Patent Application
20220072475
This application claims priority from a provisional patent application filed in India bearing no. 201841042518 titled “CONTINUOUS BATCH REVERSE OSMOSIS PROCESS” filed on Dec. 12, 2018.
The present invention generally relates to desalination systems, and in particular to batch and semi-batch desalination apparatus and methods of operation thereof.
Batch and semi-batch separations have multiple advantages over continuous separation processes. Major advantages are improved second law efficiency for separation process and significantly lower potential of fouling on equipment surface. In contrast to continuous membrane separations, batch and semi-batch separations operate with continuously varying solution properties and corresponding system operating conditions. State of the art batch separation process suffers from various challenges. Challenges described below corresponds to batch mode of separation.
For state of the art batch separations, it is often required to replace process solution in various system segments with a new process solution external to the circuit. This operation is typically required between consecutive batch separations. A major challenge for batch separations is the batch reset time. Batch reset time is the time required to replace process solution in the system's hydraulic circuit as described above. In order to overcome this limitation for a given desalination duty (i.e. increase in solute concentration, osmotic pressure and recovery) compared to a continuous separation (e.g. continuous reverse osmosis), additional equipment capacity (e.g. membrane area) needs to be provided or the system needs to be operated at higher flux (e.g. permeate flux). Both of these result in higher capital and/or operating costs.
One option to mitigate the limitations of batch reset time is to increase the batch volume. This increases the liquid container or reservoir volume that in turn increases the proportion of active separation duration of the batch. On the downside, this also leads to difference in salinity between process solution in the liquid container and concentrate returned from the separation unit. This causes entropy generation and lowers process efficiency. Further in large volume liquid containers it is difficult to maintain homogenous or well mixed solution. This will lead to spatially varying solution properties (e.g. concentration, osmotic pressure) of process solution in the liquid container. On the other hand, in small batch volumes the mixing of retentate with feed is minimized and it is practical to maintain a well-mixed solution in the liquid container. However with small batch volumes the batch reset time constitutes a major portion of total batch time thereby increasing the proportion of non-active duration of the batch. To realise optimal operations the batch-reset time must be minimized or eliminated completely.
Another problem with state of the art batch separation is the significant mixing of solutions during operation and solution change over. The retentate mixes with feed continuously during the batch separation. This increases salinity of the feed that causes the system to operate at higher than required osmotic pressures. Such mixing also occurs during replacement of final batch retentate solution from the fluid hold up volume of system using feed solution for next batch. Significant mixing leads to increased salinity of feed solution for next batch and associated efficiency loss.
An example state of the art system described in the patent application WO 2017132301A1 to Warsinger et al. describing a liquid-separation module including a membrane that passes at least partially purified solvent as filtrate while diverting the impurity in a retentate. The substantially pure water is extracted from the permeate side of the liquid-separation module, while the feed is passed from the upstream side of the liquid-separation module through the pressure exchanger, where pressure is recovered from the downstream retentate. The retentate is then passed from the pressure exchanger to the reservoir and recirculated as a component of the feed via the above steps. This method and other existing solutions do not minimize or eliminate non-permeation period between batches or address the detrimental effects of mixing.
Systems using multiple liquid containers attempt to reduce the non-permeation duration by using two service liquid containers. One liquid container provides feed solution and also collects the retentate solution. While simultaneously another liquid container, disconnected from the system, fills up with feed solution for the subsequent batch in parallel. This system still has non-permeation duration during flushing of residual brine with feed solution for next batch. Further it does not address the mixing of retentate and feed solutions in the liquid container or between retetante of a batch and feed of next batch during switchover of liquid containers.
The present invention discloses pressure- and osmotically-driven batch and semi-batch desalination apparatus and methods of operation thereof. The method and device eliminates batch reset time.
In one aspect, the invention relates to a method of performing batch and semi batch separations in a separation system. A system level feed solution is received from by at least one reservoir from an external source to initiate a first pass of a batch separation. The batch separation may include one or more pass level separations. A pass level feed solution is supplied by the at least one reservoir with at least one of the system level feed solution and a pass level retentate solution to a first side of a semi-permeable membrane of a separation unit. Pressure is exerted by the pressurizing unit in the pass level feed solution in fluid communication with the first side of the semipermeable membrane such that a pass level permeate solution from the pass level feed solution passes from the first side of the semipermeable membrane to a second side of the semipermeable membrane of the separation unit. The pressurizing unit includes at least one of an energy recovery device (ERD) device, a high-pressure pump, a booster pump, a piston, an hydraulic fluid and pneumatic fluid. A pass level retentate solution is discharged on passing the pass level permeate solution from the first side of the semipermeable membrane to the second side of the semipermeable membrane by the separation unit from the first side of the semi-permeable membrane. The discharged pass level retentate solution is stored in one of the at least one reservoir and supplied as the pass level feed solution to any of its subsequent pass until a system level retentate solution is generated. The pass level permeate solution is removed as a system level permeate solution from the separation system. The generated system level retentate solution from the separation system is removed by the separation unit in fluid communication with the at least one reservoir and the pressurizing unit.
In some aspects, the method further includes repeating, by the separation system, the described steps to continue with one or more subsequent batch separations and semi batch separations. In one aspect, the method further includes mixing a system level process solution with a pass level process solution thereby achieving the semi-batch separations. The system level process solution includes a system level feed solution, a system level permeate solution and a system level retentate solution. The pass level process solution includes a pass level feed solution, a pass level permeate solution and a pass level retentate solution. In one aspect, the method further includes filling in parallel one of the at least one reservoir with a system level feed solution for the one or more subsequent separation cycles to achieve at least one of the batch separation and the semi batch separation. In one aspect, a reservoir switchover sequence is used to enable the separation system to switch connections to supply at least one of the pass level retentate solution and the pass level permeate solution stored in one of the at least one reservoir as the pass level feed solution to any of its subsequent pass. The reservoir switchover sequence includes enabling different hydraulic segments of the separation system to replace the pass level feed solution, the pass level permeate solution and the pass level retentate solution corresponding to an earlier pass with a pass level feed solution, a pass level permeate solution and a pass level retentate solution of a next pass. In one aspect, the method further includes collecting the pass level permeate solution in one of the at least one reservoir and supplying as a pass level feed solution to any of its subsequent pass until a system level permeate solution is generated. In one aspect, the pressure exerted on the pass level feed solution in fluid communication with the first side of the semipermeable membrane is maintained by at least one of a) varying pressurized boundaries of a liquid container enclosing the at least one reservoir, b) displacing a hydraulic fluid between the at least one reservoir, c) adding hydraulic fluid to the at least one reservoir, d) transporting the pass level retentate solution and the pass level feed solution through the pressurizing unit to recover a portion of energy released by reducing the pressure of the pass level retentate solution and e) utilizing the recovered energy to pressurize the pass level feed solution. In one aspect, a process solution acts as the hydraulic fluid to maintain the pressure exerted on the pass level feed solution in fluid communication with first side of the semipermeable membrane, wherein the process solution includes at least one of the system level feed solution, the system level permeate solution, the system level retentate solution, the pass level feed solution, the pass level permeate solution and the pass level retentate solution. In another aspect, the generated system level retentate solution is removed by the separation by discharging the system level retentate solution to one of the at least one reservoir; isolating one of the at least one reservoir from the separation unit; depressurizing one of the at least one reservoir to an ambient pressure; and removing the generated system level retentate solution from and filling the system level feed solution in one of the at least one reservoir by at least one of a sequential process or by a simultaneous process. In one aspect, the generated system level retentate solution removed by separation system includes: passing the generated system level retentate solution and the system level feed solution partially or completely of the subsequent batch separations and the semi batch separations through the ERD to recover a portion of energy released upon reducing a pressure in the generated system level retentate solution and utilizing the recovered energy to pressurize the system level feed solution, wherein the pressurized system level feed solution from the ERD is collected in one of the at least one reservoir; and removing the system level retentate solution from the ERD on transferring the recovered energy to the system level feed solution. In one aspect, the pass level retentate solution is discharged from the first side of the semi-permeable membrane by: exerting, by the pressurizing unit, the pressure on the pass level feed solution on the first side of the semipermeable membrane to discharge the pass level retentate solution from the first side of the semi-permeable membrane and the pass level permeate solution from the second side of the semipermeable membrane; and recovering, by the pressurizing unit, a portion of energy released upon depressurising the pass level retentate solution and utilizing the recovered energy to pressurize the pass level feed solution.
In one aspect, the at least one reservoir comprises at least one of: an unpressurized liquid container, a piston pressurized liquid container, a piston pressurized liquid container with at least two chambers separated by at least one movable partition, wherein the at least two chambers acts as two different reservoirs; an indirect hydraulically pressurized liquid container with at least two chambers separated by at least one movable partition, wherein the at least two chambers acts as two different reservoirs; a direct hydraulically pressurized liquid container with the hydraulic fluid, wherein the hydraulic fluid is in direct fluid communication with the process solution in the reservoir; a direct feed pressurized reservoir; an unpressurized liquid container with at least two chambers separated by at least one movable partition, wherein the at least two chambers acts as two different reservoirs; an unpressurized liquid container with at least one chamber enclosed by a bladder, wherein the at least one chamber acts as a reservoir and includes one or more connections for supplying and receiving the process solutions and a pressurized liquid container with at least one chamber enclosed by a bladder. wherein the at least one chamber acts as a reservoir and includes one or more connections for supplying and receiving the process solutions. In one aspect, the at least one of the generated system level retentate solution from a batch separation is used as the system level feed solution to another batch separation and the generated system level permeate solution from the batch separation is used as the system level feed solution to another batch separation. In one aspect, the semipermeable membrane used is at least one of a reverse osmosis membrane, a nanofiltration membrane and an ultrafiltration membrane.
In one aspect, a method of performing batch and semi batch separations in a separation system is provided. The method includes a) receiving, by the separation system, a system level feed solution to at least one feed side reservoir and a system level draw solution to at least one draw side reservoir to initiate a first pass of a batch separation, wherein the batch separation includes one or more pass level separations, wherein the system level draw solution having a higher osmotic pressure than an osmotic pressure of the system level feed solution; b) supplying, by the at least one feed side reservoir, one of the system level feed solution and a pass level retentate solution as a pass level feed solution to a first side of a semi-permeable membrane of a separation unit; c) supplying, by the at least one draw side reservoir, one of the system level draw solution and a pass level diluate draw solution as a pass level draw solution to a second side of a semi-permeable membrane of the separation unit, wherein the pass level draw solution having a higher osmotic pressure than an osmotic pressure of the pass level feed solution; d) discharging, by the separation unit, a pass level retentate solution from the first side of the semi-permeable membrane and a pass level diluate draw solution from the second side of the semi permeable membrane, on extracting a pass level permeate solution having a lower osmotic pressure than the osmotic pressure of pass level draw solution by the pass level draw solution to the second side of the semipermeable membrane, wherein the discharged pass level retentate solution is stored in one of the at least one feed side reservoir and supplied as the pass level feed solution to any of its subsequent pass until a system level retentate solution is generated, wherein the discharged pass level diluate draw solution is stored in one of the at least one draw side reservoir and supplied as the pass level draw solution to any of its subsequent pass until a system level diluate draw solution is generated; and e) removing, by the separation unit in fluid communication with the at least one reservoir, the generated system level retentate solution and the system level diluate draw solution from the separation system.
In one aspect, the method further comprises repeating, by the separation system, the described steps (a-e) to continue with one or more subsequent batch separations and semi batch separations. In one aspect, the method further comprises mixing a system level process solution with a pass level process solution thereby achieving the semi-batch separations, wherein the system level process solution includes a system level feed solution, a system level draw solution and a system level retentate solution and system level diluate draw solution, wherein the pass level process solution includes a pass level feed solution, a pass level draw solution and a pass level retentate solution and a pass level diluate draw solution. In one aspect, the method further comprises parallel filling of the one of the at least one feed side reservoir and one of the at least one draw side reservoir with the system level feed solution and the system level draw solution respectively for the one or more subsequent separation cycles to achieve at least one of the batch separation and the semi batch separation. In one aspect, a reservoir switchover sequence is used to enable the separation system to switch connections to supply one of the system level feed solution and the pass level retentate solution stored in one of the at least one feed side reservoir as the pass level feed solution and to supply one of the system level draw solution and the pass level diluate draw solution stored in one of the at least one draw side reservoir as the pass level draw solution to any of its subsequent pass, the reservoir switchover sequence comprises: enabling different hydraulic segments of the separation system to replace the pass level feed solution, the pass level draw solution, the pass level retentate solution and the pass level diluate draw solution corresponding to an earlier pass with a pass level feed solution, a pass level draw solution, a pass level retentate solution and a pass level diluate draw solution of a next pass. In one aspect, the separation system is an osmotically driven separation system. In one aspect, a flow of the feed solution on the first side of the membrane and a flow of the draw solution on the second side of the membrane are one of a counter current, a co-current and a cross-current to each other. In one aspect, one of the generated system level retentate solution from one batch separation or semi batch separation is used as system level feed solution to another batch separation or semi batch separation and the generated system level diluate draw solution from one batch separation or semi batch separation is used as a system level draw solution to another batch separation or semi batch separation.
In one aspect, a separation system for performing batch and semi batch separations is provided. The separation system includes at least one reservoir configured to: receive a system level feed solution from an external source to initiate a first pass of a batch separation, wherein the batch separation includes one or more pass level separations; supply at least one of the system level feed solution and a pass level retentate solution as a pass level feed solution to a first side of a semi-permeable membrane of a separation unit; a pressurizing unit configured to: exert a pressure on the pass level feed solution in fluid communication with the first side of the semipermeable membrane such that a pass level permeate solution from the pass level feed solution passes from the first side of the semipermeable membrane to a second side of the semipermeable membrane of the separation unit, wherein the pressurizing unit includes at least one of an energy recovery device (ERD) device, an high pressure pump, a booster pump, a piston, an hydraulic fluid and pneumatic fluid; the separation unit configured to: discharge a pass level retentate solution from the first side of the semi-permeable membrane, on passing the pass level permeate solution to the second side of the semipermeable membrane, wherein the discharged pass level retentate solution is stored in one of the at least one reservoir and supplied as the pass level feed solution to any of its subsequent pass until a system level retentate solution is generated, wherein the pass level permeate solution is removed as a system level permeate solution; and the separation unit in fluid communication with the at least one reservoir and the pressurizing unit configured to remove the generated system level retentate solution.
In one aspect, the separation system configured to repeat the described steps (a-e) to continue with one or more subsequent batch separations and semi batch separations. In one aspect, the separation system is configured to mix a system level process solution with a pass level process solution thereby achieving the semi-batch separations, wherein the system level process solution includes a system level feed solution, a system level permeate solution and a system level retentate solution, wherein the pass level process solution includes a pass level feed solution, a pass level permeate solution and a pass level retentate solution.
In one aspect, the separation system configured to fill in parallel one of the at least one reservoir with a system level feed solution for the one or more subsequent separation cycles to achieve at least one of the batch separation and the semi batch separation. In one aspect, the separation system configured to enable a reservoir switchover sequence to switch connections to supply at least one of the pass level retentate solution and the pass level permeate solution stored in one of the at least one reservoir as the pass level feed solution to any of its subsequent pass by: enabling different hydraulic segments of the separation system to replace the pass level feed solution, the pass level permeate solution and the pass level retentate solution corresponding to an earlier pass with a pass level feed solution, a pass level permeate solution and a pass level retentate solution of a next pass. In one aspect, the separation system is configured to collect the pass level permeate solution in one of the at least one reservoir and supply as the pass level feed solution to any of its subsequent pass until a system level permeate solution is generated. In one aspect, the pressure exerted on the pass level feed solution in fluid communication with the first side of the semipermeable membrane is maintained by at least one of varying pressurized boundaries of a liquid container enclosing the at least one reservoir, displacing a hydraulic fluid between the at least one reservoir, adding hydraulic fluid to the at least one reservoir, transporting the pass level retentate solution and the pass level feed solution through the pressurizing unit to recover a portion of energy released by reducing the pressure of the pass level retentate solution and utilizing the recovered energy to pressurize the pass level feed solution. In one aspect, a process solution acts as the hydraulic fluid to maintain the pressure exerted on the pass level feed solution in fluid communication with first side of the semipermeable membrane, wherein the process solution includes at least one of the system level feed solution, the system level permeate solution, the system level retentate solution, the pass level feed solution, the pass level permeate solution and the pass level retentate solution. In one aspect, the separation system is configured to remove the generated system level retentate solution by: discharging the system level retentate solution to one of the at least one reservoir; isolating the at least one reservoir from the separation unit; depressurizing one of the at least one reservoir to an ambient pressure; and removing the generated system level retentate solution from and filling the system level feed solution in one of the at least one reservoir by at least one of a sequential process or by a simultaneous process.
In one embodiment, the separation system is configured to remove the generated system level retentate solution by: passing the generated system level retentate solution and the system level feed solution partially or completely of the subsequent batch separations and the semi batch separations through the ERD to recover a portion of energy released upon reducing a pressure in the generated system level retentate solution and utilizing the recovered energy to pressurize the system level feed solution, wherein the pressurized system level feed solution from the ERD is collected in one of the at least one reservoir; and removing the system level retentate solution from the ERD on transferring the recovered energy to the system level feed solution. In one embodiment, the separation unit is configured to discharge a pass level retentate solution from the first side of the semi-permeable membrane by: configuring the pressurizing unit to exert a pressure on the pass level feed solution on the first side of the semipermeable membrane to discharge the pass level retentate solution from the first side of the semi-permeable membrane and a pass level permeate solution from the second side of the semipermeable membrane; and configuring the pressurizing unit to recover a portion of energy released upon depressurising the pass level retentate solution and utilizing the recovered energy to pressurize the pass level feed solution. In one embodiment, the at least one reservoir comprises at least one of: an unpressurized liquid container; a piston pressurized liquid container; a piston pressurized liquid container with at least two chambers separated by at least one movable partition, wherein the at least two chambers acts as two different reservoirs; an indirect hydraulically pressurized liquid container with at least two chambers separated by at least one movable partition; a direct hydraulically pressurized liquid container with the hydraulic fluid in direct fluid communication with the process solution in the reservoir, a direct feed pressurized reservoir, an unpressurized liquid container with at least two chambers separated by at least one movable partition, wherein the at least two chambers acts as two different reservoirs; an unpressurized liquid container with at least one chamber enclosed by a bladder, wherein the at least one chamber acts as a reservoir and includes one or more connections for supplying and receiving the process solutions; and a pressurized liquid container with at least one chamber enclosed by a bladder, wherein the at least one chamber acts as a reservoir and includes one or more connections for supplying and receiving the process solutions. In one aspect, at least one of the generated system level retentate solution from a batch separation is used as the system level feed solution to another batch separation and the generated system level permeate solution from the batch separation is used as the system level feed solution to the another batch separation. In one aspect, the semipermeable membrane used is at least one of a reverse osmosis membrane, a nanofiltration membrane and an ultrafiltration membrane.
In one aspect, a separation system for performing batch and semi batch separations. The separation system includes at least one feed side reservoir configured to: receive a system level feed solution to the at least one feed side reservoir and supply one of the system level feed solution and a pass level retentate solution as a pass level feed solution to a first side of a semi-permeable membrane of a separation unit for a batch separation, wherein the batch separation includes one or more pass level separations, wherein the system level draw solution having a higher osmotic pressure than an osmotic pressure of the system level feed solution; at least one draw side reservoir configured to: receive a system level draw solution to at least one draw side reservoir for the batch separation and supply one of the system level draw solution and a pass level diluate draw solution as a pass level draw solution to a second side of a semi-permeable membrane of the separation unit, wherein the system level draw solution having a higher osmotic pressure than an osmotic pressure of the system level feed solution; the separation unit configured to: discharge a pass level retentate solution from the first side of the semi-permeable membrane and a pass level diluate draw solution from the second side of the semi permeable membrane, on extracting a pass level permeate solution having a lower osmotic pressure than the osmotic pressure of pass level draw solution by the pass level draw solution to the second side of the semipermeable membrane, wherein the discharged pass level retentate solution is stored in one of the at least one feed side reservoir and supplied as the pass level feed solution to any of its subsequent pass until a system level retentate solution is generated, wherein the discharged pass level diluate draw solution is stored in one of the at least one draw side reservoir and supplied as the pass level draw solution to any of its subsequent pass until a system level diluate draw solution is generated; and the separation unit in fluid communication with the at least one reservoir, configured to: remove the generated system level retentate solution and the system level diluate draw solution from the separation system. In one aspect, the separation system is further configured to repeat the described steps to continue with one or more subsequent batch separations and semi batch separations. In one aspect, the separation system is configured to mix a system level process solution with a pass level process solution thereby achieving the semi-batch separations, the system level process solution includes a system level feed solution, a system level draw solution and a system level retentate solution and system level diluate draw solution, wherein the pass level process solution includes a pass level feed solution, a pass level draw solution and a pass level retentate solution and a pass level diluate draw solution. In one aspect, the separation system is configured to fill in parallel one of the at least one feed side reservoir and one of the at least one draw side reservoir with a system level feed solution and the system level draw solution for the one or more subsequent separation cycles to achieve at least one of the batch separation and the semi batch separation. In one aspect, the separation system is configured to enable a reservoir switchover to switch connections to supply one of the system level feed solution and the pass level retentate solution stored in one of the at least one feed side reservoir as the pass level feed solution and to supply one of the system level draw solution and the pass level diluate draw solution stored in one of the at least one draw side reservoir as the pass level draw solution to any of its subsequent pass by: enabling different hydraulic segments of the separation system to replace the pass level feed solution, the pass level draw solution, the pass level retentate solution and the pass level diluate draw solution corresponding to an earlier pass with a pass level feed solution, a pass level draw solution, a pass level retentate solution and a pass level diluate draw solution of a next pass. In one aspect, the separation system is an osmotically driven separation system. In one aspect, a flow of the feed solution on the first side of the membrane and a flow of the draw solution on the second side of the membrane are one of a counter current, a co-current and a cross-current to each other. In one aspect, one of the generated system level retentate solution from one batch separation or semi batch separation is used as system level feed solution to another batch separation or semi batch separation and the generated system level diluate draw solution from one batch separation or semi batch separation is used as a system level draw solution to another batch separation or semi batch separation.
In one aspect, a method of performing batch and semi batch separations in a separation system is provided. The method includes a) receiving, by at least one feed side reservoir, a system level feed solution and supplying as a pass level feed solution to the first side of the semi permeable membrane for a first pass of a first batch; b) supplying, by the at least one draw side reservoir, a pass level draw solution having a higher osmotic pressure than an osmotic pressure of the pass level feed solution corresponding to the first pass to the second side of the semi permeable membrane; c) discharging, by the separation unit, a pass level retentate solution from the first side of the semi-permeable membrane and the pass level diluate draw solution from the second side of the semi permeable membrane, on extracting a pass level permeate solution having a lower osmotic pressure than the osmotic pressure of pass level draw solution by the pass level draw solution from the first side of the semipermeable membrane to the second side of the semipermeable membrane, wherein the discharged pass level retentate solution is stored in one of the at least one feed side reservoir and supplied as the pass level feed solution to any of its subsequent pass, wherein the discharged pass level diluate draw solution is removed as a system level diluate draw solution; d) supplying, by the at least one feed side reservoir, a pass level retentate produced in the first pass as a pass level feed solution to the first side of the semi permeable membrane for a second pass; e) supplying by the at least one draw side reservoir, a pass level draw solution corresponding to the second pass, to the second side of the semi permeable membrane, wherein the pass level draw solution having a higher osmotic pressure than an osmotic pressure of the pass level feed solution; f) discharging, by the separation unit, a pass level retentate solution from the first side of the semi-permeable membrane and the pass level diluate draw solution from the second side of the semi permeable membrane corresponding to the second pass, on extracting a pass level permeate solution having a lower osmotic pressure than the osmotic pressure of pass level draw solution by the pass level draw solution from the first side of the semipermeable membrane to the second side of the semipermeable membrane, wherein the discharged pass level retentate solution is stored in one of the at least one feed side reservoir and supplied as the pass level feed solution to a third pass, wherein the discharged pass level diluate draw solution is stored in one of the at least one draw side reservoir and supplied as the pass level draw solution to a first pass of a second batch; g) repeating steps (d-f) for further passes till pass n-1 of the first batch to produce a pass level retentate of pass n-1, wherein the discharged pass level diluate draw solution of every pass of the first batch is stored in one of the at least one draw side reservoir and supplied as the pass level draw solution to an earlier pass of a second batch; h) supplying the pass level retentate of pass n-1 as a pass level feed solution to the first side of the semi permeable membrane for a pass n; and i) receiving and supplying, by the at least one draw side reservoir, a system level draw solution having a higher osmotic pressure than the osmotic pressure of the pass level feed solution of the pass n in step h as a pass level draw solution to the second side of the semi permeable membrane; j) discharging, by the separation unit, a pass level retentate solution from the first side of the semi-permeable membrane and the pass level diluate draw solution from the second side of the semi permeable membrane, on extracting a pass level permeate solution having a lower osmotic pressure than the osmotic pressure of pass level draw solution by the pass level draw solution from the first side of the semipermeable membrane to the second side of the semipermeable membrane, wherein the discharged pass level retentate solution is removed as system level retentate solution, wherein the discharged pass level diluate draw solution is stored in one of the at least one draw side reservoir and supplied as pass level draw solution to n−1 pass of the second batch; k) repeating the steps, a-j for further batches, wherein the system level feed solution and system level draw solution are converted to corresponding system level retentate solution and a system level diluate draw solution.
In one aspect, the method includes receiving and supplying by the at least one draw side reservoir a system level draw solution as a pass level draw solution corresponding to the second pass, to the to second side of the semi permeable membrane and removing the discharged pass level retentate solution corresponding to the second pass, from the first side of the semi-permeable membrane as a system level retentate when a batch consists of maximum of two passes, wherein the pass level draw solution having a higher osmotic pressure than an osmotic pressure of the pass level feed solution. In one aspect, the method includes mixing a system level process solution with a pass level process solution thereby achieving a semi-batch separation, wherein the system level process solution includes a system level feed solution, a system level draw solution, a system level retentate solution and a system level diluate draw solution, wherein the pass level process solution includes a pass level feed solution, a pass level draw solution, a pass level retentate solution and a pass level diluate draw solution.
In one aspect, the method further comprises filling in parallel the at least one feed side reservoir with a system level feed solution and the at least one draw side reservoir with a system level draw solution for the one or more subsequent separation cycles to achieve at least one of the batch separation and the semi batch separation. In one aspect, a reservoir switchover sequence is used to enable the separation system to switch connections to supply one of the system level feed solution and the pass level retentate solution stored in one of the at least one feed side reservoir and one of the system level draw solution and the pass level diluate draw solution stored in one of the at least one draw side reservoir as the pass level feed solution and the pass level draw solution respectively having a higher osmotic pressure than an osmotic pressure of pass level feed solution to any of its subsequent pass, the reservoir switchover sequence comprises: enabling different hydraulic segments of the separation system to replace the pass level feed solution, the pass level draw solution, the pass level retentate solution and the pass level diluate draw solution corresponding to an earlier pass with a pass level feed solution, a pass level draw solution, a pass level retentate solution and a pass level diluate draw solution of a next pass. In one aspect, the flow of feed solution on the first side of the semipermeable membrane and the flow of draw solution on the second side of the semipermeable membrane are one of counter current, co-current and cross-current to each other. In one aspect, at least one of the generated system level retentate solution from one batch separation or semi batch separation is used as system level feed solution to another batch separation or semi batch separation and the generated system level diluate draw solution from one batch separation or semi batch separation is used as system level draw solution to another batch separation or semi batch separation.
In one aspect, a separation system for performing batch and semi batch separations, the separation system comprising: at least one feed side reservoir configured to: receive a system level feed solution and supplying as a pass level feed solution to the first side of the semi-permeable membrane for a first pass of a first batch; and at least one draw side reservoir configured to: supply a pass level draw solution having a higher osmotic pressure than an osmotic pressure of pass level feed solution corresponding to the first pass to the second side of the semi-permeable membrane; a separation unit configured to: discharge a pass level retentate solution from the first side of the semi-permeable membrane and the pass level diluate draw solution from the second side of the semi permeable membrane, on extracting a pass level permeate solution having a lower osmotic pressure than the osmotic pressure of pass level draw solution by the pass level draw solution from the first side of the semipermeable membrane to the second side of the semipermeable membrane, wherein the discharged pass level retentate solution is stored in one of the at least one feed side reservoir and supplied as the pass level feed solution to any of its subsequent pass, wherein the discharged pass level diluate draw solution is removed as a system level diluate draw solution; the at least one feed side reservoir configured to: supply a pass level retentate produced in the first pass as a pass level feed solution to the first side of the semi-permeable membrane for a second pass; the at least one draw side reservoir configured to: supply a pass level draw solution corresponding to the second pass, to the second side of the semi permeable membrane, wherein the pass level draw solution having a higher osmotic pressure than an osmotic pressure of pass level feed solution; the separation unit configured to: discharge a pass level retentate solution from the first side of the semi-permeable membrane and the pass level diluate draw solution from the second side of the semi permeable membrane corresponding to the second pass, on extracting a pass level permeate solution having a lower osmotic pressure than the osmotic pressure of pass level draw solution by the pass level draw solution from the first side of the semipermeable membrane to the second side of the semipermeable membrane, wherein the discharged pass level retentate solution is stored in one of the at least one feed side reservoir and supplied as the pass level feed solution to a third pass, wherein the discharged pass level diluate draw solution is stored in one of the at least one draw side reservoir and supplied as the pass level draw solution to a first pass of a second batch; repeating steps (d-f) for further passes till pass n-1 of the first batch to produce a pass level retentate of pass n-1, wherein the discharged pass level diluate draw solution of every pass of the first batch is stored in one of the at least one draw side reservoir and supplied as the pass level draw solution to an earlier pass of a second batch; the at least one feed side reservoir configured to: supply the pass level retentate of pass n-1 as a pass level feed solution to the first side of the semi permeable membrane for a pass n; and the at least one draw side reservoir configured to: receive and supply a system level draw solution as a pass level draw solution having a higher osmotic pressure than an osmotic pressure of pass level feed solution of the pass n in step h as a pass level draw solution to the second side of the semi permeable membrane; the separation unit configured to: discharge a pass level retentate solution from the first side of the semi-permeable membrane and the pass level diluate draw solution from the second side of the semi permeable membrane, on extracting a pass level permeate solution having a lower osmotic pressure than the osmotic pressure of pass level draw solution by the pass level draw solution from the first side of the semipermeable membrane to the second side of the semipermeable membrane, wherein the discharged pass level retentate solution is removed as system level retentate solution, wherein the discharged pass level diluate draw solution is stored in one of the at least one draw side reservoir and supplied as pass level draw solution to n−1 pass of the second batch; repeat the steps a-j for further batches, wherein the system level feed solution and system level draw solution are converted to corresponding system level retentate solution and a system level diluate draw solution.
In one aspect, the at least one draw side reservoir is configured to receive and supply a system level draw solution as a pass level draw solution corresponding to the second pass, to the second side of the semi permeable membrane and removing the discharged pass level retentate solution corresponding to the second pass, from the first side of the semi-permeable membrane as a system level retentate when a batch consists of maximum of two passes, wherein the pass level draw solution having a higher osmotic pressure than an osmotic pressure of the pass level feed solution. In one aspect, the separation system further configured to mix a system level process solution with a pass level process solution thereby achieving a semi-batch separation, wherein the system level process solution includes a system level feed solution, a system level draw solution, a system level retentate solution and a system level diluate draw solution, wherein the pass level process solution includes a pass level feed solution, a pass level draw solution, a pass level retentate solution and a pass level diluate draw solution. In one aspect, the separation system further configured to fill in parallel the at least one feed side reservoir with a system level feed solution and the at least one draw side reservoir with a system level draw solution for the one or more subsequent separation cycles to achieve at least one of the batch separation and the semi batch separation. In one aspect, the separation system further configured to enable a reservoir switchover sequence to switch connections to supply one of the system level feed solution and the pass level retentate solution stored in one of the at least one feed side reservoir and one of the system level draw solution and the pass level diluate draw solution stored in one of the at least one draw side reservoir as the pass level feed solution and the pass level draw solution having a higher osmotic pressure than an osmotic pressure of pass level feed solution to any of its subsequent pass by: enabling different hydraulic segments of the separation system to replace the pass level feed solution, the pass level draw solution, the pass level retentate solution and the pass level diluate draw solution corresponding to an earlier pass with a pass level feed solution, a pass level draw solution, a pass level retentate solution and a pass level diluate draw solution of a next pass. In one aspect, the flow of feed solution on the first side of the semipermeable membrane and the flow of draw solution on the second side of the semipermeable membrane are one of counter current, co-current and cross-current to each other. In one aspect, at least one of the generated system level retentate solution from one batch separation or semi batch separation is used as system level feed solution to another batch separation or semi batch separation and the generated system level diluate draw solution from one batch separation or semi batch separation is used as system level draw solution to another batch separation or semi batch separation.
In one aspect, a method of performing batch and semi batch separations in a separation system, the method comprising: a) receiving, by a at least one draw side reservoir, a system level draw solution and supplying as a pass level draw solution to the second side of the semi permeable membrane for a first pass of a first batch; b) supplying, by the at least one feed side reservoir, a pass level feed solution having a lower osmotic pressure than an osmotic pressure of the pass level draw solution corresponding to the first pass to the first side of the semi permeable membrane; c) discharging, by the separation unit, a pass level retentate solution from the first side of the semi-permeable membrane and the pass level diluate draw solution from the second side of the semi permeable membrane, on extracting a pass level permeate solution having a lower osmotic pressure than the osmotic pressure of pass level draw solution by the pass level draw solution from the first side of the semipermeable membrane to the second side of the semipermeable membrane, wherein the discharged pass level retentate solution is removed as a system level retentate solution, wherein the discharged pass level diluate draw solution is stored in one of the at least one draw side reservoir and supplied as the pass level draw solution to any of its subsequent pass; d) supplying, by the at least one draw side reservoir, a pass level diluate draw solution produced in the first pass as a pass level draw solution to the second side of the semi permeable membrane for a second pass; e) supplying by the at least one feed side reservoir, a pass level feed solution corresponding to the second pass, to the first side of the semi permeable membrane, wherein the pass level feed solution having a lower osmotic pressure than an osmotic pressure of the pass level draw solution; f) discharging, by the separation unit, a pass level retentate solution from the first side of the semi-permeable membrane and the pass level diluate draw solution from the second side of the semi permeable membrane corresponding to the second pass, on extracting a pass level permeate solution having a lower osmotic pressure than the osmotic pressure of pass level draw solution by the pass level draw solution from the first side of the semipermeable membrane to the second side of the semipermeable membrane, wherein the discharged pass level retentate solution is stored in one of the at least one feed side reservoir and supplied as the pass level feed solution to a first pass of a second batch, wherein the discharged pass level diluate draw solution is stored in one of the at least one draw side reservoir and supplied as the pass level draw solution to a third pass; g) repeating steps (d-f) for further passes till pass n−1 of the first batch to produce a pass level diluate draw of pass n−1, wherein the discharged pass level retentate solution of every pass of the first batch is stored in one of the at least one feed side reservoir and supplied as the pass level feed solution to an earlier pass of a second batch; h) supplying the pass level diluate draw of pass n−1 as a pass level draw solution to the second side of the semi permeable membrane for a pass n; i) receiving and supplying, by the at least one feed side reservoir, a system level feed solution having a lower osmotic pressure than the osmotic pressure of the pass level draw solution of the pass n in step h as a pass level feed solution to the first side of the semi permeable membrane; j) discharging, by the separation unit, a pass level retentate solution from the first side of the semi-permeable membrane and the pass level diluate draw solution from the second side of the semi permeable membrane, on extracting a pass level permeate solution having a lower osmotic pressure than the osmotic pressure of pass level draw solution by the pass level draw solution from the first side of the semipermeable membrane to the second side of the semipermeable membrane, wherein the discharged pass level retentate solution is stored in one of the at least one feed side reservoir and supplied as pass level feed solution to n−1 pass of the second batch, wherein the discharged pass level diluate draw solution is removed as system level diluate draw solution; k) repeating the steps, a-j for further batches, wherein the system level feed solution and system level draw solution are converted to corresponding system level retentate solution and a system level diluate draw solution.
In one aspect, the method comprises receiving and supplying by the at least one feed side reservoir a system level feed solution as a pass level feed solution corresponding to the second pass, to the to first side of the semi permeable membrane and removing the discharged pass level diluate draw solution corresponding to the second pass, from the second side of the semi permeable membrane as a system level diluate draw solution when a batch consists of maximum of two passes, wherein the pass level draw solution having a higher osmotic pressure than an osmotic pressure of the pass level feed solution. In one aspect, the method further comprises mixing a system level process solution with a pass level process solution thereby achieving a semi-batch separation, wherein the system level process solution includes a system level feed solution, a system level draw solution, a system level retentate solution and a system level diluate draw solution, wherein the pass level process solution includes a pass level feed solution, a pass level draw solution, a pass level retentate solution and a pass level diluate draw solution. In one aspect, the method further comprises filling in parallel the at least one feed side reservoir with a system level feed solution and the at least one draw side reservoir with a system level draw solution for the one or more subsequent separation cycles to achieve at least one of the batch separation and the semi batch separation. In one aspect, a reservoir switchover sequence is used to enable the separation system to switch connections to supply one of the system level feed solution and the pass level retentate solution stored in one of the at least one feed side reservoir and one of the system level draw solution and the pass level diluate draw solution stored in one of the at least one draw side reservoir as the pass level feed solution and the pass level draw solution respectively having a higher osmotic pressure than an osmotic pressure of pass level feed solution to any of its subsequent pass, the reservoir switchover sequence comprises: enabling different hydraulic segments of the separation system to replace the pass level feed solution, the pass level draw solution, the pass level retentate solution and the pass level diluate draw solution corresponding to an earlier pass with a pass level feed solution, a pass level draw solution, a pass level retentate solution and a pass level diluate draw solution of a next pass. In one aspect, the flow of feed solution on the first side of the semipermeable membrane and the flow of draw solution on the second side of the semipermeable membrane are one of counter current, co-current and cross-current to each other. In one aspect, at least one of the generated system level retentate solution from one batch separation or semi batch separation is used as system level feed solution to another batch separation or semi batch separation and the generated system level diluate draw solution from one batch separation or semi batch separation is used as system level draw solution to another batch separation or semi batch separation.
In one aspect, a separation system for performing batch and semi batch separation is provided. The separation system includes at least one draw side reservoir configured to: a) receive a system level draw solution and supplying as a pass level draw solution to the second side of the semi-permeable membrane for a first pass of a first batch; and at least one feed side reservoir configured to: b) supply a pass level feed solution having a lower osmotic pressure than an osmotic pressure of pass level draw solution corresponding to the first pass to the first side of the semi-permeable membrane; a separation unit configured to: c) discharge a pass level retentate solution from the first side of the semi-permeable membrane and the pass level diluate draw solution from the second side of the semi permeable membrane, on extracting a pass level permeate solution having a lower osmotic pressure than the osmotic pressure of pass level draw solution by the pass level draw solution from the first side of the semipermeable membrane to the second side of the semipermeable membrane, wherein the discharged pass level retentate solution is removed as a system level retentate solution, wherein the discharged pass level diluate draw solution is stored in one of the at least one draw side reservoir and supplied as the pass level draw solution to any of its subsequent pass; the at least one draw side reservoir configured to: d) supply a pass level diluate draw solution produced in the first pass as a pass level draw solution to the second side of the semi-permeable membrane for a second pass; the at least one feed side reservoir configured to: e) supply a pass level feed solution corresponding to the second pass, to the first side of the semi permeable membrane, wherein the pass level feed solution having a lower osmotic pressure than an osmotic pressure of pass level draw solution; the separation unit configured to: f) discharge a pass level retentate solution from the first side of the semi-permeable membrane and the pass level diluate draw solution from the second side of the semi permeable membrane corresponding to the second pass, on extracting a pass level permeate solution having a lower osmotic pressure than the osmotic pressure of pass level draw solution by the pass level draw solution from the first side of the semipermeable membrane to the second side of the semipermeable membrane, wherein the discharged pass level retentate solution is stored in one of the at least one feed side reservoir and supplied as the pass level feed solution to a first pass of a second batch, wherein the discharged pass level diluate draw solution is stored in one of the at least one draw side reservoir and supplied as the pass level draw solution to a third pass; g) repeating steps (d-f) for further passes till pass n−1 of the first batch to produce a pass level diluate draw of pass n−1, wherein the discharged pass level retentate solution of every pass of the first batch is stored in one of the at least one feed side reservoir and supplied as the pass level feed solution to an earlier pass of a second batch; the at least one draw side reservoir configured to: h) supply the pass level diluate draw of pass n−1 as a pass level draw solution to the second side of the semi permeable membrane for a pass n; and the at least one feed side reservoir configured to: i) receive and supply a system level feed solution having a lower osmotic pressure than an osmotic pressure of pass level draw solution of the pass n in step h as a pass level feed solution to the second side of the semi permeable membrane; the separation unit configured to: j) discharge a pass level retentate solution from the first side of the semi-permeable membrane and the pass level diluate draw solution from the second side of the semi permeable membrane, on extracting a pass level permeate solution having a lower osmotic pressure than the osmotic pressure of pass level draw solution by the pass level draw solution from the first side of the semipermeable membrane to the second side of the semipermeable membrane, wherein the discharged pass level retentate solution is stored in one of the at least one feed side reservoir and supplied as pass level feed solution to n−1 pass of the second batch, wherein the discharged pass level diluate draw solution is removed as system level diluate draw solution; k) repeat the steps a-j for further batches, wherein the system level feed solution and system level draw solution are converted to corresponding system level retentate solution and a system level diluate draw solution.
In one aspect, the at least one feed side reservoir configured to receive and supply a system level feed solution as a pass level feed solution corresponding to the second pass, to the first side of the semi permeable membrane and removing the discharged pass level diluate draw solution corresponding to the second pass, from the second side of the semi permeable membrane as a system level diluate draw solution when a batch consists of maximum of two passes, wherein the pass level draw solution having a higher osmotic pressure than an osmotic pressure of the pass level feed solution. In one aspect, the separation system further configured to mix a system level process solution with a pass level process solution thereby achieving a semi-batch separation, wherein the system level process solution includes a system level feed solution, a system level draw solution, a system level retentate solution and a system level diluate draw solution, wherein the pass level process solution includes a pass level feed solution, a pass level draw solution, a pass level retentate solution and a pass level diluate draw solution. In one aspect, the separation system further configured to fill in parallel the at least one feed side reservoir with a system level feed solution and the at least one draw side reservoir with a system level draw solution for the one or more subsequent separation cycles to achieve at least one of the batch separation and the semi batch separation. In one aspect, the separation system further configured to enable a reservoir switchover sequence to switch connections to supply one of the system level feed solution and the pass level retentate solution stored in one of the at least one feed side reservoir and one of the system level draw solution and the pass level diluate draw solution stored in one of the at least one draw side reservoir as the pass level feed solution and the pass level draw solution respectively having a higher osmotic pressure than an osmotic pressure of pass level feed solution to any of its subsequent pass by: enabling different hydraulic segments of the separation system to replace the pass level feed solution, the pass level draw solution, the pass level retentate solution and the pass level diluate draw solution corresponding to an earlier pass with a pass level feed solution, a pass level draw solution, a pass level retentate solution and a pass level diluate draw solution of a next pass. In one aspect, the flow of feed solution on the first side of the semipermeable membrane and the flow of draw solution on the second side of the semipermeable membrane are one of counter current, co-current and cross-current to each other. In one aspect, the at least one of the generated system level retentate solution from one batch separation or semi batch separation is used as system level feed solution to another batch separation or semi batch separation and the generated system level diluate draw solution from one batch separation or semi batch separation is used as system level draw solution to another batch separation or semi batch separation.
This and other aspects are disclosed herein.
The invention has other advantages and features which will be more readily apparent from the following detailed description of the invention and the appended claims, when taken in conjunction with the accompanying drawings, in which:
While the invention has been disclosed with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt to a particular situation or material to the teachings of the invention without departing from its scope.
Throughout the specification and claims, the following terms take the meanings explicitly associated herein unless the context clearly dictates otherwise. The meaning of “a”, “an”, and “the” include plural references. The meaning of “in” includes “in” and “on.” Referring to the drawings, like numbers indicate like parts throughout the views. Additionally, a reference to the singular includes a reference to the plural unless otherwise stated or inconsistent with the disclosure herein.
Key inventive features: Without being bound to any particular separation system, benefits of batch and semi-batch (i.e. transient) separations over steady state separations is described below. Transient separation processes are able to achieve higher process efficiency than steady state processes, because time is available as an additional process dimension for distribution of driving force of separation and thus achieve equipartitioning of entropy generation. Equipartitioning of entropy generation is known to improve thermodynamic efficiency of separation processes. For a pressure driven separation this translates to optimal spacial and temporal distribution of net driving pressure while for osmotically driven separation this corresponds to optimal spacial and temporal distribution of gradient in osmotic pressures. The extent of separation achieved (e.g. recovery in RO processes) is limited either by solution osmotic pressures or by precipitation of sparingly soluble salts or deposition of other foulants. Typically at high degrees of separations the tendency for precipitation by sparingly soluble salts is high. In steady state separations, if equipment is operated at this condition, there is sufficient time for precipitation of these salts on the equipment that adversely affects performance. However in transient separations, duration of exposure of the system at this operating condition may be controlled so that the kinetics of salt precipitation (or deposition of any other foulants) is slower than the duration for which precipitation or scaling conditions exist. This allows for simultaneous gains in operational efficiency and equipment life. An additional benefit of operating a transient process is the varying application of separation energy (i.e. pressure or osmotic pressure or both) during separation process. This creates conditions difficult for microbes to survive thereby lowering fouling potential of biofouling agents that may be present in process solutions. Particularly for zero liquid discharge applications the disclosed methods will significantly enhance energy efficiency, reduce operation and investment costs as it significantly simplifies treatment scheme.
For batch systems in prior art, challenges are experienced in achieving continuity between batches, with unintended continuous mixing of solutions at different concentrations during a batch and during change over of reservoirs as described earlier. In various embodiments, the invention enables continuous batch separation where batch reset time is eliminated in all modes of operation and un-intended mixing (semi-batch is an intended mixing) of solutions at different concentrations is either minimized or eliminated. The invention disclosed realizes a true batch process by employing following features,
1) The batch separation is achieved by passing a batch of process solution through the separation unit 100 in multiple passes with each pass performing incremental separation. In each pass the batch of process solution flows from a reservoir through the separation unit 100 where separation is performed on it and a smaller portion is returned to another reservoir. Reservoirs are used to supply process solution to and collect process solution from the separation unit 100.
2) Volume compensation techniques described enable pressurized reservoirs to maintain required operating conditions during changes in volume of pressurized fluids in the system.
3) System level solutions corresponding to batch initial and final solutions are filled or removed in parallel during operation of another batch by direct exchange method and by collection and exchange methods. Such removal and filling of batch solutions occur in reservoirs disconnected from the separation unit while the separation unit operates another batch with other reservoir(s). This allows the removal of batch end solutions and filling of batch initial solutions while continuously achieving separation in separation unit.
4) Precise continuity is maintained between consecutive passes and consecutive batches by following a reservoir switchover sequence. Further, separation is continuously achieved during this reservoir switch over sequence. Thus the process achieves continuous batch separation requiring no redundancy in separation capacity to compensate for non-active duration of process.
5) Careful hydraulic design and system operation minimize or eliminate mixing of solutions at different concentrations.
6) In some system configurations, continuous batch separation is achieved without the use of energy recovery devices (ERD). This improves process efficiency over systems using ERDs.
7) Counter current changes in process solutions for batch and semi-batch osmotic separations is achieved by novel method of stocking of intermediate pass level solutions, by transverse cascading and bleeding techniques. This counter current change is accomplished with change in process time.
Further differences between individual system configurations are explained below.
For the purpose of this invention certain definitions are used to aid with explanation of the concepts and are explained as follows.
Process solutions refer to any solution that undergoes separation in the disclosed system. Process solutions in the simplest case may be composed of a single solvent and single solute solution such as water and sodium chloride. Alternatively process solution may be composed of multiple solvents and multiple solutes such as sodium chloride, calcium acetate, benzoic acid as solutes and water, ethanol as solvents. Process solution may comprise of multiple solvents, solutes and chemical entities, all of them might be collectively referred as solution components. Hydraulic fluid refers to any fluid that is used for transmitting pressure in the systems of this invention. A process solution may also be used as hydraulic fluid. Example of hydraulic fluid that is not a process solution includes hydraulic oil. Semi-permeable membrane refers to a physical barrier that preferentially permits transport of solvent and/or solute molecules such that the composition of permeate solution is different from that of feed solution from which the permeate solution originates. When process solutions contain multiple solvents and multiple solutes, the semi-permeable membrane may exhibit different selectivity towards each solute and each solvent. In many applications of interest to the present invention, the process solutions possess osmotic pressures that result from interaction between solvent and solute molecules. Semi-permeable membrane may also be referred as membrane in the description. Depending on the semi-permeable membrane and process solutions components, two broad types of separations may be performed by the semi-permeable membrane.
Osmotic separations correspond to separations wherein the composition of permeate solution that is transported across the semi-permeable membrane from the first side to the second side is such that its osmotic pressure is different from the osmotic pressure of corresponding feed solution supplied to the separation unit. For osmotic separations, depending on the semi-permeable membrane and process solutions used, osmotic pressure of permeate solution can be greater than or less than the osmotic pressure of feed solution. Osmotic separations described in this invention may be achieved by pressure difference of process solutions (pressure driven), osmotic pressure difference (osmotically driven) or a combination of pressure and osmotic difference (pressure and osmotically driven) of process solutions across the two sides of the semi-permeable membrane. In pressure driven separations, pressure is applied on feed solution to effect separation. An example of pressure driven separation is desalination of seawater by reverse osmosis, wherein incoming saline feed solution is separated by RO membrane to produce a salt lean desalinated permeate solution with substantially reduced osmotic pressure and concentrated retentate solution with increased osmotic pressure. In osmotically driven separation, difference in osmotic pressures of process solutions on the two sides of semi-permeable membrane is used to effect separation. An example is forward osmosis desalination using electrolytic, thermolytic or switchable polarity draw solutions. Pressure assisted osmosis is an example of a combination of pressure driven and osmotically driven separations. Osmotic separation can be achieved using various categories of membranes irrespective of the size or nature of solutes the membrane is capable of rejecting as long as it alters the concentration(s) of solute(s) responsible for at least a portion of solution osmotic pressure in the permeated solution. For separations with process solution circulation on one side, this causes a change in osmotic pressure from feed to permeate and retentate solutions, while for separations with process solution circulation on both sides, this causes a change in osmotic pressure from feed to retentate and from draw to diluate draw solutions.
Non-osmotic separations correspond to separations wherein the composition of permeate solution that is transported across the semi-permeable membrane from the first side to the second side is such that its osmotic pressure is predominantly same as the osmotic pressure of corresponding feed solution supplied to the separation unit and from which the permeate solution originates. An example is separation of water with ions from milk such that ionic components are allowed to pass through the membrane while other components such as colloids and whey are rejected. Separation yields a permeate solution with nearly same ionic strength and osmotic pressure as that of feed solution. All osmotic and non-osmotic separations can be achieved using the systems and methods of this invention. Batch separation refers to separation wherein system level input solutions undergo separation to produce system level output solutions without mixing with system level solutions during separation. Semi-batch separation refers to those separations where system level solutions are mixed with process solution undergoing separations. A separation cycle refers to any separation process executed once.
Semi-permeable membranes have two sides with which process solutions are in fluidic communication.
The semi-permeable membrane 104 is housed in a separation unit. This separation unit facilitates transport of process solutions to and from the semi-permeable membrane and also facilitates fluidic communication between the process solution and the semi-permeable membrane. Two configurations of separation unit are possible. In the first configuration, process solution is circulated on one side of the semi-permeable membrane (e.g. reverse osmosis separation or non-osmotic separation).
Process solution associations with the separation unit 100 and the system XXXX are distinguished by prefixing these levels of association when referring them. System level process solutions refer to process solutions of the batch or semi-batch. This includes system level feed (XXXXF) and system level draw (XXXXDI) that represent the initial or input solutions of a batch separation, system level retentate (XXXXR), system level permeate (XXXXP) and system level diluate draw (XXXXDO) that represent the final or output solutions of a batch separation. Pass level process solutions refer to process solutions of individual passes. This includes pass level feed (100F) and pass level draw (100DI) that represent the initial or input solutions of a pass separation, pass level retentate (100R), pass level permeate (100P), and pass level diluate draw (100DO) that represent the final or output solutions of a pass separation. Flow of process solution through the separation unit may be referred as streams. First stream refers to the process solution that is in fluidic communication with a first side of the semi-permeable membrane. Second stream refers to the process solution that is in fluidic communication with a second side of the semi-permeable membrane. In many embodiments, process solution on feed side is used as first stream and process solution on draw side is used as second stream. The connections to separation unit 100, housing the semi-permeable membrane 104 are classified based on the connecting stream. First stream inlet 1.1 and first stream outlet 1.2 refer to inlet and outlet connections respectively of first stream with separation unit 100. Second stream inlet 2.1 and second stream outlet 2.2 refer to inlet and outlet connections respectively of second stream with separation unit 100. Fouling refers to the process of material deposition on membrane surface during separation. Process solutions and hydraulic fluids are contained in liquid containers with at least one chamber. The walls of these liquid containers form the outermost boundary surface that separates process solutions and hydraulic fluids inside the containers from the surroundings. In some embodiments, liquid containers may further be partitioned internally to form one or more chambers. Each chamber may be used as a reservoir for any fluid used in this invention. A reservoir is a chamber for holding, supplying and receiving process solutions and hydraulic fluids at required pressures. These pressures may be at or near system operating pressure for pressurized reservoirs and at or near ambient pressures for pressurized and unpressurized reservoirs. Boundary of a reservoir is defined by at least one of the boundary walls of the liquid container and the boundary walls of a chamber. Unpressurised reservoirs may be open to the surroundings and may have an open boundary on one side. A movable partition or a bladder may form the partitions inside liquid containers. These partitions are impervious to solution components and hydraulic fluids that may be present on either side of the partitions. These fluids are fluidically isolated from each other by the partition. In the preferred embodiments, the process operates in passes whereby an entire batch of process solution is transported across one side of a semi-permeable membrane and separation is performed on the batch of process solution in each pass. During a pass, process solution stored in a reservoir is transported across the membrane surface in the separation unit 100 where separation is performed as a result producing a process solution with different composition that is returned to another reservoir. The reservoir from which process solution is supplied to the separation unit is called the source reservoir and the reservoir where process solution is collected from the separation unit is called the sink reservoir. In a pass, plurality of reservoirs may be used as source reservoir(s), as sink reservoirs or for both types of reservoirs on a side. In some embodiments, two fluid regions are formed in a single physical reservoir when employing hydraulic fluids that is immiscible with process solution and in direct contact with it. System components collectively refers to all fluid handling components of the system. This includes all pumps, energy recovery devices, separation unit, membrane, conduits, reservoirs and valves. The valves (not shown in figures) are state of the art flow control devices widely used in the systems of the invention for control of flow paths of all fluids through system components.
In the methods described, separations are preferably performed in non-recirculation mode, wherein output solution of a pass is not mixed with input solution to that pass. This is achieved by using different source and sink reservoirs for pass level input and output solutions thereby keeping the solutions unmixed. In alternative recirculation mode of separation, output solution of a pass is mixed with input solution to that pass. This is achieved by using same reservoir(s) as source and sink reservoir(s) thereby mixing the solutions. Further the methods of the invention may combine both of the above processes as follows. Initially the system may be operated in non-recirculation mode while towards the end of the batch it may be operated in re-circulation mode. Such a combination is useful practically, because at the start of a batch difference between osmotic pressures of pass level input and output solutions could be high when pass recovery is high. Towards end of the batch, pass recovery is usually low and difference between osmotic pressures of input and output solutions is relatively lower. Such mixing of retentate and feed solutions when their difference in osmotic pressures is smaller leads to correspondingly smaller entropy generation, which may be acceptable for operational flexibility. Recovery of a separation process may be defined as the ratio of the quantity of permeate transported through 104 to the quantity of feed solution from which it originates. Recovery of a pass is the ratio of 100 P to 100 F corresponding to that pass. Recovery of a batch or semi-batch separation is the ratio of XXXX P to XXXX F corresponding to that separation.
The multiple pass batch separation with flow on a single side of semi-permeable membrane is illustrated in
The multiple pass batch separation with flow on both sides of a semi-permeable membrane is illustrated in
Although the batch separations illustrated in
Separations described in this invention operate on the principle of cascading wherein output process solutions of a pass or a batch or semi-batch separation is used as input process solutions to another pass or another batch or semi-batch separation. In linear method of cascading, process solution output from one side of membrane 104 is used as input process solution on the same side of the same or another membrane 104. In transverse method of cascading, process solution output from one side of membrane 104 is used as input process solution on the other side of the same or another membrane 104.
This concept of cascading process solutions can be extended to batches. Cascading of system level solutions for separations with process solution circulation on a single side of semi-permeable membrane is illustrated in
All liquid containers depicted in
Working systems of the invention integrating various system components are represented in
The invention may have variations in the method of operation different from those described below, while employing at least a part of the key features of the invention. These variations include a different method of cascading separations and different sequence of flow between reservoirs than described. Methods of separation described for the systems typically employ single source reservoir and single sink reservoir for each pass. The same systems and methods may use a plurality of reservoirs as source and/or sink reservoirs in a pass. The system may also be operated in semi-batch mode by addition of system level process solution (e.g. 1000-F) to the reservoirs. All batch separations described in this invention may be converted into semi-batch separations by addition of system level process solution(s) and mixing with process solution(s) undergoing separation in a batch.
The method of separation in both systems involves certain essential operations as follows. Towards the end of one pass and prior to the start of a next pass, a reservoir switchover sequence (
Further in the methods of separation in both systems 1000 and 1100, 100-P may either be removed as system level permeate solution XXXX-P or be collected in a feed side reservoir and used as 100-F to achieve further separation by transverse cascading method in the same batch until required system level permeate 1100-P is produced. Similarly 100-R may be removed as XXXX-R or collected in a reservoir and supplied as 100-F for a subsequent pass to achieve further separation by linear cascading method in the same batch until required system level retentate XXXX-R is produced. The subsequent pass may be the next pass or a non-consecutive pass. For instance, when 100-P is removed as XXXX-P without collection in a reservoir, 100-R collected in previous pass may be used as 100-F in next pass. Alternatively if 100P is collected in a reservoir and supplied as 100F in next pass, then 100R may be used in a subsequent pass.
Further depending on the ERD technology used in 1000 and 1100 (e.g. isobaric pressure exchanger) a high pressure pump 503-1 may optionally be used to pressurize that quantity of stream entering 501-3 which is in excess to the stream entering 501-1. This excess quantity is typically equal to the permeate solution removed in a pass, batch or semi-batch and in addition some lubrication or mixing flow experienced in 501. In some embodiments when hydraulic fluid 150 is used, a separate pressurizing unit may be used for 150 different from the unit used for 160. In addition a pressure reducing valve 530 may be used to depressurize process solution bypassing 501. These individual devices 501, 502 and 503-1 shown in
Table 1 depicts a general multi pass separation for a system with three reservoirs applicable to embodiments in
For general embodiments in figures,
In the following embodiments, different segments of hydraulic fluid have the following connections with reservoirs and purposes. Every reservoir containing hydraulic fluid is connected to 201 for distribution of hydraulic fluid 150 between reservoirs, 207 for receiving 150 at system operating pressure, 208 for receiving 150 at near ambient pressures and to 209 for addition and removal of 150 at near ambient pressures required by collection and exchange method. Every reservoir on first side containing process solution is connected to 202 for supplying 100F to 100, to 203 for receiving 100R from 100, 204 for receiving XXXXF at system operating pressure, 205 for receiving XXXXF at near ambient pressure and 206 for removal of XXXXR at near ambient pressures in collection and exchange method. Every reservoir on second side containing process solution for separation is connected to 212 for supplying 100DI, to 213 for supplying 100DO, and 215 for supplying XXXXDI
An exemplary separation process in non-recirculation method is depicted in Table 1 as explained earlier. For the system 2000 shown in
An exemplary separation process in non-recirculation method is depicted in Table 1 as explained earlier. For the system 2200 shown in
System 2200 may be operated by using process solution 160 as hydraulic fluid 150 in both chambers. This is explained in the following exemplary scenario. The two chambers 120-1 and 120-2 of liquid container 101-2 may be used as the source and sink reservoirs respectively for a pass. At the start of the pass, 120-1 contains process solution while 120-2 is empty. During separation at 100, 100 F is supplied from 120-1 and 100 R is collected at 120-2. In this configuration, the same piston pressurizes source reservoir 120-1 and sink reservoir 120-2. As a result volume compensation 1 is not required. To compensate for change in volume due to removal of 100P, piston 130 moves downward, to reduce combined volume of process solution in 120-1 and 120-2. The separation process may be converted into semi-batch by addition of system level feed 2200 F to process solution undergoing separation in the system with the use of high pressure pump 503-1.
Addition of 2200F and removal of system level retentate 2200R may be achieved in parallel to the operation of another batch or semi-batch by collection and exchange method as follows. 120-2 of 101-1 may contain 2200R of a previous batch and 120-1 of 101-1 shall contain hydraulic solution present at the end of previous batch. 101-2 and 101-3 may be in use in the current batch. 101-1 is first isolated from the system and then depressurized to atmospheric pressure. 2200 R is then removed at near ambient pressures from 120-2 of 101-1. Subsequently 2200 F is added at near ambient pressures to 120-2 of 101-1. This process is performed in parallel to operation of another batch, similar to parallel filling of liquid container 3 in Table 1. For direct exchange method, an energy recovery device 501 (shown in
When removing by direct exchange method, ERD 501 and booster pump 502 (shown for system 1100 in
When removing by direct exchange method in the last pass, ERD 501 (shown for system 1100 in
2500 R may be removed either by direct exchange method or by collection and exchange method. When removing directly in the last pass, ERD (shown in system 1100 in
When removing system level retentate 2500 R by collection and exchange method, 100 R produced in the last pass of a batch is collected in chambers 120-1 and 120-2 of one liquid container which is isolated from system 2500 after completion of last pass and depressurized. Subsequently external permeate solution at near ambient pressures is added to the permeate chamber 120-3 of same liquid container containing 100R of last pass in 120-1 and 120-2 thereby displacing 100R as 2500R of previous batch. Subsequently 2500 F for a new batch is added at near ambient pressures to the same 120-1 and 120-2 of the same liquid container. This displaces external permeate solution that was added to displace 2500 R and 2500P of previous batch while simultaneously filling 2500 F for subsequent batch.
Another preferred method of removing 2500 R from 120-1 and 120-2 of the liquid container containing the retentate 2500 R is by filling 2500 F in 120-1 and 120-2 at near ambient pressure via connection on one end, displacing 2500 R via connection on the other end and further displacing 2500 P from 120-3 of the same liquid container simultaneously. Bladders and their multiple connections in liquid container type
The liquid containers
For systems performing low pressure driven separation with process solution flow across the first side of 104 and for systems performing osmotically driven separation with process solution flow across the first and second sides of 104, these methods may be simplified as follows. System level feed XXXX F on feed side and system level draw XXXX DI on draw side of a subsequent batch may be filled in parallel to the operation of a batch in corresponding empty reservoir(s) at near ambient pressures. In direct exchange method, pass level retentate 100 R and pass level diluate draw 100 DO may be removed from first stream outlet 1.2 and second stream outlet 2.2 of separation unit 100 respectively. In the collection and exchange method 100 R and 100 DO may be collected in empty reservoirs on corresponding sides and subsequently replaced with XXXX F on feed side and XXXX DI on draw side in parallel to operation of another separation cycle.
For a separation system 100 liquid containers capable of holding liquid under the operating conditions may be used as reservoirs. The types of liquid containers that may be used are shown in
All pressurized liquid containers may also be operated without exerting pressure in unpressurized systems. All liquid containers 101 and all chambers 120 in them (for liquid containers with partition and bladders) are designed to permit filling them completely with hydraulic fluid 150 or process solution 160. Further the design is such that fluid in all liquid containers and all chambers in them may be emptied completely leaving minimal to no residual solution. This is an essential feature of the invention and especially important for minimizing entropy generation due to mixing of process solutions at different concentrations in the reservoir(s). For pressure driven separations, unpressurized and pressurized reservoirs in
Essential features of methods and systems in invention: For achieving batch and semi-batch separation certain key operations are essential. These include (a) Volume compensation (b) Regulation of driving force for separation (c) Recuperation of driving force (d) supplying and removing system level process solutions to achieve continuity between batches (e) Reservoir(s) switchover sequence.
Volume compensation techniques: Volume compensation refers to system adjustments corresponding to changes in volume of process solution in a reservoir due to removal or addition of process solution for performing separation at unit 100. Volume changes can be segregated to facilitate understanding. Volume changes can occur due to removal of pass level output solutions (retentate or diluate draw or permeate) from reservoir(s) and addition of pass level input solutions (feed or draw) to reservoir(s). The means by which system adjusts to these volume changes may be referred to as volume compensation 1. Volume changes can also occur due to permeate removal from first stream, permeate addition into second stream and due to changes in density of process solution during separation. The means by which system adjusts to these volume changes may be referred to as volume compensation 2. The means of volume compensations depends on the reservoir. Table 3 below summarizes the means of achieving volume compensation 1 and 2 for different types of reservoirs. In Table 3, reservoirs are grouped based on the outermost fluid boundary. This is outermost physical boundary of liquid containers that is contacted by the fluids inside. For single reservoir liquid containers, the total volume of fluid in reservoir defines this boundary. For liquid containers with multiple reservoirs, this boundary is defined by total volume enclosed by the outermost physical boundary contacted by the fluids inside. When a reservoir is operated in re-circulation mode or the source and sink reservoirs of a pass are contained in the same liquid container, the pass level retentate corresponding to the pass level feed is returned to the same reservoir or liquid container, volume compensation 1 is not required for the portion of pass level retentate returned to the liquid container.
Regulation of driving force: Regulation of driving force during separation is essential to realize potential gains in energy efficiency resulting from equipartitioning of driving force at the required performance. For pressure driven separations operating pressure may be applied by high pressure pumps either directly on process solution or on hydraulic fluids that in turn transmit the pressure to process solution. Alternatively, piston movement can be used to apply pressure directly on either process solution or on hydraulic fluids that in turn transmit the pressure to process solution. Yet another method is to apply pressure pneumatically on process solution, for example using compressed air supply. For osmotically driven separations, the difference between osmotic pressure of process solution on feed side and osmotic pressure of process solution on draw side of 104 is regulated in order to achieve efficient separation using the total available difference between the osmotic pressures of system level feed and draw solutions. This regulation may be achieved by a variety of means. This includes controlling the rate of transport of process solutions on the two sides of 104, varying the number of passes of the batch or semi-batch, use of appropriate flow arrangement, flow conditions and turbulence inducers.
Recuperation of driving force: For pressure driven separations energy recovery is required during operation, towards the start or end of a pass, a batch or semi-batch, to recover energy from process solution or hydraulic fluid exiting the pressurized region of the system that might otherwise be wasted. For pressure driven separations, pressure exchanger or energy recovery turbine or other ERDs may be used. When using unpressurized reservoirs, energy recovery during a separation cycle is performed between pass level retentate and pass level feed during every pass using ERDs. ERDs have operational in-efficiencies and capital costs associated with them. In certain system configurations energy recovery devices may be minimized or eliminated. When using pressurized reservoirs, energy is recovered between passes by collecting the retentate at the operating pressures. Pressurized reservoirs are capable of collecting and storing process solution from separation unit 100 at or near system operating pressures. The pressurized region extends to include the feed side reservoirs. Energy loss associated with circulation of pass level process solution through the system components is compensated by energy supplied by circulation pump 504 on feed side and 505 on draw side. For osmotically driven separations, osmotic energy available in pass level diluate draw solution is reused in a subsequent pass.
Supply of system level input and removal of system level output solutions: For all types of separations, system level output solutions are required to be removed and system level input solutions are required to be added between one batch or semi-batch and the next. This removal and addition is performed while achieving uninterrupted separation between separation cycles and minimizing energy loss due to depressurization of high pressure stream and pressurization of low pressure stream. For pressure driven separations operating at high pressures, system level retentate XXXXR may be removed by direct exchange method wherein energy is recovered from XXXXR and supplied to system level feed XXXXF. The retentate from last pass 100 R of a batch is XXXXR and it may be directly removed through ERD 501 in the pressurizing unit. Further for systems operating with unpressurized reservoirs, XXXXF corresponding to first pass of next batch is added to the source reservoir(s) of that pass at near ambient pressures prior to its transport through ERD for direct exchange of XXXXR. This addition may be done during operation of a batch as shown in Table 1. For systems operating with pressurized reservoirs, XXXXF corresponding to first pass of next batch is added through ERD 501 and pressurizing unit components during direct exchange of XXXXR in the last pass of previous batch.
System level output solutions may be removed by collection and discharge method. For pressurized reservoirs, system level retentate XXXXR is collected in reservoir(s) at system operating pressures. Subsequently all hydraulic connections between the reservoir(s) containing XXXXR and separation unit 100 are disconnected and the reservoir(s) is depressurized to ambient or near atmospheric pressures. Further removal of system level retentate XXXXR and filling of system level feed XXXXF occurs at ambient or near atmospheric pressures. This may be accomplished either by a sequential process or a simultaneous process. In the sequential process, XXXXR is removed first which is then followed by filling of XXXXF in the same reservoir. In the simultaneous process, XXXXF is filled in the same reservoir while XXXXR is simultaneously removed by displacement. XXXXF may be filled in opposite end to the end from where XXXXR is removed, filled in an adjoining reservoir or filled in another reservoir in fluidic communication with the reservoir containing XXXXR. Subsequently the system level feed solution XXXXF added to the reservoir is pressurized to bring it to required operating pressure. The change in volume with pressure for most of the liquids is practically negligible and for such incompressible fluids, the work done in pressurizing and the energy lost in depressurizing is negligible and do not affect overall process efficiency. Later all hydraulic connections of the reservoir containing system level feed) XXXXF with separation unit 100 is re-established.
In the direct exchange method the last pass would only have a source reservoir but not a sink reservoir. On contrary, in collection and exchange method, the last pass would have source and sink reservoir(s). Further in systems using pressurized reservoirs, the rate of filling of XXXX-F in direct exchange method will be higher compared to collection and exchange methods. This is because in direct filling entire quantity of XXXX-F has to be added in the last pass of previous batch while in collection and exchange methods XXXX-F can be added parallel.
The disclosed systems can be used to achieve batch separation using pressure driven and osmotically driven separations. Some examples of these separation systems is given in Table 4 below,
Switchover sequence is followed between every consecutive passes in cascading methods to achieve continuous separation between passes, batches and semi-batches. It enables precise replacement of process solution in various system components from the process solution corresponding to a previous pass with the process solution of next pass with minimal or no mixing of process solutions at different concentrations. The switchover sequence is designed to replace the entire hold up volume of process solution corresponding to a previous pass in the system components with process solutions of the upcoming pass. Importantly during this switchover sequence, separation continues in the separation unit 100 un-interrupted.
Osmotically driven separations are accomplished by exploiting difference in osmotic pressure of process solutions on two side of membrane 104.
For co-current concentration change osmotic separations, process as shown in Table 1 may be performed and concentrations of final system level process solutions approach each other. For an exemplary scenario, an aqueous salt solution of sodium chloride is considered as process solution on both sides. Process solution concentration is expressed in grams of salt per liter (gpl) of solution.
For continuous batch and semi-batch osmotically driven separations performed with counter current changes in concentration of process solutions on feed side and draw side, intermediate pass level process solutions are required on one side of the separation system. These intermediate pass level process solutions must be available prior to initiating continuous batch and semi-batch separations. The intermediate pass level process solutions may be generated from system level process solutions in a preparatory sequence. The side of the system that contains pre-synthesized intermediate pass level process solutions may be referred to as stocked side. The other side of the system may be referred as the un-stocked side.
Preparatory sequence is initiated using system level feed and system level draw solutions to prepare and stock intermediate pass level process solutions on the stocked side for use in batch and semi-batch separations. For the stocked side, system level solution is supplied corresponding to each intermediate pass level solution generated. System level process solution on other side is used correspondingly to prepare intermediate stock solutions. Any intermediate process solution on the un-stocked side may be discarded back to the source of system level feed solution. This preparatory sequence is described for an exemplary process solution for a separation with an exemplary number of passes. The methods can be used for any other process solution for separation with any number of passes.
An exemplary preparation cycle is schematically illustrated in
For preparing intermediate pass level process solutions on draw side, steps 6.2 and 7.2 may be followed. In step 6.2, process solution at 160 gpl on draw side and process solution at 100 gpl on feed side are supplied as pass level draw solution to second side of 104 and pass level feed solution to first side of 104 respectively to generate pass level diluate draw solution at 140 gpl and pass level retentate solution at 120 gpl respectively. Simultaneously system level feed solution at 80 gpl is supplied to at least one feed side reservoir. In step 7.2, process solution at 120 gpl on draw side and process solution at 80 gpl on feed side are supplied as pass level draw solution to second side of 104 and pass level feed solution to first side of 104 respectively to generate pass level diluate draw solution at 100 gpl that is removed from the system as system level diluate draw solution and pass level retentate solution at 100 gpl. Further the process solution at 140 gpl on draw side is removed from the system and may be sent to the source of system level draw solution. At this stage the system is considered ready with intermediate pass level feed solutions stocked in feed side reservoirs to begin continuous batch and semi-batch separations. Stocked process solutions at concentrations of 140 gpl, 120 gpl and 100 gpl are used as pass level feed solutions 100F in pass 1, 2 and 3 respectively of a four pass continuous batch and semi-batch separations.
For counter current concentration change, the progression of passes will follow the change in concentration of process solution on the un-stocked side. The concentrations of final system level process solutions used on each side of 104 approach the concentrations of initial system level process solutions on the other side. This may be explained further considering an exemplary four pass counter-current concentration change osmotic separation in
When draw side is the stocked side progression of passes follow changes in the concentration of process solutions on feed side (the un-stocked side) with progress of process time as shown in
When feed side is the stocked side progression of passes follow changes in the concentration of process solutions on draw side (the un-stocked side) with progress of process time is as shown in
When shutting down the system, the stocked intermediate pass level solutions can be stored in the corresponding reservoirs for use in further batches upon system start up. This way preparatory sequence may be eliminated between consecutive systems shut down and start up.
In the above methods in
Application of the invention is exemplified in an industrial scale system similar to embodiment shown in
A state of the art continuous reverse osmosis system is used for comparison. It consists of two stages in series with an inter-stage booster pump with the same processing capacity of 7.5 m3/hr of system level feed and a total of 16 elements (10 in stage 1 and 6 in stage 2). Both systems are operated with same flux of 9 LMH. The continuous system recovers 40% in stage 1 and 40% in stage 2. Both systems achieve the same total permeate recovery of 64%. The total dissolved solids (TDS) reduction of greater than 95% from 100F to 100P indicates substantial removal of sodium chloride responsible for osmotic pressure of process solution. Work done for a pass level separation is calculated based on applied pressure (PF) on 100F for a pass, quantity of 100R and 100P, efficiencies of high pressure pump 503-1 η503-1, energy recovery device 501 η501 and booster pump 502 η502 as follows,
Work done for continuous separation is calculated based on feed quantity to stage 1 (i.e. system level feed VF1), feed quantity to stage 2 (i.e. system level feed VF2), applied pressure in stage 1 (PF1), applied pressure in stage 2 (PF2), efficiencies of high pressure pump 503-1 and inter-stage booster pump 502 as follows,
Efficiency of ERD 501 is taken as 96%, that is typical of isobaric pressure exchangers used in the system of the invention while efficiencies of all high pressure pump 503-1 and booster pump 502 are taken as 75%. Efficiency of ERD corresponds to its energy recovery process while that of 503-1 and 502 corresponds to efficiency of conversion from electrical power input to the motor to work performed by the pumps.
As seen in Table 6 above, total specific work done per unit of permeate recovered by the method of the invention is 2.3 kwh/m3 while for a 2 stage continuous separation is 3.5 kWh/m3. An energy savings of 35% is achievable by a 4 pass batch separation over a 2 stage continuous separation. Both systems can be optimized to achieve higher efficiencies. In particular the efficiency of continuous separation can be improved by increasing the number of stages at the cost of increased investment. However even when the separation is achieved using 4 stage continuous separation, the specific energy decreases to about 3.34 kWh/m3 which is still 32% higher than specific energy consumption for the method and system of the invention. This difference is attributable to high efficiency of 501 compared to 503-1 the components of pressurizing units responsible for major work done in the system of the invention and a continuous separation system respectively.
Further Table 6 indicates the concentrations of 100R of a pass and 100F of next pass. It can be seen that the difference in TDS due to mixing in switchover sequence in less than 5% in all passes. Thus continuous separation between passes is accomplished with minimal mixing of process solutions corresponding to different passes.
A standard dead end stirred cell set-up is used to hold the membrane and the feed solution under pressurized conditions. Feed solutions used correspond to untreated industrial washing cycles effluents from textile production and weak black liquor effluent resulting from pulp production from hard wood and bagasse. The feed solution is contained in a closed cylindrical compartment and pneumatically connected to a source of compressed nitrogen gas. Pressure was applied to feed solution using compressed nitrogen gas. Turbulence was induced near the membrane on feed side using magnetic stirrer from IKA to simulate turbulent flow conditions on the feed side in order to limit feed side concentration polarization near the membrane. Applied pressure on feed solution varied from 1 bar to 70 bar. The membrane is placed on a sintered porous disc which facilitates in collection of permeate solution. Commercially available seawater reverse osmosis membrane from Dow is used as the semi-permeable membrane. Geometric membrane area in hydraulic contact with feed side solution is approximately 14.5 cm2. Flux and recovery were calculated from change in mass of permeate solution measured. Parameters of feed solutions used are shown in Table 7 below. It may be observed that the levels of hardness, alkalinity and organic pollutants exceed acceptable levels by RO membrane suppliers for continuous separation. 10 separation batches with the same system level feed solutions were performed. Table 8 compares the performance between batch 1 and batch 10 without any cleaning cycles performed in between. Cleaning cycles are typically performed to maintain designed performance in membrane separation systems. Flux and applied pressures during initial and final part of batch separations may be used to infer change in performance. It is evident from Table 8 that there is marginal decline (<10%) in performance of the membrane between the two batches. This demonstrates the fouling tolerance of batch separations as per the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201841042518 | Dec 2018 | IN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IN2019/050912 | 12/12/2019 | WO | 00 |
