This invention relates to water purification methods using a batch crystallization process, where a fraction of water is frozen then separated from the non-frozen fraction and then thawed.
Water purification describes any process where dissolved impurities are removed from the input water. There is no quantification of this process other than the output “purified” water containing fewer dissolved and suspended impurities than the input “unpurified” water. Other examples of water treatments include water softening—the removal of calcium and magnesium cations from water, and water sterilization—the removal or inactivation of microorganisms such as pathogenic bacteria from water.
Water purification by freezing has been shown to significantly reduce concentrations of chemical and biological species. (See US EPA report “Traces of Heavy Metals in Water Removal Processes and Monitoring” 1973 EPA-902/9-74-001; Conlon 1992 http://www.wmconlon.com/wp-content/uploads/papers/IATC92.pdf accessed 26/09/13 09:45.) If a fraction of a volume of water is frozen, the increased solubility of dissolved species in the liquid phase means that impurities are concentrated in the non-frozen component. By separating the frozen and non-frozen components and then thawing the ice, the resultant water is of higher purity than the input water. Repeating this freeze-thaw process increases the percentage removal of impurities. The energy cost of multiple freeze-thaw processes can be prohibitively high for a domestic purification system, so methods of recycling the sensible and latent heat removed from the water during the freeze purification process have been developed by others to improve the efficiency of the process:
Chang (U.S. Pat. No. 4,799,945 issued Jan. 24, 1989) describes a dual chamber freezing system for water purification. In such systems the two chambers are out-of-phase with one another; when one is freezing water the other is thawing ice. The purported advantages of such devices over a continuous freezing process are the decreased engineering complexity and improved energy efficiency, making it more suitable for domestic or small scale use. However, the energy consumption of a device of this type is still not competitive with other water purification techniques.
Conlon (U.S. Pat. No. 5,438,843 issued Aug. 8, 1995) discloses an advanced batch crystallization system, whereby the energy efficiency is increased by using a cascading two stage refrigeration system and rejecting heat to the environment via an auxiliary cooling water circuit. Energy to thaw the purified ice is provided by recirculating purified water through the primary refrigerant condenser and one batch crystallization chamber whilst the evaporating refrigerant froze water in the alternate batch crystallization chamber. A design of this type also decreases the engineering complexity of the system by using fewer valves to control the flow of refrigerant to each freezing chamber.
In both the Chang and Conlon disclosures, the water is frozen by direct heat exchange with the refrigerant whose direction of flow is reversed to alternate the function of each chamber (freezing to thawing). Crucially, both inventions are limited in terms of energy efficiency by the use of cascading two-stage refrigeration systems to enable heat to be rejected to the environment at high temperature through the use of an auxiliary cooling water circuit.
In other methods to improve the energy efficiency of the freeze purification process, freeze purification has been combined with other cooling demands such as a domestic fridge/freezer (see Ashley U.S. Pat. No. 3,338,065 issued Aug. 29, 1967; Ruff U.S. Pat. No. 5,207,761 issued May 4, 1993). U.S. Pat. No. 3,338,065 describes an elongated water tank with a cooling bottom surface where ice is formed and floats to the top of the tank. The water tank is not stirred to enable the ice to float to the top of the tank, and therefore the purification process is considered static. The ice and water are separated and the ice subsequently melted to produce purified water. Aspects of this system also include combining with a domestic fridge/freezer by coupling the required evaporators in series (i.e. freezing performed by direct heat exchange with the refrigerant); heat from the refrigerator would be used to defrost the ice. Such a process has a number of potential drawbacks such as a low level of impurity removal due to the static freezing purification method and low energy efficiency of the process.
U.S. Pat. No. 5,207,761 describes a refrigerator and water purifier with a common evaporator. A device of this type uses an ice forming plate cooled by direct contact with the refrigerant for the purpose of freezing water to purify it. The process is dynamic as the water is flowed over the ice forming plate; this enhances the purification process (see R. A. Baker, Water Research, 1967, 1, 61-77). When an appropriate amount of ice has been formed on the plate, the surface is heated to release the ice into a bin where it is either stored as ice cubes or to a storage tank where it is thawed. The surface can either be heated directly with hot gas as part of the refrigerant cycle or using an electric heater. On the other side of the ice forming plate is a storage space which is cooled by the use of a fan to aid thermal advection. Such a system requires a complex series of valves to ensure that the required volume of purified ice/water is produced in addition to maintaining a stable temperature in the storage space. Furthermore, the energy efficiency is limited by the method of cooling the storage space.
Other conventional systems are based on the use of two four-way reversing valves to permit the reversing of the direction of refrigerant flow to the heat exchangers. For example, Komori et al (WO 2012147366 published Nov. 1, 2012) and Heys et al (EP 1471316 published Oct. 27, 2004) describe reversible heat pumps for air conditioning systems using two four-way valves. In both systems a reversible heat pump uses two four-way switching valves to enable the suction and discharge refrigerant flows to be switched between the “inside” and “outside” heat exchangers whilst the flow through the expansion means is maintained as unidirectional. Neither of these disclosures describes the use of unidirectional superheaters and desuperheaters as part of the reversible circuit, and so they are not capable of maximizing the specific cooling capacity, through the use of a superheater, nor removing superheat from the refrigerant with a minimal supply of cooling liquid.
Other circuits which use desuperheaters include Yaeger et al. (U.S. Pat. No. 4,316,367 issued on Feb. 23, 1982) and Holm et al. (EP 2368081 published on Sep. 28, 2011). Both of the aforementioned systems use a desuperheater to transfer refrigerant superheat to a low flow of water through a contraflow heat exchanger. These systems offer higher outlet water temperatures than can be achieved with a condenser, but their application is clearly described as being for a hot water or heating system, not for heat rejection to assist a cooling circuit. Furthermore these systems lack any means for the condenser and evaporator to be reversed whilst the function of the desuperheater remains continuous.
Therefore, none of the described conventional systems provides for a system or device which purifies water via an energy efficient process based on at least one freeze/thaw cycle, using multiple out-of-phase batch crystallisation chambers for energy recovery, wherein excess heat in the refrigerant is transferred to waste water through a contraflow desuperheater without requiring an auxiliary cooling circuit.
The object of this invention is to provide an economical method of water purification by a batch crystallization method. No conventional system minimizes energy and water consumption in a way that provides a batch crystallization method that is comparable to other water purification techniques such as reverse osmosis.
Described is a system which balances energy and water demand by recycling sensible and latent heat between the freezing and thawing processes of the purification and transferring the waste heat from the system to a mixed stream of supply and waste-water through a contraflow desuperheater. The desuperheater acts to reduce the condensing pressure thereby reducing specific electrical load on the compressor. This process is economical by using out-of-phase batch crystallization processes with internal heat recovery, to reduce the net cost of operation. Specifically, electricity consumption is reduced by dumping waste heat to cold wastewater from the purification process through a refrigerant desuperheater, thus eliminating the need for an auxiliary heat sink.
Exemplary embodiments of the invention include the following five components:
The use of two four-way switching valves to permits the reversing of the direction of refrigerant flow to the batch crystallization chambers; i.e. the chambers can switch between freezing and thawing modes without affecting the unidirectional flow of refrigerant required by components such as the superheater and desuperheater.
The use of a desuperheater permits the removal of heat from the circuit with a minimal pre-cooled supply of fluid (i.e. the waste-water from the purification process) by contraflow heat exchange with the refrigerant.
In accordance with the above features, and aspect of the invention is a water purifier. In exemplary embodiments, the water purifier includes a first crystallization chamber and a second crystallization chamber that each receives a supply of input water; wherein each of the first and second crystallization chambers is a freeze/thaw chamber in which water is alternately frozen and thawed. A refrigerant circuit alternately supplies cold refrigerant to freeze the input water in one of the crystallization chambers, and supplies heated refrigerant to the other of the crystallization chambers to thaw the input water. The first and second crystallization chambers operate concurrently and out-of-phase whereby heat recovered from freezing in one of the crystallization chambers is transferred by the refrigerant circuit for use in thawing in the other of the crystallization chambers. The refrigerant circuit includes a desuperheater that at least partially condenses heated refrigerant such that waste heat of compression generated by the desuperheater is rejected into wastewater via contraflow heat exchange with the heated refrigerant.
Another aspect of the invention is a method of purifying water. In exemplary embodiments, the method of purifying water includes the steps of:
supplying input water to each of a first crystallization chamber and a second crystallization chamber; wherein each of the first and second crystallization chambers is a freeze/thaw chamber in which water is alternately frozen and thawed; and circulating a refrigerant through a refrigerant circuit to alternately supply cold refrigerant to freeze the input water in one of the crystallization chambers, and supply heated refrigerant to the other of the crystallization chambers to thaw the input water. The first and second crystallization chambers are operated concurrently and out-of-phase whereby heat recovered from freezing in one of the crystallization chambers is transferred by the refrigerant circuit for use in thawing in the other of the crystallization chambers. The refrigerant circuit includes a desuperheater that at least partially condenses heated refrigerant such that waste heat of compression generated by the desuperheater is rejected into wastewater via contraflow heat exchange with the heated refrigerant.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
In the annexed drawings, like references indicate like parts or features:
a is a schematic diagram of a further embodiment depicting a water purifier based on multiple out-of-phase batch crystallization chambers with two four-way switching valves and a unidirectional desuperheater and a secondary cooling demand with thermostatic regulation means.
b shows the system of
A schematic diagram of an exemplary embodiment is shown in
The order of the components as described above is efficient in terms of consumption of energy and supply water; however other embodiments may have these components in a different position. The embodiment of
As described above, the crystallization chambers may contain multiple compartments to enable the use of sequential freeze-thaw processes to improve the efficacy of impurity removal. In another embodiment of the invention, the user may override this procedure to demand a single freeze-thaw cycle with lower impurity removal but lower energy and water consumption.
In another embodiment of the invention, a supply of the input water is fed to the waste water reservoir, increasing the outgoing water flow rate and thereby reducing the condensing temperature of the refrigerant.
In another embodiment of the invention, a fixed speed compressor is used with a varying duty cycle dependent on the cooling demand and the user-defined volume of purified water.
In another embodiment of the invention, shown in
b shows a modification of the embodiment of
In a further embodiment, shown in
In another embodiment of the invention, shown in
In another embodiment of the invention, shown in
In another embodiment of the invention, shown in
In another embodiment of the invention, shown in
In accordance with the above description, an aspect of the invention is a water purifier. In exemplary embodiments, the water purifier includes a first crystallization chamber and a second crystallization chamber that each receives a supply of input water; wherein each of the first and second crystallization chambers is a freeze/thaw chamber in which water is alternately frozen and thawed, and a refrigerant circuit that alternately supplies cold refrigerant to freeze the input water in one of the crystallization chambers, and supplies heated refrigerant to the other of the crystallization chambers to thaw the input water. The first and second crystallization chambers operate concurrently and out-of-phase whereby heat recovered from freezing in one of the crystallization chambers is transferred by the refrigerant circuit for use in thawing in the other of the crystallization chambers. The refrigerant circuit includes a desuperheater that sensibly cools and at least partially condenses heated refrigerant such that the waste heat of compression is rejected into wastewater via contraflow heat exchange with the heated refrigerant.
In an exemplary embodiment of the water purifier, the refrigerant circuit includes at least two valves that are switched to alternate the direction of refrigerant flow through the first and second crystallization chambers to alternate states of the crystallization chambers between freezing and thawing while maintaining unidirectional refrigerant flow through the desuperheater.
In an exemplary embodiment of the water purifier, the valves are electromechanical four-way valves.
In an exemplary embodiment of the water purifier, the refrigerant circuit further includes a heat exchanger in thermal contact with a water supply that provides the input water, wherein the heat exchanger receives heated refrigerant after freezing input water in one of the crystallization chambers, and acts as a superheater whereby the refrigerant removes heat from the water supply to pre-cool the input water.
In an exemplary embodiment of the water purifier, the refrigerant circuit further includes a compression means that receives and compresses the superheated refrigerant from the heat exchanger.
In an exemplary embodiment of the water purifier, the desuperheater receives the compressed refrigerant from the compression means and at least partially condenses the refrigerant.
In an exemplary embodiment of the water purifier, the refrigerant circuit further includes a wastewater reservoir that supplies chilled wastewater to the desuperheater to at least partially condense the refrigerant.
In an exemplary embodiment of the water purifier, excess supply water drains from at least one of the crystallization chambers into the wastewater reservoir to provide the wastewater.
In an exemplary embodiment of the water purifier, a portion of water from the input water supply is part of the wastewater received by the wastewater reservoir.
In an exemplary embodiment of the water purifier, the water purifier further includes a second heat exchanger in series with the compressor, wherein the second heat exchanger performs an auxiliary cooling function.
In an exemplary embodiment of the water purifier, the first and second crystallization chambers each comprises a primary crystallization chamber and a secondary crystallization chamber.
In an exemplary embodiment of the water purifier, the water purifier further includes a pure water reservoir for collecting thawed water from the crystallization chambers.
In an exemplary embodiment of the water purifier, the water purifier further includes a float valve for isolating the supply of input water from a mains water supply, thereby cutting off the input water supply to the first and second crystallization chambers.
In an exemplary embodiment of the water purifier, the refrigerant is one of a pure refrigerant, an azeotropic refrigerant, or a zeotropic blend of refrigerants.
In an exemplary embodiment of the water purifier, the refrigerant circuit includes a vapor compression circuit with a compression means and a mechanical expansion structure.
Another aspect of the invention is a method of purifying water. In exemplary embodiments, the method of purifying water includes the steps of supplying input water to each of a first crystallization chamber and a second crystallization chamber; wherein each of the first and second crystallization chambers is a freeze/thaw chamber in which water is alternately frozen and thawed, and circulating a refrigerant through a refrigerant circuit to alternately supply cold refrigerant to freeze the input water in one of the crystallization chambers, and supply heated refrigerant to the other of the crystallization chambers to thaw the input water. The first and second crystallization chambers are operated concurrently and out-of-phase whereby heat recovered from freezing in one of the crystallization chambers is transferred by the refrigerant circuit for use in thawing in the other of the crystallization chambers. The refrigerant circuit comprises a desuperheater that sensibly cools and at least partially condenses heated refrigerant such that the waste heat of compression is rejected into wastewater via contraflow heat exchange with the heated refrigerant.
In an exemplary embodiment of the method of water purifier, the method further includes providing a heat exchanger in thermal contact with a water supply that provides the input water, wherein the heat exchanger receives heated refrigerant after freezing input water in one of the crystallization chambers, and acts as a superheater whereby the refrigerant removes heat from the water supply to pre-cool the input water.
In an exemplary embodiment of the method of water purifier, the method further includes compressing the superheated refrigerant from the heat exchanger.
In an exemplary embodiment of the method of water purifier, the desuperheater receives the compressed refrigerant to at least partially condense the refrigerant.
In an exemplary embodiment of the method of water purifier, the method further includes collecting the thawed water from the crystallization chambers into a pure water reservoir.
Although the invention has been shown and described with respect to a certain embodiment or embodiments, equivalent alterations and modifications may occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.
The invention may be utilized in the manufacture of energy efficient domestic water purifying units based on a batch crystallization purification process. Such units would provide water purification and possibly additional cooling demand applications such as a refrigerator or air conditioning unit.