Patent Application
20110315257
Embodiments of the present invention relate to an energy recovery system. More particularly, the embodiments of the present invention relate to a valve system for the energy recovery system.
An energy recovery system is a device that utilizes a fluid stream at a higher pressure to pressurize another fluid at a lower pressure. Energy recovery systems are generally used in desalination plants to pressurize a feed stream by using high pressure concentrate.
An energy recovery system may include a pressure exchanger tube and a piston reciprocating inside the pressure exchanger tube. Further, a valve system may control the flow of feed water into the pressure exchanger tube and the concentrate out of the pressure exchanger tube. One form of the energy recovery system may include two or more pressure exchanger tubes. Various valve systems are known in the art, for example, rotary valve systems and linear valve systems.
Valve systems are generally connected to the two pressure exchanger tubes and synchronized with the movement of the two pistons. Such valve systems are usually complicated, heavy, expensive, and more susceptible to failure. Moreover, independent operation of the pressure exchanger tubes may not be possible.
During operation, the valve systems are subjected to various hydraulic loads, for example, radial loads and axial loads. Some of these hydraulic loads may be unbalanced and may oppose an applied actuating load. Consequently, higher actuation energy may be necessary to operate the valve system. This may increase the cost of actuating the valve system and may also reduce the efficiency of the energy recovery system. Also, unbalanced loads may reduce the overall life of the sealing system.
Further, known pressure exchanger tubes and valve systems may be actuated by various means: electromagnetic, hydraulic, pneumatic, and the like. In the case of hydraulic or pneumatic means, one or more shafts may have to penetrate into the pressure exchanger tubes and the valve systems through separate sealing system. This may increase the cost and complexity of the energy recovery system. The sealing system themselves may be vulnerable to leakage.
Therefore, there is a need for a valve system for pressure exchange tubes of an energy recovery system, which overcomes these, and other related problems.
The present invention provides a valve system for pressure exchanger tubes of an energy recovery system that overcomes the aforementioned drawbacks. The valve system enables appropriate actuation of the high-pressure ports and the low-pressure ports to allow pressure exchange.
According to an aspect of the present invention, the valve system includes a valve housing, a flow distributor, a hollow spool and a sealing system. The valve housing may comprise a set of high-pressure ports and a set of low-pressure ports. The flow distributor allows the flow to and from the set of high-pressure ports and low-pressure ports within the valve housing. The hollow spool may be configured to reciprocate axially in a radial clearance between the valve housing and the flow distributor. The hollow spool may connect the pressure exchanger tube in fluid communication with the high-pressure ports or the low-pressure ports. The sealing system may be configured to provide substantial hydraulic balance to the hollow spool. Due to the axial hydraulic balance, lower actuation force may be required for controlling the movement of the hollow spool. Accordingly, the low actuation force may permit the use of an externally driven hollow spool which overcomes previous challenges with the actuators that penetrate the pressure exchanger tubes or the valve body.
These and other advantages and features will be more readily understood from the following detailed description of the embodiments of the invention that is provided in connection with the accompanying drawings.
Various embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It will be apparent, however, that these embodiments may be practiced without some or all of these specific details. In other instances, well known process steps or elements have not been described in detail in order to not to unnecessarily obscure the description of the invention. The following example embodiments and their aspects are described and illustrated in conjunction with apparatuses, methods, and systems which are meant to be illustrative examples, not limiting in scope.
The invention provides a valve system for pressure exchanger tubes of an energy recovery system. The energy recovery system is a device that utilizes a waste stream of a sub-system to minimize the input of energy to the whole system by exchange of energy from one sub-system to another. In desalination systems, the energy recovery system may be utilized to transfer the pressure between the incoming and outgoing flow of a reverse osmosis system. More specifically, pressure may be extracted from the high pressure concentrate solution and transferred to the low pressure feed water resulting in improved desalination system energy efficiency. Thus, cost of production of portable water may be reduced by employing the energy recovery system.
In an exemplary embodiment of the present invention, the energy recovery system 100 may be employed in a desalination plant. In a desalination system, the energy recovery system 100 may be utilized to achieve pressure exchange between discharge concentrate solution (at relatively high pressure) and feed water (at relatively low pressure). Referring to
Initially, the piston 106 may be at the extreme left position inside the pressure exchanger tube 102 and all the ports of the valves 110 and 114 may be closed. In this position, the pressure exchanger tube 102 is filled with the concentrate solution. The low-pressure ports of the valves 110 and 114 may then be opened. Due to opening of the low-pressure ports of the valve 110, the feed water (at relatively low pressure) may be drawn into the pressure exchanger tube 102. The feed water pushes the piston 106 from the left side and drains out the concentrate solution. The piston 106 thus moves to the extreme right and the pressure exchanger tube 102 is now filled with the feed water. When the piston 106 reaches the extreme right position, the low-pressure ports of the valves 110 and 114 are closed. This completes a first half of the cycle of pressure exchange involving the movement of the piston 106 from the extreme left position to the extreme right position.
In a second half of the cycle of pressure exchange, the high-pressure ports of the valve 110 may be opened. The concentrate solution may push the piston 106 towards left with a high pressure. As the feed water is incompressible, the pressure of the feed water in the pressure exchanger tube 102 may increase to the pressure of the concentrate solution. The high-pressure ports of the valve 114 may then be opened. An extra boost may be provided to the piston 106 by an electromagnetic force. The concentrate solution (at relatively high pressure) along with the extra boost may drive the feed water out of the high-pressure ports of the valve 114 resulting in movement of the piston 106 to the extreme left position. The movement of the piston 106 from the extreme right position to the extreme left position defines the second half of the cycle of pressure exchange. Pressure is thus exchanged from the high pressure concentrate solution to the low pressure feed water. Further, these steps may be repeated to achieve pressure exchange in every cycle. The pressure exchanger tube 104 may be operated in the similar manner as the pressure exchanger tube 102.
For maintaining continuous flow of the feed water out of the energy recovery system 100, the pistons 106 and 108 of the pressure exchanger tubes 102 and 104 respectively may be operationally synchronized to move with a phase difference of about 180 degrees. Specifically, the piston 106 and the piston 108 may be actuated with a phase difference of 180 degrees.
In an embodiment of the present invention, the valve system 200 may include a valve actuator 208 for controlling the opening/closing of the valve. Further, a sensor may be used to sense the position of the piston 106. The valve actuator 208 may control the opening/closing of the valve depending on the sensed position of the piston 106. Specifically, timing of the piston 106 reaching its extreme position (at either end of the pressure exchanger tube 102) and the opening/closing of the valve may be controlled by the valve actuator 208. Referring to
Although
As shown in
Referring to
The valve actuator 208 may control the movement of the hollow spool 302. In an embodiment of the present invention, the valve actuator 208 includes an actuator housing 316, an actuator piston 318 and an actuator shaft 320. The actuator housing 316 may be tubular in shape and is connected to the valve housing 304. Actuator coils 322 may be wound around the actuator housing 316. Further, the actuator piston 318 may reciprocate within the actuator housing 316. The actuator piston 318 may be hollow in shape. Further, the actuator shaft 320 may connect the actuator piston 318 to the hollow spool 302 for controlling the movement of the hollow spool 302. The hollow spool 302 may have a connecting member at one end for receiving the actuator shaft 320. Further, the flow distributor 310 may have an opening to allow the connecting member of the hollow spool 302 to reciprocate between various positions (between the first axial position and the second axial position) of the hollow spool 302. An actuating means may be used to control the movement of the actuator piston 318. The actuating means may include, for example, electromagnetic means, pneumatic means, hydraulic means, and the like. Those skilled in the art will appreciate that other means of actuation could be limited and the aforementioned examples are a non-limiting set.
The actuating means may use the position of the piston sliding within the pressure exchanger tube to control the opening/closing of the valve system 200. A sensor may be used to obtain the position of the piston. The sensed position may be used to control the opening/closing of the high-pressure ports 306 and the low-pressure ports 308. The sensed position of the piston may be used by the actuating means to control the movement of the actuator piston 318 such that the timing of the piston reaching its extreme position at the either end of the pressure exchanger tube and the opening/closing of the high-pressure ports 306 and the low-pressure ports 308 may be synchronized.
Further, the valve system 200 may include a sealing system provided inside the valve housing 304. In an embodiment of the present invention, the sealing system may include axial seals 326 at both the ends of the flow distributor 310 as shown in the
In an embodiment of the present invention, the hollow spool 302 may have radial openings near the axial ends, which may provide substantial hydraulic balance to the hollow spool 302 when the hollow spool 302 is in the first axial position or the second axial position. A leakage path may be provided between the high-pressure ports 306 and the low-pressure ports 308. The leakage path may allow mixing of the high pressure fluid stream and the low pressure fluid stream to provide hydraulic balance to the hollow spool 302. Presence of the leakage path may provide hydraulic balance to the hollow spool 302 in substantially all positions of the hollow spool 302. Although fluid communication is allowed to balance the forces on each end of the hollow spool 302, leakage in and out of the high-pressure ports 306 and the low-pressure ports 308 may be minimized through the sealing system. The radial seals 328 may minimize the fluid flow between set of high-pressure ports 306 and set of low-pressure ports 308 when the hollow spool 302 is at the first axial position or the second axial position.
In various embodiments of the present invention, the valve system 200 has been explained in conjunction with the energy recovery system 100, with pistons 106 and 108 configured to boost the pressure of the feed water. However, those of ordinary skilled in the art may appreciate that the valve system 200 may also be utilized in any reverse osmosis systems, for example, reverse osmosis systems having energy recovery systems with passive pressure exchanger tubes and utilizing booster pumps.
The present invention has been described in terms of several embodiments solely for the purpose of illustration. Persons skilled in the art will recognize from this description that the invention is not limited to the embodiments described, but may be practiced with modifications and alterations limited only by the spirit and scope of the appended claims.
