WO2016053356A1

WO2016053356A1 - Energy recovery valves for integrated pumping energy recovery systems

Info

Publication number: WO2016053356A1
Application number: PCT/US2014/059201
Authority: WO
Inventors: Shyam Sivaramakrishnan; Matthew David D'artenay; Michael Connor
Original assignee: General Electric Company
Priority date: 2014-10-03
Filing date: 2014-10-03
Publication date: 2016-04-07

Abstract

A self-piloted energy recovery valve comprises an inlet chamber (806) and an outlet chamber (808), with one of the inlet and outlet chambers in fluid communication with a working fluid chamber of a cylinder pumping an operating fluid, and the other of the inlet and outlet chambers in fluid communication with to one of a working fluid supply line and a working fluid discharge line. A valve piston (816) is moveable into and out of engagement with a valve seat (818) to block and unblock a flow path from the inlet chamber to the outlet chamber. A biasing mechanism (820) is configured to provide a biasing force to urge the valve piston into or out of engagement with the valve seat. A pilot chamber (803) is in fluid communication with an operating fluid chamber of the cylinder. A pilot piston (812) is operatively coupled to the valve piston and moveable to expand and contract the pilot chamber such that expansion of the pilot chamber moves the valve piston in an opposite direction to the biasing force to unblock or block the flow path.

Description

ENERGY RECOVERY VALVES FOR INTEGRATED PUMPING ENERGY RECOVERY

SYSTEMS

FIELD

[0001] This specification relates to pumping systems with energy recovery.

BACKGROUND

[0002] To desalinate seawater by reverse osmosis (RO), the feed water must be pressurized above the osmotic pressure of the feed water. Energy costs, primarily resulting from electrical consumption by the feed water pumps, are the largest component of the operating cost of a seawater reverse osmosis (SWRO) plant. However, energy costs can be reduced by recovering energy from the pressurized brine leaving an RO unit.

[0003] Childs et al. described a piston based pumping and energy recovery system in

US Patent Number 6,017,200, entitled Integrated Pumping and/or Energy Recovery System. This system uses a piston driven by a hydraulic pump to provide pressurized feed water to an RO membrane module. The front face of the piston drives the feed water to the RO module. The back face of the piston receives brine from the RO module. The pressure of the brine acting on the back face of the piston reduces the power required from the hydraulic pump to move the piston.

[0004] In the Childs et al. system, "energy recovery" valves admit brine to the back face of the piston on a forward stroke. Additional valves allow the brine to leave the piston on a backward stroke. The energy recovery valves are controlled by a control unit that also operates the hydraulic pump. The control unit synchronizes the movements of the valves with the movement of the piston. Because the piston reciprocates, it must accelerate and decelerate and therefore inherently produces an uneven rate of flow and pressure of the feed water. However, when a set of pistons are used their output may be synchronized to produce a nearly constant combined output pressure.

[0005] US Patent Application Publication No. US 2013/0082000, entitled Desalination

System with Energy Recovery and Related Pumps, Valves and Controller, describes various improvements to a piston based pumping and energy recovery system. According to one improvement, the energy recovery valves are designed to begin closing when the velocity of an associated piston decreases. SUMMARY

[0006] The following paragraphs are intended to introduce the reader to the detailed description to follow and not to limit or define any claimed invention.

[0007] This specification describes an energy recovery valve for a pump that lets high pressure fluid into and out of the pump. The energy recovery valve is operated using pressure from the output chamber of the pump.

[0008] Some embodiments of the present disclosure provide a valve comprising an inlet chamber and an outlet chamber, one of the inlet and outlet chambers in fluid

communication with a working fluid chamber of a cylinder pumping an operating fluid, and the other of the inlet and outlet chambers in fluid communication with to one of a working fluid supply line and a working fluid discharge line; a valve piston moveable into and out of engagement with a valve seat to block and unblock a flow path from the inlet chamber to the outlet chamber; a biasing mechanism configured to provide a biasing force to urge the valve piston into or out of engagement with the valve seat; a pilot chamber in fluid communication with an operating fluid chamber of the cylinder; and a pilot piston operatively coupled to the valve piston and moveable to expand and contract the pilot chamber such that expansion of the pilot chamber moves the valve piston in an opposite direction to the biasing force to unblock or block the flow path.

[0009] Some embodiments of the present disclosure provide a process for controlling flow of high pressure concentrate into and out of a water cylinder having a feed water chamber and a concentrate chamber comprising a step of using feed water pressure from the feed water chamber to operate a pilot valve to open or close a flow path between the concentrate chamber and one of a concentrate supply line and a concentrate discharge line.

[0010] Some embodiments of the present disclosure provide a system comprising an

RO unit and a water displacement unit comprising a plurality of water cylinders for providing high pressure feed water to the RO unit, each water cylinder having an energy recovery valve connected to selectively open and close a flow path between a concentrate output of the RO unit and a concentrate chamber of the water cylinder, wherein the energy recovery valve is operated by pressure in a feed water chamber of the water cylinder.

[0011] Other aspects and features of the present disclosure will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a schematic drawing of a fluid pumping and energy recovery system in combination with a reverse osmosis system.

[0013] Figure 1A is a schematic drawing of a fluid pumping and energy recovery system in combination with a reverse osmosis system similar to that of Figure 1 except that there are four energy recovery valves associated with each cylinder in Figure 1A.

[0014] Figure 2 is a cross-sectional, schematic view of an example water cylinder used in the system of Figure 1 .

[0015] Figure 3 is a cross-sectional, schematic view of an example water cylinder with energy recovery valves used in the system of Figure 1 illustrating connections between the water cylinder and the energy recovery valves.

[0016] Figure 4 is a cross-sectional, schematic view of one of the energy recovery valves, alternatively called a brine valve, shown in Figure 3.

[0017] Figure 5 is a graph showing displacement over time and pressure over time for the cylinder and valves of Figure 3.

[0018] Figure 6 is a cross-sectional, schematic view of another example water cylinder with energy recovery valves used in the system of Figure 1 illustrating connections between the water cylinder and the energy recovery valves.

[0019] Figure 7 is a cross-sectional, schematic view of one of the energy recovery valves, alternatively called a brine valve, shown in Figure 6.

[0020] Figure 8 is a graph showing displacement over time and pressure over time for the cylinder and valves of Figure 6.

[0021] Figure 9A is a cross-sectional, schematic view of another type of energy recovery valve in a closed position that may be used in the system of Figure 1.

[0022] Figure 9B shows the valve of Figure 9A in an open position.

DETAILED DESCRIPTION

[0023] Generally, the present disclosure provides energy recovery valves for the cylinders of pumps used to supply high pressure feed water to a reverse osmosis (RO) unit. The RO unit receives high pressure feed water, and outputs product water at a relatively low pressure, as well as concentrate (which may also be referred to as "retentate" or "brine") at a relatively high pressure. The concentrate leaving the RO unit typically has a pressure slightly lower than the feed water provided to the RO unit, but still has a significant amount of energy. The energy of the concentrate may be used to assist in driving the pumps, as described in US Patent No. 6,017,200 and US Patent Application Publication No. US

2013/0082000, which are hereby incorporated by reference herein.

[0024] This specification provides energy recovery valves that are operated using the pressure of the feed water in the pump, and do not require any additional pressurized fluid (e.g. compressed air). Elimination of the need for compressed air may provide a number of advantages, including increased reliability due to the lack of a compressor as a potential failure-mechanism, and reduced cost, energy consumption and noise by elimination of the cost, energy consumption and noise associated with compressors.

[0025] As depicted in Figure 1 , a system 10 includes a source of feed water 1 10, three hydraulic pumps 12, a water cylinder 200 for each hydraulic pump 12, an RO membrane unit 216, and a control unit 100. The system 10 is similar to the systems described in US Patent Number 6,017,200 and US Patent Application Publication No. US 2013/0082000, but will also be described below. The hydraulic pumps 12 are driven by a motor, not shown. Optionally, the three hydraulic pumps 12 may be replaced with a single hydraulic pump and a system of pipes and valves suitable for producing an output associated with each water cylinder 200. The system 10 has three double acting water cylinders 200, which in effect provide six water cylinders, but other numbers and arrangements of water cylinders, and means of powering them, may also be used.

[0026] Under instruction from the control unit 100, each hydraulic pump 12 controls the movement of a piston rod 14. The piston rod 14 is mechanically coupled to two opposed pistons 224, 226 (not shown in Figure 1 ) that are housed within a water cylinder 200. As will be further described below, the hydraulic output of each hydraulic pump 12 causes a piston rod 14 to move. Due to the mechanical coupling, the movement of the piston rod 14 causes the two pistons 224, 226 to move in unison with the movement of the piston rod 14. The piston rod 14 and the pistons 224, 226 may be referred to collectively as a reciprocating assembly 300. For brevity, this specification may at times describe the features of a single hydraulic pump 12, reciprocating assembly 300, water cylinder or other repeated elements of the system 10, but the description similarly applies to the other similar elements.

[0027] The source of feed water 1 10, which may provide sea water, brackish water, produced water or any other feed water requiring separation, is connected to the water cylinder 200 by low pressure feed water lines 254, 256. The system 10 also includes high pressure feed water lines 262, 264 to direct a high pressure feed water from the water cylinder 200 to the RO membrane unit 216.

[0028] The RO membrane unit 216 produces a flow of permeate (alternatively called filtrate), for example desalted potable water, which is directed through a permeate line 217 for the desired uses of the permeate. The RO membrane unit 216 also produces a flow of high pressure brine, alternatively called concentrate or retentate. The high pressure brine is directed from the RO membrane unit 216 by high pressure brine lines 218, 219 back to the water cylinder 200.

[0029] The water cylinders 200 also include a low pressure brine outlet that is connected to low pressure brine lines, also referred to a discharge lines 250, 252. The low pressure brine may be directed to a waste or recycle stream.

[0030] From a simplified perspective, there are four pressures within this system. The first pressure P1 is the pressure that supplies the feed water from the source 1 10, through low pressure feed water lines 254, 256, to the water cylinder 200. P1 can be provided by gravity or one of a variety of known pumps. The second pressure P2, which is substantially higher than P1 , is the pressure exerted on the feed water from the water cylinder 200 and carried through high pressure feed water lines 262, 264, to the RO membrane unit 216. As described below, P2 is provided by the pistons 224, 226 of the water cylinder 200. The third pressure P3 is the pressure of the brine as it leaves the RO membrane unit 216 to return to the water cylinder 200 via high pressure brine lines 218, 219. P3 is less than P2 because energy is required to filter the feed water and permeate leaves the system 10. The fourth pressure P4 is the pressure of the brine as it leaves the water cylinder 200 via low pressure brine lines 250, 252. P4 is less than P3.

[0031] For example, P1 may be in the range of about 5 to 100 psig; P2 may be in the range of about 600 to 1000 psig; P3 may be in the range of 500 to 950 psig; and P4 may be in the range of about 1 to 50 psig. The pressures may fluctuate to some extent over time, and the system 10 may include one or more accumulators, pressure release valves or other components of hydraulic systems effective to compensate for recurring or emergency flow or pressure variations.

[0032] Under the control of the control unit 100, the hydraulic pump 12 imparts a desired velocity or displacement profile upon the piston rod 14. The hydraulic pump 12 is driven by a motor and translates the rotational energy of the motor into a flow of hydraulic fluid. Therefore, the hydraulic pump 12, on command from the control unit 100, produces a hydraulic output that can range from a maximal hydraulic output to zero hydraulic output to maximal hydraulic output in the opposite direction. The hydraulic output of pump 12 is translated into the reciprocating displacement of the piston rod 14.

[0033] The piston rod 14 is connected to a hydraulic piston 20 within a hydraulic cylinder 18. Attached at one end of hydraulic cylinder is line 26 and attached at the other end of hydraulic cylinder 18 is line 28. The lines 26 and 28 direct the hydraulic output of the pump 12 to either side of the hydraulic piston 20. Optionally, the piston rod 14 may be connected to one face of the hydraulic piston 20 and another rod 30 (shown in Figure 6) may be connected to the opposite face of the hydraulic piston 20.

[0034] Details of example hydraulic pumps are described in US Patent Application Publication No. US 2013/0082000, as well as US Provisional Patent Application No. 61/985, 144, filed April 28, 2014 and entitled Energy Recovery Pump with Pressure Balancing Hole and Pressure Transitioning Step, which is hereby incorporated by reference herein.

[0035] As shown in Figure 2, the water cylinder 200 is generally tubular in shape with two end plates 204, 206 and a lateral wall 208 that extends between the end plates. The water cylinder 200 also includes intermediate plates 203 and 205, which divide the internal bore of the water cylinder 200 into two piston chambers 220 and 222. Within each piston chamber 220 and 222 there is a reciprocating, dual-action piston 224 and 226, each of which defines a feed water working chamber 228, 234 and a concentrate working chamber 230, 232. The dual-action pistons 224, 226 are mechanically coupled by a connection rod 278 which extends through an aperture in both of the intermediate plates 203, 205. The connection rod 278 also extends out of the water cylinder, through a bearing and seal assembly 209 within the end plate 206 so that no pressure or fluid leaks across the end plate 206 from the feed water working chamber 234.

[0036] The feed water working chamber 228 is defined by the inner surface of end plate 204, the inner surface of lateral wall 208 and the front face 236, also called the feed water face, of the piston 224. The feed water working chamber 234 is defined by the inner surface of end plate 206, the inner surface of lateral wall 208 and the front face 237, also called the feed water face, of the piston 226. The feed water chambers 228, 234 each have a feed water access port 212, 213 to provide fluid communication across the lateral wall 208 of the feed water working chambers 228, 234, for example to allow the inlet and outlet of feed water.

[0037] The concentrate working chamber 230 is defined by the inner surface of the intermediate plate 203, the inner surface of the lateral wall 208 and the back face 238, also called the concentrate face, of piston 224. The concentrate working chamber 232 is defined by the inner surface of the intermediate plate 205, the inner surface of the lateral wall 208 and the back face 240, also called the concentrate face, of piston 226. The feed water face 236, 237 is positioned opposite to the back face 238, 240 of the pistons. The concentrate working chambers 230, 232 each have a concentrate access port 242, 244 to provide fluid communication across the lateral wall 208 of the concentrate working chambers 230, 232, for example to allow the inlet and outlet of concentrate.

[0038] The dual-action pistons 224, 226 include one or more seals 280 between the perimeter of the dual-action pistons 224, 226 and the lateral wall 208 to prevent the movement of fluid between the feed water working chambers 228, 234 and the concentrate working chambers 230, 232 so that there is no fluidic communication across the dual-action pistons 224, 226. The one or more seals 280 are sufficiently resilient to withstand the differential pressure across the pistons 224, 226 causes by different hydrostatic pressures within the feed water working chambers 228, 234 and the respective concentrate working chambers 230, 232.

[0039] As described above, the dual-action pistons 224 and 226 are mechanically coupled by a connection rod 278. The connection rod 278 is also mechanically coupled to the piston rod 14 so that both dual-action pistons 224 and 226 move in unison with the piston rod 14. As described above, the piston rod 14, the connection rod 278 and the dual-action pistons 224 and 226 are collectively referred to as the reciprocating assembly 300.

[0040] As described herein below, the movement of the reciprocating assembly 300, including the actual stroke distance of the dual-action pistons 224, 226 within the water cylinder 200 can change. Therefore, the volume of the feed water working chambers 228, 234 and the volume of the concentrate working chambers 230, 232 can also be defined by the cross-sectional area of the dual-action pistons 224, 226 multiplied by the differential position of the dual-action pistons 224, 226 at the beginning and the end of a stroke of the reciprocating assembly 300.

[0041] In the water cylinder 200 shown, the ports 212, 213, 242 and 244 are each respectively connected to valve bodies 258, 260, 400 and 401 that are in turn each connected to a low pressure and a high pressure valve. Optionally, the water cylinder 200 may have twice as many ports, with each port connected to a single low pressure or high pressure valve. For example, Figure 1A shows a system wherein valve bodies 400 and 401 are each replaced with a high pressure valve body 400A, 401 A and a low pressure valve body 400B, 401 B.

[0042] Referring back to Figure 1 , the RO membrane unit 216 includes a set of RO modules each having one or more selectively permeable membranes. The feed water, at pressure P2, enters the RO unit 216 and permeate crosses the selectively permeable membranes to enter into a permeate line 217. Effectively, the RO unit 216 removes a volume of permeate from every input volume of feed water. This causes a decrease in the flow of water that enters the high pressure brine lines 218, 219 and ultimately enters the concentrate working chambers 230 and 232. This difference is referred to as the recovery ratio.

[0043] To compensate for the recovery ratio, a ratio sleeve 282 is placed around the connection rod 278, between the back faces 238, 240 of the dual-action pistons 224, 226. The ratio sleeve 282, also referred to as a ratio rod, is of greater diameter than the connection rod 278 and this decreases the working volume of the concentrate working chamber 230, 232, in comparison to the volume of the feed water working chambers 228, 234. For example, if the recovery ratio of the RO membrane unit 216 is 30%, then the diameter of the ratio sleeve 282 is such that the volume of concentrate pumped out of the concentrate working chamber 230, 232 is 30% smaller than the volume of feed water pumped out of the feed water working chambers 228, 232.

[0044] As shown in Figure 2, the ratio sleeve 282 is part of the reciprocating assembly 300 and the ratio sleeve 282 moves through both the intermediate plates 203, 205. To prevent the communication of fluid or pressure between the concentrate working chambers 230, 232, a ratio sleeve seal assembly 284 is positioned on the inner surface of the lateral wall 208 at the apertures to provide one or more seals 286 against the outer surface of the ratio sleeve 282.

[0045] Each piston 224, 226 also has a hole 225 extending between its faces: between feed water face 237 and back face 240 for piston 226 and between feed water face 236 and back face 238 for piston 224. These holes 225 allow water to move through the pistons 224, 226, in particular when all valves associated with concentrate access ports 242, 244 are closed. Because of the differential area of the pistons 224, 226 (or because the ratio sleeve 282 is present and larger than connection rod 278), moving the reciprocating assembly 300 to the right in Figure 3 causes a decrease in the total volume of right side feed water working chamber 228 and concentrate working chamber 230. The hole 225 allows some liquid to flow from feed water working chamber 228 to concentrate working chamber 230. However, the decrease in total volume causes the pressure in both the feed water working chamber 228 and the concentrate working chamber 230 to rise. Conversely, the pressures in the left side feed water working chamber 234 and concentrate working chamber 232 decreases. When the reciprocating assembly 300 moves to the left, the pressure in left side chambers 232, 234 increases while the pressure in right side chambers 228, 230 decreases.

[0046] Optionally, the holes 225 could be replaced by another type of opening that provides a fluid passageway between feed water face 237 and back face 240 for piston 226 or between feed water face 236 and back face 238 for piston 224. For example, the holes 225 could be replaced by a notch in the side of a piston 226, 224. A hole 225 or other opening can pass through either the main body of a piston 226, 224 or through a seal 280 of the piston 226, 224. Alternatively, the opening can be provided in the lateral wall 208 of the water cylinder 300. Such an opening only needs to provide a fluid passageway while a piston 226, 224 is at its fully extended or retracted position (but preferably at both of these positions), plus the length of a bump. The length of a bump is optionally about 2 to 5% of the stroke of a piston 226, 224. An opening in the lateral wall 208 does not need to be provided at intermediate positions. This would reduce salt leakage through the opening but the lateral wall 208 might then need to be strengthened to allow the water cylinder 300 to withstand its operating pressures. In another alternative, the opening might be provided by way of a loose tolerance between one or more of the seal 280, the rest of a piston 226, 224, and the lateral wall 208. However, an opening preferably has an area of at least 0.02%, or at least 0.04%, of a feed water face 236, 237 and it would be difficult to provide a selected size of opening and have a smoothly operating piston 226, 224 with an opening of that size provided by loose tolerances alone.

[0047] As will be described further below, these motions occur in an exemplary process while all inlet valves 402 and outlet valves 502 connected to concentrate access ports 242, 244 are closed and the reciprocating assembly 300 is starting a transition from movement in one direction to movement in another direction. Further, feed water access ports 212, 213 are each connected to a feed water valve assembly 258, 260 which provide feed water inlet and outlet one way check valves. The one way valves allow water to enter or leave the feed water working chambers 228, 234, but only when the pressure inside each of the feed water working chambers 228 and 234 is near to the pressure on the opposite side of the check valve within a feed water valve assembly 258, 260 that is capable of opening. Accordingly, when moving the reciprocating assembly 300 causes the pressure inside either of the feed water working chambers 228, 234 to increase, it increases only to about, or slightly above, the high feed water pressure P2. When the movement causes the pressure inside of either of feed water working chambers 228, 234 to decrease, it decreases to about, or slightly below, the low feed water pressure P1 . The size of the holes 225 and the timing and size of the movement can be adjusted to cause similar or different pressure variations in the concentrate working chambers 230, 232. In particular, the pressure in concentrate working chambers 230, 232 is preferably increased to near, but not above, the high brine pressure P3. Although it is a lesser concern, the pressure in concentrate working chambers 230, 232 is preferably decreased to near, but not below, the low brine pressure P4.

[0048] The water cylinder 200 and other parts of the system 10 may use the materials and other details of construction described in US Patent Application Publication No. US 2013/0082000, Desalination System with Energy Recovery and Related Pumps, Valves and Controller. US Patent Application Publication No. US 2013/0082000 is incorporated by reference.

[0049] As shown in Figure 2, the piston chambers 220, 222 include a feed water valve assembly 258, 260 which regulate the flow of feed water through the feed water access ports 212, 213 to the feed water working chambers 228, 234. For example, when feed water is desired to be supplied to feed water working chamber 228, feed water valve assembly 258 is open to line 254 so that feed water can flow from the source 1 10, through line 254, and into the feed water working chamber 228 via feed water access port 212. If the feed water valve assembly 258 is closed to line 254, no feed water will flow into the feed water working chamber 228. To supply feed water to the feed water working chamber 234, feed water valve assembly 260 can open to line 256 so that feed water flows from the source 1 10, through line 256 to the working chamber 234, via feed water access port 213. If feed water valve assembly 260 is closed to line 256 then no feed water will flow into the feed water working chamber 234.

[0050] For feed water to exit the feed water working chambers 228, 234 the feed water valve assembly 258, 260 are closed to lines 254, 256 and open to lines 262, 264.

Details of example feed water assemblies are described in US Patent Application Publication No. US 2013/0082000.

[0051] The water cylinder 200 also includes two concentrate (or brine) valve bodies

400, 401 , alternatively called energy recovery valves. The concentrate valve bodies 400,

401 are positioned between lines 218, 219, and the concentrate access ports 242, 244 and the respective concentrate working chambers 230, 232 and lines 250, 252 (see Figure 1 ). In some embodiments, a separate valve body may be provided for each of lines 218, 219, 250, 252, such as for example valve bodies 400A, 401 A, 400B, 401 B. In some embodiments, the specific features and functions of the concentrate valve bodies 400 and 401 are the same, with the exception of the specific connections between the concentrate working chamber and the high pressure concentrate lines.

[0052] Figure 3 shows example concentrate valve bodies 400A, 400B, 401A, and

401 B connected between high pressure brine lines 218, 219 and discharge lines 250, 252 and a water cylinder. As discussed above, the water cylinder has two piston chambers, each divided into a feed water chamber 220F, 222F and a concentrate chamber 220C, 220C. As shown in Figure 3, each of the concentrate valve bodies 400A, 400B, 401 A, 401 B includes a poppet-type valve 800 (individually labeled 800-HP1 , 800-LP1 , 800-HP2, 800-LP2 in Figure 3). In some embodiments, the high pressure and low pressure valves may be differently configured. In other embodiments, all of the valves 800 may be substantially identical.

[0053] Details of an example valve 800 are shown in Figure 4. Each valve 800 comprises a casing 801 with a pilot port 802, an inlet port 806 and an outlet port 808. The pilot port 802 is connected by a pilot line 804 to a feed water chamber 220F/222F (see Figure 3). A pilot piston 812 is movable to expand or contract the size of a pilot chamber 803. The piston 812 is connected by a rod 814 to a valve piston 816, which is moveable into and out of engagement with a valve seat 818 to selectively block and unblock a flow path from the inlet port 806 to the outlet port 808. The pilot piston 812, rod 814 and valve piston 816 may be referred to as the reciprocating assembly 810 of the valve 800. A biasing member such as, for example, a compression spring 820 biases the valve piston 816 into

engagement with the valve seat 818, such that the valve is "normally closed." As discussed further below, the valve 800 is configured to open when the pressure in the pilot chamber 803 exceeds an opening threshold.

[0054] The opening threshold for the "high pressure" valves (800-HP1 , 800-HP2 in

Figure 3) connected to the brine lines 218, 219 may be selected to be in the range of about

60-100% of the pressure at which feed water is delivered (the "operating pressure" of the system), or about 75% of the operating pressure in some embodiments. In a system delivering RO feed water at 750 psi, the opening threshold may, for example, be in the range of about 500-750 psi. The opening threshold and for the "low pressure" valves (800-LP1 ,

800-LP2 in Figure 3) connected to the discharge lines 250, 252 may be selected to be no greater than about 25% of the operating pressure. In general, a higher opening threshold or "cracking pressure" minimizes ripple recovery time for the high pressure valves connected to the brine lines 218, 219, and a lower opening threshold or "cracking pressure" minimizes ripple recovery time for the low pressure valves connected to the discharge lines 250, 252.

[0055] In some embodiments, the pilot area ratio of the valves 800 connected to the brine lines 218, 219 is preferably 4 or greater to minimize any contribution of the system pressure on the cracking pressure of the valve. In some embodiments the pilot area ratio may be about 5.

[0056] Referring back to Figure 3, the operation of valve bodies 400A and 400B to control brine flow to and from concentrate chamber 220C will be briefly described in relation to the pressures in 220F and 222F. Valve bodies 401 A and 401 B operate in substantially the same way with respect to concentrate chamber 222C. As the reciprocating assembly in the water cylinder moves in a first direction (up in Figure 3), the pressure in feed water chamber 220F rises, which is transmitted to high pressure valve 800-HP1 through a pilot line 804. This pressure increase causes the high pressure valve 800-HP1 to open, allowing high pressure brine into the chamber 220C through line 809. As the reciprocating assembly in the water cylinder moves in a second direction (down in Figure 3), the pressure in feed water chamber 222F rises, which is transmitted to low pressure valve 800-LP1 through a pilot line 804. At the same time, the pressure in feed water chamber 220F falls. The pressure increase in chamber 222F causes the low pressure valve 800-LP1 to open, allowing brine to leave the chamber 220C through line 807, and the pressure decrease in chamber 220F causes the high pressure valve 800-HP1 to close. The relative timing of the opening and closing of the low and high pressure valves 800-LP1 and 800-HP1 is determined by selection of the cracking pressures of the valves.

[0057] In some embodiments, each of lines 807 and 809 have their own port for connecting to the chamber 220C. In other embodiments, lines 807 and 809 may share a port (e.g. if valve bodies 400A and 400B were combined into a single body 400 as shown in Figure 1 ).

[0058] Figure 5 is a graph illustrating the timing of the opening and closing of valves 800-HP1 , 800-LP1 in Figure 3. The top plot of Figure 5 represents the position of the reciprocating assembly within the water cylinder, with up representing the direction toward chamber 220F and down representing the direction toward chamber 222F. The middle and bottom plots represent the pressures in chambers 220F and 222F, respectively. The reciprocating assembly cycles back and forth through its range of motion in the water cylinder, with a relatively short "dwell time" at either end of its stroke where the reciprocating assembly remains stationary. In some embodiments, there may be a "bump" in the motion profile of the reciprocating assembly of the water cylinder at each end of its stroke, as described in US Provisional Patent Application No. 61/985, 144, filed April 28, 2014 and entitled Energy Recovery Pump with Pressure Balancing Hole and Pressure Transitioning Step. The bump is indicated by 502 in Figure 5. The bump provides for

pressurizing/depressurizing the chambers of the cylinder before the main motion of the stroke begins.

[0059] The states of the valves 800-HP1 and 800-LP1 during one pumping cycle will now be described, beginning at time T₀ when the reciprocating assembly is moving toward chamber 220F. At time T₀, valve 800-HP1 is held open by the feed water pressure in chamber 220F, and valve 800-LP1 is closed. At time T-i , shortly after the reciprocating assembly has stopped moving, the feed water pressure in chamber 200F drops below the opening pressure of valve 800-HP1 and valve 800-HP1 closes (valve 800-LP1 remains closed). At time T₂, shortly after the bump and before the reciprocating assembly has started its main motion in the direction toward chamber 222F, the feed water pressure in chamber 222F rises above the opening pressure of valve 800-LP1 and valve 800-LP1 opens (valve 800-HP1 remains closed). At time T₃, shortly after the reciprocating assembly has stopped moving again, the feed water pressure in chamber 220F drops below the opening pressure of valve 800-LP1 and valve 800-LP1 closes (valve 800-HP1 remains closed). At time T₄, shortly after the bump and before the reciprocating assembly has started its main motion in the direction toward chamber 220F again, the feed water pressure in chamber 220F rises above the opening pressure of valve 800-HP1 and valve 800-HP1 opens (valve 800-LP1 remains closed). In some embodiments, valves 800-HP1 and 800-LP1 are configured such that the interval between T-i and T₂, and the interval between T₃ and T₄, are each at least 40 milliseconds. As discussed above, selection of the cracking pressures of valves 800-HP1 and 800-LP1 determines the relative opening and closing times.

[0060] The operability of a system with self-piloted energy recovery valves during steady state (i.e., once the system is up and running at operating pressure and pumping feed water) is clear. To validate operability during start up, dynamic computer simulations were conducted. The following table shows a comparison of efficiencies between simulations a system with pilot-operated energy recovery valves operated using compressed air, and a system with self-piloted energy recovery valves operated using feed water pressure similar to those described herein.

[0061] The simulations suggest that systems with self-piloted energy recovery valves such as those described herein will be able to start up normally.

[0062] Figure 6 shows example concentrate valve bodies 400A, 400B, 401 A, 401 B according to another embodiment connected between high pressure brine lines 218, 219 and discharge lines 250, 252 and a water cylinder. As discussed above, the water cylinder has two piston chambers, each divided into a feed water chamber 220F, 222F and a concentrate chamber 220C, 220C. As shown in Figure 6, each pair of concentrate valve bodies 400A B, 401 A/B includes one "normally closed" high pressure valve 800 and one "normally open" low pressure valve 900.

[0063] Details of an example valve 900 are shown in Figure 7. Each valve 900 comprises a casing 901 with a pilot port 902, an inlet port 906 and an outlet port 908. The pilot port 902 is connected by a pilot line 904 to a feed water chamber 220F/222F (see Figure 3A). A pilot piston 912 is movable to expand or contract the size of a pilot chamber 903. Another chamber 905 on the opposite side of the pilot piston 912 from the pilot chamber 903 may be open to the atmosphere, or filled with a compressible gas such as for example air, nitrogen or an inert gas. The piston 912 is connected by a rod 914 to a valve piston 916, which is moveable into and out of engagement with a valve seat 918 to selectively block and unblock a flow path from the inlet port 906 to the outlet port 908. The pilot piston 912, rod 914 and valve piston 916 may be referred to as the reciprocating assembly 910 of the valve 900. A biasing member such as, for example, a compression spring 920 biases the valve piston 916 away from the valve seat 918, such that the valve is "normally open." As discussed further below, the valve 900 is configured to close when the pressure in the pilot chamber 803 exceeds a closing threshold, which may for example be no greater than about 25% of the operating pressure of the system.

[0064] Referring back to Figure 6, the operation of valve bodies 400A and 400B to control brine flow to and from concentrate chamber 220C will be briefly described in relation to the pressures in 220F. Valve bodies 401 A and 401 B operate in substantially the same way with respect to concentrate chamber 222C. As the reciprocating assembly in the water cylinder moves in a first direction (up in Figure 6), the pressure in feed water chamber 220F rises, which is transmitted to high pressure valve 800 through a pilot line 804 and to low pressure valve 900 through a pilot line 904. The closing pressure of the low pressure valve 900 is selected to be lower than the opening pressure of the high pressure valve 800, such that as pressure increases in the feed water chamber 220F, the low pressure valve 900 closes, preventing brine from leave the chamber 200C through line 907, and then subsequently the high pressure valve 800 opens, allowing high pressure brine into the chamber 220C through line 809. When the reciprocating assembly stops moving, the pressure in feed water chamber 200F drops, causing the high pressure valve 800 to close and then subsequently the low pressure valve 900 to open.

[0065] Figure 8 is a graph illustrating the timing of the opening and closing of valves

800 and 900 in Figure 6. The top plot of Figure 8 represents the position of the reciprocating assembly within the water cylinder, with up representing the direction toward chamber 220F and down representing the direction toward chamber 222F. The motion profile of the reciprocating assembly may be substantially the same as discussed above with respect to Figure 5. The bottom plot represents the pressures in chamber 220F.

[0066] The states of the valves 800, 900 during one pumping cycle will now be described, beginning at time T₀ when the reciprocating assembly is moving toward chamber 220F. At time T₀, valve 800 is held open and valve 900 is held closed by the feed water pressure in chamber 220F. At time T_{1 ;} shortly after the reciprocating assembly has stopped moving, the feed water pressure in chamber 200F drops below the opening pressure of valve 800 and valve 800 closes (valve 900 remains closed). At time T₂, shortly after the bump and before the reciprocating assembly has started its main motion toward chamber 222F, the feed water pressure in chamber 220F drops below the closing pressure of valve 900 and valve 900 opens (valve 800 remains closed). At time T₃, shortly after the bump, and before the reciprocating assembly has started its main motion toward chamber 220F again, the feed water pressure in chamber 220F rises above the closing pressure of valve 900 and valve 900 closes (valve 800 remains closed). At time T₄, the feed water pressure in chamber 220F rises above the opening pressure of valve 800 and valve 800 opens (valve 900 remains closed). In some embodiments, valves 800 and 900 are configured such that the interval between ΤΊ and T₂, and the interval between T₃ and T₄, are each at least 40 milliseconds.

[0067] The above examples describe ER valves are poppet-type valves. In other embodiments, ER valves may comprise other types of valves, such as ball valves, spool valves, etc. For example Figures 9A and 9B show an example ER valve 1000 that comprises a spool-type valve 1020.

[0068] Figure 9A shows the ER valve 1000 in the closed position, and Figure 9B shows the ER valve in the open position. The ER valve 1000 comprises a main valve body 1002 having an inlet 1004 and an outlet 1006. The inlet 1004 is connected to a higher- pressure line or port than the outlet 1006 (e.g. the inlet 1004 may be connected to one of bine lines 218, 219 in the case of a high pressure valve or to a port on a concentrate chamber in the case of a low pressure valve, and the outlet may be connected to a port on a concentrate chamber in the case of a high pressure valve or one of discharge lines 250, 252 in the case of a low pressure valve). A flow path 1008 is provided between the inlet 1004 and outlet 1008.

[0069] A main piston 1010 is positioned to be moveable into and out or engagement with a valve seat 1012 to selectively block and unblock the flow of fluid between the inlet

1004 and the outlet 1006. A small orifice 1014 in the main piston 1010 allows fluid to pass from the front face of the main piston 1010 (which faces the inlet 1004) to a back face of the main piston 1010 (which faces a chamber 1016). The surface area of the back face of the main piston 1010 is larger than the surface area of the front face, such that the pressure of fluid provided at the inlet tends to urge the main piston 1010 into the closed position shown in

Figure 9A. One or more biasing members such as for example springs 1018 may be provided to assist in moving the main piston 1010 into the closed position.

[0070] A port 1019 provides fluid communication between the chamber 1016 behind the main piston 1010 and the spool-type valve 1020. The spool-type valve 1020 comprises a spool body 1022 having a passage therein within which a spool 1024 is slidably received.

The spool 1024 is moveable to expand and contract a pilot chamber 1023, which is connected to receive feed water through a port 1028. The spool 1024 has a passage 1025 therein which selectively provides fluid communication between the port 1019 connected to the chamber 1016 behind the main piston 1010, and a pressure release port 1027. A biasing member such as for example spring 1026 urges the spool 1024 into the closed position shown in Figure 9A, where the port 1019 connected to the chamber 1016 behind the main piston 1010 is blocked. When feed water pressure provided to port 1028 increases beyond the cracking pressure, as indicated by arrow 1029 in Figure 9B, the spool 1024 is moved such that the passage 1025 provides fluid communication between the port 1019 connected to the chamber 1016 behind the main piston 1010, and the pressure release port 1027. The pressure release port 1027 has a larger cross-sectional area than the orifice 1014 in the main piston 1010. In some embodiments, the orifice 1014 has a generally circular cross- section with a diameter of ¼ inch or less. The pressure release port 1027 may be connected to the outlet 1006 in some embodiments, or may be connected to any chamber with lower pressure than the inlet 1004. When the spool-type valve 1020 is in the open position shown in Figure 9B, the pressure in chamber 1016 drops such that the forces acting on the back face of the main piston 1010 are no longer sufficient to overcome the force of the fluid pressure on the front face of the main piston 1010, which moves into the open position thereby opening the flow path between the inlet 1004 and the outlet 1006. The example valve 1000 shown in Figures 9A and 9B is a normally closed valve, but it is to be understood that a similar valve could be provided that is configured to be normally open.

[0071] The above examples describe ER valves are self piloted, and the feed water pressure directly controls the opening and closing of the ER valves. In other embodiments, ER valves may comprise solenoids or the like that are triggered by changes in the feed water pressure.

[0072] This written description uses examples to disclose the invention, including the best mode, to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art.

[0073] The above-described embodiments are intended to be examples only.

Alterations, modifications and variations can be effected to the particular embodiments by those of skill in the art. The scope of the claims should not be limited by the particular embodiments set forth herein, but should be construed in a manner consistent with the specification as a whole.

Claims

WHAT IS CLAIMED IS:

1. A valve comprising:

an inlet chamber and an outlet chamber, one of the inlet and outlet chambers in fluid communication with a working fluid chamber of a cylinder pumping an operating fluid, and the other of the inlet and outlet chambers in fluid communication with to one of a working fluid supply line and a working fluid discharge line;

a valve piston moveable into and out of engagement with a valve seat to block and unblock a flow path from the inlet chamber to the outlet chamber;

a biasing mechanism configured to provide a biasing force to urge the valve piston into or out of engagement with the valve seat;

a pilot chamber in fluid communication with an operating fluid chamber of the cylinder; and

a pilot piston operatively coupled to the valve piston and moveable to expand and contract the pilot chamber such that expansion of the pilot chamber moves the valve piston in an opposite direction to the biasing force to unblock or block the flow path.

2. A valve according to claim 1 wherein the pilot piston is physically connected to the valve piston.

3. A valve according to claim 2 wherein the valve comprises a poppet-type valve and the biasing mechanism comprises a spring.

4. A valve according to claim 3 wherein the spring is connected to bias the valve piston into engagement with the valve seat.

5. A valve according to claim 3 wherein the spring is connected to bias the valve piston out of engagement with the valve seat.

6. A valve according to claim 1 wherein the pilot piston is fluidically coupled to the valve piston, whereby movement of the pilot piston to expand the pilot chamber reduces the biasing force.

7. A valve according to claim 6 wherein the biasing mechanism comprises an orifice in the valve piston providing fluid communication between a front face of the valve piston facing the inlet chamber and a back face of the valve piston.

8. A valve according to claim 7 comprising a port in fluid communication with a chamber at the back face of the valve piston, wherein the pilot piston is moveable to selectively block and unblock the port in fluid communication with the chamber at the back face of the valve piston such that when the port in fluid communication with the chamber at the back face of the valve piston is unblocked fluid pressure on the back face of the valve piston is reduced.

9. A valve according to claim 8 wherein the pilot piston comprises a spool moveable within a spool-type valve body.

10. A valve according to claim 9 wherein the spool is biased to block the port in fluid communication with the chamber at the back face of the valve piston.

1 1 . A process for controlling flow of high pressure concentrate into and out of a water cylinder having a feed water chamber and a concentrate chamber comprising a step of using feed water pressure from the feed water chamber to operate a pilot valve to open or close a flow path between the concentrate chamber and one of a concentrate supply line and a concentrate discharge line.

12. A process according to claim 1 1 wherein using feed water pressure comprises providing fluid communication between a pilot chamber of the pilot valve and the feed water chamber.

13. A process according to claim 12 wherein the pilot valve comprises a valve piston moveable to open or close the flow path and a pilot piston operatively coupled to the valve piston, the process comprising biasing the valve piston to close the flow path and using feed water pressure to move the valve piston to open the flow path.

14. A process according to claim 12 wherein the pilot valve comprises a valve piston moveable to open or close the flow path and a pilot piston operatively coupled to the valve piston, the process comprising biasing the valve piston to open the flow path and using feed water pressure to move the valve piston to close the flow path.

15. A system comprising:

an RO unit;

a water displacement unit comprising a plurality of water cylinders for providing high pressure feed water to the RO unit, each water cylinder having an energy recovery valve connected to selectively open and close a flow path between a concentrate output of the RO unit and a concentrate chamber of the water cylinder, wherein the energy recovery valve is operated by pressure in a feed water chamber of the water cylinder.

16. A system according to claim 15 wherein the energy recovery valve connected to selectively open and close the flow path between the concentrate output of the RO unit and the concentrate chamber of the water cylinder comprises a high pressure energy recovery valve, and wherein each water cylinder also has a low pressure energy recovery valve connected to selectively open and close a flow path between the concentrate chamber of the water cylinder and a discharge line, wherein the low pressure energy recovery valve is operated by pressure in a feed water chamber of the water cylinder.

17. A system according to claim 16 wherein each water cylinder comprises two feed water chambers and two concentrate chambers, and wherein each of the concentrate chambers has both a high pressure energy recovery valve and a low pressure energy recovery valve coupled thereto, wherein the high pressure and low pressure energy recovery valves of both concentrate chambers are operated by pressure in one of the feed water chambers.

18. A system according to claim 17 where each of the high pressure and low pressure energy recovery valves is connected to one of the concentrate chambers by a separate port.