Valves

Abstract

An apparatus (10) for compressing and expanding a gas includes a chamber (22), a positive displacement device (24) moveable relative thereto, first and second valves (26, 28) activatable to control flow of gas into and out of the chamber (22), and a controller (80) for controlling activation of the valves (26, 28) that selectively switches operation between a compression and an expansion mode with selective switching between modes being achieved by selectively changing the activation timing of at least one of the valves during the first mode. An energy storage system including the device may be operatively coupled via a rotary device for power transmission to an input/output device, whereby the direction and speed of rotation are preserved during switching, and the input/output device may be synchronized to the grid.

Claims

1. A method of gas compression and expansion, the method comprising: receiving a gas in a chamber for which first and second valves are operable to control gas flow into and out of the chamber; and selectively changing, with a controller, an activation timing of at least one of the first and second valves to selectively switch operation of a positive displacement device moveable relative to the chamber between a compression mode in which the gas received in the chamber is compressed by the positive displacement device and an expansion mode in which the gas received in the chamber is expanded by the positive displacement device, wherein the activation timing is changed during the operation of the positive displacement device in one of the compression and expansion modes.

2. The method according to claim 1, further comprising: transmitting, via the positive displacement device being coupled to a rotary device, mechanical power between the positive displacement device and an input/output device; and selectively switching, via the controller, from one of the compression and expansion modes to the other of the compression and expansion modes of operation whilst the rotary device continues to move in a predetermined direction associated with the one of the compression and expansion modes.

3. The method according to claim 2, further comprising switching of a grid synchronised motor/generator of the input/output device between operation as a motor and a generator during a switch between the compression and expansion modes, without losing grid synchronisation.

4. The method according to claim 1, further comprising selectively connecting, via the first and second valves, the chamber to either a high pressure region or a low pressure region.

5. The method according to claim 4, further comprising allowing only one of the low pressure and high pressure regions to be connected to the chamber at any one time.

6. The method according to claim 1, further comprising: opening at least one of the first and second valves when gas pressures on either side of said at least one valve are equal; and altering, via the controller, a valve closure timing of said at least one valve to selectively switch from the one of the compression and expansion modes to the other of the compression and expansion modes.

7. The method according to claim 6, further comprising self-opening of at least one of the first and second valves when gas pressures on either side of said at least one valve are equal.

8. The method according to claim 1, further comprising reversing, upon switching between the compression and expansion modes, functions of the first and second valves such that the gas flows in a reversed direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which:

(2) FIG. 1 shows a schematic representation of apparatus according to an embodiment of the present invention;

(3) FIGS. 2A-2D illustrate valve operation in a compression mode;

(4) FIGS. 3A-3F illustrate valve operation in an expansion mode;

(5) FIGS. 4a and 4b are schematic illustrations of mobile and static energy storage systems respectively comprising the apparatus according to the present invention; and

(6) FIG. 5 is a schematic illustration of a pumped heat storage system comprising the apparatus according to the present invention.

(7) FIG. 1 shows apparatus 10 for compressing and expanding gas, comprising first and second piston assemblies 20, 30 coupled to an input/output device 50 via a rotary crankshaft 60. Crankshaft 60 may be in turn coupled to a flywheel (not shown).

(8) First piston assembly 20 comprises a first chamber (e.g. cylinder) 22 for receiving a gas, a first reciprocating piston 24 moveable in the first chamber 22, and first and second valves 26, 28 activatable to control flow of gas into and out of the first chamber 22. Second piston assembly 30 comprises a second chamber (e.g. cylinder) 32 for receiving a gas, a second reciprocating piston 34 moveable in the second chamber 32, and third and fourth valves 36, 38 activatable to control flow of gas into and out of the second chamber 32. The first and third valves 26, 36 are configured to selectively connect first and second chambers 22, 32 respectively to a low pressure region (e.g. ambient air source or low pressure cold store of the type used in WO 2009/044139). The second and fourth valves 28, 38 are configured to selectively connect first and second chambers 22, 32 respectively to a high pressure region (e.g. a high pressure hot store or high pressure heat exchanger).

(9) In use, activation timing of all closure events of the first, second, third and fourth valves 26, 28, 36, 38 are controlled by a controller 80 coupled to the valves (e.g. by an electrical, mechanical, pneumatic or hydraulic connection or by any other suitable means). As discussed in more detail below, controller 80 is configured (e.g. programmed) to selectively switch operation of first piston 24 between a compression mode in which gas received in first chamber 22 is compressed by first piston 24 and an expansion mode in which gas received in first chamber 22 is expanded by first piston 24 (i.e. with expansion of gas contained in the chamber occurring as the gas does work to move the piston), with selective switching from a first of the two modes to a second of the two modes being achieved by selectively changing the activation timing of at least one of the first and second valves 26, 28 during operation in the first mode. The first and second valves 26, 28 will then reverse their function and the gas flows automatically start to reverse. Similarly, controller 80 is also configured to selectively switch operation of second piston 34 between a compression mode in which gas received in second chamber 32 is compressed by second piston 34 and an expansion mode in which gas received in second chamber 32 is expanded by second piston 34, with selective switching from a first of the two modes to a second of the two modes being achieved by selectively changing the activation timing of at least one of the third and fourth valves 36, 38 during operation in the first mode.

(10) Each of the first, second, third and fourth valves 26, 28, 36, 38 are held closed by friction locking and are configured to open automatically only when gas pressures on either side of the valve are substantially equal. Accordingly, only one of the first and second valves 26, 28 may be open in the first piston assembly 20 at the same time. Similarly, only one of the third and fourth valves 36, 38 may be open in the second piston assembly 20 at the same time. In the case of the first piston assembly, controller 80 is configured to close one of the first and second valves 26, 28 if the switching operation requires the other valve to open. In the case of the second piston assembly, controller 80 is configured to close one of the third and fourth valves 36, 38 if the switching operation requires the other valve to open.

(11) Operation of controller 80 is now described with reference to FIGS. 2A-2D and FIGS. 3A-3F in which valve A corresponds to first or third valves 26, 36 connected to the low pressure region and valve B corresponds to second or fourth valves 28, 38 connected to the high pressure region.

(12) Compression Mode

(13) With reference to FIGS. 2A-2D, the valve timing for first and second piston assemblies 20, 30 in the compression mode are set out below, where: TDC=top dead centre; BDC=bottom dead centre.

(14) TABLE-US-00001 A B Compressor Mode (INLET) (OUTLET) START C1 TDC CLOSED CLOSES C2 Just after TDC on way down at OPENS CLOSED or near pressure equalisation with low pressure side C3 BDC CLOSES CLOSED C4 Partway through upstroke at CLOSED OPENS or near pressure equalisation with high pressure side REPEATS C1 TDC CLOSED CLOSES
Expansion Mode

(15) With reference to FIGS. 3A-3F, the valve timing for first and second piston assemblies 20, 30 in the expansion mode is as follows:

(16) TABLE-US-00002 A B Expander Mode (OUTLET) (INLET) START E1 TDC CLOSED OPEN E2 After TDC on way down CLOSED CLOSES E3 Prior to BDC at or near pressure equalisation with low pressure OPENS CLOSED side E4 BDC OPEN CLOSED E5 Before TDC and allowing for enough space to recompress CLOSES CLOSED remaining gas to high pressure E6 Just before TDC and at or near pressure equalisation with high CLOSED OPENS pressure side REPEATS E1 TDC CLOSED OPEN
Change from Compression Mode to Expansion Mode

(17) Controller 80 is configured in this embodiment to switch operation of first and second piston assemblies 20, 30 from the compression mode to the expansion mode by changing valve closure timing after either valve A or valve B have closed. The change of timing for two different switching modes is listed below:

(18) TABLE-US-00003 Switching from Compressor to Expander 1 A B START C1 TDC CLOSED CLOSES C2 Just after TDC on way down at or near pressure equalisation with low pressure side OPENS CLOSED SWITCH E4 BDC OPEN CLOSED E5 Before TDC and allowing for CLOSES CLOSED enough space to recompress re- maining gas to high pressure E6 Just before TDC and at or near CLOSED OPENS pressure equalisation with high pressure side E1 TDC CLOSED OPEN E2 After TDC on way down CLOSED CLOSES E3 Prior to BDC at or near pressure OPENS CLOSED equalisation with low pressure side REPEATS E4 BDC OPEN CLOSED Valve B Closes as Normal then switch Valve A Closure changes from BDC to just before TDC on way up Valve B Closure changes from TDC to after TDC on way down Switching from Compressor to Expander 2 A B START C3 BDC CLOSES CLOSED C4 Partway through upstroke at or near pressure equalisation with high pressure side CLOSED OPENS SWITCH E1 TDC CLOSED OPEN E2 After TDC on way down CLOSED CLOSES E3 Prior to BDC at or near OPENS CLOSED pressure equalisation with low pressure side E4 BDC OPEN CLOSED E5 Before TDC and allowing for CLOSES CLOSED enough space to recompress re- maining gas to high pressure E6 Just before TDC and at or near CLOSED OPENS pressure equalisation with high pressure side REPEATS E1 TDC CLOSED OPEN Valve A Closes as Normal then switch Valve B Closure changes from TDC to after TDC on way down Valve A Closure changes from BDC to just before TDC on way up
Change from Expansion Mode to Compression Mode

(19) Controller 80 is further configured in this embodiment to switch operation of first and second piston assemblies 20, 30 from the expansion mode to the compression mode by changing valve closure timing after either valve A or valve B have closed. The change of timing for two different switching modes is listed below:

(20) TABLE-US-00004 Switching from Expander A B to Compressor 1 (OUTLET) (INLET) START E1 TDC CLOSED OPEN E2 After TDC on way down CLOSED CLOSES E3 Prior to BDC at or near pressure OPENS CLOSED equalisation with low pressure side SWITCH C3 BDC CLOSES CLOSED C4 Partway through upstroke at or CLOSED OPENS near pressure equalisation with high pressure side C1 TDC CLOSED CLOSES C2 Just after TDC on way down at OPENS CLOSED or near pressure equalisation with low pressure side REPEATS C3 BDC CLOSES CLOSED Valve B Closes as Normal then switch Valve A Closure changes from just before TDC on way up to BDC Valve B from after TDC on way down to TDC Switching from Expander A B to Compressor 2 (OUTLET) (INLET) START E4 BDC OPEN CLOSED E5 Before TDC and allowing for CLOSES CLOSED enough space to recompress re- maining gas to high pressure E6 Just before TDC and at or near CLOSED OPENS pressure equalisation with high pressure side SWITCH C1 TDC CLOSED CLOSES C2 Just after TDC on way down at OPENS CLOSED or near pressure equalisation with low pressure side C3 BDC CLOSES CLOSED C4 Partway through upstroke at or CLOSED OPENS near pressure equalisation with high pressure side REPEATS C1 TDC CLOSED CLOSES Valve A Closes as Normal then switch Valve B from after TDC on way down to TDC Valve A Closure changes from just before TDC on way up to BDC

(21) In all four switching modes identified above, the change to the valve actuation timing is configured to occur whilst crankshaft 60 continues to rotate in a predetermined direction (i.e. clockwise or anticlockwise) associated with the first mode. Advantageously, this configuration allows switching between the first and second modes of operation with minimal impact to the motion of crankshaft 60 and input/output device 50 thereby allowing fast mode switching.

(22) In all switching modes, if a valve is already closed and a closing actuator is fired this has no effect on the valve which remains closed. This means that a defined positional closing event can be nullified if the valve is placed in a closed configuration prior to this event. Accordingly, controller 80 may be configured to provide a valve closure signal at the same point in the cycle when acting in either the compression or expansion mode.

(23) Input/output device 50 may for example be a grid synchronised motor/generator and the apparatus may be configured to run as a compressor to store energy as compressed air and as an expander to recover the energy as electricity. In another example, input/output device 50 may be a vehicle motor and the apparatus may be configured to run as a compressor to store energy as compressed air (e.g. during braking) and as an expander to recover the energy (e.g. to give a power boost).

(24) In a further mode, each of the first and second piston assemblies 20, 30 may be unloaded by ensuring that either at least one valve is either kept closed (e.g. so that gas in one of the chambers 22, 32 is compressed and re-expanded) or held open (e.g. so that no compression of gas in chambers 22, 32 can occur). In this way, apparatus 10 may be configured to operate in a minimum energy consumption pattern.

(25) Although the present embodiment illustrated two piston assemblies, the apparatus may comprise at least one further piston assembly. In one mode of operation, controller 80 may be configured to operate a fixed proportion of the piston assemblies (e.g. half) in the compression mode and a fixed proportion of the piston assemblies (e.g. half) in the expansion mode. In another mode of operation, controller 80 may be configured to operate all piston assemblies in the compression mode or all of the piston assemblies in the expansion mode. In yet another mode, controller 80 may be configured to have varying proportions of compressor and expanders. In yet another mode, controller 80 may be configured to operate at least one of the piston assemblies in the unloaded mode described above so that the piston assemblies may be configured to act as compressors, expanders, unloaded or a combination of all three. Advantageously, the piston assemblies may change modes of operation between expander, compressor and unloaded as required without crankshaft 60 changing direction of rotation.

(26) In one compression mode, controller 80 may be configured to partially unload a piston assembly ensuring the inlet valve is fired shut late (i.e. on the up stroke or the outlet valve is fired shut early, i.e. after TDC during the down stroke). In this way the overall capacity of gas compressed is reduced and the apparatus can operate in a part loaded manner.

(27) In one expansion mode, controller 80 may be configured to partially unload a piston assembly by ensuring that the inlet valve is fired shut earlier on the down stroke (i.e. nearer TDC) or the outlet valve is fired shut early i.e. before TDC. In this way the overall capacity of gas expanded is reduced and the machine can operate in a part loaded manner.

(28) FIG. 4a is a schematic illustration of an energy storage system in which apparatus 300 according to the present invention includes a positive displacement device 310 preferably a linear device (e.g. reciprocating piston), operatively coupled via rotary device 320 for power transmission to an input/output device 330, whereby the direction of rotation (and in one embodiment advantageously also the speed of rotation) are preserved during switching between modes. The system may be used in a mobile application (e.g. a regenerative braking system in a vehicle), or, as shown in FIG. 4b, a similar system may be employed in a static application where the input/output device 330 is optionally synchronised to the national grid 340.

(29) FIG. 5 is a schematic illustration of one example of a pumped heat storage system 400 comprising apparatus 430, 440 according to the present invention, a first heat storage vessel 410 for receiving and storing thermal energy from compressed gas (forming a high pressure hot store) and a second heat storage vessel 420 for transferring thermal energy to expanded gas (forming a low pressure cold store). The pumped heat storage system 400 is operable in a charging mode to store electrical energy as thermal energy, and operable in a discharging mode to generate electrical energy from the stored thermal energy, and the system comprises at least two respective chambers 430, 440 each containing the positive displacement devices according to the invention, these being respectively configured to act in a compression mode and expansion mode during the charging mode and vice versa in the discharging mode, whereby the switching of the devices is achieved according to the invention. This particular arrangement of using a hot and cold store in a heat storage system corresponds to the system described above in relation to the applicant's earlier application WO2009/044139. In that prior art system, the two displacement devices can be split into separate devices or can be combined into a single device acting as a heat pump/heat engine.