GB2416196A

GB2416196A - Valve control system for a reciprocating compressor

Info

Publication number: GB2416196A
Application number: GB0419574A
Authority: GB
Inventors: Thomas Tsoi Hei Ma
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-07-14
Filing date: 2004-09-03
Publication date: 2006-01-18
Also published as: GB0415730D0; GB0419574D0

Abstract

A valve control system for a reciprocating gas compressor having at least on suction valve 180 between a gas supply and a compressor cylinder 100. The suction valve opens and closes automatically in response to pressure in the cylinder but has a locking assembly 10 which holds it in the open position for a selected period after it has opened, in synchronisation with the piston strokes of the compressor. This allows gas to enter and exit the compressor via the suction valve during the cycle for which the valve is open so that heat is removed along with the gas thus allowing the cylinder chamber to cool. The valve may be a disk or reed valve and the locking assembly may be electromagnetic or pneumatic. The compressor may have a heat regenerator 140 mounted within the compressor cylinder for enabling transfer of heat out of the cylinder.

Description

VALVE CONTROL SYSTEM FOR A RECIPROCATING COMPRESSOR

Field of the invention

The invention relates to a valve control system for influencing the operating cycle of a reciprocating gas compressor.

Background of the invention

GB2396667 and WO2004/059155 describe a reciprocating gas compressor operating according to an extended cycle of 4, 6 or more strokes, wherein the first two strokes are sequential induction and compression strokes using a low pressure gas as working fluid and compressing it to a high pressure gas, and the remaining strokes are pairs of sequential filling and emptying strokes using more of the low pressure gas as heat transfer fluid for transferring heat from inside the gas compressor to outside the gas compressor. The gas compressor also contains an in-cylinder heat regenerator for absorbing heat from the compressed gas and releasing heat to the heat transfer fluid thus achieving near-isothermal compression. Isothermal compression is the ideal thermodynamic process giving the highest compressor efficiency and the lowest power consumption.

In the above invention, it was suggested that the self- actuated suction valve conventionally used as intake in the compressor is replaced by an externally actuated flow valve which has higher flow coefficient and the opening and closing timings are programmable according to the additional strokes of the extended cycle and according to the instantaneous cylinder pressure while mimicking the operation of the suction valve. However, this externally actuated valve arrangement is complicated and involves substantial modification to the design of the conventional compressor. - 2

Summary of the invention

With the aim of simplifying the design while keeping to the above invention objective of achieving near-isothermal compression, there is provided according to the present invention a valve control system for a reciprocating gas compressor having at least one suction valve connecting between a gas supply and a compressor cylinder and the said suction valve opens and closes automatically while being lo moved by pressure in the cylinder, characterized in that a locking assembly is provided for holding the said suction valve at the open position for a selected period after it has opened, and is controlled in synchronization with the reciprocating strokes of the compressor.

In the invention, the said locking assembly acts to keep the said suction valve open by preventing it from being closed by subsequent change in pressure in the cylinder.

The said suction valve may be a reed valve or a disk valve of conventional design and the said locking assembly is attached to the moveable reed or disk of the suction valve.

Thus, in keeping with the invention described in GB2396667 and WO2004/059155, the locking assembly is timed to sequentially lock and unlock the said suction valve in synchronization with an extended cycle of the reciprocating gas compressor having extra gas exchange strokes following the normal suction and compression strokes of the compressor. During the said gas exchange strokes, the suction valve is kept open and prevented from being closed by pressure in the cylinder, thus permitting gas flow back and forth between the said gas supply and the compressor cylinder during this period.

When used in conjunction with a heat regenerator mounted within the compressor cylinder, the invention enables transfer of heat out of the heat regenerator during - 3 the extra gas exchange strokes and absorption of heat into the heat regenerator during the subsequent compression stroke of the compressor thus achieving near-isothermal compression of the gas.

The locking assembly may be designed in a variety of ways to provide a holding force on the suction valve after it has opened. In a preferred example, the locking assembly comprises an electro-magnetic linkage for holding the lo moveable reed or disk of the valve at a predetermined fully open position when the electro-magnet is energised for a selected period in synchronization with the reciprocating strokes of the compressor. In this case, the reed or disk valve first opens automatically while being moved by pressure in the cylinder, then opens further to a predetermined fully open position while being moved by the force of the electro-magnet and is held by the electro- magnet at the fully open position for a selected period in synchronization with the reciprocating strokes of the compressor. This ensures high gas flow through the reed valve in both directions and low pressure loss across the valve during the gas exchange strokes of the compressor.

Such locking assembly will be beneficial for holding the suction valve in the fully open position during the suction period of any gas compressor (with or without the extended cycle of extra gas exchange strokes) for increasing the volumetric efficiency and mass throughput of the compressor including the conventional compressor.

Preferably a valve position sensor is provided for detecting and confirming that the suction valve has started to open before a signal is sent by the valve control system to energise the electro-magnet. This prevents the suction valve from being opened prematurely before the start of the suction period, which occurs at a variable timing relative to TDC of the compressor depending on the re-expansion of the gas retained in the compressor.

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In an alternative example, the locking assembly comprises a moveable linkage attached to the said suction valve, a hydraulic chamber containing hydraulic fluid displaced freely by movement of the moveable linkage, and a non-return fluid valve for preventing closing displacement of the hydraulic fluid after the valve has opened, thereby hydraulically locking the moveable linkage and the said suction valve in the open position. A bypass fluid valve connected in parallel with the said non- return fluid valve lo is provided to allow free displacement of the hydraulic fluid after the locking period and is controlled by an actuator in synchronization with the reciprocating strokes of the compressor.

Brief description of the drawing

The invention will now be described further, by way of example, with reference to the accompanying drawings in which Figure 1 shows a schematic view of an extended cycle reciprocating gas compressor have a valve control system of the present invention, Figure 2 shows an enlarged schematic view of a preferred design of the valve control system shown in Figure 1, and Figure 3 shows an enlarged schematic view of an alternative design of the valve control system shown in Figure 1.

Detailed description of the preferred embodiment

Figure 1 shows a reciprocating air compressor comprising at least one cylinder 100 having a variable volume defined by a reciprocating piston 120 which draws ambient air (work fluid) through a suction valve 180 into the cylinder 100 during the induction stroke and compresses the air to a high pressure before the air is released - 5 - through a non-return valve 160 to a high pressure air reservoir 320 during the compression stroke. The suction valve 180 opens and closes automatically while being moved by pressure in the cylinder 100. This could be a reed valve or disk valve of conventional design. In so far described, the compressor is conventional.

In order to achieve the invention objective described in GB2396667 and W02004/059155, a locking assembly 10 is lo provided for preventing the suction valve 180 from being closed after it has opened during selected strokes of the reciprocating compressor according to an extended cycle comprising after the said induction and compression stroke, at least one pair of extra strokes during which the suction valve 180 is locked open, each pair consisting of a filling stroke in which more ambient air (heat transfer fluid) is drawn by the piston 120 (as shown by the ingoing arrow) into the cylinder 100 to fill the cylinder followed immediately by an emptying stroke in which the filled air is expelled by the piston 120 (as shown by the outgoing arrow) out of the cylinder 100 back to the ambient. In use, the filled heat transfer fluid air cools the cylinder 100 and piston 120 and lowers the air compressor temperature close to the temperature of the filled air during the extra strokes, before the extended cycle is repeated with the working fluid of fresh air inducted into the cylinder 100 and compressed during the next compression stroke.

An open matrix heat regenerator 140 constructed in fine mesh or thin wall cell structure of high heat capacity material is also provided occupying the clearance space in the cylinder 100 and in intimate thermal contact with the air inside the cylinder 100. The heat regenerator 140 serves efficiently to absorb and store heat from the compressed air during the compression stroke, and to release the stored heat to the filled air during the extra filling and emptying strokes of the extended cycle. - 6 -

Figure 1 shows the piston position during a filling stroke of the extended cycle when ambient air is drawn into the cylinder 100 through a one-way valve 220 along a filling port 200 through the suction valve 180 which is locked in the open position. The filling air passes through the open matrix of the heat regenerator 140 and rapidly attains equilibrium temperature with the heat regenerator 140 while absorbing heat from the heat regenerator 140. The hot air is then expelled through the one-way valve 240. This is followed by the normal induction and compression strokes of the compressor cycle with the suction valve 180 unlocked so that it can freely open and close while being moved by the pressure in the cylinder 100. The inducted working fluid air is cooled by the heat regenerator 140 and continues to be cooled while being compressed and staying at substantially the same temperature as the heat regenerator thus achieving a compression process which is near- isothermal.

Because the filling and emptying of the heat transfer air during the extra strokes of the extended cycle take place with the suction valve 180 locked open, the pumping work associated with these two extra strokes will be small and does not significantly affect the mechanical efficiency of the air compressor. On the other hand, the rated delivery of the gas compressor will be reduced because of the extra strokes, though the breathing efficiency during the induction stroke would be improved because of more efficient gas flow and cooler gas charge. On balance the work efficiency of the compressor will be improved while the mass throughput will be substantially unchanged.

If necessary, the sequential filling and emptying strokes may be repeated in pairs to allow the heat regenerator 140 to give up more heat more thoroughly. Thus the reciprocating air compressor could be operated according to an extended cycle of 4, 6 or more strokes, where the - 7 first two strokes with the suction valve 180 unlocked are the working strokes for inducting and compressing the air, and the remaining pairs of strokes with the suction valve locked open are the cooling strokes using more air as heat transfer fluid for transferring heat out of the cylinder 100 which also contains a heat regenerator 140 acting as a cold storage.

The locking assembly 10 in Figure 1 may be designed in lo a variety of ways to provide a holding force on the suction valve 180 after it has opened. In a preferred design example shown in Figure 2, the locking assembly 10 comprises an electro-magnetic linkage 20, 30 for holding the moveable reed or disk of the suction valve 180 at a predetermined fully open position when the electro-magnet 30 is energised for a selected period in synchronization with the reciprocating strokes of the compressor. In this case, the reed or disk valve 180 first opens automatically while being moved by pressure in the cylinder, then opens further to a predetermined fully open position while being moved by the force of the electro-magnet 30 and is held by the electro- magnet 30 at the fully open position for a selected period in synchronization with the reciprocating strokes of the compressor. This ensures high gas flow through the reed valve 180 in both directions and low pressure loss across the valve 180 during the gas exchange strokes of the compressor. Such locking assembly will be beneficial for holding the suction valve in the fully open position during the suction period of any gas compressor (with or without the extended cycle of extra gas exchange strokes) for increasing the volumetric efficiency and mass throughput of the compressor including the conventional compressor.

Preferably a valve position sensor 40 is provided for detecting and confirming that the suction valve 180 has started to open before a signal is sent by a controller 50 to energise the electro-magnet 30. This prevents the - 8 suction valve 180 from being opened prematurely before the start of the suction period, which occurs at a variable timing relative to TDC of the compressor depending on the re-expansion of the gas retained in the compressor.

In an alternative design example shown in Figure 3, the locking assembly 10 comprises a moveable linkage 60 attached to the suction valve 180, a hydraulic chamber 70, 72, 74 containing hydraulic fluid displaced freely by movement of lo the moveable linkage 60, and a non-return fluid valve 80 for preventing closing displacement of the hydraulic fluid after the valve 180 has opened, thereby hydraulically locking the moveable linkage 60 and the suction valve 180 in the open position. A bypass fluid valve 90 connected in parallel with the non-return fluid valve 80 is provided to allow free displacement of the hydraulic fluid after the locking period and is controlled by an actuator (not shown) in synchronization with the reciprocating strokes of the compressor.

The invention of Figures 2 and 3 has low power consumption for the locking of the suction valve 180 and only requires modification to the suction valve 180 and the associated cylinder head of a conventional reciprocating gas compressor. - 9 -

Claims

1. A valve control system for a reciprocating gas compressor having at least one suction valve connecting between a gas supply and a compressor cylinder and the said suction valve opens and closes automatically while being moved by pressure in the cylinder, characterized in that a locking assembly is provided for holding the said suction valve at the open position for a selected period after it lo has opened, and is controlled in synchronization with the reciprocating strokes of the compressor.

2. A valve control system as claimed in claim 1, wherein the said locking assembly is timed to sequentially lock and unlock the said suction valve in synchronization with an extended cycle of the reciprocating gas compressor having extra gas exchange strokes following the normal suction and compression strokes of the compressor, the said valve being locked in the open position to permit gas flow back and forth between the said gas supply and the compressor cylinder during the said gas exchange strokes.

3. A valve control system as claimed in claim 2, used in conjunction with a heat regenerator mounted within the compressor cylinder for enabling transfer of heat out of the heat regenerator during the extra gas exchange strokes and absorption of heat into the heat regenerator during the subsequent compression stroke of the compressor thus achieving nearisothermal compression of the gas.

4. A valve control system as claimed in any preceding claim, wherein the said suction valve is a reed valve or a disk valve and the said locking assembly is attached to the moveable reed or disk of the suction valve.

5. A valve control system as claimed in any preceding claim, wherein the locking assembly comprises an electro - To magnetic linkage for holding the moveable reed or disk of the valve at a predetermined fully open position when the electro-magnet is energised for a selected period in synchronization with the reciprocating strokes of the compressor.

6. A valve control system as claimed in claim 5, wherein the reed or disk valve first opens automatically while being moved by pressure in the cylinder, then opens lo further to a predetermined fully open position while being moved by the force of the electro-magnet and is held by the electro-magnet at the fully open position for a selected period in synchronization with the reciprocating strokes of the compressor.

7. A valve control system as claimed in claim 5 or 6, wherein a valve position sensor is provided for detecting and confirming that the suction valve has started to open before a signal is sent by the valve control system to energise the electro-magnet.

8. A valve control system as claimed in claims 7, wherein a bypass fluid valve connected in parallel with the said non-return fluid valve is provided to allow free 2-way displacement of the hydraulic fluid after the locking period is over and is controlled by an actuator in synchronization with the reciprocating strokes of the compressor.

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8. A valve control system as claimed in any one of claims 1 to 4, wherein the locking assembly comprises a moveable linkage attached to the said suction valve, a hydraulic chamber containing hydraulic fluid displaced freely by movement of the moveable linkage, and a non-return fluid valve for preventing closing displacement of the hydraulic fluid after the valve has opened, thereby hydraulically locking the moveable linkage and the said suction valve in the open position.

9. A valve control system as claimed in claims 8, wherein a bypass fluid valve connected in parallel with the said non-return fluid valve is provided to allow free displacement of the hydraulic fluid after the locking period and is controlled by an actuator in synchronization with the reciprocating strokes of the compressor. 1'

Amendments to the claims have been filed IS follows

1. A valve control system for a reciprocating gas compressor having at least one suction valve connecting between a gas supply and a compressor cylinder and the said suction valve opens and closes automatically while being moved by pressure in the cylinder, characterized in that a locking assembly is provided for holding the said suction valve at the open position for a selected period after it lo has opened, and further characterized in that the said locking assembly is timed to sequentially lock and unlock the said suction valve in synchronization with an extended cycle of the reciprocating gas compressor having extra gas exchange strokes following the normal suction and compression strokes of the compressor, the said valve being locked in the open position to permit gas flow back and forth between the said gas supply and the compressor cylinder during the said gas exchange strokes.

2. A valve control system as claimed in claim 1, used in conjunction with a heat regenerator mounted within the compressor cylinder for enabling transfer of heat out of the heat regenerator during the extra gas exchange strokes and absorption of heat into the heat regenerator during the subsequent compression stroke of the compressor thus achieving nearisothermal compression of the gas.

3. A valve control system as claimed in claim 1 or 2, wherein the said suction valve is a reed valve or a disk valve and the said locking assembly is attached to the moveable reed or disk of the suction valve.

4. A valve control system as claimed in any preceding claim, wherein the locking assembly comprises an electro magnetic linkage for holding the moveable reed or disk of the valve at a predetermined fully open position when the electro-magnet is energised for a selected period in ë. ëe e -.

. e e . . synchronization with the reciprocating strokes of the compressor.

5. A valve control system as claimed in claim 4, wherein the reed or disk valve first opens automatically while being moved by pressure in the cylinder, then opens further to a predetermined fully open position while being moved by the force of the electro-magnet and is held by the electromagnet at the fully open position for a selected lo period in synchronization with the reciprocating strokes of the compressor.

6. A valve control system as claimed in claim 4 or 5, wherein a valve position sensor is provided for detecting and confirming that the suction valve has started to open before a signal is sent by the valve control system to energise the electro-magnet.

7. A valve control system as claimed in any one of claims 1 to 3, wherein the locking assembly comprises a moveable linkage attached to the said suction valve, a hydraulic chamber containing hydraulic fluid displaced freely by movement of the moveable linkage, and a non-return fluid valve for preventing closing displacement of the hydraulic fluid after the valve has opened, thereby hydraulically locking the moveable linkage and the said suction valve in the open position.