GB2579402A

GB2579402A - Method of filling a pressurised gas reservoir

Info

Publication number: GB2579402A
Application number: GB1819560.2A
Authority: GB
Inventors: Anderson Stewart; Philby Rhoy; Peter Duffy Liam
Original assignee: Haskel Europe Ltd
Current assignee: Haskel Europe Ltd
Priority date: 2018-11-30
Filing date: 2018-11-30
Publication date: 2020-06-24
Anticipated expiration: 2038-11-30
Also published as: GB201819560D0; GB2579402B

Abstract

A method of filing a pressurized gas reservoir 40, such as a vehicle fuel supply station tank, comprises connecting a reciprocating compressor 80, operating the compressor to supply compressed gas to the reservoir, monitoring the pressure within the gas reservoir, such as by means of a pressure sensor 50, and reducing the compressor output when the pressure reaches a predetermined point. Also disclosed is a system for filling a gas reservoir comprising a reciprocating compressor, a pressure sensor, and a control system 90, which is suitable to reduce the compressor output when the pressure reaches a certain limit. In some embodiments there may be a second compressor 85, or a second gas reservoir 41, 42.

Description

Method of filling a pressurised gas reservoir This invention relates to a method and system for filling a pressurised gas reservoir, typically a fuel gas reservoir.

A typical gas-fuelled vehicle has a reservoir or tank for holding fuel gas in a pressurised state. When the vehicle comes to be refuelled, gas under pressure is introduced into the vehicle's tank from one or more supply reservoirs. During use, the pressure within the supply reservoirs decreases as gas is expelled, and the pressure within a receiving gas reservoir increases. The supply reservoir(s) therefore need periodic refilling to ensure that not only is a sufficient volume of pressurised gas maintained, but also that the supply pressure is sufficient to meet the needs of the vehicle to be filled.

It is known to have use various methods to refill a supply reservoir including, but not limited to being topped up from time to time from other storage units held at higher pressure than the reservoir being refilled, or it may be topped up from a local gas generator and may be supplied into the containers using a pump, a compressor or any other suitable device for delivering gas under pressure. A gas generator may synthesise or concentrate gas from another resource: for instance it may extract hydrogen from water by electrolysis and then deliver it to supply reservoir.

Whenever a compressor is used to deliver pressurised gas to the supply reservoir, a pressure pulse is generated within each cycle of the compressor. This is particularly true when the compressor is a reciprocating compressor having one or more reciprocating pistons. The pressure pulse is generally most evident at the end of the compression stroke and can be up to 40% higher than the intended compressor outlet pressure. The pressure pulse may exist only for a relatively short period of time, but they can still affect the system.

Such pressure pulses however have a detrimental effect upon the reservoirs and the entire pressurised gas supply system. For example, safety valves, which are intended to prevent the system being operated at pressures that are too high and therefor potentially unsafe, can be triggered by the pressure pulses. This leads to a shutting down of the refilling process and to any supply. Resetting the system inevitably takes time, so unnecessary shutdowns are costly. Furthermore, the pressure pulses set up shockwaves which travel through the system and which can lead to degradation of joints and/or of individual components and adversely affect the mechanical integrity of the system over time. Given the high pressures (up 600-700bar or more) that the system can contain, failure of any component could lead to catastrophic consequences.

Therefore the present invention aims to provide a method and system which can avoid or reduce the generation of the pressure pulses.

According to the present invention there is provided a method of filling a gas reservoir with pressurised gas, the method comprising the steps of: connecting a reciprocating compressor to the gas reservoir to be filled; operating the compressor to supply pressurised gas to the reservoir; monitoring the pressure within the gas reservoir; and reducing the operational output of the compressor once the monitored reservoir pressure is within a predetermined amount of a target pressure.

The step of reducing the speed may include reducing the speed by more than 10%, more than 25% or more than 50%.

The predetermined amount may be a predetermined percentage of the target pressure or may be an absolute pressure differential between the target pressure and the monitored outlet pressure.

The method may further comprise the step of connecting a second compressor to the first reservoir. Such connection may be in series or in parallel.

The second compressor may pressurise the gas reservoir to a different pressure to that of the first compressor.

The method may further comprise the step of connecting a second reservoir to the same compressor(s) as the first reservoir.

The invention also provides a system for filling a gas reservoir with pressurised gas, the system comprising: a reciprocating compressor configured for connection to the gas reservoir to be filled; a pressure sensor for monitoring the pressure within the gas reservoir; and a control system configured to monitor the pressure within the reservoir and reduce the operational output of the compressor once the monitored pressure is within a predetermined amount of a target pressure.

The system may further comprise a second compressor connected in either series or parallel with the first compressor. A second gas reservoir may be in series with the first reservoir or may be connected to a second compressor.

The system is preferably configured to carry out the method as described above.

The present invention will now be described by way of example with reference to the accompanying drawings. In the drawings: Figure 1 shows an exemplary pressurised gas supply system.

Figure 2 shows a further exemplary pressurised gas supply system.

Figure 3 shows a yet further exemplary pressurised gas supply system.

Figure 4 is a graph illustrating the problem with known system.

Figure 5 is a graph illustrating the effect of the invention on the cyclic pressure from a compressor.

In Figure 1, an exemplary pressurised gas supply system is shown. Three supply reservoirs or cascades 40, 41, 42 are provided (although it will be recognised that two, or four or more could be used) and these contain pressurised gas and are used to fill a vehicle reservoir 43. A control valve 401, 411, 421 is associated with a respective supply reservoir. Each valve 401, 411, 421 is located on, and controls the flow through, a respective flow line 402, 412, 422. The flow lines are joined so as to form a common supply line 44 which connects for example via a nozzle (not shown) to the reservoir 43 in the vehicle, typically the fuel tank. By opening one more of the control valves, the vehicle reservoir 43 is placed in fluid communication with the respective supply reservoir(s) via the common supply line and pressurised gas can then flow from higher to lower pressure, typically to fill the vehicle reservoir 43.

Pressure sensors 50 are typically provided in numerous locations throughout the system. The pressure sensors may be of any suitable type and can be located on one or more, or each, fluid pathway, before and/or after a respective control valve. As examples, the figures show how a sensor may be placed only after a valve (valve 401), on both sides of a valve (valve 411), or only before a valve (valve 421). The exact locations would be determined on a system by system basis depending upon the specific requirements. Pressure sensors may be located within the individual supply reservoirs 40, 41, 42 and/or may be located in the common supply pathway 44 and/or in the dispensing nozzle (not shown). The pressure sensors preferably provide pressure readings to a valve controller (not shown).

The three supply reservoirs 40, 41, 42 store pre-pressurised gas, although different numbers of tanks could be used. Conveniently the gas source is at a higher pressure than the receiving vessel. For example, it may be at a pressure at least 100 bar above the initial pressure of the receiving vessel. The reservoir 21 may store gas at a pressure in the range from 100 to 500 bar, conveniently more than 400 bar. The initial pressure in the receiving vessel may be in the range from 40 to 400 bar, conveniently less than 200 bar. Other pressures are also suitable. The individual reservoirs may be rated to store gas at the same pressure. Alternatively, one or more reservoirs may be rated at a lower or higher pressure than other reservoirs. The reservoirs may have the same capacity, or may have different capacities. Larger capacity reservoirs may be used for the lower pressure storage. A larger capacity lower pressure reservoir has the advantage that the filling of a single tank reduces the pressure less than filling from a smaller tank, meaning that a greater number of receiving reservoirs can be filled before needing to recharge.

As gas is dispensed from a particular supply reservoir, the pressure of the retained gas reduces. Whilst the pressure of the retained gas is above a certain level, dependent upon the particular configuration of each individual system, the supply reservoir can still be useful for refilling purposes. However, at some stage, it is necessary to refill one or many of the supply reservoirs 40, 41, 42.

As shown in Figure 1, a compressor 80 can be connected to any or all of the supply reservoirs 40, 41, 42 by way of respective recharge lines 81, 82, 83 -one or more recharge valves (not shown) may be provided on each recharge line or within the compressor itself to allow the compressor to be placed in fluid communication with the desired supply reservoir for recharging. The compressor 80 and/or the recharge valves may be operated by a recharge controller 90 by way of one or more signal lines 91, which may be physical connections or may be made by any suitable wireless protocol.

The recharge controller 90 preferably comprises a processor 93 and a memory 94. The memory 94 stores in a non-transient manner program code that is executable by the processor to implement the functions described of the controller herein.

The control signal may be, for example, an electrical signal. In one example, the controllable valve may comprise a valve body defining a passageway for gas through the valve, and a closure element such as a needle or a moveable plug that can be moved across the passageway to adjust the flow therethrough. The closure element may be coupled to a solenoid or a motor so that it can be moved in response to the control signal. The controllable valve may be an automatic pressure regulator valve.

Alternative configurations are shown in Figure 2 and 3. Common features are not described again, but reference is made to the description of Figure 1.

In Figure 2, a second compressor 85 is provided and can be connected to any or all of the supply reservoirs 40, 41, 42 by way of respective recharge lines 86, 87, 88 one or more recharge valves (not shown) may be provided on each recharge line 86, 87, 88 or within the compressor 85 itself to allow the compressor to be placed in fluid communication with the desired supply reservoir for recharging. The compressor 85 and/or the recharge valves may be operated by a recharge controller 90 by way of one or more signal lines 92, which may be physical connections or may be made by any suitable wireless protocol. In this way, one supply reservoir may be refilled by two compressors, either simultaneously for faster refilling or sequentially such that one compressor can generated a higher pressure, so is used to top-up a supply reservoir after a lower rated compressor is used. Typically, a higher pressure rated compressor will be more expensive and/or larger in size, so using differing compressors of different ratings can be more economic. Figure 2 shows two compressors in parallel. As an alternative, two compressors may be used in series. This is beneficial especially when the pressure of the incoming flow to the compressor is low, as typically the compressors only have an 8 to 1 compression ratio, so a series configuration allows for greater compression. More than two compressors could be used in series or in parallel.

In Figure 3, a third compressor 95 is provided, but each compressor now acts to supply only a single supply reservoir. In the configurations of either Figure 2 or Figure 3, one or multiple recharge controllers could be utilised. One recharge controller may be associated with each compressor.

In all example, each compressor is preferably a reciprocating compressor, which may be hydraulic, having a reciprocating piston. On the compression stroke of the compressor, a pressure pulse is generated within the pressurised gas being supplied. The pressure pulse can be up to 40% higher than the normal outlet pressure of the compressor.

This pressure pulse places significant strain and stress on the physical structures of the refilling system, and also leads to unwanted activation of safety cut -offs and the like, which can be triggered when an unacceptably high pressure is sensed. The recharge controller 90 is therefore configured to be able to adjust the operation of the compressors, either individually or in groups, to mitigate against this pressure pulse. It does this by sensing when the pressure in the receiving supply reservoir reaches a predetermined level and then adjust the operation of the compressor, for example by reducing the operating speed and/or frequency of the compressor. By reducing the speed and/or frequency, the peak pressure generated by the compressor is reduced and prevents such large pressure pulse being sent through the refilling system.

The pressures within a standard system are illustrated in the graph of Figure 4 which shows the pressure cycles (line 100) within the compressor output (which is of course the input to the receiving reservoir), as the pressure in the receiving reservoir (line 101) increases. As can be seen, the pressure of the compressor output 100 spikes on every cycle well beyond the pressure within the receiving reservoir 101. As the pressure in the receiving reservoir increases, those pressure peaks 103 get closer to, and then exceed the substantially horizontal line 102, which represents the safety pressure above which the system can automatically shut down.

The corresponding graph using the method of the invention is shown in Figure 5 in which, as the spikes of line 100 approach the safety limit 102, the compressor output has been reduced by being slowed down/having the frequency reduced or the like, so as to reduce the pressure peak 103 from the compressor to below the threshold at which the safety cut out is activated.

For example, as the receiving supply reservoir pressure becomes within 10% of the target outlet pressure, the operation of the compressor may be reduced by upto 50%, although benefits can be achieved by as little as a 10% reduction. Such operational reduction of the compressor may be achieved by reducing the frequency of the compressor cycling, reducing the inlet pressure of fluid to the compressor, reducing the speed of the compressor. In essence, any change in operation of the compressor which reduces the output pressure to the desired level is an option, although reducing the frequency is the most preferable. Such a reduction can preferably limit the pressure pulse to no more than 10% and preferably no more than 5% of the intended compressor outlet pressure or the desired pressure level in the receiving reservoir.

The configuration shown in Figure 1 has the advantage that the refilling of multiple reservoirs simultaneously assists in reducing the effect of the pressure pulse as any spike in pressure is buffered by the larger volume (when compared to refilling a single reservoir). Thus the full effect of any pressure pulse is only felt once the volume left to be filled in each reservoir is much smaller.

The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Claims

CLAIMS1. A method of filling a gas reservoir with pressurised gas, the method comprising the steps of: connecting a reciprocating compressor to the gas reservoir to be filled; operating the compressor to supply pressurised gas to the reservoir; monitoring the pressure within the gas reservoir; and reducing the operational output of the compressor once the monitored reservoir pressure is within a predetermined amount of a target pressure.
2. A method according to claim 1, wherein the step of reducing the speed includes reducing the speed by more than 10%.
3. A method according to claim 2, wherein the step of reducing the speed includes reducing the speed by more than 25%.
4. A method according to claim 3, wherein the step of reducing the speed includes reducing the speed by 50% or more.
5. A method according to any one of the preceding claims, wherein the predetermined amount is a predetermined percentage of the target pressure.
6. A method according to any one of the preceding claims, wherein the predetermined amount is an absolute pressure differential between the target pressure and the monitored outlet pressure.
7. A method according to any one of the preceding claims, further comprising the step of connecting a second compressor to the first reservoir.
8. A method according to claim 7, wherein the first and second compressors are connected in parallel.
9. A method according to claim 7, wherein the first and second compressors are connected in series.
10. A method according to claim 8 or claim 9, wherein the second compressor pressurises the gas reservoir to a different pressure to that of the first compressor.
11. A method according to any one of the preceding claims, further comprising the step of connecting a second reservoir to the same compressor(s) as the first reservoir.
12. A system for filling a gas reservoir with pressurised gas, the system comprising: a reciprocating compressor configured for connection to the gas reservoir to be filled; a pressure sensor for monitoring the pressure within the gas reservoir; and a control system configured to monitor the pressure within the reservoir and reduce the operational output of the compressor once the monitored pressure is within a predetermined amount of a target pressure.
13. A system according to claim 12, further comprising a second compressor connected in either series or parallel with the first compressor.
14. A system according to claim 12 or claim 13, further comprising a second reservoir.
15. A system according to any of claims 12 to 14, wherein the control system is configured to carry out the method of any of claims 1 to 11.