Portable washing system for cleaning a gas compressor

Abstract

A portable washing unit 10 for supplying a liquid cleaning agent to a gas compressor 6 in situ in a fluid processing system. The washing unit comprises a cleaning agent storage tank 11, a cleaning agent supply line 12 for supplying a liquid cleaning agent from the tank to a tie-in point 7 of the fluid processing system, and a pump 15 in the cleaning agent supply line. The compressor has a gas inlet and a gas outlet, and the tie-in point is upstream of the inlet. A supply, non-return, pressure relief and / or isolation valve 14, 16 may be provided in the fluid supply line, and a shut-off valve 8 may be provided at the tie-in point. A connector 13 may connect the supply line to the tie-in point. The tank, pump and / or supply line may be arranged on a skid or a trolley. The pump may increase the pressure of the cleaning agent to a pressure higher than the suction pressure of the compressor.

Description

The present invention relates to cleaning of a gas compressor in situ in a fluid processing system, and in particular a portable washing unit for cleaning a gas compressor in a fluid processing system. In the oil and gas industry, gas compressors are used during the processing of well fluids to compress the gas to help transport the well fluid from one location to the next. Indeed, it can be necessary to use gas compressors to achieve a sufficiently high rate of production from the well. In multiphase fluid processing, it is common to remove as much liquid as possible from the gas before the gas is passed through the compressor and compressed. This is because liquid passing through the compressor can cause damage or fouling of the compressor. Processing components located upstream of the compressor may be used to try to reduce or minimise the liquid content in the gas before it reaches the compressor. For example, a multiphase flow may be separated into gas and liquid in a separator upstream of the compressor. Preparation of the gas upstream of the compressor may be imperfect, such that the gas entering the compressor may contain some liquid or moisture in very small quantities. High temperatures inside the compressor can cause the liquid entrained in the gas to vaporize away resulting in solid materials such as salts and scale being deposited on surfaces inside the compressor. Such deposits can detrimentally affect compressor performance and reduce the service life of the compressor. “Online” cleaning solutions have been proposed in which a liquid cleaning agent (e.g. liquid hydrocarbons, condensed hydrocarbon gas, glycol, water, or mixtures thereof) is passed through the compressor, during operation of the compressor, to clean deposited solid material from a fouled portion of the compressor. It has been found that adding a relatively small quantity of liquid to the gas stream can effectively remove deposited solid or “greasy” materials that have accumulated within the compressor without damaging the compressor. The cleaning is primarily mechanical, due to the impact of the liquid against the deposited material which acts to knock the deposits away from the internal surface of the compressor. This is caused by rotation of the compressor impellers, which generate a spray of liquid droplets travelling at high speeds towards the internal surfaces of the compressor. There remains a need for techniques for supplying cleaning solutions to gas compressors whilst they are operating in a fluid processing system so that they can undergo online cleaning. Viewed from a first aspect, the present invention provides a portable washing unit for supplying a liquid cleaning agent to a gas compressor in situ in a fluid processing system during a cleaning operation, comprising: a cleaning agent storage tank for storing a liquid cleaning agent; a cleaning agent supply line fluidly connected to the cleaning agent storage tank for supplying a liquid cleaning agent from the cleaning agent storage tank to a tie-in point of a fluid processing system; and a pump arranged for drawing a liquid cleaning agent from the cleaning agent storage tank and pumping it through the cleaning agent supply line. The above portable washing unit advantageously provides added flexibility when cleaning gas compressors in fluid processing systems. The portable washing unit can be easily installed in or removed from a fluid processing system, and moved between different fluid processing systems (e.g. at different locations). This means that the fluid processing systems do not require dedicated processing components to enable compressor cleaning, and instead they can rely on the portable washing unit to provide a cleaning solution. In addition to providing greater flexibility, this may provide a cost saving, since it avoids the need to provide multiple fluid processing systems with dedicated washing units. It will also be appreciated that the portable nature of the washing unit means that a component thereof (or indeed the entire unit) can be more easily repaired or replaced if it becomes damaged or reaches the end of its service life. Without the need for a dedicated washing unit, fluid processing systems can be made simpler since they will require fewer processing components. Rather, cleaning can be initiated without (substantial) modification of a fluid processing system, with only a simple tie-in point or interface being required to enable the portable washing unit to be coupled to the system for supplying a liquid cleaning agent. It will also be easier to fill the storage tank with cleaning liquid compared to a dedicated (non-portable) system, since the portable unit can be moved to a source of cleaning liquid, such as a filling station, where it can easily be filled. Replacing a cleaning liquid with another, different liquid is similarly made easier. A first end of the cleaning agent supply line may be fluidly connected to the cleaning agent storage tank. A second end of the cleaning agent supply line may be configured to be fluidly connected to a tie-in point of a fluid processing system. The supply line may comprise a connector for fluidly connecting the supply line to a tie-in point of a fluid processing system. The connector may be configured to connect to an existing tie-in point in a fluid processing system. In this way, the portable washing unit may be connected to the fluid processing system without modification to the fluid processing system. The connector may be arranged at the second end of the supply line (i.e. the end of the supply line not connected to the storage tank). The pump can be used to increase the pressure of the liquid cleaning agent to a sufficient pressure so that it can be injected into a fluid stream (e.g. a gas stream) in a fluid processing system to facilitate cleaning of a gas compressor in situ in the fluid processing system. The pump may be arranged in the cleaning agent supply line. By “arranged in” it is meant that the pump (or other component) is installed inline of and in between two sections forming the cleaning agent supply line. The portable washing unit may comprise a controllable supply valve (e.g. a control valve) in the cleaning agent supply line configured to control flow of liquid cleaning agent along the liquid cleaning agent supply line. The supply valve may be arranged upstream of the pump (i.e. in a flow path between the cleaning agent storage tank and the pump) or downstream of the pump. The terms “upstream” and “downstream” should be understood to refer to the flow of fluid during normal operation of a system, with fluid flowing from upstream to downstream. During normal operation of the portable washing unit, operation of the pump will cause liquid cleaning agent to flow from the cleaning agent storage tank and through the cleaning agent supply line. The supply valve is preferably configured such that when it is closed, liquid is prevented from flowing from the cleaning agent storage tank and out of the portable washing unit via the cleaning agent supply line. Hence, a supply of liquid (e.g. a liquid cleaning agent) output from the portable washing unit via the cleaning agent supply line can be stopped by closing the supply valve. The portable washing unit may comprise a non-return valve in the cleaning agent supply line to prevent back-flow of fluid in the cleaning agent supply line towards the cleaning agent storage tank. Preferably, the non-return valve is arranged downstream of the pump to prevent back-flow of fluid into the pump. The portable washing unit may comprise a pressure relief valve in the cleaning agent supply line for relieving pressure within the portable washing unit. The pressure relief valve may be configured to allow fluid to be vented from the portable washing unit when the pressure within the portable washing unit exceeds a threshold pressure. Fluid may be prevented from being vented from the portable washing unit via the pressure relief valve when the pressure within the portable washing unit is at or below the threshold pressure. The threshold pressure may vary between portable washing units, and will depend on the intended application of the portable washing unit. It should be set high enough to permit the liquid cleaning agent to reach a sufficiently high pressure within the portable washing unit so that it can be injected into a fluid stream of a fluid processing system. In particular, the pressure in the supply line should be able to exceed the suction pressure (inlet pressure) of the gas compressor which is to be cleaned using the portable washing unit. The suction pressure of a gas compressor may vary from 1 bar (100 kPa) to several hundred bar, e.g. 100 bar, 200 bar or 300 bar (10 MPa, 20 MPa or 30 MPa), depending on the application. The threshold pressure may be sufficiently high to overcome any pressure losses in the supply line, including e.g. any valves therein and restrictions at the connector (i.e. the tie-in point). The pressure relief valve may be arranged downstream of the pump. Through provision of the pressure relief valve, over-pressurisation of the portable washing unit can be avoided, helping to maintain integrity of the system and prevent damage to components of the portable washing unit, such as the pump and / or the storage tank. The pressure relief valve also helps to avoid rupture and / or explosion of the unit. Hence, safety of the portable washing unit can be improved. The portable washing unit may comprise a flow measurement device (e.g. a flow meter) in the cleaning agent supply line for measuring a quantity of liquid cleaning agent supplied by the portable washing unit. The flow measurement device may be arranged upstream of the supply valve and / or the non-return valve. The portable washing unit may comprise one or more (controllable) isolation valves in the cleaning agent supply line. The isolation valve(s) may be used to selectively prevent liquid from being expelled from the portable washing unit via the cleaning agent supply line. When closed, the one or more isolation valves may serve to prevent liquid from flowing out of the portable washing unit via the cleaning agent supply line, thereby isolating the portable washing unit from a system that it is connected to, e.g. a gas processing system. When open, the isolation valve(s) may permit liquid to exit the portable washing unit via the cleaning agent supply line. The portable washing unit may comprise an isolation valve directly upstream of the connector. That is, there may be no processing components or equipment in the flow path between the isolation valve and the connector. The storage tank preferably includes an inlet for introducing liquid (e.g. a liquid cleaning agent) into the storage tank. The inlet is preferably separate from the cleaning agent supply line. In some embodiments the portable washing unit includes a spray nozzle, e.g. arranged on the cleaning agent supply line, for forming the liquid cleaning agent into a spray. In this way, droplets of liquid cleaning agent can be formed by the spray nozzle to facilitate cleaning of a gas compressor (or other components of a fluid processing system) by the liquid cleaning agent. However, in a preferred embodiment, the portable washing unit does not include a spray nozzle. For instance, a spray nozzle may not be arranged on the cleaning agent supply line. For cleaning of a centrifugal compressor operating at normal velocity, it may not be necessary to provide a dedicated spray nozzle to atomise (i.e. form a spray) the liquid cleaning agent since the action of the compressor impellers themselves may be sufficient to generate a spray of the liquid cleaning agent to facilitate cleaning of the compressor. Preferably, the cleaning agent supply line (or at least a portion thereof) comprises a flexible hose. For example, part of the cleaning agent supply line at its second end may comprise a flexible hose. In some arrangements, a section of the cleaning agent supply line between the pump and the second end of the cleaning agent supply line comprises a flexible hose and / or a section of the cleaning agent supply line between the cleaning agent storage tank and the pump comprises a flexible hose. The flexibility of the hose may make it easier to connect the portable washing unit (e.g. the cleaning agent supply line) to a fluid processing system. The cleaning agent supply line may comprise rigid pipe, for instance one or more sections of rigid pipe. Rigid pipe may be required when a flow measuring device is arranged in the cleaning agent supply line, since the fluid measuring device may require straight piping directly upstream and downstream of the flow measuring device in order to provide accurate measurements. Hence, straight sections of rigid pipe may be provided directly upstream and downstream of the flow measuring device. One or more or all of the cleaning agent storage tank, the pump, and the cleaning agent supply line may be arranged on a skid or trolley. In this way, the portable washing unit can be easily moved (e.g. between compressor stages and / or fluid processing systems) and stored (e.g. when not in use). The skid and / or trolley may be mounted on wheels, making it easy to move the portable washing unit and manoeuvre it into position for a cleaning operation. The invention may also extend to a fluid processing facility that is configured to enable cleaning of a gas compressor of the fluid processing facility using a portable washing unit. Hence, viewed from a second aspect, the invention provides a fluid processing system, comprising: a gas compressor having a gas inlet and a gas outlet; and a tie-in point for fluidly connecting the fluid processing system to a portable washing unit, wherein the tie-in point is arranged upstream of the gas inlet of the gas compressor. This aspect of the invention is preferably compatible with the portable washing unit of the first aspect. Hence, the tie-in point is preferably configured such that it can be fluidly connected to the portable washing unit of the first aspect. For instance, the tie-in point may be compatible with the connector of the portable washing unit such that the portable washing unit can be fluidly connected to the fluid processing system by connecting the connector to the tie-in point. Hence, the present invention may provide a fluid processing system, comprising: a gas compressor having a gas inlet and a gas outlet; and a tie-in point for fluidly connecting the fluid processing system to the portable washing unit of the first aspect, wherein the tie-in point is arranged upstream of the gas inlet of the gas compressor. Since the tie-in point is arranged upstream of the gas inlet of the gas compressor, during normal operation of the fluid processing system fluid introduced into the system via the tie-in point will flow towards the gas inlet of the compressor (which is downstream of the tie-in point). Hence, during a cleaning operation, a liquid cleaning agent may be introduced to the fluid processing system via the tie-in point and flow downstream to the gas compressor, where it can act to clean the compressor. The tie-in point is preferably arranged directly upstream of the gas compressor. That is, there may be no processing components or equipment in the flow path between the tie-in point and the gas compressor. The fluid processing system may include an anti-surge control system comprising instrumentation such as a flow sensor, a temperature sensor and / or a pressure sensor for measuring the flow rate, temperature and / or pressure of the fluid at the inlet of the compressor. The tie-in point is preferably arranged downstream of the instrumentation of the anti-surge control system. In this way, fluid supplied to the gas compressor via the tie-in point will not impact anti-surge control and the anti-surge control functionality will be maintained intact during a cleaning operation. The tie-in point preferably comprises a (controllable) shut-off valve for preventing flow of liquid into the fluid processing system via the tie-in point. The shut-off valve may be configured such that when it is closed, fluid is prevented from flowing into the fluid processing system via the tie-in point. In the closed state, the fluid processing system may be isolated from other components or systems (e.g. a portable washing unit) connected via the tie-in point. The shut-off valve may be adjustable between a closed configuration in which fluid is prevented from flowing into the fluid processing facility and an open configuration in which fluid can flow into the fluid processing facility via the tie-in point. Preferably the fluid processing system is operable when the shut-off valve is completely closed. Moreover, the fluid processing system is preferably configured to be normally operable with the shut-off valve closed, i.e. when fluid cannot be introduced into the fluid processing system via the tie-in point. Preferably, the fluid processing system is operable when the shut-off valve is open. Moreover, the tie-in point is preferably configured such that it does not block or impede the flow of fluid through the fluid processing system when the shutoff valve is open. Hence, the fluid processing system may be configured to be operable when fluid can be (and is being) introduced into the fluid processing system via the tie-in point. In this way, the fluid processing system may remain in operation during cleaning of the gas compressor. The fluid processing system may comprise a separator arranged upstream of the gas compressor. The separator may be configured to receive a multi-phase fluid and to output a gas phase output and a liquid phase output. The gas compressor may be arranged to receive the gas phase output of the separator at the gas inlet. The tie-in point may be arranged downstream of the separator (and upstream of the gas compressor). In this way, fluid can be injected into the gas phase from the separator via the tie-in point. Preferably, the fluid processing system is a natural gas processing system. The separator may be arranged to receive a multi-phase fluid from a hydrocarbon well. Hence, the separator may be configured to output a gas phase comprising hydrocarbon gas and a liquid phase comprising hydrocarbon liquid. Viewed from a third aspect, the present invention provides a system for cleaning a gas compressor in situ in a fluid processing system, comprising: a fluid processing system including a gas compressor having a gas inlet and a gas outlet, and a portable washing unit. The fluid processing system of the third aspect is preferably the fluid processing system of the second aspect, and may include one or more or all of the previously described optional features described above. The portable washing unit of the third aspect is preferably the portable washing unit of the first aspect, and may include one or more or all of the previously described optional features described above. Hence, the present invention may provide a system for cleaning a gas compressor in situ in a fluid processing system, comprising: the fluid processing system of the second aspect; and the portable washing unit of the first aspect. The cleaning agent supply line of the portable washing unit may be fluidly connected to the tie-in of the fluid processing system. Preferably, the connector on the cleaning agent supply line is fluidly connected to the tie in point. Accordingly, the system may be arranged so that liquid cleaning agent can be supplied to the fluid processing system from the portable washing unit in order to clean the compressor. The present invention also extends to a method of cleaning deposited solid material from a fouled portion of a gas compressor. Hence, viewed from a forth aspect, the present invention provides a method of cleaning deposited solid material from a fouled portion of a gas compressor whilst the gas compressor is in situ in a fluid processing system, the method comprising: supplying a liquid cleaning agent from a portable washing unit to a gas inlet of the gas compressor, wherein the liquid cleaning agent is capable of removing the deposited solid material. It will be appreciated that the benefits described above in respect of the first to third aspects are equally applicable to the fourth aspect. During cleaning, the liquid cleaning agent may remain in the liquid form as it passes a fouled portion of the gas compressor, and preferably downstream of an impeller of the compressor. Removal of deposited solid material from the gas compressor is primarily mechanical, i.e. due to impact from the liquid against the fouling. However, the cleaning agent may also use chemical action to remove the solid material and / or may dissolve the solid material. Once the cleaning agent has passed the fouled portion, it may be allowed to evaporate leaving the solid material flowing in a gas stream. Preferably, at least a portion of the cleaning agent remains in the liquid form all the way through the gas compressor, e.g. such that a portion of the cleaning agent remains in the liquid form at a gas outlet of the gas compressor. This will prevent additional fouling of the gas compressor which could occur if the cleaning agent is completely vaporised within the gas compressor, thereby ensuring efficient cleaning. This can be achieved by controlling the flowrate of cleaning agent supplied to the gas compressor to ensure a portion of the cleaning agent remains in the liquid form at the gas outlet of the gas compressor. Preferably, the fluid processing system is a natural gas processing system. Supplying the liquid cleaning agent may comprise fluidly connecting the portable washing unit to the fluid processing system. Preferably, the portable washing unit is fluidly connected to the fluid processing system upstream of the gas inlet of the gas compressor. In this way, liquid cleaning agent from the portable washing unit can be injected into a flow of process fluid (e.g. gas) in the fluid processing system upstream of the gas compressor, and then subsequently flow through the gas compressor to clean the gas compressor. The portable washing unit may comprise a cleaning agent supply tank for storing a liquid cleaning agent, and a cleaning agent supply line fluidly connected to the cleaning agent storage tank for supplying a liquid cleaning agent from the cleaning agent storage tank to the fluid processing system. The fluid processing system may comprise a tie-in point for fluidly connecting the fluid processing system to the portable washing unit. Supplying the liquid cleaning agent may comprise fluidly connecting the cleaning agent supply line to the tie-in point of the fluid processing system. The method may comprise, prior to a cleaning operation, moving the portable washing unit into place adjacent to the fluid processing system (e.g. a tie-in point of the fluid processing system) so that the portable washing unit (e.g. the cleaning agent supply line) may be connected to the fluid processing system. Supplying a liquid cleaning agent may comprise mixing the liquid cleaning agent with a gas stream being supplied to the gas inlet of the gas compressor. The liquid cleaning agent is preferably supplied by the portable washing unit at a pressure higher than the pressure at the gas inlet of the gas compressor. For instance, the liquid cleaning agent may be supplied at a pressure of 1 bar (or more) higher than the pressure at the gas inlet of the gas compressor. This may comprise pumping the liquid cleaning agent to a pressure higher than the pressure at the gas inlet, for example by using a pump of the portable washing unit to increase the pressure of the liquid cleaning agent to a pressure higher than the pressure at the gas inlet of the gas compressor. Supplying the liquid cleaning agent may comprise supplying the liquid cleaning agent from a storage tank of the portable washing unit. Supplying the liquid cleaning agent may comprise opening a supply valve of the portable washing unit to permit liquid cleaning agent to flow from the portable washing unit. The supply valve may be controlled so as to supply sufficient liquid cleaning agent to the compressor such that a portion of the liquid cleaning agent remains in the liquid form as it passes a fouled portion of the compressor. In some embodiments, the supply valve may be controlled so as to supply sufficient liquid cleaning agent to the compressor such that a portion of the liquid cleaning agent remains in liquid form at a gas outlet of the gas compressor. Supplying the liquid cleaning agent may comprise opening a shut-off valve of the tie-in point to permit liquid cleaning agent to flow into the fluid processing system via the tie-in point. The liquid cleaning agent may comprise liquid hydrocarbons (e.g. oil), condensed hydrocarbon gas, glycol, alcohol, water, or mixtures thereof. The fluid processing system may comprise a separator upstream of the gas compressor, the separator outputting a gas phase output and a liquid phase output. Preferably, the gas phase output is supplied to the gas compressor during normal operation of the fluid processing system. The method of cleaning may be a method of online cleaning. That is, the cleaning process can be performed without shutting down the compressor and / or the fluid processing system. Hence, the gas phase output from the separator may be supplied to the gas compressor during a cleaning operation. The method may comprise determining the presence or potential presence of a deposit of solid material on the gas compressor. Supplying the liquid cleaning agent may be performed responsive to this determination. The determination may be performed during normal operation of the gas compressor. For example, operation preferably does not need to be stopped to perform the determination. The method may comprise measuring a property of a fluid at the gas inlet and / or at the gas outlet of the gas compressor, preferably during normal operation of the gas compressor. The measured property of the gas may be used to identify a presence or possible presence of the deposit. The determining may comprise identifying a changed performance of the gas compressor, the changed performance being suggestive of a need for cleaning. The determining may comprise comparing a measured property of a fluid at the gas inlet and / or gas outlet of the compressor or a performance of the gas compressor with a reference value. The method of cleaning may be performed for limited period of time. The limited period of time is preferably less than a day, more preferably less than four hours, more preferably less than one hour, more preferably less than 30 minutes, more preferably less than 10 minutes, and most preferably less than 1 minute. Preferably, after the limited period of time, the gas processing system resumes normal operation. Preferably, during normal operation, a liquid content in the gas at the gas inlet to the gas compressor is below 5wt.%, more preferably below 3wt.% and yet more preferably below 1wt.%. Most preferably, during normal operation, the gas at the gas inlet to the gas compressor contains substantially no fluid in the liquid phase. Preferably, during normal operation, a liquid content in the gas at the gas outlet to the gas compressor is substantially zero. After completing a cleaning operation, the supply valve of the portable washing unit may be closed to stop the supply of cleaning fluid from the portable washing unit. After completing a cleaning operation, the shut-off valve of the fluid processing system may be closed. In this way, the flow of liquid cleaning agent from the portable washing unit to the fluid processing system can be stopped. After completing a cleaning operation, the pump of the portable washing unit may be stopped. The portable washing unit may be disconnected from the fluid processing system after a cleaning operation has been completed. Disconnection preferably occurs after the supply valve and / or shut-off valve has been closed. Disconnecting the portable washing unit from the fluid processing system may comprise disconnecting a connector of the portable washing unit from a tie-in point of the fluid processing system. The portable washing unit may then be moved away from the processing system, for instance to be used elsewhere (e.g. to clean a different system or component) or to be placed in storage. In another embodiment, the portable washing unit may remain connected to the fluid processing system (for at least a predetermined amount of time) after a cleaning operation has been completed. The cleaning method of the fourth aspect may be performed using the portable washing unit of the first aspect and / or the fluid processing system of the second aspect. Hence, the method may include corresponding optional features. An embodiment of the present invention will now be described in greater detail by way of example only and with reference to the following figures, in which: Figure 1 illustrates a gas compressor in situ in a fluid processing system; and Figure 2 illustrates an arrangement for cleaning a gas compressor in a fluid processing system. Figure 1 shows a fluid processing system 1 for processing fluids from one or more well(s). In hydrocarbon wells, these fluids may include oil, gas, water, and gas condensate. The system 1 includes a gas compressor 6 through which gas from the well is passed. The compressor 6 operates to compress the gas, to facilitate transport of the gas onward for further processing or utilisation downstream of the compressor 6. The compressor 6 has an inlet for intake of the gas to be compressed, and an outlet fluidly connected to the inlet to output compressed gas (not shown). The compressor 6 may have a compressor body extending between the inlet and outlet and defining a flow channel for conveying gas therebetween (not shown). During normal operation, a gas stream is passed into the inlet, through the compressor body, where it is compressed, and out of the outlet. In this example, the system 1 has a separator 3 located upstream of the compressor 6. The separator 3 receives a multiphase fluid from a hydrocarbon well via conduit 2 comprising liquid and gas. The separator 3 acts to separate gas and liquid from the conduit 2 into a gas stream 4 and a liquid stream 5. The gas phase 4 is supplied to the gas compressor 6. The system 1 additionally has a tie-in point 7 for fluidly connecting a portable washing unit 10 (shown in Figure 2) to the fluid processing system 1. The tie-in point provides a controllable inlet to permit a liquid cleaning agent to be introduced into the fluid processing system 1. It includes a shut-off valve 8 that can be opened, when required, to allow liquid to be introduced into the fluid processing system 1 via the tie-in point 7. When the shut-off valve 8 is closed, input of fluid into (or egress of fluid from) the fluid processing system 1 via the tie-in point 7 may not be possible. In the example shown in Figure 1, the tie-in point is arranged downstream of the separator 3 and upstream of the gas compressor 6, so that liquid (e.g. liquid cleaning agent) can be injected into the gas stream 4 upstream of the compressor 6 via the tie-in point 7. Figure 2 shows a portable washing unit 10 connected to the tie-in point 7 of the fluid processing facility 1. The portable washing unit 10 is used to supply a liquid cleaning agent to the fluid processing system 1. It includes a cleaning agent storage tank 11 for storing a liquid cleaning agent. The liquid cleaning agent may be any cleaning agent suitable for removing the type of solids deposited in the compressor 6, for example deposited by the vaporisation of a multiphase fluid. Examples of suitable cleaning agents may include liquid hydrocarbons, condensed hydrocarbon gas, a glycol, an alcohol, water, and mixtures thereof. A liquid cleaning agent supply line 12 is fluidly connected to the storage tank 11, with a free end of the supply line including a connector 13. The connector is configured to be connected to the tie-in point 7 of the fluid processing system 1 to form a fluid connection between the portable washing unit 10 (specifically the supply line 12) and the fluid processing system 1 (specifically the tie-in point 7). The portable washing unit 10 includes a controllable supply valve 14 arranged in the cleaning agent supply line 12. The supply valve 14 may be opened, when required, to permit liquid cleaning agent to flow from the storage tank 11 and through the supply line 12. As shown in Figure 2, the connector 13 is fluidly connected to the tie-in point 7 of the fluid processing system such that, if the supply valve 14 and the shut-off valve 8 are open, liquid cleaning agent can be supplied from the portable washing unit 10 to the fluid processing system 1. The portable washing unit 10 includes a pump 15 to pump the liquid cleaning agent in the supply line 12 to a pressure higher than the gas in the gas stream 4. For instance, the pump 15 may be used to increase the pressure of the liquid cleaning agent to a pressure 0.5 bar to 1 bar over the pressure of the gas in the gas stream 4. In this way, the liquid cleaning agent can be supplied at a sufficient pressure to inject the liquid cleaning agent into the gas stream 4. This also prevents back-flow of gas from the gas stream 4 into the portable washing unit 10. However, a non-return valve 16 may also be provided in the supply line 12 downstream of the pump 15 to prevent back-flow if the pressure provided by the pump 15 is not sufficient, e.g. in the event that the pump 15 is shutdown or otherwise does not provide the required pressure increase. During normal operation of the fluid processing system 1, the shut-off valve 8 is closed so that liquid cleaning agent cannot be introduced in to the gas stream 4 via the tie-in point 7. The gas stream 4 is received by the compressor 6 and the compressor 6 compresses the gas. The portable washing unit 10 may or may not be connected to the fluid processing system 1 during normal operation. The fluid processing system 1 may have no need for the portable washing unit 10 during normal operation, and may only require it during a cleaning operation. Hence, the portable washing unit 10 may be disconnected from the system 1 during normal operation. During this time, the portable washing unit 10 may be serviced, refilled with liquid cleaning agent, or used to clean another compressor e.g. in a different fluid processing system. To make it easier to move the portable washing unit 10, it may be mounted on a skid or trolley (not shown). When it is desired to clean the compressor 6, if it is not already connected, the connector 13 is fluidly connected to the tie-in point 7. To initiate a cleaning operation of the compressor 6, the supply valve 14 and the shut off valve 8 are opened, and the pump 15 is turned on. As a result, liquid cleaning agent is introduced from the portable washing unit 10 into the gas stream 4. The multiphase stream (i.e. gas stream 4 with liquid entrained therein) is received by the compressor 6, which compresses the mixture. A flow measurement device (not shown) may be provided on the supply line 12, for example upstream the supply valve 14 and / or the non-return valve 16, to measure the quantity of liquid cleaning agent supplied to the gas stream 4. The supply valve 14 may be controlled so as to supply sufficient liquid cleaning agent to the compressor 6 such that a portion of the liquid cleaning agent remains in liquid form at the outlet of the gas compressor 6. The flow rate needed to perform efficient washing may be estimated prior to the washing operation, and the control valve 14 may be used during a washing operation, together with the flow measurement device, to provide the desired flow rate. Typically, the condition of the gas stream upstream and downstream of the compressor 6 and / or the performance of the compressor are monitored. The condition of the gas (e.g. a wet, liquid-containing gas) may be the flow rate, temperature, pressure and / or composition of the gas stream. The performance of the compressor 6 may be calculated based on the increase in pressure or temperature between the inlet and outlet of the compressor. In this example, the monitoring of conditions or performance can be carried out by applying measurement apparatuses (not shown) upstream and downstream of the compressor 6. The measurement apparatuses may each comprise a multiphase flow meter and / or a temperature sensor and / or a pressure sensor. The measurements may be used to calculate the performance of the compressor. The measured conditions or performance may be compared with previous or expected (modelled) performance. A change in the measured conditions and / or performance of the compressor 6 (e.g. a decrease in compressor performance) compared to previous or expected performance may indicate that deposits have formed on surfaces inside the compressor 6. Detection of fouling may be performed by detecting that the compressor efficiency is reduced compared to the reference value. This is because the compressor’s ability to create a pressure increase at a given speed will be reduced by the fouling. This is especially observed on higher volumetric flow rates. If the presence of a deposit on a surface inside the compressor 6 is detected from measured data, the cleaning operation is initiated as described above. Conventional compressors are not designed for handling liquids, and operation with a significant amount of liquid over a sustained period of time can cause erosion or instability which can be detrimental for the integrity of the compressor. Thus, liquids are typically removed from fluids upstream the compressor to provide a dry gas to the compressor. However, the upstream process may be imperfect and may not be sufficient to remove all liquid from the fluid. The remaining liquid may cause fouling to the interior surfaces of the compressor. Fouling will often occur when the liquid content in the gas stream is very low, e.g. when steps have been taken to limit the amount of liquid within the fluid passed to the compressor. Liquid cleaning agent can be injected into the gas of gas stream 4, such that the gas stream passed into the compressor 6 comprises gas with an increased amount of liquid entrained therein. As the gas-liquid stream 4 passes through the compressor 6, a spray of liquid droplets is generated due to the forces of the fastrotating impellers of the compressor 6. The liquid spray impacts on the interior surfaces of the compressor and acts to remove the deposited material from these surfaces. Thus, the gas with liquid acts to clean or wash the internal surfaces of the compressor across which the gas is passed. Such surfaces may be surfaces that define the flow channel of the compressor body that come into contact with the gas. In a centrifugal compressor, these surfaces may include those of a rotating impeller and static parts of the compressor internals. In order to provide efficient cleaning upon detecting the deposit, the amount of liquid in the gas is made sufficiently great that complete vaporization of the liquid does not occur upon passing the gas through the compressor 6. In other words, the gas remains as a two-phase gas-liquid mixture, i.e. a gas with liquid entrained therein, as it exits the discharge side of the compressor 6. If there is insufficient liquid in the gas stream as it enters the compressor, the liquid may vaporise away and deposits may form inside the compressor. The amount of liquid cleaning agent injected is controlled using the supply valve 14. The amount of liquid passed to the compressor may be estimated using the flow measurement device. The amount of liquid at the outlet of the compressor may be monitored using the measurement apparatuses described above. When the washing operation is completed, the supply valve 14 and the shutoff valve 8 may be closed, and the pump 15 shut down to stop liquid injection into the gas stream 4. The portable washing unit 10 may additionally be disconnected from the fluid processing system (i.e. the tie-in point 7). After cleaning, with at least a portion of the deposit removed, the compressor 6 may perform with a higher efficiency, close to the specified level of performance. The removal of the deposit may be detectable as an increase in performance, or change in the conditions of the gas upstream or downstream of the compressor back to previous values. Alternatively, or in addition, the removal of the deposit may be assumed to be complete after a predetermined period of cleaning operation. Similar cycles of cleaning may be performed as and when further deposit build-up is detected or suspected, and / or at regular intervals. Upon inserting liquid into the gas stream 4 via the tie-in point 7, the fluid processing system 1 is moved from a condition in which fouling occurs to one in which cleaning occurs. In order to provide cleaning, the liquid content in the gas stream 4 upstream of the compressor 6 may be increased up to around 20 times greater than the liquid content in normal operating conditions where deposits form. This may be 2 to 20 times greater, but higher amounts may also be feasible. Gas having a liquid content in an amount of up to around 5% by weight may result in deposits forming inside the compressor. For example, a content of liquid of 0.2% to 0.6% by weight may result in a deposit. In general, it will be appreciated that the amount of liquid required in order to remove deposits from surfaces inside the compressor 6 is dependent on how much liquid evaporates from the gas as it passes through the compressor 6. This is in turn dependent upon the pressure and temperature conditions of the gas. Computer modelling packages are commercially available to allow fluid processing systems 1 such as that shown in Figure 1 to be modelled. Such packages can be used to determine the amount of liquid required in the gas supplied to the compressor 6 at the inlet for purposes of cleaning. The models may define relationships between parameters for different parts of the system, including relationships between temperature, pressure and liquid content for a given configuration of processing components and fluids. In the example described above, the compressor is situated in a gas processing facility for processing well fluids, and is arranged downstream of a separator. However, it will be appreciated that the present invention is applicable to other arrangements in which a separator is not present, or other processing stages are present between the separator and the compressor. For instance, the compressor may be situated in downstream applications, e.g. in a gas terminal or refinery. Such compressors may also require cleaning due to material deposited on internal surfaces of the compressor by the fluid passing therethrough. Moreover, whilst the present invention has been described with reference to a fluid processing system that is arranged for and used for processing fluids from one or more well(s), it will be appreciated that the invention is equally applicable to other fluid processing systems handling other fluids and / or other applications that utilise gas compressors where fouling may occur.

Claims

1. A portable washing unit for supplying a liquid cleaning agent to a gas compressor in situ in a fluid processing system during a cleaning operation, comprising:a cleaning agent storage tank for storing a liquid cleaning agent;a cleaning agent supply line fluidly connected to the cleaning agent storage tank for supplying a liquid cleaning agent from the cleaning agent storage tank to a tie-in point of a fluid processing system; anda pump arranged for drawing a liquid cleaning agent from the cleaning agent storage tank and pumping it through the cleaning agent supply line.

2. A portable washing unit as claimed in claim 1, comprising a supply valve in the cleaning agent supply line configured to control flow of liquid cleaning agent along the liquid cleaning agent supply line.

3. A portable washing unit as claimed in claim 1 or 2, wherein the supply line comprises a connector for fluidly connecting the supply line to a tie-in point of a fluid processing system.

4. A portable washing unit as claimed in claim 1,2 or 3, comprising a nonreturn valve in the cleaning agent supply line to prevent back-flow of liquid cleaning agent in the cleaning agent supply line towards the cleaning agent storage tank.

5. A portable washing unit as claimed in any preceding claim, comprising a pressure relief valve in the cleaning agent supply line for relieving pressure within the portable washing unit.

6. A portable washing unit as claimed in any preceding claim, comprising an isolation valve in the cleaning agent supply line for preventing liquid flowing out of the portable washing unit via the cleaning agent supply line.

7. A portable washing unit as claimed in any preceding claim, wherein the portable washing unit does not include a spray nozzle.

8. A portable washing unit as claimed in any preceding claim, wherein the cleaning agent storage tank, the pump, and / or the cleaning agent supply line are arranged on a skid or a trolley.

9. A portable washing unit as claimed in any preceding claim, wherein the cleaning agent supply line comprises a flexible hose.

10. A fluid processing system, comprising:a gas compressor having a gas inlet and a gas outlet; anda tie-in point for fluidly connecting the fluid processing system to the portable washing unit of any preceding claim, wherein the tie-in point is arranged upstream of the gas inlet of the gas compressor.

11. A fluid processing system as claimed in claim 10, wherein the tie-in point comprises a shut-off valve for preventing flow of liquid into the fluid processing system via the tie-in point.

12. A fluid processing system as claimed in claim 11, wherein the fluid processing system is operable when the shut-off valve is open.

13. A system for cleaning a gas compressor in situ in a fluid processing system, comprising:the fluid processing system of any of claims 10 to 12; and the portable washing unit of any of claims 1 to 9.

14. A method of cleaning deposited solid material from a fouled portion of a gas compressor whilst the gas compressor is in situ in a fluid processing system, the method comprising:supplying a liquid cleaning agent from a portable washing unit to a gas inlet of the gas compressor, wherein the liquid cleaning agent is capable of removing the deposited solid material.

15. A method as claimed in claim 14, wherein supplying the liquid cleaning agent comprises fluidly connecting the portable washing unit to the fluid processing system.

16. A method as claimed in claim 14 or 15, wherein supplying the liquid cleaning agent comprises opening a supply valve of the portable washing unit to permit liquid cleaning agent to flow from the portable washing unit.

17. A method as claimed in claim 14, 15 or 16, wherein supplying the liquid cleaning agent comprises opening a shut-off valve of the fluid processing system to permit liquid cleaning agent to flow into the fluid processing system.

18. A method as claimed in any of claims 14 to 17, wherein supplying the liquid cleaning agent comprises mixing the liquid cleaning agent with a gas stream being supplied to the gas inlet of the gas compressor.

19. A method as claimed in any of claims 14 to 18, comprising using a pump of the portable washing unit to increase the pressure of the liquid cleaning agent to a pressure higher than the suction pressure of the gas compressor.

20. A method as claimed in any of claims 14 to 19, comprising, after completing a cleaning operation, closing a supply valve of the portable washing unit and / or closing a shut-off valve of the fluid processing system to stop supply of liquid cleaning agent from the portable washing unit.

21. A method as claimed in any of claims 14 to 20, comprising, after completing a cleaning operation, disconnecting the portable washing unit from the fluid processing system.

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