NO341968B1 - Method for controlling liquid content in gas flow to a wet gas compressor - Google Patents
Method for controlling liquid content in gas flow to a wet gas compressor Download PDFInfo
- Publication number
- NO341968B1 NO341968B1 NO20151362A NO20151362A NO341968B1 NO 341968 B1 NO341968 B1 NO 341968B1 NO 20151362 A NO20151362 A NO 20151362A NO 20151362 A NO20151362 A NO 20151362A NO 341968 B1 NO341968 B1 NO 341968B1
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- liquid
- compressor
- flow
- line
- controlling
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- 239000007788 liquid Substances 0.000 title claims abstract description 306
- 238000000034 method Methods 0.000 title claims abstract description 29
- 230000001276 controlling effect Effects 0.000 claims abstract description 50
- 238000011144 upstream manufacturing Methods 0.000 claims abstract description 8
- 230000001105 regulatory effect Effects 0.000 claims abstract description 5
- 230000033228 biological regulation Effects 0.000 claims description 16
- 230000001965 increasing effect Effects 0.000 claims description 11
- 238000005406 washing Methods 0.000 claims description 11
- 239000007789 gas Substances 0.000 description 61
- 239000012530 fluid Substances 0.000 description 14
- 230000006835 compression Effects 0.000 description 8
- 238000007906 compression Methods 0.000 description 8
- 238000005259 measurement Methods 0.000 description 8
- 239000000243 solution Substances 0.000 description 6
- 230000001419 dependent effect Effects 0.000 description 4
- 238000001514 detection method Methods 0.000 description 3
- 238000007599 discharging Methods 0.000 description 3
- 239000007791 liquid phase Substances 0.000 description 3
- 239000012071 phase Substances 0.000 description 3
- 230000002829 reductive effect Effects 0.000 description 3
- 238000000605 extraction Methods 0.000 description 2
- 239000007792 gaseous phase Substances 0.000 description 2
- 230000000670 limiting effect Effects 0.000 description 2
- 238000012423 maintenance Methods 0.000 description 2
- 238000000926 separation method Methods 0.000 description 2
- 239000002912 waste gas Substances 0.000 description 2
- 238000004140 cleaning Methods 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000003628 erosive effect Effects 0.000 description 1
- 230000000763 evoking effect Effects 0.000 description 1
- 230000009123 feedback regulation Effects 0.000 description 1
- 230000003116 impacting effect Effects 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000036961 partial effect Effects 0.000 description 1
- 230000002265 prevention Effects 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 238000004064 recycling Methods 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 230000003245 working effect Effects 0.000 description 1
Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
- F04B49/00—Control, e.g. of pump delivery, or pump pressure of, or safety measures for, machines, pumps, or pumping installations, not otherwise provided for, or of interest apart from, groups F04B1/00 - F04B47/00
- F04B49/02—Stopping, starting, unloading or idling control
- F04B49/03—Stopping, starting, unloading or idling control by means of valves
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
- F04B49/00—Control, e.g. of pump delivery, or pump pressure of, or safety measures for, machines, pumps, or pumping installations, not otherwise provided for, or of interest apart from, groups F04B1/00 - F04B47/00
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
- F04B49/00—Control, e.g. of pump delivery, or pump pressure of, or safety measures for, machines, pumps, or pumping installations, not otherwise provided for, or of interest apart from, groups F04B1/00 - F04B47/00
- F04B49/02—Stopping, starting, unloading or idling control
- F04B49/03—Stopping, starting, unloading or idling control by means of valves
- F04B49/035—Bypassing
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D27/00—Control, e.g. regulation, of pumps, pumping installations or pumping systems specially adapted for elastic fluids
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Control Of Positive-Displacement Pumps (AREA)
Abstract
The invention concerns a method for controlling the quantity of liquid flowing into an inlet flow of a compressor based on the acceptance limits of the compressor as a directive for determining the allowed quantity of liquid in the compressor inlet flow, wherein - providing a liquid hold up tank upstream of the compressor, - providing a compressor inlet line between the hold up tank and the compressor, - providing a liquid line between the hold up tank and the compressor inlet line, - equipping the liquid line with a flow control means -providing measuring means for providing a measured value of compressor operation parameters), -connecting a control system to the flow control means and measuring means, for controlling the flow through the liquid line, wherein this operation comprises the steps of -acquiring data input representative of measured values of compressor operational parameteres), - regulating the flow through the liquid line into the compressor inlet flow by operating the flow control means, based on comparing the data input, or computations based on the data input, with the acceptance limits of the compressor.The invention concerns a method for controlling the quantity of liquid flowing into an inlet flow of a compressor based on the acceptance limits of the compressor as a directive for determining the allowed quantity of liquid in the compressor inlet flow, wherein - providing a liquid hold up tank upstream of the compressor, - providing a compressor inlet line between the hold up tank and the compressor, - providing a liquid line between the hold up tank and the compressor inlet line, - equipping the liquid line with a flow control means -providing measuring means for providing a measured value of compressor operation parameters), -connecting a control system to the flow control means and measuring means, for controlling the flow through the liquid line, wherein this operation comprises the steps of -acquiring data input representative of measured values of compressor operational parameters), - regulating the flow through the liquid line into the compressor inlet flow by operating the f low control means, based on comparing the data input, or computations based on the data input, with the acceptance limits of the compressor.
Description
FIELD OF THE INVENTION
The present invention relates to a method and a system for controlling the quantity of liquid flowing into an inlet flow of a compressor.
The inventive method and system is applicable for controlling the conditions of the compressor inlet flow and especially applicable for a so called wet gas compressor.
The compressor inlet flow may in most circumstances comprise a mixing of liquid and gas. The gas fraction usually constitutes a larger part of the inlet flow than the liquid fraction, such as during a working mode of the compressor.
However, the fractions of gas and liquid may vary and in some mode of operations the gas fraction is reduced and the liquid fraction is increased compared to a working mode of the compressor. These modes of operations are typical shut-down mode, start up mode, washing mode and energy optimizing mode.
DESCRIPTION OF THE BACKGROUND ART
In accordance with a conventional method for controlling the operational conditions of a wet gas boosting system, the incoming multiphase flow is separated into a gas flow and a liquid flow for separate boosting of gas by a use of a compressor and liquid by use of a pump.
Prior art methods also include solutions where the multiphase incoming flow is boosted directly by a wet gas compressor without any upstream separation of gas and liquid phases.
The operating condition of a wet gas compressor is dependent on the liquid quantity in the compressor inlet flow. Both the liquid volume fraction (LVF) and the liquid mass fraction (LMF) of the compressor inlet flow influence the compressor performance. Of these, the liquid mass fraction (LMF) has a larger effect on the thermodynamic behavior of the compressor and the mechanical loads impacting the compressor. The liquid mass fraction (LMF) is largely effected by the gas/liquid density ratio (which again is dependent of pressure).
When the liquid volume flow (LVF) is increased 1%, the liquid mass fraction (LMF) typically increases by 10-30% dependent of pressure. Various studies and tests conclude that compressor torque and power demand increases almost linearly with the added mass from liquid in a one to one (1:1) relationship, meaning that 10% added mass from liquid requires approximately 10% added compressor torque and power.
Due to the fact that the performance and also the mechanical integrity of the compressor are effected by the liquid fraction (LVF and LMF) of the compressor inlet flow, the compressor has a specific limit for acceptable fraction of liquid in the compressor inlet flow.
Although an averaged incoming flow condition to a wet gas compressor system is within the acceptance limit of the compressor, intermittent situations may occur where the liquid/gas fraction exceeds such acceptance limit. Hence, it is important to control the liquid/gas fraction of the compressor inlet flow to be within a predefined range. In a situation with high liquid/gas fraction in the incoming flow, the target would normally be to control the liquid/gas fraction into the compressor to the highest possibly value giving minimum operational disturbance caused by the increased power demand, and without jeopardizing compressor integrity due to load and wear. With this methodology, the size of an upstream liquid hold-up volume can be minimized.
As the compressor performance is affected when the liquid fraction of the compressor inlet flow is altered it is important to control the variations in liquid/gas fraction of the compressor inlet flow.
Examples of prior art solutions include WO 2011081528, EP 2247858 and EP2425890.
WO 2011081528 describes a control system for a subsea compressor system comprising sensor means for measuring and determining the liquid droplet size distribution and liquid volume fraction. This system suggests supplying high pressure gas from the outlet side of the compressor into liquid line to control the liquid in the compressor inlet flow. The high pressure gas let out from the compressor is directed into an injection pump or ejector for mixing of the liquid in the gas flow. The flow enters an atomiser for dissolving the liquid into droplets of tolerable size before entering the compressor in order to reduce both droplet size and liquid volume fraction in the compressor inlet flow.
EP 2247858 describes a method to operate a compressor unit, where the suction line of the compressor has at least one detection device provided to identify non-gaseous fluid amounts in the fluid to enter the compressor, the detection device is connected to a control unit in a signal transmitting manner. In case the detection device identifies a liquid/gas ratio in excess of a certain limit, gas is routed from the compressor discharge to the compressor inlet in order to reduce the liquid/gas ratio.
EP 2425890 describes an apparatus for passive dampening of variations in liquid/gas ratio of multi-phase fluid comprising a gaseous phase and a liquid phase fluid. The apparatus comprising an inner reservoir with an inlet for the multiphase fluid and is arranged with separate outlets for the gaseous phase and the liquid phase into an outer receptacle. The outer receptacle has an outlet conduit for gas and the inner reservoir has an outlet conduit for the liquid.
US 4,273,514 shows a waste gas recovery system employing a compressor 20 which takes in waste gas from an inlet knockout drum 10 and passes compressed gas to a heat exchanger 24. The heat exchanger 24 cools the gas prior to passage of the gas through a further outlet knockout drum 11.
In accordance with recent demands within the technical field for simplifying subsea processes and subsea equipment, a need has evoked for controlling the liquid/gas fraction of the inlet compressor flow in a way that limit the power consumption and at the same time ensure the integrity of the of the compressor.
It is an object of the invention to provide a solution for controlling the quantity of liquid in the inlet flow of a compressor to avoid excess power and torque consumption. It is further an object of to provide a solution as an alternative to the prior art solutions, utilizing principles for actively controlling the liquid to flow into the compressor inlet flow for easy manipulation between the various modes of compressor operation. Further, it is an object to provide a solution that is independent of the achieved liquid quality (droplet size or equivalent) and liquid distribution in the compressor inlet flow.
SUMMARY OF THE INVENTION
In accordance with the invention the independent claims define a method and arrangement for controlling the fraction of liquid in a compressor inlet flow. The dependent claims define advantageous embodiments of the invention as defined in the independent claims.
Accordingly the invention specifies a method for controlling the quantity of liquid flowing into an inlet flow of a compressor based on the acceptance limits of the compressor as a directive for determining the allowed quantity of liquid in the compressor inlet flow. The allowed quantity of liquid in the compressor inlet flow may be determined independent of the achieved liquid quality (droplet size or equivalent) and liquid distribution of the compressor inlet flow.
The performance of the compressor is effected by the quantity of liquid in the compressor inlet flow and by the using the compressor acceptance limits as a bases for the determining the allowed quantity of liquid in the compressor inlet flow, the allowable quantity of liquid is supplied into the compressor inlet flow while keeping the capacity of the compressor at an acceptable level. The compressor acceptance limits may be defined by the allowed quantity of liquid in the compressor inlet flow ( maximum gas liquid/fraction that the compressor allows at the inlet flow) restricted by one or more of following parameters; power, torque, erosion, mechanical stresses, rotor dynamic stability, flow stability. For instance maximum power or torque or other power/torque values selected by the operator. The limiting current of the compressor driving motor may also be used for defining the compressor acceptance limit.
The inventive method comprises the step of providing a liquid hold up tank upstream of the compressor and providing a compressor inlet line between the hold up tank and the compressor. Further the method comprises providing a liquid line between the hold up tank and the compressor inlet line and equipping the liquid line with flow control means.
Equipping the liquid line with flow control means such as a control valve or an equivalent, ensures a control of the liquid flow entering the compressor inlet flow. The flow control means may be operated to allow more liquid to enter the compressor inlet flow, to reduce the liquid flow into the compressor inlet flow and to prevent liquid flow to occur at all.
The method also comprises providing measuring means for providing a measured value of compressor operational parameter(s).
The compressor operational parameter(s) are variable working factors of the compressor instrumental for determining the allowable quantity of liquid in the compressor inlet flow. The compressor operational parameter(s) is described by variable factors such as pressure, flow, torque, power etc or other parameters describing the compressor working conditions.
The measured value of the compressor operational parameter is a numerical factor specifying the actual working condition of the compressor at the time when the measurements take place.
A control system connects measuring means and the flow control means and is designed for determining the allowed quantity of liquid in the compressor inlet flow and for controlling the flow through the liquid line in accordance with the allowed liquid quantity. The allowed quantity of liquid in the compressor inlet flow may be determined independent of the achieved liquid quality (droplet size or equivalent) and liquid distribution of the compressor inlet flow.
The measured value of compressor operational parameter(s) as obtained by measuring means is supplied to the control system as a data input and is compared to acceptance limit of the of the compressor to determine the allowed liquid quantity in the compressor inlet flow. The control system has the following operational steps:
-acquiring data input representative of the measured values of compressor operational parameter(s) and
- regulating the flow through the liquid line into the compressor inlet flow by operating the flow control means, based on comparing the data input, or computations based on the data input, with the acceptance limits of the compressor.
The control system compares the data input or computations based on the data input with the acceptance limits of the compressor, and controls the operation of the flow control means accordingly depending on the results of the comparisons to regulate the flow into the compressor inlet flow from the liquid line. The quantity of liquid to be allowed into the compressor inlet flow is determined in this aforementioned comparison by the difference between the data input or computations based on the data input and the acceptance limits of the compressor.
If the difference between the data input and the acceptance limits of the compressor is positive, the flow control means may then be operated to allow more liquid to enter the compressor inlet flow. And if the difference between the data input and the acceptance limits of the compressor is zero or negative, the control means may not be modified or the flow control means may be operated to reduce the liquid flow into respectively.
If the data input representative of measured values compressor operational parameter is provided by the characteristics of the compressor inlet flow such as a liquid volume flow or liquid mass flow etc, the data input may need to be computerized or recalculated in order to compare the data input to the acceptance limits of the compressor. If the data input representative of measured values compressor operational parameter computations may not be necessary.
The regulation of the flow in the liquid line may be based on the characteristics of the compressor inlet flow as represented by the acquired data input.
In one embodiment of the inventive method, the provided measured values of the compressor operational parameter(s) may be the liquid volume fraction, the gas volume fraction and/or the liquid volume flow in the compressor inlet flow. The regulation of the flow in the liquid line is then determined by comparing the data input with corresponding acceptable values representative of the compressor acceptance limits.
In another embodiment of the inventive method, the provided measured values of the compressor operational parameter(s) may be the liquid mass fraction, the gas mass fraction and/or the liquid mass flow in the compressor inlet flow, and the regulation of the flow in the liquid line is then determined by comparing the data input with corresponding acceptable values representative of the compressor acceptance limits.
In a further embodiment of the inventive method, the provided measured values of compressor operational parameter(s) may be the density of the gas, the density of the liquid and/or the density of the multiphase flow in the compressor inlet flow, and the regulation of the flow in the liquid line is then determined by comparing the data input with corresponding acceptable values representative of the compressor acceptance limits.
In yet a further embodiment of the inventive method the provided measured values of compressor operational parameter(s) may be compressor absorbed power, absorbed torque and/or the actual current in the driving motor, or any other parameter that allows to determine the compressor power, and wherein the regulation of the flow in the liquid line is then determined by comparing the data input with corresponding acceptable values representative of the compressor acceptance limits.
A multiphase flow meter or at least two single phase meters may be used as measuring means for measuring the compressor inlet flow. A suitable sensing arrangement may be used for reading absorbed power, absorbed torque, actual current in the driving motor.
The arrangement of the control system to control the operation of the flow control means of the liquid line, enables the possibility of an easily executed compressor shut down mode, as well as enabling a reliable control of compressor start up mode, an energy optimizing mode and compressor washing mode.
The control system may have a compressor shut down mode comprising controlling the flow control means to increase or decrease the flow through the liquid line into the compressor inlet flow to drive the liquid level in liquid hold-up tank towards a specified target level before or during shut down.
The target level may be a minimum requested liquid level liquid in the hold up tank.
When the liquid level in liquid hold-up tank is above the specified target level in the compressor shut down mode, the flow through the liquid line is increased or maximized to reduce or empty the upstream liquid volume, improving the startupcondition for next compressor start-up.
If the liquid level in liquid hold-up tank is below the specified target level in the compressor shut down mode, the flow through the liquid line is decreased or minimized to increase the liquid level in liquid hold-up tank towards the specified target level.
The control system may have a washing mode comprising controlling the flow control means to let the liquid level build up in the liquid hold up tank when such level is not already above an identified reference level, thereafter controlling the flow control means to increase the flow through the liquid line into the compressor inlet flow, ensuring liquid presence throughout the compressor for washing. If the liquid level is already above the identified reference level the washing mode may be carried out without preceding procedure for filling to increase the liquid level.
Further the control system may have an energy optimizing mode comprising the steps of controlling the flow control means by,
- first reducing the quantity of liquid into the compressor inlet flow to operate the compressor at a higher efficiency, allowing a liquid level buildup in the liquid hold up tank,
- thereafter increasing the quantity of liquid into the compressor inlet flow to reduce the liquid level in the liquid hold up tank to a lower value.
The invention also concerns a system for controlling the quantity of liquid flowing into the inlet flow of a compressor based on the acceptance limits of the compressor as a directive for determining the allowed quantity of liquid in the compressor inlet flow. The system comprises a compressor inlet line connected to a liquid hold up tank and to the compressor for supplying the compressor inlet flow. A liquid line is connected to the liquid hold up tank and to the compressor inlet line. The liquid line is provided with flow control means for controlling the flow through the line. The system also has measuring means in the system for providing a measured value of compressor operation parameter(s). Further a control system is connected to the flow control means and to the measuring means for controlling the flow through the liquid line. The control system is arranged to acquire data input representative of measured values of the compressor operational parameter(s), and regulate the flow through the liquid line into the compressor inlet flow by operating the flow control means, based on comparing the data input, or computations based on the data input, with the acceptance limits of the compressor.
The liquid line may be connected to a lower portion of the liquid hold up tank, and the compressor inlet line may be connected to an upper portion of the liquid hold up tank. The liquid line and the compressor inlet line may then be configured for connection in a connection point. A liquid column in the hold up tank then exerts a driving pressure for a liquid flow to enter through the compressor inlet line. By this configuration the system is prepared so that flow through the liquid line at the connection point has equal or higher pressure than the flow through the compressor inlet line.
As an alternative to or in combination with the use of liquid column in the hold up tank to exert a driving pressure for the liquid floe, a device is provided to generate the driving pressure for the liquid flow by utilizing the gas velocity in the connection point between the gas line and liquid line out of the hold up tank. The device may then generate the required pressure alone, or in combination with a liquid column in the hold up tank.
The device that generates a differential pressure for the liquid flow may be a venturi. The device that generates a differential pressure for the liquid flow may be an ejector.
The control system may have a mode of operation where the provided measured values of compressor operational parameter(s) are the liquid volume fraction, the gas volume fraction and/or the liquid volume flow of the compressor inlet flow.
The control system may have another mode of operation where the provided measured values of compressor operational parameter(s) are driving characteristics of the compressor. The driving characteristics may be based on the compressor absorbed power, absorbed torque or on actual current in the driving motor of the compressor.
The measuring means for measuring the compressor inlet flow comprise a multiphase flow meter or at least two single phase meters.
In one embodiment of the system a recycle line may be arranged extending from the compressor outlet and is connected to the compressor inlet flow line between the liquid hold up tank and the compressor.
In another embodiment of the system a recycle line may be arranged extending from the compressor outlet and is connected to the liquid hold up tank, or alternatively to the an inlet flow line upstream the liquid hold-up tank.
By this arrangement of the recycle line the system is prepared for various compressor operational modes such as a compressor start up mode where liquid accumulates in the compressor discharge pipe prior to startup. The accumulated liquid will then be dumped into the hold up tank during recycle at startup.
The provision of flow control means to regulate the liquid flow through the liquid line provides a versatile system that is applicable to changing operation conditions and future demands to the system as not yet established. For instance changing compressor liquid tolerances or other application of compressors might be solved by regulation the liquid flow into the compressor inlet flow.
DETAILED DESCRIPTION
In the following, embodiments of the invention will be described in detail with reference to the enclosed drawings, where:
Fig. 1 shows a principle sketch of a wet gas compression system in accordance with prior art.
Fig. 2 shows an embodiment of a system for controlling the liquid quantity in a compressor inlet flow in accordance with an embodiment of the invention.
Fig. 3 shows a further embodiment of the system as shown in fig 2.
In the gas compression system as illustrated in Fig 1 a flow of fluid enters from a manifold at system inlet 1 and is either directed into a liquid hold up tank 2 here illustrated as a slug damper, or let through a bypass line 3 to an export pipeline through system outlet 15. The bypass line 3 is provided with a bypass valve 4 for opening and closing for the fluid flow through the bypass line 3. The system inlet 1 is connected to a tank inlet line 8 and an inlet valve 5 opens and closes for the fluid flow through the liquid hold up tank inlet line 8. An outlet valve 9 is arranged in a compressor outlet line 10. When the inlet valve 5 and the outlet valve 9 are closed, the compression station 30 is isolated, and the bypass valve 4 may be opened for forwarding the fluid from the system inlet to system outlet 15. The fluid may flow through the bypass line 3 during operation modes that do not necessitate compression.
When the bypass valve 4 is in a closed position and the inlet valve 5 is in an open position the fluid enters from the system inlet 1 and is collected in the liquid hold up tank 2. The liquid hold up tank 2 captures liquid peaks in the well stream flow entering through system inlet 1 and is arranged for passively discharging liquid from the liquid hold up tank 2 over a time period. The discharging of liquid may in some circumstance occur over a long period of time. The liquid is discharged from the liquid hold up tank 2 along with the gas through a compressor inlet line 11 forwarding the gas and the liquid as a compressor inlet flow into a compressor 12. The compressor 12 is driven by an electric motor 13, which may be regulated by speed variation. At least one cooler 14 and a check valve 15 are included in the compressor outlet line 10.
A recycle line 7 is connected to the compressor outlet line 10 and the tank inlet line 8 and is arranged with a recycle valve 6 for controlling the flow of fluid through the recycle line 7. The recycle line 7 is provided to protect the compressor from surge, enable operation with low forward flow and to allow startup and shutdown sequences.
A discharge device 16 is shown in the liquid hold up tank 2 in the enlarged detail A of fig 1. As seen from the enlarged detail A, the discharge device 16 is provided as a perforated pipe part and the discharging of liquid from the liquid hold up tank depend on the liquid level in the liquid hold up tank 2. As long as the liquid level in the liquid hold up tank 2 is above the lowest pipe perforations of the discharge device 16 , the liquid is let into the discharge device together with the gas, and the multiphase fluid flows out from the liquid hold up tank and into the compressor inlet line 11 leading to the compressor 12. By this arrangement of the discharge device 16 the liquid will flow into the compressor with a flow rate that increases with the liquid level in the liquid hold up tank , but other than that there is no provision for regulating the liquid flow into the compressor. Hence the system must be arranged for tolerating excessive liquid out of liquid hold up tank. Or the liquid hold up tank size and discharge device must be conservatively designed in order ensure acceptable liquid/gas fraction for all operating conditions. Because the liquid rate out of the liquid hold up tank has no or low dependency on the gas rate, means must be provided not to exceed liquid/gas fraction limitations during low flow operations such as e.g. startup and shutdown.
Figure 2 shows an example of an inventive system 20 for controlling the liquid in the compressor inlet flow flowing through compressor inlet line 11 and into the compressor 12. In figure 2 the system 20 is shown included in the gas compression system of fig 1. The components shown in fig 2 and explained above when describing the gas compression system of fig 1 are given the same reference numbers.
The well stream flow entering tank inlet line 8 is illustrated by arrow F in the enlarged section B showing the details of the system 20 in fig 2. The liquid hold up tank 2 is arranged with a gas flow line 21 extracting a gas flow from an upper portion of the liquid hold up tank 2. A liquid line 22 draws a liquid flow from a lower portion of the liquid hold up tank 2. Flow control means such as a control valve 23 is provided for regulation of the liquid flow into the compressor inlet line 11. The gas flow line 21 is connected to the compressor inlet line 11 downstream to the control valve 23.
The system 20 has a control system comprising a control unit 24, a measurement unit 25 for measuring the characteristic of the compressor inlet flow, a level control device 26 for measuring the liquid level in the liquid hold up tank 2 and an operation unit 27 for the control valve 23 to regulate the flow through the control valve and into the compressor inlet line 11. The measurement unit 25 measures parameters such as liquid mass flow (LMF) and/or liquid volume flow (LVF) of the compressor inlet flow. As an alternative to measuring characteristic of the compressor inlet flow for regulation of the control valve 23, parameters such as for instance compressor power and compressor torque are supplied from a compressor power and control system 50.
Signal lines 28, 29, 30, 32 are provided for communication between the control unit 24 and the measurement unit 25 or the compressor power and control system 50 , the level control device 26 and the operation unit 27. Based on the acceptance limits of the compressor (for instance compressor torque or power limit) and measured data provided by the measurement unit 25 or the compressor power and control system 50 and the level control device 26 , the control unit 24 communicates signals for operation of the control valve 23 to the operation unit 27. The control valve 23 then regulates the liquid flow into the compressor inlet line 11 in accordance with the signals received by the operation unit 27.
In addition to the measurements provided by the measurement unit 25 and the level control device 26 the regulation of the liquid flow also depends on liquid density and compressor suction pressure.
A small variations in the liquid quantity such as liquid volume fraction (LVF) has a considerable impact on the performance of the compressor, and the regulation of the liquid flow into the compressor inlet flow is therefore important to hold the power consumption at an acceptable level. The control system provides a feedback regulation where the liquid volume fraction (LVF)/ liquid mass fraction (LMF) is controlled in accordance with the measured data of the measurement unit 25 or the compressor power and control system 50 and the level control device 26 to avoid exceeding capabilities of the compressor, set by torque or power limitation, wear limitation or other constraints the compressor may have related to high liquid content in gas.
The arrangement of the control valve 23 to regulate the liquid flow into the compressor inlet flow provides the gas compression system with the opportunity of arranging for a compressor start up mode where the compressor inlet flow initially contains essentially gas. In such a start up mode the control valve 23 is initially in a closed position preventing liquid flow into the compressor inlet. To carry out this start up mode the recycle line 7 may be used for returning the compressor outlet flow as illustrated with arrow O to the compressor inlet line 11 via the tank inlet line 8, the liquid hold up tank 2 and gas extraction line 21.
Fig 3 shows an alternative arrangement where the recycle line 7 has a connection 30 to the gas extraction line 21 and a gas extractor 51 for separation gas and liquid to ensure that the flow returning to the compressor inlet flow in recirculation mode is reduced to a minimum By this arrangement the fluid path for the gas in the start up mode is shorter and the surge protection system may operate more effectively. Alternatively the recycle line 7 could be connected directly to the liquid hold up tank 2.
When an effective circulation of gas has been established through the compressor in the start up mode, the liquid flow may then supplied into the compressor inlet flow by opening of the control valve 23. These different sequences of initially recycling gas in the start up mode and then operating the control valve for letting the liquid flow into the compressor inlet flow may be carried out by the control system in a compressor start up mode communicating signals to the operation unit 27 for opening and closing of the control valve 23.
The arrangement of the control valve 23 also provides for a compressor shut down mode, where the liquid level in the liquid hold up tank is reduced by increasing the liquid flow into compressor and out of the compression station. This may better facilitate hydrate prevention during standstill and improve the startup condition for next startup.
Further the provision of control valve 23 provides for a compressor washing mode, operating the control valve 23 for increasing the liquid quantity in the compressor inlet flow to ensure wet gas from compressor inlet to compressor outlet. The compressor washing mode may be initiated by the control system in a compressor washing mode and may necessitate an increased liquid level to reach an identified reference level in the liquid hold up tank 2 before starting the washing cycle.
The compressor 12 also has a maintenance mode where the liquid volume fraction (LVF) is increased in the compressor inlet flow, compared to the liquid volume fraction (LVF) of the compressor inlet flow in compressor operational mode. In maintenance mode partial cleaning of the compressor is carried out while the compressor is operating partially.
The control system has an energy optimizing operational mode comprising the steps of first operating the control valve 23 to reduce the liquid flow into the compressor inlet flow to operate the compressor 12 at a higher efficiency. By reducing the liquid flow into the compressor inlet flow the liquid builds up in the liquid hold up tank 2, increasing the liquid level in the liquid hold up tank 2. Subsequent to this increase of liquid in the liquid hold up tank 2, the control valve 23 is operated to reduce the liquid level in the liquid hold up tank 2 to a lower value.
In the preceding description, various aspects of the apparatus according to the invention have been described with reference to the illustrative embodiment. For purposes of explanation, specific numbers, systems and configurations were set forth in order to provide a thorough understanding of the apparatus and its workings. However, this description is not intended to be construed in a limiting sense. Various modifications and variations of the illustrative embodiment, as well as other embodiments of the apparatus, which are apparent to persons skilled in the art to which the disclosed subject matter pertains, are deemed to lie within the scope of the present invention as defined in the set of claims.
Claims (24)
1. Method for controlling the quantity of liquid flowing into an inlet flow of a compressor (12) based on an allowable parameter range of at least one parameter of the compressor (12) as a directive for determining the allowed quantity of liquid in the compressor inlet flow, comprising the steps of:
- providing a liquid hold up tank (2) upstream of the compressor (12) for receiving a multiphase flow,
- providing a compressor inlet line (11) between the hold up tank (2) and the compressor (12),
characterised by the steps of:
- providing a liquid line (22) between the hold up tank (2) and the compressor inlet line (11),
- equipping the liquid line (22) with a flow control means (23),
- providing measuring means (25) for providing a measured value of compressor operation parameter(s),
- connecting a control system (24) to the flow control means (23) and measuring means (25), for controlling the flow through the liquid line (22), wherein this operation comprises the steps of:
- acquiring data input representative of measured values of compressor operational parameter(s),
- regulating the flow through the liquid line (22) into the compressor inlet flow by operating the flow control means (23), based on comparing the data input, or computations based on the data input, with the allowable parameter range.
2. Method for controlling the quantity of liquid in accordance with claim 1, wherein the regulation of the flow in the liquid line is based on characteristics of the compressor inlet flow as represented by the acquired data input.
3. Method for controlling the quantity of liquid in accordance with claim 1 or 2, wherein the provided measured values of compressor operational parameter(s) are the liquid volume fraction, the gas volume fraction and/or the liquid volume flow in the compressor inlet flow, and wherein the regulation of the flow in the liquid line is determined by comparing the data input with corresponding acceptable values representative of the allowable parameter range.
4. Method for controlling the quantity of liquid in accordance with claim 1 or 2, wherein the provided measured values of compressor operational parameter(s) are the liquid mass fraction, the gas mass fraction and/or the liquid mass flow in the compressor inlet flow, and wherein the regulation of the flow in the liquid line is determined by comparing the data input with corresponding acceptable values representative of the allowable parameter range.
5. Method for controlling the quantity of liquid in accordance with claim 1 or 2, wherein the provided measured values of compressor operational parameter(s) are the density of the gas, the density of the liquid and/or the density of the multiphase flow in the compressor inlet flow, and wherein the regulation of the flow in the liquid line is determined by comparing the data input with corresponding acceptable values representative of the allowable parameter range.
Method for controlling the quantity of liquid in accordance with claim 1, wherein the provided measured values of compressor operational parameter(s) are the compressor absorbed power, absorbed torque and/or the actual current in the driving motor, or any other parameter that allows to determine the compressor power, and wherein the regulation of the flow in the liquid line is determined by comparing the data input with corresponding acceptable values representative of the allowable parameter range.
Method for controlling the quantity of liquid in accordance with one of the preceding claims 1-5, wherein arranging a multiphase meter or several single phase meters as measuring means for providing the data input to the control system.
Method for controlling the quantity of liquid in accordance with one of the preceding claims, wherein the control system has a compressor shut down mode comprising controlling the flow control means to increase or decrease the flow through the liquid line into the compressor inlet flow to drive the liquid level in liquid hold-up tank towards a specified target level before or during shut down.
Method for controlling the quantity of liquid in accordance with one of the preceding claims, wherein the control system has a compressor start up mode, comprising controlling an initial operation of the flow control means to prevent flow through the liquid line into the compressor inlet flow.
Method for controlling the quantity of liquid in accordance with one of the preceding claims, wherein the control system has a washing mode comprising controlling the flow control means to let the liquid level build up in the liquid hold up tank when such level is not already above an identified reference level, thereafter controlling the flow control means to increase the flow through the liquid line into the compressor inlet flow, ensuring liquid presence throughout the compressor for washing.
Method for controlling the quantity of liquid in accordance with one of the preceding claims, wherein the control system has an energy optimizing mode comprising the steps of controlling the flow control means by,
- first reducing the quantity of liquid into the compressor inlet flow to operate the compressor at a higher efficiency, allowing a liquid level buildup in the liquid hold up tank,
- thereafter increasing the quantity of liquid into the compressor inlet flow to reduce the liquid level in the liquid hold up tank to a lower value.
12. System (20) for controlling the quantity of liquid flowing into the inlet flow of a compressor (12) based on an allowable parameter range of at least one parameter of the compressor as a directive for determining the allowed quantity of liquid in the compressor inlet flow, wherein it comprises a compressor inlet line (11) connected to a liquid hold up tank (2) for receiving a multiphase flow, and to the compressor (12) for supplying the compressor inlet flow, characterised in that:
- a liquid line (22) is connected to the liquid hold up tank (2) and to the compressor inlet line (11),
- the liquid line (22) being provided with flow control means (23) for controlling the flow through the line,
- measuring means (25) in the system for providing a measured value of compressor operation parameter(s), and
- a control system (24) connected to the flow control means (23) and to the measuring means (25) for controlling the flow through the liquid line (22), and arranged to acquire data input representative of measured values of the compressor operational parameter(s), and regulate the flow through the liquid line (22) into the compressor inlet flow by operating the flow control means (23), based on comparing the data input, or computations based on the allowable parameter range.
13. System for controlling the quantity of liquid according to claim 12, wherein the liquid line is connected to a lower portion of the liquid hold up tank, the compressor inlet line is connected to an upper portion of the liquid hold up tank, and the liquid line and the compressor inlet line are configured for connection in a connection point wherein a liquid column in the hold up tank exerts a driving pressure for a liquid flow to enter through the compressor inlet line.
14. System in accordance with claim 13, as an alternative to or in combination with the liquid column in the hold up tank, a device is provided to generate the driving pressure for the liquid flow by utilizing the gas velocity in the connection point between the gas line and liquid line out of the hold up tank.
15. System in accordance with claim 14, where the device that generates a differential pressure for the liquid flow is a venturi.
16. System in accordance with claim 14 or 15, where the device that generates a differential pressure for the liquid flow is an ejector.
17. System for controlling the quantity of liquid in accordance with one of the claims 12-16, wherein the regulation of the flow in the liquid line is based on characteristics of the compressor inlet flow as represented by the acquired data input.
18. System for controlling the quantity of liquid in accordance with one of the claims 12-17, wherein the control system has a mode of operation where the provided measured values of compressor operational parameter(s) are the liquid volume fraction, the gas volume fraction and/or the liquid volume flow of the compressor inlet flow.
19. System for controlling the quantity of liquid in accordance with one of the claims 12-16, wherein the control system has a mode of operation where the provided measured values of compressor operational parameter(s) are driving characteristics of the compressor.
20. System for controlling the quantity of liquid in accordance with claim 19, wherein the driving characteristics are based on the compressor absorbed power, absorbed torque or on actual current in the driving motor of the compressor.
21. System for controlling the quantity of liquid in accordance with one of the claims 12-18, wherein the measuring means for measuring the compressor inlet flow comprise a multiphase flow meter or at least two single phase meters.
22. System for controlling the quantity of liquid in accordance with one of the claims 12-21, wherein a recycle line extending from the compressor outlet is connected to the compressor inlet flow line between the liquid hold up tank and the compressor.
23. System for controlling the quantity of liquid in accordance with one of the claims 12-21, wherein a recycle line extending from the compressor outlet is connected to the liquid hold up tank.
24. System for controlling the quantity of liquid in accordance with one of the claims 12-21, wherein a recycle line extending from the compressor outlet is connected to the inlet flow line upstream the liquid hold-up tank.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NO20151362A NO341968B1 (en) | 2015-10-09 | 2015-10-09 | Method for controlling liquid content in gas flow to a wet gas compressor |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NO20151362A NO341968B1 (en) | 2015-10-09 | 2015-10-09 | Method for controlling liquid content in gas flow to a wet gas compressor |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| NO20151362A1 NO20151362A1 (en) | 2017-04-10 |
| NO341968B1 true NO341968B1 (en) | 2018-03-05 |
Family
ID=58668687
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| NO20151362A NO341968B1 (en) | 2015-10-09 | 2015-10-09 | Method for controlling liquid content in gas flow to a wet gas compressor |
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| Country | Link |
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| NO (1) | NO341968B1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2021191354A1 (en) | 2020-03-26 | 2021-09-30 | Fmc Kongsberg Subsea As | Modularized subsea compressor train and method of installation |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4156578A (en) * | 1977-08-02 | 1979-05-29 | Agar Instrumentation Incorporated | Control of centrifugal compressors |
| US4273514A (en) * | 1978-10-06 | 1981-06-16 | Ferakarn Limited | Waste gas recovery systems |
| US4493608A (en) * | 1982-12-27 | 1985-01-15 | General Electric Company | Surge control in compressor |
| WO2009131462A2 (en) * | 2008-04-21 | 2009-10-29 | Statoilhydro Asa | Gas compression system |
| US20130170952A1 (en) * | 2010-07-14 | 2013-07-04 | Statoil Asa | Method and apparatus for composition based compressor control and performance monitoring |
-
2015
- 2015-10-09 NO NO20151362A patent/NO341968B1/en unknown
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4156578A (en) * | 1977-08-02 | 1979-05-29 | Agar Instrumentation Incorporated | Control of centrifugal compressors |
| US4273514A (en) * | 1978-10-06 | 1981-06-16 | Ferakarn Limited | Waste gas recovery systems |
| US4493608A (en) * | 1982-12-27 | 1985-01-15 | General Electric Company | Surge control in compressor |
| WO2009131462A2 (en) * | 2008-04-21 | 2009-10-29 | Statoilhydro Asa | Gas compression system |
| US20130170952A1 (en) * | 2010-07-14 | 2013-07-04 | Statoil Asa | Method and apparatus for composition based compressor control and performance monitoring |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2021191354A1 (en) | 2020-03-26 | 2021-09-30 | Fmc Kongsberg Subsea As | Modularized subsea compressor train and method of installation |
Also Published As
| Publication number | Publication date |
|---|---|
| NO20151362A1 (en) | 2017-04-10 |
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