A BOG flow control system for a tank farm receiving station

Abstract

The application relates to a BOG flow control system of a tank group receiving station, comprising: a tank pressure controller for monitoring the pressure of an LNG storage tank and controlling a BOG compressor according to the pressure value; the BOG compressor is arranged in a BOG pipeline communicated with the LNG storage tank, and is used for receiving BOG of the LNG storage tank, processing the BOG and then conveying the BOG to a recondenser; the BOG compressor comprises a centrifugal compressor set and a reciprocating compressor set in parallel, the centrifugal compressor set is used for covering a preset basic flow, and the reciprocating compressor set is used for covering a peak flow outside the basic flow in cooperation with the centrifugal compressor set. The application can meet the demand of increasing BOG processing capacity, and meanwhile, the economy of investment is ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of LNG (Liquefied Natural Gas) receiving stations, in particular to a BOG flow control system of a tank group receiving station. BACKGROUND

[0002] With the continuous expansion of the LNG receiving station's external transport scale, a phenomenon of "tank cluster" is formed, which makes the amount of BOG (Boil-Off Gas) of the LNG receiving station continue to increase.

[0003] The existing technology usually transports the BOG to the BOG compressor for pressure compression, and then transports it to the condenser to condense into LNG.

[0004] However, the present inventors found in the research that the existing BOG compressor is usually a reciprocating compressor, and with the continuous expansion of the BOG amount, a single compressor with a capacity of 12t / h cannot meet the processing capacity requirement, and only the number of reciprocating compressors can be increased to increase the processing capacity. In the scene of the LNG receiving station, due to the limitation of the site, the investment mode of merely increasing the number of compressors is not economical. SUMMARY

[0005] In view of the above problems, the purpose of the present application is to provide a BOG flow control system of a tank group receiving station, which can meet the increasing demand for BOG processing capacity while ensuring the economy of investment.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] The present application provides a BOG flow control system of a tank group receiving station, comprising: a tank pressure controller for monitoring the pressure of the LNG storage tank and controlling the BOG compressor according to the pressure value;

[0008] The BOG compressor is arranged in the BOG pipeline in communication with the LNG storage tank, and is used to receive the BOG of the LNG storage tank for processing and then deliver it to the recondenser;

[0009] The BOG compressor comprises a centrifugal compressor group and a reciprocating compressor group connected in parallel, the centrifugal compressor group is used to cover the preset basic flow, and the reciprocating compressor group is used to cooperate with the centrifugal compressor group to cover the peak flow beyond the basic flow.

[0010] In an implementation manner of the present application, the control mode of the tank pressure controller comprises:

[0011] DCS control mode based on automatic remote operation position;

[0012] UCP control mode based on manual remote operation position; and

[0013] LP control mode based on local operation position.

[0014] In an implementation form of the application, the control mode of the tank pressure controller, the operation mode of the BOG compressor comprises an automatic mode, a manual step mode and a test mode;

[0015] The automatic mode corresponds to the DCS control mode and the UCP control mode of the tank pressure controller;

[0016] The manual step mode corresponds to the DCS control mode, the UCP control mode and the LP control mode of the tank pressure controller;

[0017] The test mode corresponds to the LP control mode of the tank pressure controller.

[0018] In an implementation form of the application, the control mode of the tank pressure controller, the tank pressure controller comprises a DSC pressure indicator, a pressure signal selector, a buffer signal selector and a priority device selector connected in sequence.

[0019] In an implementation form of the application, the control mode of the tank pressure controller, the centrifugal compressor unit is used to realize continuous load variation covering the preset basic flow through inlet guide vanes and outlet guide vanes;

[0020] The reciprocating compressor unit is used to realize a preset number of step control load variations through clearance adjustment and unloading valve adjustment.

[0021] In an implementation form of the application, the control mode of the tank pressure controller, the reciprocating compressor unit realizes step load variation of 0%-25%-50%-75%-100%.

[0022] In an implementation form of the application, the control mode of the tank pressure controller, the compressor in the centrifugal compressor unit gradually closes the IGV opening when the flow decreases; when the flow decreases to the anti-surge line, the backflow valve is opened to ensure the safety of the compressor itself.

[0023] In an implementation form of the application, the control mode of the tank pressure controller, the compressor in the centrifugal compressor unit has an inlet liquid amount with a particle size of not more than 10 μm and a concentration of not more than 50 ppm.

[0024] In an implementation form of the application, the control mode of the tank pressure controller, the tank pressure controller is provided with a high pressure set value and a low pressure set value for gap control.

[0025] In an implementation form of the application, the control mode of the tank pressure controller, the application mode of the control system includes an LNG unloading mode, an LNG loading mode or a circulation mode.

[0026] The BOG flow control system of the tank group receiving station of the application has the following advantages: the tank pressure controller is used for monitoring the pressure of the LNG tank and controlling the BOG compressor according to the pressure value. The BOG compressor includes a centrifugal compressor set and a reciprocating compressor set connected in parallel, wherein the centrifugal compressor set is used to cover the preset basic flow, and the reciprocating compressor set is used to cover the peak flow in addition to the basic flow in cooperation with the centrifugal compressor set. The centrifugal compressor has the advantages of large single machine gas capacity, continuous operation, simple and compact structure, light weight, small unit size, small land occupation area, easy realization of automatic control, high operation reliability, few friction parts, low spare parts demand, long service life, low maintenance cost and personnel, stable centrifugal compressor exhaust pressure, no pulse, reciprocating compressor exhaust pulse, and the cooperation of the two can reduce the exhaust pressure fluctuation range. Therefore, compared with the prior art, the BOG processing capacity can meet the increasing demand, and the investment economy is ensured. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a whole structure schematic diagram of a BOG flow control system of a tank group receiving station provided by an embodiment of the application;

[0028] Figure 2 is a centrifugal compressor load adjustment schematic diagram in the embodiment of the application;

[0029] Figure 3 is a reciprocating compressor load adjustment schematic diagram in the embodiment of the application. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical scheme and advantages of the embodiments of the application clearer, the technical scheme of the embodiments of the application will be described clearly and completely below with reference to the drawings of the embodiments of the application. Obviously, the described embodiments are part of the embodiments of the application, not all the embodiments. Based on the described embodiments of the application, all other embodiments obtained by those skilled in the art belong to the scope of protection of the application.

[0031] In view of the problem in the prior art that as the amount of BOG continuously expands, the investment benefit is reduced by simply increasing the number of reciprocating compressors to meet the BOG processing capacity, the application correspondingly provides a BOG flow control system of a tank group receiving station, which comprises: a tank pressure controller configured to monitor the pressure of an LNG storage tank and control a BOG compressor according to the pressure value; the BOG compressor is arranged in a BOG pipeline in communication with the LNG storage tank, and is configured to receive BOG of the LNG storage tank for processing and then deliver the BOG to a recondenser; the BOG compressor comprises a centrifugal compressor set and a reciprocating compressor set connected in parallel, the centrifugal compressor set is configured to cover a preset basic flow, and the reciprocating compressor set is configured to cover a peak flow in addition to the basic flow in cooperation with the centrifugal compressor set. The technical scheme of the application can meet the demand for increasing BOG processing capacity while ensuring the economy of investment.

[0032] Referring to Figure 1 In one embodiment of the application, a BOG flow control system of a tank group receiving station is provided, which adopts inlet guide vanes (IGV) and outlet guide vanes of a centrifugal compressor for base load BOG processing, and adopts traditional reciprocating compressor clearance adjustment and unloading valve adjustment for incremental BOG adjustment.

[0033] The BOG flow control system of the tank group receiving station in the embodiment of the application comprises: a tank pressure controller configured to monitor the pressure of an LNG storage tank 1 and control a BOG compressor according to the pressure value;

[0034] The BOG compressor is arranged in a BOG pipeline 8 in communication with the LNG storage tank 1, and is configured to receive BOG of the LNG storage tank for processing and then deliver the BOG to a recondenser 9;

[0035] The BOG compressor comprises a centrifugal compressor set 6 (for example, at least two centrifugal compressors) and a reciprocating compressor set 7 (for example, at least two reciprocating compressors) connected in parallel, the centrifugal compressor set 6 is configured to cover a preset basic flow, and the reciprocating compressor set 7 is configured to cover a peak flow in addition to the basic flow in cooperation with the centrifugal compressor set 6.

[0036] In one specific embodiment of the application, the control mode of the tank pressure controller comprises: a DCS control mode based on an automatic remote operating position; a UCP control mode based on a manual remote operating position; and an LP control mode based on an on-site operating position.

[0037] Further, the three BOG compressor operation modes include an automatic mode, a manual step mode and a test mode. The automatic mode can be selected from two ways of DCS and UCP; the manual step mode can be selected from three ways of DCS, UCP and LP; and the test mode can only be operated by the way of LP.

[0038] The tank pressure controller comprises a DSC pressure indicator 2, a pressure signal selector 3, a buffer signal selector 4 and a priority device selector 5 connected in sequence.

[0039] The control system in the embodiment of the application has application modes including an LNG unloading mode, an LNG loading mode or a circulation mode. The LNG unloading mode is switched when the LNG transport ship unloads LNG into the tank, the LNG loading mode is switched when the tank unloads LNG into the LNG transport ship, and the non-LNG unloading mode and the LNG loading mode are the circulation mode. Considering that the buffer capacity of the LNG tank is large, the tank pressure is controlled by setting a high pressure set value and a low pressure set value, and the pressure set value can be changed by the operator according to the operation mode. Therefore, the pressure value of the DSC pressure indicator 2 can represent the flow state of the BOG of the LNG tank, so as to control the start and stop state of the BOG compressor.

[0040] Since the capacity of the tank is relatively large, the tank pressure changes relatively slowly in the pressure stabilization process, which allows the controller to be stopped for 15 minutes after each load increase in the "non-unloading mode". If the tank pressure still remains above the set value after the allowed time, the controller will automatically increase the load of the same compressor. Similarly, during the pressure stabilization process after each load decrease, the tank pressure also changes relatively slowly, which allows the controller to be stopped for 15 minutes after each unloading in the "circulation mode". If the tank pressure still remains below the set value within the allowed time, the controller will automatically decrease the load of the same compressor. During the unloading and loading operations, the allowed time is reduced to 5 minutes.

[0041] In the embodiment of the application, the centrifugal compressor unit is used to realize continuous load change covering the preset basic flow through the inlet guide vane and the outlet guide vane; and the reciprocating compressor unit is used to realize preset number of step control load changes, for example, 5 step control load changes: 0%-25%-50%-75%-100%, through the clearance adjustment and the unloading valve adjustment.

[0042] The centrifugal compressor is provided with a PLC, has perfect anti-surge protection function, when the flow rate decreases, the centrifugal compressor IGV will gradually close the IGV opening; when the flow rate decreases to the anti-surge line, the backflow valve will first open, to ensure the safety of the centrifugal compressor itself, and will inform the main control PLC to distribute the load, start and stop according to the preset logic, and re-achieve the optimal working condition. In the embodiment, the centrifugal compressor has certain requirements for the inlet liquid amount and the particle size, and the size is required to be below 10 μm and the concentration is required to be below 50 ppm.

[0043] Since the centrifugal compressor has the advantages of large and continuous single machine gas volume, simple and compact structure, light weight, small unit size, small land occupation area, and easy realization of automatic control; and the centrifugal compressor has high operation reliability, few friction parts, thus the required amount of spare parts is small, the service life is long, the maintenance cost and personnel are small, the exhaust pressure of the centrifugal compressor is stable, there is no pulse, the exhaust of the reciprocating compressor has pulse, and the two are used in cooperation to reduce the exhaust pressure fluctuation range, thus the technical scheme saves the maintenance period of the compressor of the receiving station, reduces the land occupation area of the compressor workshop of the receiving station, and achieves the synergistic effect of the reciprocating and centrifugal compressors for BOG treatment.

[0044] In the following, the specific operation process and control parameters of the technical scheme of the application are described in some specific application scenarios. Figure 1 , Figure 2 and Figure 3 .

[0045] Specifically, in the application scenario of the application, the compressor is started and stopped according to the change of the inlet pressure; when the BOG amount rises, the inlet pressure rises, the centrifugal compressor regulating valve actuator (IGV) can be opened or one reciprocating compressor can be started. When the BOG amount decreases, the inlet pressure decreases, the IGV of the centrifugal compressor can be closed or one reciprocating compressor can be stopped. In one application scenario, the LNG receiving station project is provided with two 12-ton / hour low-pressure reciprocating BOG compressors and two 12-ton low-pressure centrifugal BOG compressors, the reciprocating compressor can be adjusted at 25% / 50% / 75% / 100% flow rate, and the centrifugal compressor can be adjusted at 75%-100% flow rate.

[0046] The up-down difference of the exhaust pressure of the centrifugal compressor is 0.016 Bar, the up-down difference of the exhaust pressure of the reciprocating compressor is 0.12 Bar, and the waveform is in the form of pulse. After being used in cooperation with the centrifugal compressor, the up-down difference of the exhaust pressure can be reduced to 0.0424 Bar, and the influence of the pressure pulse on the rear-end equipment is effectively reduced.

[0047] The operator can start or stop the BOG compressor and sequence the auxiliary equipment from the DCS. The operator can select the load control mode to be automatic or manual. When load control is available, the operator can select the compressor load from the DCS to be step mode, which can achieve 70% - 100% for centrifugal compressors and 25%, 50%, 75%, and 100% for reciprocating compressors.

[0048] The operator can start or stop the BOG compressor and sequence the auxiliary equipment from the HMI of the UCP (MCB). When load control is available, the operator can select the centrifugal compressor load from the UCP to be 70% - 100% and the reciprocating compressor load to be 0%, 25%, 50%, 75%, and 100%.

[0049] The operator can start or stop the auxiliary equipment individually from the local control panel located near the compressor. The operator can simulate the compressor run sequence without running the BOG compressor. The "remote" or "local" mode cannot be switched to "trial" mode during compressor operation.

[0050] Before starting the compressor, the motor purge needs to be completed; the operation mode is selected to be "remote" mode in the local panel; the load control mode is selected to be "step (manual)" mode in the main control room (DCS); the start button "auxiliary sequence" is pressed in the DCS to start the auxiliary oil pump and the oil cooling fan; then the main motor is started, and the suction BOG temperature is checked to be lower than -90°C; after the BOG compressor runs at 0% load for 30 seconds, the capacity control can be performed, in which the centrifugal compressor can control the backflow valve to gradually close, the IGV to gradually open, and the compressor capacity to be adjusted at 70% - 100%, the reciprocating compressor can be adjusted at 0% - 25% - 50% - 75% - 100%, or the capacity control can be automatically performed by the storage tank pressure; when the compressor is in the running state and is stopped, the centrifugal compressor should have all the backflow valves fully open, the IGV opening degree is 10%, then the main motor is stopped, the auxiliary oil pump is opened, the IGV is fully closed, the backflow valve is fully opened, and the auxiliary oil pump is closed after 30 minutes.

[0051] The BOG compressor can also be load regulated by the pressure of the LNG storage tank 1, in which the centrifugal compressor 6 can be adjusted at 70% - 100% capacity, and the reciprocating compressor 7 can be adjusted at 0% - 25% - 50% - 75% - 100% capacity. The pressure of the LNG storage tank 1 is controlled by the BOG compressor through two DCS pressure indicators 2 on each LNG storage tank. The pressure signal selector 3 selects the highest pressure, and the buffer signal selector sets two set values: a high pressure set value (more than 11.6 kPa absolute pressure) and a low pressure set value (more than 11.2 kPa absolute pressure).

[0052] In the unloading condition, the compressor is in automatic mode, and the reciprocating compressor 7 is used for adjustment. If the pressure of the LNG storage tank 1 rises above the high pressure set value, the reciprocating compressor 7 in operation will automatically increase one level of capacity (for example, from 25% to 50%, from 75% to 100%, etc.). Similarly, if the pressure of the storage tank decreases below the low pressure set value, the reciprocating compressor 7 in operation will automatically decrease one level of capacity (for example, from 100% to 75%, from 50% to 25%, etc.).

[0053] In the cycle mode, only the centrifugal compressor 6 is normally sufficient to handle the BOG generated by the LNG receiving station. The centrifugal compressor 6 in operation is selected as the "priority device". There is a selection switch in the DCS priority device selector 5 to select the centrifugal compressor 6 and the reciprocating compressor 7. The signal (70%-100%) is transmitted to the BOG compressor device selected as the "priority device". If the capacity of the centrifugal compressor 6 reaches 100% and the "100%-125%" signal is activated, the reciprocating compressor 7 is started manually by the operator, and it operates at a capacity of 25% (totaling 125% capacity), and the capacity control of the compressor is set to automatic mode.

[0054] The operator can adjust the capacity loading mode of the compressor to manual mode, at which time the operator can manually reduce the load, increase the load, or stop the compressor. The operator adjusts the loading and unloading mode of the compressor back to automatic mode.

[0055] In summary, the BOG flow control system of the tank group receiving station of the present application includes a storage tank pressure controller for monitoring the pressure of the LNG storage tank and controlling the BOG compressor according to the pressure value. The BOG compressor includes a centrifugal compressor set and a reciprocating compressor set connected in parallel, wherein the centrifugal compressor set is used to cover the preset basic flow, and the reciprocating compressor set is used to cooperate with the centrifugal compressor set to cover the peak flow beyond the basic flow. Since the centrifugal compressor has the advantages of large single machine gas capacity and continuity, simple and compact structure, light weight, small unit size, small land occupation area, easy realization of automatic control, high operation reliability, few friction parts, and thus less need for spare parts, long service life, low maintenance cost and personnel, stable centrifugal compressor exhaust pressure, no pulse, and pulsed exhaust of the reciprocating compressor, the use of the two in combination can reduce the exhaust pressure fluctuation range, thereby meeting the increasing demand for BOG processing capacity while ensuring the economy of investment, compared with the prior art.

[0056] The above merely describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A BOG flow control system for a tank group receiving station, characterized in that, include: A tank pressure controller used to monitor the pressure of LNG storage tanks and control the BOG compressor based on the pressure value. The BOG compressor is installed in the BOG pipeline connected to the LNG storage tank, and is used to receive the BOG from the LNG storage tank, process it, and then send it to the recondenser. The BOG compressor includes a parallel centrifugal compressor unit and a reciprocating compressor unit. The tank pressure controller includes a DSC pressure indicator, a pressure signal selector, a buffer signal selector, and a priority device selector, which are connected in sequence. The pressure of the LNG storage tank is controlled by two DCS pressure indicators on each LNG storage tank. The pressure signal selector selects the maximum pressure, and the buffer signal selector sets the high pressure setting value and the low pressure setting value. The reciprocating compressor unit achieves a stepped load change of 0%-25%-50%-75%-100%; specifically, when the pressure of the LNG storage tank rises above the high-pressure set value, the operating reciprocating compressor unit will increase its capacity by one level; and when the pressure of the LNG storage tank drops below the low-pressure set value, the operating reciprocating compressor unit will automatically decrease its capacity by one level. The control modes of the tank pressure controller include: DCS control mode based on automatic remote operation position; UCP control mode based on manual remote operation position; and LP control mode based on local operation position. The BOG compressor has three operating modes: automatic mode, manual step mode, and test mode. The automatic mode corresponds to the DCS control mode and UCP control mode of the tank pressure controller. The manual step mode corresponds to the DCS control mode, UCP control mode, and LP control mode of the tank pressure controller. The test mode corresponds to the LP control mode of the tank pressure controller. The reciprocating compressor unit is used to achieve a preset number of stepped load changes through clearance adjustment and unloading valve adjustment; In the centrifugal compressor unit, when the flow rate decreases, the compressor gradually closes the IGV opening; when the flow rate drops to the anti-surge line, the return valve is opened to ensure the compressor's own safety.

2. The BOG flow control system for the tank group receiving station according to claim 1, characterized in that, The compressor in the centrifugal compressor unit has an inlet liquid volume with a particle size not exceeding 10 μm and a concentration not exceeding 50 ppm.

3. The BOG flow control system for the tank group receiving station according to claim 2, characterized in that, The tank pressure controller is pre-set with a high pressure setting and a low pressure setting for intermittent control.

4. The BOG flow control system for a tank group receiving station according to claim 1, characterized in that, The application modes of the control system include LNG unloading mode, LNG loading mode, or circulation mode.

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