CN115751180A - A method and system for detecting and controlling the net positive pressure head of an LNG submersible pump - Google Patents

Abstract

The invention provides a net positive pressure head detection regulation and control method and system of an LNG immersed pump, wherein the regulation and control method comprises the following steps: after the liquid source components of the gas station are stable, measuring an LNG saturation temperature-pressure curve; obtaining the net positive pressure head P required by the normal operation of the immersed pump _N (ii) a After precooling of the LNG immersed pump is completed, acquiring real-time temperature of a pump inlet and real-time pressure P in the immersed pump tank before starting the pump _{Fruit of Chinese wolfberry} Obtaining the saturation pressure P at the saturation temperature according to the saturation temperature-pressure curve _{Full of} (ii) a Obtaining a real-time net positive head of LNG: p _{Fruit of N} ＝P _{Fruit of Chinese wolfberry} ‑P _{Full of} (ii) a Judgment of P _N And P _{Fruit of N} The size relationship of (1): if P _{N shi >} P _N When the LNG immersed pump runs, the required net positive pressure head is enough; if P _{N is less than or equal to} P _N And meanwhile, the clean positive pressure head required by the operation of the LNG immersed pump is insufficient. The invention detects and adjusts the net positive pressure head of the LNG immersed pump, so that the net positive pressure head always accurately meets the working requirement, cavitation is prevented, the immersed pump is protected, the service life of the immersed pump is prolonged, and the LNG immersed pump is liftedThe filling efficiency is improved.

Description

A net positive pressure head detection and control method and system for an LNG submersible pump

technical field

The invention belongs to the technical field of filling devices for marine and vehicle LNG gas filling stations, and in particular relates to a method and system for detecting and controlling the net positive pressure head of an LNG submersible pump.

Background technique

LNG (L i quef i ed Natural Gas, liquefied natural gas) gas filling station uses LNG submersible pump as pressurization equipment to pressurize the LNG in the LNG storage tank from 0 to 1.2 MPa to a maximum of 1.6 MPa, and then fill it with LNG After metering by the machine, it is filled to LNG fuel vehicles.

When LNG is stored in a closed and insulated container, it often exists as a boiling liquid and is in a temperature-pressure equilibrium state. When the pressure of LNG drops below the boiling point pressure or LNG absorbs heat from the outside, a certain amount of liquid will evaporate into gas. (LNG flashing), at the same time, the temperature of the liquid is also reduced to its boiling point at the pressure until a new equilibrium is formed. When the pressure of LNG rises above the boiling point pressure or LNG with a lower temperature is supplemented from the outside, the evaporation of LNG is suppressed, and the liquefaction of BOG (Boil Off Gas, volatile gas of LNG) is intensified until a new equilibrium is formed.

The LNG filling station adopts the submersible pump as the LNG delivery pressurization equipment. The submersible pump is a centrifugal pump. When the centrifugal pump is working, a certain pressure drop is generated at the inlet of the impeller due to the suction of the pump, which causes local evaporation of LNG and cavitation. . In order to avoid cavitation, the LNG at the suction port needs to have a certain net positive pressure head when the pump is working, so as to prevent the pressure from falling below the boiling point pressure to generate flash gas, thereby causing cavitation.

At present, when the submersible pump of LNG filling station is running, the control is based on the phenomenon in operation to judge whether there is cavitation. After cavitation occurs, stop the pump to protect the pump. At this time, the pump has more or less caused some damage. In addition, due to the different gas sources, the components of LNG in gas filling stations are quite different. It is difficult to judge whether the net positive pressure head required by the submersible pump is sufficient before operation. big error.

Contents of the invention

The invention aims to solve the technical problems existing in the prior art, and provides a method and system for detecting and controlling the net positive pressure head of an LNG submersible pump.

According to a first aspect of the present invention, the present invention provides a method for detecting and controlling the net positive pressure head of an LNG submersible pump, which comprises the following steps:

S1, after the liquid source components of the gas filling station are stabilized, the LNG saturation temperature-pressure curve is measured when the LNG in the storage tank reaches 50% to 90%;

S2, obtaining the net positive pressure head P _N required for the normal operation of the submersible pump;

S3. After the precooling of the LNG submersible pump is completed, before starting the pump, collect _the real-time temperature of the pump inlet and the real-time pressure P in the submersible pump pool, and obtain the saturation pressure P at this temperature according to the saturation temperature-pressure curve obtained in step S1. _full

S4, obtain the real-time net positive pressure head of LNG: P _{N real} = P _real - P _full ;

S5, judging the size relationship _{between PN and PN :}

If P _{N is greater than} P _N , the net positive pressure head required for the operation of the LNG submersible pump is sufficient, the submersible pump can run, and exit;

If P _{N is ≤} P _N , the net positive pressure head required for the operation of the LNG submersible pump is insufficient, and the submersible pump cannot operate, then the system starts the pressurization program and returns to step S3 until the net positive pressure head requirement is met.

The invention detects and adjusts the net positive pressure head of the LNG submersible pump, so that the net positive pressure head always accurately meets the working requirements, prevents cavitation, protects the submersible pump, prolongs the service life of the submersible pump, and improves filling efficiency.

In the prior art, it is empirically determined that the actual net positive head cannot be measured. However, the present invention detects the relationship between the temperature and the saturation pressure of natural gas with unknown components, and obtains real-time net positive pressure head through the test, and the result is more accurate.

According to a preferred embodiment of the present invention, the method for measuring the LNG saturation temperature-pressure curve is:

After the LNG in the LNG storage tank is transported by the submersible pump, it is sent to the liquid inlet on the top of the LNG storage tank. After running for t1 time, let it stand for t2 time, t1<t2, and collect the temperature and pressure transmitters in the storage tank. LNG temperature and pressure;

Adjust the saturation pressure of the storage tank, use the submersible pump to operate at a low speed, and the low-speed operation frequency does not exceed 30Hz, transport the LNG in the storage tank to the LNG vaporizer for heating, and enter the liquid into the LNG storage tank through the bottom of the storage tank to process the LNG. Heating, during the heating process, every time the temperature rises by 1°C, the pressure of the storage tank is collected once until the pressure of the storage tank reaches 0.8MPa;

Put the collected storage tank temperature and pressure data into the controller to control the submersible pump, and other uncollected parameters are calculated by interpolation method.

The invention detects the relationship between the temperature and the saturation pressure of the natural gas with unknown components, and obtains the real-time net positive pressure head through the test, and the result is more accurate.

According to the second aspect of the present invention, the present invention provides a net positive pressure head detection and control system for LNG submersible pumps. A temperature transmitter and a pressure transmitter are arranged in the LNG storage tank, and a temperature transmitter and a pressure transmitter are installed outside the LNG storage tank. An LNG submersible pump is installed on the pipeline, and the temperature and pressure transmitters collect the temperature and pressure signals in the LNG storage tank and transmit them to the controller. The controller measures the LNG saturation temperature-pressure curve, and uses The method for detecting and controlling the net positive pressure head described in claim 1 detects and regulates the net positive pressure head of the LNG submersible pump.

The invention detects and adjusts the net positive pressure head of the LNG submersible pump, so that the net positive pressure head always accurately meets the working requirements, prevents cavitation, protects the submersible pump, prolongs the service life of the submersible pump, and improves filling efficiency.

Additional aspects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

Detailed ways

Embodiments of the present invention are described in detail below, and the embodiments described below are exemplary and are only used for explaining the present invention, and should not be construed as limiting the present invention.

In describing the present invention, it should be understood that the terms "longitudinal", "transverse", "vertical", "upper", "lower", "front", "rear", "left", "right", The orientations or positional relationships indicated by "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplified descriptions, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and thus should not be construed as limiting the invention.

In the description of the present invention, unless otherwise specified and limited, it should be noted that the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be mechanical connection or electrical connection, or two The internal communication of each element may be directly connected or indirectly connected through an intermediary. Those skilled in the art can understand the specific meanings of the above terms according to specific situations.

The invention provides a net positive pressure head detection and control method of an LNG submersible pump, which comprises the following steps:

S1, after the liquid source composition of the gas filling station is stabilized, unload a truck with a liquid whose saturation pressure is close to 0 (gauge pressure), and carry out LNG when the LNG in the storage tank reaches 50% to 90% (preferably 80% to 90%) Saturation temperature-pressure curve determination, if the specific gas source comes from the same factory, the gas source is stable by default;

S2, obtaining the net positive pressure head P _N required for the normal operation of the submersible pump;

S3. After the precooling of the LNG submersible pump is completed, before starting the pump, collect _the real-time temperature of the pump inlet and the real-time pressure P in the submersible pump pool, and obtain the saturation pressure P at this temperature according to the saturation temperature-pressure curve obtained in step S1. _full

S4, obtain the real-time net positive pressure head of LNG: P _{N real} = P _real - P _full ;

S5, judging the size relationship _{between PN and PN :}

If P _{N is greater than} P _N , the net positive pressure head required for the operation of the LNG submersible pump is sufficient, the submersible pump can run, and exit;

If P _{N is ≤} P _N , the net positive pressure head required for the operation of the LNG submersible pump is insufficient, and the submersible pump cannot operate, then the system starts the pressurization program and returns to step S3 until the net positive pressure head requirement is met.

In this embodiment, the method for measuring the LNG saturation temperature-pressure curve is:

After the LNG in the LNG storage tank is transported by the submersible pump, it is sent to the top liquid inlet of the LNG storage tank. After running for t1 time, it is left to stand for t2 time, t1<t2, preferably t1 is 2 minutes, and t2 is 30 minutes. The temperature and pressure of LNG in the storage tank are collected through temperature transmitters and pressure transmitters.

Adjust the saturation pressure of the storage tank, use the submersible pump to operate at a low speed, and the low-speed operation frequency does not exceed 30Hz, transport the LNG in the storage tank to the LNG vaporizer for heating, and enter the liquid into the LNG storage tank through the bottom of the storage tank to process the LNG. Heating. During the heating process, the pressure of the storage tank is collected every time the temperature rises by 1°C until the pressure of the storage tank reaches the operating pressure threshold of the storage tank (for example, 0.8MPa). Since the pressure of the storage tank is actually in the range of 0-1.2MPa, and it is generally maintained between 0.1-0.8MPa during operation, if it exceeds 0.1-0.8MPa, an approximate value can be obtained by curve fitting.

Put the collected storage tank temperature and pressure data into the controller to control the submersible pump, and other uncollected parameters are calculated by interpolation method.

The present invention also provides a net positive head detection and control system for the LNG submersible pump, in which a temperature transmitter and a pressure transmitter are arranged in the LNG storage tank, and an LNG submersible pump is arranged on the external pipeline of the LNG storage tank , the temperature transmitter and the pressure transmitter collect the temperature signal and pressure signal in the LNG storage tank and transmit them to the controller, and the controller measures the LNG saturation temperature-pressure curve, and uses the net positive pressure head of the present invention to detect The regulation method detects and regulates the net positive pressure head of the LNG submersible pump.

In the description of this specification, descriptions referring to the terms "preferred embodiment", "one embodiment", "some embodiments", "examples", "specific examples" or "some examples" etc. mean that the embodiments are combined A specific feature, structure, material, or characteristic described by or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

Although the embodiments of the present invention have been shown and described, those skilled in the art can understand that various changes, modifications, substitutions and modifications can be made to these embodiments without departing from the principle and spirit of the present invention. The scope of the invention is defined by the claims and their equivalents.

Claims (4)

1. a net positive pressure head detection and control method of LNG submersible pump, is characterized in that, comprises the steps: S1, after the liquid source components of the gas filling station are stabilized, the LNG saturation temperature-pressure curve is measured when the LNG in the storage tank reaches 50% to 90%; S2, obtaining the net positive pressure head P _N required for the normal operation of the submersible pump; S3. After the precooling of the LNG submersible pump is completed, before starting the pump, collect _the real-time temperature of the pump inlet and the real-time pressure P in the submersible pump pool, and obtain the saturation pressure P at this temperature according to the saturation temperature-pressure curve obtained in step S1. _full S4, obtain the real-time net positive pressure head of LNG: P _{N real} = P _real - P _full ; S5, judging the size relationship _{between PN and PN :} If P _{N is greater than} P _N , the net positive pressure head required for the operation of the LNG submersible pump is sufficient, the submersible pump can run, and exit; If P _{N is ≤} P _N , the net positive pressure head required for the operation of the LNG submersible pump is insufficient, and the submersible pump cannot operate, then the system starts the pressurization program and returns to step S3 until the net positive pressure head requirement is met. 2. the net positive pressure head detection control method of LNG submersible pump according to claim 1 is characterized in that, the method for carrying out LNG saturation temperature-pressure curve measurement is: After the LNG in the LNG storage tank is transported by the submersible pump, it is sent to the liquid inlet on the top of the LNG storage tank. After running for t1 time, let it stand for t2 time, t1<t2, and collect the temperature and pressure transmitters in the storage tank. LNG temperature and pressure; Adjust the saturation pressure of the storage tank, use the submersible pump to operate at a low speed, and the low-speed operation frequency does not exceed 30Hz, transport the LNG in the storage tank to the LNG vaporizer for heating, and enter the liquid into the LNG storage tank through the bottom of the storage tank to process the LNG. Heating, during the heating process, every time the temperature rises by 1°C, the pressure of the storage tank is collected once until the pressure of the storage tank reaches the operating pressure threshold of the storage tank; Put the collected storage tank temperature and pressure data into the controller to control the submersible pump, and other uncollected parameters are calculated by interpolation method. 3. The method for detecting and controlling the net positive pressure head of the LNG submersible pump according to claim 2, wherein the t1 is 2 minutes, and the t2 is 30 minutes. 4. A net positive pressure head detection and control system for an LNG submersible pump, characterized in that a temperature transmitter and a pressure transmitter are arranged in the LNG storage tank, and an LNG submersible liquid is provided on the external pipeline of the LNG storage tank. pump, the temperature transmitter and pressure transmitter collect the temperature signal and pressure signal in the LNG storage tank and send them to the controller, and the controller measures the LNG saturation temperature-pressure curve, and utilizes the net pressure signal described in claim 1 The positive pressure head detection and control method detects and regulates the net positive pressure head of the LNG submersible pump.