CN102937240A - Back pressure control method and application system for liquefied gas loading - Google Patents
Back pressure control method and application system for liquefied gas loading Download PDFInfo
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- CN102937240A CN102937240A CN2012104190773A CN201210419077A CN102937240A CN 102937240 A CN102937240 A CN 102937240A CN 2012104190773 A CN2012104190773 A CN 2012104190773A CN 201210419077 A CN201210419077 A CN 201210419077A CN 102937240 A CN102937240 A CN 102937240A
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Abstract
The invention relates to a back pressure control method and an application system for in liquefied gas loading. The method comprises the following steps of: acquiring control pressure required by liquefied gas filling with a table look-up method according to known medium compositions and working condition temperatures; detecting back pressure of a liquefied gas filling pipeline flow meter; judging whether the back pressure of the filling pipeline is greater than the control pressure obtained from the first step, and if so, finishing the control process, otherwise, carrying out the next step; and controlling actual pressure of the filling pipeline according to density signals of the flow meter and diagnosis signals of the filling pipeline. The back pressure control method and the application system provided by the invention have less control links, are high in safety and reliability, and are convenient to operate and maintain.
Description
Technical field
The invention belongs to field of measuring techniques, relate to the controlling method in a kind of metering process, relate in particular to back pressure control method and application system in a kind of liquid gas entrucking.
Background technique
Liquid gas entrucking metering is petrochemical industry key link for sale, usually uses in recent years Coriolis flowmeter as measuring instrument, because the liquid gas component is complicated, physical property shows as: density varies with temperature greatly (liquefaction); Saturation vapour pressure varies with temperature greatly, easily gasification; State changes greatly with temperature, pressure, easily forms the gas-liquid mixed state and is not easy accurate-metering.
In the liquid gas loading system, the gasification of medium mainly is present in opening stage beginning of entrucking, this is because in airtight pouring process, because being higher than tank car pressure, pipeline pressure impel liquid gas in tank car, to flow, when empty lng tanker is come, the tank car internal pressure is generally less than the saturation vapour pressure (being generally about 0.2MPa) of liquid gas, thereby the pipeline decompression that links to each other with tank car is very fast, and the fast reducing of pressure gasifies liquid gas very soon.Usually before Coriolis flowmeter is contained in the entrucking oil filling riser, be close to the oil filling riser outlet, the liquid gas of the Coriolis flowmeter (hereinafter to be referred as flowmeter) of flowing through like this is very soon gasification also, forms gas, liquid two phases in measuring channel, so that flowmeter is operated in not normal state, the metering effect can't be assessed.After pressure in the tank car raises and satisfies the liquefaction pressure of liquid gas, the outlet end pressure that is flowmeter (is designated hereinafter simply as the back pressure of flowmeter, namely liquid gas is at the saturation vapour pressure under this operating mode) satisfy the liquefaction pressure of liquid gas after, flowmeter could work, and good metering effect just can be arranged.
In addition, pressure, ambient temperature in the static pressure of pipeline, the empty wagons all can be brought impact to the endurance of gas, liquid two phases in the measuring channel, the gas-liquid two-phase metering is the biggest problem in the fluid metering, there is not at present the directly solution of measurement, so become pure liquid state or pure gaseous state to the state of medium, the metering effect of flowmeter just can be protected.Usually the accumulating of liquid gas all is that pressurization or cooling make medium liquefaction, because the back pressure that improves flowmeter is adopted in the restriction of process conditions, makes it greater than the liquid gas saturation vapour pressure of working temperature, thereby make medium liquefaction, this mode is more rational selection scheme.
Usually in order to guarantee back pressure, use pressure instrument in conjunction with the mode of pressure control valve at the outlet end of flowmeter, this mode can only provide suitable back pressure theoretically, but because that the saturation vapour pressure of liquid gas changes with process conditions such as medium composition compositions, temperature is larger, so respective change is also wanted in the back pressure requirement.The variation of temperature can be passed through temperature sensor measurement, but the medium composition changes relatively difficulty of detection, be difficult for realizing, so manual tune is many in actual implementation process, back pressure effective controlled poor, final result is bad when being exactly the degree of accuracy fashion of loading system, and stability is not high.
Summary of the invention
In order to solve the above-mentioned technical problem that exists in the background technique, the invention provides that a kind of controlling unit is few, safety reliability is high and the liquid gas entrucking of convenient operation and maintenance in back pressure control method and application system.
Technical solution of the present invention is: the invention provides the back pressure control method in a kind of liquid gas entrucking, its special way is: said method comprising the steps of:
1) utilize look-up table to obtain the required pilot pressure of city gas bottling according to known medium composition and working temperature;
2) back pressure of detection city gas bottling pipeline flow meters;
3) judge that whether the back pressure of can pipeline is greater than the resulting pilot pressure of step 1).If then finish this control procedure; If not, then carry out step 4);
4) with density signal and self diagnostic signal of flowmeter the actual pressure of can pipeline is controlled.
The specific implementation of step 4) is:
4.1) regulate the back pressure of can pipeline by controlling opening of valve, and make it near the saturation vapour pressure of liquid gas under working temperature;
4.2) take the density signal of flowmeter and self diagnostic signal as setting value, the fine tuning valve aperture makes the back pressure of city gas bottling pipeline greater than the required saturation vapour pressure of liquefaction under this working temperature.
Above-mentioned saturation vapour pressure is to obtain with look-up table with reference to SH/T0221-92 and GB/T12576-97 liquefied petroleum gas (LPG) vapor tension and relative density and octane value numeration.
Back pressure control application system in a kind of liquid gas entrucking, its special way is: described system comprises by equipment formations such as flowmeter, pressure transmitter, flow batch controller (hereinafter to be referred as controller) and regulating valves.The unlatching of described controller regulating and controlling valve or close, described flowmeter gathers regulating valve open after in liquid gas entrucking pipeline density, temperature signal and signal is transferred to controller, described pressure transmitter gathers regulating valve open after in liquefied gas tank body actual pressure signal and signal is transferred to controller.
Above-mentioned controller has and flowmeter digital communication function, and it gathers required temperature, density, the flux signal of controller, judges the flowing medium state by the parameter of flowmeter.
Advantage of the present invention is:
The present invention utilizes known medium composition and working temperature to learn the pilot pressure of the cardinal principle that system is required (being the saturation vapour pressure of medium under operating mode in the pipeline), regulating valve makes and detects the flowmeter back pressure obtain on the city gas bottling pipeline substantially near the demand pilot pressure, again with the density signal of flowmeter, self diagnostic signal is setting value, the fine tuning valve aperture, use PID to regulate that (PID is adjusted in that to belong to term: PID in the process control be ratio, integration, the abbreviation of differential) satisfies setting range, carrying out along with the entrucking process, increase valve opening satisfying under the condition of back pressure, improve entrucking efficient.The present invention is in conjunction with the measurement parameter (density of flowmeter itself, temperature), flowmeter running state self-diagnostic function and pressure transmitter, modulating valve, controller forms the backpressure regulation control system, the utilization of this control mode novelty the measuring multiple parameters function of flowmeter and the self-diagnostic function that flowmeter has, combine the prescription memory, recipe download, PID regulates, self diagnosis, the various control algorithms such as self-correction, the validity of system's control is improved greatly, the energy self adaption is followed and is adjusted accordingly when pipeline state of the art or interior media ingredient change, need not manual intervention, it is more convenient to operate, safeguard convenient; Because flowmeter is under the Measurement accuracy state, allow pipeline internal medium to contain a small amount of gas, system's actual back pressure control is that diagnostic signal take flowmeter is as benchmark, with reference to the medium saturation vapour pressure in the pipeline, namely actual back pressure is slightly less than the required saturation vapour pressure of medium, the crushing that produces in pipeline like this is just little, and the energy loss of whole loading system is reduced, and satisfies industry to the demand of energy-conservation aspect; The operating mode little in line pressure variations also can reduce the wherein input of pressure transmitter according to actual conditions, and the equipment investment amount is few, controlling unit is few, system security reliability is high.
Description of drawings
Fig. 1 is the principle schematic of the back pressure control application system in the liquid gas entrucking provided by the present invention.
Embodiment
Working principle of the present invention is to utilize known medium composition and working temperature to learn the back pressure that system is required, regulating valve makes to detect and obtains pressure substantially near the demand pilot pressure, again take the density signal of flowmeter, self diagnostic signal as setting value, the fine tuning valve aperture is used the PID adjusting to satisfy setting range and is got final product.Along with the carrying out of entrucking process, increase valve opening satisfying under the condition of back pressure, improve the entrucking efficient of system, reduce system energy consumption.The required back pressure of known medium composition requires to table look-up as can be known, needs the Diagnostic parameters of reference flow meter self when the medium composition changes.
For the foregoing reasons, the invention provides the back pressure control method in a kind of liquid gas entrucking, the method may further comprise the steps:
1) according to look-up table known medium composition and working temperature are obtained the required pilot pressure of city gas bottling;
2) back pressure of flowmeter in the detection city gas bottling pipeline;
3) judge that whether the back pressure of can pipeline is greater than the resulting pilot pressure of step 1), if then finish this control procedure; If not, then carry out step 4);
4) with density signal and self diagnostic signal of flowmeter the actual pressure of can pipeline is controlled.
The specific implementation of step 4) is:
4.1) regulate the back pressure of can pipeline by controlling opening of valve, and make it near the saturation vapour pressure of liquid gas under working temperature;
4.2) take the density signal of flowmeter and self diagnostic signal as setting value, the fine tuning valve aperture makes the back pressure of city gas bottling pipeline greater than the required saturation vapour pressure of liquefaction under this working temperature.
Referring to Fig. 1, in the back pressure control method of the present invention in a kind of liquid gas entrucking is provided, a kind of application system based on the method also is provided, and this application controls system is made of equipment such as flowmeter, pressure transmitter, flow batch controller (hereinafter to be referred as controller) and regulating valves.The unlatching of controller regulating and controlling valve or close; Flowmeter gathers regulating valve open after in liquid gas entrucking pipeline density, temperature signal and signal is transferred to controller; Pressure transmitter gathers the rear actual pressure signal in liquefied gas tank body of regulating valve unlatching and also this signal is transferred to controller.
Controller has and flowmeter digital communication function, gathers required temperature, density, flux signal and judges the flowing medium state by the parameter of flowmeter.
To use the ZLJ Coriolis flowmeter as example, during city gas bottling, table look-up by the Coriolis flowmeter temperature signal that collects and known media composition and to obtain the saturation vapour pressure of liquid gas in the measuring channel, the theoretic saturation vapour pressure that the show value of pressure transmitter is obtained greater than system, the slug flow alarm signal that density value and flowmeter by flowmeter has, just can do detection to medium state in the sounding pipe, judge that can the medium state in the pipeline satisfy the normal measuring condition of flowmeter.System's automatic regulating valve door aperture, satisfy the required minimum back pressure value of flowmeter survey, when the gas-liquid two-phase attitude appears in medium in the sounding pipe, mass flowmenter can send alarm signal, characterize this state and can not satisfy flowmeter Measurement accuracy condition, occur reducing valve opening when this reports to the police, improve back pressure, reporting to the police to eliminate stops to adjust (PID regulatory function).After first adjusting at the scene, the back pressure demand is recorded in the controller (prescription memory function) under operating mode corresponding to control valve opening, the using process system combination parameter last time in later stage, directly use the formulation parameter (recipe download) of memory at the state of the art same case, utilize simultaneously the sensor measurement parameter, controller carries out self-correction (self diagnosis, self-correction function) in conjunction with the diagnostic function of flowmeter to parameter, and the response time of system is reduced.
Claims (4)
1. the back pressure control method in the liquid gas entrucking, it is characterized in that: the back pressure control method in the described liquid gas entrucking may further comprise the steps:
1) according to look-up table known medium composition and working temperature are obtained the liquid gas saturation vapour pressure; Described liquid gas saturation vapour pressure is approximately equal to the required pilot pressure of system;
2) actual pressure of flowmeter outlet end in the detection city gas bottling pipeline; The actual pressure of described city gas bottling pipeline flow meters outlet end, the i.e. actual back pressure of flowmeter;
3) judge that whether the back pressure of flowmeter in the can pipeline is greater than saturation vapour pressure; If then finish this control procedure; If not, then carry out step 4);
4) with density signal and self diagnostic signal of flowmeter the flowmeter back pressure of can pipeline is regulated.
2. the back pressure control method in the liquid gas entrucking according to claim 1, it is characterized in that: the specific implementation of described step 4) is:
4.1) regulate the back pressure of flowmeter in the can pipeline, and make it near the saturation vapour pressure of liquid gas under working temperature;
4.2) take the density signal of flowmeter and self diagnostic signal as setting value, fine setting LPG (liquefied petroleum gas) valve aperture makes the flowmeter back pressure of city gas bottling pipeline greater than the saturation vapour pressure under this working temperature.
3. the back pressure control method in the liquid gas entrucking according to claim 1 and 2, it is characterized in that: described look-up table is with reference to SH/T0221-92 and GB/T12576-97 liquefied petroleum gas (LPG) vapor tension and relative density and octane value numeration.
4. application system based on the back pressure control method in the described liquid gas entrucking of the arbitrary claim of claim 1-3 is characterized in that: described system comprises Coriolis flowmeter, pressure transmitter, flow in batches controller and regulating valve; Described flow in batches controller regulating and controlling valve unlatching or close, described Coriolis flowmeter gathers regulating valve open after in liquid gas entrucking pipeline density, temperature signal and signal is transferred in batches controller of flow, described pressure transmitter gathers regulating valve open after in liquefied gas tank body actual pressure signal and signal is transferred in batches controller of flow.
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| CN2012104190773A CN102937240A (en) | 2012-10-26 | 2012-10-26 | Back pressure control method and application system for liquefied gas loading |
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| CN2012104190773A CN102937240A (en) | 2012-10-26 | 2012-10-26 | Back pressure control method and application system for liquefied gas loading |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103697956A (en) * | 2013-12-09 | 2014-04-02 | 上海齐耀动力技术有限公司 | System for measuring evaporation rate of cryogenic vessel with stable back pressure |
| JP2021501898A (en) * | 2017-11-13 | 2021-01-21 | マイクロ モーション インコーポレイテッド | Flow vapor pressure device and related methods |
| JP2022527984A (en) * | 2019-04-03 | 2022-06-07 | マイクロ モーション インコーポレイテッド | Vapor pressure verification using fluid density measurements |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103697956A (en) * | 2013-12-09 | 2014-04-02 | 上海齐耀动力技术有限公司 | System for measuring evaporation rate of cryogenic vessel with stable back pressure |
| JP2021501898A (en) * | 2017-11-13 | 2021-01-21 | マイクロ モーション インコーポレイテッド | Flow vapor pressure device and related methods |
| JP2022527984A (en) * | 2019-04-03 | 2022-06-07 | マイクロ モーション インコーポレイテッド | Vapor pressure verification using fluid density measurements |
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Application publication date: 20130220 |