1. Natural gas pressurized dewatering process
According to the process calculation, the natural gas pressure of the terminal in the eastern part of the Shengli Oilfield is 5.1 MPa (gauge pressure), while the natural gas pressure of the slug flow trap in the oil and gas inlet of the CB30 block is about 0.4 MPa (gauge pressure). Therefore, in the design of the Shenghai Oilfield Haiwu United Station, a companion gas booster was installed to pressurize the natural gas to 5.2 MPa (gauge pressure). In addition, if natural gas enters the external pipeline, if there is water condensation, it may form a gas hydrate to block the pipeline, reduce the pipeline transportation efficiency; it will also cause serious corrosion to the pipeline and affect the pipeline life. Therefore, dehydration must be carried out after the natural gas is pressurized, so a triethylene glycol dehydration device is designed in the process.
The process of natural gas pressurized dewatering of Haiwu United Station can be summarized as follows: the natural gas from the outlet manifold of the slug flow trap enters the compressor inlet separator. After the gas-liquid two-phase separation, the sewage in the liquid phase is discharged into the station sewage. The treatment system, the light oil to liquefy the hydrocarbon storage tank; the natural gas enters the compressor, after being pressurized, cooled, separated, enters the dryer to remove moisture, and after drying, the natural gas is dusted, metered, and exported.
The basic parameters of the natural gas pressurized dewatering device are as follows:\
Size: 48 × 104 m3 / d
Feeding device pressure: 0.5MPa
Inlet temperature: normal temperature Outlet pressure: 5.2MPa
Device temperature: 40 ° C
Inlet water: saturated water Outlet water: water dew point is less than -80 °C
2. Introduction to the booster compressor block
The Haiwu United Station is pressurized with three imported reciprocating compressors, modeled after Ariel JGC/2. The compressor has a single processing capacity of 240,000 m3/d, of which the inlet pressure is 0.5 MPa and the outlet pressure is 5.2 MPa. Each compressor block contains a compressor, drive motor, lubricating oil system, cooling water system, pulsation buffer system, scrubber, outlet separator, bottom sump and coating.
The working process of the compressor block is: from the associated gas of the slug flow trap to the compressor inlet and the scrubber (equivalent to the separator) → the first-stage inlet pulsation buffer tank → the compressor first-stage cylinder for pressurization → one Stage outlet pulsation buffer tank→First stage compression intercooler→Secondary inlet scrubber (equivalent to separator)→Secondary inlet pulsation buffer tank→Compressor secondary cylinder for pressurization→Secondary outlet pulsation buffer tank→Secondary Intercooler → outlet separator → natural gas pipeline.
Second, the problem analysis of the natural gas booster system in the station
Since the natural gas booster system of Haiwu United Station has been put into production, it has exposed some shortcomings in the process design of the natural gas booster system during operation, and has affected the safety and economic operation of the compressor. The analysis is as follows:
1. Compressor discharge is not smooth, resulting in compressor failure
(1) Compressor sewage discharge process In order to prevent the liquid and natural gas contained in the natural gas from being cooled and then the liquid is discharged into the compressor cylinder, causing the compressor to be accidental, the compressor block is designed with a primary inlet scrubber and a secondary inlet. a scrubber and an outlet separator: the first stage inlet scrubber is arranged in front of the compressor stage cylinder, and the gas entering the compressor is washed to separate the liquid contained therein; the secondary inlet scrubber is arranged in the first stage compression intermediate cooling After the second stage cylinder, the second-stage pressurized and cooled natural gas is gas-liquid separated. The bottom of the scrubber and outlet separator of the compressor block is equipped with a drain pipe. After the bottom of the compressor is merged, the three tanks are connected to the outlet line of the stabilized compressor through a DN2.5 line. A low pressure separator 2 meters above the ground leading to the condensate zone.
(2) Analysis of the reasons for the unsmooth discharge of the compressor
The DN25 sewage line outside the compressor block is buried after connecting the drain pipe of the compressor block, and is buried for about 50 meters. It is about 3 meters above the ground and is connected to the stable compressor outlet to the low pressure separator. The low pressure separator is about 2 meters above the ground. Since the compressor discharge is not discharged to a lower vessel than the compressor block, a certain pressure is required for the compressor to discharge, and when the pressure in the scrubber and outlet separator is insufficient. The liquid in the drain line will flow back to the scrubber and outlet separator, causing the scrubber and outlet separators to have a high liquid level, causing a downtime.
In addition, after the stable compressor is put into production, its outlet pressure reaches about 0.4 MPa, and the discharge pressure of the booster compressor is about 0.2 MPa. The operation of the stabilized compressor will cause certain difficulties for the discharge of the booster compressor.
2. Two compressors cannot be operated at the same time, resulting in waste of natural gas
When it is necessary to reverse the machine (stop one compressor and run another compressor), the compressor to be operated can only be started after the compressor is stopped first. Because the discharge of the three compressor blocks is discharged to the same manifold, and the sewage pipeline has a part of 3 meters from the ground, it is determined that some of the liquid buried in the pipeline cannot be discharged into the low pressure separator. If the non-stop compressor directly starts another compressor, the liquid of the compressor can not be discharged due to the discharge pressure of the original compressor, and even running the compressor will press the liquid to the compressor that is turned on, resulting in The level of the first and second scrubbers of the after-compressor is too high, causing a downtime. Therefore, it is necessary to stop and start, and then the natural gas can only be vented during this period of time. Generally, it takes at least 10 minutes to start a compressor, which causes waste of natural gas.
Third, the improvement measures of natural gas increase system
In view of the problems existing in the above natural gas boosting system, the process design of the natural gas boosting zone was further improved, and good results were obtained.
1. Reset the drain sensitivity
The scrubber and outlet separator of the compressor consists of a mist trap, a pneumatic level controller, an automatic drain valve, a discharge ball valve, a discharge check valve (provided in the primary scrubber), a reflective see-through glass gauge valve, and a discharge The ball valve and the high liquid level switch are composed. When the liquid level of the scrubber or the outlet separator reaches the set point, the pneumatic valve controls the instrument valve to open the pneumatic valve, and the liquid is removed through the natural gas pressure in the scrubber and the separator.
The pressure levels in the first and second stage scrubbers and the outlet separator are 0.4 MPa, 3.0 MPa and 5.2 MPa, respectively. If the sewage sensitivities of the first and second scrubbers and the outlet separator are the same, the first and second stage scrubbers The liquid level will slowly rise, eventually leading to a downtime. This is because the discharge pressure of the outlet separator is greater than that of the primary and secondary scrubbers, while the secondary scrubber has a higher discharge pressure than the primary scrubber. Therefore, when setting the sewage discharge sensitivity of the first and second scrubbers and the outlet separator, the sewage discharge sensitivity of the compressor primary scrubber is greater than the sensitivity of the secondary scrubber, and the sewage scrubber sensitivity of the secondary scrubber is greater than that of the outlet separator. Sensitivity, so that the discharge time of the first and second scrubbers and the outlet separator are staggered, so that each of the three tanks can discharge the liquid in the tank in time without the pressure of the other two tanks, ensuring the compressor Safe to run.
2. Add check valve
In order to meet the requirements of simultaneous operation of two compressors, it is necessary to stop and start natural gas waste, and install a DN25 check valve at the outlet of the sewage pipe of each compressor block to improve the compressor pressurization system process. , preventing the liquid in the sewage pipeline from flowing back to the first and second scrubbers and the outlet separator of the compressor; and when the second compressor is started, the running compressor does not press the discharged liquid to the second compression Inside the machine.
In short, in order to solve the problems of the natural gas booster system, it is necessary to combine the actuality in production and adopt advanced and effective operation methods and improvement measures to ensure the safe and economic operation of the booster compressor. Meet the requirements of production.
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