Journal of Beijing Institute of Petro-chemical Engineering Natural Gas Compressor Automatic Control Technology Gao Zhao, Liu Dejun, Wang Fu, Ma Yan, Li Xiaoyue, Gao Jiqing (Liaoning University of Petroleum & Chemical Technology, Fushun 113001, Liaoning) Due to the relatively low production of associated gas in Tanhai Oilfield, natural gas compressors need to start and stop frequently during the compression process.
In order to save energy, reduce costs and improve the stability of machine operation, natural gas compressors can be controlled automatically. The author introduces a natural gas compressor automatic control method, which does not require manual control of natural gas can be compressed into high pressure gas cylinders.
Through the design of the method, design and design should pay attention to some of the problems described, for the high-pressure compressor to provide automatic control research.
As energy becomes more and more tense, the position of natural gas in energy becomes more and more important. Associated gas in the beach sea oil field is a kind of natural gas, which is gradually being valued by people. At present, due to the economic benefits brought about by its recovery, it is not obvious. Therefore, most of the domestic and foreign enterprises take the approach of venting or burning to deal with associated gas. In order to increase the efficiency of the oilfield, the economical and reasonable scheme should be designed to recover the associated gas. 2. 1NG recovery process Compressed natural gas (CNG) pressurizes the natural gas to about 25MPa to reduce its volume. When the natural gas is at 25MPa, the volume is 1/250 before compression, which effectively utilizes the compression characteristics of natural gas and improves the storage and transportation efficiency. CNG pretreatment and compression process is relatively simple, more sophisticated processing technology and equipment, the investment cost is moderate.
The process of recovering the associated gas in the Tanhai oilfield by using CNG technology: The associated gas after pretreatment (desulfurization, decarburization, dehydration, dust removal, etc.) is metered into the buffer tank (about 100m3) after it is supercharged and stored. When the buffer tank pressure reaches After a certain value, the compressor is started and the gas is compressed under high pressure to about 25MPa. The standard high-pressure gas cylinder of 630mmX11580mm is charged with a capacity of about 2.82m3. The high-pressure gas cylinder is transported by ship: 2013-03-20 to the destination.
After the recovery process is determined, taking into account less associated gas production, the compressor can not work continuously, you can set a buffer tank at the compressor inlet gas storage, according to the gas pressure in the buffer tank, the compressor can be automatically controlled. This will not only save human resources, but also improve the stability of the operation of the machine. The principle of the automation system is based on the pressure changes, the use of PLC control cabinet on the compressor and electric valve automatic control.
2 automatic control system With the development of science and technology, PLC technology is more and more mature, its flexibility and expansibility than the relay has been greatly improved, and less susceptible to environmental impact, has been widely used in automation. Therefore, I use PLC and relay joint control, not only has the characteristics of compact structure, less electrical, small size, easy to maintain, but also can make the system equipment to adapt to harsh working environment, while reducing costs.
2.1 system operation process requirements In order to ensure the normal work, the system should meet the following requirements: the normal compressor start and stop and the normal electric valve opening and closing; normal production, should ensure that at least two high-pressure gas cylinders can work;) can At any time on the operation of the machine to detect.
Beijing Institute of Petrochemical Technology 2.2 The working principle of the control system After the treatment of natural gas into the buffer tank, when the pressure in the buffer tank reaches a certain value, the compressor starts, the compressed natural gas into the high-pressure gas cylinders for storage and transportation. When the high-pressure gas cylinder for storing natural gas is full, in order not to affect the normal production, another high-pressure gas cylinder needs to be replaced for storage and transportation. During this process, the compressor continues to work normally. When the buffer tank gas pressure drops to a certain value, the compressor stops working until the buffer tank pressure reaches a fixed value, the compressor restarts, the cycle of the above process. According to the above process, I design a set of programs to make the entire system automatically cycle production, without the need for manual operation, as long as the regular maintenance, to ensure the normal production equipment can be, the system's control theory as shown.
Sui Chong tank 1it Power Meter-i force container control system works 2.3 Control System Design Proposal by the electric contact pressure gauge, electric valves and PLC and other components. Pressure changes in the electrical contact pressure gauge to promote PLC control circuit in the system for automatic control to ensure the start and stop natural gas compressor and electric valve switch. Project drawings as shown.
One set of electric contact pressure gauge capable of detecting the air pressure in the buffer tank is set at the outlet end of the buffer tank, and one electric valve is set at the inlet end of the compressor. Electric valves and electric contact pressure gauge are connected with the control circuit in the PLC. When the electric contact pressure gauge detects that the natural gas pressure in the buffer tank reaches a preset pressure value, the control circuit controls the electric valve to be opened and the compressor starts. When the electric contact pressure gauge detects that the natural gas pressure in the buffer tank is lower than the second preset pressure value, the electric valve is closed and the compressor stops working. Check valve is used between high pressure gas cylinder and compressor to prevent backflow when the compressor stops. An electrical contact pressure gauge is located near the air inlet of each high pressure gas cylinder. The electrical contact pressure gauge can detect the pressure in the high pressure gas cylinder. Electricity between the pressure gauge and the check valve to install an electric valve, the valve controlled by the PLC control system. When the pressure in the high-pressure gas cylinder reaches the preset value, the control circuit controls the electric valve corresponding to the high-pressure gas cylinder to be closed and the other one electric valve to be opened.
2.3.1 Natural gas compressor automatic start-stop compressor automatic start-stop circuit as shown. When the pressure gauge connected with the buffer tank detects that the pressure in the buffer tank reaches the preset pressure value, the pressure gauge upper limit contact P1 closes the switch 3, which is equivalent to pressing the start button 1 of the PLC control cabinet, The compressor starts; when the pressure gauge of the electric contact detects that the pressure in the buffer tank is lower than the second preset value, the lower limit contact P2 of the electric contact pressure gauge closes the switch 4, at this moment, the relay 1 is closed and the normally open switch of the relay 1 to 1 closed, equivalent to press the shutdown button PLC control cabinet 2, then the compressor stops working.
2.3.2 automatic switching between electric valves electric valve control motor control by the PLC control cabinet.
Electric valve automatically switches between the circuit shown. KM for PLC control cabinet contactor, when the compressor starts, due to the contactor KM normally closed contact 5 is closed, the relay 2 is energized, the normally closed switch 2-1 is disconnected, the normally open switch 2-2 is closed, the electric Valve control switch K2 open, natural gas through the valve into the corresponding pressure vessel. When the electrical contact pressure gauge connected with the pressure vessel detects that the pressure in the pressure vessel is higher than a preset value, the electrical contact pressure gauge contact P4 closes the normally open contact 6 of the contactor, and the corresponding normally closed contact 5 open. The relay 3 is energized, the normally closed switch 3-1 is opened, the normally open switch 3-2 is closed, and the other electrically operated valve K3 is opened; at this time, the normally open switch 2-2 is disconnected and the electrically driven valve K2 is closed. During normal operation, this process is repeated.
Point; a contactor KM normally closed contact; a contactor KM normally open contact; 2-1 a relay normally closed switch; 2-2,3-2- relay normally open switch electric valve automatic switching circuit 2.3.3 Automatic control of electric valve Electric valve control motor for the three-phase asynchronous motor, and contactors KM2, KM3 is connected through the control of contactors KM2, KM3 to achieve three-phase three-phase asynchronous motor into the power supply commutation, and then control the motor is Reverse, to achieve the purpose of automatic opening and closing electric valve. The circuit diagram as shown.
KM1 is contactor in PLC control cabinet. When KM1 is on, KM1 normally open contact 1 is on, normally closed contact 2 is off, relay 4 is on, then contactor KM2 is on, normally open-2 is closed , The motor is energized to open the valve; KM1 power failure, the normally open contact 1 is disconnected, normally closed contact 2 is closed, the relay 5 is energized, normally open switch 5-2 is closed, KM3 is power, normally closed contact KM3- 2 closed, motor reversal, electric valve closed.
3 The actual basis of system design According to the actual gas production and local conditions and other specific conditions of the oil field, the compressor, buffer tank and pressure vessel need to be selected to meet the actual production requirements, according to the parameters of various equipment automation system design; During the design process, the compressor should be avoided to start and stop several times in succession, exceeding the stipulated number of times to cause the compressor to fail to produce normally. In addition, the automatic control system in the implementation, must be based on the actual situation in the oil field and work environment, select the appropriate hardware and equipment, after the installation, commissioning and tuning equipment, and then put into production.
4 Conclusion mainly introduced a natural gas compressor automatic control system, through the PLC control cabinet on the compressor and electric valve control, natural gas compression and canning. Compressor prone to damage during the long run and so on, through the PLC to determine the operation of the machine, the compressor can produce a fault before its predictive maintenance and repair. This will improve the stability of the operation of the machine, prolong its service life and avoid the normal production of the unit due to equipment failure. The system has the following advantages: Reliable work, rapid response, high efficiency;) Compressors and other equipment can be detected to improve operational safety;) can reduce energy consumption and reduce unnecessary losses; (4) Small investment, can reduce production costs and improve economic efficiency of the oilfield.