(I. Overview
In recent years, due to the country's development and utilization of natural gas fields, natural gas has played a huge role in driving my country's economic development and has driven the development of related industries. Because of its high calorific value, cleanliness, non-polluting, non-toxic, and convenient transportation, natural gas has been widely used. Called green energy, environmentally friendly energy.
With the increase of fuel cost and the enhancement of human's awareness of environmental protection, compressed natural gas (CNG) for vehicles is widely used in urban taxis, buses and private vehicles. At present, a standard CNG filling station is mainly composed of pressure regulation and measurement, purification system, compression system, gas storage system, and CNG gas sales system.
The natural gas compressor set consisting of the compressor, its driving motor and related equipment is the core part of the entire process system of the natural gas filling station, and it is also one of the important equipment. The control system of the compressor unit is the central pivot button for the safe operation of the compressor, which controls the normal operation, automatic protection, and sequential charging of the compressor unit.
The quality of the compressor unit control system directly affects the safe operation of the compressor unit, and directly affects the output and benefit of compressed natural gas production. The factors that affect the safety of production mainly include the over-temperature, over-pressure, water-cut, oil-cut and other factors of the compressor.
With the rapid development of the gas station network, the requirements for the equipment of gas stations are getting higher and higher, and the construction of intrinsically safe gas stations has become the core of the production and construction of gas stations in the future. Equipment is constantly updated and improved, and reliability, ease of operation, monitorability, and ease of maintenance are the most basic requirements. The control circuit built with relays has poor reliability, is difficult to maintain, and is not easy to monitor, and can no longer meet the current requirements. There are also some hidden dangers to safety production. With the rapid development of electronic technology, software technology and control technology, the programmable logic controller (PLC) has developed rapidly, with high performance and reasonable price. On the unit, the safety and stability of the equipment are greatly improved.
(2) The role of PLC in natural gas compressors
Programmable Logic Controller (PLC) is a new type of general-purpose control device, which integrates traditional relay control technology, computer control technology and communication technology. It is specially designed for industrial control and has strong functions, general flexibility, and reliability. It has a series of advantages such as strong, good environmental adaptability, simple compilation, convenient use, small size, light weight and low power consumption.
1. Process flow of natural gas filling station
After the raw gas is pressure-regulated and dried, the natural gas enters the compressor, compresses and pressurizes it to 20MPa, and inflates the high, medium and low-pressure underground gas storage wells in turn through the sequence control panel. After the high-pressure underground gas storage wells are fully filled, the compressor Automatically stop running.
When CNG vehicles come to the station for filling, the high-pressure natural gas in the high-pressure underground gas storage wells fills the CNG vehicles through the gas vending machine. When the natural gas in the high-pressure underground gas storage well is too small to satisfy the filling of CNG vehicles, the compressor starts, and the high-pressure underground gas storage well is charged while satisfying the filling of CNG vehicles, until the high-pressure underground gas storage wells are fully filled. The compressor stops automatically.
2.PLC control function and control principle in natural gas compressor
The programmable logic controller (PLC) is used as the core controller, and the compressor is automatically inspected and controlled by the detection instrument to provide the PLC with the signal parameters required in the control. The main parameters to be monitored are compressor intake pressure, compression cylinder temperature, lubricating oil pressure, temperature, motor temperature, circulating water pressure, temperature; compressor discharge pressure, gas storage well high, medium and low pressure detection and other parameters.
(1) Protection and control functions: ① Detection of motor current and voltage; ② Detection of oil temperature and oil pressure of the first, second, third, and fourth cylinders; ③ Detection of exhaust temperature, pressure, and motor temperature of the first, second, and third stages; ;⑤Instrument wind pressure detection;⑥Circulating water temperature and pressure detection;⑦Gas storage well pressure detection;
(2) Protection and control principle: Before starting the main engine, open the intake valve and control the pressure to the normal starting pressure. First, open the oil pump to lubricate the compressor cylinder. After 10s, the water pump starts. When the starting conditions are met, there is no fault. After the start button is pressed, the PLC receives the command and starts to execute the running program. The motor is started with no load. When the motor runs normally for 10s, the intake solenoid valve is opened, the first, second, third and fourth stage interstage valves of the compressor are energized to open, and the compressor runs normally. PLC analyzes and processes all on-site collected data, and monitors whether each data is abnormal.
When the water temperature exceeds the set value, the fan starts to cool the circulating water. When the compressor is running and one of the monitoring parameters fails within the set range, the PLC will issue an alarm command to remind the staff to pay attention to abnormal parameter changes. When the monitoring and processing data reaches the shutdown condition, the PLC will immediately send a shutdown command. After the compressor receives the PLC shutdown command, the main motor of the compressor will stop working, and the raw gas inlet valve will be closed at the same time. The four-stage interstage valve is de-energized and closed. At the same time, the pressure relief valve of the compressor is turned on when the compressor is stopped, and the pressure between the stages of the compressor is discharged from the compressor. At this time, the compressor oil pump, circulating water pump and fan will work intermittently. After the oil temperature and water temperature of the compressor are reduced to normal values, they will automatically stop working.
The operation instructions of the compressor are all issued by the controller PLC, which essentially ensures the safe and stable operation of the compressor.
(3) Summary
Through the successful application of PLC technology in natural gas compressors, it not only solves many problems existing in the natural gas compressor system, but also makes the whole system configuration of natural gas compressors perfect and reasonable, safe and reliable in operation, and simple and convenient in maintenance. The application has accumulated successful experience.