The role of PLC in natural gas compressors

The role of PLC in natural gas compressors

Programmable Logic Controller (PLC) is a new type of general control device, which integrates traditional relay control technology, computer control technology and communication technology, and is designed for industrial control. It has a series of advantages such as strong function, universal sensitivity, strong reliability, good environmental adaptability, simple programming, convenient use, small size, light weight and low power consumption.

1. Natural gas filling station process flow

After the raw gas is pressure-regulated and dried, it enters the compressor, where it is compressed and pressurized to 20MPa. It is then charged to high, medium, and low pressure open gas storage wells in sequence through the control panel. When the high pressure open gas storage wells are fully filled, the compressor automatically stops running.

When a CNG vehicle comes to the station for refueling, the high-pressure natural gas in the high-pressure open gas storage well is used to refuel the CNG vehicle through the gas vending machine. When the natural gas in the high-pressure open gas storage well is too little and is insufficient to meet the refueling needs of the CNG vehicle, the compressor starts to refuel the high-pressure open gas storage well while meeting the refueling needs of the CNG vehicle. When the high-pressure open gas storage well is fully filled, the compressor automatically stops running.

2. PLC control function and control principle in natural gas compressor

The programmable controller (PLC) is used as the central controller. The detection instrument provides the PLC with the signal parameters required in the control to automatically patrol and control the compressor. The main parameters to be monitored include the compressor intake pressure, compression cylinder temperature, lubricating oil pressure, temperature, motor temperature, circulating water pressure, temperature; compressor exhaust pressure, high, medium and low pressure detection parameters of the gas storage well, etc.

(1) Maintenance control function: ① detection of motor current and voltage; ② detection of oil temperature and oil pressure of 234-stage cylinder; ③ detection of exhaust temperature, pressure and motor temperature of 234-stage; ④ detection of intake pressure; ⑤ detection of instrument air pressure; ⑥ detection of circulating water temperature and pressure; ⑦ detection of pressure of gas storage well;

(2) Maintenance control principle Before starting the main engine, open the air intake valve and control the pressure to the normal starting pressure. First, turn on the oil pump to lubricate the compressor cylinder. After 10 seconds, the water pump starts. When the starting conditions are met and there is no fault signal, the indicator light on the control panel that allows the start will light up, and the compressor can be started. After pressing the start button, the PLC receives the command and starts to execute the operation program. The motor is started without load. After the motor runs normally for 10 seconds, the air intake solenoid valve opens, and the compressor 1, 2, 3, 4 interstage valves are powered on and opened, and the compressor starts to operate normally. The PLC analyzes and processes all the data collected on site and monitors whether there are any abnormalities in each data.

When the water temperature exceeds the set value, the fan starts to cool the circulating water. When the compressor is running, if 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 processing data reaches the shutdown condition, the PLC will immediately issue a shutdown command. After the compressor receives the PLC shutdown command, the compressor main motor stops working, and the raw gas inlet valve is closed at the same time. The compressor 1, 2, 3, and 4 interstage valves lose power and close. At the same time, the compressor shutdown pressure relief valve is powered on and opened to discharge the pressure between the compressor stages out of the compressor. At this time, the compressor oil pump, circulating water pump, and fan will work intermittently, and the compressor will automatically stop working after the oil temperature and water temperature drop to normal values.

The operating instructions of the compressor are all issued by the controller PLC, which essentially ensures the safe and stable operation of the compressor.