CNG hydraulic piston compressor

1 Introduction

CNG hydraulic piston compressor is composed of the hydraulic system, compression system, cooling system, control system, safety system, rainproof and noise reduction, and other main units. It is integrated into a rainproof and noise-reduction box through valve pipelines. The compression cylinder adopts a hydraulic reciprocating double force structure design and is equipped with a piston position sensing system. The motor drives the hydraulic oil pump to supply oil, and through the integrated reversing system, the hydraulic oil continuously pushes the piston to reciprocate to compress the natural gas. The compressor adopts a two-stage compression mode, and the unit adopts a water circulation air cooling method for cooling. The compressor uses a PLC control cabinet to fully automatically control the unit, which has the advantages of a high degree of automation, simple operation, safe and reliable operation, and convenient maintenance. The entire unit is skid-mounted and fully unattended.

2. Hydraulic system

The hydraulic system consists of an oil tank, oil suction filter, oil pump motor unit, reversing valve group, hydraulic cylinder, oil buffer tank, oil cooler, oil return filter, and hydraulic pipeline. The main motor is connected to the oil pump through an elastic coupling. When the motor is running, the oil pump is driven to pressurize the hydraulic oil to provide power for the operation of the compression cylinder. The hydraulic oil controls the flow direction through the reversing control system and sequentially enters one side of the hydraulic cylinder to push the piston. Run to compress the gas. The hydraulic oil on the other side of the hydraulic cylinder enters the hydraulic oil radiator for cooling through the reversing control system. The cooled hydraulic oil returns to the tank through the oil return filter, completing a hydraulic oil circuit cycle. Because the compressor is controlled by the hydraulic system, the operation of the motor and the operation of the piston in the cylinder are relatively isolated, so there is no need to evacuate the high-pressure gas in the compressor cylinder when the motor is started. It can be started at any time to save energy and improve the working efficiency of the compressor.

Hydraulic system

3. Gas compression system

The gas compression system consists of high-pressure gas filters, solenoid ball valves, gas check valves, gas compression cylinders, gas heat exchangers, and gas pipelines. The compression cylinder in the gas compression system adopts a hydraulic reciprocating double-action design structure. The cylinder body is a three-stage cylinder with two-stage compression and is equipped with a piston position sensing system. From left to right, the compression cylinder is divided into the left primary compression chamber, the left secondary compression chamber, the left hydraulic oil chamber, the right hydraulic oil chamber, the right secondary compression chamber, and the right primary compression chamber. The chambers are arranged symmetrically with the middle cylinder piston as the center. As shown in the figure, when the left hydraulic oil chamber is filled with oil, the right hydraulic oil chamber is drained. The high-pressure oil pushes the oil piston to drive the piston rod, and the left and right cylinder pistons move to the right. At this time, the left first-stage compression chamber sucks air. The right primary compression chamber compresses and exhausts air; the primary exhaust gas is cooled and enters the right secondary compression chamber that is inhaling air. At the same time, the left secondary compression chamber compresses and exhausts the natural gas, enters the gas cooler, and is cooled before entering the gas storage cylinder group to complete the two-stage compression of natural gas.

Compression cylinder structure diagram

The gas compression cylinder of the compressor is completely separated from the hydraulic cylinder, and the cylinder piston adopts oil-free lubrication. Both the air chamber seal and the oil chamber seal adopt multi-stage sealing, so the compressed medium will not be polluted during the compression process. The unique design of the compression cylinder ensures that even in the event of seal leakage, oil and gas will not mix with each other; this not only solves the problem of natural gas oil and gas pollution, but also saves lubricating oil costs, and eliminates the need for lubricating oil pumps and oil and gas separation and filtration. equipment, sewage tanks, and other facilities. At the same time, it also reduces the damage caused by oil pollution to compressors, gas pipelines, gas dispensers, automobile pipelines, and automobile engines.

4. Cooling system

The CNG substation system uses a water circulation air cooling system, and the entire cooling system consists of three independent heat dissipation systems. They are natural gas cooling systems, hydraulic oil cooling systems, and compression cylinder cooling systems.

Fin-type high-pressure stainless steel tube radiators are used in the natural gas heat dissipation system. Natural gas compressed at all levels can be fully cooled after passing through the radiator. The hydraulic oil cooling system buffers the high-temperature hydraulic oil in the compression cylinder and enters the oil radiator for cooling, and the cooled hydraulic oil returns to the oil tank. The refrigerant in the compression cylinder cooling system is antifreeze. After the antifreeze is cooled through the radiator, it can fully dissipate heat for the compression cylinder, thus effectively protecting the compression cylinder and the sealing components in the cylinder.

Cooling system

5. Control system

The main function of the control system is to continuously monitor and control the operating status and operating parameters of the CNG substation system, and record and generate alarm information, so that the entire CNG substation system is in a monitorable, safe, reliable, and stable operation state. The control system has automatic alarm and automatic emergency handling processes, which can effectively monitor the status and operating parameters of the gas compressor; the production operation process realizes automated control and can realize data storage and historical data traceability.

6. Security system

The CNG substation integrates a compressor, and the skid is equipped with pressure sensors, combustible gas detectors, oil level, oil temperature, safety valves, etc. All electrical systems in the compressor adopt an explosion-proof design, making the operation safe and reliable. During the operation of the equipment, if the system detects abnormalities in the protection pressure, oil level, and oil temperature, it will promptly sound and light alarm and automatically shut down. When the gas concentration reaches 15% of the lower explosion limit of natural gas (%LEL), the exhaust fan starts; when the gas concentration reaches 30% of the lower explosion limit of natural gas (%LEL), the equipment gives audible and visual alarms and automatically shuts down.

7. Rainproof and noise reduction system

The box of the integrated compressor of the CNG substation has the functions of sound insulation, noise reduction, and rainproofing. The inner layer of the box is made of two layers of sound insulation and sound-absorbing materials, which can absorb high-frequency noise and block the transmission of low-frequency noise. The equipment box adopts a modular design, which is convenient for maintenance, disassembly, and assembly. The ceiling of the box is an integrated ceiling, which completely eliminates rain leakage.

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