As the core equipment of a CNG filling station, the compressor directly affects the operating efficiency and economy of the filling station. Therefore, it is particularly necessary to choose a suitable compressor. What this issue brings is how to correctly choose the right compressor.
1. Matching of CNG filling station and compressor
1.1 The compressor is the main energy-consuming equipment of the gas filling station. No matter what type of gas filling station it is,
the site should be located in an area with high pressure in the natural gas pipeline network to reduce the power of the compressor and the operating energy of the gas filling station. consumption and equipment purchase costs.
1.2 The gas filling capacity of the gas filling station should meet the actual operational needs. Excessive or serious insufficient gas filling capacity will affect the economic benefits of the gas filling station.
1.3 After determining the gas filling capacity of the gas filling station, rationally select the number and displacement of compressors,
comprehensively analyze the relationship between the unit price of the compressor and land occupation,
and consider the impact of compressor failure or maintenance shutdown. For example, for a gas filling station with a gas filling capacity of 3000Nm3/h, the price of a compressor with a displacement of 3000Nm3/h is often more than the sum of two compressors with a displacement of 1500Nm3/h, and large-displacement compressors have special components.
Unfavorable factors such as long production and maintenance cycles, high power consumption per unit, and strict demands on the power grid must be taken into consideration.
On the contrary, the disadvantages of multiple low-displacement compressors are that they occupy a large area and the pipelines are relatively complex.
2. Type of compressor
2.1 Mechanical compressor
As the earliest applied compressor, it has the advantages of low price, mature technology, wide displacement range, and strong adaptability, and is widely used in various types of CNG filling stations.
It adopts the technical principle of a very mature crank-link mechanism reciprocating piston compressor but has poor adaptability to working conditions with a wide inlet pressure range and large fluctuations in air supply volume.
It is mostly used in CNG standard stations or CNG mother stations. The disadvantage is that the leakage rate is high (1%~3%).
The crank drives the piston to run. The packing and piston rings in the body need to have necessary gaps. Leakage is inevitable under high pressure.
The power of the motor is relatively large. Under high-voltage conditions, the reactive power loss of the motor is large, and when it is stopped,
it needs to be depressurized and unloaded before it can be started again, which increases the production cost of unit gas. It is not suitable for frequent starts,
has many wearing parts, makes the unit noisy and vibrating, and requires frequent maintenance.
2.2 Hydraulic push type
This type of compressor is mostly used in substations. The advantages are that the process flow is simple, no gas storage facilities and exhaust gas recovery systems are required,
the motor power is small, and the displacement is constant. It has excellent energy-saving effects, and the system pressure compensation response is fast and stable.
The equipment is easy to install, can be put into production quickly, and does not require excessive land resources. It is simple to operate and easy to maintain.
Adopting a hydraulic structure, the vibration is small and the noise is relatively low. However, the shortcomings of this device are equally obvious. First of all,
because this type of compressor requires a special tank truck, the unit price of the equipment is often 4-5 times that of a mechanical compressor. It is limited by the power of the compressor and the displacement is constant,
so it is not suitable for gas filling stations with large fluctuations in gas demand. Since the hydraulic oil is in direct contact with natural gas,
it is easy to contaminate precision equipment, and the hydraulic oil loss is large, which increases operating expenses.
2.3 Hydraulic piston type
Between the above two types of compressors, hydraulic piston compressors can significantly reduce construction costs and do not require excessive gas storage facilities. They have small motor power and low leakage rates and have the characteristics of low energy consumption, low leakage, and low noise. The inlet pressure range is large, no pressure stabilization is required, and it is hydraulically driven. It can start and stop frequently and quickly without unloading. Use oil-free lubrication to reduce natural gas pollution and damage to precision equipment. Smooth operation, small vibration, and low noise. The disadvantage is that the single machine displacement is low, generally no more than 1500Nm3/h, and the single machine price is slightly higher than that of the mechanical type, and it is mostly used in CNG substations.