Influence of compressor selection on the operation of CNG refueling substation

The influence of compressor selection on the operation of CNG refueling substation The equipment currently operated by Sinopec in the CNG refueling station substations is nothing more than tank trucks, degassing columns, bottle groups, compressors, refueling machines, etc. Equipment maintenance and operation costs such as degassing columns, bottle sets, and air compressors, and personnel management costs are relatively stable. The real impact on operating costs is compressor operating costs. This effect is manifested in three points: 1. the cost of electricity required for compressor boost; 2. the cost of leakage generated when the compressor is working; 3. the cost of equipment maintenance.

First, the cost of electricity

The cost of electricity required for compressor boosting is reflected in the amount of electricity used, calculated in kW·h/square (JB11422-2013 “The Natural Gas Hydraulic Compressor for Automobile Refueling Stations” is called: specific energy consumption), Can be calculated using the formula:

F1=x1·/V;

F1: power consumption per unit of gas (kW·h/square);

X1: The power consumption (degree or kW·h) of the compressor during the unloading process of the tank truck;

V: the amount of outgassing of the tanker (square)

Let us analyze the difference in the specific energy consumption values ​​of various compressors. Substation compressors or supercharging equipment used in the market today include mechanical compressors, vertical hydraulic compressors, horizontal hydraulic compressors, and hydraulic pushers. Their respective principles are:

1) Traditional mechanical substation compressor

The transmission mode is a crank-link mechanism: the motor drives the crankshaft to rotate, and the piston, the crosshead, and the piston rod drive the piston to reciprocate in the cylinder to realize the gas compression process and achieve the purpose of supercharging. As shown below:

2) Hydraulic flat push substation equipment system

The working principle is as follows: the hydraulic working skid provides high-pressure oil, and is successively injected into each long-tube cylinder of the special tank truck through a series of control valves, and the natural gas in the long-tube cylinder is pushed out at a constant pressure of 20MPA, thereby passing through the gas selling machine. Refill the car. As shown below: The left side is the special tank truck, and the right side is the hydraulic working raft.

3) Vertical hydraulic compressor (vertical cylinder)

Structure principle:

The I-shaped piston rod divides the upper cylinder into two chambers A and B, and divides the lower cylinder into two chambers C and D, as shown below:

Process flow:

1 The high-pressure oil output from the hydraulic station enters the C-cavity, and the oil in the B-chamber is returned to the tank (approx. The oil pressure of the return tank is 0), the piston rod moves downward, and the gas in the tank enters the A-cavity (first-stage intake). The gas in the D chamber is compressed and flows out (first-stage compression), and enters the cooler to complete the first-stage compression process; when the piston runs to the pole, the hydraulic station reversing valve will be reversed, and the output high-pressure oil enters the B-cavity. The oil in the C chamber is returned to the oil tank, the piston rod moves upward, the gas in the tank car enters the D chamber, (first stage intake air), and the gas in the A chamber flows out after compression (first stage compression), enters the cooler, and completes one. Stage compression process

2 When two such cylinders are connected in series, it constitutes two-stage compression.

4) Horizontal hydraulic compressor

Structural principle: One cylinder in the middle drives two cylinders on both sides, and each cylinder is divided into two stages of compression. As shown below.

Process flow:

1 When the piston rod moves to the right, the gas in the tank car enters the first-stage cavity of the left cylinder (first-stage intake air), while the gas in the right-stage cavity is compressed and flows out through B, enters the cooler, and completes the first-stage compression. At the same time, the cooled gas enters the secondary chamber (secondary intake) from G, and the gas in the secondary chamber of the left cylinder is compressed and then flows through D into the secondary cooler and then discharged.

2 On the contrary, when the piston rod moves to the left, the gas in the tank car enters the first-stage cavity of the right cylinder (first-stage intake air), while the gas in the left-stage cavity is compressed and flows out through F, enters the cooler, and completes one. At the same time, the cooled gas enters the secondary cavity (secondary intake) from C, and the gas in the secondary cavity of the right cylinder is compressed and then flows into the secondary cooler through H, and then discharged.

The theoretical power consumption of the four seed station compressors is compared as follows:

	Mechanical compressor	Vertical hydraulic compressor	Horizontal hydraulic compressor	Hydraulic push
Average displacement	1000	1000	1000	1000
Main motor power (kW)	75	44	44	37
Actual hourly power consumption (kWh)	75x0.8=60	44x0.8=35.2	44x0.8=35.2	37
Specific energy consumption (kW·h/square)	0.06	0.0352	0.0352	0.037

Note: The first three motors are not fully loaded for most of the time, and the average current is calculated as 80% of full load.

As can be seen from the above table, in terms of energy consumption, the substation compressor should give priority to the hydraulic equipment.

Second, the cost of leakage

The compressor always produces leakage during the working process. The leakage is large and the gas is lost. On the contrary, less leakage can increase the income of the gas station, which also constitutes the operating cost of the gas station. Looking at the monthly CNG entry and exit data of multiple gas stations, we can conclude that the leakage rates of these four compressors are as follows:

	Mechanical compressor	Vertical hydraulic compressor	Horizontal hydraulic compressor	Hydraulic push
Leakage rate (%)	0.6-3	0.03-0.06	0.03-1	1.5-1.8
Average leak rate (%)	1.8	0.045	0.5	1.65
Annual leakage calculated on a scale of 15,000 square meters per day (square)	15000x1.8%x 360 days = 97200	15000x0.045%x 360 days = 2430	15000x0.5%x 360 days = 27000	15000x1.65%x 360 days = 89100

Third, maintenance costs

In the gas station equipment, the main maintenance tasks, and have a greater impact on the gas sales of the gas station, is still the compressor equipment, so the maintenance cost of the compressor equipment is more prominent. Here is a list of normal working conditions, annual consumables costs and repair costs of consumables:

	Mechanical compressor	Vertical hydraulic compressor	Horizontal hydraulic compressor	Hydraulic push
Accessories costs (ten thousand yuan)	12	4	4	8 (fuel consumption)
Repair time (hours)	8	3	20	Waste of natural gas during maintenance

Maintenance costs are also reflected in the credit damage of the gas station. When the driver comes to refill, there is a device failure to stop refueling. If the driver appears 2-3 times in a short period of time, the driver may not be willing to refill, and this information is transmitted inside the driver through the intercom. The speed of communication is quite fast, so that many users are lost invisibly. Therefore, the maintainability and failure rate of the compressor are even more important.

Fourth, the conclusion:

From the above three cost analysis, it can be seen that the compressor for CNG refueling substation should be selected as the hydraulic compressor, and the hydraulic compressor should be preferred in the hydraulic compressor. This kind of compressor can be seen from its working principle: energy saving, no leakage, full air cooling, etc., in the use of gas station, it also shows its advantages in energy saving, environmental protection and good maintainability. At present, this type of vertical hydraulic compressor has been used in China. It was first developed by Wuhan Qidakang Environmental Protection Technology Co., Ltd. and first used in China. After successful use, it has now been established by Sichuan Jinke and Shandong Jerry. Follow up. There is another good choice for CNG refueling substation compressors.


Http://news.chinawj.com.cn Editor: (Hardware Business Network Information Center) http://news.chinawj.com.cn

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