Analysis On Compressor Selection For Different Types Of Hydrogen Refueling Stations

Analysis On Compressor Selection For Different Types Of Hydrogen Refueling Stations

1.Analysis of hydrogen refueling station types

Depending on the source of hydrogen, hydrogen refueling stations can be divided into on-site hydrogen refueling stations and off-site hydrogen refueling stations. On-site hydrogen refueling stations produce hydrogen directly at the station through various methods (such as water electrolysis, reforming natural gas, etc.), and then refuel fuel cell vehicles. This method reduces the cost and complexity of hydrogen transportation. Off-site hydrogen refueling stations obtain hydrogen from external suppliers, transport it to the station by tank trucks for storage, and then refuel. This method is more common, especially in the initial stage of hydrogen energy infrastructure construction. 

According to different equipment configurations, hydrogen refueling stations can be divided into fixed hydrogen refueling stations and skid-mounted hydrogen refueling stations. Fixed hydrogen refueling stations are usually large-scale, permanently built hydrogen refueling facilities, suitable for areas with large and stable hydrogen demand. Skid-mounted hydrogen refueling stations are characterized by modular design and skid-mounted installation, which are easy to deploy and relocate quickly, and are suitable for initial market exploration or temporary demand occasions.

According to the different refueling pressure levels, hydrogen refueling stations can be divided into 35MPa hydrogen refueling stations, 70MPa hydrogen refueling stations and 35MPa+70MPa hydrogen refueling stations.  35MPa hydrogen refueling stations usually serve hydrogen heavy trucks, muck trucks, buses and logistics vehicles. 70MPa hydrogen refueling stations serve fuel cell vehicles equipped with 70MPa high-pressure hydrogen storage bottles, especially passenger cars. The mixed pressure level of +35MPa+70MPa hydrogen refueling stations can meet the needs of vehicles with two pressures at the same time, providing greater flexibility for hydrogen refueling stations and ensuring that hydrogen refueling stations can adapt to a wider range of hydrogen vehicle markets.

2.1 Diaphragm compressor

The diaphragm compressor compresses gas through a reciprocating metal diaphragm. The advantages are that the gas is completely isolated from the piston and there is no oil pollution. The membrane cavity adopts a static seal with low leakage rate. The gas directly contacts the end cover and the metal diaphragm group to form a good heat transfer effect, which can achieve a very high volume efficiency and simple maintenance and operation. The disadvantage of the diaphragm compressor is that it cannot be started or stopped at will, the compressor vibrates slightly, and a special design foundation is required. Due to its high throughput, low power consumption and low cooling requirements, it has been proven to be very effective in hydrogen applications, and is usually used in fixed hydrogen refueling stations that require long-term operation and high hydrogen purity requirements.

2.2 Liquid-driven piston compressor

The liquid-driven piston compressor is a process in which the hydraulic oil drives the piston of the hydraulic cylinder body, driving the gas compression chamber piston installed on the same piston rod to reciprocate, realizing the process of gas suction and exhaust. The advantage is that due to the use of hydraulic drive without crankshaft connecting rod movement, it can adapt to frequent start-stop conditions, and the compression frequency is low and the vibration is small, and the requirements for the compressor foundation are not high. 

The disadvantage of the liquid-driven piston compressor is that the single-stage compressor is low, the cooling requirements are high, and wear will inevitably occur during the reciprocating movement of the piston, resulting in dust particles contaminating the cleanliness of the hydrogen, and the leakage is higher than that of the diaphragm compressor. The piston cylinder parts are large in size and complex to repair and replace. Because its cost is adapted to frequent start-stop conditions and has low requirements for equipment foundation, it is usually used in skid-mounted hydrogen refueling stations or mobile hydrogen refueling stations that do not require long-term operation.

2.3 Liquid-driven diaphragm compressor

The liquid-driven diaphragm compressor adopts a single-stage, double-diaphragm compression scheme and a "hydraulic pump + rotary reversing valve" drive scheme. The advantage is that the hydraulic pump drives the hydraulic oil instead of the traditional piston and crank-connecting rod driving the hydraulic oil, reducing the piston assembly, crank-connecting rod mechanism assembly, crankshaft and other mechanical transmission parts, and the layout is more compact. 

It combines the advantages of high sealing and oil-free pollution of diaphragm compressors and the advantages of liquid-driven piston compressors in adapting to frequent start and stop. The disadvantage of the liquid-driven diaphragm compressor is that the need to use two diaphragm heads increases the risk of diaphragm rupture, and the hydraulic oil pump pressure needs to be higher than the exhaust pressure, which has high requirements for oil circuit sealing performance. At present, the liquid-driven diaphragm compressor is similar to the liquid-driven piston compressor, and is mainly used in skid-mounted hydrogenation stations or mobile hydrogenation stations. The common specifications and parameters of the liquid-driven diaphragm compressor are similar to those of the diaphragm compressor.

3.Conclusion

Hydrogen compressors for hydrogen refueling stations have made great progress in terms of displacement, working pressure, maintenance cycle and specific power, and have continuously narrowed the technical gap with foreign products. Domestic hydrogen compressors have gradually replaced foreign products. From the above-mentioned typical hydrogen refueling station examples, diaphragm compressors and liquid-driven compressors have achieved relatively good operating results in their respective application scenarios. The 90 MPa domestic liquid-driven compressor has been successfully developed, but there are no commercial application cases yet. There is still a large gap between compression technologies such as high-pressure piston compressors, ionic liquid compressors, and metal hydride compressors and foreign ones. Technology iteration and market testing are important development directions in the future.

In the current construction stage, hydrogen refueling station compressors should focus on the maturity of use, hydrogen compression ratio, working condition stability and project-actual operation. In the scenarios of off-site hydrogen production fixed hydrogen refueling stations and on-site hydrogen production hydrogen refueling stations, diaphragm compressors can be used first. In the scenarios of skid-mounted hydrogen refueling stations and 90 MPa hydrogen refueling stations where the filling frequency is relatively low and frequent start and stop are required, liquid-driven compressors can be given priority.