What is a hydrogen liquefaction system?

Fig1: Hydrogen liquefaction process

Process flow:

The raw material hydrogen enters the cold box, is pre-cooled by the cold nitrogen pre-cooled primary heat exchanger HX-1, and then enters the liquid nitrogen pre-cooled secondary heat exchanger HX-2 to cool down, and then enters the liquid nitrogen immersed primary positive Parahydrogen converter for constant temperature conversion. The converted hydrogen gas is cooled by the third and fourth heat exchangers HX-3 and HX-4, and then enters the second-stage positive and secondary hydrogen converter for adiabatic conversion. At the same time, after exothermic heating, it returns to the four-stage heat exchanger HX-4 for cooling. . The cooled hydrogen gas is cooled by the fifth and sixth heat exchangers HX-5 and HX-6, and then enters the three-stage positive and secondary hydrogen converter for adiabatic conversion. At the same time, the heat is released and returned to the six-stage heat exchanger HX-6 for cooling. . The cooled hydrogen is cooled by a seven-stage heat exchanger HX-7, then cooled by a JT valve throttle, and then cooled by an eighth stage heat exchanger HX-8, and enters the fourth-stage positive-hydrogen converter for adiabatic conversion, while exothermic After the temperature rises, it will return to the eight-stage heat exchanger HX-8 again. After cooling, it will enter the liquid hydrogen storage dewar. The high-pressure helium gas discharged by the helium screw compressor is cooled by a water cooler, precooled by a cold nitrogen pre-cooled primary heat exchanger HEX1, and then enters a liquid nitrogen pre-cooled secondary heat exchanger HX-2. Then enter the three or four stage heat exchangers HX-3, HX-4 to cool down to a lower temperature, and then pass through a two-stage turbine in series. After the adiabatic expansion refrigeration in the middle of the cooling circuit, it becomes low temperature and low pressure helium gas. Eight-stage heat exchanger HX-8 low pressure side inlet. The returned low-temperature and low-pressure helium flows through the eighth to first-stage heat exchangers (HX-8~HX-1) in reverse flow in order to recover the cooling capacity, then exit the cold box, and then return to the suction side of the compressor for recirculation.

Comparative advantages:

1. Diffusion welding without solder, high and low temperature resistance (-200℃~900℃), high compactness, high heat exchange efficiency, low leakage rate (1*10-9Pa·m3/s), high bonding strength (10MPa). At the same time, the secondary bonding has no effect on the core weld, etc.

2. The heat exchangers used in the domestic hydrogen liquefaction system are mainly aluminum alloy plate-fin heat exchangers. Due to the stringent product leakage rate requirements, the aluminum alloy plate-fin heat exchanger plates are selected to be thick, large, and heavy. And problems such as brazing are not easy to repair. Aluminum alloy plate-fin heat exchangers and stainless steel pipelines will face difficulties in welding aluminum alloy and stainless steel.

The first domestic large-scale hydrogen liquefaction system developed by Shenshi's domestically produced diffusion-bonded stainless steel plate-fin heat exchanger solves the above problems and fills the blank of the steel plate-fin heat exchanger in the domestic hydrogen liquefaction field.

Fig2: Hydrogen liquefaction system and steel plate-fin heat exchanger for low temperature