In the rapid development of the LNG industry, the demand for its supporting cryogenic valves is increasing day by day. Because LNG is flammable, explosive, and ultra-low temperature, and LNG plants are usually located in a seaside salt spray environment, higher requirements are placed on the selection and design of cryogenic valves. At present, most of the domestic LNG cryogenic valves still need to be imported, and some cryogenic valves for severe working conditions are still monopolized by foreign countries, such as J-T valves, breathing valves for large LNG storage tanks, large-diameter, high-pound valves, etc. Although the domestic material design meets the low temperature requirements, the pressure bearing and sealing performance of some parts still need to be improved.
Cryogenic valve type for LNG
In small natural gas liquefaction plants, low-temperature valves are mainly concentrated in the liquefaction unit and LNG storage unit. This kind of multi-stage pressure-reducing regulating valve. According to rough statistics, the number of cryogenic valves used in general liquefaction plants accounts for about 30% of the total number of valves in the entire plant. In the LNG receiving station (mainly refers to the large station with a receiving capacity of more than 2 million tons/year), the number of low-temperature valves is about 2,000, of which the number of small-sized valves is about 700, and the low-temperature valves account for more than 90% of all valves. The valve has a higher pressure rating and a larger diameter.
The low temperature and ultra-low temperature valves involved in the LNG field mainly include single-seat straight-through valves (including angle valves), ball valves, butterfly valves, globe valves, check valves and safety valves.
Selection points of valves for LNG harsh working conditions
Examples of valves for LNG harsh conditions
J-T valve is one of the control valves with the worst operating conditions in LNG liquefaction plants. At present, the most widely used liquefaction process is the mixed refrigerant cycle, which uses the refrigerant J-T valve and the LNG J-T valve to throttle and depressurize the mixed refrigerant and natural gas. The two J-T valves used in the mixed refrigeration cycle are both in an ultra-low temperature environment below -150 °C. Under the condition that the valves are normally opened, the pressure at both ends of the J-T valve is usually between 30 and 80 bar. Because the J-T valve is in a high pressure differential and ultra-low temperature environment, cavitation is prone to occur, and the surface of the valve core, valve seat and valve body is easily damaged. If the valve core is damaged and not closed tightly, the valve will leak and frost in the fully closed position. Moreover, the performance requirements of the J-T valve are relatively high in the process. In order to achieve the cooling effect, the pressure difference at both ends of the valve and the outlet temperature should be kept stable during use, and the J-T valve should be precisely adjusted when the load of the device changes. Therefore, in the selection of J-T valve, in addition to complying with the general rules of low temperature valve design, it is also necessary to consider the special requirements for the selection and design of valve trims under high pressure differential conditions.
Special requirements for J-T valve selection
Application Status of Cryogenic Valves in LNG Field - Zorgon (Zhejiang) Automation Technology Co.,Ltd. (cnzorgon.com)
www.cnzorgon.com/application-status-of-cryogenic-valves-in-lng-field.html
