[ valves ] warm generates a heat flow . Ice may form in the warmer section of the bonnet cavity , compromising the stem sealant and thus the operability of the valve .
The -253 ° C temperature demands optimal insulation technology for the valves to maintain LH 2 at this temperature and minimize hydrogen losses via boil-off . Any heat transfer to the liquid causes hydrogen to evaporate and leak . Furthermore , a break in the insulation causes oxygen condensation . Any contact between oxygen and hydrogen or other combustible material will increase the likelihood of fire hazard . Therefore , when considering the susceptibility of valves to the risk of fire , the valve design must be explosion-proof and include a fireproof actuator , instruments , and wiring , in conformance with the most stringent certifications . This will ensure that the valve will function safely during a fire .
Pressure buildup is another potential issue that may render the valve inoperable . The accumulation may occur when liquid is trapped in the valve cavity , and under certain conditions of heat transfer and vapor formation . In the case of high differential pressure , cavitation and / or noise can occur , which will damage the valve prematurely and result in unacceptable process failures .
Velan engineer providing support at the Westcoast hydrogen liquefaction plant in North Las Vegas
characteristics make zero leakage an absolute necessity .
Valve solutions
Regardless of their functionality or type , all valves in LH 2 service must meet certain common requirements . These include the use of appropriate construction materials that ensure structural integrity at very low temperatures , as well as materials that are inherently fire safe . Similarly , the sealing and packing materials used in these valves must also meet these basic requirements .
Austenitic stainless steel is a preferred material for LH 2 valves . It offers excellent impact strength , minimal heat loss , and can handle steep temperature gradients . Other materials are also available that are compatible with hydrogen but depend on the process conditions .
By considering these aspects regardless of the process conditions , appropriate design features are integrated into the design process , thus providing a safe and reliable operation .
Other key design challenges are related to environmental issues such as fugitive emissions . Hydrogen has unique characteristics : small molecular size being colorless , odorless , and explosive . These
Besides the choice of materials , other design details such as extending the stem with a gas column protect the sealing packing from the effects of extremely low temperature . In addition , the stem extension can be supplemented with a thermal collar to avoid condensation in the insulated area .
Unique features tailored to each valve design offer enhanced technical solutions to different challenges .
Hydrogen Tech World | Issue 9 | April 2023 27