The oxygen content in inert gases is 3%; how can the oxygen content in the system after displacement be reduced to less than 0.5%?
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In the safety technical regulations for hydrogen use, section 5.2 states that the inert gas displacement method shall meet the following requirements: a) the volume fraction of oxygen in the inert gas shall not exceed 3%. c) The oxygen or hydrogen content in the hydrogen system must pass testing on at least two consecutive occasions. Purging is completed when the volume fraction of oxygen in the hydrogen system is less than or equal to 0.5%, and the volume fraction of hydrogen is less than or equal to 0.4%. The oxygen content in inert gases is 3%; how can the oxygen content in the system after displacement be reduced to less than 0.5%? The limiting oxygen concentration for hydrogen is 5%; why does the oxygen level need to be reduced to 0.5% after displacement?
When the oxygen content in the inert gas is 3%, the method of multiple purges can be employed, with successive purges carried out; analysis and testing are conducted after each purge until the volume fraction of oxygen in the hydrogen system is less than or equal to 0.5%, and the volume fraction of hydrogen is less than or equal to 0.4%, at which point the purification process is completed. This allows the oxygen content to be reduced gradually, ensuring safety. Generally speaking, keeping the oxygen content below 0.5% ensures the safe use of hydrogen, as the lower the oxygen concentration, the weaker the flammability of hydrogen. .
When the oxygen content in the inert gas is 3%, no matter how many times you perform the displacement process, the oxygen content in the system will remain at least 3%; it is not possible to reduce it to below 0.5%
It is indeed stated that the oxygen content in the nitrogen used for displacement should not exceed 3%, but when it is required that this value be below 0.5% after displacement, then it should be specified that the oxygen content in the nitrogen used for displacement must not exceed 0.5%.
Yes, you are right. If the oxygen content in the system after displacement is required to be less than 0.5% (i.e., less than 0.5%), then the volume fraction of oxygen in the inert gas should be kept as low as possible. One method is to use a purer inert gas as the displacement gas, such as high-purity nitrogen with an oxygen content of no more than 0.1%. Additionally, the method of multiple replacements can be used, with analysis and testing performed after each replacement, gradually reducing the oxygen content until it meets the required level. These methods can ensure that the oxygen content in the hydrogen system meets safety standards. .