Regarding the nitrogen displacement issue for gas compressors
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When hydrogen and dry gas compressors need to be started, generally nitrogen is used for sealing and pressure building, followed by pressure release; 3 such cycles are sufficient for replacement； For some nitrogen purging processes, the oxygen content needs to be less than or equal to 0.5%. What are the regulations in your respective companies?
Before starting a combustible gas compressor, it is essential to purge and replace the air with nitrogen; whether it is a dry gas compressor or a hydrogen compressor, it is necessary to ensure that the oxygen level inside the compressor unit does not exceed 0.5%. Do not hesitate to take the extra steps to guarantee safety.
May I ask: Is the same criterion applied for replacing NO compressors as well?
How was 0.5% determined?
Our company’s policy states that, in the case of nitrogen replacement, when the readings from the two on-site oxygen analyzers show values approaching zero and remain stable for two hours without any changes, it can be assumed that the oxygen has been completely replaced. Only then can the hydrogen connection tube be attached and hydrogen can be introduced.
Replacing with nitrogen to a level of less than 05% is the standard to prevent explosions, and this is beyond doubt; whether it is done by purging with nitrogen or by pressurizing with nitrogen makes no difference. However, pressure holding replacement yields better results, as it prevents the formation of dead zones.
Under normal circumstances, purging and displacement are used; pressure holding for displacement is too troublesome and wasteful
For larger containers, pressure variation is generally used for displacement, while purging is a faster method for pipes.
:lol :lol Agree with the person above! But the pressure increase should not exceed 80% of the designed pressure.:handshake
:handshake Thank you all for the discussions
Our unit uses purging and displacement; although it is theoretically safer to use nitrogen for displacement, it presents many practical difficulties. Generally, using the process gas itself for purging and displacement is sufficient, as it is both time-saving and relatively safe.
Can directly purging and displacing the feed gas ensure safety? How is it determined what constitutes a relatively safe option? Would it be considered a violation of the rules if something goes wrong?
Generally, purging is sufficient; it basically meets the oxygen removal requirements. Holding pressure is too wasteful
Our unit uses pressure retention replacement, and it is required that the oxygen content in the samples analyzed be less than 0.5% (**the specified value seems to be 1%); stricter requirements are set for greater safety. Pressure retention replacement is safer as there are no dead zones.
I am currently studying*, and I thank everyone for their discussions, which have enriched my knowledge. Thank you
Everyone is talking about the control parameters for replacement. So which method of replacement should be used to ensure that the internal parts of the machine (including the cylinder block) meet the requirements for proper replacement? Also, from which location should samples be taken to guarantee that the oxygen content meets the specifications set by the process rules? This is especially relevant when it comes to replacing components in reciprocating compressors. I would appreciate your advice on this matter.
In our facility, we use purging and displacement: first, nitrogen is used to displace the air, and once that is satisfactory, process gas is used to displace the nitrogen, after which the system is brought online. The oxygen content level is less than 0.5%.