Problem of using nitrogen with hydrogen compressors
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When the site is airtight, nitrogen is pumped in using a hydrogen compressor; the compressor is of the reciprocating type, and it makes a loud and harsh noise. According to the information available, when using the adiabatic compression model to calculate the power of reciprocating compressors, the calculation is primarily influenced by the adiabatic index K. In various sources, the adiabatic index for both nitrogen and hydrogen is slightly over 1.4, with little difference between them; as a result, the calculated powers are also similar. This suggests that a compressor capable of handling hydrogen can also handle nitrogen, which does not correspond to reality in practice. I would appreciate some guidance from those with more experience.
The adiabatic factor is one of them; changing the compression medium – it seems there are many other things to take into consideration
The molecular weights of hydrogen and nitrogen differ by so much that it has a significant impact on the thrust and flow rate in the propulsion system!
I’d like to tell the original poster that our unit also used it in this way; later on, due to the high temperature of the valve, the flow rate couldn’t be too high. Therefore, when using a compressor to supply nitrogen, we switched to a nitrogen-specific valve. Since the molecular weight of nitrogen is more than ten times that of hydrogen, and the flow rate at the compressor outlet is a volume flow rate, when the same volume of nitrogen and hydrogen is fed into a hydrogen valve, the temperature rise of that valve is different. The lift of the valve leaflets in a hydrogen valve is much smaller compared to that in a nitrogen valve, so a hydrogen valve cannot be used for supplying nitrogen. I’m not sure if it’s clear now.
As for signs of overload, it’s still possible to fight. The pressure needs to be reduced in order to lower the flow rate; nitrogen is much denser than hydrogen. It’s like using a water pump to draw up mercury; it’s strange if the motor doesn’t burn out.
When designing the compressor, it is necessary to take into account the nitrogen testing conditions; the manufacturer is required to meet these conditions. Moreover, the anti-surge valve must have a full-backflow design, otherwise testing will be difficult
Excuse me, I would like to ask: why does the temperature rise when the valve resistance increases? What is the theoretical basis?
The most obvious symptom when a dry gas compressor uses nitrogen is an increase in the exhaust temperature. The main reason for this is that nitrogen molecules have a higher molecular weight than hydrogen, which means they are easier to compress. When considering the back pressure at the outlet of a reciprocating compressor, if nitrogen is used, the piston cannot reach the required exhaust pressure at the end of compression; as a result, the gas does not get discharged and suction continues, thereby increasing the clearance volume. This leads to a reduced compression capacity of the compressor, and more compression is needed to achieve the desired exhaust pressure, which in turn causes the exhaust temperature to rise.