Hydrogen Reciprocating Compressor Flow Rate

[seungwon2]

When we start H2 reciprocating compressor with N2 gas, manufacturer's manual shows reduced operating flow limit (8,450 Nm2/h) compared to rated hydrogen capacity(49,500 Nm3/h) for 1st stage.
If the compressor is operated with the same rated flow as H2 gas, what problem will happen?

 

[pmover]

think about the moleweight difference between the gases . . . and the consequences of operating the compressor. the compressor driver may not have sufficient power available to operate at the higher N2 flow rates.

hope this helps.
-pmover

 

[25362]

What are the actual operating pressures with nitrogen and with hydrogen? Assuming both gases are at the same ambient temperature, the "actual" (not "normal") displaced volumes could still be the same for both gases if nitrogen is at atmospheric pressure and hydrogen is at, say 5.86 atm.

Quoted from Lieberman & Lieberman's A working guide to process equipment:

A reciprocating compressor is a direct-volume reduction machine. The gas is simpkly squeezed out of a cylinder by a piston and pushed into the discharge line. The molecular weight of the gas does not influence the suction or discharge pressure of the compressor. The gas density does not influence the compressor performance or the work required by the driver.

 

[seungwon2]

I attach operating limit and inlet line orifice calculation sheet for this compressors.
I know N2 purge and circulation is needed during startup and commissioning period.
My concern is for the operation of compressor with n2 at rated flow of h2, it may cause a problem on the compressor.

 

[seungwon2]

another attach

 

[25362]

seungwon2

From the sheet taken from the Safety & Operating manual I could learn that the operation on nitrogen is taken at 50% load of the normal rated capacity, after correcting for inlet pressures.

I imagine, but I cannot be entirely sure (better ask the maker), that the intercoolers are much more effective with the hydrogen-rich gas than with nitrogen, therefore, in order not to unduely heat the gas and possibly ruin the lubricant there is a limitation on nitrogen flowrate. This is also confirmed by the lower overall compression ratio indicated for nitrogen.

FYI, the lubricant I used to work with in hydrogen compressors was based on PAG which is claimed as not leaving any deposits in service up to 200^oC.

Normally these type of compressors are provided with a high-temp trip for such reasons.