We have the following Hyrogen compr

[NiravK]

We have the following Hyrogen compressors in our Diesel Hydrotreater. The op.pressure of reactor is of the range of 115 - 120 kg/cm2g.

Compressor desing pressures are...

[1] Make-up Gas Compressor MUGC - 2 Stage Reciprocating.
With Nitrogen->
1st STAGE :: Suction P=6.0 kg/cm2 g; Disch P=14.0 kg/cm2 g
2nd STAGE :: Suction P=13.5 kg/cm2 g; Disch P=33.7 kg/cm2 g
And
With Hydrogen->
1st STAGE :: Suction P=20.0 kg/cm2 g; Disch P=47.0 kg/cm2 g
2nd STAGE :: Suction P=45.4 kg/cm2 g; Disch P=104.0 kg/cm2 g

[2] Recycle Gas Compressor RGC - Single Stage Reciprocating.
With Nitrogen->
Suction P = 32.5 kg/cm2 g
Disch P = 43.0 kg/cm2 g
And
With Hydrogen->
Suction P = 104.0 kg/cm2 g
Disch P = 126.0 kg/cm2 g


We have to keep reactor pressure below 30 kg/cm2 g pressure during start-up before we reach pre-defined Min Pressurisation Temp(MPT).
So, we want to run Recycle Gas compressor with suction of 20-23 kg/cm2 g pressure with minimum possible discharge pressure. This are the conditions during Reactor dryout with Nitrogen.

Make up gas compressor can fulfill the requirement BUT it does not have configuration to have re-circulation of flow from reactor and also, the capacity is also low. So we have to run Recycle Gas Compressor. But compressor vendor is recommending not to start the compressor with low suction in any case.

I want to know if someone can explain me why is it not possible to start with low suction with same compression ratio.

During commissioning, plant start-up procedure also requires to run recycle gas compressor with 20 kg/cm2 g suction pressure of Hydrogen. The circulate hydrogen through reactor, increase temperature of the reactor catalyst bed and then start pressurising gradually with Make-up gas compressor upto operating pressure. But under the circumstances, we CAN NOT start recycle gas compressor.

What could be the feasible solution???

thanx in adv.

 

[25362]

I'll concentrate on valves, since they are the heart of the compressor, but may be other mechanical and lubrication factors are also of importance in your case. Valve failures represent more than 40% of reciprocating mechanical failures. Compressor valves operate on pressure differentials, not pressure ratios. Valves open and close against the return force of their springs. On a indicator card plot one sees that the actual pressures inside the cylinders are much lower at suction, and much higher at discharge, than on the process side. Thus valve fluttering, actual pressure ratios, and gas heat up may be larger than expected.

The technical literature stresses that poppet valves are considered the best of all types (including plates, rings and channels). Besides, valve lifts of 0.04" have been shown to prolonge valve lifes from 1 year to 3 years.

Anyway, valves' (and their springs') design is delicate, even the molecular mass of the gas bears an effect on their design.

Try

http://www.dresserrand.com/e-tech/PDF Files/tp102.pdf

And ask the compressor manufacturer about acceptable solutions to your problem. Good luck.

 

[NiravK]

Thanks for the reply.
I may need to contact vendor again. Any more suggestions or comment???