Cryo vs. Stabilizer vs. Other Options 1

[ChEMatt]

I'm sure this is an incredibly broad question, but I'll give it a go.

At what point does the design go from a stabilizer unit with mechanical refrigeration (propane loop) to a cryo unit?

I'm looking at a gas stream that simply won't pass muster on the sales gas side Btu limit (1050 Btu/scf) for the pipeline. I've got a stabilizer skid that will, hydraulically, handle the flow. But even the gas coming off the separator is higher than required.

Is there a rule of thumb for reviewing a gas stream that determines "hey, this just won't make it in a stabilize, you need a cryo"?

Sorry for the nebulous question, thanks for any pointers you may have.


Thanks,

-m

 

[EmmanuelTop]

If gas pressure is above the Cricondenbar, refrigeration will not produce any liquids. Also, depending on the shape of the phase envelope, the amount of condensation can be quite small and refrigeration process will not produce the desired effect. That's one example.

Second example is based on economy. If you can recover NGL from feed gas at a price that gives you positive NPV at whatever discount rate your company uses in economic calculations, and you have a market and the infrastructure for NGL, in 99.9% cases that's a straightforward winner. Cryogenic processes require removal of Hg, CO2, Hg, down to ppm/ppb levels so technology and the associated costs of gas treatment will be much higher for cryogenic plants.

I have seen refrigeration units employed mostly in cases where a very small amount of liquids had to be removed from the gas (i.e. less than 1%), and typically when unit pressures were in the range of 20-40 barg. How would you handle liquid stream within the plant can also be a significant factor.

Dejan IVANOVIC
Process Engineer, MSChE

 

[georgeverghese]

A non refrigerated stabiliser unit should typically give you an overheads gas stream that is devoid in C4 and heavier, while a propane refrigerated unit should give you an over heads stream that is partially or completely devoid in C3 and heavier depending roughly on what temperature you've got at the overheads condensor and the operating pressure of the deC3 column.