9 replies to this topic

[rasyid93]

Hello all,

I have a problem in determining the most suitable process for ngl recovery process for rich feed gas (rich heavy hydrocarbon). The feed gas composition is 2% CO2; 75% C1; 7% C2; 6,8 % C3; around 9 % C4+. Furthermore the gas pressure is low (3,5 bar).

 

I want to reject (almost) all the C2 (>97%), and recover >98% C3+ in my deethanizer.

 

From what i have learnt, turboexpander process isn't suitable for rich feed gas, because it will need additional external refrigerant, so increasing CAPEX and OPEX. And also, turboexpander process require high pressure feed (around 70 bar).

 

While conventional mechanical refrigerant (propane refrigerant) doesn't require high pressure feed, but the process can't achieve high recovery (typical C3+ recovery is 50%). And I think i won't consider using extreme refrigerant (like Nitrogen refrigerant and else)

 

So, do you know any other process that is suitable for my case? Any licensed technology or anything

This is for my final project, I hope someone could help me

 

Thanks in advance

 

Regards,

 

Rasyid

[RockDock]

I think you will need to combine a turbo expander and mechanical refrigeration. What is your flowrate? 

 

What you are describing is an Ortloff unit with a true reflux (RSV). This process takes some of your rejected gas and sends it through a JT valve before putting it back into the column. You will need to compress your feed gas, though. I expect you will need to put a C3 chiller upstream of the Low Temperature Separator. You have to lower the temperature somehow. Combining a TE, JT and C3 refrigeration is your best bet. Ortloff RSV would get you the product you desire.

[rasyid93]

Hello RockDOck

 

Thank you for your help. The sweet gas flowrate entering deethanizer is 11,2 MMSCFD. Is the flowrate suitable for TE combined with mechanical refrigerant?

 

I guess I really should compress the feed gas to really high pressure for this TE process . But I really hope that there's a process that is not require high pressure but can achieve the spec of product i mentioned above.

 

Thanks again. I will try to simulate this RSV process

[ColinR33]

That is a pretty small flow rate. RockDock is correct, with that rich a feed you will need to combine mechanical refrig with a turboexpander, or use a refrigerated lean oil process, both of which will work (we have designed and built both types), but the lean oil processes aren't used very much any more. At 11.2 you will probably be running the smallest expander frame size. Not sure what the economics would be like off the top of my head, but with refrigerated lean oil you probably would not need to compress the feed gas nearly as much.

[RockDock]

No problem.

 

With that low of a flowrate, it will not have a very good return on investment with the specifications you require. Maybe 15-20 year pay off period... Perhaps you could get better economics with just a 50% C3 recovery. You may be able to use just a simple gas plant with that specification

[rasyid93]

Hello ColinR33 and RockDock

Why the lean oil processes aren't used very much anymore? Is there any particular disadvantage of lean oil process? And with the spec of feed gas that i have mentioned above, can the lean oil process achieve high propane recovery while ejecting almost all of ethane?

 

I am worrying about the economics now

I did some search, and found a process patented by Lummus Technology, Inc named IPOR (Iso-Pressure Open Refrigeration NGL Recovery), It doesn't require high pressure, has open refrigerant and external propane refrigerant, and can achieve high propane recovery. It looks good to me. Do any of you have any experience in this technology?

Sorry if I ask too much. Thanks

[RockDock]

I've never dealt with an IPOR plant before, but it is a legitimate option for you. It utilizes the propane in your plant as the refrigerant. There will still be a good deal of compression with this option. You'll have to model them and compare the compressing powers to see which one to use. I expect the IPOR process to have a higher compression cost, unless you are able to run it at a lower pressure.

 

I imagine lean oil processes are not common because it requires external energy in many cases. The benefit of the RSV and conventional Ortloff units is that they are self sustaining in most cases - no external energy is required, except for recompression (if required).

[rasyid93]

Thank you for your suggestion, I have simulate the IPOR and RSV process for the spec of product i want. I am currently trying to make some some optimization and then i will compare the two processes.

 

But I have some question left. Is 11.2 MMSCFD really that small that make it will probably be running the smallest expander frame size? I read the list of ortloff experience, they have experienced in 1.3 MMSCFD feed gas by OHR technology. OHR technology is also a Turbo Expander process right? What do you think about that? This is the link to list of ortloff experience: http://www.ortloff.c...GasPPLicAll.pdf

[ColinR33]

Yes, that is a turboexpander process as well, and having worked on several of the plants listed in Ortloffs experience list I can say with a fair degree of certainty it will use pretty much the smallest expander frame size available. I am not familiar with the 1.3 MMSCFD unit shown, but as you can see, that is the only one of that size, most start around the 15-17 MMSCFD capacity range. I don't know what the economics of that unit were like or if it was environmentally driven, or what the expander efficiency was like, but it certainly can be done, just a matter of what payback would be like.

The Lean Oil plants do have somewhat higher energy requirements, but this is partially offset by reduced feed gas compression requirements (also depend on what sales gas pressure you require), and they are also more tricky to operate, but there are some companies that specialize in proprietary designs that can achieve 90%+ C3 recovery. The only way to be sure is to evaluate all the options. Good luck!

[rasyid93]

That really answer my question.

Having discussion in this forum is really helpful.Thank you ColinR33 and RockDock