Liquid ring compressors Vs Ejector for VRU

[uritse]

Hi all,
I'll really appreciate some help regarding equipment selection.
Please see attached process parameters I am working with. Vendor has already specified LRC for this application but the process guys are of the opinion that an Ejector VRU could be a better selection. As you can see from the data we are looking at a pressure ratio of around 10, are LRC's suitable for this application? I have worked before with rotating compressors but don't have experience with positive displacement compressors. any experience sharing is highly welcomed.

 

[zdas04]

I have designed ejectors that can do 10 compression ratios, but the mass flow rate of power fluid was very very high and the range of suction mass flow rate was very very limited. A small change in suction conditions caused the process to become very unstable.

This is absolutely not a 10 ratio application. If I assume you are at sea level, then you are going from (11.7+14.7)/(1.09+14.7)=1.67 ratios. A piece of cake for any technology.

With a positive pressure of 1 psig, this becomes the easiest VRU I've ever looked at. Just for scoping, I would look at a unit with a power gas pressure around 40 psig that can give you around 350 MSCF/day. Then make sure that your sink can handle an extra 350 MSCF/day. If you can meet the power-gas and exhaust-gas requirements there are a dozen different vendors that could source this off the shelf.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[uritse]

Thanks a lot for the prompt feedback David!
I have obviously overlooked the units there. I am not sure if I clearly understood your point on the sizing figures. FYI, the discharge of this compressor is routed to the suction line of the Flash Gas Compressors.

BR/Yared

 

[georgeverghese]

You may need to refine this datasheet to include a operating suction pressure range, else you might trip the compressor driver if you dont have sufficient margin on power if are running a fixed speed motor.
If your suction pressure could go subatmospheric, there may be a risk of air / O2 getting into this gas ?
- materials of construction may be affected if you have chlorides etc etc.
Also no range specified for operating suction temp.
As advised, either technology will be okay for this low compression ratio
presume you are aware that ejectors have poor turndown on motive gas demand vs suction gas flow. Also the ejector may fail if discharge pressure varies some what from design. The suction pressure variation on the flash gas compressors - this is also not reflected as discharge pressure range on this datasheet.