7 replies to this topic

[rajarshi2016]

Hi all,

 

A gas with attached composition (MW: 24.12) needs to be compressed. Conditions are as follows:

 

Suction pressure: 4.6 kg/cm2g, Discharge pressure: 37 kg/cm2g, Suction Temperature: 56 DegC

 

We are planning to use a multistage centrifugal compressor for this purpose.

 

As you can see, there is a high percentage of olefins in the gas.

 

Is there any special consideration/ safeguard that needs to be taken for compressing this gas, say w.r.t. maximum allowable outlet temperature, risk of polymerization etc.?

 

Awaiting your response and thank you for your time.

 

Regards,

Rajarshi

 

 

 

Attached Files

•  composition_.pdf   39.93KB   24 downloads

[Bobby Strain]

What is the source of this gas? And what is the volume?

 

Bobby

[abhi_agrawa]

Rajarshi,

 

The composition you provided did not show an di-olefins (butadiene, acetylene etc). It is important to establish their limits for proper design. Therefore it is important to know the source. If there are no di-olefins, then you should be able to design the compressor for 100 to 120 deg C discharge temperature.

 

Abhishek

[manojkaila]

Dear Rajarshi,

 

I already worked with High Olefin FCC where olefin % is very high even with some Di-olefins. We are using normal multi stage axial centrifugal compressor and we did not face any problem in any system.

 

Though we have naphtha wash facility for compressor but till today It is not used as per my last information.

 

I hope this will help

 

Regards, 

[rajarshi2016]

Hi all,

 

Thank you for your inputs and apologies for my delayed response

 

The flow rate is about 16200 kg/h

 

Unfortunately, I do not have any information about the source; this is feed gas for a H2 unit coming from some other section of the plant - the exact source is not known to us.

 

@ Abhishek: It seems from your reply that some sort of precaution needs to be taken if there is some di-olefins in the gas. Can you please elaborate why and also

 

what is the maximum percentage of di-olefins that can be allowed without taking any additional precaution.

 

Can you also tell from where this temperature limit of 120 DegC comes from (any standard/ any safety concern)?

 

Inputs will be highly appreciated.

 

Regards,

Rajarshi 

[PingPong]

this is feed gas for a H2 unit

Olefin rich gas is not a suitable feedstock for a Hydrogen Unit.

 

You should contact the licensor of your H2 unit to find out what feed olefin content their unit design can handle.

Probably they will advise you no more than 1 mol% olefins in feed to the H2 unit, so you would need to dilute this olefin rich gas with a lot of olefin free gas before feeding it to the H2 unit.

 

With regard to compressing this gas: I don't know of any standards that give maximum limits on concentration or temperature, but the higher the diolefin concentration or temperature the more severe the fouling of the compressor. Keep discharge temperature below 100 ^oC when diolefins are present.

In ethylene plants usually water injection on the charge gas compressor stages is applied to limit discharge temperature of each stage to 90 - 95 ^oC. Discuss this with compressor vendor for your specific application.

 

If however, after compression, you would preheat a gas containing diolefins in exchangers or the convection bank of a fired heater (like in a H2 unit) then the fouling problem will still occur there.

Edited by PingPong, 01 April 2016 - 04:19 AM.

[abhi_agrawa]

Rajarshi,

 

As PingPong pointed out, it is advisable to restrict the compressor discharge temperature to 100°C if you have diolefins in the process gas. The diolefins have a high tendency to polymerize and would therefore lead to fouling and loss of efficiency in the compressor. In order to counter the same, there are several options available. The chosen option depends on several other factors.

 

Hope this clarifies.

 

Abhishek

[rajarshi2016]

Hi PingPong and Abhishek,

 

Thank you very much for your inputs.

 

Just to clarify, we are the unit licensors and we have taken adequate protection in order to handle the olefin rich gas.

 

I will convey the concerns regarding diolefins to concerned person handling this project and will tell them to enquire about the possibility of diolefines.

 

Thanks a lot for your time; it is much appreciated.

 

Regards,

Rajarshi