REGENERATION GAS DESIGN

[dvd111]

Dear All,
In C2+ recovery plant a stream of 30000 kg/hr natural gas is branched from main sales gas stream for regeneration of C3 and C4 sulfur treaters. This stream has a pressure of 31 bar. Regeneration gas is heated, entered to the treaters and and sulfur-rich gas is re-injected to the sales gas stream after compressed to 66 bar.
There is an idea that regeneration gas could be branched from sales gas compressor discharge (66 bar pressure), depressurized to about 34 bar, then heated and used as regeneration gas in treaters; after that re-injected to sales gas suction line (30 bar). In this case the regeneration gas compressor will be removed from process resulting in saving in energy and maintenance costs.
What is your idea?
Link to brief PFD of two cases:

https://drive.google.com/open?id=0BwWID2uo-gZHdk5qR0t2N3VfT3M

https://drive.google.com/open?id=0BwWID2uo-gZHa0NCQmtkaERrQXM

 

[georgeverghese]

In your proposed new scheme, the regen circuit pressure is the same as the booster compressor suction press, so what is the suction pressure to the booster compressor ? - conflicting information on the diagram..

 

[dvd111]

Dear Georgeverghese,
The suction pressure of booster compressor is 30.5 bar. This booster is a small machine connected to an expander.

 

[georgeverghese]

At the outset, it is obvious that you will lose some 30tons/hr in sales gas capacity.
Also, the regen gas heater feedgas temp will be low due to the JT effect upon letdown from 66barg - is it not better then to take this regen gas stream from upstream of the sales gas export cooler ?

Also, the regen gas cooler should account for the spike in gas cooler feedgas temp that occurs during the changeover from one bed to the other.

 

[georgeverghese]

Info I get from the internet is that Sulfa Treat is a non regenerable iron oxide based H2S removal agent, so what is the regenerable process you have here ? From your scheme, merely cooling this H2S rich regen gas stream / separation in the KOD removes most of the H2S released from the reactor bed..