Saturday, June 20, 2015

Evaluating Options for LPG recovery in Refinery Gas Plant

Evaluating Options for LPG recovery in Refinery Gas Plant- By Raj Bhadra Singh & Abhishek Sinha

Introduction

LPG recovery in a refinery follows a standard arrangement – The feed is compressed to a higher pressure followed by absorption with a solvent such as stabilized/ unstabilized naphtha. The lighters, methane and ethane, absorbed in the process are removed in a stripper column. The rich solvent stream from the stripper bottom is then routed to a debutanizer column where LPG is separated from the rich solvent stream. The LPG so recovered and Fuel Gas undergo further treatment in amine absorbers to meet H2S specifications.


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Line Sizing Calculation


Simple Rules:

1. How much pressure drop you can afford.

2. What is the maximum velocity your pipe MOC can afford?
Is it all!!

Yes basic funda is this only. The only thing remaining is to understand this.

Scenario 1:
As we decrease the line size, our velocity increases (for fixed flow rate) and pressure drop also increases with approximately square of the velocity increase. So if I have lot of pressure is available to be consumed (e.g. Pump discharge of 3 barg to effluent treatment pit where pressure is atmospheric than i have total 3 barg pressure for consumption and i will size the line. check pressure drop and match it to just below 3 barg, say 2.5 barg ( i will still keep 0.5 barg safety margin in my hand)

The limiting factor is rule 2 (limit of maximum velocity)
I.e. I have 3 barg to consume but I can’t go above certain value of velocity which is erosion velocity of the pipe material (Usually this value is valve above than your available pressure drop limit.

Scenario 2:

Outlet of one of the equipment is going to equipment and the operating pressure difference is only 1 barg. Head increase is 0.5 barg (due to elevation difference) so i can afford only 0.5 barg pressure drop. I will size the line with such a size that total pressure drop is not more than 0.4 barg (i would definitely like to still keep 0.1 barg pressure drop in my hand)

Pressure drop calculation equation can be refer from company excel sheets or standard text book  ( i never advise to mesmerize the things which can be easily borrowed from books - Einstein)

Please share your knowledge in comments section 

 




Worldwidesimulation won't die


This is my first blog after shut down of my Website Worldwidesimulation.com
I would still encourage Knowledge sharing So I am putting again my blogs from WWS.