Q & A > Question Details
For a Cracked Gas Compressor in an Ethylene Plant, I am doing a simulation for determining optimum wash oil rate for the CGC. As a rule of thumb, 0.01 to 0.25 percent of cracked gas rate is taken as wash oil rate in plant. But I want to know how to calculate it using simulation now. I do not have compressor curves, so to start with I am doing it like this : three phase separator I have taken . I am flashing cracked gas outlet from compressor and wash oil and wash water in this three phase separator here. Now I want to know what is the point where I can say that it is an optimum flow of wash oil ? Do I need to run more wash oil to get dienes from the cracked gas outlet into the wash oil ?
22/02/2020 A: keith bowers, B and B Consulting, kebowers47@gmail.com
You are embarked on a 'fools errand' trying to calculate an 'optimum wash oil rate' based on cracked gas composition. CGC 'wash oil' is used to keep polymerization products from accumulating on the compressor wheels. This 'rate' is experimentally determined by 'trial and error' on the particular compressor and cracked gas composition. The 'amount needed' is far too small to be determined by any analytical test of which I am aware.
Wash oil excess is detrimental to compressor efficiency, reducing efficiency up to 3% if the rotor wheels are liquid wet.

As an experimental approach, one can slowly increment wash oil rate and test the wash oil for polymer content---is it removing the stuff or not. Eventually the crud content will peak and then decline with increasing wash oil rate. The goal of wash oil is to keep compressor efficiency high throughout the entire 'run length.'