Reduce operating pressure in residue coker unit

[rumirav]

Dear all,
Here are several different options to increase liquid production and reduce coke yield in residue coker units. One of the most widely used is try to operate coker drum at low pressure.
But, what are the possible options to reduce further the operating pressure in the coker drum?
Could the minimum pressure limit (alarm) at the wet gas compressor inlet be reduced? We currently operate at 0,4 kg/cm2. Has anyone experience operating at lower pressure at this point?
Has anyone experience installing an on-line water wash in top of main fractionator or condenser to remove salts? In that case, which is the maximum DP reduced with this option?
Has anyone experience implementing any other modifications (increase vapor lines diameter, etc)?

Thanks in advance for your help

Best regards

 

[TD2K]

< Could the minimum pressure limit (alarm) at the wet gas compressor inlet be reduced? >

Maybe, you'll need to research why was that pressure selected and are there any risks to operating at a lower pressure? Do you have the compressor capacity at a lower suction pressure?

< Has anyone experience installing an on-line water wash in top of main fractionator or condenser to remove salts? >

Water washes on exchangers are not uncommon. What is your dP compared to what it should be per design at the conditions you are operating at?

< In that case, which is the maximum DP reduced with this option? >

A lot to a little. With no numbers, I'm not sure how you expect someone to answer this. If the salts have heavily fouled the exchanger or tower and are water soluble, you could see a significant reduction in pressure drop. But it very much depends on your existing situation.

 

[georgeverghese]

0.4kg/cm2(g) isnt far from atmospheric - depending on how well the suction PIC / speed controls work when there are flow disturbances, the transient low pressure should be kept above atmospheric, else the compressor may pull in air at subatmospheric conditions. The compressor recycle line should also kick back discharge gas back to suction as this low limit is approached.

 

[gocougs1]

Coke drums normally operate 15-25 PSIG, and what you have is 14 PSIG (0.4 kg/cm^2), so you probably will not be able to go much lower due to the main frac gas compressor suction limitations. Lowering pressure further can cause other issues like the formation of shot coke.