Q & A > Question Details
In flare header line, we keep positive pressure by water seal in water seal drum upstream of flare stack. During steam out operation in turn-around period, we plan to steam out the hydrocarbon in the process system to the flare system for reduced VOC emission to atmosphere. Since the condensation of steam may cause negative pressure in flare header line, this operation is safety concerned. Please advise.
 
Answers
03/04/2010 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
I agree, purge gas is good practice in this case.
02/04/2010 A: Marcello Ferrara, ITW SrL, mferrara@itw.it
You can reduce steam requirements by adding a patented chemical to quickly degass and decontaminate the equipment. If heavy hydrocarbons deposits are to be removed, a preliminary patented online cleaning of the system (including blowdown accumulator) can be performed.
31/03/2010 A: Mike Watson, Tube Tech International Ltd, mike.watson@tubetech.com
A solution is to clean the Flare Line ON-LINE without Steam or Chemicals and avoid shutting the refinery down.
31/03/2010 A: keith bowers, B and B Consulting, kebowers47@gmail.com
It will be necessary to keep enough purge gas (fuel gas, natural gas) going into the flare header, upstream of the steam-out to keep a positive pressure on the flare header. Otherwise there is risk of sucking in the water seal and getting air in the header, resulting in flammable or even explosive conditions.
This is not to say there is a significant probability of any combustion taking place, but the RISK (exposure) would be high if there is not sufficient purge gas. It is not prudent to allow such a risk to develop when low cost mitigation is readily available.