connecting existed flare system with new system

[MohdYaseen2010]

Our case as follow:
We have an existing degassing station & we are in process of building a new degassing station adjacent to the existing one.

The existing degassing station consist of:
Test Separator (DP/OP = 2.2MPag/1MPag) & (DT/OT 100/55°C)
1st Stage Separator (DP/OP = 2.2MPag/1MPag) & (DT/OT 100/55°C)
2nd Stage Separator (DP/OP = 2.2MPag/0.5MPag) & (DT/OT 100/55°C)
Note: both 1st Stage Separators allowed to work in parallel to flow to 3rd Stage Separator
3rd Stage Separator (DP/OP = 0.5MPag/0.2MPag) & (DT/OT 100/55°C)
HP flare stack receipting gas from Test Separator, 1st Stage Separator & 2nd Stage Separator
LP flare stack receipting gas from 3rd Stage Separator
Separate flare header for each (HP & LP) are underground

The new degassing station consists of:
Test Separator (DP/OP = 2.2MPag/1.2MPag) & (DT//OT 125/65-100°C)
1st Stage Separator (DP/OP = 2.2MPag/1.2MPag) & (DT//OT 125/65-100°C)
2nd Stage Separator (DP/OP = 2.2MPag/1MPag) & (DT//OT 125/65-100°C)
Elevated FKOD (flare knockout drum) (DP = 0.35MPag) & (DT 80°C)
HP flare stack receipting gas from Test Separator, 1st Stage Separator & 2nd Stage Separator
Flare header is aboveground (elevated)

As per the contract the existing flare piping should be incorporated into the new flare system

We think that, if the two system (new & existing) are connected together (tie-in will be in lowest point-no other way) the condensate will be accumulated at the tie-in point of the new & existing headers.

We think that due to low pressure of the existing LP flare system, the new flare system should be connected to the existing HP flare system.

Our Contractor is suggesting to add auxiliary facilities (FKOD & unloading pumps) to the existing system, otherwise, leave the idea of connecting both flare systems together. This suggestion to avoid high back pressure on the existing HP flare.

For the existing LP flare, the operating pressure of the 3rd separator is so low that the exhaust gas can only go to the LP flare. In order to keep the function of old station, it is recommended to keep the existing LP flare instead of connecting the exiting LP flare into the new HP flare.


Mohd Yaseen

 

[georgeverghese]

From the information provided:
a) Agree tie in of the existing HP flare header (at its low point) to the new HP flare header is going to cause problems
(i)for the new HP FKOD - probably high velocity liquid slugs resulting in high level trip
(ii)high and erratic backpressure on new and existing PSV's
(iii)erratic operating backpressure at PCV on stage 1 and 2 seps

b) Agree to keeping existing LP flare dedicated to old degassing station 3rd stage sep.

To enable tiein of the old HP flare header to the new, you may most likely have to install a new above ground HP flare collection header for the existing degasssing station, so that all condensate will free flow to the new HP FKOD.

Strange you are still flaring all this gas. In most oil companies, this practice is no longer permitted - most, if not all , flare gas is recovered. Any offgas sent to flare ( due to overload or shutdown of the flare gas recovery unit) is totalised and reported to Operations Management and to state / federal environmental agencies. You may find recovery of the CAPEX for this unit is easily realised in a few years if you can use this gas locally as fuel gas and/or have it exported as sales gas after suitable treatment.

 

[MohdYaseen2010]

Dear george;
thanks for your response

Yes installing new flare header for the existing is the optimum way to solve this problem, but our management don't want to add more cost on the project.

Do you think erratic back pressure will attend on the Existed 1st separator also (it has the same operating conditions as the New separators)

((i)for the new HP FKOD - probably high velocity liquid slugs resulting in high level trip) would you elaborate more on this point

Regarding the wasted gas, part of the gas going to natural flare knockout drum & hence sent to our CPF to be processed for the utilize of the Gas Power Plant.

Mohd Yaseen

 

[georgeverghese]

Condensate will gradually accumulate at the low point of the existing flare header. When there is a transient high velocity gas surge through this header from one or more separators, this condensate will be swept out at high velocity into the new FKOD. This may damage (a) the flare header due to high momentum liquid slug (b) result in high level in the FKOD resulting in facility shutdown.

When there are liquid slugs appearing at the new FKOD, backpressure on all connected separators will rise rapidly, then backpressure will fall off.

If you have a means of recycling this waste gas, high level events will also occur at the feed gas separator / scrubber of the recovery unit due to this awkward arrangement of this existing HP flare header tiein to the new flare header.