5 replies to this topic

[Light]

Dear members,

 

I am currently involved in the engineering of an ethylene cracker. In the entire petrochemical complex, there are three different types of flares:

(i) Process Flare (For combusting hot and cold flare hydrocarbon gases released during an event such as flare control valves opening, relief valves popping, etc.)

(ii) Sour Gas Flare (For H2S and oxygen containing gases released from various sections of the plant like caustic wash towers, spent caustic treatment unit)

(iii) Acetylene Flare (For flaring acetylene containing gases from butadiene extraction and MTBE units)

 

My questions are as follows:

 

(i) What is/are the reasons for having a different flare stack for acid gas and acetylene containing gases, why can't we put them directly in the common flare header going to the process flare?

 

(ii) For the process flare system, we have a cold blowdown drum, which receives cold flare liquids and gases (less than 0 deg C). This drum has a vaporizer in which the cold liquid is vaporized by heating with condensing methanol. The condensed methanol is then revaporized by heating with low pressure steam in another exchanger. My question is that, why can't we directly use condensing LP steam to heat the cold flare liquid instead of having two exchangers with a separate methanol cycle?

 

Thanks.

[Phenol]

Member,

 

Flare system is also function of the gases that are flared.

 

Segregation of flare, particularly acetylene, may be connected with the flame prorogation velocity. It is to be checked. Generally hydrogen is also not flared with other gases for this reason.

 

Regarding usage of steam directly, check the HAZOP finding done for this section. Did they consider any tube leak condition & steam getting into flare side directly discussed. Steam, condensing nature is not acceptable on process side of flare, because condensation can create vacuum condition and sucking in of air/oxgen into the system from the tip. 

 

Rajan

[Light]

Thanks Rajan. Atleast, someone replied to my question. 

[siroos]

Sour gas flare is continues flaring for normal operation and is low pressure flare(the gas is coming from low pressure system).It needs separate system and should not interrupt with other flaring.
For process flare(cold flare) we can use steam as a heating medium directly in vaporizer if no heavy hydrocarbon exist in mixture(not heavier than c3).DIrect heating by steam when heavy hydrocarbon present will block the tubes.Using methanol as intermediate heating medium is more reliable and more safe.By controlling the methanol pressure and then temperature it is possible to have some different temperature in vaporizer.
But when using steam the temperature is fixed.
Also by using methanol the freezing of steam in some situation, is never happened.

[Pham Hong Phuc]

Dear Light

In my understanding, the segregated flare collection systems for corrosive and non-corrosive service have been provided to collect the relief valve release to the flare system. On the another hand, in normal operation, all relief gas not only from sour gas but also from Acetylene  will be burnt at sour gas flare.In case of emergency or the plant shutdown or sour gas in maintenance...all relief gas will be sent to Acetylene flare.From this, the capacity of each flare should be diffirent. Of cours, the sour gas directly send to flare not through a seal drum.

For your second quesion, because i dont know your system so i can not answer your question.

Hope this information for yours

[senthil13]

Apart from process /process safety/compatibility issues.There may be permitting issues if you have all the streams into one flare system. Please check with your environmental department regarding this. 

 

Composition and quantity of flare gases makes a big difference on what type of flare to use.

 

Just my 2 cents.,