5 replies to this topic

[mav9rick]

Hi,
I am looking to define a criteria to determine which relief streams should discharge to the Acid Gas Flare. Does anyone know what is the typical criteria that is used when deciding if a particular stream should be routed to acid flare or normal (HHP/LP) flare? I am looking for some quantitavice criteria to be used as a cutoff, such as partial pressure of H2S or mole fraction in the vented stream. Also, I would like to know the reason behind the suggested criteria.
Thanks in advance
K

[fallah]

Hi,
I am looking to define a criteria to determine which relief streams should discharge to the Acid Gas Flare. Does anyone know what is the typical criteria that is used when deciding if a particular stream should be routed to acid flare or normal (HHP/LP) flare? I am looking for some quantitavice criteria to be used as a cutoff, such as partial pressure of H2S or mole fraction in the vented stream. Also, I would like to know the reason behind the suggested criteria.
Thanks in advance
K

mav9rick,

Relief streams that need "sour service" should be routed to acid gas flare network.On the other hand "sour service" refers to a material that shall be NACE MR0175 compliant as minimum.

Thus, sour service conditions shall be evaluated considering H2S partial pressure and the total pressure (as per NACE MR0175 requirements).

Fallah

[mav9rick]

Thanks for your input Fallah. However I am not entirely satisfied that NACE criteria for sour service applies to the Flare headers as such. There are other numerous issues such as ammonium bisulphite salt formation, elemental sulfer deposition and water condensation that goes into the decision making process of where to rout the vent gasses. Also, NACE stipulates that MR0175 criteria does not apply to low pressure gas (<65psi). The Flare header is going to be low pressure and therefor I cannot directly apply the rule.
Also, the gas that we are venting does not have free water present and therefore rules are presented in NACE MR0175 para 1.41 is hard to apply.
I am looking for some industry accepted practices (based on the H2S concentration in vented gas or the source of emission) that are used for deciding wheather to rout the gas to normal flare or acid flare.
cheers

[rasprocess]

Hi.
usually gas streams which have more than 10%(mole basis) H2S, are known as acid gas and routed to flare system.

[Propacket]

Hi,
I am looking to define a criteria to determine which relief streams should discharge to the Acid Gas Flare. Does anyone know what is the typical criteria that is used when deciding if a particular stream should be routed to acid flare or normal (HHP/LP) flare? I am looking for some quantitavice criteria to be used as a cutoff, such as partial pressure of H2S or mole fraction in the vented stream. Also, I would like to know the reason behind the suggested criteria.
Thanks in advance
K

What is the composition of your gas?
Which gases should be sent to Acid Gas Flare. In my opinion, It depends upon your own philosophy. I worked on a project in which our client required Acid gas Flare for “appropriate steams”. We recommended them that all acid gas steams should be sent to the acid gas flare. You disagree? Let me explain.
If you talk to flare experts ( I am not), they will tell you that acid gas flaring is never a good idea.
Reason: If you flare acid gases, you will be emitting a large amount of SO2 (Get ready for acid rain).
However, in most instances, acid gases are difficult to burn completely to SO2 under operating conditions of flare. The best way to handle acid gases is to use a thermal oxidizer with supplement fuel gas to achieve high temperatures enough to oxidize the H2S.
In a flare, oxidizing situation can be created by sending low H2S (high HCs/high heating value). That’s why we decided to send all the acid gas streams to the acid gas flare despite the fact some of which had small amount of H2S.
So remember, if you only send rich acid gases (and no HC gases) to the acid flare, there will be incomplete conversion to SO2 and formation of elemental sulfur. I would recommend a proper thermal oxidizer.
Even SO2 emission is not allowed in most of the countries. A sulfur recovery unit is the best solution to get rid of acid gases.
P.S. With Acid Gas Flare, You need to perform a dispersion analyses along with the radiation analysis, however, the dispersion analysis will govern the flare height.

Edited by Propacket, 01 November 2012 - 08:49 AM.

[ankur2061]

mav9rick,

Quantitative criteria are not generalized. These are company or organization specific. I know BP guidelines for hydrogen sulfide rich waste gas streams where they have quantitatively defined how to treat hydrogen sulfide rich waste gas streams with different concentrations of hydrogen sulfide. BP provides the following guidelines:

% volume by H2S Disposal of Waste Stream

Less than 1% Atmosphere (Note 1)
1-2% BP to approve the disposal method
2-10% Flare
>10% Flare, with separate line

Note 1: The waste gas stream may be disposed to atmosphere only if a dispersion analysis proves that no accumulation of toxic or flammable waste gases can occur endangering life or the environment and the atmospheric emission is in conformance with local emission laws for air pollutants through atmospheric vents.

Note that these are guidelines only and an in-depth study is required to ascertain how to dispose any waste gas stream to the environment.

The current trend is not to release any waste gas streams to the environment without treatment (flaring / thermal oxidizers) due to long-term effects of waste gases to the environment such as acid rain and green-house effect of hydrocarbon gases such as methane.

Hope this helps.

Regards,
Ankur.