12 replies to this topic

[azizhamad]

In our gas plant "especially in gas treating unit" . Flashed gas is one of products from fuel gas stripper "after the flash drum". We utilize this flashed gas to be used as fuel gas in the boilers but recently, we have been experienced a sulfur deposit in tubes boilers.

The questions are:

1. Can we prevent this deposited from happing again? "we checked H2S in fuel gas , it's less than 10 ppm"

2. Is the boiler very sensitive "in case of fuel gas composition changed???"

3. What is the general practice that’s followed worldwide to deal with flashed gas?

4. Is there any way to utilize the flashed gas inside the plant?

5. If you were in my place what you will doJ?

[azizhamad]

is it so difficult ?

[azizhamad]

any support ?

[vista]

aziz,

Are you taking about flash tank of Dehydration unit or some natural gas sweetening plant?

[Dacs]

I tend to believe the gas comes from either Sulfur Recovery or Tail Gas Treatment Unit.

Edited by Dacs, 25 September 2012 - 07:07 PM.

[Dacs]

Can we prevent this deposited from happing again? "we checked H2S in fuel gas , it's less than 10 ppm"

You said sulfur deposit. Formation of elemental Sulfur reacts at very high temperature (>800°C if I'm not mistaken) so the offgas streams must have come from a process similar to SRU or TGTU (as with my last post).

Or is it really sulfur? Have you had it qualitatively checked? Is it possible that it may be ammonium salts (from NH3)?

Is the boiler very sensitive "in case of fuel gas composition changed???"

That depends whether if you rely on offgases as your primary source of fuel. My thinking is normally boilers use fuel gas as primary source of fuel and this is just supplemented by offgas from various refinery units.

That may or may not be the case in your system, but anyhow it's the HV (heating value) that matters in boiler operation. Changes in composition may affect the heating value of your fuel gas. By how much? That I can't answer.

What is the general practice that’s followed worldwide to deal with flashed gas?

General practice is you normally treat the flashed gas with amine to scrub the sour gases that may cause emission problems in your boiler.

In your case, without any idea on how your plant works, my guess is as good as anyone's here in the forum.

If you were in my place what you will doJ?

I'll check for ammonia content of your offgas. That's just me though

Good luck!

[azizhamad]

thanks Dacs for your support

the fuel gas is one of by-product from gas sweetening unit "treating unit"

[azizhamad]

you may find the simple drawing in the following link
http://www.4shared.c.../_online.html?#

your support is highly appreciated

[Dacs]

Upon seeing your schematic, there's less reason to believe that you're having sulfur deposits.

I still stand in my previous answer. Have the deposits analyzed in your lab. Although if that is flashed gas from Rich Amine, it may contain little NH3.

Nevertheless, check it for NH3 concentration and analyze the deposits for ammonium salts.

[RoyenG]

Hi Aziz,

1. Can we prevent this deposited from happing again? "we checked H2S in fuel gas , it's less than 10 ppm"
you may prevent this deposited if you can provide lower H2S content in the flashed gas. in my opinion, the best way will be by changing source of the fuel gas to the boiler from the flashed gas to the treated gas from your gas treating system, say outlet of your Acid Gas Removal Unit (treated gas), because you will always gambling with H2S content if flashed gas from the rich amine is used as the fuel gas.
if you have low H2S content in your flashed gas, that's mean your amine does not absorb H2S, or your treated gas contains more H2S.
but if you have high H2S content in your flashed gas, that's mean your amine has remove acid gas from your treated gas, but later there will be another problem, H2S in the fuel gas to boiler.

2. Is the boiler very sensitive "in case of fuel gas composition changed???"
yes it is, that's why Boiler vendor always request all possibility of fuel gas composition to see the range of LHV they have and also maximum acid gas content.

3. What is the general practice that’s followed worldwide to deal with flashed gas?
if if is not economic enough to be treated, sent it to the flare.

4. Is there any way to utilize the flashed gas inside the plant?
recycle back to the inlet gas treatment unit if need to be used as the fuel gas or it could be used as the fuel gas for the flaring system with not too big sensitivity in the H2S content.

5. If you were in my place what you will doJ?
checked how long is the time range for the H2S to form deposit,
checked with the boiler vendor what is the impact of this deposit
propose to change the source of the fuel gas to boiler to not to use the flashed gas if possible.

Regards,
Royen

[Dacs]

Just to comment on the treatment of flashed gas, if you check the schematic provided, the flashed gas is usually treated (check the "inverted boot" area on top of the flash drum, it's in fact an absorber column with trays) with Lean Amine before sending it to downstream.

I've seen this in a number of projects I've been involved with.

It's a matter of economics if you're going to send offgas to flare. Some companies will opt for maximum recovery of HCs produced.

[RoyenG]

with respect to Dacs experience,

that is not treated gas, flashed gas shown in the sketch is from the rich amine, which treated gas must be on top of the column/contactor upstream of this flash drum.

or may be if it is mis-understanding, treated gas i mean is the sweet gas (sour gas after contacted with lean amine).

[Padmakar Katre]

In our gas plant "especially in gas treating unit" . Flashed gas is one of products from fuel gas stripper "after the flash drum". We utilize this flashed gas to be used as fuel gas in the boilers but recently, we have been experienced a sulfur deposit in tubes boilers.

The questions are:

1. Can we prevent this deposited from happing again? "we checked H2S in fuel gas , it's less than 10 ppm"

Hi,

The answer is "Yes" but it calls for lot many inputs such as the fuel gas quantity, specifications, margin in current fuel gas treatment unit (generally amine treatment). H2S level of 10 ppm is average value or one time sample after your boiler has issues.

2. Is the boiler very sensitive "in case of fuel gas composition changed???"

You need to discuss this with the material specialist with the MOC data and fuel gas composition (mainly acid gases partial pressure)

3. What is the general practice that’s followed worldwide to deal with flashed gas?

It is treated with to remove the acid gases/other impurities to a certain quality specified by the end users.

4. Is there any way to utilize the flashed gas inside the plant?

Depends on flashed gas composition and economics involved.

5. If you were in my place what you will doJ?

The answers to all the questions above will answer this last question.

Thanks

Edited by Padmakar, 12 December 2012 - 04:01 AM.