Process air coil Quencher

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mohsinmkr
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Process air coil Quencher

Post by mohsinmkr » Wed Sep 13, 2017 3:50 am

Hey,

We are operating Topsoe design Ammonia Plant, due to change in furnace fuel gas composition, Protection steam remains lined up in PAC coil to maintain its temperature. average flow of steam is ~15 tph. Is it possible to replace steam with quencher by lining up BFW in coil during normal operation only and Steam will remain there for tripping case? has it be done somewhere in world?

debjyoti0047
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Re: Process air coil Quencher

Post by debjyoti0047 » Wed Sep 13, 2017 5:55 am

Hello Sir,

Normally BFW to steam drum temperature is around 250-270 degC (after preheating, it is still in sub-cooled form) and pressure is maintained at around 120-130 Kscg. The saturation temperature at this pressure range is 320-325 degC.

That means if we inject BFW in the PAC coil, a two-phase flow will occur in the coil and the liquid BFW drops might prove detrimental to the coil's mechanical integrity as a result of hammering and turbulence caused by high density liquid phase. It is better to consult the coil designer / OEM to confirm about the equipment's resilience towards such a phenomenon and then take any decision.

Also liquid water must not enter downstream shift reactors, especially LT converter.

Regards
Debjyoti Ghosh

mohsinmkr
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Re: Process air coil Quencher

Post by mohsinmkr » Thu Sep 14, 2017 8:09 am

debjyoti0047 wrote:
Wed Sep 13, 2017 5:55 am
Hello Sir,

Normally BFW to steam drum temperature is around 250-270 degC (after preheating, it is still in sub-cooled form) and pressure is maintained at around 120-130 Kscg. The saturation temperature at this pressure range is 320-325 degC.

That means if we inject BFW in the PAC coil, a two-phase flow will occur in the coil and the liquid BFW drops might prove detrimental to the coil's mechanical integrity as a result of hammering and turbulence caused by high density liquid phase. It is better to consult the coil designer / OEM to confirm about the equipment's resilience towards such a phenomenon and then take any decision.

Also liquid water must not enter downstream shift reactors, especially LT converter.

Regards
Debjyoti Ghosh
Thanks sir...we have BFW available at 60 kg/cm2 and 130 C. I am talking about normla plant operation. During start / Stop, steam will be lined up as per original design.

debjyoti0047
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Re: Process air coil Quencher

Post by debjyoti0047 » Thu Sep 14, 2017 8:35 am

Sir, I too was referring to normal plant operations. Even at 60 Kscg and 130 °C BFW will be in liquid phase, so PA and BFW will make a two phase flow.

mohsinmkr
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Re: Process air coil Quencher

Post by mohsinmkr » Thu Sep 14, 2017 9:06 am

debjyoti0047 wrote:
Thu Sep 14, 2017 8:35 am
Sir, I too was referring to normal plant operations. Even at 60 Kscg and 130 °C BFW will be in liquid phase, so PA and BFW will make a two phase flow.
Ohh Ok Thanks alot

rajneesh_jauhari
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Re: Process air coil Quencher

Post by rajneesh_jauhari » Mon Sep 25, 2017 4:25 pm

Dear
Can u provide the process conditions of the PA coil and S/C ratio & plant capacity. Dog house top Flue gas temperature and Reformer process outlet temperature.
Rgds
Rajneesh
mohsinmkr wrote:
Wed Sep 13, 2017 3:50 am
Hey,

We are operating Topsoe design Ammonia Plant, due to change in furnace fuel gas composition, Protection steam remains lined up in PAC coil to maintain its temperature. average flow of steam is ~15 tph. Is it possible to replace steam with quencher by lining up BFW in coil during normal operation only and Steam will remain there for tripping case? has it be done somewhere in world?

chinh
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Re: Process air coil Quencher

Post by chinh » Wed Nov 21, 2018 8:44 am

Hi
I think you can use Protection steam

bedmonds
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Re: Process air coil Quencher

Post by bedmonds » Wed Nov 28, 2018 2:03 pm

Hi,
Regarding this situation, making a bunch of assumptions re: plant size and using typical convection bank details for Topsoe plants I have the air coil temperature being reduced by about 55 deg and to do so with 130 deg BFW would require 2500 kg/h of BFW which would only increase dewpoint of the air to around 120 deg C so well below the air temperature which would cooled from 240 deg to about 148 so I think it is doable but require good atomization of the BFW. There are licensors who have a cold and a hot air coil that have attemperation between the two coils and there are good desuperheating valves for this application (Narvik-Yarway for example). Since BFW contains more chloride than steam there is a small price to pay in terms of LTS catalyst poisoning rate. I don't know if any licensor provide this solution when there is only one air coil. The driving force to fully evaporate the BFW is rather small to be 100% sure no water enters the coil.

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