VDU off-gases are being routed to LP flare header through a water seal drum (VDU ISBL). It has H2S content around 2 mol%. Is it possible to burn it in VDU furnace? Constraint is higher H2S content. Can we use water seal as amine seal to absorbe H2S?
Any other destination of these gases?
Answers
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13/10/2019
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GAURAV BURDE, Bharat Petroleum corporation limited , burdegaurav88@gmail.com
Yes, you can burn it in either a CDU or VDU heater. But, firstly it will have to treated with low pressure difference Offgas Amine absorber.
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22/10/2009
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Prakash Pimparkar, Environmental Consulting Services , prakash.pimparkar@yahoo.in
The H2S contents of 2% is too high to be burnt either through flare or furnace. Burning through flare will cross all pollution limits as no country on earth will allow this as this would result in severe SO2 pollution during proper operation of flare and really toxic conditions in case of flame out or incomplete burning in flare.
The VDU furnace option is no good either as normally the metallurgy of furnace do not allow 2% H2S is fuel gas (you may refer your furnace data sheet for design gas composition.) Also the H2S will get converted to SO2 again not permitted beyond 100 ppm or so.
You can not use water seal to absorb all the H2S on a continuous basis as soon the Amine will get saturated and will not absorb any further H2S ( this will happen in few minutes only)
The best option is to provide an ATU with absorbed/desorber.You would normally have an fuel gas ATU in the refinery and could probably use to clean this gas.
It is advisable to use ATU as you can recover the VDU off gas as fuel gas and the ATU unit would pay for itself say within a year or so (you have not given the quantity). The technology is open art, simple and easy to implement so best of luck !
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21/10/2009
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Raghavendra Sangam, Libra Techcon Ltd., rsangam0504@yahoo.co.in
Check environmental norms. H2S is lethal and is not allowed above 10 ppmv in gaseous effluents. 2 mol% is very high. Even after getting diluted in the main flare header after VDU, it may not be below the limit. And is not destructed completely in the flare.
Water has limited solubility for H2S. Can not remove all H2S in water seal. Amine seal is not advisable. Rich amine has to be removed and replenished time to time. Bets and the only way is to pass the gas through amine absorber column, bring H2S down below permissible limits and send the gas out.
Check VDU furnace design for burning corrosive H2S. In any case, local authorities may not allow disposal of H2S in any way other than proven approved processes such as continuous amine absorption system. Check with a process engineer in a refinery for more details.
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21/10/2009
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Morgan Rodwell, Fluor Canada Limited, morgan.rodwell@fluor.com
You can but you will probably need a small amine column to clean up the gas to meet emissions limits, and you might need a blower to get enough head. I doubt you would get enough H2S removal with a single stage seal drum filled with amine.
If you have a delayed coker or FCC, a small compressor can be used to get into the suction of the wet gas compressor, but some facilities may frown on this as it will allow small quantities of oxygen (air-leaks from VDU) into the coker or FCC fuel gas.
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