2 replies to this topic

[Atul Borse]

This is typical case of High H2S (10 to 12%) and CO2 (4 to 5%)in Natural Gas in Off Shore Field. Normal practice of producing Power in Off Shore Field is by using Gas Turbines. Here I would like to hear from experts what are the practical / feasible ways of producing power from such high H2S gas in the off shore field. I am proposing some of the following options and request you all to share your experience for the same. Any additional suggestions / experiences are welcomed. The tentative amount of Fuel Gas Requirement is 25 MMSCFD. Gas Turbine Power capacity is 75 MW.
1) Use the same high H2S Natural Gas as fuel for the Gas Turbine.(Experts opinion on hot gas path corrosion, Turbine vendors todays state of art technology accepts how much maximum H2S and Reliability of Machine)
2)Use suitable Sweetening Process to reduce H2S to acceptable level of Gas Turbine Fuel. (Experts opinion on which method should be used for sweetening in off shore, how the removed H2S shall be further processed and where to discharge it safely and Safety concern).
3) Find out a sweet gas well in nearby area and put a well their and bring the good quality fuel gas by sub sea pipe to this high sour field.
4) Generate power On shore by power plant and use sub sea cable to transfer power to off shore and run the off shore platform. (Expert opinion on amount of KVA for such power, any danger / safety concern in sub sea cable etc).
In my opinion many small sour fields are available in the world which can not be developed due to above problems. Let us approach this problem together.

[daryon]

This is an interesting field development post, I think you would certainly require gas sweetening with the H2S concentrations you are anticipating. You suggest this is a small development but your power generating capacity is quite large 75 MW. What is using all this power? Compression trains? What gas flowrates and export pressures are we talking about?

If you are planing to sell your gas you're unlikely to get much money for it if 15% of the gas is H2S or CO2, which will have to be removed onshore. Compressing and exporting these components is a large waste of energy and will cause corrosion problems.

Further information that would be useful:
a) How far offshore is the field?
Are you exporting via pipeline?
c) Do you have a sales gas specification to meet?
d) IS there condensate to produce also? What's the GOR?


1)It is typical to limit H2S to a concentration of less than approximately 20 ppmv. Turbines may be able to burn higher concentrations (H2S is flammable) but corrosion and SOx emissions poses limits. There is also the health perspective GPSA handbook gives a figure of 10 ppmv as the thershold limit value for prolonged exposure. Concentrations of >1000 ppmv can cause death in 30 minutes. With the H2S and CO2 concentrations the process fluids will be very corrosive, with Chloride and Sulfide Stress Corrosion Cracking an additional concern.

2) I recommend you read through the GPSA Handbook for the different techniques for gas sweetening. Amine units have been successfully installed and operated offshore for H2S & CO2 removal, and the Claus process to recover the sulphur. There is a lack of data in your post to discuss this further.

3) Good option, if there's sweet gas nearby shouldn't you be focusing you field development plans around recovery of this gas in preference of the sour gas?

4)Depends how far offshore you are and how much voltage loss you will experience along the transmission line. Probably not feasible, you will have high CAPEX (probably comparable to GT) with this option as the cable and installation is expensive, and also increased OPEX as you have to pay for electricity.

I think your right, a lot of these sour gas fields are simple not economically viable to develop. Still always good to investigate.

rgds,
daryon

[Rock_Dock]

This is typical case of High H2S (10 to 12%) and CO2 (4 to 5%)in Natural Gas in Off Shore Field. Normal practice of producing Power in Off Shore Field is by using Gas Turbines. Here I would like to hear from experts what are the practical / feasible ways of producing power from such high H2S gas in the off shore field. I am proposing some of the following options and request you all to share your experience for the same. Any additional suggestions / experiences are welcomed. The tentative amount of Fuel Gas Requirement is 25 MMSCFD. Gas Turbine Power capacity is 75 MW.
1) Use the same high H2S Natural Gas as fuel for the Gas Turbine.(Experts opinion on hot gas path corrosion, Turbine vendors todays state of art technology accepts how much maximum H2S and Reliability of Machine)
2)Use suitable Sweetening Process to reduce H2S to acceptable level of Gas Turbine Fuel. (Experts opinion on which method should be used for sweetening in off shore, how the removed H2S shall be further processed and where to discharge it safely and Safety concern).
3) Find out a sweet gas well in nearby area and put a well their and bring the good quality fuel gas by sub sea pipe to this high sour field.
4) Generate power On shore by power plant and use sub sea cable to transfer power to off shore and run the off shore platform. (Expert opinion on amount of KVA for such power, any danger / safety concern in sub sea cable etc).
In my opinion many small sour fields are available in the world which can not be developed due to above problems. Let us approach this problem together.

It sounds like you will need to use an amine to remove the H2S (and CO2 if you are compressing the gas).