Problem Of Wet Fuel Gas From Fuel Gas System

[asade]

Hello,

Am troubleshooting on the cause of wet gas supply to gas generator from the fuel gas system at a flowstation. the fuel gas skid consists of the FG scrubber and FG filter separator. The gas supply is from the gas outlet of HP Separator.

Kindly advise me about possible scenarios taht can lead to the problem and ideas on how it can be mitigated.

Am considering the introduction of heater to the system.

Your input is highly appreciated.

Regards,
AOA

I am what I am by His grace

 

[LittleInch]

Errr, water saturated gas coming off the scrubber???

To get dry gas from a gas supply which has water vapour in t you need some sort of de-hydration equipment. The scrubber and filter separator will remove the liquid drops, but the water still contained in the gas will remain and as temperature drops this will condense further down the line.

Please advise what the gas supply is and some details of it, but normally you either need to send it through a MEG / TEG unit, a dessicant dryer or heat it up to go above the condensation temperature.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[zdas04]

asade,
You didn't say much about your process at all. Is it a single wellsite with a 35 hp compressor, a BCF/day cryogenic gas plant, or something in between? This is one where scale is kind of important. For wellsite-scale loads, you can often get adequate fuel gas from a deliquescent dryer which results in about a 20°F dew point depression. Bigger loads can served with a mole sieve (if you can use the waste heat to regenerate it, if not they tend to be non-starters). If you go to TEG/MEG in a system with very low wellhead pressures then there is so much water vapor in the gas that the fuel load for the reboiler will be orders of magnitude greater than your base fuel load.

Some unsolicited advice? Your beliefs are your own concern, but when asking strangers for advice it is generally a good idea to minimize information that is not related to the question. Some people will be attracted by your signature. Others won't care. Others will be put off by it. It would be unfortunate if THE person who can answer your question is in the last group. The risk/reward balance is a personal choice, but when asking strangers from all over the world for free consulting I know how I would fall on that analysis.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[georgeverghese]

If you are running an internal combustion gas engine with this gas, it is acceptable to use dewpoint gas, provided there are no low points in the piping leading to the generator i.e. the supply line to the gen set must slope continously back the filter sep. If you dont have this feature, there are 2 choices (a) install low point drip legs which should be manually or automatically drained out before startup or (b) re arrange the piping to avoid the low points, which may involve relocating the filter sep. Option b would be better since you dont have to rely on operating procedures.

The filter sep should be fitted with an independant LSHH safeguard in addition to the auto level control. Be wary of quirky "cost saving" arrangements to drain out liquids from filter seps, which may result in liquids entrainment into the gas exit stream. Obviously a PDIA H is necessary also to remind operators to change out the filter elements.

Fuel gas to gas turbines should typically be dewpoint conditioned (by at least 10degC margin to min ambient temp) and superheated by some 10-15degC or so, referencing the min - max supply fuel gas supply press range.