Gas Quality High Btu Swings 1

[McMoe]

I am trying to identify what is the operating impact of varying Btu in a natual gas fuel source to process or power generating loads. I am talking about swings of 60 - 70 Btu within hours of a day. Please state your concerns and experience with problems if available.

 

[SAFC]

It rather depends on what composition changes (Inerts and / or C's) are causing the heating value of the gas to change? Do you have typical gas analysis range?

 

[pablo02]

What percentage in heating value does 60 to 70 Btu/CF represent? At a large gas-fired plant, our heating value was typically 960 to 1020 Btu/CF and had no significant impact other than efficiency (due to how the combustion controls were set up) -- we were down stream of a stripper plant (removes high Btu 'goodies' like propane, etc); it tripped off once and as I recall (it's been 25 years or so), the Btu went to about 1200 in a matter of seconds; fortunately the operator biased his air up immediately when he got the call -- rode the swing out without any combustion upsets....

chemically, the higher Btu gas requires more air (volume) than a lower value for combustion.. I guess for your consideration, you need to make sure that your combustion controls are set up to allow sufficient air for the higher Btu content

 

[ElwoodGreen]

McMoe, It sounds like you are on the delivery side of the situation, and you want to know what problems you are going to cause someone like me on the recieving end. My landfill gas fuel averages about 540 Btu/scf SLHV. If it varies by more than about 5%, my fuel system can't compensate.

If it varies too high, I can adjust my fuel ratio controller parameters and keep operating, as long as the plant operator sees the change before the engine goes into detonation and shuts down. If the detonation sensing system fails, then I experience severe engine damage.

If the fuel heat content drops more than 5%, then my fuel system can't supply enough to make full power. Therefore, the plant can't produce rated output. If my power is being sold via contract or is pre-scheduled into the grid for the open market, then I have to buy replacement power. If the market is high, I am going to be real mad.

For either case, I would be on the phone to my GasCo right away to find out what is going on.

Even with pipeline fuel, assuming just under 1000 btu/scf, your 60-70 Btu change would be outside the 5% variance allowed by my engine's fuel system. Your inability to control fuel quality is going to impact your customer negatively, if his system is similar to mine.