Eng-Tips is the largest engineering community on the Internet
Intelligent Work Forums for Engineering Professionals
-
Congratulations waross on being selected by the Tek-Tips community for having the most helpful posts in the forums last week. Way to Go!
Looking for a natural gas additive (Combustion improver)
- Thread starter lombardo
- Start date
- Thread starter
- #3
Yes, but adding liquid to dry NG is generally not a good idea. What liquids came with it from the ground have been taken out for a reason. Standard burners would require modification, as they are built for typical NG Btu content, you would increase pressure drops in handling lines, not to mention create some type of 2-phase flow (slugging, possible vapor locks). Compressors don't like liquids either. Just about any device made for pure NG would have to be modified, making its ultimate usefullness doubtful.
You could add gasoline, but that gets pretty expensive if you want to add enough to make a difference.
Seriously, gas ain't liquid. With a liquid, you can add chemicals to do most anything from controlling salt to enhancing combustion. With a gas the tendency is for any liquid atomized into the flow to eventually (nanoseconds? microseconds? not very long) coalesce into larger drops and settle to the bottom of the pipe. I've seen hundreds of different chemicals added to thousands of natural gas lines and have never seen a single case where it achieved the desired results.
The common scenario is for people to have a corrosion failure in part of their gathering system (due to localized conditions) and start adding chemicals to prevent a recurrence. Sometime in the future (months, generally not years) they'll start looking at their upstream line pressure and find that it has gone up dramatically. If the lines are piggable and they can make themselves analyze the liquid they find that the corrosion chemical has come home all at once. For a non-piggable line they have very few diagnostic options but eventually either install more compression or stop the chemicals.
Gas simply lacks the specific mass (density) to transport liquids any significant distance or with any reliably repeatable results. I don't think your octane enhancer has a chance.
David
Seriously, gas ain't liquid. With a liquid, you can add chemicals to do most anything from controlling salt to enhancing combustion. With a gas the tendency is for any liquid atomized into the flow to eventually (nanoseconds? microseconds? not very long) coalesce into larger drops and settle to the bottom of the pipe. I've seen hundreds of different chemicals added to thousands of natural gas lines and have never seen a single case where it achieved the desired results.
The common scenario is for people to have a corrosion failure in part of their gathering system (due to localized conditions) and start adding chemicals to prevent a recurrence. Sometime in the future (months, generally not years) they'll start looking at their upstream line pressure and find that it has gone up dramatically. If the lines are piggable and they can make themselves analyze the liquid they find that the corrosion chemical has come home all at once. For a non-piggable line they have very few diagnostic options but eventually either install more compression or stop the chemicals.
Gas simply lacks the specific mass (density) to transport liquids any significant distance or with any reliably repeatable results. I don't think your octane enhancer has a chance.
David
I am just thinking out loud but couldn't you just add some NG heavies to the low BTU NG. So add some pentane or butane to the Methane-ethane mix to bring up the BTUs. You would have to worry about adding too much but your should eaily know the final BTU contant with just analysing the gas and Pentane and Butane remain gaseous at certain pressure and temperatures. There is obvious draw backs to this and where you can get it eaily I don't know but it is only and idea.
What do you think zdas and dcasto?
gsteng
What do you think zdas and dcasto?
gsteng
Its low Btu because its got N2 or CO2, or air or something other than 100% ng. Why not just add more natural gas to bring up the NG% ???
BTU content does not increase octane rateing, ie increased efffiency from running a higher compression ratio?supercharged engine that the OP desires.
Adding natural gas heavires will lower the octane. Iso Butane is 98 octane, normal pentane is 62 octane, iso butane is very valuable commodity, don't want to burn it.
When we run 1350 BTU/cf field gas, we have to retard the ignition, lower the boost and unload the engine from the nameplated Horsepower. Instead, we send back the leanest gas we have back to the fuel so we can load up the engine. Catapillar and Waukesha have a fuel rateing program that will take a gas composition and rerate the engine from its designed 1000 BTU/cf to the new composition.
Adding natural gas heavires will lower the octane. Iso Butane is 98 octane, normal pentane is 62 octane, iso butane is very valuable commodity, don't want to burn it.
When we run 1350 BTU/cf field gas, we have to retard the ignition, lower the boost and unload the engine from the nameplated Horsepower. Instead, we send back the leanest gas we have back to the fuel so we can load up the engine. Catapillar and Waukesha have a fuel rateing program that will take a gas composition and rerate the engine from its designed 1000 BTU/cf to the new composition.
dcasto,
lombardo asked "I want to know if already exist a good additive (combustion improver) for natural gas, "
Wouldn't increasing the BTU content improve the combustion? Even thought it would not increase the octane?
I understand what you are saying about the problems with high BTU content, we also face the same issues and I did not know about what you said about octane rating. But I am making the assumption that for some reason (CO2, N2...) lombardo has a low btu gas that he is having trouble with. THat being said if he has less than 1000BTU/cf he should addres the removal of the non combustibles before attempting to add some high dollar heavies.
The cost factor aside, would adding pentane or butane help improve combustion? or would there be other issues I am not aware of?
lombardo asked "I want to know if already exist a good additive (combustion improver) for natural gas, "
Wouldn't increasing the BTU content improve the combustion? Even thought it would not increase the octane?
I understand what you are saying about the problems with high BTU content, we also face the same issues and I did not know about what you said about octane rating. But I am making the assumption that for some reason (CO2, N2...) lombardo has a low btu gas that he is having trouble with. THat being said if he has less than 1000BTU/cf he should addres the removal of the non combustibles before attempting to add some high dollar heavies.
The cost factor aside, would adding pentane or butane help improve combustion? or would there be other issues I am not aware of?
Solar turbines can burn gas with 600 BTU/cf. I've seen gas engines burn 600 BTU/cf gas. We had boilers using 700 BTU/cf gas. The gas company in my area dilutes natural gas with air down to 930 BTU/cf.
To remove inerts can be quite expensive with N2 being the most expensive so injection of high btu componets is better.
I've injected propane to increase BTU/cf because it was in the contract that the gas had to be 950 BTU/cf, but more importantly, the gas had to meet certain Wobie or Wobbie index values.
To remove inerts can be quite expensive with N2 being the most expensive so injection of high btu componets is better.
I've injected propane to increase BTU/cf because it was in the contract that the gas had to be 950 BTU/cf, but more importantly, the gas had to meet certain Wobie or Wobbie index values.
If you need more BTU/CF add propane. It's easy to handle and also has a high octane value. Pentanes injected will cause an engine to knock because it has low octane number. Iso butane has a high octane, but its very expensive.
You will have a heck of a time controlling the BTU content and therefore the the AFR when mixing propane or other heavier HC's. Be ready to derate your engines HP. Most engine manufacturers have methane index computers to adjust the AFR (or ECU) based on a given gas composition.
You will have a heck of a time controlling the BTU content and therefore the the AFR when mixing propane or other heavier HC's. Be ready to derate your engines HP. Most engine manufacturers have methane index computers to adjust the AFR (or ECU) based on a given gas composition.
- Status
Similar threads
- Question
- Question
- Locked
- Question