SNG - Simulated Natural Gas

Cucumberer

Hi all. I'm trying to determine the chemical formula of Propane-air SNG. Anyone got any data on this? Wondering if it is basically the same as standard Natural Gas - CH4?

EdTheHeaterMan

Not very common in the USA for heating homes unless the gas company does it to supplement their supply when Natural gas demand is extra high. SNG may mean Synthetic Natural Gas or Simulated Natural Gas. I believe that Simulated NG is C3H8 with air added so it will perform as CH4 Not sure how that process is done.

mattmia2

probably just mix it approximately 4 parts air to 1 part propane.

JakeCK

Wouldn't that seriously screw up the air to fuel ratio when it's burned?

mattmia2

JakeCK said:

Wouldn't that seriously screw up the air to fuel ratio when it's burned?

no. that is why the air is added so the energy content per volume is the same.

kcopp

I believe the City of Keene NH distributes their gas system w/ SNG.
https://new-hampshire.libertyutilities.com/keene/residential/about/what-we-do/propane-air.html

Jamie Hall

JakeCK said:

Wouldn't that seriously screw up the air to fuel ratio when it's burned?

Consider. Propane is C3H8; butane, which may also be added, is C4H10. Methane -- natural gas -- is CH4. When you burn methane, you need 2 molecules of oxygen for every molecule of methane. When you burn propane, though, you need 7 and butane takes 9. That extra oxygen has to come from somewhere, and if the gas company doesn't add air to the SNG mix to provide that oxygen, you would have to adjust all the burners everywhere to provide the extra air. NOT something you want to have to do!

JakeCK

Yea you're right about the extra o2. just feels that with an atmospheric appliance it would throw it all off.

Why 7 extra molecules of O2 and not 5 for propane? It looks balanced at 5. Sorry it's been 17 years or so since I last did any chemistry. 

2O2 + CH4 -> CO2 + 2H20
5O2 + C3H8 -> 3CO2 + 4H2O

This also asks the question of sealed combustion. Wouldn't it be possible for the entire system to be designed to supply both the combustion air and fuel in the same pipe so no outside air is required at the appliance? Would that be safer?
Granted it would take a total redesign of basically everything. 

EBEBRATT-Ed

The gas companies have been adding propane to NG for years especially during high demand when they can't keep the pressure up in their crummy old mains that have been in the ground for 100 years.

I installed a large gas burner 4,000,000 btu and was working with the gas company beforehand to determine what pressure was available and what size gas train and regulator we would need. They could only supply 6"wc

I said to the gas co rep "turn up the pressure" He said "we can't, we would give away a lot of free gas"

Old leaking cast iron gas mains in the street. Why they are not required to change this stuff out I don't know

mattmia2

JakeCK said:

This also asks the question of sealed combustion. Wouldn't it be possible for the entire system to be designed to supply both the combustion air and fuel in the same pipe so no outside air is required at the appliance? Would that be safer?

The gas in the pipe having the right mixture to explode would very much be not safer.

When I was thinking about this, I looked at the upper explosive limit for propane to make sure that adding the 4-5 parts oxygen wouldn't bring it below the upper explosive limit.

JakeCK

Good point, wasn't thinking that through, would be fun to watch from afar tho.


The whole idea of piping explosive gas into everyone's homes is pretty dangerous considering all that has to happen is a leak and it has plenty of air to work with. Hit the magic fuel to air ratio and Yippee-ki-yay.


Yes I know things only explode like this in Hollywood. 

mattmia2

JakeCK said:

Good point, wasn't thinking that through, would be fun to watch from afar tho.

Maybe that's what happened in Flint. It seems very questionable that even the state lab couldn't figure out where it leaked from.

EdTheHeaterMan

EBEBRATT-Ed said:

I said to the gas co rep "turn up the pressure" He said "we can't, we would give away a lot of free gas"

Old leaking cast iron gas mains in the street. Why they are not required to change this stuff out I don't know

Who is going to pay for that? If my political representative mandated a law that caused my price for gas to triple so that all the leaks were repaired, I might not vote for them again.

There is a margin of safety that a small leak at 6" WC will not cause a problem. That same leak at 1 PSI will no longer be within the margin of safety. It all comes down to $$$

When that section of town goes from low pressure mains to high pressure mains, the new gas mains will be able to provide higher pressure without leaking. Just don't forget to call 811 if you dig near a High pressure gas main.

JakeCK

ron said:

The whole idea of piping explosive gas into everyone's homes is pretty dangerous considering all that has to happen is a leak and it has plenty of air to work with. Hit the magic fuel to air ratio and...

20 years ago, in the fire department (volunteer), the gas company gave a demo / training session. Demonstrated propane and how rather safe it is...

• vented propane into pitcher of water, than drank the water, no affect, propane does not mix at all with water... i can't remember if there was mercaptan in that though
• vented high pressure propane (20 lb tank no regulator but a pipe setup off the valve) to a lighter, within the room within the building. Extinguished the lighter flame, or nothing happened. Hitting the "magic" air to fuel ration is not as easy as you might think. The gallon gasoline container in your garage/shed is likely more dangerous..

And yet every year you hear about numerous houses exploding, and some times entire cities are set on fire. 

But yes gas cans are dangerous too. I've can happily say I have retired all of my gas lawn implements with battery electric versions. Snow blower, lawn mower, weed Wacker, leaf blower... And I very rarely park my truck in the garage. It fits but not easily. Last time I pulled it in I had less then an inch on both ends and if I was any fatter(I'm only 160) I wouldn't have been able to squeeze out of the drivers side door. In other words there are no flammable liquids in my garage any more.

DJD775

ron said:

JakeCK said:

The whole idea of piping explosive gas into everyone's homes is pretty dangerous considering all that has to happen is a leak and it has plenty of air to work with. Hit the magic fuel to air ratio and...

20 years ago, in the fire department (volunteer), the gas company gave a demo / training session. Demonstrated propane and how rather safe it is...

• vented propane into pitcher of water, than drank the water, no affect, propane does not mix at all with water... i can't remember if there was mercaptan in that though
  
• vented high pressure propane (20 lb tank no regulator but a pipe setup off the valve) to a lighter, within the room within the building. Extinguished the lighter flame, or nothing happened. Hitting the "magic" air to fuel ration is not as easy as you might think. The gallon gasoline container in your garage/shed is likely more dangerous..
  

Remember, like dissolves like, so you shouldn't expect an alkane(non-polar) like propane to have any significant solubility in water(polar).

A 20lb cylinder of propane is not something I would worry about too much. It's when you have a much larger source of propane that empties into your house and pools in your basement.

mattmia2

You hear about it because it is very rare. far more people are killed in car accidents and house fires but they are common so they only make local news

DJD775

mattmia2 said:

You hear about it because it is very rare. far more people are killed in car accidents and house fires but they are common so they only make local news

I agree. I have a friend that is a fire investigator and from the stories I hear from him the most common things are electrical issues, portable space heaters, and battery charging gone wrong.