LPG (Propane) to CNG Conversion for Stove – Anyone Done It?

[Doug in Lakeview]

We are currently restoring a new to us 1984 Beneteau First 38. It has a mid-1980’s vintage propane (LPG) 2 burner stove with oven manufactured by ELECTROLUX. It is stainless steel, gimbaled and still in “like new” condition. Apparently not used much. It is currently set up with propane as fuel with propane locker in the port lazarette. The storage locker has the required gas “drain” to allow heavy propane gas to escape from the locker.

We are considering changing over from propane (LPG) to CNG. Has anyone done this?

Since the LHV (Low Heating Value) of LPG and CNG are different, I would expect that it might be necessary to change the jets on the burners where the fuel and air are mixed. When you change over a cooking stove or gas furnace in your home (from LPG to natural gas or reverse) you need to change the jets. I would expect the same when changing from CNG to LPG or the reverse for a marine stove.

Why CNG? Here in Chicago many of the taxis use CNG for fuel so refilling tanks will not be a problem. With the abundance of natural gas here in the USA, I expect both LNG & CNG to become popular fuels for buses, taxis, 18 wheelers, etc. CNG filling stations will become more common.

CNG, which is mostly methane (CH4) and LPG, which is mostly propane (C3H8) & butane (C4H10) have drastically different vapor densities. CNG, lighter than air, will rise and dissipate if there is a leak while LPG, heavier than air, will descend to low points, accumulate, & concentrate to the point where the mixture can become explosive if there is an ignition source.

Also, CNG, which is mainly derived from natural gas, will probably continue to be rather inexpensive here in the USA while LPG which is mainly propane and butane will be more expensive since it is a feedstock that can be processed/upgraded to more valuable products.

 

[Ross]

Re: LPG (Propane) to CNG Conversion for Stove – Anyone Done

The cost of the conversion will exceed a lifetime of use savings. The heat value of propane(LPG) far exceeds that of natural gas per unit volume or unit weight and the CNG cylinder will likely exceed the weight of the LPG cylinder.

 

[higgs]

Re: LPG (Propane) to CNG Conversion for Stove – Anyone Done

IMHO you are going to a lot of trouble for nothing. For the amount of gas you are going to use over the next several years the savings would not cover the expense and trouble of conversion. I usually cruise 3 to 4 weeks each season and have filled my small propane tank once in the last 9 years.

 

[mitiempo]

You will also have to have a place to store the cng cylinder outside the cabin. It is the size of a scuba tank.

 

[Bill Roosa]

converting to CNG

You can safely store the CNG tanks inside the cabin. CNG is lighter than air so there are no "locker" requirements. Hunter does this on several models.
To convert you will need a two stage regulator, high pressure to go from the tank (3000+psi) to the low pressure regulator (which is just your old propane regulator adjusted for the new delivery pressure BTW), a tank filler adapter (they don't come with the CNG gas pump connector so you have to make one, see photos), the tanks, some high pressure plumbing stuff to connect to it all together and connect to a dedicated emergency vent line (goes through a thru hull and vents the tank if it gets too hot)
I switched from CNG to propane and did not have to re-jet the stove. I did have to turn the delivery pressure down a tad on the regulator though.
you do not need a locker or solenoid cut off valve.
IMHO the cost of the tanks (if you can find them) will make this a non starter as you will never be able to recover your cost in the life of the boat. Note that there are lots of tanks out ther but they are very large and very heavy. you are looking for a "20 hour bottle"

 

[Bill Roosa]

Re: LPG (Propane) to CNG Conversion for Stove – Anyone Done

Also, you need to check your local CNG gas station and check the delivery pressure. There are 3200 and 3600 psi stations. Some have both and 3600 is becoming the standard. You can buy the tanks in a verity of working pressures. You can't take a cheap 1800 psi tank and connect it to a 3600 psi pump. doing so will rupture the tank and ruin your day and everybody else at the station.

 

[Benny17441]

Re: LPG (Propane) to CNG Conversion for Stove – Anyone Done

It might become a problem finding CNG refills. It is true they are setting up vehicle refill stations but it is also evident that these stations for safety and liability concerns will refuse to accept the use of adapters to fill portable tanks. Yes people sneak in and charge tanks but as soon as an accident happen the penalties will get too stiff to risk. CNG is stored at very high pressure. At a time when most people are forced to consider switching to propane from CNG to go the other way I do not think it is wise move.

 

[walmsleyc]

Went the other way ...

I converted from the factory CNG system on my Hunter Legend 35 to LPG. It was a necessity. One by one, the places that were willing to fill my tank either closed or refused to fill them. I thought about getting a second tank, so I wouldn't be stuck if one ran out. I found a valve, but couldn't easily find a tank with the correct threads. for the LPG, I change the jets in the stove, and put in all the necessary safety solenoids, sensors, storage, etc. needed. Cost a bunch, but at least it's always easy to find a place to fill.

I now have a CNG tank, regulators, spare tank shutoff value looking for a home though.

 

[mitiempo]

You can safely store the CNG tanks inside the cabin. CNG is lighter than air so there are no "locker" requirements.

Some surveyors disagree with that.

 

[Stu Jackson]

Re: LPG (Propane) to CNG Conversion for Stove – Anyone Done

That is simply not a good idea. Why go backwards?

And this is from someone who is:

1) Tired of all the CNG/propane discussions. Google can answer all those repetitive questions.

2) A boat owner who has CNG. I also have a CNG supplier right down the street from our boat. I also have a backup CNG tank on the boat. I never run out of stove fuel. We use our boat weekly and get about six months out of a tank. Yet again, thanks to Steve Dion: http://www.cngnow.com/stations/Pages/information.aspx

3) A proponent of the "If you have propane, keep it" school of thought, your resale value, if you even care, will be much higher, or at least not lower.

4) Tired of dealing with the recurring CNG or propane questions.

 

[Doug in Lakeview]

Thanks for the valuable input.

I fully agree that any fuel cost savings (if any) between CNG and propane will never be enough to pay off any conversion. My comments on the cost difference were made support the idea that CNG fueling stations are becoming more common and that, possibly, refilling CNG tanks for marine use will become easier. Here in Chicago, there is a CNG refilling station 2 blocks from where I work and a 2nd station about 20 blocks from the marina.

The only reason for even contemplating switching to CNG from propane is safety. My experience is in the oil & gas industry where the occurrence of propane/butane leaks leading to a vapor cloud which “hugs” the ground until it is ignited by a source is all too frequent. Methane leaks, on the other hand, have a good chance of rising and escaping. The methane release is diluted and does not become an explosive mixture. For me the idea of having an appliance that uses propane as a fuel in an enclosed space seems a 2nd best choice. Stainless steel tubing, Swagelok type fittings, solenoid valves (which don’t seal tightly if there is any debris on the seat), etc, onboard a vessel which is never stable all seem to be possible failure modes. Yes, propane has been used for years but is there an alternate fuel that is inherently safer? Thus, my questions.

Since the current propane system is nearly 30 years old, I will be replacing everything except the stove itself. This includes all fittings, manual shut-off valves, pressure regulator, tubing, connections, etc. The current system does not have a 12volt solenoid valve so I will add one. The existing propane locker is in the port lazarette with tubing running through the port aft berth on its way to the galley. With the valve in the aft berth, it could be dangerous to have to pass by the stove in an emergency to shut-off the fuel line. I plan on moving the manual valve to the port lazarette. The 12volt solenoid valve (closed when e-energized) would also be located there.

 

[Doug in Lakeview]

Stu,

Please don't read previous post

Everyone else………………..

Another great October day sailing Lake Michigan. We did nearly 30 nm today and our moving average was 6.8 knots.

Yesterday met up with 2 guys who have a new Beneteau Oceanis 38. They came aboard our 30 year old First 38 and were frankly shocked how much space we have – especially main cabin & aft berths. They already have their boat on the hard for the winter. We will have to do a bit of racing next spring to see how these 2 Beneteau 38s compare.

 

[higgs]

That is simply not a good idea. Why go backwards?

And this is from someone who is:

1) Tired of all the CNG/propane discussions. Google can answer all those repetitive questions.



4) Tired of dealing with the recurring CNG or propane questions.

Stu-If these discussions bother you, why do you respond? Why not just ignore them?

 

[Stu Jackson]

Stu-If these discussions bother you, why do you respond? Why not just ignore them?

Only 'cuz this one was pretty unique, never heard of anyone even considering doing this. Not bothered, actually, just amazed that folks could type in CNG in the search box and read for weeks.

 

[Benny17441]

Re: LPG (Propane) to CNG Conversion for Stove – Anyone Done

I find it surprising that in Chicago they are opening up CNG filling stations when in the rest of the country they are rapidly disappearing due to cost and dwindling demand. Tanks are getting harder to find as most manufacturers have eliminated them from their product line and existing supply is being diminished by attrition. Are we confusing automotive filling stations with portable tank filling stations?

 

[Ron20324]

.... Tired of dealing with the recurring CNG or propane questions.

So true, Stu, but then again, that would apply to just about every question in these forums.

 

[Stu Jackson]

CNG Availability

http://forums.catalina.sailboatowners.com/showthread.php?p=1157161#post1157161

Maybe it's just the part of the country...or...conflicting input?

 

[Head Sail]

To reiterate previous posts, ,how often do you think you will use CNG? My guess is not too much. I've had a small propane bottle (5lb?) for the last year and have not refilled yet. I'd use your current setup. You can upgrade your fittings but I'd leave well enough alone unless you detect a leak. You can install a propane detector as I did if you want to feel safer. Propane is much more compact, and on a boat, that means a lot. There a millions of boats out there. When was the last time you heard of a propane explosion? Propane tanks have valves that can be turned off if you don't feel comfortable with the solenoid. Probably a good idea when the boat is not in use. When your ready to cook your pot roast, turn it on.

 

[Gunni]

Doug: Are you really that short of boat projects? Get her back into the water next spring and triage the list. If you need to fix what ain't broke there will be plenty of time (and projects).