Bill;
Your boat, your barbeques grill, and a forklift (or a car outfitted with an LPG conversion kit) all burn LPG vapor. But your friend was correct that in that vehicle applications all use tanks that are designed to deliver liquid LPG out of the tank, instead of vapor. There are both horizontal and vertical tanks for forklifts (cars and trucks usually have permanently mounted tanks) that have a pickup tube internally that goes to the bottom of the tank. Vapor pressure in the top of the tank pushes liquid LPG up the pickup tube and out of the tank valve. AFIK, there are no tanks for boats or barbeques that are available for horizontal applications because there is no way to ensure the horizontal tank would not provide liquid instead of vapor. (Liquid instead of vapor would turn your stove into a flame thrower.) What is different in a vehicle application is the regulator, which is a rather large two-stage device commonly called a vaporizer. Liquid is delivered to the first stage, where pressure is reduced from about 125 PSI to 4 or 5 using ambient or engine heat. A second stage regulator further reduces the vapor to about 1.5 PSI for delivery to the carburetor (or throttle body injectors) on the engine. The two stage process provides better control of the fuel flow for consistent engine performance. The boat or barbeque has a 1 stage regulator to provide LPG to the flame, but the amount of fuel delivered depends on the pressure in the tank and the temperature in the environment. LPG is a different animal than CNG. LPG is a liquid at above something near 125PSI, or temperatures below about minus 45 or 50 degrees. CNG can only be converted to liquid at very high pressures (IIRC something between 4500 and 6000 PSI) or a few degrees above absolute zero. As Joe pointed out, a CNG tank for a boat (or home barbeque) is essentially a diving tank with a different regulator, containing gas pressurized to 2500-3000 PSI. CNG is cheap (as Joe said about $2 per fill up), and I think the energy content is higher than LPG. But it has never really caught on as a motor fuel for two basic reasons – it is difficult to get enough gas squeezed into a tank to give you decent run time for a vehicle, and the cost of the compressor/fill station needed to fill the tanks is quite high. Before I left the forklift industry, the entry level cost of a CNG fill station (essentially a high pressure pump that takes the CNG from the city gas line at 3-4PSI and brings it up to 3000 PSI, and then stores it in a flask for transfer to your mobile CNG tank) was around $3000-$3500US for a fill station that would fill a fuel tank every couple of hours. So the only practical application for CNG is something like a city bus line where high volume of fuel use and federal subsidies can offset the very high capital cost of setting up a fill station. CNG is really nice as a stove fuel. Safer than LPG, higher energy & cooking times like you’d get on your stove at home, and cheap. But the cost of creating a fill station will probably mean that it’s never going to be convenient to refill a CNG tank at a marina or local hardware store. Rick Brass Washington, NC From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of coltrek via CnC-List Sent: Sunday, December 31, 2017 3:28 PM To: cnc-list@cnc-list.com Cc: coltrek <colt...@verizon.net> Subject: Re: Stus-List CNG tank refill location I'm a little out of my area of expertise here, but I tried to get an adapter for a forklift propane tank, which is laid sideways. And after talking to a friend of mine in the propane business, he told me that forklifts use liquid propane which was what happens when you laid on its side, and Flames used vapor gas which comes straight up. I think for that reason, there were no adapters readily available. Just a thought. Bill Coleman C&C 39
_______________________________________________ Thanks everyone for supporting this list with your contributions. Each and every one is greatly appreciated. If you want to support the list - use PayPal to send contribution -- https://www.paypal.me/stumurray
