Natural gas usage

To talk about gas in terms of volume with no reference to pressure is completely ridiculous.

I am trying to determine how many cubic feet of propane I have with two 1500 gal tanks

Note that propane and natural gas are not the same. A gallon of propane has about 91,500 BTU which is about 137 million BTU. A 100 cu ft of natural gas varies depending on impurities and amounts of butane and ethane along with the methane (this is the main ingrediant) anywhere from 100,000 to 103,000 BTU (100,000 BTU are called a Therm) so about 1370 CCF (CCF means 100 cubic feet) of natural gas has the same heat content as 1500 gallons of propane. 100 cu ft of natural gas (1 therm or 100,000 BTU)= 1.095 gallons of propane.

I assume that 1 CCF is 100 cubic feet of gas at standard atmospheric pressure (14.7 psia). As a theoretical problem, if I had a heavy steel wall container that was exactly 100 cubic feet in volume, evacuated to a perfect vacuum (0 psia), and I pumped in NG to a pressure of 2 atmospheres (2 x 14.7 = 29.4 psia), would the NG meter indicate that I had consumed 200 cubic feet (2 CCF)? If I pressurized to 4 atmospheres (4x14.7=58.8psia or 58.8-14.7=44.1psig), would that be 4CCF consumed?

[JohnS]

Originally Posted by Unregistered

I assume that 1 CCF is 100 cubic feet of gas at standard atmospheric pressure (14.7 psia). As a theoretical problem, if I had a heavy steel wall container that was exactly 100 cubic feet in volume, evacuated to a perfect vacuum (0 psia), and I pumped in NG to a pressure of 2 atmospheres (2 x 14.7 = 29.4 psia), would the NG meter indicate that I had consumed 200 cubic feet (2 CCF)? If I pressurized to 4 atmospheres (4x14.7=58.8psia or 58.8-14.7=44.1psig), would that be 4CCF consumed?

Yes, if you did it agonizingly slowly and let the temperature settle to the original value.

Gas volume is a function of pressure and temperature, as well as the weight or number of moles of gas. In the real world, compression/expansion of the gas will change the temperature and influence your results. But in ideal isothermal case, yes.

Thank you. I asked the question about calculating pressurized gas and CCF because I was trying to get an estimate of how much CCF a cylinder 16" x 48" pressurized to 3000psi would contain. I don't know the wall thickness or the actual volume of the cylinder, but as a rough estimate I came up with about 11CCF (ball-park number). If this is a reasonable estimate, then it would cost about $11 worth of NG to fill. I get this from my gas bill because I paid about $17 for 18CCF to run my water heater (this does not include the flat $10/month fee that is independent of usage). The supplier of this cylinder is a company that makes equipment to convert cars to run on CNG and says that this cylinder at 3000psi is a gasoline equivalent of 8.4 gallons. I assume that this means that the car should travel about a far on the 3000psi CNG tank as 8.4 gal of gasoline. That is $11->$15 of NG instead of about $28.50 for the gasoline.

[JohnS]

Originally Posted by Unregistered

Thank you. I asked the question about calculating pressurized gas and CCF because I was trying to get an estimate of how much CCF a cylinder 16" x 48" pressurized to 3000psi would contain. I don't know the wall thickness or the actual volume of the cylinder, but as a rough estimate I came up with about 11CCF (ball-park number). If this is a reasonable estimate, then it would cost about $11 worth of NG to fill. I get this from my gas bill because I paid about $17 for 18CCF to run my water heater (this does not include the flat $10/month fee that is independent of usage). The supplier of this cylinder is a company that makes equipment to convert cars to run on CNG and says that this cylinder at 3000psi is a gasoline equivalent of 8.4 gallons. I assume that this means that the car should travel about a far on the 3000psi CNG tank as 8.4 gal of gasoline. That is $11->$15 of NG instead of about $28.50 for the gasoline.

Per unit of energy content, natural gas is cheaper. At 3000 psi the ideal gas law is not too accurate. In your calculations you would need to consider a correction factor commonly called "compressibility" which depends on temperature and pressure, or use a more sophisticated equation of state.

Originally Posted by Unregistered

If a Therm is 100,000 btu and a ccf is a 1000 btu, where is the one to one conversion? 1 therm is about 100 ccf not 1 ccf.

if I used 1,200,000 btu in 24hr how many terms is it

[JohnS]

Originally Posted by Unregistered ban02

if I used 1,200,000 btu in 24hr how many terms is it

1 therm = 100 000 BTU, so 12 therm

Just look at your gas bill. It usually shows the "Therm Conversion Factor." For instance, in Indiana in July, Vectren indicated a Therm Conversion Factor of 1.007 Therms-per-CCF (very close to 1-to-1 ratio).