has anyone built their own cng compressor

[assistance]

thinking of buying a $250 dollar scuba compressor (4500psi) on amazon to compress CNG for cars.

The CNG stations charge 1.60 / GGE, and homefill would be 30 cents per GGE.

The plan would be to have a flash back arrester on the intake to the compressor to prevent any accidents from going back into the main line.

Might also have a check valve to make sure the gas only goes one way.

It would appear impossible to have a flashback arrestor on the tank line due to 4500psi.

I havent been able to source cng service nozzles, i found fill ones but not the service handles like at the station, so i will be using a diy connector system that is rated for 4500psi, probably ball valves instead.

What u think of the plan?

[teoman]

Did you calculate how much cng you would need? And how many tanks you need to fill?

I had a look at those 250 compressors, the ones where you also attach a bucket of cold water. they are mainly for filling airgun tanks. So with such high volumes, i do not know how long they would last.


What car do you have?

[teoman]

1m^3 is roughly 1l of liquid fuel.

A 10L scooba tank will hold 2000L at 200 bars. So 2 liters worth of fuel.

[MeteorGray]

I would research the project thoroughly before attempting it. Compressing natural gas sounds like a daunting venture in view of the potential for disaster and liability.

[ksa8907]

At those pressures you would need supercompressibility calculations to more accurately determine how much energy you can put inside your tank.

However, (atmospheric pressure [absolute] + final cng pressure) ÷ (utility base delivery pressure [absolute]) = standard cubic feet per one actual cubic foot.

So a 1 cubic foot tank can store roughly 308 cf at 4500 psig.

I think what you're going to find is that to have a relatively safe and reliable system it will cost more money than it is worth.
Also, what are you going to do with the condensate?

[rmay635703]

If it’s not rated for flammable gases I wouldn’t waste time on it, not worth explosions

[ksa8907]

Originally Posted by rmay635703

If it’s not rated for flammable gases I wouldn’t waste time on it, not worth explosions

Things do fail in spectacular ways, luckily though for NG, it's basically inert above 15% concentration in air. If no oxygen is mixed, it's quite safe.

[Piotrsko]

Don't know about your specific community, but in many cities, they inject atmosphere into the natural gas stream in the winter to boost flow and pressure during the winter, typically below 10%. The utilities state this is quite safe and other than loss of range, the 3000 psi CNG bus I drove had no issues.

[ksa8907]

Originally Posted by Piotrsko

Don't know about your specific community, but in many cities, they inject atmosphere into the natural gas stream in the winter to boost flow and pressure during the winter, typically below 10%. The utilities state this is quite safe and other than loss of range, the 3000 psi CNG bus I drove had no issues.

Atmosphere? Like air? I've never heard of that in the industry but propane-air injection is fairly common. Though that is also being displaced by LNG.

[Piotrsko]

Yup: air consisting of whatever is at the input filter of the diesel pump. Have a friend that did maintenance inspections of them yearly all over the country.