CNG Vessel Sizing
CNG Vessel Sizing
(OP)
I am interested in a Compressed Natural Gas (CNG) vessel to supply natural gas to heat a building because the piping from our existing infrastructure is far away and it's going to cost an insane amount in scaffolding, etc. to pipe it, there. All I know is that the building's HVAC units require a total of about 34m³/hr of gas (1200ft³/hr). I would like the vessel sized to last something near 4 weeks.
My pathetic Google searching keeps showing wet capacity of vessels and "gas capacities" that don't really mean much without the pressure. I suppose my 34m³/hr also does not mean much without a pressure; but, IIRC, gas is delivered to heaters at barely any pressure at all, isn't it? Something like 1psi? Arbitrarily close to atmospheric?
My crack at it would be something along the lines of (24hr/day)(30days/month)(34m³/hr) = 24480 m³ of atmospheric gas per month.
Then, convert that gas to a volume of liquid by looking up what pressure natural gas liquifies at. Find a vessel that is 1.25x the wet volume of natural gas (because you can't fill them >80%). Verify that it is rated for a suitable pressure and see what it costs.
Profit?
Please point out my errors and mock or flame accordingly.
Thanks!
My pathetic Google searching keeps showing wet capacity of vessels and "gas capacities" that don't really mean much without the pressure. I suppose my 34m³/hr also does not mean much without a pressure; but, IIRC, gas is delivered to heaters at barely any pressure at all, isn't it? Something like 1psi? Arbitrarily close to atmospheric?
My crack at it would be something along the lines of (24hr/day)(30days/month)(34m³/hr) = 24480 m³ of atmospheric gas per month.
Then, convert that gas to a volume of liquid by looking up what pressure natural gas liquifies at. Find a vessel that is 1.25x the wet volume of natural gas (because you can't fill them >80%). Verify that it is rated for a suitable pressure and see what it costs.
Profit?
Please point out my errors and mock or flame accordingly.
Thanks!





RE: CNG Vessel Sizing
RE: CNG Vessel Sizing
Density of methane at 14.73 psia [101.56 kPaa] and 60F [15.56 C] is 0.0451 lbm/SCF [0.723 kg/SCM] (assuming compressibility is negligible). CNG is stored at a nominal 3600 psia [24.8 MPaa] and 70F [21.1 C] so the density is 12.346 lbm/ft^3 [197.7 kg/m3] (calculating compressibility as 0.876). This is all you need. The volume of the vessel (with no safety factor) is:
Volreceiver = Q*ρSCF/ρCNG=2950 ft3 [84 m3]
If you pick a 90-inch [2.3 m] diameter receiver then it would have to be 67 ft [20.3 m] long. Getting a vessel rated for CNG pressures much bigger than 90 inch is outrageously expensive, but then getting a 90-inch pressure vessel 67 ft long would be tens of millions of dollars.
The storage gets smaller with LNG, but sources of LNG and the gassification equipment for your load are hard to come by. There is a reason that people pay the cost to run pipe to their buildings.
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: CNG Vessel Sizing
In some locals LPG (propane, butane) sell for the same cost per BTU as nat gas.
I would check with suppliers and see what they can offer.
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P.E. Metallurgy, Plymouth Tube
RE: CNG Vessel Sizing
RE: CNG Vessel Sizing
How much? Don't know but they often make these things from fibre glass a multiple small tubes.
Search CNG containers.
Here's an example. www.weldship.com/about-us/recent-news-and-events1....
Don't confuse LNG, LPG with CNG. LNG is not currently available in that size of system, LPG is, but usually more expensive than gas. CNG is now very common in lots of places so the cost of equipment is low and safety issues have been worked out.
Let us know if you're going ahead.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: CNG Vessel Sizing
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: CNG Vessel Sizing
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: CNG Vessel Sizing
I think the idea is dead before it's off the ground. We are unfortunately stuck with Natural Gas which is infuriating me that those selections are set in stone when propane should work just as well and is super prevalent.
I pictured the LNG equivalent of a rental propane bullet that a company like Superior could supply and fill in required intervals. The filling is what kills it as I don't think there are any LNG trucks that can supply us in our region.