Well, couple reasons...
It's too wide a ranging variable - some oxygen goes a few miles, some goes 200+ miles... I guess I could add the caveat that the further you are from the point of production the more sense a concentrator would make if your primary concern is energy use and pollution...most people seem more concerned with total cost and convenience. There's really nothing "green" about being a glass blower.
But mainly because it's not part of this equation - it's not that it's not an issue and can just be ignored, but I am talking about production, not delivery.
The cost of oxygen is directly tied to the cost of the energy used to produce it, with little margin. I think it would be interesting to know what percentage of the total energy cost of getting oxygen to your torch is comprised of transportation. I'll ask someone at Airgas next time I'm there. I suspect it's a pretty major concern for suppliers, and they'll have some figures. What I don't think is that it's significant, my guess is something less than 1%.
Follow the rest if you want, it's more of a worksheet to get my head around the energy costs of production based on various web source, mostly http://www.uigi.com/new_cryo_plants.html
My hypothesis is that post production plant to consumer delivery costs of oxygen comprises less than 1% of the total cost to deliver.
here's what I know:
A 5,000 gallon (23.8 ton) delivery to Airgas comes 2 or 3 times a day, and travels about 20 miles each trip, so really 40 miles round trip... 80-120 miles a day, and probably burns about 12-16 gallons of diesel to do it (modern semis run 6-8 mpg diesel.)
Large industrial air sep / liquifaction plants consume 1 to 10 megawatts of power, and produce 100-900 tons of LOX per day.
5,000 gallons LOX is about 23.8 tons (1.141gm/cm^3), a smaller "large" plant would supply Airgas with their 48-70 tons of liquid a day for about 1 megawatt.
It takes about 3800 tons of coal to make 12000 megawatts or a bit over 3 tons coal per megawatt...
So large tank worth of liquid oxygen, 5,000 gallons, takes a ton or two of coal to produce.
last I checked 1 or 2 tons of coal is more pollution than 15 gallons of diesel fuel.
Please feel free to check my math, I used google calculator, windows calculator, wikipedia, ww.uigi.com and www.fibatech.com...
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