VigIIPeaBurner wrote:This is not an accurate answer to your question but the formula you post, 13,250 * 0.94, is based on weight percent subtracted from the BTU/carbon content. Apples to oranges as it were. I'm get from your question is how many BTU are consumed by the 6% water content in you example. The equation would have to be normalized to BTU. Here goes my shot ...
I'm not representing that this is the actual laboratory procedure to analyze the effect of the moisture. It's pretty close but I'm just trying to convert apples to apples.
- A BTU is the amount of heat it takes to raise one Lb of water 1*F
- Given that definition, raising the temperature of the water from 60* F to 212*F, boiling temperature @ST&P, it would require ~1,200 BTU to do this.
- If a Lb of coal at 60*F has 6% moisture content then it would take 6% of the 1,200 BTU to boil the 1 Lb of water off: .06 x 1,200 BTU = 72 BTU
- In your example that would leave 13,178 BTU heat content remaining in the Lb of coal after the 72 BTU is used by boiling the 6% moisture off.
Pacowy wrote:I think the 1200 btu estimate is for a gallon, not a pound. For a pound, by definition the btu requirement would be (212-60=) 152 btu's.
The thing that's been left out of these figures is the "latent heat of vaporization" required to evaporate the water at 212 deg. I believe that is about 970 btu/lb, so the total would be around 1120 btu/lb.
lsayre wrote:So where does that leave the "real world" BTU's/lb. for anthracite?
lsayre wrote: Surprisingly, bituminous coal often has a higher MAF rating for BTU's than does anthracite.
Pacowy wrote:I think the 13,451 number, for which the testing basis is not stated, results from a mathematical adjustment to "put the ash back in" to the 14,876 number -
i.e., 14,876 x (1-.0958 [ash content]) is exactly equal to 13,451. The 13,451 therefore still assumes the coal is dry, so the "real world" yield from burning the coal as received would be around 12,300 btu/lb after the water is taken into account.
P.S. Source of numbers is http://penncoal.com/wst_page6.html .