Supplemental Heat: Act III How Long to Heat Grain 5 C

In my last blog, I was preaching about the dangers of over heating the grain because it could cause condensation.  In fact I recommended that the grain should not be more than 5 deg C warmer than the outside air.  But how long would it take to raise the grain 5 C?  What would it cost?  How many cubic meters of natural gas would be required?  How much water would the combustion of that much natural gas be?

We will use Jim S. situation in which he has 3500 bu of wheat in a hopper bottom bin at 5 C and wants to heat it to 10 C with his 50,000 btu furnace.

Wheat is 60 lbs/bu.  So in kg 3500 bushels weighs 60 x 3500/2.204 = 95,281 kg.

Specific Heat of Wheat is 1.36 kJ/kg C

For 1 C rise in   1.36 kJ/kg C  x 95,281 kg = 129,582 kJ/C

For 5 rise (5 t0 10)  5 x 129,582 = 647,910 (assume that all energy went into wheat)

Our furnace puts out 50,000 btu and there is 1.055 kJ/btu so furnace puts out 52,750 kJ/hr.  But we need 647,910 kJ, so it will take us 647,910/52,570 = 12.3 hrs to raise the temp of the wheat by 5 C.

Cost  1 GJ = $4.30   so .647 GJ = $2.78  (Sask Energy price)

Estimated Water Removal   .2 %  (MC 17% to 16.8%) – Assume that we will pull the wheat back to 0 C.  This would be 190 kg of water removed.  We would have to do this everyday for two weeks to get wheat from 17 to 14.4% and this would cost about $36 in natural gas.

1 cubic meter of natural gas produces 0.688 lbs of water in its combustion.  There are 26.94 cubic meters required to produce a GJ of energy.  But we only need 0.647 GJ to raise the temp 5 C, or  0.647 x 26.94 = 17.43 m^3.  which would produce  17.43 x 0.688 = 12 lbs  (5.44 kg.) of water.   If we would use a tiger torch instead of the furnace, we would have taken 190 kg of water out of the wheat, but would have added 5.44 kg of water back into the wheat from the combustion of the natural gas.  I think it is a good idea to prevent the flue or the smoke from getting into the grain.  People are throwing out their conventional low efficiency furnaces,  you could pick one out of the junk for almost nothing.  All you need is the burner and the heat exchange. Even if the heat exchange is cracked, it would not be a problem.

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