I got a call a couple of days ago from Jim S from Wainwright, Alberta. He said this night drying thing wasn’t working for him, and that he was considering buying a natural gas furnace to add some supplemental heat to the process. Would that work? I told him I thought so, but I would have to work out the numbers to see; but I’ll save that for another blog. First let’s have a look at why this night drying isn’t working out.
Jim has tough wheat, 17%, that was harvested cold and put in a 3500 bushel hopper bin. Attempts at night drying brought the temperature down, but because of the nasty wet weather they have been having, the moisture has remained close to 17. Jim thought that water may have been added. I told Jim that once you got the temperature of the grain down, you have taken the energy out of it that could have been used for drying. So it is quite possible that now that the grain is cold, that drying will cease.
Here is what I did to get a handle on what was happening in Jim’s case. I went to the website for BINcast and got the hourly temperature and relative humidity for Wainwright from Sunday Oct 14 til Thurs Oct 18. The temperature was bouncing around the freezing point, from +4 to -6 C. The relative humidity was high throughout this time, 90% – 95%. We didn’t know the temperature of the wheat, but we knew it was cold, so I assumed it was 4 C. I modeled the temperature of grain, so that it would chase the outside temp in a similar fashion as I saw how the grain temperature changed in our trials at Indian Head. At the end of this simulation, the grain temp was close to -1.5 C.
I now had all the information I needed to calculate the amount of hourly drying. To make a long story short, I used the principle of absolute humidity, and EMC equations to calculate the amount of drying for each hour. For the first few hours we did take out a bit of moisture until the temp of the grain came down, and then we started adding small amounts of water. We did get some drying when the temp went down to -5, but this was short lived. In the end we did indeed add water, 7.52 kg. This actually isn’t that much, it would raise the MC from 17% to 17.001% however we can definitely say that night drying did not work in these conditions. Maybe we should consider supplemental heat? Maybe Jim should buy his furnace. Using supplemental heat brings forth a whole host of other questions. What fuel should I use? How much will this cost? At what time of day do we apply the heat? How hot should we get the grain? Should we have a cooling cycle, or should we just apply the heat continuously. How long should the cooling cycle be?
In my previous blogs, I showed that a 15 deg C cooling of the grain resulted in a 1 percent decrease in moisture. So let’s say we want to raise the temp of the wheat by 15 C. The specific heat of wheat varies, but it is about 1.36 kJ/kg C. I will spare you the details but to heat 3500 bushels, 15 C, requires 2 GJoules.
I checked with SaskEnergy and used the internet to check out the cost of the different fuels for 1 GJ.
Natural Gas $6.48 /GJ
Gasoline $16 /GJ
Fuel Oil (Diesel) $21.65 /GJ
Propane $14.66 /GJ
Electricity $32.81/ GJ
So, we can see there is no decision, if you have natural gas, it is by far the cheapest supplemental fuel. Also 1 GJ , at least, is the required energy to remove 0.5% MC. Maybe we can get Jim’s wheat dry for $40 — if we do everything just right? As our benchmark, and challenge, we will use the same nasty weather conditions above, with the supplemental heat and see what happens?
Stay tuned for the next blog on playing with supplemental heat.