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Burning sawdust in a pellet stove4/22
Warning, this is for your knowledge only!.
System for burning sawdust in a U.S. Stove American Harvest Model 1039; Arrived at after much trial and error.
1. Auger motor at 6 rpm to compensate for lower bulk density of sawdust.
My frirst purchase was a Corn Flame Stove to reduce heating cost for my house in Indiana. It worked well and I then purchased a Danson's Cheap Charlie for heating my house in the U.P. fo Michigan. When the price of corn went thru the roof, I started making pellets with an 8" mill. Because of the higher ash content of pellets made from a combination of sawdust, leaves and paper, the corn burner had to be cleaned every 8 hours. The mill that I have can not make pellets from straight sawdust. After seaching the web for pellet stoves suitable for burning biomass pellets, I decided to try a U.S. Stove(used model 6039) because it had a burn pot agitator.
This worked well with my home made pellets which I screened prior to burning to remove fines. Even with the screening when the hopper was nearly empty, there would be a lot of fines and smaller pellets. The auger would feed the finer material with no problem. The agaitator worked well to help the ash fall through the burn pot and running for a week was no problem.
I have now used this system for two winters burning about 25-30 gallons of sawdust a week. The sawdust is all screened through 1/4" mesh to remove larger wood chips screws.
Sawdust burning tests:
Because the fine material fed and burned well, I began seaching the web for ways to burn sawdust in a pellet stove. There are several stoves that will burn sawdust, but they are not pellet stoves. My first attemp with burning sawdust in the U.S. Stove was to empty the hopper of pellets an fill it with about 10 pounds of sawdust. Pellets were put in the burn pot and a fire started, the sawdust burned well. At the maximum auger setting there was a lot of fluidization of the sawdust and particles carried out the exhaust with sparks being visable. Bridging of the sawdust in the hopper was a problem.
Since the sawdust burned well, my next step was to evaluate the design of the 6039 stove and decide what changes were required for proper sawdust burning.
1. I added a agitator to the feed hopper, powered by a 2rpm auger gearmotor.
Based on this to get the same amount of heat, the the 4rpm auger motor would have to run at the maximum setting of 9 instead of the 3-4 that I had been running with pellets.
This system was run for several hours. Bridging in the feed hopper was still a problem.
A vibrator taken out of a back massage pad was pop riveted to the outside of the hopper.
A test was run as follows. The auger motor was powered directly by 110v to operate continuously.(not a good idea for a permanent setup because it by passes the safety shut down controls). Since on this stove the auger motor speed controller also controls the combustion blower speed, the setting was reduced until a minimum of fluidization occurred. This system was run for 8 hours with no problems.
The feed hopper was extended adapting a hopper extension I had for the Danson pellet burner. The lid was spilt and the agitator shaft extended. This allows filling with out removing the agitator. The agitator shaft is attached to the gearmotor shaft with clip that can be removed after the lid is raised only a few inches, the lid can then be fully opened for the removal of the shaft.
Next since the 4rpm auger running full time worked okay, ( through with the controller at maximum speed it only runs about 75%of the time) a 6rpm auger motor was installed .
This system is working well with little fluidization. More frequent cleaning of the exhaust duct is required. I clean it about once/month.
Sawdust is dust and it is difficult to keep the area clean.
Pellet stove is in the basement and the hopper is fed by a screw conveyor from the garage. Feed hopper has a shop vac connection for dust control when filling..
Hopper agitator: Uses 1/2" pvc pipe with screen door springs tipped with plastic hose to prevent hopper wear. Needs to be centered over the auger feed throat. Bottom bar of 1/4" plastic tube.
Made a mistake in this post: Should read 25-30 gallons per day of sawdust.
Fluidization is when the sawdust particle is lifted by the upward flow of the air used for combustion. This can lead to it being carried out the exhaust pipe while it is still burning.