After some modifications to my grate design I was able to have a one hour continuous test run with a self sustained flare. I shut it down not because of any problems but because it was time to eat supper!
Day one is when I had my 10 – 15 minute runs, day two was the one hour run and day three was the mixed bag of fuel day.
First the burner design can be seen in the pictures “Burner” and “Burner Parts”. It is made of a length of exhaust pipe with reinforcing rod welded to it. Next a piece of duct work pipe was slid over the reinforcing rod. This allows the duct work pipe to slide thus adjusting the air to fuel ratio. Seems to be working good for me at this time.
Over the course of three days I had some short runs of about 10 to 15 minutes of self sustained flare that helped me make some changes. After making those changes I was able to have that one hour run as stated above. This was on hardwood pellets. I decided to use this fuel for my point of reference.
After the gasifier warmed up the flare can be seen in the picture “Flare 1” (day two). This was an odd colored flame, at least for me. At first I though it was purple but the more I looked at it I could start to see it was composed of blue and maybe white flames. Is there such a thing as a white flame? Also, you can notice that the reinforcing rod was red hot. It was also windy on this test day and the flame never blew out. This flare doesn't burn your eyes (I mean emissions NOT HEAT) or smell bad, it smells clean. Also, the inside of the burner is very clean. At the end of the one hour run the gasifier consumed 20 lbs of hardwood pellets. Other interesting flares can be seen in the other pictures.
OK, it's time for day three: First the gasifier was started with hardwood pellets then switchgrass pellets were loaded. It seemed that as soon as the switchgrass pellets started to react or shortly after, the flare stared to go a stray, next get smoky and went out. So I poked around and it seemed kind of crusty in the char zone but I am not sure.
Next more hardwood pellets were added and a flare was lit. After some settling time went by paper fireballs were added to the fire tube. This is were things got interesting.... I was observing the flare and it started to look like water going down a sink drain. This odd looking flame seemed to be rather hot but was getting smaller and now the exhaust pipe (part of the burner) was starting to glow red hot, not just the reinforcing rod..... It seemed to be falling down my pipes and the pipe that I am using are just something like dryer vent material, aluminum accordion tubing. This pipe was something that was discarded from my HeatHut project and is a little on the swiss cheese side. In other words lots of air leaks. Also my suction fan motor cools it's self by passing air through the motor and into the fan housing. Of course with woodgas a little extra air helps with the air to fuel ratio mixing BUT with this paper fireball gas (hydrogen rich gas ???) things change. By now you should be getting the picture..... The flame gets bored with my burner and goes for a trip down my pipes! So I let it go out and relight the burner and in no time the same thing happens (this gas lights nice). It also doesn't stop at the fan but it will also heads towards the cyclone filter. OK, it's time to replace this pipe with some solid exhaust pipe!!
Looks like the paper fireballs lived up to their name but I'll have to wait for my pipe up grade before I can do more testing. So now it's time to try some switchgrass fireballs. Guess what? They do the same thing that the switchgrass pellets do. They stop the gasifier from gasifying. I'm starting to wonder if switchgrass could be used to put out forest fires? I also tried rice hulls with no luck.
Jeff Davis
The Rig: My set up.
Flare 9: Day one
Flare 8: Day one.
Flare 7: Day one.
Flare 6: Day one.
Flare 5: Day two.
Flare 4: Day two
Flare 3: Not sure which day.
Flare 2: Not sure
Flare 1: Day two.
Burner Parts: Here you can see the rod welded to the pipe.
Burner: The outer pipe can side on the rods.
Day 3 Pictures
Here are my day three pictures and what was inside the gasifier.
Tom Miles wrote
Jeff,
The slag encapsulation that you see is not unsual when heating straw. Dirt sually just bulks up the slag rather than melting itself. You rinse out some of the principle slagging constituents (potassium, chlorine)in the
wetting and milling but you don't get them all. Even with
the rinse you'll stil have an ash content of 4-5% in the swtichgrass fireballs. If you subject the ash to temperatures above 1450 F (750C) you'll get slagging.
One way to dilute the slagging is to mix in paper and
switchgrass fireballs or switchgrass and wood.
Tom
Tom wrote
Dear Jeff:
Gorgeous pictures and an interesting gasifier. If I'm reading it right, it is a downdraft gasifier.
I note that you got a LOT of slag. This is the problem with agricultural residues. Wood typically contains less than 1% ash, and so can be completely gasified without slag buildup. However, with 2-20% slag it is impossible to get complete gasification of the carbon without the slag buildup.
If you don't have a good bed of charcoal, you will get
combustion on the grate. This is the Achilles heel of switchgrass and other non-woody biomass being used for clean gas for engines etc.
Try filling the tube with charcoal briquettes and then running.
COMMENTS?
TOM REED THE BIOMASS ENERGY FOUNDATION