Making Stove Pellets from Shavings and Sawdust
A look at the technology for turning wood waste into wood-stove briquettes or pellets. Is it practical? January 25, 2010
Question
I stumbled on an old thread here on WOODWEB that discussed making pellets out of wood scrap. I had often thought of that myself and even found a pellet machine I like. The machine is relatively affordable and it would be interesting to try making pellets for my own use - perhaps heating the shop or my home. The discussion here (I don't know how old it was) made the process sound more complicated then it appears to be on the Pellet Pro website. I'd be interested in hearing what others know about this.
Forum Responses
(WOODnetWORK Forum)
From contributor K:
Tthis is very cool! I love the idea. I think I would love to incorporate it into my dream shop some day. I wonder how clean burning it is and how much smoke it actually produces?
From contributor Z:
We already heat the shop with our scraps but still have lots of shavings to deal with. I’m going to look into these further.
From contributor G:
I looked very hard at Pellet Pro. I talked to them over the phone (they seemed very knowledgeable), looked at their website and viewed their CD. I was told the machines are meant to be tended to at all times while running which is too labor intensive. I was also told the pellets must be cooled. The little cooling rack system in the video is also too labor intensive. They do have a cooling bin but it seemed disproportionately oversized and overpriced compared to the pellet machines.
I want to process the 5-7 semiloads of sawdust we produce in a year so I can burn it for heat. Now I am looking at a used Weima briquette maker which seems to fit my needs better. From my research, briquettes are not quite as fussy about the initial moisture content of the sawdust as pellets. 6-8% MC sawdust is too dry for pellets from what I have read. I suppose moisture could be added somehow but that is another step. Granule size of the sawdust is also fussier with pellet makers. These are conclusions I have made from my research so far and are the reasons influencing my decision to go with briquettes. I am very open for corrections or other ideas. I am very motivated and excited about this project. I think this technology is in its infancy for us small scale users but will likely advance as current fuel prices make it more attractive. Right now the payback on even my used equipment isn't that great. It just seems to be the right thing to do.
From contributor S:
We also looked into producing wood pellets from our sawdust and shavings. We actually visited a pellet producing plant just to see what equipment is involved. I noticed the output rating on pellet pro machines was as much as the output on the larger HP pelletizers. Pellet Pro recommended using a binder with sawdust in their machines which would require another process and more expense. We aborted the project and purchased a Taylor hot water furnace which will be converted into a waste fired hot water furnace. We are using a fairly large auger. I welded a hopper over the auger which we will load kiln dried moulder shavings and sawdust with a skid steer. We plan on blowing our shavings into the Taylor wood furnace (incorporating antiblowback devices of course). The sawdust/shaving/oxygen mixture should burn very well. We will use this energy to heat our dry kilns.
From contributor U:
I'd think that as long as you're going to burn the waste at the site of production making pellets first would be a wasted step. The technology to burn the waste as produced is proven and has been available for years. Making pellets makes sense if you are going to transport and resell to consumers, but large scale production seems to be the answer to any money gain.
From the original questioner:
To contributor U: now that's kind of the point. We are a small four person operation that goes through hundreds of board feet a week as versus thousands. The question is whether pellets have an advantage when we are talking about only around 120 cubic feet of shavings every couple weeks.I doubt we would produce enough shavings to feed a commercial shavings boiler system (which until this discussion I didn't even know existed).
From contributor G:
At first I also thought processing the sawdust as a wasted step. I also looked into sawdust fired boilers. We do not produce enough dust in the cold months alone and that means storing sawdust until winter. That, I decided, is less practical in our case then making the dust into briquettes which is a 10 to 1 reduction in volume, easier and cleaner to handle. Make sure you don't spend a dollar on labor to save a dime on fuel costs. Even at eight dollars an hour it could add up. Another reason I am going to make briquettes is so a couple of my employees and myself can burn them at home also. They agreed to make and bag my briquettes, as well as their own, on their time in return for free briquettes. Without the free labor it would not be worth it. Making the briquettes is easier than making firewood for them so it should be a win, win situation. I'm not even making them yet and have had interest from people wanting to buy briquettes. Interesting idea but I don't think we will make enough dust for that. Like I said earlier, I am excited about this.
From contributor T:
Be sure to let us know how you make out with the briquette machine should you go that route. We produce about four semitrailer loads a year as well. I am currently having a hard time getting rid of the dust. The MDF plant that used to take it no longer takes hardwood shavings. We do have a wood boiler that we use to burn our scraps during the winter for heat. So I would have no trouble burning either the pellets or briquettes. I looked that the Pellet Pro video online, looks simple. But as someone else mentioned, I thought you had to add a binder to the dust before adding it to the machine. Maybe wax of some sort. They don't seem to show that in the video or the cool down requirements you mentioned. Anyway if the dies only last only 200 hours or so, I can't see that as a great payback. Running it four hours a week, it would only last a year or so. I guess it depends on the price of the dies. I haven't really checked out the Weima briquetter but I think I will get some literature on their system. I wonder how well both the pellets and the briquettes burn as well as how much smoke they generate and how long they burn. Anyone out there burn pellets or briquettes and care to share their experience with them?
From contributor G:
Pellets are more moisture sensitive than briquettes from my research. If the moisture is correct, about 12% no binder is needed. Lignum, a natural binder in wood gets reactivated in the pressure process. Introducing moisture to 6% MC sawdust is another hassle. I am buying the Weima briquette maker, stove, and bagger all used from the same guy. He has been successfully using them for two years. He does not add moisture although he says it would work a little better if he did. He used to burn firewood and said he would not want to back to that. The briquettes burned best for him in his particular stove if he bagged them in feed sacks first, about 30 lbs per bag and 30 bags to a stove full. That’s 900 lbs at a time and they lasted 24 hours on the coldest days at 10-25 degrees below zero. My shop is way better insulated than his so it will not take as many briquettes. I do have a 24" exhaust fan going all day most days so that is a huge heat loss. That’s a bigger fan than we had last winter so that is one of the reasons for burning briquettes.
From the original questioner:
To contributor G: is that correct - 900 lbs a day?
From contributor G:
Yes that is correct, 900 lbs. That was on the coldest below zero days. Last winter was a very long cold one here in the midwest. His shop is 10,000 sq ft. of very poorly insulated space. That is why he got into burning wood then briquettes. He could not afford to heat with LP. He also has an exhaust fan going most of the time in the finish room. His woodburner is rated for 24,000 sq.ft. so he was able to keep his shop very warm. He figured he burned 3-4 semiloads of sawdust made into briqs per year. I gave him about 4 semiloads over the last 1.5 yrs. The rest I gave away to farmers for bedding. He had the learning curve of this briquette thing mostly concurred and I had asked a lot of questions over that time because I thought it was a great idea.
From contributor K:
Do any of you that have spent time researching burning with pellets and briquettes know if one burns longer that the other, per pound of fuel? Contributor U mentioned about burning plain unprocessed sawdust. It seems to me the whole point of compacting the material is to slowdown the rate of burning on the fuel in order to control the BTU'S it puts out so not to waste the fuel. I would think the briquettes would be a better, more economical choice because I believe they would burn longer that pellets.
From contributor G:
Someone please correct me if I'm wrong but this is what I've learned. All species of wood or wood byproducts contain about the same BTU's per pound. A pound of hickory is smaller and denser than a pound of pine. Obviously volume wise the hickory is smaller and burns longer. Weight wise they both contain about the amount of BTU’s per pound. You have to reload the stove more often with pine because you can't get as many pounds in. Volume wise pine burns faster but weight wise it does not. No matter what you are burning the trick is to deliver the fuel (air and wood) at a controlled rate only as it is needed so as to not waste fuel. Weight wise whether you burn firewood, sawdust, pellets or briquettes should not matter, they burn the same. The difference is in the handling and delivery system. I can't store the volume of seven truckloads of sawdust through summer until winter. I can store the volume of it after it is made into briquettes. Both weigh the same but one takes less space.
From contributor K:
I requested literature from Pellet Pro and it says that hardwood sawdust (doesn't say what species so I'll assume mixed) burns at 8573 BTU/lb. and softwood sawdust at 7000 BTU/lb. If this is correct, it speaks for itself to that question. The point I was thinking about but didn't say was that the more surface area exposed in the burning chamber of the furnace, like one would have with uncompacted sawdust, the less one can control the burns and the less BTU'S you will benefit from the burn. the larger and denser the briquette is, I guess the less time you will have to spend loading. Am I thinking right?
From contributor G:
I Googled "wood BTU and BTU conversion" and many different species of wood were listed. They first list the weight of a chord of firewood of a particular species and among other things the BTU in that cord. In all the charts I read, if a species was half the weight of another species the BTU was also half. According to those charts there was no difference in BTU per pound per species. Right or wrong in the real world it probably doesn't matter because if any of us make pellets or briquettes we will make them out of whatever type of sawdust we have available. The point I did not clearly make is that a controlled burn in the stove is at least as important as the type (sawdust, pellets, briquettes) of wood fuel. Controlling the air intake of the burner via a dampener is how this is done. The air intake will vary depending on the type of fuel, its surface area, density, heat demand at that particular time, and burn rate of the fuel.
From contributor U:
I've been researching for a way to utilize small quantities of wood waste for over a year and here's some of my thoughts and things I've learned or think I've learned. No argument about the reduction in size advantage of compressing wood waste to reduce volume. Pellets and briquettes are more easily transported whether it's across town or across the state. Storage of uncompressed wood can become a problem. However, one of the things that pellet making needs (and I assume) briquettes need is a uniform particle size and consistent moisture level. Size seems to be a "less than" situation to be able to go through the dies. Moisture is needed to get everything to stick together. Uniform sized fuel is also needed to configure a burner for efficiency. Wood pieces larger than small shavings would need to be reduced in size to compress which would require a machine of some sort like a grinder of hammer mill - more expense and more floor space needed.
I would assume that your wood is KD and less than 10% MC which as mentioned can create a binding problem. Adding uniform moisture would be needed. How should be considered. I'd also assume a wood shop would have a variety of sizes ranging from very fine sawdust to small end and side cuts. Two distinct problems when it comes to burning. Burning just sawdust is a problem because the dust tends to smother the flame so a controlled feed rate is needed. You can't just shovel it in. You might consider a way to standardize particle size and get a furnace optimized for that size. Do a web search for sawdust burner, gasification furnace, or waste wood burner. Some I'm aware of are Wood Gun, EKO furnace and Woodmizer. Woodmizer has specialized toward sawdust burning to support the dust generated by their mills and is still somewhat in the Beta testing stage but all reports have been favorable and they are a good company to deal with. I have no vested interest.
From contributor G:
In my case all of the dust is dry to about 8% - definitely on the dry side. The guy I am buying the briquette maker has processed and burned seven semi loads of mine and his dry dust. He has learned higher moisture makes a prettier briquette but the dry stuff did work good enough for him to burn. Planer and moulder shavings made the best briquettes. Finer dust also worked (he made a lot of sanding dust) and made an acceptable but crumbly briq. Over the last two years of his briquette making he experimented with moisture and chip size and showed me many samples. In the end he settled on processing the dust as it was. He said the briqs maybe were not always pretty enough to sell but they all burned very well in his Central Boiler brand outdoor wood burner. Wood scraps were also burned buy just tossing them in the stove. I will probably eventually grind mine for ease of handling and storage.
From contributor G:
We now have all the equipment on our site. The Weima briquette maker is in place and operatable. We made some briqs and it worked good with both fine and coarse dust. We are now in the process of repairing (rust and bearings) an 8' diam. x 20' high sawdust holding bin. The shop dust collector will blow into this bin. It has beaters, to stop the sawdust from bridging, right above a cross auger that will discharge into the Weima's hopper. So far so good.
From contributor H:
Any thought’s using the briquette machine for barbecues? Would it work or is too much smoke?
From contributor G:
Briquettes burn like small pieces of wood. I would think there would be smoke but I have never tried it.
From contributor N:
You can briquette them with a barbeque briquette machine. Essentially, charcoal is just heated wood in like a gasifier system. It is heated and gives off the gases but doesn't actually burn. Charcoal is the leftover residue that is pressed together. If you just use the briquettes in a stove, without charring them, It will burn quickly like small pieces of wood, but it will work.
From contributor G:
The guy I bought my briquetter from said he sold briquettes to people for campfire wood. Once bagged it was cleaner and easier to haul to the campground.
