Charcoal Making Indirect Method by Dan Gill

You really can make your own charcoal at home – even if you live in the suburbs!

If you use the indirect method, which burns the gasses, and use a clean burning fuel (such as natural or LP gas) the emissions are mostly water vapors with very little smoke. It is not difficult to do and, even when burning waste wood to provide the carbonizing heat , the process requires less time and attention than barbecuing a rack of ribs in a wood burning smoker.

55 GALLON DRUM CHARCOAL RETORT 12

Introduction

Why would anyone want to make their own charcoal? For one thing, good hardwood lump burns hotter and cleaner than briquettes and is much easier to light. You also know where it came from, what it contains and what was done to it en route. There are endeavors other than barbecue that require high quality natural charcoal: It is still the preferred fuel for forges and blacksmithing.

Folks who make their own fireworks and black powder need specialty charcoals with specific burning properties such as that made from willow or grapevine. When grilling or even barbecuing in open pits with charcoal and wood, the quality of the charcoal is really not that critical. There is enough airflow to dilute impurities. Now that I have a Weber Smoky Mountain, though, charcoal quality, impurities and additives become very important. It is a great little cooker and will do everything folks say it will, BUT there is precious little airflow and the meat is bathed in smoke for hours.

What you burn, you eat! I have read how the major manufacturers make briquettes. That leaves me either burning to coals, which is impractical for the small amount of coals needed by the WSM, or making my own lump, which is just a way to burn to coals and store them for use as needed.

Being somewhat of a skinflint, I would rather utilize the resources at hand and make my own lump as opposed to buying it. My objective in this endeavor was to use existing technology to design a simple, cheap, reliable and efficient method for the small-scale production of charcoal for home use utilizing readily available materials and minimizing the release of pollutants.

How to make Charcoal:

Timing is important. Plan to start your burn on the hottest, muggiest day of the year with a comfort index of at least 105 and air quality just above the minimum to sustain life. These conditions won’t affect the charcoal process at all but will ensure that the experience is memorable.

There are two basic methods of making charcoal: direct and indirect:

  • The direct method uses heat from the incomplete combustion of the organic matter, which is to become charcoal. The rate of combustion is controlled by regulating the amount of oxygen allowed into the burn and is stopped by excluding oxygen before the charcoal itself begins to burn. This is the ages old method used by colliers to make charcoal in a pit, pile (clamp) or, more recently, in metal or masonry chambers (kilns). See the links below for more information.
  • The indirect method uses an external heat source to “cook” organic matter contained in a closed but vented airless chamber (retort). This is usually carried out in a metal or masonry chamber (furnace). The indirect method results in a higher yield of high quality charcoal with less smoke and pollutants and requires less skill and attention than the direct method.

For my first tests, I decided to try the indirect method. There had been some posts on a pyrotechnics newsgroup describing a procedure for making small quantities of willow or grapevine charcoal in a cookie tin or five gallon bucket. For the furnace, I used a 55 gal oil drum with the top cut out and a 12″ wide X 10″ high hole cut in the lower side for maintaining the fire. I used two iron rods stuck through the sides about 8″ from the bottom to support the retort. I also kept the top which had been cut out. After the fire was well established , the top was placed on the drum and supported by rods to help hold the heat in yet allow a good draft. The retort was a 16 gal. steel drum with lid and I cut about six 3/8″ holes in the bottom with an acetylene torch. I burned it out well in the furnace to eliminate petroleum residues. These drums are used for lubricants such as transmission fluid and gear grease and are readily available.

After the retort was loaded with air dried hickory the top was sealed and the drum was placed in the furnace or burn barrel. Wood scraps and bark were placed under the retort and around the sides and lit with newspaper assisted by a little burnt motor oil to get things off to a fast start. There was right much smoke for the first hour, but as things heated up and the moisture was driven off, it burned so clean that all you could see were heat waves. With the vent holes located in the bottom of the retort, the vapors and gasses were discharged into the hottest part of the fire and burned.

I stopped the first test too soon and only had about 1/3 charcoal. The rest was charred chunks of wood. The second test burned for about 3 hours, until the gasses had just stopped burning around the holes in the bottom. Results: 56# of wood yielded 17 1/2# charcoal or 32% by wet weight. Assuming an EMC (equilibrium moisture content) of 12%, The yield exceeds 35% on a dry matter basis. This is very good as most direct burns result in 20 to 25% at the best. I got over 2 1/2 five gallon buckets of good lump and only one large (4″X6″) chunk showed signs of incomplete conversion with some brown in the center.

I was going to run a series of trials to compare the indirect method with direct (bottom lit) and direct (top lit). After several burns using the retort, I decided that there were such obvious advantages to the indirect method that I abandoned studies of direct burns. The retort method is easy, reliable, and does not require the skill and attention of direct burns. The equipment and materials which I used are readily available worldwide. As the gasses and volatiles are discharged into a hot bed of coals, I believe that most of the pollutants are burned, adding to the furnace heat. I also suspect that yield and quality are better. From what I have read, 35% by dry weight is excellent; the resulting charcoal burns hot and clean; you can almost light it with a match.

The indirect method also appears to be more compatible with heat recovery and waste wood utilization systems.

I live on a farm in Virginia and my wife operates a small sawmill. Disposing of slabs and wood waste is a serious problem. I can burn a lot of the hardwood slabs in my indoor masonry heater/cooker.

We have not found an economical use for pine slabs (we can’t give them away) and have started burning them in a field. This is obviously a wasteful and polluting practice. My ultimate goal is to build a small masonry furnace that would hold several 55 gallon drum retorts and recover heat for domestic space heating during the winter.

Charcoal could be a marketable by-product. I would burn pine slabs and waste wood in the furnace and make charcoal from hardwoods in 55 gallon drums. This approach appears to be very energy efficient as the gasses released by destructive distillation are utilized.

 Indirect method Charcoal Making Log and Results

Furnace: 55 gal drum with lid cut out and a 12″ wide by 10″ high opening in the side at the bottom. Holes were burned about 8″ up on the sides to put two 3/8″ electric fence rods in for the retort to rest on. The idea was to be able to pull the rods out at the end of the burn and allow the retort to settle in the ashes to exclude air.Retort: 16 gal oil drum with sealable lid. 6, 3/8″ holes were burned in the bottom with a torch to allow gasses to escape.

Wood: 51.5# of air dried chunks (+/- 20% EMC not measured). Mostly hickory ranging up to 3″ thick.

Heat source: hardwood slabs and bark in bottom and around sides. Newspaper and burnt motor oil as accelerants.

Misc: Welders gloves, shovel, platform scales,

Conditions: overcast, spitting rain occasionally. temp about 80 deg.F breezy with variable winds 8-12 mph

 

 

Procedure

2:40 started fire. Rods started to soften and bend within 10 minutes allowing retort to settle against one side.

3:00 (+20 min) After the fire was going good, I placed two rods across the top of the furnace barrel and positioned the cut-off top to hold heat in yet allow good draft.

3:30 (+50 min) Roaring sound as gasses burned off through holes in bottom of retort and around leaks in top.

3:40 (+1 hr.) No smoke – nothing but heat.

3:45 (+1 hr. 5 min) Tried to pull rods to allow drum bottom to settle in ashes to seal but they had melted too much to pull out. Fire mostly burned to coals.

3:50 (+1 hr. 10 min.) Outgassing stopped rather abruptly.

4:00 (+1hr. 20 min.) Carefully dumped over burn barrel to remove retort. Could hear charcoal clinking inside. Retort was fairly heavy (not a good sign). Set retort upright in dirt and packed dirt around base to exclude air. Left to cool.

7:00 (+4hrs. 20 min.) Retort cool to the touch. removed top. Contents had not settled much. Smaller pieces and the outside of larger pieces had become charcoal; larger pieces were still brown indicating incomplete conversion.

Results: The burn was stopped too soon yielding about a five gallon bucket of good charcoal and a lot of charred chunks of wood. Possibly the fire had cooled some so that the retort stopped outgassing and I thought the burn was complete. There was no sign of ash or any indication of flame in the retort.

Methods and materials:As above except as noted.

Wood: 56# of 2 yr. old hardwood (mostly hickory) air dried to about 29% EMC.

Used 1/2″ square hardened rod to hold up retort.

Conditions: 80_ F. light wind.

Procedure:

2:35 (start) lit fire with newspaper and some burnt motor oil.

3:10 (+35 min.) Outgassing starts. Added enough wood during the burn to keep temp up.

5:00 (+2 hrs 25min.) Outgassing about complete. Pulled rods to allow can bottom to settle in coals and ashes sealing holes.

6:00 (+3 hrs 25 min.) Lifted retort can – feels light indicating a complete burn. To ensure an oxygen-free condition and to facilitate faster cooling, I removed the retort from the furnace barrel and placed it on dirt, pulling dirt up around the bottom.

7:35 (+ 5 hrs.) Can cool enough to handle. Opened top and found the results of a good burn. Volume had decreased by about 1/3 and all of the wood appeared to have converted to charcoal.

Results: 56# of wood yielded 17 1/2# charcoal or 32% by weight. This is very good as most direct burns result in 25% at the best. I got over 2 1/2 five gallon buckets of good lump and only one large (4″X6″) chunk showed signs of incomplete conversion with some brown in the center.

Read this article for making charcoal in direct method

Source : pine3.info/Charmake.htm

by Dan Gill Published in Pleasant Living March-April ’07

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