operating the big box biochar kiln to maximize biochar production

Operating a Large Biochar Kiln and Implementing Best Practices

Hazardous fuels are a major problem on wildlands throughout the West1. As fire managers can do little to control the weather, controlling fuels is their best option2. The goal of this method is to provide a new, scalable tool for reducing waste wood while producing biochar in an economically and practically accessible manner. Foresters traditionally pile and burn material from logging and fuel reduction projects, but air quality restrictions and longer fire seasons have made open pile burning much more difficult over the past decades3. Furthermore, open pile burning has been shown to cause potential long-term damage to soils from the excessive heat4. All these challenges provide the reason why the UBRG is developing this technique for biochar production. The UBRG set out to provide a low-cost, high-accessibility approach to hazardous fuel reduction that results in a valuable product5. This approach of turning fuels into feedstocks and attempting to make value from low-value wood is rife with challenges. This approach conserves a portion of that carbon, which is otherwise lost to burning or rotting, and processes it into a durable form, with a half-life approaching 1,000 years in the soil6; this is 10-1,000 times longer than residence times of most soil organic matter7.
The Big Box kiln design process began with a review of other derivatives of a technology that originated in Japan. In 2011, Inoue et al.8 reported on the carbonizing efficiency and quality of biochar produced in the &#34;smokeless charcoal kiln M50&#34; manufactured by the Moki company in Japan. Biochar was produced in these small, cone-shaped kilns with conversion efficiencies ranging between 13% and 19.5% on a dry mass basis. The authors found that the values of fixed carbon and carbon content of the char were equal to those of charcoal made in a retort method at the temperature of about 600 &#176;C.
The Big Box shape was first suggested by Kelpie Wilson in a feasibility study for the North Dakota Forest Service on carbonizing shelterbelt tree removals. Wilson suggested using a modified steel trash dumpster as a flame cap kiln for processing larger-sized material. The Big Box kiln design includes several improvements to the concept that help with durability, usability, and mobility, as described below. Wilson&#39;s figure includes suggestions for repurposing containers such as dumpsters and oil tanks for this purpose; however, repurposed material generally has been painted or galvanized and may expose workshop participants to harmful chemicals in the air.
Emissions from the Big Box Kiln have not yet been reported, but Cornelissen et al.9 conducted emissions testing on several different types of Kon-Tiki kilns (a deep cone kiln) and found that emissions were generally lower than those from open burning of biomass feedstocks. They also tested the biochars produced for polycyclic aromatic hydrocarbons (PAH) and found that PAH levels were well below the Norwegian maximum tolerable risk (MTR) level for soils. A life-cycle analysis of the Oregon Kiln (a shallow pyramid-shaped kiln) showed that the in-woods operation of a flame cap kiln was carbon-negative, resulting in a net sequestration of atmospheric carbon in soil10.
One limitation of the Big Box approach is wet feedstock. While two batches per day of large-diameter material in these kilns is a reasonable expectation in arid climates and dry feedstock, one batch a day is a more reasonable expectation in locations with higher humidity and fuel moisture. Dry feedstock is more productive; wet feedstock will limit the productivity of the kiln. Wet feedstock on a wet day does not work well. Wet feedstock less than 10 cm in diameter will pyrolyze more completely than larger-diameter wet feedstock. Dry material can easily be pyrolyzed in wet and/or snowy weather. Big Box kilns have successfully pyrolyzed kiln-length dry logs upwards of 0.76 m (30 inches) in diameter and branches down to less than 1 cm in diameter.
Kiln operation is treated like open pile burning by most air quality regulators and, in Utah, permission is only granted three&#160;days in advance, which makes planning difficult, especially in winter months when atmospheric inversions are common around our communities. The cost of conducting a biochar burn is much higher than simply burning the piles, which presents another limitation of this approach. This technique is the first published low-tech method for biochar production at a scale that forgoes expensive preprocessing of feedstocks such as grinding and chipping prior to pyrolyzing. This method is useful for most woody debris that has not been chipped or processed beyond cutting into manageable piece sizes. This method is not useful for small piece-size feedstocks or feedstocks that will form mats or globs of material such as grasses, corn stover, and rice hulls.
Kiln design 
The BB12 is a double-walled kiln that is 3.7 m (12 feet) long, 1.8 m (6 feet) wide, and 1.2 m (4 feet tall), made from 14-gauge steel. The size and shape can be varied. Plans are available on the UBRG Website11. No air is allowed into the kiln except at the top; this is critical to developing the flame cap that consumes most of the combustibles as they rise through the heat column. See Figure 1 for details of the inside corners of the kiln. The exception is a drainage port, referred to as the dog door, shown in Figure 2 because it is similar in size to a common dog door. It has a sliding piece of metal with a handle so it can be pushed down closed when operating the kiln and lifted (Caution: Hot) when ready to dump the kiln.
The two walls are separated to provide an air gap12 and are open on the top and not completely sealed on the bottom, except on the interior of the kiln. See Figure 3 for details of the air gap and the top of walls. Avoid sealed spaces to avoid problems during heat expansion and resultant contraction. Single-walled kilns are still effective at reducing hazardous fuels and producing biochar, but the double-walled kiln allows for equipment and operators to get close with less heat exposure. If biochar production is the most important goal, a double-walled kiln might be more effective. If hazardous fuels reduction is the primary goal and biochar is secondary, a single-walled kiln is likely adequate.

Installation of the Big Box Biochar Kiln for Biochar Production

Big Box Biochar Kiln Operation and Best Practices

Begin by loading the BB12 onto a trailer for transport, using either a mini excavator and chains or a four by four forklift using the fork pockets. Next, with the help of ratchet straps, with a breaking strength of over 1, 361 kilograms each, secure the kiln to the trailer. Proceed to unload the kiln, either by using the mini excavator or forklift, or by tying it to a tree or vehicle and driving away, allowing the kiln to fall to the ground.At the site, use a pickup truck and straps to drag the kiln on skids. Next, place the BB12 on a flat surface near the wood pile, and ensure the dog door draining panel faces downhill if placed on a slope. Select feedstocks of any woody species, and use small, dry material to start the kiln, particularly when working with wet feedstock.Gather an adequate amount of feedstock and cut it to lengths shorter than the maximum kiln dimensions for easy fitting. Then, construct a fire line around the kiln, ensuring the fire cannot escape. Make sure to have a charged hose with sufficient water supply on hand for fire control before starting the kiln, considering the current fire hazard.

Operating the Big Box Biochar Kiln to Maximize Biochar Production

After installing the kiln, using a mini excavator, load the kiln randomly with feedstock, disregarding the size or order of added feedstocks. Next, pile a layer of small diameter fuels on top of the kiln to facilitate a quick ignition. When ready, use a drip torch, propane torch, or other ignition device to light the top of the kiln first.Allow the kiln to burn down. Add fuels gradually as needed, and tend the kiln similarly to a campfire. Monitor the kiln and surrounding vegetation for sparks or embers that could cause unwanted ignition.Proceed with tending and loading the kiln until it is full, the feedstock is depleted, or the shift ends. Once the kiln is full or nearly full of coals and flaming combustion turns into smoldering or glowing combustion, use a 3.8 centimeter diameter hose and a water pump from a water source or a water truck to quench the kiln with approximately 300 gallons of water. After quenching the kiln, open the dog door to drain the water, making the kiln lighter for tipping out the biochar.Dump the kiln contents onto the ground next to the kiln after it's fully quenched and drained. Using chains or straps attached to the machine, pull the kiln towards the machine. Before leaving the site, ensure the fire is out by moving hands through the entire amount of biochar that was produced.

operating-the-big-box-biochar-kiln-to-maximize-biochar-production

Research

JoVE Journal

Environment

233 Views.  Utah State University. After installing the kiln, using a mini excavator, load the kiln randomly with feedstock, disregarding the size or order of added feedstocks. Next, pile a layer of small diameter fuels on top of the kiln to facilitate a quick ignition. When ready, use a drip torch, propane torch, or other ignition device to light the top of the kiln first.Allow the kiln to burn down. Add fuels gradually as needed, and tend the kiln similarly to a campfire. Monitor the kiln and surrounding vegetation fo...

Video: Operating the Big Box Biochar Kiln to Maximize Biochar Production

Big Box biochar kilns are an alternative to open pile burning that allows for in-woods biochar production in a simple metal box with no moving parts. This approach is based on technology used by charcoal makers for centuries but with a modern, mechanized approach. A mini-excavator or other piece of machinery is used to load, tend, and empty the kilns. This article will outline Big Box biochar kiln best practices, including the design, transportation, placement, loading, lighting, quenching, and dumping procedures for beginners developing their own Big Box biochar kiln programs. 
Biochar production requires a low oxygen burning environment, and the Big Box kilns use a flame-cap (sometimes referred to as a flame-curtain) method to burn material with limited smoke production. These kilns have been designed to be easily transferred to the site using an adequately rated trailer. A mini-excavator or other piece of machinery is used to load, tend, and empty the kilns. The author is not aware of a more accessible means for people to sequester durable carbon on the farm, ranch, or in the backyard. This article outlines Big Box biochar kiln best practices, including the design, transportation, placement, loading, lighting, quenching, and dumping procedures for beginners developing their own Big Box biochar kiln programs.

The Utah Biomass Resources Group (UBRG) has scaled-up simple biochar kilns in an innovative approach to hazardous fuel reduction and biochar production using metal boxes, called Big Box kilns, that allow for in-woods biochar production. This article outlines Big Box biochar kiln operation and best practices.

Big Box biochar kilns are an alternative to open pile burning that allows for in-woods biochar production in a simple metal box with no moving parts. This ...