Choosing a biochar reactor to meet your needs - Biochar for Sustainable Soils (2022)

Operation of a Kon-Tiki

Firing

  1. Build an upside down fire on the bottom of the kiln to nearly the rim (so it is easy to light and sustain plenty of air), either by:
    • Partially filling the kiln with dry brushy material to near the rim
    • Building a crisscross pier of sticks, progressing to smaller sticks towards the top (don’t use big or moist sticks on the bottom – they may get buried and cooled before they are fully charred
  2. Insert some kindling and tinder into the pier or into the top of the brush
  3. If using liquid starter fuel, spray only on top, or use a gel. Do NOT use highly flammable liquid like petrol. It will fall into the lower kiln and be explosive in a confined space.
  4. Once flaming hotly, feed the flame to build a complete fire cap and a strong fire bed.

Choosing a biochar reactor to meet your needs - Biochar for Sustainable Soils (1)

Method of Firing

  1. A fire is started inside the Kon-Tiki. Once the fire is burning well, and flaming across the bottom of the kiln, it provides the heat to dry and pyrolysethe next layer of wood, and the flame cover to burn the smoke.
  2. Each new layer of material in the kiln blackens and chars, and white ash may form on the outside of the biomass, indicating the material has dried out, reached pyrolysis temperature and has begun carbonizing. At this stage the wood will continue to pyrolyse (an exothermic process) even without oxygen, as long as the material stays in a heat field sufficient to overcome heat loss by conduction, convection and radiation. Ash formation is minimized by adding the next layer of wood early in that process so the flame cap is maintained.
  3. The flame cap consumes the smoke diffusing upwards off the pyrolysing wood, radiates heat down onto the wood to continue the pyrolysis, and protects the the biochar formed from oxygen by consuming it before it gets to the char.

During the run

The goal in operating the Kon-Tiki is to maintain a full flame cap in the cone to:

  • dry and heat the biomass,
  • burn the smoke,
  • shield the char from oxygen.

For the cleanest, fastest production add material at a rate that keeps the flames high and the smoke low.Material can be added more rapidly once the kiln is over half full.

  • If the flame is too small or smoky, feed dry thin material
  • If the flame is large, take advantage of the heat to feed heavier or moister material.
  • Do not leave the burn unattended for more than 10 minutes.A 20 minute break might result in the fire dying back and some char turning to ash. Even though ash may not be bad for the biochar, it will reduce the yield, and it may take effort and small material to build the intensity again.

Feedstock Size

  • The length is best kept shorter than the kiln diameter.
  • Don’t use material thicker than will char fully during the duration of the run (roughly 2 hours for a 1.2m kiln and 4-6 hours for a 1.6m kiln).
  • It takes about 1 hour per inch (2.5cm) of radius to fully carbonize wood, so a 4in piece will take about 2 hours to fully carbonize.
  • Don’t use large or moist wood at the start. It may become buried and cooled on the kiln floor before it is fully charred.
  • Similarly don’t let big wood or moist wood roll to the walls of the kiln.
  • Insert bigger wood into the middle of the kiln and of the run. Taper to finish with small wood.

Choosing a biochar reactor to meet your needs - Biochar for Sustainable Soils (2)

(Video) Top Reason Why Biochar Doesn't Increase Crop Yields & 5 Ways to Fix it

Finishing

  • It takes about an hour to finish after the final fuel is added to a 1.6m Kon-Tiki.
  • Yellow flames die away indicating that most pyrogas has been evolved.
  • Quenching from below can be started during this process. Steam generated will be adsorbed by hot char, where it probably cracks and opens up the char.
  • As the flame cap dies fine material can be added that will fully carbonize before the end: fine sticks, bark, straw, leaves, grass clippings. These keep flames going, to burn the remaining volatiles being released. This new material also adds some different ash components that may complex with and enhance the biochar.
  • Remaining flaming embers can be raked into a pile to finish.
  • Apply water mist to the finished hot coals, avoiding remaining flaming areas, to slow ashing and generate steam, activating surfaces.
  • When you are losing char to ash faster than it is being created from remaining uncarbonized wood, flood the kiln fully to stop combustion of the biochar (quenching).
  • The top-most layer of red hot char will float on the water. Quench it with a top spray.
  • Drain kiln overnight, or for a few hours, saving quench/nutrient water if desired.

Choosing a biochar reactor to meet your needs - Biochar for Sustainable Soils (3)

Quenching & Adding Nutrients

A special feature of the Kon-Tiki is the ability to quench the hot char with nutrient laden water right in the kiln at the end of the run. The rapid cooling of the hot char, and the steam that is flashed off and re-adsorbed in higher char layers, cracks the char, activates surfaces, and opens it to nutrients.

You can add to the quench water the minerals and nutrients your soil and plants need. These could include rock dust, acids (phosphoric or acetic acid or wood vinegar ) to neutralize the pH, or manure slurries. Only limited N will be lost from the nutrient rich waterbecause volatilized N will be adsorbed by char. The char is quickly cooled from the bottom up in the first flood, so microorganisms in the quench water will attach to the cooled char and survive.

Quench water e.g. from 1000L bulk liquid tank (optionally with nutrients) is:

  • pumped into the kiln through the bottom drain
  • soaked overnight
  • drained back into the tank next morning

Smoke water/nutrients are recycled and used.

Alternatively, nutrient/quench water can be gravity-flowed from a high tank, and drained to a low tank, or nutrients can be stirred into the biochar slurry.

Choosing a biochar reactor to meet your needs - Biochar for Sustainable Soils (4)

Drying the Biochar

  • Once thoroughly drained the biochar is easy to shovel out.
  • A 1.6m kiln in a cradle kiln is easily tilted and propped for emptying.
  • Biochar is raked out on tarpaulins and sundried for at least 2 to 4 days, covered at nights.
  • Moisture content of sundried biochar has ranged from 34 to 63% weight basis (wb)

Choosing a biochar reactor to meet your needs - Biochar for Sustainable Soils (5)

(Video) Does Biochar Deliver Carbon-Negative Energy?

Choosing a biochar reactor to meet your needs - Biochar for Sustainable Soils (6)

Crushing the Biochar

  • The biochar can be crushed in various ways.
  • Here the sundried biochar is passed through a hammer mill. Too much moisture in the biochar can clog the mill when grinding, and too little causes dust.
  • The milled biochar, raked out on the tarpaulin, may be sprayed with phosphoric acid or organic acid to adjust pH and then further sun-dried.
  • Moisture content of original biomass and sun-dried biochar can be determined by oven drying samples. E.G.
    • Wood feedstock = 15%, wb
    • Biochar = 15-63%, wb (sundried)

Running the Kon-Tiki with agricultural residues

In many places wood is not readily available or it has a high moisture content or the soils have low nutrient content. To efficiently convert high nutrient content biomass that has small particle sizes (e.gmanures , straw etc) simple retorts can be placed in the Kon-tiki to use the residual heat from the biochar

Operation: Find used drums (10-20l) that have a lid.

Load with straw, manure etcwith a moisture content of less than 25%. Loosely fix the lid onto the drum so that the pyrolysing gases can escape and burn in the flame from the pyrolysing wood. Keep adding wood until the kiln is full of biochar and the flame from the drum has ceased. Then quench.

Choosing a biochar reactor to meet your needs - Biochar for Sustainable Soils (7)

Using the residual heat in the biochar to pyrolyse a mixture of manure, grasses, compost and minerals

Quenching with Compost in Peru

Once the kiln has been half to ¾ filled with biochar it can be quenched with a mixture high in organic nitrogen and minerals to promote growth of beneficial micro-organisms.

(Video) Evaluation of Biochar for Agricultural Soil Management in California

Choosing a biochar reactor to meet your needs - Biochar for Sustainable Soils (8)

Choosing a biochar reactor to meet your needs - Biochar for Sustainable Soils (9)

In this production run in Australia the biochar produced from wood was covered in a mixture of

  • 52 kg compost
  • 14 kg soil
  • 63 kg of red clay
  • 23 kg of lump biochar
  • 20kg animal manure

We covered the biomass clay mixture with biochar to capture any smoke that was emitted but no smoke was observed

How pyrolysis of the quenched material takes place

Choosing a biochar reactor to meet your needs - Biochar for Sustainable Soils (10)

Example: Biochar-clay complex from wet feedstock

Vietnam, May 2016

Choosing a biochar reactor to meet your needs - Biochar for Sustainable Soils (11)

(Video) An Alternative to Biochar for Carbon Sequestration • Exaquest Carbon

Biochar-clay complex from wet feedstock

Vietnam, May 2016

Choosing a biochar reactor to meet your needs - Biochar for Sustainable Soils (12)

Waste heat capture from Kon-Tiki in Nepal

Example: Capturing heat from Kon-tiki for distillation of essential oil

Choosing a biochar reactor to meet your needs - Biochar for Sustainable Soils (13)

Choosing a biochar reactor to meet your needs - Biochar for Sustainable Soils (14)

Choosing a biochar reactor to meet your needs - Biochar for Sustainable Soils (15)

(Video) The Science Behind Biochar

FAQs

Which biochar is best? ›

Some authors suggested bamboo, rice, and corn/maize feedstocks are excellent biomass products. Hard bio materials are producing good quality biochar with high recovery percentage. Biochar produced with high pyrolysis temperature gives stronger level of recalcitrant carbon with lesser recovery of carbon and nutrients.

How do you make a big scale biochar? ›

Farm Scale Biochar Part 5 System Design - YouTube

Which technology is used for biochar production? ›

Biochar is produced by heating biomass in the total or partial absence of oxygen. Pyrolysis is the most common technology employed to produce biochar, and also occurs in the early stages of the combustion and gasification processes.

How do you make a biochar retort? ›

Energy Corps Montana: Building a Biochar Retort Kiln - YouTube

What are the disadvantages of biochar? ›

However, when biochar is applied in the agricultural land, some previous studies highlighted some drawbacks of biochar implementation: (i) loss of land due to erosion, (ii) soil compaction during the application, (iii) risk of contamination, (iv) removal of crop residues, and (vii) reduction in worm life rates.

What is the best size for biochar? ›

Most biochar intrapores have diameters (d) <0.01 mm [33, 34]. Based on these constraints, Eq 4 provides ψ < -16.5 kPa when d is less than 0.01 mm. This suggests that the pores smaller than 0.01 mm control water retention of our biochar-sand mixtures when ψ is less than -16.5 kPa.

Can you use green wood for biochar? ›

By choosing clean, non-toxic wood 'waste' we can intercept the carbon before it has a chance to go back into the atmosphere. Make sure your feedstock is dry. Using green or wet material will create smoke which will outweigh any carbon savings achieved through making biochar.

What is a biochar kiln? ›

Introduction to the RoCC Biochar Kiln - YouTube

What is biochar retort? ›

A biochar retort

Biomass (such as wood) will produce gas when heated without access to air. The re- tort drum is sealed except for the vent. It is placed inside a brick kiln to help hold in the heat. The loaded retort inside the kiln. Wood gas burns in self-sustaining reaction.

How long does it take to produce biochar? ›

2. Methods of biochar production
TechniqueTemperature (°C)Residence time
Pyrolysis500−1000 (fast)Hour-day (fast)
Hydrothermal carbonization180−3001−16 h
Gasification750−90010−20 s
Torrefaction29010−60 min
3 more rows

Is biochar the same as charcoal? ›

One major difference between charcoal and biochar is the temperature at which it is made. Charcoal is made at roughly 400 degrees Celsius whereas biochar is made between 600–1000 Celsius. Making biochar at lower temperatures causes volatiles (smokeyness) to be left behind, which has been found to limit plant growth.

Is biochar environmentally friendly? ›

Biochar is considered as a potentially attractive, sustainable, and green support and coating material for CRNFs, because of the cost effectiveness, environmental friendliness, recyclability, renewability, and desirable physical-chemical properties for industrial scale application3,9,10.

Can you make biochar at home? ›

Industrial production of biochar employs pyrolysis; a means of combustion without much air or oxygen and is more efficient in that it produces little ash. However, for most uses, including gardening, biochar can be made at home in a purchased or homemade burner as explained further in this publication.

How do you make a burn barrel biochar? ›

HOW TO MAKE BIOCHAR REACTOR - TLUD BURN BARREL for TERRA ...

What are the benefits of biochar? ›

A special kind of carbon-rich charcoal, it offers gardeners and growers so many benefits:
  • Improvement of soil fertility. ...
  • Increase in crop yields. ...
  • Better water retention and drainage. ...
  • Reduction of soil acidity. ...
  • Adsorption of soil pollutants. ...
  • Increase in plant disease resistance. ...
  • Catching and storing carbon.
Feb 6, 2019

What is the difference between charcoal and bio char? ›

One major difference between charcoal and biochar is the temperature at which it is made. Charcoal is made at roughly 400 degrees Celsius whereas biochar is made between 600–1000 Celsius. Making biochar at lower temperatures causes volatiles (smokeyness) to be left behind, which has been found to limit plant growth.

Is biochar better than compost? ›

Biochar outperforms straw and compost only with regards to sorption. Comparability criteria for experimental studies are recommended (C, N, H, pH, etc.). Constant laboratory conditions often mask amendment effects in soils.

Is biochar the same as activated charcoal? ›

Biochar vs charcoal

Biochar is made in the same manner as charcoal, but it is intended for utilization as an adsorbent and/or a soil amendment. Basically, the key is the end use of the material. It is charcoal if it is intended to be used as a fuel; hence it is manufactured with optimal fuel properties.

Are all Biochars the same? ›

Depending on the feedstock source, biochar may have varying levels of macronutrients (like Phosphorus) and micronutrients (like Zinc) that are essential for plant growth.

Videos

1. Deep Dive: Biomass to Biochar, March 10, 2021
(SSU Center for Environmental Inquiry)
2. Biochar in United States and Southwest - Overview
(University of Arizona Cooperative Extension)
3. Dr Nate Anderson: Forest Biomass for Biochar Production
(US Biochar Initiative)
4. Biochar: Properties and Potential as an Ag Amendment - Webinar
(Cultivating Success Idaho)
5. Hamish Fallside: Demonstration of biochar reactor (Climate Foundation, USA), Part 2
(Sustainable Sanitation Alliance (SuSanA))
6. Biochar and The circular economy - 2021
(Bio360 Expo)

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