All biochar reactors should be designed to:
- be easy to load and unload,
- handle the high heat,
- burn the released gases without emissions that exceed local environmental limits
- be safe to operate.
Varying with specific kiln design and cost, most kiln categories can be constructed:
Important physical properties of fresh and aged biochars include:
The chemical, electrical and magnetic properties include:
All biochar reactors should be designed to:
Continuous devices are more complex and expensive, but provide:
Traditionally, production of charcoal occurred in batch earth, brick or metal kilns and had very high emissions (particulates, methane and other unburnt hydrocarbons). These polluting kilns are not acceptable today.
Modern batch devices achieve low emissions by efficient mixing of air and gas.
The advantages of modern batch kilns are the low cost, capacity to use larger feedstock (e.g. logs), ease of operation, portability and relatively low emissions when operated correctly.
The disadvantages can include:
Kirk Harris – Natural Draft TLUD stove
Fill pyrolysis chamber with biomass, place wood in main chamber and start fire. Heat from the fire is transferred to the pyrolysis chamber, releasing volatile gases. These gases are burnt in the wood flame.
Secondary air is provided to efficiently combust the pyrolysis gases.
The cone kiln was developed in Japan and has been used to make wood and bamboo biochar for over 200 years. It consists of a steel cone that can sit on the ground. Pyrolysis occurs inside the kiln and burning occurs at the top of the kiln.
Why do you get efficient burning in a cone kiln?
Air updrafts past the rim of the kiln, pushed from below by convection up the hot kiln wall, and pulled from above by the low pressure created by the updraft above the kiln.
Emission factors for CO2, CO, CH4, TSP (aerosols, derived from PM10), non-methane volatile organic carbon (NMVOC), nitrogen oxide and nitrogen dioxide (NOx), and the sum of all products of incomplete combustion (PIC). Error bars represent standard deviations from 50 to 250 individual measurements
Method of Firing
The goal in operating the Kon-Tiki is to maintain a full flame cap in the cone to:
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.
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 water because 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:
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.
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.
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.
In this production run in Australia the biochar produced from wood was covered in a mixture of
We covered the biomass clay mixture with biochar to capture any smoke that was emitted but no smoke was observed
Vietnam, May 2016
Vietnam, May 2016
For larger scale applications many companies and organisationsmay want to either purchase the kiln and associated materials handling and biochar processing equipment or manufacture all of some of the the plant.
It is recommended that a functional specification of both the whole plant and the plant components is prepared to ensure that the unit is fit for purpose.
A functional specification can have the following contents:
Include a detailed specification of the equipment items that comprise the whole plant, from feed reception to discharge of solids, liquids and gases.
The desired biochar properties will determine the type of plant that will be purchased (or designed and manufactured)
Start by defining the desired qualities and properties of the biochar. These could include:
See guide “Properties of Fresh and Aged Biochar” for more detail
Specify the following
Consider the risks for operators and the public, along with all relevant regulations, for each phase of the process including loading, start-up, operation, shut-down, unloading and storage.
Risks could include:
A check list should include the following topics:
Suitability of the equipment for purpose & location
Regulatory requirements for:
Health and Safety
Air and water emissions
Application of biochar to soil
Control system for plant operation
Cost benefit analysis
Training, Staffing & Commissioning requirements
Warranties and support offered
What pressure relief system is provided to prevent/minimize explosions?
What deviation from the specification is permissible without causing safety issues?
What warranties are offered on sub-contracted items and what level of support can be expected and for how long?
Have the materials, components and manufacturing process been appropriately selected to withstand temperature, pressure and weight stresses during operation?
Does the feedstock come from a sustainably produced source?
Are there risks associated with a particular feedstock? For example carcinogens may be produced when pyrolysing certain feedstocks under certain conditions.
Does obtaining the feedstock have any other negative environmental implications (on humans, animals, plants, biodiversity, water, land-use)? Does the biochar have any components which are toxic to certain organisms or plants growing in the soil?
Are there any solid or liquid (e.g., tar) wastes to be disposed of? What are the relevant regulations and how will this/these material/materials be effectively dealt with?
Have all relevant standards been complied with?
Gaseous and particulate emissions standards, obtained from the applicable Environmental Protection Agency (or equivalent).
Manufacturing standards (e.g. CE certification mark).
Ratings for regional classifications such as the ATEX rating for explosive atmospheres in the EU.
Noise and odour standards beyond the site boundary.
Standards for water disposal.
Standards for application of biochar to soil.
Does the plant need to be fully automated? If so, what level of sophistication is required?
Does the plant instrumentation provide sufficient data on the process so that a life cycle assessment and cost benefit analysis may be performed to measure the energy, greenhouse gas and economic impacts of the process?
What level of training is required for plant operation?
How many shifts are required to operate the plant?
How will staff be trained and certified that they are proficient in its operation, with the required awareness of the nature of the process, operating conditions, safety issues and potential hazards?
Who is responsible for plant commissioning, start-up and handover?
Are long term operation and maintenance contracts available from the plant provider (if purchased)?
There are now a number of companies producing pyrolysers that can be taken to the biomass in the field to convert it to biochar. These have been designed to have minimal emissions. There are two types of machines: batch and continuous.
Batch and continuous kilns are transported on a truck, or integrated into a trailer.
Emissions are minimised through careful management of air introduced into the flaming combustion zone.
Water must be available to quench the biochar and prevent fires.
Temperature of the biochar can be controlled with water sprays.
In operation in Peru B4SS project
Example: Exeter Kiln
Wood is placed in the inner chamber and the inner door is shut. A wood fire is started under the inner chamber. The water vapour and the volatile gases come out of the inner chamber and pass through the wood fire where they are burnt. Once the temperature reaches 300-350°C then the retort does not need any external heat.
The Kansai kiln uses a screw feeder that sits inside a trough. The pyrolysis gases are combusted above the trough and the heat is reflected down onto the moving biomass. The biomass must have a diameter less than 10mm. The reactor biochar temperature is approximately 450°C. The yield varies between 25 and 40% depending on feedstock. The kiln has a biomass feed input of 300-1000kg/hr.
Biomass Tech & Equip Pty Ltd is manufacturing a trough pyrolyser. The principle used is similar to the Kansai kiln. Water is injected to give flameless very low emissions combustion. The input is 300kg/hr of poultry litter.
Leakage of gases is prevented by a negative interior pressure, maintained by draft & process controls.
All Power Labs Power Pallet
Example: ICM Auger Kiln Gasifier
Drying as well as gasification takes place in the kiln. To achieve this, air is introduced along the kiln to cause some of the biomass to burn. At the front of the kiln the water vapor is removed and taken to the exit. An auger moves the biomass along the kiln where it is pyrolysed and gasified. A gas rich in CO, hydrogen and methane is produced.