Biochar: how to make it into granular fertilizer?
The use of biochar as soil improver and climate change mitigation strategy has gained much attention.
The amount of agricultural and forestry waste generated each year is huge, and the total volume still maintains a growing trend. At present, the mainstream treatment method is to dispose of it or directly stack it for incineration, which not only wastes resources but also pollutes the environment. Therefore, the use of agricultural and forestry waste has gradually become a hot issue, and it is imperative to find new ways to use this valuable resource efficiently.
On the other hand, the huge role played by fertilizers in crop growth and yield increase is self-evident. Data shows that fertilizer use is increasing year by year. The release of nutrients from common fertilizers is fast, and a large number of nutrients are easily lost, the utilization rate is not high, and environmental damage is caused. Therefore, it has become an important research direction to develop and develop environmentally friendly new fertilizers, improve the utilization efficiency of chemical fertilizers, and reduce the damage to the environment.
Although biochar is a new term, the application of biochar into soils is not a new concept. Native pre-Columbian civilisations in the Amazon Basin added biochar to their soils and increased their fertility. Whether they did it on purpose or by accident is uncertain. Because of their black colour and origins, these soils are known in Portuguese as Terra Preta de Indio (Indian black earth). Today, biochar is especially valuable in areas with inadequate water supplies and severely depleted soil.
What is Biochar?
Biochar is defined by the International Biochar Initiative as "The solid material obtained from the thermochemical conversion of biomass in an oxygen-limited environment".
Biochar is the solid product remaining after biomass is heated to temperatures typically between 300°C and 700°C under oxygen-deprived conditions, a process known as “pyrolysis. In contrast to the original biomass feedstock that mainly contains cellulose, hemicellulose, and lignin, biochar falls into the spectrum of materials called “charcoal” or “black carbon” but excludes black carbon derived from fossil fuels or non-biomass wastes.
Biochar can be produced from many types of feedstock including: agricultural wastes, rice husks, bagasse, paper products, animal manures, and even urban green waste.
8 Benefits of Biochar
Biochar is a valuable Soil Amendment
1) Enhance plant growth and reduce need for water and fertilizer.
This is because more moisture and nutrients remain in the soil and don’t leach into the groundwater.
2) Improve water quality and quantity by increasing soil retention of nutrients and agrochemicals for plant and crop utilization.
More nutrients stay in the soil instead of leaching into groundwater and causing pollution.
3) Due to its adsorption ability, some biochars have the potential to immobilise heavy metals, pesticides, herbicides, and hormones; prevent nitrate leaching and faecal bacteria into waterways; and reduce N2O and CH4 emissions from soils.
Biochar is a Powerfully Simple Tool to Combat Climate Change
Carbon in biochar can persist in soils over long time scales. Beyond the carbon sequestered in the biochar itself.
1) Soil Fertility: Biochar can improve soil fertility, stimulating plant growth, which then consumes more CO2 in a positive feedback effect.
Reduced fertilizer inputs: Biochar can reduce the need for chemical fertilizers, resulting in reduced emissions of greenhouse gases from fertilizer manufacture
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2) Reduced N2O and CH4 emissions: Biochar can reduce emissions of nitrous oxide (N2O) and methane (CH4)—two potent greenhouse gases—from agricultural soils.
3) Enhanced soil microbial life: Biochar can increase soil microbial life, resulting in more carbon storage in soil.
4) Reduced emissions from feedstocks: Converting agricultural and forestry waste into biochar can avoid CO2 and CH4 emissions otherwise generated by the natural decomposition or burning of the waste.
5) Energy generation: The heat energy—and also the bio-oils and synthesis gases—generated during biochar production can be used to displace carbon positive energy from fossil fuels.
3 Types of Biochar fertilizer
Various possible applications of biochar have been suggested including using it as a fuel source, composting additive or heavy metal adsorbent in wastewater. However, the most promising uses for biochar are as a carbon sequestration technique or soil amendment. The physical and chemical properties of biochar make it an ideal candidate for these applications.
Biochar fertilizer can be split into 3 types: carbon-based Organic Fertilizer, carbon-based Inorganic Fertilizer and carbon-based Compound Fertilizer
1) Carbon-based Organic Fertilizer,
refers to the ecological fertilizer formed by the reasonable compatibility of biochar powder with organic fertilizer.
2) Carbon-based Inorganic Fertilizer,
refers to the ecological fertilizer formed by the reasonable compatibility of biochar powder with inorganic fertilizer.
3) Carbon-based Compound Fertilizer,
refers to the ecological fertilizer formed by the reasonable compatibility of biochar powder with organic inorganic compound fertilizer (compound fertilizer).
Disadvantage of biochar powder
Biochar has shown potential as a soil amendment, but it is difficult to package, transport, and handle due to its size. Biochar is a fine powder with a particle size between 1 and 100 microns and can easily become airborne during processing and application to soils. Application to soil in Quebec, Canada, using standard farm machinery resulted in an estimated 30% loss of biochar through entrainment into the air. Entrained biochar can negatively affect human health through respiratory irritation and lung damage.
How to solve the problem? Making biochar pellets
Techniques have been proposed to reduce biochar dust hazards including pelletization, increasing biochar powder moisture and the addition of biochar to aerobically digested slurry.
The on-site addition of water or slurry to biochar powder to dampen it could decrease dust problems during spreading. But it requires additional manual labour and may not reduce all dust issues. Although beneficial, these applications do not completely eliminate dust hazards and do not consider other possible problems.
Wet granulation of biochar could eliminate both processing and cultivation problems. The compaction of biochar powder into pellets increases the ease of handling of biochar and decreases transportation cost through increased packing efficiency. It also potentially increase biochar's consumer appeal.
How to make granular biochar fertilizer? Using granulator machine
There are many kinds of granulators in the market, such as disc pan granulator, rotary drum granulator, double roller granulator and Ring die granulator, which kind granulator should be selected? It depends on properties of the final granular fertilizer.
Key properties for granular fertilizers are the granule size, flowability and strength.
A specified granule size range must be maintained to ensure granules can be used in standard fertilizer equipment. Granule size is also important for even distribution of fertilizer nutrients during cultivation. If the fertilizer nutrients are not evenly distributed, some plants can receive fertilizer burns from over fertilization or a lack of growth from under fertilization.
Granule flowability is important during processing and application to soils where granules need to flow through equipment.
Fertilizer granules must be strong enough to maintain their shape during storage, transportation or application.
4 kinds of fertilizer granulator machine
The granulator selected must ensure that the product granules meet the required specifications for these fertilizer properties.
1) Disc pan granulator
It is mainly composed of Motor, Reducer, Spindle, Disc, Scaffold, Scraper, etc. The working principle as below,
The pan revolves at a certain angle with horizontal plane driven by the motor through reducer. The powder will ride along with the revolving pan under the friction between the powder and the pan. On the other hand, the powder will fall down under the function of its gravity. At the same time, the powder is to the pan edge because of the centrifugal force. The power material rolls in a certain trace under the function of these three forces. It gradually becomes the required size, then overflows by the pan edge.
The Disc granulator could produce granules with 0.16-6 mm, but the granules are very soft, not dense enough. They are very easily broken to powder during storage and transportation. The pellet rat is only about 50-60%, much material should be returned for second process. What's more, a lot of dust will be generated during the production process and it is dangerous and harmful for workers' health. This disc pan granulator is mainly used for chemical fertilizer.
2) Rotary drum granulator
It is mainly composed of Motor, Reducer, Drum, Driving gear, Gear ring, Track ring, Support roller, etc. The work principle as below,
The pulley is driven by the motor, and the power is transmitted to the driving gear on the shaft through the speed reducer, which leads to the rotation of the gear ring that meshes with the driving gear, and the drum rotates together as it is connected with gear ring. Fed the material into the drum from the hopper, then it rolls with the drum and gradually forms spherical balls under the action of the wavy inner wall of the drum, and discharges from the discharge end.
The rotary drum granulator has the same disadvantage as disc granulator. The output granules are very soft and the pellet rate is low. It is also mainly used for chemical fertilizer production.
3) Double roller granulator
It is mainly composed of Motor, Reducer, Spindle, Roller, Screw feed hopper, Hopper, etc. The machine has a pair of rollers with the same diameter. The rollers rotates in the opposite direction at the same speed. The same concave pits are distributed on the surface of the roller. The material is added into the screw feed hopper, and pass through the double rollers and molded into granules.
The granules made by the double roller granulator are strong enough, but they are oval.
4) Ring die granulator
The entire ring die granulator includes two parts, Pellets part and Balling part (Polishing machine). The pellets part turns the raw material that fed into the granulator into cylindrical pellets, and then the cylindrical pellets are polished to spherical granules by the balling part. So both round ball granules and cylindrical pellets could be produced by the Ring die system granulation machine.
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| Ring die granulator machine from Harbin Dadi Machinery |
The detailed working process as below,
The raw material goes into working chamber and fall on the ‘dump tray’, then thrown into the ring die by centrifugal effect. The ring die and rollers system turning drive by reduction gears & transmission which energy from motor. The pressure come from ring die and rollers system running, cylinder form are forced extrusion from ring die hole which cut into small pellets as required by cutting line.
The cylinder form pellets fall onto the disk in the polishing drum, and thrown onto the wall of drum with circumferential movement by high-speed rotating disk, the granules in a circular motion at the same time also in radial rotation motion due to centrifugal effect . Mutual friction make the granules with edges and corners into balls gradually due to granules’ moving . At the same time, ball shape granules gradually floating on the top, final granules overflow along with quantity of granules increased in the drum .
The granules produced by ring die granulator are strong enough to keep their shape during storage, transportation and application. Pellet rate is higher than 90%.
Both cylinder form pellets and spherical granules can be made by the Ring die system granulator machine.
It is the best choice for making biochar pellets.
Any further question, feel free to contact me.
Amy Lee
Tel / Whats app / Skype / Wechat: +86 13475961259
Email: amylee516@outlook.com
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