Biochar (Carbonized Organic Matter)
Understand what is Biochar and its importance as an effective soil amendments with multiple benefits to the agriculture sector.
Know more on Biochar as a soil amendment
Introduction
Soils have the ability to absorb carbon dioxide and influence its concentration in the atmosphere. Biochar can be used to increase the ability of soils to sequester carbon and simultaneously improve soil health. The goal of this paper is to introduce the concept and origins of biochar, discuss its production process, potential uses, and the benefits and costs of biochar in its key roles in agriculture and climate change mitigation.
What is biochar?
Biochar is just charcoal made from biomass—which is plant material and agricultural waste—hence the name ‘biochar’. It is a fine-grained charcoal produced from pyrolysis: the slow burning of organic matter in a low- or no-oxygen environment. What differentiates biochar from charcoal is its purpose; it is produced as an additive to soils, mainly to improve nutrient retention and carbon storage. 1 Although the history of biochar extends thousands of years, its science is still relatively poorly understood. History of biochar The term ‘biochar’ was coined in recent times, but the origins of the concept are ancient.2 Throughout the Amazon Basin there are regions—up to two metres in depth—of terra preta. 3 This is a highly fertile dark-coloured soil that has for centuries supported the agricultural needs of the Amazonians. Analyses of the dark soils have revealed high concentrations of charcoal and organic matter, such as plant and animal remains (manure, bones and fish). Terra preta’s productivity is due to good nutrient retention and a neutral pH, in areas where soils are generally acidic.4 Interestingly, terra preta exists only in inhabited areas, suggesting that humans are responsible for its creation. What has not been confirmed is how terra preta was created so many years ago. Many theories exist. A frontrunner is the suggestion that ancient techniques of slash-and-char are responsible for the dark earth. Similar to slash-and-burn techniques, slash-and-char involves clearing vegetation within a small plot and igniting it, but only allowing the refuse to smoulder (rather than burn). 5 Combined with other biomass and buried under a layer of dirt, the smouldering char eventually forms terra preta. 6 It is from these hypotheses of early slash-and-char practices that modern scientists have developed methods for producing biochar.
Biochar production
The biochar production process begins with biomass being fed into a pyrolysis kiln—a furnace that burns with little or no oxygen. The biomass could be crop residue, wood and wood waste, certain animal manure, or various other organic materials. At the end of this, two main products come out of the kiln.7 The first is biochar, usually representing about 50 per cent of the carbon content of the biomass. The other is biofuel. The biofuel is often syngas, which is a mixture of mainly hydrogen and carbon monoxide, with a little carbon dioxide. The proportions of the three gases vary according to the processes used to create the syngas. However, the important point is that syngas is combustible and so can be used as a fuel source. Depending on the process, the biofuel from the kiln could also be biooil, which can be used as a substitute for diesel in some engines. The pyrolysis occurs at temperatures below 700˚C; but some parameters can be altered, such as the rate of pyrolysis, or the quantity of oxygen. Generally, faster pyrolysis results in more oils and liquids, slower pyrolysis produces more syngas. Minimising the oxygen present during pyrolysis optimises the production of biochar.8 Pyrolysis can be followed by a second stage: gasification. Gasification liberates more energyrich syngases from the char (usually hydrogen-based). There may also be a ‘gas cleanup’ stage to remove some of the particulates, hydrocarbons and soluble matter from the gas.9 The biofuel generated from the pyrolysis process can be used to create the electricity needed to power the kiln or secondary stages of the process. So it is possible for the system to run autonomous of external power sources. The pyrolysis process described is summarised in Figure 1.
Simplified pyrolysis process flow diagram An important advantage of biochar is that it can be produced either from small, simple mobile units or from larger, stationary ones. Small-scale systems for biomass inputs of 50 to 1000 kilograms per hour can be used on farms, while large units of up to 8000 kilograms per hour can be operated by large industries.10 There are potentially three broad types of pyrolysis systems: • central pyrolysis plants for processing all the biomass in a region. • lower-tech pyrolysis kilns for individual farmers or small groups of farmers (these kilns may not include some secondary stages such as the gasification or gas cleanup). • pyrolysis trucks powered by syngas that could be driven around for processing biomass within a region. The biochar and bio-oil would be transported on the truck back to the customers.
Understand what is Biochar and its importance as an effective soil amendments with multiple benefits to the agriculture sector.
Know more on Biochar as a soil amendment
Introduction
Soils have the ability to absorb carbon dioxide and influence its concentration in the atmosphere. Biochar can be used to increase the ability of soils to sequester carbon and simultaneously improve soil health. The goal of this paper is to introduce the concept and origins of biochar, discuss its production process, potential uses, and the benefits and costs of biochar in its key roles in agriculture and climate change mitigation.
What is biochar?
Biochar is just charcoal made from biomass—which is plant material and agricultural waste—hence the name ‘biochar’. It is a fine-grained charcoal produced from pyrolysis: the slow burning of organic matter in a low- or no-oxygen environment. What differentiates biochar from charcoal is its purpose; it is produced as an additive to soils, mainly to improve nutrient retention and carbon storage. 1 Although the history of biochar extends thousands of years, its science is still relatively poorly understood. History of biochar The term ‘biochar’ was coined in recent times, but the origins of the concept are ancient.2 Throughout the Amazon Basin there are regions—up to two metres in depth—of terra preta. 3 This is a highly fertile dark-coloured soil that has for centuries supported the agricultural needs of the Amazonians. Analyses of the dark soils have revealed high concentrations of charcoal and organic matter, such as plant and animal remains (manure, bones and fish). Terra preta’s productivity is due to good nutrient retention and a neutral pH, in areas where soils are generally acidic.4 Interestingly, terra preta exists only in inhabited areas, suggesting that humans are responsible for its creation. What has not been confirmed is how terra preta was created so many years ago. Many theories exist. A frontrunner is the suggestion that ancient techniques of slash-and-char are responsible for the dark earth. Similar to slash-and-burn techniques, slash-and-char involves clearing vegetation within a small plot and igniting it, but only allowing the refuse to smoulder (rather than burn). 5 Combined with other biomass and buried under a layer of dirt, the smouldering char eventually forms terra preta. 6 It is from these hypotheses of early slash-and-char practices that modern scientists have developed methods for producing biochar.
Biochar production
The biochar production process begins with biomass being fed into a pyrolysis kiln—a furnace that burns with little or no oxygen. The biomass could be crop residue, wood and wood waste, certain animal manure, or various other organic materials. At the end of this, two main products come out of the kiln.7 The first is biochar, usually representing about 50 per cent of the carbon content of the biomass. The other is biofuel. The biofuel is often syngas, which is a mixture of mainly hydrogen and carbon monoxide, with a little carbon dioxide. The proportions of the three gases vary according to the processes used to create the syngas. However, the important point is that syngas is combustible and so can be used as a fuel source. Depending on the process, the biofuel from the kiln could also be biooil, which can be used as a substitute for diesel in some engines. The pyrolysis occurs at temperatures below 700˚C; but some parameters can be altered, such as the rate of pyrolysis, or the quantity of oxygen. Generally, faster pyrolysis results in more oils and liquids, slower pyrolysis produces more syngas. Minimising the oxygen present during pyrolysis optimises the production of biochar.8 Pyrolysis can be followed by a second stage: gasification. Gasification liberates more energyrich syngases from the char (usually hydrogen-based). There may also be a ‘gas cleanup’ stage to remove some of the particulates, hydrocarbons and soluble matter from the gas.9 The biofuel generated from the pyrolysis process can be used to create the electricity needed to power the kiln or secondary stages of the process. So it is possible for the system to run autonomous of external power sources. The pyrolysis process described is summarised in Figure 1.
Simplified pyrolysis process flow diagram An important advantage of biochar is that it can be produced either from small, simple mobile units or from larger, stationary ones. Small-scale systems for biomass inputs of 50 to 1000 kilograms per hour can be used on farms, while large units of up to 8000 kilograms per hour can be operated by large industries.10 There are potentially three broad types of pyrolysis systems: • central pyrolysis plants for processing all the biomass in a region. • lower-tech pyrolysis kilns for individual farmers or small groups of farmers (these kilns may not include some secondary stages such as the gasification or gas cleanup). • pyrolysis trucks powered by syngas that could be driven around for processing biomass within a region. The biochar and bio-oil would be transported on the truck back to the customers.
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