Differences Between Torrefaction & Carbonization

As the reduced burning of coal, the global demand for biomass energy is increasing rapidly in recent decades of years. As the largest global source of renewable energy, the biomass energy contributes an estimate 10% of global primary energy production. Given the rising concern about the global warming and sustainable development, this share is expected to rise.

The most common use of the biomass energy is direct combustion, followed by gasification, carbonization, torrefaction etc. Even though emission out of the direct biomass combustion is much lower than the coal, people are seeking the much cleaner way to reduce the carbon emission. Having gone through the carbonization and torrefaction, the biomass products have higher heating calorific value and lower flue gas emission.

Carbonization that produces charcoal from biomass was widely practiced for extraction of iron from iron ore in ancient India and China ( 4000 BCE ). Charcoal is still being used in many parts of the world as a smokeless fuel as well as a medium for filtration of water or gas.

Torrefaction (French word for “roasting”), a relatively new biomass conversion option, is similar to carbonization that produces solid fuels from biomass but has some important differences. In any case, this option is also attracting much attention especially in its near term application in co-firing biomass in coal-fired power plants and possibly for replacement of coke in metallurgy.

What is torrefaction?
It is a thermochemical process in an inert or limited oxygen environment, where biomass is slowly heated to within a specified temperature range and retained there for a stipulated time so that it results in near complete degradation of its hemicellulose content while maximizing mass and energy yield of solid product. Typical temperature range for this process is between 200℃ and 300℃. When the temperature is higher than 300℃, it would cause the loss of lignin in biomass, which could make it difficult to form pellets from torrefied products.

What is carbonization?
Carbonization (or carbonisation) is the term for the conversion of an organic substance into carbon or a carbon-containing residue through pyrolysis or destructive distillation. The temperature range of this process is above 300℃.

What are the differences between the the carbonization and torrefaction?
The torrefaction process is sometimes confused with carbonization, but the motivation, process conditions and usages of this two processes are not necessarily the same.

1. Major Objective:
A major objective of torrefaction is to increase the energy density of the biomass by increasing its carbon content while decreasing its oxygen and hydrogen content. This objective is similar to that of carbonization that produces charcoal but with an important difference that the latter does not retain maximum amount of energy of the biomass, and thereby gives low energy yield.

2. Process Condition:
Carbonization is similar to torrefaction in many respects, both carbonization and torrefaction require relatively slow rates of heating. Carbonization takes place at higher temperatures with a certain level of oxygen that allows sufficient combustion to supply the heat for the process. The torrefaction process on the other hand tries to avoid oxygen as well as combustion. Torrefaction is a thermal decomposition that takes place at low temperature and within a narrow temperature range of 200~300℃, while carbonization is 600℃ destructive distillation process. Carbonization produces more energy dense fuel than torrefaction, but it has a much lower energy yield.

3. Usages:
Both of the torrefaction pellets and carbonization pellets can be used as fuel. In addition, the carbonization pellets can be used in the following industries:

- Manufacture of carbon disulfide, sodium cyanide, and carbides;
- Smelting and sintering of iron ores, case hardening of steel, and purification in smelting of nonferrous metals;
- The carbonization pellets can be converted to activated carbon, which apply to water purification, gas purification, solvent recover, and waste water treatment;
- Carbon sequestration and soil remediation. Torrefied chicken manure and biomass can also be used in soil improvement.

SIMEC has started the R&D of torrefaction & carbonization technology since 2004. It is the technology that upgrade the value of biomass. Torrefaction and pelletization can be combined to maximize the commercial value of biomass. The final product is also called Black Pellets. Accompany with the increasing market demand of Black Pellets, we believe SIMEC technology will benefit more and more clients and investors.
Torrefaction is the future of biomass!

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