What is Torrefaction

 

What is Torrefaction?

Torrefaction is a biomass pretreatment method. It involves heating raw biomass to temperatures between 200 and 300°C in low or no oxygen conditions to produce a solid mass similar to charcoal. Torrefaction is driven by the combustion of volatile gases, which are released from the biomass and subsequently recovered and recycled as fuel for the process. The reduction of volatiles and moisture reduces the weight of the plant material while retaining 70% to 90% of the original energy content, making the torrefied product more energy dense and storable.

Biomass Torrefaction Process

The first step in torrefaction is to feed the raw biomass into the torrefaction system. Particle size may vary depending on the source of the feedstock. Typically, feedstock with uniform size works better. Next, the biomass is slowly heated in an oxygen-free torrefaction chamber to temperatures between 200 and 300°C for 10 to 30 minutes. This partially decomposes the biomass and releases some volatiles, including water, VOCs, and hemicellulose. The remaining solid portion is torrefied biomass, which is the main end product. Volatiles, steam and gases produced during torrefaction can be burned in the combustion section to generate heat, which can be used to preheat the incoming raw biomass before torrefaction.

Benefits of Biomass Torrefaction

Agricultural and forestry residues, energy crops and animal manure can all be used as feedstocks for biomass torrefaction, which results in various energy products such as ethanol, heat and electricity. However, these feedstocks generally have lower bulk density and energy density. By torrefaction of biomass, their properties can be modified to improve storage, transportation, pre-handling and conversion. The advantages of torrefied biomass over raw biomass include:
 

Lower moisture, more hydrophobic

After torrefaction, the moisture content of biomass is significantly reduced to less than 1%. It produces a relatively hydrophobic product that absorbs very little moisture from the atmosphere, so the moisture content increases very little during storage, which reduces the deterioration of the biomass. Moreover, the low moisture content also reduces transportation costs.  

Increased brittleness

Torrefaction destroys the original structure of the biomass, which increases the brittleness of the material. Biomass often needs to be reduced in size before it can be converted into end products such as fuels, chemicals or other materials. The increased friability of torrefied biomass reduces the energy required for grinding by 80% to 90%.
 

Higher Energy Density

After torrefaction, the heating value of biomass typically increases from 5,000-7,000 BTU per pound to 8,500-10,500 BTU per pound. This makes it ideal for thermal chemical plants as well as home burners.
 

Less Smoke

Raw biomass has a wide range of moisture content and VOCs, depending on type, source and harvest conditions. Torrefaction significantly reduces moisture content and VOCs, resulting in a homogenous solid fuel that produces less smoke during combustion.
 

Removes Odors and Pathogens

Torrefying biomass at high temperatures eliminates pathogenic microorganisms and most odorous VOCs, effectively reducing potential pathogen threats.
 

Torrefaction and Pyrolysis Carbonization: Similarities and Differences

Although both Torrefaction and Pyrolysis Carbonization involve thermal treatment of biomass, they differ significantly in temperature range, product characteristics, and end-use applications.
 

Similarities of Torrefaction and Pyrolysis Carbonization

Oxygen-free or oxygen-deficient heating: They are both conducted in an oxygen-free or low-oxygen environment to prevent the biomass from burning.
Solid carbonization products: Both Torrefaction and Pyrolysis Carbonization convert biomass into solid materials with a high carbon content.
Reduce volatile matter and increase fixed carbon: They both cause the biomass to lose some volatile matter and increase the fixed carbon ratio.
Applicable to similar feedstocks: Biomass such as wood, straw, and bamboo can be used for both processes.
 

Difference between torrefaction and pyrolysis carbonization

 

	Torrefaction	Pyrolysis Carbonization
Temperature Range	200-300°C	300-800°C
Main Products	Solid (torrefied biomass)	Solid (biochar), small amount of gas
Solid Yield	70-80%	25-40% (high-temperature pyrolysis)
Fixed Carbon Content	30-50%	60-90%
Pyrolysis oil Yield	Very little	Some pyrolysis oil in low-temperature carbonization
Gas Yield	Small amount	More significant
Solid Characteristics	Increased energy density, reduced moisture, but retains some volatiles	High carbon content, high porosity, strong adsorption capacity
Application Fields	Fuel alternative (coal, pellet fuel), gasification feedstock	Biochar (soil improvement, adsorbent), activated carbon, metallurgical reductant

Torrefaction and pyrolysis both play a vital role in the growing biomass energy sector. At HaiQi, we are proud to be at the forefront of providing advanced biomass torrefaction and biomass pyrolysis equipment. Whether you prefer the stable, high-energy output of torrefaction biomass, or the production of versatile pyrolysis products such as biochar production and cogeneration solutions, HaiQi has the expertise and biomass pyrolysis equipment to meet your diverse energy needs. Contact HiaQi today to embark on a sustainable biomass utilization journey and realize the full potential of your biomass resources!