Factors Related to Biochar Yield

Biochar yield is not a fixed value, but varies according to many factors such as pyrolysis temperature, pyrolysis speed, raw material type and so on. Usually, the biochar yield can be measured by the output ratio, which is the ratio of the mass of biochar to the mass of raw material.

Under different pyrolysis conditions, the output ratio of biochar can vary greatly. For example, slow pyrolysis methods (performed at lower temperatures and longer reaction times) typically produce higher yields of biochar, with output ratios of 30 per cent or more, while fast pyrolysis methods (performed at relatively high temperatures and very fast ramp-up rates) produce lower yields of biochar, with output ratios of about 12 per cent or less, and with a high proportion of liquid product. The yield of biochar is mainly influenced by the following factors:
 

Type of Feedstock

Different types of biomass feedstocks have different densities and carbon contents, which directly affect the yield and quality of biochar after carbonization. In general, biomass feedstock with higher lignin content has higher biochar yield, such as forest wood (pine, spruce, oak, bamboo, etc.), nut shells; straw and rice straw feedstock are also one of the main raw materials for biochar production although their lignin content is lower than that of forest wood feedstock.
 

Pyrolysis Time

Pyrolysis time is also one of the important factors affecting the yield of biochar. Generally, the yield of biochar may decrease as the charring time increases. Prolonged pyrolysis may result in the release of more gases and volatiles from the surface of the biomass, which is favourable to the production of a pore structure and increased surface area of the biochar, but the biochar yield will become lower.
 

Pyrolysis Rate

The rate of pyrolysis (i.e., the rate of temperature rise) will similarly affect the biochar yield. In the case of fast pyrolysis, the biomass feedstock is heated at a super-fast rate in the pyrolysis furnace, and thus the pyrolysis gas condenses quickly into liquid, which results in maximum liquid yield and lower biochar yield; slow pyrolysis, also called carbonization, i.e., heating of the biomass feedstock at a slower rate, results in higher biochar yield than that of fast pyrolysis.
 

Moisture

The moisture content of the feedstock is also an important factor affecting the biochar yield. The moisture in the feedstock will absorb a lot of heat at the beginning of the pyrolysis process, which affects the pyrolysis temperature and heating rate of the biomass, thus affecting the final biochar yield. Moreover, part of the moisture will also participate in the pyrolysis reaction, which will increase the complexity of the pyrolysis process. Therefore, when the moisture of the raw material is too high, we need to pre-dry the raw material, and when the biomass material is less than 20% moisture, it can enter the carbonization furnace.

In summary, biochar yield is affected by a number of factors, which is a complex process to consider. Even for the same feedstock, the characteristics of the same feedstock from different origins are very different. A certain subtle difference may affect the final solution programme configuration, when considering biochar pyrolysis equipment you need to choose the right solution according to your actual needs. Turn to Haiqi's Professional Team!