Pyrolysis Essay

Which other pyrolysis types are available? Compare torrefaction to other pyrolytic techniques.

Pyrolysis

Pyrolysis is a rapid thermal decomposition process of organic biomass, in absence or little supply of oxygen, brought about by high temperatures into useful biofuel products such as pyrolysis oil, ethanol, biodiesel, methanol etc. During the process, large hydrocarbon molecule’s chemical composition structure breaks down into relatively smaller molecules into solid (char), liquid or gas phase (Figure 1). The process is very similar to many other biomass decomposition processes such as torrefaction, carbonization, devolatilization etc. however pyrolysis cannot be compared to gasification due to external activation required for gasification.

On the other hand torrefaction of bio waste is carried out at lower temperature, at slower rate, than pyrolysis and solid fuels produced from torrefaction can replace coal usage industry and many other different applications. Torrefaction is initial pretreatment of pyrolysis process as biomass is heated and prepared for next stage processes. Typical temperature range for torrefaction process is between 200°C to 300°C. torrefaction process increases the energy density of biomass by increase in carbon content and decreasing oxygen and hydrogen content.

Torrefaction of bio-solid is the preparation stage of pyrolysis. However based on heating rate, pyrolysis can be further divided into many types, such as slow pyrolysis, fast pyrolysis, flash pyrolysis and hydropyrolysis. Once the temperature reaches its peak level (650°C) initial state of gasification process initiates. The main difference between fast and slow pyrolysis is the heating time (theating) vs. pyrolysis reaction time (tr). For example if the time required to heat biomass or bio-solid is larger than pyrolysis reaction time, it is considered as slow pyrolysis and vice

The heating rate of biomass for fast pyrolysis can be high as 1000°C/s- 10,000°C/s, however maximum temperature for the process is maintained below 650°C. the primary interest is to produce for tis process is to produce bio-oil, however temperature can be increased up to 1000°C produce fuel gases in the same process (Table 1). There are 4 important factors that can affect the liquid yield heating rate, reaction temperature, residence time and rapid quenching of the product gas. Maintaining these factors can increase the liquid yield of biomass and maximize the production of bio-oil.

Flash Pyrolysis

Flash pyrolysis process takes place when heat is increased rapidly in the absence of oxygen and temperature is kept between 450°C- 650°C. within 30-1500 microsecond, condensable and incondensable gases leave the pyrolyzer. After cooling condensable vapors are collected as bio-oil fuel. With rapid increase in heat, liquid yield increases rapidly, results drop in char content. Such operation can maximize bio-oil up to 70%-75% of the pyrolysis product.