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What is pyrolysis?.

Pyrolysis – definition

Pyrolysis is a form of thermochemical treatment of any organic (carbon-based) product, where material is exposed to high temperature, and in the absence of oxygen undergoes chemical and physical decomposition.

In contrary to combustion and gasifications processes, which involve entire or partial oxidation of material, pyrolysis is based on heating products in the absence of air. This makes it mostly endothermic process which allows to obtain high energy content in the products received.

Pyrolysis products always produce solid (charcoal, biochar), liquid and non-condensable gases (H2, CH4, CnHm, CO, CO2 and N). As the liquid phase is extracted from pyrolysis gas only during it’s cooling down, in some applications, these two streams can be used together when providing hot syngas directly to the burner or oxidation chamber (see « Directions of hot syngas utilisation »).

During the pyrolysis, a particle of material is heated up from the ambient to defined temperature (setup temperature of Biogreen® equipment). The material remains inside the pyrolysis unit and is transported by screw conveyor at defined speed, until the completion of the process. Chosen temperature of pyrolysis defines the composition and yields of products (pyrolysis oil, syngas and char).

Biogreen pyrolysis process

What influences pyrolysis process results?

    • treated material composition – each of the major constituents of biomass and waste feature different temperatures of thermal decomposition, which means they contribute to the results of process in different way. Due to high diversity of material compositions it is always recommended to perform a pilot tests to forecast the pyrolysis process performance in most accurate way.
    • temperature of process – has a major influence to the treatment results. Higher temperatures of pyrolysis provide greater quantity of non-condensable gases (syngas, synthetic gas), while lower temperatures favour the production of high quality solid product (charcoal, bio-coal, torrefied fuels). Temperature is a factor fully controllable in Biogreen® process thanks to electrically heated screw conveyor that allows precise setup of treatment conditions.
    • residence time of material in the pyrolysis chamber – influences the degree of thermal conversion of received solid product as well as the residence time of the vapour, which influences the composition of vapours (condensable / non-condensable phase). Residence time can be precisely controlled in Biogreen® process by changing the rotation speed of screw conveyor (Spirajoule®) transporting material along the reactor.
    • particle size and physical structure – influences the speed in which material is subjected to pyrolysis. In general, lower particle size materials are quicker affected by the thermal decomposition, which can result in greater quantities of pyrolysis oil than in case of larger particle size.
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