Introduction to Pyrolysis | Advantages,Classification, Modes Of Pyrolysis


• The word Pyrolysis is derived from Greek words 

– Pyr: Fire

– Lysis: Separating

• Pyrolysis is one of the dry chemical processes. 

• It is thermal decomposition occurring in the absence of
oxygen. It is destructive distillation of wood, biomass in the
absence of air or oxygen.

• It is always also the first step in combustion and
gasification processes where it is followed by total or partial
oxidation of the primary products.


• Among the thermo-chemical processes, pyrolysis has become an
attractive alternative because of the ease of operation. 

• Its suitability as fuel for energy production and as
feedstock for chemical industries, 

• relatively few polluting emissions,

• CO2 neutral cycle and 

• ease of reproduction make pyrolytic oil.

Classification of Pyrolysis

• The pyrolysis can be classified as allothermal and

• Allothermal: The process in which heat is supplied from an
external agency.

• Autothermal: heating by fuel wood itself.

Allothermal Process

• Pyrolysis is achieved by using an external heat source such
as exhaust gas, electrical energy etc, However, the process is
unsuitable for pyrolysis since

1) There is no control over the products in an integrated

2) If a non-reacting medium such as N2 is used for heat
transfer & uniform heating, there is the problem of
purification at the gas collection points.

3) If the spatially differentiated system  of heating is
adopted, the coefficient of heat transfer between the source
& wood/biomass is reduced. This is because the presence of
wall enables only conductive transfer instead of convection
& radiation . This reduces the net energy efficiency.

4) Allothermal process may involve the use of a high grade
source (electric energy) for producing a low grade product.


• In this process a small amount of air or oxygen is supplied
to the wood/biomass & combustion is initiated with sole
objective of causing pyrolysis.

• If combustion is excessive , fuel energy instead of going
into the production of secondary fuel  is escaped as
sensible heat of the fuel gas.

• Therefore, combustion must be kept at minimum level.

Different modes of Pyrolysis

-The proportion of gas, liquid, and solid products depend very
much on the pyrolysis technique used and on the reaction

-Depending on the operating conditions, the pyrolysis process
can be divided into three sub classes.