Page 30 - Refining Biomass Residues for Sustainable Energy and Bioproducts

Solid waste biorefineries 9

Pretreatment of biomass can be used to facilitate the conversion of SWs into bioenergy or
biofuels (Nunes et al., 2017).

1.4 Pyrolysis

Pyrolysis is the process of thermal decomposition of materials at higher tempera-
tures in a latent environment with absence of air or oxygen. It includes the differ-
ence in chemical composition and is irreversible. It is the most usually utilized
technique for the pretreatment of organic material in thermochemical conversion
processes. Pyrolysis of natural substances produces unpredictable items and leaves
a solid residue enriched in carbon. In biorefineries that at first fractionate the bio-
mass in hemicellulose, cellulose, and lignin, pyrolysis can assume a significant job
as a handling unit for no less than one of these segments. Quick pyrolysis has been
made to change over biomass into extraordinary returns of bio-oil (normally up to
80 wt.% of the dry feedstock), gas, and roast. Quick pyrolysis plays a significant
role in biorefineries because of its flexibility, which is the upside of a storable and
transportable bio-oil item. Carbonization is the extreme stage of pyrolysis in which
the carbon leaves as residue. This is commonly used is many industries, including
petroleum, coal, and wood, for the production of several valuable chemicals such as
ethylene and others forms of carbon. Pyrolysis can be classified into two types
based on the heating time (t heating ) and the pyrolysis reaction time (t r ).

1. Slow pyrolysis—t heating ct r
2. Fast pyrolysis—t heating {t r

1.4.1 Methods characterizing
Pyrolysis methods are characterized based on several factors, such as residence
time, heating rate, final temperature, and the products obtained from pyrolysis
include torrefied biomass, charcoal, bio-oil, chemicals, and gases. Pyrolysis is pre-
cursor of both combustion and gasification forms, yet requiring external specialists
such as oxygen and steam. It has likeness with techniques such as splitting, devola-
tilization, carbonization, torrefaction, dry refining, dangerous refining, and thermo-
lysis, yet it has no comparability with gasification. Gasification incorporates
synthetic responses with an outer master known as gasification medium. Pyrolysis
of biomass is consistently done in a temperature extent of 300 C 650 C appeared

differently in relation to 800 C 1000 C for gasification and 200 C 300 C for tor-

refaction. The characterized pyrolysis methods and their products are as follows:
Torrefaction—torrefied biomass
Carbonization—charcoal
Fast pyrolysis—bio-oil
Flash pyrolysis—chemicals, gases, and bio-oil
Ultrarapid pyrolysis—chemicals and gases
Vacuum pyrolysis—bio-oil