Page 387 - Refining Biomass Residues for Sustainable Energy and Bioproducts

350 Refining Biomass Residues for Sustainable Energy and Bioproducts

various process parameters, such as temperature, heating rate, inert flow rate, particle
size, and residence time. Based on these parameters, it can be classified as slow, fast, or
flash pyrolysis. Slow pyrolysis is performed as lower temperature, lower heating rate, and
longer vapor residence time, and fast pyrolysis is operated at high temperature, high heat-
ing rate, and short vapor residence time. The primary end product for slow pyrolysis is
biochar which is around 35% 40%, and biooil and pyrolytic gas are 30% and 30%
35%, respectively, whereas for fast and flash pyrolysis, the primary product is biooil
which is around 75%, and biochar and pyrolytic gas are 12% and 13%, respectively
(Hossain and Davies, 2013).
Agricultural waste 1 heat 1 inertðN 2 =ArÞ! Biooil 1 biochar 1 pyrolytic gas

Gasification is another thermochemical process that is performed in the partial oxidative

(air, oxygen, or carbon dioxide) atmosphere at certain high-temperature range from 800 C

to 1000 C. The substrates for the gasification are similar to that are used in pyrolysis pro-

cess, such as agricultural wastes, woody biomass, and energy crops. The main end product
of the gasification process is syngas (CO 1 H 2 ) around 85% along with some amount of
tar with around 5% and biochar around 10% (Bridgwater, 2004; Ram and Mondal, 2018).
Some amount of CH 4 and other hydrocarbons are also produced. The gases produced
have ample amount of calorific value and can be used as fuel for engines or turbines.
Syngas produced can be used in the Fisher Tropsh synthesis for the production of valu-
able liquid hydrocarbon mixtures (methanol, ethanol, etc.). The process parameters are
temperature, heating rate, particle size, biomass feed rate, equivalence ratio, etc.
Gasification can be performed in two different modes; fixed and fluidized bed. Fixed bed
3
process gases with lower calorific value (4 6 MJ/N m ). Today, fluidized bed gasification
process is mostly preferred since it provides uniform temperature distribution in the gasifi-
cation zone.

Agricultural waste 1 heat 1 partial oxidation ! Syngas 1 tar 1 biochar

Combustion is a fully oxidative high-temperature thermal degradation process that
involves the conversion of chemical energy of biomass to heat and power along with car-
bon dioxide and water. The energy produced can be utilized in steam turbines, boilers,
furnaces, etc. The substrates for this process are similar as used in pyrolysis and gasifica-
tion processes. For any biomass to be combusted, the moisture content should be below
50%. The net bioenergy conversion biomass combustion is up to 40%. However, its effi-
ciency can be upgraded by cofiring the biomass with coal.

Agricultural waste 1 heat 1 excess air=oxygen ! Heat=power

15.6 Enrichment of end products

The various end products obtained after thermal and biological conversion of bio-
mass contain certain impurities and thus cannot be used directly as energy source.