BIOMASS GASIFICATION,gasification and gasifier. A slide about biomass gasification including brief description about thermo-chemical conversion process and applications

1. BIOMASS
GASIFICATION
{Thermo chemical conversion}

2. Introduction
The word “GASIFICATION” means ‘converting solid fuel in to
gaseous fuel by Thermo Chemical process , without leaving any
solid carbonaceous residue. Actually biomass gasification means
incomplete combustion of biomass resulting in production of
combustible gases, consisting:
•Carbon monoxide, CO,
•Hydrogen, H2 and traces of
•Methane, CH4
THE MIXTURE IS CALLED PRODUCER GAS

3. Cont.
• Gasification is the process in which the supply of oxygen is
controlled and the raw materials are converted into
chemical product called producer gas/ syngas
• This process transfers the majority of the chemically bound
energy of the solid fuel into the gas phase.
• The oxygen supply will be 20 to 40 per cent of the
stochiometric air requirement.
• In combustion process, raw materials are directly converted
into heat energy,
• where as in gasification raw materials are converted into an
intermediate chemical product, which constitutes mainly of
carbon monoxide and hydrogen.
Describing the quantitative relationships among substances as they participate in
chemical reactions is known as reaction stoichiometry.

4. Cont.
The equipment in which the gasification process takes place it is
known as Gasifier.
Gasifiers are used to convert the solid fuel materials into producer
gas.
The calorific value of producer gas is 950-1200 kcal /m3.
The main components of producer gas are :
• carbon monoxide (13-19%),
• hydrogen (18-22%),
• carbon dioxide (9-12%),
• nitrogen (45-55%),
• methane (1-5%)
• water vapour (4%).
It has the thermochemical conversion efficiency of about 70 to 90
per cent.

5. GASIFIER

6. Thermo-chemical Process
•The solid fuel is subjected to a
series of thermochemical
processes like drying, pyrolysis,
oxidation and reduction.
•The resultant product is
producer gas.

7. Thermo-chemical Process
Drying zone
• As a result of heat transfer from the lower parts of the gasifier
drying of feedstock occurs in this zone. biomass + heat ⇢ loss of
water
Pyrolysis zone
• At this zone feedstock starts pyrolysing. Large molecules such
cellulose, hemi cellulose and lignin break down into medium size
molecules and char.
• biomass + heat ⇢ carbon + gas (CO, CO2 ,H 2 , H 2 O, CH 4 , tar
vapors)
Pyrolysis: Pyrolysis is the application of heat to raw biomass, in an
absence of air, so as to break it down into charcoal and various tar
gasses and liquids. It is essentially the process of charring.
*Tar is a dark brown or black viscous liquid of hydrocarbons and free carbon, obtained
from a wide variety of organic materials through destructive distillation.

8. Thermo-chemical Process
Oxidation zone
Air is introduced at this zone.
Reaction with oxygen are highly exothermic and result in a sharp
rise of the temperature. Actual combustion of tar and charcoal
takes place producing carbondioxide and water vapour and
nitrogen.
Reduction zone
The reaction products of the oxidation zone (charcoal and hot
gases) move downward into the reduction zone. carbon dioxide
is reduced to form CO and hydrogen.
3C+2H 2 O+2CO 2 +2H 2 +heat ⇢5CO+4H 2 +H 2 O

9. Pyrolysis
• Biomass begins to rapidly decompose with heat once its
temperature rises above around 240°C.
• The biomass breaks down into a combination of solids,
liquids and gasses. The solids that remain commonly; we
call charcoal. The gasses and liquids that are released we
collectively call tars.
• The gasses and liquids produced during lower temp
pyrolysis are simply fragments of the original biomass
that break off with heat.
• pyrolysis is the application of heat to biomass in the
absence of air/oxygen. The volatiles in the biomass are
evaporated off as tar gases, and the fixed carbon-to-
carbon chains are what remains— otherwise known as
charcoal.

10. Reduction
• Reduction is the process of stripping oxygen atoms off
combustion products of hydrocarbon (HC) molecules, so as to
return the molecules to forms that can burn again.
• Reduction is the direct reverse process of combustion.
• Combustion is the combination of combustible gases with
oxygen to release heat, producing water vapor and carbon
dioxide as waste products.
• Reduction is the removal of oxygen from these waste products
at high temperature to produce combusitable gases.
• Reduction in a gasifier is accomplished by passing carbon
dioxide (CO2) or water vapor (H2O) across a bed of red hot
charcoal (C).

13. Applications of Producer gas:
• Electric power generation from few kW to MW, either for local
consumption or for grid power
• To operate diesel engine on dual fuel mode with 80-85%
diesel replacement
• To operate gas engine on 100% mode
• To operate water pumps for irrigation purpose

14. Applications of Gasifier