BIOMASS GASIFICATION

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, H 2 and traces of Methane, CH 4 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 /m 3 .  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, CO 2 ,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 carbon dioxide 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 (CO 2 ) or water vapor (H 2 O) across a bed of red hot charcoal (C).

11. 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

12. Applications of Gasifier