01-12-2012, 06:18 PM
BIOMASS
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INTRODUCTION:
Biomass is organic matter from plants, animals and micro-organism grown on land and water and their derivatives.
Biomass is considered as a renewable sources of energy because the organic matter is generated everyday.
Biomass resources are classified into three groups:
Biomass from cultivated fields, crops, forests, etc.
Biomass derived from wastes like municipal wastes and animal dung.
Biomass converted into liquid fuels.
PRINCIPLE OF GENERATION OF BIOGAS:
Biogas can be produced by fermenting organic materials in the absence of air or oxygen with the help of bacteria to break down materials to intermediates such as alcohols and fatty acids finally to methane, CO2 and water. The process is called anaerobic fermentation.
Anaerobic fermentation has three phases:
Enzymatic hydrolysis
Acid formation
Production of methane
Factor affecting biogas generation:
Hydrogen ion concentration
Temperature
Total solid content of feed material
Loading rate
Seeding
Nutrients
Digester size and shape
TYPES OF BIOGAS PLANTS:
Continuous and batch type
Continuous type single stage
Continuous type two stage
Fixed dome collector type
Floating drum collector type
CONTINUOUS BIOMASS PLANT:
There is a single digester in which raw materials charged regularly and the process goes on without interruption except for repair and cleaning etc.
The continuous process may be completed in a single stage or separated in two stages:
Single stage process:
In this type, phase-I (acid formation) and phase-II (methanation) are carried out in the same chamber without barrier such plants are simple, easier, economical to operate and control.
This chamber is regularly fed with the raw materials while the spent residue keeps moving out.
Serious problems are encountered with agricultural residues when fermented in a single stage continuous process.
BATCH TYPE BIOGAS PLANT:
The feeding is between intervals the plant is emptied once the process of digestion is complete.
In this type, battery of digesters are charged along with lime, urea etc. and allowed to produce gas for 40-50 days.
These are charged and emptied one by one in a synchronous manner which maintains a regular supply of gas through a common gas holder.