OCTOBER 19-20, 2012 - YMCA University of Science & Technology

Proceedings of the National Conference on
Trends and Advances in Mechanical Engineering,
YMCA University of Science & Technology, Faridabad, Haryana, Oct 19-20, 2012
+24, 2) CH 4 of +8, CO 2 of 0.The energy balance can be calculated as follows: Organic material, which is built
up by photosynthesis
CO 2 +H 2 O→CH 2 O+O 2 contain the energy.
1.2 Design Parameter
A) Selection of materials
B) Total solid (TS) contains calculations of organic materials
Solid part: Total solid contained in a certain amount of materials is usually used as the material unit to indicate
the biogas- producing rate of the materials. Most favorable TS value desired is 08%.
Liquid part: contain 20% to 80 %.
C) Favorable condition for good fermentation-
Temperature: 20 o c to 35 o c.
PH value: Neutral PH and ranges 6.8 to 7.2.
C/N ratio: Ranges from 20:1 to 30:1.
Pressure: A minimum pressure of 6-10 cm of water column that is 1.2 bar is considered ideal for the proper
functioning of plant. It should never be allowed to exceed 40-50 cm of water column.
Seeding of Biomass with Bacteria: To start and accelerate fermentation processes, small amount of digested
slurry, containing Methane-forming bacteria is added to the freshly charged plant. This is known Seeding.
Mixing: Mixing has three important effects: Maintains uniformity in substrate concentration, temp. & other
environmental factors. Minimise the formation of scum on the surface. Prevents the deposition of solid at the
bottom.
Hydraulic retention time (HRT): For digestion where temperature varies from 20 o c to 35 o C and HRT is
greater than 20 days.
TABLE-1
Materials and their main
Yield of Biogas
Methane Content (%)
components
m 3 /kg
Green Grass 0.630 70
Leaves 0.210~0.294 58
Carbohydrates 0.750 49
Liquid 1.440 72
Protein 0.980 50
1.3 Properties of Biogas
Composition: 60 to 70 per cent Methane, 30 to 40 per cent carbon dioxide, traces of hydrogen sulfide, ammonia
and water vapor.
It is about 20% lighter than air (density is about 1.2 gm/litre).
Calorific value is 18.7 to 26 MJ/ m3 (500 to 700 Btu/ ft3.)
Calorific value without CO2: is between 33.5 to35.3 MJ/ m3
Explosion limit: 5 to 14 % in air.
Removal of CO2: Scrubbing with limewater or ethanol amine solution.
Removal of H2S: Adsorption on a bed of iron sponge and wood shavings.
Air to Methane ratio for complete combustion is 10 to 1 by volume.
One cubic meter of biogas is equivalent to 1.613 liter of kerosene or 2.309 kg of LPG or
0.213 kW of electricity.
1.4 Different Wastes Under Consideration
All biodegradable wastes can be use for the production of bio gas which may be listed as:
1. Agriculture waste
2. Household waste
3. Industrial liquid waste
4. Slaughterhouse wastes
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