INTRODUCTION TO BIOGAS

Biogas is generated when bacteria degrade biological material in the absence of oxygen, in a process known as anaerobic digestion.

           Since biogas is a mixture of methane (also known as marsh gas or natural gas, CH4) and carbon dioxide it is a renewable fuel produced from waste treatment. Anaerobic digestion is basically a simple process carried out in a number of steps that can use almost any organic material as a substrate - it occurs in digestive systems, marshes, rubbish  dumps,  septic  tanks  and  the  Arctic Tundra.

Humans  tend to make the process as complicated  as  possible by trying  to  improve on nature in complex  machines but a simple approach is still possible.  Conventional anaerobic digestion has been a "liquid" process, where waste is mixed with water to facilitate digestion, but a "solid" process is also possible, as occurs in landfill sites.

THE POTENTIAL OF BIO GAS

The enormous potential of biogas, estimated at 17,000 MW can be seen from table 1. The capacity was derived principally from estimated agricultural residues and dung from India's 300 million cattle. Biogas technology may have the potential to short-circuit the 'energy transition' Leach (1987) describes from biomass to 'modern' fuels. Biogas technology is a particularly useful system in the Indian rural economy, and can fulfill several end uses.

With the bourgeoning population in metro cities and growth of urban centres, the enormity of waste generated is proving to be a huge task for disposal by city municipal  authorities. Therefore, this process, driven further can turnout to be best boon in waste management. The scope for saving huge funds used for transporting the waste as at present is immeasurable. Also the search and location for land-fills and promotion of pollution in areas nearer to urban centres can be avoided.

The gas is useful as a fuel substitute for firewood, dung, agricultural residues, petrol, diesel, and electricity, depending on the nature of the task, and local supply conditions and constraints (Lichtman, 1983), thus supplying energy for cooking and lighting.

Biogas systems also provide a residue organic waste, after anaerobic digestion, that has superior nutrient qualities over the usual organic fertilizer, cattle dung, as it is in the form of ammonia (Sasse et al, 1991).    

Anaerobic digesters also function as a waste disposal system, particularly for human waste, and can, therefore, prevent potential sources of environmental contamination and the spread of pathogens (Lichtman, 1983). Small-scale industries are also made possible, from the sale of surplus gas to the provision of power for a rural-based industry, therefore, biogas may also provide the user with income generating opportunities (KVIC, 1993). The gas can also be used to power engines, in a dual fuel mix with petrol (Jawurek et al, 1987) and diesel (KVIC, 1993), and can aid in pumped irrigation systems.

 Apart from the direct benefits gleaned from biogas systems, there are other, perhaps less tangible benefits associated with this renewable technology. By providing an alternative source of fuel, biogas can replace the traditional biomass based fuels, notably wood. Introduced on a significant scale, biogas may reduce the dependence on wood from forests, and create a vacuum in the market, at least for firewood (whether this might reduce pressure on forests however, is contestable).

       

BIO GAS AND GLOBAL CARBON CYCLE

Each year some 590-880 million tons of methane are  released worldwide into the atmosphere through microbial activity. About 90% of the emitted methane derives from biogenic sources, i.e. from the decomposition of biomass. The remainder is of fossil origin (e.g. petrochemical processes). In the northern hemisphere, the present tropospheric methane concentration amounts to about 1.65 ppm(parts per million).  

Unlike fossil fuel combustion, biogas production from biomass is considered CO₂ neutral and therefore does not emit additional Greenhouse Gases (GHG) into the atmosphere.  

However, if biogas is not recovered properly, it will contribute to a GHG effect 20 times worse than if methane is simply combusted. Therefore, there is a real incentive to transfer biogas combustion energy into heat and/or electricity.

Finally, biogas production from anaerobic digester   presents the additional advantage of treating organic waste and reducing the environmental impact of these wastes. It contributes to a better image of the farming community while reducing odor, pathogens and weeds from the manure and producing an enhanced fertilizer easily assimilated by plants.  

FLOW-CHART SHOWING BIO GAS PRODUCTION TO USAGE

PEOPLE BEHIND CHETANA

President

K. USHANATH, M.Sc.                      :  9611842417

Vice President

S.P. ARADHYA, M.A. (Rur.Devp.): 9740588345

Secretary

G.N.N. ARADHYA                           : 9663293984

Treasurer     

R. PRATHIBHA PREM KUMAR

          B.Sc. (Bio-Tech) : 9740090866

Executive Committee Members

K.R. PRASAD B.E. (Mech) : 9845161509

B. UMESH, B.E. (Civil) : 9845497613

G.N. KIRAN KUMAR, B.E.(E&C) : 9035253847

PROPOSED MANUFACTURING OF BIO-GAS AT CENTRALIZED PLANT

Our method of producing bio-gas is shown as under:

STAGE 1 : Bio-waste collection - Municipal Waste, Agro-waste, Fruits and Vegetables waste, hotel and dairy rejects etc.

STAGE 2 : Bio-gas Production : Process of manufacturing of concentrated raw slurry  - fed into digesters of 250m³ - process of purification using - compressor - water scrubber - 3 stage compressor of bio-gas, ready to be use as fuel - bottling of the project.

STAGE 3 :  The bio-waste collected by us and processed as raw slurry is transferred to Digesters of 100m³ set up by semi-educated interested village population. After due process of slurry, the raw bio-gas is collected in tankers for transportation to the centralized plant for purification.

STAGE 4 : The centralized plant produces pure bio-gas of high methane content out of the raw gas collected from each of the digesters.

USES OF BIO-GAS: The pure bio-gas is useful as:

· Fuel for motor vehicles as alternate to petroleum products

· Can be used as cooking gas for house-holds

· Can be used as alternate power-generation to lift water for farming purpose, house-hold, street lighting.

· Residuals can be used as high quality bio-mature.

WASTE MANAGEMENT: At village level, Taluk and District levels, the waste management is effectively carried out by optimum utilization of bio-waste for producing bio-gas. In addition, the spending by local self governments is drastically cut down by using the Bio-waste for producing bio-gas and thereby contribute for better environment.

INCOME & EMPLOYMENT GENERATION:  By introducing the digesters at individual households, ample employment is generated for villagers, income by way of sale of bio-gas, sale of residuals etc.

ECONOMICS OF BIOGAS PLANT

Scope of the Technology : Enriched biogas is made moisture free by passing it through filters, after which it is compressed up to 200 bar pressure using a three stage gas compressor. Compressed gas is stored in high pressure steel cylinders as used for CNG . There is large potential of this technology in buses, tractors, cars, auto rickshaws, irrigation pump sets and in  rural  industries. This will help to meet energy demand for rural masses thus reducing burden of petroleum demand, moving towards energy security and will improve economic status by creating employment generation in rural area.

Cylinders filled from one 120m³ biogas bottling plant = 8 cylinders/day

(Capacity 6kg/cylinder)

As 6 kg CNG cylinder = 6 liter petrol

So, gas filled in these cylinders will be equivalent to = 6 x 8 = 48 liters of petrol/day or

Diesel/Petrol savings = 17520 liters/annum = Rs.13,44,000/annum approx. from one bottling plant.

Therefore, from only one Biogas  bottling plant, enriched biogas filled cylinders will be able to replace fuel worth Rs.13 lakh annually. Increasing the number of bottling plants will be subsequently increase the diesel/petrol savings. The whole cost can be recovered within two-three years from the installation of the plant.

Cost estimate for the proposed technology

Cost estimate for the proposed technology

120m³ biogas/day Digester cost :                                         Rs.  8,00,000/-

1. Biogas scrubbing/enrichment unit                                   Rs.  3,50,000/-

2. High pressure compressor to fill CNG cylinders          Rs.  7,00,000/-

3. CNG conversion kit and filling into cylinders Rs.  1,50,000/-

        TOTAL Rs.20,00,000/-