BIOGAS PURIFICATION USING WATER SCRUBBING SYSTEMS

Dr.Virendra K.Vijay CentreforRuralDevelopment&Technology Coordinator BiogasDevelopmentandTrainingCentre IndianInstituteofTechnology,Delhi Hauz Khas,NewDelhi,India Email:vkvijay@rdat.iitd.ernet.in

INTRODUCTION

Biogas is clean environment friendly fuel that can be obtained by anaerobic digestion of animal residues and domestic and farm wastes, abundantly available in the countryside. Biogas is an important renewable energy resource for rural areas in India Biogas generally comprise of 55-65 % methane, 35-45 % carbon dioxide, 0.5-1.0 % hydrogen sulfide and traces of water vapor. Average calorific value of biogas is 20 MJ/m3 (4713 kcal/m3).

INTRODUCTIONBiogas like Liquefied Petroleum Gas (LPG) cannot be liquefied under normal temperature and pressure. Critical temperature required for liquefaction of methane is -82.1oC at 4.71MPa pressure, therefore use of biogas is limited nearby the biogas plant. An estimate indicates that India has a potential of generating 6.38 X 1010 m3 of biogas from 980 million tones of cattle dung produced annually. The heat value of this gas amounts to 1.3 X 1012 MJ. In addition, 350 million tones of manure would also produce along with biogas.

ORGANIC WASTES & THEIR ESTIMATED AVAILABILITY IN INDIASr. Organic Wastes No. 1. 2. 3. 4. 5. 6. 7. 8. Municipal Solid waste Municipal liquid waste Distillery (243 units) Press mud Food & fruit processing wastes Willow dust Dairy industry waste Paper & pulp industry waste (300 mills) Tannery (2000 units) Estimated Quantity 30 million tons/year 12000 million litres/day 8057 kilolitres/day 9 million tons/year 4.5 million tons/year 30000 tons/year 50-60 million litres/day 1600 m3/day

9.

52500 m3 waste water/day

Source: MNES Report, Renewable Energy in India and business opportunities, MNES. Govt. of India, New Delhi, 2001

BIOGAS PROGRAMMESOn-going Programmes:

National Biogas and Manure Management Programme (NBMMP). Biogas Based Distributed/ Grid Power Generation Programme.

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BIOGAS PRODUCTION PROCESSBiogas production process (Anaerobic digestion) is a multiple-stage process in which some main stages are:

Chemicalreactionsinvolvedinbiogasproduction:C6H12O6 3CO2 + 3CH4 CO2 + 4H2 > CH4 + 2H2O CH3COOH > CH4 + CO2

THE QUANTITY, RATE AND COMPOSITION OF BIOGAS GENERATED DEPENDS ON

The nature and concentration of the substrate, Feed rate, pH value, Bacterial population, Temperature, and Chemical inducers.

BIOGAS PRODUCTION POTENTIAL FROM DIFFERENT WASTES

UTILIZATION OF BIOGASCooking: Biogas can be used in a specially designed burner for cooking purpose. A biogas plant of 2 cubic metres capacity is sufficient for providing cooking fuel needs of a family of about five persons. Lighting: Biogas is used in silk mantle lamps for lighting purpose. The requirement of gas for powering a 100 candle lamp (60 W) is 0.13 cubic metre per hour. Power Generation: Biogas can be used to operate a dual fuel engine to replace up to 80 % of diesel-oil. Diesel engines have been modified to run 100 per cent on biogas. Petrol and CNG engines can also be modified easily to use biogas. Transport Fuel: After removal of CO2, H2S and water vapor, biogas can be converted to natural gas quality for use in vehicles.

BIOGAS DEVELOPMENT AND TRAINING CENTRES (BDTCS)

For training and publicity purposes, Eleven Biogas Development and Training Centres (BDTCs) are functioning, one each in Assam, Himachal Pradesh, Karnataka, Madhya Pradesh, Punjab; Rajasthan, Tamil Nadu, Uttar Pradesh, West Bengal and Uttarakhand. One BDTC has been started in IIT Delhi in 2008. Central financial assistance is provided to these Centres for staff and training courses. BDTCs focus on the training of masons and entrepreneurs to improve quality of construction of biogas plants and to follow standard specifications & approved construction techniques.

NEED FOR THE BIOGAS REFINING AND BOTTLING Potential of biogas is not fully utilized and commercialized so far. For commercialization, its area of application may widen; from cooking fuel to vehicle fuel. For use as a vehicle fuel, it should be bottled like CNG. Before bottling, it should enriched in methane content from 55 % to 95 %; similar to CNG.

CO2 & H2S REMOVAL PROCESSES FROM BIOGASProcess PSA Advantage Disadvantage Economy in production with comparatively Not much scalability in production. high purity. Capital costs are moderate. Equipment maintenance on the higher Relatively quick installation and start up. side ,Chemical regeneration is required Simple process, remove both H2S and CO2 High pressure, difficulty in recovery of using a water stream. CO2 High purity . Capital cost high. Requirement of large sites. Longer start-up and shut down process. Limited scalability in production.

Water Scrubbing Cryogenic

Membrane

Fast installation and start up .Production of Economically not viable. Not suitable output is flexible .Purity and flow rate can for high purity needs. Consumes vary. relatively more electricity per unit of gas produced. The chemical absorbents are more efficient Regeneration of the solvent requires a in low pressure relatively high energy input. Disposal of by product formed due to chemical reaction is a problem

Chemical Absorption

THE DESIGNING OF THE PACKED BED SCRUBBER INVOLVED THE FOLLOWING STEPS:Assumptions of basic data Solubility data generation Material balance and determination of water flow rate Selection of packing material Determination of column diameter Determination of the height of the packed bed column Selection of packing support and water distributor

WORKING OF SCRUBBING SYSTEM

Water scrubbing method is found most suitable for biogas enrichment in rural areas. Water is good solvent for CO2. The solubility of CO2 in water is governed by variation in pressures and temperatures.

SYSTEM OPERATION

Raw biogas is compressed up to 1.0 MPa pressure to enhance solubility of CO2 in water. Pressurized biogas is sent into bottom section of the scrubber. Packing material is used to enhance the contact time (interfacial area) between gas and water. Pressurized water is sprayed from top to absorb the CO2 from pressurized biogas.

COMPRESSION UNIT

Multi stage compressor : compression of methane enriched biogas at 20 MPa Pressure in cylinder. Filters : for moisture removal. Cylinders: High pressure, seamless, steel cylinders that are already in being use for CNG application. Pipe fittings and accessories : G.I.

Biogas Digester Biogas (CH4 CO2) Moisture Removal

Single Stage Compressor Water Tank Pump Flow Meter Gas Storage Pressure Vessel Water Biogas Scrubber Dissolved CO2 in Water Enriched Biogas

Gas Storage Pressure Vessel Moisture Filters Pressure Reducers Three Stage Gas Compressor High Pressure Cylinders for Storage of Enriched Gas

BIOGAS ENRICHMENT AND BOTTLING SYSTEM1-Biogas plant 2-Ball valve 3-Water remover 4-Receiver mounted compressor 5-Pressure gauge 6-Gas Storage Vessel 7-Rotameter 8-Supporting stand 9-Reshching rings 10-Scrubber 11-Safety valve 12-Water sprayer 13-Flange 14-View glass 15-Water outlet 16-Water pump 17-Gas filter 18-Pressure reducer 19-Three stage gas compressor 20-CNG Cylinder

NOT TO SCALE11

12

13 14

10

20 9 5 2 3 1 6 7 8 17

19 16 18 4 15

Fig.1: Experimental setup for biogas purification and bottling

Enriched Biogas

CO2 SCRUBBING SYSTEM

Not to scale

Water InTop Section 500 mm

150 mm

Enriched Biogas Water In

Middle Section

Packing 3500 mm Supporting Stand

Raw Biogas

Bottom Section

Raw Biogas 800 mm

Water Out Schematic Diagram of Packed Bed Column

Water Out

SUCCESS CASE STUDIES OF BIOGAS AS AUTOMOTIVE FUEL Rajasthan Go Sewa Sangh, Durgapura, Rajasthan: Plant started in 2007 and has been running successfully. A three wheeler runs on biogas daily about 100 km. and approximate 4 kg Bio-CNG is required. Shri Krishna Goshala, Ghaziabad: Plant started in 2009 and has been running successfully. Shri Madhav Go Vigyan Anusandhan Sansthan, Bhilwara, Rajasthan: Plant started in 2009 and has been running successfully.

AUTOMOTIVE CAR AND THREE WHEELER RUNNING ON ENRICHED BIOGAS

COST- ECONOMICS OF THE SYSTEMThe Cost of Biogas plant (1000 NM3/Day Capacity) is approx. Rs. 60 lakhs Biogas purification and bottling system is approx. Rs. 55 lakhs (excluding the cost of cylinder for gas storage) slurry management and processing cost to produce dry manure is Rs. 20 Lakhs other costs like land preparation, civil work, high pressure gas storage cylinders Taxes, logistic etc. is appox. Rs.15 Lakhs. total initial cost is Rs. 1.5 Crores of the whole system with annual profit of approx. Rs. 34.125 Lakhs.

POSSIBLE ENTREPRENEURIAL AVENUES Large Scale/ Community level Biogas Enterprises for 1. Cooking needs- Pipeline supply 2. Electricity Production and Supply 3. Rural sanitation & bio manure production 4. Cylindering of methane available from biogas plant for vehicles and production of bio manure

CONCLUSIONS India has second largest biogas programme in the world at rural and as well as urban levels. Many technologies/models have been successfully developed in India for biogas programme. There is need to develop a sustainable renewable energy programme on biogas for replacing petroleum products by utilization of biogas in the country. This will help in green energy technology and reducing green house gases emissions.

Biogas is a potential renewable energy source for rural India and other developing countries. Biogas generation and subsequent bottling will cater the energy needs of villages, supply enriched manure and maintain village sanitation. The bottling system will work as a decentralize source of power with uninterrupted supply using local resources, generate ample opportunities for employment and income of the rural people.

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