Monday, April 30, 2007
Friday, December 02, 2005
ENERGY FROM BIOMASS
The availability of Energy in rural areas is at stake. The energy poverty in rural areas is increasing. Moreover the demand for energy is ever growing and the oil prices are increasing everyday. Keeping in view the above facts there is need to look for decentralized energy options in rural areas.Energy from Biomass is one of the most widely used options. With the availability of new technologies there are various means to convert biomass into energy efficiently.
The biogas yield from Gobar or cow dung is very low as compared to various other biomass, therefore there is a need to design biogas plants for digestion of other efficient material. The widely available vegetative biomass (usually weeds) and Kitchen waste form the important material for designing efficient biogas models. At the same time not compromising on food security issues, developing countries could also take up Energy Farming (Production of biomass on fields for energy utilization - beside food production and organic waste utilization). Anaerobic digestion and gasification technology are possibilities for Energy Farming.
I have developed a prototype mini-biogas plant called 'SRUSHTI' means creation. This model works with vegetative biomass (grass, leaves) and kitchen waste as raw material. It was created last year. This requires 2 kilograms of Kitchen waste and other green matter as feed, and releases about 2 cubic meters of biogas. Initially to activate dung of cattle should be added for introducing methane generating bacteria.
The challenge was to develop a very low cost and efficient bio-gas plant, for communities to adopt with out subsidy. This prototype was costing about Rs. 3,500/- or about $80 (USD).
The yield of biogas increases in this order for same quantity by weight of the raw material as it is : cowdung, pig litter, vegetable, poultry litter, bush waste, sewage, food waste, grass and vegetable oil. As compared to the lowest and the maximum the difference is at least 5 to 10 times.
Features:
Digester: A GI sheet drum as digester, an inlet (feed) and an outlet (digested slurry) system.
Controlling the temperature of the digester: Regarding keeping the temperature of the microbes at 37 degree centrigrade there are three options. The other option is to heat water through a simple solar water heater and circulate the water in the drum through copper tubes used for air conditioners which is adopted in this design. Other alternative options are to have an aquarium glass / steel water heater (temp is adjustable) this does not consume much electricity, which will be inserted into the drum through the slurry tube and it will lie at the bottom. The other option is to have a water bath around the drum and link the water bath to solar water heater. The whole digester should be insulated from outside.
Mixing the biomass: At the top of the drum a stirrer with handle arrangement is made, for rotating the material inside the drum. The shaft of the stirrer should be gas leak proof. Another traditional method is to rotate the floating drum.
Storing the gas: The gas is first stored in the floating drum and also in the extra plastic drum linked.
I am keeping it under 'Open Source Technology' - any one could use the design as it is or modify for community and common good.SUGGESTIONS FOR IMPROVEMENT OF THE DESIGN
My name is Borja Diaz and I live in Spain. During the last 2 years I have been surfing the net, reading articles about alternative energy sources for producing heat and electricity and I was really impressed when I found your works on the internet.
I have some questions concerning your mini biogas plant SHRUSHTI. Everytime I look at it, I have the feeling that the lid cannot hold too much pressure and that it must be really dificult to get it so tight that the biogas doesn´t go out. Same applies for the holes for stirring the tank´s liquids.
I humbly want to share with you some modifications I made to your design (never tested, it´s just theory), hoping that they will be useful.
First I added a metal pipe that goes vertically from top to bottom. That pipe is held in the center of the tank by radial supports that allow the pipe to spin (rotate?). Attached to that pipe are several little propellers that stir the mix of solids and liquids inside the tank. On the top of the pipe there is a crankshaft that makes the pipe spin.
Secondly on the top of the tank I substituted the metal lid by a loose plastic bag resistant to corrosion. That way, the biogas reactions would take place in complete anaerobic conditions, and as the biogas is generated the bag would get filled
The upsides of my modifications are that it is much easier to create an airtight environment using plastic materials since they are cheap and require little qualification for reparing it: as simple as reparing a flat bicycle tire.
The problems with those modifications is that the plastic must be kept away from direct sunlight exposure in order to enhance it´s lifespan ( 2 or 3 years tops ) and it wouldn´t hold as much gas pressure as the former lid. For that problem I was thinking about using old truck tires as auxiliary gas reservoirs in cases when the gas input is much bigger that the gas output. The crankshaft may be an obstacle for the plastic bag as it gets filled with gas, but it can be easily solved by using a large pipe and adjusting the sealing device (flange clamps)
