BIOMASS AS ENERGY SOURCE -II
Posted June 23, 2008on:
Another form of standardised fuel which is already being used in the rural areas is that of biogenous methane. The biological process of methane production results in a mixture of methane and carbon dioxide, which is called biogas. Burnt in a properly designed burner, biogas produces a blue flame, which is absolutely clean. This technology is at least 150 years old.
Traditionally, cattle dung is used as feedstock for producing biogas, and therefore it is also called gobar gas in India. During the last 50 years, the Government of India has made great efforts to popularise the gobar gas technology, but the present figures indicate that there are only about 2.5 million working domestic biogas plants in India, covering hardly 1.8% of the rural households. The failure of the gobar gas technology in India was due to the fact that it is not a very user-friendly technology. It requires dung from at least 6 to 8 heads of cattle. In order that the dung be easily available, the cattle must be penned and not allowed to roam.
The present technology also requires the dung to be mixed with equal volume of water to form a slurry. Villagers do not have tap water in their houses. Therefore, the water has to be fetched by the women from a source that is often far away from the house. The water is generally carried in pots balanced on their heads. Fetching water for the household is itself quite a strenuous task. Fetching daily additional 40 to 50 litres of water for the biogas plant only adds to the women’s burden, which they generally resent. The drudgery doesn’t just stop at fetching dung and water. Disposal of daily about 80 litres of spent slurry is also often a problem.
The new proposed system produced a more user-friendly biogas system based on starchy or sugary feedstock. Just 2 kg of sugar yield as much biogas as 40 kg of dung, and while dung requires a retention period of about 40 days, sugar yields the gas within just a single day. Starch also works equally well as feedstock. Our novel biogas system operates on waste starchy or sugary material such as leftover food, oilcake of non-edible oilseeds, fruits, tubers, rhizomes or grain that cannot be marketed due to poor quality, or non-edible material like rhizomes of banana, fruits of wild ficus etc.
A biogas plant based on this technology is quite small, having a capacity of just 1000 litres, and its cost is also much less, only about Rs.6000. About 200 of such gas plants are already installed, in various parts of Maharashtra, and this number is going to increase to 2000 in the next year.
Biogas can also be used as fuel in internal combustion engines. The CNG technology that is currently available in India can be used in both ways as bigas and an automotive fuel. Wood gas is the third alternative representing standardized fuel made from biomass. This technology does not lend itself well to being used in domestic cookstoves, but larger stoves, used in bakeries, langars or restaurants can be based on it.
However, wood gas is currently being used as fuel in internal combustion engines for generating electricity. Many such units are being operated all over the country. Biogas based electricity generation should be seriously considered by our planners and administrators as a means of supplying electricity to villages.
The electricity demand of a village is not very high. Supply of such small amount of electricity from a central generating facility is generally very costly because of the capital expense of the conduction system. There are also losses and theft of electricity when it is transmitted over such long distances. The village level generators should be operated by the villagers themselves. They can then generate electricity as and when they want and also use it for whatever purpose they want.
This discussion would not be completed without mentioning biodiesel and alcohol. Biodiesel is made from vegetable oil. In the Western countries, edible oil like soybean oil or rapeseed oil are used as a source of biodiesel. Our country, currently imports almost 50% of its total demand of edible oil. Under such circumstances, using edible oils for biodiesel is out of question.
Among our indigenous plant species, castor and rice are the only sources of oil that are produced by farmers. Castor oil, having special chemical composition, is not only being used by industries but it is also exported, while rice bran oil is used almost entirely by the organised soap industry. The remaining non-edible oils, being produced from seeds of various uncultivated tree species, play only a minor role in our economy. Being uncultivated, their supply is unreliable and therefore one cannot base a major industry like biodiesel on them. Currently India requires annually about 50 million tonnes of diesel. Substituing just 5% of this by biodiesel would require 2.5 million tonnes of vegetable oil. Considering average yield of 500 kg oil per hectare, one would require an area of 5 million hectares under oilseed production. I quote these figures only to bring into focus the magnitude of this endeavour. There is talk of introducing Jatropha curcas as a new oil bearing plant. It is claimed that Jatropha requires very little water.
It is clear that all plant species, irrespective of whether they are drought tolerant or not, require monthly about 200 mm water, if they are to give a good yield. Tolerance to drought means only that the plant can survive under conditions of drought and that it does not die under drought. It does not mean that it would give high yield under such conditions. It has been shown that even Jatropha needs about 800 to 900 mm of water to become economically viable. If a farmer has at his disposal this much water, he would rather grow a cash crop like cotton, groundnut, soybean or onion, than a low yielding plant like Jatropha.
The situation of alcohol is similar to that of biodiesel. Currently, alcohol is made from
molasses, a free by product of the sugar industry. As the cost of sugarcane, its harvest, transport, and processing are borne by sugar, the present cost of alcohol is low. But if crops like sugarcane, sugar beet or sweet sorghum are grown exclusively for alcohol production, the above mentioned costs would have to be borne by alcohol, which then would not be so cheap. Also the area required to be planted to produce alcohol would be of the same magnitude as that required by biodiesel.
Production of biomass in any form requires the use of land, and it would require the
involvement of rural people to do it. Chemical fertilizers, an important input required in agriculture, need a large quantities of fossil fuel in their production.
This concept is based on the assumption that soil micro-organisms degrade the soil minerals to provide the green plants with all the mineral nutrients that they need. If the soil micro-organisms are adequately fed with organic matter, there is theoretically no need to apply chemical fertilizers to the soil. Traditional agricultural scientists recommend the application of organic matter in the form of compost. However, the nutritional value of composted organic matter is so low, that one has to apply 20 to 50 tonnes of compost per hectare. In practical terms, it means that one has to use the biomass produced in about 10 hectares for providing organic matter to one hectare.
Research has shown that if organic matter having high nutritive value, like sugar, starch, protein etc. is used as manure, application of just 10 to 25 kg per hectare of it is enough to produce high crop yield without using any other form of chemical or organic nutrients. This new discovery would reduce the cost of agriculture substantially and would also reduce the cost of producing biomass.