Flexi Biogas Plants for the Domestic Cooking Need of Rural Sikkim

In India, where there are 535.78 million livestock, including approximately 302 million bovines there is sufficient room for the construction of biogas facilities. The GDP contribution of India’s cattle industry is large and is projected to rise. With its direct and indirect benefits, the spread of biogas technology is a boon for Indian farmers. In FY 2022, India’s installed biomass capacity was 10,205.61 MW. To ensure that all the advantages are obtained, the Ministry of New and Renewable Energy (MNRE) has started several programmes to promote effective technology for using biomass in various economic sectors.

Sikkim, which occupies an area of 7096 km2 and located in the Eastern Himalayan Region, is mostly a hilly region surrounded by high Himalayan ranges. Sikkim has a considerable number of animals, including cattle, buffaloes, pigs, sheep, goats, yaks, and a few other types. In the north-eastern ranges bordering Tibet, Bhutan, and the western portion bordering Nepal, yaks are reared. The availability of animal excreta (organic waste) and their potential to produce biogas from various animals are shown in Table 1.
 

 

In hilly places, like Sikkim, where high transportation cost of construction material adds significantly to their expenses, conventional biogas plants are not feasible. Furthermore, conventional underground digesters are not suitable for use along India’s coastlines. Flexible balloon-style digesters made of neoprene-rubber can operate effectively in mountainous and coastal areas. Flexi biogas plants can be easily and affordably installed at any time above the ground and are readily transportable to remote locations.

Technology of Flexi Biogas Plant
Flexi biogas plant is a prefabricated air cushion type (flexi) household biogas digester with a high-density polyethylene gas container. The flexi biogas digester and gas holder are made from fabric that has been PVC coated. The gas holder of the flexi digester is above ground in an earthen pit. The biogas digester requires minimal maintenance and is simple to build without the need for civil construction. Installation of a 1m3, 2m3, or 3m3 flexi biogas plant requires no civil work, whereas 5m3 and bigger flexi biogas plants require just minimal civil work. The biogas digester for a 2m3 flexi biogas plant is made up of a 6-inch feeding funnel, a 0.5-inch gas opening and shutting valve, a 3-inch inlet PVC pipe, and a 3-inch elbow on the 3-inch outlet PVC pipe. Cattle dung and water are mixed before feeding in a mixing tank (a plastic drum) using a hand-operated agitator. To supply pressurised biogas to the cooking stove, a 20 watt (200 V, 50 Hz) biogas booster pump should be installed in the kitchen (Fig. 1). When the plant is being fed, the biogas outlet valve is closed. Due to pressure from the biogas that accumulates in the gas holder, the digested slurry flows out of the outlet pipe into the slurry drying pit. Flexi biogas models provide the most advanced technology while continuing to be the most affordable in the market.

Substrates for 2 m3 Biogas Production
• Farm manure up to 50 kg/day– poultry, cattle, pig, horse, poultry (when mixed with other) manure.
• Plant wastes up to 55 kg/day – leaves, twigs, little branches(shredded) waste.
• Food waste up to 18 kg/day raw and 40kg/ day cooked; from restaurants, cafeterias, groceries – food wastes like leftover food, fruit and vegetable peelings, over-ripped or spoiled fruits and vegetables, date expired food (shredded) waste.
 

Advantages of Utilising Biogas as a Cooking Fuel
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. Some of its advantages are as follows:
• Biogas burns very cleanly, and produces fewer pollutants during cooking than any other fuel except electricity.
• Biogas provides instant heat upon ignition, no pre-heating or waiting time is required.
• Most biogas burners are able to regulate the flow-rate to turn down fire-power from high heat to small low heat for simmering.
• Biogas can be used for lighting as well.
• The by-product (slurry) from the digester can be used as fertilizer.
• Biogas is a renewable fuel that is ‘carbon negative’: unless there are leakages in the system, burning biogas in a cook stove releases less greenhouse gases than if the dung was left on the ground to decompose naturally.

Employment Opportunities
India has the highest youth population in the world, with more than 808 million people under the age of 35, which accounts for close to 40 percent of the Indian population (according to the National Youth Policy). The youth unemployment rate in India was 6.8 percent during January-March 2023 according to National Sample Survey Office, out of which Sikkim accounts for 20.7 percent. This flexi biogas plant installation will provide employment opportunities to the rural youth as well as the women of the state, in the maintenance and installation of these biogas plants. Every nation’s economic development is based on the strength of its women. Women must be involved in industrial activities that not only assist women’s economic empowerment but also contribute to their empowerment. Flexi biogas digester construction requires soft labour that women can accomplish with ease.
 

Sikkim - Target and Way Forward with Flexi Biogas Plant
The annual target of MNRE for installation of biogas plants under the Biogas Programme for FY 2022-23 for Sikkim is 50 biogas plants under SREDA and the target for sanitary toilet’s linked biogas plant is 10 plants. The way forward with flexi biogas plant is that, the rural as well as the urban population should be sensitised regarding the flexi biogas plant or the bag type biogas plant. The benefits along with the simplicity of such technology should be highlighted and should be made popular among the masses, so that people understand the advantages of using biogas over LPG.

Conclusion
Flexi biogas plants are a better, more affordable alternative for those who live in rural and distant places. The Flexi biogas plant is simple to construct and operate. A rural family’s requirements for cooking and lighting are met by the biogas produced. The desired target of Sikkim can be achieved by encouraging the population to shift towards biogas utilisation for their energy needs as well as focusing on the need to adopt advanced technologies like the flexi biogas plant which are cost-effective and come in ready to install packages. The adaptation and use of flexi biogas plants helps mitigate the impact of global warming and hazardous environmental emissions in addition to converting accessible organic waste into usable gaseous fuel. A clean and hygienic environment would be developed in rural and distant areas of India thanks to the use of flexi biogas technology, which also strengthens energy security, creates employment possibilities, and improves the environment.

- Anisha Pradhan; Pradip Narale; Mahendra S. Seveda, Department of Renewable Energy Engineering, CAEPHT Ranipool