Table of Contents
Biomass is renewable, widely available, carbon-neutral and has the potential to provide significant productive employment in rural areas. Biomass is derived from numerous sources including by-product from sugar and wood industry, agricultural crops, forests etc. Biomass is an important source of energy and the most important fuel worldwide after coal, oil and natural gas.
Biomass Briquetting: The process of densifying loose agro-waste into a solidified biomass of high density. Briquette is also termed as "Bio-coal". It is pollution free and eco-friendly. Some of the agricultural and forestry residues can be briquetted after suitable pre-treatment. The advantages of briquetting is high calorific value with low ash content, absence of polluting gases like sulphur, phosphorus fumes and fly ash, which eliminate the need for pollution control equipment, complete combustion, ease of handling, transportation & storage because of uniform size and convenient lengths.
Three main technologies for utilization of biomass are:
- Bagasse-based cogeneration in sugar mills.
- Biomass power generation.
- Bimass gasification for thermal and electrical applications.
Technology: Cogeneration is the process of using a single fuel to produce more than one form of energy in sequence. Cogeneration of steam and electricity increases overall efficiency, where heat and electricity is simultaneously required, as in sugar industry. In electricity production, thermodynamics requires rejection of large quantity of heat at lower temperature. In normal electricity generation stations, heat rejection takes place in condensers, where upto 70 % of heat of steam is converted to water vapour and hot water which can be recycled as boiler feed water. In cogeneration, this heat is used for process heating, thus increasing the overall efficiency of fuel utilization to 60 % or even higher. Capacity of cogeneration plants can range from few kW to several MW.
Cogeneration in Sugar Industry: Traditionally, worldwide, sugar industries utilize bagasse-based cogeneration. Almost all sugar mills in India have some form of cogeneration, even mills set up 80 years ago has. Now technology is available for high-temperature and high-pressure steam generation using bagasse. With this new technology, energy efficiency increases and sugar mills generate more electricity than they need. Typically, when steam generation temperature / pressure is increased from 400 °C / 32 bar to 485 °C / 66 bar, more than 80 kW⋅h of additional electricity is produced per tonne of cane. It has been estimated by MNRE that 'optimum cogeneration' can result in net value addition of ₹ 70 - 100 per tonne at current electricity prices.
Cost: ₹ 4.5 - 5.5 crore/MW, depending on configuration. As typical sugar mill has average crushing season of 160 days, cogeneration is beneficial in long-term.
Biomass-based Power Generation
India produces a huge quantity of biomass material in its agriculture, agro-industrial and forestry operations. According to some estimates, over 500 Mt of agri-cultural and agro-industrial residue is generated every year. At least 150 - 200 Mt of biomass residue is wasted and can be used for energy production. These materials include a variety of husks and straws. This spare biomass is sufficient to generate 18 000 - 20 000 MW electricity.
Technology: The technology for generation of electricity from biomass is similiar to that of coal based thermal plants. The biomass is burnt in boilers to generate steam, which drives turbo alternator. Recent innovation uses air-cooled condensers to reduce water consumption.
- These projects can be designed to match the electric loads, as biomass can be stored and used at demand.
- Equipment and technology is same as for coal-based, no new development is required.
- As they are in proximity to the rural areas, they improve quality of electricity supply there.
- A variety of biomass can be used in the same plant, thus providing flexibility of operations.
Cost: ₹ 4.0 - 5.0 crore/MW, depending on cost of biomass, plant load factor and efficiency.
Biomass gasifiers have the potential to provide captive electrical and thermal energy needs of industries to replace conventional fuels. More importantly, it is also capable to produce electricity for off-grid application in rural areas ans well as feed into the tail end of the grid, which is imperative and sustainable solution, as there is acute shortage of electricity in rural areas.
A variety of biomass such as rice husk, corn cab & stalks, arhar staltks, cotton stalks, and small wooden chips are available. Rice husk is abundantly available in rice growing eastern part of the country comprising of Eastern UP, Bihar, Orissa, and WB. These areas also have the lowest per capita energy consumption and hence remain backward.
Biomass gasifiers convert the solid biomass into a combustible gas mixture normally called as producer gas. The producer gas consists of mainly methane, carbon-monoxide, hydrogen and nitrogen and has a lower calorific value (1000–1200 kcal/N⋅m³). The conversion efficiency of the gasification process is in the range of 60 %–70 %. Gasification of biomass and using it in place of conventional direct burning devices will result in savings of atleast 50 % in fuel consumption. The gas has been found suitable for combustion in the internal combustion engines for the production of power. Methane can also be used as the 'fuel' in fuel cell. Fuel cell work much like batteries, but never need recharging, producing electricity as long as there is fuel.
Biomass gasifier system is different from 'direct-fired system' in which biomass is burned directly in the boiler to produce steam, which drives turbine. Gasifier systems use high temperature and oxygen-starved environment to convert biomass into producer gas. This process is called anaerobic digestion.
The energy from biomass can meet the demand of electricity in villages for lighting, water pumping and micro enterprise. It is specially suitable where biomass production and electricity consumption points are nearer. The following use cases are for gasifiers:
- Biomass gasifier based distributed/off-grid power programme for rural areas with a view to provide distributed power generation for lighting, irrigation and other commercial establishments.
- Biomass gasifier based captive power generation in rice mills and other industries for meeting their captive electrical and thermal needs.
- Biomass gasifier based grid-connected power projects with 100 % producer gas engines or biomass based grid connected boiler-turbine-generator (BTG) projects, preferrably at the tail end of a grid and having a decentralized distribution component. The maximum installed capacity of such project would be 2 MW.
Central Financial Assistance.
- ₹ 15 000 per kW for distributed/off-grid power projects in rural areas and grid connected power projects with 100 % producer gas engines or biomass based conbustion projects.
- ₹ 10.00 lakh per 100 kW for projects involving installation of 100 % gas engines with an existing gasifier.
- ₹ 10 000 per kW for captive power projects with 100 % producer gas engines in industries including rice mills.
- ₹ 2 500 per kW for biomass gasifier systems retrofitted with duel fuel mode engines.
- ₹ 2.0 lakh per 300 kW for the gasifier system in thermal application in industries.
- 20 % higher CFA for special category states.
- Support to activities such as awareness creation, publicity measures, seminars, workshops, business meets, training programs etc. and to expand local manufacturing capacity and also support service facilities under the programme.
Thirty-two years old, Mr Vivek Gupta has started Saran Renewable Energy in 2006. He has built a 120 kW biomass gasifier plant in Garkha and uses the gas to generate electricity. He has lit up more than 200 houses, dozen small units, a school and a medical center in Garkha. Recently, Airtel has also become his customer. He supplies 8-10 hours of regular supply at ₹ 8-10 per unit, 40 % cheaper than EA set.
He has further identified Dhaincha, a local woody plant which can be easily and profitabily grown by local farmers on uncultivable and waterlogged land, now used as their 85 % of fuel. The cultivation of plant has attracted villagers and strengthened plant's backward integration and in return villagers gets money. With this fuel, little carbon footprint is there and saves over 200 tonnes of carbon dioxide per year which makes it eligible for carbon credit. He is approaching corporates to bur carbon credit.
He has further chalked out plans to build small plants with capacity of 30-60 kW to power small villages and 4-6 MW for neighbouring districts of Dewan, Viashali and Muzaffarpur.
Unlike other renewable energy sources, biomass can be converted directly into liquid fuels - biofuels - for our transportation needs (cars, trucks, buses, airplanes, and trains). The two most common types of biofuels are ethanol and biodiesel.
Ethanol is an alcohol, similar to that used in beer and wine. It is made by fermenting any biomass high in carbohydrates (starches, sugars, or celluloses) through a process similar to brewing beer. Ethanol is mostly used as a fuel additive to cut down a vehicle's carbon monoxide and other smog-causing emissions. Flexible-fuel vehicles, which run on mixtures of gasoline and up to 85 % ethanol, are now available.
Biodiesel, produced by plants such as sunflowers and soybeans, can be extracted and refined into fuel, which can be burned in diesel engines and buses. Biodiesel can also made by combining alcohol with vegetable oil, or recycled cooking greases. It can be used as an additive to reduce vehicle emissions (typically 20 %) or in its pure form as a renewable alternative fuel for diesel engines.
Liquid fuels can be produced from biomass through a process called pyrolysis. Pyrolysis occurs when biomass is heated in the absence of oxygen. The biomass then turns into liquid called pyrolysis oil, which can be burned like petroleum to generate electricity.