Biomass gasifier-based power generation system

Biomass gasifier-based power generation system

Back to basics, with a difference

A mobile 7-kilowatt dual-fuel power plant in operation in a village

Think of the 18 000 Indian villages that will continue to be without electricity for at least the next 10 years. Though they fall under the government's rural electrification programme, it is not feasible at present to connect them to the grid. Then, there are other 62 000 villages that are still waiting to be wired. And in villages that are already wired, supply continues to be erratic. To electrify rural India so as to usher in development uniformly is an uphill task.

India being a large agrarian economy, biomass – wood, agricultural residues, animal dung, etc. – is available in enormous quantities. And, hence, over 40% of India's total energy requirement is met through biomass burning. However, biomass burning has been characterized with energy inefficiency and environmental hazards. Working towards a sustainable solution to the energy scarcity in rural India, researchers at TERI have arrived at a technological innovation to exploit the vast biomass resource and generate power in an environment-friendly and profitable proposition. TERI's biomass-based power generation systems for rural applications could effectively make up for the absence of grid electricity supply in many remote areas.

The innovation

A gasifier is a reactor that converts biomass into clean gaseous fuel called producer gas (having calorific value of the order of 1000–1200 kilocalories per normalized cubic metre). TERI's biomass gasifier system optimally utilizes biomass for power generation. It consists of a downdraft gasifier, a gas-cleaning train, and an engine. The technological innovation provided users with the option of dual-fuel operation. The existing diesel genset could run on both diesel and producer gas, instead of running only on diesel. The producer gas is fed into the diesel engine to let the engine operate in a dual-fuel mode, thereby reducing diesel consumption by more than 70%

 

A 40-kilowatt dual-fuel gasifier system at TERI's Gurgaon facility (left) and its schematic diagram

 

TERI's research then moved a step ahead to develop a modified engine that runs only on producer gas, eliminating the need for diesel altogether (Figure 3). In this, along with other design changes, the diesel injector set-up was replaced with a spark plug, and the fuel pump (governing system) with a distributor set-up coupled to the shaft.

 

The modified engine that runs only on producer gas and its schematic diagram

 

TERI's gasifier system comprises a downdraft throat-less gasifier, has multi-fuel capability and end-use Biomass gasifier-based power generation system Back to basics, with a difference Figure 2 flexibility. Fuelwood or briquettes produced from agricultural residues can be used in this gasifier. The throatless design makes for smooth fuel movement, with the gasifier allowing comparatively larger pieces of wood or fuel briquettes. Water seal arrangement with continuous grate-shaking mechanism simplifies ash and char removal without shutting down the system, thus enabling long uninterrupted operation. Entry of preheated air at two levels helps obtain good quality gas, with low impurities in raw gas. This also reduces the load on the gas-cleaning system. Induction of a cooling tower minimizes water requirement for gas cleaning and also reduces the quantities of tar-laden water to be disposed of.

 

The 10-kilowatt, 100% producer gas system installed in a village in Orissa

 

Towards self-sustenance

Village applications, such as water pumps for irrigation, can immensely benefit from the new technology. It can also be a boon to many agro-processing enterprises (those working with coffee, cashew, tobacco, plywood, and so on) that can recycle their biomass by-products to generate power. Using this technology, the tea industry in South India alone has the potential of generating 2000 megawatt of power from its biomass by-products.

The available biomass in the country (excluding animal residues) can support electrical power plants of 16 000 megawatts. Tapping this potential, two TERI gasifier systems have already been successfully installed: one in Orissa (10-kW, 100% producer gas system [Figures 4 and 5]) and the other in Uttaranchal (50-kW dual-fuel system). Installation of several other gasifiers is in the pipeline.

Applications/benefits

The biomass-based gasifier technology carries an environment-friendly and sustainable solution to the power crisis in rural India. It can reduce the use of fossil fuels in village applications. The technology can recycle bio-waste, be localized, and made available on demand without the need for separate storage. It also provides livelihood opportunities to the local population through various activities–biomass generation, processing, and operation of the plant.

The electricity produced from a biomass–based gasifier system can be used for lighting houses, powering irrigation pumps, and operating machines such as chillers. Table 1 explains the economics of a biomassbased power plant as compared to power plants based on other renewable energy sources.

Table 1 Economics of power plants (of 10–100 kilowatt capacity) based on biomass and other renewable energy source

Type of energy Capital investment
Type of energy (million rupees per megawatt)
Solar photovoltaic 300–400
Micro-hydel 40–60
Wind 40–50
Biomass Biomass 20–40