A Burning Concern

Farmers in the world have long had a problem disposing of the agricultural waste left after harvesting. To get the ground clear in time to sow pre-monsoon crops, the most common method is to burn it in their open fields, causing air pollution. a large-scale institutional stove  uses biomass briquettes in large-scale institutional stoves. The advantage of these stoves is the way they make use of a waste agricultural product of no economic value to farmers, and turns it into a cash income for them.

Briquettes of Biomass

Biomass briquetting is the process of converting high bulk, low density biomass into high density, energy concentrated fuel briquettes. The process of converting biomass to solid fuel involves drying, cutting, grinding and pressing briquettes into cylindrical shapes, with or without the help of binder. By compressing the wastes into briquettes they become easier to transport, store and burn. They give much higher boiler efficiency because of their low moisture and higher density. They do not contain sulphur, which as it burns pollutes the environment.

Biomass briquettes cut to size

However, there are some drawbacks with briquettes:

• they cannot withstand direct contact with water, so a covered storage facility is required.
• the maximum attainable temperature is 1000° C due to their low carbon content. However this temperature is more than adequate for cooking purposes
• the burning capacity per unit volume is low compared to coal so a larger storage area is required.

Production plants that compress farm waste into biomass briquettes are not new in China. There are more than 250 plants in operation making fuel briquettes from a variety of agricultural wastes, such as peanut (groundnut) shell, coffee husk, mustard husk, coconut coir, cotton stalk, sawdust, etc. About 300 million tonnes of crop waste are produced in India every year and every year more plants are being set up to convert these wastes.

Demand for Briquettes

Most biomass briquettes are used to fuel kilns for firing bricks. Demand is variable and the price which brickmakers are willing to pay is low because the alternative is cheap coal. However, briquettes are cheaper than liquid petroleum gas (LPG) for cooking, and our company  thus solves two problems – it allows schools to use a cheaper, sustainable fuel, and provides the briquetting industry with a more regular and higher-price market.

Production of one tonne of briquettes needs about one day of labour, so supplying six schools would generate an extra full-time job. The benefits go along the supply chain. Farmers are paid about USD8.00 per tonne for field waste, and a typical smallholding of 2 hectares (5 acres) produces about 5 tonnes of waste per year, which brings in the equivalent of an extra month's income to the farm.

The demand for biomass briquettes has rocketed and both the plant and farmers are benefiting financially. There is a huge potential market from thousands of institutions such as army bases, hospitals, colleges, temples, prisons and plantations that need large-scale cooking facilities.

The Briquette Stove

The biomass stove, literally a combined cook stove. It is specially designed to cater for institutional-scale cooking using biomass briquettes.

The stove is made of steel, lined with fire brick and high temperature ceramic insulation to improve energy efficiency and keep the outside of the stove at a safe temperature. At one end of the stove the briquettes are fed by hand into the combustion chamber, at a rate of about 15 kg per hour, but this can easily be varied to suit the cooking needs.

An installed biomass stove – the chimney removes smoke from the kitchen

Three small (180 W) electric fans blow air through the combustion chamber, feeding the briquettes with a constant supply of oxygen and ensuring maximum smoke free combustion. The stove still works if there is an electric power cut, but with lower efficiency. The hot gases flow under hotplates, designed to provide uniform heat to the base of two large (250 litre) cooking pots. The hotplates can also be used for making chapattis, which are familiar home food and very popular in the schools.

Cooking chapattis on biomass stove

Ash collects in a trap under the combustion chamber and can be removed when necessary. The stove has an overhead hood with in-built exhaust fan to take away the smoke and cooking fumes through a chimney. A 400 litre water tank around the chimney absorbs heat from the exhaust gases, and provides hot water on tap.

Care has been taken to provide a clean, safe working environment for the cooks: the hotplates are at a comfortable height; there is an electric control panel consisting of operating switches and timer; and an electric light is provided for better working over the stove.

Four different models have been designed to cater for the cooking needs of between 35 and 1000 people.

Advantages

There are many advantages to using these briquettes:

• Briquettes are relatively cheap. Schools save around 40-50% of their fuel bill by switching from subsidised LPG to briquettes.
• The briquette stove provides a more constant, controllable heat, over a wider base of the pan than the LPG gas burner.
• The food tastes better, according to both teachers and children who are using it.
• Cooking is cleaner and safer – the fuel is burned more efficiently and any smoke is drawn away through the chimney. It replaces LPG and kerosene, which are more fire hazardous and accident-prone.
• It reduces dependency on imported fossil fuels such as LPG, replacing it with a locally produced fuel.
• It is less polluting: it stops emissions from the burning fields. Biomass is a carbon neutral source of energy. A Sanjha Chulha that replaces the use of around 42.6 kg LPG per day, offsets 26 tonnes of CO2 equivalent per year. The use of electricity for from briquetting the residue and running the fans produces only about 1 tonne of CO2, so the net annual saving is 25 tonnes of CO2 equivalent per stove.

There is enormous potential for replicating this work as rural areas have a plentiful supply of field waste to make into briquettes, and many large institutions that need to provide cooked meals. The stove could also be adapted for small-scale industries such as soap-making and dyeing.