Every year the sugar cane fields of Maharashtra State in India produce a staggering four and half million tonnes of leaves, which are left behind when the cane is harvested.
The leaves contain lignin and silica, so they don't decompose easily, and they aren't good for animal fodder. So what can be done with them? Traditionally, the answer has been to burn them in the field.
The Appropriate Rural Technology Institute of India (ARTI) came up with a better solution. It developed a special portable kiln that burns the leaves to produce char. The powdered char is mixed into a paste with water and a binder, and a hand-operated press is used to turn the paste into briquettes, which are then dried in the sun. ARTI has developed the efficient ‘Sarai’ cookstove that uses the char-briquettes, but they can also be used in other charcoal stoves.
Charring the sugar cane trash in kilns instead of burning it in the open reduces local pollution. By replacing charcoal from unsustainable sources, it also cuts greenhouse gas emissions and deforestation. ARTI estimates that a rural family could make 100 kg of char-briquettes per day and earn about US$50 per week by selling them.
Charring the sugar cane trash in kilns instead of burning it in the open is helping to keep the skies clear and is reducing unnecessary carbon emissions. ARTI has also developed a new, improved, cooker that can use these briquettes as fuel. This 'Sarai' cooker uses only 100g of briquettes to cook food that would normally need 3Kg of firewood. The aim of this project is to increase the production of briquettes from sugar cane trash and to popularise the use of briquettes for cooking.
Charcoal has always been a favourite fuel for cooking with in Maharashtra. It burns cleanly, produces little smoke and has traditionally been cheaper than petrol products like kerosene. In the 1950s, the government of India banned charcoal production and subsidised the price of kerosene in order to try and stop deforestation. The ban on charcoal making (from wood) is still in place, but in 2000 the Government reduced the subsidy on kerosene, forcing people to return to using wood as fuel. The production of charcoal from sugar cane trash therefore provides a muchneeded source of cheap fuel. The briquettes are expected to displace the use of about 30 times their weight in wood. This could mean saving about 15,000 hectares of dry deciduous forest a year in Maharashtra alone.
Sugar cane leaves are extremely tough and won't decompose easily. They are long and springy and the farmer has to get them out of the way before ploughing and replanting can begin. The burning of four and a half million tonnes of sugar cane trash in Maharashtra each year produces a massive amount of smoke and atmospheric pollution.
Technology and use
The first kiln that ARTI built was fixed to the ground, but more recent versions are portable and can be taken to the fields as they are ready for clearing. This is an important improvement as collecting up the trash and taking it to a kiln is not economically viable.
The leaves are packed tightly into lidded stainless steel cans. Seven of these are loaded into the metal drum that forms the body of the kiln, and supported by a grate. Sugar can trash is burned below the grate and used to fire the charring process. Flue gases are forced to move between the cans on their way to the chimney, transferring their heat as they go.
Being starved of oxygen in the lidded cans, the cane trash is forced to pyrolise rather than burn as it heats up, and so it turns into a mass of charcoal. An innovative twist to the kiln design is that a small hole in the bottom of each can allows gases produced in the process of pyrolysis to escape at the level of the grate and be burned as fuel. This reduces atmospheric pollution and means that the charring process is exceptionally efficient.
It takes 45 minutes to fire one load of trash. At this rate one kiln, working full time, would take 40 days to char the trash from a one-hectare cane field. The farmers are generally in a hurry to get their fields cleared, so the project usually puts 10 kilns into a field at a time. The harvest lasts about five months, and after that the kilns can be used to char other things like wheat straw and leaf litter.
At the end of a firing, the cans contain a charcoal mass that needs to be pulverised with a light roller and then mixed with a liquid binder before being formed into briquettes. Starch paste, made from the floor sweepings of flour mills, cattle slurry or sugar cane juice can all be used as binders. The resulting charcoal paste is pushed into briquette moulds or extruded from a handoperated briquette extruder, and left out in the sun to dry.
Briquette making can only be done when the sun is strong enough to dry the briquettes. Good sun usually lasts for about 35 weeks a year. During this time a family could make enough briquettes to earn about 100,000 rupees, equivalent to the annual salary of an urban white-collar worker. This would clearly make a dramatic improvement to the quality of life for a rural family.
ARTI's Sarai cooker, which uses the cane trash briquettes, uses a neat system of three cans stacked inside a large cooking pot. A small amount of water at the bottom of the large pot quickly turns to steam and cooks the contents of the cans. Rice, beans and vegetables can be cooked in one go. The Sarai system has proved popular, and cookers are being produced on a commercial basis in the city of Pune. They are marketed through a rural cooperative at a price of 350 rupees (about £5).