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Biomass gasifiers for cardamom drying, silk reeling, and cremation
Faster way up the energy carrier

Electricity and LPG (liquefied petroleum gas) are clean and convenient fuels but are not easily available in villages—and they are not cheap. Firewood, dry leaves, and stubble left in the field after a crop is harvested are easily available and cheap—but they are smoky. Enter the gasifier, a device that uses firewood and other forms of loose biomass in the form of briquettes and turns it into a gas that burns with a clean smokeless flame. And TERI has developed a variety of gasifiers for applications ranging from curing cardamom to cremation.

A gasifier ensures that woody biomass is burnt more efficiently. Biomass that feeds an open fire loses about two-thirds of its energy to the environment in the form of smoke. Though the technique of converting wood energy into a combustible gas is not new – it was widespread in Europe during the Second World War when oil supplies were low – TERI’s work has focused on developing gasifiers for specific applications, namely drying of large cardamom, boiling cocoons in silk-reeling, cremation, and power generation.

Preserving the aroma of large cardamom
Though less widely known than its green-skinned cousin, large cardamom occupies a niche in south-east Asian cuisine owing to its characteristic aroma. Sikkim is the major producer of large cardamom: during the curing season, nearly a quarter of a million people are gainfully employed in the business, and the crop is the mainstay of small farmers, whose plantations are 2 hectares or smaller.

Traditionally, large cardamom is dried over fire within a stone-walled drying chamber. The capsules are spread out in a 25- to 30-cm-thick layer on a wire mesh placed above a small fire. The firewood consists of freshly cut twigs and small branches, not quite dry, which burn unevenly and emit copious smoke. The key to the gasifier’s success is in its controlled and clean application of heat: the capsules fetch a premium in the market because they retain their natural red colour and carry a richer aroma (35% more volatile oils than those dried in the traditional bhattis) and the consumption of fuelwood is more than halved. And the design of the gasifier has been kept simple enough so that it can be manufactured cheaply – it uses discarded barrels of oil – in local workshops.

Spinning a yarn
In the production of silk on a small scale, cocoons or the pupae of the silkworm are boiled to dissolve sericin, the gummy secretion that holds the thread together. This process frees one end of the silk yarn, which can then be reeled. The temperature of the hot water has to be maintained within narrow limits. The process requires substantial quantities of firewood—the gasifier reduced those by improving the energy efficiency of the process by as much as 60%. Better control over the process also enhanced the quality of silk yarn (longer unbroken threads) and its yield (more yarn for the same weight of cocoons). The gasifier was also successful in lowering the amount of water required for the process by nearly 30%.

Dust to dust; ashes to ashes
Modern electric or diesel-based crematoria are found mostly in very large cities. They are expensive and cause pollution. It was the ordeal of the bereaved – open-air funeral pyres not only take hours to reduce a body to ashes but require half a tonne of firewood – that led TERI researchers to think of an alternative; the gasifier they developed consumes less than 100 kilos of wood and takes less than an hour to do its job.

In electric crematoria, the cremation chamber requires to be heated to a temperature of 700 °C, which has to be maintained till it is put to use. This takes nearly 10 hours. For cremation, the required temperature is 800 °C, which has to be maintained over an hour. Approximately 165 kilowatt-hours of energy is consumed for every cremation even when the system is operated round the clock (an average of eight bodies a day). Diesel-based systems consume about 25 litres of diesel in the process. The capital cost is also very high (up to five million rupees, whereas the gasifier-based crematorium developed by TERI can be set up for less than a million rupees).

The gasifier-based crematorium also helps check pollution and air pollution. Often, because fuelwood is scarce and expensive, and because a traditional open-air pyre can take hours to reduce the body to ashes, a large number of partially burnt bodies are released into rivers, a major source of water pollution. And because a gasifier burns gas produced from wood instead of burning wood directly, it is not smoky. The gasifier is also more resource-efficient in that it can use sawdust and crop residues also, so long as they are compacted into briquettes.

A wood-gasifier-based crematorium in Ambarnath

The first successful gasifier-based crematorium that TERI developed was operational in July 2002 in Ambarnath, about 65 kilometres from Mumbai, thanks to the determined efforts by the Nagrik Seva Mandal, the Ambarnath Municipal Corporation, TERI, and financial support from the MNES, the Ministry of Non-conventional Energy Sources, Government of India. Two more similar crematoria are now being commissioned in Goa (one in Ponda and the other in Mapusa) and enquiries keep coming in from all over India.

Applications/benefits
Biomass gasification promises a faster way up the ‘energy carrier’ (firewood, dung-cakes, and crop residues represent the lowest rung whereas electricity is at the top) because it delivers a clean and convenient fuel. The process also offers better control over combustion and higher efficiency. Depending on the application, better control has such benefits as dried cardamom capsules of superior quality and a longer silk yarn whereas higher efficiency directly translates to lower costs.

Large cardamom drying
The investment cost of the gasifier-based system is about 10 000–15 000 rupees, as compared to 4000–6000 rupees in the traditional bhatti system. Although fuel consumption is less than one-third of the traditional system, it does need some pieces of dry cut wood. The major benefit is in terms of savings in fuelwood and a clean smoke-free working environment.

Commercial prototype of the gasifier for silk industry

Silk reeling
Though the upfront investment costs of the biomass gasifier (65 000 rupees) for silk reeling are higher to that of regular cooking ovens (8000 rupees), the latter has additional maintenance costs of 2000 rupees every two years. Moreover, the T ERI-modelled gasifier uses only about 60% energy as compared to the traditional ones (translates into savings of 72 rupees per day). Moreover, with a 10% discount rate and a life-span of 15 years, the present value of the traditional technology and T ERI’s technology are not very different. Moreover, if benefits in terms of additional silk production and improved quality of silk (450 rupees per day and 180 working days) are internalized, the NPV (net present value) is positive at 0.6 million rupees.

Crematoria
The gasifier-based crematorium is better than other new technologies such as the diesel and electric crematoria, in terms of investment and running costs. In comparison with the conventional wood crematorium, it needs an additional investment of 0.5 to 1 million rupees. Assuming a 10% rate of discount, and one cremation per day, it carries an NPV of 50 000 rupees. The 0.5-million rupees investment for conventional technology has a positive NPV of 4600 rupees. If two bodies are cremated in a day, with an investment of 1 million rupees, the NPV is positive at 9200 rupees. Hence, this technology would become viable with low capital costs and high utilization. The gasifier-based crematorium has positive environmental effects due to lower emissions and substantial savings in the use of wood.