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Technology Development in Thermal Gasifiers
Thermal Gasifier

TERI develops and disseminates biomass-based gasifier systems that serve as a source of heat for a various uses. Customised gasifer systems have been developed for large-scale cooking; cremation; sericulture; dyeing; extraction of chemicals; metal smelting; and drying tobacco, rubber, and large cardamom. During the past two decades, more than 300 gasifier systems have been installed throughout India with a cumulative capacity of 12 MWthermal. These gasifiers burn locally available low-grade biomass fuels such as twigs, husk, shells of coconut and cashew, mustard stalks, and other crop residues in briquetted form, but offer the convenience associated with high-grade fuels such as gas and electricity. The technology has been licensed to six manufacturers for commercialization. It has also crossed international borders; TERI gasifiers are found in neighbouring countries like Myanmar, Nepal, and Bhutan.

Improvement in system design and associated benefits with product development approach followed

The salient features of TERI gasifier design are:
Throat less design
Low specific gasification rate
Use of castable insulation of firebox
Use of water-seal ash-pit and gasifier top cover (fuel charging door) for quick and easy ash removal without disturbing operation and quick fuel charging respectively

The various gasifier designs developed by TERI so far along with its advantages and limitations are as follows:

Down-draft gasifier

Relatively clean gas
Can handle relatively smaller wood pieces with low moisture content (upto 15%)

Up-draft gasifier

Relatively dirty gas (more tar content)
Can handle relatively larger wood pieces and high moisture content (upto 20-25%)
Needs relatively smaller capacity air blower

Up-draft gasifier operating under natural draft mode

Can be operated in remote areas where electricity is not available for using blower
Relatively dirty gas (more tar content)
Can handle relatively larger wood pieces
Operates under narrow range of designed gas production rates

Recently, TERI also developed a small sized wood gas stove operating on IDG (inverted downdraft gasifier) principle. This can be operated for given (design) output power under natural draft mode or can be used for varying output power using tiny sized blower (turbo stove), which can be operated using small battery. These batteries can be charged using small solar cell in remote areas. These turbo stoves or updraft gasifier can even be used as efficient charcoal making devices utilizing volatiles for some useful thermal applications. Turbo stoves can be operated with efficiency levels of about 30-35% with charcoal yield of about 20-22%.

As mentioned earlier, TERI has been working on developing tailor-made packages for thermal applications of gasifiers—both updraft and downdraft type—over two decades. Gasifier development work was initiated in TERI much before TERI-SDC (Swiss Agency for Development and Cooperation) partnership came into being. The partnership boosted the work being pursued in the field in SMiEs (Small and Micro Enterprises), which accelerated the pace of intervention. It also gave an opportunity to work systematically in collaborative manner involving users, sector experts, and product developers. It further provided an insight on development of complete package of gasifier system for utilizing producer gas efficiently. This helped in achieving higher overall efficiency levels since in most of the cases this resulted in development of better processes, making it faster, cleaner, and of better quality.

Various gasifier thermal application packages developed by TERI under TERI-SDC partnership projects include:

Down-draft gasifer along with improved SERI 2 000 oven for silk reeling units
Down-draft gasifier system for silk yarn dyeing along with improved oven
Up-draft gasifier system as retrofit option for Italian cottage basin oven in Siddlaghatta cluster along with options for silk yarn drying using either waste heat of flue gases or by obtaining the req
uired charcoal as byproduct using gasifier
Improved charka oven (about 25% fuel saving) using HRU (heat recovery unit) concept for producing hot water and for silk yarn drying
Down-draft gasifier application for namkeen making and sweet (sohan halwa) making
Down-draft and updraft gasifier systems for puffed rice making along with improved bhatti, HRU and simple retrofitting devices for reducing particulate emissions from the chimney
Up-draft gasifier for bamboo-mat factory boiler
Up-draft gasifier (either using blower or under natural draft operation) for community cooking in residential hostels
Refining turbo stove design

In addition to these, other gasifier thermal applications developed so far under various other projects include:

Up-draft gasifier for magnesium chloride manufacturing
Down-draft gasifier for carbon dioxide production
Down-draft gasifier for large scale community cooking
Up-draft and down draft gasifiers for crum rubber drying
Down-draft gasifier based crematorium
Down-draft gasifier for tobacco curing
Down-draft gasifier for plaster of paris making
Down-draft gasifier for copper smelting
Down-draft gasifier for lead melting
Down-draft gasifier for bakeries
Up-draft gasifier operating under natural draft mode for green brick drying