Biomass Gasifier Systems for Thermal Applications by Debajit Palit and Sanjay Mande

Boiling Point
Issue 53 (2007) Technologies that really work
Article	Biomass Gasifier Systems for Thermal
Author	Debajit Palit, Sanjay Mande

[top] [end]Introduction

Biomass fuels continue to play an important role both in the domestic and industrial sector in India, as it is an agricultural-based economy. Biomass is the main source of energy for a large number of small, rural, and cottage industries along with the majority of rural households. The majority of these enterprises belong to an unstructured sector and hence information and data on these industries are scarce. These industries provide employment to millions of people and form a very important part of the rural economy. The biomass-consuming industries can be divided into two categories, namely traditional industries and new or potential industries.

Traditional biomass-based industries are essentially rural cottage and smallscale industries. These industries depend predominantly on biomass fuels such as wood, agricultural residues, and animal dung because biomass is cheap and its supply is assured. Biomass energy is used in these industries for direct heating (fi ring of bricks,lime), indirect fi ring (drying, baking), boiling, steam raising and distillation.

New or potential biomass-based industries include many medium- and small-sized enterprises that currently use fossil fuels and are willing to switch over, at least partially, to biomass fuels available locally at lower prices. Examples of these industries include textile mills, brick kilns, mini cement plants, steel re-rolling and lime kilns.

This situation calls for the development of a biomass-based but energy efficient and environment friendly system with better environmental acceptability, economic viability, and good process control. The biomass gasifier system is ideal for such applications as it can offer all these qualities.

Biomass gasifi cation is the process of conversion, through partial combustion of solid biomass feed material into combustible gas. The technology may be regarded as fuel switching to convert solid fuel to gaseous fuel. Gasification is achieved in the presence of heat and a limited supply of oxygen, resulting in incomplete combustion of the solid biomass material. The resulting combustible gas mixture can be burnt directly in an oven/burner for thermal applications or cooled, cleaned and fed into a diesel engine to generate electricity.

Figure 1: Downdraft gasifier for cooking(photo: Dr Sanjay Mande & Debajit Palit )

For over two decades, TERI (The Energy and Resources Institute) has been working on the development of various biomass gasifi er designs (downdraft, updraft and natural draft) for both thermal applications as well as for decentralized power generation. So far, more than 350 TERI gasifier systems have been successfully installed in the fi eld throughout India with a cumulative installed capacity of over 13 MWth. This paper gives an account of TERIâs efforts in developing and promoting biomass gasifi cation as a sustainable and eco-friendly option to meet energy demand for three selected rural applications: cardamom drying, arecanut processing and community cooking.

[top] [end]Gasifier system for community cooking

Figure 2: Updraft gasifier for cooking (photo:Dr Sanjay Mande & Debajit Palit)

In a developing country like India, biomass is still and will remain the major fuel for cooking energy. There are several residential schools and religious places that consume substantial quantities of fuelwood daily. Apart from contributing to deforestation, it also consumes a lot of time and labour in its collection. TERI has designed both downdraft and updraft gasifi er based cooking systems and installed these at residential tribal schools at Doimukh in Arunachal Pradesh and Kankia in Orissa (Figure 1 and Figure 2). The updraft gasifi er system can also be operated without a blower under natural draft mode in unelectrifi ed villages.The fuel consumption data and time required for cooking using the gasifier system is tabulated in Tables 1 and 2 along with a comparison to the traditional stove.

Table 1: Summary of performance data of gasifier based cooking system at Doimukh, Arunachal Pradesh

Table 2: Summary of performance data of gasifeer based cooking system at Kankia, Orissa

[top] [end]Wood gas system for large cardamom curing

Figure 3: Gasifier for cardamom drying(photo: Dr Sanjay Mande & Debajit Palit)

With an annual production capacity of more than 4 000 Metric Tonnes (MT), India is the largest producer of large cardamom with a 54% share in world production, followed by Nepal and Bhutan. Within India more than 85% of production comes from Sikkim and Darjeeling. To achieve a long storage time and to bring out the characteristic aroma, cardamom capsules have to be dried to reduce the moisture content from about 70-80% to below 10%.Traditionally, an ineffi cient smoking method is employed, using a bhatti (oven) system. Out of the total argecardamom cultivation area in Sikkim, more than 85% plantations are very small with an area of less than 2 ha, with over 34 000 traditional bhattis, making it a small farmerâs business.

The bhatti is made-up of locally available construction materials. It has a 0.60 m thick stonewall structure on three sides and a wide opening in the front for burning large wood logs. About 400-600 kg fresh, large-cardamom capsules are loaded as a thick bed on a bamboo or wiremesh platform and placed on the stonewalls. Large wood logs from within plantations are fed and burnt in the front opening of the bhatti, and the capsules are exposed to a large amount of smoke to dry them. Thus the cardamom bed is exposed to the thick smoke generated during the burning of wet wood and it takes about 30-50 hours to dry the cardamom (Mande et al. 1999).

Figure 4: Comparative performance of traditional and gasifier based cardamom-curing system (Diagram: Dr Sanjay Mande)

TERI has developed an appropriate gasifier based large-cardamom dryer system (Figure 3) to suit local conditions. The system is made of locally available material and can be easily transported into remote forested areas where cardamom plantations are found. More than 150 systems have been installed in the state in collaboration with the state Horticulture Department and these systems have also been pilot tested in Nagaland state in India, as well as in Nepal and Bhutan. Through extensive fi eld performance monitoring it was observed that use of gasifi er not only resulted in more than 62% fuelwood saving but also resulted in improving the quality of the product, as the dried cardamom retained 35% more volatile oils and natural reddish colour (Figure 4). Thus induction of a gasifier system cannot only help in the preservation of natural forest but also in increasing the income for farmers.A greater oil content without a burnt smell could also open new industries for large-cardamom by way of extracting its oil.

[top] [end]Arecanut processing

Figure 5: Traditional arecanut boiling (photo:Dr Sanjay Mande & Debajit Palit)

Arecanut palm (Areca catechu L.) is cultivated for its kernel, which is chewed in its tender, ripe or processed form. The north-eastern region of India is a major producer of arecanut in India, producing 21% of the total national production. Most of the production is exported to outside the region. The major processing clusters are in northeast India with large (5-7 tonnes of processed arecanut produced weekly) and medium sized (2-3 tonne of processed arecanut produced weekly) units located in Rupahi and Howly, in the state of Assam. Apart from these clusters, thousands of cottage-level processing units are also found in Cachar, Karimganj, Darrang, Dhubri and Kokrajhar districts of Assam.

There are two varieties of processed arecanut processed in the state of Assam and other states in India: Boiled, dried nuts (red in colour, called chikni) and non-boiled, sun dried nuts (called supari). Tender green arecanut are dehusked, boiled and dried to obtain the chikni. Boiling is done in batches in fl at, open, iron pans (4-5 feet diameter) where chopped nut pieces are mixed with colour and boiled at 70-80°C, to cook and absorb the colour (Figure 5). The first batch of boiling in a day takes 50 minutes and subsequent batches take 30 minutes. Though the nuts should be boiled for 20 minutes to get a good quality boiled nut, owners restrict the boiling time to save the scarce fuelwood. The drying (slow heating) is done in brick-cement/brick-mud frame sheds (7 feet height and 7.5 feet width) with vertical partitions. Thick bamboo mats are used to spread the chopped nuts out for drying and wood is fi red in each partition on the ground, well below the bamboo mats. In the large and medium sized units, fi re curing is initially done for 12 hours at a temperature of 70-75°C and then the dried product is further sun dried for 2-3 days to remove any residual moisture.

On average 100 to 150 kg fuelwood is used to produce 100 kg of processed arecanut, of which 60% is used for boiling and the rest for drying. The average wood-burning rate for boiling is 115 kg per hour, with SFC (specific fuel consumption) of 0.70 kg wood per kg boiled nut. Detailed water boiling tests carried out on the vessel-bhatti combination currently used, revealed that the useful power requirement is 30-35 kWth.

TERI has successfully developed an integrated gasifi er-based system for boiling, as well as drying, and has successfully demonstrated the application in the Rupahi cluster (Figure 6). The gasifi er with a wood consumption rate of about 20 kg/hr capacity, was used for boiling arecanut in the existing boiling pan and also utilized the hot fl ue gases for drying. The gasifi er could also be operated successfully using waste arecanut husk (a by-product during de-husking operation) that makes the gasifi er option even more attractive (Table 3). Further improvements in energy effi ciency are achieved by utilizing the hot gases for drying instead of traditionally burning fuelwood.

Table 3: Field performance of gasifier-based cooking system for arecanut boiling

TERI has successfully developed an integrated gasifi er-based system for boiling, as well as drying, and has successfully demonstrated the application in the Rupahi cluster (Figure 6). The gasifier with a wood consumption rate of about 20 kg/hr capacity, was used for boiling arecanut in the existing boiling pan and also utilized the hot fl ue gases for drying. The gasifi er could also be operated successfully using waste arecanut husk (a by-product during de-husking operation) that makes the gasifi er option even more attractive (Table 3). Further improvements in energy efficiency are achieved by utilizing the hot gases for drying instead of traditionally burning fuelwood.

[top] [end]Conclusions

Biomass gasifi cation technology can help in taking a rural population using biomass as a fuel two steps up on energy ladder (from solid to gaseous fuel). Application of gasifi er for heat applications in rural areas has significant fuel saving potential coupled with other benefi ts such as improving the working environment, improving product quality and processing rates, due to controlled burning of gaseous fuel obtained through gasifi cation of solid biomass.

[top] [end]References

1). IEA 1998. World Energy Outlook; Paris: International Energy Agency.

2). IEA 2003. Energy Balances of non-OECD countries 2000-2001. Paris: International Energy Agency

3). Fisher, G., and Schrattenholzer, L., 2001. Global Bio-energy Potentials. Biomass and Bioenergy 20 (3): 151-159.

4). Mande S, Kumar A and Kishore V V N, 1999. "A study of large cardamom curing chambers in Sikkim"? Biomass and Bioenergy, Vol 16, No 6, pp. 463-473, 1999.

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[top] [end]Contents: Boiling Point 53 - Technologies that really work

Theme Editorial - Taking Science to Hearth - Good technologies - but do they really work - Rocket mud stoves in Kenya - Green Power -Lighting up rural India - The Biogas Programme in Vietnam - Pico hydro for cost-effective lighting - Biomass gasifier systems for thermal applications - GTZ News BP53 - Energy News From Practical Action BP53- Whats Cooking On The Solar Cooker Front? - Getting Technologies To The Market - SODIS - Solar Water Disinfection - A story of improving cooking stoves in a Dogon village - Micro-gasification what it is and why it works - What's happening in household energy BP53?

Categories: Boiling Point 53| Biomass| India| Heating| Gasification

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