11. Basic Requirements of Promising Options

For any option to be promising, it must satisfy the following basic conditions:

a) It must allow use of major plant and equipment of the option for some of the activities essential for farming community, such as:
- Pumping of water for irrigation and/or drainage;
- Harvesting operation, like threshing, winnowing, etc;
- Preparation of fodder;
- Generation of motive power required by the farming community for various applications, including proceeding of produce, and/or production of higher value added products or improving its quality/marketability;
- Generation of electrical power to improve the quality of life, and/or improve their earning capacities.

Increased utilization of major investments on the option will reduce the cost of drying significantly.

b) It must allow the actual user to obtain major plant and equipment of the option, on softer terms and /or obtain subsidy on its procurement and installment.

c) It must use locally available fuel, ideally surplus agricultural residues.

d) It should provide 100 percent (notional) reliability in carrying out drying operations even under adverse weather conditions.

e) The farmer should be able to re-install it at an alternative site, should the need arise, without major investments.

12. Availability of Surplus Crop Residues & Agro By-products

A detailed study on the production, consumption and surplus of available crop residues and agro by-products on All India basis, was carried out by National Productivity Council. The study revealed:

i) Sufficient surplus crop residue and agro industrial by-products are available in all states for usage as fuel for any promising option.

ii) Surplus crop residue available at the village farm are:
- Paddy straw in all states
- Sugarcane trash in Andhra Pradesh, Gujarat and Karnataka only.

iii) Surplus agro- industry by-products available are:
- Rice husk (sometime also called paddy husk) in all states.
- Groundnut shell, in Andhra, Gujarat, Orissa and Uttar Paradesh. Uttar
- Cotton Gin waste, in Gujarat and Orissa.
- Saw dust in Himachal and Maharashtra.

Thus, the fuels which the promising option should use, in order of preference, are:

- Paddy straw; and/or
- Rice husk.

Usage of paddy straw is likely to be preferred as the same is available at the farm/village and, hence, cost of transportation will be expected to the minimal.

13. Routes Available for Usage of Paddy Straw or Rice Husk in Promising Option

Three routes are available to use paddy straw and/or rice husk to provide operable energy for the probable options. These are:

• Biogas,
• Gasification,
• Combustion

14. Biogas Route

Basic constituent of both paddy straw and rice husk is cellulose. Technology for bio-degradation of cellulose to produce gas has not yet been established, although considerable efforts are afoot in this direction.

15. Gassification Route

As on date, gasification of loose biomas is not possible. Normal methods used for gasification of biomas are:

i) Fluidized bed gasification. This method of gasification is not easily amenable for small size units.
ii) Briquetting and gasification in drawn draft gassifier. This method is amenable for small sizes. For a gassifier using this technology, a briquetting machine has an important bearing on the overall economics, as the cost of the briquetting machine is substantial.

Analysis of thermogram of rice husk shows that, it is not easily amenable to gasification. Thermogram of rice straw is not readily available, it is likely to be similar to that of rice husk. Gaccifier drying system has the following limitations:

• Capital cost is likely to be higher.
• Use of diluted exhaust gas of internal combustion engine for drying may affect the quality of dried product.
• Even under most optimal conditions, diesel will be required, at least to start the engine.

16. Combustion Route

Energy required by the promising option can be obtained by direct combustion of paddy straw or rice husk. Heat so produced can be used by either of the following methods:

- Steam route;
- Directly

The steam boiler operating in a farm environment will necessarily have to be a low pressure type, due to safety considerations.

Direct Utilization of Heat Obtained by Combustion of Biomass

Heat produced by combustion of biomass ca be directly used for drying by either of two methods, namely:

- Direct utilization of combustion gases.
- By hot air engineers to produce mechanical power and heat in combustion gases in cogeneration made.

In both the methods, a controlled combustion is required. The technology for controlled combustion of rice husk is well established. The technology for controlled combustion of paddy straw on a large scale is also established. However, controlled combustion of paddy straw on a small scale is yet to be established. The rout which shows promise consists of mechanical disintegration of paddy straw. Disintegrated paddy straw can be used in rice husk combustor with appropriate modification in the feeding mechanism.