AIR HEATER The air heater basically exchanges the heat, released from the combustion of fuels, indirectly to raise the temperature of ambient air for drying purposes. Tea drying is a high thermal energy consuming operation. Hence, it is essential to know the basis of combustion for the efficient operation of heater or stove.

Air heaters commonly used in South India are of two types. In the first type, the hot flue gas from the combustion chamber passes through the tubes of a heat exchanger. In the other type, it flows outside the multitubular heat exchanger. The former is most common and suitable for fluidized bed driers. The selection of the stove should be based on the compatibility with the drier in regard to heat requirement as decided by the fan characteristics such as air volume and total pressure. Any under rating of the air heater implies burning more fuel than the stipulated quantity and results in higher flue temperatures. The efficiency of the heater is mainly determined by the heat transfer area, insulation, type of fuel used, combustion control and design of the furnace itself.

GRADING AND SORTING Sorting is the operation in which tea particles of the bulk are separated into various grades of different sizes and forms confirming to trade requirements. In other words, it basically converts the bulk into finished products.

The process of sorting has two objectives (i) to enhance the value (ii) to impart quality. Grading of the manufactured bulk is therefore, undertaken to improve its marketability and to obtain the premium that different buyers are willing to pay for the size of their preference. Cleaning of fiber is also part of the sorting procedure which is directly related to value enhancement.

Sorting enhances the appearance and quality of liquor; at the same time it can also deteriorate the quality. The presence of fibre or flakes of coarse leaf in a primary grade causes harshness and their removal makes the liquor mellow. The cleaning of fibre also improves the black appearance of tea which is desirable. Bloom is indicative of liquor character; over sorting and over cleaning can result in loss of bloom. Usually a tea which has not been well fired, loses bloom more quickly. If tea absorbs moisture during the cleaning process, liquors can deteriorate and its keeping quality reduces.

Sorting of bulk has to be done in three stages.
1. Cleaning of fibre
2. Grading
3. Winnowing

Currently, PVC rollers are being widely used to remove the fibres as well as flaky teas from the rest of the bulk. The principle involved here is that PVC rollers are (static) electrically charged by the contact of a sponge like material known as felt. Fibre and flaky teas differ in many characters like moisture content and density from the rest of the tea. These electrically charged rollers preferentially attracts the fibre and flaky teas which are higher in moisture content and thereby, they are removed from the bulk. If teas are exposed for longer time in the humid conditions, the difference of moisture content between fibre and rest of bulk narrows down; this reduces the efficiency of the removal from the bulk.