TYPICAL APPLICATIONS FOR THE FLUID BED DRYER

1. Simple drying of material to give moisture content and the drying time required

2. Fluidising curves give the variation of pressure drop with air flow rate showing the feasibility of fluidisation and the conditions for minimum and operating fluidisation velocity

3. Determination of drying curves, to assess feasibility of fluidised bed drying of a material on an industrial scale. Drying curves are relevant to the mechanism of drying. They may be used as a basis for heat and mass balances, thermal efficiency of drying and drier design

4. Calculation of heat transfer coefficients for different conditions, relevant to dryer design and comparison of fluidised beds with other drying methods

RANGE OF MATERIALS

The wide range of materials which can be dried include foodstuffs such as peas, wheat and lentils, may be dried at relatively low temperatures, diced onions may be dried at higher temperatures to produce the value added caramelisation flavours

Because the high heat and mass transfer rates obtainable, drying times for the laboratory fluid bed dryer are much less than for the more traditional methods available and many materials can be dried in less than 15 minutes

OPTIMUM BED DEPTH

The optimum bed depth is that which can be fluidised at the required temperature be a relatively high air velocity. This optimum bed depth will vary appreciably with the material, an initial bed depth of about 75mm is typical and a trial and error procedure is generally used to identify the optimum. Particle size in the range 0.1mm to 5mm are most suitable and the size ratio largest : smallest should not be more than 8

OPERATING PROCEDURE - DRYING OF MATERIAL AND DETERMINATION OF MOISTURE CONTENT

Remove any excess water from the sample be decanting or using a filter pump. Place the sample in the dryer at a pre-determined bed depth compatible with the operating range of the dryer as previously indicated. In some cases the moisture content may be too high for immediate fluidisation to be effected, but after some initial drying fluidisation becomes possible.

Weigh container empty, then with material. Fit a clean bag over the container, locating the sealing ring into its groove on the tub.

Switch on the mains supply. Select the drying temperature. Select manual or automatic mode of operation. Push cycle start button

Select blower and heat settings. Adjust blower speed to achieve good fluidisation

In normal mode, when drying nears completion as judged by a rise in temperature of outlet air or visual observation, push stop button to stop cycle

Remove the tub with contents and re-weigh, continue repeating the drying cycle until a constant weight is obtained.

For each weighing the dryer is stopped and then restarted. The difference in initial and final weights of the material can be expressed as the moisture content on wet or dry basis. This is the equilibrium moisture content

In the automatic mode, once the pre-set time has elapsed the cycle will automatically stop and the alarm will sound. This can be reset by means of the red stop button

The total drying time for the material can be calculated by multiplying the interval cycle time by the number of cycles required. The dry material is removed from the dryer and may be stored for further analysis or processing