INDUTHERM® - Inductive Heating for Evaporators and Dryers

Introduction

Thin film evaporators, thin film dryers and short path evaporators all work on the basis of processing a product in a thin turbulent film. The heart of the thin film technology is the rotor which creates the thin product film. The product is picked up by the rotor blades and immediately formed into a thin turbulent film on the heat transfer surface ( fig. 1). Due to the low film thickness (from 0,5 mm) the heat and mass transfer rates are significantly improved compared to non agitated heat transfer equipment. The volatile component of the feed stock is therefore very quickly evaporated. For this reason the thin film technology has become a generally recognised and accepted solution for the most difficult and demanding processing problems in the areas of distillation, concentration, degassing, drying, cooling and reaction. Without thin film technology the efficient processing of many products from the chemical, pharmaceutical, food and polymer industries be either extremely difficult or impossible.

Commonly thin film equipment is jacketed on the thermal surface. Mostly a double jacket is used for steam or liquid heat transfer agents. When working with high pressure, half coils welded to the inner shell are required.

: Productfilm in a thin film evaporator

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Features of inductive heating

Thin film equipment with an inductive heating system is designed without any jacket in the evaporation zone. Inductive heating is generated in the inner shell by wrap-around copper coils. Inductive heating permits temperatures of up to 500 °C for any type of thin film equipment, either of cylindrical or conical design of the evaporation zone.

Thin film technology is commonly the last stage of a thermal separation process requiring the highest temperature. The possibility of avoiding installing a special hot oil system for this last stage can often prove an economically interesting alternative for the following reasons:

High operational safety (no rotating parts, e. g. pumps, no oil leakages)
Easy erection (control cabinet only)
Smaller space requirements (no hot-oil unit, no piping)
Reduced inspection and testing by minimising the number of pressure retaining parts
High specific heat transfer rates
Short heat up time
High overall thermal efficiency due to reduced radiation from a hot oil unit and associated pipework
Fine temperature control
Safety requirements for hot oil are not required<o:p>

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Mode of operation

Heating of the equipment is effected by generating inductive energy in copper coils which are in intimate contact with the body shell (fig. 2) , using mains frequency (50 to 60 Hz).

Nearly any electrically conductive metals can be heated . Practical installations require the use of mains frequency with high efficiency and cos. phi. The optimum case is attained with magnetic metal shells (either solid material or clad with stainless steel).

The inductive heating unit is directly connected to AC. With the exception of a few special cases, connection to the supply grid is possible without a intermediate transformer. Larger units are equipped with several separately controlled coils.

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Performance Data

Heating temperature at continuos operation: 100 ? 500 °C

Temperature accuracy: ± 3 °C

Specific heat transfer rate: up to 60 kW/m 2

Efficiency: approx. 93 %

Protection class: IP 54 (optional EEx)