Thin Film Evaporator - Evaporation Technology
Using a Thin Film Evaporator for Evaporation which is the removal of volatile solvent (usually water) in the vapor phase, from a solution, while discharging the concentrate in a liquid or pumpable form.
Read more about thin film evaporator.
Film Type Evaporation
Film Type Evaporation involves generation of a thin product film (thin film evaporator) over the heat transfer surface to promote minimal resistance to heat transfer. Parameters are set such that optimum filmboiling occurs within the evaporator body. Caution must be used to ensure a continuous filmhydraulic condition (wetting rate) and to prevent nucleate boiling; otherwise, the rate of heat transfer will fall off dramatically, while the rate of scaling on the heat transfer surface will increase.
Vapor Induced Film
- Falling Film (tubular and plate)
- Rising Film (tubular and plate)
Mechanically Induced Film
- Mechanically Agitated Thin Film
(Thin Film, Wiped Film)
Suppressed Boiling Type Evaporation
Suppressed boiling type evaporation involves superheating a product above its boiling point, while maintaining back pressure within the system to prevent boiling in the evaporator body. The superheated product is passed to a flash vessel or separator, where the equivalent flash vapor is removed. This is commonly referred to as a “heat and flash” principle.
Forced Circulation (tubular, plate, spiral)
Energy Efficiency of a GEA Thin Film Evaporator is a key consideration in the design and operation for each customer’s particular application.
Generally speaking, an equivalent of approximately 1,000 BTU for each pound of water to be evaporated must be available to the heating media side of the evaporator. In addition, to affect heat transfer to the product, this energy input must also be available at a higher temperature (pressure) than the boiling product. The heating media, almost exclusively, consists of condensing water vapor. An external energy source, in the form of live steam, dryer off gases, or electrical power is commonly used.
Mechanical Vapor Recompression (MVR)
Evaporated vapors are compressed to a higher pressure (temperature) in either a low speed blower or turbofan, or a high speed turbo-compressor. The compressor is typically driven by either electricity or a steam turbine. Equivalent compression ranges of 7-12oF for turbofans, and 18-32oF for turbo-compressors, are not uncommon.
Due to the high initial cost of a high speed turbocompressor, it may be more economical to arrange multiple low speed turbofans in series to achieve the equivalent compression .T.
MVR technology yields the greatest energy efficiency for evaporators, and results in the lowest cooling water requirement for the waste heat condenser. MVR evaporators may also be coupled with TVR and/or multiple effect evaporation stages.
The high initial capital cost of an MVR unit must be weighed against the operating cost savings. Generally, when considering medium to high evaporation duties in the range of 40,000 – 200,000 lb/hr of water removal, savings associated with operating costs of MVR evaporators (over those of a multiple effect or TVR plant) will usually offset the added capital expenditure within three months to two years of operation.
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