DOUB LE EFFE CT EVAP ORATOR Conservation of energy is one major consideration that needs to be well-treated in the application of an evaporator system. This is due to the fact that the larger the evaporation process unit, the more crucial it is to conserve energy. One of the techniques available for this purpose is by applying double or multiple effect evaporator. The invention of multiple effect evaporators is generally credited to Norbert Rillieux. Backthen, Rillieux developed a multiple pan evaporation system for use in sugar refining. Double-effect evaporation generally involves processing the steam generated from evaporation in first effect, where it is condensed in the heating element in order to provide the heat for product evaporation in a second effect maintained at lower pressu re. The boiling temperature is usually high enough so that the evaporated water can serve as heating medium in second effect. The first effect will however has the highestpressure. The effects in an evaporator are usually the same in terms of size, construction and heat transfer and unless thermal oses are significant, the capacity willbe the same as well. The steam e conomy rises as the number of effects used is increased. Increasing the number of effect does increase the capital investments; therefore careful evaluation is necessary for such systems. In general, when the evaporation rate is no lower than 3,000 lbs/h (1350 kg/h), thus application of multi-effectevaporator should be considered.The feed for double effect evaporator is normallytransferred from first effect to another. This will in turn leads to the ultimate productconcentration to reach only in either one of the effect. However, there are three differentways for feed introduction in double effect evaporator. The feed order is not according to the number of effects, whereas effects are always numbered according to reducingpressure. The first feed way is byforward feed arrangement, where the raw feed is introduced in the first effect and then to the second parallel to steam flows. Operatingcosts are increased since the feed is raised to the highest operating temperature. The liquor produced are however most concentrated and viscous in lowest temperature, and
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Conservation of energy is one major consideration that needs to be well-treated in
the application of an evaporator system. This is due to the fact that the larger the
evaporation process unit, the more crucial it is to conserve energy. One of the
techniques available for this purpose is by applying double or multiple effect evaporator.
The invention of multiple effect evaporators is generally credited to Norbert Rillieux. Back
then, Rillieux developed a multiple pan evaporation system for use in sugar refining.
Double-effect evaporation generally involves processing the steam generated from
evaporation in first effect, where it is condensed in the heating element in order to
provide the heat for product evaporation in a second effect maintained at lower pressure.
The boiling temperature is usually high enough so that the evaporated water can serve
as heating medium in second effect. The first effect will however has the highest
pressure. The effects in an evaporator are usually the same in terms of size,
construction and heat transfer and unless thermal oses are significant, the capacity will
be the same as well. The steam economy rises as the number of effects used is
increased. Increasing the number of effect does increase the capital investments;therefore careful evaluation is necessary for such systems. In general, when the
evaporation rate is no lower than 3,000 lbs/h (1350 kg/h), thus application of multi-effect
evaporator should be considered.The feed for double effect evaporator is normally
transferred from first effect to another. This will in turn leads to the ultimate product
concentration to reach only in either one of the effect. However, there are three different
ways for feed introduction in double effect evaporator. The feed order is not according to
the number of effects, whereas effects are always numbered according to reducing
pressure.
The first feed way is by forward feed arrangement , where the raw feed is
introduced in the first effect and then to the second parallel to steam flows. Operating
costs are increased since the feed is raised to the highest operating temperature. The
liquor produced are however most concentrated and viscous in lowest temperature, and
more frequent. Thus, on the finisher, it is preferable to use duplex heat exchangers, so
that one can be cleaned while the other is in operation.
Black Liquor
Literally, black water is caustic waste water generated at paper plants. Typically
black liquor contains 3% solids, and half of it is caustic soda. This results in merely high
boiling point elevation as the concentration increases, thus most black liquor evaporators
are double-effect evaporators.
Sugar Refining
Crystallization of very coarse refined sugar is done by using double-effect
evaporator in conjunction with thermal vapour compression. Conservation of energy is practised in this case where vacuum is used from batch pans evaporator as heating
steam. A controllable thermo-compressor increases this vapour from 0.2 bar to 0.3 bar.
In addition, vapour is supplied at approximately 0.35 bars, thus reducing the heating