Gas separation: processes – Miscellaneous
Patent
1997-01-21
1999-01-26
Smith, Duane S.
Gas separation: processes
Miscellaneous
95211, 96296, B01D 4714
Patent
active
058633189
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a new absorption dryer adapted especially to dry humid gas, especially humid air. In other words, the invention relates to the technical field in which the humid gas is contacted with a liquid drying agent, such that the drying agent absorbs moisture from the gas at issue. The drying agent is then regenerated, i.e. relieved of the absorbed moisture, and is again used in the dryer. The novelty of the invention is a drastically simplified and improved construction of the contact means for establishing contact between the humid gas and the liquid drying agent. Moreover, the invention relates to this new contact means itself.
BACKGROUND OF THE INVENTION
The absorption dryer is one of several types of dryer. Two other important types are the adsorption dryer and the condenser dryer. The adsorption dryer operates with a solid drying agent, which is usually regenerated with the aid of electrically heated hot air. The adsorption dryer frequently consists of a fabric structure similar to corrugated fibreboard and impregnated with a drying agent. This structure usually is in the form of a rotor, and the humid air is blown through the flutes and dehumidified. The drying agent can be regenerated by a sector of the rotor being reserved for the regenerating function. The sector is sealed in some suitable manner on both sides of the rotor, and hot air is blown through the rotor material which at that very moment is located in the sector. The advantage of such an adsorption dryer is that it can dehumidify down to low relative moisture contents, since solid drying agents, as a rule, have very low vapour pressures of equilibrium with water vapour in, for instance, air. 10-30% RH thus is quite possible to achieve in exit air, but if supply air is not too humid, suitably not exceeding 50-60% RH.
Although the adsorption dryer must be considered relatively simple in respect of design, it must, however, comprise a driving motor and a comparatively complex rotor. Its great disadvantage is, however, its lack of operation economy. By operation economy is meant the power requirements in kWh per kg of removed water. 1.2-1.5 kWh per kg of water is reasonable for an adsorption dryer. The theoretical power requirements are about 0.75 kWh per kg of water. The reason for the losses in the adsorption dryer is that the rotor, during its continuous rotation between the cold and the warm sector, consumes a considerable amount of power during the exchange of heat. Moreover, the adsorption dryer is not very convenient at high moisture contents and temperatures, or when large amounts of water are to be removed, such as in the case of damage by water or in operating situations in moist and warm climates, including laundry rooms. A further disadvantage of the adsorption dryer is that it is difficult to exchange the heat of warm and humid regeneration air in an inexpensive fashion. In other words, a gas/gas heat exchanger is necessary, and therefore usually just the warm and humid regeneration air is released outdoors. Otherwise, by heat exchange/condensation of moisture it is possible to recover the supplied power as heat, thereby avoiding wall ducts.
The condenser dryer, is built more or less like an ordinary refrigerating or freezing machine. Humid air is dehumidified by contacting the cold surface of the evaporator. The condenser dryer has good operation economy and can process air having a high moisture content and a high temperature. The supplied power remains in the room, and humid hot air need not be wasted outdoors. However, the condenser dryer suffers from the drawback that a compressor having a driving motor is necessary. In continuous operation, the life of the most expensive components of the dryer will be just about a year. A further drawback of the condenser dryer is that it contains FREON fluorocarbon, which, as is well known, is a much discussed substance these days from the environmental point of view. Besides, the condenser dryer is relatively expensive, possibly excluding the
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