Humidity control is a primary concern in many industries. Accordingly, over the years, various techniques have been developed to address these concerns. One such technique to control humidity combines cooling and condensation principles to remove humidity from air. The air in an enclosed space is cooled until it reaches a temperature below its dew point temperature at which time the moisture in the air condenses on the nearest surface. Conventional cooling-based dehumidification systems typically include a cooling coil, a condensing coil and a compressor.
While these types of systems are capable of extracting moisture from the air, it should be noted that they are primarily designed for cooling air. Nonetheless, the use of cooling-based dehumidification systems in industrial facilities and installations remains relatively widespread. Some cooling-based dehumidification systems have even been used on work sites located in generally hazardous environments where significant explosion or ignition hazards tend to exist. A readily apparent advantage associated with these cooling-based dehumidification systems resides in the fact that these systems do not generate high temperature air streams which could otherwise ignite flammable vapours or gases in the ambient air. The use of such systems however has had mixed results. While these systems have tended to be effective at removing moisture from the air in regions where the ambient temperature is generally warm and the humidity is relatively high, they have tended not to perform well in regions where the climate tends to be colder. In particular, cooling-based dehumidification systems tend to become inefficient at removing moisture from the air when the dew point of the air approaches 0° C. because at that temperature the moisture freezes on the condensing coil. Accordingly, cooling-based dehumidification systems have been found to be ill-suited for use in hazardous environments located in cold climates.
Another known humidity control technique relies on differences in vapour pressure to remove water vapour from air. When air is humid it has a relatively high water vapor pressure. In contrast, a dry desiccant surface tends to have a low water vapour pressure. When the moist air comes in contact with the desiccant surface, the water molecules will move from the humid air to the desiccant surface in an effort to equalize the differential pressure. In the result, the humid air will be dried. Since these systems do not involve any liquid condensate, they can continue to remove moisture efficiently even when the dew point of the air is below freezing. In fact, the performance of such desiccant-based dehumidification systems tends to improve in colder temperatures. It will thus be appreciated that such systems do not suffer from the same drawback traditionally associated with cooling-based dehumidification systems.
Desiccant-type dehumidification systems typically employ a rotating desiccant wheel whose core is impregnated with desiccant material. The desiccant wheel includes a process section and a regeneration section. In operation, an air stream from the enclosed space flows through the process section in one direction, while simultaneously another, heated air stream through the regeneration section in an opposite direction, all the while the desiccant wheel rotates slowly about its longitudinal axis. As the air flows through the process section, the desiccant material in the core extracts moisture from the air. The thus treated air is returned to the enclosed space in a dehumidified state. The desiccant material is regenerated by the heated air stream which flows through the reactivation section of the desiccant wheel.
While such systems tend perform well in colder climates, conventional desiccant-type dehumidification systems have tended not to be employed in hazardous environments. This is because proper functioning of a conventional desiccant wheel requires the use of a heated air stream and a thermal energy source for regeneration (usually electricity). Both of these requirements tend to create significant explosion and ignition risks in a hazardous environment. Moreover, the risk of explosion or ignition is further compounded by the fact that rotation of the wheel and the drying action of the desiccant tend to promote the generation of significant static electrical charges. The build-up of these static electrical charges can result in electrostatic discharge causing sparking. In a hazardous location, sparking can ignite flammable or combustible vapours in the ambient air.
Accordingly, there is a need for a desiccant-based dehumidification system that is versatile and that may be safely deployed in hazardous environments while minimizing the risks of explosion and/or ignition.