Heat wheel regenerators

Boilers and low temperature applications sometimes use a heat wheel regenerator—a massive cylindrical metal latticework that slowly rotates through a side-by-side hot flue gas duct and a cold combustion air duct. 

ASHRAE, Atlanta (1992)]. Process air stream 6, to be conditioned, passes through the adsorbent wheel, where it is dried. This is a non-isothermal process due to the release of heat of adsorption and transfer of heat from a wheel that may be above ambient temperature. The dry but heated air (7) is cooled in a heat exchanger that can be a thermal wheel. This stream (8) is further cooled, and the humidity adjusted back up to a comfort range by direct contact evaporative cooling to provide supply air. Regeneration air stream 1, which can be ambient air or exhausted air, is evaporatively cooled to provide a heat sink for the hot,... 

The use of rotary desiccant wheels for dehydration has been practiced for several decades. Carl Munters [13] created the first rotary adsorbers by impregnating corrugated paper with LiCl and then ran the rotor using direct heat exchange to regenerate the sorbent. More recently Munters, NTI and others have developed improved adsorbents for rotary dehydrators. 

The rotary bed adsorber (also called adsorption wheel) provides a truly continuous TSA system. It uses a shallow wheel-shaped adsorption bed that continuously turns about an axis inside a fixed supporting frame. A section of the wheel is continuously used for adsorbing impurities from a gas while the other section is continuously regenerated by heating it with an impurity free gas. The adsorbent is made from a honeycomb-shaped alumina substrate that can be coated with layers of silica gels, activated carbons, or zeolites [14], It has been used for gas dehumidification, solvent vapor recovery, VOC removal, and deodorization of a gas stream. 

The regeneration air stream starts at approximately 75°F db, 40% rh. From state 5 to state 6, this air stream acquires heat from the process air stream through a heat exchanger, and from state 6 to state 7, the regeneration stream is further heated to an appropriate temperature for desiccant regeneration. Finally, the regeneration air is cooled and humidified as it extracts moisture from the desiccant wheel (state 7 to state 8). At state 8, the regeneration stream is exhausted to the outside. 

Several investigators [15, 17-19] studied the effect of balanced and unbalanced flows in both the heat exchangers and in the desiccant wheel. In the balanced flow mode of the operation, entire regeneration flow is heated to a maximum regeneration temperature. When an unbalanced flow is used, a portion of the preheated regeneration air stream from the sensible heat exchanger is vented to the atmosphere. An increase of 10 to 15 percent in the COP value was reported when unbalanced flow was used compared to a balanced flow system. 

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