Session: 16-01: Poster Presentations

Paper Number: 131881

131881 - Implementing an Independent Air-Cooled Purge Section to Enhance the Desiccant Wheel Efficiency 

Abstract: 

Desiccant wheels are essential in industries requiring precise humidity control, such as lithium battery and pharmaceutical manufacturing. The principle of a desiccant wheel involves using a desiccant that absorbs moisture from the air at varying capacities based on temperature. In the process, the dry desiccant first absorbs moisture from the process air in the process sector, then moves to the regeneration sector, where it is heated to release the absorbed moisture, and cycles back to the process sector to absorb more moisture. A key challenge is that the desiccant is too hot to absorb moisture efficiently right after leaving the regeneration sector.

 

Previous study has shown that incorporating a purge sector between the regeneration and process sectors can significantly improve the efficiency of the desiccant wheel. However, these studies used a part of the processed air in the purge sector, which is usually pre-cooled by a leading cooling coil, leading to energy waste. This study introduces a new approach by proposing an independent ambient temperature cooling coil air cycle as the working fluid for the purge sector. This method avoids using processed air, thereby enhancing the efficiency of the desiccant wheel.

 

To demonstrate the benefits of this system, an industrial case study was conducted to compare the economic efficiency of different desiccant wheel layouts. The economic efficiency here refers to the total energy cost (including heating costs in the regeneration sector, costs of chilled water for pre-cooling and re-cooling coils, and fan power costs) to produce 1 cubic meter of processed air under the same external conditions.

 

The factory in the study required relative humidity below 10% and temperature within ±1 degree of 21°C, thus the process air has to be pre-cooled to 7°C before passing through the desiccant wheel. Three layouts were examined: a standard regeneration-process layout; a regeneration-purge-process layout using part of the process air for purge sector; and a similar layout but with the purge sector supplied by an independent ambient temperature coil air cycle. In this third layout, air firstly passes through a cooling coil with flowing ambient temperature water, then enters the purge sector of the desiccant wheel, contacts the hot desiccant from the regeneration sector, leaves the purge sector as heated air, and is then re-cooled by the ambient water cooling coil. Meanwhile, the cooled desiccant exits the purge sector to the process sector to more effectively absorb moisture from the process air.

 

The study concludes that under the specified conditions, the traditional layout has the poorest economic efficiency. Compared to the second layout, the proposed independent ambient temperature coil air cycle for the purification zone can further save over 10% in energy costs, making it a promising direction for further research.

Presenting Author: Cheng-Yan Tsai National Taiwan Normal University

Presenting Author Biography: A faculty member of Undergraduate Program of Vehicle and Energy Engineering at National Taiwan Normal University, who is also an engineer with various project experiences and familiar with building energy efficiency measures.

Authors:

Wei-Jen Chen National Taiwan Normal University
Yu-Chia Huang National Taiwan Normal University
Cheng-Yan Tsai National Taiwan Normal University