This study is about an operation method and a proposal to save energy from the adsorption dryer in the process of purifying compressed air (ISO 8573-1, class 1) which is required for a clean room production site in "A" company. The adsorption dryer is a facility which removes the moisture in the air; meanwhile, consuming a lot of energy. Energy consumption of the adsorption dryer can be lowered by altering the operating conditions: time, pressure, temperature, and so on.
Therefore, based on the current operating experiences of the adsorption dryer in the CDA (clean and dried air) production system, I have searched for the operating method that saves the most energy by varying the operating conditions of the dryer while comparing the energy usage of each alteration. Doing this is very risky as the system supplies CDA in the mass production process. Therefore I approached this experiment with a sequential method, which changes each factor and searches for the best condition one factor at a time rather than just conducting a complex simultaneous experiment.
In testing the regenerating pressure, all four conditions (2.5, 2.7, 3.0, 3.3 bar) were satisfied below ?80℃ of the dew point temperature. Among them, the dew point temperature and regenerating cost were the lowest at a 2.5 bar. During the heating temperature assessment, all four conditions (200∼210, 210∼220, 220∼230, 230∼240℃) were met at the dew point temperature. The regenerating cost was the most efficient at 200∼210℃.
For the regenerating time evaluation, I conducted tests under three conditions (12, 14, 16 hours). The result was that 14 hours of regenerating time was more economical than 16 hours. However, anything under 12 hours of regenerating time was insufficient for regeneration. Through these time operating tests, I used a 2.5 bar, 200∼210℃ and 14 hours in the regeneration process as the basic conditions of improvement.
Under the dew point operating tests, I set a ?80℃ dew point temperature as the tower exchanging condition and conducted tests with a 14 and 16 hour regenerating time while keeping all other conditions of improvement the same. As a result, I discovered that there is a limited supplying time of 24 hours. Therefore, managing the safety device is necessary to prevent an error in the quality of CDA.
I applied the delay time of 8 hours after finishing the 14 hours of regeneration under the basic conditions of improvement. As a result, the delay time function worked. However, the purge temperature was 50℃ lower than the reference temperature, that is because the regenerating time of 14 hours was too short to dry all of the moisture, which was absorbed in 22 hours. Therefore, I continued to search for the needed regenerating time.
To find the regenerating time necessary for the limited supply time of 24 hours. I applied a PSR (Purge Stop Regeneration) function with a heating and cooling temperature of 100℃ and 40℃ respectfully, as the purge temperature which served as the reference to judge the finished regeneration. As a result, the PSR function properly operated and the regeneration was completed in 16.5 hours. On these conditions, I decided this was the necessary time for successful regeneration.
Under the condition of a 16 hour regenerating time, a 6 hour delay time (with 22 hours of supply time), with a purge temperature of 100℃ heating and 40℃ cooling, I conducted the next test by changing the pressure and temperature. As a result, all of them satisfied the mass production standard. I also confirmed that operations were achieved within a heating time of 10 hours and a cooling time of 6 hours in the regenerating time process.
Based on these results, I further experimented with the application of a delay time and the PSR function by changing the temperature and pressure under the common conditions of a regenerating time of 22 hours (heating 11, cooling 11), a delay time 2 hours (24 hours of supply time), and a purge temperature of 100℃ heating and 30℃ cooling. As a result, the dew point temperature, heating temperature, and purge temperature all satisfied the supply conditions. Furthermore, I found that the regenerating cost was the most efficient in the 2.5 bar of regenerating pressure and a heating temperature of 200∼210℃.
This result leads me to conclude that 18% of the energy used can be saved compared to the time operating method currently in use; thus, these conditions were adopted as the new operation method for the adsorption dryer in the process of purifying compressed air at “A” company and have been in operation since September of 2015. I believe this study would improve the performance of the current operation method of the adsorption dryer by saving energy and can be used as basic data for other facilities as well.