As the price of fossil fuels escalates, engineers and operators are being asked to mitigate operating costs by recycling process streams, thereby minimizing their utility consumption per unit production. Thermal drying of super absorbent polymer (SAP) is a prime application where reusing exhaust air and condensate streams benefit the energy footprint of the conveyor dryer. SAP drying yields effluent streams with sufficient internal energy to financially justify modifying the configuration of the dryer for heat recovery.
Buhler Aeroglide in Cary, N.C., conducted a study using a numerical approach to identify and quantify potential energy savings through mass and energy balances. Opportunities for heat recovery include cascading airflow, air-to-air heat recovery and condensate flashing.
During the study, Buhler analyzed six modules. Every module maintained the same dryer dimensions, production rate, physical properties of the inlet/outlet product streams, and operating parameters such as air temperature and velocity.
- Module 1 was a basic design and assumed no heat recovery.
- Module 2 recycled exhaust air from the cooling zone by transferring it as preheated makeup air to the heating zones.
- Module 3 adapted the same cascading airflow concept; however, the exhaust was internally cascaded as makeup air.
- Module 4 incorporated a flash steam system to recycle low pressure steam from high pressure condensate. The low pressure steam was used to preheat the makeup air entering the heating zones.
- Module 5 recycled thermal energy from the exhaust air using an air-to-air heat exchanger to preheat the makeup air entering the heating zones.
- Module 6 was a combination of the energy saving modules.
During the study, Modules 2 through 6 were compared to Module 1 to determine the theoretical energy savings. A nominal throughput of 5 tons/hr was selected as the production rate for the SAP dryer, and operating parameters were consistent with the industry’s standard. The study estimated a potential energy savings of 18.7 percent and improved the thermal efficiency of the dryer by nearly 12.5 percent.
To learn more about the study and the results, contact Frank Poandl at Buhler Aeroglide at 919-851-2000, ext. 2868, or firstname.lastname@example.org.