Integration of High Temperature Heat Pumps in the Drying Process of Packaging Paper and Tissue
The paper drying process is highly energy intensive and contributes significantly to CO2 emissions. Integrating high temperature heat pumps for waste heat recovery and electrifying this process, offers a pathway to reduce fossil fuel use in the paper industry. This study evaluates the integration of a high temperature heat pump into two distinct drying methods: cylinder drying for packaging paper and Yankee cylinder drying for tissue. It aims to compare how high temperature heat pump integration affects each process in comparison to a conventional natural gas boiler. Key variables include refrigerant type, exhaust air (source) properties, steam (sink) properties, and system configurations. The simulation quantifies the coefficient of performance, and the reduction in final energy consumption per ton of paper in the dryer section. In addition, a pinch analysis estimates the maximum recoverable waste heat potential. The best-performing model uses R601a in a high temperature heat pump with an internal heat exchanger, a turboexpander- coupled to a steam compressor to boost steam conditions to the dryer, and water injection to control steam superheating. In this case the total coefficient of performance reaches 2.8 for packaging paper drying and 1.9 for tissue drying, while the energy consumption per ton of paper (just the thermal energy for the drying section) falls by 68 % and 61.7 %, respectively, compared to a conventional natural gas boiler. Pinch analysis of the packaging paper dryer shows that a drying section with high temperature heat pump integrated, can eliminate hot utility demand, shifting 885 kWh/tpaper of thermal demand to 293 kWh/tpaper of electricity, and cut unused waste heat by 54%. The study demonstrates that heat pump integration can substantially improve energy efficiency in energy supply system for paper drying, with performance varying by paper grade and drying method.