Improving the energy effectivity of biomass drying for utilisation in energy systems by combining convective and contact drying

Abstract

The article deals with reducing the energy consumption of biomass drying before combustion in energy plants. The combination of traditionally used convective hot air drying and less applies contact drying is analyzed. To determine the basic drying characteristics, the experiments on a contact dryer and a convective hot air dryer were carried out with wet wood chips. A heat balance model of a system with serial connection of a convective air dryer and a contact dryer was compiled. In the model, the utilization of condensation heat from the waste vapor leaving contact drying to preheat the drying air for convective drying was considered. Based on these results, the system could be optimized to achieve the lowest energy consumption, drying time, and dryer sizing. This solution can significantly improve the energy efficiency of drying moist biomass before combustion from 3.29 and 2.76 MJ per kg of evaporated water for only convective drying and only contact drying, respectively, to 1.48 or 1.33 MJ per kg of evaporated water, depending on the order of the dryers in their connection.

Keywords:

• Wood chips
• indirect dryer
• hot air dryer
• drying rate
• heat recovery

Disclosure statement

The authors report there are no competing interests to declare.

Additional information

Funding

This work was supported by the Ministry of Education, Youth and Sports under OP RDE grant number CZ.02.1.01/0.0/0.0/16-019/0000753 “Research centre for low-carbon energy technologies”.

Notes on contributors

Jan Havlík

Jan Havlík is an assistant professor at the Faculty of Mechanical Engineering, Czech Technical University in Prague, Czech Republic. His major research areas include heat exchanger design, heat transfer, advanced drying technologies for energy systems, condensation technologies, thermal process optimization.

Tomáš Dlouhý

Tomáš Dlouhý is a professor at the Faculty of Mechanical Engineering, Czech Technical University in Prague, Czech Republic. His major research areas include combustion technologies, boiler design, advanced drying technologies for energy systems, thermal process optimization.