Mechanical Engineering - Mohiodin Nazemi

Doctoral candidate:
Mohiodin Nazemi

Title of thesis:
Intermittent Drying of Biomass: A Systematic Reassessment of Energy Efficiency

Opponents:
Dr. Shiplu Sarker, Associate Professor at the Norwegian University of Science and Technology (NTNU) in Norway
Dr. Anderson Assuah, Associate Professor at University College of the North in Canada

Advisor:
Dr. Rúnar Unnþórsson, Professor at the Faculty of Industrial Engineering, Mechanical Engineering, and Computer Science, University of Iceland

Other members of the doctoral committee:
Dr. Christiaan Petrus Richter, Professor at the Faculty of Industrial Engineering, Mechanical Engineering, and Computer Science, University of Iceland
Dr. Ragnheiður I. Þórarinsdóttir, Rector at Agricultural University of Iceland

Chair of Ceremony:
Dr. Sigrún Nanna Karlsdóttir, Professor at the Faculty of Industrial Engineering, Mechanical Engineering and Computer Science

Abstract:
Drying is one of the most energy-intensive steps in the processing of high-moisture biomass, such as seaweed. In research, intermittent drying has often been reported as more energy-efficient than continuous drying. However, the results of previous studies have often not been compared under equivalent conditions, making it unclear whether the reported energy savings stem from genuine advantages of intermittent drying or from methodological artefacts. The objective of this thesis is to systematically reassess the energy efficiency of intermittent drying. The research originated from studies on seaweed pelletization, where it was demonstrated that the majority of the energy in the preprocessing chain was used for drying. Therefore, a new comparison framework was developed to evaluate intermittent and continuous drying under identical operating conditions. A systematic literature review and meta-analysis of published studies were conducted. The reassessment of the results showed that many of the advantages previously attributed to intermittent drying diminish or disappear when the comparison is made on an equivalent basis. Furthermore, the results revealed that material thickness, initial moisture content, and drying temperature are the main parameters influencing the relative performance of the two drying methods. The effects of material thickness and initial moisture content were further investigated through controlled experiments using a porous sponge model, while tests with Bladderwrack were used to evaluate the framework using a representative high-moisture biomass. The results demonstrate that intermittent drying is not inherently energy-efficient; rather, its performance depends on material properties and operating conditions. The benefits of intermittent drying are most likely to occur when internal moisture transport limits the drying process. The thesis establishes a framework for the fair evaluation of intermittent drying and demonstrates that the feasibility of high-moisture biomass utilization depends strongly on drying performance, which is influenced more by material properties and operating conditions than by intermittency itself.

About the doctoral candidate:
Mohiodin Nazemi was born and raised in Iran. He completed his B.Sc. in Mechanical Engineering in 2009 and his M.Sc. in Applied Design in 2015. Before moving to Iceland, he worked for several years as a mechanical engineer, mainly in machine design and industrial manufacturing. He moved to Iceland in 2019 and completed an M.Sc. in Mechanical Engineering at the University of Iceland in 2021. He began his Ph.D. studies in Mechanical Engineering at the University of Iceland later that year. He lives in Reykjavík with his wife.