Heat transfer studies of a 150 kWth cement rotary kiln

Other conference contribution, 2023

Due to the global warming caused by the emissions of greenhouse gases, heavy-emitting industries must convert their present processes to become more environmentally sustainable as well as competitive in the future. Several such industrial processes include rotary kilns where fossil fuels are combusted to heat a passing bed material to sufficiently high temperatures. One example is the cement industry which is one of the largest emitters worldwide. Various process modifications for carbon-neutral cement production are being evaluated. This study explores the feasibility of replacing the current burner in the rotary kiln with plasma torches, thereby substituting fossil fuels with an electrically generated thermal plasma. However, such changes require substantial investment in equipment and are accompanied by uncertainties about how the new process should be designed and how the new heat transfer conditions will affect the product. Therefore, experimental and modeling work should be carried out to further examine the total heat transfer in the rotary kiln and how it may change using a thermal plasma. The aim of this work was to study the overall mass and energy balance inside an experimental rotary kiln to find the energy demand, theoretical excess air coefficient, and radius of a build-up layer of bed material formed inside the shell of the kiln for different bed materials. Building on these findings, upcoming experimental work will focus on an in-depth examination of convective heat transfer, regenerative heat transfer, and the influence of specific operational parameters.