Preparational work of a small rotary kiln for cement production and plasma installation – An experimental study of the heat transfer conditions for calcination and clinkerization reactions

Other conference contribution, 2023

Due to the alarming 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. For some high temperature processes, a heat source exchange from fossil to electrically generated plasma may be suitable. However, such a change is related to many uncertainties and should be evaluated at a smaller scale before it can be implemented at an industrial scale.

This work presents heat transfer conditions for cement production examined in an experimental rotary kiln available at Heidelberg Materials. The kiln has a length of about 2.9 m, is cylindrical with an inner diameter of 0.58 m, refractory lined, rotating, and slightly tilting. The heat is supplied from a propane flame in the range 100-155 kWth, with the burner located at the lower end of the kiln. Two experimental campaigns have been conducted in the experimental kiln. The first campaign aimed at calcinate a bed feed of raw meal as well as two types of limestone, with varying composition and size distribution. The second campaign aimed at creating clinker from the calcinated meal (produced in the same kiln). During the campaign measurements of the gas composition, radiative intensity, radiative heat flux and temperature through ports along the wall of the kiln as well as chemical analysis of the bed material were conducted. Such measurements were possible in the kiln with optical measurements and the traversing of probes along the kiln diameter in ports available along the kiln axis. Such detailed studies of the total heat transfer in rotary kilns with a present bed material have earlier been limited to the authors best knowledge. In addition, the radiative heat transfer from a small, standalone, plasma torch of 50 kW has been studied and a first evaluation is presented.

This work presents a first evaluation of the experimental findings, using mass and energy balances as well as employing a detailed in-house modelling tool for rotary kilns with a passing bed material. The work aims to obtain a better understanding of the overall heat transfer in a rotary kiln for cement production and to give guidelines for the continuing work with exchanging the burner for a plasma torch.