Novel design of a rotary calciner internally heated with electrical axial heaters: Experiments and modelling

Abstract

As the share of renewable energy increases, green electricity may help reduce the carbon footprint in the lime industry. Electrifying the calciner can produce relatively pure CO2 from the calcination process (CaCO3 → CaO + CO2), which may be utilized or stored. All the previous literature studied electrically heated rotary calciner with external heating. This work presents a novel design of an electrical rotary calciner through which internal heating is possible. The design can utilize existing kiln drums made from relatively inexpensive refractory and steel materials. The designed calciner operated smoothly for around four days, and the concept was technically feasible. The outer wall temperature and calcination degree was measured during the condition of a pseudo-steady state in the calciner. A model was developed and implemented in OpenModelica, which was validated by comparing it against measured variables. The modelling results revealed that the current setup had low thermal efficiency, as the heat loss amounted to around 60%, and the average heat transfer coefficient was around 101 W/(m2K). A step-by-step procedure with the help of the model was discussed to improve heat efficiency and reduce heat loss by up to 11% by improving thermal insulation and increasing the residence time of particles. With the improved thermal efficiency, energy intensity and electricity cost per unit CO2 were reduced from 35 to 7 MJ/kg-CO2 and 4.9 to 1 NOK/kg-CO2, respectively. So, improving thermal efficiency can improve both the environmental and economic aspect of the process.