Current activities to restrain climate change are evaluated to be insufficient to meet the international and national climate targets. Cement industry is one of the main CO2 emitters in industry sector. Electrification and carbon capture and utilization or storage (CCUS) technologies are seen as potential solutions to reduce greenhouse gas emissions from heavy industries. Traditionally, heat required for cement and lime production is generated by combustion of fossil fuels. This thesis focuses on potential and effects of deploying electric heating in rotary kilns used in lime and cement production. The thesis consists of two sections. In the first section, literature review is conducted. Lime and cement production processes are introduced. Calcination reaction, lime uses, kiln types and CO2 emissions and emission reduction methods are discussed. Electric heated kiln concept and its advantages and downsides compared to traditional kiln technologies are presented. Additionally, heat transfer in electric heated kiln is studied. Literature review shows that the main difference of process conditions in the electric heated rotary kiln compared to traditional rotary kiln is high partial pressure of CO2 in the kiln gases. The main advantages of electric heating are the reduction of energy related emissions, transformation of process emissions into usable product, and easier process control. In the second section, controlled experiments with laboratory scale electric heated rotary kiln are performed. The objective is to study calcination in CO2 rich gas atmosphere. Experiments are performed for three different calcium carbonate based materials. Calcination of the raw materials is studied in different gas atmospheres, temperatures and pressures. The results are analyzed with thermogravimetry, differential scanning calorimetry, reactivity measurements, and particle size and dry matter content measurements. The performed experiments showed promising results for calcination degree and reactivity in CO2 rich gas atmosphere. However, recarbonation and blockages in the rotary tube caused challenges that require more studying. Recarbonation occurred in experiments in CO2 rich gas atmosphere both in slight positive pressure relative to atmospheric pressure and in vacuum. Recarbonation can be prevented with rapid cooling and change of gas atmosphere, however the technological solutions need to be studied and tested. Small scale of the kiln used in the experiments is a possible reason for the blockages but it requires confirmation from pilot scale experiments. Measurement range of CO2 concentration of the gas analyzer used in the experiments was too narrow which affected the evaluation of direct capture potentials. Thus, a more comprehensive analysis of the kiln off-gases is suggested. In further experiments, sintering of the particles need to be considered as well. Additionally, further research on economic feasibility of electric heated rotary kiln is recommended.
|Award date||9 Nov 2020|
|Publication status||Published - 5 Nov 2020|
|MoE publication type||G2 Master's thesis, polytechnic Master's thesis|