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CPOTE2020 logo
6th International Conference on
Contemporary Problems of Thermal Engineering
Online | 21-24 September 2020

Abstract CPOTE2020-1188-A

Book of abstracts draft
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Exergy-based assessment of shaft kiln efficiency

Risto FILKOSKI, Ss Cyril and Methodius University, North Macedonia (Republic of)

Vertical shaft kilns are widely used in the minerals' thermal processing industry, including sintered dolomite manufacturing. The calcination of the dolomite stone (CaMg(CO3)2) for the production of sintered dolomite (CaO and MgO), is a high-temperature energy-intensive process accompanied by a significant CO2 emission. The exergy concept is a suitable scientific approach in the efforts towards sustainable development. This work is based on energy and exergy analysis of the operation of a vertical shaft kiln. The objective is to identify the factors affecting the kiln's economical operation, by analyzing the energy and exergy balances of the calcination process. Data on energy and exergy consumption and losses throughout the calcination process are presented for a shaft kiln with a production capacity of 3 tonnes sintered dolomite per hour. It is found that the energy efficiency of the kiln process is significantly higher than the exergy efficiency. The largest irreversibilities taking place in the kiln are the exergy dissipation due to fuel combustion and due to internal heat transfer, accounting in total for about 50% of the efficiency loss. The main exergy loss through the kiln boundaries is the loss with the exhaust gases contributing to about 10% of the efficiency loss. Improvements on both the energy and the exergy efficiencies can be achieved through a complex of measures, including the recovery of waste heat of flue gases for preheating of air and drying of raw material, better control of the kiln operational parameters, optimisation of the excess air and limestone/fuel supply, operation with an optimal average size of the limestone fed to the kiln and exit temperature of quicklime flow. The present study proposes a tool for the analysis of energy and exergy utilization of the calcination process in lime kilns, and also provides some measures for energy efficiency enhancement.

Keywords: Shaft kiln, Exergy efficiency, Waste energy recovery, Combustion, Dolomite calcination