Total lime kiln gas compression for CO₂ mineral sequestration

This work deals with the optimization of the compression of flue gas from a lime kiln for mineral carbonation. The production of lime is a CO₂ intensive process and the high CO₂ content in the flue gas makes it highly suitable for CO₂ capture and mineralization. Exergy analysis is used as the tool for the evaluation of different compression strategies. The goal of the analysis is to find the strategy which requires the least of external exergy fed to the process and the one in which the least amount of exergy is destroyed. Several different compressor configurations are compared and evaluated based on the exergy balance and financial costs. The compression of lime kiln gas in order to pressurize a fluidized bed reactor for Mg(OH)2 carbonation is an exergy consuming operation (1.225-1.675 GJ/ton CO₂ compressed). Exergy input can be reduced significantly if the gas is compressed in multiple steps between which the temperature of the gas is lowered as much as feasibly possible; the lowest temperature used in this study is 40°C. The exergy destruction, on the other hand, can be significantly reduced by removing the cooling medium at as high a temperatures as possible but still below the boiling point. In order to minimize the costs related to operation of compressors it is essential to find and acquire efficient equipment. It was found that a five-stage compressor with higher compression ratio in the last compression step was the most exergy and cost efficient configuration.