2025 AIChE Annual Meeting

(296a) Calcination of Calcium Carbonate in a Steam and CO2 Environment

Authors

Nathan Schroeder - Presenter, Sandia National Labs
H. Evan Bush, Sandia National Laboratories
Javier Martell, Sandia National Labs
The production of calcium oxide, commonly known as quicklime, is an energy-intensive process that significantly contributes to anthropogenic CO2 emissions, particularly in the cement industry. Traditionally, fossil fuels serve as the heat source for this process; however, a novel approach is being explored that utilizes solar-heated steam and CO2 as the heat transfer fluid.

This study presents two experimental setups: an entrained flow reactor and a counterflow calcination reactor. Both systems are designed to calcine cement raw meal while varying the mass fractions of steam within a steam and CO2 mixture to assist with model validation and design of large scale calciners using the alternative heat transfer fluid.

The entrained flow reactor experiment aims to assess the onset temperature of the calcination reaction across different mass fractions of steam and CO2, without the limitations on heat transfer rates or steam concentrations that are often encountered in furnace-heated thermogravimetric analyzer (TGA) systems. This reactor is equipped with a Residual Gas Analyzer (RGA) that monitors changes in CO2 concentration above a baseline level, allowing for the estimation of the onset temperature as a function of the steam and CO2 mass fractions.

The counterflow calcination system serves as an analogue for large-scale calcination operations, where the raw meal descends through a counterflowing gas stream, undergoing calcination before entering the kiln. This calciner consists of a vertical cylinder measuring 2 meters in height and 1 meter in diameter, equipped with a vibrating material feeder, an eductor sample cooler, and a cyclonic separator for sample collection. A sparger tube at the bottom of the cylinder introduces high-temperature steam and CO2, which rise through the falling stream of cement raw meal. The heat transfer fluid is vented from the top of the system, while the reacted material is drawn into the eductor, where it is cooled using an ambient temperature motive gas stream before being conveyed to the sample collection system. The reacted material is then separated from the gas stream using a cyclonic separator. A loss of ignition test is conducted to determine the extent of the reaction within the small calciner.

Results from the entrained flow reactor experiment indicates that the onset temperature of the calcination reaction increases with higher CO2 concentrations and decreases with increased steam relative to an air baseline case.