A novel gas removal method for the removal of C2H2 in calcium carbide slag slurry by fine bubbles combined with air purging: performance, mechanism, and in situ bubble imaging analysis

Abstract

About 60% of carbon emissions in the cement industry come from the decomposition of limestone. As a key low-carbon technology of raw material substitution, calcium carbide slag (CCS, low-carbon calcareous material) can replace limestone to produce cement, desulfurizer, and other products, which can achieve carbon emission reduction and the upcycling of CCS. However, the release of residual C2H2 in CCS brings safety and environmental risks, which seriously restricts the upcycling of CCS. In this study, a novel gas removal method of fine bubbles (FBs) degassing was proposed for the removal of C2H2 in solid CCS particles, and an advanced in situ bubble imaging technology was used to investigate the performance and mechanism of C2H2 removal. The results indicated that approximately 70% of C2H2 (encapsulated C2H2) in CCS was difficult to remove by drying or slurrying. Under the optimal condition, the C2H2 removal efficiency was approximately 61.0%, and the amount of C2H2 released from the CCS slurry decreased by 92.9%. In the process of FBs degassing, large CCS particles in the CCS slurry were broken up into fine particles via the erosion mechanism, thus promoting the reaction of the encapsulated calcium carbide with water to produce C2H2. The generated C2H2 was dissolved in the slurry and could be quickly removed by FBs (<500 μm) with a fast mass transfer rate under the slight negative pressure. This work provides a novel gas removal method for effectively removing C2H2 in CCS and avoiding security and environmental risks, provides technical support for the upcycling of CCS, and provides a reference for the separation of other similar multiphase systems (e.g., gas–liquid/gas–liquid–solid, oil-liquid/oil-liquid–solid).