A COST EFFECTIVE, ENERGY SAVING BOOSTED EVAPORATION PROCESS FOR ALUMINA REFINERIES

Zhang, H., Chua, H.T., Boom, E., Cochrane, D.

Evaporation process is a significant section in the alumina production by the Bayer Process. It consumes a large amount of thermal energy and helps to manage water balance. We introduce a novel flash boosted evaporation process that can reduce live steam consumption for evaporation purposes, by using the available waste flash vapour from the last stage of the evaporation unit. The process can economise on the consumption of live steam, as waste flash vapour injection into the patent pending Flash Boosted Thermal-Vapour Compression Multi-Effect Evaporation (FB-TVC- MEE) process is able to minimise the motive steam usage of the Thermal-Vapour Compressor (TVC). We compare this novel FB-TVC-MEE process with the conventional Thermal-Vapour Compression Multi-Effect Evaporation (TVC-MEE) process and the current Multi-Stage Flash (MSF) process in terms of the amount of saved live steam, Gain Output Ratio (GOR), and specific pumping power consumption.

Our result shows that 82% of the current live steam consumption can be saved, with our process having the ability to exploit all the available flashed vapour for the evaporation of feed spent liquor. The Gain Output Ratio of our design is 468% better than the current MSF system and 98% better than the conventional TVC-MEE process. With regards to the pumping power consumption, the FB-TVC-MEE process shows a 5% increase as compared to the TVC-MEE process. Importantly, at a risk discount rate of 10%, the FB-TVC-MEE process has been shown to cost the least (both capex and opex considered), auguring 57% net present cost savings compared to the standard MSF technology that consumes 40 ton per hour of live steam with a baseline capex of $30 mil.