Calcium Looping for Carbon Dioxide and Sulfur Dioxide Co-capture from Sulfurous Flue Gas
Sally L. Homsy, Chemical Engineering Ph.D Student, supervised by Professor Bill Roberts
Monday, November 30, 2020
04:00 PM - 05:00 PM
Global decarbonization requires addressing local challenges and advancing appropriate technologies. The overarching objective of this project is the investigation of appropriate carbon capture technologies for CO2 capture from heavy fuel oil (HFO) fired power plants, common locally. Two emerging technologies are considered, chemical looping combustion (CLC) and calcium looping (CaL). In a preliminary study, CLC and CaL implementation at an HFO-fired power plant are modeled using Aspen software, and based on the results, CaL is selected for further experimental investigation. Briefly, CaL is a high temperature separation process that utilizes limestone-derived CaO to simultaneously concentrate CO2 and capture SO2 from flue gas. The solid CaO particles are cycled between carbonation and calcination, CaO + CO2 ⇋ CaCO3, in a dual fluidized bed system and experience capture capacity decay with cycling.
Structurally distinct limestones were procured from the two geologic regions where limestone is mined in Saudi Arabia. Using bubbling fluidized bed reactor systems, the capture performance of these two limestones, and a German limestone of known performance, were compared. The combined and individual influence of flue gas H2O and SO2 content, the influence of textural changes caused by sequential calcination/carbonation cycles, and the impact of CaSO4 accumulation on the sorbents’ capture performance were examined. It was discovered that metamorphosed limestone-derived sorbents exhibit atypical capture behavior: flue gas H2O negatively influences CO2 capture performance, while limited sulfation can positively influence CO2 capture. The morphological characteristics influencing sorbent capture behavior were examined using imaging and material characterization tools, and a detailed discussion is presented.
Saudi Arabian limestones’ deactivation rates were examined by thermogravimetric analysis. A semi-empirical deactivation model accounting for sorbent sulfation and reactivation was developed. The validity of this model was supported by subsequent pilot scale (20 kWth) experiments. Solving process mass and energy balances, reasonable limits on operating parameters for CaL implementation at HFO-fired power plants were calculated. The influence of power plant configuration, carbonator design, and limestone source on power plant energy efficiency is considered and a discussion is presented. Finally a commentary on the potential of this technology for local implementation and required future work is presented.