Process modeling and analysis of CO₂ purification for oxy-coal combustion

Abstract

Oxy-coal combustion technology has great potential as one of the major CO2 capture technologies for power generation from coal. The distinguishing feature of oxy-coal combustion is that the oxygen source is a high concentration oxygen stream and the product flue gas consists primarily of CO₂ and H₂0 with contaminants like NOx, SOx, and non-condensable gases like argon, oxygen and nitrogen. For carbon sequestration and Enhanced Oil Recovery (EOR) applications, pipeline transport standards as well as storage specifications impose concentration limits on these contaminants. These must be removed to ensure that the transported CO₂-rich stream stays within specified limits to prevent aqueous phase separation, hydrate formation, and corrosion due to acids, water or oxygen. The purification process however constitutes additional energy consumption and lowers overall cycle efficiency. Purification options like traditional flue gas desulfurization (FGD), selective catalytic reduction (SCR), catalytic O₂ consumption, packed bed adsorption and low temperature flash separation have been proposed. In this thesis, we develop a novel CO2 purification process model for oxy combustion systems that utilizes high-pressure reactive absorption columns for NOx and SOxrem oval and distillation strategies for noncondensable gas removal. This process results in significant cost savings and lower energy consumption compared to the traditional systems. We conduct a sensitivity analysis NOx and SOx removal system to determine the key performance parameters and based on the results present a modification to the base case that results in further cost and energy savings. Different strategies for the removal of non-condensable gases are developed and compared. This study also explores opportunities for integrating the CO₂ purification unit (CPU) with the base cycle and the impacts of the different strategies on the overall oxy combustion cycle efficiency are presented. A cost analysis for the proposed purification process is also presented.