Date of Award
Doctor of Philosophy (PhD)
Oxy-combustion and post-combustion carbon capture technologies are two of the most promising strategies for carbon capture and storage (CCS), which is a commonly accepted approach to address the challenge of climate change. Pressurized oxy-combustion has been actively studied due to its great potential to enhance the power plant energy efficiency by recovering latent heat from water vapor condensation without incurring additional gas compression cost. On the other hand, amine-based CO2 scrubbers have been demonstrated to have high removal efficiency of CO2 with the possibility to recycle amine solutions, which makes the technology a promising candidate for post-combustion carbon capture. Nonetheless, the existence of submicrometer particles (diameters < 1Âµm) in coal combustion exhaust can pose various challenges to both advanced technologies: (1) particle control device used widely in coal-fired power plants such as electrostatic precipitator (ESP) is only designed for normal pressure operation, while submicrometer particles are needed to be removed efficiently under high pressure in a pressurized combustion system; (2) it has been shown that submicrometer particles in flue gas can induce amine loss in scrubbers by carrying the solution out due to condensation. In light of those technological challenges, this dissertation focuses on developing an understanding of how pressure affect characteristics and electrostatic precipitation of submicrometer particles in coal combustion exhaust gas through experimental and modeling approach, and investigates characteristics of submicrometer particles with and without pretreatment upstream amine-based CO2 scrubbers in real coal-fired power plants.
A lab-scale pressurized ESP was constructed to investigate the effect of pressure on electrostatic collection of submicrometer particles. Current-voltage characteristics were measured using different feeding gases. Removal efficiency of the pressurized ESP was studied under various pressure conditions. A semi-empirical Deutsch-Anderson equation was developed using multivariate regression to fit the experimental removal efficiency data under high pressure with minimized error, which was thus used to design a pilot-scale pressurized ESP in a pressurized combustion system. To better understand the effect of particle properties on electrostatic precipitation, coal fly ash generated from combustion of different coal seams from China, US and India were characterized in terms of particle size distribution, charge fraction and electrostatic precipitation efficiency. How combustion pressure affects the mineralogy, morphology and chemical composition of coal fly ash was also examined for a more detailed understanding of submicrometer particles in pressurized combustion exhaust.
To investigate the characteristics of submicrometer particles upstream amine-based CO2 scrubber, a field study on variation of particle number concentration and gas pollutants concentration under different operating scenarios in a utility-scale power plant was conducted. Five operating modes including soot blow of boilers, bypass of flue gas desulfurization (FGD) scrubber and derating of reheat burner (0%, 27% and 42%) were studied. Significant differences in mode diameter and number concentration were observed for both wet and dry aerosols across those operating modes. A photo-ionizer enhanced ESP was demonstrated with higher removal efficiency of submicrometer particles than a conventional ESP. Another field study was conducted at a utility-scale coal-fired power plant with a pilot-scale amine-based CO2 scrubber to investigate how different pretreatment methods affect the particle size distribution in coal combustion exhaust. Pretreatment methods including steam injection, desiccation and electrostatic precipitation were studied. Steam injection showed different effects on particle number concentration in different submicrometer size ranges. Although particles in certain small sizes showed higher concentration with ESP turned on probably due to secondary aerosol generation, ESP with an optimal voltage could remove submicrometer particles effectively, which evidenced its candidacy as a promising pretreatment technique for amine-based CO2 scrubbing.
Richard Axelbaum, Rajan Chakrabarty, Yongqi Lu, Brent Williams,