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CO2 Separation from Coal-Fired Power Plants by Regenerable Mg(OH)2 Solutions

Cheng, Lei
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1378216250

Abstract Details

, PhD, University of Cincinnati, Engineering and Applied Science: Environmental Engineering.
A novel carbon dioxide (CO2) capture method by using environment-friendly chemical magnesium hydroxide (Mg(OH)2) solution has been proposed and is currently under investigation in response to controlling the CO2 emissions from coal-fired power plant in the post-combustion control area. The major goal of this research is to (1). Select and design an appropriate absorber which can offer 90% plus CO2 removal efficiency with low energy costs; (2). Find and optimize the operation conditions for the regeneration step. The results of experimental investigation and discussion of desorption energy requirement are presented. Turbulent contacting absorber (TCA) and bubble column absorber have been tested as primary CO2 mass transfer devices. Both batch and continuous mode of operations were performed. Important parameters including liquid-to-gas ratio, residence time, lean solvent concentration, pressure drop, bed height, CO2 partial pressure, bubble size, pH, and temperature have been carefully evaluated. The n-CSTR model has been developed to analyze the TCA absorption data. It is found that TCA reactor used in this research can be adequately modeled when n=7. Also, the mass transfer controlling step of TCA was examined. It is found that TCA operation might be divided into two regimes based on the OH- concentration. The bubble column absorber results reveal that the scrubbing performance heavily depends on the gas residence time and size of bubble. It is found that 90% plus CO2 removal efficiency can be achieved at L/G ratio of 120 gal liquid/1000 acf gas and 8 seconds of gas residence. A bubble column reactor model was developed for CO2 removal data analysis. The model incorporated physical absorption between CO2 and water, dissolution of Mg(OH)2 solid particles, diffusion within the gas and liquid phases, and chemical reactions of the ions. The overall mass transfer coefficient, a key designing parameter, is found to be a function of the hydrodynamic parameters, Henry’s constant, CO2 partial pressure in the gas phase, diffusivities, solid dissolution constant and temperature. The overall mass transfer coefficients found from this study are comparable to the other widely studied scrubbing chemicals, such as MEA and ammonia solutions. Also, the experimental investigations of regeneration are given. Regeneration conditions have been identified and a possible regeneration mechanism was found. Mg(HCO3)2 is completely soluble and can be reversed by temperature, but MgCO3, when formed, is a solid and very energy intensive to regenerate. A temperature swing regeneration process has been shown to be effective in recovering CO2 and regenerating Mg(OH)2. Finally, the vapor-liquid equilibrium data of CO2-Mg(OH)2 system and energy analysis of desorption step have been presented. It is found that the total desorption energy consumption mainly consists of heat of desorption, water vaporization energy, and the energy required for temperature raise in the stripper. The results suggest that 167 MW is required for bicarbonate only desorption case; while 232 MW is required for carbonate solid only desorption case at a scale of 500 MW coal-fired power plant.
Timothy Keener, Ph.D. (Committee Chair)
Margaret Kupferle, Ph.D. P.E. (Committee Member)
Joo Youp Lee, Ph.D. (Committee Member)
Mingming Lu, Ph.D. (Committee Member)
147 p.
Environmental Engineering
CO2 capture; coal-fired power plant; bubble column reactor; TCA; magnesium hydroxide; mass transfer

Recommended Citations

Citations

  • Cheng, L. (n.d.). CO2 Separation from Coal-Fired Power Plants by Regenerable Mg(OH)2 Solutions [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1378216250

    APA Style (7th edition)

  • Cheng, Lei. CO2 Separation from Coal-Fired Power Plants by Regenerable Mg(OH)2 Solutions. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1378216250.

    MLA Style (8th edition)

  • Cheng, Lei. "CO2 Separation from Coal-Fired Power Plants by Regenerable Mg(OH)2 Solutions." Doctoral dissertation, University of Cincinnati. Accessed APRIL 17, 2024. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1378216250

    Chicago Manual of Style (17th edition)

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