Absorption of Nitric Oxide from Flue Gas Using Ammoniacal Cobalt(II) Solutions
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Absorption of Nitric Oxide from Flue Gas Using Ammoniacal Cobalt(II) Solutions by Hesheng Yu A thesis presented to the University of Waterloo in fulfillment of the thesis requirement for the degree of Doctor of Philosophy in Mechanical Engineering Waterloo, Ontario, Canada, 2012 © Hesheng Yu 2012 Author's Declaration I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, including any required final revisions, as accepted by my examiners. I understand that my thesis may be made electronically available to the public. Hesheng Yu ii Abstract Air emissions from the combustion of fossil fuel, including carbon dioxide, sulfur dioxide, nitrogen dioxide and nitric oxide, have caused severe health and environmental problems. The post- combustion wet scrubbing has been employed for control of carbon dioxide and sulfur dioxide emissions. However, it is restricted by the sparingly water soluble nitric oxide, which accounts for 90- 95% of nitrogen oxides. It is desirable and cost-effective to remove nitric oxide from flue gas by existing wet scrubbers for reduced capital costs and foot prints. In this research, absorption of nitric oxide from simulated flue gas using three different absorbents was first conducted in a bubble column system at room temperature and atmospheric pressure. Through performance comparison, ammoniacal cobalt(II) solutions were chosen as the optimum absorbent for nitric oxide absorption. Then the effects of fresh absorbent composition, pH value and temperature on nitric oxide absorption were investigated. Experimental results showed that the best initial NO removal efficiency of 96.45% was measured at the inlet flow rate of 500 mL∙min-1; the room temperature of 292.2 K; the pH value of 10.50; and the concentrations of cobalt(II) solution, -1 NO and O2 of 0.06 mol∙L , 500 ppmv and 5.0%, respectively. For in-depth understanding of NO absorption into ammoniacal cobalt(II) complexes, equilibrium constants of reactions between nitric oxide and penta- and haxa-amminecobalt(II) solutions, respectively were determined using a bubble column reactor, in which the operation was performed continuously with respect to gas phase and batch-wise with respect to liquid phase. The experiments were conducted at temperatures from 298.2 to 310.2 K and pH from 9.06 to 9.37, all under atmospheric pressure. All experimental data fitted well to the following equations: and , which give the enthalpy of reactions between NO and penta- and hexa-amminecobalt (II) nitrates as and . In kinetic study, a number of experiments were conducted in a home-made double-stirred reactor at temperatures of 298.2 and 303.2 K and pH from 8.50 to 9.87 under atmospheric pressure. The reaction rate constants were calculated with the use of enhancement factor derived for gas absorption accompanied by parallel chemical reactions. The reaction between NO and pentaaminecobalt(II) was first order with respect to NO and pentaamminecobalt(II) ion, respectively. Similarly, the reaction between NO and hexaaminecobalt(II) was also first order with respect to NO and hexaamminecobalt(II) ion, respectively. The forward reaction rate constants of these two reactions iii were 6.43×106 and 1.00×107 L∙mol-1∙s-1, respectively at 298.2 K, and increased to 7.57×106 and 1.12×107 L∙mol-1∙s-1, respectively at 303.2 K. Furthermore, regeneration of used absorbent was attempted but fails. None of the additives tested herein including potassium iodide (KI), sodium persulphate (Na2S5O8) and activated carbon (AC) showed capability of regeneration at room temperature and atmospheric pressure. In addition, the effect of oxygen was investigated. With ammoniacal cobalt(II) compounds a positive effect of oxygen on NO absorption was observed. Calculated NO amount absorbed into the aqueous solution showed that with the oxygen the absorption reaction could be considered as irreversible. This fact was probably the reason for the failure of regeneration of the tested reagents. Last but not least, volumetric liquid-phase mass transfer coefficient, kLa, in some popular industrial absorbers including bubble column (BC), conventional stirred tank reactor (CSTR) and gas-inducing agitated tank (GIAT) were determined by modeling removal of oxygen from water. The experimental results could be well interpreted by mathematical models with 90% of deviations less than ±10 %. iv Acknowledgements I would like to acknowledge my supervisor, Dr. Zhongchao Tan, for his guidance, supervision, and patience throughout the course of this research project. His encouragement and support are greatly appreciated. I would also like to thank other members of my thesis examining committee, Drs. Eric Croiset, Xiangguo Li, Mark J. Rood, and John Z. Wen, for their contributions to this dissertation. In addition, support from Dr. Qunyi Zhu in Harbin Institute of Technology is highly acknowledged. Thank you is also extended to Professor Guangyuan Xie, Dr. Jimmy Yu and Ms. Lin Wu. My dream of studying overseas could not be realized without their encouragement and assistance. I am grateful to them from my very bottom of heart. Financial support and scholarships from Natural Sciences and Engineering Research Council of Canada (NSERC), Imperial Oil Ltd., Enersul Inc., the University of Calgary, and the University of Waterloo are also highly appreciated. I would also like to thank Jim Baleshta, Jason Benninger, Charlie Boyle and Mark Kuntz for their technical support. To those I have worked with during my PhD program both in Calgary and Waterloo, Dr. Sudong Yin, Grace Pan, Chao Yan, Harry Lei, Ke Zhang, Stephen Kuan, Zhe Li, Fang Liu, Raheleh Givhechi and Qixia Zhang, thank you for your assistance, friendship and a pleasant studying environment. Rose Jin, Hanwen Liu, Jianchen Tao and Yuzan Yang, thanks for your friendship over the course of my degree. I would like to thank all my family members, my parents, my parents-in-law, my sister and brother- in-law. This thesis could not be completed without your great understanding and unconditional support. I especially thank Qianqian Nie, my dear wife, for her love, patience and consistent encouragement she gave so that I could concentrate on studying and working on this project. Her trust is the source of power that drives me to courageously face any challenges. v Dedication To my loving wife Qianqian and my parents vi Table of Contents Author's Declaration ............................................................................................................................ ii Abstract ................................................................................................................................................ iii Acknowledgements ............................................................................................................................... v Dedication ............................................................................................................................................. vi Table of Contents ................................................................................................................................ vii List of Figures ...................................................................................................................................... xi List of Tables ...................................................................................................................................... xiii List of Symbols ................................................................................................................................... xiv Chapter 1 Introduction ........................................................................................................................ 1 1.1 Research Motivations ................................................................................................................... 1 1.2 Research Opportunities ................................................................................................................ 4 1.3 Research Objectives ..................................................................................................................... 7 1.4 Thesis Structure ............................................................................................................................ 8 1.5 Original Contributions .................................................................................................................. 9 Chapter 2 Literature Review ............................................................................................................. 10 2.1 Characterization of Nitrogen Oxides .......................................................................................... 10 2.1.1 Definition and Source of Nitrogen Oxides .......................................................................... 10 2.1.2 Formation of NOx in Fuel Combustion ............................................................................... 10 2.1.3 Negative Impacts of NOx ..................................................................................................... 12 2.2 NOx Abatement Technologies .................................................................................................... 12 2.2.1 Fuel Switching ..................................................................................................................... 12 2.2.2 Combustion Modification .................................................................................................... 13 2.2.3 Post-combustion