Abstract
This study investigates the use of calcium-based slurry for simultaneous removal NO and SO2 from oxy-fuel combustion flue gas, and recovery of the sulfur and nitrogen species in resulting solutions. The experiments were performed in a bubbling reactor in a transient mode under the pressure of 20 bar. The various influencing factors including the CaO amount, carrier gas (N2/CO2), and absorption time on the simultaneous NO and SO2 removal process, and the solution products were studied comprehensively. The results show that the NO2 removal efficiency can be improved by the presence of CO2, and the gas phase HNO2 produces in this process. The addition of CaO has positive effects not only on the NO2 removal efficiency but also on the formation of stable HNO3. With the presence of CO2, CaCO3 is formed in a solution initially. With the decrease of pH, CaCO3 is gradually converted to CaSO4, and in particular CaCO3 can be fully avoided through decreasing the pH of an absorption solution to 1.14. At the same time, the formation of unstable S(IV) and NO2- can be prevented when the solution pH is lower than 1.37. The nitrogen and sulfur compounds in the absorption solution (at pH 1.14) were further separated by the addition of different amounts of CaO. In particular, 95% of SO42- finally can be recovered in the form of CaSO4.2H2O with nitrogen in solution existing as NO3- by controlling the Ca/S ratio at 4.70. The effectiveness of calcium-based slurry on the removal and recovery of SO2 and NO is confirmed.
Highlights
In order to reduce the greenhouse gas CO2 emission, various pre-combustion, post-combustion and combustion enhanced technologies have been proposed[1]
The selective catalytic reduction (SCR) and selective noncatalytic reduction (SNCR) technologies are adopted for NO removal[6], while the wet flue gas desulfurization (WFGD) technology using calcium based solution is adopted for SO2 removal[7]
The slow increase of NO and NO2 after the quick initial increase may come from the complex chemical reactions between the gas phase NO and NO2 with water
Summary
In order to reduce the greenhouse gas CO2 emission, various pre-combustion, post-combustion (e.g., carbon capture and storage, CCS) and combustion enhanced (e.g., oxy-fuel combustion) technologies have been proposed[1]. Oxy-fuel combustion technology is considered to be one of the most promising ways for carbon capture[2] This technology effectively enriches flue gas with high CO2 concentration[3], and effectively reduces NO and SO2 emissions per unit mass of fuel[4]. The NO and SO2 concentrations are higher in the oxy-fuel combustion flue gas than those in conventional aircombustion flue gas[5] These acid gases (mainly includes NO and SO2) must be removed from CO2 stream considering the safety of transport pipelines and sequestration sites. Thereupon, oxidizing insoluble NO to soluble NO2 before wet scrubbing method is necessary In this oxidizing process, many oxidation-absorption combined processes have been studied extensively to oxidize NO to NO2 for the purpose of simultaneous removal of NO and SO2, including strong oxidizing agent injection[9], selective catalytic oxidation[10,11], and photo-catalytic oxidation[12]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
