Removal and recovery of SO₂ and NO in oxy-fuel combustion flue gas by calcium-based slurry

¹ School of Energy and Power Engineering, University of Shanghai for Science and Technology, 200093 Shanghai, China
² Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power Engineering, University of Shanghai for Science and Technology, 200093 Shanghai, China
³ Department of Computer Science, George Mason University, Commonwealth of Virginia, USA
⁴ DONGFANG TURBINE Co.,LTD, 618000 Deyang, China

^* Corresponding author: Dunyu Liu; Email address: liudunyu@usst.edu.cn; Jun Chen; Email address: j.chen@usst.edu.cn

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 SO₄^2- 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.