Energy conservation and efficiency improvement by coupling wet flue gas desulfurization with condensation desulfurization

Abstract

Limestone–gypsum wet flue gas desulfurization (WFGD) is the most effective desulfurization technique. However, to achieve ultralow SO2 emissions, the efficiency of WFGD should be improved and its energy consumption reduced. To address these aims, a technology of coupling WFGD with condensation desulfurization using a condensing heat exchanger (CHE) was proposed in this study. The results show that, as the WFGD approaches the limiting desulfurization efficiency, a small increase in the efficiency may cause a high energy consumption. However, the energy consumption can be reduced significantly through the synergistic absorption of SO2 during the wet flue gas condensation. The synergistic absorption efficiency is affected by the SO2 concentration at the inlet of the CHE, flue gas flow, and the amplitude and rate of temperature drop. Injecting Ca(OH)2 into the flue gas during wet flue gas condensation can form dispersive heterogeneous cores of Ca(OH)2 in the flue gas, thereby enhancing SO2 mass transfer and improving the desulfurization efficiency considerably. The increased amount of Ca(OH)2 is small, and the unreacted Ca(OH)2 can be fully utilized by collecting the condensed solution and returning it to the WFGD system. When the coupling desulfurization technology is applied to achieve ultralow SO2 emissions, at inlet SO2 concentrations of 2000 and 4000 mg/Nm3, the circulating pump power consumption decreases by 351–449 kW and 1661.5–2125.5 kW for 300- and 1000-MW units, respectively, demonstrating the significant energy-saving potential of the coupling desulfurization technology.