Investigation and improvement of the desulfurization performance of molten carbonates under the influence of typical pyrolysis gases

Abstract

Co-pyrolysis with oxygen-lean waste tires could improve the quality of pyrolytic oil from the bio-wastes while H2S/COS generated during co-pyrolysis process has a negative impact on the utilization of oil/syngas as well as the flue gas pollution control. Compared to traditional wet desulfurization process, high-temperature desulfurization via molten carbonates could reduce heat loss and favor the recycling of captured sulfur. Notably, small-molecule pyrolytic gases might change the species of sulfur-containing gases and promote the re-emission of absorbed sulfur from the molten salts. To fully understand the effects of pyrolysis gases (H2/CO/H2O/CO2) on molten salts desulfurization efficiency as well as mutual conversion mechanism of H2S and COS, equilibrium compositions calculations and adsorption experiments were carried out in the present study. The results showed that H2/CO had few effects on molten salts desulfurization performance and mutual conversion of H2S/COS. In contrast, CO2 and H2O had obvious adverse effects on desulfurization efficiency through the transferring of free S2− into emitted sulfur-containing gases. More specifically, only a small amount of CO2 reacted with S2− to produce COS while more S2− was converted to H2S and released from the reactor outlet when H2O was introduced. Fortunately, the impact of H2O or CO2 on molten salts desulfurization could be weakened with the addition of CaCO3 by transferring the molten free S2− into precipitated CaS. Besides, multi-stage desulfurization units connected in series and parallel were proposed and estimated, which was confirmed to show good performance to maintain the high desulfurization efficiency from the complicated pyrolytic gases.