The calcium-based sorbent for simultaneous removal of SO 2 /NO was prepared with KMnO 4 as additive. The activity of sorbent was studied individually in a fixed bed at low temperature. The experimental results showed that KMnO 4 could highly enhance the sorbent ability for NO capture. It was found that temperature rise could improve SO 2 capture, but could not influence NO removal so distinctively. The presence of water vapor in the gas could prominently improve the sorbent's ability to capture SO 2 and NO, and an optimal relative humidity existed for NO removal. O 2 and KMnO 4 were found to play an important role in NO removal. The optimum condition for simultaneous SO 2 /NO removal was studied, including reaction temperature, O 2 concentration, and relative humidity in the flue gas. XRD and IC analysis indicated that SO 2 was absorbed as sulfate with KMnO 4 present and as calcium sulfite with KMnO 4 absent. It was further deduced from the experimental results that NO was first oxidized into NO 2 and then was removed by reaction with calcium hydroxide and calcium sulfite into nitrate and nitrite.
The production of polyvinyl chloride (PVC) via the calcium carbide process utilizes a catalyst containing large amounts of mercury (Hg) and is therefore one of the most important sources of anthropogenic Hg in China. To measure the emission of Hg from PVC production, we established a flowchart for the calcium carbide process, for which we quantified the Hg content of the material/product at each step. Results indicated that 71.5% of the total Hg (Hg(T)) was lost from the catalyst, most of which was recovered by the Hg remover, accounting for 46.0% of the total Hg (Hg(T)). We determined that 3.7% of the Hg(T) was released into the environment, mostly in solid wastes and byproducts such as hydrochloric acid. Furthermore, no Hg has been detected in the PVC end product. However, we were only able to account for 78.1% of the Hg across the whole system, leaving 21.7% unaccounted for in the mass balance. A rough estimation indicates that most of the "missing" Hg had accumulated in deposits on the inner surface of converters and downstream pipelines; however, the emission to the atmosphere was ≤ 1% of the Hg(T). For a PVC production line equipped with a Hg remover, emissions of Hg to the atmosphere have been estimated to be 4.9 g per tonne PVC. Currently, almost all calcium carbide facilities have been equipped with a Hg remover, which may reduce the release of Hg in China by ∼ 500 t/year.
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