Department of Chemical Engineering, University of South Carolina, 541 Main St., Columbia, SC 29201, USA.
Southern Company Services, Inc. 600 18th Street North, Birmingham, AL 35203, USA.
J Environ Sci (China). 2019 May;79:67-73. doi: 10.1016/j.jes.2018.10.012. Epub 2018 Oct 30.
Mercury (Hg) is a toxic and bio-accumulating heavy metal that is predominantly released via the combustion of coal. Due to its toxicity, the Environmental Protection Agency (EPA) has introduced Mercury and Air Toxics Standards (MATS) Rule regarding allowable Hg emissions. In order to reduce emissions, power plants have widely adopted activated carbon (AC) injection. AC injection has proven to be an effective method to reduce Hg emissions, but the re-emission of previously adsorbed Hg during unit operation, likely due to changing temperature or flue gas composition, could be problematic. This study specifically examined the effects of temperature and sulfur trioxide (SO) concentration, by ramping temperature and SO concentration independently and simultaneously, on AC samples that are already exposed to flue gas and saturated in presence of Hg, sulfur dioxide (SO) and nitric oxide (NO). Of these two suspected factors to cause re-emission, temperature had the greater impact and resulted in re-emission of both elemental and oxidized Hg with a greater fraction of oxidized Hg, which can be attributed to elemental Hg being more strongly bonded to the AC surface. Surprisingly, exposing the samples to increasing concentrations of SO had nearly no effect under the conditions examined in this study, possibly as a result of the samples being already saturated with sulfur prior to the SO ramp tests to simulate transient conditions in the plant.
汞（Hg）是一种有毒且具有生物累积性的重金属，主要通过煤炭燃烧释放。由于其毒性，美国环境保护署（EPA）引入了汞和空气有毒物质标准（MATS）法规，以限制可允许的汞排放量。为了减少排放，发电厂广泛采用活性炭（AC）注入。事实证明，活性炭注入是一种有效减少汞排放的方法，但由于温度或烟道气成分的变化，在单元操作过程中先前吸附的汞再次释放可能会成为问题。本研究专门研究了温度和三氧化硫（SO）浓度的影响，通过独立和同时升高温度和 SO 浓度，考察了已经暴露于烟道气并在存在汞、二氧化硫（SO）和一氧化氮（NO）的情况下达到饱和的活性炭样品。在这两个可能导致再次排放的因素中，温度的影响更大，导致元素汞和氧化汞重新释放，其中氧化汞的比例更大，这可以归因于元素汞与活性炭表面的结合更强。令人惊讶的是，在本研究中考察的条件下，将样品暴露于逐渐增加的 SO 浓度下几乎没有效果，这可能是由于在进行 SO 斜坡测试以模拟工厂中的瞬变条件之前，样品已经被硫饱和的结果。
