酸改性对褐煤半焦脱除烟气中元素态汞性能的影响

为减少燃煤烟气中零价汞的排放,利用HCl和HNO3溶液对褐煤半焦改性研制了一种高效、低成本的吸附剂.运用酸碱滴定、Boehm滴定、BET、SEM和FTIR等技术对半焦吸附剂的表面特性进行表征与分析,利用固定床吸附实验装置及烟气测汞仪在线考察了半焦吸附剂对气态Hg0的吸附特性.结果表明,酸改性使半焦灰分含量降低,增加了半焦比表面积和羧基、酚羟基等官能团含量.酸改性处理可提高半焦对元素态单质汞的脱除效率,特别是盐酸溶液改性褐煤半焦可使吸附温度为140℃时的脱汞效率显著提高,这与改性半焦表面羧基、酚羟基和C-Cl官能团的含量及性质有关,半焦表面这些官能团能为Hg0的化学吸附提供活性位.

Effect of lignite semi-coke by acid solution treatment on its performance for elemental mercury removal in the flue gas

The adsorption performance of modified lignite semi-coke with HCl or HNO3solution for gaseous Hg0was investigated to develop more effective and lower price adsorbents for reducing emission of elemental mercury in coal combustion flue. The surface properties of these lignite semi-coke adsorbents were characterized with methods of acid-base titration, Boehm titration, Brunauer-Emmett-Teller (BET) measurement, scanning electron microscope (SEM) and Fourier Transform infrared spectroscopy (FTIR), respectively. The adsorption experiments of semi-coke adsorbents for gas-phase Hg0have been carried out with a laboratory-scale fixed-bed reactor, and elemental mercury analyzer was used to determine the on-line concentrations of gas-phase Hg0. Nitric acid or hydrochloric acid treatment of lignite semi-coke resulted in the decrease in ash content of semi-coke sample, and the values of specific surface area, surface oxygen and phenolic hydroxyl group increasing of modified semi-cokes. Compared to raw lignite semi-coke (NM-SC), the modified lignite semi-coke with HCl or HNO3 solution (Cl-SC or N-SC sample) could improve removal performance for gas-phase Hg0. Especially, the removal performance for gas-phase Hg0of Cl-SC semi-coke was obviously improved when adsorption temperature increased to 140℃. These results were related to the surface properties of modified semi-coke and its contents of carboxyl group, phenolic hydroxyl and C-Cl functional groups, which can provide active sites for gaseous Hg0chemical adsorption.