Evaluation of mercury sorbents in a lab-scale multiphase flow reactor, a pilot-scale slipstream reactor and full-scale power plant

Due to its adverse effects on human health and ecosystem, mercury emission from the coal-fired utility boiler has been generating more and more concern. Sorbent injection upstream of the electrostatic precipitator (ESP) or bag-house has been deemed one of the recommended mature technologies to reduce mercury emission. Before a sorbent is used in practice, its mercury capture ability needs to be evaluated, but has until recently only been demonstrated in bench-, pilot- or full-scale experiments separately. In this paper, a lab-scale multiphase flow reactor and a pilot-scale slipstream reactor were set up and conducted such evaluation on the two scales. After that, some kinds of sorbents were injected at a full-scale power station. The experimental results show that the lab- and pilot-scale reactor systems in this paper can provide accurate information of sorbent evaluation under flue gas atmosphere. There was significant difference between the mercury removal efficiency of tested sorbents, varying from 98.3% down to 23%. SO2 in the flue gas was shown to inhibit mercury oxidization and capture. The sorbents have higher mercury capturing efficiency with higher injection rate and longer residence time when other conditions were held constant. In the pilot-scale, four injection ports vertical to the flue gas flow direction could help improve mixture of sorbent and flue gas so that the mercury removal efficiency became higher. The pilot-scale data can be used to predict the full-scale results. Some of the chemical and physical mechanisms responsible for the mercury removal of the sorbents were identified.