Process Optimization Guidance (POG and iPOG) for Mercury Emissions Control

This paper introduces two new tools to quickly identify and assess a broad range of Hg emissions controls for utility gas cleaning systems worldwide. The Process Optimization Guidance (POG) document summarizes the available options for mercury control at most coal-fired power plants, covering everything from efficiency improvements and fuel switching through co-benefit effects (maximizing Hg capture in existing pollution control systems) to Hg-specific sorbent and oxidation technologies. The POG includes a "decision tree" concept that helps the reader determine the potential compliance strategies for particular coal-fired gas cleaning systems. The Interactive Process Optimization Guidance (iPOG) is a user-friendly software package that formalizes the "decision tree" concept in the POG document. It accurately estimates Hg removals and emissions rates for broad ranges of coal quality, the most common configurations for furnace firing and flue gas cleaning, and Hg controls, both inherent and external. Two case studies presented in this paper show its utility in addressing "What if...?" scenarios, in which the impact of adding Hg controls to existing cleaning systems can be quickly and conveniently evaluated. The iPOG supports compliance strategies based on coal cleaning and blending, stronger inherent Hg removal in new air pollution control units for NO and SOx control, and dedicated external Hg controls, such as activated carbon injection (ACT) and halogen addition. This flexibility is compounded by minimal input data requirements and extremely fast execution times. This makes the iPOG useful for those who are new to the technicalities within the issue of Hg control, such as policy makers or even operators in developed countries or countries with economies in transition. Relative novices can "play" with the iPOG, selecting generic coals and simple plant design options, and then discover just how much simple changes in coal characteristics or plant operation may affect emissions. Being based on statistical regressions of an American Hg field test database :and streamlined input data requirements, iPOG cannot possibly resolve differences among different Hg control strategies within the measurement uncertainties or depict the distinctive features of particular gas cleaning systems. Such limitations are especially pronounced whenever SO3 adsorption interferes with Hg removal via ACI and also when distinctive selective catalytic reduction (SCR) design specifications strongly affect Hg-0 oxidation along a SCR catalyst monolith. Whereas the Hg removals for such situations are accurately predicted by previously reported reaction mechanisms, they are beyond the current scope of iPOG. However, the iPOG is fully capable of estimating Hg emissions from a preferred control scenario ahead of expert analysis.