IEA Clean Coal Centre

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 NOx and SOx control, and dedicated external Hg controls, such as activated carbon injection (ACI) 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 Hg0 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.

Certainties and uncertainties in the issue of the greenhouse gases are discussed. It is an established fact that the concentrations of these trace gases — CO 2 chlorofluorocarbons (CFC), methane, nitrous oxide and ozone — are increasing in the lower atmosphere as a result of human activities. The contribution of coal use to the greenhouse effect is about 15 to 20%. Future emissions of the greenhouse gases form one of the greatest sources of uncertainty. The potential for reducing emissions of the greenhouse gases is discussed. While steps are being taken to control CFC, the greenhouse gases with the greatest rate of increase, the scope for reducing CO 2 emissions is limited. Climatic model results suggest that there will be a noticeable global warming in one or two decades with more uncertain regional changes. Observations are consistent with these results but there is as yet no conclusive causal link with increases in the greenhouse gases.