Nick D. Hutson

Effect of solution pH on SO2, NOx, and Hg removal from simulated coal combustion flue gas in an oxidant-enhanced wet scrubber

This paper presents a study on the simultaneous removal of SO2, NOx and Hg (both Hg0 and Hg2+) from a simulated flue gas by oxidant injection in a bench-simulated wet limestone scrubber for a wide range of slurry pH. The slurry pH strongly influenced the chemical mechanism in the scrubber and, therefore, affected pollutant removal. This paper also examines the potential ClO2(gas) reemission from a developed multipollutant scrubber at different slurry pHs. To better understand the chemical mechanisms at each slurry pH and to apply a mass balance to the process, detailed product ion analyses were performed for all experiments. Ion analysis covered three different chlorine species (chlorite, chloride, chlorate), sulfate, nitrite and nitrate. Different NOx removal efficiencies and mechanisms were found in acidic and alkaline pHs in the multipollutant scrubber. The acidic solution was favorable for NO and Hg0 oxidation, but increasing the slurry pH above 7.0 was disadvantageous for NO and Hg oxidation/removal. However, the rate of NOx absorption (by percentage) was higher for the alkaline solution. Implications This paper demonstrated a method for controlling multipollutant (SO2, NOx, Hg) emissions from a gas stream of a stationary combustion source in a wet limestone wet-FGD scrubber enhanced by an oxidizing additive. This paper explores how the flue gas conditions, especially the slurry pH, affect the chemical mechanisms of the multipollutant process and the pollutant removal efficiencies. The pH may be important when considering the location of oxidant injection into the scrubber/channel, where local parameters such as pH strongly vary. The usage of chlorite additive is potentially threatens ClO2(gas) emission; therefore, research in this area was also presented in this paper.

The importance of the location of sodium chlorite application in a multipollutant flue gas cleaning system

In this study, removing sulfur dioxide (SO2), nitrogen oxides (NOx), and mercury (Hg) from simulated flue gas was investigated in two laboratory-sized bubbling reactors that simulated an oxidizing reactor (where the NO and Hg0 oxidation reactions are expected to occur) and a wet limestone scrubber, respectively. A sodium chlorite solution was used as the oxidizing agent. The sodium chlorite solution was an effective additive that enhanced the NOx, Hg, and SO2 capture from the flue gas. Furthermore, it was discovered that the location of the sodium chlorite application (before, in, or after the wet scrubber) greatly influences which pollutants are removed and the amount removed. This effect is related to the chemical conditions (pH, absence/presence of particular gases) that are present at different positions throughout the flue gas cleaning system profile. The research results indicated that there is a potential to achieve nearly zero SO2, NOx, and Hg emissions (complete SO2, NO, and Hg removals and ∼90% of NOx absorption from initial values of 1500 ppmv of SO2, 200 ppmv of NOx, and 206 μg/m3 of Hg0) from the flue gas when sodium chlorite was applied before the wet limestone scrubber. However, applying the oxidizer after the wet limestone scrubber was the most effective configuration for Hg and NOx control for extremely low chlorite concentrations (below 0.002 M) and therefore appears to be the best configuration for Hg control or as an additional step in NOx recleaning (after other NOx control facilities). The multipollutant scrubber, into which the chlorite was injected simultaneously with the calcium carbonate slurry, appeared to be the least expensive solution (when consider only capital cost), but exhibited the lowest NOx absorption at ∼50%. The bench-scale test results presented can be used to develop performance predictions for a full- or pilot-scale multipollutant flue gas cleaning system equipped with wet flue gas desulfurization scrubber. Implications The control of NOx, Hg, and SO2 emissions from coal-fired combustors is an important, worldwide concern affecting environmental pollution. In both the European Union and the United States, NOx and SO2 emissions are subject to newly tightened emission limits. This paper investigated the NOx, Hg, and SO2 removals in a flue gas cleaning system equipped with a classical wet limestone scrubber, enhanced by a solution of sodium chlorite. This paper demonstrated that the location at which the sodium chlorite is applied in a flue gas cleaning system affects the control of these pollutants and discusses how possible solutions could be practically implemented.

Novel Catalytic Process for Flue Gas Conditioning In Electrostatic Precipitators of Coal-Fired Power Plants

Abstract One of the most important environmental protection problems for coal-fired power plants is prevention of atmospheric pollution of flying ash. The ash particles are typically removed from flue gases by means of electro-static precipitators, for which the efficiency may be significantly increased by lowering the resistance of fly ash, which may be achieved by controlled addition of micro-amounts of sulfur trioxide (SO3) into the flue gases. This paper describes the novel technology for production of SO3 by sulfur dioxide (SO2) oxidation using the combined catalytic system consisting of conventional vanadium catalyst and novel platinum catalyst on the base of silica-zirconia glass-fiber supports. This combination provides highly efficient SO2 oxidation in a wide temperature range with achievement of high SO2 conversion. The performed pilot tests have demonstrated reliable and stable operation, excellent resistance of the novel catalytic system to deactivation, and high overall efficiency of the proposed process. The scale of the plant was equivalent to the commercial prototype; therefore, no further scale-up of the oxidation process is required.

Binding of vapour-phase mercury (Hg0) on chemically treated bauxite residues (red mud)

Environmental context. Mercury (Hg) is a toxic, persistent pollutant that accumulates in the food chain. Atmospheric Hg is a global problem with many sources of emissions, of which anthropogenic sources are estimated to account for approximately one-third. Stationary combustion (coal combustion, municipal waste incinerators, etc.) are the largest worldwide sources of anthropogenic Hg emissions, and great effort has been taken to develop control technologies for capture of mercury from these sources. In the present study, Hg capture using bauxite residue (red mud) – a waste product from the aluminium industry – is evaluated and compared with other, more conventional sorbent materials. Abstract. The development and testing of novel control technologies and advanced adsorbent materials continue to be active areas of research. In the present study, Hg capture using adsorbent material derived from the bauxite residue (red mud) from two North American refineries was studied. The red mud, seawater-neutralised red mud, and acid-treated red mud were evaluated for their mercury adsorption capacity and compared with other, more conventional sorbent materials. Two different seawater-neutralised red mud (Bauxsol) samples were treated with HCl and HBr in an effort to increase the mercury sorption capacity. In all cases, the acid treatment resulted in a significant increase in the total surface area and an increase in the total pore volume. The fixed-bed mercury capture experimental results showed that the HBr activation treatment was very effective at increasing the mercury capture performance of both Bauxsol samples whereas the HCl treatment had no effect on the mercury capture performance. Entrained-flow experiments revealed that the Br-Bauxsol was not effective for in-flight mercury capture. This indicates that the mechanism of mercury capture is likely mass-transfer-limited in the entrained-flow experiments.

Mercury Control for Coal-fired Power Plants

Mercury is a toxic, persistent pollutant that accumulates in the food chain, especially in fish, and causes major environmental health concerns. There are many sources of natural and anthropogenic emissions, but combustion of coal is known to be the major anthropogenic source of mercury (Hg) emissions in the U.S. and worldwide. To address this, the U. S. Environmental Protection Agency (EPA) has recently promulgated the Clean Air Mercury Rule (CAMR) to reduce Hg emissions from coal-fired utility boilers. This rule makes the United States the first country in the world to regulate mercury emissions from such plants. However, atmospheric mercury is a global problem and mercury emissions from U.S. coal-fired boilers represent only a small fraction of the total worldwide emissions. Mercury emissions from Asia — especially from countries with rapidly growing economies, such as China and India — account for almost 60% of worldwide anthropogenic mercury emissions. Mercury can be controlled as a co-benefit of existing NO x , SO x , and PM control technologies and via sorbent injection technology. The level of control is strongly affected by the type of mercury emitted (elemental, ionic, or particulate-bound), coal type, chlorine levels, and type of air pollution controls used. With knowledge of the impact of each of these, mercury can be controlled, and improved methods to achieve further control can be developed.