Mercury (Hg) is one of the most toxic heavy metals, harmful to both the environment and human health. Hg is released into the atmosphere from natural and anthropogenic sources and its emission control has caused much concern. This book introduces readers to Hg pollution from natural and anthropogenic sources and systematically describes coal-fired flue gas mercury emission control in industry, especially from coal-fired power stations. Mercury emission control theory and experimental research are demonstrated, including how elemental mercury is oxidized into oxidized mercury and the effect of flue gas contents on the mercury speciation transformation process. Mercury emission control methods, such as existing APCDs (air pollution control devices) at power stations, sorbent injection, additives in coal combustion and photo-catalytic methods are introduced in detail. Lab-scale, pilot-scale and full-scale experimental studies of sorbent injection conducted by the authors are presented systematically, helping researchers and engineers to understand how this approach reduces the mercury emissions in flue gas and to apply the methods in mercury emission control at coal-fired power stations. Readers will arrive at a comprehensive understanding of various mercury emission control methods that are suitable for industrial applications. The book is intended for scientists, researchers, engineers and graduate students in the fields of energy science and technology, environmental science and technology and chemical engineering.
This essential handbook and ready reference offers a detailed overview of the existing and currently researched technologies available for the control of mercury in coal-derived gas streams and that are viable for meeting the strict standards set by environmental protection agencies. Written by an internationally acclaimed author team from government agencies, academia and industry, it details US, EU, Asia-Pacific and other international perspectives, regulations and guidelines.
Mercury is a leading concern among the air toxic metals addressed in the 1990 Clean Air Act Amendments (CAAA) because of its volatility, persistence, and bioaccumulation as methylmercury in the environment and its neurological health impacts. The Environmental Protection Agency (EPA) reports for 2001 shows that total mercury emissions from all sources in USA is about 145 tons per annum, of which coal fired power plants contribute around 33% of it, about 48 tons per annum. Unlike other trace metals that are emitted in particulate form, mercury is released in vapor phase in elemental (Hg0) or oxidized (Hg2+, mainly HgCl2) form. To date, there is no post combustion treatment which can effectively capture elemental mercury vapor, but the oxidized form of mercury can be captured in traditional emission control devices such as wet flue gas defulrization (WFGD) units, since oxidized mercury (HgCl2) is soluble in water. The chlorine concentration present during coal combustion plays a major role in mercury oxidation, which is evident from the fact that plants burning coal having high chlorine content have less elemental mercury emissions. A novel method of co-firing blends of low chlorine content coal with high chlorine content cattle manure/biomass was used in order to study its effect on mercury oxidation. For Texas Lignite and Wyoming coal the concentrations of chlorine are 139 ppm and 309 ppm on dry ash free basis, while for Low Ash Partially Composted Dairy Biomass it is 2,691 ppm. Co-firing experiments were performed in a 100,000 BTU/hr (29.3 kWt) Boiler Burner facility located in the Coal and Biomass Energy laboratory (CBEL); coal and biomass blends in proportions of 80:20, 90:10, 95:5 and 100:0 were investigated as fuels. The percentage reduction of Hg with 95:5, 90:10 and 80:20 blends were measured to be 28- 50%, 42-62% and 71-75% respectively. Though cattle biomass serves as an additive to coal, to increase the chlorine concentration, it leads to higher ash loading. Low Ash and High Ash Partially Composted Dairy Biomass have 164% and 962% more ash than Wyoming coal respectively. As the fraction of cattle biomass in blend increases in proportion, ash loading problems increase simultaneously. An optimum blend ratio is arrived and suggested as 90:10 blend with good reduction in mercury emissions without any compromise on ash loading.
"Mercury Emission and its Control in Chinese Coal-Fired Power Plants" focuses on investigating mercury emissions samplings and measurement in Chinese coal-fired power plants, mercury emission estimations and future trends, mercury speciation transformation during coal combustion, mercury control and mercury stability in byproducts. The book not only introduces mercury emissions from actual coal-fired power plants, but also presents studies on the mechanism of mercury emission and its control. This is a valuable reference for engineering thermal physicists, thermal engineers, and chemical engineers. Jinsong Zhou, Zhongyang Luo, and Mengxiang Fang are Professors in the College of Mechanical and Energy Engineering, Zhejiang University, China. Yanqun Zhu is Associate Professor in the College of Mechanical and Energy Engineering, Zhejiang University, China.
In March 2005, the EPA issued a rule that will limit mercury emissions (ME) -- a toxic element that causes neurological problems -- from coal-fired power plants, the nation's largest ind'l. source of ME. Under the rule, ME are to be reduced from a baseline of 48 tons/yr. to 38 tons in 2010 & to 15 tons in 2018. The ME target for 2010 is based on the level of ME achievable with technol. for controlling other pollutants -- which also capture some mercury -- because it believed emerging mercury controls had not been adequately demonstrated. This report: describes the use, availability, & effectiveness of technol. to reduce ME at power plants; & identifies the factors that influence the cost of these technol. & reports on available cost estimates. Tables.
The emission of hazardous air pollutants (air toxics) from various industrial processes has emerged as a major environmental issue that was singled out for particular attention in the Clean Air Act Amendments of 1990. In particular, mercury emissions are the subject of several current EPA studies because of concerns over possible serious effects on human health. Some of those emissions originate in the combustion of coal, which contains trace amounts of mercury, and are likely to be the subject of control requirements in the relatively near future. Data collected by the Department of Energy (DOE) and the Electric Power Research Institute (EPRI) at operating electric-power plants have shown that conventional flue-gas cleanup (FGC) technologies are not very effective in controlling emissions of mercury in general, and are particularly poor at controlling emissions of elemental mercury. This paper gives an overview of research being conducted at Argonne National Laboratory on improving the capture of mercury in flue gas through the use of dry sorbents and/or wet scrubbers. The results and conclusions to date from the Argonne research on dry sorbents can be summarized as follows: lime hydrates, either regular or high-surface-area, are not effective in removing elemental mercury; mercury removals are enhanced by the addition of activated carbon; mercury removals with activated carbon decrease with increasing temperature, larger particle size, and decreasing mercury concentration in the gas; chemical pretreatment (e.g., with sulfur or CaCl2) can greatly increase the removal capacity of activated carbon; chemically treated mineral substrates have the potential to be developed into effective and economical mercury sorbents; sorbents treated with different chemicals respond in significantly different ways to changes in flue-gas temperature.
Coal-fired power plants are a major anthropogenic source of worldwide mercury (Hg) emissions. Since mercury is considered to be one of the most toxic metals found in the environment, Hg emissions from coal-fired power plants is of major environmental concern. Mercury in coal is vaporized into its gaseous elemental form throughout the coal combustion process. Elemental Hg can be oxidized in subsequent reactions with other gaseous components (homogeneous) and solid materials (heterogeneous) in coal-fired flue gases. While oxidized Hg in coal-fired flue gases is readily controlled by its adsorption onto fly ash and/or its dissolution into existing solution-based sulfur dioxide (SO2) scrubbers, elemental Hg is not controlled. The extent of elemental Hg formed during coal combustion is difficult to predict since it is dependent on the type of coal burned, combustion conditions, and existing control technologies installed. Therefore, it is important to understand heterogeneous Hg reaction mechanisms to predict the speciation of Hg emissions from coal-fired power plants to design and effectively determine the best applicable control technologies. In this work, theoretical and experimental investigations have been performed to investigate the adsorption and in some cases the oxidation, of Hg on solid surfaces, e.g., calcium oxide (CaO), noble metals and activated carbon (AC). The objective of this research is to identify potential materials that can be used as multi-pollutant sorbents in power plants by carrying out both high-level density functional theory (DFT) electronic structure calculations and experiments to understand heterogeneous chemical pathways of Hg. This research uses a fundamental science-based approach to understand the environmental problems caused by coal-fired energy production and provides solutions to the power generation industry for emissions reductions. Understanding the mechanism associated with Hg and SO2 adsorption on CaO will help to optimize the conditions or material to limit Hg emissions from the flue gas desulfurization process. Plane-wave DFT calculations were used to investigate the binding mechanism of Hg species and SO2 on the CaO(100) surface. The binding strengths on the high-symmetry CaO adsorption sites have been investigated for elemental Hg, SO2, mercury chlorides (HgCl and HgCl2) and mercuric oxide (HgO). It has been discovered that HgCl, HgCl2, and SO2 chemisorb on the CaO(100) surface at 0.125 ML coverage. Binding energies of elemental Hg are minimal indicating a physisorption mechanism. Noble metals such as palladium (Pd), gold (Au), silver (Ag), and copper (Cu) have been proposed to capture elemental Hg. Plane-wave DFT calculations have been carried out to investigate the mercury interactions with Pd binary alloys and overlays in addition to pure Pd, Au, Ag, and Cu surfaces. It has been determined that Pd has the highest mercury binding energy in comparison to other noble metals. In addition, Pd is found to be the primary surface atom responsible for increasing the adsorption of Hg with the surface in both Pd binary alloys and overlays. Deposition of Pd overlays on Au and Ag has been found to enhance the reactivity of the surface by shifting the d-states of surface atoms up in energy. The possible binding mechanisms of elemental Hg onto virgin, brominated and sulfonated AC fiber and brominated powder AC sorbents have been investigated through packed-bed experiments in a stream of air and simulated flue gas conditions, including SO2, hydrogen chloride (HCl), nitrogen oxide (NO) nitrogen dioxide (NO2). A combination of spectroscopy and plane-wave DFT calculations was used to characterize the sorption process. X-ray photoelectron spectroscopy (XPS) and x-ray absorption fine structure (XAFS) spectroscopy were used to analyze the surface and bulk chemical compositions of brominated AC sorbents reacted with Hg0. Through XPS surface characterization studies it was found that Hg adsorption is primarily associated with halogens on the surface. Elemental Hg is oxidized on AC surfaces and the oxidation state of adsorbed Hg is found to be Hg2+. Though plane-wave DFT and density of states (DOS) calculations indicate that Hg is more stable when it is bound to the edge carbon atom interacting with a single bromine bound atop of Hg, a model that includes an interaction between the Hg and an additional Br atom matches best with experimental data obtained from extended x-ray absorption fine structure (EXAFS) spectroscopy. The flue gas species such as HCl and bromine (Br2) enhance the Hg adsorption, while SO2 is found to decrease the Hg adsorption significantly by poisoning the active sites on the AC surface. The AC sorbents represent the most market-ready technology for Hg capture and therefore have been investigated by both theory and experiment in this work. Future work will include similar characterization and bench-scale experiments to test the metal-based materials for the sorbent and oxidation performance.
The Subbituminous Energy Coalition (SEC) identified a need to re-test stack gas emissions from power plants that burn subbituminous coal relative to compliance with the EPA mercury control regulations for coal-fired plants. In addition, the SEC has also identified the specialized monitoring needs associated with mercury continuous emissions monitors (CEM). The overall objectives of the program were to develop and demonstrate solutions for the unique emission characteristics found when burning subbituminous coals. The program was executed in two phases; Phase I of the project covered mercury emission testing programs at ten subbituminous coal-fired plants. Phase II compared the performance of continuous emission monitors for mercury at subbituminous coal-fired power plants and is reported separately. Western Research Institute and a number of SEC members have partnered with Eta Energy and Air Pollution Testing to assess the Phase I objective. Results of the mercury (Hg) source sampling at ten power plants burning subbituminous coal concluded Hg emissions measurements from Powder River Basin (PBR) coal-fired units showed large variations during both ICR and SEC testing. Mercury captures across the Air Pollution Control Devices (APCDs) present much more reliable numbers (i.e., the mercury captures across the APCDs are positive numbers as one would expect compared to negative removal across the APCDs for the ICR data). Three of the seven units tested in the SEC study had previously shown negative removals in the ICR testing. The average emission rate is 6.08 lb/TBtu for seven ICR units compared to 5.18 lb/TBtu for ten units in the SEC testing. Out of the ten (10) SEC units, Nelson Dewey Unit 1, burned a subbituminous coal and petcoke blend thus lowering the total emission rate by generating less elemental mercury. The major difference between the ICR and SEC data is in the APCD performance and the mercury closure around the APCD. The average mercury removal values across the APCDs are 2.1% and 39.4% with standard deviations (STDs) of 1990 and 75%, respectively for the ICR and SEC tests. This clearly demonstrates that variability is an issue irrespective of using 'similar' fuels at the plants and the same source sampling team measuring the species. The study also concluded that elemental mercury is the main Hg specie that needs to be controlled. 2004 technologies such as activated carbon injection (ACI) may capture up to 60% with double digit lb/MMacf addition of sorbent. PRB coal-fired units have an Hg input of 7-15 lb/TBtu; hence, these units must operate at over 60% mercury efficiency in order to bring the emission level below 5.8 lb/TBtu. This was non-achievable with the best technology available as of 2004. Other key findings include: (1) Conventional particulate collectors, such as Cold-side Electro-Static Precipitators (CESPs), Hot-side Electro-Static Precipitator (HESP), and Fabric Filter (FF) remove nearly all of the particulate bound mercury; (2) CESPs perform better highlighting the flue gas temperature effect on the mercury removal. Impact of speciation with flue gas cooling is apparent; (3) SDA's do not help in enhancing adsorption of mercury vapor species; and (4) Due to consistently low chlorine values in fuels, it was not possible to analyze the impact of chlorine. In summary, it is difficult to predict the speciation at two plants that burn the same fuel. Non-fuel issues, such as flue gas cooling, impact the speciation and consequently mercury capture potential.
The Development of Advanced Environmental Control Technology project at Argonne is designed to investigate new concepts leading to advanced control technologies for fossil-energy systems. Within that project, specific research tasks are focused on the development of combined NO(subscript x)/SO2control technologies, evaluation of waste/byproduct materials from advanced flue-gas-cleanup (FGC) systems, and development of new or improved control measures for the abatement of emissions of hazardous air pollutants (HAPs) from fossil-fuel combustion. The last task, which is the subject of this paper, also includes the evaluation of any possible effects of captured HAP species on waste disposal, as well as the evaluation of HAP measuring techniques and instruments. The HAPs currently under investigation in this task include mercury and arsenic compounds. Only experimental activities concerning mercury control are reported in this paper.
