Wet Flue Gas Desulfurization Unit Research Articles

Aqueous Bromide Discharges from U.S. Coal-Fired Power Plants: Points of Origin, Concentration Ranges, and Effluent Treatment Costs

Bromide discharges from coal-fired power plants have received increased attention from regulatory bodies due to their contribution to the formation of disinfection byproducts (DBPs) in downstream drinking water treatment plants. This paper characterizes the relative contributions of bromide from coal feedstocks and bromine-based mercury control processes, estimates the distribution of bromide concentrations at 85 active coal-fired power plants across the United States (U.S.) with wet flue gas desulfurization units, and estimates the cost of bromide removal from wastewater discharge using year 2020 data. Bromide discharges are estimated at the plant level using a combination of the reported coal rank and composition combusted, estimates of bromide addition in mercury control techniques under multiple halogen addition scenarios, and the estimated flue gas desulfurization (FGD) wastewater flow rate. The median, simulated plant-level estimation of total FGD wastewater flow is 18.3 gallons/min at a bromide concentration of 319 mg/L, equivalent to ∼11.6 tonnes/year of bromide discharges to the environment. Next, we evaluated the expected cost of employing the best available technology (BAT) to control bromide discharges in FGD wastewater to prevent contributions to DBP formation. Treatment would need to remove more than 99.8% of bromide to reach the 0.2 mg/L voluntary incentive program (VIP) limit. The total cost of treatment depends on whether disposal is on- or off-site; the average costs for all plants combined come to an average of $110 million ($95.2/kgal) in 2021 U.S. dollars for on-site disposal, or $134 million ($115/kgal) for off-site disposal.

Effect of modified fly ash injection on As, Se, and Pb emissions in coal-fired power plant

Modified fly ash injection was installed at the outlet of selective catalytic reduction (SCR) systems in a 1000 MW coal-fired power plant, reaching 94% mercury capture rate. Due to chemical and mechanical treatment of raw fly ash, the modified fly ash has a higher oxidation capability, finer particle size, and more active sites. The co-benefit of the reduction of trace elements (TEs), such as arsenic (As), selenium (Se), and lead (Pb), when using on-line modified fly ash was investigated in this study. The results between with and without modified fly ash indicated that it is between 30% and 74% of reduction on the three TEs’ emission in both electrostatic precipitator (ESP) and wet flue gas desulfurization (WFGD) systems with the additional fly ash injection. The finer particle property is the dominant factor to reduce the emission of Se and Pb at such lower temperature (Temp) range. The Se itself also has the higher volatility to make capture more difficult than that of Pb. The strong chemical reaction between As and calcium with the smaller particle size reduced the As in the gas phase. The materials balance including solid, liquid, and gas phase also establish to confirm the sampling and measurement are validated of each value in this study. Above 97% of As and Pb are in the fly ash. Around 67% of the Se was captured in the WFGD unit. The Se had the higher emission in the stack.

Evaluation of Ultralow Emission Performance of Magnesium Oxide (MgO) Wet Flue Gas Desulfurization Unit for Coal-fired Units

Performance tests and evaluations were carried out on the magnesium oxide (MgO) wet flue gas desulfurization unit being used in the ultra-low emission reformation of coal-fired units. It is of reference for units that have not yet carried out ultra-low emission transformation. Taking a magnesium oxide (MgO) wet flue gas desulfurization device of a 350MW coal-fired unit that has completed ultra-low emission modification as the research object, The main performance indexes such as desulfurization efficiency, GGH air leakage rate and reducing agent consumption of the device were tested, and the system operation status were mastered. The test proves that when the magnesium oxide (MgO) wet flue gas desulfurization device used in the desulfurization ultra-low emission reform of the unit is operated under design conditions, It can maintain high desulfurization efficiency and low SO2 emission concentration for a long time, and the main design indicators can meet the design value requirements. The effect of GGH leakage rate on SO2 emission concentration is obvious, resulting in system desulfurization efficiency slightly lower than that of absorption tower desulfurization efficiency.

Lignites and subbituminous coals combustion in Polish power plants as a source of anthropogenic mercury emission

Coal combustion is one of the main anthropogenic sources of mercury emission to the atmosphere. A total of 121 subbituminous coal samples and 29 lignite samples representative for coals burned in Polish power and heat and power plants were acquired and examined. The average mercury content in subbituminous coal samples was 104μgkg−1 (4.591gHgTJ−1), varying from 18 to 518μgkg−1. The average chlorine and bromine content were 2200ppm and 12ppm, respectively. For lignite samples the average mercury content was 197μgkg−1 (21.380gHgTJ−1), varying from 60 to 665μgkg−1. Lignite samples contained significantly less chlorine (40ppm on average) and bromine (4ppm) than coal samples. The Cl·Hg−1 ratio for subbituminous coal samples varied between 103 and 105. For lignite samples this ratio was around 10. Mercury mass balances were performed for two subbituminous coal-fired plants and one lignite-fired plant. The chemical composition of each type of coal had a significant influence on mercury concentration and speciation in the flue gas. The proportion of oxidized mercury (Hg2+) correlated with chlorine content. The relatively large proportion of particulate-bound mercury (Hgp) and Hg2+ measured favored mercury removal by the electrostatic precipitator (65% on average), and by the wet flue gas desulfurization units (32%). Results of mercury emissions from the stack to the atmosphere were 2.0–5.0 and 15.1μgm−3, for plants burning subbituminous coal and lignite, respectively. The mercury leaving the stack from three plants was over 90% elemental mercury (Hg0). Calculated mercury emission factors for plants burning subbituminous coal and lignite were: 0.71–1.80gHgTJ−1 (subbituminous coal) and 6.09gHgTJ−1 (lignite).

Using Wet-FGD systems for mercury removal

A plan to control mercury emissions to the atmosphere and to establish mercury emission limits has recently been elaborated by the European Commission, making it necessary to devise an efficient and cost effective mercury removal technology. Towards this end wet flue gas desulfurization units appear as a promising option for multi-pollutant control. However, more investigation on mercury removal and a greater mercury removal efficiency are required to achieve this objective. In the present work scrubber chemistry and the application of various solid additives to enhance mercury removal in wet scrubbers is evaluated. The results obtained show a significant correlation between mercury removal efficiency and the pH of the scrubber slurry and SO2 concentration. A weaker correlation was observed between oxygen or slurry concentration and removal efficiency. Finally several solid oxides were found to be effective additives for enhancing mercury capture in wet scrubbers.

Status review of mercury control options for coal-fired power plants

Status review of mercury control options for coal-fired power plants