A prediction of arsenic and selenium emission during the process of bituminous and lignite coal co-combustion

Kinetics Analysis of the NH3-SCR Denitration Reaction over Sintered Ore Catalysts

Utilizing sintered ore catalysts (SOC), which are used in the sintering industry for NH3-SCR denitration, is a feasible and economical way to reduce NOx emission in sintering flue gas. Therefore, in order to enhance the denitration efficiency of SOC, sintered ore modified by sulfuric acid and sulfated sintered ore catalysts (SSOC-5) were prepared. Kinetic analyses of these two catalysts for denitration were carried out in this study. On the basis of eliminating the influence of internal and external diffusion, the relationship between reactants and reaction rate was studied by a power function kinetic model. This clarified that the adsorption ability of the acid-modified catalyst for reaction gas adsorption was stronger than that of sintered ore catalysts, and the reaction rate was also accelerated. The NO, NH3 and O2 reaction orders of SOC were 1, 0.3 and 0.16 at 250~300 °C, while these values of SSOC-5 were 0.8, 0.06 and 0.09, respectively. The apparent activation energy of SOC was 83.66 kJ/mol, while the value of SSOC-5 decreased to 59.93 kJ/mol.

Comprehensive Effect of Oxidant Addition in an FGD Slurry on the Removal and Distribution of Selenium: A Field Study

Flue gas desulfurization (FGD) scrubbers capture selenium in coal-fired power plants, leading to a high concentration of selenium in the slurry. This research proves that SO₃^2- is preferentially oxidized compared to SeO₃^2- by S₂O₈^2-. With the increase in the oxidation-reduction potential (ORP) caused by S₂O₈^2- addition, the conversion rate of SO₃^2- increased and the size of gypsum grains grew from 31.2 to 34.6 μm. SeO₃^2- migrates into gypsum grains during the growth of CaSO₄·2H₂O, leading to selenium fixation in gypsum. In a field study of a 350 MW unit, the ORP increased from 142 to 450 mV when Na₂S₂O₈ was fed into the FGD slurry. With the addition of the oxidant, 65.1% of selenium in the liquid phase migrated into gypsum. The concentration of selenium in the leachate of gypsum after oxidant addition decreased by 68.0%. A 2.34% increase in the selenium removal rate was observed in the scrubber. This study focuses on the migration and conversion of selenium in an actual FGD slurry via a field test. The results found in the 350 MW unit are consistent with laboratory results. The change in ORP has been proven to be effective in adjusting the selenium distribution in the FGD slurry.

A Model for Predicting Arsenic Volatilization during Coal Combustion Based on the Ash Fusion Temperature and Coal Characteristic

Arsenic emission from coal combustion power plants has attracted increasing attention due to its high toxicity. In this study, it was found that there was a close relationship between the ash fusion temperature (AFT) and arsenic distribution based on the thermodynamic equilibrium calculation. In addition to the AFT, coal characteristics and combustion temperature also considerably affected the distribution and morphology of arsenic during coal combustion. Thus, an arsenic volatilization model based on the AFT, coal type, and combustion temperature during coal combustion was developed. To test the accuracy of the model, blending coal combustion experiments were carried out. The experimental results and published data proved that the developed arsenic volatilization model can accurately predict arsenic emission during co-combustion, and the errors of the predicted value for bituminous and lignite were 2.3–9.8%, with the exception of JingLong (JL) coal when combusted at 1500 °C.

Effect of Molybdenum on the Activity Temperature Enlarging of Mn-Based Catalyst for Mercury Oxidation

The MnO2/TiO2 (TM5) catalyst modified by molybdenum was used for mercury oxidation at different temperatures in a fixed-bed reactor. The addition of molybdenum into TM5 was identified as significantly enlarging the optimal temperature range for mercury oxidation. The optimal mercury oxidation temperature of TM5 was only 200 °C, with an oxidation efficiency of 95%. However, the mercury oxidation efficiency of TM5 was lower than 60% at other temperatures. As for MnO2–MoO3/TiO2 (TM5Mo5), the mercury oxidation efficiency was above 80% at 200–350 °C. In particular at 250 °C, the mercury oxidation efficiency of TM5Mo5 was over 93%. Otherwise, the gaseous O2, which could supplement the lattice oxygen in the catalytic reaction, played an important role in the process of mercury oxidation over TM5Mo5. The results of X-ray photoelectron spectroscopy (XPS) suggested that mercury oxidized by O2 over TM5Mo5 followed the Mars–Maessen mechanism.