Influence of Recirculated Flue Gas Distribution on Combustion and NOx Formation Characteristics in S-CO_(2) Coal-fired Boiler

Supercritical carbon dioxide(S-CO_(2))Brayton power cycle power generation technology,has attracted more and more scholars'attention in recent years because of its advantages of high efficiency and flexibility.Compared with conventional steam boilers,S-CO_(2) has different heat transfer characteristics,it is easy to cause the temperature of the cooling wall of the boiler to rise,which leads to higher combustion gas temperature in the furnace,higher NOX generation concentration.The adoption of flue gas recirculation has a significance impact on the combustion process of pulverized coal in the boiler,and it is the most effective ways to reduce the emission of NOX and the combustion temperature in the boiler.This paper takes 1000MW S-CO_(2) T-type coal-fired boiler as the research target to investigate the combustion and NOX generation characteristics of S-CO_(2) coal-fired boilers under flue gas recirculation condition,the influence of recirculated flue gas distribution along the furnace height on the characteristics of NOX formation and the combustion of pulverized coal.The results show that the recirculated flue gas distribution has the great impact on the concentration of NOX at the boiler outlet.When the bottom recirculation flue gas rate is gradually increased,the average temperature of the lower boiler decreases and the average temperature of the upper boiler increases slightly;The concentration of NOx at the furnace outlet increases.

Mercury Speciation of Flue Gas Desulphurization By-Products in Coal-Fired Power Plants in China

The aim of this study was to develop and examine the morphology and distribution of mercury (Hg) in flue gas desulfurization (FGD) by-product. Mercury in the coal of coal-fired power plants is concentrated in the by-products of desulfurization process, and it is widely used as an additive in cement, building materials and other industries. Due to the different stability of various forms of mercury in the environment, subsequent use of products containing desulfurization by-product additives will continue to be released into the environment, endangering human health. Therefore, it is very necessary to study the form and distribution of mercury in the by-products of desulfurization in coal-fired power plants to provide a theoretical basis for subsequent harmless treatment. For content and morphology of mercury analysis, 1 sample of dry FGD ash and 6 samples of wet FGD gypsum were analyzed. The total 7 samples were extracted using a modification of sequential chemical extractions (SCE) method, which was employed for the partitioning Hg into four fractions: water soluble, acid soluble, H2O2 soluble, and residual. The Hg analysis was done with United States Environmental Protection Agency (USEPA) method 7471B. Comparing with the wet FGD gypsums of coal-fired boilers, the total Hg content in the dry FGD by-product was as high as 1.22 mg/kg, while the total Hg content in the FGD gypsum is 0.23 - 0.74 mg/kg, which was 2 times over the wet FGD gypsum. The concentration of water soluble Hg in the dry FGD by-product was the highest amount (0.72 mg/kg), accounting for 59.02% of the total mercury. While residual Hg content was 0.16 mg/kg, only about 13.11% of the total mercury. Mercury content in FGD gypsum was expressed in the form of ρ (residual Hg) > ρ (H2O2 soluble Hg) > ρ (water soluble Hg) > ρ (acid soluble Hg). The morphology and distribution of mercury in FGD by-products is supposed to be analyzed before utilization, and the impact of mercury on the environment should be considered.

Gas-phase and particle-phase PCDD/F congener distributions in the flue gas from an iron ore sintering plant

The activated carbon injection-circulating fluidized bed（ACI-CFB）-bag filter coupling technique was studied in an iron ore sintering plant. For comparison, the removal efficiencies under the conditions without or with ACI technology were both evaluated. It was found that the polychlorinated dibenzo-p-dioxins and dibenzofuran（PCDD/F） removal efficiency for total international toxic equivalence quantity（I-TEQ） concentration was improved from 91.61% to 97.36% when ACI was employed, revealing that ACI was very conducive to further controlling the PCDD/F emissions. Detailed congener distributions of PCDD/Fs in the gas-phase and particle-phase of the Inlet and Outlet samples were determined. Additionally, the PCDD/F distribution for the Fly ash-with ACI sample of was also studied.

Effect of wet flue gas desulfurization(WFGD) on fine particle(PM_(2.5)) emission from coal-fired boilers

In this study, the characteristics of fine particles before and after wet flue gas desulfurization(WFGD) in three coal-fired heating boilers in northern China were investigated by using a dilution-based emission sampling experimental system. The influences of the WFGD process on the mass and number concentrations as well as the chemical composition of fine particles were analyzed. The removal efficiency of desulfurization processes on particulate matter mass was 30.06%–56.25% for the three study units. The WFGD had a great influence on the size distributions of particle mass concentration and number concentration. A significant increase in the number and mass concentration of particles in the size range of 0.094–0.946 μm was observed. The watersoluble ion content accounted for a very large proportion of PM_(2.5) mass, and its proportion in PM_(2.5) increased from 28.39%–41.08% to 48.96%–61.21% after the WFGD process for the three units. The desulfurizing process also drastically increased the proportion of cation component(Ca^(2+) for unit A, Mg^(2+) for unit B, and Na+for unit C) and the proportion of SO_4^(2-) in PM_(2.5), and it increased the CE/AE values of PM_(2.5) from 0.82–0.98 to 0.93–1.27 for the three study units.