Search Results (4)

In order to realize the full-time denitration of a boiler, high-temperature flue gas needs to be introduced when SCR is conducted during the boiler start-up stage, and there is a fire risk due to the presence of combustible fly ash at this time. Therefore, research on reburning and the explosion risk of tail flue gas encountering high-temperature flue gas during start-up and shutdown was carried out. A small testbed was designed to record the temperature of the flue gas and the composition of the flue gas before and after the test, and the ignition characteristics of combustible fly ash in the flue gas were systematically studied. The ignition temperature of combustible fly ash in various conditions was obtained, the ignition characteristics of combustible fly ash in the airflow were analyzed, and the effects of combustible gas, high-temperature flue gas temperature, and fly ash composition on ignition were also analyzed. The results show that the flue gas temperature in the test section was about 400 °C, the low-temperature flue gas temperature increased from 650 °C to 813 °C, and the combustible fly ash did not ignite regardless of whether alcohol was added as a combustible gas component. When the volatile content of combustible fly ash was 10~26.7%, the ignition temperature was 660~760 °C. The lower the volatile content of combustible fly ash was, the higher the ignition point was. When alcohol was added as a combustible component of gas, the ignition point decreased by about 50 °C. The critical ignition temperature of combustible fly ash in this test was lower than that under actual power plant operation conditions. Full article

The flue evaporation of desulfurization wastewater can solve the problem that it is difficult to remove some heavy metal ions and chloride ions by conventional methods. A large amount of chloride ions in desulfurization wastewater can also promote the catalytic oxidation removal of Hg in the flue gas. The migration character of chloride ions in the flue evaporation process of desulfurization wastewater was studied by using the coal-fired thermal state experimental platform. The concentrations of Hg⁰ and Hg²⁺ in the flue gas at the inlet and outlet of selective catalytic reduction denitration (SCR), electrostatic precipitator (ESP), and wet desulfurization (WFGD) devices were tested, and the synergistic removal of traditional pollutant removal equipment by flue evaporation of desulfurization wastewater was analyzed. The influence of Hg and the effect of the evaporation of desulfurization wastewater at different positions on the removal of Hg in the flue gas were compared and analyzed, and the catalytic mechanism of Hg on the SCR surface was further revealed. The results show that 10% chloride ions enter the flue gas after the desulfurization wastewater evaporates. The content of chlorine elements and evaporation temperature influence the evaporation of desulfurization wastewater. The mechanism of SCR catalytic oxidation of Hg⁰ was explored; oxygen atoms have catalytic oxidation effects on Hg⁰ at different positions in the V₂O₅ molecule in SCR; and chloride ions can enhance the catalytic oxidation of Hg⁰ by V₂O₅. The intermediate product HgCl is generated, which is finally converted into HgCl₂. The oxidation efficiency of Hg⁰ in electrostatic precipitation (ESP) is increased from 3% to 18%, and the removal efficiency of Hg is increased from 5% to 10%. The removal efficiency of Hg²⁺ in WFGD is basically maintained at approximately 85%. In addition, a small amount of Hg²⁺ was restored to Hg⁰ in WFGD. The removal efficiency of Hg⁰ in the flue gas of evaporative desulfurization wastewater before SCR is 65%, and the removal efficiency of gaseous Hg is 62%. When the evaporative desulfurization wastewater before ESP, the synergistic removal efficiency of Hg⁰ is 39%, and the gaseous Hg removal efficiency is 39%, and the removal efficiency of Hg is 40%. Evaporation of the desulfurization wastewater before SCR was more conducive to the coordinated removal of Hg by the device. Full article

Selective catalytic reduction (SCR) technology plays a crucial role in flue gas denitration. The nonuniform distribution of catalyst inlet parameters causes the nonuniform distribution of NO concentration at the outlet, thus affecting accuracy of ammonia injection. Regarding this issue, this paper describes the impacts of nonuniform velocity and temperature on both the confidence of NO concentration measured at a single measuring point at the outlet and the denitration efficiency, which can provide a basis for structural optimization of SCR denitration reactor and decrease in ammonia slip. The random distribution form of velocity and temperature above the catalyst layer are derived from the actual gas volume and the actual SCR reactor model, and then the catalyst inlet boundary conditions were generated with different relative standard deviation of velocity and temperature accordingly. The confidence of outlet NO concentration measurement results can be counted by means of Monte Carlo simulation. Finally, the relation model can be obtained to calculate the confidence of outlet NO concentration measurement results at different working conditions. The results show that within the gas volume range of this work, in order to ensure the confidence of the NO concentration measurement results, the relative standard deviation of temperature before the catalyst inlet must be within 0.005 and the relative standard deviation of velocity before the catalyst inlet must be within 0.1. With the increase in relative standard difference in temperature, there is a slight decrease in the efficiency of denitration. With the different mean value of temperature, the variation range of denitration efficiency is similar to that of temperature-relative standard difference. With the different mean value of velocity, the deviation range of corresponding efficiency is similar to that of the temperature-relative standard difference. When the relative standard difference in velocity increases, the denitration efficiency decreases slightly. The greater velocity value, the decreasing range of denitration efficiency is larger than the variation range of relative standard difference in velocity. Full article

Currently, energy policy is associated with the increase in the share of renewable sources in systemic energy production. Due to this trend, coal-fired power units must increase their work flexibility. Adapting a coal power plant to work with a lower load often causes the issue of maintaining the temperature before the selective catalytic reduction (SCR) installation at a sufficiently high level. This paper presents a CFD analysis of the mixing area of two flue gas streams before the SCR installation with various methods for mixing flue gas streams. The novelty of the work is mixing the flue gas streams of different temperatures using a flap shape developed by the authors. A series of numerical simulations were performed to develop the location and method of introducing the higher temperature gas, obtaining a uniform distribution of the exhaust gas temperature. The simulation scheme was applied to a series of geometrical modifications of the boundary conditions. The tested solution using only a single, straight flap in the flue gas duct allows the amplitude to be reduced from 298 K to 144 K. As a result of the research, a mixing flap design was developed to reduce the initial temperature amplitude of the flue gas streams from 298 K to 43 K. Full article