Desulfurization characteristics of slaked lime and regulation optimization of circulating fluidized bed flue gas desulfurization process--A combined experimental and numerical simulation study

Circulating fluidized bed flue gas desulfurization(CFB-FGD) process has been widely applied in recent years. However, high cost caused by the use of high-quality slaked lime and difficult operation due to the complex flow field are two issues which have received great attention. Accordingly, a laboratory-scale fluidized bed reactor was constructed to investigate the effects of physical properties and external conditions on desulfurization performance of slaked lime, and the conclusions were tried out in an industrial-scale CFB-FGD tower. After that, a numerical model of the tower was established based on computational particle fluid dynamics(CPFD) and two-film theory. After comparison and validation with actual operation data, the effects of operating parameters on gas-solid distribution and desulfurization characteristics were investigated. The results of experiments and industrial trials showed that the use of slaked lime with a calcium hydroxide content of approximately 80% and particle size greater than 40 μm could significantly reduce the cost of desulfurizer. Simulation results showed that the flow field in the desulfurization tower was skewed under the influence of circulating ash. We obtained optimal operating conditions of 7.5 kg·s^(-1)for the atomized water flow, 70 kg·s^(-1)for circulating ash flow, and 0.56 kg·s^(-1)for slaked lime flow, with desulfurization efficiency reaching 98.19% and the exit flue gas meeting the ultraclean emission and safety requirements. All parameters selected in the simulation were based on engineering examples and had certain application reference significance.

Effect of H_2O(g)Content in Circulating Flue Gas on Iron Ore Sintering with Flue Gas Recirculation

The influence of H2O （g） content in circulating flue gas on sintering was studied by simulating the flue gas circulating sintering. The results show that the burning speed of solid fuel and the heat transfer rate during sintering process are improved when the H2O （g） content increases from 0 to 6%, which accelerates the sintering speed. However, when the H2O （g） content exceeds 6 %, the over-wet zone in sinter bed is thickened, which deteriorates the permeability of sintering bed. In addition, the magnetite content in sinter increases, while the acicular calcium ferrite content decreases. Accordingly, the sinter yield and tumble index decrease with excessive H2O （g） content. To guarantee the yield and quality of sinter, the favourable H2O （g） content in circulating flue gas should be controlled to be less than 6%.

Influence of O_2 Content in Circulating Flue Gas on Iron Ore Sintering

Circulating flue gas can reduce the emission of flue gas , and furthermore , it can reuse the waste heat effectively in the sintering process.Compared with conventional sintering , O2 that gets through the sintering bed decreases because of substituting circulating gas for air.The influences of O2 content on sintering process are studied through simulating the flue gas circulation sintering with artificial gas.It shows that , with the reducing of O2 content in circulating gas , the combustion speed of fuel decreases and incomplete combustion degree increases , which makes the flame front fall behind the heat front and reduces the heat utilization efficiency of fuel.The ultimate result is that the temperature of sintering bed decreases and the liquid phase reduces.In addition , the reducing atmosphere is strengthened because of flue gas circulation , which makes the magnetite increase yet calcium ferrite reduce gradually. Because the content of calcium ferrite with good strength reduces , the sinter yield and tumble strength decrease.To ensure the sinter index , the favorable O2 content of circulating flue gas is no less than 15%.

Activity and characteristics of ＂Oxygen-enriched＂ highly reactive absorbent for simultaneous flue gas desulfurization and denitrification

An ＂Oxygen-enriched＂ highly reactive absor- bent was prepared by mixing fly ash, lime and a small quantity of KMnO4 for simultaneous desulfiarization and denitrification. Removal of SO2 and NO simultaneously was carried out using this absorbent in a flue gas circulating fluidized bed （CFB）. The highest simultaneous removal efficiency, 94.5% of SO2 and 64.2% of NO, was achieved under the optimal experiment conditions. Scanning Electron Microscope （SEM） and Accessory X-ray Energy Spectrometer （EDX） were used to observe the surface characteristics of fly ash, lime, ＂Oxygen-enriched＂ highly reactive absorbent and the spent absorbent. An ion chromatograph （IC） and chemical analysis methods were used to determine the contents of sulfate, sulfite, nitrate and nitrite in the spent absorbents, the results showed that sulfate and nitrite were the main products for desulfurization and denitrification respectively. The mechanism of removing SO2 and NO simultaneously was proposed based on the analysis results of SEM, EDX, IC and the chemical analysis methods.