Effects of Magnesium and Ferric Ions on Crystallization of Calcium Sulfate Dihydrate Under the Simulated Conditions of Wet Flue-gas Desulfurization

The influences of magnesium and ferric ions in their different ratios on the rate of gypsum crystallization were studied under the conditions similar to those of wet flue-gas desulfurization（WFGD）. The results show that addition of both Mg^2＋ and Fe^3＋ increased induction time and decreased the growth efficiency up to 50% compared with the baseline（without impurities） depending on the concentration and the type of impurity. The effects of Mg^2＋ and Fe^3＋ on the surface energy and the rate of nucleation were estimated by employing the classical nucleation theory. The surface energy decreased by 8% and 14% with the addition of 0.02 mol/L magnesium or ferric ions, respectively, compared to the baseline. Mg^2＋ and Fe^3＋ made the growth rate of the （020）, （021） and （040） faces of gypsum crystal a much greater reduction, which leads to the formation of needle crystals compared to the baseline which favors the formation of plate or flakes. Furthermore, an edge detection program was developed to quantify the effects of impurities on the filtration rate of gypsum product. The results show that the inhibition efficiency of the presence of 0.02 mol/L Mg^2＋ and Fe^3＋ on the filtration rate of gypsum crystal ranges from 22% to 39%.

Gas-solid flow field numerical simulation of different feeding and returning formations of flue-gas circulating fluidized bed

3D Euler double-fluid model was applied and three different feedstocks and reverts formations were simulated. By calculating and analyzing the state of gas and solid fluxion in absorber using three different methods of the feedstocks and reverts in recirculating fluidized bed, described the behavior of gas and solid through the gas-phase velocity, turbulence intensity, gas-solid sliding velocity, and density of particles. The results show that the feedstocks and reverts enters into absorption tower through two symmetrical feedings and are mixed with flue gas. Based on the respective analysis of each model and the com- parison analysis of the three models, this paper drew conclusions. The turbulence intensity of absorption tower is high, gas-solid sliding speed is big, and granule concentration near the axis is high, which has advantages for desulfurization and im- proving the utilization rate of absorbent.

Temperature Distribution in Ethylene Pyrolyzer

A good understanding of the detailed temperature distribution in the furnace plays an important role in the implementation of operation optimization and design improvement of ethylene pyrolyzer. Numerical simulation of the turbulent flow, combustion and heat transfer was carried out to investigate the temperature distribution in industrial furnace. Inhomogeneities of the flue-gas temperature distribution were observed in X, Y, and Z direction of the furnace from the simulated results. Along the height of the furnace, the average flue-gas temperature increased initially and decreased afterward, and reached its peak at the height of 5 m. The reactor tube skin temperature varied not only along the height of the furnace, but also around the circumference of the tube. The heat flux profiles from the furnace towards the reactor tubes followed the shape of the average flue-gas temperature profile. The heat flux of the inlet tubes was constantly higher than that of the outlet tubes at the same height in the furnace.

Flue gas analysis for biomass and coal co‑fring in fuidized bed:process simulation and validation

Coal-conversion technologies,although used ubiquitously,are often discredited due to high pollutant emissions,thereby emphasizing a dire need to optimize the combustion process.The co-fring of coal/biomass in a fuidized bed reactor has been an efcient way to optimize the pollutants emission.Herein,a new model has been designed in Aspen Plus®to simultaneously include detailed reaction kinetics,volatile compositions,tar combustion,and hydrodynamics of the reactor.Validation of the process model was done with variations in the fuel including high-sulfur Spanish lignite,high-ash Ekibastuz coal,wood pellets,and locally collected municipal solid waste(MSW)and the temperature ranging from 1073 to 1223 K.The composition of the exhaust gases,namely,CO/CO_(2)/NO/SO_(2)were determined from the model to be within 2%of the experimental observations.Co-combustion of local MSW with Ekibastuz coal had fue gas composition ranging from 1000 to 5000 ppm of CO,16.2%–17.2%of CO_(2),200–550 ppm of NO,and 130–210 ppm of SO_(2).A sensitivity analysis on co-fring of local biomass and Ekibastuz coal demonstrated the optimal operating temperature for fuidized bed reactor at 1148 K with the recommended biomass-to-coal ratio is 1/4,leading to minimum emissions of CO,NO,and SO_(2).

Effect of additives on mercury partitioning in wet-limestone flue-gas desulfurization

The wet-flue-gas desulfurization(FGD)process plays an important role in removing water-soluble flue-gas components such as sulphur dioxide(SO_(2))and oxidized mercury compounds.Under the reducing environment of the FGD,there is the possibility of re-emission of the already absorbed mercury(Hg)to the gas phase,which may be diminished by the utilization of specific additives.In this study,the effect of two different additives on Hg re-emission from the aqueous phase and Hg partitioning in gypsum and filtrate of a lab-scale wet-limestone FGD is investigated.Furthermore,the behaviour of additives in the presence of different halides is studied.The studied additives are TMT 15■as a sulphidic precipitating agent,which forms non-soluble mercury compounds,and activated lignite(AL)as a carbon-based sorbent,which adsorbs Hg compounds from the aqueous phase.TMT 15■has no significant effect on SO_(2) absorption;on the other hand,addition of AL improves the SO_(2)-removal efficiency by up to 30%.Using both additives,Hg re-emission is suppressed in all the experimented cases except for AL in the absence of halides,in which Hg re-emission shows no change.Thus,the need to form nucleophilic oxidized mercury compounds in the slurry for the adsorption of oxidized mercury on AL can be concluded.Usage of both additives improves Hg retention in the slurry to different extents.It is shown that,for the additive-free slurries,the Hg-adsorption capacity of the solid fraction of the slurry is the limiting parameter.Moreover,the utilization of both additives results in a significant increase in the Hg concentration of solid fraction.The correlation between redox potential and partitioning of Hg in the slurry is presented by comparing the change in the redox potential of slurries when additives are used.

Sulphite measurement and its influence on Hg behaviour in wet-limestone flue-gas desulphurization

The most abundant and typical reducing agent for oxidized mercury in the slurry of wet flue-gas desulphurization(FGD)is the absorbed sulphur dioxide(SO_(2)),which is present as different species of bisulphite or sulphite,depending on the pH of the slurry.In this study,two different measurement principles for continuous sulphite measurement in the slurry of lab-scale FGD were investigated to check their feasibility to be implemented in a wet FGD.The first method is based on light absorbance at the characteristic wavelength of sulphite measurement using a spectrophotometer and,in the second method,sulphite is measured as sulphur dioxide using a gas sensor.In addition,the correlation of sulphite concentration and mercury(Hg)in the slurry can be shown by measuring sulphite semi-continuously.It was concluded that using a spectrophotometer leads to distorted results.In contrast,measuring sulphite as SO2 in the gas phase proved to be more selective.The implementation of the measurement technique in the lab-scale FGD showed promising results for sulphite measurement.Thus,the correlation of Hg and sulphite concentration could be shown at different synthetic slurries containing different halides.Using a slurry without halides demonstrated the ambivalent influence of sulphite in reactions involving Hg,in which sulphite acts as a ligand for Hg complexes as well as a reducing agent,depending on the existing concentration.However,in the presence of halides,the role of sulphite was less significant.

The Thermal Behavior of Coal-Ash Deposits on Heat Exchangers

A theoretical model for predicting the thermal behavior of coal-ash deposits on heat exchangers is desveloped. The heat transfer modes of heat conduction, convection, and thermal radiation are consideredfor the system. The effective thermal conductivities and emissivities of the ash deposits are temperaturedependent. Heat fluxes and dimensionless temperatures in the three layers (loose, sintered, and fused)of the ash deposit are determined. Results are presented for the first two rows of tubes in aligned andstaggered tube banks.

Applications of functionalized ionic liquids

Recent developments of the synthesis and applications of functionalized ionic liquids (including dual-functionalized ionic liquids) have been highlighted in this review. Ionic liquids are at-tracting attention as alternative solvents in green chemistry, but as more functionalized ILs are pre-pared, a greater number of applications in increasingly diverse fields are found.

Emission characteristics of flue gas during the chemical-looping combustion process for multi-component solid waste

Solid waste has interactions with its flue-gas products during combustion,which offers the possibility of regulating its pollutant emissions.Especially,these interaction pathways would be clearer under anaerobic conditions when the chemical-looping combus-tion(CLC)process is used.The CLC experiments of multi-component solid waste were conducted on a homemade twin-bed reactor and the characteristics of flue gas were investigated for the effect of the mixing ratio of sewage sludge and polyvinyl chloride(PVC).The results indicated that the combustion efficiency was>99.9%for these CLC processes;the highest carbon-conversion rate was obtained at 96.3%for PVC with 60%sludge.The highest NO and SO_(2)emissions were 26%and 19%,respectively,when the sludge was mixed with 20%PVC.As the proportion of PVC blended into the sludge increased,the time when the concentration of NO in the flue-gas peaks moved backwards,while peak SO_(2)concentration moved forward.The general trend was to increase first and then de-crease.In addition,there were multiple peaks in carbon emissions,corresponding to~10%,30%and~70%of the carbon-conversion rate;nitrogen emissions reached 90%of total emissions before the carbon-conversion rate was 40%;sulphur emissions had a longer cycle and were mainly emitted between 10%and 60%of the carbon-conversion rate.The results are expected to provide a reference for solid-waste source suppressing to inhibit the generation of pollutants.