Wet flue gas desulfurization performance of 330 MW coal-fired power unit based on computational fluid dynamics region identification of flow pattern and transfer process

Wet Flue Gas Desulfurization(WFGD)unit based upon spray scrubber has beenwidely employed to control SO_(2) emissions from flue gas in coal-fired power plant.To clarify the dependence of desulfurization performance on inter-phase transfer behaviors with non-ideal contacting patterns of flue gas and slurry droplets,three regions in spray scrubber are distinguished in terms of gas-slurry flow structures using CFD method in the Eulerian-Lagrangian framework.A comprehensive model is established by involving the transfer process between two phases and chemical reactions in aqueous phase,which is validatedwith the measured data froma WFGD scrubber of 330 MW coal-fired power unit.Numerical results show that the overall uniformity degree of flue gas in whole scrubber is largely determined by the force-balanced droplets in the middle part of scrubber,which is dominated by counter-current mode.Both momentum transfer behavior and SO_(2) chemical absorption process present the synchronicity with the evolution of gas-slurry flow pattern,whilst the heat transfer together with H_(2)O evaporation has little effect on overall absorption process.Three regions are firstly defined as Gas Inlet Region(GIR),Dominant Absorption Region(DAR)and Slurry Dispersed Region(SDR)from the bottom to top of scrubber.SO_(2) is mainly scrubbed in DAR,which provides much more intensive interaction between two phases compared to GIR or SDR.A better understanding of the desulfurization process is obtained from the fundamental relationship between transport phenomena and chemical reactions based upon the complicated hydrodynamics of gas-slurry two-phase flow,which should be useful for designing and optimizing the scrubber in coal-fired power unit.

Experimental study on prediction model of wet gas pressure drop across single-orifice plate in horizontal pipes in the low gas phase Froude number region

The pressure drop prediction of wet gas across single-orifice plate in horizontal pipes had been solved satisfactorily under an annular-mist flow in the upstream of orifice plates.However,this pressure drop prediction is still not clearly determined when the upstream is in an intermittent flow or stratified flow,which is corresponding to a region of low FrG(gas phase Froude number)in the flow pattern map of wet gases.In this study,the wet gas pressure drop across a single-orifice plate was experimentally investigated in the low FrG region.By the experiment,the flow pattern transition in the downstream of single-orifice plates,as well as the effects of FrG and FrL(liquid phase Froude number)on UG(gas phase multiplier),were determined and compared when the upstream is in the flow pattern transition and the stratified flow region,respectively.Prediction performances were examined on the available pressure drop models.It was found that no model could be capable of jointly predicting the wet gas pressure drop in the low FrG region with an acceptable accuracy.With a new method of correlating FrG and FrL simultaneously,new correlations were proposed for the low FrG region.Among which the modified Chisholm model shows the best prediction accuracies,with the prediction deviations of UG being within 7%and 3%when the upstream is in flow pattern transition and stratified flow region,respectively.

Dynamic optimization oriented modeling and nonlinear model predictive control of the wet limestone FGD system

Nonlinear model predictive control(NMPC)scheme is an effective method of multi-objective optimization control in complex industrial systems.In this paper,a NMPC scheme for the wet limestone flue gas desulphurization(WFGD)system is proposed which provides a more flexible framework of optimal control and decision-making compared with PID scheme.At first,a mathematical model of the FGD process is deduced which is suitable for NMPC structure.To equipoise the model’s accuracy and conciseness,the wet limestone FGD system is separated into several modules.Based on the conservation laws,a model with reasonable simplification is developed to describe dynamics of different modules for the purpose of controller design.Then,by addressing economic objectives directly into the NMPC scheme,the NMPC controller can minimize economic cost and track the set-point simultaneously.The accuracy of model is validated by the field data of a 1000 MW thermal power plant in Henan Province,China.The simulation results show that the NMPC strategy improves the economic performance and ensures the emission requirement at the same time.In the meantime,the control scheme satisfies the multiobjective control requirements under complex operation conditions(e.g.,boiler load fluctuation and set point variation).The mathematical model and NMPC structure provides the basic work for the future development of advanced optimized control algorithms in the wet limestone FGD systems.

Gas cyclone-liquid jet absorption separator used for treatment of tail gas containing HCl in titanium dioxide industry

In the titanium dioxide industry,there is a lack of a low-cost and high-efficiency treatment method for chloride containing tail gas.In this paper,the removal of HCl from the titanium dioxide industry by gas cyclone-liquid jet separator was studied,while Ca(OH)_(2),Na_(2)CO_(3),NaOH solution,and water were used as absorbents.This paper investigated the influence of gas cyclone-liquid jet separator’s various process parameters on the removal rate of hydrogen chloride gas.The mechanism of mass transfer in the process of removing hydrogen chloride was discussed,and the effect and feasibility of HCl gas removal in the gas cyclone-liquid jet absorption separator were studied.The results showd that the removal efficiency of hydrogen chloride maintained above 95%,up to 99.9%,and the total mass transfer coefficient reached0.28 mol·m^(-3)·s^(-1)·k Pa^(-1).Under the same conditions,the absorption effect and total mass transfer coefficient of weak basic absorption liquid can be greatly improved by increasing the flow rate of absorption liquid,but the absorption effect and total mass transfer coefficient of strong alkaline absorption liquid can’t be improved obviously.The larger the inlet gas volume,the higher the gas concentration,the lower the absorption efficiency and the lower the total volumetric mass transfer coefficient.

Wet air oxidation treatment of H-acid wastewater

１ＩｎｔｒｏｄｕｃｔｉｏｎＨａｃｉｄｍｏｎｏｓｏｄｉｕｍｓａｌｔ（４ａｍｉｎｏ５ｈｙｄｒｏｘｙ２，７Ｎａｐｈｔｈａｌｅｎｅｄｉｓｃｕｌｆｏｎｉｃａｃｉｄｍｏｎｏｓｏｄｉｕｍｓａｌｔ，ｈｅｒｅｉｎａｆｔｅｒｒｅｆｅｒｅｅｄｔｏａｓ“Ｈａ...

Evaluation of the Gas Turbine Inlet Temperature with Relation to the Excess Air

This paper shows the effect of excess air on combustion gas temperature at turbine inlet, and how it determines power and thermal efficiency of a gas turbine at different pressure ratios and excess air. In such a way an analytic Equation that allows calculating the turbine inlet temperature as a function of excess air, pressure ratio and relative humidity is given. Humidity Impact on excess air calculation is also analyzed and presented. Likewise it is demonstrated that dry air calculations determine a higher level for calculations that can be performed on wet air.

Experimental research on influencing factors of wet removal of NO from coal-fired flue gas by UV/H_2O_2 advanced oxidation process

Wet removal of NO from coal-fired flue gas by UV/H2O2 Advanced Oxidation Process (AOP) were investigated in a self-designed UV-bubble reactor. Several main influencing factors (UV intensity, H2O2 initial concentration, initial pH value, solution temperature, NO initial concentration, liquid-gas ratio and O2 percentage content) on the NO removal efficiency were studied. The results showed that UV intensity, H2O2 initial concentration, NO initial concentration and liquid-gas ratio are the main influencing factors. In the best conditions, the highest NO removal efficiency by UV/H2O2 advanced oxidation process could reach 82.9%. Based on the experimental study, the influencing mechanism of the relevant influencing factors were discussed in depth.

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.

Influence of Chromium on Corrosion Behavior of Low-alloy Steel in Cargo Oil Tank O_2-CO_2-SO_2-H_2S Wet Gas Environment

As international maritime organization （IMO） draft 289 was adopted to develop a low-alloy anti-corrosion steel for the deck of cargo oil tank and to understand corrosion mechanism, corrosion behavior of a low-alloy steel with chromium contents was studied in O2-CO2-SO2-H2 S wet gas environment. Corrosion rate was measured, and the microstructure and morphology of corrosion product film were characterized by scanning electron microscopy （SEM）. The phase and chemical composition of the corrosion product film were investigated by X-ray diffraction （XRD） and energy dispersive spectroscopy （EDS）, respectively. The effect of misorientation distribution on corro- sion resistance of steel was evaluated by electron backscattered diffraction （EBSD）. The results showed that corro- sion rate decreased with increasing chromium content in the low-alloy steel, and the corrosion type was general corrosion. The phenomenon of chromium enrichment was found in corrosion product film consisting of a-FeOOH, γ- FeOOH, sulphur, FeS2 and Fel-xS. The increase of chromium content decreases the amount of high-angle grain boundaries, thus resulting in the improvement of corrosion resistance.

Transformation and removal of ammonium sulfate aerosols and ammonia slip from selective catalytic reduction in wet flue gas desulfurization system

Selective catalytic reduction(SCR) denitration may increase the emission of NH4+and NH3.The removal and transformation characteristics of ammonium sulfate aerosols and ammonia slip during the wet flue gas desulfurization(WFGD) process, as well as the effect of desulfurization parameters, were investigated in an experimental system equipped with a simulated SCR flue gas generation system and a limestone-based WFGD system.The results indicate that the ammonium sulfate aerosols and ammonia slip in the flue gas from SCR can be partly removed by slurry scrubbing, while the entrainment and evaporation of desulfurization slurry with accumulated NH4+will generate new ammoniumcontaining particles and gaseous ammonia.The ammonium-containing particles formed by desulfurization are not only derived from the entrainment of slurry droplets, but also from the re-condensation of gaseous ammonia generated by slurry evaporation.Therefore,even if the concentration of NH4+in the desulfurization slurry is quite low, a high level of NH4+was still contained in the fine particles at the outlet of the scrubber.When the accumulated NH4+in the desulfurization slurry was high enough, the WFGD system promoted the conversion of NH3 to NH4+and increased the additional emission of primary NH4+aerosols.With the decline of the liquid/gas ratio and flue gas temperature, the removal efficiency of ammonia sulfate aerosols increased, and the NH4+emitted from entrainment and evaporation of the desulfurization slurry decreased.In addition, the volatile ammonia concentration after the WFGD system was reduced with the decrease of the NH4+concentration and p H values of the slurry.

Investigation on the relationship between the fine particle emission and crystallization characteristics of gypsum during wet flue gas desulfurization process

The relationship between the fine particles emitted after desulfurization and gypsum crystals in the desulfurization slurry was investigated,and the crystallization characteristics varying with the operation parameters and compositions of the desulfurization slurry were discussed.The results showed that the fine particles generated during the desulfurization process were closely related to the crystal characteristics in the desulfurization slurry by comparison of their morphology and elements. With the higher proportion of fine crystals in the desulfurization slurry,the number concentration of fine particles after desulfurization was increased and their particle sizes were smaller,indicating that the optimization of gypsum crystallization was beneficial for the reduction of the fine particle emission. The lower p H value and an optimal temperature of the desulfurization slurry were beneficial to restrain the generation of fine crystals in the desulfurization slurry. In addition,the higher concentrations of the Fe3＋ions and the F- ions in the desulfurization slurry both promoted the generation of fine crystals with corresponding change of the morphology and the effect of the Fe3＋ ions was more obvious.With the application of the desulfurization synergist additive,it was beneficial for the inhibition of fine crystals while the thinner crystals were generated.

Field Studies on the Removal Characteristics of Particulate Matter and SO_(x) in Ultra-Low Emission Coal-Fired Power Plant

In order to reduce the environmental smog caused by coal combustion,air pollution control devices have been widely used in coal-fired power plants,especially of wet flue gas desulfurization(WFGD)and wet electrostatic precipitator(WESP).In this work,particulate matter with aerodynamic diameter less than 10μm(PM_(10))and sulfur oxides(SO_(x))have been studied in a coal-fired power plant.The plant is equipped with selective catalytic reduction,electrostatic precipitator,WFGD,WESP.The results show that the PM_(10)removal efficiencies in WFGD and WESP are 54.34%and 50.39%,respectively,and the overall removal efficiency is 77.35%.WFGD and WESP have effects on the particle size distribution.After WFGD,the peak of particles shifts from 1.62 to 0.95μm,and the mass concentration of fine particles with aerodynamic diameter less than 0.61μm increases.After WESP,the peak of particle size shifts from 0.95 to 1.61μm.The differences are due to the agglomeration and growth of small particles.The SO_(3)mass concentration increases after SCR,but WFGD has a great influence on SO_(x)with the efficiency of 96.56%.WESP can remove SO_(x),but the efficiency is 20.91%.The final emission factors of SO_(2),SO_(3),PM_(1),PM_(2.5)and PM_(10)are 0.1597,0.0450,0.0154,0.0267 and 0.0215(kg·t^(−1)),respectively.Compared with the research results without ultra-low emission retrofit,the emission factors are reduced by 1~2 orders of magnitude,and the emission control level of air pollutants is greatly improved.

Model Free Adaptive Predictive Control of Desulfurization Slurry pH Based on CPS Framework

In order to improve the slurry pH control accuracy of the absorption tower in the wet flue gas desulfurization process,a model free adaptive predictive control algorithm for the desulfurization slurry pH which is based on a cyber physical systems framework is proposed.First,aiming to address system characteristics of non-linearity and pure hysteresis in slurry pH change process,a model free adaptive predictive control algorithm based on compact form dynamic linearization is proposed by combining model free adaptive control algorithm with model predictive control algorithm.Then,by integrating information resources with the physical resources in the absorption tower slurry pH control process,an absorption tower slurry pH optimization control system based on cyber physical systems is constructed.It is turned out that the model free adaptive predictive control algorithm under the framework of the cyber physical systems can effectively realize the high-precision tracking control of the slurry pH of the absorption tower,and it has strong robustness.

Calculating densities and viscosities of natural gas with a high content of C_(2+) to predict two-phase liquid-gas flow pattern

The paper is devoted to the two-phase flow simulation.The gas-condensate mixture flow in a horizontal pipe under high pressure is considered.The influence of the equation of state(EOS)choice for mixture properties modelling on the flow regime calculation results is studied for gas with high content of methane homologues.An analytical overview of the methods to predict the flow pattern is provided.Based on this analysis,two techniques are selected.For these techniques,values of density and viscosity for each phase are required.Density calculation for the gas phase is performed with Van der Waals based EOS.The propriate EOS is selected based on studies of calculation errors for test mixtures.Calculation of liquid phase density is done by means of Patela-Teja and Guo-Du equations,two different models are considered for viscosity estimation.The flow patterns of gas-condensate mixture in a range of temperatures and pressures are calculated and verified via probability map.The results of study allow to recommend the Brusilovsky EOS for calculation of densities for similar gas mixtures and make more rigorous flow regime evaluation.The probability map shows that for the chosen composition and parameters of media the flow pattern is mostly transitional between segregated and annular independent from EOS.

Distribution and Accumulation of Major and Trace Elements in Gypsum Samples from Lignite Combustion Power Plant

Flue gas containing volatile elements, fine fly ash particulates not retained by particle control devices, and limestone are the most important sources of trace and major elements (TMEs) in wet flue gas desulphurization (WFGD) gypsum. In this study, samples of gypsum slurry were separated into fine and coarse fractions. Multi-elemental analysis of 45 elements in the different size fractions of gypsum, slurry waters and lignite were performed by k0-INAA (k0-instrumental neutron activation analyses). The study found that the volatile elements (Hg, Se and halogens) in the flue gas accumulate in the fine fractions of gypsum. Moreover, the concentrations of most TMEs are considerably higher in the fine fractions compared to the coarse fractions. The exceptions are Ca and Sr that primarily originate from the limestone. Variations of TMEs in the finer fractions are dependent on the presence of CaSO4·2H2O that is the main constituent of the coarse fraction. Consequently, the content of TMEs in the fine fraction is highly dependent on the efficiency of separating the fine fraction from the coarse fraction. Separation of the finer fraction, representing about 10% of the total gypsum, offers the possibility to remove effectively TMEs from WFGD slurry.

Low-temperature oxidation behavior and mechanism of semi-dry desulfurization ash from iron ore sintering flue gas

The low-temperature wet oxidation behavior of semi-dry desulfurization ash from iron ore sintering flue gas in ammonium citrate solution was investigated for efficiently utilizing the low-quality desulfurization ash. The effects of the ammonium citrate concentration, oxidation temperature, solid/liquid ratio, and oxidation time on the wet oxidation behavior of desulfurization ash were studied. Simultaneously, the oxidation mechanism of desulfurization ash was revealed by means of X-ray diffraction, Zeta electric resistance, and X-ray photoelectron spectroscopy (XPS) analysis. Under the optimal conditions with ammonium citrate, the oxidation ratio of CaSO_(3) was up to the maximum value (98.49%), while that of CaSO_(3) was only 8.92% without ammonium citrate. Zeta electric resistance and XPS results indicate that the dissolution process of CaSO_(3) could be significantly promoted by complexation derived from the ammonium citrate hydrolysis. As a result, the oxidation process of CaSO_(3) was transformed from particle oxidation to SO_(3)^(2−) ion oxidation, realizing the rapid transformation of desulfurization ash from CaSO_(3) to CaSO_(4) at low temperature. It provides a reference for the application of semi-dry desulfurization ash and contributes to sustainable management for semi-dry desulfurization ash.

Characterization of a new total heat recovery system using CaCl_(2) as working fluid:Thermal modeling and physical analysis

This paper introduces a kind of open cycle absorption heat wet flue gas heat recovery system,which use CaCl_(2) as the working medium.The system will use the wet heat recovery method and combined with an efficient heat pump system for flue gas as a heat source generator.Through direct contact with the solution in the absorber,the flue gas is going to carry out gas,liquid heat transfer between heat exchanger,realization of sensible heat and latent heat step by step.As the key part of the system,absorber is established by one-dimensional steady-state heat transfer and mass transfer model.This paper uses the finite difference method to model the discrete numerical methods,and an-alyzes the characteristics of heat and mass transfer in the absorber.We obtain the concentration curves of the three kinds of working medium’s temperature and flow along the height direction.We also analyze the influence of CaCl_(2) solution parameters changes on the absorption process,parsing the reason of the temperature change by analyzing the three working medium’s energy flow trend.We found that the temperature change of flue gas is non-monotonic,which decreases gradually in the range of absorption tower height 0-0.9 m,and then increases gradually.The reason for this change is that sensible heat exchange and latent heat exchange exist between flue gas and solution.Although such a change has an impact on the efficiency of the system,it prevents the"white smoke"from condensing in the air,which effectively protects the environment.Compared with conventional LiBr absorption heat pump,the system constructed in this paper has certain advantages in latent heat recovery,flue gas heat energy utilization,energy conservation and emission reduction and economy.

Experimental study on the control of black smoke pollution from the ceramic kilns based on the mechanism of the surfactant and coagulant

Aiming at the characteristics of carbon black,a new method of controlling the black smoke from the industrial coal-burning ceramic kilns by wetting was brought forward.The carbon black in the flue of coal-burning ceramic kiln was collected for the experiments,and its physical and chemical properties were studied in detail.In order to change the sedimentation and wettabil-ity state of the carbon black,the complex solution of the coagulant and surfactant was applied.After a series of orthogonal experiments,the complex solutions with bet-ter effects were chosen.Then,the sedimentation percent-age of carbon black treated by the selected complex solutions was measured.The optimized complex solutions included Na 2 SO 4(100 mmol/L),sodium dodecylbenzene-sulfonate(SDBS)(1.2 mmol/L)and polyacrylamide(PAM)(40 mg/L).After carbon black was absorbed,the complex solutions were clear and colorless.The complex solutions can be recycled,and the sedimentation percent-age of carbon black is 94%.