Removal of SO2 in Semi‐Dry Flue Gas Desulfurization Process with a Powder‐Particle Spouted Bed

Semi‐dry flue gas desulfurization was investigated with several kinds of SO₂ sorbents, such as slaked lime, limestone, Mg(OH)₂ and concrete pile sludge, in a powder‐particle spouted bed. Slurry droplets including sorbent fine particles were fed to a spouted bed of coarse inert particles spouted with hot gas containing SO₂. SO₂ removal efficiency was strongly affected by the approach to saturation temperature, Ca/S molar ratio and particle size of sorbent. Slaked lime showed the highest desulfurization efficiency. In this process, despite very short gas residence time, more than 90% SO₂ removal was easily achieved by choosing appropriate conditions.     

Simultaneous Removal of NO and SO2 from Flue Gas by UV/H2O2/CaO

The effects of several influencing factors (CaO and H₂O₂ concentration, gas flow, solution temperature, NO, SO₂, O₂ and CO₂ concentration) on the simultaneous removal of NO and SO₂ from flue gas by using a UV/H₂O₂/CaO process were studied. In addition, the anions in the liquid phase were measured by ion chromatography and the material balances for NO and SO₂ were calculated. It was found that, under all experimental conditions, this process achieved a SO₂ removal efficiency of 100 %. With the increase in CaO concentration, NO removal efficiency first increased and then remained almost unchanged. With the increase in H₂O₂ concentration, NO removal efficiency increased but the changes gradually became smaller. NO removal efficiency greatly decreased with increasing gas flow, NO concentration and CO₂ concentration. Slightly increasing the solution temperature and SO₂ concentration reduced NO removal efficiency. Increasing O₂ concentration can promote the removal of NO. The anions in the liquid phase were mainly SO₄^2– and NO₃^–. Most of the low valence nitrogen elements in NO and the low valence sulfur elements in SO₂ transformed into the high valence nitrogen element in NO₃^– and the high sulfur element in SO₄^2–.     

Flue Gas Desulfurization by a Powder‐Particle Spouted Bed

The powder‐particle spouted bed process is one of the semi‐dry processes that have been developed for flue gas desulfurization. In this study, which is designed for SO₂ removal by a powder‐particle spouted bed, the reaction term is included in one‐dimensional and streamtube models that were presented previously for spouted beds. Hydrated lime is used as the sorbent in this process. The predictions of the models are compared with some published experimental data and it is found that the developed models are valid. The results of two models are compared with each other and their various properties are evaluated. The effects of different operating conditions on SO₂ removal efficiency are also investigated and preferred operating conditions are discussed.     

气-固-固流化床用于燃煤电厂尾气同时脱硫脱硝

采用新型干法气–固–固流化床反应器进行模拟燃煤电厂尾气的高效同时脱硫、脱硝. 在内径53 mm的流化床中,以砂粒作为固相介质、自制的K2CO3/Al2O3为吸附剂,考察了温度、吸附剂粒径、吸附剂活性组份(K)与气相中污染组份(SO2,NO)的摩尔比、模拟气中SO2/NO摩尔比等工艺条件对脱硫脱硝效率的影响. 在无氨条件下同时脱硫、脱硝的效率可分别达到100%和92%. 大量数据表明,尾气中的SO2对吸附剂表面NO的脱除反应有显著促进作用.     

Removal of SO2 Using a Magnetically Fluidized Bed in the Semi‐Dry Flue Gas Desulfurization Process: Roles of Ferromagnetic Particles and Applied Magnetic Field in the Desulfurization Reaction

A new semidry flue gas desulfurization (FGD) process is proposed. The process uses a magnetically fluidized bed (MFB) as the reactor in which ferromagnetic particles are fluidized with simulated flue gas under the influence of an external magnetic field. A slurry of lime is continuously sprayed into the reactor by an atomizer fixed at the top of the bed. As a consequence, the desulfurization reaction and slurry drying take place simultaneously in a same reactor. Experiments with a laboratory‐scale apparatus were carried out to investigate the roles of the ferromagnetic particles and the magnetic field applied in the desulfurization reaction. The results show that when ferromagnetic particles are used as the fluidization material, both sulfite (SO₃^2–) salts and sulfate (SO₄^2–) salts are found in the desulfurization products. When quartz particles are used, only sulfite (SO₃^2–) salts are found. This suggests that the Fe(III) ions and Fe(II) ions result from the ferromagnetic particles dissolving in the liquid phase. In addition, the ions act as catalysts in the oxidation of S(IV) to S(VI) and react with SO₂ producing FeSO₃ and Fe₂(SO₄)₃ as the products. On the other hand, the level of the sulfate (SO₄^2–) salts in the products increases with increasing intensity of applied field intensity, which suggests that the oxidation of S(IV) can be enhanced by the applied magnetic field. The oxidation of S(IV) can increase the solubility of SO₂, and therefore, intensify the reaction between SO₂ and Ca(OH)₂, leading to an increased SO₂ removal efficiency.     

Expansion Behavior of a Binary‐Solid Liquid Fluidized Bed with Large Particle Size Difference

The overall expansion of two dissimilar solid particle species with over a tenfold difference in their size and substantial density difference is investigated here for different compositions of the fluidized bed. Contrary to the widely held notion that the total bed height would be the sum of the heights of the two segregated mono‐component beds, the actual bed heights were, in fact, found to be lower. This volume contraction is found to strongly depend upon the mixing behavior prevailing in the binary‐solid fluidized bed. At the complete mixing of the two solid species, the bed‐contraction versus liquid velocity profile shows a global maximum. As a result, the overall bulk density profiles are similarly affected. Moreover, it is found here that correlations meant for predicting the porosity of the packing of binary particle mixtures can be satisfactorily extended to binary‐solid fluidized beds where solid species differ significantly in size.     

Regeneration/Optimization of Activated Carbon Monolith in Simultaneous SO2/NOx Removal from Flue Gas

Due to the adverse effects of SO₂/NO_x on humans and the environment, environmental regulations necessitate the control of their emission. In this study, an activated carbon monolith was synthesized with cobalt oxide (ACM‐Co₃O₄) for the purpose of simultaneous SO₂/NO_x removal from flue gas generated by coal combustion. Average regeneration efficiencies of 92.7 and 94.2 % were obtained for SO₂ and NO_x, respectively. The Langmuir model can adequately describe the experimental results of the ACM‐Co₃O₄ adsorbent in SO₂ and NO_x removal. The key regeneration parameters were optimized by using the response surface methodology (RSM). The RSM results revealed that the statistical prediction and experimental results were in agreement.     

Prediction of the Removal Efficiency of a Novel Two‐Stage Hybrid Scrubber for Flue Gas Desulfurization

Emission of SO₂ from various industrial sources occurs in varying concentrations and quantities. The operation of scrubbers as SO₂ control devices is getting more and more attention as pollution control regulations are tightened. Experimental investigations on the scrubbing of SO₂ in a novel two‐stage hybrid (spray‐cum‐bubble column) scrubber using water and dilute sodium alkali are reported. Empirical and semi‐empirical correlations are developed for the prediction of the performances of the bubble and the spray sections in terms of various pertinent variables of the system for water and alkaline scrubbing, respectively. The contribution of the mass transfer enhancement factor towards the removal of SO₂ has been exploited while developing the semi‐empirical correlation for the prediction of performance in alkaline scrubbing. The predicted values are in excellent agreement with the experimental values. Finally, the operating features of the scrubber and design aspects are discussed in order to develop our understanding for practical applications.     

液相催化氧化法脱除烟气中SO2的研究

采用含Mn2 的吸收液催化氧化脱除烟气中SO2,研究了吸收液硫酸浓度、吸收液催化剂浓度、气体分布器和气体流量等控制条件对SO2的吸收率的影响。试验结果表明,采用w(MnSO4)为0.05%~1.00%的吸收液,其中的w(H2SO4)为2%~6%,选择理想的吸收设备,脱硫率可达98%以上。针对中小型燃煤锅炉中的废气和硫酸生产尾气,液相催化氧化法是一种很有前途的脱硫方法。     

Experimental Study on Flow Behavior in a Gas‐Solid Fluidized Bed for the Methanol‐to‐Olefins Process

A cold model experimental system is established to investigate the flow behavior in a gas‐solid fluidized bed for the methanol‐to‐olefins process catalyzed by SAPO‐34. The system comprises a gas distributor in a F 300 × 5000 mm acrylic column, double fiber optic probe system and a series of cyclones. The experiments are carried out under conditions of atmospheric pressure and room temperature with different superficial velocities (0.3930–0.7860 m s^–1) and different initial bed heights (600–1200 mm). The effects of radial distance, axial distance, superficial gas velocity, and initial bed height on the solid concentration and particle velocity in the bed are discussed. The time‐averaged solid concentration and rising particle velocity profiles under different conditions are obtained. The results show that an increase in the value of r/R or initial bed height results in an increase in the solid concentration but a decrease in the rising particle velocity in the dense phase area, while improvement of the superficial gas velocity has a negative influence on the solid concentration but results in an increase in the rising particle velocity.     

Bubbling and Bed Expansion Behavior Under Vibration in a Gas‐Solid Fluidized Bed

The effect of vibration on the flow patterns and fluidization characteristics including the minimum fluidization velocity (u_mf), the void fraction (ϵ_mf) at u_mf and the bed expansion ratio were examined. The powders used were spherical glass beads and their diameters were 6, 20, 30, 60 and 100μm. For group A powders, the manner in which the vibration affects the bubble formation was examined from the bed expansion ratio and the index of n/4.65. The area of the homogeneous fluidization region was also observed. The homogeneous fluidization region was broadened at a certain vibration strength, where the value of n/4.65 was a minimum. The bubble formation was observed even for 20μm powder (group C), at large vibration strengths and at high gas velocities. Under such conditions, the bed expansion ratio increased suddenly due to bubble formation. The bubbles broke the irregular bed structure, including various properties of agglomerates. Although the channel breakage was dominant flow pattern for group C powders, the bubbles also played an important role in the improvement of the fluidization.     

Critical Bed Height for Solid Circulation in a Compartmented Gas‐Fluidized Bed

The influence of design and operating parameters on minimum upstream bed height required for steady solid circulation across a compartmented gas‐fluidized bed has been studied. The partition plate in the compartmented bed is fitted with two pairs of V‐valve and riser with orifices in them. Silica sand of three different sizes, viz., 490 μm, 325 μm and 250 μm, has been used and the range of the aeration rate tested covers 1–3U_mf through the bed, 5–60U_mf through the V‐valve and 0–60U_mf through the riser. A model incorporating pressure balance across the circulation loop has been developed to analyze the experimental findings. Studies show the existence of a unique critical bed height for a given set of fluidization velocities through the bed, V‐valve, riser and the size of the solids.     

Development of Catalyst-Sorbents for Simultaneous Removal of SO2 From Flue Gas by Low Temperature Ozone Oxidation

One technological process employing ozone and heterogeneous catalyst-sorbents was proposed for removal of SO₂ from flue gas. The catalyst-sorbents were developed and tested especially for adsorption and oxidation of SO₂. Alternative catalyst-supporters including γ-Al₂O₃, permutite, silica gel, activated carbon and diatomite combined with different metal oxides (MnO₂, Cr₂O₃, Fe₂O₃, CuO, CoO and NiO) were evaluated and tested. It was found that γ-Al₂O₃ doped with MnO₂ can be considered as removal-effective sorbent for adsorption and oxidation of SO₂. The synergetic effect between ozone and catalyst was found to be dominated. Effects of catalyst preparation parameters like calcination temperature, metal loaded and reaction temperature, etc. were investigated based on the MnO₂/Al₂O₃ catalyst-sorbents. Results show that γ-Al₂O₃ combined with 8% Mn, calcinated under 573 K and reacted at 413 K are the optimal parameters for removal of SO₂. Extra NO in flue gas can slightly enhance the capture efficiency of SO₂.     

Dry SO2 Removal Process Using Calcium/Siliceous‐Based Sorbents: Deactivation Kinetics Based on Breakthrough Curves

The removal of sulfur dioxide (SO₂) from simulated flue gas was investigated in a laboratory‐scale stainless steel fixed‐bed reactor using sorbents prepared from various siliceous materials, i.e., coal fly ash (CFA), oil palm ash (OPA) and rice husk ash (RHA) mixed with lime (CaO) by means of the water hydration method. Experiments were carried out with a flue gas flow rate of 150 mL/min, reaction temperature of 100 °C, and SO₂ concentration of 1000 ppm. It was found that sorbents prepared from RHA have high BET surface areas and high SO₂ sorption capacities, based on breakthrough curve analysis. In addition, the SO₂ breakthrough curves were also described in terms of a simple first‐order deactivation model containing only two rate constants, one of which, k_s, describes the surface reaction rate constant while the other, k_d, describes the deactivation rate constant. The values of k_s and k_d obtained from the deactivation kinetics model were in good agreement with the experimental breakthrough curves and were also compared with those available in the literature.     

臭氧氧化同时脱除烟气中NO和SO_2的研究

燃煤烟气往往含有大量NO和SO2,它们会引起严重的光化学污染和酸雨现象。采用臭氧氧化-碱液吸收工艺,实现同时脱硫脱硝,使出口烟气能够稳定达标排放。实验结果表明,当温度≤150℃,O3∶NO物质的量比为1时,NO氧化率高于90%,当温度达到200℃后,臭氧分解速率显著增加,NO氧化率显著降低。烟气中SO2的存在会使NO的去除率略微降低,但是影响不大,且O3对SO2的氧化率约为5%左右。将臭氧氧化后的烟气分别采用NaOH和Ca(OH)2溶液吸收,研究发现,相同质量浓度时,NaOH溶液对NOx具有更好的吸收效果;当pH值大于4时,NOx和SO2的去除率分别能达到80%以上和接近100%。     

Radial Gas Mixing in a Fluidized Bed with a Multi‐Horizontal Nozzle Distributor using Response Surface Methodology

The gas mixing in the radial direction within a fluidized bed equipped with a multi‐horizontal nozzle distributor was studied using response surface methodology (RSM), which enables the examination of parameters with a moderate number of experiments. All experiments were carried out in a circular fluidized bed of 0.29 m I.D. cold model fluidized bed. The distributor is placed beside twenty‐two horizontal nozzles that are arranged in three concentric circles with all existing discharge directed clockwise. The tracer gas (CO₂) was discharged into the bed as a tracer gas and the analysis was performed with a gas chromatograph. In order to compare the different internal circulations, the tracer gas was discharged in the center area or annular area of the bed. In RSM, the static bed height, superficial velocity and the open area ratio of the distributor are chosen as the research variables, and the standard deviation of the time averaged radial tracer concentration is used as the objection function. A mathematical model for the gas mixing as a function of the operating parameters was empirically proposed. The results show that the standard deviation of time averaged radial tracer concentration is well correlated with the operating and geometry parameters, (U – U_mf)/U_mf, H_s/D and ψ_d, and that the tracer gas injected to the center position has a better dispersion than when injected to the annular position. This model can be used for optimizing the design of fluidized bed reactors at a required performance level.     

Characteristics of a Pressurized Gas‐Solid Magnetically Fluidized Bed

The hydrodynamic, heat and mass transfer characteristics of a pressurized co‐current gas‐solid magnetically fluidized bed (MFB) were systematically investigated considering major influence factors, such as magnetic field strength, superficial gas velocity, and operating pressure. It was shown that this pressurized gas‐solid MFB has the advantages of a wider operation range of the superficial gas velocity under bubble‐free particulate fluidization, a larger bed voidage with smaller pressure drop across the bed, and larger heat transfer efficiency, compared with a conventional fluidized bed. Moreover, the minimum bubbling velocity, gas‐solid mass, and heat transfer coefficients were correlated at high accuracy within the investigated range of operating conditions.     

Estimation of Sorption Isotherms for Dry Desulphurization of Flue Gas in a Fluidized Bed Reactor

A model approach is presented here to obtain sorption isotherms that are connected with a low cost breakthrough analysis for dry desulphurization of flue gas in a fluidized bed reactor. Experiments were conducted at different temperatures (600–900°C) providing constant feedstock concentration (0.6% SO₂). The fluidizing gas entered the bed through a distributor and fluidized the single charge of 15 g sorbent. The space velocity ranged from 3100 to 5700 h^?1. Each run was terminated when the steady state was reached. Sulfate layer thickness was calculated from conversion ratio and the structural parameter. Inserting this value and the particle size parameter into the mass transfer equation then extracted the process parameters. Equilibrium relationships involving these parameters were compared with different isotherms. The agreement between the experimental and predicted values of the sorption isotherms validated the model. The latter may be successfully used to design reactors for e.g., sulfating or desulphurization.     

Hydrodynamic Characteristics of a Powder‐Particle Spouted Bed with Powder Entrained in Spouting Gas

Spouting of 3.7 mm polyvinyl chloride particles in a cone‐based cylindrical column is subjected to entrainment of FCC powder in the spouting air. It is found that the powder entrainment reduces the minimum spouting velocity, increases the bed pressure drop and reduces the maximum spoutable bed height. At any given bed height and value of U/U_ms, there is a critical value of powder loading ratio above which spouting gives way to slugging.