颗粒包覆过程的数值模拟方法比较研究

综述全颗粒和单颗粒均匀包覆的颗粒包覆研究层次;对比表面更新模型、蒙特卡罗模拟方法、分区群体平衡模型、DEM-C-PBM模型、CFD-DEM模型等包覆过程数值模拟方法,提出CFD-DEM模型是单颗粒层次的数值模拟方法;基于颗粒包覆数值模拟方法的比较分析,针对颗粒包覆过程的多场耦合特征,提出CFD-DEM-CVD多尺度模型,将宏观流体尺度、介观颗粒尺度、微观材料沉积尺度耦合起来进行包覆过程数值模拟;提出颗粒包覆过程准确数值模拟的发展趋势是基于单颗粒尺度的表面均匀包覆机理研究和基于反应器尺度的物理场分布研究相耦合的多尺度研究方法。     

水基铜纳米流体管内颗粒凝并的数值模拟研究

采用大涡模型和泰勒展开矩方法对三维水平圆管中水基铜纳米流体的运动和颗粒扩散及凝并过程进行了数值模拟,主要研究了纳米流体中纳米颗粒在管内的演化过程.结果显示,随着颗粒凝并的进行,颗粒粒径增加,数密度减小;小颗粒的混合和颗粒凝并同时改变颗粒粒径,最终使粒径在径向呈现抛物线分布;流场雷诺数越大对凝并的抑制作用越强.     

基于介尺度曳力模型双组分颗粒混合的CFD模拟

为了对鼓泡流化床内双组分颗粒混合过程进行更精准的计算流体力学(CFD)数值模拟,结合颗粒动力学理论和欧拉多流体模型,建立以气泡为介尺度的双组分曳力模型,在三维鼓泡流化床反应器中模拟了双组分颗粒的分离和混合过程,并通过实验数据验证该模型的准确性,分析外界操作条件和颗粒物性参数对双组分颗粒的分离和混合过程的影响。结果表明:固相颗粒直径的减小、气体入口表观速度的增大以及床层温度的升高都将会加大两相间曳力的非均质性,固相颗粒混合程度逐渐加大;随着颗粒直径和入口气体表观速度的减小,两相颗粒分离程度加大,混合指数随之减小;颗粒物性和外界操作条件的合理匹配有利于双组分颗粒的分离。     

270t/h锅炉烟气循环流化床半干法脱硫除尘系统分析改造

近年来锅炉烟气脱硫利用半干法循环流化床脱硫技术越来越普遍,但在过去的几年里,由于很多环保公司对半干法循环流化床脱硫技术的理解、经验等多方面不足的原因,导致以前很多锅炉烟气治理系统很不理想,出现的主要问题有:结壁、塌床、塔差压不稳定、Ca/S比偏高、布袋除尘器阻力偏高等。现以一个最具代表性的改造项目作为例子供借鉴和参考。     

基于混烧循环流化床锅炉炉内优化脱硫技术的研究

通过对混烧循环流化床锅炉炉内喷钙系统脱硫机理研究,分析了影响脱硫效果的主要因素,提出循环流化床锅炉实际脱硫过程中存在的诸多问题,通过对存在的问题提出控制优化方案,能达到循环流化床锅炉烟气达标排放,减少污染,利于环保。     

循环流化床底部区域流动特性的数值模拟

基于欧拉两相流模型计算循环流化床底部区域的流动特性。在低气速(1.0～2.5m/s)、低循环量下(5.2～34.5kg/(m2·s)),模拟时黏性采用层流模型取得了较好的效果。实验采用光导纤维探头测量仪测量流化床底部区域3个截面的局部颗粒浓度,模拟计算了循环流化床底部3个截面的颗粒浓度的径向分布,并同循环流化床装置的实验数据进行了对比。结果表明,数值模拟计算与实验结果相吻合。     

颗粒流体系统Euler/Lagrange模型中自适应三角网格的生成

针对二维颗粒流体系统Euler／Lagrange模型的有限元模拟,建立了三角网格生成的自适应算法。该算法能够根据颗粒分布与颗粒大小自适应地调整网格的疏密程度,使其网格密度在系统边界附近及颗粒边缘附近较大,而在其它地方较小。与此同时,网格的光滑化也提高了网格质量, 从而为颗粒流体系统介观尺度的有限元模拟奠定了基础。     

液-液循环流化床制取流体冰过程的颗粒形成与运动特性

采用水与另一种非相溶载冷液体直接接触换热制取流体冰的液-液循环流化床是一种全新的动态制冰方法，在所建立的循环流化床试验台上针对制冰过程的关键问题——颗粒（液滴、冰颗粒）形成及其运动特性展开研究，研究过程中采用快速摄像与图像处理相结合的方法，获得颗粒形成及其沿程运动过程的图像以及循环流化床不同高度上颗粒的粒径信息。研究发现射流形状、射流长度及其波动的变化规律直接影响形成液滴的粒径大小与均匀性；颗粒的沿程粒径分布具有向粒径增大方向倾斜与移动特征，并随射流液体流量的增大，颗粒的粒径分布范围与倾斜程度增大；颗粒在流化床内沿程运动过程中具有明显的颗粒聚团、聚并与分散现象，且颗粒的聚并现象不可避免，主要出现在流化床0．50m高度以上，并随射流液体流量增大出现颗粒聚并现象的高度在增高。     

催化裂化烟气脱硫技术分析

催化裂化烟气脱硫技术是现阶段主要的污染物控制措施,我国催化裂化装置(FCC装置)在运行过程中可经过内部结构与烟气内二氧化硫的一系列反应,结合配套污水处理单元及外排污水管网,保证烟气的有效脱硫,同时可减少外环境负担。本文从可再生循环技术、抛弃法、干法烟气脱硫等方面对催化裂化烟气脱硫技术进行了分析。     

气流磨超细粉碎循环流化床锅炉脱硫灰的试验研究

为提高循环流化床燃煤锅炉脱硫灰在工程上的利用率,利用气流磨对循环流化床脱硫灰进行超细粉碎,通过调节分级机频率大小进行分组实验。结果表明:CaO和SO3组分含量在循环流化床脱硫灰中所占比例大,质量分数分别达26.84%和12.25%;采用气流磨粉碎循环流化床脱硫灰,有效地增大了CaO的比表面积,通过调节分级机的频率可获得窄粒度段分布的超细脱硫灰,获得的超细脱硫灰颗粒表面粗糙,凹凸不平,呈不规则形状。     

Sulfation and attrition of calcium sorbent in a bubbling fluidized bed

A bubbling fluidized bed reactor was used as a desulfurization apparatus in this study. The height of the bed was 2.5 m, and the inner diameter was 9 cm. The bed materials were calcium sorbent and silica sand. The effects of the operating parameters of the flue gas desulfurization including relative humidity, temperature, superficial gas velocity, and the particle size of calcium sorbent on SO₂ removal efficiency and calcium sorbent conversion and attrition rate in the fluidized bed were investigated. It was found that the temperature effect in our system was negligible from 40 to 65°C. A higher relative humidity had a higher calcium conversion and a higher sulfur dioxide removal efficiency. Moreover, a smaller particle size of calcium sorbent had a lower calcium conversion in the cyclone but a higher sulfur dioxide removal efficiency. A lower superficial gas velocity resulted in a higher sulfur dioxide removal efficiency and a higher calcium conversion, thus, the total volume of the flue gas treated was maximum near the minimum fluidization velocity. Finally, an attrition rate model proposed in this study could predict the elutriation rate satisfactorily.     

A modeling and experimental study of flue gas desulfurization in a dense phase tower

We used a dense phase tower as the reactor in a novel semi-dry flue gas desulfurization process to achieve a high desulfurization efficiency of over 95% when the Ca/S molar ratio reaches 1.3. Pilot-scale experiments were conducted for choosing the parameters of the full-scale reactor. Results show that with an increase in the flue gas flow rate the rate of the pressure drop in the dense phase tower also increases, however, the rate of the temperature drop decreases in the non-load hot gas. We chose a water flow rate of 0.6 kg/min to minimize the approach to adiabatic saturation temperature difference and maximize the desulfurization efficiency. To study the flue gas characteristics under different processing parameters, we simulated the desulfurization process in the reactor. The simulated data matched very well with the experimental data. We also found that with an increase in the Ca/S molar ratio, the differences between the simulation and experimental data tend to decrease; conversely, an increase in the flue gas flow rate increases the difference; this may be associated with the surface reactions caused by collision, coalescence and fragmentation between the dispersed phases.     

Multi-functional sorbents for the simultaneous removal of sulfur and lead compounds from hot flue gases

A multi-functional sorbent is developed for the simultaneous removal of PbCl(2) vapor and sulfur dioxide from the combustion gases. The sorbent is tested in a bench-scale reactor at the temperature of 700 degrees C, using simulated flue gas (SFG) containing controlled amounts of PbCl(2) and SO(2) compounds. The removal characteristics of PbCl(2) and SO(2), individually and in combination, are investigated. The results show that the mechanism of capture by the sorbent is not a simple physical adsorption process but seems to involve a chemical reaction between the Ca-based sorbent and the contaminants from the simulated flue gas. The porous product layer in the case of individual SO(2) sorption is in a molten state at the reaction temperature. In contrast, the combined sorption of lead and sulfur compounds generates a flower-shaped polycrystalline product layer.     

High temperature removal of hydrogen sulfide using an N-150 sorbent

In this study, an N-150 sorbent was used as a high temperature desulfurization sorbent for the removal of hydrogen sulfide from coal gas in a fixed bed reactor. The results indicate that the N-150 sorbent could be used for H(2)S removal in the tested temperature ranges. Regeneration test also reveals that utilization of the N-150 sorbent maintains up to 85% compared to the fresh sorbent. No significant degeneration occurs on the N-150 sorbent. In addition, various concentrations of H(2)S, H(2) and CO were also considered in the performance test of the N-150 sorbent. Except for H(2)S, H(2) and CO act the important roles in the high temperature desulfurization. By increasing the H(2) concentration, the sulfur capacity of the sorbent decreases and an adverse result is observed in the case of increasing CO concentration. This can be explained via water-shift reaction. On the basis of the instrument analysis, X-ray powder diffraction determination and SEM images with EDS spectrum characterization, residual sulfur is found in the regenerated N-150 sorbent and this sulfur species is sulfate which resulted by incomplete regeneration. The sulfate formation and sintering effect are major reasons to cause activity loss in the sulfidation/regeneration cycles.     

湿法烟气脱硫塔能效特性研究

针对湿法烟气脱硫能效规律欠缺问题,以150 MW超低排放机组湿法脱硫塔为研究对象,基于脱硫设备的主要能耗和脱硫效率构建了脱硫能效指标——脱硫能效值,并采用数值模拟和理论分析相结合的方法,探究了液气比、入口烟气量、烟气流速、入口SO₂质量浓度、烟气温度等参数以及不同喷淋层组合方式对脱硫能效特性的影响规律。结果表明：脱硫能效值为0.22~0.96 kg/（kW·h）,并随入口SO₂质量浓度增加呈正比例变化,随喷淋层组合数、液气比和入口烟气温度增加呈反比例变化,随入口烟气量和塔内烟气流速增加先上升后下降。研究结果可为脱硫技术评价和脱硫系统节能运行提供参考。     

Interactions between mercury and dry FGD ash in simulated post combustion conditions

Two different flue gas desulfurization (FGD) ash samples were exposed to a simulated flue gas stream containing elemental mercury vapor to evaluate the interactions and determine the effects of gas components, dry FGD ash samples, and temperature on adsorption and heterogeneous oxidation of mercury. Both samples were characterized for surface area, unburned carbon content, element content, and mineralogical composition. Mercury speciation downstream from the sample was determined using Ontario Hydro Method. Results showed that higher levels of mercury oxidation were associated with higher levels of mercury capture. The NO(2), HCl, and Cl(2) promoted mercury oxidation, while SO(2) and NO had inhibitory effects on mercury oxidation. Unburned carbon of dry FGD ash sample played an important role in mercury capture. Whether the surface area was caused by unburned carbon or by calcium-based sorbents might be more significant than the level of surface area. Extent of mercury oxidation and capture increased slightly and then decreased as the temperature rising due to the interaction of mass transfer and reaction rates control.     

燃煤烟气中Hg迁移转化特性研究

研究了300 MW煤粉锅炉系统选择性催化还原（selective catalytic reduction,SCR）、低低温电除尘器、海水脱硫、湿式电除尘器等超低排放设施在不同工况、不同煤种情况下的Hg迁移特性和脱除能力。结果表明：各工况下总汞排放浓度为1.16~2.90 μg/m³。最终排入大气中的汞主要以单质汞存在,还有少量氧化态汞,颗粒态汞被全部脱除;汞主要是在海水法烟气脱硫中被去除的,低低温电除尘器、海水脱硫、湿式电除尘器对总汞平均脱除率分别为25%、62%、37%;Hg²⁺占比是影响烟气中汞脱除效率的关键,气相中较高的Hg²⁺份额有利于在电除尘器和海水脱硫装置中获得较高的脱除效率;在该配备SCR脱硝、低低温电除尘器、海水脱硫、湿式电除尘器等超低排放设施的300 MW煤粉锅炉电厂中,总汞平均脱除率约为83%,能够实现较大程度的汞脱除。     

Numerical simulation of semi-dry flue gas desulfurization process in the powder-particle spouted bed

Computational fluid dynamics (CFD) combined with the two-fluid model (TFM) was used for simulation of water vaporization and semi-dry flue gas desulfurization process in a two dimensional powder-particle spouted bed (PPSB), on the basis of gas-solid two-phase flow, the mathematical and physical models of water vaporization process and flue gas desulfurization reaction process have been established through reasonable hypothesis and simplification of the system. The numerical method was used to simulate the desulfurization reaction process and the heat and mass transfer in the powder-particle spouted bed. Simulation results indicate that water vaporization rate was high in spout and annular regions. The main area where flue gas desulfurization reaction occurs was annular area, as a result, the maximum value of desulfurization product rate appears in the annulus. Under the same condition, the desulfurization efficiency of simulation value is 75.75% when the value of slurry water content equals 40 kg-H₂O/kg-dry_sorbent, which is close to but greater than the experimental value (75.03%). The desulfurization efficiency of spouted bed increases first and then decreases with the increase of water content of desulfurization slurry, and the optimum slurry water content for desulfurization process in powder-particle spouted bed was obtained by numerical simulation, which was 40 kg-H₂O/kg-dry_sorbent.     

Life cycle test of the NOXSO SO2 and NOX flue gas treatment process: Process modeling

The NOXSO process uses a regenerable sorbent that removes SO₂ and NO_X simultaneously from flue gas. The sorbent is a γ-alumina bead impregnated with sodium carbonate. The process was successfully tested at three different scales, equivalent to 0.017, 0.06, and 0.75 MW of flue gas generated from a coal-fired power plant. These test results were used to develop a mathematical model for the NOXSO fluid-bed adsorber (NOXSO Corp., Library, PA). The model predicts SO₂ and NO_X removal efficiencies as a function of process conditions and sorbent properties. The spent sorbent was successfully regenerated with either hydrogen or natural gas. The presence of steam during regeneration helps to remove the residual sulfur, but the benefit of steam diminishes when its inlet concentration exceeds 25%. A design equation for a moving-bed regenerator using natural gas as the regenerant was developed from the 0.06 MW results. The adsorber model and the regenerator design equation were used together to determine the optimum residual sulfur content of the regenerated sorbent. It was concluded that the NOXSO LCTU (0.06 MW) would operate at the minimum cycle time of sorption and regeneration if the sulfur content of the regenerated sorbent was controlled at 0.8 wt%.     

海水烟气脱硫膜吸收单元及工艺研究

以海水作为吸收剂,采用自行研制的中空纤维管式膜接触器作为吸收单元,进行膜吸收法海水烟气脱硫过程模拟试验研究.考察膜接触器结构、膜填充密度、膜吸收单元工艺方式、模拟烟气SO2浓度、温度、气液流量等因素对脱硫效率的影响.结果表明,提高烟气温度、海水流量、膜接触器内气液分布均匀程度、气液相有效接触面积、增加膜吸收级数,均有利于提高脱硫率;烟气流量及SO2浓度的增大不利于SO2的脱除;烟气流经管程的气液流程方式利于提高脱硫率,但是气阻大,进气压力高,工程化应用难以实现.提高膜材料传质特性和优化设计膜接触器结构是提高膜吸收法烟气脱硫效率的根本途径.