Experimental study on secondary air mixing along the bed height in a circulating fluidized bed with a multitracer-gas method

A multitracer-gas method was proposed to study the secondary air(SA)mixing along the bed height in a circulating fluidized bed(CFB)using carbon monoxide(CO),oxygen(O_(2)),and carbon dioxide(CO_(2))as tracer gases.Experiments were carried out on a cold CFB test rig with a cross-section of 0.42 m×0.73 m and a height of 5.50 m.The effects of superficial velocity,SA ratio,bed inventory,and particle diameter on the SA mixing were investigated.The results indicate that there are some differences in the measurement results obtained using different tracer gases,wherein the deviation between CO and CO_(2) ranges from 42%to 66%and that between O_(2) and CO_(2) ranges from 45%to 71%in the lower part of the fluidized bed.However,these differences became less pronounced as the bed height increased.Besides,the high solid concentration and fine particle diameter in the CFB may weaken the difference.The measurement results of different tracer gases show the same trends under the variation of operating parameters.Increasing superficial velocity and SA ratio and decreasing particle diameter result in better mixing of the SA.The effect of bed inventory on SA mixing is not monotonic.

Modeling and Simulation Study on Reverse Swirl of Secondary Air in Large Tangentially Fired Boiler

Based on the porosity method and the improved non uniform QUICK scheme, this paper describes a three dimensional computer simulation to predict the flow characteristics in a tangentially fired boiler. The model is applied to a 600?MW boiler modeling under different operating conditions of reverse swirl of secondary air. The numerical results achieve reasonable agreement with experimental data. The calculated results of flow field, the pressure distribution, the relative diameter of tangential circle, angular momentum flux in furnace and the velocity distribution index in horizontal gas pass are analyzed in detail. And then the effects of the reverse swirl of secondary air on flue gas imbalance are discussed. Finally a reasonable operating condition of the reverse swirl of secondary air is presented.

Research and Development of Hot Primary Air Heater for Coal-Fired Boilers in Power Plant

The reasons of introducing cold air into pulverizer are analyzed for boilers with large capacity and high parameters. The temperature rises of the exhaust gas are calculated when varying the amount of the cold air. The hot primary air heater, a new technology, is developed to eliminate the cold air from the pulverized coal system. The applications, advantages and disadvantages are introduced in detail for the new device and system. It is concluded that introducing cold air into pulverizer is one of the major factors that causes the exhaust gas temperature of boilers with large capacity to be high. The amount of the cold air could be reduced signif icantly, even to zero in some cases by adopting the hot primary air heater, which drops the exhaust gas temperature of the boiler effectively. The hot primary air heater, which could play part roles of the steam-air heater or the hot air recirculation system, could also be used to adjust the exhaust gas temperature within the range of 20 ℃ by controlling the flow rate of the cooling medium. Moreover, the startup period of the steam-air heater or the hot air recirculation system will be shortened, which is a unique advantage of the hot primary air heater among the measures to drop the exhaust gas temperature.

Study and Application of W-Flame Boiler Startup Aided by Adjacent Hot Primary Air

In this paper,the designed features of a W-flame coal-fired boiler are introduced.A scheme of joint primary air for two boilers is made and technical measures are also taken based on corresponding analyses and studies.The scheme and the measures provide a reference for technicians to improve the efficiencies and reduce the startup costs of other similar large boilers.

Effect of the secondary air distribution layer on separation density in a dense-phase gas–solid fluidized bed

Dry coal separation has been the most significant process in the field of coal beneficiation to date, because of its special advantage of operation with no water consumption. Mineral dry separation research has received wide attention, particularly in countries and regions experiencing drought and water shortages. During the process of dense coal gas-solid fluidized bed beneficiation, the material is stratified according to its density; the high density material layer remains at the bed bottom, and thus the high density coarse particle bed becomes an important infuencing factor in fluidized bed stability. In the steady fluidization stage, a small number of large radius bubbles are the direct cause of unsteady fluidization in the tradi- tional fluidized bed. The dispersion effect of the secondary air distribution bed for air flow is mainly apparent in the gas region; when the particle size exceeds 13 mm, the secondary air distribution bed has a synergistic effect on the density stability of the upper fluidized layer. When the particle size is small, especially when less than 6 ram, particles will constantly move, accounting for instability of the secondary air distribution bed and distorting the stability of the upper fluidized bed. Under optimum operation conditions, the probable deviation E of gas-solid separation fluidized with a high density coarse particle layer can be as low as 0.085 g/cm3.

Simulation on Soot Emission Control in Stoker-Fired Boiler by Secondary Air

A work on soot emission control simulation in stoker-fired boiler by secondary air has been done. Some models such as k-e, combustion, radiation, and soot Khan-Greeves have been adopted. Soot production and emission has been reduced by secondary air; the highest mass concentration is reduced from 7.46 × 10^-14 to 6.94 × 10^15; mass concentration of soot is decreased from 1.12 ×10^-15 to 9.25 ×10^-32 in the upper areas.

Effects of Interaction between Axial and Radial Secondary Air and Reductive Intensity in Reduction Region on Combustion Characteristics and NO_(x) Emission of Coal Preheated by a Self-Preheating Burner

The study focused on the effects of the interaction between axial and radial secondary air and the reductive intensity in reduction region on combustion characteristics and NO_(x) emission in a 30 kW preheating combustion system.The results revealed that the interaction and reductive intensity influenced the combustion in the down-fired combustor(DFC) and NO_(x) emission greatly.For the temperature distribution,the interaction caused the position of the main combustion region to shift down as R_(2-12)(ratio of axial secondary air flow to radial secondary air flow) decreased or λ_(2)(total secondary air ratio) increased,and there was the interplay between both of their effects.As R_(3-12)(ratio of first-staged tertiary air flow to second-staged tertiary air flow)increased,the decrease in the reductive intensity also caused the above phenomenon,and the peak temperature increased in this region.For the NO_(x) emission,the interaction affected the NO_(x) reduction adversely when λ_(2) or R_(2-12) was higher,and the range of this effect was larger,so that the NO_x emission increased obviously as they increased.The decrease in the reductive intensity caused the NO_(x) emission increased under the homogeneous reduction mechanism,while was unchanged at a high level under the heterogeneous reduction mechanism.For the combustion efficiency,the interaction improved the combustion efficiency as λ_(2) increased when R_(2-12) was lower,while reduced it as λ_(2) increased excessively when R_(2-12) was higher.The proper decrease in the reductive intensity caused the combustion efficiency increased obviously,while was hardly improved further when the intensity decreased excessively.In this study,the lowest NO_(x) emission was only 41.75 mg/m^(3) without sacrificing the combustion efficiency by optimizing the interaction and reductive intensity.

Simulation of the secondary air system of turbofan engines:Insights from 1D-3D modeling

Focusing on the internal flow and heat transfer analysis,a platform for the performance evaluation of the Secondary Air System(SAS)is developed.A multi-fidelity modeling technique has been developed in a turbofan engine model under different flight conditions.A turbine blade cool-ing model which integrates external heat transfer calculations and coolant side modeling with com-mon components is proposed.In addition,the Computational Fluid Dynamics(CFD)method is selected to capture the complex flow field structure in the preswirl system.The validity of the SAS models is compared with publicly available data.An elaborately designed cooling system for the AGTF30 engine is analyzed through three main branches.It is found that the 1D-3D mod-eling technique can provide more accurate predictions of the SAS for the AGTF30 engine.The results demonstrate the versatility and flexibility of the SAS models,thereby indicating the capacity of meeting most of the demands of flow and thermal analysis of the SAS.

Effect of secondary air on NO emission in a 440 t/h circulating fluidized bed boiler based on CPFD method

The 440 t/h circulating fluidized bed boiler was numerically simulated by the Computational Particle Fluid Dynamics(CPFD)method.The combustion characteristics of circulating fluidized bed boiler and the effect of secondary air on NO emission were investigated.The full-scale three-dimensional model of a 440 t/h circulating fluidized bed boiler was established.The rationality of the grid was validated by the experimental data of material layer resistance.The accuracy of the simulation was validated by measuring the temperature of each measuring point in the dense phase area.The combustion conditions in the furnace under different setting modes were simulated.The effects of secondary air rates on NO formation in fluidized bed were predicted.The results show that when the secondary air rate increases to 27%,the proper secondary air rate has a positive effect on the inhibition of NO generation,and the proper strengthening of the central air supply will improve the permeability of the secondary air and make the combustion more uniform and stable.When the secondary air rate increases to 33%,excessive improvement of air classification and central air distribution will affect the stability of circulating fluidized bed operation.Therefore,air classification and strengthening of central air supply can be used together to inhibit the generation of NO.

Efficacy of graphene nanocomposites for air disinfection in dental clinics: A randomized controlled study

BACKGROUND Aerosols containing disease-causing microorganisms are produced during oral diagnosis and treatment can cause secondary contamination.AIM To investigate the use of graphene material for air disinfection in dental clinics by leveraging its adsorption and antibacterial properties.METHODS Patients who received ultrasonic cleaning at our hospital from April 2023 to April 2024.They were randomly assigned to three groups(n=20 each):Graphene nanocomposite material suction group(Group A),ordinary filter suction group(Group B),and no air suction device group(Group C).The air quality and air colony count in the clinic rooms were assessed before,during,and after the procedure.Additionally,bacterial colony counts were obtained from the air outlets of the suction devices and the filter screens in Groups A and B.RESULTS Before ultrasonic cleaning,no significant differences in air quality PM2.5 and colony counts were observed among the three groups.However,significant differences in air quality PM2.5 and colony counts were noted among the three groups during ultrasonic cleaning and after ultrasonic treatment.Additionally,the number of colonies on the exhaust port of the suction device and the surface of the filter were significantly lower in Group A than in Group B(P=0.000 and P=0.000,respectively).CONCLUSION Graphene nanocomposites can effectively sterilize the air in dental clinics by exerting their antimicrobial effects and may be used to reduce secondary pollution.

Numerical investigation of gas-particle flow in the primary air pipe of a low NO_x swirl burner-The DEM-CFD method

The gas-particle flow in the primary air pipe （PAP） of a low NOx swirl burner was investigated using the computational fluid dynamics （CFD） coupled with the discrete element method （DEM）. The mathematical models were validated using the measured values obtained at the outlet of the primary pipe through a phase Doppler anemometer （PDA） system. Particles of different Stokes numbers in the primary air pipe （PAP） were investigated, and the effects of the structure of the primary air pipe and the particle-particle interaction on particle dispersion were analyzed. The results indicate that particles under the combined effects of the Venturi pipe and the spindle body are concentrated into a narrow band area and that the PAP structure can more efficiently concentrate particles with large Stokes numbers. The formed fuel rich/lean jet persists for a long distance out of the burner, thereby favoring of air-staged combustion and NOx reduction. The particle collision frequency and its fluctuation range increase as the particle Stokes number increases. The collisions among particles result in an increase of the spanwise dispersion of particles. Experimental results indicate that the models that take particle-particle collision into consideration are more able to predict particle concentration.

Simulation of Unsteady State Performance of a Secondary Air System by the 1D-3D-Structure Coupled Method

This paper describes the calculation method for unsteady state conditions in the secondary air systems in gas turbines. The 1D-3D-Structure coupled method was applied. A 1D code was used to model the standard components that have typical geometric characteristics. Their flow and heat transfer were described by empirical correlations based on experimental data or CFD calculations. A 3D code was used to model the non-standard components that cannot be described by typical geometric languages, while a finite element analysis was carried out to compute the structural deformation and heat conduction at certain important positions. These codes were coupled through their interfaces. Thus, the changes in heat transfer and structure and their interactions caused by exterior disturbances can be reflected. The results of the coupling method in an unsteady state showed an apparent deviation from the existing data, while the results in the steady state were highly consistent with the existing data. The difference in the results in the unsteady state was caused primarily by structural deformation that cannot be predicted by the 1D method. Thus, in order to obtain the unsteady state performance of a secondary air system more accurately and efficiently, the 1D-3D-Structure coupled method should be used.

Modeling of air quality with a modified two-dimensional Eulerian model: A case study in the Pearl River Delta (PRD) region of China

A modified two-dimensional Eulerian air quality model was used to simulate both the gaseous and particulate pollutant concentrations during October 21-24, 2004 in the Pearl River Delta （PRD） region, China. The most significant improvement to the model is the added capability to predict the secondary organic aerosols （SOA） concentrations because of the inclusion of the SOA formation chemistry. The meteorological input data were prepared using the CALMET meteorological model. The concentrations of aerosol-bound species such as NO3^-, NH4^＋, SO4^2-, and SOA were calculated in the fine particle size range （〈2.5 μm）. The results of the two-dimensional model were compared to the measurements at the ground level during the PRD Intensive Monitoring Campaign （IMC）. Overall, there were good agreements between the measured and modeled concentrations of inorganic aerosol components and O3. Both the measured and the modeled results indicated that the maximum hourly O3 concentrations exceeded the China National Air Quality Standard. The predicted 24-h average SOA concentrations were in reasonable agreement with those predicted by the method of minimum OC/EC ratio.

Aircraft Clean Air Requirements Using Bleed Air Systems

There are certification and airworthiness requirements relevant to the provision of clean breathing air in the crew and passenger compartments. There have been continuing reports and studies over the years regarding oil fumes in aircraft, including impaired crew performance. Oil fumes are viewed in varying ways ranging from rare seal bearing failures, to low level leakage in normal flight. A Masters of Science (MSc) research degree was undertaken to assess whether there is any gap between the certification requirements for the provision of clean air in crew and passenger compartments, and the theoretical and practical implementation of the requirements using the bleed air system. A comprehensive literature search reviewed applicable certification standards, documented and theoretical understanding of oil leakage. Two types of interviews were conducted to address the research questions. Key aviation regulators were questioned about the process by which they certify and ensure compliance with the clean air requirements. Aerospace engineers and sealing professionals were interviewed about their understanding of how oil may leak past compressor oil bearing seals, and into the air supply under various flight conditions. The outcome of the research showed that there is a gap between the clean air certification requirements, and the theoretical and practical implementation of the requirements using the bleed air system. Low level oil leakage into the aircraft cabin in normal flight operations is a function of the design of the engine lubricating system and bleed air systems, both utilising pressurised air. The use of the bleed air system to supply the regulatory required air quality standards is not being met or being enforced as required.

A new geometrical and mechanical relation in the respiratory system with airflow limitation—From the perspective of analytical respiratory mechanics

Classic respiratory mechanics is a branch of vectorial mechanics, which aims to recognize all forces acting on the respiratory system. Another branch of mechanics, analytical mechanics, has been used for analyzing the motions of complicated systems with constraints through equilibrium among scalar quantities such as kinetic energy and potential energy. However, until now, there have not been any studies concerning about analytical respiratory mechanics. In this paper, the author has obtained two types of motion equations (linear and nonlinear) for the airflow limitation from formulation of the analytical respiratory mechanics. Reconstructed flow-volume trajectories of the linear equation revealed a new relationship among the slope of the linear portion of trajectory, the coefficient of the dissipation function and the coefficient of the potential function. Reconstructed trajectories of the nonlinear equation suggested that a curved flow-volume trajectory would be caused by the emergence of regional hypoventilated clusters with airtrapped lobules. In conclusion, analytical respiratory mechanics will provide the basis for analyzing the mechanical properties of the respiratory system con cerning pulmonary functional images made by newly developed technologies.

空调二次泵系统在地铁车站中的应用

杭州地铁机场轨道快线工程杭州西站为地铁四线换乘车站,地铁车站体量大、空调系统末端多、运营要求高。针对本工程特点,经过比较分析水系统采用二次泵变流量系统,根据不同区域负荷特点和运营需求进行分区划分,可有效的降低空调水系统输送能耗,为运营后的稳定运行和场所管理创造了了良好条件。同时,文中给出了二次泵系统分区划分、设备选型及运行控制方案,并对选用条件进行了验证,可为类似工程提供参考。

低负荷下CFB锅炉二次风优化对NO_(x)排放影响的数值模拟

为控制循环流化床(circulating fluidized bed,CFB)锅炉低负荷下NO_(x)的原始排放,以某350 MW超临界CFB锅炉为研究对象,基于计算颗粒流体力学(computational particle fluid dynamics,CPFD)方法对40%负荷下燃烧过程进行数值模拟。分析了不同二次风角度、新增二次风量对NO_(x)排放的影响。结果表明:随着射流角度的减小,炉膛出口NO浓度逐渐降低,CO浓度无明显增加。部分二次风上移后炉膛密相区氧浓度降低,不完全燃烧增加,还原性氛围增强,抑制了NO的生成。当新增风量从10%增加到30%时,NO排放浓度降低了17.2%。但随着比例的进一步提高,炉膛密相区的缺氧环境造成燃烧效率下降,温度大幅降低。因此,在不影响燃烧的前提下可以通过提高新增二次风比例来降低NO的原始排放浓度。

黄河三角洲地区大气复合污染特征、成因与VOCs来源解析

为了解黄河三角洲区域细颗粒物(PM_(2.5))和臭氧(O_(3))大气复合污染特征和成因,本文利用2021年和2022年夏秋季黄河三角洲中心城市东营市、滨州市的挥发性有机物(VOCs)连续观测数据及常规污染物数据,识别对O_(3)和二次有机气溶胶(SOA)生成有显著贡献的VOCs物种并对VOCs进行来源解析,同时利用基于观测的化学盒子模型探讨O_(3)的生成敏感性.结果表明:①黄河三角洲地区PM_(2.5)和O_(3)浓度“双高”的大气复合污染主要出现在秋季,夏季东营市和滨州市首要污染物均为O_(3),距离入海口越远的站点O_(3)超标天占比越高;秋季东营市和滨州市首要污染物均为PM_(2.5),且超标情况相近.②烯烃和含氧挥发性有机物(OVOCs)对臭氧生成潜势(OFP)的贡献大,优势物种为乙醛;芳香烃对SOA生成潜势(SOAFP)的贡献大,优势物种为1,2,3-三甲苯.③东营市夏秋季O_(3)生成均处于VOCs和NO_(x)协同控制区,且夏季O_(3)对NO_(x)更为敏感;滨州市夏秋季O_(3)生成分别处于VOCs和NO_(x)协同控制区、VOCs控制区,且夏季O_(3)对NO_(x)敏感性更高,秋季对VOCs敏感.④油气挥发源、工业排放源和机动车尾气排放源为该区域VOCs的主要来源,且VOCs来源解析结果存在空间上和季节上的差异.夏季,区域溶剂源和生物源VOCs的贡献率增加,东营市溶剂源贡献率(28.2%)明显高于滨州市(6%),机动车尾气排放源贡献率(11.5%)低于滨州市(29.6%);秋季,区域燃烧源和生物质燃烧源贡献率增加,东营市(25.9%)油气挥发源贡献率明显低于滨州市(42.4%).研究显示,黄河三角洲地区夏季应实施VOCs和NO_(x)的协同减排,秋季应优先控制VOCs排放;其次需要加强对油气挥发源、工业排放源和机动车尾气源VOCs的管控.

基于粉管动压和煤粉分配的热态条件下中速磨煤机入口风量标定试验方法

针对中速磨煤机输运介质特点及入口管路、空间等限制,冷态纯空气条件下的测试方法无法保证磨煤机入口风量标定测试及时性的问题,热态运行工况下,选取流场稳定的磨煤机出口管道,采用等截面网格法测试各粉管动压和煤粉分配特性,并用循环迭代法获取风粉混合物流速,最终以实测的磨煤机出口风粉混合物流量与煤量、设计密封风量的差值对磨煤机入口风量进行标定。试验结果表明,在相同的实测原始数据基础上,采用上述方法获取的磨煤机入口流量更接近真实值,准确性较采用冷态纯空气条件下的计算结果提升约15百分点。该方法测试简单,实操性强,可有效提升中速磨煤机入口风量标定结果的准确性和及时性,同时,对相似工业环境中含粉气流流量的测试也有一定的指导作用。

燃煤锅炉燃烧利用矿井乏风甲烷改造经济性及运行影响分析

为处理矿井大流量乏风中的超低浓度甲烷,拟采用将乏风作为锅炉二次风进行处理利用。对此类工程改造的锅炉引风、投资运行成本、项目改造收益、锅炉效率影响进行了分析。结果表明,矿井乏风甲烷利用工程改造减小了原来锅炉烟气的产生量,且烟气量改变很小,无需对锅炉侧进行改造。管道及保温材料的采购与安装是此类改造工程的主要投资部分。该类项目的主要收益为乏风处理的碳汇补贴收益。乏风流速越低,工程投资成本变高,但运行成本变低,有助于项目的长周期盈利。绘制了不同输运长度下乏风总量与瓦斯绝对涌出量的20年期盈利平衡曲线。提出了优化矿井侧及二次风侧的乏风输送系统,并对乏风温度、湿度等因素对锅炉效率的影响进行了分析。对矿井乏风利用项目的立项及可行性分析提供了指导。