燃焦炉煤气锅炉尾部受热面和烟道的腐蚀及对策

0引言 在目前的燃焦炉煤气锅炉中,空气预热器都安装在锅炉对流烟道的最后面,进入该部的烟气温度不高,故将其称为低温受热面或尾部受热面。而该受热面最容易出现的影响锅炉运行的故障就是低温腐蚀和堵塞。烟道处于空气预热器后、引风机前,烟气温度相对较低,更易出现低温腐蚀。     

层燃锅炉受热面结焦堵灰原因分析和清除措施

<正> 层然锅炉的燃煤入炉经过燃烧后,大部分炉渣由炉徘排掉,但仍有部分飞灰因燃烧情况的不同,随着烟气的流程在辐射受热面、对流受热面、省煤器、空气预热器、过热器上不同程度的发生结焦或堵灰.从而使     

CFB锅炉防磨技改工程

我厂2×35 t/h CFB锅炉受热面磨损严重,低温过热器及省煤器的频繁泄漏、爆管事故长期困扰热电厂锅炉的安全、经济运行,降低热电厂开车率。 为减缓锅炉受热面管壁的磨损,延长受热面寿命,根据CFB锅炉受热面磨损机理,采用主动与被动两种的防磨措施,降低受热面磨损速度,延长电厂锅炉的运行周期,达到热电厂安全、经济、稳定运行的目的。 所谓主动措施系指通过改进不合理结构,降低烟气流速,降低烟气含尘浓度等措施。这是降低受热     

基于热力学第二定律的ORC蒸气发生器性能优化

为了更深入地研究低温余热驱动ORC系统的设计与优化,建立了有机朗肯循环蒸气发生器主要热力性能计算模型,基于热力学第二定律,以蒸气发生器单位换热面积工质?升作为性能优化目标函数,选取了R245fa作为循环工质,在给定烟气进口温度以及保证循环工质在蒸气发生器出口为饱和蒸气条件下,对不同工况下的工质质量流速进行优化,并分析了在一系列换热管管径下,烟气入口温度、工质入口压力、管外对流传热系数、单根换热管烟气质量流量对目标函数及工质最优质量流速的影响。结果表明：工质入口压力与管外对流传热系数对最优工质质量流速影响显著,随着工质入口压力与管外对流传热系数的增大,最优工质质量流速增大,对应的换热管径减小;而烟气入口温度、单根换热管烟气质量流量对最优工质质量流速影响甚微。     

基于热力学第二定律的ORC蒸气发生器性能优化

为了更深入地研究低温余热驱动ORC系统的设计与优化,建立了有机朗肯循环蒸气发生器主要热力性能计算模型,基于热力学第二定律,以蒸气发生器单位换热面积工质?升作为性能优化目标函数,选取了R245fa作为循环工质,在给定烟气进口温度以及保证循环工质在蒸气发生器出口为饱和蒸气条件下,对不同工况下的工质质量流速进行优化,并分析了在一系列换热管管径下,烟气入口温度、工质入口压力、管外对流传热系数、单根换热管烟气质量流量对目标函数及工质最优质量流速的影响。结果表明:工质入口压力与管外对流传热系数对最优工质质量流速影响显著,随着工质入口压力与管外对流传热系数的增大,最优工质质量流速增大,对应的换热管径减小;而烟气入口温度、单根换热管烟气质量流量对最优工质质量流速影响甚微。     

增压强化烟气对流传热机理及其计算方法

增压锅炉装置因其容积热负荷高、体积小、质量轻等优点广泛应用于大中型船舶主动力装置。利用分子动力学原理及流体分子微观理论与性质,分析了增压对烟气导热与热对流的影响机理,并利用Illes教授与前苏联的两种计算方法,分别计算了不同增压比下增压锅炉对流受热面烟气流速、密度以及传热系数等参数并进行了对比。经分析可知烟气压力的提高使分子碰撞频率增加、平均自由程减小、烟气密度增大,从而对流传热得到强化。同时计算结果表明烟气压力较低时两方法计算结果相差不大,但在压力接近0.3 MPa时,Illes教授推荐的热力计算方法所得传热系数可达到前苏联方法的1.3倍。     

超临界压力注汽锅炉膜式水冷壁传热特性数值模拟研究

由于体积较大,超临界压力油田注汽锅炉在采油现场的运输较为困难。本文将辐射段水平受热面水冷壁设计为膜式结构,增大了水冷壁角系数和吸热量,减小了对流段所需换热面积,对油田注汽锅炉进行了小型化改造。本文利用ANSYS 14.5件对单根管(φ89 mm×12 mm×2500 mm)与管内26 MPa超临界水的传热进行研究,得到了膜式水冷壁危险点温度与入口处工质温度(550K、600K、650K)、入口处工质流量(100%Q_(m0)、70%Q_(m0)、50%Q_(m0))之间的关系,确定了不同工况下的危险点及温度。本文为油田注汽锅炉水冷壁结构设计及其小型化改造提供参考。     

导热油炉的传热计算分析

分析了导热油炉的传热计算方法,包括炉子热平衡、炉膛辐射换热和对流换热计算。并论述了炉膛出口烟气温度、炉膛辐射受热面、对流段烟气流速和排烟热损失等问题。     

载热体加热炉对流受热面中的烟气流速分析

分别介绍了载热体加热炉对流受热面中的无灰燃料最佳烟气流速，有灰燃料烟气的极限流速，空气预热器中烟气流速和空气流速的选取。     

基于离散元方法的高碱煤灰沉积过程数值模拟研究

针对锅炉燃用高碱煤产生的受热面积灰问题,以流化床锅炉对流过热器为研究对象,采用离散元方法（discrete element method）建立黏性颗粒碰撞黏附模型,对过热器对流受热面的积灰过程进行数值模拟。分别研究了烟气流速、颗粒粒径、烟气温度以及壁面温度对积灰特性的影响规律。模拟结果表明：烟气流速增大、颗粒粒径减小会导致颗粒的碰撞率上升、捕集率下降;烟气温度和壁面温度提升时,颗粒表面能上升,导致颗粒捕集率上升,且壁面温度的影响更为显著;不同工况下最大积灰厚度、沉积物形状变化较小。     

Observation of Cell Structures Developed by Marangoni Convection in Glass Thick Films

Cell structures developed by convection in glass thick films have been studied with special emphasis on the effects of material parameters and heating conditions on the cell structure. Borosilicate glass films from 10 to 30 μm thick were prepared on alumina substrates by printing and firing at temperatures between 750° and 950°C up to 2 h, and surface flow patterns were observed with an optical microscope under dark-field illumination. In most cases a flow pattern developed and changed with time, finally reaching a steady state. Cell structures with regular polygons of four to seven sides from 15 to 150 μm across developed, depending on the glass composition. The effects of heating time, temperature, film thickness, and glass chemistry on the cell structure have been examined. From observations of cell structures, the driving force for the convection in glass thick films has been identified to be the gradient in surface tension due to small temperature fluctuations on the surface. Hence, it is concluded that the convection in glass thick films is of Marangoni type.     

Numerical study on effects of coal properties on spontaneous heating in longwall gob areas

A computational fluid dynamics (CFD) study was conducted to model effects of coal properties on the potential for spontaneous heating in longwall gob (mined-out) areas. A two longwall panel district using a bleeder ventilation system was simulated. The permeability and porosity profiles for the longwall gob were generated from a geotechnical model and were used as inputs for the three-dimensional CFD modeling. The spontaneous heating is modeled as the low-temperature oxidation of coal in the gob using kinetic data obtained from previous laboratory-scale spontaneous combustion studies. Heat generated from coal oxidation is dissipated by convection and conduction, while oxygen and oxidation products are transported by convection and diffusion. Unsteady state simulations were conducted for three different US coals and simulation results were compared with some available test results. The effects of coal surface area and heat of reaction on the spontaneous heating process were also examined.     

Physicochemical properties of edible films from chitosan composites obtained by microwave heating

Summary  Chitosan films were prepared by casting, using microwave and dried by air convection. No scientific literature covers the use of microwave heating in the preparation of chitosan films by casting technique. Effects of heating time, molecular weight and plasticizer on structure, thermal behavior, surface, barrier properties and light transmission were investigated. Heating time showed that the microwave heating did not affect the structural composition and thermal decomposition of chitosan films. UV-vis light barrier properties, equilibrium moisture content and water vapor permeability varied significantly with the heating treatment. Surface film analysis revealed no captured differences between different heating treatments.     

THE RELATIVE MAGNITUDE OF RADIATION AND CONVECTION HEATING IN A MUFFLE KILN1

Rates of Heating by Convection and by Radiation in a Muffle Kiln, 38°×18°× 36° high, were each determined for temperatures from 350° to 800°C from measurements with a steady flow water calorimeter whose surface was first gold plated and then covered with a mixture of platinum black and lamp black. Taking the reflecting powers as 91 and 4 per cent, respectively, for the two surfaces, the radiation heating increases approximately according to the Stefan-Boltzmann fourth power law, while the convection heating comes out proportional to the temperature difference between calorimeter and muffle; that is, C=γ(T-t) where γ= 2.34×10⁻⁴ gm. cal./cm.² sec. The ratio of convection to radiation decreases from about .40 at 350° to .10 at 800°C, so that for the higher temperatures the convection heating may be neglected in rough computations of the rate of heating in such a kiln.     

Forced convection subcooled boiling of binary mixtures

A mode based on an additive mechanism of heat transfer is proposed for forced convection subcooled boiling of binary mixtures. The contributing modes of heat transfer are: (i) the heat transferred as latent heat by the rising bubbles, (ii) the heat transferred as the heat contained in the superheated thermal layer that is removed from the surface in the wake of the rising bubbles and (iii) the single phase forced convection heat transfer from the heating surface not influenced by the bubbles. Experimental data from the literature on binary systems show good agreement with the model, validating the postulated mechanism.     

Analysis of Thermal Stress Resistance of Partially Absorbing Ceramic Plate Subjected to Asymmetric Radiation, II: Convective Cooling at Front Surface

Thermal stresses in a partially absorbing brittle ceramic plate asymmetrically heated by radiation and cooled by convection on the same surface with finite and infinite heat transfer coefficients are analyzed. Comparison of the results from this study with those obtained in Part I, where the plate is subjected to radiation heating in the front surface and cooled by convection at the rear surface, indicates that the magnitudes of the maximum steady-state tensile thermal stresses are nearly identical. Significant differences are found in the transient thermal stresses and the temperature distribution. The relative temperature levels in the present case are found to be significantly lower than those obtained in Part I. Implications of these results to the design and operation of engineering structures such as concentrated solar receivers are discussed.     

蒸馏装置常压炉新增冷进料改造方案核算与探讨

加热炉的能耗问题是炼油厂非常关键的问题,将需要加热的低温介质脱后原油引入对流室末端,将增加对流室吸收热量,对提高管式炉热效率,减少燃料消耗具有重要的意义。对已建炼油厂管式加热炉新增冷进料技术改造应注意的问题进行初步探讨,并提出相应措施。     

Study of heat and mass transfer from sugarcane juice for evaporation

The study of heat and mass transfer during natural convection heating for preparation of Jaggery was carried out for the open and closed conditions. An indoor experiment was conducted for simulation of developed thermal model for heat and mass transfer for maximum evaporation. Evaporated water was condensed at the inner surface for the closed system as fresh water. The effect of different rates of heating (varying voltage) and heat capacity of sugar cane juice on heat and mass transfer were also carried out. It was observed that the evaporative heat transfer coefficient depends significantly on the rate of heating and heat capacity.     

富氧燃烧技术在锅炉节能方面的应用探讨

介绍了富氧燃烧方式的技术特点,对其节能机理进行了较为详细的阐述,并以某电站300MW电站锅炉为例,采用ASMEPTC4-1998得出了空气和富氧（30%O2/70%CO2）2种气氛下锅炉的热效率,详细计算分析了煤粉在空气气氛和富氧气氛下锅炉各受热面的传热特性。计算结果表明：采用O2/CO2的富氧燃烧技术可大大提高锅炉热效率,且锅炉的辐射吸热量增加、对流吸热量降低,在炉内的辐射受热面积变化不大的情况下,锅炉的对流受热面积降低很多,同时烟气中高浓度的CO2将会降低分离回收CO2的成本。     

加热方式对管壳式相变蓄热单元强化传热的可视化及数值模拟

为了提高相变蓄热系统在实际应用中的蓄热速率,本文建立了管壳式相变蓄热单元可视化实验平台,提出了一种外部加热法的强化传热方式,讨论了相变蓄热单元在外部加热法时的熔化特性和传热机理。通过Fluent软件模拟对比了外部加热法和内部加热法在熔化过程中的液相分数、熔化速率和均匀性等方面的差异。研究结果表明：外部加热法的使用能大幅提升蓄热单元的蓄热效率。与内部加热法相比,外部加热法在熔化过程中的传热和相变更加均匀。相比于内部加热法,由于外部加热法传热面积较大,熔化时间缩短了69.1%;在消除传热面积的影响后,外加热方法依靠广泛而强烈的自然对流使熔化时间减少了23.2%。