蒸汽二次风在锅炉中的应用

介绍了蒸汽二次风的原理及特性,分析了蒸汽二次风在锅炉中的作用,此技术结构简单、安装方便、节能效果显著,同时还阐述了蒸汽二次风在应用中应注意的问题。     

Monitoring of transient temperature and thermal stresses in pressure components of steam boilers

Two methods of solving the transient inverse heat conduction problens in complex shaped elements are presented in this paper. The time-space temperature distribution in whole element cross-section is reconstructed using the measured temperature histories at several points placed inside the element or on its easily accessible outer surface. Thermal stresses are then evaluated involving Finite Element Analysis. In both methods the heat transfer coefficient at the element inner surface is the unknown value. Four examples are presented, two for one method showing the high accuracy of the presented methods and possibility of their practical application.     

角管式蒸汽锅炉汽水分离装置的设计特点

角管式锅炉由于设计了炉外再循环系统,减少了进入锅筒的汽水混合物数量,降低了汽水混合物的动能,在达到同样目的的情况下,锅内分离设备变得十分简单,不仅降低了锅内设备的耗钢量和制造工作量,而且缩小了锅筒直径及壁厚.根据锅筒内部汽水分离原理以及由各分离原理衍生的分离方法,分析和介绍了角管式锅炉锅内装置的设计理念,供业内人士参考...     

Estimation of performance of steam turbines using a simple predictive tool

Mechanical drive steam turbines are major prime movers for compressor, blower, and pump applications. Steam turbines are available for a wide range of steam conditions, power ratings and speeds. In this work, a simple predictive tool, which is easier than existing approaches, less complicated with fewer computations, is presented for rapid prediction of steam rate, turbine efficiency, and the inlet and exhaust nozzle diameters to determine the actual steam rate (ASR) and total steam requirements for both multi-stage and single-stage turbines. The proposed method predicts the above mentioned parameters for inlet steam pressures up to 12,000 kPa, turbine ratings up to 10,000 kW as well as the exhaust air over inlet air ratios of up to 0.55. The predictions from the proposed predictive tool have been compared with reported data and found good agreement with average absolute deviation hovering around 1.4%.     

电站锅炉蒸汽吹灰器压损问题分析与处理

本文通过结合某电站工程锅炉蒸汽吹灰器出现的压损问题,从吹灰器本体与管路参数匹配性和压损问题位置查找两方面进行分析,找出压损问题根本原因,并制定针对性处理措施,为后续电站锅炉蒸汽吹灰器同类问题处理和质量控制提升提供宝贵借鉴参考.     

Theoretical evaluation of various configurations of silica membrane reactor in methanol steam reforming using CFD method

The main purposes of this work was to evaluate from a theoretical point of view the performance of silica membrane reactors (MRs) in various configurations for generating hydrogen via methanol steam reforming (MSR) reaction using a two dimensional computational fluid dynamic (CFD) method, presenting details about molar fractions of gas species, velocity and pressure distributions at the simulated conditions. The CFD model was firstly validated and, then, used for the simulations, achieving an acceptable agreement between numerical outcomes and experimental data. The simulations were realized for MSR reaction carried out in three types of silica MRs, namely: 1) silica MR with cocurrent flow pattern (MR1); 2) silica MR with countercurrent flow pattern (MR2); 3) silica MR with countercurrent flow pattern including a water gas shift (WGS) reaction stage in the permeate side (MR3), meanwhile comparing the results with a traditional reactor (TR). The influence of several operating parameters (reaction temperature and pressure, and feed flow rate) on the performance of the aforementioned silica MRs in terms of methanol conversion, hydrogen yield and CO-selectivity was evaluated and the results compared with an equivalent TR. The simulations via CFD method indicated the MR3 results to be the best solution over the other MR proposed configurations and the TR as well, presenting the best simulation results at 10 bar of transmembrane pressure, 513 K, SF = 6, GHSV = 6000 h⁻¹ and feed molar ratio = 3/1 with CO selectivity ≤0.04%, methanol conversion and hydrogen yield >90%.     

Optimum heating of pressure components of steam boilers with regard to thermal stresses

A method for determining time–optimum fluid temperature changes is presented. In contrast to current standards, stepwise fluid temperature changes are allowed. The optimum fluid temperature changes are assumed in the form of a simple time function. It is possible to increase the fluid temperature stepwise, and then the fluid temperature can be increased with a constant rate at the beginning of the heating process. The permissible rates of the fluid temperature change determined by the proposed method are smaller than those obtained by boiler standards. But, due to the abrupt increase in fluid temperature, the heating time of a thick-walled component is of the same order as in the case of calculations according to EN 12952-3 European Standard. However, the total circumferential stresses on the edge of the hole do not exceed the allowable value.     

Linear correlation of heat transfer and friction in helically-finned tubes using five simple groups of parameters

A linear regression approach was used to correlate experimentally-determined Colburn j-factors and Fanning friction factors for flow of liquid water in helically-finned tubes. Experimental data came from eight enhanced tubes with helix angles between 25° and 48°, number of fin starts between 10 and 45, fin height-to-diameter ratios between 0.0199 and 0.0327, and Reynolds numbers ranging from 12,000 to 60,000. The current study revealed that, in helically-finned tubes, logarithms of both friction and Colburn j-factors can be correlated with linear combinations of the same five simple groups of parameters and a constant. The proposed functional relationship was tested with independent experimental data yielding excellent results.     

Prediction of compressed air transport properties at elevated pressures and high temperatures using simple method

Compressed air energy storage is a way to store energy generated at one time for use at another time. At utility scale, energy generated during periods of low energy demand can be released to meet higher demand periods. Also compressed air is a commonly used utility across most manufacturing and processing industries as its production and handling are safe and easy. Compressed air systems are critical and play a pivotal role in the proper operation of many processing facilities since most of the instruments and controls depend on pressurized instrumentation air for operation. In this work, a simple predictive tool, which is easier than current available models involving a large number of parameters, requiring more complicated and longer computations, is presented here for the prediction of transport properties (namely thermal conductivity and viscosity) of compressed air at elevated pressures as a function of temperature and pressure using a simple Arrhenius-type function. The proposed correlation predicts the transport properties of air for temperature range between 260 and 1000 K, and pressures up to 1000 bar (100 MPa). Estimations are found to be in excellent agreement with the reliable data in the literature with average absolute deviation being around 1.28% and 0.68% for thermal conductivity and viscosity respectively.     

排烟中水蒸气汽化潜热的回收与燃油燃气锅炉热效率的改善

锅炉的热效率在很大程度上取决于排烟热损失的大小。把排烟温度降至水露点以下 ,不仅可以减少排烟中不凝气体的显热 ,而且可以回收排烟中水蒸气的潜热 ,因而能大幅度减小排烟热损失和提高锅炉热效率。燃油燃气锅炉排烟中水蒸气含量比较多 ,热效率改善效果更显著。但必须采取适当的措施防止凝结下来的硫酸和亚硫酸对低温受热面的酸腐蚀。     

闭式回收技术在蒸汽冷凝水回收利用中的应用

分析了企业蒸汽冷凝水排放和利用的现状,提出采用闭式回收蒸汽冷凝水技术对全厂蒸汽冷凝水系统进行改造。结果表明,采用闭式回收技术,各路蒸汽冷凝水可以完全得到回收,并用于工艺管线和设备的伴热;伴热温度均在规定的范围之内,伴热后的热水用于橡胶生产之中,起到了节能节水的作用。     

Prediction of the effective coefficient of thermal expansion of heterogeneous media using two-point correlation functions

Statistical continuum mechanics is used to predict the coefficient of thermal expansion (CTE) for solid oxide fuel cell glass-ceramic seal materials with different morphology and crystallinity. Two-point correlation functions are utilized to represent the heterogeneous microstructure morphology and phase distribution. The model uses two-point correlation functions in conjunction with local properties to predict the effective CTE. Prediction results are comparable to experimental CTE results. The advantage of using the statistical continuum mechanics model in predicting the effective properties of anisotropic media is shown, using the ability to take the microstructure into consideration.     

Prediction of PVT properties for dissociated steam by molecular simulation

A water molecule is dissociated at high temperatures. The PVT properties of dissociated steam have been calculated with molecular simulation of the general Monte Carlo method using the 1 center Lennard–Jones 12‐6 potential model for temperatures from 1000 K to 3000 K at pressures from 0.1 MPa to 300 MPa. The uncertainty in density calculations with NPT ensemble is estimated to be ±1%. Density values of dissociated steam become smaller than those of pure steam with increasing temperature and decreasing pressure. Percentage deviation of density for dissociated steam from density for pure steam at 3000 K and 0.1 MPa is calculated to be 17.1%. Comparison of density between the present calculations and values in thermophysical property tables by Vargaftik is reported. © 2000 Scripta Technica, Heat Trans Asian Res, 29(3): 181–192, 2000     

基于改进差分极端学习机的燃煤锅炉NOx预测

低NOx燃烧优化是一种简单、高效、廉价的燃煤电站NOx减排方法.建立NOx预测模型是该方法的重要组成部分.极端学习机(extreme learning machine,ELM)是一种简单有效的建模方法,但随机生成的输入权值和隐层阈值会影响ELM的泛化性能和逼近能力.针对该问题,利用一种改进的差分进化算法(improve...     

Prediction of the heat flux profile on the furnace wall of circulating fluidized bed boilers

The purpose of this work is to investigate and develop a correlation for predicting the profile of heat flux on the crest of the membrane water wall tube along the height of circulating fluidized bed furnaces. The heat conduction equation for the tube was solved numerically under various operating conditions and furnace sizes. It was found that the temperature and heat flux profiles decreased rapidly in the region above the secondary air ports and then were found to be nearly constant. In addition, the heat flux increased as the Froude number increased or as the bed particle to the furnace diameter ratio decreased. The results were used to develop a correlation for predicting the heat flux profiles of the boilers having capacities from 12 MW_th to 165 MW_th in terms of dimensionless temperature, the Froude number, the diameter ratio and the height from the ports to the total height ratio.     

Prediction of selling price of hydrogen produced from methanol steam reforming

Hydrogen is a clean energy carrier. However, it is not naturally available and should be supplied from other organic materials such as biomass or other chemicals such as dimethyl ether. In this article, we estimated the selling price of hydrogen produced by methanol steam reforming and evaluated the effect of some influential factors on selling price using Aspen Plus. Validation process showed that the model and experimental results well agree with each other, especially in high temperatures where reaching equilibrium is followed more rapidly. Similar to temperature, pressure can directly affect the economics of methanol synthesis. As pressure increases from 5 atm to 20 atm, selling price decreases.     

CFB锅炉应用福建无烟煤的技术探讨

本文根据试验结果 ,总结循环流化床锅炉应用我省无烟煤的运行经验 ,针对福建无烟煤的难燃特性 ,在大型循环流化床锅炉设计中如何降低飞灰含炭量 ,提高燃烧效率提出了一些建议。     

Porous bamboo-like CNTs prepared by a simple and low-cost steam activation for supercapacitors

How to prepare porous carbons with appropriate structure for supercapacitors is a big challenge. In general, activation is the simplest way to obtain porous carbons. Porous bamboo-like CNTs were fabricated by simple activating sulfonated polymer nanotubes with steam at 800°C. Compared with the un-activated one, activated carbon nanotubes (ACNTs) have good tubular structure, larger specific surface area and rich porosity thanks to the protection of steam during the activation. The ACNTs electrode for supercapacitors displays a specific capacity of 276 F g⁻¹ at 1 A g⁻¹. When assembling ACNTs into a symmetrical supercapacitor, the specific capacity of the device can retain 98% after 10 000 cycles, and this result shows the great application prospect of ACNTs for supercapacitors.     

燃煤锅炉房自身排放碱性物质的脱硫工艺及其应用

主要介绍利用锅炉燃煤灰渣及排污水中碱性物质脱硫工艺,以达到以废治废,降低脱硫运行费用的目的,同时还对灰渣中碱性物质溶出量的有关影响因素及其脱硫机理进行了探讨。