Combustion and energy balance of aluminum holding furnace with bottom porous brick purging system

For acquiring the details in aluminum holding furnace with bottom porous brick purging system, efforts were performed to try to find out the potential optimal operation schemes. By adopting transient analysis scheme and constant boundary temperature, combustion in the furnace was investigated numerically using computational fluid dynamics (CFD). The predicted gas temperature shows good agreement with the measured results, and the predicted energy distribution of the furnace is consistent with that obtained from energy balance experiment, which confirms the reliability of the numerical solution. The results show that as the fuel-air mixture temperature rises up from 300 K to 500 K, the energy utilization of the furnace could increase from 34.55% to 37.14%. However, as the excess air coefficient increases from 1.0 to 1.4, energy utilization drops from 34.55% to 29.56%. Increasing the combustion temperature is the most effective way to improve the energy efficiency of the furnace. High reactant temperature and medium excess air coefficient are recommended for high operation performance, and keeping the furnace jamb sealed well for avoiding leakage has to be emphasized.     

Dynamic simulation on effect of flame arrangement on thermal process of regenerative reheating furnace

By analyzing the characteristics of combustion and billet heating process, a 3-D transient computer fluid dynamic simulation system based on commercial software CFX4.3 and some self-programmed codes were developed to simulate the thermal process in a continuous heating furnace using high temperature air combustion technology. The effects of different switching modes on injection entrancement of multi burners, combustion and billet heating process in furnace were analyzed numerically, and the computational results were compared with on-site measurement, which verified the practicability of this numerical simulation system. The results indicate that the flow pattern and distribution of temperature in regenerative reheating furnace with partial same-side-switching combustion mode are favorable to satisfy the high quality requirements of reheating, in which the terminal heating temperature of billets is more than 1 460 K and the temperature difference between two nodes is not more than 10 K. But since the surface average temperature of billets apart fi＇om heating zone is only about 1 350 K and continued heating is needed in soaking zone, the design and operation of current state are still needed to be optimized to improve the temperature schedule of billet heating. The distribution of velocity and temperature in regenerative reheating furnace with same-side-switching combustion mode cannot satisfy the even and fast heating process. The terminal heating temperature of billets is lower than that of the former case by 30 K. The distribution of flow and temperature can be improved by using cross-switching combustion mode, whose terminal temperature of billets is about 1 470 K with small temperature difference within 10 K.     

The study on Sanmenxia annual flow forecasting in the Yellow River with mix regression model

This paper established mix regression model for simulating annual flow, in which annual runoff is auto-regression factor, precipitation, air temperature and water consumption are regression factors; we adopted 9 hypothesis climate change schemes to forecast the change of annual flow of Sanmenxia Station. The results show: (1) When temperature is steady, the average annual runoff will increase by 8.3% if precipitation increases by 10%; when precipitation decreases by 10%, the average annual runoff will decrease by 8.2%; when precipitation is steady, the average annual runoff will decrease by 2.4% if temperature increases 1°C; if temperature decreases 1°C, runoff will increase by 1.2%. The mix regression model can well simulate annual runoff. (2) As to 9 different temperature and precipitation scenarios, scenario 9 is the most adverse to the runoff of Sanmenxia Station of Yellow River; i.e. temperature increases 1°C and precipitation decreases by 10%. Under this condition, the simulated average annual runoff decreases by 10.8%. On the contrary, scenario 1 is the best to the enhancement of runoff; i.e. when temperature decreases 1°C precipitation will increase by 10%, which will make the annual runoff of Sanmenxia increase by 10.6%.     

W火焰锅炉炉内三维流场和颗粒运动轨迹的数值模拟

W火焰锅炉具有独特的炉膛和烟气流动结构,适用于低挥发份劣质煤发电,炉膛配风和煤粉颗粒对W火焰锅炉形成良好的炉内燃烧和保证安全高效洁净燃烧影响显著.针对300 MW W火焰锅炉,采用RNGk~ε和DPM模型数值研究了不同工况下W火焰锅炉炉内三维流场和煤粉颗粒运动轨迹,分析了炉膛配风和煤粉粒径对流场特性的影响.研究表明:配风对流场对称性影响很大,不合理的配风可导致火焰"短路"和气流冲刷冷灰斗.炉膛折焰角结构决定了对称的配风形成非对称流场,但增加前墙配风速度可有效平衡折焰角效应.当前后墙配风比为1.05时流场对称性最佳.下炉膛冷灰斗区双旋涡流动结构可增强煤粉气流热质交换,增加煤粉停留时间,有利于煤粉燃尽.随粒径增大,煤粉深入下炉膛平均深度越大,煤粉在燃烧炉膛内停留时间先增大后减小,存在最佳煤粉粒径.研究结果对大容量W火焰锅炉设计和燃烧调整有意义.     

Shrinkage Behavior of High Performance Concrete at Different Elevated Temperatures under Different Sealing Conditions

The shrinkage behavior of high performance cement concrete made from Portland cement, ultra fine granulated blast furnace slag and pulverized fly ash with addition of superplasticizer at different temperatures from ambient temperature to 120 ℃ under different seuliug conditions was investigated by means of length change measurement on cylindrical concrete specimens along with curing age. Results show that drying shrinkage deformations of titled concrete specimens increased rapidly as the curing temperature rose. The development of dryiing shrinkage deformatian can be efficiently controlled with the aid of aluminum tape sealing as compared with the unsealed specimens, especially when the curing temperature is below 60℃ , although it will increase dramatically when the curing temperature is elevated to above 90%＂ . Polymer coating on concrete specimens showed a similar effect on the control of drying shrinkage as the sealing operation with aluminum tape.     

逆向式蓄热高温空气燃烧换向的动态分析

模拟了逆向式蓄热高温空气燃烧换向的动态燃烧特性．研究表明,随着时间的推移,炉膛内火焰的最高温度降低,平均温度升高,炉膛温度变得更加均匀;随着氧气质量分数的降低,氮氧化物质量分数随时间变化产生的变化幅度减小,燃烧变化更加平稳;随着预热空气温度上升,炉膛内的最高温度和平均温度都有不同程度的上升,氮氧化物生成量也相应增加,但随着氧气质量分数降低,影响逐步减小．在燃料速度为0．25、0．5 m／s对比分析中,综合考虑了温度场、氮氧化物和二氧化碳的质量分数,在低氧条件下应优先采用燃料速度为0．25 m／s的燃烧方式．     

某2 027 t/h锅炉变工况掺烧污泥燃烧特性研究

采用Fluent软件,针对某2 027 t/h四角切圆煤粉锅炉不同负荷下单独燃烧煤粉、煤粉和污泥混烧工况进行了数值模拟,研究了炉内流动、燃烧和NOx排放特性。结果表明：模型能够模拟锅炉燃烧过程,模拟误差在10%以内;掺混污泥对炉内速度场影响较小,掺混污泥后,水分蒸发吸热,炉膛整体温度水平下降,中上层燃烧器区域CO和HCN生成量增加,还原性气氛增强,NOx生成受到抑制;掺混10%比例污泥后,600 MW,510 MW,450 MW工况下平均温度峰值分别降低了15.5 K,8.2 K,3.1 K,NOx排放分别降低10.9%,13.1%,8.1%。     

Combustion characteristics of semicokes derived from pyrolysis of low rank bituminous coal

Various semicokes were obtained from medium-low temperature pyrolysis of Dongrong long flame coal. The proximate analysis, calorific value and Hardgrove grindability index (HGI) of semicokes were determined, and the ignition temperature, burnout temperature, ignition index, burnout index, burnout ratio, combustion characteristic index of semicokes were measured and analyzed using thermogravimetry analysis (TGA). The effects of pyrolysis temperature, heating rate, and pyrolysis time on yield, composition and calorific value of long flame coal derived semicokes were investigated, especially the influence of pyrolysis temperature on combustion characteristics and grindability of the semicokes was studied combined with X-ray diffraction (XRD) analysis of semicokes. The results show that the volatile content, ash content and calorific value of semicokes pyrolyzed at all process parameters studied meet the technical specifications of the pulverized coal-fired furnaces (PCFF) referring to China Standards GB/T 7562-1998. The pyrolysis temperature is the most influential factor among pyrolysis process parameters. As pyrolysis temperature increases, the yield, ignition index, combustion reactivity and burnout index of semicokes show a decreasing tend, but the ash content increases. In the range of 400 and 450 °C, the grindability of semicokes is rational, especially the grindability of semicokes pyrolyzed at 450 °C is suitable. Except for the decrease of volatile content and increase of ash content, the decrease of combustion performance of semicokes pyrolyzed at higher temperature should be attributed to the improvement of the degree of structural ordering and the increase of aromaticity and average crystallite size of char. It is concluded that the semicokes pyrolyzed at the temperature of 450 °C is the proper fuel for PCFF.     

Preparation and characterization of Bi4Ti3O12 platelets by a novel low-temperature molten salt system

Bismuth titanate (Bi₄Ti₃O₁₂) platelets were prepared by molten salt method in a new salt system of CaC_l2-NaCl at 650–750 °C, using bismuth nitrate pentahydrate (Bi(NO₃)₃―H₂O) and titanium butoxide (Ti (OC₄H₉)₄) as raw materials. The synthesis temperature of Bi₄Ti₃O₁₂ platelets was decreased to 650 °C from 900–1100 °C. The phase compositions and crystalline morphology of Bi₄Ti₃O₁₂ platelets were investigated by XRD and SEM. The experimental results indicate that Bi₄Ti₃O₁₂ platelets containing tetragonal and orthorhombic phase with the size of 1–3 μm can be synthesized at 650 °C for 2 h, and the orthorhombic phase becomes the dominant phase at 750 °C for 5 h. The size and proportion of Bi₄Ti₃O₁₂ platelets increase with the increment of the calcining temperature and holding time. The proportion of platelets increases to about ninety percent, and the platelets grow up to about 3–10 μm at 750 °C for 5 h from 1–2 μm at 650 °C for 2 h. This technical route provides a new low-temperature molten salt system for preparing platelets by molten salt methods.     

Numerical simulation of heat transfer process in cement grate cooler based on dynamic mesh technique

A grate cooler is key equipment in quenching clinker and recovering heat in cement production. A two-dimensional numerical model based on a 5000 t/d cement plant is proposed to for a study on the gas-solid coupled heat transfer process between the cooling air and clinker in a grate cooler. In this study, we use the Fluent dynamic mesh technique and porous media model through which the transient temperature distribution with the clinker motion process and steady temperature and pressure distribution are obtained. We validate the numerical model with the operating data of the cooling air outlet temperature. Then, we discuss the amount of mid-temperature air outlet and average diameter of clinker particles, which affect the heat effective utilization and cooling air pressure drop in clinker layer. We found that after adding one more mid-temperature air outlet, the average temperature of the air flowing into the heat recovery boiler increases by 29.04°C and the ratio of heat effective utilization increases by 5.3%. This means heat recovery is more effective on adding one more mid-temperature air outlet. Further, the smaller the clinker particles, the more is the pressure drop in clinker layer; thus more power consumption is needed by the cooling fan.     

Fluid-solid coupling numerical simulation of charge process in variable-mass thermodynamic system

A joint solution model of variable-mass flow in two-phase region and fluid-solid coupling heat transfer, concerned about the charge process of variable-mass thermodynamic system, is built up and calculated by the finite element method (FEM). The results are basically consistent with relative experimental data. The calculated average heat transfer coefficient reaches 1.7×10⁵ W/(m² · K). When the equal percentage valve is used, the system needs the minimum requirements of valve control, but brings the highest construction cost. With the decrease of initial steam pressure, the heat transfer intensity also weakens but the steam flow increases. With the initial water filling coefficient increasing or the temperature of steam supply decreasing, the amount of accumulative steam flow increases with the growth of steam pressure. When the pressure of steam supply drops, the steam flow gradient increases during the maximum opening period of control valve, and causes the maximum steam flow to increase.     

Numerical simulation of high temperature air combustion flames properties

Ａｎａｔｔｒａｃｔｉｖｅｔｅｃｈｎｏｌｏｇｉｃａｌｐｒｏｇｒｅｓｓｉｎｆｕｅｌｃｏｍｂｕｓ ｔｉｏｎｆｉｅｌｄｈａｓｂｅｅｎｏｂｔａｉｎｅｄｉｎ 1990′ｓ ,ｗｈｉｃｈｃｒｅａｔｅｓａｐｏｓｓｉｂｉｌｉｔｙｏｆｅｎｅｒｇｙｓａｖｉｎｇｗｉｔｈｅｆｆｅｃｔｉｖｅｃｏｎｔｒｏｌｏｆｐｏｌｌｕ ｔａｎｔｅｍｉｓｓｉｏｎｏｎｌａｒｇｅｓｃａｌｅ[1～ 4 ] .Ｈｉｇｈｔｅｍｐｅｒａｔｕｒｅａｉｒｃｏｍｂｕｓｔｉｏｎ(ＨＴＡＣ)ｔｅｃｈｎｏｌｏｇｙ ,ｄｅｖｅｌｏｐｅｄｉｎＪａｐａｎｉｎｃｏ ｏｐｅｒａｔｉｏｎｗｉｔｈｒ…     

Effects of annealing on microstructure, mechanical and electrical properties of AlCrCuFeMnTi high entropy alloy

The multi-component A1CrCuFeMnTi high entropy alloy was prepared using a vacuum arc melting process. Serial annealing processes were subsequently performed at 590 ℃, 750 ℃, 955 ℃ and 1 100 ℃ respectively with a holding time of 4 h at each temperature. The effects of annealing on microstructure, mechanical and electrical properties of as-cast alloy were investigated by using differential thermal analysis （DTA）, X-ray diffraction （XRD）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The experimental results show that two C14 hexagonal structures remain unchanged after annealing the as-cast A1CrCuFeMnTi alloy specimens being heated to 1 100℃. Both annealed and as-cast microstructures show typical cast-dendrite morphology and similar elemental segregation. The hardness of alloys declines as the annealing temperature increases while the strength of as-cast alloy improves obviously by the annealing treatment. The electrical conductivities of annealed and as-cast alloys are influenced by the distribution of interdendrite re~ions which is rich in Cu element.     

贵州无烟煤的燃烧特性和NOx排放特性试验

为了探究氧量及温度对贵州无烟煤的燃烧特性及NOx排放特性的影响,选用粒径为58～75 μm的贵州无烟煤,利用一维沉降炉进行相关试验.研究结果发现,贵州无烟煤NOx排放量随着氧气量的增加而增加,当过量空气系数大于0.9后增幅趋缓;随着燃烧温度的上升,NOx生成量增加,在达到1 400 ℃后,由于生成大量热力型NOx,NOx排放量呈指数型大幅增长;氧量主要影响贵州无烟煤在燃烧过程的0.2 s之前以及2.0 s之后的NOx生成量,对于0.2～2.0 s的主燃烧区域的NOx生成量影响不大.研究认为氧量是影响贵州无烟煤NOx排放及燃烧的最主要因素,燃料型NOx对温度并不十分敏感.     

Thermal fatigue behavior of 441 ferritic stainless steel in air and synthetic automotive exhaust gas

The thermal fatigue behavior of 441 ferritic stainless steel was investigated in air and synthetic automotive exhaust gas by the cyclic tests under 100°C–800°C and 900°C conditions. After the fracture failure, the microstructure, oxide film, and precipitated phases were analyzed using optical microscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. In both atmospheres, increasing the maximum temperature from 800°C to 900°C results in lower strength and fatigue life and higher elongation and grain size. At the same maximum temperature, the thermal fatigue life of the specimen is lower in the synthetic exhaust gas than in the air. Both the higher maximum temperature and the synthetic exhaust gas facilitate fatigue failure. The failure mechanism is discussed according to the grain size, thermal stress, high-temperature oxidation rate, and the precipitation of secondary phases. Some precipitated carbides play an important role in the rapid fatigue failure of specimens in the synthetic exhaust gas.

     

太阳能在煤粉锅炉上的应用

通过对煤粉锅炉炉膛内的燃烧、传热过程进行数值计算研究,预测了不同空气温度下炉膛内的温度分布和污染物体积分数分布。结果表明,在达到工业生产要求的炉内温度时,二、三次风使用高温空气,可降低总空气量和煤粉消耗量,同时还可减少污染物的生成量,达到节能减排的目的;随着空气温度的升高,炉膛内同一截面的温度更加趋于均匀,这样水冷壁各管吸热均匀,有利于锅炉水循环的稳定性,有利于煤粉锅炉应用高温低氧燃烧技术。为了实现空气高温,可在锅炉尾部增设太阳能空气加热器,利用太阳能辅助烟气余热将二、三次风加热到873K以上。     

大型切圆燃烧锅炉炉膛燃烧和辐射的修正模型

应用于实时仿真培训的锅炉炉膛燃烧和辐射的零维模型对总风量扰动过于敏感,表现为总风量增加时,主蒸汽压力下降过多,不符合实际电厂的特性。根据煤粉燃烧理论和配风方式对此进行分析,指出其主要原因在于模型计算绝热燃烧温度公式的不合理,并建立其修正模型。验证结果表明:修正模型改善了对总风量扰动的敏感性,仿真结果合理。该模型已经应用于某300 MW仿真机工程中。     

亚临界煤粉锅炉流体流动和燃烧的数值模拟

以一300MW Hg1025/18.2-YM13型亚临界自然循环、四角切圆燃煤锅炉为研究对象,应用可实现化k-ε湍流模型、颗粒相随机轨道模型、即混即燃气相燃烧模型、P-1辐射换热模型,根据燃烧测试试验得到的边界条件,运用FLUENT软件对锅炉炉内流体流动和燃烧过程进行了三维数值研究。模拟预测结果与试验结果吻合较好,温度分布规律和趋势与试验研究结果一致。运用该模型对炉内速度场、压力场、温度场以及燃烧释热场进行了多场耦合仿真,并全面系统地研究了各种操作参数对炉内燃烧工况的定量影响规律,确定了燃烧器和锅炉合理的操作参数:过剩空气系数为1.2、一次风率为20%、一次风温度为608K、二次风温度为620K且均匀投粉。在该条件下炉内温度分布较合理,煤粉能正常稳定地燃烧,炉膛高温区较集中,炉膛出口温度合理。     

Influences of heat treatments on crystallization in SiO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-MgO-K<Subscript>2</Subscript>O-F glass-ceramics

Five kinds of heating treatment processing were chosen according to the experiment result of differential scanning calorimeter to prepare SiO2-Al2O3-MgO-K2O-F glass ceramics samples.The effects of heat treatment processing on the crystallization of these samples were explored by X-ray diffraction and scanning electron microscopy techniques.The results indicate that phase separations can occur in the bulk regions of the glass sample when holding at 670 ℃ for 3 h.The phase separation can accelerate the precip...     

Influence of elemental iron on hydrogen content in superheated aluminum-iron melts

The hydrogen content in liquid binary aluminum alloys with 1,3,5 and 8 wt% iron has been determined in the temperature range from 973K to 1103K. The hydrogen content in molten Al-Fe alloys increases remarkably when the temperature of the meh rises to about 1053K. This work indicates that the alloying element iron plays an important role in hydrogen content in snperheated Al-Fe alloy melts below about 1053K. The results make it clear that the hydrogen content in the mekt ahuminum reduces with the increasing element levels. A conclusion is drawn that the degree of gassing in molten AL-Fe alloys is hound up with the properties of oxide film of aluminum alloy melts. The element iron has no effect on the compact stntcture of oxide film in aluminum melts. The effects of alloying element are theoretically analyced in terms of Wagner interaction parameter. According to the values of the first order interaction parameter, it is concluded that the interaction between iron atom and aluminum is much stronger than that between hydrogen atom and ahanintum, and the addition of the alloying element decreases the affinity of liquid aluminum for hydrogen.