Numerical simulation of the influence factors of NO_(x) emission on a W-type radiant tube

The radiant tube burner was modeled and analyzed by the numerical simulation method to investigate the influence factors and rules of NO_(x) emissions in a W-type radiant tube.These factors,which include air preheating temperature,excess air coefficient,and fuel gas composition,were modified to study their effects on NO_(x) emissions under varying working conditions.Simulation results were compared with the theoretical calculation value based on chemical reaction equilibrium theory and the onsite experimental value to verify the simulation accuracy.The results show that NO_(x) emissions rise with increasing air preheating temperatures.NO_(x) production increases to an extreme value and then decreases during the oxygen-poor to oxygen-enriched process with the rise of the excess air coefficient.Enhancing the proportion of coke oven gas in the fuel gas raises the combustion temperature as well as the NO_(x) discharge.Both the thermal efficiency and NO_(x) emissions should be balanced.Therefore,the recommended values based on the simulation results are as follows:the air preheating temperature should not exceed 400℃,the excess air coefficient should be between 1.1 and 1.2,and the volume fraction of the coke oven gas should not exceed 30%.

NOx Emission Characteristics in Radiant Tube Burner with Oscillating Combustion Technology

An experimental study was carried out in a small-scale furnace to investigate the performance, such as NOx emission, enhancement of heat transfer, uniformity of temperature, and etc., of oscillating combustion applied in radiant tube burner sy stem for heat treatment furnace. A premixed type burner and a solenoid type oscillating control valve were designed and used. The fuel was used commercial LPG in this study and the fuel flow was oscillated by periodically opening and shutoff of the solenoid valve. From the tests, it was found that NOx emission, compared to no oscillation, could be reduced by 32% at 2.0 Hz. However, as oscillating frequency was increased, abatement of NOx emission was gradually reduced. At the high NOx abatement of 1.0 Hz, carbon monoxide was emitted above 10,000 ppm. Although rate of NOx abatement was low, oscillation condition of 2.5 Hz and duty ratio of 10-30% was recommended for low carbon monoxide emission. From the measurement of furnace heating time from 100 ℃ to 720 ℃, it was shown that heat transfer was increased by 11.5% at 2 Hz oscillating frequency. Temperature distribution of radiant tube surface was more uniform at 2 Hz oscillating frequency with drop of the peak temperature and rise of low temperature. From these results, it was confirmed that oscillating combustion was useful in radiant tube burner system.

Application and practice of regenerative combustion technology on radiant-tube furnace

High Temperature Air Combustion(HTAC) based on regenerative theory has been used in developed countries in recent years,it has many advantages such as efficient recovery of waste heat,high temperature preheating air,low pollution discharge,and so on.This Technology can be used in various furnaces in mechanical,petroleum,chemical industry.To rebuild traditional radiant-tube combustion system with HTAC technology has become important.In the transformation process,The biggest difficulty encountered is that the stability of burner combustion and control system. Because the exhaust gas heat is absorbed by the regenerator,exhaust gas discharge can be controlled at a very low temperature to realize maximum waste heat recovery.At the same time,it improves the temperature uniformity and improve the heating intensity.Thermal efficiency of the device can reach more than 80%.And compared to the traditional air preheating,21.55%energy can be saved. Revamping on traditional radiant-tube combustion system is technically feasible,but a lot of problems will be involved since the rebuild work is on the old system,this article discusses on the main problem encountered in rebuild process in site. to optimize temperature control and obtain not so high exhaust gas temperature,digital combustion control system is necessary.This control loop consists of big loop and small loop,Big loop controls the load distribution of all burners in each heating zone.Small loop controls each heating zone burner's burning time. Compared performance of tradition radiant-tube heater with regenerative radiant-tube heater,result that regenerative radiant-tube heater have many advantage in consume fuel.Accordance with experience of replacing tradition radiant-tube heater with regenerative type,give a proposition in combustion control system, pilot burner,flame detection and prevent trouble to rebuild work of CAPL and CGL. It is recommended to use regenerative combustion technology in new annealing Line.Although the investment is 1/3 much more than the traditional combustion system,the energy saving effect is obvious and operating costs decreases.Revamping can be taken step by step according to different heating zones.Although taking a long time,it is safer and it influences the production less. Regenerative combustion burner revamping has become successful.However,the revamping work on different furnaces,particular on continuous annealing furnace with high request for temperature control,need further exploration and research.

The application of the regenerative combustion technology to a radiant-tube furnace and its practice

This study compares the regenerative radiant-tube heater with the traditional radiant-tube heater, showing the regenerative radiant-tube heaters have many advantages in fuel consumption. Based on the experience of changing a heating system with traditional radiant-tube burners to a heating system with regenerative combustion, propositions are given for the combustion control system, pilot burner, flame detection and for trouble prevention in rebuilding the continuous annealing production line（CAPL） and the continuous galvanizing line（CGL）.

高烟气循环W型辐射管烧嘴研究

为了提高热效率、优化辐射管表面温度均匀性及降低NO_(x)排放,文章设计了一款双行程换热高烟气循环W型辐射管烧嘴,并搭建了实验平台,进行了大量实验研究,得出以下结论:得益双行程管式换热,空气预热温度在500℃以上,满负荷时预热温度可达755℃;设计的卷吸结构能够卷吸大量烟气,使助燃空气氧含量低至13.34%,辐射管表面最大温差小于120℃,NO_(x)排放低于53×10^(-6)。

燃气辐射管换热器结构优化与数值模拟研究

为解决燃气辐射管换热器排烟温度高的问题,设计带有换热管簇及烟气引射回流的高效换热器装置。通过对换热器的换热管长度、折流板数目和引射器尺寸变化的数值模拟分析,进而对换热器结构进行优化,以达到节约燃气、提高加热质量、降低NOx的目的。

燃气辐射管高效换热器性能分析

对采用换热管簇及带烟气引射回流的U型辐射管换热器的性能进行了热态模拟试验研究,结果表明,换热管簇大幅增加了有效换热面积,提高换热系数,强化换热效果,换热器换热效率在77.5%~87.1%,回收率在50%左右;而烟气引射回流降低了NOX排放,烟气中NOX体积含量在77.3~123.4 mg/m3,相比于现有辐射管换热器具有明显的优势。

基于Fluent的埋管式辐射地板传热及供冷能力研究

充分了解辐射供冷系统的传热特性有助于该系统的设计、推广及应用。构建了埋管式辐射地板的三维稳态传热模型,进行供冷工况下地板内部传热情况的数值模拟,得到了辐射地板内部及表面的温度场。经实验验证,建立的传热模型与实际误差小于9.01%。模拟分析了换热盘管长度与供水温度对辐射地板的供回水温差、供冷能力及温度分布的影响。结果表明:在相同供水温度下,换热盘管越长,埋管式辐射地板的供冷能力越弱,温度分布均匀性越差,管长每增加10 m,单位面积辐射地板供冷量约降低1.5 W/m^(2);在相同换热盘管长度下,供水温度越高,地板的供冷能力越弱,温度分布均匀性越好。

换热管间距对冷辐射板换热性能的影响

冷辐射空调以较好的热舒适性和较大的节能潜力越来越受到人们重视,但其表面易结露及单位面积制冷能力偏低影响了其工程应用。本文通过建立金属辐射板传热过程模型,分析了辐射板换热管间距排列对换热性能的影响。结果表明:对常规等管间距排列铜管辐射换热表面,在供水温度及流速分别为17℃和0.3 m/s时,对某1.2 m×0.4 m辐射板,当管间距由100 mm降至68 mm时,辐射板表面平均温度和最高温度分别下降0.58、0.76℃,温度不均匀系数分别降低3.56%、9.41%。在此基础上,设计了4排、5排、6排三类共9种变管间距排列辐射板,分别与相应等管间距排列辐射板对比,表面平均温度最高分别下降0.37、0.56、0.36℃,温度不均匀系数最高分别下降19.3%、23.5%、30.3%,换热管变管距排列表面温度更均匀。

U型蓄热式辐射管表面温度分布数值模拟研究

以一支燃烧能力为 5 8kW的蓄热式辐射管为对象 ,利用商业CFD软件CFX4 3对蓄热式辐射管表面温度分布进行数值模拟 ,并进行试验验证 ,重点分析了辐射管沿长度方向温度分布的规律及其影响因素。结果表明 ,高速煤气射流产生的湍动燃烧动力 ,能搅拌炉膛、消除炉内的温差 ,有利于提高烟气的加热能力 ,改善其加热性能。但煤气喷射速度不能无限制增大 ,对于该类型的蓄热式辐射管燃烧器 ,煤气喷射速度可限制在 80m/s～ 1 1 0m/s。

U型辐射管的表面温度分布实验研究

对抽吸式U型辐射管进行了实验研究,重点研究了辐射管沿长度方向的温度分布规律,实验表明,使用可靠、实用的拉杆技术,可以灵活地调节一次、二次进风量的配比,从而有效地改善辐射管的表面温度分布,使辐射管的表面最大温差明显低于同类型的辐射管,此项技术成本低、易于实施,为工业化应用打下了良好的基础.此外,实验表明,提高空气预热温度和改进烧嘴安装精度也可有效改善辐射管表面温度分布.

U型辐射管的表面温度分布

本文分析了影响大型辐射管表面温度分布的因素，通过实验说明，对于单端吸入空气的扩散型燃烧辐射管，使用芯块可以明显地提高燃料的利用率，较好地控制空气消耗系数，强化气体与辐射管管壁之间的对流传热，从而改善辐射管的表面温度分布。

大型渗碳炉用CrNiNRE耐热钢辐射管的失效机理研究

应用SEM电镜、能谱分析及X射线衍射等方法研究了高镍铬含氮和稀土的奥氏体型CrNiNRE耐热钢辐射管在长期高温渗碳中的失效机理和组织特征。结果表明,CrNiNRE钢在长期高温和单边渗碳作用下,使得M7C3碳化物持续长大,并促使奥氏体区域退缩和沿碳化物周边形成裂隙;合金元素的重新分布造成基体贫铬;管内壁氧的侵入形成氧化空洞和疏松;这些因素的综合作用导致构件最终贯通穿孔而失效。

毛细管地板辐射采暖特性试验研究

描述了毛细管地板辐射采暖试验系统、毛细管辐射板铺设形式、地板构造以及具体试验方法;通过试验分析了毛细管辐射板供热能力、辐射板加热层温度、地板表面温度以及室内温度的变化特性。研究得出了毛细管辐射板供热能力较强,毛细管辐射采暖时室内温度响应较快,室内温度场分布均匀性较好。

蓄热式辐射管表面温度分布的实验研究

论述了应用高温空气燃烧技术的蓄热式辐射管的实验研究工作,重点研究了辐射管沿长度方向的温度分布规律及其影响因素。结果表明,蓄热式辐射管与常规辐射管相比不仅在节能、环保方面具有优势,而且在加热均匀性方面也有优越性。

W型蓄热式辐射管表面温度分布的数值模拟

以一套W型蓄热式辐射管实验装置为对象,利用商业CFD软件CFX4.3对蓄热式辐射管表面温度分布进行数值模拟,并与实验结果进行对比,重点分析了辐射管沿长度方向温度分布的规律及其影响因素。结果表明,高速煤气射流有利于提高辐射管表面温度,降低温差,改善温度分布均匀性。

P型蓄热式辐射管设计与数值模拟

开发了P型蓄热式辐射管。在开发设计过程中,应用CFD技术,对设计方案进行三维流动、传热与燃烧过程的数值模拟。根据模拟结果,改进和优化设计方案,大大减少了实验次数。实践表明,CFD技术是提高燃烧设备开发设计水平和增强技术创新能力的有效工具。

蓄热式高温空气燃烧技术在燃气辐射管中的应用

介绍了一种利用高温空气燃烧技术改造W型燃气辐射管加热装置的方案,并通过计算举例,论证了其可行性,分析了新型燃气辐射管的技术性能。蓄热式改造后的装置具有热效率高,表面温度分布均匀,使用寿命延长,污染物排放浓度降低等特点。

连续退火线辐射管炉内传热过程模型

建立连续退火辐射管加热炉内传热的数学模型,推导了模型的解析式,并给出了无量纲解的图像。引入当量灰平面法来简化带钢与辐射管之间的辐射换热计算,讨论了辐射管布置对系统黑度和机组长度的影响。计算表明,辐射管的间距直径比增加,系统黑度降低,机组长度增加。采用实际生产数据,分析了机组带钢厚度与机组速度的乘积(TV值)变化对带钢加热温度的影响。

采用辐射管加热的辊底式热处理炉数值仿真及其分析

以某公司拟建的采用辐射管加热的辊底式热处理炉为研究对象,在详细分析其传热机理的基础上,建立了炉内钢坯加热过程的二维传热数学模型。采用交替隐式格式的TDMA数值计算方法,开发出了采用辐射管加热的辊底式热处理炉钢坯加热过程二维传热模型计算机数值仿真系统,并进行了大量的数值仿真计算。所得结论为该公司即将开展的辊底式热处理炉模型优化控制奠定了坚实的理论基础。