Numerical Heat Transfer Modelling for Rapid Impact Assessment of Limiting Thermostat Reliability on Fuel-Oil Burner Pre-Heaters： A Case Study

In this paper, the impact of limiting thermostat on the rupture event occuring in Fuel-Oil burner fuel pre-heaters＇ resistant （heat generating） wires is inspected numerically. Gaseous fuel content in the pipeline has also been issued as a possibility. Heater＇s inner temperature distributions have been simulated by an in-house MATrix LABoratory （MATLAB） script in order to understand the resistant wire exposure to high temperatures by numerous scenarios. It is concluded that the effect of fuel flowrate is not a major effect on the wires＇ fate because of the limiting thermostat co-working. The main difference between the calculations is the effect of thermostat cut off function. The numerical simulations enlightened the dominant effect of thermostat sensing delay, so the overheating event. Intolerable delay results with a quick drop in the thermal efficiency and an increased possibility on wire rupture due to overheating which means a burner malfunction. Referring to the first numerical simulation results, a distributed and reduced heat flux was implemented with the same fluid and thermodynamic properties on a revised pre-heater model with an increased heater plate. The increment, thus the reduction on the heat flux of the ribbon wires has been noted as the key for safe operation.

氢燃料的制储运及其在燃气轮机中的应用

氢燃料具有来源广泛、燃烧无碳排放等优点,燃气轮机作为工业、电力等领域不可或缺的设备,将氢燃料用于燃气轮机可有效降低碳排放并解决可再生能源发电的波动问题。为向我国节能减排提供技术参考,本文围绕氢燃料的制、储、运以及在燃气轮机中的应用这四个环节进行综述,对比总结了各环节技术原理及优缺点。灰氢虽制备技术成熟、成本较低,但碳排放最高,随着CCUS(碳捕集、利用与封存)技术及绿氢制备技术的发展,蓝氢、绿氢将逐步取代灰氢。高压气态储氢、低温液态储氢是目前最成熟的储氢方式,储氢密度较高的固态、液态储氢是未来储氢技术发展的主流,但其目前存在的主要挑战为储氢材料吸放氢条件苛刻,需研制高效催化剂。液态船舶及管道掺氢运输是前景较好的输氢方式。氢燃气轮机分为掺氢、纯氢燃气轮机,目前示范项目基本为掺氢燃气轮机,扩散型掺氢燃烧器可燃烧掺氢比例高达90%的燃料,预混型掺氢燃烧器掺氢比例较低,纯氢燃烧器大多还处于试验阶段,但从长期来看,纯氢燃烧器是未来氢燃气轮机发展的主要方向。

松木生物质颗粒预热燃烧特性试验

使用于松木生物质颗粒作为燃料,结合先进的自预热燃烧技术,实现燃料在炉膛内的流态化燃烧。通过千瓦级预热燃烧试验平台,对木本生物质颗粒在不同预热温度下的预热改性进行了全面深入的探索。使用BET、SEM扫描电镜与拉曼光谱带对比的方法对高温生物质半焦的比表面积、总孔容积、氮气等温吸附脱附特性、颗粒表明形态等关键物性参数进行检测和分析。分析结果显示,随着预热温度的升高,氮气吸附量明显增加,说明改性后的生物质半焦具有更多的孔隙结构。结合碳微晶结构分析,松木生物质颗粒在高加热速率下解聚脱挥发导致大分子碳链断裂产生小分子挥发物从而改善反应活性。在燃烧特性方面,改性后的高温生物质半焦可在下行燃烧室内迅速实现稳定燃烧,且燃烧效率高达99%以上。在NO_(x)排放上,所有实验工况均将燃烧温度控制在1 100℃以下避免产生热力型NO_(x)。预热后松木生物质颗粒的NO_(x)排放浓度并未随预热温度的单调变化而增减。842℃时,NO_(x)排放质量浓度达到峰值,随后开始下降。在试验温度范围内,当预热温度设定为705℃时,NO_(x)排放质量浓度达到最低值,即97.79 mg/m^(3)。综上,为确保松木生物质预热燃烧后具有较低的NO_(x)排放和高燃烧效率,推荐的最佳预热温度为705℃。

烘炉燃烧器空燃比精细化控制研究与现场应用

为提高燃烧器的燃烧效率,并研究精细化控制空燃比在燃烧器中的应用效果。采用燃气和空气量分别精细化控制的方法和装置,在燃烧器运行过程中,获取多个最佳空燃比数据,根据空燃比数据生成控制曲线。燃烧器控制系统可根据控制曲线,自主控制空气阀门和燃气阀门开度。通过测量尾烟的CO含量进行节能评价。结果表明,精细化控制空燃比,可精准控制空气阀门和燃气阀门开度,不同阀门开度情况下空燃比可调,尾烟的的CO含量低。说明精细化控制空燃比可有效提高燃烧器的燃烧效率、节约燃气耗量、降低碳排放。

Improved combustion stability of biogas at different CO_(2) concentrations using inhomogeneous partially premixed stratified flames

Biogas is a renewable and clean energy source that plays an important role in the current environment of lowcarbon transition.If high-content CO_(2) in biogas can be separated,transformed,and utilized,it not only realizes high-value utilization of biogas but also promotes carbon reduction in the biogas field.To improve the combustion stability of biogas,an inhomogeneous,partially premixed stratified(IPPS)combustion model was adopted in this study.The thermal flame structure and stability were investigated for a wide range of mixture inhomogeneities,turbulence levels,CO_(2) concentrations,air-to-fuel velocity ratios,and combustion energies in a concentric flow slot burner(CFSB).A fine-wire thermocouple is used to resolve the thermal flame structure.The flame size was reduced by increasing the CO_(2) concentration and the flames became lighter blue.The flame temperature also decreased with increase in CO_(2) concentration.Flame stability was reduced by increasing the CO_(2) concentration.However,at a certain level of mixture inhomogeneity,the concentration of CO_(2) in the IPPS mode did not affect the stability.Accordingly,the IPPS mode of combustion should be suitable for the combustion and stabilization of biogas.This should support the design of highly stabilized biogas turbulent flames independent of CO_(2) concentration.The data show that the lower stability conditions are partially due to the change in fuel combustion energy,which is characterized by the Wobbe index(WI).In addition,at a certain level of mixture inhomogeneity,the effect of the WI on flame stability becomes dominant.

燃油超低NO燃烧器结构的大涡模拟

采用Fluent软件的大涡模拟(Large Eddy Simulation,LES)方法,对3种旋流非预混低NOx燃烧器进行数值模拟,分析它们的温度、速度场和污染物排放特性,探讨燃烧器结构对涡旋与火焰相互作用的影响。研究结果表明,旋流内置结构和旋流文丘里结构能有效降低燃烧温度,最高温度降幅可达300 K;超低NOx燃烧器的NOx生成主要集中在炉膛中下游区域。与常规旋流结构相比,旋流文丘里结构和旋流内置结构的NOx排放量分别降低了13.77%和12.32%,其中旋流内置结构的NOx排放量最低为11.9 mg·kg^(-1)。在炉膛出口处,旋流内置结构的碳烟排放量较常规结构降低了5.56%,降至20.4 mg·kg^(-1),而旋流文丘里结构的碳烟排放量则上升了18.06%,表现不佳。

低温加热炉低CO燃烧器试验研究

低氮燃烧器采用提高喷速、回流烟气、扩大火焰面等弱化燃烧的措施,达到降低NOx产生的目的。但在低温环境运行时,存在燃料无法完全燃烧、火焰稳定性差、排烟中CO含量偏高的问题。针对以上问题,提出了增设中心枪局部强化燃烧的方法,设计了2.8 MW的低CO燃烧器,在试验加热炉上开展了燃烧性能试验。性能试验表明,炉膛温度低于700℃时,低CO燃烧器中心枪燃料占比为25%~35%,NOx和CO含量才能满足相关标准及规定要求。选取了中心枪燃料占比30%的低CO燃烧器进行了燃烧效果试验,试验结果表明,炉膛温度为530~700℃时,低CO燃烧器有效解决了低氮燃烧器在炉低温环境下出现的问题,在满足国家排放标准的前提下,大幅降低了排烟中的CO含量,提升了燃烧火焰的稳定性,能够满足工业现场的使用要求。

玻璃熔窑全氧燃烧技术现状及发展趋势

全氧燃烧技术因其在高效熔化、节能、减排等方面的优势,在玻璃生产线上的应用场景越来越多,通过分析全氧燃烧技术的特点、燃烧方式变化,提出了全氧窑炉的燃烧器、控制系统、氧气供应和耐火材料是全氧燃烧技术发展的重要节点,并对全氧燃烧技术的发展提出了研发方向。

PRP燃烧技术在热电厂超低排放的应用

为降低锅炉NO_(x)排放,解决燃烧不稳、低负荷稳燃范围小、锅炉掉焦灭火等问题,文章通过采用清华大学新型PRP燃烧技术对某电厂270t/h锅炉进行燃烧器改造,提高了锅炉安全稳定性及燃烧效率,实现了安全生产与节能双丰收。

Response Surface Modeling of Fuel Rich and Fuel Lean Catalytic Combustion of the Stabilized Confined Turbulent Gaseous Diffusion Flames

The Response Surface Methodology (RSM) has been applied to explore the thermal structure of the experimentally studied catalytic combustion of stabilized confined turbulent gaseous diffusion flames. The Pt/γAl2O3 and Pd/γAl2O3 disc burners were situated in the combustion domain and the experiments were performed under both fuel-rich and fuel-lean conditions at a modified equivalence (fuel/air) ratio (ø) of 0.75 and 0.25 respectively. The thermal structure of these catalytic flames developed over the Pt and Pd disc burners were inspected via measuring the mean temperature profiles in the radial direction at different discrete axial locations along the flames. The RSM considers the effect of the two operating parameters explicitly (r), the radial distance from the center line of the flame, and (x), axial distance along the flame over the disc, on the measured temperature of the flames and finds the predicted maximum temperature and the corresponding process variables. Also the RSM has been employed to elucidate such effects in the three and two dimensions and displays the location of the predicted maximum temperature.

Response Surface Methodology and Artificial Neural Network Methods Comparative Assessment for Fuel Rich and Fuel Lean Catalytic Combustion

Modeling, predictive and generalization capabilities of response surface methodology (RSM) and artificial neural network (ANN) have been performed to assess the thermal structure of the experimentally studied catalytic combustion of stabilized confined turbulent gaseous diffusion flames. The Pt/γAl2O3 and Pd/γAl2O3 disc burners were located in the combustion domain and the experiments were accomplished under both fuel-rich and fuel-lean conditions at a modified equivalence (fuel/air) ratio (ø) of 0.75 and 0.25, respectively. The thermal structure of these catalytic flames developed over the Pt and Pd disc burners was scrutinized via measuring the mean temperature profiles in the radial direction at different discrete axial locations along with the flames. The RSM and ANN methods investigated the effect of the two operating parameters namely (r), the radial distance from the center line of the flame, and (x), axial distance along with the flame over the disc, on the measured temperature of the flames and predicted the corresponding temperatures beside predicting the maximum temperature and the corresponding input process variables. A three-layered Feed Forward Neural Network was developed in conjugation with the hyperbolic tangent sigmoid (tansig) transfer function and an optimized topology of 2:10:1 (input neurons:hidden neurons:output neurons). Also the ANN method has been exploited to illustrate the effects of coded R and X input variables on the response in the three and two dimensions and to locate the predicted maximum temperature. The results indicated the superiority of ANN in the prediction capability as the ranges of & F_Ratio are 0.9181 - 0.9809 & 634.5 - 3528.8 for RSM method compared to 0.9857 - 0.9951 & 7636.4 - 24,028.4 for ANN method beside lower values for error analysis terms.

Evaluation of a Pulse Width Modulated Bypass Nozzle for the Development of a Variable Load Residential Oil Burner

Due to the need for energy conservation in buildings and the simultaneous benefit of cost savings, the development of a low firing rate load modulating residential oil burner is very desirable. One of the two main requirements of such a burner is the development of a burner nozzle that is able to maintain the particle size distribution of the fuel spray in the desirable (small) size range for efficient and stable combustion. The other being the ability to vary the air flow rate and air distribution around the fuel nozzle in the burner for optimal combustion at the current fuel firing rate. In this paper, which deals with the first requirement, we show that by using pulse width modulation in the bypass channel of a commercial off-the-shelf bypass nozzle, this objective can be met. Here we present results of spray patterns and particle size distribution for a range of fuel firing rates. The results show that a desirable fuel spray pattern can be maintained over a fuel firing rate turndown ratio (Maximum Fuel Flow Rate/Minimum Fuel Flow Rate) of 3.7. Thus here we successfully demonstrate the ability to electronically vary the fuel firing rate by more than a factor of 3 while simultaneously maintaining good atomization.

一种新型中心富燃料直流煤粉燃烧器燃烧性能试验研究

为提升直流煤粉燃烧器在促进煤粉着火燃尽及降低NO_(x)生成方面的性能,哈尔滨锅炉厂在某原型燃烧器基础上,通过构建两级煤粉浓缩、设置钝体稳燃板及稳燃齿等点火强化及分级燃烧措施,设计开发一种中心富燃料直流煤粉燃烧器。为研究该燃烧器的综合性能,结合燃烧器冷态流动及热态燃烧试验,对比分析原型燃烧器及新型燃烧器的回流区形成、燃烧及NO_(x)生成特性。研究表明,相比于原型燃烧器,新型燃烧器能够在出口处构建更大的回流区分布,且煤粉气流着火位置由90cm附近大幅缩短至10~20cm,煤粉燃烧稳定性明显改善。新型燃烧器在兼顾115mg/m^(3)(O_(2)=6%)较低NO_(x)排放浓度的同时,能够明显提升煤粉燃尽效果,对应飞灰可燃物含量由6.5~9.5%降低至1.5~3.9%,CO排放浓度由800mg/m^(3)(O_(2)=6%)以上降低至160mg/m^(3)(O_(2)=6%)以内,在综合燃烧性能方面较原型燃烧器显现出了更好的优越性。

微混喷嘴结构对氢混燃料/空气掺混均匀性的影响分析

采用数值仿真方法开展了燃气轮机燃烧室微混喷嘴中富氢燃料/空气掺混均匀性问题研究。首先分析了三种不同微混喷嘴结构的燃料浓度分布和掺混均匀性指数变化规律,发现采用燃料轴向进气、空气径向进气的燃料/空气掺混方式,能够在合理的总压损失范围内,获得更好的掺混均匀性。然后分析了三种喷嘴的流场特性,不同径向位置处的轴向速度分布表明,燃料和空气的射流速度会对喷嘴内燃料/空气掺混水平造成影响,燃料径向喷入和从喷嘴中心区域轴向喷入在轴向高速射流作用下被吹向下游,不能均匀的沿径向扩散并分布到喷嘴流道内部,使燃料/空气掺混均匀性提高受限。最后分析了富氢燃料中氢含量变化对掺混均匀性的影响,研究结果表明,氢含量变化会带来燃料射流速度的改变,当燃料射流速度超出合理范围后,会导致掺混均匀性下降。研究结果为微混喷嘴燃料/空气喷注策略设计提供参考。

不同雾化角燃油超低NOx燃烧器的大涡模拟

采用大涡模拟方法分析不同雾化角对旋流非预混燃油低NOx燃烧器燃烧性能的影响。在充分燃尽的基础上,进行收敛性研究,对比分析两工况的温度场、速度场以及污染物排放情况,结果表明:大雾化角压力频谱低频段信息增加,燃烧室压力振荡强度增强,更易发生燃烧不稳定现象;雾化角的增大使得火焰集中分布在射流锥内侧,角回流区极少有火焰分布;大雾化角使得燃油径向雾化效果增强,轴向刺透深度减小,导致着火点提前,燃烧反应速率增大,使得炉膛最高温度升高,导致污染物排放水平升高。

低压纯氧燃烧技术在玻纤窑炉的应用

纯氧燃烧技术能够助力玻璃企业实现节约燃料、减少氮氧化物排放并改善玻璃品质等经济和环保双重效益。经过在玻璃行业三十多年的发展,纯氧燃烧技术已经逐渐获得业内的认可和肯定。本文主要介绍最新低压纯氧燃烧技术和设备及其在增强玻纤窑炉领域的成功应用。采用低压纯氧燃烧技术可进一步提升玻璃窑炉燃烧效率并实现节能降耗减排的可持续发展。

防火试验用NexGen油燃烧器火焰温度特性研究

为深入研究NexGen油燃烧器的火焰温度特性,在不同燃油压力、空气压力下测量火焰温度,研究燃油流量和空气流量对油燃烧器火焰温度特性的影响。结果表明:NexGen油燃烧器配置的音速节流器及其空气分配结构使其火焰具有更好的均匀性及稳定性;在100~150 psi燃油压力范围内,随着燃油流量的增大,NexGen油燃烧器火焰平均温度逐渐增大;在40~60 psi空气压力范围内,随着空气流量的增大,火焰平均温度逐渐减小;NexGen燃烧器垂直状态下,距离燃烧筒6 in位置处温度分布最均匀饱满;水平状态下,距离燃烧筒4 in位置处温度分布最均匀饱满。

柴油加氢装置加热炉烟气NO_(x)排放量大的原因分析及改进措施

为解决柴油加氢装置加热炉运行末期烟气中NO_(x)排放量升高的问题,对加热炉烟气NO_(x)排放量的影响因素进行了分析,并提出了相应的改进措施。结果表明:燃料气中氮气体积分数、炉膛氧体积分数、加热炉负荷、各主燃烧器火焰高度、各燃烧器配风量均对加热炉烟气NO_(x)排放量有影响;通过采取降低燃料气氮气体积分数,炉膛氧体积分数和加热炉负荷,调整优化各主燃烧器火焰高度及配风量后,将烟气NO_(x)排放量由优化前的11.9 kg/d逐月降至4.2 kg/d。

典型生物质颗粒燃料燃烧特性试验

为研究生物质颗粒燃料的燃烧特性及污染物排放特性,该文以国外引进的生物质颗粒燃料燃烧器为试验装置,选择了8种典型的生物质颗粒燃料进行试验研究。试验结果表明,挥发份含量越高,含水率越低,生物质颗粒燃料所需的点火时间越短,SO2、NOx等污染物排放质量浓度远低于国家标准,但存在着部分生物质颗粒燃料灰分含量过大、结渣严重等问题。对大多数颗粒燃料来说,软化温度越高,结渣率越低,当软化温度超过1389℃时,不会发生结渣;Si元素、碱金属元素含量越高,越容易结渣,碱土金属元素含量越高,越抗结渣。玉米秸中Si的质量分数为27.70%,底灰结渣率达到48.84%,落叶松中Si的质量分数仅为9.76%,不结渣;使用添加剂后,玉米秸的底灰结渣率降低了22.77%。这将为设计适合中国国情的生物质颗粒燃料燃烧设备及改善燃料的燃烧性能提供依据。

不同进料方式燃烧器对生物质燃料颗粒物排放特性的影响

为摸清不同进料方式的燃烧器对生物质成型燃料燃烧后颗粒物排放的影响，该文对上进料式（A 型）、水平进料式（B型）和下进料式（C型）等3种类型的燃烧器进行燃烧颗粒排放试验，采用低压电子冲击仪对玉米秸秆、棉秆、木质3种成型燃料燃烧后颗粒物排放开展数量浓度和质量浓度研究，并计算出每种燃料在3种燃烧器中每秒排放的颗粒物数量和质量分布。试验结果表明：3种燃烧器中的颗粒物质量分布都成双峰分布，主要集中在5～7级和12级，占总颗粒物质量的90%；木质和棉杆燃料在A型燃烧器中的颗粒物质量排放最少，玉米秸秆燃料在B型中颗粒物质量最少。3种燃烧器中的颗粒物数量分布都成单峰分布玉米秸秆和木质在B型燃烧器上的颗粒物数量主要集中在1～5级，在A型和C型燃烧器上颗粒物数量主要集中在3～6级；棉杆在C型燃烧器上集中在1～5级，在A型和B型燃烧器上颗粒物数量主要集中在3～6级。3种燃烧器对颗粒物质量的分布影响不大。根据试验结果，建议不同的燃料匹配不同的燃烧器。从颗粒物排放总量角度，玉米秸秆应该匹配B型燃烧器，棉杆和木质燃料应该匹配A型燃烧器。从PM2.5所占比例得出，玉米秸秆燃料应匹配C型燃烧器，棉杆匹配 B 型燃烧器，木质匹配 A 型燃烧器。并建议生物质成型燃料燃烧器结构应具有以下特点：进料连续平稳；带有主动清渣装置并且清渣波动小；鼓风配风，保证过量空气系数高。研究结果为中国生物质固体成型燃料的颗粒物排放法规的制定提供参考。