阳极焙烧炉内煤气流动和燃烧的数值模拟

采用计算燃烧学的原理和模型以及CFD软件对燃烧煤气的阳极焙烧炉炉内的流动和燃烧过程进行了数值模拟计算,讨论了炉内温度场、流场、O2浓度场的分布规律,分析了这些因素对阳极炭块焙烧质量的影响。研究表明,在设计阳极焙烧炉时应考虑对气流分布有影响的各种因素。     

基于CFD的焙烧炉技术改进

基于计算燃烧学的原理和CFD软件对燃烧重油的焙烧炉炉内的流动和燃烧过程进行了数值模拟计算,讨论了炉内温度场、流场的分布规律,分析了结构因素对焙烧炉内流动和燃烧分布的影响.从炉子结构的设计角度提出了解决炉内温度场、流场的分布不均匀的方案.研究表明,在设计焙烧炉时合理地布置拉砖的位置有利于改善炉内流动和燃烧的分布.     

基于PDF模型的阳极焙烧炉仿真分析研究

为了探索阳极焙烧炉在焙烧质量方面存在的问题,研究分析了阳极焙烧炉现场实际情况,进行了模型简化处理和假设。借助商业软件Fluent,根据边界条件和模型近似假设,建立了阳极焙烧炉的物理模型。基于PDF(Probability Density Function)模型,结合计算传热学和计算流体力学的原理和数学模型,对焙烧炉进行了数值仿真分析研究。重点研究了火道内的流场、温度场和浓度场及其在火道内的分布规律,流场、温度场和浓度场之间的关系及其对阳极焙烧质量的影响。分析得到现有焙烧炉炉型存在的不足,     

辊道窑烧成带火焰空间在富氧气氛下NO_x生成的研究

采用FLUENT软件对气烧明焰陶瓷辊道窑烧成带的火焰空间进行数值模拟研究,对在富氧气氛下以天然气和炉煤气为燃料时辊道窑烧成带的NO_x生成进行分析,并与空气气氛下进行对比。数值模拟结果表明:当燃料种类和燃料量一定时,富氧燃烧可以提高燃烧的火焰温度,w(O_2)由23%升至35%时,各截面温度均升高200～250K,燃烧发生炉煤气时比天然气平均温度高、增幅大。随w(O_2)增加,以发生炉煤气为燃料时炉内NO生成先增后减然后缓慢回升,燃用天然气时,NO持续缓慢增加,但两者w(NO)均持续增大,相比于空气气氛下,分别增长了141.48%和107.73%。以天然气为燃料时炉内NO生成以快速型为主导,以发生炉煤气为燃料时以热力型为主导;富氧燃烧时气氛中的w(NO_x)增加而烟气量减少,采用不同燃料时出口处NO_x生成速率有不同变化。     

基于燃烧风预热下铜精炼炉烟气热损失研究

根据能量平衡原理，建立了基于燃烧风预热下铜精炼阳极炉高温烟气热损失数学模型，并根据不同预热燃烧风温度对铜精炼阳极炉氧化期高温烟气热损失数学模型进行计算。结果表明，随着燃烧风预热温度增加，铜精炼阳极炉氧化期重油流量和高温烟气热损失减少趋势十分明显，节能效果显著。此外，给出了一些合理化建议，有利于铜精炼阳极炉氧化期节能效果进一步提高。     

提高电极焙烧炉的热效率途径与探讨

该论文从炉子结构形式,燃烧装置形式和炉子热工控制装置三方面阐述了提高碳素制品焙烧炉热效率的途径,在理论上作了探讨。 上海碳素厂是以生产石墨电极为主的工厂,焙烧炉在整个工艺流程中是一个关键设备,它的运行是当正常,能源的消耗是同电极的质量、生产成本的高低有密切的关系,在炉型的选择上,有火井和无火井炉,各有利弊,都应于以肯定,在具体采用炉型上取决于该炉用什么燃料,燃烧装置的位置尺寸,要根据燃料的热值,压力来确定,(煤气)燃烧装置的数量要     

镀锌板生产线退火炉辐射管燃烧实验研究

建造一座模拟退火炉作为煤气燃烧试验装置，通过模拟不同热值的发生炉煤气在炉内辐射管中燃烧，探索辐射管换热性能和烟气热损失大小的变化规律，为将燃烧半水煤气更换成燃烧发生炉煤气提供技术依据。模拟在线辐射管的运行状态，找出改变助燃空气量和排烟负压对辐射管壁温和炉温的影响，寻求一种最佳的运行方案，从而使生产线达到节能降耗目的。     

混合煤气成分变化对加热炉内温度场影响的数值模拟研究

以燃用高炉、焦炉混合煤气的实验加热炉为研究对象,建立炉内二维稳态传热、流动及燃烧的数学模型,研究混合煤气成分变化对加热炉内温度场的影响,计算结果显示高炉煤气含量在一定范围内增加时,炉内温度水平和钢坯加热区温度均匀性逐渐降低.这些与华凌涟钢集团轧钢加热炉的实际情况基本一致.     

空气预热温度对NOX排放量的影响

空气预热温度是影响炉内煤气燃烧过程中氧化氮生成量的主要因素之一。在其他条件相同时 ,空气预热温度越高 ,燃烧产物的温度越高 ,从而使 NOX的生成量增加。文中以天然气为例进行了计算。在冶金炉中 ,由于燃烧产物在高温区停留的时间有限 ,因此 ,在大多数情况下 ,烟气中氧化氮浓度达不到化学平衡浓度。而当空气预热温度达 2 5 0～ 30 0℃时(此时燃烧温度将高于 195 0℃ ) ,燃烧产物中氧化氮浓度达到最大值 ,接近于化学平衡浓度。当预热温度再高时 ,氧化氮浓度的计算值与实测值相差较大 ,因为该浓度将取决于燃烧过程的组织和热交换条件。文…     

现有燃烧设备改烧天然气的可行性初探

通过分析天然气和城市煤气的燃烧计算结果，并用AGA法判断了它们的互换性，发现它们不能互换。进而从反应机理、火焰传播速度、火焰稳定性3方面分析其中的原因，提出了一些现有燃烧设备改烧天然气的措施。     

Assessment of natural gas/hydrogen blends as an alternative fuel for industrial heat treatment furnaces

The present study investigates the application of natural gas/hydrogen blends as an alternative fuel for industrial heat treatment furnaces and their economic potential for decreasing carbon dioxide emissions in this field of application. Doing so, a detailed technological analysis of several influencing parameters on the heating system was performed as well as a consideration of furnace heating technology challenges. Starting with an evaluation of the main thermophysical properties of the blends and their corresponding flue gases, requirements for the heating systems were identified. Potential ways of decreasing flue gas losses and increasing the heat transfer are shown. In the radiant tube application, an increased overall combustion efficiency of about 1.2% was measured at 40 vol% hydrogen in the fuel gas. Influences on the air to gas ratio control system of the furnace is a further important point, which was considered in this study. Two commonly used control systems were evaluated concerning their capabilities to regulate the gas flow rates of blends with varying hydrogen contents and combustion properties, such as Wobbe Index. This is important, since it shows the capability to retrofit existing furnaces. Two types of burners were tested with different natural gas/hydrogen blends. This includes an open jet burner with air-staged and flameless combustion operation modes. A recuperative burner for radiant tube application was considered as well in these tests. Doing so, the nitrogen oxide formation of both systems under different operating conditions and different fuel blends were evaluated. An increase by about 10% at air-staged combustion and about 100% at flameless combustion was measured by a hydrogen content of 40 vol% in comparison to pure natural gas firing. Finally, the additional fuel costs of natural gas hydrogen blends and different cases are presented in an economic analysis. The driving force for the use of hydrogen as a fuel is the price of the CO2 certificates, which are considered in the analysis at a current price of 25.2 €/t CO2.     

天然气锅炉NOx及CO排放控制试验研究

为了响应政府业及民用天然气锅炉达到超低氮排放,要求绝大多数天然气锅炉采用低氮燃烧器+烟气再循环系统的技术路线,实施后普遍出现NO_x、CO含量偏高、炉膛振动较大等问题。借助116 MW天然气锅炉进行试验研究,研究了燃烧器燃料配比、燃烧火焰长度、助燃空气氧含量三个因素对NO_x及CO的影响,并对投入烟气再循环前后炉膛振动情况进行了检测。试验表明:燃烧器燃料内外配比对NO_x、CO生成影响较大,两者呈现相反趋势变化;燃烧火焰长度对NO_x生成影响较大,对CO含量影响较小;助燃空气氧含量对NO_x、CO生成以及锅炉振动影响较大。三种影响因素相比,助燃空气氧含量影响更为突出。     

Utilization of combustible waste gas as a supplementary fuel in coal‐fired boilers

A system is proposed to use the combustible waste gas as a supplementary fuel in coal‐fired boilers. The combustion air can be partially or fully substituted by ventilation air methane or diluted combustible waste gases. The recommended volume fraction of combustible waste gas in combustion air is no more than 1.0%. The effect of waste gas introduction on thermodynamic parameters of boiler is evaluated through thermal calculation based on material balance, heat balance, and heat transfer principles. A case study is conducted by referring to a 600 MW supercritical pressure boiler. The results show that no retrofit of boiler is required. The operation of boiler is scarcely influenced, and the original forced and induced draft fans can meet the requirement. With increasing volume fraction of combustible waste gas, the flue gas temperature at the furnace exit decreases monotonically, resulting in an increment of heat absorption in furnace and a decrement of heat transferred in convective heating surfaces. When 1.0% volume fraction of hydrocarbon gas is introduced, the thermal efficiency of boiler is increased by 0.5%, and the coal consumption rate is reduced by 25.4%. The cost analysis of the proposed system is conducted, and break‐even curves are given as references for the utilization of waste gas as a supplementary fuel. The economic velocity of the combustion air is suggested to be 18.2 m s^?1.     

Development of high intensity CDC combustor for gas turbine engines

Colorless distributed combustion (CDC) has been demonstrated to provide ultra-low emission of NOx and CO, improved pattern factor and reduced combustion noise in high intensity gas turbine combustors. The key feature to achieve CDC is the controlled flow distribution, reduce ignition delay, and high speed injection of air and fuel jets and their controlled mixing to promote distributed reaction zone in the entire combustion volume without any flame stabilizer. Large gas recirculation and high turbulent mixing rates are desirable to achieve distributed reactions thus avoiding hot spot zones in the flame. The high temperature air combustion (HiTAC) technology has been successfully demonstrated in industrial furnaces which inherently possess low heat release intensity. However, gas turbine combustors operate at high heat release intensity and this result in many challenges for combustor design, which include lower residence time, high flow velocity and difficulty to contain the flame within a given volume. The focus here is on colorless distributed combustion for stationary gas turbine applications. In the first part of investigation effect of fuel injection diameter and air injection diameter is investigated in detail to elucidate the effect fuel/air mixing and gas recirculation on characteristics of CDC at relatively lower heat release intensity of 5 MW/m³ atm. Based on favorable conditions at lower heat release intensity the effect of confinement size (reduction in combustor volume at same heat load) is investigated to examine heat release intensity up to 40 MW/m³ atm. Three confinement sizes with same length and different diameters resulting in heat release intensity of 20 MW/m³ atm, 30 MW/m³ atm and 40 MW/m³ atm have been investigated. Both non-premixed and premixed modes were examined for the range of heat release intensities. The heat load for the combustor was 25 kW with methane fuel. The air and fuel injection temperature was at normal 300 K. The combustor was operated at 1 atm pressure. The results were evaluated for flow field, fuel/air mixing and gas recirculation from numerical simulations and global flame images, and emissions of NO, CO from experiments. It was observed that the larger air injection diameter resulted in significantly higher levels of NO and CO whereas increase in fuel injection diameter had minimal effect on the NO and resulted in small increase of CO emissions. Increase in heat release intensity had minimal effect on NO emissions, however it resulted in significantly higher CO emissions. The premixed combustion mode resulted in ultra-low NO levels (<1 ppm) and NO emission as low as 5 ppm was obtained with the non-premixed flame mode.     

Simulation of producer gas flameless combustion with fresh reactant diluted by hot flue gas

Flameless combustion is considered as a flexible and efficient combustion process for low heating value gas fuel. This paper presents numerical simulations of premixed flameless combustion using producer gas as a fuel. Different initial conditions of the premixed fresh reactant (air/fuel mixture) and dilution levels are taken into account for the investigation. The numerical simulations were investigated using a network of chemical reactor models with the detailed reaction mechanism of GRI‐Mech 3.0. A threshold dilution level for flameless combustion fuelled by producer gas was determined. The numerical results show that dilution of the fresh reactant with hot combustion products and initial fresh reactant temperature play important roles in flameless combustion formation and its auto‐ignition behaviour, rather than equivalence ratio of the fresh reactant. In the flameless combustion regime, temperature and chemical concentrations were reduced while chemical kinetics process was decelerated, resulting in delay of the auto‐ignition process.     

Influence of nozzle design parameters on exhaust gas characteristics in practical-scale flameless hydrogen combustion

Considering the trend toward decarbonization, hydrogen is expected to be used as a fuel in industrial furnace burners. One of the challenges in using hydrogen as a fuel is the increase in thermal-NOx emission compared to hydrocarbon fuel owing to its high flame temperature. This study experimentally evaluated the combustion characteristics of flameless combustion, which is a low-NO_x combustion technology, with hydrogen as a fuel in a practical-scale experimental furnace as well as the effect of nozzle design parameters on the combustion characteristics. Through comparative tests with city gas by considering parameters, such as the fuel gas velocity, combustion air velocity, and air nozzle pitch, the low-NO_x effect of flameless combustion was confirmed in hydrogen combustion with appropriate nozzle design parameters. The optimal nozzle design parameters to achieve this effect differ from those for city gas, and the design guidelines are summarized.     

Effect of natural gas enrichment with hydrogen on combustion characteristics of a dual fuel diesel engine

Environmental benefits are one of the main motivations encouraging the use of natural gas as fuel for internal combustion engines. In addition to the better impact on pollution, natural gas is available in many areas. In this context, the present work investigates the effect of hydrogen addition to natural gas in dual fuel mode, on combustion characteristics improvement, in relation with engine performance. Various hydrogen fractions (10, 20 and 30 by v%) are examined. Results showed that natural gas enrichment with hydrogen leads in general to an improved gaseous fuel combustion, which corresponds to an enhanced heat release rate during gaseous fuel premixed phase, resulting in an increase in the in-cylinder peak pressure, especially at high engine load (4.1 bar at 70% load). The highest cumulative and rate of heat release correspond to 10% Hydrogen addition. The combustion duration of gaseous fuel combustion phase is reduced for all hydrogen blends. Moreover, this technique resulted in better combustion stability. For all hydrogen test blends, COV_IMEP does not exceed 10%. However, no major effect on combustion noise was noticed and the ignition delay was not affected significantly. Regarding performance, an important improvement in energy conversion was obtained with almost all hydrogen blends as a result of improved gaseous fuel combustion. A maximum thermal efficiency of 32.5%, almost similar to the one under diesel operation, and a minimum fuel consumption of 236 g/kWh, are achieved with 10% hydrogen enrichment at 70% engine load.     

Improving cost-effectiveness for the furnace in a full-scale refinery plant with reuse of waste tail gas fuel

The waste tail gas fuel emitted from refinery plant in Taiwan e.g. catalytic reforming unit, catalytic cracking unit and residue desulfurization unit, was recovered and reused as a replacement fuel. In this study, it was slowly added to the fuel stream of a heater furnace to replace natural gas for powering a full-scale distillation process. The waste tail gas fuel contained on average 60 mol% of hydrogen. On-site experimental results show that both the flame length and orange-yellowish brightness decrease with increasing proportion of waste gas fuel in the original natural gas fuel. Moreover, the adiabatic flame temperature increases as the content of waste gas fuel is increased in the fuel mixture since waste gas fuel has a higher adiabatic flame temperature than that of natural gas. The complete replacement of natural gas by waste gas fuel for a heater furnace operating at 70% loading (i.e. 3.6 × 10⁷ kcal/h of combustion capacity) will save 5.8 × 10⁶ m³ of natural gas consumption, and 3.5 × 10⁴ tons (or 53.4%) of CO₂ emission annually. Recovering and reusing the waste tail gas fuel as natural gas replacement will achieve tremendous savings of natural gas usage and effectively lower the emission of carbon dioxide.     

Physicochemical effects of varying fuel composition on knock characteristics of natural gas mixtures

The physicochemical origins of how changes in fuel composition affect autoignition of the end gas, leading to engine knock, are analyzed for a natural gas engine. Experiments in a lean-burn, high-speed medium-BMEP gas engine are performed using a reference natural gas with systematically varied fractions of admixed ethane, propane and hydrogen. Thermodynamic analysis of the measured non-knocking pressure histories shows that, in addition to the expected changes arising from changes in the heat capacity of the mixture, changes in the combustion duration relative to the compression cycle (the combustion “phasing”) caused by variations in burning velocity dominate the effects of fuel composition on the temperature (and pressure) of the end gas. Thus, despite the increase in the heat capacity of the fuel–air mixture with addition of ethane and propane, the change in combustion phasing is actually seen to increase the maximum end-gas temperature slightly for these fuel components. By the same token, the substantial change in combustion duration upon hydrogen addition strongly increases the end-gas temperature, beyond that caused by the decrease in mixture heat capacity. The impact of these variations in in-cylinder conditions on the knock tendency of the fuel have been assessed using autoignition delay times computed using SENKIN and a detailed chemical mechanism for the end gas under the conditions extant in the engine. The results show that the ignition-promoting effect of hydrogen is mainly the result of the increase in end-gas temperature and pressure, while addition of ethane and propane promotes ignition primarily by changing the chemical autoignition behavior of the fuel itself. Comparison of the computed end-gas autoignition delay time, based on the complete measured pressure history of each gas, with the measured Knock-Limited Spark Timing shows that the computed delay time accurately reflects the measured knock tendency of the fuels.     

Experimental study on combustion characteristics of compost using New‐type combustor

The aim of the present study is to develop the biomass furnace combustor, which can effectively use the compost as a fuel. Here, the compost that is made from pig's waste and has the calorific value of 2000 kcal/kg is employed here. Emphasis is placed on the optimum conditions of fuel and air flow rates and moisture content of the compost and the corresponding combustion gas components and combustion gas temperature in the combustor. It is found from the study that (i) except 40% of the compost's moisture content, the self‐combustion of compost as the fuel takes place, (ii) the combustion gas concentrations are affected by gas temperature, and (iii) the optimum value of the air‐to‐fuel ratio is obtained based on the gas temperature and the concentration of combustion gases. Copyright © 2016 John Wiley & Sons, Ltd.