微通道内甲烷/湿空气重整转化效率实验研究

用沉淀法制备了涂覆在微通道内壁面的Ni/Al2O3催化剂,在自行搭建的实验系统上进行了微通道内甲烷/湿空气催化重整的实验研究,考察了催化壁面温度、空碳比及甲烷体积流量对甲烷/湿空气重整转化效率的影响,并与数值计算结果进行对比.结果表明,随着催化温度的升高,甲烷转化率不断升高;相同水碳比下,甲烷的催化转化率随着空碳比的增大而增大;随着甲烷体积流量的增大,甲烷转化效率呈现先增大后减小的变化规律.反应温度为1 023 K,甲烷体积流量为20 mL/min时,实验所得甲烷转化率达到最大值,为61.3％.     

微纤包结细粒子结构化微燃烧器的催化燃烧性能

具有三维微米孔道的烧结Ni微纤包结Pt/Al2O3细粒子催化剂复合材料结构化于毫米尺度流道中的微催化燃烧器,可以作为微型吸热反应的热量来源.考察了操作条件及Pt负载量对微燃烧器中氢气/空气催化燃烧性能的影响,并对催化剂进行了表征.结果表明处于爆炸极限内的氢气催化燃烧反应可以在微燃烧器中安全进行,过高Pt负载量会降低催化燃烧性能.在反应温度83℃,体积空速2.0×105 h-1,氢气入口摩尔分数28.5%,负载5%质量分数Pt的条件下,氢气转化率高达92-2%.     

甲烷微尺度燃烧中气相反应与催化反应间的相互作用

以往对甲烷微尺度催化燃烧的研究中,甲烷的气相反应往往没有受到足够的重视,有时候甚至被忽略。为了了解气相反应在甲烷的微尺度燃烧中所起的作用,本文使用了计算流体力学软件Fluent对CH_4和空气的预混气体在微尺度平板燃烧器中的催化燃烧过程进行了数值模拟,对比在0.2mm和1mm两种间距的微尺度平板燃烧器内CH_4的催化燃烧过程,研究了微尺度平板燃烧器内CH_4气相反应与CH_4催化反应的相互影响,其中重点研究了CH_4气相反应对CH_4催化反应的影响。模拟结果显示:(1)在间距为0.2mm和1mm的微尺度平板燃烧器中,CH_4气相反应均是由CH_4催化反应所引起;(2)在0.2mm间距的微尺度平板燃烧器中,CH_4气相反应产生的OH促进了CH_4催化反应的进行;(3)在1mm间距的微尺度平板燃烧器中,CH_4气相反应对CH_4催化反应仍然具有促进作用,但对CH_4催化反应的抑制作用更为显著。研究结果可以为设计和开发高效稳定的微尺度平板燃烧器提供参考。     

甲烷与正丁烷微小尺度催化燃烧性能比较

对微圆管内甲烷和正丁烷在Pt/ZSM-5上的催化燃烧进行实验研究,获得并分析了二者的稳燃范围、产物浓度、壁温分布和壁面散热等燃烧性能。发现在富燃条件下甲烷和正丁烷能够在大当量比下实现催化自稳燃烧。相同流量下正丁烷稳燃当量比范围宽于甲烷,贫燃范围在0.4附近。流量由200 ml·min^-1增大至1000 ml·min^-1,甲烷和正丁烷转化率出现大幅下降。在实验范围内,正丁烷和甲烷的转化率差异不大。化学当量比条件下随流量增大,正丁烷的转化率在600 ml·min^-1开始高于甲烷。甲烷和正丁烷能够在散热比例高达70%的情况下自稳催化燃烧且转化率在95%以上。相同流量下,与甲烷相比,正丁烷催化燃烧的壁温、散热功率和散热比例都更高。整体来看,正丁烷催化稳燃范围较甲烷略宽,两者转化率曲线相近,放热功率和壁面散热功率相差较小,正丁烷在必要时可作为甲烷的替代燃料。     

甲烷与正丁烷微小尺度催化燃烧性能比较

对微圆管内甲烷和正丁烷在Pt/ZSM-5上的催化燃烧进行实验研究,获得并分析了二者的稳燃范围、产物浓度、壁温分布和壁面散热等燃烧性能。发现在富燃条件下甲烷和正丁烷能够在大当量比下实现催化自稳燃烧。相同流量下正丁烷稳燃当量比范围宽于甲烷,贫燃范围在0.4附近。流量由200 ml·min~(-1)增大至1000 ml·min-1,甲烷和正丁烷转化率出现大幅下降。在实验范围内,正丁烷和甲烷的转化率差异不大。化学当量比条件下随流量增大,正丁烷的转化率在600 ml·min~(-1)开始高于甲烷。甲烷和正丁烷能够在散热比例高达70%的情况下自稳催化燃烧且转化率在95%以上。相同流量下,与甲烷相比,正丁烷催化燃烧的壁温、散热功率和散热比例都更高。整体来看,正丁烷催化稳燃范围较甲烷略宽,两者转化率曲线相近,放热功率和壁面散热功率相差较小,正丁烷在必要时可作为甲烷的替代燃料。     

微尺度催化燃烧的研究进展

阐述了微尺度催化燃烧的重要意义,描述了它的概念、特点、分类和发展概况。综述了微尺度催化燃烧在微型动力系统(MEMS)中的应用,重点介绍了几种典型的微尺度催化燃烧器的应用和研究概况。指出数值模拟的方法,为研究微尺度催化燃烧提供了方便而高效的途径。微尺度催化燃烧在国防和经济建设中具有广阔的应用前景。     

控制一氧化碳能提高炉子燃烧效率

通常炉子在燃烧过程中,大部分燃烧控制系统只测量燃料流量和空气流量以控制炉子的燃烧效率。由于燃烧热值和流量配比不同,流量计量控制方法需要考虑过量空气来确保燃烧的安全,通常需要20—35%的过量空气,这样的控制方法必然要增加烟道气带出的热量(因为烟道气带出的热量与过量空气成正比)。同时,在燃烧过程中,燃料热值、流量压力、温     

天然气冲天炉富氧燃烧器火焰特性的数值模拟

设计了一种新型天然气冲天炉富氧燃烧器,并建立物理模型和数学模型。利用CFD软件fluent模拟了不同甲烷喷入量和过量空气系数对燃烧室最高温度、体积平均温度、出口平均温度等的影响规律,为今后相关燃烧器设计工作提供理论依据。     

煤层气燃烧器流动及NO_x生成特性数值研究

针对煤层气热值低的特点,设计了一台煤层气旋流燃烧器,采用数值模拟方法研究了不同热负荷及过量空气系数对燃烧性能的影响,并计算了燃烧污染物的生成.结果表明,在燃烧区域存在逆压梯度,加强了烟气的扰动,有利于形成稳定的高温区,提高燃烧效率.燃烧器负荷调节范围大,低负荷时仍能保持较高的燃烧温度和燃烧效率.过量空气系数为1.05时燃烧温度最高,此时NOx生成最多,仅为25.1 mg/m3.     

合成氨转化炉高效节能燃烧器的研究与应用

通过分析燃烧过程中助燃空气的过剩量,对合成氨一段转化炉现有燃烧器存在的问题进行了诊断。采用对比实验的方法研究了混合方式对燃烧器特性的影响,开发了一种新型燃烧器,经过工业性试验和试用,取得了良好效果。新型燃烧器消耗的助燃空气量明显减少,燃烧状况良好,转化管的传热特性改善,在不增加燃料消耗的情况下,炉膛温度和转化气温度显著升高,排烟温度降低,二段转化炉耗氧量下降,甲烷转化率提高,年增产氨5 700 t。     

O2/CO2气氛中水蒸气预混CH4燃烧特性与烟气余热梯级利用方案

对O2/CO2气氛中甲烷预混水蒸气燃烧特性及主要污染物生成进行了数值模拟研究,在加湿燃烧的基础上提出一种全新的清洁燃烧方式,即在保证甲烷流量一定时,通过改变入口处水蒸气的质量分数,研究水蒸气预混比Rf(0, 0.1, 0.2, 0.3, 0.4和0.5)对燃烧流场、燃烧组分和污染物浓度的影响。结果表明,随Rf增大,燃烧反应速率上升、燃烧效率提高且污染物排放量降低。模拟所得甲烷预混水蒸气的最优气氛为81%CH4/19%H2O,提出了一种高效节能的O2/CO2气氛下水蒸气预混CH4燃烧与烟气余热梯级利用方案。     

Numerical simulation of the combustion of hydrogen-air mixture in micro-scaled chambers. Part I: Fundamental study

Understanding of micro-scale combustion mechanism is very essential to the development of combustion-based micro-power devices, which may supply much higher energy density than the batteries used nowadays. In part I of this paper, Computational Fluid Dynamics (CFD)-based numerical simulations have been performed to study the combustion of premixed hydrogen-air mixture in a series of chambers with same shape aspect ratio but various dimensions from millimetre to micron level. The transition of the combustion phenomena in the chambers from relatively large scale to micro-scale has been studied numerically to investigate the micro-combustion mechanism. The combustion model of premixed hydrogen-air mixture represents the detailed reaction mechanism with 19 reversible elementary reactions and nine species. The effect of various heat transfer conditions at chamber wall, e.g. adiabatic wall, with heat loss and heat conduction within the wall, on the combustion is analysed. These thermal conditions have strong effects on the combustion especially when the chamber dimension goes smaller and the ratio of surface area to volume becomes larger. Both factors, such as larger heat loss through the chamber wall and smaller chamber dimension size, may lead to the thermal quenching of micro-scale combustion. The simulation results also indicate that the stable combustion in a micro-scaled chamber may be sustained through increasing the ratio of flow residence time in chamber to chemical reaction time, and maintaining proper thermal condition. In part II of this paper, the numerical modelling method developed here is applied to analyse the micro-combustion characteristics in a three-dimensional micro-combustor based on the prototype developed by the MIT group for a micro gas turbine engine.     

甲烷催化燃烧反应工艺研究进展

甲烷催化燃烧是一种清洁高效的甲烷燃烧技术,在节能减排中具有重要的应用价值。从催化剂、反应工艺和过程强化等方面对近年来甲烷催化燃烧技术进行综述,重点介绍颗粒催化剂固定床反应工艺、整体式催化剂反应工艺、流化床反应工艺和吸放热耦合反应工艺研究进展。用于固定床反应器的颗粒催化剂主要为负载型贵金属催化剂和非贵金属氧化物催化剂。贵金属催化剂活性好,起燃温度低,适合低浓度甲烷的催化燃烧。非贵金属氧化物催化剂耐高温性好,适合较高浓度甲烷燃烧体系。整体式催化剂的甲烷催化燃烧反应工艺中,最常用的是蜂窝陶瓷和金属合金等整体式催化剂的多段式催化燃烧反应器的设计。设计直接采用多段式整体催化剂,催化剂的位置不同,发挥的催化作用也不同。流化床催化燃烧装置具有燃烧过程接触面积广、热容量大和换热效率高等特点,可有效避免传统的固定床催化燃烧反应工艺存在的问题,非常适合应用于低浓度甲烷的催化燃烧过程。利用甲烷催化燃烧强放热的特点,将催化燃烧产生的热量进行时间或空间的耦合,可以开发出吸-放热耦合反应工艺。其中,固定床催化反应器中的流向变换强制周期操作作为一种高效的过程强化技术,在节约反应器成本的同时,可以提高反应热量的利用率。     

1kW SOFC-CHP系统用催化燃烧耦合蒸汽重整反应器的实验研究

针对1 kW 固体氧化物燃料电池热电联供(SOFC-CHP)系统开发了集成催化燃烧、换热及蒸汽重整的反应器,搭建了性能评价系统,系统研究了燃烧侧气体组分及工艺参数对该反应器性能的影响规律。实验结果表明:在反应器燃烧侧气体入口温度为300℃、空燃比为10:1、电堆燃料利用率为65%、水碳比为3 的条件下,重整侧转化率达到73.6%,重整尾气中H₂ 含量为67.5%。电堆燃料利用率对重整反应转化效率影响较大,其值大于80%时,采用尾气燃烧的余热回收方式无法有效为蒸汽重整提供所需热量。在150~350℃范围内,降低燃烧侧气体入口温度对重整反应效率影响较小,建议采用尾气先换热再进行催化燃烧的流程设计,保证重整效率的前提下可有效提升系统热效率。空燃比的降低可小幅度提升重整效率,在保证电堆反应温度稳定的前提下,适当降低空燃比可减少空气压缩机的功耗,从而提升整个系统的效率。研究成果对SOFC-CHP 系统的优化和整体效率提升具有指导意义。     

肋片对微小燃烧室内甲烷燃烧与传热特性影响

建立含有肋片的微小通道内甲烷/空气燃烧模型,研究了带肋片的导热壁面对微小尺度燃烧和传热特性的影响。结果表明,纵向肋片对于微小通道中的燃烧和传热过程有着非常重要的影响,与没有肋片的光滑通道相比,带有肋片的壁面起到了良好的导热作用,燃烧室内区域的温度分布梯度大幅降低;纵向肋片的数量对燃烧和传热特性的影响作用要优于肋片高度的影响;横向肋片的高度对火焰位置有着很大的影响,肋片高度增加火焰位置后移且流体区域的温度分布梯度加大;横向肋片宽度和肋片位置对微燃烧和传热过程的影响甚小;两个肋片及肋间距大的通道,其微燃烧和传热特性得到了较大的改善。     

Numerical simulation of the combustion of hydrogen-air mixture in micro-scaled chambers Part II: CFD analysis for a micro-combustor

Understanding of the flow dynamics, chemical kinetics and heat transfer mechanism within micro-combustors is essential for the development of combustion-based power MEMS devices. In Part I, CFD based numerical simulation has been proven to be an effective approach to analyse the performance of the micro-combustor under various conditions. In this paper, numerical simulations are performed to analyse the combustion behaviour in a three-dimensional micro-combustor based on the prototype used in the MIT micro-gas turbine engine. The CFD model of the micro-combustor includes fuel/air flow path, combustion chamber as well as solid walls used to construct the combustor. The simulation analysis includes not only the detailed chemical reactions occurred in the combustion chamber, but also the fluid flow dynamics, heat transfer within the combustor and heat loss to the ambient. The performance of the combustor is evaluated under various fuel/air ratio, flow rate and heat loss conditions. Through such systematic numerical analysis, a proper operation space for the micro-combustor is suggested, which may be used as the guideline for micro-combustor design. In addition, the results reported in this paper illustrate that the numerical simulation can be one of the most powerful and beneficial tools for the micro-combustor design, optimisation and performance analysis.     

Controlled three-stage heat release of stratified charge compression ignition (SCCI) combustion with a two-stage primary reference fuel supply

This paper discusses the heat release mode and its effect on combustion characteristics of stratified charge compression ignition (SCCI) combustion with a two-stage fuel supply. To create and control the fuel concentration stratification, composition stratification, and temperature stratification, primary reference fuels or their mixtures were supplied from the intake port, while n-heptane was directly injected into the cylinder near the top dead center of the compression stroke. To achieve a controllable staged heat release and to optimize the thermal efficiency and emissions, important factors, including premixed fuel properties, direct injection timing, the overall equivalence ratio, and the premixed ratio were tuned to modulate the heat release pattern. The experimental results revealed that, with the port fuel injection of a two-stage reaction fuel, the heat release curve of the SCCI combustion exhibits a three-stage heat release pattern. The in-cylinder fuel delivery advance angle plays an important role in the indicated thermal efficiency, and the earlier fuel delivery angle has a positive effect on the indicated thermal efficiency. It should be noted that an excessively advanced fuel delivery angle will lead to a sharp increase of NOx emissions. With the port fuel injection of PRF50, both fuel efficiency and ultra-low NOx emissions were obtained over wide ranges of the premixed ratio and the equivalence ratio. Moreover, the experimental results suggest that a higher premixed ratio for low-to-medium equivalence ratios and a smaller premixed ratio for larger equivalence ratios are preferred. The maximum thermal efficiency was observed at the zone with the earlier CA50 but with shorter burn duration. NOx levels were determined not only by CA50 and burn duration but also by the heat release mode. One-stage SCCI combustion, which was dominated by the diffusion burn, exhausted considerable NOx emissions, compared to the staged heat release mode.     

Application concepts and evaluation of small-scale catalytic combustors for natural gas

Basic application concepts of catalytic combustion are roughly classified into three types, and the development of catalysts, combustion performance and applicability are stated. On the diffusive catalytic combustion method, completeness of methane combustion and its reaction mechanism have been demonstrated by detailed combustion analysis of the burner and reaction kinetics. On the adiabatic lean premixed catalytic combustion method, applicability of a high-temperature catalyst system based on Mn-substituted hexaaluminate monolithic honeycomb to a 1.5 MW gas turbine combustor has been investigated through pressurized combustion tests and prototype engine-rig tests. As a result, a good outlook of the basic technical problems to overcome including the catalyst durability and the combustor control method was obtained, but another problem was that of the combustor capacity. In view of the progress of the non-catalytic lean premixed combustion method, it was concluded that a hybrid catalytic combustion method limiting catalytic combustion to the low-temperature range in this concept might become efficient in the future, but that it would depend on the development of efficient catalysts initiating their activity at about 350°C and having durability at 1000°C.     

Development of a catalytically assisted combustor for a gas turbine

A catalytically assisted low NO_x combustor has been developed which has the advantage of catalyst durability. This combustor is composed of a burner section and a premixed combustion section behind the burner section. The burner system consists of six catalytic combustor segments and six premixing nozzles, which are arranged alternately and in parallel. Fuel flow rate for the catalysts and the premixing nozzles are controlled independently. The catalytic combustion temperature is maintained under 1000°C, additional premixed gas is injected from the premixing nozzles into the catalytic combustion gas, and lean premixed combustion at 1300°C is carried out in the premixed combustion section. This system was designed to avoid catalytic deactivation at high temperature and thermal or mechanical shock fracture of the honeycomb monolith. In order to maintain the catalyst temperature under 1000°C, the combustion characteristics of catalysts at high pressure were investigated using a bench scale reactor and an improved catalyst was selected for the combustor test. A combustor for a 20 MW class multi-can type gas turbine was designed and tested under high pressure conditions using LNG fuel. Measurements of NO_x, CO and unburned hydrocarbon were made and other measurements were made to evaluate combustor performance under various combustion temperatures and pressures. As a result of the tests, it was proved that NO_x emission was lower than 10 ppm converted at 16% O₂, combustion efficiency was almost 100% at 1300°C of combustor outlet temperature and 13.5 ata of combustor inlet pressure.     

自由堆积多孔介质内预混燃烧火焰传播

为了解多孔介质内预混燃烧火焰前沿的传播特性,对不同化学当量比（=0.7～1.0）的甲烷/空气预混气体在不同孔隙率（ε为0.37和0.42）的多孔介质内的火焰前沿传播特性进行了研究,多孔介质采用3 mm和6 mm直径的Al₂O₃小球在陶瓷管中堆积而成。结果表明,预混气体在多孔介质中能够形成低速燃烧的稳定燃烧波;其火焰传播速度随化学当量比增大而加快,最大的火焰传播速度为3.52×10^-3 cm·s^-1;多孔介质的结构对火焰前沿传播速度影响很大,即使在孔隙率差别不大的情况下,大球堆积而成的多孔介质比小球具有更高的火焰前沿传播速度。