Thermochemical conversion of fuels into hydrogen-containing gas using recuperative heat of internal combustion engines

The problem of the thermochemical recuperation of heat from the exhaust gases of internal combustion engines (ICEs) as a method of increasing of the efficiency of fuels has been considered. The thermodynamic analysis of thermochemical recuperation conditions was performed, and maximum efficiency conditions were determined. Catalysts for the steam conversion of oxygen-containing fuels into syngas were developed, and the Co-Mn/Al₂O₃ catalyst was shown to be the most promising. The model of a thermochemical heat recuperation system was developed and manufactured, and its bench tests in the conversion of alcohols were performed using the simulated exhaust gases from a heating device. Mathematical models for calculating units of the heat recuperation system were developed. A recuperation system was manufactured and tested in the ICE-free and ICE-integrated variants. Based on the test results, the equivalent fuel consumption characteristics of a recuperative ICE was revealed to decrease by 11–22% depending on its load with a decrease in the concentration of hazardous emissions by 8–12 times for CO, 2–3.5 times for CH, and 18–25 times for NO _x .     

新型低氮燃气分级燃烧器燃烧特性和NOx排放的CFD研究

应用CFD软件Fluent数值模拟了某二甲苯塔再沸炉在役油气联合燃烧器燃烧和NOx排放特性,分析了其NOx排放浓度较高的原因,提出了新型低NOx燃气分级燃烧器的改造方案,并数值模拟了新型燃烧器空气预热温度Tair、过剩空气系数α和主辅喷枪燃气质量分率Rp对辐射室壁面热通量、出口温度、火焰高度和炉膛出口NOx排放浓度的影响。针对在役燃烧器的模拟结果与现场运行数据吻合良好,说明所选模型能够正确模拟炉膛内部的流动、辐射、燃烧和NOx生成过程。新型燃烧器模拟结果表明,增加Tair会增加辐射壁面热通量,同时也会增加NO的排放;辐射壁面热通量随α增加而降低,NOx排放浓度随α增加而增加;Rp对炉内传热和NOx排放的影响并不明显。当Tair = 220℃、α = 1.05及Rp= 0.24时,新型燃烧器在模拟范围内达到最佳运行工况,辐射壁热通量为37.45kW/m2,NOx排放浓度为12.1μL/L。     

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。     

Microwave plasma combustion of coal

Microwave plasma is studied as an alternative to oil or gas fuel for ignition and stabilisation of burning of lean coal. The study is performed on an experimental set-up, which includes a burner with a microwave plasma generator, coal and air supply systems, and measurement equipment. Power and thermochemical characteristics of the coal-plasma interaction have been measured and analysed. The obtained results indicate an essential intensification of ignition and combustion processes in the microwave burner compared to those in conventional burners. In particular, it has been demonstrated that the microwave energy consumption is only about 10% of the required expenditure of oil or gas, measured in heat equivalent. A design of an industrial microwave-plasma burner is proposed. Prospects of such burner for applications at industrial boilers of power plants are discussed.     

热解燃烧链条炉低NOx排放特性的数值模拟

利用Fluent软件,对功率为1.4 MW的新型热解燃烧链条炉的NOx排放特性进行了数值模拟,其中,煤热解产生的还原性可燃气简化为CH4,采用添加元素N的乙烯-空气混合物模拟链条炉排半焦层燃烧及其生成的NO. 数值计算结果表明,在过量空气系数为1.2、再燃比为30%的燃烧条件下,热解燃烧比传统燃烧可降低NO排放14.6%. 热解燃烧链条炉由于热解气的再燃作用,在炉膛中形成一局部还原区,可较有效地降低NOx排放,证明了热解燃烧技术的可行性. 增大再燃比和减小炉排前段风室配风量可提高出口NO还原率,减小炉膛前拱长度和前后拱间距会使NO还原作用增强.     

Catalytic oxidation of natural gas using flameless burners of a new design

Various aspects of operating burners traditionally used for oxidizing gaseous hydrocarbons and heat exchangers used for heat recovery are considered. A method developed by FAST ENGINEERING LTD. for the efficient burning of fuel with deep heat recovery of waste gases while maintaining a given adiabatic temperature is described. The method is based on using a flameless burner and heat exchangers of a new design. Burner operation is tested on an experimental stand with determination of the dependences for the aerodynamic drag of a granular layer and the content of unburned hydrocarbons, CO, and NO _x in combustion products on the consumption of the fuel-air mixture and the adiabatic temperature of fuel combustion. The described method for burning fuel is shown to provide the desired temperature of combustion products for a consumer of heat energy and to reduce the consumption of fuel by 5–20%. Burning fuel at an adiabatic combustion temperature of no more than 1200°C virtually eliminates the CO and NO _x content in the combustion products. Designed flameless burner, new generation of heat exchangers, and technology for the efficient burning of fuel can be applied to vapor and water-heating boilers, gas turbines, and catalytic reactors to produce synthesis gas from natural gas for processing into hydrogen, ammonia, methanol, synthetic liquid hydrocarbons, and so on.     

Combination of thermochemical recuperative coal gasification cycle and fuel cell for power generation

An integrated power generation cycle combining thermochemical recuperation, brown coal gasification and a solid oxide fuel cell (SOFC) was proposed based on the concept of thermochemical recuperative energy. Process simulation combining the coal gasifier, gas turbine cycle, and SOFC module was conducted using the ASPEN Plus process simulation tool. The simulation indicated that the cycle efficiency increases from 39.5% (HHV) without the SOFC to about 45% (HHV) with the SOFC.     

Premixed gas combustion stabilized in fiber felt and its application to a novel radiant burner

Premixed gas combustion stabilized in a unique ceramic fiber felt has been investigated. Our aim was to better understand the flame structure and flame stabilization mechanisms in the porous felt medium in order to develop a new radiant burner. A novel recuperative radiant burner was designed and constructed. A flame stabilizes near the downstream interface of the porous medium that is an excellent selective thermal emitter. The burner was developed for use as a gas-fired light source. The combustion performance of the burner at various operating conditions and the effect of heat recuperation are presented. Combustion modes on the fiber felt were examined carefully. An optimal flame structure for the premixed gas combustion is attained and the flame stabilizes in the porous fiber felt at radiant mode combustion over a wide range of firing rates. The burner emits desired spectral radiation and generates fairly intense light at the conditions of heat recuperation. The light radiant burner could be used as an alternative low-glare light source in an integrated heat and light system in which the light is distributed through light pipes.     

催化燃烧蒸发器热态流场分布研究

为了改善催化燃烧蒸发器中反应和蒸发的耦合行为,提高蒸发器的热效率,文章对催化燃烧蒸发器进行了热态实验研究和数值模拟,确定燃料完全燃烧需要的过氧系数随着空速的增加而降低;同时,通过对催化燃烧蒸发器内初始浓度场和温度场的分析比较,说明当放热反应速率较快时,燃烧腔内温度场的空间分布主要受初始浓度场分布决定。实验和模拟结果的很好吻合,说明建立的多孔介质模型能够很好地预测燃烧腔内的流场分布。     

Characteristics of diesel fuel combustion in a burner with injection of a superheated steam jet

Basic characteristics of combustion of the diesel fuel in a novel autonomous burner with injection of superheated steam into the combustion region are studied. The temperature distribution in the flame is obtained. Calorimetric measurements of heat release and gas analysis of combustion products are performed. The environmental effects of fuel combustion are compared for regimes with injection of a steam jet and an air jet. It is demonstrated that the combustion regime with steam gasification ensures high combustion intensity and combustion efficiency; moreover, the combustion process becomes more environmentally friendly.     

掺氢天然气在家用燃烧器中的燃烧特性

为了降低CO2排放,缓解天然气供应压力,促进氢能规模消纳,掺氢天然气被认为是最有前途的途径之一。目前,掺氢天然气的研究主要集中在工业上,本工作基于以掺氢天然气为燃料的家用大气式燃烧器的燃烧特性,利用Fluent软件结合GRI 2.11化学反应机理文件,建立燃烧器二维轴对称模型,对比数值模拟结果与实验结果,验证了数值模型的合理性;分析了燃料与空气不同预混量以及二次风流速对燃烧器的燃烧温度、主要自由基含量、燃烧污染物等的影响规律。结果表明,随着预混量(一次空气系数)增大,峰值温度大幅度升高,NO峰值质量分数先增大后降低,CO峰值质量分数逐渐增大;随着二次风流速(过量空气系数)增大,温度与污染物含量变化很小,与预混量的影响相比,二次风流速的影响几乎可以忽略不计。     

载体孔道密度对天然气催化燃烧的影响

制备了不同载体孔道密度的Pd/γ-Al_2O_3和六铝酸盐蜂窝催化剂,在自行设计的催化燃烧实验装置上进行了天然气催化燃烧实验。考察了载体孔道密度、空燃比和燃气流量对催化燃烧效果的影响。结果表明,载体孔道密度影响孔道内壁面反应和气相反应变化以及燃烧流体孔道内的流动及燃烧过程的传热传质,当载体孔道密度为200目时,流速减小,加强了气流与壁面上的浓度边界层中反应物质的交换,温度峰值增大,HC排放少;载体孔道密度为400目,气相反应减少,不会产生局部高温区,NO_x排放小。空燃比影响催化反应炉内各床层轴心温度以及炉内温度峰值的出现位置。随着燃气流量的增加,温度随之上升,1200℃以上时会产生较多的NO_x。     

Stability of lean combustion in mini-scale porous media combustor with heat recuperation

In miniaturization of burners, it is very difficult to organize stable self-sustained combustion. A mini-scale porous media combustor with heat recuperation was set up to study the stability of lean combustion and its emission. The diameter of the porous media was only 20 mm and the burner was about 140 mm in length. Experimental results showed that when the mass flow rate of the premixed gas was 0.163 g/s, the extinction limit was extended to Φ = 0.40 in the methane combustion and Φ = 0.39 in the propane combustion. For most cases, the emission of CO was lower than 100 ppm in both methane and propane combustion. The maximal concentration of NO_x was 63 ppm in the methane combustion. The ultra-lean combustion was also predicted by a numerical simulation with a 2D two-temperature model. The heat recuperation efficiency η, as high as 40%, made the ultra-lean combustion extremely stable. Although the maximal flame temperature in the porous media reached above 2000 K, the exhausts temperature was lower than 900 K.     

Ignition of Particles of Wet Woody Biomass under Convective Diffusion of Water Vapor in the Near-Wall Region

This paper presents the results of an experimental and theoretical study of heat and mass transfer during ignition of wet wood particles in a high-temperature gas medium. Experiments were carried out in a setup which provides conditions similar to the combustion spaces of boiler units. The main heat transfer parameters (ambient temperature) and integrated ignition characteristics (ignition delay) were measured. The measurement error of these parameters did not exceed 18%. The convective transfer of water vapor formed during evaporation of pore moisture and pyrolysis products were found to have an insignificant effect on the ignition characteristics and conditions. From the results of the experiments, a mathematical model of the ignition process was developed which describes the simultaneous occurrence of the main processes of thermal preparation under conditions of intense phase (evaporation of water) and thermochemical transformations (thermal decomposition of the organic part of the fuel, thermochemical interaction between water vapor and carbon coke, ignition of volatiles) taking into account the convective diffusion of water vapor and pyrolysis products in the near-wall gas area during the induction period. The theoretical ignition delay is in satisfactory (within the confidence interval) agreement with the experimental value. The numerical model of the diffusion flame adequately (good agreement between experimental and theoretical ignition delays) describes the ignition of a wet wood particle.     

回转窑二次风富氧燃烧的数值模拟

针对一实际尺寸的回转窑建立模型，分别进行了空气助燃(21% O2)和二次风富氧(23% O2)燃烧的数值模拟研究。结果表明，二次风富氧后，高温区覆盖形状没有明显变化，仍呈“棒槌状”；在回转窑前端，煤粉挥发分与焦炭燃烧速度加快，整体温度有所提升，最高温度由2386 K增至2427 K，壁面所接收的辐射量得到了提升；但NOx的生成量也大幅度提高，其中出口处NOx由247 mg/m3增至367 mg/m3。考虑到制氧成本问题及NOx排放问题，在二次风中进行富氧燃烧的总体效果不够理想。     

Development of a catalytic heating system for external combustion engines

A catalytic heater design was proposed for an external combustion engine. This design is based on the partial oxidation or autothermal conversion of hydrocarbon fuel to syngas and its further oxidation with heat generation in a radial catalytic reactor integrated with a tubular heat exchanger. The theoretical analysis of operational regimes for a catalytic heater with a thermal power of 25–50 kW was performed with regard to the distribution of gas and the mathematical modeling of processes in a catalyst bed integrated with a heat exchanger, and some estimates were given for the performance of an external combustion engine. The conditions providing a uniform distribution of gas along the length of a radial reactor with suction of a reaction mixture into the catalyst bed were determined. A design of catalytic heating system elements was developed, and some layout solutions that provide a rational mutual arrangement of system components were created.     

EFFECT OF FURNACE GASES UPON GLASS ENAMELS1

The effect of various fuel gases of products of combustion, and pressures on bonding of ground coat, physical condition and gloss of the enamel were studied under laboratory controlled conditions to determine the comparative results of firing in open and muffle furnaces and with fuel of different sorts. The benefits of recuperation are shown to he in complete combustion rather than in excess oxygen. Very hot diluted air would increase the efficiency of either oil or gas burners and produce better enamels.     

低NOx燃气燃烧技术研究进展

气体燃料具有易于点火、燃烧迅速、燃烧完全等特点,且氮、硫、灰分低,因此燃烧后产生的污染物相对较少,属于较清洁的燃料,且国家燃气补贴政策的实施,使气体燃料燃烧近年来有很好的发展前景。但随着国家对大气污染物的控制更加严格,控制气体燃料燃烧过程中NOx的生成至关重要。笔者介绍了不同种类NOx的产生机理及影响因素,并基于NOx的产生机理提出控制措施,分析目前应用较广泛的燃气燃烧技术的低氮原理及应用现状,最后提出燃气燃烧器应用的展望。燃气燃烧过程中主要以热力型NOx及快速型NOx为主,温度和过量空气系数是影响NOx生成的主要影响因素。燃烧温度高于1 500℃时,热力型NOx呈指数型增长,温度是影响NOx生成的最重要因素。根据NOx产生机理,低NOx燃烧技术的实质是降低最高燃烧温度,控制燃烧区燃料浓度以及氧浓度,缩短烟气在高温区的停留时间,破坏NOx生成的最佳条件,最终抑制NOx的生成。低NOx燃烧技术一定程度降低了NOx的生成,但又会破坏整个燃烧进程,对燃烧和放热过程造成不利影响,降低了燃烧效率和传热效率,因此如何解决这些矛盾是亟需解决的问题。在实际应用中,应根据需求选择合适的燃烧技术,同时可将不同燃烧技术相结合起到稳燃、低氮的效果。应用较广泛的燃气燃烧技术主要是阶段型燃烧技术、烟气再循环燃烧技术、无焰燃烧技术等,其中催化燃烧技术发展前景较好,目前已应用于多个领域,其催化剂的热稳定性和寿命问题是限制其工业上广泛应用的核心问题。     

65t／h生物质循环流化床锅炉热效率性能实验

介绍了以农林废弃物为主要燃料的生物质直燃循环流化床锅炉。对生物质循环流化床锅炉进行了额定、常用及最大负荷下的热效率测试实验,并对其热效率进行了修正。结果表明：锅炉热损失主要来自排烟热损失q4和固体未完全燃烧热损失q4;对进风温度、给水温度、燃料特性进行了修正,在12,13．5,15MW工况下修正后的热锅炉效率分别为87．57％,88。77％和88．72％。     

Modeling and simulating combustion and generation of NOx

This paper deals with the modeling and simulation of combustion processes and generation of NO_x in a combustion chamber and boiler, with supplementary combustion in a gas turbine installation. The fuel burned in the combustion chamber was rich gas with a chemical composition more complex than natural gas. Pitcoal was used in the regenerative boiler. From the resulting combustion products, 17 compounds were retained, including nitrogen and sulphur compounds. Using the developed model, the simulation resulted in excess air for a temperature imposed at the combustion chamber exhaust. These simulations made it possible to determine the concentrations of combustion compounds with a variation in excess combustion.