熔渣气化炉喷嘴燃烧区行为的数值模拟研究

燃烧区是熔渣气化炉的重要区域,其对熔渣气化炉的工作状态具有明显影响。基于双欧拉模型探究了燃烧区的速度场、温度场和组分场的分布特征及燃烧区空腔的形成过程。研究发现：工业级熔渣气化炉燃烧区呈“羽”状,其先向炉中心延伸再斜向上发展;气体在熔渣气化炉中心区域的流动速度为2.5 m/s左右,但未形成“高速对撞区”;高温区出现在燃烧空腔外表面附近特别是正对喷嘴且靠近炉中心的区域,该区域的温度可以达到约2000℃;氧气主要分布在气化剂喷嘴前端约0.5 m的空腔内,一氧化碳的分布区域与水蒸气在空间上有较大程度重叠,二氧化碳主要在喷嘴前端空腔外壳附近生成,氢气浓度较高的区域则出现在燃烧区对应空腔的上沿;沿喷嘴轴线方向,气体温度呈先升至峰值再逐渐下降的趋势。随着气化剂流量的增大,燃烧温度极大值出现的位置逐渐朝炉中心处移动,并呈较明显的线性变化规律。     

基于双色法测量气化火焰温度场的研究

基于双色法测温原理,测量了多喷嘴对置式气化炉内气化火焰的温度场.为减少测量误差,对CCD摄像机系统进行了标定,并对拍摄的气化火焰图像进行了处理,提高了测量的精度.结果表明:两喷嘴运行时,撞击气化火焰不规则,火焰末梢有时会冲刷炉壁,火焰主体温度分布范围为1 400 ℃～1 600 ℃;四喷嘴运行时,撞击气化火焰呈单峰十字型,集中在炉膛中心且更均匀,火焰主体温度分布范围为l 500 ℃～1 800 ℃.气化炉在两喷嘴工业运行时,另一对不使用的烧嘴应采用氮气保护,并尽量避免两喷嘴在长周期下运行,以延长耐火砖和喷嘴的使用寿命.     

载气对两段式干煤粉加压气化炉气化特性的影响

相比于N_2,CO_2作为气化炉煤粉载气会降低合成气中N_2的含量而有利于后续CO_2捕集,但O_2在CO_2中较小的扩散系数会影响焦炭的反应特性,进而影响气化炉运行结果。为此,考虑到气化炉中较高的CO含量及其对煤气化反应的抑制作用,将Langmuir-Hinshelwood动力学模型与缩核模型相结合,提出一个改进的焦炭反应模型,并对两段式干煤粉气化炉内的流场、温度场和组分浓度场进行了模拟分析,结果与实炉实测数据一致。在此基础上,模拟分析了气化炉在不同煤粉载气(N_2、CO_2)、两种二段给煤量下的气化特性。结果表明,煤粉载气由N_2改为CO_2后,由于O_2在CO_2中较低的扩散速率,一段气化室喷嘴区域气体温度和碳转化率降低,该区域CO_2增多对焦炭-CO_2反应的促进作用对提高碳转化率的影响较小;在一段气化室喷嘴区域之上,O_2浓度较低导致O_2扩散性影响减弱,同时CO_2增多促进焦炭-CO_2反应进而提高碳转化率。研究结果还证实,煤粉载气由N_2改为CO_2会促进CO的生成,抑制H_2的生成。     

水煤浆添加剂的研制开发和应用

0引言 水煤浆加压气化技术是当今世界上比较先进和成熟的气流床煤气化技术,其气化过程是：一定浓度的水煤浆和纯净的氧气通过特殊的喷嘴进入气化炉反应室反应,生成以CO和H2为主要成分的粗合成气,用于生产NH3、H2、甲醇和联合发电等。该技术对煤种的适应性强、碳转化率高,粗合成气中有效气体含量高,并且不会产生焦油等副产物。水煤浆中水分含量的高低影响着气化炉的能耗,水分含量越高,气化炉的能耗也就越高,     

Texaco水煤浆气化过程的数值模拟

基于CFD算法,采用Fluent软件对某企业的Texaco气化炉气化过程进行模拟,考察CO、H_2、CO_2与H_2O(g)四种主要气体在气化炉内的速度与浓度的分布特征及气化室内的温度场特性。模拟结果表明,炉内气体的速度场分布具有区域性,并导致气化炉的拱顶超温,同时气体浓度分布与炉内温度分布特征相关。出口煤气成分浓度的模拟值接近于工业数据,证明模型的正确性。     

水煤浆气化炉内飞灰的形成机理

基于实验室规模的多喷嘴对置式水煤浆气化炉,利用SEM、马尔文激光粒度仪和XRD表征气化炉内飞灰的粒径分布和组成,并分析了气化炉内飞灰的形成机理。结果表明,喷嘴平面处飞灰与气化炉出口处飞灰的粒径分布及化学组成存在显著差异,不同气化阶段飞灰的形成机理也不同。气化燃烧阶段飞灰的形成机理为部分固定碳燃烧和外在矿物转化,而在焦炭气化反应阶段,飞灰的形成机理为焦炭破碎和内在矿物释放及转化。     

焦炉煤气非催化部分氧化的数值模拟

用Fluent软件对焦炉煤气非催化部分氧化制取合成气的反应器内的温度场、浓度场和平衡气体组成进行了数值模拟.结果表明,氧气与焦炉煤气比是决定气化温度和出口合成气成分的关键.随着氧气与焦炉煤气比的增加,气化温度升高.在氧气与焦炉煤气质量比为0.14时,反应器出口的有效气体(H2+CO)含量达到最大值,焦炉煤气中的CH4几乎完全转化.在距反应器喷嘴0.05 m处反应器内达到了最高温度3 300 K,在0.1 m处H2和CO及CO2均达到平衡,CH4在该点降到最低点.     

二段组合式气化炉的数值模拟

二段组合式气化炉利用化学反应方式回收高温煤气中的显热,能有效地提高现有气流床气化技术的能量利用效率。文中利用Fluent中的PDF燃烧模型和多孔介质模型,对该组合式气化炉进行了数值模拟研究,模拟计算结果与实验值吻合较好,验证了模型的可行性。模拟结果表明:一段燃烧区的撞击流有效促进了热质传递,在一段喷嘴平面区域产生了强烈的回流,并且模拟得到了2股射流火焰撞击形成的"花瓣型"火焰形状;在二段固定床两侧存在压降,气流和温度在床层内的径向分布更加均匀,并且二段固定床能够影响水蒸气变换反应的进行。文中的模拟结果为二段组合式气化炉的工艺和结构设计提供参考。     

多喷嘴对置式气化炉内颗粒挥发分火焰可视化研究

基于实验室规模多喷嘴对置式水煤浆气化炉及其可视化装置,研究了气化炉喷嘴平面非射流区颗粒挥发分燃烧过程。结合图像处理技术,在气化条件下对粒径小于300 μm颗粒挥发分火焰尾迹形态及变化过程进行分析。研究结果表明,颗粒挥发分火焰非典型包络型火焰,而是形成挥发分火焰尾迹。颗粒挥发分尾迹形态受颗粒脱挥发分所处阶段和颗粒相对于气流的运动状态的影响,随时间不断变化。颗粒挥发分最大火焰尺寸随颗粒粒径增加而增加。气流床气化还原性气氛条件下颗粒挥发分燃烧时间较颗粒在富氧气氛中燃烧时间显著增加。     

双通道喷嘴渣油气化过程(Ⅱ)区域模型

根据实验所得模型气化炉流场结构,提出了8.53MPa双通道喷嘴渣油气化炉气化反应的区域模型。与传统模式不同,本模型指出回流组分参与燃烧反应,系统出口进行逆变换反应,并就气体成分、耐火砖与激冷环寿命短等工程现象与问题给出了合理解释。     

Experimental study on CH* chemiluminescence characteristics of impinging flames in an opposed multi‐burner gasifier

The bandpass filtered images of impinging flames in an opposed multi‐burner (OMB) gasifier was visualized by a CCD camera combined with a high temperature endoscope. A filtering and image processing method by use of three bandpass filters was applied to subtract soot and CO₂* contributions in the CH* band and obtain the CH* chemiluminescence of impinging flames. The results show that a clear reaction core is generated in the impinging zone of four‐burner impinging flames. The size of the reaction core is affected by the O/C equivalence ratio ([O/C]_e) and the impingement effect is relatively stronger at lower [O/C]_e. The flame lift‐off length in the gasifier is jointly controlled by the syngas concentration and the diesel atomization effect. The impingement effect shortens the flame lift‐off length. The relationship between the syngas concentration and the maximum CH* intensity makes it possible to evaluate the syngas concentration from CH* intensity. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2007–2018, 2017     

提高水煤浆气化有效气成分的途径

通过对多元料浆气化装置中A、C气化炉运行情况的对比,找出影响有效气（CO＋H2）含量的主要因素是烧嘴结构和煤浆浓度,提出调整烧嘴喷口尺寸改变中心氧量、烧嘴压差的改进措施,提高工艺气中有效气含量。     

多喷嘴对置式水煤浆气化炉内火焰声学特性分析

气化炉内火焰声学信号是表征水煤浆气化炉内火焰燃烧及流动特性的重要信息。为了更好地了解气流床气化炉内撞击火焰的燃烧特性及其对气化炉的影响,在多喷嘴对置式气流床气化炉中,进行了两喷嘴撞击火焰和四喷嘴撞击火焰的变工况试验。应用统计理论和Hilbert-Huang变换对炉内火焰声学信号分别进行了时域和频域的分析。结果表明,随着燃料或氧气的增大,火焰化学反应速率加快,燃烧越来越剧烈,火焰的稳定性越来越差,其中氧气对火焰的影响大于燃料。四喷嘴工况的撞击火焰噪声的标准偏差值要大于两喷嘴,但标准偏差随工况的变化小于两喷嘴,说明四喷嘴撞击火焰燃烧剧烈但稳定。低氧燃比工况时,四喷嘴能量和频率的分布主要集中在45 Hz以下的低频段和45～100 Hz的中频段,比两喷嘴工况更集中于低频段。     

Support studies for the U-GAS coal gasification process. Part II: Combustion characteristics

This is the second part of a series of papers providing the details of support studies conducted as part of the development of the U-GAS fluidized-bed coal gasification process. (Part I: Fluidization; published in Fuel Processing Technology, Vol. 17(2) (1987) 169–186). The medium-Btu industrial fuel gas (IFG) produced in the gasifier, which consists mainly of CO, H₂, CO₂, and CH₄, was evaluated for its combustion characteristics in a sub-scale, spud-type boiler burner. The gas was evaluated for flame stability, furnace efficiency, flame temperatures, flame size, and pollutants created. In the event of planned or unscheduled gasifier downtime, a gas mixture consisting of 30% natural gas and 70% air has been proposed as a backup to the industrial fuel gas-produced in the U-GAS process. The proposed backup gas was tested according to the same criteria to determine its suitability as a temporary replacement fuel. The combustion characteristics of these gases were compared with the combustion characteristics of natural gas.     

撞击流对火焰稳定性影响的试验研究

研究了射流火焰噪声和撞击式火焰噪声,对比两者以探求撞击流对火焰稳定性的影响。对火焰噪声信号进行频谱分析（FFT）,结果表明,射流火焰噪声包含燃烧噪声和喷流噪声,火焰噪声以燃烧噪声为主,撞击式火焰噪声是主频约420Hz的高频噪声,由燃烧噪声、喷流噪声和撞击区燃烧噪声组成。撞击式火焰噪声频谱图表明,撞击流强化了气化燃烧,有利于火焰的稳定,对气化炉的稳定运行有重大意义。     

Stochastic Modeling of the Particle Residence Time Distribution in an Opposed Multi‐Burner Gasifier

The gasification technology of impinging streams has been extensively applied to chemical production and power generation. Particle residence time distribution (RTD) is an important parameter required for modeling, designing and optimization of an impinging stream gasifier. A stochastic mathematical model based on the Markov chains model is developed for the opposed multi‐burner gasifier (OMBG), which closely describes the behavior of the flow pattern and particle RTD in the gasification system. The model simulates the motion of single particle moving in the gasifier using the Markov chains. The predicted results give a reasonable fit to the experimental data. This shows that the flow process of particles in the gasifier has recirculation eddies, which have a downward flow direction near the downflow core and an upward flow direction near the wall, but no short‐circuit. Finally, the effect of particle flux rate on the RTD is predicted, and the contrast between gas and particles RTDs at a laboratory scale and in an industrial gasifier are presented.     

Experimental measurement of gas concentration distribution in an impinging entrained-flow gasifier

On a laboratory-scale testing platform of impinging entrained-flow gasifier with two opposed burners, the detailed measurements of gas concentration distribution have been performed for carbonaceous compound (diesel oil) at atmospheric pressure. Under the condition of 1.48–2.36 O/C ratios (kg/kg), radial gas samples are collected at three axial positions and the syngas exit position with stainless steel water-cooled probes, the concentration distribution of the major gases (H₂, CO, CO₂, CH₄ and O₂) under stable operating state was determined with a mass spectrometry. These data are used to clarify mixing and reaction characteristics within the reactor, to give insight into the combustion process and provide a database for evaluating predictive mathematical models.     

Numerical Simulation and Assessment of a Two‐Stage Gasifier Modified from an Opposed Multi‐Burner Gasifier

An opposed multi‐burner (OMB) entrained‐flow gasifier with coal water slurry feeding is developed by the East China University of Science and Technology. A 3D model is employed to numerically simulate the gas flow field, motion of char particles, and distributions of temperature and gaseous components in an OMB gasifier and in a conceptual two‐stage gasifier modified from the OMB gasifier (TS‐OMB gasifier). Results show that the TS‐OMB gasifier produces higher concentration and productivity of the effective gases (CO+H₂) with a slightly higher carbon conversion than the OMB gasifier. The reasons for the differences between these two types of gasifier are discussed by means of numerical simulation. This information is valuable for guiding the design of an advanced OMB gasifier.     

二氧化碳和富氧空气对甲烷与乙烯燃烧的影响

利用碳氢燃烧实验台,研究了二氧化碳和富氧空气对甲烷、乙烯层流燃烧火焰的特性影响,分析了不同气氛下火焰结构特性和温度分布规律. 结果表明,随氧浓度从21%增加到50%(j),甲烷、乙烯火焰高度下降70%,火焰温度和亮度同时增加,且发光区域呈向下收缩趋势;相同氧浓度下,乙烯火焰亮度高于甲烷. 随CO2浓度由0增加到20%(j),火焰高度增加28%,各高度处火焰边缘温度平均下降290℃,中心温度平均下降132℃. 火焰亮度降低,由黄色变为暗黄色,底部亮度更低,CO2浓度超过20%(j)后,火焰出现悬浮状态,最终被吹熄.     

Emission studies of impinging premixed flames

This paper reports the results of an experimental investigation of emissions from an impinging flame to a flat cold surface. This study pertains to the fuel rich premixed flame issuing from a 8-mm diameter nozzle burner. The effects of burner to plate spacing, equivalence ratio and Reynolds numbers on the flame structure and emission are investigated. The flame structure is characterized by temperature measurement. The axial temperature profiles show that it is strongly dependent on the distance between the burner and cold surface. The temperature in the radial direction declines sharply after certain distance from the center of the plate which is also seen to depend on the separation distance. It has been found out that the CO level increases for separation distance greater than 12 nozzle diameter for all Reynolds number which may be attributed to the excess entrainment of air leading to the dilution of mixture. However, the CO level also increases with increase in equivalence ratio for same separation distance. The NO level decreases with increase in equivalence ratio and Reynolds number. The separation distance of 12 nozzle diameter case gives higher NO level for all Reynolds number. The CO₂ level increases with equivalence ratio for all Reynolds number. It is believed that these experimental data will be useful for designing and developing rapid heating devices.