Effect of slag composition on corrosion resistance of high chromia refractory bricks for industrial entrained-flow gasifier

The slag composition corresponding to different coals varies significantly,which directly affects the operation of industrial entrained-flow gasifier and the service life of refractory bricks.In this study,the corrosion resistance of several typical coal slags for gasification on high chromia refractory bricks was comparatively investigated by static laboratory crucible tests and thermodynamic simulations.The results demonstrated that the corrosion degree of high chromia refractory bricks by different coal slags was high-Ca/Na slag>high-Fe slag>high-Si/Al slag.The surface structure of the refractory was relatively flat after corrosion by high-Si/Al slag,and the primary corrosion reaction was the partial dissolution of the matrix by the slag.High-Fe slag was prone to the precipitation of iron phases as well as the formation of(Mg,Fe)(Al,Cr)_(2)O_(4)composite spinel layer at the slag/refractory interface.The high-Ca/Na slag was susceptible to react with the refractory to yield a low melting point phase,which led to the destruction of the matrix structure of the refractory and an isolated distribution of particles.In addition,the monoclinic ZrO_(2) in the refractory reacted with CaO in the slag to formed calcium zirconate,which loosened its phase toughening effect,was the primary factor that aggravated the refractory corrosion.

Implementation of a Demoisturization and Devolatilization Model in Multi-Phase Simulation of a Hybrid Entrained-Flow and Fluidized Bed Mild Gasifier

A mild gasification process has been implemented to provide an alternative form of clean coal technology called the Integrated Mild Gasification Combined Cycle (IMGCC), which can be utilized to build a new, highly efficient, and compact power plant or to retrofit an existing coal-fired power plant in order to achieve lower emissions and significantly improved thermal efficiency. The core technology of the mild gasification power plant lies on the design of a compact and effective mild gasifier that can produce synthesis gases with high energy volatiles through a hybrid system: utilizing the features of both entrained-flow and fluidized bed gasifiers. To aid in the design of the mild gasifier, a computational model has been implemented to investigate the thermal-flow and gasification process inside this mild gasifier using the commercial CFD (Computational Fluid Dynamics) solver ANSYS/FLUENT. The Eulerian-Eulerian method is employed to model both the primary phase (air) and the secondary phase (coal particles). However, the Eulerian-Eulerian model used in the software does not facilitate any built-in devolatilization model. The objective of this study is therefore to implement a devolatilization model (along with demoisturization) and incorporate it into the existing code. The Navier-Stokes equations and seven species transport equations are solved with three heterogeneous (gas-solid) and two homogeneous (gas-gas) global gasification reactions. Implementation of the complete model starts from adding demoisturization first, then devolatilization, and then adding one chemical equation at a time until finally all reactions are included in the multiphase flow. The result shows that the demoisturization and devolatilization models are successfully incorporated and a large amount of volatiles are preserved as high-energy fuels in the syngas stream without being further cracked or reacted into lighter gases. The overall results are encouraging but require future experimental data for verification.

Characterization of Size and Density Separated Fractions of a Bituminous Coal as a Feedstock for Entrained Slagging Gasification

Coal is one of the main sources of energy in many parts of the world and has one of the largest reserves/production ratios amongst all the non-renewable energy sources. Gasification of coal is one among the advanced technologies that has potential to be used in a carbon constrained economy. However, gasification availability at several commercial demonstrations had run into problems associated with fouling of syngas coolers due to unpredictable flyash formation and unburnt carbon losses. Computer models of gasifiers are emerging as a powerful tool to predict gasifier performance and reliability, without expensive testing. Most computer models used to simulate gasifiers tend to model coal as a homogenous entity based on bulk properties. However, coal is a heterogeneous material and comminution during feedstock preparation produces particle classes with different physical and chemical properties. It is crucial to characterize the heterogeneity of the feedstocks used by entrained flow gasifiers. To this end, a low ash US bituminous coal that could be used as a gasifier feedstock was segregated into density and size fractions to represent the major mineral matter distributions in the coal. Float and sink method and sieving were employed to partition the ground coal. The organic and inorganic content of all density fractions was characterized for particle size distribution, heating value, ultimate analysis, proximate analysis, mineral matter composition, ash composition, and petrographic components, while size fractions were characterized for heating value, ash composition, ultimate and proximate analysis. The proximate, ultimate and high heating value analysis showed that variation in these values is limited across the range of size fractions, while the heterogeneity is significant over the range of density fractions. With respect to inorganics, the mineral matter in the heavy density fractions contribute significantly to the ash yield in the coal while contributing very little to its heating value. The ash yield across the size fractions exhibits a bimodal distribution. The heterogeneity is also significant with respect to the base-to-acid ratio across the size and density fractions. The results indicate that the variations in organic and inorganic content over a range of density and size classes are significant, even in the low ash, vitrinite rich coal sample characterized here. Incorporating this information appropriately into particle population models used in gasifier simulations will significantly enhance their accuracy of performance predictions.

CPFD simulation on particle behaviour in an entrained-flow gasifier

A computational particle fluid dynamics simulation model for entrained-flow gasification was established in this study.The simulation results agree with the experimental data.The detailed particle information and residence-time distribution were obtained by injecting particle tracers in the simulation.The results show that the particles in the gasifier can be classified into three flowing zones,i.e.a fast-flowing zone,a recirculation zone and a spreading zone.The criterion for this classification was also provided.The rapid gas expansion caused by the fast reactions plays a significant role in forming the particle stream into these three zones.It accelerates the particles in the centre of the gasifier while pushing the particles near the expansion edge into the gas recirculation.Also,the concentrated oxygen distribution in the gasifier results in the formation of high-and low-temperature regions.The particles in the fast-flowing zone flow directly through the high-temperature region and most of these particles in this zone were fully reacted with a short residence time.Since particles in the recirculation zone are in a relatively low-temperature region,most of these particles are not fully gasified,although with a long residence time.The rest of particles in the spreading zone show moderate properties between the above two zones.

Study for entrained-flow gasifier modeling and measurement

The syngas composition change during the measurement process was analyzed using a detailed gas phase reaction mechanism.Results showed that the measurement error induced by the temperature and pressure change in the measurement process cannot be ignored.Based on the results,suggestions were proposed for syngas concentration measurement and temperature measurement.

气流床气化炉内颗粒停留时间分布

The particle residence time distributions in the entrained-flow gasifier as the important parameters in the gasification process were studied by using a new stimulus response method.The differences of the particle residence time distributions in the opposed multi-burner entrained-flow(OMBEF) and Texaco gasifier were compared.The influence of gas velocity and particle diameter on particle residence time distributions was discussed.The experimental results showed that the new stimulus response method was reliable and could be used to measure the particle residence time distributions in the entrained-flow gasifier and the particle residence time in the OMBEF gasifier was more favorable than in the Texaco gasifier.The results also showed that with increasing gas velocity and decreasing particle diameter,the mean and variance of particle residence time increased in both kinds of entrained-flow gasifier.

撞击流气化炉内气固两相流动与颗粒附壁沉积数值模拟

对多喷嘴对置式气化炉内复杂的气固两相流动与颗粒附壁沉积进行3D数值模拟。采用Realizable k-ε湍流模型计算炉内气相湍流流场,应用Euler-Lagrange模型模拟气固两相流动,颗粒轨迹跟踪采用随机轨道模型。根据液态排渣气化炉本身特点,描述炉壁熔渣流的形成过程,建立适用于液态排渣气化炉的颗粒附壁沉积模型,模拟结果与实验值吻合较好。模拟结果表明,数值模拟再现了撞击流气化炉内分区流动的情况;射流撞击使颗粒在气化炉内分布较为均匀,撞击中心和撞击流股区域浓度略高;颗粒在炉壁沉积基本覆盖整个气化炉,不存在局部积渣;当气化炉操作压力达到4.0MPa时,渣口气流夹带颗粒量有所提高,气流流速的增大而提高,颗粒停留时间缩短,影响碳转化率。

撞击流气化炉内气粒两相流动的数值模拟

对撞击流气化炉内气粒两相流动进行了三维数值模拟。在Euler坐标系中计算气相流场,在Lagrange坐标系中跟踪颗粒运动轨迹,考虑了熔融灰渣颗粒间的碰撞合并、反弹。模拟结果与冷模流场测试数据、热模实验现象一致。通过考察不同工况下的流场计算发现:增加喷嘴以上直段高度使流场更对称,物料停留时间增加,若同时提高入口气速将使颗粒在炉壁的沉积量增加;模拟结果与热模实验都表明撞击形成的强烈湍流和火焰主要集中在撞击中心;颗粒碰撞合并使炉内颗粒选择性团聚,但炉内颗粒浓度分布整体比较合理;Stokes数为0.19的小颗粒跟随性较好,较大Stokes数颗粒不易被流场控制,且对流场具有较大的影响。

两喷嘴撞击气化火焰结构特性研究

撞击火焰是多喷嘴对置式气流床气化炉的主要特征。文中利用高速摄像仪和计算机图像处理技术,对两喷嘴撞击气化火焰的结构特性进行了研究,通过计算图像灰度相关系数定量描述了两喷嘴撞击气化火焰的结构特征。研究结果表明:在撞击前单股火焰仍能较好地保持其几何结构,但在撞击区内单股火焰的几何结构迅速消失。随着撞击速度的增大,火焰整体分布更为均匀,互相关系数标准差降低;单股火焰的湍流拟序结构分区变得不明显,互相关系数小幅波动的区域增多;撞击区内火焰分布不均匀,互相关系数降低。

多喷嘴气化炉气体浓度及撞击火焰高度分析

基于多喷嘴对置热模实验平台,以柴油为模拟介质,对其气化过程进行了实验研究.采用水冷取样管,对气化炉喷嘴平面及轴线上方进行气体取样,经气体净化系统,由质谱仪实时在线分析.结果表明,喷嘴平面内,距中心5 cm处,CO,CO2和H2浓度开始发生较大变化,即为火焰撞击区域,且该区域同由火焰图象拍摄结果一致;气化炉中心轴线方向,气体浓度曲线在距离中心29 cm处出现拐点,表明气化火焰高度与炉内径之比约为1.0.

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300μm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。

撞击气流床气化炉内雾化过程中颗粒运动特性

基于实验室规模的撞击气流床气化炉,以水煤浆为原料进行气化实验,采用高温内窥镜及工业相机组成的可视化成像系统,在操作条件下,对水煤浆雾化过程进行拍摄。运用图像处理算法来识别和检测所得图像中的颗粒信息,利用颗粒示踪算法对颗粒进行轨迹测算。对颗粒的平均粒径、速度及角度进行统计分析。结果表明,喷嘴出口射流区内平均粒径主要集中在325~375μm,相较于原煤颗粒较大;大部分颗粒速度集中在1~2m·s^-1且运动过程中速度变化不大;大部分颗粒运动方向不随时间而变化,呈简单直线运动;颗粒轨迹呈现以喷嘴为起始点的扇形射线。

气化炉内柴油火焰光谱辐射特性及CH~*二维辐射特性研究

火焰的自发辐射光谱与火焰的结构、温度分布等燃烧特征参数密切相关。对激发态自由基辐射的辐射强度与二维分布进行研究,可清晰地反映火焰燃烧状态而不对火焰产生扰动。基于多喷嘴对置式气流床气化实验平台,利用光纤光谱仪和配置CCD相机的高温内窥镜,对柴油扩散火焰的辐射光谱及CH^*辐射二维分布特性进行研究。考察了当量比和撞击作用对火焰辐射光谱和CH^*辐射分布的影响。结果表明,柴油火焰在306.47及309.12nm处存在OH^*辐射特征峰,在431.42nm处存在CH^*辐射特征峰,且存在明显的碱金属原子Na^*(589.45nm),K^*(766.91和770.06nm)发射光谱。此外,由于柴油不完全燃烧生成大量碳黑,在辐射光谱的可见光波段产生了强烈的连续黑体辐射。火焰中的黑体辐射对CH^*辐射特征峰的检测存在干扰,且当量比越低时背景辐射越强,对自由基特征峰检测干扰越大。基于普朗克定律利用插值法可扣除430nm附近波段背景辐射。柴油火焰中CH^*辐射峰值随当量比的增加单调减小,CH^*辐射等值线沿火焰发展方向依次出现三峰状、双峰状及单峰状,最终收缩为以反应核心区为中心的圆核。随着当量比的提高,出现各个形状的CH^*辐射强度阈值不断降低,火焰主反应区面积减小且向下游移动,当量比增加到1.0附近时,理论上柴油完全燃烧,CH^*辐射强度显著降低,贫燃火焰的CH^*辐射强度及分布区域几乎稳定不变。利用CH^*辐射强度值判定火焰举升长度,对于单喷嘴射流火焰,火焰举升长度随当量比的增加经历了显著增加后小幅下降的过程。相同当量比时两喷嘴撞击火焰CH^*辐射强度峰值始终高于单喷嘴射流火焰对应值;火焰举升长度随当量比的增加小幅增加。火焰撞击的约束作用使得火焰举升长度不易随着当量比变化发生较大波动,燃烧更加稳定。这为定量判断火焰燃烧状态提供了一种直观、有效的方法,同时为柴油燃烧的化学动力学研究提供了实验依据。

气流床气化炉内撞击火焰的Na~*、K~*二维辐射特性

气流床气化炉内火焰的辐射光谱包含着大量与火焰结构、火焰温度及当量比等有关特性的信息,因此对火焰进行有效的光谱诊断,是实现燃料高效利用、监控和优化气化过程的必要手段.基于实验室规模多喷嘴对置式气化实验平台,以柴油及水煤浆为原料,重点研究了气化炉内撞击火焰Na~*、K~*二维辐射分布特征,进而表征气化炉内火焰温度分布.结果表明,相比较两喷嘴火焰,四喷嘴火焰撞击区自由基辐射强度明显增大;Na~*的二维强度分布明显强于K~*的二维强度分布,且柴油中K含量高于Na,说明在相同条件下,Na比K更加容易被激发;随O/C摩尔比增大,Na~*及K~*辐射强度均增大,撞击区温度升高;在不同O/C摩尔比条件下,撞击中心辐射强度均最大且撞击中心火焰温度最高.

预膜式烧嘴在新型撞击流水煤浆气化炉上的首次应用与改进措施

介绍了预膜式烧嘴的结构和工作机理,总结了预膜式烧嘴在新型撞击流水煤浆气化炉上的使用经验和技术优势,分析了其在工业应用中出现的问题,提出了改进措施。

撞击气流床气化炉内浓度场和温度场的数值模拟

运用PDF燃烧模型模拟以柴油为模拟气化介质的撞击气流床气化炉气化时的过程,结果与实验较吻合。还考察氧燃料比与合成气组成的关系,分析了气化炉中的温度和浓度分布情况。模拟结果表明:氧燃料比与合成气组成关系很大,随着氧燃料比例降低合成气中有效气(CO+H2)浓度升高;通过温度变化预测撞击火焰上升的高度,得出模拟条件下撞击火焰上升的高度与气化炉内径之比在1.0左右;随着反应进行,气化炉轴向上O2浓度迅速下降,H2浓度逐渐升高,H2O浓度逐渐降低。