基于Aspen Plus的固定床高温煤气化模拟

文章以过程模拟软件Aspen Plus为工具,建立了以高温空气为气化剂的固定床煤气化的数学模型,模拟计算了逆流式固定床气化的制气过程;并利用该模型模拟研究了不同空煤比以及不同的空气预热温度对煤气化指标的影响,结果表明:在相同空煤比与汽煤比的工况下,提高空气的预热温度可以使气化过程得到强化。     

Gasification of greek lignite in an indirect heat (allothermal) rotary kiln gasifier

This work reports the performance results of a pilot-size lignite gasification plant. The feed material was Greek lignite (Megalopolis), currently being employed for electricity generation in pulverized lignite-fired thermoelectric stations. Low energy conversion efficiency, low station availability, and environmental issues call for developing improved processes, e.g., an IGCC (Integrated Gasification Combined Cycle). An indirect heat (allothermal) rotary kiln was selected as the lignite gasification reactor for developing an overall gasification process of improved efficiency. Weeklong gasification runs, at near atmospheric pressure and maximum temperature in the range 900-950°C, validated high DAF lignite conversions, i.e., 90-95%, and the production of a medium heating value synthesis gas (i.e., 11-13 MJ/Nm 3 dry basis), despite the use of air for burning recycled product gas for process heating. Gas composition is equivalent to that of autothermal gasifiers (e.g., Lurgi, Winkler, Koppers-Totzek), which operate on oxygen, under pressure and strict moisture and particle size specifications. Similarly, the kiln gas is comparable to that of an allothermal, high-pressure, fluidized bed gasifier running with a high rank coal feed. The data indicate satisfactory gasification efficiency and a good thermal efficiency that should be improved further through heat integration of a scaled-up process based on an indirect heat rotary kiln gasifier.     

GASIFICATION OF GREEK LIGNITE IN AN INDIRECT HEAT (ALLOTHERMAL) ROTARY KILN GASIFIER

This work reports the performance results of a pilot-size lignite gasification plant. The feed material was Greek lignite (Megalopolis), currently being employed for electricity generation in pulverized lignite-fired thermoelectric stations. Low energy conversion efficiency, low station availability, and environmental issues call for developing improved processes, e.g., an IGCC (Integrated Gasification Combined Cycle). An indirect heat (allothermal) rotary kiln was selected as the lignite gasification reactor for developing an overall gasification process of improved efficiency. Weeklong gasification runs, at near atmospheric pressure and maximum temperature in the range 900-950°C, validated high DAF lignite conversions, i.e., 90-95%, and the production of a medium heating value synthesis gas (i.e., 11-13 MJ/Nm 3 dry basis), despite the use of air for burning recycled product gas for process heating. Gas composition is equivalent to that of autothermal gasifiers (e.g., Lurgi, Winkler, Koppers-Totzek), which operate on oxygen, under pressure and strict moisture and particle size specifications. Similarly, the kiln gas is comparable to that of an allothermal, high-pressure, fluidized bed gasifier running with a high rank coal feed. The data indicate satisfactory gasification efficiency and a good thermal efficiency that should be improved further through heat integration of a scaled-up process based on an indirect heat rotary kiln gasifier.     

COAL GASIFICATION AND THERMODYNAMIC CALCULATION OF MOVING BED COAL GASIFIER WITH DRAFT TUBE

The coal gasification experiment and thermodynamic calculation of the newly developed moving bed coal gasifier with a draft tube are done according to the thermodynamic calculating model built on the basis of chemical reaction equilibrium, mass balance and heat balance. The obtained experimental results are quite approaching to the thermodynamically calculated values. The effects of steam/coal ratio, air/coal ratio, reaction temperature, reaction pressure, steam temperature, air temperature on the thermodynamic indexes of the gasifier are examined through thermodynamic simulating calculations. Under the optimal simulating conditions, gas calorific value, cold gas thermodynamic efficiency and available energy efficiency can reach 12 MJ/Nm³, 88.6% and 95.4% respectively, when air is used as the oxidizer. Compared with the directly-burning-coal-gasifier, the gasifier exhibits good characteristics and prospects for industrial application.     

串行流化床煤气化试验

针对串行流化床煤气化技术特点,以水蒸气为气化剂,在串行流化床试验装置上进行煤气化特性的试验研究,考察了气化反应器温度、蒸汽煤比对煤气组成、热值、冷煤气效率和碳转化率的影响。结果表明,燃烧反应器内燃烧烟气不会串混至气化反应器,该煤气化技术能够稳定连续地从气化反应器获得不含N₂的高品质合成气。随着气化反应器温度的升高、蒸汽煤比的增加,煤气热值和冷煤气效率均会提高,但对碳转化率影响有所不同。在试验阶段获得的最高煤气热值为6.9 MJ•m^-3,冷煤气效率为68％,碳转化率为92％。     

Predictive model for countercurrent coal gasifiers

The paper deals with a model able to predict the stationary operating conditions of a moving bed gasifier with upflow of gas. The model was used to simulate coal gasifiers but the proposed approach can also be useful for biomass gasifiers. The model considers the different phenomena that occur along the reactor: drying and pyrolysis take place at the top, while the behaviour of the lower part is dominated by the combustion and gasification reactions between the coal char and the oxidizing gas. The model is structured into two levels: particle level and reactor level. At the particle level, the strong gradients of temperature in the single pellet caused by external heating were taken into account. Literature kinetic models developed with isothermal particles were employed. The calculated results of fixed carbon yield and gas were compared with experimental results obtained in our laboratory.At the whole apparatus level, the reactor was subdivided into two zones: pyrolysis (upper) zone and gasification/combustion (lower) zone. The upper zone was modelled by coupling convective heating of the particles, temperature gradients inside the particles and kinetics. In the lower zone transport of heat by radiation was taken into consideration. The governing equations were solved as a boundary condition problem, leading to a stable and reliable solution. The model was validated by comparison with some literature data of full scale gasifiers.     

现代煤气化技术及其煤种的适应性分析

结合国内外煤气化技术发展现状与趋势,讨论了煤质特性对气化过程的影响及其在不同气化炉型中的适应性。分析表明,煤种的多样性及气化工艺的选择促进了煤气化技术的快速发展,气流床和流化床代替固定床是煤气化技术发展的必然所趋。在充分认识各类煤气化技术优缺点的基础上,应发挥优势,针对煤种选用炉型,开发具有单炉生产能力高、煤种适应性强、气体成分可调等优势的加压气化技术以及可有效利用煤气高温显热的两段或多段式气化技术。     

恩德炉与两段炉煤气化技术的选择与应用

通过对恩德炉与两段炉煤气化技术进行的分析和比较,论述了两种炉的不同气化方式。由于两项技术的气化方法和气化原理不同,因此在气化条件、气化过程、气化产品及煤气应用等方面都有所不同。恩德炉粉煤气化技术用煤范围广,单炉生产能力大,煤气生产成本低,是未来煤气化技术的发展趋势。     

Nutzung biogener Festbrennstoffe in Vergasungsanlagen

Utilization of Biogenic Solids in Gasifiers As a result of shrinking fossil fuels biomass as a regenerative energy source gains in importance. To realize biomass projects it is essential to investigate convenient thermal procedures. On this evidence an analysis and evaluation of diverse gasification technologies with different boundary conditions and diverse biomasses is indispensable. Form and kind of the biomass as well as the type of the gasification plant cause different compositions of the product gas. The gasifiers show advantages and disadvantages concerning the biomass and the produced gas quality, depending on reactor type, kind of heat supply, gasification medium, and the pressure ratio in the reactor. As the ideal gasifier for different biomass is presently not available it will be shown which biomass is suitable for fixed bed or fluidised bed gasifiers.     

煤气化技术的发展与应用

综述了煤气化技术的现状及发展趋势,对煤气化技术的原理进行了阐述,概括介绍了固定床、流化床和气流床三种不同煤气化技术的特点,并对鲁奇炉、德士古炉、壳牌炉、恩德炉等几种常用气化炉的性能做了比较,重点介绍了恩德粉煤气化炉的发展历史、特点及应用现状,认为恩德粉煤气化技术具有自己独特的优势,是国内实力比较薄弱的合成氨企业进行技术改造的适宜技术.     

Gasification of Biogenic Solid Fuels

As a result of shrinking fossil fuels, biomass as a regenerative energy source gains importance. To realize biomass projects it is essential to investigate in convenient thermal procedures. On this evidence an analysis and evaluation of diverse gasification technologies with different boundary conditions and diverse biomasses are indispensable. Form and kind of the biomass as well as the type of the gasification plant cause different compositions of the product gas. The gasifiers show advantages and disadvantages concerning the biomass and the produced gas quality, depending on reactor type, kind of heat supply, gasification medium, and the pressure ratio in the reactor. As the ideal gasifier for different biomass is presently not available, it will be shown, which biomass is suitable for fixed bed or fluidized bed gasifiers.     

PERFORMANCE OF A PRESSURIZED TWO-STAGE FLUIDIZED GASIFICATION PROCESS FOR PRODUCTION OF LOW-BTU GAS FROM COAL CHAR

A two-stage pressurized fluidized-bed gasification process has been developed to produce low-heating value gases from coal char. The reactor was 0.075 m id. and 1.4 m long, and gasification experiments were conducted under pressures up to 790 kPa and at temperatures up to 1323 K. A partition disc was used to divide the fluidized bed into two stages, using the first stage as a partial combuster and gasifier and the second stage as a gasifier. The disc was designed to control compositions of coal char particles in both stages so that the heat required for the endothermic gasification reaction in the second stage can be provided by the heat of combustion in the first

For conditions examined here, the disc with an opening ratio of 40° was found to give optimum distribution of the char particles in both stages without ash agglomeration. It was also shown that all oxygen gas was completely consumed within the first stage

The heating value of the product gas increased with the char feed rale. However, there may be an oplimum Teed ratio of char and sand-particles since the higher char feed rate causes more frequent ash agglomeration as well as less carbon conversion     

化肥造气技术的现状和前景

评述了近年来煤气化领域的最新进展;提出了对改造或新建合成氨厂的具体建议,即对于小型合成氨厂, 可以采用连续气化代替间歇气化、气化型煤代替无烟煤 （或焦炭） 或选用循环流化床气化炉; 对于中型合成氨厂, 可以采用连续气化或气流床气化技术; 对于大型合成氨厂,则采用气流床气化技术、流化床气化燃烧一体化技术或者采取Ｌｕｒｇｉ炉和湿法气流床（如Ｔｅｘａｃｏ炉） 联用的方法．     

鼓泡流化床内高灰煤气化过程的颗粒尺度特性研究

基于多相流体质点网格方法(MP-PIC)对高灰煤在三维鼓泡流化床气化过程进行了数值模拟研究。在欧拉-拉格朗日框架下将气相和固相分别视作连续介质和离散相处理。首先,将模拟得到的出口处气体组分结果与实验数据进行对比,实验数据与模拟结果具有良好的一致性。其次,研究了煤颗粒在气化炉内的温度、传热系数、速度和停留时间,从颗粒尺度揭示了鼓泡流化床气化炉内的颗粒分布特性和气固流动特征。结果表明:在气化炉入口附近煤颗粒与床层温差最大,传热系数最大;由于流化床内强非线性的气固流动,床中煤温度和传热系数的空间分布不均匀;煤颗粒和床料的瞬时速度具有稳定的波动幅度,其中垂直方向速度波动最明显,且煤颗粒的瞬时速度比床料的瞬时速度略大;由于颗粒间的剧烈碰撞,延长了煤颗粒停留时间。此外,对鼓泡流化床中煤气化过程颗粒尺度的研究,有助于深入了解固体颗粒的流动行为以及气固相相互作用特性,对鼓泡流化床反应器的设计优化具有重要意义。     

Numerical simulation of coal gasification in entrained flow coal gasifier

This paper presents modeling of a coal gasification reaction, and prediction of gasification performance for an entrained flow coal gasifier. The purposes of this study are to develop an evaluation technique for design and performance optimization of coal gasifiers using a numerical simulation technique, and to confirm the validity of the model. The coal gasification model suggested in this paper is composed of a pyrolysis model, char gasification model, and gas phase reaction model. A numerical simulation with the coal gasification model is performed on the CRIEPI 2 tons/day (T/D) research scale coal gasifier. Influence of the air ratio on gasification performance, such as a per pass carbon conversion efficiency, amount of product char, a heating value of the product gas, and cold gas efficiency is presented with regard to the 2 T/D gasifier. Gas temperature distribution and product gas composition are also presented. A comparison between the calculation and experimental data shows that most features of the gasification performance were identified accurately by the numerical simulation, confirming the validity of the current model.     

煤炭气化产业的发展现状和工业化前景

论述了煤炭地面气化技术和地下气化技术的技术特点、发展现状和工业应用;对比和分析了固定床、流化床和气流床气化炉的气化特点和工程应用概况;提出了目前国内可采用优先发展工业化成熟的Texaco气化技术和自主开发的对置式多喷嘴气化技术,适时发展具有广阔发展潜力的干煤粉气化技术的参考性意见。     

Coal combustion characteristics in a fluidized bed combustor with a draft tube

The effects of gas velocity to draft tube (3–6 U_m), bed temperature (800–900°C) and excess air ratio (0–30%) on the total entrainment rate, overall combustion efficiency and heat transfer coefficient have been determined in an internally circulating fluidized bed combustor with a draft tube. The total entrainment rate increases with an increase in gas velocity to draft tube, but decreases with increasing bed temperature and excess air ratio. The overall combustion efficiency increases with increasing excess air ratio, but decreases with increasing gas velocity to draft tube. The overall combustion efficiency obtained in internally circulating fluidized beds was found to be somewhat higher than that in a bubbling fluidized bed combustor.     

The behavior of iron-sulfur species in fluidized-bed gasification on coal

The behavior of iron-sulfur species derived from pyrite, especially that present in the coal feed as particles of free pyrite, is of concern in the operation of fluidized-bed coal gasifiers. Work conducted at the Institute of Gas Technology (IGT) has shown that the decomposition of pyrite in a U-GAS® pilot plant has yielded a liquid phase that spreads on the surface of ash particles. Formation of a liquid phase in decomposition of pyrite in an inert atmosphere has also been observed in connection with the investigation of boiler deposits. To aid in understanding the behavior of iron-sulfur species, we have prepared an Fe---S phase diagram at temperatures relevant to coal gasification and with equilibrium sulfur potentials exhibited, for the most part, as hydrogen sulfide to hydrogen mole ratios; in a fluidized-bed gasifier, the latter can easily be obtained from the composition of the reactor product gas, which closely approximates that in the back-mixed fluidized bed. To show, in addition, the effect of oxygen potential in the bed, we have also prepared phase stability diagrams at 100°F intervals from 1500 to 2000°F (816 to 1093°C). According to the Fe---S diagram, formation of an iron-sulfur liquid in the gasifier or in an inert atmosphere cannot be explained on the basis of equilibrium considerations. Instead, a kinetic explanation, based on increased concentration of iron in the exterior regions of the decomposing pyrite particle, as sulfur is removed from the surface, is much more plausible. Phase stability diagrams indicate that a liquid composed of iron, sulfur, and oxygen could be formed in steam-oxygen gasification of high-sulfur coal at temperatures above 1850°F (1010°C). However, no evidence of its formation was found by optical petrography in the examination of solids from the U-GAS pilot plant in which steam-to-hydrogen mole ratios ranged up to about 2, but formation of a submicroscopic liquid layer on iron sulfide particles could have been responsible for deposition of these particles in the hot cyclone of the U-GAS pilot plant. Its formation in steam-air gasification, where the steam-to-hydrogen mole ratio typically is about 0.6, is less likely.     

反应器结构对多段气化炉内颗粒分布的影响

针对多段气化炉(上部快速床、下部鼓泡床),采用MP-PIC(Multi-Phase Particle In Cell)方法模拟了多粒径煤粉颗粒的三维全循环流化过程,考察了鼓泡床与快速床床径比及鼓泡床和快速床之间的过渡段高度对气化炉内流动特性的影响。结果表明,基本工况下,大颗粒主要存在于下部鼓泡床中,细颗粒主要存在于上部快速床内,但细颗粒会通过旋风分离器和回料管再次进入鼓泡床参与循环。进入旋风分离器的大部分为半径622 ?m以下的小颗粒,无1216 ?m以上的大颗粒。旋风分离器对小颗粒的分离效率为99.75%,分离效率良好。增大床径比(即减小快速床直径),快速床中气速增大,整个气化床更快达到稳定状态,被夹带到快速床中的颗粒增多,所夹带的颗粒粒径增大。过渡段高度存在一个适当值(炉高0.6~1.0 m),升高或降低过渡段高度,快速床中颗粒浓度均增大,颗粒通量均升高,旋风分离效率降低。     

Identification of reaction zones in a commercial Sasol-Lurgi fixed bed dry bottom gasifier operating on North Dakota lignite

The Sasol-Lurgi fixed bed dry bottom gasification technology has the biggest market share in the world with 101 gasifiers in operation. To be able to further improve the technology and also to optimise the operating plants, it is important that the fundamentals of the process are understood. The main objective of this study was to determine the reaction zones occurring in the Sasol-Lurgi fixed bed dry bottom (S-L FBDB) gasifier operating on North Dakota lignite. A Turn-Out sampling method and subsequent chemical analyses of the gasifier fuel bed samples was used to determine the reaction zones occurring in the commercial MK IV, S-L FBDB gasifier operating on North Dakota lignite. The reaction zones were further compared with the same reactor operating on bituminous coal.Based on the results obtained from this study it was found that about two thirds of the gasifier volume was used for drying and de-volatilising the lignite thus leaving only about a third of the reactor volume for gasification and combustion. Nonetheless, due to the high reactivity of the lignite, the char was consumed within a third of the remaining gasifier volume. Clear overlaps between the reaction zones were observed in the gasifiers thus confirming the gradual transition from one reaction zone to another as reported in literature. Due to the high moisture content in the lignite, the pyrolysis zone in the gasifiers operating on North Dakota lignite occurred lower/deeper in the gasifier fuel bed as compared to the same gasifier operating on South African bituminous coal from the Highveld coalfield. All the other reaction zones in the gasifier operating on bituminous coal were also higher in the bed compared to the lignite operation. This can therefore explain the higher gas outlet temperatures for the S-L FBDB gasifiers operating on higher rank coals when compared to the gasifiers operating on lignite. The fact that the entire reactor volume was utilized for drying, de-volatilisation, gasification and combustion with carbon conversion of >98% makes the S-L FBDB gasifier very suitable for lignite gasification.