Coal devolatilization in fluidized-bed combustors

Experimental data for devolatilization of coal in sizes and at operating conditions pertinent to fluidizedbed combustors are examined. The time for devolatilization is shown to be characteristic of a diffusion-limited situation. A model, in which the diffusion of the volatiles outwards through the char is the rate-controlling step, is shown to agree with the data.     

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.     

灰熔聚流化床粉煤气化技术生产甲醇的工业优化

灰熔聚流化床粉煤气化技术为"三高"劣质煤的洁净化利用提供了一条切实可行的道路。针对灰熔聚技术的种种技术缺陷导致甲醇生产成本极高问题,采取了多项工业优化措施。3年多的运行实践表明,全系统及单炉稳定运行周期稳步增加,系统负荷大幅提升,甲醇单耗逐步下降。     

煤气化工艺的比较

我国以油为原料的氮肥企业不能满负荷生产,很多厂在做“以煤代油”的方案研究。目前世界上技术成熟的煤气化工艺主要有以下5种:德士古水煤浆气化(Texaco)、谢尔干煤粉气化(Shell)、鲁奇公司循环流化床技术(CFB)、鲁奇公司块煤加压气化技术(Lurgi)、固定层常压气化(UGI)。各种气化工艺各有特色,对不同煤种各有优缺点,所以选择不同的气化工艺适应煤的不同性质,是工艺方案选择的原则,以达到投资最低、操作费用最少、生产成本最低的目的。1　各气化工艺特点1.1　德士古水煤浆气化技术德士古水煤浆气化技术属于气流床气化技术,是将粗煤磨碎,…     

灰熔聚旋风分离系统的优化设计

灰熔聚流化床粉煤气化技术在天溪煤制油分公司的应用,为晋城"三高"劣质无烟煤的洁净化利用做出了技术上的探索。然而,旋风分离系统的设计缺陷影响了气化技术的应用。通过与上海化工研究院合作,天溪公司对旋风分离系统进行了深入研究,运用系统工程的原理进行了优化设计,最终改善了旋风分离系统的运行。     

Coal gasification studies: Part I. Single stage complete gasification of coal using water as the hydrogen source

The complete gasification of coal to low molecular weight hydrocarbons has been achieved in a single stage process using water as the source of hydrogen. Reaction times of one hour, and a temperature of 600°C were required. The reactions were carried out in a stainless steel reactor with iodine or FeI₂ as a catalyst. It is shown that FeI₂ is a catalyst for the reaction Stainless Steel + H₂O → H₂ + Metal Oxide and also for the coal hydrogenation reaction. The apparent excellent reduction efficiency is probably a consequence of the good contact between the coal sample and the catalyst, which at the reaction temperature has a significant vapor pressure.     

Support studies for the U-GAS coal gasification process. Part I: Fluidization

This is the first part of a series of papers providing the details of support studies conducted as part of the development of the U-GAS fluidized-bed ash-agglomerating coal gasification process. The fluidized-bed gasifier in the U-GAS process behaves much like a conventional well-mixed bed, having a uniform bed composition and temperature in the bulk of the region, but it exhibits some departure in a small localized area confined to the proximity of the central spout, where a somewhat higher temperature is maintained for producing ash agglomerates. Extensive cold-flow experimental studies have been conducted to predict the solids discharge rates and agglomerates classification from the venturi/classifier system in the gasifier; these studies have resulted in a generalized analytical expression in terms of operating velocities, gas properties, and venturi/classifier configuration for the gasifier scale-up.Large-scale U-GAS gasifiers can have single-cone or multiple-cone grid configurations. X-ray cinematographic studies have been conducted in a program at University College London to compare the fluidization behaviors in the one-cone and three-cone grid configuration systems. The objective of this test program was to visually examine the solids circulation and study the bubble dynamics in the fluidized beds with these different configurations.     

灰熔聚流化床粉煤气化技术0.6MPa工业炉运行概况

介绍了中科院山西煤炭化学研究所开发的灰熔聚流化床粉煤气化技术及其适用范围、工业应用情况。灰熔聚流化床粉煤气化技术具有气化温度适中、氧耗量较低、煤种适应性宽、产品气不含焦油、气化炉耐火材料要求低等优点。同时,对0.6 MPa工业装置的运行情况进行了介绍,总结了0.6 MPa工业装置运行结果,并指出当前需要改进和完善之处。     

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.     

Texaco煤气化工艺的影响因素

介绍了Texaco煤气化流程的特点,分别对影响工艺操作的煤种性质、煤浆浓度、气化温度和气化压力等方面进行了分析,对如何合理、有效利用煤炭资源以及气化炉如何能达到最佳的长周期稳定运行状态,具有一定的借鉴意义。     

Texaco水煤浆气化装置配煤模型及其优化

优化配煤对Texaco水煤浆加压气化装置的优化运行具有重要的意义。针对Texaco水煤浆气化装置优化配煤问题,建立了一个管理决策级视角下的配煤优化模型。模型综合考虑了混煤指标、库存成本、市场价格、操作成本、堆存和转运消耗。采用预交叉差分进化粒子群优化算法对模型进行求解,算法将粒子群和差分进化相结合,避免算法早熟,提高了全局搜索能力和收敛精度。最后,以某化肥厂水煤浆配煤优化过程为研究实例进行仿真,计算结果验证了模型和算法的可行性。     

采用Prenflo气化技术的IGCC流程

Prenflo气化属于粉煤气化技术 ,与Shell的粉煤气化技术相似 ,同属气流床气化工艺 ;整体煤气化燃气 蒸汽联合循环(IGCC)是先进的洁净煤技术 ,具有广阔的应用前景。介绍了IGCC技术的起源、进展、特色 ,重点介绍采用Prenflo煤气化工艺的IGCC流程。     

典型加压煤气化工艺的比较

介绍鲁奇固定床回压煤气化工艺、德士古和壳牌气流床加压煤气化工艺的特点,并对三者进行比较,认为壳牌粉煤加压气化工艺更具竞争力。     

Second-law efficiency analysis of a coal gasification process

The present paper summarizes a comprehensive Second-Law analysis of the SYNTHANE process of coal gasification⁽¹⁾, based on the available-energy concept as applied to design conditions and data. The analysis yields an overall process efficiency of 46%. For every 100 MJ of useful energy supplied with coal, 51 MJ are consumed during the various unit operations while effluents carry 3 MJ. Unit 30, Steam and Power Production, consumes nearly 20 MJ; Unit 15, Gasification, used up nearly 16 MJ; Units 12 and 14, Coal Preparation and Feeding, about 5 MJ; Units 16 and 17, Raw Gas Quenching and Shift Conversion, 4 MJ; Unit 32, Oxygen Plant, approximately 2 MJ; other miscellaneous units contribute a combined available-energy destruction of 4 MJ. The Second-Law analysis unveils the inefficiencies present in the process and their sources, thus pinpointing the opportunities for improvement in the SYNTHANE process.     

Parametric studies on devolatilization of a subbituminous coal in a reactive gas environment

A laboratory scale fixed bed coal gasifier was set up to simulate the conditions existing in the devolatilization zone of an air-blown, fixed-bed coal gasifier. Devolatilization behaviour of a subbituminous coal was evaluated in the temperature range 350 °C to 550 °C and at pressures 30, 300 and 375 psig. Three feed coal particle sizes, (−2, +1), (−4, +3) and (−9, +6)mm, were studied. The gas feed was a synthetic mixture of composition similar to that leaving the gasification zone of a fixed bed gasifier and contained 30% by volume of steam. Devolatilization runs were conducted over coal residence times of 5, 10, 20 and 30 min durations. The gas evolution rates showed a peak around 5 min from the start of a run and most of the gas evolution tapered off just under 30 min. Thirty key components in the tars were quantified and these included aliphatic and aromatic homologues, as well as sulphur and nitrogen substituted structures. The molecular weights of the tar samples showed a maximum between 300 and 500. A first order kinetic model applied to the total weight loss data yielded activation energies in the range 4 to 11 kcal mol⁻¹. Differential equations for obtaining concentration profiles for tar and gas inside the coal particle were solved numerically. From these calculations it was concluded that the pressure buildup (due to evolution of tar and gas) inside the coal particle was higher for larger particles, at a given external pressure, but decreased with external pressure. The concentration of tar inside the particle did not appear to be sensitive to low pressures (around 1 atm), but increased in the higher range of pressure (above 20 atm) and also with particle size.     

Evolution of fuel nitrogen in coal devolatilization

The distribution of fuel nitrogen in the devolatilization products of a lignite and 12 bituminous coals has been observed experimentally. For these coals under isothermal conditions (300 < T < 1000 °Cand 5 < t < 80 s) the behaviour of the nitrogen evolution was found to be similar. Nitrogen which is initially released is contained almost entirely in the tar. The chemical composition, ¹³C-n.m.r. spectra and infrared spectra of the tars and parent coals are strikingly similar and it is reasonable to suspect that the tar nitrogen occurs in the same structures as in the parent coal. Secondary release of nitrogen into nontar volatiles occurs only at high temperature. Results can be described with first-order kinetics using the same rate constant for all the coals studied. Initial nitrogen release is described by the tar release rate constant, k = 81 exp (−5800/T) (s⁻¹), which is similar to the rate constant for initial nitrogen release measured by Pohl and Sarofim. Secondary release of nitrogen is described with a rate constant which is similar to the results measured by Blair, Wendt and Bartok. This rate is smaller than that measured for the decomposition of nitrogen-ring compounds such as pyridines or pyrroles. The results suggest that coal nitrogen is contained almost entirely in tightly bound rings which are released without breakage in the tar during the initial stage of devolatilization; the remainder is released at higher temperatures when rings are ruptured.     

型煤在碎煤加压气化工艺中的可行性论证

碎煤加压气化工艺广泛应用在现代化工企业中,其产生大量的粉煤剩余,尤其是以褐煤为原料的化工企业,因此粉煤的合理利用就显得尤为重要。型煤技术是一种先进处理粉煤技术,但型煤能否在碎煤加压气化工艺中成功应用,还有待验证。文章以三次型煤试烧为基础,对试烧过程中的各项参数进行比较,找出影响气化炉运行的关键因素,并对型煤在碎煤加压气化工艺中是否可行进行论证。     

WSA工艺在煤气化超高硫回收中的应用

介绍托普索公司WSA工艺在Rentech公司煤气化项目废气净化中的应用.该技术的主要设备是WSA冷凝器.与传统硫酸生产技术相比,WSA工艺所需设备较少,因此投资、操作和维修费用较低.WSA装置可脱除原料气中高达99.98%的硫化合物.该技术可确保Rentech公司在满足严格排放要求的同时生产有价值的商品硫酸,并且输出高压过热蒸汽来解决整个煤气化联合装置的能量平衡问题.     

浅谈两段式煤气发生炉的节能

通过对影响两段式发生炉节能因素的分析，说明理论上的节能措施与实践相结合，加以合理的节能设计可在一定程度上大大降低煤气生产成本，取得较好的经济效益、社会效益。     

Gasification of hydrogenation residues using the Texaco coal gasification process

Since early 1978 the two West German companies Ruhrchemie AG and Ruhrkohle AG have been operating a Texaco coal gasifier on the premises of Ruhrchemie at Oberhausen, West Germany. The gasifier is a pressurised entrained slagging gasifier working at a pressure of 40 bar and at temperatures between 1200 and 1600°C. The demonstration plant generates up to 15,000 m³/h of pure gas from around 8 t/h of coal. Within the first four years of operation the plant was run on domestic coal as well as on several imported hard coals, some of them tested under contract for various companies.The aim of a second experimental program is to adapt the existing coal gasification facility to the conversion of liquefaction residues and to demonstrate the generation of syngas from liquefaction bottoms on a semi-commercial scale. This feedstock is a high-melting material which can be fed to the gasifier either as a solid or in a molten form. The application of solid feedstock resembles that of coal and requires the equipment necessary to prepare an aqueous suspension, the characteristic feed material for a Texaco gasifier. It has already been tested extensively using the residues from two different coal hydrogenation processes. The feeding of molten residue requires a special feed system which in principle resembles that of a heavy residual oil gasifier adapted to the higher melting temperatures of the feedstock and the handling of high amounts of ash. The system is operating in close cooperation with Ruhrkohle/VEBA's coal—oil plant at Bottrop, West Germany, near Oberhausen. It consists of road transportation of the molten residue from Bottrop to Oberhausen, storage and feeding to the gasifier.The equipment necessary was built and commissioned in December 1983. In an initial three weeks uninterrupted test run it operated in a decidedly steady manner with a high degree of reliability and without any trouble of note. Due to the high reactivity of the feedstock and the low temperature at which the gasifier operated, excellent performance data have been recorded.