Use of new reaction kinetics for COS formation to achieve reduced sulfur emissions from claus plants

A simulation study of COS formation in the tubes of the waste heat boiler (WHB) located just after the reaction furnace of a Claus plant is reported. First, the kinetics of the COS forming reaction were obtained from a recently completed experimental program in our laboratory. The predictions for COS formation from the newly developed kinetic model were compared with the data from an actual industrial waste heat boiler and found to be in good agreement. The simulation results showed that up to a 50% reduction in the COS production may be achieved by operating the WHB at the maximum allowable gas mass velocity in the WHB tubes coupled with the use of a smaller diameter tube. These reductions have major implications on the overall sulfur recovery from Claus plants.     

The fate of methane in a claus plant reaction furnace

Experimental kinetic data are reported for key side reactions occurring in the front end [i. e. the reaction furnace (RF) and the waste heat boiler (WHB)] of modified Claus plants used for sulfur recovery from the sour gases evolved in the treatment of natural gas. An extensive experimental study was conducted in a high temperature tubular reactor system for two important homogenous gas‐phase reactions. Firstly, experiments were carried out to study the oxidation of hydrogen sulfide and methane mixtures in the presence of oxygen. Secondly, the reaction between methane and sulfur dioxide was investigated experimentally. These results showed that methane was much less competitive for oxygen than hydrogen sulfide. Hence, in a partially oxidizing environment of a RF, data showed that methane reacted significantly with other major sulfur containing species, as secondary reactions, to form COS and especially CS². This is highly problematic from an environmental point of view.     

Efficiency of a Claus furnace in the coke-oven gas desulphurization circuit of MMK

The poor efficiency of the Claus furnace in sulfur removal at the coke plant of OAO Magnitogorskii Metallurgicheskii Kombinat (MMK) is analyzed on the basis of monitoring data for the sulfur recovery unit and thermodynamic calculations. The low level of sulfur removal from coke-oven gas (~60%) at OAO MMK is mainly due to thermodynamic limitations on the thermal stage of hydrogen-sulfide oxidation with the specific composition of the sour gas at coke plants: low hydrogen-sulfide concentration and combustion of the additional fuel (natural gas). With the kinetic constraints in the Claus furnace, the high CO₂ content in the sour gas (up to 37 vol %) results in increased yield of carbonyl sulfide (~14%). That calls for particular care in optimizing the temperature during the catalytic stages and selecting the best catalysts.     

超级克劳斯装置的工艺和控制

介绍了超级克劳斯装置的工艺特点,阐述了燃烧炉控制系统和氧化空气控制系统的设计意图,将该装置与常规克劳斯工艺进行了比较。结果表明,超级克劳斯装置硫回收率超过99.5％;从化学反应的根本上实现了对催化剂活性的保护和对SO2、H2S的抑制。     

SULFUR RECOVERY WITH REDUCED EMISSIONS, LOW CAPITAL INVESTMENT AND HYDROGEN CO-PRODUCTION

The main disadvantage of the Claus process is that by introducing air as oxidant a large volume of tail gas is produced. This must be treated to reduce atmospheric emissions of sulfur-containing gases. The costs of the tail-gas unit are a significant fraction of the total capital and operating costs for sulfur recovery. A new process uses thermal decomposition of hydrogen sulfide in the presence of carbon dioxide instead of air oxidation. The products of this reaction are hydrogen, carbon monoxide, elemental sulfur, water vapor and carbonyl sulfide. Carbonyl sulfide is easily converted to H₂S and C0₂ by liquid- or vapor-phase hydrolysis. Unreacted H₂S and C0₂ are recovered by absorption and recycled to the reactor. Since no air is introduced, there is no tail gas and the tail-gas unit is eliminated, giving a substantial reduction in capital investment. The concentrations of sulfur-containing gases in the product streams depend only on the operation of the absorber and stripper units and can be controlled to very low levels by increasing stripper boil-up. Process operating costs depend on the level of sulfur recovery required and can also be much lower than those of the modified Claus Process.

The process chemistry depends on a shift in the equilibrium of H₂S decomposition caused by reaction of hydrogen with C0₂ by the reverse of the water-gas-shift reaction. Catalysts for this chemistry have been identified. Reactor conversion is further improved by rapid cooling of the reactor effluent gas. Other aspects of process design and operation confer further advantages with respect to the Claus process; however, the process equipment used is similar to that used in a Claus plant. Retrofit of existing plant to the new technology can therefore be considered.     

Poisoning and regeneration of claus alumina catalysts

Samples of poisoned alumina catalysts obtained from Claus sulfur recovery plants in Alberta have been regenerated. Poisoned catalysts had SO₄⁼, NO₃^?, sulfur and carbon deposits, discoloration, and low surface areas. Whereas the Claus catalytic activity of the poisoned catalysts varied widely, regeneration uniformly enhanced the catalytic activity to the same level as fresh alumina. The activity comparisons were made under conditions similar to those of a third Claus converter of low partial pressures of H₂S and SO₂ and high partial pressure of H₂O, where maximum catalytic activity is required to promote Claus reaction.     

Fluidized bed Claus reactor studies

Fluidized bed studies have been performed on the Claus reaction to determine whether the conversion efficiency of the Claus process could be improved by replacing conventional fixed bed reactors with fluidized bed reactors. Various idealized Claus plants, incorporating fluidized bed technology, were simulated using the equilibrium constant method. The results of the simulation indicated that, for feed gases consisting of pure H₂S, sulphur conversions in excess of 99% are attainable by using a Claus furnace and two fluidized bed reactors in series. To substantiate the theoretical predictions, experimental studies were performed using a single fluidized bed reactor (0.1 m I.D.) containing Kaiser alumina S-501 catalyst. The effects of temperature (150–300°C), flow rates (15–30 l min⁻¹), feed composition (0.06 < H₂S < 18%, 0.03 < SO₂ < 9%, 73 < N₂ < 99.91%) and bed height (0.12, 0.25 m) on the sulphur conversion were examined. The experimental results showed the same general trends as the theoretical predictions but the measured sulphur conversions exceed the theoretical values by up to 8%.     

Adsorptive reactors for enhancing equilibrium gas-phase reactions—two case studies

The conversion enhancement potential of fixed-bed adsorptive reactors has been evaluated for two heterogeneously catalysed gas-phase equilibrium reactions: the Claus reaction used in sulphur recovery and the direct synthesis of hydrogen cyanide from carbon monoxide and ammonia. It was found that kinetics of both reaction and adsorption as well as adsorbent capacity have to be very compatible to achieve high conversions. The specific parameters of the reaction/catalyst system, such as the deposition of solids (e.g. sulphur, coke) or the formation of undesirable by-products have to be taken into account for the successful application of adsorptive reactor concepts. A crucial point is the selection of the reaction conditions (i.e. temperature), since the occurrence of side reactions may be enhanced in adsorptive reactor operation due to the inherently distorted concentration profiles.     

SRT-Ⅲ型裂解炉改造及效果

通过分析原乙烯装置生产存在的“瓶颈”，提出了SRT-Ⅲ型裂解炉改造的设计方案，并对改造后效果进行测量，热效率和乙烯收率均比设计值有所提高，乙烯裂解炉的生产能力提高了，能耗降低了。     

Simulation of natural gas steam reforming furnace

A mathematical model for natural gas reformer is established to draw up homogeneous phase one-dimensional reaction kinetics equation in the reforming tubes, and compute the tube external radiant heat transfer with zone method. Simulation result is compared with the operating data carried on Selas reformer used in Brown and Root Braun 1000 t NH₃/day production system in Urumqi Second Ammonia Plant, and they match well. This model has laid the foundation for the design variable optimization research, for example, the relations among specific heat transfer area of furnace tube, tube outlet temperature, tube pressure drop and maximum tube-wall temperature, as well as the effect of tube pitch, furnace chamber width, burner arrangement, furnace wall blackness, production load, water carbon ratio and fuel distribution on operation behaviors.     

A study on the reactivity of Ce-based Claus catalysts and the mechanism of its catalysis for removal of H2S contained in coal gas

In this study, Claus reaction was applied for the selective removal of H₂S contained in the gasified coal gas, and the characteristics of Claus reaction over the Ce-based catalysts were investigated to propose the reaction mechanism. The Ce-based catalysts showed a high activity on Claus reaction. Specially, Ce_0.8Zr_0.2O₂ catalyst had a higher activity than CeO. On the basis of our experimental results, it was proposed that the selective oxidation of H₂S was carried out by the lattice oxygen in the Ce-based catalysts and that the reduction of SO₂ was performed by the lattice oxygen vacancy in the reduced catalyst. Since the mobility of the lattice oxygen in Ce_0.8Zr_0.2O₂ composite catalyst was better than the one in CeO₂, Ce_0.8Zr_0.2O₂ provided more lattice oxygen for the selective oxidation of H₂S. It was presumed that the reaction mechanism to convert H₂S and SO₂ into elemental sulphur over our prepared catalysts was different from the mechanism over the solid-acid catalysts. It is believed that Claus reaction over the Ce-based catalysts was carried out by the redox mechanism. Since the moisture was contained in the major components, CO and H, of the gasified fuel gas, the effects of CO and H₂O on the catalytic reaction were investigated over a Ce-based catalyst. The conversion of H₂S and SO₂ was decreased in Claus reaction over the Ce-based catalysts as the concentration of either H₂O or CO in the gasified coal gas was increased. Under the circumstances of the coexistence of both moisture and CO, however, the conversion was increased as the concentration of CO was increased. The reactivity of Claus reaction was varied in terms of the concentration ratio of CO to H₂O. The maximum conversion of H₂S and SO₂ was achieved in the condition of that the concentration of CO contained in the reacting gas was higher than the one of H₂O. The conversions of H₂S and SO₂ did not match to the stoichiometric ratios of Claus reaction. The higher conversion of H₂S was obtained in the higher concentration of H₂O, while the higher conversion of SO₂ was achieved in the higher concentration of CO. It was another evidence to indicate that the Claus reaction over the Ce-based catalysts was carried out by the redox mechanism.     

硫磺回收装置过程气加热方式比较

介绍了国内硫磺回收工艺特点及过程气加热方式。分析比较高温热掺合法、在线加热炉加热法、蒸汽加热法、气-气换热法和电加热法等过程气加热方式的优缺点,并探讨了高温掺合阀的安装位置及选材、Claus尾气加热方式选择等。建议设计人员根据各企业热源的可靠性、装置规模、装置操作弹性、酸性气组成、装置平面布局及投资情况等综合考虑,选择最佳的过程气加热方式。     

Economic Evaluation and Environmental Assessment of the Shale Gas Sweetening Process

An appraisal on economic and environmental performance of shale gas processing is significant for energy utilization. A framework on economic evaluation and environmental assessment of the shale gas sweetening process is proposed. The sweetening process is simulated by Aspen Plus, coupled with Claus sulfur recovery by energy integration. The economic evaluation is conducted by purchased cost curves. In environmental assessment, a hybrid life cycle inventory model is established to investigate the emissions from upstream manufacture and process operation. The results demonstrate that exhaust gas is the dominant source in carbon emission while utility consumption produces more SO₂ and NO_x. The study provides guidance in energy management and pollution control for shale gas plants.     

煤化工装置中硫回收单元的模拟设计

采用Sulsim软件,对煤化工装置中硫回收单元进行流程模拟设计。采用不同浓度的氧气与同一原料酸性气发生燃烧反应,讨论了氧气浓度对燃烧反应的影响,分析了采用Sulsim软件中不同的燃烧反应经验模式设计对模拟结果的影响。模拟结果表明,使用纯氧可大幅度提高装置处理能力,且在Sulsim软件模拟中,炉膛燃烧反应模式选用富氧燃烧模式更为可靠。模拟结果与国内外研究资料及实际工厂运行情况吻合,并分析了该模拟结果产生的原因及其对于工业设计的意义。     

CPS 硫磺回收工艺在塔中某处理厂的应用

塔中某处理厂硫磺回收采用分流法低温克劳斯工艺,通过一级常规克劳斯和三级低温克劳斯反应完成单质硫的回收和尾气的处理,保证硫收率达到99.25％以上及尾气排放合格。文中对装置的工艺特点进行简单介绍,并对生产过程中遇到的问题与应对措施进行分析和说明,充分证明了CPS硫磺回收工艺非常适合该处理厂的实际情况。     

Activity monitoring of Claus catalysts in sulfur recovery units

Methodical principles of catalyst activity monitoring in Claus reactors based on the determination of the rate constant of the reaction of hydrogen sulfide conversion at catalyst temperatures lower than 280°C are discussed. The procedure is justified by data from laboratory experiments (in the range of concentrations [H₂S]₀ = 1.5–7 vol %), pilot tests ([H₂S]₀ = 0.8–37.4 vol %) of an alumina-based catalyst AO-NKZ-2 produced by ZAO Novomichurinsk Catalyst Plant, and by the results of its test in the Claus reactor of the department for coke oven gas purification of by-product-coke plant at the OAO Magnitogorsk Integrated Iron-and-Steel Works. The procedure is recommended for reliable monitoring of the current activity and estimation of the residual life of catalysts in the Claus industrial reactors operating under conditions of substantial variations in the composition of the process gas, as well as for comparative estimates of catalyst activity in the Claus process.     

Kinetic modelling of a fluidized bed claus plant

A kinetic model of a fluidized bed Claus reactor was developed using the Modified Bubble Assemblage Model (MBAM) to establish the practical implications of fluid bed technology for this new application. Simulations predicted that a two stage sub-dewpoint fluidized bed Claus plant is capable of achieving a recovery efficiency of 97.1%, which is comparable to a conventional three stage fixed bed plant, but considerably less than the overall equilibrium conversion of 99.5%. Conversion is limited by gas-bypassing, particularly in the downstream sub-dewpoint reactor. In the fluidized bed process, about half the catalyst is required and the pressure drop is significantly lower compared with a conventional plant of equivalent capacity. Moreover, the capital cost estimate for a two reactor fluid bed Claus plant (200 t/d sulphur) was estimated to be $20 million (Can) which is within 10% of a conventional plant.     

基于Aspen Plus的克劳斯硫回收过程模拟

采用Aspen P lus工艺模拟计算软件模拟了克劳斯硫回收工艺过程,模拟数据与硫回收专用模拟软件的标定数据吻合较好;在此基础上,利用Aspen P lus模块化分析功能,研究了克劳斯工艺的关键数据对工艺过程的影响,其结论与实际生产过程相符合;结果表明,基于Aspen P lus的克劳斯硫回收过程模拟,对设计计算和生产...     

超优克劳斯硫回收工艺技术及应用前景

超优克劳斯硫回收工艺是在传统克劳斯工艺基础上开发的硫回收工艺,在硫回收率、尾气达标、装置投资费用等方面更具优势。介绍了超优克劳斯硫回收的工艺原理、技术特点以及国内装置的建设概况;将超优克劳斯与其他硫横回收工艺的相对投资和效益进行了比较。结果表明,该工艺不仅适用于现有克劳斯装置的技术改造,也适用于新建装置;在不改变克劳斯工艺基本特点及没有进一步尾气处理的情况下,可将硫回收率提高到99．4％以上。     

A model of acid gas absorption/stripping using methyldiethanolamine with added acid

A nonequilibrium stage model was developed for the absorption and stripping of H₂S and CO₂ using aqueous methyldiethanolamine (MDEA). Heat and mass transfer are calculated for each stage assuming the liquid is well mixed and the gas moves in plug flow. The vapour-liquid equilibrium is represented by an empirical expression that was fit to experimental data. The mass transfer enhancement factor for CO₂ is based on the surface renewal theory with approximations made to the reaction term by the method of DeCoursey. Calculation of H₂S absorption assumes an instantaneous reaction rate at the gas/liquid interface and accounts for enhancement by equilibrium chemical reactions. Results were generated at Claus tail gas conditions using available equilibrium and rate data for 50 wt% MDEA. The amount of H₂S in the absorber outlet gas, or H₂S leak, was used to measure system performance. The base case resulted in a H₂S leak of 98 ppm with 20 absorber stages, 25 stripper stages, and a steam rate of 1.7 lb/gal solvent. Adding 0.05 equivalents of acid per mole of MDEA to the aqueous solution reduced the H₂S leak to 6 ppm and the steam rate to 1.2 lb/gal. Reducing the base case stripper pressure of 2.0 atm to 1.0 atm reduced the H₂S leak to 22 ppm. Analysis of McCabe-Thiele plots generated by the model showed that system performance improved after adding acid or reducing the stripper pressure because the H₂S equilibrium in the stripper was linearized.