Coupling pinch analysis and rigorous process simulation for hydrogen networks with light hydrocarbon recovery

In refineries, some hydrogen-rich streams contain considerable light hydrocarbons that are important raw materials for the chemical industry. Integrating hydrogen networks with light hydrocarbon recovery can enhance the reuse of both hydrogen and light hydrocarbons. This work proposes an automated method for targeting hydrogen networks with light hydrocarbon recovery. A pinch-based algebraic method is improved to determine the minimum fresh hydrogen consumption and hydrogen sources fed into the light hydrocarbon recovery unit automatically. Rigorous process simulation is conducted to determine the mass and energy balances of the light hydrocarbon recovery process. The targeting procedures are developed through combination of the improved pinch method and rigorous process simulation. This hybrid method is realized by coupling the Matlab and Aspen HYSYS platforms. A refinery hydrogen network is analyzed to illustrate application of the proposed method. The integration of hydrogen network with light hydrocarbon recovery further reduces fresh hydrogen requirement by 463.0 m³·h^-1 and recovers liquefied petroleum gas and gasoline of 1711.5 kg·h^-1 and 643 kg·h^-1, respectively. A payback period of 9.2 months indicates that investment in light hydrocarbon recovery is economically attractive.     

REACTOR-MEMBRANE PERMEATOR CASCADE FOR ENHANCED PRODUCTION AND RECOVERY OF H2 AND CO2 FROM THE CATALYTIC METHANE-STEAM REFORMING REACTION

The catalytic reforming of methane by steam is an important industrial process that produces H₂, CO and CO₂, thus chemically transforming natural gas, coal gas and light hydrocarbon feedstocks to synthesis gas or hydrogen fuel. Methane-steam reforming may consist of a number of reactions depending on the reforming catalyst, operating conditions and feedstock composition, The typical industrially desirable reactions are the reverse of methanation (CH₄ + H₂O = CO + 3H₂) and the water-gas shift (CO + H₂O = CO₂ + H₂). Both reactions are equilibrium limited and the composition of the mixture that exits the reformer is in accordance with the one calculated thermodynarmically. Removal of reaction products at the reactor exit by means of selective membrane permeation can offer improved CH₄ conversions and CO₂ and H₂ yields, assuming the subsequent utilization of the reject streams by a second methane-steam reformer. We numerically investigated the feasibility of a system of two tubular methane-steam reformers, in series with an intermediate permselective polyimide membrane permeator, as means of improving the overall CH₄ conversion and the H₂, CO₂ yields over conventional methane-steam reforming equilibrium reaction-separation schemes that are currently in industrial practice. The unique feature of the permselective polyimide separator is the simultaneous removal of H₂ and CO₂ versus CH₄ and CO from the reformed streams. The utilized 6FDA-3,3', 5,5'-TMB aromatic polyimide was reportedly characterized [10] and found to exhibit superior permselective properties compared with other polyimides of the same or different dianhydride sequence. Conversion and yield of the designed reactor-membrane permeator reforming system can be maximized by optimizing the permselective properties of the membrane material and the design variables of the reactors and the permeator. Product recovery and purity in the permeate stream need to be compromised to overall enhance methane conversion and product yield. The operating variables that were varied to investigate their effect on the magnitude of conversion and yield included the inlet pressure of the first reformer, the temperature of both reformers, and the permeator dimensionless Pe' number (variation of the first two variables results to a drastic change in the composition of the reformed stream that enters into the permeator). The numerical results show that the new reformer-membrane permeator cascade process can be more effective (it can offer increased CH₄ conversions and H₂, CO₂ yields) than conventional equilibrium methane-steam reforming reaction-separation processes currently in practice.     

高炉煤气特征组分分析及其对脱硫过程的影响研究进展

高炉煤气（BFG）作为炼铁过程中副产的可燃气体,具有明显的资源回收价值,但其同时存在热值低、成分复杂等问题。目前大多数研究集中在对羰基硫（COS）、硫化氢（H₂S）等有害成分的脱除,而鲜有对高炉煤气特征组分的研究或报道。研究者对高炉煤气特征组分的来源、生成路径等不明朗,导致在研究过程中忽略了煤气复杂组分的相互影响,很多技术在工业应用时问题频发。本文阐述并分析了高炉煤气特征组分的来源及生成路径,进而讨论了高炉煤气特征组分对脱硫过程的影响。高炉原料、燃料和空气在高温条件下经过复杂的化学反应,生成粉尘、N₂、O₂、CO、CO₂、H₂、CH₄、H₂O、HCl、HCN、硫化物等共同组成高炉荒煤气,荒煤气中的O₂、CO_x、H₂、H₂O、HCl、硫化物等化学成分对COS转化或H₂S脱除过程产生影响,导致催化剂中毒或转化率下降。本文通过分析探讨特征组分在高炉煤气产生和脱硫净化过程中的相互作用及影响规律,为超低排放背景下高炉煤气的净化和资源化提供方向和参考。     

RESEARCH NOTES Unified model of purification units in hydrogen networks

Purification processes are widely used in hydrogen networks of refineries to increase hydrogen reuse. In refineries, hydrogen purification techniques include hydrocarbon, hydrogen sulfide and CO removal units. In addition, light hydrocarbon recovery from the hydrogen source streams can also result in hydrogen purification. In order to simplify the superstructure and mathematical model of hydrogen network integration, the models of different purification processes are unified in this paper, including mass balance and the expressions for hydrogen recovery and impurity removal ratios, which are given for all the purification units in refineries. Based on the proposed unified model, a superstructure of hydrogen networks with purification processes is constructed.     

柴油加氢尾气中氢气的水合物法回收工业侧线试验

常规氢气回收方法的产品氢气压力偏低,需多级增压后才可被高压加氢装置利用,具有较高的氢气增压成本。水合物法回收加氢尾气具有压降损失小、产品氢气压力高的优点,可降低高压加氢装置的氢气增压成本。为降低高压加氢装置的用氢成本,本文开发了高压尾气的水合物法氢气回收技术。针对高压柴油加氢尾气,在茂名炼油厂建立了一套柴油加氢尾气中氢气水合物法回收的工业侧线试验装置,考察了不同条件下连续搅拌釜法回收柴油加氢尾气中氢气的分离效果。试验结果表明,水合物法可高效脱除CH₄和大部分的H₂S。连续进气工况下,处理脱硫后尾气时可将氢气体积分数从83.76%提高至91.65%,处理含硫尾气时可将H₂S体积分数从0.73%降至0.07%。     

SIMULTANEOUS ABSORPTION OF AN ACID GAS (H2S) AND A BASIC GAS (NH3) IN A SCRUBBING DEVICE

H₂S and NH₃ are major contaminants in many synfuel process gas streams. The H₂S is frequently removed by dissociation and reaction in scrubbers using alkaline scrubbing liquids. Some of the NH₃ is removed by simple dissolution in the same unit; the remaining NH₃ can be removed in a second scrubber using a mildly acidic liquid. The first scrubbing stage in such a system is novel in that an acidic gas (H₂S) and a basic gas (NH₃) are absorbed simultaneously. In this paper, the interesting behavior of this simultaneous acid gas-basic gas scrubbing process is described and discussed. The percentage H₂S and NH₃, absorption as a function of the injected liquid pH, the liquid-to-gas ratio, and the NH₃ content of the gas stream have been determined.     

Microbial reduction of sulfur dioxide and nitric oxide

Two process concepts have been developed for a microbial contribution to the problem of flue gas desulfurization and NO_x removal. We have demonstrated that the sulfate-reducing bacterium Desulfovibrio desulfuricans can be grown in a mixed culture with fermentative heterotrophs in a medium in which glucose served as the only carbon source. Beneficial cross-feeding resulted in vigorous growth of D. desulfuricans, which used SO₂(g) as a terminal electron acceptor, with complete reduction of SO₂ to H₂S in 1–2 s of contact time. We have proposed that the concentrated SO₂ stream, obtained from regeneration of the sorbent in regenerable processes for flue gas desulfurization, could be split with two-thirds of the SO₂ reduced to H₂S by contact with a culture of sulfate-reducing bacteria. The resulting H₂S could then be combined with the remaining SO₂ and used as feed to a Claus reactor to produce elemental sulfur. However, the use of glucose as an electron donor in microbial SO₂ reducing cultures would be prohibitively expensive. Therefore, if microbial reduction of SO₂ is to be economically viable, less expensive electron donors must be found. Consequently, we have evaluated the use of municipal sewage sludge and elemental hydrogen as carbon and/or energy sources for SO₂ reducing cultures. Heat and alkali pretreated sewage sludge has been successfully used as a carbon and energy source to support SO₂ reduction in a continuous, anaerobic mixed culture containing D. desulfuricans. The culture operated for nine months with complete reduction of SO₂ and H₂S. Another sulfate-reducing bacterium, Desulfotomaculum orientis, has also been grown in batch cultures on a feed of SO₂, H₂ and CO₂. Complete reduction of SO₂ to H₂S was observed with gas-liquid contact times of 1–2 s. We have also demonstrated that the facultative anaerobe and chemoautotroph, Thiobacillus denitrificans, can be cultured anoxically in batch reactors using NO(g) as a terminal electron acceptor with reduction to elemental nitrogen. We have proposed that the concentrated stream of NO_x, as obtained from certain regenerable processes for flue gas desulfurization and NO_x removal, could be converted to elemental nitrogen for disposal by contact with a culture T. denitrificans. Two heterotrophic bacteria have also been identified which may be grown in batch cultures with succinate or heat and alkali pretreated sewage sludge as carbon and energy sources and NO as a terminal electron acceptor. These are Paracoccus denitrificans and Pseudomonas denitrificans.     

ALTERNATIVE GENERATION OF H2, CO AND H2, CO2 MIXTURES FROM STEAM-CARBON DIOXIDE REFORMING OF METHANE AND THE WATER GAS SHIFT WITH PERMEABLE (MEMBRANE) REACTORS

A new process is proposed which converts CO₂ and CH₄ containing gas streams to synthesis gas, a mixture of CO and H₂ via the catalytic reaction scheme of steam-carbon dioxide reforming of methane or the respective one of only carbon dioxide reforming of methane, in permeable (membrane) reactors. The membrane reformer (permreactor) can be made by reactive or inert materials such as metal alloys, microporous ceramics, glasses and composites which all are hydrogen permselective. The rejected CO reacts with steam and converted catalytically to CO₂ and H₂ via the water gas shift in a consecutive permreactor made by similar to the reformer materials and alternatively by high glass transition temperature polymers. Both permreactors can recover H₂ in permeate by using metal membranes, and H₂ rich mixtures by using ceramic, glass and composite type permselective membranes. H₂ and CO₂ can be recovered simultaneously in water gas shift step after steam condensation by using organic polymer membranes. Product yields are increased through permreactor equilibrium shift and reaction separation process integration.

CO and H₂ can be combined in first step to be used for chemical synthesis or as fuel in power generation cycles. Mixtures of CO₂ and H₂ in second step can be used for synthesis as well (e.g., alternative methanol synthesis) and as direct feed in molten carbonate fuel cells. Pure H₂ from the above processes can be used also for synthesis or as fuel in power systems and fuel cells. The overall process can be considered environmentally benign because it offers an in-situ abatement of the greenhouse CO₂ and CH₄ gases and related hydrocarbon-CO₂ feedstocks (e.g., coal, landfill, natural, flue gases), through chemical reactions, to the upgraded calorific value synthesis gas and H₂, H₂ mixture products.     

Integration strategies of hydrogen network in a refinery based on operational optimization of hydrotreating units

Inferior crude oil and fuel oil upgrading lead to escalating increase of hydrogen consumption in refineries. It is imperative to reduce the hydrogen consumption for energy-saving operations of refineries. An integration strategy of hydrogen network and an operational optimization model of hydrotreating (HDT) units are proposed based on the characteristics of reaction kinetics of HDT units. By solving the proposed model, the operating conditions of HDT units are optimized, and the parameters of hydrogen sinks are determined by coupling hydrodesulfurization (HDS), hydrodenitrification (HDN) and aromatic hydrogenation (HDA) kinetics. An example case of a refinery with annual processing capacity of eight million tons is adopted to demonstrate the feasibility of the proposed optimization strategies and the model. Results show that HDS, HDN and HDA reactions are the major source of hydrogen consumption in the refinery. The total hydrogen consumption can be reduced by 18.9% by applying conventional hydrogen network optimization model. When the hydrogen network is optimized after the operational optimization of HDT units is performed, the hydrogen consumption is reduced by 28.2%. When the benefit of the fuel gas recovery is further considered, the total annual cost of hydrogen network can be reduced by 3.21×10₇ CNY·a_-1, decreased by 11.9%. Therefore, the operational optimization of the HDT units in refineries should be imposed to determine the parameters of hydrogen sinks base on the characteristics of reaction kinetics of the hydrogenation processes before the optimization of the hydrogen network is performed through the source-sink matching methods.     

Solubility and mass transfer of H2, CH4, and their mixtures in vacuum gas oil: An experimental and modeling study

In this work, the solubility data and liquid-phase mass transfer coefficients of hydrogen (H₂), methane (CH₄) and their mixtures in vacuum gas oil (VGO) at temperatures (353.15-453.15 K) and pressures (1-7 MPa) were measured, which are necessary for catalytic cracking process simulation and design. The solubility of H₂ and CH₄ in VGO increases with the increase of pressure, but decreases with the increase of temperature. Henry's constants of H₂ and CH₄ follow the relation of ln H=-413.05/T + 5.27 and ln H=-990.67/T + 5.87, respectively. The molar fractions of H₂ and system pressures at different equilibrium time were measured to estimate the liquid-phase mass transfer coefficients. The results showed that with the increase of pressure, the liquid-phase mass transfer coefficients increase. Furthermore, the solubility of H₂ and CH₄ in VGO was predicted by the predictive COSMO-RS model, and the predicted values agree well with experimental data. In addition, the gas-liquid equilibrium (GLE) for H₂ + CH₄ + VGO system at different feeding gas ratios in volume fraction (i.e., H₂ 85% + CH₄ 15% and H₂ 90% + CH₄ 10%) was measured. The selectivity of H₂ to CH₄ predicted by the COSMO-RS model agrees well with experimental data. This work provides the basic thermodynamic and dynamic data for fuel oil catalytic cracking processes.     

集成轻烃回收单元代理模型的氢气网络多目标优化

当前炼油企业氢气需求持续增长,导致炼厂成本及生产过程温室气体排放增加,炼油企业通过增设轻烃回收单元对氢气和轻烃组分进行回收利用,能有效缓解这一现状。因此,在氢气网络优化中有必要考虑轻烃回收单元。本研究提出了一种集成轻烃回收单元的氢气网络多目标数学规划模型,对轻烃回收单元采用代理模型建模方法,解决了直接嵌入严格机理模型可能导致的高计算成本问题,以总年度费用最小为优化目标,同时将系统的环境影响也纳入优化目标。实例计算表明,所提出的方法能够有效降低氢气网络的年度费用及温室气体排放,并揭示了集成轻烃回收单元的氢气网络经济性能与环境影响之间的权衡关系,为工业应用提供了一定的理论基础。     

ABSORPTION OF SO2 AND H2S IN SMALL-SCALE VENTURI SCRUBBERS

Small-scale venturi scrubbers having geometries of typical large-scale units were constructed from glass and were operated in a laboratory system. Carrier gas streams consisting of air or nitrogen and up to 30% (by volume) CO₂ were mixed with SO₂ or H₂S to give SO₂ or H₂S concentrations in the range of 1890-4400 ppm. These gas mixtures were then scrubbed in the Venturis using various injected liquids (plain water, NaOH solutions, NH₄OH solutions, and NaOH/NaHCO₃ solutions) at L/G ratios of 0.0004-0.0040 m³ liquid per standard (1 atm, 60°F)m³ of gas (3-30 gallons liquid per 1000 standard ft³ of gas). Absorption percentages for SO₂ and H₂S were determined as functions of the L/G ratio, initial liquid pH, and liquid composition. The effects of venturi throat length, gas velocity, and the presence of CO₂ in the gas stream were also determined.     

Conversion of sulfur dioxide to sulfate and hydrogen sulfide by Desulfotomaculum orientis

The autotrophic, sulfate-reducing bacterium, Desulfotomaculum orientis, grew in batch culture with molecular hydrogen (H₂) as an energy source, carbon dioxide (CO₂) as a carbon source and sulfur dioxide (SO₂) as the terminal electron acceptor. At high H₂ partial pressure, SO₂ was stoichiometrically reduced to hydrogen sulfide (H₂S). At low partial pressures of hydrogen (< 0.025 atm), SO₂ was both oxidized to sulfate and reduced to hydrogen sulfide. These results indicated a new mode of sulfur metabolism for D. orientis.     

H2O-CO2、H2O-N2、H2O-He水平管外自然对流凝结换热特性研究

不凝性气体制约换热设备安全和系统效率,为研究不凝性气体-蒸气于水平管外自然对流凝结换热机理和特性,实验测量了不凝性气体He、N₂、CO₂质量分数分别为1.16%~18.18%、7.56%~60.86%、11.39%~70.95%,壁面过冷度为5~25 K,总压力为5~101 kPa的H₂O-He、H₂O-N₂、H₂O-CO₂自然对流条件下水平管外凝结换热特性,对比分析了H₂O-He、H₂O-N₂、H₂O-CO₂的不凝性气体质量含量、壁面过冷度以及压力因素的影响。压力和壁面过冷度一定,相同质量分数时,实验凝结传热系数与Nusselt理论解的比值(Q/Q_Nu)由大到小依次为：H₂O-CO₂、H₂O-N₂、H₂O-He;相同摩尔分数时,Q/Q_Nu由大到小依次为：H₂O-He、H₂O-N₂、H₂O-CO₂。相同总压力和不凝性气体质量分数时,H₂O-He的Q/Q_Nu随着壁面过冷度的增加下降最为缓慢。相同不凝性气体质量分数和壁面过冷度时,H₂O-He的Q/Q_Nu值最小,其受压力影响最为显著。     

Explosion limits estimation and process optimization of direct propylene epoxidation with H2 and O2

Direct propylene epoxidation with H₂ and O₂, an attractive process to produce propylene oxide (PO), has a potential explosion danger due to the coexistence of flammable gases (i.e., C₃H₆ and H₂) and oxidizer (i.e., O₂). The unknown explosion limits of the multi-component feed gas mixture make it difficult to optimize the reaction process under safe operation conditions. In this work, a distribution method is proposed and verified to be effective by comparing estimated and experimental explosion limits of more than 200 kinds of flammable gas mixture. Then, it is employed to estimate the explosion limits of the feed gas mixture, some results of which are also validated by the classic Le Chatelier's Rule and flammable resistance method. Based on the estimated explosion limits, process optimization is carried out using commercially high and inherently safe reactant concentrations to enhance reaction performance. The promising results are directly obtained through the interface called gOPT in gPROMS only by using a simple, easy-constructed and mature packed-bed reactor, such as the PO yield of 13.3%, PO selectivity of 85.1% and outlet PO fraction of 1.8%. These results can be rationalized by indepth analyses and discussion about the effects of the decision variables on the operation safety and reaction performance. The insights revealed here could shed new light on the process development of the PO production based on the estimation of the explosion limits of the multi-component feed gas mixture containing flammable gases, inert gas and O₂, followed by process optimization.     

锆基双金属氧化物催化剂硫中毒的研究

在工业二氧化碳加氢制甲醇过程中,硫化氢气体的引入将对该过程中使用的催化剂活性及稳定性带来负面的影响。基于此,采用微反应合成法成功制备了InZrO_x和ZnZrO_x锆基催化剂,并研究了在二氧化碳加氢反应中,硫化氢气体对锆基催化剂的结构性质及其催化性能的影响规律。结果表明,在T=573 K、p=3.0 MPa和GHSV=18 000 mL/(g_cat·h)条件下,仅通入二氧化碳/氢气反应气时,InZrO_x和ZnZrO_x催化剂的二氧化碳转化率和甲醇选择性分别为7.2%、9.3%和93%、92%。在二氧化碳/氢气原料气中通入体积分数为5×10^-3硫化氢气体时,InZrO_x和ZnZrO_x催化剂的二氧化碳转化率和甲醇选择性都降为0,这主要是因为硫化氢气体占据了氧空位,导致锆基双金属氧化物催化剂硫中毒失活。当停止通硫化氢气体时,InZrO_x和ZnZrO_x催化剂的二氧化碳转化率和甲醇选择...     

H2O-CO2、H2O-N2、H2O-He水平管外自然对流凝结换热特性研究

不凝性气体制约换热设备安全和系统效率,为研究不凝性气体-蒸气于水平管外自然对流凝结换热机理和特性,实验测量了不凝性气体He、N₂、CO₂质量分数分别为1.16%~18.18%、7.56%~60.86%、11.39%~70.95%,壁面过冷度为5~25 K,总压力为5~101 kPa的H₂O-He、H₂O-N₂、H₂O-CO₂自然对流条件下水平管外凝结换热特性,对比分析了H₂O-He、H₂O-N₂、H₂O-CO₂的不凝性气体质量含量、壁面过冷度以及压力因素的影响。压力和壁面过冷度一定,相同质量分数时,实验凝结传热系数与Nusselt理论解的比值(Q/Q_Nu)由大到小依次为：H₂O-CO₂、H₂O-N₂、H₂O-He;相同摩尔分数时,Q/Q_Nu由大到小依次为：H₂O-He、H₂O-N₂、H₂O-CO₂。相同总压力和不凝性气体质量分数时,H₂O-He的Q/Q_Nu随着壁面过冷度的增加下降最为缓慢。相同不凝性气体质量分数和壁面过冷度时,H₂O-He的Q/Q_Nu值最小,其受压力影响最为显著。     

双反应器选择性氧化硫回收工艺改进与优化

陕西某天然气净化厂采用干法双反应器选择性氧化硫回收工艺,该硫磺回收装置自2016年1月投产以来,存在等温反应器床层热点温度>300℃、硫磺夹带严重等问题,造成焚烧后φ（SO₂）偏高。通过对运行数据分析,结合实验室评价和模拟计算,确定汽包管路的不对称性分布为热点温度高的主因,硫分离器内流速低于设计值为硫磺夹带的主因,并提出汽包管路均布、降低硫分离器内件流通面积及增加在线仪表蒸汽吹扫等改进措施,使得装置运行平稳,热点温度降低至300℃以下,硫磺收率增加,外排SO₂降低至4 000 mg/m³（标准状态,下同）以下。     

石化园区厂际提纯回用氢气系统优化

石化园区化肥厂、乙烯厂等富氢气体送往炼油厂,能够缓解炼油厂的氢气亏缺,因而石化园区厂际氢气系统优化具有重要的意义.本文构建了石化园区厂际提纯回用氢气系统超结构模型,以年度化总费用为目标函数,建立优化的数学模型,使用商业优化软件GAMS平台建模,用DICOPT作为求解器.对某石化园区的氢气系统进行了优化,结果表明,总的年度化费用比现行的系统降低了33.1%.     

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.