甲醇模块化生产中分时储热系统的优化设计

以“数量放大”为特征的模块化化工生产为克服原料供给和产品市场需求波动的生产流程优化操作提供新途径。为了提高生产系统的能量利用效率,需对生产系统中随时间变化的流股预热、冷却和反应热分时段进行储存和调度。针对可再生能源驱动的甲醇模块化生产系统,本文提出了分时储热策略,通过储罐设置及流股匹配、储罐储热温区确定和储罐容量配置及调度三步对甲醇模块化生产中分时储热系统进行优化设计,获得了分时储热系统的最优配置和优化调度方案。研究表明：在甲醇模块化生产系统中,分时储热系统可将前阶段的热量储存供后续阶段调用,以实现系统能量的最大化利用,而储热的适量废弃可降低储热系统的投资费用。本文所提出的储热系统优化方法可为波动生产过程中分时储热系统的优化设计提供分析工具。     

Techno-economic optimization of IGCC integrated with utility system for CO2 emissions reduction—Maximum power production in IGCC

Environmental legislation, with its increasing pressure on the energy sector to control greenhouse gases, is a driving force to reduce CO₂ emissions. In this paper, pre-combustion CO₂ capture through integration of a site utility system with an integrated gasification combined cycle (IGCC) is investigated as an option to provide a compressed CO₂-rich stream from a process site for sequestration. This work presents a two-step procedure for integration and optimization of a site utility system with an IGCC plant: (i) screening and optimization of IGCC plant performance parameters; (ii) integration and optimization of the utility system of the site with the IGCC plant. In the first step, an optimization approach applies the results of screening studies based on rigorous simulation of the IGCC. Having fixed the inlet fuel flow rate, the IGCC design parameters (including oxygen consumption, diluent flow rate and turbine exit pressure) are optimized for maximum power generation. Energy flows between the IGCC and CO₂ compression train are considered. In the second step, the economic and operating performance of the utility system integrated with the IGCC plant are modeled and optimized for minimum operating cost to find the most appropriate level of integration. In a case study illustrating the approach, 94% of the fuel is gasified; additional power generation offsets the operating costs of pre-combustion CO₂ capture.     

Effects of catalyst composition on methanol synthesis from CO2/H2

Effects of catalyst composition have been studied for Cu/support and Cu/ZnO/supports in methanol synthesis from CO₂/H₂. A strong effect of support has been observed. Different supports brought about different behavior in temperature-programmed reduction of copper, different copper surface areas, and different catalytic activity and selectivity. It seemed possible to find catalyst supports that might perform better than commercial Cu/ZnO/Al₂O₃ catalysts. A correlation was observed between catalytic activity and the copper surface area which was varied by using different supports. However, the sup]>orts appeared to influence other catalytic properties as well, for example, the surface oxygen coverage.     

CO_2捕集的吸收溶解度计算和过程模拟

为了降低CO2吸收法捕集技术的能耗和成本,以目前常用的单乙醇胺(MEA)溶液吸收CO2为例,采用电解质非随机双流体热力学模型(E-NRTL),对溶液中的CO2气体溶解度进行计算,计算过程包含了化学反应平衡和汽液平衡,计算结果和文献数据相吻合。在此基础上,建立了CO2吸收过程模拟程序和包括解吸能耗、气体压缩能耗以及液体输送能耗的过程总体能耗的计算方法,继而通过过程模拟分析了吸收塔和解吸塔压力、溶液浓度和流量等因素对吸收捕集过程的总体能耗的影响,获取了最优的工艺条件,为以后新CO2吸收捕集过程提供能耗分析方法基础。     

Modeling and simulation for the methane steam reforming enhanced by in situ CO2 removal utilizing the CaO carbonation for H2 production

The transient behavior of catalytic methane steam reforming (MSR) coupled with simultaneous carbon dioxide removal by carbonation of CaO pellets in a packed bed reactor for hydrogen production has been analyzed through a mathematical model with reaction experiments for model verification. A dynamic model has been developed to describe both the MSR reaction and the CaO carbonation-enhanced MSR reaction at non-isothermal, non-adiabatic, and non-isobaric operating conditions assuming that the rate of the CaO carbonation in a local zone of the packed bed is governed by kinetic limitation or by mass transfer limitation of the reactant CO₂. Apparent carbonation kinetics of the CaO pellet prepared has been determined using the TGA carbonation experiments at various temperatures, and incorporated into the model. The resulting model is shown to successfully depict the transient behavior of the in situ CaO carbonation-enhanced MSR reaction. The effects of major operating parameters on the transient behavior of the CaO carbonation-enhanced MSR have been investigated using the model. The bed temperature is the most important parameter for determining the amount of CO₂ removed by carbonation of CaO, and at temperatures of 600°C, 650°C, 700°C and 750°C, the CO₂ uptake is 1.43, 2.29, 3.5 and -CO₂/kg-CaO, respectively. Simultaneously with the increase in CO₂ uptake with increasing temperature, the corresponding amounts of hydrogen produced are 1.56, 2.54, 3.91 and -H₂/kg-CaO, at the same temperatures as above. Operation at high pressure, high steam to methane feed ratio, and the decreased feed rate at a given temperature are favorable for increasing the degree of the overall utilization of CaO pellets in the reactor bed, and for lowering the CO concentration in the product.     

Post-combustion CO2 capture process: Equilibrium stage mathematical model of the chemical absorption of CO2 into monoethanolamine (MEA) aqueous solution

This paper deals with the modeling and optimization of the chemical absorption process to CO₂ removal using monoethanolamine (MEA) aqueous solution. Precisely, an optimization mathematical model is proposed to determine the best operating conditions of the CO₂ post-combustion process in order to maximize the CO₂ removal efficiency. Certainly, the following two objective functions are considered for maximization: (a) ratio between the total absorbed CO₂ and the total heating and cooling utilities and (b) ratio between total absorbed CO₂ and the total amine flow-rate.Temperature, composition and flow-rate profiles of the aqueous solution and gas streams along the absorber and regenerator as well as the reboiler and condenser duties are considered as optimization variables. The number of trays or height equivalent to a theoretical plate (HETP) on the absorber and regenerator columns as well as the CO₂ composition in flue gas are treated as model parameters. Correlations used to compute physical-chemical properties of the aqueous amine solution are taken from different specialized literature and are valid for a wide range of operating conditions. For the modeling, both columns (absorber and regenerator) are divided into a number of segments assuming that liquid and gas phases are well mixed.GAMS (General Algebraic Modeling System) and CONOPT are used, respectively, to implement and to solve the resulting mathematical model.The robustness and computational performance of the proposed model and a detailed discussion of the optimization results will be presented through different case studies. Finally, the proposed model cannot only be used as optimizer but also as a simulator by fixing the degree of freedom of the equation system.     

Partial oxidation of methane with air for methanol production in a post-plasma catalytic system

Partial oxidation of methane to methanol via post-plasma catalysis using a dielectric-barrier discharge was performed under mild reaction conditions. Air was used as the oxidizing co-reactant because of its economical practicality. Three catalysts impregnated with Pt, Fe₂O₃, CeO₂ on ceramic supports located downstream of the discharge zone were examined for increased selectivity towards methanol. It was found that all three catalysts had no significant effect on the conversion of methane, but enhanced methanol selectivity, which could be explained by a two-stage reaction mechanism. The Fe₂O₃-based catalyst showed the best catalytic activity, and high stability in the reaction. The methanol selectivity of the Fe₂O₃-assisted plasma process was 36% higher than that of the non-catalytic system at a rather low catalyst temperature (150 °C). In addition, the effects of input power, discharge frequency, discharge gap distance, total flow rate, and methane/air ratio on methane conversion and methanol yield were also studied.     

Promoting effect of an aluminum emulsion on catalytic performance of Cu-based catalysts for methanol synthesis from syngas

Copper-based catalysts modified with aluminum precursors having different morphologies for methanol synthesis were prepared and the effect of the addition of aluminum emulsion on the characteristics of the catalyst was studied by using X-ray diffraction (XRD), temperature-programmed reduction (TPR) and differential thermal gravity (DTG). The experiment results show that the copper-based catalyst prepared by mixing a Cu-Zn precipitate with an amorphous aluminum emulsion prepared in advance by precipitating an aluminum salt with ammonia exhibits higher specific surface area and catalytic performance for methanol synthesis from synthesis gas. The catalysts thus prepared were found to have more (Cu,Zn)₂CO₃(OH)₂ phase, from which more Cu/Zn sosoloid was produced during calcination. More sosoloid phase produced and stronger synergy between Cu and ZnO were verified to enhance the activity of the catalyst for methanol synthesis.     

Influence of preparation method on performance of Cu(Zn)(Zr)-alumina catalysts for the hydrogen production via steam reforming of methanol

The selective production of hydrogen via steam reforming of methanol (SRM) was performed using prepared catalysts at atmospheric pressure over a temperature range 200–260^∘C. Reverse water gas shift reaction and methanol decomposition reactions also take place simultaneously with the steam reforming reaction producing carbon monoxide which is highly poisonous to the platinum anode of PEM fuel cell, therefore the detailed study of effect of catalyst preparation method and of different promoters on SRM has been carried out for the minimization of carbon monoxide formation and maximization of hydrogen production. Wet impregnation and co-precipitation methods have been comparatively examined for the preparation of precursors to Cu(Zn)(Al₂O₃) and Cu(Zn)(Zr)(Al₂O₃). The catalyst preparation method affected the methanol conversion, hydrogen yield and carbon monoxide formation significantly. Incorporation of zirconia in Cu(Zn)(Al₂O₃) catalyst enhanced the catalytic activity, hydrogen selectivity and also lower the CO formation. Catalyst Cu(Zn)(Zr)(Al₂O₃) with composition Cu/Zn/Zr/Al:12/4/4/80 prepared by co-precipitation method was the most active catalyst giving methanol conversion up to 97% and CO concentration up to 400 ppm. Catalysts were characterized by atomic absorption spectroscopy (AAS), Brunauer-Emett-Teller (BET) surface area, pore volume, pore size and X-ray powder diffraction (XRPD). The XRPD patterns revealed that the addition of zirconia improves the dispersion of copper which resulted in the better catalytic performance of Cu(Zn)(Zr)(Al₂O₃). The time-on-stream (TOS) catalysts stability test was also conducted for which the Cu(Zn)(Zr)(Al₂O₃) catalyst gave the consistent performance for a long time compared to other catalysts.     

Kinetics study of carbon dioxide absorption in aqueous solutions of 1,6-hexamethyldiamine (HMDA) and 1,6-hexamethyldiamine, N,N′ di-methyl (HMDA, N,N′)

A study towards the kinetics of CO₂ in aqueous solutions of 1,6-hexamethyl diamine (HMDA) and 1,6-hexamethyl diamine, N,N′ di-methyl (HMDA, N,N′) was performed at concentrations ranging from 0.5 to 2.5 mol/L and temperatures from 283 up to 303 K. The kinetics data were determined by CO₂ absorption experiments using a stirred cell reactor with a flat interface between gas and liquid. These new CO₂ solvents were identified in earlier work for their high CO₂ capacity and limited corrosiveness. The experimental technique was validated using kinetic experiments for a 2.5 mol/L monoethanolamine solution. In view of double amine functionality and the six carbon chain between the amine groups, attention was paid to whether the amine groups acted independently and whether or not internal cyclisation would affect the carbamate forming mechanism. The reaction order with respect to HMDA was found to vary from 1.4 to 1.8 with increasing temperature. Absorption experiments in an equimolar solution of HMDA with HCl showed that the two amine groups react independently from each other towards CO₂. The reactivity of both diamines was more than five times larger than for monoethanolamine. The secondary diamine HMDA, N,N′ was found to be even more reactive towards CO₂. Additionally, the effect of CO₂ loading on the kinetics was studied for 0.5 mol/L aqueous solutions of HMDA and HMDA, N,N′ at 293 K. Both solvents are from absorption kinetics point of view good candidates for further evaluation as solvent (-component) for CO₂ capture.     

Carbon dioxide hydrogenation to methanol over the pre-reduced LaCr0.5Cu0.5O3 catalyst

The synthesis of methanol from CO₂ hydrogenation was carried out over the pre-reduced Cu-based LaCr_0.5Cu_0.5O₃ catalyst. It showed a much higher catalytic performance (X_CO2 = 10.4% and S_MeOH = 90.8%) at 250 °C than over 13% Cu/LaCrO₃ prepared by wet-impregnation method (X_CO2 = 4.8% and S_MeOH = 46.6%). XRD, H₂/CO₂-TPD and XPS measurements illustrated that hydrogen was adsorbed on the Cu^α+ sites and that CO₂ was activated on the medium basic sites for the reduced LaCr_0.5Cu_0.5O₃. This phenomenon was responsible for its catalytic activity.     

Integrated solvent and process design using a SAFT-VR thermodynamic description: High-pressure separation of carbon dioxide and methane

The increasing importance of natural gas as an energy source poses separation challenges, due to the high pressures and high carbon dioxide concentrations of many natural gas streams. A methodology for computer-aided molecular and process design (CAMPD) applicable to such extreme conditions is presented, based on the integration of process and cost models with an advanced molecular-based equation of state, the statistical associating fluid theory for potentials of variable range (SAFT-VR). The approach is applied to carbon dioxide capture from methane using physical absorption. The search for an optimal solvent is focused on n-alkane blends. A simple flowsheet is optimised using two objectives: maximum purity and maximum net present value. The best equipment sizes, operating conditions, and average chain length of the solvent (the n-alkane) are identified, indicating n-alkane solvents offer a promising alternative. The proposed methodology can readily be extended to wider classes of solvents and to other challenging processes.     

Process modeling for parametric study on oil palm empty fruit bunch steam gasification for hydrogen production

Biomass steam gasification with in-situ carbon dioxide capture using CaO exhibits good prospects for the production of hydrogen rich gas. The present work focuses on the process modeling for hydrogen production from oil palm empty fruit bunch (EFB) using MATLAB for parametric study. The model incorporates the reaction kinetics calculations of the steam gasification of EFB (C_3.4H_4.1O_3.3) with in-situ CO₂ capture, as well as mass and energy balances calculations. The developed model is used to investigate the effect of temperature and steam/biomass ratio on the hydrogen purity, yield and efficiency. Based on the results, hydrogen purity of more than 76.1 vol.% can be achieved. The maximum hydrogen yield predicted at the outlet of the gasifier is 102.6 g/kg of EFB. It is found that increment in temperature and steam/biomass ratio promotes hydrogen production. However, it is also predicted that the efficiency decreases when using more steam. Due to the still on-going empirical work, the results are compared with published literatures on different systems. The comparison shows that the results are in agreement to some extent due to the different basis.     

Tackling increased CO2 concentration in feeds for existing acid gas removal units: A simulation study based on a customized CO2 kinetics model

A Middle East-based amine sweetening unit, with an overall capacity of about 2.2 BSCFD of gas, is among the world’s largest process plants and currently processes sour gas with 10 mol% of hydrogen sulfide (H₂S) and carbon dioxide (CO₂) put together. Current expectation is that acid gas contents in the feed may increase beyond the design limit of the plant. The present work is an effort to quantify the effects of the feed gas CO₂ increase on the plant and to proffer solutions to handle these effects efficiently. We revised the kinetics of amine-based CO₂ absorption correlation of an existing model using real-data-driven parameters re-estimation. Evolutionary technique that employs particle swarm optimization algorithm is used for this purpose. The new CO₂ kinetic model is inserted in a first-principle process simulator, ProMax® V4.0, in order to analyze various solutions necessary to mitigate the operational challenges due to increased feed CO₂. The process plant with present design and operating conditions is determined to handle up to 8.45 mol% CO₂ contents in the sour gas feed. Further results revealed that methyldiethanolamine, diethanolamine, and dimethyl ether propylene glycol (DEPG) could not handle this high feed CO₂ challenge, even at maximum (design) steam and solvent usage. However, diglycolamine exclusively renders the solution as it treats high CO₂ feed gas efficiently with allowable utility consumption, while satisfying the constraints imposed by product gas specifications.     

The phenol steam reforming reaction towards H2 production on natural calcite

The steam reforming of phenol towards H₂ production was studied in the 650–800 °C range over a natural pre-calcined (air, 850 °C) calcite material. The effects of reaction temperature, water, hydrogen, and carbon dioxide feed concentrations, and gas hourly space velocity (GHSV, h⁻¹) were investigated. The increase of reaction temperature in the 650–800 °C range and water feed concentration in the 40–50 vol% range were found to be beneficial for catalyst activity and H₂-yield. A similar result was also obtained in the case of decreasing the GHSV from 85,000 to 30,000 h⁻¹. The effect of concentration of carbon dioxide and hydrogen in the phenol/water feed stream was found to significantly decrease the rate of phenol steam reforming reaction. The latter was probed to be related to the reduction in the rate of water dissociation as evidenced by the significant decrease in the concentration of adsorbed bicarbonate and OH species on the surface of CaO according to in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS)-CO₂ adsorption experiments in the presence of water and hydrogen in the feed stream. Details of the CO₂ adsorption on the CaO surface at different reaction temperatures and gas atmospheres using in situ DRIFTS and transient isothermal adsorption experiments with mass spectrometry were obtained. Bridged, bicarbonate and unidentate carbonate species were formed under CO₂/H₂O/He gas mixtures at 600 °C with the latter being the most populated. A substantial decrease in the surface concentration of bicarbonate and OH species was observed when the CaO surface was exposed to CO₂/H₂O/H₂/He gas mixtures at 600 °C, result that probes for the inhibiting effect of H₂ on the phenol steam reforming activity. Phenol steam reforming reaction followed by isothermal oxygen titration allowed the measurement of accumulated “carbonaceous” species formed during phenol steam reforming as a function of reaction temperature and short time on stream. An increase in the amount of “carbonaceous” species with reaction time (650–800 °C range) was evidenced, in particular at 800 °C (4.7 vs. 6.7 mg C/g solid after 5 and 20 min on stream, respectively).     

低温甲醇脱碳工艺热力学模型和过程模拟研究

为了进行含高压气体和强极性物质的体系的低温甲醇脱碳工艺的模拟研究,建立相应的热力学模型.采用Soave-Redlich-Kwong(SRK)立方型状态方程,结合Huron-Vidal混合规则和非随机双流体Non-Random-Two-Liquid(NRTL)活度系数模型建立的热力学模型,从气体溶解度和气液平衡数据拟合获...     

Techno-economical assessment of coal and biomass gasification-based hydrogen production supply chain system

Hydrogen is an energy carrier that represents a possible clean fuel of the future. This paper assesses the effect of biomass co-firing on gasification based hydrogen production supply chain, with carbon dioxide capture and storage, from technical, economical and environmental point of view. Several cases consisting of various feedstocks to the gasification reactor are investigated (coal only and coal in mixture with sawdust or wheat straw). Considered plant concepts generate between 330 and 460 MW hydrogen of 99.99% (vol.) purity.     

Carbon nanotube-supported Pd–ZnO catalyst for hydrogenation of CO2 to methanol

A type of Pd–ZnO catalysts supported on multi-walled carbon nanotubes (MWCNTs) were developed, with excellent performance for CO₂ hydrogenation to methanol. Under reaction conditions of 3.0 MPa and 523 K, the observed turnover-frequency of CO₂ hydrogenation reached 1.15 × 10⁻² s⁻¹ over the 16%Pd_0.1Zn₁/CNTs(h-type). This value was 1.17 and 1.18 times that (0.98 × 10⁻² and 0.97 × 10⁻² s⁻¹) of the 35%Pd_0.1Zn₁/AC and 20%Pd_0.1Zn₁/γ-Al₂O₃ catalysts with the respective optimal Pd_0.1Zn₁-loading. Using the MWCNTs in place of AC or γ-Al₂O₃ as the catalyst support displayed little change in the apparent activation energy for the CO₂ hydrogenation, but led to an increase of surface concentration of the Pd⁰-species in the form of PdZn alloys, a kind of catalytically active Pd⁰-species closely associated with the methanol generation. On the other hand, the MWCNT-supported Pd–ZnO catalyst could reversibly adsorb a greater amount of hydrogen at temperatures ranging from room temperature to 623 K. This unique feature would help to generate a micro-environment with higher concentration of active H-adspecies at the surface of the functioning catalyst, thus increasing the rate of surface hydrogenation reactions. In comparison with the “Parallel-type (p-type)” MWCNTs, the “Herringbone-type (h-type)” MWCNTs possess more active surface (with more dangling bonds), and thus, higher capacity for adsorbing H₂, which make their promoting action more remarkable.     

Promotion through gas phase induced surface segregation: methanol synthesis from CO, CO2 and H2 over Ni/Cu(100)

We have studied the rate of methanol formation over Cu(100) and Ni/Cu(100) from various mixtures of CO, CO₂ and H₂. It is found that the presence of submonolayer quantities of Ni leads to a strong increase in the rate of methanol formation from mixtures containing all three components whereas Ni does not influence the rate from mixtures of CO₂/H₂ and CO/H₂, respectively. The influence of the partial pressures of CO and CO₂ on the rate indicates that the role of CO is strictly promoting. From temperature-programmed desorption spectra it follows that the surface concentration of Ni depends strongly on the partial pressure of CO. In this way the increase in reactivity is interpreted as a CO-induced structural promotion introduced by the stronger bonding of CO to Ni as compared to Cu. It is suggested that this type of promotional behavior will be of general importance in existent catalysts and perhaps even more relevant in the development of new or improved bimetallic catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.