煤制天然气过程全局能量集成优化

我国正在大力发展煤制天然气项目实现清洁能源供给。然而现有煤制天然气示范项目存在能耗大、CO₂排放高、生产成本缺少竞争力的问题。本文从煤制天然气能量系统出发,通过全局能量集成实现煤制天然气项目的节能减排与经济效益的提高。根据煤化工示范项目特点,提出了煤制天然气过程全厂能量系统集成优化策略：建立了煤制天然气各单元过程模型,对全流程的物流和能流展开了详细的模拟计算;利用夹点技术对全厂内各单元过程的能量系统展开了用能分析;利用全局温焓曲线对全厂能量系统进行了分析,揭示出全厂能量利用效率低是由于高品位热量降质利用和低品位余热未得到合理利用引起的。通过装置间热回收集成和增设有机朗肯余热回收装置可有效地提高热回收率。通过全厂能量系统优化集成,燃料煤消耗由现有过程1.26t/kNm³（0℃、101325Pa标准状态）天然气下降到1.07t/kNm³天然气。由于公用工程系统消耗的减少,全厂能量利用效率由原来的57.2%提高到59.6%,同时CO₂排放可以由原来5.02t/kNm³天然气下降到4.66t/kNm³天然气。相比于现有过程,改进过程的总投资仅增加了2%左右,而单位生产成本由1.65CNY/Nm³下降到了1.59CNY/Nm³,对于年产20亿立方米煤制天然气厂每年可节约生产成本1.2亿元。     

煤制天然气过程变换单元建模与能量集成

我国煤制天然气项目经过国家"十二五"时期进一步升级示范,工艺上取得了突破性进展。然而煤制天然气项目面临集成度不高,整体能耗较大的问题。高效回收利用变换单元放出的反应热是降低煤制天然气项目能耗的一条有效途径。本文首先建立了基于反应动力学的固定床反应器模型,在满足变换反应调整氢碳比要求下,通过对反应操作参数的优化,提高了系统（火用）输出。在对优化后变换单元过程能量分析的基础上,建立了新的变换单元热回收网络。实现了过程反应参数优化和换热网络的集成优化。新工艺的能效比现行工艺提高9个百分点,达到86.3%,投资增加了5.5%,投资回收期为2.1年。     

A new process for synthesis gas by co-gasifying coal and natural gas

Production of synthesis gas with coal and natural gas co-gasification is a new process based on coupling of methane steam-reforming and coal gasification. The process concept is discussed in this paper. Experiments are carried out in a laboratory fixed-bed gasifying reactor to investigate the effect of feedstock on composition, ratio of hydrogen to carbon monoxide, concentrations of hydrogen and carbon monoxide in the produced raw synthesis gas. Preliminary experimental results indicate that the effect of steam flow rate on component, ratio of hydrogen to carbon monoxide and concentrations of hydrogen and carbon monoxide of the raw synthesis gas is slight, while the effect of oxygen flow rate is pronounced. When the ratio of oxygen to methane in feedstock is below 1, the ratio of hydrogen to carbon monoxide is greater than 1 and the total concentration of hydrogen and carbon monoxide is above 90%. Comparison of experimental results with calculated results shows that the composition of raw synthesis gas is near equilibrium.     

Experimental study of synthesis gas production by coal and natural gas co-conversion process

A moving bed was used as the reactor in experiments to produce synthesis gas by coal and natural gas co-conversion process. The effects of coal types on the temperature in the flame zone, the ingredients and the H₂/CO ratio of synthesis gas, together with the methane and steam conversions were investigated by using coke, anthracite, lean and fat coals as the raw materials. By comparing the results between coals and coke, it can be seen that the temperatures in the flame zone and the content of the active compounds (H₂, CO) of coals are higher than those of coke. In addition, the H₂/CO ratio of synthesis gas closes to the calculated value by thermodynamic equilibrium. For the produced crude synthesis gas with coals by coal and natural gas co-conversion process, in which the H₂/CO ratio varies in 1.0–2.0, the content of the active compounds (H₂, CO) is more than 92%, and the residual methane is less than 2%, the methane and steam conversion rates are more than 90% and 75%, respectively. All these results demonstrated that the concept of coal and natural gas co-conversion process is positive and feasible.     

Process synthesis of hybrid coal,biomass, and natural gas to liquids via Fischer–Tropsch synthesis,ZSM-5 catalytic conversion,methanol synthesis,methanol-to-gasoline,and methanol-to-olefins/distillate technologies

Several technologies for synthesis gas (syngas) refining are introduced into a thermochemical based superstructure that will convert biomass, coal, and natural gas to liquid transportation fuels using Fischer–Tropsch (FT) synthesis or methanol synthesis. The FT effluent can be (i) refined into gasoline, diesel, and kerosene or (ii) catalytically converted to gasoline and distillate over a ZSM-5 zeolite. Methanol can be converted using ZSM-5 (i) directly to gasoline or to (ii) distillate via olefin intermediates. A mixed-integer nonlinear optimization model that includes simultaneous heat, power, and water integration is solved to global optimality to determine the process topologies that will produce the liquid fuels at the lowest cost. Twenty-four case studies consisting of different (a) liquid fuel combinations, (b) refinery capacities, and (c) superstructure possibilities are analyzed to identify important process topological differences and their effect on the overall system cost, the process material/energy balances, and the well-to-wheel greenhouse gas emissions.     

Simultaneous process optimization and heat integration based on rigorous process simulations

This paper introduces a simultaneous process optimization and heat integration approach, which can be used directly with the rigorous models in process simulators. In this approach, the overall process is optimized utilizing external derivative-free optimizers, which interact directly with the process simulation. The heat integration subproblem is formulated as an LP model and solved simultaneously during optimization of the flowsheet to update the minimum utility and heat exchanger area targets. A piecewise linear approximation for the composite curve is applied to obtain more accurate heat integration results. This paper describes the application of this simultaneous approach for three cases: a recycle process, a separation process and a power plant with carbon capture. Case study results indicate that this simultaneous approach is relatively easy to implement and achieves higher profit and lower operating cost and, in the case of the power plant example, higher net efficiency than the sequential approach.     

Simultaneous MINLP synthesis of heat and power integrated heat exchanger networks

This paper describes the simultaneous MINLP synthesis of heat and power integrated heat exchanger networks. The objective of this work is to obtain feasible networks with optimal tradeoffs between investment, utility and power consumption caused by pressure drops in heat exchangers, and to use a detailed design model for exchangers in the synthesis in order to represent pressure drops and heat transfer coefficients as functions of exchanger design variables. In this way, the simultaneous synthesis of HEN and the detailed exchanger design become completely consistent and optimal.     

Thermodynamic modelling of co-firing coal and biomass pyrolysis gas in a power plant

The Austrian utility company EVN AG is investigating possibilities to substitute part of the hard coal used in their Dürnrohr power station by biomass pyrolysis gas produced in an upstream rotary kiln at relatively low temperatures of ≤ 600 °C. A major advantage of the low temperature is the retention of alkalis and halogenes in the coke. The aim of the present work was to set up a working thermo-chemical computer model in order to calculate the possible effects that this co-firing may have on corrosion phenomena in the boiler. The work was carried out using the software packages FactSage^® and SimuSage^®. A model was successfully developed and validated using data from laboratory analyses as well as from the power station and a biomass pyrolysis test facility set up next to the plant. The results of the calculations show that the gas produced in the rotary kiln at the planned scale very likely does not pose any potential threat to the power plant.     

A superstructure-based framework for simultaneous process synthesis,heat integration,and utility plant design

We propose a superstructure optimization framework for process synthesis with simultaneous heat integration and utility plant design. Processing units in the chemical plant can be modeled using rigorous unit models or surrogate models generated from experimental results or off-line calculations. The utility plant subsystem includes multiple steam types with variable temperature and pressure. For the heat integration subsystem, we consider variable heat loads of process streams as well as variable intervals for the utilities. To enhance the solution of the resulting mixed-integer nonlinear programming models, we develop (1) new methods for the calculation of steam properties, (2) algorithms for variable bound calculation, and (3) systematic methods for the generation of redundant constraints. The applicability of our framework is illustrated through a biofuel case study which includes a novel non-enzymatic hydrolysis technology and new separation technologies, both of which are modeled based on experimental results.     

Simultaneous synthesis of heat exchanger networks with pressure recovery: Optimal integration between heat and work

The optimal integration between heat and work may significantly reduce the energy demand and consequently the process cost. This article introduces a new mathematical model for the simultaneous synthesis of heat exchanger networks (HENs), in which the pressure levels of the process streams can be adjusted to enhance the heat integration. A superstructure is proposed for the HEN design with pressure recovery, developed via generalized disjunctive programming, and mixed‐integer nonlinear programming formulation. The process conditions (stream temperature and pressure) must be optimized. Furthermore, the approach allows for coupling of the turbines and compressors and selection of the turbines and valves to minimize the total annualized cost, which consists of the operational and capital expenses. The model is tested for its applicability in three case studies, including a cryogenic application. The results indicate that the energy integration reduces the quantity of utilities required, thus decreasing the overall cost. © 2013 American Institute of Chemical Engineers AIChE J, 60: 893–908, 2014     

移动床煤与天然气共气化制备合成气的工艺技术

煤与天然气共气化是基于天然气蒸汽转化和煤气化工艺耦合的一种新工艺.阐述了煤与天然气共气化制合成气的技术原理.实验研究表明合成气最佳出口温度为1000 ℃,氧气、水蒸气和天然气在同一位置进入反应器能有效降低火焰区温度;理论计算得到的合成气有效气体浓度（CO+H₂）大于95%.实验研究和理论计算结果都表明,煤与天然气共气化可以直接得到H₂/CO在1.0～1.5之间可以调节的合成气.     

煤制天然气工艺及甲烷化催化剂研究进展

随着人们生活水平的不断提高以及世界工业的高速发展,作为一种高效清洁能源,天然气的需求越来越大,中国在较长时间内将会出现供不应求的局面。煤制天然气技术的大力发展不仅可有效缓解中国的能源危机,而且可有效地改善中国的环境状况。综述了煤制天然气的现状,包括国内外煤制天然气工艺技术的发展现状以及甲烷化催化剂研究现状。重点介绍了甲烷化催化剂的活性组分、助剂及载体方面的研究进展,提出了中国煤制天然气技术所面临的机遇与挑战。     

Kinetic investigations for hybrid process of water electrolysis and chemical coal desulphurization

Chemical coal desulphurization combined with water electrolysis has been systematically studied. Pyritic sulphur in pulverized coals was oxidized by Fe(III) ions to elemental sulphur and sulphate ions in an acidic solution. The removal of pyritic sulphur at 363–383 K in a solution of 0.89 M Fe(III) and l M HCl was about 100% for Illinois No. 6 coal and 87% for Miike coal. Fe(II) ions which were produced by the reaction between Fe(III) ions and coal slurries were utilized to depolarize the anode potential for the water electrolysis. The use of a three-dimensional electrode cell packed with graphite felt drastically increased the current density per unit feeder area to 1000 A m⁻² at the cell voltage of 1 V. No deactivation of the graphite felt electrode was observed after the 20 h continuous electrolysis using the Illinois No. 6 coal filtrate. The energy consumption with respect to the hydrogen production was about half that of conventional electrolysis cells.     

Simultaneous optimal integration of water utilization and heat exchange networks using holistic mathematical programming

A systematic holistic mathematical programming (HMP) is proposed to formulate a mixed integer nonlinear programming (MINLP) model for one-step optimization of water-allocation and heat exchange network (WAHEN) designs with single- or multi-contaminant water streams. The proposed model formulation and solution strategy are believed to be superior to the available ones in the following aspects. First, a comprehensive representation combining two separate superstructures is adopted to capture the structural characteristics of the integrated WAHEN. Then, a hybrid optimization strategy integrating stochastic and deterministic components is developed for the resulting MINLP model and, also, an interactive iteration method is adopted based on sensitivity analysis to guide the search toward a potential global optimum. Finally, evolutionary strategies and manipulations are executed to enhance WAHEN configurations. Two illustrative examples are presented to demonstrate the validity and advantages of the proposed approach.     

具有完全热集成和水集成的合成甲醇精制工艺

提出了一种新的三塔精馏工艺用于合成甲醇的精制过程。在采用差压双效精馏实现系统内热集成的方案中,新工艺将加压塔塔顶蒸汽分为两部分,一部分作为预塔再沸器的供热源,其余部分作为常压塔再沸器的供热源,实现了供热蒸汽的完全热集成。同时将常压塔塔底出料的高纯软水和加压塔塔底部分含盐水回用为预塔萃取水,实现了系统内工艺软水的完全集成,既节约了工艺软水,又减少了系统的废水排放量。运用Aspen Plus定态模拟方法,对Lurgi工艺,文献中提到的W-C工艺和新的Z-W工艺进行对比研究,研究结果表明Z-W工艺比现有Lurgi工艺节约能量21.4 %,节约软水100 %,减少废水排出量81.4 %;比文献中W-C工艺节约能量11.7 %,节约软水100 %,减少废水排出量68.5 %。     

具有热集成和水集成的甲醇精馏新工艺及其模拟

提出了一种新的三塔精馏工艺用于合成甲醇的精制过程.在采用差压双效精馏实现系统内的热集成方案中,新工艺从加压精馏塔进料板上部的侧线采出中等甲醇浓度的物料作为常压精馏塔的进料,有效地平衡了两塔的分离负荷,进一步降低了双效精馏的总能耗,同时,将预精馏塔产生的盐碱类物质浓缩分离到加压塔底采出,使常压塔底出料为高纯度软水,将其循环复用为预塔萃取水,实现了系统内的工艺软水集成,不但降低了新鲜工艺软水的消耗,而且还减少了系统的废水排放量.运用计算机稳态模拟方法对传统的两塔工艺、现有的三塔双效精馏工艺和本文提出的新工艺进行了对比研究,研究结果表明：新工艺可以比两塔工艺节能49.2%,节水38.0%;比现有三塔工艺节能24.7%,节水38.0%.     

煤制天然气的Aspen Plus过程模拟研究进展

简要介绍了大型化工流程模拟软件Aspen Plus,并对其构建煤制天然气流程模型的方法进行概述。同时,针对近年来Aspen Plus软件在煤制天然气领域中的工艺模拟、反应器研究、设计优化等方面的应用情况进行综述,并指出当前研究的不足和今后的发展方向。