Optimal design and integration of an air separation unit (ASU) for an integrated gasification combined cycle (IGCC) power plant with CO2 capture

The air separation unit (ASU) plays a key role in improving the efficiency, availability, and operability of an oxygen-fed integrated gasification combined cycle (IGCC) power plant. An optimal integration between the ASU and the balance of the plant, especially the gasifier and the gas turbine (GT), has significant potential for enhancing the overall plant efficiency. Considering the higher operating pressure of the GT, an elevated-pressure air separation unit (EP-ASU) is usually favored instead of the conventional low-pressure air separation units (LP-ASU). In addition, a pumped liquid oxygen (PLOX) cycle is usually chosen if the operating pressure of the gasifier is high. A PLOX cycle helps to improve plant safety and availability and to decrease the capital cost by reducing the size of the oxygen compressor or by eliminating it completely. However, the refrigeration lost in withdrawn liquid oxygen must be efficiently recovered. This paper considers five different configurations of an ASU with PLOX cycle and compares their power consumptions with an EP-ASU with a traditional gaseous oxygen (GOX) cycle. The study shows that an optimally designed EP-ASU with a PLOX cycle can have similar power consumption to that of an EP-ASU with GOX cycle in the case of 100% nitrogen integration. In the case of an IGCC with pre-combustion CO₂ capture, the lower heating value (LHV) of the shifted syngas, both on a mass and volumetric basis, is in between the LHV of the unshifted syngas from an IGCC plant and the LHV of natural gas, for which the GTs are generally designed. The optimal air integration in the case of a shifted syngas is found to be much lower than that of an unshifted syngas. This paper concurs with the existing literature that the optimal integration occurs when air extracted from the GT can be replaced with the nitrogen from the ASU without exceeding mass/volumetric flow limitations of the GT. Considering nitrogen and air integration between the ASU and the GT, this paper compares the power savings in an LP-ASU with a PLOX cycle to the power savings in an EP-ASU with GOX cycle and EP-ASU with PLOX cycle. The results show that an LP-ASU with a PLOX cycle has less power consumption if the nitrogen integration levels are less than 50-60%. In addition, a study is carried out by varying the concentration of nitrogen and steam in the fuel diluents to the GT while the NOx level was maintained constant. The study shows that when the nitrogen injection rate exceeds 50%, an EP-ASU with a PLOX cycle is a better option than an LP-ASU with a PLOX cycle. This paper shows that an optimal design and integration of an ASU with the balance of the plant can help to increase the net power generation from an IGCC plant with CO₂ capture.     

电厂CO2捕集工艺夹点分析与过程集成节能

电厂一乙醇胺（MEA）法烟气CO2捕集（CCS）工艺换热网络能量流密集,固有能耗高,对该工艺进行过程集成节能研究,具有重要意义。对CO2捕集工艺换热网络的夹点分析说明该换热网络存在跨越夹点的热量传递。冷热物流的总复合曲线特征说明了CO2捕集工艺固有能耗高的特性。对换热网络进行调优并提出了节能技术方案：（1）在夹点之上利用MEA贫液的部分高温位热量加热预吸附塔再生气;(2)采用MEA再生塔产生的湿CO2混合物作为驱动热源,跨越夹点设置一台氨吸收式制冷机以替代CO2液化所需部分制冷量。基于过程集成节能提出的换热集成节能措施可有效降低CO2捕集工艺固有能耗,使蒸汽耗量降低21%,冷却水耗量降低17.2%,CO2液化所需低温冷却公用工程降低43.4%。     

Performance analysis of integrated biomass gasification fuel cell (BGFC) and biomass gasification combined cycle (BGCC) systems

Biomass gasification processes are more commonly integrated to gas turbine based combined heat and power (CHP) generation systems. However, efficiency can be greatly enhanced by the use of more advanced power generation technology such as solid oxide fuel cells (SOFC). The key objective of this work is to develop systematic site-wide process integration strategies, based on detailed process simulation in Aspen Plus, in view to improve heat recovery including waste heat, energy efficiency and cleaner operation, of biomass gasification fuel cell (BGFC) systems. The BGFC system considers integration of the exhaust gas as a source of steam and unreacted fuel from the SOFC to the steam gasifier, utilising biomass volatilised gases and tars, which is separately carried out from the combustion of the remaining char of the biomass in the presence of depleted air from the SOFC. The high grade process heat is utilised into direct heating of the process streams, e.g. heating of the syngas feed to the SOFC after cooling, condensation and ultra-cleaning with the Rectisol^® process, using the hot product gas from the steam gasifier and heating of air to the SOFC using exhaust gas from the char combustor. The medium to low grade process heat is extracted into excess steam and hot water generation from the BGFC site. This study presents a comprehensive comparison of energetic and emission performances between BGFC and biomass gasification combined cycle (BGCC) systems, based on a 4th generation biomass waste resource, straws. The former integrated system provides as much as twice the power, than the latter. Furthermore, the performance of the integrated BGFC system is thoroughly analysed for a range of power generations, ～100–997 kW. Increasing power generation from a BGFC system decreases its power generation efficiency (69–63%), while increasing CHP generation efficiency (80–85%).     

Techno-economic assessment of pulverized coal boilers and IGCC power plants with CO 2 capture

The current studies on power plant technologies suggest that Integrated Gasification Combined Cycle (IGCC) systems are an effective and economic CO₂ capture technology pathway. In addition, the system in conventional configuration has the advantage of being more “CO₂ capture ready” than other technologies. Pulverized coal boilers (PC) have, however, proven high technical performance attributes and are economically often most practical technologies. To highlight the pros and cons of both technologies in connection with an integrated CO₂ capture, a comparative analysis of ultrasupercritical PC and IGCC is carried out in this paper. The technical design, the mass and energy balance and the system optimizations are implemented by using the ECLIPSE chemical plant simulation software package. Built upon these technologies, the CO₂ capture facilities are incorporated within the system. The most appropriate CO₂ capture systems for the PC system selected for this work are the oxy-fuel system and the postcombustion scheme using Monoethanolamine solvent scrubber column (MEA). The IGCC systems are designed in two configurations: Water gas shift reactor and Selexol-based separation. Both options generate CO₂-rich and hydrogen rich-gas streams. Following the comparative analysis of the technical performance attributes of the above cycles, the economic assessment is carried out using the economic toolbox of ECLIPSE is seamlessly connected to the results of the mass and energy balance as well as the utility usages. The total cost assessment is implemented according to the step-count exponential costing method using the dominant factors and/or a combination of parameters. Subsequently, based on a set of assumptions, the net present value estimation is implemented to calculate the breakeven electricity selling prices and the CO₂ avoidance cost.     

Control strategies for flexible operation of power plant with CO2 capture plant

About 20% power output penalties will be incurred for implementing CO₂ capture from power plant. This loss can be partially compensated by flexible operation of capture plant. However, daily large variations of liquid and gas flows may cause operation problems to packed columns. Control schemes were proposed to improve the flexibility of power output without causing substantial hydraulic disturbances in capture plant is presented. Simulations were implemented using ASPEN Plus. In varying lean solvent flow strategy, the flow rate of recycling solvent was manipulated to control the CO₂ capture rate. The liquid flow of the absorber and gas flow of the stripper will vary substantially. In an alternative strategy, the lean solvent loading will be varied. Variation of gas throughput in the stripper is avoided by recycling part of CO₂ vapor to stripper. This strategy provided more stable hydraulics condition in both columns and is recommended for flexible operation. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

整体煤气化燃料电池联合发电(IGFC)技术研究进展

整体煤气化燃料电池联合发电技术(IGFC)是一种新型煤基洁净高效发电技术,不考虑热电联供的情况下,发电效率达60%以上,可有效控制污染物的排放,为CO₂捕集和回收创造了条件,可实现CO₂的近零排放。IGFC系统一般由煤气化净化、燃料电池发电、余热回收及CO₂捕集和封存等子系统构成,其中燃料电池发电技术是制约IGFC发展的关键技术。固体氧化物燃料电池(SOFC)及熔融碳酸盐燃料电池(MCFC)是适配IGFC系统的2种燃料电池技术,其中SOFC在生产成本及发电效率方面更具优越性。2017年国家能源集团牵头,联合中国矿业大学(北京)、北京低碳清洁能源研究院、华能清洁能源技术研究院、清华大学等,在国家重点研发计划项目支持下承担了开发100 kW级SOFC和MCFC发电单元,建成MW_th级CO₂近零排放的IGFC示范工程任务,项目成果推动了我国IGFC系统从基础技术研发向产业化迈进的步伐。     

液化天然气冷能回收混合动力循环参数分析

提出了以氨水为工质的朗肯循环、燃气动力循环和液化天然气循环组成的混合动力循环系统,用于液化天然气冷能回收。建立了混合动力循环中换热和动力设备的能量平衡方程和可用能平衡方程,并以朗肯循环冷凝温度、朗肯循环透平进出口压力、液化天然气循环透平进出口压力为关键参数,分析了上述关键参数对混合动力循环热效率和可用能效率的影响。分析结果表明,混合动力循环热效率和可用能效率随朗肯循环冷凝温度升高、朗肯循环透平进口压力和液化天然气循环透平进口压力增大而提高,随朗肯循环透平出口压力和液化天然气循环透平出口压力增大而降低。     

Techno-economic evaluation of a PVAm CO2-selective membrane in an IGCC power plant with CO2 capture

Published data for an operating power plant, the ELCOGAS 315 MWe Puertollano plant, has been used as a basis for the simulation of an integrated gasification combined cycle process with CO₂ capture. This incorporated a fixed site carrier polyvinylamine membrane to separate the CO₂ from a CO-shifted syngas stream. It appears that the modified process, using a sour shift catalyst prior to sulphur removal, could achieve greater than 85% CO₂ recovery at 95 vol% purity. The efficiency penalty for such a process would be approximately 10% points, including CO₂ compression. A modified plant with CO₂ capture and compression was calculated to cost €2320/kW, producing electricity at a cost of 7.6 € cents/kWh and a CO₂ avoidance cost of about €40/tonne CO₂.     

Performance analysis of a zeotropic mixture (R290/CO2) for trans-critical power cycle☆

Low critical temperature limits the application of CO2 trans-critical power cycle. The binary mixture of R290/CO2 has higher critical temperature. Using mixture fluid may solve the problem that subcrit...     

一种低能耗捕集CO2煤基甲醇和电力联产过程设计

传统的煤制甲醇过程所需合成气的氢碳比为2.1左右,而煤气化粗合成气氢碳比仅为0.7左右,因此需要将部分合成气进行变换来调节氢碳比。然而,变换气与未变换气混合后使得CO₂浓度降低,从而导致CO₂捕集能耗增加。提出了一种低能耗捕集CO₂煤基甲醇和电力联产过程。新联产过程中部分粗合成气首先经过变换,将CO转变为H₂和CO₂,CO₂浓度提高,在此时进行CO₂捕集可实现捕集能耗的降低。经CO₂捕集后,得到富H₂气体,富H₂气体分流后与另一部分煤气化粗合成气混合调节甲醇合成的氢碳比。对新的过程进行了建模、模拟与分析。结果表明相比传统的带CO₂捕集的煤制甲醇和IGCC发电过程,新的联产过程的能量节约率可达到16.5%,CO₂捕集能耗下降30.3%。     

The multi-period optimisation of an amine-based CO2 capture process integrated with a super-critical coal-fired power station for flexible operation

In this work, we present a model of a super-critical coal-fired power plant integrated with an amine-based CO₂ capture process. We use this model to solve a multi-period dynamic optimisation problem aimed at decoupling the operation of the power plant from the efficiency penalty imposed by the CO₂ capture plant, thus providing the power plant sufficient flexibility to exploit price variation within an electricity market. We evaluate four distinct scenarios: load following, solvent storage, exhaust gas by-pass and time-varying solvent regeneration. The objective is to maximise the decarbonised power plant's short run marginal cost profitability. It is found that while the solvent storage option provides a marginal improvement of 4% in comparison to the load following scenario, the exhaust gas bypass scenario results in a profit reduction of 17% whereas the time-varying solvent regeneration option increases the profitability of the power plant by 16% in comparison to the reference scenario.     

Process analysis for polygeneration of Fischer-Tropsch liquids and power with CO2 capture based on coal gasification

This paper designs four cases to investigate the performances of the polygeneration processes, which depend on the commercially ready technology to convert coal to liquid fuels (CTL) and electricity with CO₂ sequestration. With Excel-Aspen Plus based models, mass and energy conversion are calculated in detail. The simulation shows that the thermal efficiency is down with the synfuels yield decrease though the electricity generation is increased. It also suggests that the largest low heat value (LHV) loss of coal occurs in the gasification unit. From the comparison of the four cases, prominent differences of coal energy transition appear in water-gas shift (WGS) units, Fischer-Tropsch (FT) synthesis and combined cycle processes. CO₂ capture and vent are discussed and the results show that the vent amount of CO₂ increases with the increase of percentage of the syngas going to produce electricity. The results also show that the ratio of carbon captured to total carbon increases from 58% to 93% which is an important contribution to cutting down the greenhouse gas vent.     

Experimental investigation of a 125 kW twin-fire fixed bed gasification pilot plant and comparison to the results of a 2 MW combined heat and power plant (CHP)

Fixed bed biomass gasification is a promising technology to produce heat and power from a renewable energy source. A twin-fire fixed bed gasifier based CHP plant was realized in the year 2003 in Wr. Neustadt, Austria. Wood chips are used as fuel, which are dried and sieved before being gasified to a low calorific gas of about 5.8 MJ/Nm³_dry. Before the clean gas is fed into a gas engine a cyclone and a RME (rapemethylester)/H₂O quench system followed by a wet electrostatic precipitator (ESP) is used for gas cleaning. The CHP plant has a fuel power of 2 MW_th and an electric output of 550 kW_el. As scale up and optimization tool a hot test rig with a capacity of 125 kW_th was built. Basic parameters like the type of wood chips, power and air distribution were varied to investigate the effect on gas composition, tar content in the producer gas and carbon content in the ash. Additionally a temperature profile over the height of the 125 kW hot test rig was measured. Furthermore, the results from the hot test rig are discussed and compared with the results from the 2 MW_th demonstration plant.     

660MW燃煤机组百万吨CO_2捕集系统技术经济分析

为了解常规燃煤机组碳捕集系统的技术经济性,以基准情景为基础,根据国内某10万t CO_2燃烧后捕集系统的投资情况,利用生产能力指数法对5种脱碳情景的投资进行估算。在保证内部收益率为8%的前提下,分析了5种脱碳情景的上网电价、CO_2综合减排成本及其敏感性。结果表明,CO_2综合减排成本中,厂内碳捕集成本比例最大;随着燃料价格的上涨,CO_2综合减排成本逐渐增加;随着CO_2综合收益的增加,上网电价可以逐渐下降。     

Performance assessment and system optimization of a combined cycle power plant (CCPP) based on exergoeconomic and exergoenvironmental analyses

We propose a systematic approach for performance evaluation and improvement of a combined cycle power plant (CCPP). Exergoeconomic and exergoenvironmental analyses are used to assess CCPP performance and suggest improvement potentials in economic and environmental aspects, respectively. Economic and environmental impacts of individual system components are calculated by cost functions and life cycle assessments. Both analyses are based on a CCPP case study located in Turkey, which consists of two gas turbine cycles and a steam turbine cycle with two different pressure heat recovery units. The results of the exergoeconomic analysis indicate that the combustion chamber and condenser have a high performance improvement potential by increasing capital cost. Furthermore, the exergoenvironmental analysis shows that the exergy destruction of the steam turbine and combustion chamber and/or the capacity of heat recovery units must be reduced in order to improve environmental performance. This study demonstrates that combined exergoeconomic and exergoenvironmental analyses are useful for finding improvement potentials for system optimization by simultaneously evaluating economic and environmental impacts.     

集成CO2高效利用的煤制乙二醇过程设计与系统分析

为减少传统煤制乙二醇过程资源利用效率低和CO₂排放量高等问题，提出了一种集成CO₂高效利用的煤制乙二醇过程，并对其进行了全流程建模及系统分析。与传统过程不同，新过程利用焦炉气来提高其资源利用率和能量效率，集成甲烷干重整与湿重整技术降低CO₂排放。在全流程建模的基础之上，对新工艺的关键操作参数进行了分析与优化。结果表明，焦炉气的最佳进料比和甲烷蒸汽重整反应的分配比为0.68和0.74。与传统过程相比，新工艺的CO₂排放降低了94.05％，同时?效率提高了15.17％。     

A multi-objective analysis for the retrofit of a pulverized coal power plant with a CO2 capture and compression process

The long term sustainability of fossil energy systems depends on reducing their carbon footprint and freshwater consumption. Much of the United States is or will be experiencing water shortages in the near future. Since power generation accounts for about a third of all freshwater use, reducing freshwater requirements will be of increasing importance. In addition, recent reports indicate that adding a carbon capture system may double water consumption. Thus, when designing a carbon capture and compression system, it is important to consider not only the direct costs, but also the increased environmental burden associated with increased freshwater requirements. To address these interrelated sustainability issues, a modular framework for multi-objective analysis was developed and demonstrated by minimizing freshwater consumption and levelized cost of electricity for the retrofit of a hypothetical 550 MW subcritical pulverized coal power plant with an MEA-based carbon capture and compression system.     

Gas−liquid multiphase computational fluid dynamics (CFD) of amine absorption column with structured-packing for CO2 capture

The gas−liquid multiphase Eulerian computational fluid dynamics (CFD) model was used to investigate hydrodynamics and CO₂ removal efficiency of a pilot-scale amine absorber with structured-packing. The structured-packing was represented by a porous media zone having porous resistance, gas−liquid interfacial drag force, and liquid dispersion force. This study aimed to find a reasonable way to identify four modification factors of the Ergun coefficient that determine the hydrodynamic characteristics of structured-packing. The two modification factors (a and b) for porous resistance were mainly related to the liquid holdup (h_L) with respect to the liquid load. The other two factors (c and d) for gas−liquid interfacial drag force depended on the specific wet pressure drop (ΔP_wet/L) versus the gas load factor. The h_L and ΔP_wet/L increased in parallel with the increase of a and c, respectively, while the slopes of h_L and ΔP_wet/L increased with b and d, respectively.     

Homogeneous reduction of nitrobenzene to aniline under CO/H2O, catalyzed by cis-[Rh(CO)2(amine)2]PF6. The role of the amine effect

The CO₂ reforming of methane over reduced NiO/MgO solid solution catalysts was studied at 800°C by a novel transient method, which couples a broadened pulse of CH₄/CO₂ with a step change to the carrier gas and/or with a sharp isotopic pulse of either ¹⁸O₄, CO¹⁸ ₂ or ¹³CO¹⁶ ₂. The response curves indicated that two kinds of oxygen were formed over the catalysts during reaction: adsorbed oxygen which reacts fast with C species and lattice oxygen which reacts more slowly with C species. One concludes that a redox cycle of lattice oxygen formation through the oxidation of Ni and its reaction with C species takes place on the catalyst surface. This revised version was published online in August 2006 with corrections to the Cover Date.