Proposal and Evaluation of a New‐Type Cogeneration System for Energy Saving and CO2 Emission Reduction

The paper proposes a cogeneration system which generates four types of energy or material resources: electricity, steam, hot water, and freshwater. The proposed system can capture CO₂, and be constructed on the basis of a combined cycle power generation system which consists of a gas turbine and a back‐pressure extraction turbine. In the proposed system, power is produced by driving the gas turbine system. High‐pressure saturated steam with medium temperature is produced in the heat recovery steam generator by using gas turbine exhaust gas, and then superheated with a regenerative superheater in which the fuel is burned by using oxygen instead of air for driving the steam turbine generator. Water and CO₂ are recovered from the flue gas of the regenerative superheater. It has been estimated that the proposed system has a net power generation efficiency of 41.2%, a heat generation efficiency of 41.5%, and a total efficiency of 82.7%. Freshwater of 1.34 t/h and CO₂ of 1.76 t/h can be recovered. It has also been shown, when a case study was set and evaluated, that the proposed system can save 31.3% of energy compared with the conventional energy supply system, and reduce CO₂ emission by 28.2% compared with the conventional cogeneration system. Copyright © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Proposal and characteristics evaluation of a CO2-recovering hybrid power generation system utilizing solar thermal energy

A CO₂-recovering hybrid power generation system utilizing solar thermal energy is proposed. In the system, relatively low temperature saturated steam around 220°C is produced by using solar thermal energy and is utilized as the working fluid of a gas turbine in which generated CO₂ is recovered based on the oxygen combustion method. Hence, solar thermal utilization efficiency is considerably higher as compared with that of conventional solar thermal power plants in which superheated steam near 400°C must be produced for use as the working fluid of steam turbines; the requirement for solar radiation in the location in which the system is constructed can be significantly relaxed. The proposed system is a hybrid energy system using both the fossil fuel and solar thermal energy, thus the capacity factor of the system becomes very high. The fuel can be used exergetically in the system; i.e., it can be utilized for raising the temperature of the steam heated by utilizing the turbine exhaust gas more than 1000°C. The generated CO₂ can be recovered by using an oxygen combustion method, so that a high CO₂ capturing ratio of near 100 percent as well as no thermal NO_x emission characteristics can be attained. It has been shown through simulation study that the proposed system has a net power generation efficiency of 63.4 percent, which is higher than 45.7 percent as compared with that of the conventional power plant with 43.5 percent efficiency, when the amount of utilized solar energy is neglected and the temperature of the saturated steam is 220°C.     

Characteristics evaluation of a CO2‐capturing power generation system with reheat cycle utilizing regenerative oxygen‐combustion steam‐superheater

A new CO₂‐capturing power generation system is proposed that can be easily realized by applying conventional technologies. In the proposed system, the temperature of medium‐pressure steam in a thermal power plant is raised by utilizing an oxygen‐combusting regenerative steam‐superheater. The CO₂ generated by combusting the fuel in the superheater can be easily separated and captured from the exhaust gas at the condenser outlet, and is liquefied. The superheated steam is used to drive a steam turbine power generation system. Using a high‐efficiency combined cycle power generation system as an example, it is shown that the proposed system can increase the power output by 10.8%, and decrease the CO₂ emissions of the entire integrated system by 18.6% with a power generation efficiency drop of 2.36% compared with the original power plant without CO₂ capture, when the superheated steam temperature is 750 ^°C. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(1): 35–41, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20575     

A CO2-recovering nonpolluting high-efficiency gas-turbine power-generation system utilizing saturated steam as its working gas

A carbon dioxide-recovering high-efficiency gas-turbine power-generation system is proposed in which carbon dioxide (CO₂) generated is recovered by adopting the oxygen (O₂) combustion method and no thermal nitrogen oxide is generated. In the system, saturated steam produced by utilizing waste heat is adopted as the working fluid of the gas turbine. Thus, the compressing process of the working fluid gas, which is the most energy-consuming process in generating power by using a gas turbine, is not needed. This makes the system extremely high efficient. By taking saturated steam of 210°C as an example, the characteristics of the system were simulated. The net exergetic efficiency of the system has been estimated to be 48.4 percent by considering both the exergy of the saturated steam and the electric power required not only to generate high-pressure oxygen, but also to liquefy the recovered CO₂. The value is higher than the exergetic efficiency 37.8 percent of large-scale thermal power generation plants using the same natural gas, and is 28.0 percent higher than its efficiency of 37.8 percent, the one estimated if the CO₂ generated is removed and recovered from the stack gas by using alkanolamine-based solvent and the recovered CO₂ is liquefied.     

Characteristics and economic evaluation of a CO2‐capturing solar thermal hybrid power generation system with heat storage

For wide use of a power plant utilizing solar energy, improvement of its economics is important. Both the economics and characteristics of a CO₂‐capturing solar thermal hybrid power generation system are evaluated in this paper. Since a relatively low temperature steam of 220 °C is produced by using solar thermal energy and is utilized as the working fluid of a gas turbine, the solar collector can attain high heat collecting efficiency. The net fuel‐to‐electricity conversion efficiency of the hybrid system is estimated to be higher than 60% on the lower‐heating‐value‐ basis. It has been estimated that the gross income and the period of depreciation of the proposed system are 34.8 × 10⁵ yen/year and 8.89 years, respectively, and that the system is economically feasible, under the assumptions of a solar collector area of 10 ha, a maximum net power output of 4 MW, and a heat storage capacity of 2000 m³. The amount of fuel saving and reduction of CO₂ emission of our system, compared to a conventional natural gas firing plant, are also estimated in the paper. © 1999 Scripta Technica, Electr Eng Jpn, 126(4): 21–29, 1999     

Proposal and evaluation of a gas engine and gas turbine hybrid cogeneration system in which cascaded heat is highly utilized

A high‐efficiency cogeneration system (CGS) is proposed for utilizing high‐temperature exhaust gas (HTEG) from a gas engine (GE). In the proposed system, for making use of heat energy of HTEG, H₂O turbine (HTb) is incorporated and steam produced by utilizing HTEG is used as working fluid of HTb. HTb exhaust gas is also utilized for increasing power output and for satisfying heat demand in the proposed system. Both of the thermodynamic characteristics of the proposed system and a gas engine CGS (GE‐CGS) constructed by using the original GE are estimated. Energy saving characteristics and CO₂ reduction effects of the proposed CGS and the GE‐CGS are also investigated. It was estimated that the net generated power of the proposed CGS has been increased 25.5% and net power generation efficiency 6.7%, compared with the original GE‐CGS. It was also shown that the proposed CGS could save 27.0% of energy consumption and reduce 1137 t‐CO₂/y, 1.41 times larger than those of GE‐CGS, when a case study was set and investigated. Improvements of performance by increasing turbine inlet temperature were also investigated. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(3): 37– 45, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20708     

Proposal of a high‐performance solid oxide fuel cell combined power generation system with carbon dioxide recovery

A new fossil‐fuel‐utilized high‐performance combined power generation system with liquefaction recovery of carbon dioxide is proposed. In the system, pure oxygen is used as the oxidant gas to prevent the mixture of nitrogen in the exhaust gas and to make the liquefaction recovery of carbon dioxide possible. Solid oxide fuel cell is selected as the topping cycle. The exhaust fuel gas of the solid oxide fuel cell is afterburned with its exhaust oxidant gas of pure oxygen and the heat of the combustion gas is utilized in the bottoming cycle. Nonequilibrium MHD/noble gas turbine cycle is selected as the bottoming cycle because the temperature of the combustion gas reaches about 2300 K. It is made clear through detailed examination of energy balance that the total thermal efficiency of the system using natural gas (methane) as the fuel reaches 63.24% (HHV) or 70.18% (LHV). This efficiency is very high as for the system with carbon dioxide recovery. The proposed system, therefore, has excellent performance, and further research and development is warranted. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 143(4): 12–21, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10146     

Modeling and control of distributed generation systems including PEM fuel cell and gas turbine

This paper concentrates on the modeling and control of distributed generation systems including fuel cell and gas turbine. The fuel cell is connected to the power system through a dc/ac converter, which is equipped with both voltage- and power-control loops. The gas turbine is also assumed to be equipped with both voltage-control and generation (or frequency)-control loops. Moreover the gas turbine is modeled using the d–q frame of reference. The interfacing of the gas turbine with the power system is achieved by transforming its equations from the d–q frame of reference to power system frame of reference. A multivariable supplementary fuzzy logic controller is proposed for improving the dynamics of the combined fuel cell and gas turbine system. This fuzzy logic controller is designed using the Matlab Fuzzy Logic Toolbox A distribution test system including a load, a fuel cell and a gas turbine, connected to a power grid is simulated using Matlab/Simulink software package. The dynamics of the combined distributed generation plant are analyzed for the cases of with and without controller. The accuracy of the presented model and the effectiveness of the proposed multivariable supplementary fuzzy controller are deduced from the simulation results.     

未来"绿色煤电"的思考

中国的电力工业以燃煤发电为主，燃煤发电如何走出一条全面、协调、可持续发展的新型工业化道路是电力行业的重要课题。影响煤电可持续发展的主要因素是环境污染严重和煤电转化效率低。从满足未来电力可持续发展的角度看，现有的洁净煤发电技术在提高效率和减少污染物排放方面尚未达到未来“绿色煤电”的要求。通过分析，提出了未来“绿色煤电”的设想，它是以煤气化制氢和氢能发电为主、对CO2进行分离处理的煤基发电系统，可实现煤基发电的高效和近零排放。并描述了中国华能集团公司发展“绿色煤电”的初步规划。     

Wind turbine emulator based on blade element momentum theory for variable‐speed wind power generation system

This paper proposes a wind turbine emulator (WTE) based on the blade momentum theory, and tests the variable‐speed wind power generation system using a pulse‐width modulation (PWM) converter to verify the accuracy of the emulator. The behavior of the wind turbine for natural wind is reproduced by the WTE based on the proposed theory. The variable‐speed wind power generation system employs a vector control system to control the torque and speed of the permanent magnet synchronous generator in the converter side. The windmill rotational speed is controlled to maximize the efficiency of the wind turbine against wind velocity. And the active power and reactive power are controlled in the inverter side, and the generated power is sent to the grid while controlling the DC link voltage to be constant at the same time. The behaviors of the WTE are compared with the simulation results and experimental results using a real wind turbine. These experimental and simulation results show that the test bench with the proposed WTE has sufficient performance and accuracy to verify variable‐speed wind generator systems. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Load frequency control of a realistic power system with multi-source power generation

In this paper, load frequency control (LFC) of a realistic power system with multi-source power generation is presented. The single area power system includes dynamics of thermal with reheat turbine, hydro and gas power plants. Appropriate generation rate constraints (GRCs) are considered for the thermal and hydro plants. In practice, access to all the state variables of a system is not possible and also their measurement is costly and difficult. Usually only a reduced number of state variables or linear combinations thereof, are available. To resolve this difficulty, optimal output feedback controller which uses only the output state variables is proposed. The performances of the proposed controller are compared with the full state feedback controller. The action of this proposed controller provides satisfactory balance between frequency overshoot and transient oscillations with zero steady state error in the multi-source power system environment. The effect of regulation parameter (R) on the frequency deviation response is examined. The sensitivity analysis reveals that the proposed controller is quite robust and optimum controller gains once set for nominal condition need not to be changed for ±25% variations in the system parameters and operating load condition from their nominal values. To show the effectiveness of the proposed controller on the actual power system, the LFC of hydro power plants operational in KHOZESTAN (a province in southwest of Iran) has also been presented.     

质子交换膜燃料电池发电系统建模与分析

对质子交换膜燃料电池(PEMFC)发电系统进行动态建模和分析,模型包括质子交换膜燃料电池,供气系统和直流-直流(DC-DC)变换器等部分。首先建立用于预测燃料电池电化学特性和反应气体压力特性的集中参数动态模型,同时给出了供气系统和DC-DC转换器的动态模型,也给出了比例积分型DC-DC变换控制器的设计方法。然后仿真和分析了PEMFC发电系统对快速变化负载的动态响应。采用Matlab-SIMULINK软件对5kW的PEMFC发电系统进行仿真。仿真结果表明系统模型结构简单,计算量小;PEMFC发电系统能够满足快速负载功率需求,满足不同负载的使用要求。     

生物质气化–熔融碳酸盐燃料电池联合循环发电系统性能研究

将生物质气化与熔融碳酸盐燃料电池(molten carbonate fuel cell,MCFC)构建为新型的生物质能高效清洁利用联合循环发电技术,气化产生的富氢气体作为MCFC的燃料,通过燃烧半焦以及MCFC中未利用的燃料为气化反应提供热量,进行生物质气化–MCFC联合循环发电系统的模拟研究。运用Aspen Plus软件搭建系统模型并计算,研究了燃料电池内重整及系统工作压力对系统性能的影响。结果表明：生物质气化–MCFC联合循环发电技术具有较高的系统发电效率,可达50%,比常规生物质气化驱动燃气轮机技术高出10个百分点;对于常压系统无需采用内重整,而对于增压系统,采用内重整对系统性能有较大改善;提高系统工作压力可改善其整体性能,最佳工作压力在0.8~1.2 MPa。     

适应整体煤气化联合循环燃气轮机改型方法分析

整体煤气化联合循环(IGCC)是多种设备、多种技术集成的一个复杂系统,整合了化工、发电等各方面技术为一体,包括了气化炉、空分系统、燃气轮机、余热锅炉、蒸汽轮机等设备。通过分析煤气化合成气与天然气的差异以及煤气化合成气对燃气轮机的影响,展开燃用天然气燃气轮机改型设计为燃用合成气的方法探索,总结改型设计经验,为整体煤气化联合循环燃气轮机设计奠定基础。     

太阳能热气流发电系统透平发电及其能量损失

对包含蓄热层、透平的太阳能热气流发电系统的流动及传热及发电特性进行数值模拟,建立了太阳能热气流发电系统的流动与传热数学模型,分析了太阳辐射和透平压降对系统透平发电输出功率以及系统各部件能量损失的影响.计算结果表明:当太阳辐射为800 W/m2、透平压降为400 Pa时,系统输出功率可达160 kW;此外,大流量的流体流出烟囱成为造成系统能量损失的主要因素,集热棚顶棚也造成了大量的能量损失.     

Compensation of power fluctuations of wind power generation by means of biomass gas turbine generator and flywheel energy storage equipment

Power generation using natural energy contains electric power fluctuations. Therefore, in order to put such power generation systems to practical use, compensation for system power fluctuations is needed. In this paper, we propose a power compensation method using a biomass gas turbine generator and flywheel energy storage equipment. The gas turbine generator is used for compensation of low‐frequency power fluctuations in order to decrease the required flywheel capacity. The usefulness of the proposed system is confirmed by experiments using a test plant. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(3): 1–8, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20896     

Coal-gas-burning high-efficiency power plant which recovers generated carbon dioxide

This paper describes the characteristics and construction of a coal-gas-burned high efficiency power plant which emits no carbon dioxide (CO₂) into the atmosphere. In a plant, CO₂ gas and superheated steam are used as the main and the secondary working fluids, respectively, of a closed dual fluid regenerative gas turbine power plant. Since coal gas composed of CO, H₂, CO₂ and CH₄ is burned in a combustor using oxygen, the exhaust gas let into a condenser includes only CO₂ and H₂O. Hence, CO₂ gas can be easily separated at the condenser outlet from condensate. In the plant, the combustion gas is first used to generate power by driving a turbine. High-temperature turbine exhaust gas is next utilized at a regenerator to heat the main working fluid of CO₂ gas flowing into the combustor, and then is utilized at a waste heat boiler to produce the superheated steam injected into the combustor. It is estimated that the power can be generated with gross thermal efficiency of 54.4 percent, and that the power generating efficiency is 46.7 percent. Generating efficiency is calculated by subtracting the power required for producing the high-pressure oxygen used for combustion from the generator output. It is shown that the estimated efficiency is higher by 18.1 percent than that of a conventional boiler steam turbine power generating plant into which a process for removing and recovering CO₂ from the stack gas by utilizing alkanolamine-based solvent is integrated.     

Combined carbon‐dioxide‐capturing high‐performance power generation system using a solid oxide fuel cell operating on pressurized fuel/air

The authors recently proposed a high‐performance combined carbon‐dioxide‐capturing power generation system using a solid oxide fuel cell (SOFC) and a closed‐cycle MHD generator, in which pure oxygen is used as the oxidant. This combined system makes the best use of the advantages of combustion with pure oxygen but fails to prevent the efficiency deterioration caused by high power demand for oxygen production. In the present study, the authors modified this previous system and proposed an improved combined carbon‐dioxide‐capturing power generation system using SOFC/MHD characterized by a higher overall thermal efficiency. In this system, pure oxygen is supplied only to the combustor to reduce the power required for the oxygen production, and pressurized air is used as the oxidant gas in the SOFC. The power saving amounts to about 5% of the thermal input, resulting in a very high total thermal efficiency of 67.53% (HHV) or 74.94% (LHV), which is considered to be the highest possible value of the overall thermal efficiency of carbon‐dioxide‐capturing systems. Advantages of the proposed system suggest that it is advisable to continue further research in this direction. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 149(4): 21–30, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20010     

Evaluation of output and unit cost of power generation systems utilizing solar energy under various solar radiation conditions worldwide

Characteristics and economics of three power generation systems which utilize solar energy were investigated and compared for systems located in five different regions. The three systems investigated were a solar thermal system, a solar photovoltaic system, and a CO₂‐capturing hybrid power generation system utilizing solar thermal energy (referred to as the hybrid system) which has been proposed by the authors. The net generated power energy and the net exergetic efficiency of the hybrid system have been estimated to be larger and higher, respectively, than those of the others. Economic evaluation reveals that the unit cost of generated power energy of the solar thermal system changes most widely corresponding to the change in solar radiation condition and that the cost of the hybrid system changes the least. In general, the most economical system has been estimated to be the solar thermal system in a location which is superior in solar condition and to be the hybrid system in a not so good solar condition. The solar photovoltaic system has the possibility of being the most economical if its construction cost is greatly improved, though the hybrid system is still the most economical under considerably worse solar conditions such as in Osaka. © 1999 Scripta Technica, Electr Eng Jpn, 127(3): 1–12, 1999     

整体煤气化联合循环(IGCC)发电系统性能计算与分析

针对整体煤气化联合循环(IGCC)发电系统在技术、经济、环保综合性能上具有较大的优势,阐述了IGCC发电系统分类,对4种采用空气气化型的IGCC发电系统进行了性能计算和参数分析,得到了供电效率与燃气轮机压比、入口温度之间的关系.