The influence of the legal and economical environment and the profile of activities on the optimal design features of a natural-gas-fired combined heat and power plant

The paper deals with the effect of some selected quantities occurring in the legal and economical environment on the optimal values of some selected design quantities of a natural-gas-fired CHP plant. This trend of investigations results from the newly observed legal changes in the legislation concerning new forms of mechanisms supporting the combined production of electricity and heat. Special stress was exerted on changes resulting from the formulation of two directives, viz. 2003/7/EC and 2004/8/EC.For the purpose of realising this task, a reference structure of a CHP plant was selected. For the steam-water part of the plant thirteen quantities were selected, determining the design features of the most essential components of this part of the system. These quantities served as decision variables in processes of optimisation. As the objective function the break-even price of electricity was assumed.The second part of the paper presents the results of sensitivity analyses of the fundamental indices of the energy and economical effectiveness to failures in the adherence of the optimal values of the respective design quantities, as well as the results of investigations on the effect of the operation time of the plant in the course of one year.     

Influence of the heat recovery steam generator design parameters on the thermoeconomic performances of combined cycle gas turbine power plants

This paper proposes a methodology to identify the most relevant design parameters that impact on the thermal efficiency and the economic results of combined cycle gas turbine power plants. The analysis focuses on the heat recovery steam generator (HRSG) design and more specifically on those operating parameters that have a direct influence on the economic results of the power plant. These results are obtained both at full and part load conditions using a dedicated code capable of simulating a wide number of different plant configurations. Two different thermoeconomic models aimed to select the best design point are proposed and compared: the first one analyzes the generating cost of the energy while the second one analyzes the annual cash flow of the plant. Their objective is to determine whether an increase in the investment in order to improve the thermal efficiency is worth from an economic point of view. Both models and the different HRSG configurations analysed are compared in the results section. Some parametric analysis show how the design parameters might be varied in order to improve the power plant efficiency or the economic results. Copyright © 2004 John Wiley & Sons, Ltd.     

Optimal design of gas turbine CHP plant with preheater and HRSG

Located in the south of Iran, Jiroft Paper Mill Company requires an integrated combined heat and power plant, which can provide 50 MW of electric power and 100 ton h^?1 saturated steam at 13 bar, to produce paper from an adjacent eucalyptus forest. The plant is composed of an air compressor, combustion chamber, air preheater, turbine, as well as a heat recovery steam generator. The design parameters of the plant were chosen as: compressor pressure ratio (r_c), compressor isentropic efficiency (η_AC), gas turbine isentropic efficiency (η_T), combustion chamber inlet temperature (T₃), and turbine inlet temperature (T₄). In order to optimally find the design parameters a thermoeconomic approach has been followed. An objective function representing the total cost of the plant in terms of dollar per second was defined as the sum of the operating cost related to the fuel consumption and the capital investment for equipment purchase and maintenance costs. Subsequently, different parts of the objective function have been expressed in terms of decision variables. Finally, the optimal values of decision variables were obtained by minimizing the objective function using sequential quadratic programming. The influence of changes in the demanded power and steam on the design parameters has also been studied for 40, 50, 60, and 70 MW of net power output, and 100, 120, and 150 ton h^?1 of saturated steam mass flow rate. Finally, the sensitivity analysis of change in design parameters with change in fuel or investment cost was performed. Copyright © 2009 John Wiley & Sons, Ltd.     

Energy balance and cogeneration for a cement plant

The cement industry is an energy intensive industry consuming about 4 GJ per tonne of cement produced. A thermodynamic analysis for cogeneration using the waste heat streams is not easily available. Data from a working 1 Mt per annum plant in India is used to obtain an energy balance for the system and a Sankey diagram is drawn. It is found that about 35% of the input energy is being lost with the waste heat streams. A steam cycle is selected to recover the heat from the streams using a waste heat recovery steam generator and it is estimated that about 4.4 MW of electricity can be generated. This represents about 30% of the electricity requirement of the plant and a 10% improvement in the primary energy efficiency of the plant. The payback period for the system is found to be within two years.     

Thermoeconomic analysis method for optimization of combined heat and power systems—part II

In this paper, a thermoeconomic functional analysis method based on the Second Law of Thermodynamics and applied to analyze four cogeneration systems is presented. The objective of the developed technique is to minimize the operating costs of the cogeneration plant, namely exergetic production cost (EPC), assuming fixed rates of electricity production and process steam in exergy base. In this study a comparison is made between the same four configurations of part I. The cogeneration system consisting of a gas turbine with a heat recovery steam generator, without supplementary firing, has the lowest EPC.     

Efficient utilization of waste heat from molten carbonate fuel cell in parabolic trough power plant for electricity and hydrogen coproduction

Direct steam generating parabolic trough power plant is an important technology to match future electric energy demand. One of the problems related to its emergence is energy storage. Solar-to-hydrogen is a promising technology for solar energy storage. Electrolysis is among the most processes of hydrogen production recently investigated. High temperature steam electrolysis is a clean process to efficiently produce hydrogen. In this paper, steam electrolysis process using solar energy is used to produce hydrogen. A heat recovery steam generator generates high temperature steam thanks to the molten carbonate fuel cell's waste heat. The analytical study investigates the energy efficiency of solar power plant, molten carbonate fuel cell and electrolyser. The impact of waste heat utilization on electricity and hydrogen generation is analysed. The results of calculations done with MATLAB software show that fuel cell produces 7.73 MWth of thermal energy at design conditions. 73.37 tonnes of hydrogen and 14.26 GWh of electricity are yearly produced. The annual energy efficiency of electrolyser is 70% while the annual mean electric efficiency of solar power plant is 18.30%.The proposed configuration based on the yearly electricity production and hydrogen generation has presented a good performance.     

A thermoeconomic analysis of biomass energy for trigeneration

The principal objective of this study is to formulate a calculation process, based on the second law of exergy, for evaluating the thermoeconomic potential of a steam-turbine plant for trigeneration. The plant employs biomass, namely, waste wood as its energy source. Four different plant configurations are presented and assessed. ‘Their cost effectiveness is evaluated with varying economic and operating parameters’, because only the fuel price and electricity price are varied. In case 1, high pressure superheated steam generated is supplied to meet the demand for process heat as well as chilled water production in an absorption chiller. In cases 2 and 3, steam is extracted at appropriate stages of the turbine and supplied to meet the demand for process heat and chilled water production in an absorption chiller. Steam generated in case 2 produces sufficient power to meet internal demands while case 3 generates excess electricity for sale back to the utility. In case 4, low pressure saturated steam is generated to meet the demand for process heat and electricity is bought from the utilities, including those used to power an electric vapour-compression chiller. For all cases, it was found that exergy destruction is most extensive in the furnace, amounting to nearly 60%. Exergy destruction in the steam drum is the next most extensive ranging from 11% to 16%. It was also observed that the overall production cost decreases with steam pressure and increases with steam temperature.     

凝汽式机组改为循环水供热的技术可行性研究

本文从提高汽轮机热经济性的角度出发,探讨了凝汽式机组冬季利用循环 水供热的有关理论与技术问题,包括热力学、经济指标、系统布置、经济效益等方 面的分析与计算,比较全面地论述了凝汽式机组利用循环水供热的可行性。文章 对于提高地方电厂与企业自备电厂的经济效益以及节约能源等方面,具有重要的 参考价值与指导意义。     

A performance analysis of integrated solid oxide fuel cell and heat recovery steam generator for IGFC system

Solid oxide fuel cell (SOFC) is a promising technology for electricity generation. Sulfur-free syngas from a gas-cleaning unit serves as fuel for SOFC in integrated gasification fuel cell (IGFC) power plants. It converts the chemical energy of fuel gas directly into electric energy, thus high efficiencies can be achieved. The outputs from SOFC can be utilized by heat recovery steam generator (HRSG), which drives the steam turbine for electricity production. The SOFC stack model was developed using the process flow sheet simulator Aspen Plus, which is of the equilibrium type. Various ranges of syngas properties gathered from different literature were used for the simulation. The results indicate a trade-off efficiency and power with respect to a variety of SOFC inputs. The HRSG located after SOFC was included in the current simulation study with various operating parameters. This paper describes IGFC power plants, particularly the optimization of HRSG to improve the efficiency of the heat recovery from the SOFC exhaust gas and to maximize the power production in the steam cycle in the IGFC system. HRSG output from different pressure levels varies depending on the SOFC output. The steam turbine efficiency was calculated for measuring the total power plant output. The aim of this paper is to provide a simulation model for the optimal selection of the operative parameters of HRSG and SOFC for the IGFC system by comparing it with other models. The simulation model should be flexible enough for use in future development and capable of predicting system performance under various operating conditions.     

A performance analysis of integrated solid oxide fuel cell and heat recovery steam generator for IGFC system

Solid oxide fuel cell (SOFC) is a promising technology for electricity generation. Sulfur-free syngas from a gas-cleaning unit serves as fuel for SOFC in integrated gasification fuel cell (IGFC) power plants. It converts the chemical energy of fuel gas directly into electric energy, thus high efficiencies can be achieved. The outputs from SOFC can be utilized by heat recovery steam generator (HRSG), which drives the steam turbine for electricity production. The SOFC stack model was developed using the process flow sheet simulator Aspen Plus, which is of the equilibrium type. Various ranges of syngas properties gathered from different literature were used for the simulation. The results indicate a trade-off efficiency and power with respect to a variety of SOFC inputs. The HRSG located after SOFC was included in the current simulation study with various operating parameters. This paper describes IGFC power plants, particularly the optimization of HRSG to improve the efficiency of the heat recovery from the SOFC exhaust gas and to maximize the power production in the steam cycle in the IGFC system. HRSG output from different pressure levels varies depending on the SOFC output. The steam turbine efficiency was calculated for measuring the total power plant output. The aim of this paper is to provide a simulation model for the optimal selection of the operative parameters of HRSG and SOFC for the IGFC system by comparing it with other models. The simulation model should be flexible enough for use in future development and capable of predicting system performance under various operating conditions.     

Optimal investment strategies in decentralized renewable power generation under uncertainty

This paper presents a method for evaluating investments in decentralized renewable power generation under price un certainty. The analysis is applicable for a client with an electricity load and a renewable resource that can be utilized for power generation. The investor has a deferrable opportunity to invest in one local power generating unit, with the objective to maximize the profits from the opportunity. Renewable electricity generation can serve local load when generation and load coincide in time, and surplus power can be exported to the grid. The problem is to find the price intervals and the capacity of the generator at which to invest. Results from a case with wind power generation for an office building suggests it is optimal to wait for higher prices than the net present value break-even price under price uncertainty, and that capacity choice can depend on the current market price and the price volatility. With low price volatility there can be more than one investment price interval for different units with intermediate waiting regions between them. High price volatility increases the value of the investment opportunity, and therefore makes it more attractive to postpone investment until larger units are profitable.     

燃机电厂9F型机组热电负荷优化分配研究

电厂热电负荷优化分配是指在全厂总调度负荷下,根据各机组的热力性能确定各机组应承担的热电负荷,使得全厂效益最大或能耗最小的一种最优化问题.不同于燃煤热电厂,燃机电厂9F型机组由于设计为燃气轮机加蒸汽轮机的组合方式运行,因此在联合循环热力性能模型建立上较为复杂.提出了将余热锅炉新蒸汽参数作为中间变量,建立了机组天然气燃料消耗与电负荷、热负荷之间的关系模型,确定了优化计算的目标函数和边界约束条件,并采用非线性规划方法求解.模拟与实际运行结果均表明,该优化分配方法能有效降低燃机电厂燃料消耗水平,可以为同类型燃机电厂热电负荷优化分配提供参考.     

IGCC系统关键部件的选择及其对电厂整体性能的影响——(3)气化炉合成气冷却器与余热锅炉的匹配

带有合成气冷却器的气化炉,因能将高温合成气中的显热提供给余热锅炉,其系统效率高且更具有研究价值．采用GT PRO软件,研究了余热锅炉和合成气冷却器联合运行的工作过程．模拟和对比了余热锅炉在不同位置抽取和回送冷却介质对系统整体技术、经济性能造成的影响．综合分析之后,提出了几种性价比较高的流程布置．     

Integration of Kalina cycle in a combined heat and power plant,a case study

This paper presents the integration of the Kalina cycle process in a combined heat and power plant for improvement of efficiency. In combined heat and power plants, the heat of flue gases is often available at low temperatures. This low-grade waste heat cannot be used for steam production and therefore power generation by a conventional steam cycle. Moreover, the steam supply for the purpose of heating is mostly exhausted, and therefore the waste heat at a low-grade temperature is not usable for heating. If other measures to increase the efficiency of a power plant process, like feed-water heating or combustion air heating, have been exhausted, alternative ways to generate electricity like the Kalina cycle process offer an interesting option. This process maximizes the generated electricity with recovery of heat and without demand of additional fuels by integration in existing plants. The calculations show that the net efficiency of an integrated Kalina plant is between 12.3% and 17.1% depending on the cooling water temperature and the ammonia content in the basic solution. The gross electricity power is between 320 and 440 kW for 2.3 MW of heat input to the process. The gross efficiency is between 13.5% and 18.8%.     

联合循环参数和系统结构优化研究

研究了如何提高余热锅炉型三压再热联合循环系统的效率,应用分析的方法建立了系统效率数学模型,以联合循环系统效率最高作为系统性能的评判标准。在亚临界范围内,对余热锅炉的蒸汽参数进行了优化;针对余热锅炉进气温度对余热锅炉性能的影响进行分析,在此基础上提出燃气轮机排气部分回热利用,并研究了回热利用对联合循环效率的影响。计算结果表明:经余热锅炉优化和排气部分回热利用,在基本负荷下,PG9351FA机组的联合循环热效率可提高1.33%;在75%和50%的负荷下,效率分别提高2.11%和4.17%;而具有再热的GT26机组热效率高达60.73%。     

Comprehensive methodology for identifying tariff zones of efficiency of hydrogen-thermal accumulation system at the NPP

In countries with developed nuclear energy, there are problems associated with non-uniformity of the daily electricity load, due to the economically justified need to load nuclear power plants with a maximum installed capacity utilization factor. This is due to the cheapness of nuclear fuel compared to organic and, at the same time, high investment compared to thermal power plants, as well as the presence of technological limitations on maneuverability. Most organic fuel thermal power plants are switched to half-peak mode, which negatively affects their efficiency and reliability.In addition, the ever-increasing requires on the level of safety negatively affect the economic competitiveness of nuclear power plants. Improving safety through the introduction of passive heat removal systems of the reactor core is provided for in new NPP projects. These systems have several disadvantages: maintenance costs; a significant increase in capital investment; emergency cooling mode.To solve these problems, the authors developed a system of hydrogen-thermal accumulation, which, when combined with a nuclear power plant, allows one to accumulate cheap energy during the hours of a decrease in load in the power system due to electrolysis of water to produce hydrogen and oxygen, and thermal accumulation of hot water in heat-insulating tanks. Thanks to the use of hot water tanks, investment in the accumulation system is significantly reduced. Thanks to the use of a hydrogen-oxygen steam generator, the opportunity to generate an additional main steam and to use it in the additional steam turbine unit appears, which will allow to avoid costly modernization of the main equipment of the nuclear power plant and reducing its lifetime. The presence of a low-power steam turbine unit as part of the accumulation system ensures uninterrupted autonomous power supply to consumers of the NPP own needs due to the possibility of using the energy of the reactor residual heat, when the station is completely blackout. The method of combining the hydrogen complex with thermal accumulators is completely new and has no analogues.The economic efficiency of the developed energy complex has been investigated. The accumulated net present value was determined depending on the off-peak electricity tariff for the three options of the half-peak electricity tariff, taking into account possibility to refuse expensive heat exchangers of the passive heat removal systems. It is shown that the use of the proposed scheme is advisable in regions with off-peak electricity tariffs in the range 0–0.32 cents/kW·h, 0–0.8 cents/kW·h and 0–1.25 cents/kW·h, respectively, depending on the forecast dynamics of the half-peak electricity tariff. The average payback period of the accumulation system for given conditions is equal to 3–15 years.     

Possibilities for gas turbine and waste incinerator integration

The aggressive nature of the flue gases in municipal waste incinerators does not allow the temperature of steam in the boiler to rise above 400°C. An increase in steam temperature can be achieved by external superheating in a heat recovery steam generator positioned behind a gas turbine, so that steam of a higher energy content becomes available for electricity production. The paper addresses two basic schemes. In one case, steam generated at a waste-to-energy plant is superheated in a combined-cycle plant that operates in parallel. In the other case, the exhaust from a gas turbine plant is sent through a superheater section to the waste incinerator's boiler providing preheated combustion air. Performance of these configurations together with two modified schemes was analyzed in terms of efficiency, natural gas consumption and boiler surface area. An exergy analysis of the cases was carried out. The results showed that the integrated options can effect a substantial increase in efficiency. The hot windbox configuration was found the most effective solution, offering a smaller boiler surface area along with a moderate rate of natural gas consumption.     

Solar thermodynamic plants for cogenerative industrial applications in southern Europe

The paper deals with the preliminary design and optimization of cogenerative solar thermodynamic plants for industrial users. The considered plants are all based on proven parabolic trough technology, but different schemes have been analyzed: from a conventional configuration with indirect steam cycle and a heat transfer fluid such as synthetic oil or molten salts, to a more innovative arrangement with direct steam generation in the solar field. Thermodynamic parameters of the steam cycle have been optimized considering some constraints due to the heat requirements of the user, leading to a preliminary design of the main components of the system and an estimation of costs. Resulting net electric efficiency is about 10% for conventional synthetic oil plant, while 13% for innovative molten salts and DSG.A comparison with conventional solar thermodynamic systems for electricity production and photovoltaic power plants shows the economic and energetic benefits of the cogenerative solution. Cost of electricity for solar plant is cheaper of about 20 €/MWh than conventional solar power application. Moreover, heat recovery allows to achieve a further 50% of CO₂ emission savings compared to reference solar plants for only electricity production.     

Comparative performance analysis of cogeneration gas turbine cycle for different blade cooling means

The paper compares the thermodynamic performance of MS9001 gas turbine based cogeneration cycle having a two-pressure heat recovery steam generator (HRSG) for different blade cooling means. The HRSG has a steam drum generating steam to meet coolant requirement, and a second steam drum generates steam for process heating. Gas turbine stage cooling uses open loop cooling or closed loop cooling schemes. Internal convection cooling, film cooling and transpiration cooling techniques employing steam or air as coolants are considered for the performance evaluation of the cycle. Cogeneration cycle performance is evaluated using coolant flow requirements, plant specific work, fuel utilisation efficiency, power-to-heat-ratio, which are function of compressor pressure ratio and turbine inlet temperature, and process steam drum pressure. The maximum and minimum values of power-to-heat ratio are found with steam internal convection cooling and air internal convection cooling respectively whereas maximum and minimum values of fuel utilisation efficiency are found with steam internal convection cooling and closed loop steam cooling. The analysis is useful for power plant designers to select the optimum compressor pressure ratio, turbine inlet temperature, fuel utilisation efficiency, power-to-heat ratio, and appropriate cooling means for a specified value of plant specific work and process heating requirement.     

Thermoeconomic optimization of combined cycle gas turbine power plants using genetic algorithms

This paper shows a possible way to achieve a thermoeconomic optimization of combined cycle gas turbine (CCGT) power plants. The optimization has been done using a genetic algorithm, which has been tuned applying it to a single pressure CCGT power plant. Once tuned, the optimization algorithm has been used to evaluate more complex plants, with two and three pressure levels in the heat recovery steam generator (HRSG).The variables considered for the optimization were the thermodynamic parameters that establish the configuration of the HRSG.Two different objective functions are proposed: one minimizes the cost of production per unit of output and the other maximizes the annual cash flow. The results obtained with both functions are compared in order to find the better optimization strategy.The results show that it is possible to find an optimum for every design parameter. This optimum depends on the selected optimization strategy.