Recycling a hydrogen rich residual stream to the power and steam plant

The benefits of using a residual hydrogen rich stream as a clean combustion fuel in order to reduce Carbon dioxide emissions and cost is quantified. A residual stream containing 86% of hydrogen, coming from the top of the demethanizer column of the cryogenic separation sector of an ethylene plant, is recycled to be mixed with natural gas and burned in the boilers of the utility plant to generate high pressure steam and power. The main advantage is due to the fact that the hydrogen rich residual gas has a higher heating value and less CO₂ combustion emissions than the natural gas. The residual gas flowrate to be recycled is selected optimally together with other continuous and binary operating variables. A Mixed Integer Non Linear Programming problem is formulated in GAMS to select the operating conditions to minimize life cycle CO₂ emissions.     

Software system “DIORES” for the operation diagnosis of a steam power plant unit

Despite the long operating experience with steam power units in the Electric Power System of Serbia (out of which some are at the end of or had even passed their planned working lives), unfortunately, there is a lack of data for their operating regimes, process parameters and performance deviations, the economy and operating states for the previous period. These data would not only be useful for optimal process control, but also for the planning of maintenance, retrofits and repowering of power plants. For these and other equally important reasons, the software system for the diagnosis of operating conditions, control of economy and operating states of different components has been developed for the referential steam power unit. A better control of the process and operating state, thanks to the use of the results obtained with this software system, will bring a lasting benefit to the efficiency and economy increase. Furthermore, it will enable an increase of reliability and availability of steam turbine units and make their working life longer. The basic characteristics of this software system and some of the results obtained by its testing using the available data base for referential unit operation are presented in this paper.     

A comprehensive life cycle analysis of cofiring algae in a coal power plant as a solution for achieving sustainable energy

Algae cofiring scenarios in a 360 MW coal power plant were studied utilizing an ecologically based hybrid life cycle assessment methodology. The impacts on the ecological system were calculated in terms of cumulative mass, energy, industrial exergy, and ecological exergy. The environmental performance metrics, including efficiency, loading, and renewability ratios were also quantified to assess the sustainability of cofiring scenarios from a holistic perspective. The analysis results revealed that cumulative mass and ecological exergy consumption were higher for algae cofiring compared to single coal firing due to high material and energy inputs for the algae cultivation. On the contrary, total energy and industrial exergy utilization were reduced with an increasing share of algae cofiring where algae is dried with solar energy. Additionally, natural gas dried algae cofiring scenarios had a lower renewability ratio in comparison with single coal firing. The results of this study are vital for the policy makers to decide on more environmentally friendly algae cofiring options by considering the potential impacts on ecological system.     

A practical perspective on plant preservation and plant life extension in thermal power stations. Considering aspects of reliability, maintainability, cost and safety

Currently I am employed as the Assistant Power Station Manager, with responsibility for all maintenance aspects, in a thermal power station which has been on standby since 1986! Previously I have been employed as a maintenance engineer and engineering manager in base loading thermal power stations where plant life extension programmes have not only been conceived and planned, but, on most occasions, even completed.

This paper reflects on aspects of plant preservation and plant life extension programmes with which I have been, and am currently, associated; weighing the obvious desirability for such programmes against the need to achieve reliability and maintainability, at a reasonable cost. (Who knows, it may even answer the question continually asked by my wife, “If you are not generating electricity, what do you do all day?”).

The paper also looks at the retention of safety standards, and the need to improve safety standards on ageing plant, in line with ever more stringent legislation.     

Environmental assessment and extended exergy analysis of a “zero CO2 emission”, high-efficiency steam power plant

Aim of this paper is to analyze the performance of an innovative high-efficiency steam power plant by means of two “life cycle approach” methodologies, the life cycle assessment (LCA) and the “extended exergy analysis” (EEA).

The plant object of the analysis is a hydrogen-fed steam power plant in which the H₂ is produced by a “zero CO₂ emission” coal gasification process (the ZECOTECH^© cycle). The CO₂ capture system is a standard humid-CaO absorbing process and produces CaCO₃ as a by-product, which is then regenerated to CaO releasing the CO₂ for a downstream mineral sequestration process.

The steam power plant is based on an innovative combined-cycle process: the hydrogen is used as a fuel to produce high-temperature, medium-pressure steam that powers the steam turbine in the topping section, whose exhaust is used in a heat recovery boiler to feed a traditional steam power plant.

The environmental performance of the ZECOTECH^© cycle is assessed by comparison with four different processes: power plant fed by H₂ from natural gas steam reforming, two conventional coal- and natural gas power plants and a wind power plant.     

不同运行方式对联合循环电站部分负荷性能的影响

计算并分析比较了不同调节方式对部分负荷运行时某燃气－蒸汽联合循环电站各个组成部分及总体性能的影响。     

Effect of altering combustion air flow on a steam power plant: energy and exergy analysis

Energy and exergy analyses were previously performed by the authors of a coal-fired steam power plant. These analyses suggest that the steam generator (and its combustion and heat-transfer processes) is the most inefficient plant device and that significant increases in overall plant efficiency are possible by reducing steam-generator irreversibilities. Here, a possible plant alteration is examined to increase the efficiency of the plant by reducing the irreversibility rate in the steam generator. The modification involves decreasing the fraction of excess combustion air from 0.40 to 0.15. The results show that overall-plant energy and exergy efficiencies both increase by 1.4% when the fraction of excess combustion air decreases from 0.4 to 0.15.Copyright © 2006 John Wiley & Sons, Ltd.     

The effects of the control system on the thermoeconomic diagnosis of a power plant

Thermoeconomic methodologies represent a powerful tool for the energy system diagnosis when detecting possible malfunctions, localizing them and expressing their effects on the components in terms of thermodynamic and economic quantities. In this article, the role played by the control system in the propagation of malfunctions is analyzed. Its effects are proven to be relevant when the thermoeconomic diagnosis is performed and quantified for a gas turbine based cogeneration plant.     

Life Cycle Energy Assessment of biohydrogen production via biogas steam reforming: Case study of biogas plant on a farm in Serbia

The aim of this paper is to demonstrate and to quantify energy flows in a life cycle of biogas to biohydrogen production, starting from feedstock materials via anaerobic digestion, biogas upgrading, biohydrogen production, to the end of biogas system (application of digestate as fertilizer in agriculture). The performance of the biogas plant of Mirotin dairy farm in Serbia has been assessed. According to Life Cycle Energy Assessment approach, results obtained in this study have shown that biohydrogen production via biogas steam reforming has negative energy balance (with ?16,837 GJ). It has also been demonstrated that this process is energy unsustainable in an environmental context. In future analysis it would be necessary to consider the other aspects of sustainability, e.g. the economical and social factors in order to estimate the overall sustainability of the biogas utilization pathways, especially having in mind that the technology of converting biogas to hydrogen is still in the development phase.     

火力发电厂灰场对土壤及浅层地下水的影响研究

火力发电厂灰场的粉场灰对土壤和浅层地下水均有影响,其对浅层地下水影响的大小,主要取决于排灰场土壤的类型及污染物的种类和浓度,从模拟试验结果可知,土壤对砷,氮,六价铬的吸附能力远小于汞和铅。     

One feedwater heater taken out of service as a strategy to maintain full load and its effect on steam power cycle parameters and performance

The aim of this study is to analyze the suitability of one heater removal as a strategy for maintaining full load operation of steam power cycles when superheated and/or reheated temperatures (T_SS, T_RS) decrease and the effect on the net heat rate (HR_Net). For this purpose, three regenerative cycles with different numbers of closed feedwater heaters were chosen. The cycles were analyzed at different steady states with Thermoflex software. Removing a heater has an important influence on the cycle operation and performance, leading to the redistribution of extraction mass flows, with the heater immediately downstream being the most affected. This may make it necessary to reduce the load of the cycle. However, when the highest pressure heater (highest PH) is removed from service, the changes are not so significant. When T_SS and/or T_RS decrease, the plant may not achieve full load operation. Nevertheless, if the highest PH is removed from service, it can help to recover full load. This is due to the decrease in the water/steam mass flow through the steam generator, which produces an increase in T_SS and/or T_RS. On the one hand, this measure leads to higher HR_Net in comparison to that of the nominal conditions. On the other hand, there are certain conditions at which HR_Net is lower than when all the heaters are in service and the values of T_SS and/or T_RS are low. Thus, for maintaining full load, the highest PH removal can be applied and cycle parameters optimized in order to reach a HR_Net closer to its nominal value. The higher the number of closed feedwater heaters, the more adequate is the application of this strategy.     

The effect of the steam temperature fluctuations during steady state operation on the remnant life of the superheater header

Ligament cracking in superheater headers is generally understood to be associated with thermal transients that occur during starts. However, recent analysis has shown that under some circumstances stress changes due to the steam temperature fluctuations during continued operation also contribute to crack growth. The correlation of the stress range due to these temperature fluctuations has been established by carrying out a transient thermo-mechanical FE analysis. The contribution to fatigue crack propagation of existing defects has been quantified. Frequent thermal fluctuations at steady state operation were identified as the most influential factor for the remnant life of the header.     

1000MW火电机组给水泵组配置对机组运行的影响

结合国电汉川电厂1000MW机组的给水泵配置情况,分析比较多种给水泵配置方案的差异。在此基础上,针对无电动给水泵配置的情况,分析其设备运行的安全性和经济性,以及该配置方案对机组运行的影响。     

Performance of a direct steam generation solar thermal power plant for electricity production as a function of the solar multiple

This paper describes the influence of the solar multiple on the annual performance of parabolic trough solar thermal power plants with direct steam generation (DSG). The reference system selected is a 50 MW_e DSG power plant, with thermal storage and auxiliary natural gas-fired boiler. It is considered that both systems are necessary for an optimum coupling to the electricity grid. Although thermal storage is an opening issue for DSG technology, it gives an additional degree of freedom for plant performance optimization. Fossil hybridization is also a key element if a reliable electricity production must be guaranteed for a defined time span. Once the yearly parameters of the solar power plant are calculated, the economic analysis is performed, assessing the effect of the solar multiple in the levelized cost of electricity, as well as in the annual natural gas consumption.     

电厂凝结水泵运行偏离设计工况的原因分析

对电厂凝结水泵运行与设备选型的数据进行了对比分析,指出凝结水泵一般采用定速泵节流调节方式,由于设计考虑老化裕量及运行调节的不确定因素,普遍存在运行与设计的偏差情况,从而使实际运行存在节流损失,因此建议电厂根据实际负荷情况进行经济比较,选择疑泵变频技术改造。     

Dynamic characteristics and operation strategy of the discharge process in compressed air energy storage systems for applications in power systems

In the context of the rapid development of large-scale renewable energy, large-scale energy storage technology is widely considered as the most effective means of improving the quality and security of electricity. In the existing energy storage technology, advanced adiabatic compressed air energy storage (AA-CAES) technology has broad application prospects because of its advantages of low pollution, low investment, flexible site selection, and large capacity. However, the lack of an in-depth understanding of the dynamic characteristics of CAES systems has severely limited the development of system design and control strategy, resulting in a lack of commercial operation of large-scale CAES systems. This paper describes the design and implementation of a CAES plant and its controller for applications in the distribution network level. The dynamic mathematical models of AA-CAES were established and a feasible control strategy for the grid-connected process was developed to analyze the dynamic characteristics of the system in the discharge stage. The work done in this study provided a data reference for the deep understanding of the dynamic characteristics of AA-CAES, system design, and control strategy in the industry.     

联合循环机组的数学模型及其参数辨识研究

联合循环电站由于其复杂的控制系统和强耦合的非线性关系,其数学模型非常复杂,开展联合循环机组的建模和参数测试研究具有重要的学术意义和工程应用价值。本文提出了适用于电网一次调频和稳定性分析的联合循环电站模型,采用改进最小二乘参数辨识方法对某400MW联合循环机组的模型参数进行了辨识,采用辨识的参数进行了仿真分析并与机组运行的实测数据进行了对比,两者能够很好地吻合,证明了所提出模型和辨识方法的有效性,为联合循环电站的一次调频和动态特性分析奠定了基础。     

基于综合需求侧响应策略的园区多能源系统优化运行

在能源互联网的背景下,计及多类型能源市场价格传导机制的综合需求侧响应策略能够解决传统工业园区能源利用效率低、电能紧缺等问题。文章以园区多能源系统为研究对象,计及电力市场和碳交易市场价格传导机制,基于园区多能源系统模型,以系统运行成本最小化为目标,设计了园区多能源系统综合需求侧响应策略,对深圳某园区进行了实例分析,并运用粒子群算法进行优化求解。结果表明,文章所提出的策略能够提高多能源系统的运行可靠性,降低运行成本。     

Simulation of the operation of a gas turbine installation of a thermal power plant with a hydrogen fuel production system

The growth in demand for the production of heat and electricity requires an increase in fuel consumption by power equipment. At the moment, the most demanded thermal equipment for construction and modernization is gas turbine units. Gas turbines can burn a variety of fuels (natural gas, synthesis gas, methane), but the main fuel is natural gas of various compositions. The use of alternative fuels makes it possible to reduce CO₂ and NO_x emissions during the operation of a gas turbine. Under conditions of operation of thermal power plants at the wholesale power market, it becomes probable that combined cycle power units, designed to carry base load, will start to operate in variable modes. Variable operation modes lead to a decrease in the efficiency of power equipment. One way to minimize or eliminate equipment unloading is to install an electrolysis unit to produce hydrogen.In this article the technology of “Power to gas” production with the necessary pressure at the outlet of 30 kgf/cm² (this pressure is necessary for stable operation of the fuel preparation system of the gas turbine) is considered. High cost of hydrogen fuel during production affects the final cost of heat and electric energy, therefore it is necessary to burn hydrogen in mixture with natural gas. Burning a mixture of 5% hydrogen fuel and 95% natural gas requires minimal changes in the design of the gas turbine, it is necessary to supplement the fuel preparation system (install a cleaning system, compression for hydrogen fuel). In addition, the produced hydrogen can be stored, transported to the consumer. For the possibility of combustion of a mixture of natural gas and hydrogen fuel in a gas turbine the methodology of calculation of thermodynamic properties of working bodies developed by a team of authors under the guidance of Academician RAS (the Russian Academy of Sciences) V.E. Alemasov has been adapted, resulting in a program that allows to obtain an adequate mathematical model of the gas turbine. The permissible range of the working body temperature is limited to 3000 K. This paper presents the developed all-mode mathematical model of a gas turbine.On the basis of mathematical modeling of a gas turbine, a change in the main energy and environmental characteristics is shown depending on the composition of the fuel gas. Adding 5% hydrogen to natural gas has little effect on the gas turbine air treatment system, the flow rate remains virtually unchanged. CO₂ emissions decrease, but there is an increase in the amount of H₂O in the turbine exhaust gases.