基于动态网络数据包络分析模型的我国供电公司运营效率研究

为科学合理地测量和评价我国供电公司的运营效率,以分析我国电力体制改革中输配分离的必要性和可行性。应用动态SBM模型和动态网络SBM模型研究了我国31个省级供电公司2010~2012年的运营效率,分析了输配分离电力体制改革对各省级供电公司的影响,提出了在电力行业高速发展的情形下合理配置资源的方案,可为各省级电网公司应对输配分离政策提供决策参考。     

Exergy, economic & environmental (3E) analysis of inlet fogging for gas turbine power plant

In the present paper, the effects of inlet fogging system on the first and second law efficiencies are investigated for a typical power plant (Shahid Rajaee) which is located near Ghazvin in Iran. Also a new function is proposed for system optimization that includes the social cost of air pollution for power generating systems. The new function is based on the first law efficiency, energy cost and the external social cost of air pollution for an operational system. Social cost of air pollution is based on the negative effects of air pollution on the health of society and environment. The economic aspect of these effects is called external social cost of air pollution. Other pollution sources such as water, soil, etc. produced by an operational power generation system are ignored. The theoretical results obtained from the model are validated by registered practical performance results from Shahid Rajaee power plant. It is concluded that using of inlet fogging system, increases the average output power production, the first and the second law efficiencies through three months of year (June, July and August) by 7%, 5.5% and 6% respectively and reduces the objective function value by about 4%.     

Evaluation of thermal power plant operational performance in Taiwan by data envelopment analysis

Electricity is essential in the economic development of a nation. Due to the rapid growth of economy and industrial development in Taiwan, the demand for use of electricity has increased rapidly. This study evaluates the power-generation efficiency of major thermal power plants in Taiwan during 2004–2006 using the data envelopment analysis (DEA) approach. A stability test was conducted to verify the stability of the DEA model. According to the results, all power plants studied achieved acceptable overall operational efficiencies during 2004–2006, and the combined cycle power plants were the most efficient among all plants. The most important variable in this DEA model is the “heating value of total fuels”. Findings from this study can be beneficial in improving some of the existing power plants and for more efficient operational strategies and related policy-making for future power plants in Taiwan.     

A comparative study among fossil fuel power plants in PJM and California ISO by DEA environmental assessment

This study compares among fossil fuel power plants in PJM and California ISO by their unified (operational and environmental) performance. DEA (Data Envelopment Analysis) is used as a methodology. For comparative analysis, DEA incorporates strategic concepts such as natural and managerial disposability into the computational process. This study explores both how to measure Returns to Scale (RTS) under natural disposability and how to measure Damages to Scale (DTS) under managerial disposability. This empirical study obtains two implications on US energy policy. One of the two policy implications is that California ISO outperforms PJM in terms of the three unified efficiency measures. The result implies that strict regulation on undesirable outputs, as found in California, is important in enhancing the performance of US fossil fuel power plants. Thus, it is necessary for federal and local governments to regulate the fossil fuel power plants under the strict implementation of environmental protection. Under such a policy direction, it is possible for US fossil fuel power plants to attain economic prosperity (by enhancing their operational efficiencies) and to satisfy environmental regulation (by enhancing their environmental efficiencies). The other policy implication is that coal-fired and gas-fired power plants in PJM and California ISO need to reduce their operational sizes or introduce technology innovation on desirable and undesirable outputs and/or new management for environmental protection within their operations. Meanwhile, oil-fired power plants may increase their operational sizes if they can introduce technology innovation and new management on undesirable outputs.     

Environmental assessment on coal-fired power plants in U.S. north-east region by DEA non-radial measurement

This study discusses a new use of DEA (Data Envelopment Analysis) environmental assessment to measure unified (operational and environmental) and scale efficiencies among inputs, desirable and undesirable outputs. In particular, the measurement of scale efficiency is discussed by two non-radial models. That is a new methodological contribution. To discuss these efficiency measures, this study first examines a concept of disposability from the perspective of corporate strategies to adapt a regulation change on undesirable outputs. The concept is separated into natural and managerial disposability. After discussing how to measure the degree of scale efficiency within the non-radial approach, this study applies the proposed DEA environmental assessment to measure the performance of coal-fired power plants in the U.S. north-east region. The region has been long producing a large amount of coal from the Appalachian Mountains. The coal mining industry has supported U.S. energy utility and other industries. Because of the long history, the quality of coal became worse and the coal-fired power plants have been producing a large amount of undesirable gases. This study has statistically confirmed that there is a significant difference between the two types (BIT: bituminous coal and SUB: subbituminous coal) of coal-fired power plants in terms of their unified efficiency measures, including their scale efficiencies, under the concept of managerial disposability (the first priority: environment performance and the second priority: operational performance). In contrast, under the natural disposability (the first priority: operational performance and the second priority: environmental performance), this study cannot find such a statistical significance between them. The fact, in which BIT outperforms SUB in terms of their unified and scale efficiencies, suggests the policy implication that these power plants need to shift their coal combustions from SUB to BIT in the United States. Besides the empirical finding, this study cannot confirm the other hypothesis on whether coal-fired power plants with small operation (less than 50% in plant capacity factor) outperform ones with large operation (more than 50% in plant capacity factor), and vice versa, in terms of their unified and scale efficiency measures under natural and managerial disposability. An exception is found in environmental performance under variable returns to scale. The rationale is because their plant operations are frequently monitored by regulatory agencies. As a consequence, this study cannot find such a statistical difference between them on operational performance. This result implies that the regulation on coal-fired power plants has been effective on their unified performance but large power plants may have a potential to improve their environmental performance.     

Bioelectricity production on xylose with a compost enrichment culture

An exoelectrogenic culture was enriched on 1.0 g/L xylose from a compost sample in two-chamber microbial fuel cells (MFCs). Electricity production was optimized by changing mixing type, external resistance, xylose concentration and pH. Furthermore, the changes in microbial communities after each optimization step were monitored with PCR-DGGE. Electricity production was highly dependent on operational conditions that affected power densities (PD), Coulombic efficiencies (CE), substrate degradation, utilization of soluble metabolites for electricity production and stability of MFC performance. The optimum operational conditions for electricity production were without mixing, 100 Ω external resistance, 0.5 g/L xylose and pH 7. With optimized operational conditions PD of 590 mW/m² and CE of 82% were obtained. Microbial community composition, consisting mainly of Geobacter sulfurreducens, Escherichia coli, Sphaerochaeta sp. TQ1 and Bacteroides species, was mainly affected by MFC configuration, i.e. electrical connections, which likely affected the anode potential.     

Spark spread – A screening parameter for combined heating and power systems

Combined heating and power (CHP) systems may be considered for installation if they produce savings over conventional systems with separate heating and power. For a CHP system with a natural gas engine as the prime mover, the difference between the price of natural gas and the price of purchased electricity, called spark spread, is an indicator as to whether a CHP system might be considered or not. The objective of this paper is to develop a detailed model, based on the spark spread, that compares the electrical energy and heat energy produced by a CHP system against the same amounts of energy produced by a traditional, or separate heating and power (SHP) system that purchases electricity from the grid. An expression for the spark spread based on the cost of the fuel and some of the CHP system efficiencies is presented in this paper as well as an expression for the payback period for a given capital cost and spark spread. The developed expressions allow determining the required spark spread for a CHP system to produce a net operational savings over the SHP in terms of the performance of system components. Results indicate that the spark spread which might indicate favorable payback varies based on the efficiencies of the CHP system components and the desired payback period. In addition, a new expression for calculating the payback period for a CHP system based on the CHP system capital cost per unit of power output and fuel cost is proposed.     

Solar tower power plant in Germany and future perspectives of the development of the technology in Greece and Cyprus

Since the 80s power production with solar thermal power plants has been a way to substitute fossil fuels. By concentrating direct solar radiation from heliostats very high temperatures of a thermal fluid can be reached. The resulting heat is converted to mechanical energy in a steam cycle which generates electricity.High efficiencies and fast start-up are reached by using air as a heat medium, as well as using porous ceramic materials as solar receiver of the concentrated sunlight.In Germany the construction of a 1.5 MW_e solar tower power plant began in 2008. It is operational since December 2008 and started production of electricity in the spring of 2009.In Greece and Cyprus, countries with high solar potential, the development of this competitive solar thermal technology is imperative, since it has already been implemented in other Mediterranean countries.     

Thermal performance of the distributed flow, subatmospheric pressure, flat plate solar collector

Experimental thermal efficiencies for the distributed flow, subatmospheric pressure, flat plate solar collector are reported for a wide range of environmental and operational conditions, and for corrugated Filon and glass covers. Efficiencies for near normal solar incidence are correlated with a parameter formed from the difference between inlet fluid and air temperatures divided by incident solar energy. A mathematical model based on heat transfer concepts applicable to the collector yielded efficiencies which are in close agreement with the corresponding experimental efficiencies when the experimental measurements are inserted into the model.     

Understanding energy and exergy efficiencies for improved energy management in power plants

An extensive overview is provided of various energy- and exergy-based efficiencies used in the analysis of power cycles. Vapor and gas power cycles, cogeneration cycles and geothermal power cycles are examined, and consideration is given to different cycle designs. The many approaches that can be used to define efficiencies are provided and their implications discussed. Improvements of the management of energy in power plants that stem from understanding the efficiencies better are described. Examples are given to illustrate the efficiencies and their differences, with the results presented using combined energy and exergy diagrams. It is anticipated that the results will provide a convenient and practical tool for engineers and researchers dealing with the analysis, design, optimization and improvement of power cycles.     

Analysis of advanced energy chain typologies

A method for estimating the effectiveness and CO₂ emissions of advanced energy conversion systems from primary to final energy is presented. A traditional condensing power plant for electricity production and a fuel boiler for heat production based on natural gas were used as the reference system. Several potentially better energy chains were analysed including CHP, tri‐generation, heat pumps and efficiency improvements in final energy use. All above solutions could provide clear reductions in primary energy use and emissions, in most cases tens of per cents, but the results are sensitive to operational conditions. In a heat pump system, the primary energy savings are considerable but emission reductions may turn out to be marginal or even negative whereas in co‐generation the emission reductions are higher than energy savings. Striving for high conversion efficiencies would ensure sustained benefits from the advanced energy chain typologies over the reference system even in the less favourable cases. Copyright © 2007 John Wiley & Sons, Ltd.     

Measurements on a PV solar pump equipped with a piston pump with a matching valve

The work on a simple high efficient solar pump equipped with a piston pump with a matching valve, reported at the Solar World Congress in Budapest, has been continued. Quasi-static and dynamic models of the solar pump have been derived with which the operation of the system is simulated. A test rig has been built at ECN in Petten (The Netherlands) to perform some preliminary measurements. These tests show that the piston with a matching valve indeed ensures a good matching of the system components over a wide range of solar insolations. Daily average solar panel maximum power point tracking efficiencies of over 80% were measured. Daily average subsystem efficiencies (solar panel power output to hydraulic power output) measured were about 40%, which is lower than expected. These low efficiencies were caused by substantial power losses in the motor, transmission and pump. The losses can easily be reduced by appropriate design of each component; subsystem efficiencies of 50% should be attainable.     

Performance enhancement in coal fired thermal power plants. Part I: boilers

This paper presents the results of the performance enhancement study in 22 coal fired thermal power stations of capacities 30–500 MW. The efficiencies and performance indices of the equipment are evaluated which then leads to the performance evaluation route—operational optimization, simple modification of equipment or renovation. The generic problems associated with design, operation and fuel inputs is investigated and appropriate solutions are suggested to improve the boiler efficiency levels from 71–86% to 86–87% immediately and 89–90% on a long term (5–10 yr) basis. A large volume of design and operating data has been analysed and presented in the form of curve fits for computer simulation of the performance of boilers for high ash coals. Copyright © 1999 John Wiley & Sons, Ltd.     

Operational chemical storage cycles for utilization of solar energy to produce heat or electric power

A self-sufficient chemical cycle is required which will take solar energy on an intermittent basis and continuously convert it into heat and/or electric power. This paper presents engineering criteria for selection of suitable chemical reactions, and considers in detail two systems, (a) methanol cycle and (b) ammonium hydrogen sulfate (AHS) cycle. The latter appears very attractive as an operational cycle, has liquid storage on both sides of the cycle, essentially meets all criteria, and has high ΔH (reaction), heat and work efficiencies. Preliminary reactor configurations for the AHS cycle are discussed.     

Thermo-economic analysis of chlor-alkali electrolysis for hydrogen production in the electrochlorination plant: Real case

This study deals with the implementations of electrochemical technology for the on-site production of sodium hypochlorite (NaOCl) and hydrogen from seawater for utilization in the steam power plant. The effects of electrical current and seawater temperature on the performance of electrochlorination system are investigated. The obtained results show that current efficiency increases with increasing electrical current. The current efficiency of the system is calculated as 94% at a maximum electric current with a value of 4000 A and maximum temperature with a value of 30 °C. Electricity consumption increases for the unit generation of available chlorine in the case of both enhancements of electrical current and seawater. Hydrogen generation is directly proportional to the variation of the electrical current. Also, improvement in seawater temperature provides more efficient hydrogen generation. Moreover, energy and exergy efficiencies of the whole system are positively affected by an increase of current. However, energy and exergy efficiencies are determined to be 50.4% and 3.04%, respectively, under the best operational conditions. Besides, the cheapest product cost of the hydrogen gas is calculated as $4.04/kg under the greatest electrical current and seawater temperatures.     

Assessment of the Turkish utility sector through energy and exergy analyses

The present study deals with evaluating the utility sector in terms of energetic and exergetic aspects. In this regard, energy and exergy utilization efficiencies in the Turkish utility sector over a wide range of period from 1990 to 2004 are assessed in this study. Energy and exergy analyses are performed for eight power plant modes, while they are based on the actual data over the period studied. Sectoral energy and exergy analyses are conducted to study the variations of energy and exergy efficiencies for each power plants throughout the years, and overall energy and exergy efficiencies are compared for these power plants. The energy utilization efficiencies for the overall Turkish utility sector range from 32.64% to 45.69%, while the exergy utilization efficiencies vary from 32.20% to 46.81% in the analyzed years. Exergetic improvement potential for this sector are also determined to be 332 PJ in 2004. It may be concluded that the methodology used in this study is practical and useful for analyzing sectoral and subsectoral energy and exergy utilization to determine how efficient energy and exergy are used in the sector studied. It is also expected that the results of this study will be helpful in developing highly applicable and productive planning for energy policies.     

Impact of hydrogen production on optimal economic operation of a grid-parallel PEM fuel cell power plant

This paper presents an economic model of a PEM fuel cell power plant (FCPP). The model includes the operational cost, thermal recovery, power trade with the local grid, and hydrogen production. The model is used to determine the optimal operational strategy, which yields the minimum operating cost. The optimal operational strategy is achieved through estimation of the following: hourly generated power, thermal power recovered from the FCPP, power trade with the local grid, and hydrogen production. An evolutionary programming-based technique is used to solve for the optimal operational strategy. The model is tested using different seasonal load demands. The results illustrate the impact of producing hydrogen on the operational strategies of the FCPP when subjected to seasonal load variation. Results are encouraging and indicate viability of the proposed model.     

Performance enhancement in coal fired thermal power plants. Part II: steam turbines

This paper presents the results of the performance enhancement study on 22 coal fired thermal power stations of capacities 30–500 MW. The oldest units (30 MW) have served for 33yr and the newer units (500 MW) have been in operation since 7yr. The turbine efficiencies are in the range 31·00–41·90% as compared to the design range of 34·80–43·97%. The isentropic efficiencies are in the range 74·13–86·40% as compared to design values of 83·20–89·10%. Considerable scope for efficiency improvement through low cost solutions: operational optimization, capital overhaul, simple modifications, etc., exists for all classes of units. The efficiencies can be restored to their design values. The developments in turbines over the last quarter of this century which have led to improved isentropic and thermal efficiencies must be adopted for existing units through retrofits, upgrades and revamps. The turbine efficiencies can be improved to 38·0% for 30 MW units and to 47% for 500 MW units. The maximum potential is for improvement in 210 and 500 MW units followed by 110 and 120 MW units. The potential for 30 and 62·5 MW units is rather limited because of their low capacity share, lack of interest in manufacturers to sell spares (because of the low volume of requirement) and large pay back periods for modernisation schemes. Copyright © 1999 John Wiley & Sons, Ltd.     

Economics of hydrogen production and utilization strategies for the optimal operation of a grid-parallel PEM fuel cell power plant

This paper integrates the hydrogen production and utilization strategies with an economic model of a PEM fuel cell power plant (FCPP). The model includes the operational cost, thermal recovery, power trade with the local grid, and hydrogen management strategies. The model is used to determine the optimal operational strategy, which yields the minimum operating cost. The optimal operational strategy is achieved through estimation of the following: hourly generated power, thermal power recovered from the FCPP, power trade with the local grid, and hydrogen production. An evolutionary programming-based technique is used to solve for the optimal operational strategy. The model is tested using different seasonal load demands. The results illustrate the impact of hydrogen management strategies on the operational cost of the FCPP when subjected to seasonal load variation. Results are encouraging and indicate viability of the proposed model.