Evaluation of the reduction in CO2 emissions by applying Micro‐Grid to home energy supply system

Dispersed generators such as wind power systems, photovoltaic systems, and cogeneration systems are expected to mitigate the environmental burden of energy consumption, and their installation has been promoted recently. Micro‐Grid is focused on as a method to solve some problems in a commercial electric power line when installing a large number of dispersed generators, and some demonstrative research on Micro‐Grid for large‐scale systems is being carried out now. Also, small cogeneration systems for houses, such as gas engines and fuel cells, are expected to improve CO₂ emissions. However, if the power and heat demand of a family are relatively small or are unbalanced, the cogeneration system does not operate effectively. The authors have studied the application of Micro‐Grid for home energy supply, and have developed a control system to solve this problem. The system achieves a reduction of CO₂ emissions and energy costs by sharing electric power and heat among some houses with cogeneration systems. This paper presents an outline of the newly developed system, and in particular describes the effect of the reduction in CO₂ emissions compared with a conventional energy supply method, and the case in which dispersed generators are installed in some houses and operate independently. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(3): 19–27, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20879     

上海市燃气热电联产政策研究

在美国能源基金会的资助及上海有关部门和机构的合作和支持下 ,完成了燃气热电联产的政策研究。研究表明 :热电联产发展的主要障碍是电力并网难和上网电价缺乏竞争性 ,以及缺乏高素质的技术咨询队伍。研究的主要内容是 :透明和公正的热电联产机组电力并网规定 ;鼓励能源服务公司参与热电联产的投资、建设和管理 ;上海市热电联产管理办法 ;热电联产在上海的适用性 ;基于燃气热电联产的环保效益 ;应给予热电联产一定的政策优惠 ;鼓励燃气热电联产参与电力和燃气调峰     

Optimal Total Planning for Incinerator Plants in an Urban Area

This paper proposes optimal total planning for incinerator plants (IPs) in a typical urban area, which includes a method of determining the number of plants and the capacities of the IPs. Burnable municipal refuse is disposed of sanitarily by high‐temperature incineration at the IPs. At the same time, power generation from waste (PGW) is being performed at many IPs to recover energy. At present, the amount of energy generated by PGW is greater than that of wind power or photovoltaic power generation. However, PGW has a limited generation efficiency and low generation output due to the smaller capacity of IPs. To overcome the above weakness, highly efficient PGW is necessary with total integration and scaling up of IPs. Regarding total integration and scaling up, operation in larger areas is favorable from the point of view of refuse volume and collection. In the planning stage, both the cost of IPs and refuse collection, which is important for refuse disposal, should be taken into account comprehensively. Optimal total planing for IPs can be performed in two stages. First, the disposal capacity G_k of an IP versus the number of plants K is decided by constraints. G_k is about the same for all K because of maintenance and refuse collection, and is greater than 300 tons per day in steps of 100 tons per day. G_k should be decided not only by refuse volume but also by cessation of operation at plants due to maintenance or faults. Second, the cost of each value of K is calculated based on the construction and operating costs of the IPs, income from selling the energy of PGW, and refuse collection costs. Therefore, the value of K with the minimum cost is selected as the optimal number of IPs. A numerical simulation of an area with a population of 3 million indicates that the optimal plant number is 4. At present there are eight or nine IPs in cities of 3 million people. The above cost reduction effect will be about 15% from the present value. Considering the situation of aging IPs, a decreasing trend in refuse volume, and the stringent financial conditions of local governments, the proposed method is very effective and realistic.     

Optimal planning of cogeneration systems under time-of-use rates

For commercial customers with a cogeneration system (CGS), a mixed integer programming model is used to examine effects of time-of-use (TOU) rate structure on the optimal operation of the system as well as its optimal capacity. Three case studies are performed for a hotel, a hospital, and an office building (20,000 m² in total floor space, respectively). The optimal capacity of the generator under the flat rate is 50 to 70 percent of peak power demand. Effects of the on-peak/off-peak energy charge ratio are saturated at a ratio of 5. It is not until an energy charge ratio of between 2 and 5 that the purchase of off-peak power increases in summer when price reduction is applied to city gas. As the energy charge ratio is raised, cheaper off-peak power is substituted for city gas and the sum of electricity energy charge and gas energy charge decreases. The simulation results indicate that properly designed TOU rates may provide commercial customers an incentive to operate a cogeneration system with an appropriate mix of the self-generation and commercial power.     

燃气轮机热电联产系统的热力学分析及用能改进建议

给出了燃气轮机热电联产系统热力学分析(能量平衡分析和分析)评价准则及计算式。利用实测运行参数,对一个燃气轮机热电联产系统进行了运行工况下的热力学分析,找出了系统的用能薄弱环节。根据测算分析结果,提出了提高系统运行效率的三个建议。     

Increase of breakdown voltage due to composite insulation in SF6 gas

The breakdown characteristics using a hemispherical tip rod (10 ～ 60 mm) molded with epoxy resin-to-plate gap in SF₆ gas up to 0.20 MPa was studied. The result shows that breakdown characteristics are classified into three regions (A, B and C region) depending on gap length. In the A-region breakdown voltage is lowered compared with bare hemispherical tip rod-to-plate gap. In the B-region breakdown voltage is raised sharply with gap length and in the C-region it saturates. The maximum increase ratio of breakdown voltage in the B and C region are 1.95 times (ac) and 1.68 times (impulse) compared with a bare hemispherical tip rod-to-plate gap characteristic. The ratios depend on the diameter of the spherical tip rod and the thickness of epoxy resin. It is concluded that the increase of breakdown voltage is attributed to the synergism effect of the decrease of maximum electric field strength by epoxy resin and the suppression of field emission. The use of composite insulation reduces the gap length drastically in the gas-insulated switchgear, for instance, C-GIS (Cubicle-type Gas-Insulated Switchgear).     

Cogeneration systems planning using structured genetic algorithms

This paper proposes a new approach to plan cogeneration systems, that of distributed energy systems. The proposed approach uses structured genetic algorithms. Cogeneration systems planning provides optimal allocation of cogeneration systems, a layout of the pipeline network structure for distributing heat energy between cogeneration systems and demand areas, and optimal heat and electric energy supply to meet the energy demands. The planning is formalized as a combinatorial optimization problem with minimizing cost of energy supply as its objectives. The traditional solution method is based on mathematical programming methods. But it is difficult to get an optimal solution as the number of areas increases because of combinatorial explosion and nonlinearity. This paper describes a new method to solve the cogeneration systems planning based on genetic algorithms. The solution of the cogeneration systems planning problem has a network structure. The proposed method applies structured genetic algorithms whose genotype has a tree structure to represent a network structure. The characteristics of the proposed method are analyzed by applying the new method to empirical data of the area around station K. © 1997 Scripta Technica, Inc. Electr Eng Jpn 119(2): 26–35, 1997     

Moment performance of photovoltaic/thermal hybrid panel (numerical analysis and exergetic evaluation)

A photovoltaic/thermal hybrid panel (PV/T) is a high‐efficiency energy converter which supplies electrical energy and thermal energy from solar energy. In this paper, we report characteristics of two PV/T types under various environmental conditions and fluid flow rates, using numerical analysis. We found photovoltaic efficiencies to be 9.61% for PV/T_A and 10.56% for PV/T_B at T _c = 25 °C; thermal ones were 52.11% for PV/T_A and 40.14% for PV/T_B at T_f = 40 °C, I_rr = 800 W/m². From these results, we propose some design points to construct the optimum structure of PV/T. Next, we adopted exergetic evaluation to study electrical energy and thermal energy quantitatively. As a result, we could confirm the existence of flow rate maximizing the total efficiency (optimum flow rate) on some environmental condition, and could define the optimum operating condition. Moreover, we compare exergetic efficiencies on optimum operating conditions (maximum exergetic efficiency) under various environmental conditions with PV, PV/T_A, and PV/T_B. A rise of maximum exergetic efficiency with increasing irradiance yielded –3.6%/kW ⋅ m^–2, +3.6%/kW ⋅ m², and +1.4%/kW ⋅ m², respectively. Nevertheless, we could confirm a hybridizing advantage of high irradiance. © 2000 Scripta Technica, Electr Eng Jpn, 133(2): 43–51, 2000     

On the ionic conductivity of strongly acceptor doped, fluorite-type oxygen ion conductors

We present an analytical model for the ionic conductivity of a strongly acceptor doped, fluorite-type oxygen ion conductor, (A_{1 −} x _B B _{x B} )O_{2 − x B/2}, i.e. a concentrated solution of AO₂ and B₂O₃, which can be applied, e.g., to yttria doped zirconia (YSZ). The model considers nearest neighbor interactions between oxygen vacancies and dopant cations, which may be negligible, attractive or repulsive. The vacancies are distributed to the tetrahedra formed by the cations using quasi-chemical reactions for the exchange between the different sites. The resulting vacancy distribution is used in a simplified model for the oxygen ion conductivity which considers jump rates between different oxygen sites that depend on their local neighborhood and the nature of the cation-cation edge which has to be crossed during a jump between edge-sharing tetrahedra. Among the various possibilities, only attractive dopant-vacancy interaction together with reduced jump rates through A-B and B-B edges (compared to A-A edges) can explain satisfactorily the experimental findings, i.e. the maximum of the conductivity at dopant fractions x _B ≈ 0.15, the slight decrease of the activation energy with increasing temperature and the increase of activation energy with dopant fraction.     

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.     

Magnetic core properties and their thermal stability in a BCC Fe-Zr-B-Cu alloy with nanoscale grain size

A mostly single bcc phase with nanoscale grain size of 10 to 20 nm has been found to form by annealing amorphous Fe-Zr-B, Fe-Hf-B and Fe-M-B-Cu (M = Ti, Zr, Hf, Nb and Ta) alloys. It has further been clarified that the newly developed nanocrystalline bcc alloys exhibit high permeability (μ_e) combined with high saturation magnetization (B_s). Subsequently, the possible application potentials of the bcc alloys were investigated. The core loss is as small as 66 mW/kg at 1 T and 50 Hz for a nanocrystalline bcc Fe₈₆Zr₇B₆Cu₁ alloy obtained by annealing for 3.6 ks at 873 K. This value is 45 and 95 percent smaller than those for amorphous Fe₈₆Si₉B₁₃ alloy and Fe-3.5 percent Si alloy, respectively, which are presently in use as core materials in electric power transformers. The frequency dependence of the core loss for the bcc alloy at 0.2 T is almost the same as that for an amorphous Co_70.5Fe_4.5Si₁₀B₁₅ alloy with zero magnetostriction. In the frequency range of 10 to 300 kHz, the core loss for the bcc alloy is slightly smaller than the Co base amorphous which has been used as core material in high-frequency transformers. Furthermore, the core losses of the nanocrystalline Fe₈₆Zr₇B₆Cu₁ alloy also were found to have high stability against thermal aging. Thus, nanocrystalline bcc Fe-Zr-B-Cu alloys with the advantages of high B_s, high μ_e, and low core loss is expected to be used as a core material in various transformers.     

Energy Economics of a Modern Suspension Preheater Plant Compared to a Modern Plant Incorporating Cogeneration

The rising cost of fuel experienced over the past several years has caused the cement industry to look for more energy efficient systems for producing cement. Probably the most popular system has been the suspension preheater, frequently coupled with a roller mill, a flash calciner, or both. While these systems have yielded greatly improved fuel efficiencies, they have also contributed to higher consumption of electrical energy. This, coupled with the rapid rise in cost of electrical energy, has led to a renewed interest in cogeneration, wherein the heat contained in the kiln off-gases is used to produce steam to run turbine generators, thereby increasing the use of lower cost fuel energy while decreasing the use of higher cost purchased electric power energy. The production cost of a suspension preheater is different than for a plant utilizing cogeneration, so the production cost per ton of the two systems is compared, and the differences are used to determine the feasibility of cogeneration for a specific set of conditions. Two cogeneration cases will be examined. One is a plant utilizing generated power from waste heat only, all of which is consumed by the plant. The other is a plant which not only utilizes waste heat power but also produces for sale back to the utility company.     

Analysis of the fuel efficiency of gas-turbine cogeneration stations

A technique for evaluating the fuel efficiency of the combined generation of electricity and heat at a gas-turbine cogeneration station is presented. The effects the regeneration degree of the gas-turbine cycle and the temperature of gas upstream the turbine have on the fuel efficiency of a gas-turbine cogeneration station are estimated for different ratios between its thermal and electric outputs. It is shown that the use of a gas-turbine cogeneration station for generating energy allows the expenses for the fuel to be cut by as much as $2 million a month.     

Optimization of multiplant cogeneration system operation includingelectric and steam networks

The problem of optimizing the short-term operation of a multiplant cogeneration system in a large industrial complex is solved. A cogeneration system is defined as a system that simultaneously produces electric power (electricity) and thermal power (steam). The cogeneration system model includes both the electric and thermal systems. The electric system model includes generation and transmission. The thermal system model includes the individual plants, which comprise boilers, turbines, condensers, deaerators, pumps, and storage tanks and the interconnecting steam network. The optimization problem has as its objective the minimization of the overall cost of all fuels and make up water used during the scheduling horizon (1 to 24 h), subject to satisfying a number of constraints on electric and steam systems. A novel solution approach is introduced which is based on coordinated optimization of the electric and thermal systems. A production-grade computer program has been developed and tested for a real industrial complex     

CO2 reduction effect of the utilization of waste heat and solar heat in a city gas system

We evaluated total energy consumption and CO₂ emissions in the phases of a city gas utilization system from obtaining raw materials to consuming the product. Assuming monthly and hourly demand figures for electricity, heat for space heating, and hot water in a typical hospital, we explore the optimal size and operation of a city gas system that minimizes the life cycle CO₂ emissions or total cost. The cost‐effectiveness of conventional cogeneration, a solar heating system, and hybrid cogeneration utilizing solar heat is compared. We formulate a problem of mixed integer programming that includes integral parameters that express the state of system devices such as the on/off condition of switches. As a result of optimization, the hybrid cogeneration can reduce annual CO₂ emissions by 43% compared with the system without cogeneration. The sensitivity of CO₂ reduction and cost to the scale of the CGS is also analyzed. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 149(1): 22–32, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10369     

Examination of simple analytical method for calculating 60-Hz magnetic field in power substations

In the last decade, increasing attention has been paid to ELF (Extremely Low Frequency) electromagnetic environments in work areas as well as in and near homes, regarding their interaction both with electric apparatus such as CRT's and with biological systems. Experimental and theoretical analyses are presented of 60 Hz magnetic field (B-field) characteristics at and near ground level in both 187/66-kV EHV and 66/6.6-kV HV power substations. Experimental results of B-field profiles along horizontal paths as well as harmonic contents in B-field waveforms at several positions are shown and discussed. Furthermore, analytical B-field profiles calculated by using a B-field approximation method based on Biot-Savart law are shown and compared with the measured ones. The comparisons verify that the assumptions employed are applicable to the substation B-field calculation, and that the B-field calculation method employed can estimate B-field in EHV and HV power substation to significant accuracy, except for areas where localized B-field sources, such as power transformers and underground power cables, exist. The analytical profiles of three orthogonal components of B-field are also described in terms of equiflux contour maps, which show 3-D characteristics of B-field in power substations.     

考虑高比例新能源消纳的微能源网日前经济调度

能源危机是目前全球各国面临的共同难题,各国专家学者均积极研究能源可持续利用.因此,可再生能源逐渐受到研究者们的青睐,新能源并网比例不断增加.但是由此引发的新能源消纳问题是一大挑战.为解决这一问题,在由热电联产机组、燃气轮机、电锅炉、电转气设备及储能设备组成的微能源网中,在考虑电负荷需求响应的同时,在微能源网中引入电动汽...     

Electric Utility Energy Storage Systems for Peak Shaving

ABSTRACT

The state of the art of energy storage systems used by the electric utilities for peak shaving is discussed. The underlying concepts for the operation of the most important available schemes have been described. Whenever applicable the economics of the energy storage schemes as well as the cost expressed in §/Kw of electric capacity have been provided. In addition, the procedure used in modeling an energy storage system for planning purposes has been explained. The paper concludes with a prediction of the trend expected in future expansions of electric power plants.     

我国热电联产产业的发展趋势

介绍了国内外热电联产产业发展的现状和热电联产的优势,分析了今后我国热电联产机组的发展模式,指出今后我国热电联产产业应以大容量、高参数的热电联产机组和分布式能源系统这两个模式为主,并大力发展CFB锅炉、燃气轮机技术和研发高温气冷核反应堆技术。     

分布式能源供应系统的优良方式 --燃气冷热电联供

从一次能源的利用率、总热效率、节能和应用效果等方面论述了燃气冷热电联供是我国推行分布式能源供应系统的优良方式。