Design and Optimization of an Innovative Solid Oxide Fuel Cell–Gas Turbine Hybrid Cycle for Small Scale Distributed Generation

Distributed power generation and cogeneration is an attractive way toward a more rational conversion of fuel and biofuel. The fuel cell‐gas turbine hybrid cycles are emerging as the most promising candidates to achieve distributed generation with comparable or higher efficiency than large‐scale power plants. The present contribution is devoted to the design and optimization of an innovative solid oxide fuel cell–gas turbine hybrid cycle for distributed generation at small power scale, typical of residential building applications. A 5 kW planar SOFC module, operating at atmospheric pressure, is integrated with a micro gas turbine unit, including two radial turbines and one radial compressor, based on an inverted Brayton cycle. A thermodynamic optimization approach, coupled with system energy integration, is applied to evaluate several design options. The optimization results indicate the existence of optimal designs achieving exergy efficiency higher than 65%. Sensitivity analyses on the more influential parameters are carried out. The heat exchanger network design is performed for an optimal configuration and a complete system layout is proposed. An example of hybrid system integration in a common residential building is discussed.     

区域供冷供热系统冷热源方案经济性分析与比较

以某居民小区为例，对区域供冷供热系统的四种不同冷热源配置方案从初投资、年运行费用等方面进行比较和分析，从而确定出各个方案的可行性。     

Availability and reliability considerations in the design and optimisation of flexible utility systems

Industrial utility plants are usually comprised of many interconnected units that must constitute a flexible and reliable system capable of meeting process energy requirements under different circumstances (e.g. varying prices, demands, or equipment shutdowns). Also, in order to avoid large economic penalties, the design and operation of a utility plant should consider that the equipment is not fully reliable and that each item needs to receive preventive and corrective maintenance. Conventionally, these issues are handled by installing additional units according to rules of thumb or heuristics, which usually imply excessive capital costs and might even result in designs that cannot satisfy the specified demands for certain situations. In contrast, during the present work a systematic methodology has been developed to address the design and operation of flexible utility plants incorporating reliability and availability considerations. The suggested method is based on a novel modelling and optimisation framework that can address grassroots design, retrofit, or (pure) operation problems in which design and operational parameters are optimised simultaneously throughout several scenarios. Thereafter, it is possible to define maintenance and failure situations in different operating periods to ensure that the plant will be able to cope with them, while meeting process requirements at minimum cost. Hence, for design cases, the most cost-effective elements of redundancy can be determined without pre-specifying any structural options in the final configuration (e.g. equipment sizes, types, and number of units). Furthermore, the proposed (multiperiod) MILP formulation is robust enough to tackle problems of the size and complexity commonly found in industry, and has the potential of yielding significant economic savings.     

Energy and water in Kuwait: A sustainability viewpoint, Part II

In Kuwait, the daily consumption per capita of electric power is 14,000 kWh, and of desalted water is 600 L. These are among the highest in the world, and the total consumption of each is almost doubled every 10 years. The cogeneration power desalting plants CPDP producing these two commodities consumed about 54% of the total 150 millions barrels of fuel consumed in the year 2005. If these consumption and production patterns prevail, the fuel oil produced in the country can be fully consumed locally in 30 years, with nothing left for export, the main source of income. The picture can be changed if better desalted water and power production methods are used. These include changing the desalting method from multistage flash MSF known by its high energy consumption to the more energy efficient seawater reverse osmosis SWRO; and power production method of steam or gas turbine cycles to combined gas/steam turbine combined cycle known of its high efficiency. The energy consumed by the air conditioning AC systems should be reduced by using better codes of building insulation and more efficient AC systems. Other conservation methods to reduce water consumption and the energy consumed by transportation are outlined in this paper.     

甘蔗糖厂饱和渗透轻压提汁工艺及糖能联产方案分析

提出一种适应于糖能联产的甘蔗糖厂饱和渗透轻压提汁工艺,采用三辊重压、两辊轻压和饱和渗透的方法,其能耗较低,物料分配合理。比较分析了几种甘蔗加工工艺的经济效益,提出了单产糖和糖能联产生产工艺条件下简单、适应性强的利润计算公式,通过验证其准确性较好,为糖厂利润最大化提供了一种可靠方法。     

Modelling and Performance Evaluation of Solid Oxide Fuel Cell for Building Integrated Co‐ and Polygeneration

Models of fuel cell based combined heat and power systems, used in building energy performance simulation codes, are often based on simple black or grey box models. To model a specific device, input data from experiments are often required for calibration. This paper presents an approach for the theoretical derivation of such data. A generic solid oxide fuel cell (SOFC) system model is described that is specifically developed for the evaluation of building integrated co‐ or polygeneration. First, a detailed computational cell model is developed for a planar SOFC and validated with available numerical and experimental data for intermediate and high temperature SOFCs with internal reforming (IT‐DIR and HT‐DIR). Results of sensitivity analyses on fuel utilisation and air excess ratio are given. Second, the cell model is extended to the stack model, considering stack pressure losses and the radiative heat transfer effect from the stack to the air flow. Third, two system designs based on the IT‐DIR and HT‐DIR SOFCs are modelled. Electric and CHP efficiencies are given for the two systems, as well as performance characteristics, to be used in simulations of building integrated co‐ and polygeneration systems.