Optimal synthesis and design of Heat Recovery Steam Generation (HRSG) via mathematical programming

Thermal efficiency of Combined Cycle Power Plants (CCPPs) depends strongly on the Heat Recovery Steam Generation (HRSG) design which links the gas cycle with the steam cycle. Therefore, the HRSG must be carefully designed in order to maximize the heat exchanged and to improve the overall performance of the plant.In this paper, a mixed integer non-linear programming (MINLP) model to simultaneously optimize the equipment arrangement, geometric design and operating conditions of CCPPs is proposed. General Algebraic Modelling System (GAMS) is used to implement and to solve the mathematical model. The HRSG model involves discrete decisions connected with the geometric design and the selection of tube diameters as well as the length and width of each solid fin. Continuous variables are used to model the operating conditions of the HRSG and steam turbines (ST). The solution strategy for the resulting model comprises two phases: the first one focuses the process optimization but considering only global energy and mass balances and this phase provides initial-bounds values for the second phase where the complete and rigorous model involving discrete decisions is solved. Different case studies with increasing complexity have been successfully solved. Model validation and results obtained from the MINLP model by considering different objective functions are discussed.     

四大热电中心接入对北京电网的影响研究

对四大热电中心接入系统对北京电网的影响展开研究,分析了四大热电中心输电电压等级选择以及接入系统形式,研究了四大热电中心接入系统对电网短路水平、稳定、无功和调峰能力的影响,并根据研究结果提出了相关建议.     

长春市新建民用建筑采用热电联产的效果评价

本论文探讨了长春市新建民用建筑采用热电联产时的节能、环保和经济效果。由长春和东京气候条件的相似性,以东京能源消耗强度为基础,利用修正系数推算长春能源消耗强度。根据不同建筑用途的建筑面积和能源消耗强度,计算了长春市新建民用建筑的能源需要量。本研究设立了空调系统、锅炉系统、热主电从和电主热从系统。同时,设定了设备效率和价格、能源价格和二氧化碳排放强度等参数。计算四种能源供给系统的一次能源消费量、二氧化碳排放量、初期投资、运行费用和单纯回收年数。计算结果为:与空调系统相比,锅炉系统、热主电从和电主热从的热电联产系统的节能率分别为-2.1%、21.2%和6.0%;二氧化碳排放量的消减率分别为-0.7%、24.1%和9.4%;单纯回收年数分别为8.0,5.2和3.5年。     

冷热电联产技术的探讨

介绍了冷热电联产的原理及特点。现今,冷热电联产系统越来越广泛的被应用在为单个建筑物及区域内多个建筑物提供能源上。该系统不仅具有节能环保效益,而且在供电安全、缓解电力短缺及改善能源结构等方面上提供了有效的措施。     

Understanding the design and economics of distributed tri-generation systems for home and neighborhood refueling—Part I: Single family residence case studies

The potential benefits of hydrogen as a transportation fuel will not be achieved until hydrogen vehicles capture a substantial market share. However, although hydrogen fuel cell vehicle (FCV) technology has been making rapid progress, the lack of a hydrogen infrastructure remains a major barrier for FCV adoption and commercialization. The high cost of building an extensive hydrogen station network and the foreseeable low utilization in the near term discourages private investment. Based on the past experience of fuel infrastructure development for motor vehicles, innovative, distributed, small-volume hydrogen refueling methods may be required to refuel FCVs in the near term. Among small-volume refueling methods, home and neighborhood tri-generation systems (systems that produce electricity and heat for buildings, as well as hydrogen for vehicles) stand out because the technology is available and has potential to alleviate consumer's fuel availability concerns. In addition, it has features attractive to consumers such as convenience and security to refuel at home or in their neighborhood.The objective of this paper is to provide analytical tools for various stakeholders such as policy makers, manufacturers and consumers, to evaluate the design and the technical, economic, and environmental performances of tri-generation systems for home and neighborhood refueling. An interdisciplinary framework and an engineering/economic model is developed and applied to assess home tri-generation systems for single family residences (case studies on neighborhood systems will be provided in a later paper). Major tasks include modeling yearly system operation, exploring the optimal size of a system, estimating the cost of electricity, heat and hydrogen, and system CO₂ emissions, and comparing the results to alternatives. Sensitivity analysis is conducted, and the potential impacts of uncertainties in energy prices, capital cost reduction (or increase), government incentives and environmental cost are evaluated. Policy implications of the modeling results are also explored.     

家用热电联供产品(MCHP)的设计要求与原动机的选择

探讨了家用热电联供产品设计要求，展现了燃气热气机作为家用热电联供产品原动机的优势，并分析了燃气热气机家用热电联供产品的应用前景。根据我国国情，MCHP的输出功率应以1kw为主，同时可输出热水功率4～5kW。MCHP要求体积小，重量轻，噪声低，适合在居住环境下使用。燃气热气机作为MCHP的原动机，其最理想的是采用自由活塞结构，但是目前采用斜盘式或摆盘式传动结构则更为现实。     

Heat pumps and combined heat and power a technology assessment

This paper utilizes a novel system boundary and methodological framework for comparing the technical, economic and institutional factors affecting the development of advanced heating technologies. The focus is on the USA where electric heat pump technology has recently gained widespread acceptance; parts of the centralized combined heat and power (CHP) industry are in a state of decline; and a rapidly changing regulatory environment is stimulating development of small decentralized gas-fired CHP systems.     

Combined heat and power considered as a virtual steam cycle heat pump

The first aim of this paper is to shed light on the thermodynamic reasons for the practical pursuit of low temperature operation by engineers involved in the design and the operation of combined heat and power (CHP) and district heating (DH) systems. The paper shows that the steam cycle of a combined heat and power generator is thermodynamically equivalent to a conventional steam cycle generator plus an additional virtual steam cycle heat pump. This apparently novel conceptualisation leads directly to (i) the observed sensitivity of coefficient of performance of CHP to supply and return temperatures in associated DH systems, and (ii) the conclusion that the performance of CHP will tend to be significantly higher than real heat pumps operating at similar temperatures. The second aim, which is pursued more qualitatively, is to show that the thermodynamic performance advantages of CHP are consistent with the goal of deep, long-term decarbonisation of industrialised economies. As an example, estimates are presented, which suggest that CHP based on combined-cycle gas turbines with carbon capture and storage has the potential to reduce the carbon intensity of delivered heat by a factor of ∼30, compared with a base case of natural gas-fired condensing boilers.     

Biomass-Based Combined Heat and Power Systems

This study aims to identify and evaluate the biomass utilization options and evaluate the sustainable biomass production for combined heat and power (CHP) in Turkey. The total biomass energy potential of Turkey is about 32 Mtoe. The amount of usable biomass potential of Turkey is approximately 17 Mtoe. Among the biomass energy sources, fuel wood seems to be one of the most interesting because its share of the total energy production of Turkey is high at 21%. The use of biofuels for CHP on a large scale is focused mainly on forest industry sites, where considerable quantities of biomass are available. Biomass available for energy can be converted to different types of final energy (e.g., electricity, heat), of these, the production of electricity appears to be particularly important. While CHP provides several environmental benefits by making use of waste heat and waste products, air pollution is a concern any time fossil fuels or biomass are burned.     

Power plant perspectives for sugarcane mills

Biomass, integral to life, is one of the main energy sources that modern technologies could widely develop, overcoming inefficient and pollutant uses. The sugarcane bagasse is one of the more abundant biomass. Moreover, the fluctuating sugar and energy prices force the sugarcane companies to implement improved power plants. Thanks to a multiyear collaboration between University of Rome and University of Piura and Chiclayo, this paper investigates, starting from the real data of an old sugarcane plant, the energy efficiency of the plant. Furthermore, it explores possible improvements as higher temperature and pressure Rankine cycles and innovative configurations based on gasifier plus hot gas conditioning and gas turbine or molten carbonate fuel cells. Even if the process of sugar extraction from sugarcane and the relative Rankine cycles power plants are well documented in literature, this paper shows that innovative power plant configurations can increase the bagasse-based cogeneration potential. Sugarcane companies can become electricity producers, having convenience in the use of sugarcane leaves and trash (when it is feasible). The worldwide implementation of advanced power plants, answering to a market competition, will improve significantly the renewable electricity produced, reducing CO₂ emissions, and increasing economic and social benefits.     

Combined cooling, heating and power: A review

Combined cooling, heating and power (CCHP) systems, including various technologies, provide an alternative for the world to meet and solve energy-related problems, such as energy shortages, energy supply security, emission control, the economy and conservation of energy, etc. In the first part of this paper, the definition and benefits of CCHP systems are clarified; then the characteristics of CCHP technologies—especially technical performances—are presented, as well as the status of utilization and developments. In the third part, diverse CCHP configurations of existing technologies are presented, particularly four typical systems of various size ranges. The worldwide status quo of CCHP development is briefly introduced by dividing the world into four main sections: the US, Europe, Asia and the Pacific and rest of the world. It is concluded that, within decades, promising CCHP technologies can flourish with the cooperative efforts of governments, energy-related enterprises and professional associations.     

热电(冷)联产系统的优化性能

依据有限时间热力学原理导出了不可逆热电联产和热电(冷)联产系统在系统最大火用输出时的基本优化关系,确定了热电(冷)联产系统优化参数和优化构形选取范围,得到了供热(制冷)和发电间的匹配优化特性,通过数值算例得出不同参数对系统性能影响的规律。所得结论可为热电(冷)联产系统的优化设计和最佳工况选择等提供理论依据。     

Hydrogen,ethylene and power production from bioethanol: Ready for the renewable market?

The economic sustainability of renewable based sources is a matter of debate and the technology is changing very fast. We here considered three examples of exploitation of bioethanol as renewable source: a) centralised hydrogen prodution; b) heat and power cogeneration (residential scale); c) ethylene production. Bioethanol can be a suitable starting material for the production of H₂, as fuel or chemical, or syngas. After designing the process and the implementation of kinetic expressions based on experimental data collected in our lab or derived from the literature, an economic evaluation and sensitivity analysis allowed to assess the economic sustainability of hydrogen production and purification by the steam reforming of bioethanol. The attention was mainly put on diluted bioethanol solutions, easy to purify and cost effective. The centralised hydrogen production from bioethanol was considered cost effective at least starting from diluted bioethanol from first generation crops. When dowscaling the hydrogen production and purification unit to feed a 5 kW fuel cell, the most undetermined item was the fuel cell cost, since no acclarate market price is still available.Finally, ethylene market is steadily increasing by ca. 4% each year due to economic growth. The demand for renewable ethylene, as well as the increasing oil price experienced in the recent past, suggested the development of alternative routes to ethylene. Based on the increasing availability of ethanol form renewable biomass, bioethanol-to-bioethylene processes have been recently designed, finding economic sustainability, at the moment, in Brazil.     

Heat accumulators in CHP networks

In a Combined Heat and Power (CHP) network, it is sometimes optimal to install a device for storing heat from one period of time to another. Several possibilities exist. If the electricity demand is high, while at the same time the district heating load is too small to take care of the heat from the CHP plant, it could be optimal to store heat from peak periods and discharge the storage under off-peak. It might also be optimal to store heat during off-peak and use it under the district heating peak load. The storage is then used for decreasing either the district heating demand or for decreasing the electricity load used for space heating. The paper shows how a mixed integer program is developed for use in the optimization process. As a case study, the CHP system of Malmö, Sweden, is used. Further, a sensitivity analysis is elaborated in order to show how the optimal solution will vary due to changes in certain input data.     

Design of a combined heat,hydrogen, and power plant from university campus waste streams

This paper presents analysis of a combined heat, hydrogen, and power (CHHP) plant for waste-to-energy conversion in response to the 2012 Hydrogen Student Design Contest. Our team designed the CHHP plant centered on a molten carbonate fuel cell (Fuel Cell Energy DFC-1500) fueled by syngas derived primarily from an oxygen-fed municipal waste gasifier. Catalytic methanation and supplemental utility natural gas increase the fuel methane content to meet the DFC-1500 fueling requirements for maintaining stack thermal energy balance. Internal reforming converts excess fuel from the fuel cell to an H₂-rich stream, which is purified downstream in a pressure-swing adsorption system. The separated H₂ (1000 kg per day) is compressed for storage to provide fuel for a campus fleet of PEM fuel cell buses. The system provides more than 1.1 MWe for the campus grid with approximately 20% of the fuel cell power used for H₂ compression and running the plant. Heat recovery steam generators provide steam for the methanation reactor and 0.4 MW of thermal energy for district heating or steam turbine-driven chillers. Cost analysis indicates that the system requires incentives for economic viability with current estimated operating costs, but advances to reduce capital expenses of comparable urban waste-driven CHHP systems can make them attractive for future implementation.     

A novel method for the design of CHCP (combined heat,cooling and power) systems for buildings

The design of capacity and operation of CHCP (combined heat, cooling and power) plants applied to HVAC (heating, ventilation and air conditioning) in buildings entails a considerable difficulty, because efficiency and economic aspects frequently interact in a complex way. Due to the strong fluctuations in thermal demands, the evaluation of a given design usually requires detailed simulations and a significant amount of input data. This paper proposes simplified approaches to estimate the main parameters characterising the thermal performance of the plant (ATD_e method) as well as to identify optimal designs for a given application under certain encouragement policies (annual PES (primary energy savings) strategy). In the ATD_e method, the duration curve of ATD (aggregated thermal demand) is used to estimate, among others, the amount of heat and cooling effectively supplied to the final user for a given design of the plant. This procedure serves to achieve a quick, global evaluation of the thermal performance of CHP (combined heat and power) or CHCP plants with little computational effort. The annual PES strategy searches the optimal values for the engine capacity, the OP (operation period) or both for CHP and CHCP plants in a particular application, defined by its energy demands. Both methods have demonstrated a notably good performance in several test cases with different patterns of the thermal demands.     

Investigation on performance of an integrated solid oxide fuel cell and absorption chiller tri-generation system

An integrated tri-generation system incorporating a solid oxide fuel cell (SOFC) and a double-effect water/Lithium Bromide absorption chiller is presented in this paper. The proposed tri-generation system can provide power, cooling or heating simultaneously with a typical gas produced from a gasication process. The system conguration and design are discussed, and the energy and mass balances are obtained through the matrix representation method and integrated into a simulation program by MATLAB soft package. The developed model comprises of three modules: SOFC module, exhaust combusting and HRSG module, and the absorption chiller module. Validation of the SOFC model is performed by comparison with a single tubular cell of Siemens-Westinghouse, and a specific case study of the system is presented. For parametric analysis, the fuel utilization ratio, fuel flow ratio and air inlet temperature are investigated and the results are discussed in detail.     

Hydrogen and electricity co-production plant integrating steam-iron process and chemical looping combustion

In this paper, steam-iron process (Fe looping) and NiO-based chemical looping combustion (Ni looping) are integrated for hydrogen production with inherent separation of CO₂. An integrated combined cycle based on the Fe and Ni loopings is proposed and modeled using Aspen Plus software. The simulation results show that at Fe-SR 815 °C, Fe-FR 815 °C, Ni-FR 900 °C and Ni-AR 1050 °C without supplementary firing, the co-production plant has a net power efficiency 14.12%, hydrogen efficiency 33.61% and an equivalent efficiency 57.95% without CO₂ emission. At a supplementary firing temperature of 1350 °C, the net power efficiency, hydrogen efficiency and the equivalent efficiency are 27.47%, 23.39% and 70.75%, respectively; the CO₂ emission is 365.36 g/kWh. The plant is attractive because of high-energy conversion efficiency and relatively low CO₂ emission; moreover, the hydrogen/electricity ratio can be varied in response to demand. The influences of iron oxide recycle rate, supplementary firing temperature, inert support addition and other parameters on the system performance are also investigated in the sensitive analyses.     

A critical review on design aspects and developmental status of metal hydride based thermal machines

Over two decades, research in the field of metal hydride based thermal machines has gained immense attention by the researchers of different fields. Because of its capability to store large volume of hydrogen per unit mass at near ambient condition, its utilization has been spread in numerous applications such as energy storage and other biological, chemical, aerospace and nuclear applications. Though there have been several review reports published on metal hydride based hydrogen storage, but the present work is focused on the thermal management issues and worldwide developmental status of various metal hydride based thermal machines such as thermal energy storage, heat upgradation, heat pump, cooling system, and hydrogen purification and compression. With a brief discussion about the basic understanding of metal hydride alloy formation, this paper also covers screening of metal hydride alloys, design considerations and evolution of different reactor geometries for various metal hydride based thermal management systems. The review also addresses the benefit of coupling of a metal hydride based hydrogen energy system with a conventional thermal system in order to a produce hybrid system with much higher performance and almost zero environmental pollution.     

Total Site Hydrogen Integration with fresh hydrogen of multiple quality and waste hydrogen recovery in refineries

This paper proposes a novel method combining Pinch Methodology and waste hydrogen recovery, aiming to minimise fresh hydrogen consumption and waste hydrogen discharge. The method of multiple-level resource Pinch Analysis is extended to the level of Total Site Hydrogen Integration by considering fresh hydrogen sources with various quality. Waste hydrogen after Total Site Integration is further regenerated. The technical feasibility and economy of the various purification approaches are considered, demonstrated with a case study of a refinery hydrogen network in a petrochemical industrial park. The results showed that fresh hydrogen usage and waste hydrogen discharge could be reduced by 21.3% and 67.6%. The hydrogen recovery ratio is 95.2%. It has significant economic benefits and a short payback period for Total Site Hydrogen Integration with waste hydrogen purification. The proposed method facilitates the reuse of waste hydrogen before the purification process that incurs an additional environmental footprint. In line with the Circular Economy principles, hydrogen resource is retained in the system as long as possible before discharge.