Operation Of Cogeneration System Research Articles

Thermodynamic Comparison of the Steam Ejectors Integrated at Different Locations in Cogeneration Systems

Under the challenge of global energy transition, coal-fired cogeneration systems are undergoing a technical revolution towards enhanced efficiency, heating capacity, and flexibility. In this paper, four schemes using a steam ejector integrated into a cogeneration system are designed. Considering operational safety, integrated locations are selected at the front and back of high- and medium-pressure turbines. Subsequently, the thermodynamic and operational characteristics under both design and off-design conditions are analyzed based on a model built in EBSILON Professional. Finally, a sensitivity analysis of the heating process is conducted. The results show that the integration of steam ejectors can increase the waste heat recovery ratio of exhaust steam by 18.42–45.61% under design conditions. The largest waste heat recovery ratio is obtained in System 4, resulting in the power generation efficiency (ηg) and gross energy utilization efficiency (ηp) of 81.95% and 65.53%, respectively. Meanwhile, the steam ejector can expand the power-load regulation range of the cogeneration system, and System 4 has the lowest lower power limit among all the systems. The ηp values of Systems 1–4 reach extreme values at different mixed steam pressures of the ejector. Increasing the pinch point temperature difference reduces the power load ηg and ηp of Systems 1–4. The results provide technical solutions for improving the heating capacity and efficient and flexible operation of cogeneration systems.

Collaborative configuration and optimal operation of cogeneration system based on phase change heat storage

Given the low efficiency of heating and power supply caused by the low temperature in the Northeast during the heating process of the solar heat pump, the article first adds phase change hot storage device based on time-sharing control based on the traditional PVT collector — heat pump, and constructs a flexible thermoelectric coupling multi-energy system by shifting the peak and filling the valley; Secondly, based on TRNSYS software, the simulation model of PVT collector-heat pump-phase change heat storage-electrical coupling combined supply system is built. By comparing with the heat storage system using an ordinary heat storage tank, the results show that the phase change water tank system can significantly improve the system performance. Finally, Hooke-Jeeves is used to optimize the inclination angle, area, volume of the tank, and heating capacity of the air source heat pump of the PVT collector of the thermal-electric coupling system, to increase the system’s one-year operation.

Design and Modelling of Heat-Coupled Storage System with High- and Low-Pressure Bypass: Electrothermal Characteristics and Peak Regulating Performance

To achieve a balance between supply and demand during cogeneration system operation, it is necessary to improve the peak regulation capacity and regulatory flexibility of the unit. Considering the excellent performance of energy storage systems, a heat-coupled storage system with high- and low-pressure bypass is proposed to increase peak regulation capacity. Employing a 300 MW heating unit as the research object, thermal system models of a traditional-pumping steam-heating system, a high- and low-pressure bypass heating system, and a coupled system were built using Aspen Plus software. The electric heating characteristics of the three systems, as well as the peak regulation capacity and peak regulation depth of the coupled system, were analysed under different storage and heat release loads. Results indicate that the high- and low-voltage bypass system and the coupled system both improve the peak capacity and control flexibility of the unit. Moreover, the coupled system has a greater influence on the maximum thermoelectric ratio and minimum charge rate than the high- and low-voltage bypass heating system, thereby extending the range of safe operation. The peak capacity and depth of heat storage are 65.55 MW and 21.85%, respectively, while the peak capacity and the depth of the heat-release process are 39.32 MW and 13.10%.

Optimization and Control of Renewable Energy Integrated Cogeneration Plant Operation by Design of Suitable Energy Storage System

Cogeneration is preferred mostly in process industries where both thermal and electrical energies are required. Cogeneration plants are more efficient than utilizing the thermal and electrical energies independently. Present government policies in India made renewable energy generation mandatory in order to minimize fossil fuels consumption and to protect the environment. Hence, many cogeneration plants have been integrated with renewable energy generation. However, post-integration effects increase and introduce inefficiencies in the operation of cogeneration systems. In this paper, a case study of an identified typical cogeneration plant where renewable energy is integrated is considered. Post operational effects on the plant due to integration of renewable energy (solar) are studied and by practical experimentation through cost-benefit analysis the break-even point beyond which renewable energy generation introduces inefficiencies is estimated. Next, a systematic methodology is developed based on the heuristic forward-chaining approach technique to establish the breakeven point. An algorithm/flow chart is developed using an iterative method and executed through MATLAB using practical data from the industry. Suggestions for suitable energy storage devices to store renewable energy beyond the breakeven point, based on a techno-economic analysis of energy storage technologies, are made. Further, the battery energy storage system is designed and the capacity is estimated based on the practical solar irradiance data. A rule-based algorithm is developed to control the charge and discharge cycles of battery storage based on predefined conditions. The payback period is estimated based on the expected monetary benefits of proposed energy storage and the economy of the proposed system is ensured. The post-operational issues are resolved by introducing energy storage. The methodology presented in this paper can be a guiding tool for optimization of various renewable-energy-integrated cogeneration systems.

Multi-objective optimisation and planning of grid-connected cogeneration systems in presence of grid power fluctuations and energy storage dynamics

In recent years, multi-generation systems (MGS) have been at the centre of attention for incorporating various energy sources and technologies to provide a reliable and sustainable energy supply. However, deciding on the most suitable configuration and optimal operation strategy of MGSs has always been a challenging issue due to the nonlinear and complex interactions between different energy converters. Cogeneration solutions offer excellent energy efficiency through the coproduced heat from the electricity generation process. This will lead to significant economic profitability compared to conventional independent heat and power production plants. This paper presents a mixed-integer quadratic based multi-objective structural design strategy for grid-connected cogeneration systems comprising combined heat and power (CHP) devices, ancillary boiler, and energy storage devices in presence of nonlinear and dynamic behaviour of the energy storage systems. The power fluctuations smoothing index (PFSI) and energy storage depreciation factor (ESDF) are defined to effectively mitigate the power grid fluctuations and extend the lifetime of the energy storage systems. Presenting three case scenarios, the obtained results demonstrate the efficacy and applicability of the developed technique and reflect the impact of the introduced factors on the optimal configuration and operation of cogeneration systems.

Design parameters influencing the operation of a CHP plant within a micro-grid: application of the ANOVA test

Combined heat and power systems are widely recognized as a cost-effective solution for the achievement of sustainable and energy efficiency goals. During the last decade, cogeneration systems have been extensively studied from both the technological and operational viewpoints. However, the operation of a cogeneration system is a topic still worth of investigation. In fact, along with the determination of the optimal configurations of the combined heat and power systems, it is likewise fundamental to increase the awareness on the design and cost parameters affecting the operation of cogeneration systems, especially if considering the micro-grid in which they are inserted. In this direction, this paper proposed a mixed integer linear programming model with the objective of minimizing the total operational costs of the micro-grid. Different scenarios include the satisfaction of the cooling demands of the micro-grid as well as the opportuneness to include a heat storage. The influence of the main design and cost parameters on the operation of the micro-grid has been assessed by adopting the statistical tool ANOVA (Analysis Of Variance). The model and the experimental application of the ANOVA have been applied to a micro-grid serving a hospital located in the South of Italy.

Optimal operation of cogeneration system coordinated by aggregator for providing the demand and supply regulation capacity

AbstractRecent growth of renewable energy generations with natural variability, such as photovoltaic generation and wind turbine generation, would make the demand and supply control in a whole power system more difficult, and therefore, alternatives for demand and supply regulation resources would be required. The authors focus on cogeneration system (CGS) as one of regulation resources. In order to procure adequate volume of regulation capability, an aggregator coordinates a number of CGSs efficiently and flexibly considering the wide variety of electricity/thermal demands of CGS owners. This paper proposes a novel optimal operation strategy of CGS coordinated by the aggregator considering the energy balance and operation cost of individual CGS owner. This paper also demonstrates the availability of CGSs for regulation capability by numerical case studies in which the actual consumption profile is employed.

A Comprehensive Methodology for the Integrated Optimal Sizing and Operation of Cogeneration Systems with Thermal Energy Storage

Cogeneration systems are widely acknowledged as a viable solution to reduce energy consumption and costs, and CO2 emissions. Nonetheless, their performance is highly dependent on their capacity and operational strategy, and optimization methods are required to fully exploit their potential. Among the available technical possibilities to maximize their performance, the integration of thermal energy storage is recognized as one of the most effective solutions. The introduction of a storage device further complicates the identification of the optimal equipment capacity and operation. This work presents a cutting-edge methodology for the optimal design and operation of cogeneration systems with thermal energy storage. A two-level algorithm is proposed to reap the benefits of the mixed integer linear programming formulation for the optimal operation problem, while overcoming its main drawbacks by means of a genetic algorithm at the design level. Part-load effects on nominal efficiency, variation of the unitary cost of the components in relation to their size, and the effect of the storage volume on its thermal losses are considered. Moreover, a novel formulation of the optimization problem is proposed to better characterize the heat losses and operation of the thermal energy storage. A rolling-horizon technique is implemented to reduce the computational time required for the optimization, without affecting the quality of the results. Furthermore, the proposed methodology is adopted to design a cogeneration system for a secondary school in San Francisco, California, which is optimized in terms of the equivalent annual cost. The results show that the optimally sized cogeneration unit directly meets around 70% of both the electric and thermal demands, while the thermal energy storage additionally covers 16% of the heat demands.

Optimal Operation of Co-generation System Coordinated by Aggregator for Providing the Demand and Supply Regulation Capacity

Optimal Operation of Co-generation System Coordinated by Aggregator for Providing the Demand and Supply Regulation Capacity

外皮・躯体と設備・機器の総合エネルギーシミュレーションツール「BEST」の開発 （その167）デマンドレスポンスを想定したコージェネレーションの運用シミュレーションの基礎検討

外皮・躯体と設備・機器の総合エネルギーシミュレーションツール「BEST」の開発 （その167）デマンドレスポンスを想定したコージェネレーションの運用シミュレーションの基礎検討

A-1 東京工科大学CGS(コージェネレーションシステム)運転実績調査(その1 冬期)

A-1 東京工科大学CGS(コージェネレーションシステム)運転実績調査(その1 冬期)

S0830103 寒冷地の下水処理施設で並列稼働するFC-MGT CGSの性能予測

Since a micro gas turbine (MGT) generally has higher heat/electric ratio to the other prime movers in cogeneration system (CGS), it is much available at a sewage treatment plant of cold district where large amount of heat is usually required in a year. However, it sometimes gives lower generating efficiency, especially in summer, because of higher intake air density. As another problem it is difficult to keep higher level of generating efficiency on partial loads of MGT operation. On the other hand CGS with fuel cells commonly shows the higher efficiency and is significantly expected to improve the total energy performance in the system without those defections. In this study, several models with cooperative usage of MGT and PAFC are analytically proposed for a sewage treatment plant of cold district. As the result of the calculation CGS operation properly mixed with MGT and FC can produce both much generation capacity and more effective use of biogas in the plant.

Best Practices for Cogeneration System Operation

Best Practices for Cogeneration System Operation

Thermoeconomic assessment of an absorption refrigeration and hydrogen-fueled diesel power generator cogeneration system

The thermoeconomic assessment of a cogeneration application that uses a reciprocating diesel engine and an ammonia–water absorption refrigeration system for electrical power and cold production from hydrogen as fuel is presented. The purpose of the assessment is to get both exergetic and exergoeconomic costs of the cogeneration plant products at different load conditions and concentrations of hydrogen–diesel oil blends. The exhaust gas of the reciprocating diesel engine is used as an energy source for an ammonia–water absorption refrigeration system. The reciprocating diesel engine was simulated using the Gate Cycle™ software, and the ammonia–water absorption refrigeration system simulation and the thermoeconomic assessment were carried out using the Engineering Equation Solver software (EES). The results show that engine combustion is the process of higher exergy destruction in the cogeneration system. Increased hydrogen concentration in the fuel increases the system exergetic efficiency for all load conditions. Exergy destruction in the components of the ammonia–water absorption refrigeration system is increased with increasing load due to the rise of heat transfer. At intermediate and high loads energy efficiency is increased in the power system, and low values of unit exergetic cost and competitive specific exergoeconomic costs are noticed. The cogeneration system operation at intermediate and high engine loads was proven to be feasible.

Development of Multi-model for Cogeneration System Using Statistical Analysis

Cogeneration system is a nonlinear multivariate system with a wide operating regime. The efficiency of electricity generating and thermoelectric conversion coefficient of turbine generator are affected by many factors such as load variation, extracted steam change, and unstable supplied power etc. In this paper, a kind of identification algorithm has been proposed to build the statistical model of generating efficiency. Firstly, key variables are selected by using stepwise regression method. Then, statistical models are built in different operating regimes. The experimental results demonstrate the performance of the presented algorithm. The field engineer can take the developed model as a reference and determine the operating operation of cogeneration system. As a result, the performance of turbine generator is improved and the operating cost is reduced.

Case Studies of Energy Saving and CO<sub>2</sub> Reduction by Cogeneration and Heat Pump Systems

This paper describes two case studies: 1) a cogeneration system of a hospital and 2) a heat pump system installed in an aquarium that uses seawater for latent heat storage. The cogeneration system is an autonomous system that combines the generation of electrical, heating, and cooling energies in a hospital. Cogeneration systems can provide simultaneous heating and cooling. No technical obstacles were identified for implementing the cogeneration system. The average ratio between electric and thermal loads in the hospital was suitable for the cogeneration system operation. An analysis performed for a non-optimized cogeneration system predicted large potential for energy savings and CO2 reduction. The heat pump system using a low-temperature unutilized heat source is introduced on a heat source load responsive heat pump system, which combines a load variation responsive heat pump utilizing seawater with a latent heat-storage system (ice and water slurry), using nighttime electric power to level the electric power load. The experimental coefficient of performance (COP) of the proposed heat exchanger from the heat pump system, assisted by using seawater as latent heat storage for cooling, is discussed in detail.

Optimal Operation of Cogeneration Systems by Stochastic Programming

Cogeneration Systems (CGSs) are high efficiency energy generation systems which are able to generate both electricity and useful heat by the power generators and heat recovery equipment near energy consumers. It is crucial not to waste both of electricity and heat produced from a CGS for the effective use of a CGS. Therefore, the optimal scheduling problem of CGSs is important. For the CGS scheduling problem, energy demand is an essential condition. In many cases, the energy demand is uncertain, but most study on the CGS scheduling problem has treated it as the definite values.In this paper, we formulate the CGS scheduling problem as a stochastic programming problem involving recourse costs for the energy supply shortage and a chance constraint for excess of electric power contract, and propose a method to optimize the CGS operation schedule under the uncertain energy demand. In our method, the objective function includes the term of the expectation of the recourse costs, and the inequality constraints that represent the probability of meeting the maximum limit of the power purchase is added to the problem. The problem can be described as a mixed integer programming problem whose objective function is convex. By the piecewise linear approximation, it is solved with general MIP solvers. Using our method, the strict optimal operation schedule with the minimum expected operation cost, and the optimal contracted electric power is sought.

Optimal operation of a micro-combined cooling, heating and power system driven by a gas engine

The objective of this paper is to investigate the problem of energy management and optimal operation of cogeneration system for micro-combined cooling, heating and power production (CCHP). The energy system mainly consists of a gas engine, an adsorption chiller, a gas boiler, a heat exchanger and an electric chiller. On the basis of an earlier experimental research of the micro-CCHP system, a non-linear-programming cost-minimization optimization model is presented to determine the optimum operational strategies for the system. It is shown that energy management and optimal operation of the micro-CCHP system is dependent upon load conditions to be satisfied and energy cost. In view of energy cost, it would not be optimal to operate the gas engine when the electric-to-gas cost ratio (EGCR) is very low. With higher EGCR, the optimum operational strategy of the micro-CCHP system is independent of energy cost.

A study on power flow congestion relief in cooperation with customer‐side cogeneration systems

AbstractDispersed generation technologies (e.g., gas engines) have greatly advanced in recent years. Gas engines are often operated as the main component of a cogeneration system (CGS). By using exhaust heat, the total efficiency of CGSs can reach from 70% to 80%, and as a result, it is also useful for reductions of CO2 emission. Therefore, CGSs have been given preferential treatment by the Japanese government and their installation and use is expected to become widespread in the future. When customers introduce CGSs, these systems have an influence on the demand profile for electric utilities. On the other hand, CGS operational patterns depend on customers' economic requirements; thus, it is difficult to flexibly change those patterns so that they meaningfully contribute to the electric utility. As a demand response program, the authors proposed a method whereby CGSs at the customer side are used for congestion relief in transmission networks. In the proposed method, the optimal configuration of energy systems including CGSs at the customer side is determined. As well, the optimal operation of the electric utility's generators is also determined taking into account the CGS operation patterns. This paper evaluates both costs to the electric utility and the customers' cost for congestion relief in transmission networks. Further, we evaluate the influence on CO2 emission and primary energy consumption from the viewpoint of a unified energy system with CGSs providing input on a flexible operation pattern. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(4): 30– 40, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20674

需要家コージェネレーションシステムとの協調運用による送電ネットワークの混雑緩和に関する研究

Dispersed generation technologies (e.g., gas engines) have greatly advanced in recent years. Gas engines are often operated as the main component of a cogeneration system (CGS). By using exhaust heat, the total efficiency of CGSs can reach from 70% to 80%, and as a result, it is also useful for reductions of CO2 emission. Therefore, CGSs have been given preferential treatment by the Japanese government and their installation and use is expected to become widespread in the future. When customers introduce CGSs, these systems have an influence on the demand profile for electric utilities. On the other hand, CGS operational patterns depend on customers' economic requirements; thus, it is difficult to flexibly change those patterns so that they meaningfully contribute to the electric utility. As a demand response program, the authors proposed a method whereby CGSs at the customer side are used for congestion relief in transmission networks. In the proposed method, the optimal configuration of energy systems including CGSs at the customer side is determined. As well, the optimal operation of the electric utility's generators is also determined taking into account the CGS operation patterns. This paper evaluates both costs to the electric utility and the customers' cost for congestion relief in transmission networks. Further, we evaluate the influence on CO2 emission and primary energy consumption from the viewpoint of a unified energy system with CGSs providing input on a flexible operation pattern. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(4): 30– 40, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20674