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The objective of this paper was to study the sCO2 cycle as a waste heat recovery system for a 180 kW biogas engine. The research methodology adopted was numerical simulations through two models built in different programs: Aspen HYSYS and GT Suite. The models were used to optimize the design and thermodynamic parameters of a CO2 cycle in terms of system power, system efficiency, expander, and compressor efficiency. Depending on the objective function, the sCO2 cycle could provide additional power ranging from 27.9 to 11.3 kW. Based on the calculation performed, "Recuperated cycle at maximum power" was selected for further investigation. The off-design analysis of the system revealed the optimum operating point. The authors designed the preliminary dimensions of the turbomachinery, i.e., the rotor dimension is 16 mm, which will rotate at 100,000 rpm. [ABSTRACT FROM AUTHOR]

This article deals with a thermal energy storage system in the form of a water tank with a thermocline. The well-known thermocline phenomenon is modeled using computational fluid dynamics (CFD). However, the reservoir model proposed in this article is zero-dimensional. This is due to the fact that the aim of this article is to build a mathematical model that will be more useful in mathematical models of complex energy systems in which a hot water tank is one of many elements of the system. In such a zero-dimensional mathematical model, the hot water tank will be modeled using equations describing heat transfer, and the thermocline itself will be treated as a heat transfer surface with known dimensions and heat transfer coefficient. A novelty of this paper is that it addresses heat loss across the thermocline as defined in this manner. A CFD model of a thermal storage tank is created, validated with available experimental data, and used to obtain the heat transfer coefficient U. The resulting value is then analyzed quantitatively and qualitatively and the changes in the thickness of the thermocline are accounted for in the equation. The results from this groundbreaking work can be used to analyze heat storage in the form of thermocline water tanks at the level of system modeling, e.g., for the purpose of configuring the structure of other devices and control systems. [ABSTRACT FROM AUTHOR]

In recent years, due to the very intensive development of renewable sources (working in a very irregular and unpredictable way), energy storage has acquired a special importance for the stability of the power system. There are many methods of energy storage, but only two have adequate capacity and power: Pumped Hydro Storage (PHS) and Compressed Air Energy Storage (CAES). The article presents energy analysis of energy storage system based on compressed air inside underground mining caverns. A dynamic mathematical model of CAES system of parameters and structure similar to the Huntorf type power plant was constructed. Filling and emptying of the cavern with compressed air was numerically simulated. Balance calculations for selected configuration of the system was performed. Four different equations were used to describe the efficiency of the storage.

The paper contains a comprehensive summary of potential sCO2 cycle applications being considered for power generation. The authors give examples of different sCO2 based cycles used in combination with conventional energy sources like fossil fuels or nuclear as well as renewable energy sources like solar. The article presents sCO2 recompression cycle simulation model results and - using this example, cycle flexibility and parameters - discusses potential application of the cycle. [ABSTRACT FROM AUTHOR]

Summary: Growing installed capacity in renewable energy sources is driving demand for energy storage in the power systems. Compressed air energy storage (CAES) technology can provide a good alternative to pumped energy storage, with high reliability and good efficiency in terms of performance. The article presents three constant volume CAES systems: (i) without recuperation, (ii) with recuperation, and (iii) adiabatic. Dynamic mathematical models of these systems were built using Aspen HYSYS software. Adiabatic compressed air energy storage system with liquid thermal energy storage achieved round trip efficiency of 64.8%. [ABSTRACT FROM AUTHOR]

The paper presents an investigation into the three cathode layers for the Molten Carbonate Fuel Cell that were obtained by using printing techniques on various surfaces. The main differences during the manufacturing process were the substrates used when printing the layers: glass and two different sorts of paper. The cathodes were investigated at the theoretical and experimental level. To identify the influence of the substrate used we built a mathematical model of the fuel cell, in which the influence is expressed by the conductivity of the layer. The paper demonstrates the possibility of using printing techniques to manufacture Molten Carbonate Fuel Cell layers. [ABSTRACT FROM AUTHOR]

This article is a comparative analysis of two systems: Brayton-Brayton and Brayton-Diesel. These two systems were both compared with a simple cycle of a gas turbine as a benchmark. The paper compares and contrasts the various advantages and disadvantages of the systems. The comparison with the simple cycle was made possible by having the same mass flow of air at the inlet of the gas turbine compressor for all analyzed cases (in the case of the Brayton-Brayton system--at the inlet of the compressor of the first gas turbine). Compared to the simple cycle, the Brayton-Brayton cycle has greater power and the Brayton-Diesel less. In terms of efficiency both systems outperformed the simple cycle, with the Brayton-Diesel system achieving slightly better results than the Brayton-Brayton. [ABSTRACT FROM AUTHOR]

The paper presents a thermodynamic analysis of a selected hypothetical liquid air energy storage (LAES) system. The adiabatic LAES cycle is a combination of an air liquefaction cycle and a gas turbine power generation cycle without fuel combustion. In such a system, heat of compression is stored and subsequently used during the expansion process in the turbine. A mathematical model of the adiabatic LAES system was constructed. Balance calculation for a selected configuration of the energy storage system was performed. The influence of pressure in the air liquefaction cycle and the gas turbine power generation cycle on storage energy efficiency was analyzed. The results show that adiabatic liquid air energy storage systems could be very effective systems for storing electrical power, with efficiency levels reaching as high as 57%. [ABSTRACT FROM AUTHOR]

Compressed Air Energy Storage (CAES) technology and electricity generation by this system are described in this paper. General performances and possible system efficiency definitions of those kinds of systems are indicated. Hybrid systems which consist of CAES and other Renewable Technologies--RT--(e.g. wind turbines) are presented. A possible location for CAES-RT in Poland is indicated. A dynamic mathematical model of CAES is presented; using this model the results for compressing and expanding operating modes are obtained. [ABSTRACT FROM AUTHOR]

Molten Carbonate Fuel Cells (MCFC) offer several advantages that are accelerating the research and development effort. Recent advances include improved materials, new fabrication techniques and new designs, flow configurations and applications. Nevertheless, several factors are holding back large scale implementation of fuel cells, especially in distributed energy generation, a major one being their long response time to changing parameters. Whereas alternative mathematical models of the molten carbonate fuel cell stack have been developed over the last decade, there are no reported analyses of regarding the application of models for emergency scenarios such as fuel cell malfunctions. This paper presents the 0D model of MCFC, calibrated to the appropriate available experimental data. This study investigates a generic molten fuel cell stack with nominal power output of 1 kWel. As daily, weekly and monthly variations in the electrical power load are expected, there is a need to develop numerical tools to predict the unit's performance with high accuracy. Hence, a fully physical dynamic model of an MCFC stack was developed and implemented in Aspen HYSYS 10 modeling software to enable predictive analysis of the dynamic response. The model is used to simulate a number of few malfunctions with 5. 66% broken cells in the stack. Losses of performance are obtained, manifested by rising operating temperature and falling power output. Moreover, a number of emergency operation scenarios were investigated, such as sudden loss of electric load, fuel and oxidiant supply. The presented model exhibits high accuracy and accounts for thermal and electrochemical processes and parameters. The paper presents the methodology used in the study to analyze the sensitivity of key scenarios such as load changes and emergencies. Further functionality of the model, which was validated using real operating data, is discussed. • Dynamic model of a Molten Carbonate Fuel Cell 1 kW stackis proposed. • The model was calibrated to the appropriate available experimental data. • The load changes and emergency situations were examined. [ABSTRACT FROM AUTHOR]