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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]

Development of the district heating system (DHS) is needed to achieve the Renewable Energy Directive goals. To maintain the economic profitability of DHN, the increase of intensity of heat production/consumption has to be ensured. Well, a known method is a cold production using an adsorption heat pump. However, developing a system suitable for implementation in the district heating companies is very difficult. As a solution, the authors propose a composite substation equipped with the adsorption heat pump and the heat/cold storage system based on a PCM.

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]

This paper describes the model of the novel concept liquid piston engine, which is designed to convert low-grade waste heat into electricity. The proposed dynamic oriented model is implemented in Aspen Hysys that enables simulations dynamic simulation of various working agents. The simulation results were verified with experimental data obtained from the research installation. The proposed model demonstrated relatively small discrepancies with respect to experimental research, hence it could be used as a tool for research on optimization of an innovative power plant operation, i.e. various working agents, various operating pressures.

This paper presents models of three elements: heat exchanger, compressor and expander dedicated to supercritical CO2 cycles (Brayton). The models are built using Ebsilon software and validated against experimental data from available literature. Radial turbomachinery and thin plate heat exchangers were used to meet the demands of the relatively compact design of the S-CO2 cycle elements. It seems that there are no general relationships for the turbomachinery and real characteristics need to be used for constructing the models. [ABSTRACT FROM AUTHOR]

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]

The paper presents a variant analysis of the structures of closed gas turbines using supercritical carbon dioxide (super-CO2) as a working fluid. Several configurations covered in the available literature were collected, commented on and compared. The parameters of the cycles, such as operating temperature and heat supply are noted and commented on. There are three main configurations considered in the available literature: the precompression cycle, partial cooling cycle, and recompression cycle. [ABSTRACT FROM AUTHOR]

This article presents the off-design operation of a 900 MW-class steam turbine cycle upgraded with utilization of lowtemperature waste heat taken from boiler flue gas. The low-temperature heat contributes to increasing the efficiency of power plants without introducing many complex changes to the whole system. The base for investigations was a power unit operating in off-design conditions and supplied with steam from a BB-2400 boiler. Modifications to the model were made using commercially available software and by applying the Stodola equation and the SCC method. Calculations for off-design conditions show that, after making some modifications to the system, both heat and electricity generation could be increased through the addition of a low-temperature heat exchanger. [ABSTRACT FROM AUTHOR]

Abstract: The paper presents an experimental investigation of using a Molten Carbonate Fuel Cell (MCFC) to reduce CO2 emission from the flue gas of a lignite fired boiler. The MCFC is placed in the flue gas stream and separates CO2 from the cathode side to the anode side. As a result, a mixture of CO2 and H2O is obtained from which pure CO2 can be obtained through condensation of water and carbon dioxide. The main advantages of this solution are: additional electricity generated, reduced CO2 emissions and higher system efficiency. The results obtained show that the use of an MCFC could reduce CO2 emissions by 90% with over 30% efficiency in additional power generation. [Copyright &y& Elsevier]