• Energy Research

The increasing interest in small-scale renewable-energy plants for distributed power generation has led to a demand for suitable software tools to study and develop control systems able to manage advanced integrated systems. Biomass, as a renewable energy resource, needs to be processed if it is to be exploited in small CHP units and pyrolysis is one of the options available for transforming solid biomass into useful liquid and gaseous fuels. This work is concerned with the development of a time-dependent model of a rotary-kiln pyrolyser for biomass: the model is intended for the de- velopment of control systems and the simulation of integrated energy systems, where the pyrolyser is connected to a power-generation package. The model was developed within the TRANSEO environment and based on a quasi 2-D nu- merical discretisation of the rotary kiln. Results are shown for a real case that is currently under construction: the model is able to predict the impact of different operating conditions on fuel yields, as well as capturing the main transient phenom- ena occurring during changes in the pyrolyser operating conditions. Kewords: Biomass, pyrolysis, distributed generation, transient modelling.

The increasing interest in small-scale renewable-energy plants for distributed power generation has led to a demand for suitable software tools to study and develop control systems able to manage advanced integrated systems. Biomass, as a renewable energy resource, needs to be processed if it is to be exploited in small CHP units and pyrolysis is one of the options available for transforming solid biomass into useful liquid and gaseous fuels. This work is concerned with the development of a time-dependent model of a rotary-kiln pyrolyser for biomass: the model is intended for the de- velopment of control systems and the simulation of integrated energy systems, where the pyrolyser is connected to a power-generation package. The model was developed within the TRANSEO environment and based on a quasi 2-D nu- merical discretisation of the rotary kiln. Results are shown for a real case that is currently under construction: the model is able to predict the impact of different operating conditions on fuel yields, as well as capturing the main transient phenom- ena occurring during changes in the pyrolyser operating conditions. Kewords: Biomass, pyrolysis, distributed generation, transient modelling.

In this work, the National Energy Technology Laboratory (NETL) in collaboration with the Thermochemical Power Group (TPG) of the University of Genoa have developed a dynamic model of a 10 MW closed-loop supercritical CO2 (sCO2) recompression Brayton cycle plant in the MATLAB-Simulink environment. The sCO2 cycle modeled here is a closed cycle with an external thermal source used to heat the sCO2 working fluid before it is expanded in a turbine. The turbine exhaust heat is recuperated using high- and low-temperature recuperators, with mixing of two compressor outlets between the recuperators (on the cold-side). About two thirds of the low-pressure sCO2 is compressed by a main compressor, after passing through a cooler, while the remaining working fluid flows directly through a bypass compressor. The reference fluid properties (REFPROP) method by the National Institute of Standards and Technology is used to provide the thermodynamic and transport properties for sCO2 over the cycle temperature and pressure range because the sCO2 behavior is highly non-ideal, especially at the inlet of the two compressors. Dynamic simulations have been carried out to assess the behavior of the plant during a typical process disturbance.

In this work, the National Energy Technology Laboratory (NETL) in collaboration with the Thermochemical Power Group (TPG) of the University of Genoa have developed a dynamic model of a 10 MW closed-loop supercritical CO2 (sCO2) recompression Brayton cycle plant in the MATLAB-Simulink environment. The sCO2 cycle modeled here is a closed cycle with an external thermal source used to heat the sCO2 working fluid before it is expanded in a turbine. The turbine exhaust heat is recuperated using high- and low-temperature recuperators, with mixing of two compressor outlets between the recuperators (on the cold-side). About two thirds of the low-pressure sCO2 is compressed by a main compressor, after passing through a cooler, while the remaining working fluid flows directly through a bypass compressor. The reference fluid properties (REFPROP) method by the National Institute of Standards and Technology is used to provide the thermodynamic and transport properties for sCO2 over the cycle temperature and pressure range because the sCO2 behavior is highly non-ideal, especially at the inlet of the two compressors. Dynamic simulations have been carried out to assess the behavior of the plant during a typical process disturbance.

Abstract In the pursuit of increasing their profitability, the design and operation of combined cycle power plants needs to be optimized for new liberalized markets with large penetration of renewables. A clear consequence of such renewable integration is the need for these plants for being more flexible in terms of ramping-up periods and higher part-load efficiencies. Flexibility becomes an even clearer need for combined heat and power plants to be more competitive, particularly when simultaneously following the market hourly price dynamics and varying demands for both the heat and the electricity markets. In this paper, three new plant layouts have been investigated by integrating different storage concepts and heat-pump units in key sections of a traditional plant layout. The study analyses the influence that market has on determining the optimum layouts for maximizing profits in energy-only markets (in terms of plant configuration, sizing and operation strategies). The study is performed for a given location nearby Turin, Italy, for which hourly electricity and heat prices, as well as meteorological data, have been gathered. A multi-parameter modeling approach was followed using KTH’s in house techno-economic modeling tool, which uses time-dependent market data, e.g. price and weather, to determine the trade-off curves between minimizing investment and maximizing profits when varying critical size-related power plant parameters e.g. installed power capacities and storage size, for pre-defined layouts and operating strategies. A comparative analysis between the best configurations found for each of the proposed layouts and the reference plant is presented in the discussion section of the results. For the specific case study set in northern Italy, it is shown that the integration of a pre-cooling loop into baseload-like power-oriented combined cycle plants is not justified, calling for investigating new markets and different operating strategies. Only the integration of a heat pump alone was shown to improve the profitability, but within the margin of error of the study. Alternatively, a layout where district heating supply water is preheated with a combination of a heat pump with hot thermal tank was able to increase the internal rate of return of the plant by up to 0.5%, absolute, yet within the error margin and thus not justifying the added complexity in operation and in investment costs. All in all, the analysis shows that even when considering energy-only market revenue streams (i.e. heat and electricity sells) the integration of heat pump and storage units could increase the profitability of plants by making them more flexible in terms of power output levels and load variations. The latter is shown true even when excluding other flexibility-related revenue streams. It is therefore conclusively suggested to further investigate the proposed layouts in markets with larger heat and power price variations, as well as to investigate the impact of additional control logics and dispatch strategies.

Abstract In the pursuit of increasing their profitability, the design and operation of combined cycle power plants needs to be optimized for new liberalized markets with large penetration of renewables. A clear consequence of such renewable integration is the need for these plants for being more flexible in terms of ramping-up periods and higher part-load efficiencies. Flexibility becomes an even clearer need for combined heat and power plants to be more competitive, particularly when simultaneously following the market hourly price dynamics and varying demands for both the heat and the electricity markets. In this paper, three new plant layouts have been investigated by integrating different storage concepts and heat-pump units in key sections of a traditional plant layout. The study analyses the influence that market has on determining the optimum layouts for maximizing profits in energy-only markets (in terms of plant configuration, sizing and operation strategies). The study is performed for a given location nearby Turin, Italy, for which hourly electricity and heat prices, as well as meteorological data, have been gathered. A multi-parameter modeling approach was followed using KTH’s in house techno-economic modeling tool, which uses time-dependent market data, e.g. price and weather, to determine the trade-off curves between minimizing investment and maximizing profits when varying critical size-related power plant parameters e.g. installed power capacities and storage size, for pre-defined layouts and operating strategies. A comparative analysis between the best configurations found for each of the proposed layouts and the reference plant is presented in the discussion section of the results. For the specific case study set in northern Italy, it is shown that the integration of a pre-cooling loop into baseload-like power-oriented combined cycle plants is not justified, calling for investigating new markets and different operating strategies. Only the integration of a heat pump alone was shown to improve the profitability, but within the margin of error of the study. Alternatively, a layout where district heating supply water is preheated with a combination of a heat pump with hot thermal tank was able to increase the internal rate of return of the plant by up to 0.5%, absolute, yet within the error margin and thus not justifying the added complexity in operation and in investment costs. All in all, the analysis shows that even when considering energy-only market revenue streams (i.e. heat and electricity sells) the integration of heat pump and storage units could increase the profitability of plants by making them more flexible in terms of power output levels and load variations. The latter is shown true even when excluding other flexibility-related revenue streams. It is therefore conclusively suggested to further investigate the proposed layouts in markets with larger heat and power price variations, as well as to investigate the impact of additional control logics and dispatch strategies.

This paper describes and compares the results of thermodynamic and economic modelling based on integrating an existing large size steam power plant (ENEL’s Brindisi power plant-660 MWe) with hydrogen production and purification plants. ENEL is one of the main Italian power utility. The high quality of the hydrogen produced would guarantee its usability for distributed generation (e.g. by micro gas turbine, Stirling engine, fuel cell, etc.) and also for public transport (using PEM fuel cells). The proximity of an hydrogen production and purification plant to an existing steam power plant can favour connections in terms of energy requirements exchanges; the integrated system, proposed here, can represent an attractive approach to a flexible hydrogen-electricity co-production. Two different technologies for the syngas production section are considered: the pyrolysis process and direct pressurised gasification. These technologies produce syngas with different characteristics in terms of temperature, pressure and composition: this has a profound effect on the layout of the complete systems proposed in this paper. The model for the pyrolysis process is based on an existing 800 kWt coal- and biomass-fed pyrolysis ENEL’s plant placed in Bastardo (Perugia, Italy): a detailed model of the plant was created. Different coals (Ashland, South Africa, Sulcis) and biomass (Poplar, Mischantus, Wood residuals, Husk) are considered in this study to explore the real potential of mixed-fuels in terms of thermodynamic performances and costs. The results were obtained using WTEMP software, developed by the TPG of the University of Genoa, showing the performance attainable by integrating a real steam power plant with systems for hydrogen production and purification for a novel vision of clean distributed hydrogen generation.

This paper describes and compares the results of thermodynamic and economic modelling based on integrating an existing large size steam power plant (ENEL’s Brindisi power plant-660 MWe) with hydrogen production and purification plants. ENEL is one of the main Italian power utility. The high quality of the hydrogen produced would guarantee its usability for distributed generation (e.g. by micro gas turbine, Stirling engine, fuel cell, etc.) and also for public transport (using PEM fuel cells). The proximity of an hydrogen production and purification plant to an existing steam power plant can favour connections in terms of energy requirements exchanges; the integrated system, proposed here, can represent an attractive approach to a flexible hydrogen-electricity co-production. Two different technologies for the syngas production section are considered: the pyrolysis process and direct pressurised gasification. These technologies produce syngas with different characteristics in terms of temperature, pressure and composition: this has a profound effect on the layout of the complete systems proposed in this paper. The model for the pyrolysis process is based on an existing 800 kWt coal- and biomass-fed pyrolysis ENEL’s plant placed in Bastardo (Perugia, Italy): a detailed model of the plant was created. Different coals (Ashland, South Africa, Sulcis) and biomass (Poplar, Mischantus, Wood residuals, Husk) are considered in this study to explore the real potential of mixed-fuels in terms of thermodynamic performances and costs. The results were obtained using WTEMP software, developed by the TPG of the University of Genoa, showing the performance attainable by integrating a real steam power plant with systems for hydrogen production and purification for a novel vision of clean distributed hydrogen generation.