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Abstract The supercritical power plant analyzed in this paper consists of the following elements: a steam turbine, a hard-coal-fired oxy-type pulverized fuel boiler, an air separation unit with a four-end-type high-temperature membrane and a carbon dioxide capture unit. The electrical power of the steam turbine is 600 MW, the live steam thermodynamic parameters are 650°C/30 MPa, and the reheated steam parameters are 670°C/6 MPa. First of all the net efficiency was calculated as functions of the oxygen recovery rate. The net efficiency was lower than the reference efficiency by 9–10.5 pp, and a series of actions were thus proposed to reduce the loss of net efficiency. A change in the boiler structure produced an increase in the boiler efficiency of 2.5–2.74 pp. The range of the optimal air compressor pressure ratio (19–23) due to the net efficiency was also determined. The integration of all installations with the steam turbine produced an increase in the gross electric power by up to 50.5 MW. This operation enabled the replacement of the steam regenerative heat exchangers with gas–water heat exchangers. As a result of these alterations, the net efficiency of the analyzed power plant was improved to 5.5 pp less than the reference efficiency.

Abstract Increasing electrification of final uses can be a viable solution towards low-carbon energy systems, when coupled with local renewable power generation. Mountain areas can already benefit from high shares of hydro-power generation, but, at the same time, rely on oil products for transport and for the heating sector in remote areas where natural gas infrastructures are not available. This research work evaluates potential scenarios for the electrification of transport and heating sectors, by coupling the simulation tool EnergyPLAN with a multi-objective optimization algorithm to analyse economic and environmental aspects. Results show that the largest benefits are expected from the electrification of the heating sector. Indeed, a CO2 emissions reduction up to 30% can be reached by acting on the transport sector alone, while up to 65% combining it with measures on heating, industry and agriculture sectors and additional electricity generation from photovoltaic systems. Moreover, the use of heat pumps can lead to significant CO2 emissions decrease with only to a slight increase in the overall annual costs thanks to lower variable costs that partly compensate the higher required initial investment and electricity storage deployment. The optimization analyses also highlight the effect of progressive penetration of electric vehicles in the private cars fleet and hydrogen trucks in the light-duty vehicles one.

Abstract Energy conversion efficiency increase in power plants with high-temperature gas-cooled reactors via implementation of the bottoming cycle was investigated under nominal and minimal thermal load of a high-temperature reactor (HTR). Heat transfer surface area and turbine outlet volumetric flow rate in bottoming cycles was also investigated. Water and two low-boiling point working fluids (ammonia and ethanol) were analyzed. Analyzed thermodynamic cycles consisted of a closed Joule-Brayton cycle with helium as working medium, which was investigated in configurations with heat regeneration, compressor intercoolers, and in a simple design. Organic versus steam Rankine cycles were compared; low-boiling point fluids under supercritical conditions in some configurations provide higher cycle energy efficiency than the gas-steam cycle. Volumetric flow rates in the last turbine stages were reduced against the steam turbine to 38% and 0.8% with ethanol and ammonia, respectively. The steam Rankine cycle configuration provided the smallest heat transfer surface increase compared with the base cycle.

Abstract In dispersed power generation, low power devices are used for local combined generating of heat end electric power. There are developing concepts of micropower plants with electric generators driven by steam or gas microturbines. The paper presents the results of an experimental investigations of the microturbine set consists of the turbine with partial admission, permanent magnet generator and three phase AC-to-DC rectifier. The microturbine was designed for steam of HFE7100 as a working medium. The dynamic behavior of the microturbine unit was experimentally examined. Microturbine unit was tested during changes of the parameters of the working medium or the electrical load. Experiments were performed with compressed nitrogen as a working medium. The dynamic model of microturbine unit was developed. The examples of the comparison between experiment results and simulations are shown and discussed in the paper.

Abstract In the paper a novel approach to thermochemical utilization of low rank coal, flotation concentrates and municipal refuse derived fuels was presented. The economic attractiveness of low rank coals and flotation concentrates is limited and that is why they are commonly stored at excavation heaps causing additional costs and the risk of endogenous fires occurrence. One of the crucial parameters determining the attractiveness and usability of a fuel in the gasification process is its reactivity. In the study several low rank coals, flotation concentrates and municipal refuse derived fuels were tested in terms of their reactivity in the process of steam gasification. The reactivity of low rank coal and flotation concentrates at 50% of carbon conversion, R50, varied between 1.46·10−4 and 2.39·10−4 s−1, whereas the maximum reactivity, Rmax, from 3.28·10−4 to 4.62·10−4 s−1. Advanced mathematical models were developed to investigate the similarities and dissimilarities between the studied fuels as well as the relationships between the physical and chemical parameters and the reactivities of fuel chars in steam gasification. On this basis, a low rank coal was selected and blended with 20%w/w of municipal refuse derived fuel in co-gasification experiments. The aim of the research was to utilize the low rank coal characterized by the lowest reactivities (R50 and Rmax of 1.46·10−4 and 3.28·10−4 s−1, respectively) in steam co-gasification to hydrogen-rich gas with an alternative fuel in a fixed bed reactor at the temperature of 800 °C. The selected low rank coal was blended with 20%w/w of municipal refuse derived and the resulting fuel yielded the average concentration of hydrogen in the produced gas of 58.99%vol.

Abstract The article analyses to what extent ‘negative net CO2 emissions’ from decarbonised biogas-to-electricity can contribute to solving Poland’s carbon capture and sequestration dilemmas. From the criteria-based evaluation of low-carbon power technologies it is found, that biogas-to-electricity is among technologies having increasing production potential in Poland. Therefore, in future biogas will be able to contribute to solving Poland’s CCS dilemmas, because it offers carbon-neutral electricity. Moreover, by applying CCS into biogas-to-electricity the ‘negative net CO2 emissions’ can be achieved. The article examines three biogas-to-electricity technologies involving CO2 capture, i.e. biogas-to-biomethane, biogas-to-CHP and biogas-to-electricity via the ORFC cycle. It is emphasised that the ORFC cycle offers low-cost CO2 separation from a CO2–H2 mixture, low O2-intensity, and the opportunities for advanced mass and energy integration of involved processes. Besides, energy conversion calculations show that the ORFC cycle can offer comparable cycle efficiency with air- and oxy-combustion combined cycles. In regard to the design of biogas-based energy systems it is recommended to include (i) distributed production of biogas in order to avoid costs of long-distance transportation of high-moisture content biomass and (ii) centralised large-scale decarbonised biogas-to-electricity power plants since costs of pipeline transportation of gases are low but large-scale plants could benefit from increased energy and CCS efficiencies.

Adsorption technology enables construction of chillers that can be driven with a low temperature cogeneration, solar or waste heat source. As compared with absorption chillers, the adsorption devices have the unique advantages like the utilization of heat source characterized by lower temperature. The paper presents the thermodynamic model of a three-bed adsorption chiller of a cooling capacity equal to 90 kW. The chiller has been commissioned at Wroclaw Technology Park and is instrumented in a way allowing a full identification of important thermodynamic and operational parameters like COP (coefficient of performance), switching time, temperatures and pressures of adsorption and desorption processes as well as water condensation. The chiller provides cooling power at two temperature levels of about 13 and 8 °C. Experimental results of a long-term chiller investigation are presented. The dependence of the chiller COP on the adsorption bed regeneration temperature in the range from 45 °C to 70 °C has been identified. It has been demonstrated that the chiller can be driven with a hot water of 65 °C, what is a typical cogeneration heating temperature in distributed systems. It allows the utilization of cogeneration heat in trigeneration mode, what is especially important for distributed heating systems in summer time.

Abstract Under conditions of low funding for the production of “green energy” in Poland, it became necessary to search for other – cheaper sources of biomass and the development of more efficient technologies. The maize straw is waste material arising in the production of grain. Therefore currently has no wider application and the cost of acquisition is several times lower than in case of maize silage. This paper presents the results of research on biogas efficiency of the maize straw silage, the dynamics of the fermentation process and the decomposition time of biomass under the meso- and thermophilic conditions. Moreover, the exploitation costs of a biogas plant working on this substrate and maize silage have been compared. It has been proved that thermophilic fermentation is significantly shorter (17%) than mesophilic and permits to increase biogas production (8.6%) and methane content (9.3%). In turn, mesophilic fermentation has more stable pH changes in comparison with the thermophilic technology. However, it is related to inhibition of the propionic acid, which can be of great importance in case of continuous fermentation. On the basis of energetic calculations it was shown that the substitution of the maize silage with the maize straw silage allows for nearly three-fold costs reduction and thus increase of the biogas plant profitability.

Abstract In this paper, a building energy simulation tool is exploited to study the impact of multiple radiative inter-reflections exchanges in an urban environment. The aim is to evaluate their influence on the thermal energy demand of buildings. A street canyon model validated in a previous work is used in TRNSYS to investigate the effects of the related urban radiative trapping. Due to multiple shortwave and longwave reflections, the actual radiation exchanged by the buildings facades is different if compared to a street canyon building, where only shadowing phenomena due to canyon geometry are considered. Buildings energy simulation commercial codes do not take in account inter-reflections inside urban canyons. The objective of this study is to evaluate how multiple shortwave and longwave reflections affect thermal energy demand (cooling and heating) of a street canyon building depending on its orientation, its transparent/opaque surfaces ratio and on the solar absorption factor of the envelope surfaces. Increases in cooling demand up to 50% and decreases in heating demand up to 20% are found.