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The dynamic growth of renewables in national power systems is driving the development of energy storage technologies. Power and storage capacity should correspond to system-scale requirements in the field of power and capacity. One such technology is liquid air energy storage. As the main energy expenditures in this system are related to the liquefaction module, authors focused their research on analysis of the advanced liquefaction modules. The six most common liquefaction sections were considered. Depending on the regasification section pressure, various amounts of cold media can be obtained, stored, and used during liquid air energy storage system charging mode. Mathematical modelling results show that when the regasification section pressure is below 100 bar, the type of liquefaction system used has no significant influence on the unit energy expenditures of liquefaction section. Since additional air cooling is desired for higher pressure values, appropriate choice of liquefaction system type can minimise unit energy expenditures for air condensation. One of the main parameters from the efficiency point of view is the temperature before the throttling valve, as lower values contribute to a reduction in recirculated flow, leading to lower power demands for compressors. The highest efficiencies for almost all considered cases were reported for the Kapitza system: 57.72% for 100 bar regasification pressure. Importantly, the Kapitza and Heylandt systems retain good efficiency with higher regasification pressures, until 160 bar. For the other cases, the discrepancies between efficiencies for 100 bar and 160 bar are significant. The highest difference was observed for the simplest system – Linde-Hampson – where the efficiency drop exceeds 12%. For the best analysed system (Kapitza) exergy analysis were leaded. The main single component exergy destruction was reported for the Joule-Thompson valve (25.56%), which is related with isenthalpic throttling of air. In general, the highest share of exergy destruction in the system occurs in the heat exchangers (26.15% in total).

Efficiently storing energy on a large scale poses a major challenge and one that is growing in importance with the increasing share of renewables in the energy mix. The only options at present are either pumped hydro or compressed air storage. One novel alternative is to store energy using liquid air, but this technology is not yet fully mature and requires substantial research and development, including in-depth energy and exergy analysis. This paper presents an exergy analysis of the Adiabatic Liquid Air Energy Storage (A-LAES) system based on the Linde–Hampson cycle. The exergy analysis was carried out for four cases with different parameters, in particular the discharge pressure of the air at the inlet of the turbine (20, 40, 100, 150 bar). The results of the analysis show that the greatest exergy destruction can be observed in the air evaporator and in the Joule–Thompson valve. In the case of air evaporator, the destruction of exergy is greatest for the lowest discharge pressure, i.e., 20 bar, and reaches over 118 MWh/cycle. It decreases with increasing discharge pressure, down to approximately 24 MWh/cycle for 150 bar, which is caused by a decrease in the heat of vaporization of air. In the case of Joule–Thompson valve, the changes are reversed. The highest destruction of exergy is observed for the highest considered discharge pressure (150 bar) and amounts to over 183 MWh/cycle. It decreases as pressure is lowered to 57.5 MWh/cycle for 20 bar. The other components of the system do not show exergy destruction greater than approximately 50 MWh/cycle for all considered pressures. Specific liquefaction work of the system ranged from 0.189 kWh/kgLA to 0.295 kWh/kgLA and the efficiency from 44.61% to 55.18%.

A variant analysis of a potential configuration of a peak-load system which is based on SOE/SOFC module and hydrogen storage is presented in this article. The most rational configuration of the power plant with the SOE/SOFC appears to reach a high total electricity-to-electricity conversion rate with small and medium size plants. The system contains the minimum amount of devices where the anode side of the SOFC is exposed to the hydrogen storage directly. In this solution no compressors or pumps are needed and the system has no moving parts. Oxygen is then released to the surrounding environment or can be stored in an additional tank. In theory, it is possible to obtain higher efficiencies, but this requires much higher capital expenditures (additional heat exchangers, gas turbines, set of heat regeneration heat exchangers, etc.) and much higher parameters of working media in the system (1400 C, 30 bar). The absolute efficiency of the system depends on the assumptions made and the way in which the mathematical model was developed. It may change due to them, hence the presented analysis is qualitative rather than quantitative.

This paper presents the model of compressed air energy storage (CAES) expansion part with flue gas recovery. The model is built based on classic CAES expansion part and supplemented with heat recovery steam generator and steam turbine. The model is built in the GateCycle software and tested based on real data acquired from one of existing CAES plant. As a result the influence of air inlet pressure on power and efficiency of such a system is presented.

This paper presents the results of the first stage of the project, aimed at the assessment of the applicability of the new apparatus for disintegration of excess waste activated sludge. It was documented that the analysed device allows for disintegration of sewage sludge with an efficiency comparable to that obtained in other devices dedicated for mechanical disintegration of sewage sludge described in the literature. The disintegration process at energy density in a range of 35–210 kJ/l resulted in the release from activated sludge flocs of 219–515 mg SCOD/l for 35 kJ/l to 2138–4884 mg SCOD/l for 210 kJ/l.

This paper presents the model of heat exchanger dedicated to operate in supercritical CO2 cycles (Brayton). The models is built in the Ebsilon software and validated against literature available experimental data. Relatively compact design of the supercritical CO2 cycle elements required using radial turbomachinery and thin plate heat exchangers. Thus, it seems that there is no general relationships for the turbomachinery and real characteristics need to be used for constructing the models.

This paper presents the model of heat exchanger dedicated to operate in supercritical CO2 cycles (Brayton). The models is built in the EBSILON software and validated against literature available experimental data. Relatively compact design of the supercritical CO2 cycle elements required using radial turbomachinery and thin plate heat exchangers. Thus, it seems that there is no general relationships for the turbomachinery and real characteristics need to be used for constructing the models.

In the paper The Liquid Air Energy Storage (LAES) technology is described. The LAES can be constructed in every place, bases on well-known components and is dedicated for system scale and short-term energy storage. The most important issue is to increase the energy storage efficiency and its economic attractiveness. For that purpose the Organic Rankine Cycle application was proposed. The new variant of the Liquid Air Energy Storage with Organic Rankine Cycle (LAES-ORC) was developed, including technical analysis, the mathematical model implementation description, simulation results and its analysis.

The paper presents dynamic model of hot water storage tank. The literature review has been made. Analysis of effects of nodalization on the prediction error of generalized finite element method (GFEM) is provided. The model takes into account eleven various parameters, such as: flue gases volumetric flow rate to the spiral, inlet water temperature, outlet water flow rate, etc. Boiler is also described by sizing parameters, nozzle parameters and heat loss including ambient temperature. The model has been validated on existing data. Adequate laboratory experiments were provided. The comparison between 1-, 5-, 10- and 50-zone boiler is presented. Comparison between experiment and simulations for different zone numbers of the boiler model is presented on the plots. The reason of differences between experiment and simulation is explained.

The paper presents behavior of molten carbonate fuel cell fueled by ash free coal. Comparison between AFC and hydrogen as a fuel for MCFC is presented. Then, simulation gases expected from gasified ash free coal were investigated. The simulations were provided for different composition of gases based on results of AFC gasification. Current-voltage curves for investigated cases are presented as well as results are discussed.

Since carbon dioxide used as a working fluid in both supercritical and transcritical power cycles operates mostly in the supercritical area, the ideal gas model cannot be applied to obtain the working parameters and the cycle performance. In this paper some equations of state and their modifications that are usually recommended in the literature are presented. In the high-precision equations the maximum relative error can reach approximately 20% in the near critical region. That is why some of the authors using corrections. The corrected equations can precisely predict the density of supercritical CO2, and the average relative error can be restricted to within 1.5%. The Lee-Kesler equation of state is recommended for further calculations owing to its good performance and availability in the software application to design a supercritical CO2 cycle.

In this paper, a supercritical CO2 cycle concept is investigated in terms of possible use as a power conversion cycle. Three types of most popular modifications of simple Brayton cycle (pre-compression, partial cooling and recompression) are described. As the most efficient, a recompression cycle was chosen for further investigation. The model of the recompression supercritical carbon dioxide Brayton cycle was created using GateCycle software. The results of simulation performed in GateCycle software show that the cycle achieves efficiency of 44% for CO2 turbine inlet conditions of 550°C and 20 MPa. Comparison of optimum turbine inlet pressure for cycle efficiency and net output power at turbine inlet is presented.

The paper presents the influence of selected components parameters on the performance of supercritical carbon dioxide power unit. For this analysis mathematical model of supercritical recompression Brayton cycle was created. The analysis took into consideration changes in the net cycle power and efficiency for different compressor inlet temperatures. The results were obtained for a fixed minimum pressure of 7.4 MPa and fixed recompression split ratio. The studies conducted in this paper included also consideration of sensitivity of the cycle efficiency to a change in recuperators heat transfer area. In order to determine how each recuperator influences the cycle performance, an analysis of efficiency dependence on the recuperators area was made. Another parameters that were investigated are to a change in turbine and compressors isentropic efficiency and their influence on the cycle efficiency. In the reference cycle, isentropic efficiencies were set up as 88% for both the main and recompression compressor, and 90% for the turbine. Since isentropic efficiency is a sort of measure of broadly defined quality of a turbine or compressor, including airfoil shape, sealing, etc., it may be a significant cost factor that should be considered during cycle design. Therefore, a sensitivity analysis of cycle efficiency to both compressors and turbine isentropic efficiencies was conducted.

In the article the new method of energy storing, using cavern gas storage system is presented. The idea drew from the Compressed Air Energy Storage systems, but use natural gas stored in salt caverns as a medium, so can be called the Compressed Natural Gas Energy Storage (CNGES). The concept of the store charging is to pump the gas from lower pressure cavern to the higher pressure one by an electric powered compressor. In the discharging mode the gas expands through the expander connected with the generator, from the high pressure cavern to the lower pressure one with the electricity production.The paper covers the dynamic model of CNGES implemented in Aspen Hysys numerical environment. The main aim of the simulation was to determine the influence of selected parameters of the store (gas initial and terminal temperature and pressure). The article covers main model assumptions, implemented methodology description, results analysis and conclusions.In the article the new method of energy storing, using cavern gas storage system is presented. The idea drew from the Compressed Air Energy Storage systems, but use natural gas stored in salt caverns as a medium, so can be called the Compressed Natural Gas Energy Storage (CNGES). The concept of the store charging is to pump the gas from lower pressure cavern to the higher pressure one by an electric powered compressor. In the discharging mode the gas expands through the expander connected with the generator, from the high pressure cavern to the lower pressure one with the electricity production.The paper covers the dynamic model of CNGES implemented in Aspen Hysys numerical environment. The main aim of the simulation was to determine the influence of selected parameters of the store (gas initial and terminal temperature and pressure). The article covers main model assumptions, implemented methodology description, results analysis and conclusions.

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.

The paper presents a theoretical investigation of using a Seasonal Thermal Energy Storage facility (STES) to cover the heat demand of a complex of four buildings. The STES is placed in the ground and connected to both the local district heating network and solar panels. A number of scenarios were investigated to find an adequate size of the STES (tank size and solar panel area.) The results obtained show that the use of a STES could reduce heat consumption by 22100% depending on the architecture solution chosen.

This article presents an analysis on possible ways of utilizing low-temperature waste heat. If well-designed, this could contribute to increasing the efficiency of power plants without introducing many complex changes to the whole system. The main analysis focuses on the location of the regenerative heat exchanger in the facility. This could differ with varying temperatures of working media in the system. The base for investigations was a 800 MW-class power unit operating in off-design conditions and supplied with steam from an BB2400 boiler. Modifications to the model were made using commercially available software and by applying the Stodola equation and the SCC method. It allowed to determine the most suitable position for installing the low-temperature heat exchanger. 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.

The paper presents a variant analysis of the structure of SOFC hybrid system. The systems are divided into two gropus: atmospheric and pressurized. The main parameter of such systems are indicated and commented. The comparison of various configurations is shown in a view of efficiency obtained. The ultra high efficiency (65% HHV, 72% LHV) of electricity production seems to be possible by systems like these.

The paper presents a variant analysis of the structure of SOEC systems. The main parameters of such systems are indicated and commented. The comparison of various configurations is shown in terms of efficiency obtained. High efficiency (70%) hydrogen generation seems possible with systems like these.

This work considers electronic conductance in a molten carbonate fuel cell and consequences of its existence. The voltage characteristics of cells show differences between a theoretical maximum circuit voltage and open circuit voltage (OCV). A relationship is assumed between the OCV value and electronic conductance. Based on experimental measurements an appropriate mathematical model was created. The model is used to calculate the temperature dependence of electronic conductance for the most popular types of electrolyte: Li2CO3/K2CO3. The results obtained point to the possible existence of a very close relationship between electronic conductance and open circuit voltage. This relationship enables OCV to be calculated when electronic conductance is known. Appropriate formulae can be determined. Temperature is one of the factors affecting electronic conductance. Other influencing factors do exist, but their impact on OCV is not well known. This article mentions some of them.

The paper presents an experimental investigation of using a Molten Carbonate Fuel Cell (MCFC) for reducing CO2 emission from the flue gas of a lignite 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 by cryogenic 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.

The mathematical model of the Molten Carbonate Fuel Cell (MCFC) is presented. The new approach for modeling the voltage of MCFC is proposed. Electrochemical, thermal, electrical and flow parameters are collected in the 0-D mathematical model. The aim was to combine all cell working conditions in as a low number of factors as possible and to have the factors relatively easy to determine. A validation process for various experimental data was made and adequate results are shown. The presented model was validated for various fuel mixtures in relatively wide ranges of parameters. A distinction is made between the “design-point” and “off-design operation”.

A mathematical model of a Molten Carbonate Fuel Cell (MCFC) is used to simulate an experimental lab-stand single fuel cell unit with a size of 100 cm2. The comparison of simulated data against the experimental results is shown and commented. The model was used for optimizing the working parameters of the cell. The results of the optimizing procedures were validated during experiments.

The paper presents an experimental investigation of using a Molten Carbonate Fuel Cell (MCFC) for reducing CO2 emission from the flue gas of a hard coal 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 by water condensation. 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 35% efficiency in additional power generation.

The paper presents a control strategy concept for a Solid Oxide Fuel Cell (SOFC) to work in Distributed Generation. The control strategy is based on several factors and directs the operation of the SOFC in the context of changes occurring in the market, while taking into account the operating characteristics of the power unit. The control strategy is defined by an appropriate objective function: for example, work at maximum profit, maximum service life, etc. The results of simulations of a fuel cell at chosen loads are presented. Daily changes in the prices of fuel and electricity are factored into the simulations.

The paper aims to compare the models of working fluids against experimental data for carbon dioxide close to its critical conditions. Fortunately, most of the work is already done and published where the authors compared the models based on the equation of the state (EoS). There are a few other models which were not investigated, thus we would like to add a few new results here and focus only on near-critical properties where the biggest deviation between experimental and calculated properties can be observed. The area of interest was pressure range of 7.39 – 20 MPa and temperature range of 304-340 K just above fluid critical point (7.39 MPa, 304.25 K). Model validation was performed for density and heat capacity as one of the most important parameters in preliminary cycle analysis.

An MCFC model concept is presented. The MCFC model was built in HYSYS.Plant environment is based on its standard libraries. The main elements of the MCFC model and chemical reactions are presented. Selected performance characteristics at the design point of MCFC are presented. A new equation is given to define MCFC voltage, which was obtained based on new assumptions and which can be used instead of the classical approach.