The results of experimental investigations into foaming process of poly(ε-caprolactone) using supercritical CO2 are presented. The objective of the study was to explore the aspects of fabrication of biodegradable and biocompatible scaffolds that can be applied as a temporary three-dimensional extracellular matrix analog for cells to grow into a new tissue. The influence of foaming process parameters, which have been proven previously to affect significantly scaffold bioactivity, such as pressure (8-18 MPa), temperature (323-373 K) and time of saturation (1-6 h) on microstructure and mechanical properties of produced polymer porous structures is presented. The morphology and mechanical properties of considered materials were analyzed using a scanning electron microscope (SEM), x-ray microtomography (μ-CT) and a static compression test. A precise control over porosity and morphology of obtained polymer porous structures by adjusting the foaming process parameters has been proved. The obtained poly(ε-caprolactone) solid foams prepared using scCO2 have demonstrated sufficient mechanical strength to be applied as scaffolds in tissue engineering.
Binary vapour-liquid equilibrium of thymoquinone and carbon dioxide at the isothermal conditions was carried out at temperature 323.15 K and pressures from 6 to 10 MPa. The experimental data were fitted to the Soave-Redlich-Kwong equation of state. Results could be used for selection of process parameters in separation of volatiles from raw oil or for evaluation of existing separation technologies.
Power boilers should be characterized by high flexibility in terms of loads, which results from the demand for electricity. In addition to the flexibility of the boiler, it is also important for the boiler to operate under technical minimum conditions while maintaining harmful emissions standards. A boiler operating with a technical minimum should also exhibit a stable combustion process. The paper presents the results of numerical combustion research for the minimum load of the two-pass ultrasupercritical boiler with front wall swirl burners system. The combustion stability for the minimum boiler load of 40% for the three mill system configurations has been demonstrated. Based on the numerical tests carried out in terms of obtaining the most favourable combustion conditions and the emission of harmful substances, the most favourable of them cases was indicated.
Biocomposite foam scaffolds of poly(ε-caprolactone) (PCL) with different porogenes were produced with batch foaming technique using supercritical carbon dioxide (scCO2) as a blowing agent. In performed experiments composites were prepared from graphene-oxide (nGO), nano-hydroxyapatite (nHA) and nano-cellulose (nC), with various concentrations. The objective of the study was to explore the effects of porogen concentration and foaming process parameters on the morphology and mechanical properties of three-dimensional porous structures that can be used as temporary scaffolds in tissue engineering. The structures were manufactured using scCO2 as a blowing agent, at two various foaming pressures (9 MPa and 18 MPa), at three different temperatures (323 K, 343 K and 373 K) for different saturation times (0.5 h, 1 h and 4 h). In order to examine the utility of porogenes, a number of tests, such as static compression tests, thermal analysis and scanning electron microscopy, have been performed. Analysis of experimental results showed that the investigated materials demonstrated high mechanical strength and a wide range of pore sizes. The obtained results suggest that PCL porous structures are useful as biodegradable and biocompatible scaffolds for tissue engineering.
The problem presented in this paper refers to the concepts applied to the design of supercritical steam turbines. The issue under the investigation is the presence of a cooling system. Cooling systems aim to protect the main components of the turbines against overheating. However the cooling flows mix with the main flow and modify the expansion line in the steam path. This affects the expansion process in the turbine and changes the performance when compared to the uncooled turbine. The analysis described here investigates the range of the influence of the cooling system on the turbine cycle. This influence is measured mainly through the change of the power generation efficiency. The paper explains the approach towards the assessment of the cooling effects and presents results of the modeling for three supercritical steam cycles.
Among the technologies which allow to reduce greenhouse gas emission, mainly carbon dioxide, special attention deserves the idea of 'zero-emission' technology based on boilers working in oxy-combustion technology. In the paper the results of analyses of the influence of changing two quantities, namely oxygen share in oxidant produced in the air separation unit, and oxygen share in oxidant supplied to the furnace chamber on the selected characteristics of a steam boiler including the degree of exhaust gas recirculation, boiler efficiency and adiabatic flame temperature, was examined. Due to the possibility of the integration of boiler model with carbon dioxide capture, separation and storage installation, the subject of the analysis was also to determine composition of the flue gas at the outlet of a moisture condensation installation. Required calculations were made using a model of a supercritical circulating fluidized bed boiler working in oxy-combustion technology, which was built in a commercial software and in-house codes.
This paper presents an analysis of the corrosion hazard in the burner belt area of waterwalls in pulverised fuel (PF) boilers that results from low-NOx combustion. Temperature distributions along the waterwall tubes in subcritical (denoted as SUB) and supercritical (SUP) boilers were calculated and compared. Two hypothetical distributions of CO concentrations were assumed in the near-wall layer of the flue gas in the boiler furnace, and the kinetics of the waterwall corrosion were analysed as a function of the local temperature of the tubes. The predicted rate of corrosion of the boiler furnace waterwalls in the supercritical boilers was compared with that of in the subcritical boilers.
In this study, the process of membrane cleaning by supercritical fluid extraction was investigated. Polypropylene microfiltration membranes, contaminated with oils, were treated in a batch process with a supercritical fluid (SCF). As extractant, pure supercritical carbon dioxide or supercritical carbon dioxide with admixtures of methanol, ethanol and isopropanol were used. Single-stage and multi-stage extraction was carried out and process efficiency was determined. The obtained results showed that addition of organic solvents significantly enhances the cleaning performance, which increases with increase of organic solvent concentration and decreases with increasing temperature. All three solvents showed a comparable effect of efficiency enhancement. The results confirmed that supercritical fluid extraction can be applied for polypropylene membrane cleaning.
In this paper a mathematical model enabling the analysis of the heat-flow phenomena occurring in the waterwalls of the combustion chambers of the boilers for supercritical parameters is proposed. It is a one-dimensional model with distributed parameters based on the solution of equations describing the conservation laws of mass, momentum, and energy. The purpose of the numerical calculations is to determine the distributions of the fluid enthalpy and the temperature of the waterwall pipes. This temperature should not exceed the calculation temperature for particular category of steel. The derived differential equations are solved using two methods: with the use of the implicit difference scheme, in which the mesh with regular nodes was applied, and using the Runge-Kutta method. The temperature distribution of the waterwall pipes is determined using the CFD. All thermophysical properties of the fluid and waterwall pipes are computed in real-time. The time-spatial heat transfer coefficient distribution is also computed in the on-line mode. The heat calculations for the combustion chamber are carried out with the use of the zone method, thus the thermal load distribution of the waterwalls is known. The time needed for the computations is of great importance when taking into consideration calculations carried out in the on-line mode. A correctly solved one-dimensional model ensures the appropriately short computational time.
The present work is devoted to the problem of utilization of the waste heat contained in the exhaust gases having the temperature of 350 °C. Conversion of the waste heat into electricity using a power plant working with organic fluid cycles is considered. Three Organic Rankine Cycle (ORC) power plant solutions are analysed and compared: a solution with the basic, single thermodynamic conversion cycle, one with internal heat recuperation and one with external heat recuperation. It results from the analysis that it is the proper choice of the working fluid evaporation temperature that fundamentally affects the maximum of the ORC plant output power. Application of the internal heat recuperation in the plant basic cycle results in the output power increase of approx. 5%. Addition of the external heat recuperation to the plant basic cycle, in the form of a secondary supercritical ORC power cycle can rise the output power by approx. 2%.
The paper presents the results of the numerical analyses for the steam turbine rotor, dedicated for the newly-designed 900 MW steam unit with supercritical steam parameters (650 °C, 30.0 MPa). Basing on the design calculations, an optimal design solution was determined. Review of the available literature on materials for turbine rotors with supercritical steam parameters was done. Then the start-ups of the turbine were simulated. Thermal and strength states were analyzed. As a result, an optimal start-up characteristic was obtained.
The objective of the paper is to analyse thermodynamical and operational parameters of the supercritical power plant with reference conditions as well as following the introduction of the hybrid system incorporating ORC. In ORC the upper heat source is a stream of hot water from the system of heat recovery having temperature of 90 °C, which is additionally aided by heat from the bleeds of the steam turbine. Thermodynamical analysis of the supercritical plant with and without incorporation of ORC was accomplished using computational flow mechanics numerical codes. Investigated were six working fluids such as propane, isobutane, pentane, ethanol, R236ea and R245fa. In the course of calculations determined were primarily the increase of the unit power and efficiency for the reference case and that with the ORC.
The paper presents equations of a mathematical model to calculate flow parameters in characteristic cross-sections in the steam-water injector. In the model, component parts of the injector (steam nozzle, water nozzle, mixing chamber, condensation wave region, diffuser) are treated as a series of connected control volumes. At first, equations for the steam nozzle and water nozzle are written and solved for known flow parameters at the injector inlet. Next, the flow properties in two-phase flow comprising mixing chamber and condensation wave region are determined from mass, momentum and energy balance equations. Then, water compression in diffuser is taken into account to evaluate the flow parameters at the injector outlet. Irreversible losses due to friction, condensation and shock wave formation are taken into account for the flow in the steam nozzle. In two-phase flow domain, thermal and mechanical nonequilibrium between vapour and liquid is modelled. For diffuser, frictional pressure loss is considered. Comparison of the model predictions with experimental data shows good agreement, with an error not exceeding 15% for discharge (outlet) pressure and 1 K for outlet temperature.
This article describes a thermodynamic analysis of an oxy type power plant. The analyzed power plant consists of: 1) steam turbine for supercritical steam parameters of 600 °C/29 MPa with a capacity of 600 MW; 2) circulating fluidized bed boiler, in which brown coal with high moisture content (42.5%) is burned in the atmosphere enriched in oxygen; 3) air separation unit (ASU); 4) CO2 capture installation, where flue gases obtained in the combustion process are compressed to the pressure of 150 MPa. The circulated fluidized bed (CFB) boiler is integrated with a fuel dryer and a cryogenic air separation unit. Waste nitrogen from ASU is heated in the boiler, and then is used as a coal drying medium. In this study, the thermal efficiency of the boiler, steam cycle thermal efficiency and power demand were determined. These quantities made possible to determine the net efficiency of the test power plant.
The purpose of this work is to find a correlation for heat transfer to walls in a 1296 t/h supercritical circulating fluidised bed (CFB) boiler. The effect of bed-to-wall heat transfer coefficient in a long active heat transfer surface was discussed, excluding the radiation component. Experiments for four different unit loads (i.e. 100% MCR, 80% MCR, 60% MCR and 40% MCR) were conducted at a constant excess air ratio and high level of bed pressure (ca. 6 kPa) in each test run. The empirical correlation of the heat transfer coefficient in a large-scale CFB boiler was mainly determined by two key operating parameters, suspension density and bed temperature. Furthermore, data processing was used in order to develop empirical correlation ranges between 3.05 to 5.35 m·s-1 for gas superficial velocity, 0.25 to 0.51 for the ratio of the secondary to the primary air, 1028 to 1137K for bed temperature inside the furnace chamber of a commercial CFB boiler, and 1.20 to 553 kg·m-3 for suspension density. The suspension density was specified on the base of pressure measurements inside the boiler’s combustion chamber using pressure sensors. Pressure measurements were collected at the measuring ports situated on the front wall of the combustion chamber. The obtained correlation of the heat transfer coefficient is in agreement with the data obtained from typical industrial CFB boilers.