The effect of intermittent turbulence on drop size reported by Baldyga and Podgórska (1998) was analysed and the multifractal exponent ?FT was evaluated in a model system of immiscible silicon oil-water dispersion mechanically agitated by a high-shear sawtooth impeller. The ?FT values of approximately 1.64 on average and 1.46 were found for regions close to the impeller and the region outside the impeller, respectively. Finally, the relation between Sauter mean diameter d32 and maximum drop size dmax was investigated. The d32/dmax values of approximately 0.6 on average and 0.5 were found for regions close to the impeller and the region outside the impeller, respectively. The droplet sizes were obtained by the in-situ measurements technique and by the image analysis method.

The world is moving towards decarbonization policies in the energy and industrial sectors to bring down carbon dioxide release and reach net zero emissions. Technologies to capture CO2 and use it as a feedstock to produce CO2-based chemicals and biofuels via chemical or biochemical conversion pathways can potentially reduce the amount of CO2 released. The paper serves the innovative scientific knowledge for CO2 transformation via a biochemical pathway to microalgal biomass with its subsequent treatment to biofuels and bioproducts assuming milder climatic conditions (Central or Eastern Europe, Visegrad countries or climatically related world regions). The recent trends were critically reviewed for microalgal biorefinery to reach the sustainability of microalgal-based chemicals with added value, digestion, hydrothermal liquefaction, pyrolysis, and gasification of microalgal residues. Knowledge-based chemical process engineering analysis, systematic data synthesis, and critical technical evaluation of available life cycle assessment studies evaluated the sustainability of microalgal biorefinery pathways. The research showed that biological CO2 fixation using water, seawater or wastewater to produce third-generation biomass is a promising alternative for bioethanol production via pretreatment, enzymatic hydrolysis, digestion, and distillation, and can be realized on a large scale in an economically viable and environmentally sound manner. Its best economically promising and sustainable pathway is perceived in producing microalgal-based nutraceuticals, bioactive medical products, and food products such as proteins, pigments, and vitamins. Machine learning methods for data mining, process control, process optimization, and geometrical configuration of reactors and bioreactors are the crucial research needs and challenges to implementing microalgal biorefinery in an operational environment.

The specific CO2 production of fuels has commonly been expressed empirically in terms of kgCO2 (kWh)−1. No specifications regarding combustion conditions, transformation technology used, and efficiency are usually presented in detail. In this paper, however, we propose replacing this approach by the use of rigorous chemical engineering calculations based on the composition and the combustion conditions of the fuels. The MS EXCEL program, which is provided as supplementary material to this paper, calculates the specific CO2 production considering energy losses, adiabatic flame temperature, calorific value and heat of fuel combustion, flue gas temperature, energy losses through flue gas, slag, and the overall energy efficiency of the whole energy conversion process. Results are presented for three fuel groups: coal, hydrocarbons, and renewable fuels. The calculated results are compared with the literature data. A benefit of our approach is that the procedure can be generalized for any fuel of known composition and for different types of combustion-based energy transformation.

Heat transfer coefficient (HTC) was experimentally measured for saturated and subcooled pool boiling of binary mixtures of water and glycerin. Saturated boiling was studied for mixtures with water mass fractions omega(w) from 100%A to 60% on horizontal flat nickel-plated surfaces at heat fluxes from 50 to 650kWm(-2) at atmospheric pressure. Subcooled boiling was investigated in the range of subcooling from 0 to 30K at heat fluxes of approximately 250, 450 and 650kWm(-2). It was found that mixture effects have a significant impact on saturated boiling HTC even for mixtures with very low content of glycerin as significant drops of HTC were observed for subtle changes in composition for mixtures of high omega(w). Measured HTC was successfully correlated with the combination of Yagov (1999) and Inoue and Monde (2009) correlations with a mean relative error of 12 %. A simple empirical HTC correlation is also proposed. For subcooled boiling, developed subcooled boiling regime was reached for all investigated heat fluxes. For this regime, correlations, which were able to predict HTC for saturated boiling, were employed to predict subcooled boiling HTCs for all investigated concentrations, heat fluxes and subcoolings. Effect of subcooling and effect of liquid composition on total HTC were of the same importance for mixtures with higher water content. With the increase in concentration of glycerin in the mixture, decrease in total HTC with increasing subcooling became more significant.

Two variants of a four-blade axial impeller with diagonally rounded large-surface blades have been developed in order to reach two goals. First, the impeller should be hydrodynamically optimized for coagulation and flocculation processes (wastewater treatment), and second, the manufacturing severity and costs should be low (easily manufacturable impeller). The main process characteristics (power characteristics, blending characteristics, and hydrodynamic characteristics) of both variants of the impeller have been performed in various vessel-to-impeller configurations and the results are presented in the paper. The obtained values were compared with other standard impellers and TECHMIX hydrofoil impellers, and it was found that one of the proposed variants (4TR10) seems to be a perspective hydrofoil impeller for blending processes in the chemical, pharmaceutical, or mining industry. The coagulation/flocculation performance of the impeller has been tested and the results proved that the impeller produces the highest ratio of macroaggregates and the lowest ratio of non-aggregated particles compared to standard impellers.

The homogeneity of an immiscible liquid-liquid system was investigated in a baffled vessel agitated by a Rushton turbine. The dispersion homogeneity was analyzed by comparing Sauter mean diameters and drop size distribution (DSD) determined in different measured regions for various impeller speeds. The sizes of droplets were obtained by the in-situ measurement technique and by the Image Analysis (IA) method. Dispersion kinetics was successfully fitted with Hong and Lee (1983) model. The effect of intermittency turbulence on drop size reported by Baldyga and Podgorska (1998) was analyzed and the multifractal exponent alpha(FT) was evaluated.

Mixing of immiscible liquid-liquid system is the crucial process for many branches of industry. The main purpose of this process is to increase mass transfer efficiency in processes occurring in chemical and metallurgical industry. The knowledge of drop size and surface area of drops is important for the determination of mass transfer time. The aim of this contribution is to study drop size time evolution in immiscible liquid-liquid system agitated by high-shear Sawtooth impeller in baffled cylindrical vessel. The drop size evaluation was investigated in three different regions of interest. The time evolution of drop size was described by the kinetic model proposed by Hong and Lee (1983) for each region of interest. Simultaneously, the drop size distribution (DSD) was determined and compared for each regions of interest. The time evolution of drop sizes was investigated by non-invasive measurement directly in control volume. The images of illuminated region of interest were captured by a high-speed camera. The captured images were processed by the Image Analysis method.

The pressure swing adsorption (PSA) units are widely used as an oxygen source. The storage of pressurized gaseous oxygen is limited by the capacity of a pressure vessel. The increasing share of renewable electricity sources (RES) causes intraday electricity price fluctuations. These fluctuations can be an opportunity to improve the economy of a plant. This paper aims to analyze the potential of a PSA unit connected to the battery energy storage system (BESS) for more effective on-site oxygen production. The analysis was carried out for the Czech Republic, Germany, and Denmark. These countries differ significantly in the energy mix. The theoretical potential of BESS installation and use in electricity price peak was found to be around 9 - 16 % of cost-saving on average compared with the daily operation of PSA unit when the off-peak average electricity price was from 95 to 91 % of the daily average electricity price respectively. Widening the price gap due to increasing RES share, the potential is growing.

The energy required for air compression is the largest cost item for oxygen separation from air by pressure swing adsorption technology (PSA). This paper aims to demonstrate the potential of water-injected compressor technology for energy savings for small oxyfuel combustion units that use PSA technology as an oxygen source. Additionally, the utilization of waste heat from the compressor was further examined for the dewatering of biomass. Based on the performance data presented for available commercial water injected compressors, 2 % of electrical energy can be saved compared to oil lubricated single compression as a reference case. The waste compression heat released was capable of drying the burned wood and saving 10.4 % of the wood to obtain the required thermal load.

Steam methane reforming units (SMR) have been technically mastered nowadays, but most installed units are large-capacity units. In addition, the hydrogen that is produced does not reach the required purity. It would have to be purified, which increases the investment and operating costs. The development of a small SMR is described here, and marketed equipment is listed. The production of blue hydrogen by steam reforming or of green hydrogen by hydrolysis of water is an option as a source of hydrogen for these units. Hydrogen production by water electrolysis is technically more straightforward, but it requires a significant electricity supply at high current loads. This paper provides an overview of the principal published data of equipment manufacturers and essential scientific articles on both technical and economic issues of hydrogen production for these purposes. The paper contributes an assessment of recommended methods for the conversion of CAPEX units of different capacities and a rough estimate of the growth of feedstock and energy prices to OPEX. The production price of hydrogen from SMRs has increased by approximately 2.18 times and the production price of hydrogen from electrolysis units has increased by approximately 1.53 times due to the increase in the price of raw materials and electricity.

Heat transfer coefficients and nucleation parameters were experimentally measured during saturated nucleate boiling of water–glycerin mixtures on a thin smooth titanium foil. Infrared thermometry was employed to study boiling of water–glycerin mixtures at atmospheric pressure in water mass fraction range from 100 % down to 60 % and heat flux range from 0 to 200 kW m−2. Heat transfer coefficients were found to deteriorate with an increase of concentration of glycerin in the boiling mixture. The deterioration was more pronounced for mixtures with lower water mass fraction and for higher heat fluxes. Bubble departure diameters were observed to be weakly dependent on heat flux and independent of composition of the boiling mixture. Nucleation frequencies were found to increase with heat flux and to be inversely proportional to water mass fraction of the boiling mixture. Thermal energy transferred during nucleation of individual bubbles was independent of both heat flux and mixture composition. Values and trends of evaluated parameters suggest that for investigated mixtures and boiling conditions, heat transfer into the liquid phase is more important relative to the transport of latent heat by nucleating bubbles.

Experimental measurement of drop size in immiscible liquid-liquid dispersion using non-disruptive in-situ non-invasive method utilizing high-speed image capturing and Image Analysis strongly depends on the quality of captured images. This contribution aims to analyze the effect of optical properties of the image acquisition system on the determination of the drop size in a baffled vessel agitated by a high-shear sawtooth impeller. The experiments were carried out for three impeller speeds at low dispersed phase volume fraction when the drop breakage occurs only.

The pressure swing adsorption (PSA) units are widely used as oxygen sources where oxygen is produced in a gaseous form. The start-up time of minutes is an undeniable advantage of PSA technology compared to cryogenic air separation having start-up time taking hours or days. The purity of oxygen produced by PSA using nitrogen selective zeolites (type A and type X zeolites) is limited to 95 % oxygen. The pilot-plant adsorption unit utilizes two-bed pressure swing adsorption technology. The nominal capacity of this unit is 1.4 kg h-1 of gaseous oxygen with a purity of 95 % oxygen. The paper deals to analyze process characteristics of oxygen separation from the air in the pilot-plant adsorption unit for the adsorption pressure of 5.5 bar and the defined adsorption cycle. The effect of the number of cycles needed to obtain relevant results was also investigated.

Dynamic filtration is promising for microalgae harvesting and mitigation of fouling and has been used for various purposes, such as yeast separation, soy milk protein concentration, whey protein microfiltration, etc. This contribution reviews different designs of dynamic filtration systems. It aims to investigate and highlight the potential of dynamic filtration for microalgae harvesting. The performances of individual systems are compared. Dynamic filtration systems can yield permeate flux almost twice higher than systems using cross-flow filtration. Considering the filtration flux and power consumption, the optimal recommended disks for dynamic filtration are those with a gap between the disk and the membrane of 3 mm and disks with two vanes with a cross-sectional area that decreased in the outward direction from the disk center. Disks with two vanes or perforated disks are recommended to achieve a uniform distribution of shear stress along the membrane. Fluid velocity is 2-fold and shear stress 7-fold higher than those obtained for an unperforated disk. Due to the energy demand during dynamic filtration, it is not recommended to use the frequency of disk revolution higher than 1,000 rpm. The shear rate used to mitigate fouling during harvesting of microalgae typically varies between 5,000 to 90,000 s-1 and the shear stress varies between 0.6 to 29 Pa, depending on the design of the dynamic filtration system. In case of vibrating systems, a vibrating frequency of 5 Hz is capable of significantly reducing fouling.

Pool boiling of cryogenic nitrogen and oxygen is important, as both substances represent more than 99 % of all particles in the atmosphere. Boiling of cryogens is commonly utilized in gas processing, air separation, cooling, or superconducting systems. The so-called chilldown is a characteristic process when handling cryogens, which occurs when a surface at ambient temperature gets into contact with a cold cryogenic liquid. The chilldown is accompanied by transient film boiling. Investigating critical heat fluxes and film boiling of cryogens is thus more important compared with non-cryogenic liquids. This contribution deals with heat transfer during pool boiling of cryogenic nitrogen, oxygen, and nitrogen–oxygen mixtures. Knowledge of heat transfer coefficients and of critical heat fluxes is crucial for qualified design of cryogenic apparatuses and for improved handling of cryogens. In this contribution, pool boiling performance of pure nitrogen, oxygen, and their mixtures is investigated and suitable predictive correlations for the heat transfer coefficient and critical heat flux are analyzed. It was found that variations of thermophysical properties with composition are quite weak and sufficiently linear for nitrogen–oxygen mixtures. The pure-fluid correlation of McNelly is shown to be suitable for HTC estimation during boiling of pure nitrogen and oxygen. The mixture correlation of Thome was found to be suitable for nitrogen–oxygen mixtures.

Heat transfer coefficients were investigated for saturated nucleate pool boiling of binary mixtures of water and glycerin at atmospheric pressure in a wide range of concentrations and heat fluxes. Mixtures with water mass fractions from 100% to 40% were boiled on a horizontal flat copper surface at heat fluxes from about 25 up to 270kWm−2. Experiments were carried out by static and dynamic method of measurement. Results of the static method show that the impact of mixture effects on heat transfer coefficient cannot be neglected and ideal heat transfer coefficient has to be corrected for all investigated concentrations and heat fluxes. Experimental data are correlated with the empirical correlation α=0.59q0.714+0.130ωw with mean relative error of 6%. Taking mixture effects into account, data are also successfully correlated with the combination of Stephan and Abdelsalam (1980) and Schlünder (1982) correlations with mean relative error of about 15%. Recommended coefficients of Schlünder correlation C0=1 and βL=2×10−4ms−1 were found to be acceptable for all investigated mixtures. The dynamic method was developed for fast measurement of heat transfer coefficients at continuous change of composition of boiling mixture. The dynamic method was tested for water–glycerin mixtures with water mass fractions from 70% down to 35%. Results of the dynamic method were found to be comparable with the static method. For water–glycerin mixtures with higher water mass fractions, precise temperature measurements are needed.

The pressure swing adsorption (PSA) units are widely used as an oxygen source. The second PSA unit outgoing stream contains a dry mixture of O2 in N2 that is mostly exhausted into the atmosphere. Utilization of this stream's potential and waste compression heat leads to an increase in the unit's overall energetic capacity and the ecologically more friendly processing. This paper aims to demonstrate the above-described possibilities in the case of the oxy-fuel combustion unit. The following four options for integrating PSA technology were analyzed: i) single or dual compression, ii) utilization of waste compression heat for coal or biomass dewatering, iii) utilization of dry waste gas from the PSA unit for coal or biomass dewatering, and iv) energy recovery by an expansion of pressurized oxygen before combustion. The greatest potential for practical application was found for the usage of dual compression (saving of 10 % of electricity) and utilization of waste compression heat for coal or biomass dewatering. In this case, the saving of 5.3 % and 10.4 % of lignite and wood respectively can be reached depending on fuel moisture for reference fuel conditions.

Separation of microalgae from aqueous solutions still requires further optimization and knowledge. The tool for modelling of one- or two-step microalgae harvesting technology should provide a way to predict the final concentration of microalgal suspensions. The presented spreadsheet-based tool enables to determine the mass balance of the separation process and other parameters required for the equipment basic design. These parameters are the mass flow rate of individual media, an agent consumption, and the estimation of energy consumption. The tool allows a user to combine different separation processes of various separation efficiencies. A pretreatment by coagulation or flocculation before the separation process can be also included. The applicability of this approach was demonstrated on three cases.

The paper scoped to evaluate the process characteristics of polyetherimide-polyimide hollow fibre membrane module to separate CO2 of the model flue gas. The model gas was composed of 15.2 vol % CO2 + 4.5 vol % O2 + 80.3 vol % N2, as referenced to the typical composition of flue gas emitted by an LPG-fired power plant. The effect of process variables on process characteristics was researched for various differential pressures between permeate 0.2 - 0.5 MPa (a) and retentate 0.5 - 1.0 MPa (a), feed flowrates 100 g h-1 and 200 g h-1, all under the gas temperature of 30 °C. It was found out that the value of the separation factor (CO2/N2) was 6.9. The decrease of the separation factor (CO2/N2) by 4.1 compared to the ideal selectivity (CO2/N2). The separation factor (CO2/O2) was shallow; its maximum value of 1.8 was reached.