Tomáš Jirout

Lab-scale Technology for Biogas Production from Lignocellulose Wastes

Currently-operating biogas plants are based on the treatment of lignocellulose biomass, which is included in materials such as agriculture and forestry wastes, municipal solid wastes, waste paper, wood and herbaceous energy crops. Lab-scale biogas technology was specially developed for evaluating the anaerobic biodegrability and the specific methane yields of solid organic substrates. This technology falls into two main categories – pretreatment equipments, and fermentation equipments. Pretreatment units use physical principles based on mechanical comminution (ball mills, macerator) orhydrothermal treatment (liquid hot water pretreatment technology). The biochemical methane potential test is used to evaluate the specific methane yields of treated or non-treated organic substrates. This test can be performed both by lab testing units and by lab fermenter.

Effect of Organic Solvents on Microalgae Growth, Metabolism and Industrial Bioproduct Extraction: A Review

In this review, the effect of organic solvents on microalgae cultures from molecular to industrial scale is presented. Traditional organic solvents and solvents of new generation-ionic liquids (ILs), are considered. Alterations in microalgal cell metabolism and synthesis of target products (pigments, proteins, lipids), as a result of exposure to organic solvents, are summarized. Applications of organic solvents as a carbon source for microalgal growth and production of target molecules are discussed. Possible implementation of various industrial effluents containing organic solvents into microalgal cultivation media, is evaluated. The effect of organic solvents on extraction of target compounds from microalgae is also considered. Techniques for lipid and carotenoid extraction from viable microalgal biomass (milking methods) and dead microalgal biomass (classical methods) are depicted. Moreover, the economic survey of lipid and carotenoid extraction from microalgae biomass, by means of different techniques and solvents, is conducted.

Study of the Blending Efficiency of Pitched Blade Impellers

This paper presents an analysis of the blending efficiency of pitched blade impellers under a turbulent regime of flow of an agitated low viscous liquid. The conductivity method is used to determine of the blending (homogenization) time of miscible liquids in pilot plant mixing equipment with standard radial baffles. For the given homogeneity degree (98 %) a three-blade pitched blade impeller is tested with various off-bottom clearances, vessel/ impeller diameter ratios and various impeller pitch angles. The experimental results show in accordance with theoretical data from the literature, that the greatest effect on the dimensionless blending time is exhibited by the vessel/ impeller diameter ratio and the impeller pitch angle. The number of total circulations necessary for reaching the chosen homogeneity degree depends on the impeller pitch angle and amounts more than three. Finally, the energetic efficiency of the blending process is calculated. The results of this study show, that the highest energetic efficiency of the three-blade pitched blade impeller appears for the pitch angle a = 24°, the impeller/vessel diameter ratio T/D = 2 and the impeller off-bottom clearance h/D = 1.

Heat transfer similarities between impinging jets and axial-flow impellers

Similarities in the flow and heat transfer characteristics between simulation results of a round impinging jet and experimental data obtained on an agitated vessel with an axial flow impeller are presented in this paper. The electrodiffusion method was used in measuring the local heat transfer coefficients on a flat bottom of an agitated vessel. A small axial impeller has been built to provide a clearly defined flow imitating a submerged confined jet impinging the vessel bottom. Our simulation and experimental results show that the flow pattern in the impinging jet region below the axial flow impeller can be compared to the stagnation region of a round impinging jet with a corresponding tangential velocity component. CFD simulations of an impinging jet showed also the importance of different boundary conditions on small electrodes used with the electrodiffusion method and give an approximation of necessary correction factor.

Heat Transfer at the Bottom of a Cylindrical Vessel Impinged by a Swirling Flow from an Impeller in a Draft Tube

Heat transfer at the bottom of a cylindrical vessel impinged by a flow with tangential velocity component generated by an axial-flow impeller in a draft tube was measured using the electrodiffusion experimental method. Local values of the Nusselt numbers along the radial coordinate of the heat transfer surface and corresponding mean values are presented for relatively small distances of the draft tube from the impinged surface (0.25 ≤ h / d ≤ 1). Such small distances are typical for mixing of liquids, which ensures good homogenization and increases the intensity of heat and mass transfer in many industrial operations. Results are compared with literature data for unconfined impinging jets with no tangential velocity components. The additional tangential velocity component generated by the rotating impeller significantly influences the hydrodynamics of the impinging jet and decreases the heat transfer intensity in the case of small distances from the impinged surface. A correlation describing the mean Nusselt number at the vessel bottom is proposed. It can be used in a design of a real industrial piece of equipment with heat transfer situated at the bottom.

Mixing system for highly concentrated fine-grained suspensions

Mixing system for highly concentrated fine-grained suspensions The mixing equipment for highly concentrated fine-grained suspensions must be designed differently from the equipment in which a suspension with a low concentration of the solid phase or bigger particles is mixed. It is due to the different rheological properties of the suspensions. In this work we are trying to find a suitable mixing system for a highly concentrated fine-grained suspension. The aim was to determine an effect of particular geometrical parameters of the tested mixing systems on a suspension process, especially from the energetic viewpoint. The energetic costs of all the used mixing systems were compared on the basis of the power consumption which was necessary for reaching the state of sufficient suspension movement in the whole mixed bulk. As a result, it was confirmed that multistage impellers can be used even in standard vessels (with a liquid level height equal to a vessel diameter) with a profit. During experiments, the state of sufficient movement was determined by a visual observation of the suspension at the vessel bottom, at the wall and also at the suspension level.

Liquid circulation in a stirred system with an axial flow impeller and a cylindrical draft tube

This study deals with a CFD simulation of the turbulent flow of a homogeneous liquid in a cylindrical stirred system with a pitched-blade impeller and a cylindrical draft tube. Design of investigated pilot plant equipment corresponds to the shape of agitated crystallizer with a draft tube – additional cooling heat exchanger. The results of the computation are expressed by means of the circulation pattern of a stirred liquid and the main flow characteristics of the system – the flow rate numbers and the impeller power number.

Mixing of waste gypsum suspensions

The paper deals with experimental research of the waste suspensions mixing from the energy industry. Mixing experiments were carried out in a transparent baffled vessel with a diameter of 290 mm. Standard pitched six-blade turbine and folded four-blade turbine with diameters of 100 mm in two relative distances from bottom H2/d = 1 and 0.5 were used in experiments. Measurements were carried out with three volumetric concentrations of suspensions: 16, 31.5 and 47%.

Effect of rapid batch decompression on hydrolysate quality after hydrothermal pretreatment of wheat straw

The subject of this paper was to study the effect of rapid batch decompression on hydrolysate quality and on biogas yield after the hydrothermal pretreatment of wheat straw. An aqueous batch containing 5 mass % total solids of wheat straw was thermally and thermally-expansionary treated in parallel at the process temperature of 170–200°C and the residence time of 0–60 min. An analysis of the thermal and thermal-expansionary hydrolysate provided identical results in the dependences and values of chemical oxygen demand, acidities, and glucose yields of both treatments based on severity factors including the combined effects of temperature and residence time. Increases in the methane content of 33 % for thermally and of 34 % for thermally-expansionary treated wheat straw were reached in comparison to the methane yield from an untreated sample. This means that the polysaccharide cell wall was dissolved because of the high process temperature and residence time. From this it follows that all its nutrients were subsequently washed out of the cell into liquid where they caused changes in its chemical oxygen demand, glucose content, and acidities. There was therefore no rapid decompression effect on the hydrothermally treated wheat straw.

Heat transfer in a jacketed agitated vessel equipped with multistage impellers

In this work, heat transfer via the cylindrical part of the jacket in an agitated vessel has been investigated. Heat transfer coefficients were determined using the transient method based on measuring the temperature dependency of the liquid batch on time. A multistage impeller made of two impellers was used in a cylindrical vessel with dished bottom. The lower impeller was a curved blade turbine with the diameter of d = 100 mm and the upper impeller was either a pitched three-blade or pitched four-blade impeller with the diameter of d1 = 67 mm. Three different impeller clearances in a multistage configuration, H3/d1 = 1, 1.5, and 2, were used in our measurements. The vessel was equipped with two baffles. Experimental results were evaluated using the Euler’s method and nonlinear regression procedure in the Matlab® software and they are summarized in form of Nusselt number correlations describing their dependency on the Reynolds number.