Fulltext search in archive

This work is focused on determination of adsorbable organic halogens (AOX) concentration in the digested sludge from the sewage treatment plant and the losses of this component during dewatering and drying of sludge. Drying of the sludge from wastewater treatment plant is not extended too much in Czech Republic. In this work, the AOX are monitored, because AOX is one of the limits restraining use of the sludge on an agricultural land. Another reason is technological demand for using the sludge in cement processing, because chlorine in AOX can cause decrease in a heat transfer effect in a cement kiln. It is clear from the results that both centrifuged and dried sludge from the sewage treatment plant Brno fulfilled limits for using sludge on agriculture land. They can also be composted, in case they meet other requirements. If not, it is a possibility of co-incineration in cement kiln. In such case, limit for total chlorine including the AOX is required too. This limit was not exceeded. Another aim was to calculate a mass balance of AOX during the centrifugation and drying processes. It was found out, that after centrifugation the main part of AOX remained in the centrifuged sludge (96.4 %). The rest was drawn-off with reject water. 60 % of AOX in the reject water were dissolved compounds. A similar situation occurred during the drying process. More than 99 % of AOX was bound in the dried sludge. The air and vaporised water contained such quantity of AOX, which corresponded with the amount of the dust in the air and the amount of particles of sludge in vaporised water.

Some associated substances which are not innate to the drying wood may be evaporated together with moisture to the surrounding environment during the drying process. These substances in high concentrations can be dangerous and have negativ influence on the living environment. This work deals about the results of expertize condensation arose during the drying of spruce wood. Wet spruce lumber was dried by dehumidification system with low temperature conditions (55 °C). The analysis of condensate fluid (water) collected during the first part of drying process shows on a content of some volatile organic compounds. The condensed fluid was get from drying of spruce timbre of 24 mm of width. The timbre was dried in a small semi industrials scale drying kiln when the moisture of the lumber was 56% in the beginning of the process. Volume of the lumber under examination was 2.2 m³. The condensate fluid was originally from down pipe. The condensate fluid was collected during the initiatory phase of the drying, four hours after the initiation of the drying process itself. First, the value of pH of the condensate fluid was measured. Determination of volatile organic compounds was done by accredited method SOA-16. The concentration of these substances were under the limits set in the statute No. 61/2003 Law Digest.

The main aim of this work is focused on FE modeling of wood structure. This task is conditioned mainly by different organized structures/regions (tissues, anomalies...) and leads to homogenization process of multiphysics declaration of common scientific and engineering problems. The crucial role in this paper is played by derivation of coefficient form of general PDE which is solvable by nowadays numerical solvers. Generality of supposed model is given by wide range of coupled physical fields included in the model. Used approach summarizes and brings together models for various fields of matter and energy common in wood material in wood drying process, but is also suitable for a lot of different tasks of similar materials. Namely microwave drying of wood with orthotropic, visco-elastic material properties together with time, moisture and temperature dependency of structural strains by modified mechanical properties were included. Specific matrixes of elasticity for individual fields were derived. Thermal field in wood was described by conduction type of spreading. Coupling of physical fields is based on diffusive character of temperature, moisture, static pressure fields movement.

The main aim of this work is focused on weak solution of coupled physical task the microwave drying of wood with stress-strain effects and moisture/temperature dependency. Due to well known weak solution for separated physical fields without coupled effect, author concerns with coupled stress-strain relation coupled with moisture and temperature distribution. For scale dependency the subgrid upscaling method was used. Solved region is assumed to be divided into discontinual subregions according to investigated scale. This approach sugests sequential type of solution for highly coupled task. This way, very huge structures (huge according to geometry and also physics) can be solved in reasonable time and with memory consumptions. Main emphasis was putted on evaluation of structural response of the whole complex. Due to influence of moisture, temperature and time the coupled physical task of structural response is solved. Sugested aproach is of course usable not only for structural response, but for other physical fields, which were taken into account. Weak solution is based on slightly modified Ritz-Galerkin method. The work is continuing of the previous article General model of wood in typical coupled tasks: Part I. - Phenomenological approach.

This work deal with modelling of the process of drying, air flow, temperature and moisture distribution in a condensation lumber kiln. This model was made and solved in the computing system ANSYS with the use of the finite element method. There are comparationes of the 2D and 3D models, shape of wood stacks and variability of their parameters (height, width, length, cross section) in the work. The flow velocity and orientation, pressure and temperature field were observed.

The proposal of scanning and digitizing of prong test samples used for casehardening of wood is provided. The measurement of magnitude and stress state of residual stresses is usually done by prong test samples. Recently the numerical approach of given problem is more and more applied. To verify the credibility of the model, the comparison with factual specimen is needed. Therefore, the optimal methodological approach and process of specimen digitizing is out of demand. There are two means how to scan the samples, (1) using the analogical camera or (2) scanner. Both means has bean tested. The results of scanning actual prong test samples show that application of scanner gives us more satisfactory outputs.

Common parametric model of sawn wood, geometry and finite element and physical parametric model pile sawn wood and its immediate airy environment was introduced. By the help of numerical simulation with Finite Element Method utilization the description of temperature distribution, dampness and stress in wood, in dependence on temperature and moisture distribution in airy environment of sawn wood kiln was included. Discussion about problem of design model, mesh refinement and definition boundary conditions was opened. Results of simulations make possible to propound the optimization of drying process. Direction of next investigation was outlined too.