An approach for computing the thermal balance and energy consumption of pits during boiling of frozed logs intended for veneer production has been presented. With the help of our own non-stationary ...model, the boiling times of beech logs with a diameter of 0.4 m, initial temperature of −10°C, and moisture content of 0.6 kg·kg
−1
were determined at water temperatures in the pit equal to 70°C, 80°C and 90°C. Using the determined logs' boiling durations and the mentioned approach, the change in energy required for the entire boiling process and that for each of the components of the thermal balance was calculated. Computer simulations were performed for concrete pit with a volume of 20 m
3
and a degree of filling with logs 45%, 60%, and 75%. It was found that the total energy consumption of the pit increases from 169 to 205 kWh·m
−3
when the temperature of the boiling water increases from 70°C to 90°C at a pit filling level of 75%. The approach can be applied to compute thermal balances of concrete pits during boiling of frozed and non-frozed logs to any desired final average mass temperature required for the mechanical processing of the plasticized logs.
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A mathematical description of the operating temperature of each of the five constituent stages of regimes for autoclave steaming and subsequent air conditioning of wood has been proposed. This ...description has been included in the boundary conditions of two coupled own non-stationary temperature-energy models of the autoclave steaming process of wooden prisms intended for veneer production. Using these models, calculation of the durations of the initial part and of the whole regimes for steaming of beech prisms have been carried out. The variables were an initial wood temperature of 0 and -20 °C, moisture content of 0.4, 0.6, and 0.8 kg·kg
−1
, and cross-section dimensions of the prisms 0.3 × 0.3 m and 0.4 × 0.4 m; steaming autoclave with a diameter of 2.4 m, length of 10.6 m, and loading level of 40, 50, and 60% at limited thermal power of 500 kW suplied to the autoclave. The simulations carried out using Visual Fortran showed a good agreement of the proposed mathematical description with many previously obtained experimental results and confirmed the possibility of its being applied in the boundary conditions of various non-stationary models of autoclave treatment processes (steaming, impregnation, desired property modification) of wood and other materials.
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An approach for calculating the energy required for defrosting and subsequent heating of frozen wood during thermal treatment in the production of veneer has been presented. Using two own unsteady ...models the duration of regimes for steaming of prisms in an autoclave and for boiling of logs in a pit, and also the average mass temperature of the prisms and logs and the energy accumulated by them at the end of heat carrier introduction in these regimes was determined. The obtained values of average temperature were introduced in third own model for engineering calculation of the energy considered in the approach. Computer simulations were carried out for beech prisms with a cross section of 0.4 × 0.4 m and beech logs with a diameter of 0.4 m at an initial wood temperature of −10°C, −20°C, and −30°C and moisture content of 0.6 kg·kg
−1
. The operating temperature of the prism steaming regimes was equal to 130°C, and that of the log boiling regimes was 80°C. The approach can be applied using Excel for computing the energy and its components needed for defrosting and heating of different frozen capillary-porous materials subjected to multiple types of thermal treatment.
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An approach for calculation of the duration of regimes for intensive autoclave steaming of frozen wooden prisms in cases of dispatching interferences into the operating temperatures has been ...suggested. The approach is based on the use of two coupled personal mathematical models: a 2D non-linear model of the unsteady distribution of the temperature in frozen and non-frozen prismatic wood materials subjected to steaming and a model of the non-stationary thermal balance of autoclaves for steaming wood materials. Using the suggested approach, calculation of the duration of regimes for defrosting and heating of beech prisms have been carried out. The variables were an initial wood temperature of −20°C, moisture content of 0.6 kg·kg
−1
, and cross-section dimensions of the prisms 0.4 × 0.4 m; steaming autoclave with a diameter of 2. 4 m, length of 9.0 m, and loading level of 50% for the cases of lowering by the dispatcher the maximum temperature of the basic steaming regime from 130°C to 120, 110, and 100°C in the 3rd, 7th, and 11th hour of these regimes. The approach can be applied for developing optimized energy-efficient regimes for autoclave steaming of frozen wood materials with desired duration set by the dispatcher.
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A methodology for the computation of the thermal energy efficiency of modes for the heat treatment of frozen wooden prisms in an autoclave with saturated water vapor at changing operational ...conditions has been proposed. The methodology includes computer simulations with two own-coupled unsteady models: one to calculate the 2D temperature distribution in the cross-section of prismatic wood materials during their heat treatment, and the second to determine the heat balance of industrial autoclaves for such wood treatment. Simulations were carried out in order to determine the duration, energy consumption, and thermal efficiency of different modes, caused by changed operational conditions, for the autoclave steaming of frozen beech prisms with industrial parameters in the absence and presence of dispatcher intervention. The influence of nine combinations between the time of dispatcher intervention and the degree of reduction of the constant maximum temperature from the 130 °C of the basic mode on the thermal efficiency of the autoclave was investigated. The results show that all studied dispatching interventions cause an increase in both the duration and the thermal efficiency of the modes. This efficiency in the modes at changing operational conditions has values between 68.7% and 74.6%, while the efficiency in the basic steaming mode is equal to 68.0%.
This paper presents an approach for computing the heat balance of boiling pits during the plasticizing of non-frozen logs intended for the production of peeled veneer. With the help of our ...non-stationary model, the heating times of beech logs with a diameter of 0.4 m, an initial temperature of 10°C, and a moisture content of 0.6 kg∙kg-1 were determined at water temperatures in the pit equal to 70, 80, and 90°C. Using the determined logs’ boiling durations and the mentioned approach, the change in the total energy required to carry out the entire boiling process and that required for each of the individual components of the heat balance was calculated. Computer simulations were conducted for a concrete pit with overall dimensions of 8.0 × 2.6 x 2.5 m, a working volume of 20 m3, and a degree of filling with logs equal to 45, 60, and 75%. It was found that the increase in the water temperature from 70 to 90°C causes an increase in the total specific energy, as well as in the energy for the heating of the logs themselves, the construction, and the water of the pit. At the same time, the energy required to cover the heat losses of the pit decreases and the energy for heating the metal heater/radiator itself does not change. A decrease in the degree of filling of the pit with logs from 75 to 45% causes an increase in both the total energy and all its components except the energy for heating the logs, which remains unchanged.
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CEKLJ, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Abstract
Heating green wood logs by infrared (IR) radiation during peeling for veneer production has been numerically simulated, focusing on the heating kinetics of a green wood cylinder rotating ...with a decreasing radius. The results confirm those of previous experiments, that this kind of heating is a promising alternative to soaking wood prior to peeling. The model integrates the green wood parameters such as moisture content, density, distribution and ratios of earlywood and latewood, on the one hand, and the peeling conditions of veneer thickness and peeling speed, on the other. The following heat transfer processes were considered: conduction within the bolt, external heating by the IR source, and convection between the bolt surface and the external environment. The outputs were the temperatures of the bolt surface and of layers several millimeters deep. For maximal heat penetration, the bolt should turn in front of the IR source before cutting starts and the IR source should be positioned at the greatest angular distance ahead of the knife. Several heating scenarios could be simulated by the model, thus it is a useful decision-making tool for the design of an in-line IR heating system installed on the peeling lathe.
An approach for computing the heat balance of boiling pits during defrosting of logs in them intended for veneer production has been presented. With the help of our own non-stationary model, the ...defrosting times of beech logs with a diameter of 0.4 m, initial temperature of -10 °C, and moisture content of 0.6 kg.kg −1 were determined at water temperatures in the pit equal to 70, 80 and 90 °C. Using the determined logs' defrosting durations and the mentioned approach, the change in the total energy required to completely defrost the logs in the pit from their initial average mass temperature of -10 °C to 0 °C and that required for each of the individual components of the heat balance was calculated. Computer simulations were conducted for a concrete pit with overall dimensions 8.0 × 2.6 × 2.5 m, working volume of 20 m 3 , and a degree of filling with logs equal to 25, 50, and 75%. The approach can be applied to compute heat balances of pits both during defrosting only and during complete defrosting and subsequent boiling of frozed logs to a desired final average mass temperature required for the mechanical processing of the plasticized logs.
The report highlights pine veneer logs as a source of higher finacial returns to the locals trading it on roadsides compared to sawlogs which fetches much lower prices within the Zimbabwean forestry ...industry.
In the paper is discussed the aggregate optimal control of the production sector comprising wood-steaning equipment and veneer-cutting machine. As a criterion is used the minimal expenses for ...obtaining steamed wood and veneer production aut of it. In the solution of the problem is applied the maximum principle (Pontriagin, 1976). It shows the method by which the optimal duration of the wood-steaming and the optimal plastic condition of the steamed wood are calculated on the basis of the economic specifications of the wood-steaming equipment and the veneer-cutting machine in accordance with the properties of the steaming wood.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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