The kiln car is widely used as a kind of transport equipment in the current ceramic industry, and it is heated to the firing temperature and cooled down to the ambient temperature with products in the tunnel kiln. And the burning of the ceramics requires a lot of energy, and the efficiency is relatively low within 30% or even less. In addition, the mass ratio between car and ware can be more than 50%. So the energy loss of car also occupies a great part in total energy consumption. In this work, a mathematical model will be created to describe the temperature distribution inside the kiln car while it travels through the tunnel kiln. All the used parameters are from real ceramic industry. The operative process is assumed as a countercurrent heat exchanger. Both the convection and radiation are considered as boundary condition in the model. Furthermore, the thermal results of car and the specific energy consumption of car in the standard case will be demonstrated. Finally, the influences of different thermal physical parameters on the energy consumption of car will be investigated, and the possible optimization measures of car are proposed through comparing the different specific energy losses.
The mixing of the two axial flows through the ware and through the gap between ware and walls using side nozzles in the preheating zone of tunnel kiln is investigated. The three-dimensional temperature field in the cross section between the two cars is calculated using the computational fluid dynamics (CFD) tool fluent. The mixing quality is evaluated using contours, the frequency of temperature distribution, and the maximum temperature difference. The influence on the mixing behavior of injection flow rate, injection velocity, nozzles position, and nozzle number has been analyzed. The results show that using two nozzles is more effective than one nozzle if the nozzles are installed at the opposite side walls with high vertical distance. The mixing quality increases strongly until an impulse flow rate (IFR) of about 4 N. For higher values, the influence becomes relatively low. The results for the mixing temperature obtained through CFD simulation compared with analytical results show a good agreement with maximum error of 0.5%.
A simplified model is developed to predict axial gas and product temperatures along tunnel kiln with neglecting cooling zone. The plate tunnel kiln is simplified as a counter current heat exchanger. The model is solved by Finite Difference Method. Mass and energy balance equations of gas and solid in elements are derived, which consider convective and radiative heat transfer from gas to solid. Equations of elements are solved continuously from kiln ending to beginning, in which two boundary conditions are adiabatic combustion temperature and product sintering temperature in the last element. The results of a standard case and a fitting case are discussed and compared with data from an existed kiln. The standard case proves Lorenz’s Nusselt function is more accurate than infinite flat plate Nusselt function for convection description in plate tunnel kiln. The fitting case proves this simplified model is available.
Tunnel kilns are used for manufacturing coarse and fine ceramics like bricks, roof tiles and sanitary ware. Kiln cars which carry the ceramics through the tunnel kiln are considered to be one of the main contributors to energy loss. Depending upon the production capacity, a single kiln car can weigh up to 10 tonnes and there can be more than 20 kiln cars inside the tunnel kiln. In this paper, different physical properties of each layers of kiln car such as conductivity, density and specific heat capacity are analysed with the help of a mathematical model. The mathematical model developed for a generalized tunnel kiln which produces roof tiles, incorporates all modes of heat transfer taking place between the ceramic ware, gas and the kiln car. By examining the different physical properties of each layers of the kiln car, the physical properties of the first layer of kiln car is found to have an influence on energy saving.
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