Forgestal, S.L. has developed a computer program by finite elements, specifically adapted for kiln cars. It calculates the evolution of the heat inputs and outputs in the kiln car as well as the evolution of the temperatures in all the nodes of a predefined
internal network, as a function of both the kiln car properties and the evolution of conditions of temperature and gas velocity along the real firing cycle.
Modern kiln cars, made of fired refractory pieces, can look so similar between them that it is not easy to distinguish between different designs, both on the drawing and sometimes even on real new kiln cars.
But its performance in operation, regarding the cycles and real firing conditions, can be very different depending on some important design details. The calculations indicate and the experience confirms that kiln cars very similar in appearance can show
radically different performances regarding mechanical impact, thermal shock, chemical attack, vacuum cleaning possibilities, resistance to chipping penetration and fuel consumption in real cycle.

Each one of these aspects, and even more the whole of them, is important for life and profitability of a kiln car system, but we will focus this article on the last listed one: Fuel consumption.
The intuitive concept that heavy kiln cars consume more heat than light ones is basically true (1).

It is a fact that a better insulated kiln car will transmit, in steady heat flow conditions, less heat than a worse insulated kiln car.

But it would be wrong to deduce from the prior statements that two kiln cars with identical weights and identical global coefficients of transmission will have the same consumption in real cycle. In fact consumptions in real cycle can be very different even in kiln cars with identical weights and identical global coefficients of transmission. Real consumption is very little depending on global weight and global heat transmission coefficient, and much more depending on the individual densities, individual transmission coefficients and physical disposition of each one of the individual components.
The reason of this apparent contradiction is very simple: Kiln car working conditions in real cycle are very far from the ideal conditions in which the calculation of steady flow heat transmission is based (2).
In steady heat flow situation,100% of the lost heat (consumption) correspond to the transmission heat losses.

But kiln car conditions, especially in modern kilns with cycles seldom higher than 36 hours and sometimes lower than18 hours, are radically different, to such an extent that the transmission heat loss of a kiln car inside the kiln can be less than 20% of the heat retained by the same kiln car at the kiln exit.
Whilst calculation of heat loss in steady flow conditions is relatively simple, the calculation of the heat retained in the kiln car is rather more complex and requires both an accurate preparation and a powerful calculation program.

Forgestal, S.L. has developed a calculation program by finite elements (3), specifically conceived to be applicable to kiln cars. This program, calculates the evolution of the heat inputs and outputs in the kiln car as well as the evolution of the temperatures in all
the nodes of a predefined internal network, as a function of both the kiln car properties and the evolution of conditions of temperature and gas velocity along the real firing cycle.

The points of this network are usually situated at a distance between 1 and 10 mm, so that the information obtained is very vast for each kiln car section. This vast information should be excessive for presentation and study, so the program includes several
possibilities to gather and condensate it.

The results are displayed here gathered to the global level of a kiln car, but other displays much more detailed are used for the optimisation of the designs. Calculations, independently of the gathering level for display, are always done for each one of the section types constituting the kiln car.