Process for firing and cooling of ceramic products, particularly wall and floor tiles, in continuous kiln on a single layer car

Abstract

 The process provides that the material is introduced into a furnace with a first prefiring zone, a second firing zone and third cooling zone. Kiln cars move forward in the furnace on which refractory surfaces carrying the load (2) are realized in such a manner as to leave at least one longitudinal interspace (3). In the ceiling of the first zone and in correspondance with the said longitudinal interspace (3) is formed a niche (3') provided with burners (4), the gases coming from which are divided and deflected by means of deflectors (6) from a vertical passage into two horizontal passages in opposite directions. In the second zone, the firing is realized by combustion gases which are fed in horizontally and over the product to be fired, together with the heat supplied from the air originating from the cooling zone, and the distance between the ceiling and the car deck (5') of kiln cars is reduced to a very small amount.
Therefore, this results in the greatest reduction possible of the external air volume injected into a tunnel furnace resulting in improvement of the efficiency.

Description

[0001] The invention refers to a process for the firing and cooling of ceramic products, particularly floor and wall tiles, in continuous tunnel kiln on a single layer car.

[0002] The invention also refers to a kiln car to carry out the process.

[0003] It is known that ceramic products to be fired are moved forward through tunnel furnaces, supported by a refractory surface in a single layer car, the cars offering the support base for the refractory surfaces which carry the ceramic green pieces to be fired.

[0004] In the known multilayers tunnel furnaces for wall and floor tiles, the product to be fired is arranged stacked in more than one layer and on cars which therefore present a notable load density and also require longer firing cycles. In known single layer furnaces, instead, a single layer of tiles is arranged on the car refractory surface.

[0005] Then, since in this case load density is very low, the firing process can be accelerated, so it can be rapid.

[0006] In said known furnaces, the refractory.surface for the product to be fired is mounted at a considerable height relative to the car deck.

[0007] Also, to get the firing the burners are placed to the side in relation to the forward passage of the cars and mainly below the refractory surfaces of the cars on which the ceramic wares are layed.

[0008] A combustion chamber of large dimensions is required to obtain complete combustion, by means of solid fuel such as carbon, or liquid fuel such as gas oil or diesel oil, or gaseous fuel such as methane or the like.

[0009] Said known firing systems for ceramic products present various disadvantages, including e.g. that of necessitating the placement of the refractory surfaces carrying the load at a considerable distance from the car deck.

[0010] This implies the necessity of using refractory supports, for the refractory surfaces and these supporting elements consequently absorb part of the heat available for the firing, resulting in reduction of the efficiency.

[0011] A second serious inconvenience of the known systems is that space existing between the surfaces carrying the lofd and the car deck, during the preheating phase, does not promote the heat exchange with the product to be fired.

[0012] In effect, this space constitutes a preferential route for the hot fumes, originating from the firing zone, to pass through the furnace to reach the exhaust point to the chimney, in the opposite direction to that of advancement of the cars.

[0013] This does not promote the heat exchange with the product to be fired for a suitable preparation of the material for an adequate and proper firing. The insufficient heat exchange results in low furnace efficiency, leading to the aforementioned insufficient preparation of the material before undergoing the firing.

[0014] I Finally, the cooling of the product in the known firing sy - stem is also subject to great inconveniences. To be precise, after having passed through the firing zone, the product will pass through the cooling zone and will be invested in the countercurrent of ambient air which arises from the thrust of fans, _!

[0015] The heat thus recovered from the air should then be supplied to the material which is found in the firing zone, in order to improve the overall heat efficiency. However, since there is a large free space between the product and the car deck, as already indicated, said cooling air, in order to be able to reach its purpose, i.e. to cool the ceramic wares, must be admitted in proportionally large volumes.

[0016] As a result, said air will arrive in the firing zone at remarkably low temperature and will be a negative influence on the combustion and the resulting firing efficiency in that zone.

[0017] A further serious inconvenience in the known furnaces is due to the existence of the afore mentioned refractory material supports for the support of the surfaces carrying the load. In fact, since the burners are arranged laterally and below such surfaces, the flame overheats said vertical supports, reducing their life and resulting in notable maintenance costs.

[0018] The purpose of the present invention is to reduce the volume of space in a continuous tunnel with-single layer car to a maximum, that is, to limit as much as possible the distance between the surfaces carrying the load of material to be fired and the car deck.

[0019] Another object of the invention is to eliminate the necessity of supplying heat both above and below the surfaces, with resulting reduction of the height and weight of the supports of the mentioned surfaces carrying the load. According to the present invention, the described arrangements result in that the material to be fired is introduced into a furnace having preferably three zones, the first for prefiring, the second for firing and the third for cooling, and in which furnace the cars move forward with the surfaces carrying the load, realized in such a manner as to allow at least one longitudinal interspace, in the ceiling of the first zone being provided, in each longitudinal interspace, niches fitted with burners the gases coming form which are divided and deflected by means of deflectors from a fully vertical passage to two passages which are essentially horizontal and going in opposite directions; in the second zone the firing is realized by combustion gases which are fed in essentially horizontally and over the material to be fired together with the heat of the air originating form the third cooling zone; being also the distance between the ceiling in this third cooling zone and the car deck reduced to a very small amount.

[0020] The invention is shown in a nonlimiting embodiment in the attached drawing.

Figure 1 is a diagram of a partial plane view of the car of a continuous tunnel furnace, single layer.

Figure 2 is the vertical transverse partial cross section along the line II-II of Figure 1.

Figure 3 is a diagram in reduced scale of the longitudinal vertical cross section of the aforementioned furnace.

[0021] In reference to the drawings, the continuous single layer tunnel furnace according to the invention is subdivided into two firing zones, the first F ₁ for "prefiring" and the second F ₂ for the "firing".

[0022] In the furnace, cars move forward, on which refractory surfaces carrying the load are realized in such a manner as to allow at least one interspace 3.

[0023] Each interspace 3, only in the prefiring zone F₁, is surmounted by niches 3' provided with vertical burners 4. The combustion gases are divided by the deflector 6 into two opposite directions and are directed horizontally in such a manner as to impact with the refractory batts 2 carrying the load.

[0024] This results in a uniform distribution of the heat on the tiles in the prefiring, invested by the hot fumes, which as a result of their prolonged stay can give a large part of its heat content to the material to be fired.

[0025] The "firing" section within the zone F₂ (Fig. 3) follows this first phase of preheating or preparation of the product. In this zone F₂ is provided a plurality of burners 7 which are arranged laterally and in a plane over the material to be fired. Burners 7 are situated within one or more staggered recesses 8 in the walls of the furnace.

[0026] The gases discharged at high velocity from said burners create a strong turbolence to complete the process of firing of the material.

[0027] In Fig. 3 is shown an elevation 8 which includes burners 7 arranged laterally.

[0028] In their arrangement, the burners 4 and 7 concur to reduce to the minimum the free cross section of the furnace both in prefiring zone F₁ and in cooling zone F₃. Thus the inconvenience of having to place the refractory surfaces carrying the load at a great distance from the car deck, with the interposition of heavy supports of refractory material, is eliminated, which would have been unfavorable to an optimum heat exchange between the hot fumes and the material to be fired.

[0029] In fact, the above mentioned lowering of the refractory surface carrying the load with respect to the car deck presents particular advantages besides that provided for zone F₁, especially for the cooling zone F₃ wherein only the quantity of air necessary to cool the product is injected into the furnace. An optimum heat exchange is thus realized, with transfer of the heat from the product to the air, which passes into the firing zone at such a temperature as to not require a supplementary heat supply.

[0030] The remarkable lowering of the refractory surface carrying the load according to the present disclosure, is possible only with the realization of a new type of kiln car, which can for example be realized with a height of only 50mm of the refractory surface carrying the load with respect to the car deck, while the minimum height for the konwn kiln cars is approximately 170mm. The reduction is therefore on the order of 60%.

Claims

1. Process for firing and cooling of ceramic products, particularly wall and floor tiles, in a single layer in continuous tunnel furnaces, characterized in that the material to be fired is introduced into a furnace consisting preferably of three zones, the first for prefiring, the second for firing and the third for cooling, and in which kiln cars move forward, on which refractory surfaces carrying the load are realized in such a manner as to leave at least one longitudinal interspace(3),in the ceiling of the prefiring zone, being provided, in each longitudinal interspace niches (3') fitted with burners (4), the gases coming from which are divided and deflected by means of deflectors (6) from a fully vertical passage into two essentially horizontal passages in opposite directions; in the second zone (F₂) the firing is realized by combustion gases which are fed in essentially horizontally and over the material to be fired, together with the heat supplied from the air originating from the third cooling zone (F₃); being also the distance between the ceiling in this third cooling zone and the car deck (5') of the kiln car (9) reduced to a very small amount.

2. Furnace to carry out the process as in claim 1, characterized in that it preferably has three zones, the first for prefiring, the second for firing and the third for cooling, and in which furnace cars move forward, in which refractory surfaces carrying the load (2) are realized in such a manner as to leave at least one longitudinal interspace (3), in the ceiling of the first zone being provided, in each longitudinal interspace (3), niches fitted with burners (4), the gases coming from which are divided and deflected by means of deflectors (6) from a fully vertical passage into two essentially horizontal passages in opposite directions; in the second zone (F₂), the firing is realized by combustion gases which are fed in essentially horizontally and over the material to be fired, together with the heat supplied from the air originating from the third cooling zone (F₃); being also the distance between the ceiling in this third cooling zone and the sliding base (5') of the firing kiln cars (9) reduced to a very small amount.

3. Furnace as in claim 2, characterized in that the quantity of ambient air injected into cooling zone (F₃) through the open transverse section of the furnace is such as to provide with the cooling of the product, absorbing the heat therefrom in order to thereby arrive at a very high temperature in the firing zone (F₂), and thereby to promote the firing so as to not require a supplementary heat supply.

Drawing