A plant for depuration of fumes orionating, in Particular, from the production of ceramic frits.

Technical field The invention relates to a plant for depuration of fumes originating, in particular, from the production of ceramic frits.

Background Art Frit is defined, substantially, as a mixture of sand and alkaline substances used to obtain glaze to apply to ceramic products such as, for example, tiles and trim pieces.

Disclosure of Invention Frits are obtained through a procedure involving the melting of said mixture at rather high temperatures, ranging substantially, from 1100 to 1500°C.

The melted product, i. e. the melted frit, seeping out of the melting furnace is exposed to a sudden cooling and is then crushed; subsequently, the product of said crushing is reduced still further in size and finally damp- ground, during which various other components are added depending on the quality of the finished product required.

The frit is then applied to the surface of said ceramic products in the form of an aqueous suspension and fired together with said ceramic products.

The fumes originating from said melting process contain polluting substances, which will be referred to hereinafter as powders, and must therefore undergo depuration in special filters.

It should be noted that the aforesaid powders remain semi-melted until the temperature reaches approximately 500°C and, consequently, if the fumes do not undergo a first cooling, their treatment would create a good few problems for the depuration plant due to the sticky nature of the powders if the fumes are not cooled below the said temperature.

The temperature at which the fumes are immediately brought up to in order to manipulate them, without the risk of obstructive phenomena occurring in the plant, is not higher than 450°C to limit the problems

linked to the vitrification of the colloidal powders.

This first lowering of the temperature of the fumes is brought about by means of a prior dilution of said fumes in the output chimney from the melting furnace and, in the current embodiments, this dilution is effected by blowing air taken from the external ambient into said chimney.

This fact causes the drawback wherein the outgoing fumes from the chimney on the depuration plant for said fumes almost always have a percentage Of 02 above 13%, the maximum level set by law; this drawback is due to the fact that the said fumes originating from the melting furnace have undergone, following combustion, a lowering of the percentage of Oz, which would increase again and over the maximum legal limit with the insufflation, into the furnace chimney, of air taken from the ambient.

A further drawback of the commonly-known plants lies in the current design adopted for the realisation of the plant's forced draft regulation system ; in fact, since the component responsible for the intake for the entire plant is constituted of the ventilator connected to the expulsion chimney for the depurated fumes (hereinafter the said chimney will be called smokestack) if, for operational or energy-related reasons, or to limit the space occupied, a single depuration plant is used to treat the fumes from several furnaces, it will be necessary to provide systems designed to correct the draft of the fumes according to the number of furnaces still functioning if some of the furnaces have been switched off. If one or more of the furnaces are not functioning, the current design to correct the drat of the remaining functioning furnaces is constituted of valves or section shutters which constitute techniques that it has been demonstrated are somewhat precarious, given the particularly obstructive power of the powders present in the fumes to be depurated.

A still further drawback of the current depuration plants for ceramic frits is caused by the fact that the exchangers assigned to lowering the temperature of the fumes envisage, generally, a flow of cooling air directed orthogonally with respect to the flow of fumes generally flowing inside the pipes ; the drawback consists in the fact that in this way not all the external surface of the tube bundle is hit by the cooling air in the same way, leading to the creation of'shaded areas'with the decline of the total efficiency of said exchangers.

The aim of this invention is to overcome all the aforesaid drawbacks.

In particular, the depuration plant for fumes originating from the

production of ceramic frits, of the type fitted with a chimney with at least one melting furnace, said chimney being the location in which a first lowering of the temperature of the fumes takes place, one heat exchanger designed to effect a second lowering of the temperature of the fumes, filtering means and one smokestack fitted with a ventilator unit, the said smokestack being designed to expulse the depurated fumes, in question in this invention, is characterised by the fact that it comprises: - a circuit of the closed type for the recirculation of the air, supplying a first ventilator directly from the smokestack, the said first ventilator being designed to effect a first lowering of the temperature of the fumes coming out at least one furnace and flowing into the chimney of said furnace ; - a dilution system for the fumes inside the chimney in combination with a regulation system for the pressure drop AP in each furnace substantially only in the event that the plant serves a plurality of furnaces; the said dilution and regulation systems being constituted of the first ventilator, of a first and second valve and of an interception valve; - an air-fumes heat exchanger; said exchanger providing a flow of air in the same direction as the fumes but countercurrent.

These and other characteristics will better emerge in the description that follows of a preferred embodiment illustrated, purely in the form of a non- limiting example, in the plate enclosed, in which figure 1 shows a diagram of the whole plant; With reference to the figure, 1 is a furnace designed for melting ceramic frits fitted with a chimney 2.

Said chimney is reached by a first or second pipeline respectively 3 and 4 ; aforesaid first pipeline is fitted with a first valve 5 and the second pipeline is fitted with a second valve 6.

Both first and second aforesaid pipelines come from a first ventilating element 7.

There is a first fume pipeline 8 coming out the chimney which connects said chimney and a heat exchanger 9; on the first fume pipeline 8 there is both a thermal sensor 10 and a pressure sensor 11.

The thermal sensor 10 is connected, said connection not shown, with the first valve 5 and the pressure sensor 11 is connected, said connection also not shown, with the second valve 6.

The second pipeline 4 is endowed with an internal section, not shown, shaped in such a way as to generate a laminar air flow.

An upper cap 12 on the chimney 2 is fitted with a by-pass connection 13, of a commonly-known type, with the first fume pipeline 8.

The first fume pipeline 8 enters the heat exchanger 9 in position with the upper portion of the said heat exchanger; inside the said heat exchanger there is a plurality of jackets 14 obtained inside which some pipes 15 are positioned. Along the vertical length of the external wall of the heat exchanger 9 there is a plurality of inlets 16 obtained for ambient air sent by a second ventilating element 17 which takes in air from the external ambient A pipeline 18 connects the said second ventilating element with each of the inlets 16.

From the lower portion of the heat exchanger 9 comes a second fume pipeline 19, which enters a filtering element 20 in position with the lower portion of said filtering element. On said second fume pipeline there is a probe 33 of a commonly-known type connected, said connection not shown in the figure, with a modulation device 34, also of a commonly- known type, inserted in the second ventilating element 17.

A third fume pipeline 21 comes out from said filtering element in position with the upper portion of said filtering element.

Said third fume pipeline is connected to the inlet portion of a third ventilating element 22 after crossing a main modulation valve 23, of a commonly-known type. The outgoing portion of said third ventilating element ends up in position with the lower portion of a smokestack 24.

From the upper portion of said chimney, a recirculation pipeline 25 comes out, the said recirculation pipeline connecting the said chimney with the inlet portion of the first ventilating element 7.

Nos. 26, 27, 28,29 and 30 indicate the various directions of the flow of fumes along their route through the inside of the plant in question in this invention.

31 refers to the direction of the flow of dilution air and 32 indicates the direction of the flow of cooling air.

There will now follow a description of the functioning of this invention, with reference to the numbers in the figure.

The fumes originating from the melting of the ceramic frits leave the furnace 1 and are canalized along the chimney 2 following the route 26.

These fumes, upon leaving said furnace, oscillate between temperatures of, substantially, 900-1400°C and are diluted, inside the chimney 2, in order to bring their temperature to a value no higher than 450°C.

This dilution occurs by means of the blowing into said chimney of a part

of the depurated fumes leaving the smokestack 24 ; the temperature of these depurated fumes is located within an interval of approximately 100- 160°C. Therefore it ensues that this is also, substantially, the temperature of the portion of depurated fumes which are sent, by means of the recirculation pipeline 25, to the first ventilating element, which is only supplied with the depurated fumes, not the ambient air, in this way realising a closed circuit for the recirculation air.

The reason for this closed circuit is that, proceeding in this way, the 02 content of the depurated fumes leaving the smokestack 24, remains within 13%, the value set by Italian law. If, however, ambient air were used in the first ventilating element 7, this would increase the oxygen content of the air blown into the chimney 2, where the 02 content has been initially lowered by the combustion which has taken place in the furnace 1, and consequently in the fumes leaving said chimney.

In the event that the fume depuration plant in question in this invention is designed to serve one furnace 1 only, the dilution air entering the first ventilating element 7 is blown inside the chimney 2 along the first pipeline 3 ; the quantity of the dilution air transiting in said first pipeline is regulated during the passage of said air through the first valve 5 actuated by the thermal sensor 10 which therefore controls the optimum dilution air-fume mixture according to the temperature, which, as stated earlier, never exceeds 450°C and at which it is required that fumes to be depurated should be before said fumes enter the heat exchanger 9.

In the event, however, that the fume depuration plant in question in this invention is designed to serve a plurality of furnaces 1, it may happen that one or more of the furnaces are not functioning ; in this case, since the intake through the sole smokestack 24 for the depurated fumes is guaranteed by the sole third ventilating unit 22, it is necessary to make corrections to the draft of the furnaces 1 which are effectively functioning, distinguishing between the pressure AP differential furnace by furnace ; the said pressure differential referring to the difference between atmospheric pressure and the pressure inside each furnace 1.

In this operative situation, the dilution air to be blown into the chimneys 2 of the various functioning furnaces 1 is made to pass through the second pipeline 4 and the relative second valve 6, which is actuated by the pressure probe 11. The said second pipeline has an internal section shaped in such a way as to generate a laminar passageway for the dilution air.

The laminar regulation of the dilution air flow, always constituted of

portions of the depurated fumes originating from the smokestack 24, once the opportune priority has been established on the basis of the natural draft of each chimney 2, enables a modular, i. e. adjustable, barrier to be obtained in relation to the intake of said dilution air blown into each chimney 2 maintaining a pressure drop value set, according to the operative requirement of each functioning furnace 1, constant.

It should be noted that the upper cap 12 can, if needed, be opened; the by- pass connection 13, constituted of a pipeline and relative valve, is used to open the cap 12, normally in the closed position as shown in the figure, in the event of maintenance or, exceptionally, in the event of malfunctioning of the plant.

Once the fumes to be depurated have been cooled a first time to a temperature no higher than 450°C, they enter the heat exchanger 9, following the route 27, preferably from the upper portion of said heat exchanger for cleaning purposes, and also due to gravity, of the route followed by said fumes inside the said heat exchanger in which a second temperature lowering of the fumes to be depurated occurs so that the functioning of the subsequent filtering element is guaranteed.

This second lowering of the temperature of the fumes to be depurated is known, per se, but in this invention both the flow of fumes and the flow of cooling air move in the same direction, while being reciprocally countercurrent: the fumes to be depurated enter a plurality of vertical pipes 15 and proceed towards the bottom, while the cooling air, taken in from the external ambient by the second ventilating element 17 and following the first fume pipeline 8 along the route 32, proceeds towards the top inside a plurality of jackets 14 inside which said pipes 15 are positioned. With this internal arrangement, of the heat exchanger 9, it ensues that all the pipes 15 are completely enveloped by the flow of the cooling air without zones emerging which are less cooled than others as would happen if the flow of air were orthogonal to the route of the fumes.

The route 32 of the cooling air envisages the plurality of inlets 16 in said heat exchanger in order to diffuse the cooling fluid still better within said plurality of jackets 14.

The flow of fumes proceeds, inside the pipes 15, towards the bottom in order to facilitate the cleaning of said pipes by depositing the powders in the lower part of the heat exchanger 9 from where they will be evacuated by means of valves of a commonly-known type. The cleaning of the pipes 15 can also be facilitated by jets of air under pressure, this procedure

being of a commonly-known type.

The second cooling of the fumes to be depurated brings the temperature of said fumes to a variable range of between 100 and 180°C, i. e. to temperature values for which condensation phenomena dangerous for the functioning of the filtering element 20 are averted.

Following the second fume pipeline 19 along the route 28, the fumes to be depurated reach the filtering element 20, in general of the commonly- known type with sleeves, from which they come out following the third fume pipeline 21, the said fumes following the route 29 before being sucked back by the third ventilating element 22 and evacuated by the smokestack 24.

The probe 33 positioned along the pipe 19 permits said range of 100- 180°C to be respected, by operating the modulating device 34 for the inlet for the cooling air, taken from the ambient, inside the heat exchanger 9; the flow variation of the second ventilating element 17 has the task of compensating for the variations in the thermal potential of said heat exchanger rendered variable by any variations in the flow of fumes to be depurated.

The main modulation valve 23 fulfils the function of maintaining the pressure drop AP in the chimney 2 optimum and constant ; the said pressure drop will be regulated more finely by the air lamination system inserted in the second pipeline 4, as described earlier.

From the smokestack 24, a bled portion of depurated fumes will be sent once again within a closed circuit, by means of the recirculation pipeline 25, following the route 31, to the first ventilating element 7.

A first advantage of the plant in question in this invention is constituted of the possibility of easily respecting the percentage of 02 contained in the depurated fumes to be discharged into the atmosphere.

A further advantage consists in the possibility of regulating the AP of each furnace in the event that the plant in question in this invention is connected to several furnaces for the production of ceramic frits.

A still further advantage is constituted of the uniformity of the cooling, inside the heat exchanger, of the pipes through which the hot fumes to be depurated flow.

In the description, explicit reference is made to the process of production of ceramic frits, but it is extremely evident that the plant in question in this invention can also be applied, advantageously, to other production processes involving hot fumes containing impurities the percentage of which must be reduced before they are discharged into the atmosphere.