The present invention refers to a system for cyclically charging limestone in regenerating ovens equipped with an internal pressure equalizing device; moreover, the present invention refers to a charging process using the above system.

As known, parallel-flow regenerating ovens for producing lime from limestone are composed of two vats mutually interconnected through a connection channel.

Limestone is loaded in every vat and descends along the pre-heating area in which the regenerating heat exchange occurs in counter-current with fumes, passes the fuel inserting lances and arrives in the cooking/calcining area. From here, it reaches the lime cooling area.

The oven operation provides for the alternate combustion in every vat with a combustion cycle which is from 8 to 12 minutes long.

In the first step of the combustion cycle, fuel is entered through lances in the combustion vat and burns in the combustion air which is blown-in. The freed heat is partly absorbed by the limestone calcination in the first vat. Simultaneously, cooling air is entered from the base of every vat in order to cool the lime. Cooling air gf the combustion vat, together with combustion gases and carbon dioxide formed from calcination, travel into the interconnected transverse channel, thereby reaching the second vat at the temperature of about 1050° C. In the second vat, gases coming from the first vat are mixed with cooling air at the base of the second vat and rise, thereby

the second vat.

Should the above described operating mode go on, the temperature of exhaust gases would rise well above 300° C. Therefore, after a period of 8 - 12 minutes, the fuel and air flows to the first vat initially under combustion are stopped, vats are depressurised, lime is discharged, vats are recharged with fresh limestone and- the process is reversed; in traditional ovens, it is important not to exceed the 12-minute combustion cycle, in order to avoid an overheating and the possible following lime burning. After having loaded the limestone, fuel and air are supplied in the second vat and exhaust gases are expelled from the top part of the first vat towards a sleeve filter for lowering solid particulates before scavenging in the atmosphere/environment.

Two key principles are the base of this way of operating: the pre-heating area of every vat operates as a regenerating heat exchanger, recovering from fumes the excess heat not completely absorbed by the mineral in the combustion vat. This heat, after the combustion vat reversal, pre-heats the combustion air up to a temperature of about 800° C during the pre-heating cycle. As a result, fumes coming from combustion and decarbonisation are heated from the outside at a temperature which can be highly lower than 100 °C; lime calcination is completed at transverse vat connecting channel level at a moderate temperature of about 1100° C. This favours the production of very reactive burnt lime, with a reduced contents of CaCO ₃ (in-burnt) .

However, using known regenerating ovens as described above, the amount of heat contained in exhaust gases in the oven pre-heating area is much greater than the amount which can be absorbed by limestone. Moreover, in known regenerating ovens as described above, the combustion cycle length is limited by the temperature increase of exhaust gases which leave the oven.

From what is stated above, it is further clear that the vat supply with fresh limestone can occur only during the reversal phase, in which the oven is depressurised, then taken back to ambient pressure, strongly constraining the combustion/preheating cycle length.

Therefore, object of the present invention is solving the above prior art problems by providing a system for cyclically charging limestone in regenerating ovens equipped with an internal pressure equalizing device which allows supplying vats with fresh limestone during the combustion cycle.

Another object of the present invention is providing a system for cyclically charging limestone in regenerating ovens which allows prolonging the combustion cycle up to about 20 minutes, at the same time avoiding the exhaust gas temperature increase by supplying fresh limestone during the combustion cycle.

A further object of the present invention is providing a system for cyclically charging limestone in regenerating ovens which allows recovering part of the combustion gas excess heat, decreasing and settling the exhaust gas temperature.

Another object of the present invention is providing a system for cyclically charging limestone in regenerating ovens which allows increasing the lime production by increasing the combustion period length between an oven reversal and the other.

A further object of the present invention is providing a system for cyclically charging limestone in regenerating ovens which allows prolonging the delivery of exhaust gases with high CO ₂ contents during the combustion cycle, that is prolonged up to about 20 minutes.

Moreover, an object of the present invention is providing a process for charging limestone in regenerating ovens which uses the cyclic charging system according to the present invention.

The above and other objects and advantages of the invention, which will result from the following description, are reached with a system for cyclically charging limestone in regenerating ovens equipped with an internal pressure equalizing device as disclosed in claim 1. Moreover, the above and other objects and advantages of the invention are reached with a process for charging limestone in regenerating ovens as disclosed in claim 9. Preferred embodiments and non-trivial variations of the present invention are the subject matter of the dependent claims.

The present invention will be better described by some preferred embodiments thereof, provided as a non limiting example, with reference to the enclosed drawings, in which:

- FIG. 1 shows a schematic side view of an embodiment of the system for cyclically charging limestone in regenerating ovens equipped with an internal pressure equalizing device according to the present invention; and

- FIG. 2 shows a comparative graph of the combustion or preheating/reversal cycle of a regenerating oven using the system and/or the procedure according to the present invention with respect to the combustion or pre-heating/reversal cycle of a traditional regenerating oven.

With reference to FIG. 1, it is possible to note the system 10 for cyclically charging limestone according to the present invention cooperating with a known regenerating oven 20, of which mouths of the first and second vat are shown, respectively designated by references 21 andO 23. The system 10 according to the present invention, adapted to alternatively charge, according to a cyclic operation, the two vats 21, 23 with fresh limestone, comprises means for storing and supplying limestone, adapted to receive such limestone supplied by charging means, to store and supply it in turn to vats 21, 23 alternatively and cyclically by interposing the supply valves

mentioned below. In particular, in the preferred embodiment shown, such storing and supplying means comprises a first and a second intermediate tank for storing and supplying limestone, respectively designated with references 11 and 13, each one of which has an upper opening connected to the charging means, which can be a charging hopper 15, from which it receives a supply of limestone, and a lower opening connected with a respective vat 21, 23 to supply this latter one by gravity with the limestone contained therein. Both the upper and the lower opening are then equipped with respective upper and lower supply valves adapted to cyclically insulate the internal volume of intermediate tanks 11, 13 alternatively from the charging hopper 15 or the respective vat 21, 23.

Such supply valves are, in the preferred embodiment shown, upper airtightly sealed doors 11a, 13a placed in order to open or close the upper openings of intermediate tanks, respectively 11 and 13, and lower airtightly sealed doors lib, 13b placed in order to open or close the lower openings of intermediate tanks, respectively 11 and 13, such doors 11a, lib, 13a, 13b being preferably adapted to be opened in the gravity fall direction of lime from the charging hopper 15 towards the vats 21, 23. Alternatively, the supply valves could be any other type of functionally adequate airtightly sealed valve or device.

In order to allow supplying limestone to the oven 20 during the combustion step, therefore without the need of having to depressurise vats 21, 23, the system 10 according to the present invention is "further equipped with an internal pressure equalizing device for the intermediate tanks 11,13. Such device is in fact adapted, as can be seen afterwards in greater detail, to cyclically equalize the internal pressure of storing and supplying means alternatively with the pressure at which the charging means operate, or with the internal pressure of the oven 20, thereby solving the problems deriving from the

existence of not neglectable pressure differentials between the environment in which the charging means operate and the inside of the oven 20 with which the storing and supplying means must alternatively communicate. In particular, in the preferred embodiment shown, the internal pressure equalizing device operates by equalising the internal pressure of intermediate tanks 11, 13 cyclically with the charging hopper 15 pressure, typically at ambient pressure, to allow opening the upper airtightly sealed doors 11a, lib, and with the internal oven pressure, to allow opening the lower airtightly sealed doors 13a, 13b during system 10 operation.

In the preferred embodiment of the present invention, the internal pressure equalizing device is composed of at least a first and a second equalization circuits, respectively 30, 40 preferably independent and advantageously mutually equal, and each one of which is adapted to control the internal pressure of one of the two intermediate tanks 11, 13. Each equalisation circuit 30, 40 is adapted to connect, by interposing a valve system described below, the respective intermediate tank 11, 13 alternatively with an environment having the same pressure at which the charging hopper 15 operates, and with the oven 20 interior or with an environment having its same internal pressure; in this way, cyclically, each intermediate tank 11, 13 during the system 10 operation, will have an internal pressure equal to the one at which the charging hopper 15 operates, typically the ambient pressure, or equal to the internal oven 20 pressure. For such purpose, each equalisation circuit 30, 40 is preferably composed of a piping 31, 41 exiting from the respective intermediate tank 11, 13 which is divided into a first piping 33, 43 which is connected to the environment, having the same pressure at which the charging hopper 15 operates, and a second piping 35, 45 which is connected to the oven 20 interior or to an environment having its same internal

pressure; each first piping 33, 43 is equipped with a first equalisation valve 37, 47 anc each second piping 35, 45 is equipped with a second equalisation valve 39, 49. If supply valves are all closed, therefore when the first equalisation valve 37, 47 is open and the second equalisation valve 39, 49 is closed, the respective intermediate tank 11, 13 has an internal pressure equal to the 'one in the environment in which the charging hopper 15 operates; when instead the first equalisation valve 37, 47 is closed and the second equalisation valve 39, 49 is open, the respective intermediate tank 11, 13 has an internal pressure equal to the oven 20 pressure.

In order to better understand the cyclic operation of the system 10 according to the present invention, herein below a sequence of operating steps will be described, carried out by the system 10 itself, starting, as a non-limiting example, from the supply of fresh limestone to the first vat 21. Consequently, as an explanation, one starts from a status in which all supply valves and all equalisation valves are assumed as closed: the system 10 then operates as follows: the first equalisation valve 37 of the first equalisation circuit 30 is opened: in this way, the first intermediate tank 11 assumes the same internal pressure as of the environment in which the charging hopper 15 operates and it is possible to open the upper airtightly sealed door 11a without the problems deriving from pressure differentials;

- the upper airtightly sealed door 11a of the first intermediate tank 11 -is opened and the fresh limestone, due to gravity, precipitates from the charging hopper 15 inside the first intermediate tank 11;

- the upper airtightly sealed door 11a of the first intermediate tank 11 and the first equalisation valve 37 of the first equalisation circuit 30 are closed; the second equalisation valve 39 of the first equalisation

circuit 30 is opened: in this way the first intermediate tank 11 assumes the same internal pressure as of the oven 20 and it is therefore possible to open the lower airtightly sealed door lib of the first intermediate tank 11 without the problems deriving from pressure differentials; the lower airtightly sealed door lib of the first intermediate tank 11 is ^' opened and the fresh limestone contained in the first intermediate tank 11, due to gravity, precipitates inside the first vat 21;

- the lower airtightly sealed door lib of the first intermediate tank 11 and the second equalisation valve 39 of the first equalisation circuit 30 are closed;

- the first equalisation valve 47 of the second equalisation circuit 40 is opened: in this way the second intermediate tank 13 assumes the same internal pressure as of the environment in which the charging hopper 15 operates and it is possible to open the upper airtightly sealed door 13a of the second intermediate tank 13 without the problems deriving from pressure differentials; the upper airtightly sealed door 13a of the second intermediate tank 13 is opened and the fresh limestone, due to gravity, precipitates from the charging hopper 15 inside the second intermediate tank 13; the upper airtightly sealed door 13a of the second intermediate tank 13 and the first equalisation valve 47 of the second equalisation circuit 40 are closed;

- the second Equalisation valve 49 of the second equalisation circuit 40 is opened: in this way the second intermediate tank 13 assumes the same internal pressure as of the oven 20 and it is therefore possible to open the lower airtightly sealed door 13b of the second intermediate tank 13 without the problems deriving from pressure differentials; the lower airtightly sealed door 13b of the second

intermediate tank 13 is opened and the fresh limestone contained in the second intermediate tank 13, due to gravity, precipitates inside the second vat 23; the lower airtightly sealed door 13b of the second intermediate tank 13 and the second equalisation valve 49 of the second equalisation circuit 40 are closed; the sequence of previous steps is then repeated starting from the first step.

Obviously, opening and closing of supply valves and/or control of the internal pressure equalizing device can be operations managed and performed at suitable times by a human operator; alternatively, such operations can be controlled and managed by automatic controlling and managing means, such as for example PLC systems.

In an alternative embodiment, not shown, of the system 10 according to the present invention, the storing and supplying means can advantageously be a single "intermediate tank connected on its lower side both to the first vat 21 and to the second vat 23; such single intermediate tank would then receive as supply the limestone from the charging means by interposing an upper supply valve and alternatively and cyclically it would supply with the same limestone the first vat 21 or the second vat 23 by interposing related first and second lower supply valves. In this case, the pressure equalizing device could also be composed of a single equalisation circuit which cyclically equalizes the internal pressure of the intermediate tank with the environment in which charging means operate or with the internal oven 20 pressure.

In compliance with what has been described above, subject matter of the present invention is also a process for charging limestone in regenerating ovens which uses the cyclically charging system 10 according to the present invention. The process according to the present invention, starting like before

opening the upper airtightly sealed door 11a of the first intermediate tank 11; closing the upper supply valve of the first intermediate tank 11; in particular such step preferably comprises the step of closing the upper airtightly sealed door 11a of the first intermediate tank 11 and the first equalisation valve 37 of the first equalisation circuit 30; equalising the internal pressure of the first intermediate tank 11 with the internal pressure of the oven 20; in particular such step preferably comprises the step of opening the second equalisation valve 39 of the first equalisation circuit 30; opening the lower supply valve of the first intermediate tank 11 and precipitating the fresh limestone, due to gravity, inside the first intermediate tank 11 inside the first vat 21; in particular such step preferably comprises the step of opening the lower airtightly sealed door lib of the first intermediate tank 11; closing the lower supply valve of the first intermediate tank 11; in particular such step preferably comprises the step of closing the lower airtightly sealed door lib of the first intermediate tank 11 and the second equalisation valve 39 of the first equalisation circuit 30; equalising the internal pressure of the second intermediate tank 13 with the pressure of the environment in which the charging hopper 15 operates; in particular such step preferably comprises the step of opening the first equalisation valve 47 of the second equalisation circuit 40; opening the upper supply valve of the second intermediate tank 13 and precipitating the fresh limestone, due to gravity, from the charging hopper 15 inside the second intermediate tank 13; in particular such step preferably comprises the step of opening the upper airtightly sealed door 13a of the second intermediate tank 13;

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from a status in which, as an example, all supply valves and all equalisation valves are assumed as closed, then comprises the steps of: equalising the internal pressure of the storing and supplying means with the pressure of the environment in which the charging means operate; supplying the storing and supplying means with limestone from the charging means; equalising the internal pressure of the storing and supplying means with the internal pressure of the oven 20; supplying the first vat 21 with said limestone from the charging means; equalising the internal pressure of the storing and supplying means with the pressure of the environment in which the charging means operate; supplying the storing and supplying means with limestone from the charging means; equalising the internal pressure of the storing and supplying means with the internal pressure of the oven (20); supplying the second vat (23) with the limestone; cyclically repeating the previous steps.

With reference now to the preferred and shown embodiment of the system 10, the process according to the present invention comprises in particular the steps of:

- equalising the internal pressure of the first intermediate tank 11 with the pressure of the environment in which the charging hopper 15 operates; in particular such, step preferably comprises the step of opening the first equalisation valve 37 of the first equalisation circuit 30; opening the upper supply valve of the first intermediate tank 11 and precipitating the fresh limestone, due to gravity, from the charging hopper 15 inside the first intermediate tank 11; in particular such step preferably comprises the step of

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closing the upper supply valve of the second intermediate tank 13; in particular such step preferably comprises the step of closing the upper airtightly sealed door 13a of the second intermediate tank 13 and the first equalisation valve 47 of the second equalisation circuit 40; equalising the internal pressure of the second intermediate tank 13 with the internal pressure of the oven 20; in particular such step preferably comprises the step of opening the second equalisation valve 49 of the second equalisation circuit 40; opening the lower supply valve of the second intermediate tank 13 and precipitating the fresh limestone, due to gravity, inside the second intermediate tank 13 inside the second vat 23; in particular such step preferably comprises the step of opening the lower airtightly sealed door 13b of the second intermediate tank 13; closing the lower supply valve of the second intermediate tank 13; in particular such step preferably comprises the step of closing the lower airtightly sealed door 13b of the second intermediate tank 13 and the second equalisation valve 49 of the second equalisation circuit 40; cyclically repeating the previous sequence starting from the first step.

With reference now to FIG. 2, it is possible to note two diagrams which compare the time length of the reversal or preeating/reversal cycle of a traditional regenerating oven (diagram A) with respect to the ones of a regenerating oven equipped with ths system 10 according to the present invention and/or charged according to the above described process (diagram B) : from such comparison, the advantages deriving from the present invention are clear. In particular, tcl and tc2 designate the combustion cycle length respectively in the first and in the second vat 21, 23, and tp designates the length of

the pre-heating/reversal cycle; from the comparison of the two diagrams, it is clear that the use of the system and/or process according to the present invention allows prolonging the combustion cycle up to about twice the cycle length in a traditional oven due to the fact that, by supplying fresh limestone during the combustion cycle, an excessive increase of exhaust gas temperature is avoided. It is therefore clear that the use of the system and/or the process according to the present invention allows highly increasing lime production with respect to a traditional oven due to the increase in the combustion period length between a vat reversal and another.

Moreover, another advantage from the use of the system and/or the process according to the present invention is that they allow supplying limestone to vats avoiding that powders and vapours go out of the vats themselves, since insulated from the enviroment during the supply step by interposing the storing and supplying means.