CLINKER PRODUCTION PLANT AND METHOD FOR PRODUCING CLINKER IN SUCH A PLANT

Abstract

Disclosed is a clinker production plant including: a preheating unit; a calcination unit; a kiln; and a cooler. The calcination assembly includes a calcination reactor for calcination by combustion of a solid so-called alternative fuel. The calcination reactor is arranged such that at least part of the combustion fumes from the kiln pass partly through the calcination reactor before entering the preheating unit, and a tertiary gas flow including air leaving the cooler passing at least in part through the calcination reactor before entering the preheating unit. The calcination reactor includes a system for controlling the residence time of the alternative solid fuel.

Claims

1. A clinker production plant (1) comprising: a preheating unit (2), in which raw material is preheated; a calcination unit (3), in which the preheated raw material is at least partially decarbonated; a kiln (4) in which the preheated and at least partially decarbonated raw material is baked; a cooler (5) in which the fired kiln material is cooled by cooling air; plant in which the calcination assembly comprises a reactor (8) to calcinate by combustion a solid so-called alternative fuel, the calcination reactor (8) being arranged, according to the direction of flow of the gases, between the preheating assembly (2) and the kiln (4), and being connected to the cooler (5) so that: at least part of the combustion fumes from the kiln (4) pass at least partly through the calcination reactor (8) before entering the preheating unit (2), a tertiary gas flow comprising at least in part air leaving the cooler (5) passes at least in part through the calcination reactor (8) before entering the preheating unit (2), and wherein the calcination reactor (8) comprises a system for controlling the residence time of the alternative solid fuel in the calcination reactor (8).

2. The plant according to claim 1 comprising a tertiary flow rate adjustment system (13) configured to ensure, in the calcination reactor (8), a balance between the supply of oxygen necessary for the combustion reaction and the reduction of the NOx produced in the kiln (4).

3. The plant (1) according to claim 1, wherein the calcination reactor (8) is a rotary kiln, where the alternative solid fuel residence time control system is a system for controlling the rotational speed and/or slope of the calcination reactor (8).

4. The plant (1) according to claim 1, wherein the preheating unit (2) comprises at least one cyclone preheater.

5. The plant according to claim 1, in which the calcination unit (3) furthermore comprises an additional calcination reactor (10) supplied with fuel, the additional calcination reactor (10) being arranged between the calcination reactor (8) and the preheating unit (2) in the direction of gas flow, so that at least some of the fumes leaving the calcination reactor (8) pass through the additional calcination reactor (10) before entering the preheating unit (2).

6. Installation (1) according to claim 1, in which the calcination assembly (3) furthermore comprises an auxiliary calcination reactor (11), supplied with a fuel, the auxiliary reactor (11) being connected to the cooler (5) upstream of the calcination reactor (8) in the direction of flow of the gases, so that the tertiary gas flow supplying the calcination reactor (8) comprises at least some of the fumes leaving the auxiliary reactor (11).

7. A method for producing clinker in a plant (1) according to claim 1, said method comprising: preheating the raw material in the preheating unit (2); decarbonating the preheated material in the calcination unit (3); baking the preheated and decarbonated material in the kiln (4); cooling the fired material in the cooler, the cooling being carried out by means of cooling air; the method further comprising: feeding the calcination reactor (8) with at least part of the kiln (4) fumes and a tertiary gas stream comprising at least part of the cooling air leaving the cooler (5); combusting in the calcination reactor (8) of a solid alternative fuel and the adjustment of the residence time of the solid alternative fuel in the calcination reactor (8); recovering the fumes from the calcination reactor (8) to feed the preheating unit (2).

8. The method according to claim 7, wherein the solid alternative fuel is a solid fuel comprising particles having a characteristic size greater than 20 mm.

9. The method according to claim 7, wherein the solid alternative fuel is a solid fuel comprising particles having a characteristic size greater than 80 mm.

10. The method according to claim 7, wherein the tertiary gas flow to the calcination reactor (8) can be controlled so as to achieve a balance between the supply of oxygen needed for the combustion reaction and the reduction of NOx produced in the kiln (4).

11. The plant (1) according to claim 2, wherein the calcination reactor (8) is a rotary kiln, where the alternative solid fuel residence time control system is a system for controlling the rotational speed and/or slope of the calcination reactor (8).

12. The plant (1) according to claim 2, wherein the preheating unit (2) comprises at least one cyclone preheater.

13. The plant (1) according to claim 3, wherein the preheating unit (2) comprises at least one cyclone preheater.

14. The plant according to claim 2, in which the calcination unit (3) furthermore comprises an additional calcination reactor (10) supplied with fuel, the additional calcination reactor (10) being arranged between the calcination reactor (8) and the preheating unit (2) in the direction of gas flow, so that at least some of the fumes leaving the calcination reactor (8) pass through the additional calcination reactor (10) before entering the preheating unit (2).

15. The plant according to claim 3, in which the calcination unit (3) furthermore comprises an additional calcination reactor (10) supplied with fuel, the additional calcination reactor (10) being arranged between the calcination reactor (8) and the preheating unit (2) in the direction of gas flow, so that at least some of the fumes leaving the calcination reactor (8) pass through the additional calcination reactor (10) before entering the preheating unit (2).

16. The plant according to claim 4, in which the calcination unit (3) furthermore comprises an additional calcination reactor (10) supplied with fuel, the additional calcination reactor (10) being arranged between the calcination reactor (8) and the preheating unit (2) in the direction of gas flow, so that at least some of the fumes leaving the calcination reactor (8) pass through the additional calcination reactor (10) before entering the preheating unit (2).

17. Installation (1) according to claim 2, in which the calcination assembly (3) furthermore comprises an auxiliary calcination reactor (11), supplied with a fuel, the auxiliary reactor (11) being connected to the cooler (5) upstream of the calcination reactor (8) in the direction of flow of the gases, so that the tertiary gas flow supplying the calcination reactor (8) comprises at least some of the fumes leaving the auxiliary reactor (11).

18. Installation (1) according to claim 3, in which the calcination assembly (3) furthermore comprises an auxiliary calcination reactor (11), supplied with a fuel, the auxiliary reactor (11) being connected to the cooler (5) upstream of the calcination reactor (8) in the direction of flow of the gases, so that the tertiary gas flow supplying the calcination reactor (8) comprises at least some of the fumes leaving the auxiliary reactor (11).

19. Installation (1) according to claim 4, in which the calcination assembly (3) furthermore comprises an auxiliary calcination reactor (11), supplied with a fuel, the auxiliary reactor (11) being connected to the cooler (5) upstream of the calcination reactor (8) in the direction of flow of the gases, so that the tertiary gas flow supplying the calcination reactor (8) comprises at least some of the fumes leaving the auxiliary reactor (11).

20. Installation (1) according to claim 5, in which the calcination assembly (3) furthermore comprises an auxiliary calcination reactor (11), supplied with a fuel, the auxiliary reactor (11) being connected to the cooler (5) upstream of the calcination reactor (8) in the direction of flow of the gases, so that the tertiary gas flow supplying the calcination reactor (8) comprises at least some of the fumes leaving the auxiliary reactor (11).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Other features and advantages will become apparent in the light of the description of the embodiments of the invention accompanied by the figures in which:

[0061] FIG. 1 is a diagram illustrating a cement clinker production plant using a state-of-the-art embodiment;

[0062] FIG. 2 is a diagram illustrating a cement clinker production plant using according to a first embodiment of the invention;

[0063] FIG. 3 is a diagram illustrating a cement clinker production plant using according to a second embodiment of the invention;

[0064] FIG. 4 is a diagram illustrating a cement clinker production plant using according to a third embodiment of the invention; and

[0065] FIG. 5 is a diagram illustrating a cement clinker production plant using according to a fourth embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0066] FIG. 1, which represents a state of the art, has already been described above.

[0067] FIGS. 2 to 5 show four embodiments of a cement clinker production plant 1.

[0068] In a classical way, and following generally the direction of the material flow, the plant 1 includes: [0069] a preheating unit 2, in which the raw material is preheated and at least partially decarbonated; [0070] a calcination unit 3, in which the preheated raw material is at least partially decarbonated; [0071] a kiln 4 in which the preheated and at least partially decarbonated raw material is baked; [0072] a cooler 5 in which the fired kiln 4 material is cooled by cooling air.

[0073] Specifically, the preheating unit 2 comprises a plurality of cyclones, e.g. five, arranged in series, in which the material is carried from cyclone to cyclone by a carrier gas from the calcination unit 3. In FIGS. 2 to 5, the preheating unit 2 has been represented by a first block 2a representing the first cyclones, and a second block 2b representing the last cyclone(s), in order to facilitate the description that follows.

[0074] Kiln 4 is, for example, a rotary kiln, the material feed in kiln 4 to the cooler 5 being controlled by the rotation and/or inclination of kiln 4. A burner 6 is provided in kiln 4, on the side opposite to the material feed into kiln 4. This burner is fuelled by a conventional 4a fuel, i.e. by a fossil fuel or an alternative fuel in liquid or gaseous form, or by a solid alternative fuel treated so as to have characteristic particle sizes of less than 20 mm. The kiln flame generated by burner 6 is supplied with so-called primary air, i.e. air from outside the plant injected via burner 6, and is also supplied with so-called secondary air, i.e. heated air from the cooler 5.

[0075] For this purpose, cooler 5 has a cooling air inlet. This air is heated by the hot cooked material with which it comes into contact in the cooler. In order to take advantage of this heated air, some of it is recovered and sent to kiln 4 as secondary air. It can also be sent for another part to the calcination unit 3 as tertiary air.

[0076] As shown in FIGS. 2 to 5, the secondary and tertiary air are taken from the same location, in this case at the heating hood on cooler 5, so that a single distribution sheath 7 supplies the secondary and tertiary air. Of course, it can be otherwise, as the tertiary air intake can be made at a point on the cooler 5 where the heated cooling air is cooler than the secondary air taken from the heating hood.

[0077] According to the invention, the calcination unit 3 comprises a calcination reactor 8 which is arranged between the kiln 4 and the preheater 2 in the direction of flow of the fumes in plant 1, so that at least some, and preferably all, of the fumes leaving the kiln enter the calcination reactor 8 before entering the preheater 2.

[0078] In what follows, the positions of the equipment, and in particular the terms upstream and downstream, shall be understood, unless otherwise specified, in relation to the direction of flow of the gases in installation 1.

[0079] The calcination reactor 8 may include, but is not necessarily limited to, a burner. However, the fumes from furnace 4 are generally hot enough, at a temperature of around 1100 C., to provide the energy needed to burn the coarse alternative solid fuel in reactor 8. Recycling the energy of the flue gas from kiln 4 into the calcination reactor 8 thus reduces the energy costs of plant 1.

[0080] The calcination reactor 8 is also connected, directly or indirectly, to the distribution duct 7, so that it is fed by a so-called tertiary gas flow coming from cooler 5. Specifically, as will be explained later, the tertiary gas stream includes at least some tertiary air. This tertiary flow provides the oxygen necessary for the combustion reaction.

[0081] Calcining reactor 8 has a fuel inlet 8a. According to the invention, it is a coarse alternative solid fuel. The term coarse is used here to refer to a particle size larger than that of the solid fuels normally used. In particular, a coarse alternative solid fuel here comprises particles with at least one characteristic size greater than or equal to 20 mm (millimetres), and preferably greater than or equal to 80 mm. The particles of the coarse alternative solid fuel injected into the calcination reactor 8 can reach characteristic dimensions of around 500 mm, so that any preliminary shredding operation involves much lower costs than the shredding operations mentioned in the introduction for the state of the art.

[0082] The calcination reactor 8 also includes a system for adjusting the residence time of the coarse alternative solid fuel: the residence time is adjusted so that the fuel is completely consumed, so that only mineral residues fall into kiln 4 and mix with the material.

[0083] According to a particular embodiment, which is the one shown in the figures, the calcination reactor 8 is a rotary kiln. The residence time of the fuel can then be adjusted by two parameters: the inclination of reactor 8 and the rotation speed. The feeding of coarse alternative solid fuel into the calcination reactor 8 is then preferably done on the highest side, so that the fuel has the whole length of the calcination reactor 8 to burn out and only ashes reach the lowest point of the calcination reactor 8, before falling into the clinker kiln 4.

[0084] The fuel residence time adjustment system makes it possible to adapt the residence time in particular according to the nature of the coarse alternative solid fuel supplied. This is because coarse alternative solid fuel can have different origins, and therefore different combustion properties in different batches. The particle size of the alternative solid fuel may also vary depending on its origin. It is therefore advantageous to be able to adjust the residence time in the calcination reactor 8 in order to always achieve complete combustion of the coarse alternative fuel.

[0085] Preferably, the tertiary flow rate is adjusted to achieve a balance between the oxygen supply needed for the combustion reaction and the need to reduce the NOx produced in the kiln 4.

[0086] Indeed, conditions in kiln 4 are favourable to the appearance of NOx, which are highly polluting pollutants. In order to reduce NOx, and to further avoid their occurrence in the calcination reactor 8, the amount of oxygen arriving through the tertiary flow is controlled.

[0087] Preferably, the fumes from kiln 4 and the tertiary air flow mix upstream or at the inlet of the calcination reactor 8, so that the NOx reduction mechanism of the fumes from kiln 4 is controlled by the tertiary flow rate. The amount of NOx leaving plant 1 is thus advantageously limited. The control of the proportion of the tertiary flow feeding the calcination reactor 8 is such that the alternative fuel is subjected in the reactor to the high temperatures of the fumes from the kiln, in order to cause first of all at least the partial volatilisation of the alternative fuel, in a reducing atmosphere, and thus the release of pyrolysis products (from the alternative fuel) which recombine by reaction with NO to be transformed into N2, thus ensuring the reduction of NOx.

[0088] The combustion of the alternative fuel is then carried out in the same calcination reactor 8 using oxygen from tertiary air. The calcination reactor 8 thus makes it possible to combine both the control of the combustion of a coarse alternative solid fuel and the control of the reduction of NOx contained in the fumes of kiln 4.

[0089] For this purpose, the installation includes a tertiary flow rate adjustment system 13, which may include dampers and/or valves, to control the proportion of tertiary air arriving at the calcination reactor 8.

[0090] This adjustment system 13 is configured to ensure a slightly reducing atmosphere in the calcination reactor, allowing both the correct combustion of the solid alternative fuels and the reduction of the NOx produced by the kiln.

[0091] Four embodiments of this invention will now be described in detail.

[0092] According to a first embodiment illustrated in FIG. 2, the tertiary flow comprises only tertiary air, the calcination reactor 8 being directly connected to the distribution sheath 7.

[0093] The calcination reactor 8 is followed, downstream in the direction of gas flow, by a sheath 9 called gooseneck, in which the calcination of the material continues under the effect of the residual heat in the gases passing through gooseneck 9. Possibly, as shown in FIG. 2, tertiary air may be fed into gooseneck 9 to support combustion. The adjustment system 13 allows the proportion of tertiary air supplied to the inlet of the calcination reactor 8 to be adjusted, and the remaining proportion to be supplied downstream, for example a little further into the calcination reactor 8, or even downstream of the calcination reactor 8, for example in the gooseneck 9, and as shown in FIG. 2.

[0094] Specifically, material leaving the first block 2a of preheater 2 is suspended in the rising gas flow circulating through the gooseneck 9. This material is transported by the fumes and gases from kiln 4 and calcination reactor 8 to the second block 2b of preheater 2. The material is then sent to the inlet of the clinker kiln 4.

[0095] According to a second embodiment illustrated in FIG. 3, compared to the first embodiment, the calcination unit 3 includes an additional calcination reactor 10 between calcination reactor 8 and gooseneck 9. Thus, the fumes from calcination reactor 8 enter, at least in part and preferably completely, into the additional reactor 10, pass through the gooseneck 9 and enter the preheater 2. The additional reactor 10 includes in particular an inlet 10a for a conventional fuel as defined above. An additional tertiary air supply can also be provided in the additional reactor 10 to feed the combustion. This additional reactor 10 therefore makes it possible to consume conventional fuels when these are available to supplement the energy input required to achieve the targeted level of decarbonation of the material.

[0096] According to a third embodiment illustrated in FIG. 4, compared to the first embodiment, the calcination unit 3 comprises an auxiliary reactor 11, connected to the distribution sheath 7, upstream of the calcination reactor 8 according to the direction of gas flow. A burner 12 is used to ignite a fuel supplying in 11a the auxiliary reactor 11.

[0097] For example, when the available fuel is difficult to ignite, in particular because it contains little volatile matter, it is preferable to ignite the fuel in such a dedicated auxiliary reactor 11, in which the energy and the quantity of oxygen, contained in the tertiary air arriving through the distribution sheath 7, which are necessary for combustion, are supplied to ensure stable and controlled combustion.

[0098] The gases coming out of the auxiliary reactor 11, mixed with combustion fumes and tertiary air, then form the tertiary gas flow which is sent to the inlet of the calcination reactor 8, where it mixes with the fumes from kiln 4.

[0099] As in the first embodiment, the fumes from calcination reactor 8 pass through a gooseneck 9, carrying the material to be calcined, and then arrive at preheater 2 where they preheat the material before leaving plant 1.

[0100] In a fourth embodiment, shown in FIG. 5, the plant includes an additional calcination reactor 10 in the second embodiment, and an auxiliary calcination reactor 11 in the third embodiment, to combine their effects and benefits.

[0101] The clinker production plant 1 thus described offers great flexibility in the use of fuels. Indeed, depending on the nature and origin of the fuels available for plant 1, the different reactors 8, 10 and 11 can be used, adapting the proportions of the different fuels and material arriving at reactors 8, 10 and 11 according to energy requirements.

[0102] Plant 1 thus described makes it possible in particular to use alternative solid fuels in coarse form in a cement clinker manufacturing process, without any prior fuel shredding step, in an efficient manner thanks in particular to the control of the fuel residence time in the calcination reactor 8, and thanks to the use of fumes from the clinker kiln 4 and tertiary air from the cooler 7.

[0103] Plant 1 also reduces the need for a cleaning step to remove NOx from the kiln fumes. Indeed, the position of the calcination reactor 8 in the fume path of kiln 4, combined with the control of the oxygen supply to the calcination reactor 8, creates the right conditions to obtain a NOx reduction reaction.

[0104] The amount of energy consumed by plant 1 is thus increased little or not at all by the introduction of coarse alternative solid fuels. The calorific value of coarse alternative solid fuels is efficiently exploited. Clinker production costs are reduced.