EP2242975A2

EP2242975A2 - Method of heating a mineral feedstock in a firing furnace of the tunnel furnace type

Info

Publication number: EP2242975A2
Application number: EP09709567A
Authority: EP
Inventors: Mohand Amirat; Robert Kalcevic; Faustine Panier; Rémi Tsiava
Original assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 2008-02-11
Filing date: 2009-02-11
Publication date: 2010-10-27
Also published as: CN101946148A; WO2009101361A3; WO2009101361A2; US20100316969A1; FR2927409A1; FR2927409B1

Abstract

Method of heating a mineral feedstock in a firing furnace of the tunnel furnace type, having a hearth with an upstream inlet, a downstream outlet and sidewalls fitted with burners, in which method the feedstock is transported as a layer of approximately constant thickness along a treatment path in which the feedstock is heated and fired by means of said burners so as to obtain a fired product, said path being located between the upstream inlet and the downstream outlet of the furnace, characterized in that said burners comprise at least one fuel injector and at least one oxidizer injector and are positioned and oriented in such a way that their flames do not impact the layer, the at least one oxidizer injector being positioned relative to the at least one fuel injector so that the at least one fuel jet injected by the at least one fuel injector is separated from the layer by at least one oxidizer jet injected by at least one oxidizer injector.

Description

METHOD FOR HEATING A MINERAL CRU IN A TUNNEL FURNACE COOKING FURNACE

The present invention relates to a method for heating a mineral meal in a tunnel type baking oven.

CO ₂ emissions related to human activity are likely to be responsible for much of the global warming that seems to be occurring at the terrestrial level. This observation led in particular to the signing of the Kyoto Protocol. Since a growing number of countries are setting targets in terms of limiting CO ₂ emissions. In the case of the European Union, for example, the implementation of this protocol resulted in an emissions allowance system _CO2, or quotas.

With emissions of about 0.7 to 0.8 tonnes of CO ₂ per tonne of cement produced, cement manufacturers are among the largest emitters worldwide (nearly 5% of global emissions related to human activity). Cement companies must therefore be particularly active in finding ways to reduce their CO ₂ emissions.

The means implemented and the avenues for research to reduce CO2 emissions vary. Among these lines of research, we can mention the use of biofuels, the capture of CO ₂ for its sequestration, or changes in the composition of the raw, with more additions.

The question of reducing CO ₂ emissions also arises for the cooking of other mineral crus.

In the manufacture of cement, the raw material, called raw, which is a mixture of clay and limestone mainly, is: first (1) homogenized, typically by grinding, and (2) dried, then (3) reheated , typically up to about 900 ^° C., and (4) decarbonated - at the reheating temperature the calcium carbonate decomposes to give lime and carbon dioxide - and then (5) clinkerized. The clinker thus obtained is quenched in the air and then ground with gypsum to form the cement.

The clinker is obtained by firing at high temperature (clinkerization), generally between 1100 ⁰ C and 1400 ⁰ C, decarbonated raw. At this temperature, the lime and the various components of the material recombine to form the clinker. Clinkering usually takes place in a rotary kiln. It has also been proposed to implement a tunnel kiln for clinker firing. Thus it is known from WO-A-02094732 to manufacture sulfo-aluminous and / or ferroaluminous cement by clinkerization of a particular raw material in a tunnel oven, said raw material being treated until clinkerization by displacement in the furnace hearth , in a sheet of substantially constant thickness and at a substantially constant speed of movement, along a treatment path subjected to a positive gradient of temperature, and during a treatment time during which the raw material remains below its temperature of fusion, the clinkerized product being cooled at the output of the treatment path.

The firing of a mineral raw material and in particular the clinkerization in a tunnel furnace must be carried out under stable operating conditions in order to preserve the installation and to reduce the costly maintenance and to ensure the quality of the cooked product.

Except in exceptional cases, clinkering is advantageously carried out in an oxidizing medium. If this is not the case, the sulfur contained in the raw material (SO ₄ ^{2 "} ) is reduced to SO ₂ and goes off with the combustion gases, which poses two problems: the fumes must then be cleaned up and the clinker lost element SO ₄ ^{2 "} is detrimental to its quality. Similar considerations arise for the cooking of other mineral crus.

However, an excessive surplus of oxygen degrades the energy performance of the installation. In fact, a surplus of oxygen dilutes and lowers the temperatures and the overconsumption of oxygen waste oxygen which is expensive.

The object of the present invention is to provide a combustion technology, adapted to tunnel furnaces, which meets the constraints described above.

The present invention relates in particular to a method of heating a mineral meal in a tunnel furnace type baking furnace having a focus with an inlet upstream, a downstream outlet and side walls equipped with burners. The raw material travels a treatment path between the upstream inlet and the downstream outlet of the hearth. The raw material is conveyed in a substantially constant thickness web along the treatment path where the raw material is heated and cooked by means of said burners so as to obtain a cooked product, such as clinker. Said burners comprise at least one fuel injector and at least one oxidant injector, said oxidant having an oxygen content of greater than 22% vol. These burners are hereinafter referred to as "oxyburners". These oxy-burners are positioned and oriented so that their flames do not impact the sheet. According to the invention, the at least one oxidant injector is positioned relative to the at least one fuel injector so that the at least one fuel jet injected by the at least one fuel injector is separated from the fuel injector. tablecloth by at least an oxidant jet injected by at least one oxidant injector. Thus, at least one oxidant jet is interposed between each fuel jet and the web. On the other hand, as will be explained in more detail below, it is not necessary for the whole of an oxidizing jet or all the oxidant jets of an oxy-burner to be inserted between a jet of fuel and the tablecloth.

Thanks to this positioning of the fuel and oxidizer injectors, an oxidizing atmosphere is created directly above the raw material.

As indicated above, in kiln type furnaces (kiln tunnel), the raw material is transported between the inlet upstream and the outlet downstream of the hearth. For the transport of the raw material, the tunnel kilns are equipped with appropriate mechanical means of transport adapted to the temperatures that prevail in the home. Thus, the raw material can be transported through the hearth by means of rollers, as described in particular in WO-A-02094732, on a treadmill or on trolleys (in English "kiln-cars") as described in part 2.2.7.4.2 "Tunnel kilns" of the reference document of the European Commission entitled "Reference Document on Best Available Techniques in the Ceramic Manufacturing Industry" of August 2007

The tunnel type furnaces are thus distinguished from rotary kilns (in English "rotary kilns") which are not equipped with such means for the transport of the raw material and in which, in particular, the transport of the raw material is typically carried out under the effect gravity by tilting the same rotary kiln.

The cooked product is typically cooled at the outlet of the treatment path.

According to one embodiment, at least one oxy-burner is a concentric injection oxy-burner with a peripheral oxidant injection making it possible to create an oxidizing atmosphere outside the flame envelope. In this case, the oxidant jet injected by the peripheral injection surrounds the fuel jet, the lower part of the peripheral oxidant jet being interposed between the fuel jet and the sheet, thus separating the fuel jet from the fuel jet. the tablecloth. Preferably, the process will use several such concentric injection oxy-burners. Advantageously, all the oxy-burners mounted in the side walls of the furnace are such concentric injection oxy-burners.

When heating a mineral raw material in a tunnel kiln type cooking oven, the raw material is static on a moving trolley / mat. In order to obtain a homogeneous heating of the load, it is necessary to carry out a heat transfer substantially homogeneous over the width of the oven. Such heat transfer in substantially homogeneous be realized by means of an implementation mode in which at least one oxy-burner is a concentric injection oxy-burner with:

• a peripheral oxygen injection,

• a central oxygen injection, and

• a fuel injection between the peripheral oxygen injection and the central oxygen injection.

Preferably, a plurality, or all of them, of the oxy-burners are oxy-burners of this type.

The jet of oxidant injected by the central oxidant injection is advantageously injected at a higher impulse than the jet of oxidant injected by the peripheral oxidant injection.

With this type of burner with central and peripheral injection of oxidant, it is possible, in the method according to the invention, to adjust the length of the flame resulting from the burner of this type by adjusting the distribution between the injected oxidant jet. by injecting central oxidant and the oxidant jet injected by the peripheral oxidant injection. The oxidant jet injected by the central oxidant injection represents between 8% and 30% of the totality of oxygen injected by the oxy-burner.

Another advantage that this type of burners present is their good adaptability of power.

According to one embodiment, at least one of the oxy-burners comprises one or more lower oxidant injectors situated below the at least one fuel injector so that the oxidant jet (s) injected by the lower injector (s) separate the at least one fuel jet injected by the at least one fuel injector of the web. Thus, the oxidant jet (s) injected by the lower injector (s) are interposed between the fuel jet (s) and the layer. Note that it is not necessary that all oxidizer injectors are lower injectors located below the fuel or injectors. In fact, the oxy-burner may also comprise one or more oxidant injectors located at one or more fuel injectors and / or located at a level above one or more fuel injectors.

When the oxy-burner comprises one or more lower oxidant injectors as described above, the oxy-burner is advantageously an oxy-burner with a staged oxidant injection. In the case of an oxy-burner with a staged injection of oxidant, a first part oxidant, called primary oxidant, is injected near the fuel jet or jets, a second part of the oxidant, said secondary oxidant being injected at a greater distance from the fuel jet or jets, a third part of the oxidant, said tertiary oxidant, being optionally injected at an even greater distance from the fuel jet or jets. In this way, a staged combustion is carried out: in a first combustion phase, the fuel jet or jets react with the primary oxidant, the remainder of the fuel after the primary combustion and the products of combustion of this primary combustion then entering into contact with the secondary oxidant in a secondary combustion and, in the particular case where there is distribution of the oxidant in primary, secondary and tertiary oxidant, the fuel remaining after the secondary combustion and the products of combustion resulting from this secondary combustion come into contact with the tertiary oxidant in a tertiary combustion phase.

Each fuel injector is connected to a fuel source.

Each oxidant injector is connected to an oxidant source.

The fuels used are preferably low-cost fuels (coal, petcoke, waste, etc.) conventionally used by cement manufacturers. It is nevertheless conceivable to advantageously use gaseous fuels (natural gas, propane, etc.) or liquid fuels (fuel oil).

As mentioned above, the oxygen content of the oxidant is greater than 22% vol. The oxygen content of the oxidant is advantageously greater than 50% vol, preferably greater than 70% vol and more preferably greater than 80% vol.

The invention also relates to the use of the heating method described above in the manufacture of lime or clinker.

A tunnel furnace for heating a mineral raw material to produce a cooked product suitable for carrying out the process comprises a furnace having an upstream inlet, a downstream outlet and sidewalls equipped with burners. Such a furnace also comprises means for introducing a sheet of mineral raw material into the furnace through the upstream inlet, means for evacuating the layer of cooked product from the furnace via the downstream outlet and means for transporting the sheet along a treatment path between the upstream inlet and the downstream outlet, such as one or carriages, rollers or treadmills. The burners with which the side walls of the furnace are equipped are burners according to any one of the embodiments described above. These burners are therefore oxy-burners comprising at least one fuel injector and at least one oxidant injector. They are positioned and oriented so that their flames do not impact the sheet. The at least one oxidant injector of these burners is positioned relative to the at least one fuel injector so that the at least one fuel jet injected by the at least one fuel injector is separated from the sheet by at least one oxidant jet injected by at least one oxidant injector.

The proposed technology is applicable to the manufacture of various types of clinker, such as the clinker for sulfo-aluminous cement and / or ferro-aluminous cited in WO-A-02094732, the clinker for Portland cement, the manufacture of lime, or the cooking other mineral products. It is particularly useful for cooking mineral raw materials whose composition is such that their cooking requires a good control of the heat transfer to the raw material such as raw for sulfo-aluminous cement and / or ferro-aluminous.

The present invention makes it possible to create a relatively homogeneous temperature atmosphere above the sheet according to a desired longitudinal profile.

The advantages of the present invention will be better understood in light of the examples of the invention described below, reference being made to FIGS. 1 and 2, in which: FIG. 1 is a schematic representation of a suitable concentric injection burner; for the process according to the invention, Fig. 1A showing cross-section and Fig. 1B a front view; and FIG. 2 is a diagrammatic cross-sectional representation of the hearth of a tunnel furnace adapted for implementing the method according to the invention equipped with a second type of burner.

The examples below relate more particularly to clinkering.

The tunnel or hearth is equipped with oxy-burners aligned on the side of the furnace, on both sides of the sheet of material. Said burners are positioned in the side walls and oriented so that their flames do not impact the load.

The fuel used is a fuel conventionally used by cement manufacturers, such as coal, petcoke, waste. It is also possible to use gaseous fuels (natural gas, propane ...) or liquid fuels (fuel oil).

As already mentioned above, the oxygen content in the oxidizer of an oxy-burner is greater than 22% vol, preferably greater than 50%, still more preferably greater than 70% and more preferably greater than 80%. Different types of burners are proposed to create the proper atmosphere for the material: a. oxy-fuel burners with concentric fuel and oxidant injections (Figure 1)

The burner 1 in the side wall 3 is a concentric injection oxy-burner, with a peripheral oxidant injection 10 surrounding the fuel injection 11 and for creating an oxidizing atmosphere outside the flame envelope 19. oxidizing atmosphere avoids the excessive reduction of sulphates contained in the raw.

Furthermore, the need to preserve the oven or to adapt the heat transfer to the width (for example following a change in the composition of the raw or in the production rate of the oven) may lead to a need to change the length of the oven. the flame 19 produced by one or more burners. For this, it is possible to use concentric injection burners with:

The peripheral oxidant surrounding the fuel injection 11, to create an oxidizing atmosphere outside the flame envelope as mentioned above,

And central oxidant 12 surrounded by fuel injection 11 and allowing better mixing of the reactants and adjustment of the length of the flame 19.

The adjustment of the distribution between the peripheral oxidant flow rate and the central oxidant flow rate is as a function of the desired power and the desired flame length.

Typically, the central oxidant, or primary, 12 injected at a higher pulse than the secondary oxidant 10 will allow to adjust the flame length. The proportion of this oxidant is typically such that the central oxidant 12 provided between 8% and 30% of the totality of the oxygen injected by the burner, for example of the order of 15%. At constant stoichiometry, increasing the proportion of primary oxygen (oxygen supplied by the central oxidant) will reduce the length of the flame by improving the oxidant / fuel mixture.

b. oxy-burners with spaced injections of fuel and oxidant (Figure

2).

According to the second example, the injection of fuel into the furnace 2 is separated, that is to say spaced, from the injection of oxidant into the clinkerization furnace. A first line of oxidant injectors (secondary oxidant) 10 is at a level directly above the level of the sheet 20 transported on the carriage 21 and below the fuel injector or injectors 11, at least one injector primary oxidant 12 being located at a smaller distance (relative to this first line of injectors 10) of the fuel injector or injectors 11 and at a greater distance (with respect to this first line of injectors 10) from the ply 20 Such a burner 1 in the side wall 3 again makes it possible to create an oxidizing atmosphere above the sheet 20 and outside the flame envelope 19. This oxidizing atmosphere makes it possible to avoid the excessive reduction of the sulphates. contained in the raw.

In a similar manner to Example 1,

The first line of oxidant injectors (secondary oxidant) 10 makes it possible to create an oxidizing atmosphere above the sheet 20 outside the flame envelope 19,

• and the other injectors the oxidizer (primary oxidant) 12 allow better mixing of the reactants and adjustment of the length of the flame 19,

Adjusting the distribution between the oxidant flow rates of the various oxidant injectors 10, 12 is based on the desired power and the desired flame length 19.

In the example illustrated in FIG. 2, additional lines of oxidant injectors (primary oxidant) 12 are located (a) above this first line of injectors but below the fuel injector (s) 11 (line 12a) and (b) above the fuel injector (s) 11 (line 12b).

The spacing of the injection lines depends inter alia on the width of the furnace. The calculation of this spacing, and in particular the spacing between the fuel injector and the primary oxidant injectors during the design allows optimization between flame length and NOx reduction.

The power of the various oxy-burners along the fireplace 2 of the clinkerisation furnace is adjusted to obtain the desired heating profile.

The level of the oxidant injection lines and the spacing of the injections on the same line may also vary over the length of the clinkerisation furnace in order to obtain the appropriate heat transfer.

Suitable oxy-burners for the present invention that allow, among other things, to vary the length of a flame in operation and adjust it as necessary are described in patent applications and patents of the Applicant. So: EP-A-0763692, EP-A-1016825, EP-A-1195557 and FR-A-2837916 disclose oxy-burners marketed under the trade name ALGLASS VM ™ which makes it possible to modify the flame length by modifying the oxygen distribution central or peripheral ("Variable Momentum") as in Example 1 above; and

- FR-A-2823290, EP-A-1618334, EP-A-1702177 and EP-A-1704366 describe oxybrulers with separate injections with a staging of the oxygen injection and an adjustment of the distribution of oxidant marketed under the trade name ALGLASS SUN ™.

A common point of these technologies is to allow to modify the characteristics of the flame in operation.

Claims

claims

A method of heating a mineral meal in a tunnel furnace-type baking furnace having a hearth with an upstream inlet, a downstream outlet and sidewalls equipped with burners, wherein the raw is transported in a thick sheet. substantially constant along a treatment path where the raw is heated and cooked by means of said burners so as to obtain a cooked product, said path being located between the upstream inlet and the downstream outlet of the hearth, characterized in that said burners comprise at least one fuel injector and at least one oxidant injector and are positioned and oriented so that their flames do not impact the sheet, the at least one oxidant injector being positioned relative to the minus one fuel injector so that the fuel jet injected by the at least one fuel injector is separated from the ply by at least one jet of oxidant injected by at least one oxidant injector.

2. Method according to claim 1, wherein at least one burner is a concentric injection burner with a peripheral oxidant injection for creating an oxidizing atmosphere outside the flame envelope.

3. Method according to claim 2, wherein at least one burner is a concentric injection burner with a peripheral oxidant injection, a central oxidant injection and a fuel injection between the peripheral oxidant injection and the central oxidant injection.

4. The method of claim 3, wherein the oxidant jet injected by the central oxidant injection is injected at a higher pulse than the jet of oxidant injected by the peripheral oxidant injection.

5. Method according to one of claims 3 and 4, wherein is adjusted the length of the flame from a concentric injection burner with a peripheral oxygen injection, a central oxygen injection and a fuel injection between peripheral oxygen injection and central oxygen injection, by adjusting the distribution between the jet of oxidant injected by the central oxidant injection and the jet of oxidant injected by the injection of peripheral oxidant.

6. Method according to one of claims 3 to 5, wherein the oxidant jet injected by the central oxidant injection is between 8% and 30% of the total oxygen injected by the burner.

7. The method of claim 1, wherein at least one burner comprises one or lower oxidant injectors located below the at least one fuel injector so that the oxidant jets injected by said series of injectors of oxidant separate the at least one jet of fuel injected by the at least one fuel injector from the web.

The method of claim 7, wherein at least one of the burners comprising one or more lower oxidant injectors located below the at least one fuel injector is a stepped oxidant burner.

9. Process according to any one of the preceding claims, in which the oxidant has an oxygen content of at least 50% vol, preferably at least 70% vol and more preferably at least 80% vol. .

10. Use of a manufacturing method according to any one of the preceding claims in the manufacture of lime or clinker.