EP1148311B1 - Process for firing a material containing carbonates - Google Patents

Abstract

In a method for burning carbonate-containing material the latter moves as a result of gravity in counter-current to the cooling and combustion air through a shaft kiln. The fuel supply takes place by means of burning lances introduced into the granular burning material at right angles to the shaft wall. On limiting the grain size and the residence time as a result of this type of fuel supply it is possible to achieve high burning temperatures even suitable for hard burning without there being any sintering together of the granular burning material.

Description

The invention relates to a method for firing carbonate-containing Material in a shaft furnace, with gravity feed by a preheating zone, at least one firing zone and a cooling zone to a discharge device, wherein a Fuel supply in the combustion zone or adjacent to this takes place over several guided through the shaft wall burning lances and combustion air supplied as cooling air under pressure becomes.

Especially when firing small granular material, i. at a substantial proportion of material to be burned with a Grain size of less than 30 mm, the problem exists to supply the required amount of heat to the material evenly, so every grain burned to its core without the grains sintering together due to localized overheating and form fixed bridges in the oven. This problem is particularly large when going beyond a soft burn, higher degrees of combustion are required.

For small-grained fuel and a uniform Kiln furnaces are the best at firing and thus product quality suitable because an intensive material circulation a good and ensures uniform heat transfer to each grain. The disadvantage, however, is that their construction is very is expensive and that the correspondingly high investment costs still high operating costs are added, conditional due to high wear and high heat losses due to radiation and by exhaust gases, resulting in the application of higher Temperatures, as for higher fuel levels and others Product qualities, such as medium, hard and sinter firing required are, especially strong impact.

Another method, the amount of heat required for firing to feed the kiln evenly, consists in admixing of fuel, i. from metallurgical coke to the kiln in Mischfeueröfen. However, mixed-hearth furnaces are not for small-grained Fuel suitable. Moreover, they have the considerable Disadvantage that the ashes of coke burning in finished product remains and thus one with Grayscale associated, inferior product quality leads.

An energy-saving mode of operation is through multi-shaft furnaces after the DC regenerative process in so-called MAERZ ovens given. At them the fuel gets through hanging in the firing dipping arranged burning lances fed in the feed zone evenly over the Shaft cross section are arranged distributed. Such ovens known However, they are only suitable for soft fires.

In US-A-5,460,517 is described as by special Grain size distribution when feeding the furnace, combined with a special design of the chess dreams too Burning of smaller granular fuel is possible.

Although suitable for hard firing suitable amounts of fuel the combustion zone of a shaft furnace to be supplied to to achieve the required firing temperatures, exist so far not overcome difficulties, one uniform temperature distribution over the shaft cross section to achieve, and in particular a Zusammensintern of To avoid fuel by local overheating.

It has been proposed by US-A-4,094,629 to set the width of the Shaft cross section through its annular design too reduce and in the thus existing inner wall additional Burner mouths to arrange. This is how one should even downward movement of the fuel under Gravity can be maintained without the material flow is disturbed by fittings in the shaft.

Installations in the form of bar-shaped burner supports are in GB-A-1111746. These have due to the inclusion from e.g. twenty liquid-cooled burners each a relatively wide cross section and effect thus a considerable reduction of the usable furnace cross-section, associated with the danger of a local blockage the gravity of the fuel.

A summary of various combustion processes, including the aforementioned firing in regenerative multiwell furnaces can be found in the manual "Chemistry and Technology of Lime and Limestone "by Robert S. Bynton, Second Edition, 1987.

US-A-3 355 158 describes a firing furnace, distributed over its cross-section Burner are arranged, which are befastigt adjustable on the shaft wall transversely thereto.

The invention has for its object to provide a method of to find the type mentioned by the particular small-grained fuel with different degrees of combustion to the deadburn in an economical way in shaft furnaces be burned to a high quality product can.

To solve this problem, a method of the aforementioned Art proposed according to the invention thereby characterized is that the Firing lances for selecting the position of their Mouths are moved during furnace operation perpendicular to the shaft wall so that the at the Firing lances forming single flames together one Form flame area at least approximately above the entire shaft cross-section extends; to burn becomes one Material selected whose grain size ranges from 5 to 70 mm lies.

Since each burner lance preferably only for the generation of each a flame is provided, it has compared to numerous Brenner burner having a low Cross section and therefore only leads to a negligible Influencing the fuel flow. It's surprising shown that the burning lances nevertheless sufficient Flexural strength have to the pressure of it flowing around to take up granular fuel.

By the extension of each burning lance perpendicular to Shaft wall is prevented between itself and the Shaft wall forms a gap by accumulating fuel could. The local restriction of the shaft cross-section through the fire lances projecting into it decrease by adding the focal lances in multiple levels on top of each other and to those of another level in the circumferential direction be arranged offset so that the required Fuel quantity distributed over several shafts is supplied.

Fig.1

in schematischer Darstellung einen Axialschnitt durch einen Einschachtofen mit in drei Ebenen übereinander angeordneten, in den Schacht hineinragenden Brennlanzen,

Fig.2

einen Einschachtofen entsprechend Fig.1, jedoch mit im Schacht angeordneten Wärmeaustauschrohren,

Fig.3

einen nicht masstäblichen Radialschnitt durch den Ofen nach Fig.1 oder 2 im Bereich der oberen Ebene der Brennlanzenanordnung,

Fig.4

einen Radialschnitt durch den Ofen nach Fig.1 oder 2 im Bereich der mittleren Ebene der Brennlanzenanordnung,

Fig.5

einen Radialschnitt durch den Ofen nach Fig.1 oder 2 im Bereich der unteren Ebene der Brennlanzenanordnung,

Fig.6

ein Diagramm der radialen Temperaturverteilungen über einen in seiner Breite relativ angegebenen Schachtquerschnitt,

Fig.7 bis 9

Querschnittsdarstellung von an einem Schachtofen montierten Brennlanzen für pulverförmige, flüssige und gasförmige Brennstoffe,

Fig.10

ein Diagramm der vertikalen Temperaturverteilung im Schachtofen nach Fig.1 mit Brennstoffzufuhr für Weichbrand in drei Brennebenen,

Fig.11

ein Diagramm entsprechend nach Fig.10, jedoch in einem Ofen nach Fig.2,

Fig.12

ein Diagramm der vertikalen Temperaturverteilung im Schachtofen nach Fig.1 mit Brennstoffzufuhr für Hartbrand in nur einer Brennebene,

Fig.13

ein Diagramm entsprechend nach Fig.12, jedoch in einem Ofen nach Fig.2,

Fig.14

einen Mehrschachtofen nach dem Regenerativerfahren, mit hängend und quer angeordneten Brennlanzen,

Fig.15

einen Mehrschachtofen nach dem Regenerativerfahren, mit nur quer angeordneten Brennlanzen und

Fig.16

einen Mehrschachtofen nach dem Regenerativerfahren, mit nur quer angeordneten Brennlanzen und mit in den oberen Schachtbereichen angeordneten Wärmeaustauschrohren.

Der in Fig.1 im Längsschnitt dargestellte Einschachtofen 1 ist vertikal ausgerichtet und hat zumindest über den verfahrenstechnisch erheblichen Bereich seiner Länge einen Schachtraum 2 mit gleichbleibendem Querschnitt. Dieser kann verschieden, z.B. kreisrund elliptisch oder vieleckig geformt sein. Im Beispiel entsprechend seinen Querschnittsdarstellungen in Fig.2 bis 4 ist der Querschnitt kreisringförmig, mit einer Aussenwand 3 aus Stahl, die aufgrund der erforderlichen hohen Verfahrenstemperaturen auf ihrer Innenseite mindestens eine gemauerte, feuerfeste Auskleidungsschicht 4 trägt.Further advantageous embodiments of this method are the subject of the dependent claims and the following description with reference to the drawings. It shows:

Fig.1

a schematic representation of an axial section through a slot furnace with stacked in three levels, projecting into the shaft burning lances,

Fig.2

a shaft furnace according to Fig.1, but with arranged in the shaft heat exchange tubes,

Figure 3

a non-standard radial section through the furnace according to FIG. 1 or 2 in the region of the upper level of the burning lance arrangement,

Figure 4

3 shows a radial section through the furnace according to FIG. 1 or 2 in the region of the middle plane of the burning lance arrangement,

Figure 5

a radial section through the furnace of Figure 1 or 2 in the region of the lower level of the Brennlanzenanordnung,

Figure 6

a diagram of the radial temperature distributions over a relatively wide in its width shaft cross-section,

7 to 9

Cross-sectional view of burning lances for pulverulent, liquid and gaseous fuels mounted on a shaft furnace,

Figure 10

1 is a diagram of the vertical temperature distribution in the shaft furnace according to FIG. 1 with fuel supply for soft firing in three focal planes;

Figure 11

a diagram corresponding to FIG. 10, but in an oven according to FIG.

Figure 12

1 shows a diagram of the vertical temperature distribution in the shaft furnace according to FIG. 1 with fuel supply for hard firing in only one focal plane,

Figure 13

a diagram corresponding to Figure 12, but in a furnace according to Fig.2,

Figure 14

a multi-shaft furnace after the regenerative process, with hanging and crosswise arranged burning lances,

Figure 15

a multi-shaft furnace after the regenerative drive, with only transverse fire lances and

Figure 16

a multi-shaft furnace after the regenerative process, with only transversely arranged burning lances and arranged in the upper shaft areas heat exchange tubes.

The insertion shaft 1 shown in longitudinal section in Figure 1 is vertically aligned and has at least over the procedurally significant range of its length a shaft space 2 with a constant cross-section. This can be shaped differently, eg circular elliptical or polygonal. In the example according to its cross-sectional representations in Figure 2 to 4, the cross section is circular, with an outer wall 3 made of steel, which carries on the inside at least one masonry refractory lining layer 4 due to the required high process temperatures.

The height of the furnace shaft 2 is by the method in connection with the setting of the conveying speed by means of the discharge device 5 to be determined residence times of the fuel. These residence times spread over an upper, to the loading area 6 subsequent preheating zone 7, on one down following combustion zone 8 and one to the discharge device. 5 extending cooling zone 9.

The supply of gaseous, liquid or powdery Fuel, preferably together with primary combustion air, takes place over numerous, in one or more levels 10 to 12 arranged burning lances 13, extending through the Shaft wall 3,4 extend into the shaft space 2 inside.

By the axial displacement of the burning lances by hand in bulk, vertically through the bricked shaft wall 3.4 through, the positions of their mouths 14 can be and thus the flames forming on each of them, systematically or due to temperature measurements by means of arranged in the shaft cross-section probes, arrange so that in the relevant shaft level a largely uniform Burning temperature arises. Such a uniform Temperature distribution is in the diagram of Figure 6 through the straight course of the middle curve 15 shown. in the Compared to this would be in an arrangement of Lanzenmündungen 14 flush with the inside of the shaft wall 3.4 a towards the middle of the shaft decreasing temperature curve accordingly give the curve 16 and thus a different Burning degree of the product. The temperatures would be in the Near the shaft wall too high, with the risk of sintering together and in the middle of the shaft too low and below the indicated by the curve 17 minimum firing temperature. The radial positions that can be read on the abscissa of the diagram are only relative and not specific Shaft diameter related. However, the shaft diameter can a radius of 1, although larger Well dimensions can be realized, e.g. with a Diameter of three or more meters.

Due to the high temperatures in the combustion chamber 8 are at least for a far projecting into the slot 2 arrangement provided burning lances 13 with a burner tube 18th provided enclosing cooling jacket 19, the connecting piece 20,21 for the passage of a cooling liquid. On burning lances 13, where a lower temperature load can be expected instead of a cooling jacket a heat-resistant material for the relevant lance area be used. In this way, the over one Cooling medium dissipated heat reduced.

The combustion tube 18 has a connecting piece 22 for the supply line primary combustion air. Furthermore, at the rear End of the fuel lance 13 a coaxially with this running Fuel pipe 23,24 or 25 used, depending on the type of fuel to use different is executed. For powdered fuel, the fuel pipe has the shape of a short nozzle 23 accordingly Figure 7. For liquid and gaseous fuel extends the fuel pipe 24 or 25 until shortly before the mouth 14 of the burning lance 13, to there with the in the enclosing Ring channel 26 incoming primary combustion air mix.

A tight against the overpressure in the oven, but movable Passing through the firing lances 13 through the shaft wall 3,4 through is in each case by a to a wall bore 27th outwardly adjoining stuffing-box-like sealing arrangement 28 guaranteed.

Figures 3 to 5 illustrate a different angular arrangement the arranged in three levels burning lances 13, so that the burning lances 13 to those of another level are angularly offset. By the addition of different, in the illustrations exemplified insertion positions the burning lances 13 of the different focal planes 10, 11 and 12 is a special even with small flame training extensive coverage of the shaft cross-section through given at each of the mouths 14 forming flames. The size of these flames is due to several factors determined, i. the amount of fuel, the amount of primary and secondary combustion air and the grain size of the fuel. A small grain size leads to a denser bulk packing and thus to a lesser Propagation of the flame. On the other hand, the limitation of the Grain size to a range preferably less than 70 mm grain size the advantage of a lower mechanical load the transversely projecting into the flowing bulk material Burning lances 13 and the advantage of a smaller adjustable Residence time, allowing a sintering of fuel can be prevented by a short residence time. For one uniform degree of combustion should the particle size distribution in the smallest possible area.

If the method with a grain size of the fuel should be carried out in one area significantly above a maximum grain size of 70 mm, so can special measures are taken, which is an overload the far into the shaft 2 projecting fire lances 13 prevent. For example, the relevant fuel lance be held in the manner of a weighing beam, with a Force measuring point outside the shaft wall 3 and with a Device for generating mechanical oscillations in the Overshoot of a permissible force is switched on automatically becomes. In this way, the burning lance can be shake it free, if it should form a jam on it. A shaking of the burning lance can also be her pushing in facilitate the filled shaft space 2.

The fuel supply in the individual focal planes 10, 11 and 12 can be individually adjusted to zero, depending on from the desired degree of combustion or the residence time in a certain temperature range a certain temperature profile in the shaft longitudinal direction or in the flow direction to receive the incoming air from below.

This air is kept in the range of e.g. designed as a sliding table Discharge device 5 with overpressure by at least an unillustrated blower supplied so that they are in Countercurrent to the downwards moving by gravity Bulk column through the grain structure upwards flows. At first, it serves as cooling air in the cooling zone 9, then in the combustion zone 8 as, for example, secondary Combustion air and last, in the upper preheating zone. 7 the oven to preheat the fuel and thereby, accordingly a preferred embodiment of the invention, for Preheating the flowing to the fuel lances 13, primary Combustion air in there arranged hanging heat exchange tubes 29th

The invention essential arrangement of the burning lances 13 and from their mouths 14, distributed over the shaft cross-section, allows new types of process management, with special high flame temperatures in the range of 1800 ° C in a short Dwell time without being at such temperatures in itself expected sintering, i. the formation of blökken occurs, so that was previously impossible Hard burning in vertical shaft furnace with gaseous, liquid and powdered fuels is possible.

The diagrams of Figs. 10 to 13 show for a particular Dwell time due to the control of the fuel supply in conjunction with adapted primary air supply via the burning lances 13 and countercurrently supplied secondary Combustion air achievable temperature curves for the fuel lime (CaCO3), based on the longitudinal section of the shaft furnace. Here is the temperature of the fuel represented by a solid line 30, while the temperature of the forming by the combustion Fuel gas and the cooling or Sekundärverbrennungsluft the dashed line 31 corresponds.

For the production of soft firing according to Fig.10 and Fig.11 the fuel supply is graded over in the three Focal planes 10 to 12 arranged burning lances 13 in substantially less than hard firing, so that flame temperatures corresponding to the three temperature peaks 32 train up to 34. at about 1200 ° C in the first focal plane and at about 1400 ° C in the third focal plane. The fuel flowing from top to bottom thus passes in the first focal plane 30 first in contact with fuel gas of 1200 ° Celsius and in the subsequent focal planes with hotter fuel gas of a maximum of about 1400 ° C. By the in the Countercurrent upwards flowing fuel gas became the granular Fuel already on reaching the first focal plane preheated to about 1000 ° C, and it reaches in the third Focal plane has a temperature of about 1200 ° C. By the on three focal planes 10,11,12 distributed supply of the required Fuel quantity, the combustion zone 8 has a corresponding long extension in the direction of the chess with correspondingly larger Dwell time of the fuel in the firing zone 8.

This in shaft furnaces with the exception of mixing furnaces so far Not possible hard burning of lime takes place accordingly the embodiment of Figure 12 with fuel and supplying primary combustion air in only one Level 12 and at a flame temperature of about 1800 ° C. The Fuel has a particle size in the range of 5 to 70 mm. The resulting high firing temperature of about 1400 ° C surprisingly does not cause grain sintering together of fuel with lumps and bridging. This explains characterized by a short residence time at highest temperatures, according to the sharp curve of the temperature curve 31 for the fuel in diagram according to Fig.12. This Temperature profile results from the missing connection additional focal planes and the correspondingly shorter extension the combustion zone 8 in the direction of chess.

In the execution of the Einschachtofens 1 according to the Representation in Figure 1 leave the in the preheating zone 7 itself cooling fuel gases the oven at about 330 ° C, so that accordingly high heat losses occur. A recuperation in Downstream heat exchangers would be due to the high Dust in the exhaust stream for early training of the Heat transfer obstructing deposits. At a preferred development of the invention according to the Embodiment of Figure 2 is a part of the in the Fuel gases contained heat energy for the heating of exploited primary combustion air, the burning lances 13 is supplied via a line 39. This heating takes place within the furnace 1 ', by the combustion air is guided through heat exchange tubes 36, which are connected to an and return part 37, 38 hanging vertically and in the circumferential direction of the shaft 2 or evenly on the shaft cross-section distributed in the fuel of the preheating zone. 7 plunge. The arrangement of the heat exchange tubes 36 in the oven 1 'in direct contact with the kiln and the fuel gases leads to a particularly good heat transfer through heat conduction, Convection and heat radiation. In addition, will the heat exchange surfaces of the tubes 36 through the under Gravity influence on fuel flowing along them cleaned automatically. The possible savings in heat energy is compared to a furnace without preheating of primary combustion air approx. 7 to 10%, at an exhaust gas temperature from about 190 ° C instead of about 330 ° C.

Figs. 11 and 13 illustrate that due to the additional one Heat exchanges in the tubes 36 resulting different Temperature profile in the direction of the chute.

The double shaft furnaces 40, 40 'and 40 "of the embodiments the invention of Fig.14 to Fig16 are like the operated MAERZ-ovens operated by the regenerative process. This means that both shafts 41 and 42 in the transition area 43 interconnected below the combustion zone 44 with each other are that of the discharge area 45 continuously Cooling air is supplied in countercurrent and that also from the Charging region 46 from combustion air in DC alternately fed to one of the shafts 41, 42 while at the same time the discharge of the exhaust gases from the oven 40, 40 ', 40 "through the preheating zone of the adjacent shaft 42 or 41 therethrough. The switching of these flow conditions in the oven at intervals of, for example 10 to 15 minutes. The representations of Fig.14 16 illustrate by the directional arrows the operating state, in the combustion air to the shaft 41 via the line 47 supplied and the exhaust gas from the other shaft 42 is derived via line 48. Following the same switching principle can also be more than two parallel to each other Manholes 41, 42 operated with alternating operating state become.

In contrast to the direct current known as the MAERZ oven Regenerative furnace with fuel according to the operating intervals alternating only one or the other of the Manholes in direct current is supplied to the kiln, takes place the fuel supply simultaneously to both shafts 41.42, so that in one of the shafts the fuel gases direct current to the fuel and in the other shaft in countercurrent are directed. The total fuel required is thus on the Brennlanzenanordnungen both Shafts 41, 42 distributed. In contrast to DC combustion operation in a slot 41 or 42, thus takes place in another shaft 42 or 41 with the burning in the cooling zone 49 preheated combustion air, with consequently reduced Amount of exhaust gas and correspondingly improved energy balance. Versus over the known DC regenerative furnace according to system MAERZ can reduce the burning of limestone the amount of exhaust gas be 25%. This increases the concentration of the carbon dioxide, so that the exhaust advantageous for Chemical process can be used that uses a gas need high carbon dioxide content.

In the double shaft furnace according to Fig. 14, in addition to in the firing material 50 immersing firing lances 51 in near the transition region 43 across the fuel 50 inserted burning lances 52 are provided. After switching of the burning operation are thus in the same slot instead the hanging burning lances 51, the cross-inserted burning lances 52, while at the same time reverse switching of the burner 52,51 in the other Schacht. The direction of the flame development at the nozzle mouths the burning lances 51,52 in the direction of chess is through the pictures of the flames 53 and 54 can be seen. By these representations can also be seen that the transversely directed Firing lances 52 of the shaft 41 during operation the hanging in this slot 41 burning lances 51 off while in the other shaft 42 the burning lances 52 are switched on.

The double shaft furnace according to Fig.15 are in both shafts. 41,42 only transversely arranged firing lances 55 provided. Of the In contrast, double shaft furnace according to FIG Preheating area 56 hanging arranged heat exchange tubes 58th for heating of primary combustion air, as previously for Einschachtofen has been described according to Fig.2.

By the simultaneous supply of fuel in the second Manhole in countercurrent by inserted into the fuel Burning lances 52,55 is known per se, the regenerative process with good thermal efficiency for the Production of medium and hard firing advantageously suitable.

Claims (10)

1. Method for burning carbonate-containing material in a shaft kiln, with gravity conveying through a preheating zone, at least one burning zone and a cooling zone to a discharge device, in which a fuel supply in the burning zone or adjacent thereto takes place by means of several burning lances passed through the shaft wall and combustion air is supplied under overpressure as cooling air, characterized in that burning lances are displaced during kiln operation perpendicular to the shaft wall in such a way that the individual flames formed on the orifices together form a flame area, which at least approximately extends over the entire shaft cross-section, whereby for burning purposes a choice is made of a burning material with a grain size in the range 5 to 70 mm.
2. Method according to claim 1, characterized in that the fuel supply takes place by means of several superimposed groups of burning lances in each case arranged at least approximately in the same plane and as a function of the desired degree of burning in the burning zone a temperature profile passing in the kiln longitudinal direction is regulated by modifying the fuel supply to one or more of the individual lance groups.
3. Method according to claim 1 or 2, characterized in that the temperature distribution over the shaft cross-section is adjusted by displacement of the burning lances as a function of temperature values determined by probes.
4. Method according to claim 2 or 3, characterized in that for a uniform, common coverage of the shaft cross-section by individual, superimposed flame areas, the displacement direction of superimposed burning lances is mutually staggered in the circumferential direction of the shaft.
5. Method according to one of the claims 1 to 4, characterized in that the burning lances supply in addition to fuel combustion air, whose quantity is adjustable and if necessary can be reduced to zero.
6. Method according to claim 5, characterized in that the combustion air to be supplied by means of the burning lances is heated within the preheating zone by being passed through heat exchange tubes, which are positioned parallel to the shaft wall, distributed over the kiln cross-section and suspended in the preheating area of the kiln.
7. Method according to one of the claims 1 to 6 for burning in a multi-shaft kiln according to the regenerative method by the time-alternating supply between the shafts of combustion air in parallel flow and with a continuous counter-flow supply of cooling air in the lower area of the shafts, characterized in that during the fuel supply in parallel flow operation in one of the shafts, in one or more shafts transversely connected to the former shaft, fuel with or without combustion air is supplied by means of burning lances arranged in the burning zone and displaceable transversely to the kiln wall.
8. Method according to claim7, characterized in that the fuel supply takes place in each case during one of the operating periods of the regenerative method in one of the shafts in parallel flow form by means of suspended burning lances.
9. Method according to one of the Claims 1 to S, characterized in that the maximum insertion depth of the burning lance extends close to the centre of the shaft cross-section, so that the associated flame reaches the centre and the internal diameter of the shaft chamber is reduced to 3 m.
10. Method according to one of the claims 1 to 9,characterized in that a cooling medium flows at least through the burning lances projecting furthest into the shaft chamber.

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