EP2717007A1 - Method and apparatus for improving the combustion of secondary fuel in a rotary kiln - Google Patents

Abstract

The method involves providing a burner assembly (9) with a main burner (5) and supply tunnels (19). Secondary fuel (10) is supplied to the tunnels in compressed air current form. A tubular oxygen lance (12) is filled with pure oxygen gas. A bent nozzle (14) is arranged at ends of the supply tunnel of the burner assembly. The oxygen gas from the oxygen lance is passed to first beam (7) and second beam (8) through the nozzle. Carbon monoxide in portion of undesirable components is measured. An independent claim is also included for a device for improving combustion of secondary fuel in a rotary kiln.

Description

The present invention is in the field of rotary kilns, such as those used for the production of cement. Such rotary kilns are large-scale plants with a length of often over 50 m, for their heating different fuels can be used. In general, a rotary kiln has at least one main burner for primary fuel, e.g. As petroleum, natural gas or coal dust, with opportunities for adding other fuels, so-called secondary fuels may be provided. As secondary fuels, many materials are considered, including waste plastics, textile waste, old tires and the like. These secondary fuels are generally supplied as small particles, snippets or shreds by means of compressed air. Typically, a secondary fuel has a lower calorific value than the primary fuel, and therefore its complete combustion often requires additional measures, particularly to avoid or reduce the emission of pollutants.

The basic structure of a rotary kiln, for example, in the EP 0 866 295 A1 described. There, an oxygen lance for the supply of liquid oxygen is proposed to improve the combustion.

From the EP 1 065 461 B1 is also the basic structure of a rotary kiln known. There is also already proposed the improvement of the combustion of a secondary fuel with the addition of oxygen.

Also in the US Pat. No. 6,318,278 B1 a rotary kiln will be described, as it may also be constructed in the present invention. This document also already shows the use of an oxygen lance in a rear combustion area, wherein also a supply of the oxygen at an angle to the direction of a main burner is taken into consideration.

Also the EP 0 726 437 A1 deals with different oxygen lances in a rotary kiln, with one of the oxygen lances is guided centrally in a burner assembly. However, the use of secondary fuel is not dealt with here.

Object of the present invention is to improve the combustion of secondary fuel in a rotary kiln, preferably taking advantage of existing possibilities of typical burner arrangements, in particular to reduce the emission of carbon monoxide, without increasing the emission of other undesirable pollutants, such as nitrogen oxides above prescribed limits.

To achieve this object, a method according to claim 1 and a device according to claim 5. Advantageous embodiments, which can be used individually or in combination with each other, are given in the respective dependent claims.

The inventive method for improving the combustion of secondary fuel supplied in a first jet in a rotary kiln, the rotary kiln having a cylindrical burner assembly with a geometric center axis and with a main burner and with a plurality of supply tunnels for various media, one for the supply of secondary fuel, in particular in the form of particles or Schnipseln in a compressed air flow, is characterized in that a tubular oxygen lance for an oxygen-rich gas, in particular gaseous oxygen, with a angled nozzle is placed at its end in a feed tunnel of the burner assembly, wherein the oxygen lance is placed in such a position that the oxygen issuing from the nozzle forms a second beam, which meets the first beam. In general, secondary fuel is supplied above or at the top of a main burner, so that this fuel is ignited by the rising heat of the main burner flame and burned with the surrounding oxygen. Experiments have shown that the supply of oxygen to the secondary fuel before or at its ignition can significantly improve the combustion. If an oxygen jet hits the jet with secondary fuel, much less carbon monoxide is formed during later combustion than without the coincidence of the two beams. By means of the invention, the oxygen supplied by the oxygen lance can be used much more effectively than in the case of untargeted feeding into the rotary kiln. It should be noted that a typical burner arrangement for a large-scale rotary kiln itself may already have a length of about 10 m, so that there is no practical way to arrange an obliquely to the main flow direction oxygen lance, without making significant changes to the system. The oxygen lance is therefore guided by a supply tunnel not used in the respective operating state, of which typical burners have a plurality, and therefore an angled nozzle is required at the end of the oxygen lance in order to steer the second jet in a desired direction. The main burner continues to operate with the primary fuel when using secondary fuel and assists in complete combustion of the secondary fuel in the further course of the rotary kiln.

In general, it suffices to insert the oxygen lance at the correct angle of rotation with respect to the secondary fuel feed tunnel into an available feed tunnel to coincide to reach the two rays. In particular, in geometrically difficult conditions and possible swirl flows in the rotary kiln, however, it is advantageous to measure the proportion of undesirable components in the exhaust gas, in particular carbon monoxide, and to rotate the oxygen lance in a kind of fine adjustment and / or to change the supply of oxygen so that a Minimum of the components in question or an acceptable value for all the different undesirable components in the exhaust gas is achieved. This allows a particularly low-pollution combustion even with complicated flow conditions in the interior of the rotary kiln.

Preferably, the method is designed so that the second beam hits the first beam within less than 5 m after exiting the burner assembly, preferably after less than 2 m. In this way it is achieved that the oxygen from the oxygen lance does not primarily increase the temperature at the combustion of the primary fuel, which takes place further downstream in the rotary kiln, which could result in an increased production of nitrogen oxides, but mainly to promote the combustion of the secondary Fuel is used.

Nevertheless, the oxygen supplied by the oxygen lance can serve to set a slightly more than stoichiometric ratio, ie an excess of oxygen to fuel in the furnace, in order to achieve the most complete possible combustion of all fuels over the length of the rotary kiln.

An apparatus according to the invention for improving the combustion of secondary fuel supplied in a first jet in a rotary kiln, the rotary kiln having a burner assembly with a main burner and a plurality of feed tunnels for different media, one of which is for the supply of alternative Fuels, in particular of particles or Schnipseln is designed in a compressed air flow, characterized in that a tubular oxygen lance for an oxygen-rich gas, in particular gaseous oxygen with technically available purity and concentration, with an angled nozzle at its end in a supply tunnel of the burner assembly so arranged that the oxygen exiting the nozzle during operation forms a second beam, which meets the first beam. The angled nozzle of the oxygen lance is thus just aligned so that it is rotated in the direction of the secondary fuel supply tunnel.

In order to facilitate the alignment of the nozzle in the correct position, the oxygen lance preferably in a rear, protruding from the burner assembly area, means for identifying the direction of the angled nozzle, in particular a position angle display. This may be, for example, a mark applied to the outside of the lance or a directional arrow. When this mark points to the inlet of the secondary fuel feed tunnel, the nozzle inside the rotary kiln also points in the right direction. According to the invention, the angled nozzle preferably at an angle 5 ° to 25 ° from the axial direction of the lance, preferably 10 ° to 20 °. In this way it can be achieved that the second beam hits the first beam at a relatively short distance after exiting the burner arrangement.

In experiments, it has been found that certain improvements in combustion even by a non-angled nozzle of the oxygen lance, ie in the case of axial injection of oxygen, especially when the oxygen jet has a long range through a suitable nozzle. For this reason, a non-angled additional nozzle may be present as a second nozzle at the end of the oxygen lance, which assumes this function.

Since the proportion of oxygen, which is supplied to the combustion in the rotary kiln through the oxygen lance, is relatively low, according to the invention, the oxygen lance has a significantly smaller outer diameter than the inner diameter of the feed tunnel in which it is arranged, preferably at least 20% smaller outer diameter. Typical burner assemblies have several different feed tunnels for different fuels and other purposes, one of which may then be selected more suitably for the oxygen lance. The difference in diameter ensures that there is no difficulty in inserting or turning the oxygen lance, even with soiling.

Particularly preferably, the oxygen lance is arranged rotatably and displaceably in a supply tunnel, wherein it determines its position by its own weight and also fixed sufficiently. The dead weight of the oxygen lance causes it to always lie down in the relevant supply tunnel and the friction is sufficiently large to prevent undesired rotations or displacements.

Since the oxygen lance must be supplied with oxygen under relatively high pressure as needed and dimensioned, it is advantageous to provide two inlet flanges for the connection of two flexible hoses in order to minimize the pressure loss in the hoses from a reservoir to the oxygen lance.

In a preferred embodiment of the invention, the oxygen lance and its nozzle are dimensioned and connected to an oxygen supply, that the emerging from the nozzle second jet when hitting the first beam has approximately the same or a smaller beam diameter than the first beam. In this way it can be avoided that oxygen in a larger amount of the secondary fuel flows past into the top of the rotary kiln, where it can contribute little to improve combustion.

If an additional nozzle is present in the oxygen lance, this is designed so that the oxygen exiting from it has the greatest possible range, which can preferably be achieved by a Laval nozzle.

Since the existing possibilities of burner arrangements are to be utilized for the present invention, it can not always be assumed that symmetrical positions of the oxygen lance are available for the secondary fuel supply tunnel. It may even be advantageous if the connecting line of the two supply tunnel for the secondary fuel and the oxygen lance does not intersect a geometric center axis of the burner assembly. Typically, the oxygen lance is located obliquely below the first jet, so that the second jet does not strike the first jet exactly from below but somewhat laterally. This may even lead to a desirable swirling effect and a better subsequent mixing of the secondary fuel with the primary flame. Such an arrangement also ensures that the oxygen jet is not already reacting on its way mainly with the primary fuel or is strongly deflected by the combustion air for the primary fuel.

In any case, however, it is advantageous that the first jet enters the rotary kiln vertically higher than the second jet, the second jet strikes the first jet from below or obliquely from below.

• Fig. 1: eine schematische Sicht eines Drehrohrofens im Längsschnitt,
• Fig. 2: einen Querschnitt durch eine erfindungsgemäße Brenneranordnung,
• Fig. 3: einen schematischen Längsschnitt durch den Zwischenbereich einer erfindungsgemäßen Sauerstofflanze,
• Fig. 4: eine schematische Seitenansicht einer erfindungsgemäßen Sauerstofflanze und
• Fig. 5: das Funktionsprinzip der Erfindung in schematischer perspektivischer Darstellung.

In the following, the present invention will be explained in more detail with reference to some embodiments with the aid of the drawing. Show it:

• Fig. 1 : a schematic view of a rotary kiln in longitudinal section,
• Fig. 2 FIG. 2: a cross section through a burner arrangement according to the invention, FIG.
• Fig. 3 FIG. 2: a schematic longitudinal section through the intermediate region of an oxygen lance according to the invention, FIG.
• Fig. 4 a schematic side view of an oxygen lance according to the invention and
• Fig. 5 : The functional principle of the invention in a schematic perspective view.

Fig. 1 schematically shows a typical rotary kiln 1 for the production of cement 2, which passes through the rotary kiln 1 in powder form. At the lower end of the rotary kiln 1, a burner assembly 3, preferably of approximately cylindrical basic shape, is arranged, which comprises a main burner 5, which is fed with a primary fuel. During operation of the rotary kiln 1 so creates a primary flame 6, which generates the majority of the heat required. The burner assembly 3 also includes at least one secondary fuel supply pipe 10, also called a fluff, which is typically supplied in small pieces by means of an air flow. In the rotary kiln 1, this leads to a first jet 7 containing the secondary fuel 10. In the burner assembly 3 according to the invention also an oxygen lance 12 is arranged, which generates an oxygen-rich second jet 8 during operation. The first jet 7 and the second jet 8 meet in an intersection region 9, since the oxygen lance 12, although parallel to the secondary fuel supply tunnel 19, has an angled nozzle 14 at its end. It is thereby achieved that the second jet 8 emerges at an angle to the geometric center axis 4 of the burner arrangement 3 or to the geometric center axis 27 of the oxygen lance 12. The combustion gases pass out of the rotary kiln 1 to an exhaust vent 24, in which an analyzer 25 can measure the proportions of certain components, in particular of pollutants.

Fig. 2 shows a cross section through the burner assembly 3, which reveals that the burner assembly 3 has different supply tunnels in different areas, which are partially concentric with the geometric center axis 4, but partly also lie eccentrically. The entire burner assembly 3 has an outer insulation 26 which surrounds a first supply tunnel 16, which is formed as an annular space. This can be used for example for the supply of primary air. Further inside is another supply tunnel, the z. For example, it can be used as a primary fuel for the supply of pulverized coal. Still further inside is another supply tunnel, which can be reused for centrally supplied air, for example. Within this further supply tunnel 18 are in the present embodiment, at least one supply tunnel 19 for secondary fuel 10, two more supply tunnel 18 for purposes not further explained here and a feed tunnel 20 for the oxygen lance 12. This supply tunnel 20 for the oxygen lance 12 has an inner diameter D, which is considerably larger than the outer diameter of the oxygen lance 12, in particular at least 20% larger. In the embodiment of Fig. 2 For example, the secondary fuel supply tunnel 19 is slanted above the oxygen lance supply tunnel 20.

Fig. 3 shows in schematic longitudinal section with additional explanations an end portion of the oxygen lance 12 with an angled nozzle 14 and an additional nozzle 15, which can be optionally provided. The oxygen lance 12 has an outer diameter d and a geometric center axis 27. The angled nozzle 14 ejects in operation an oxygen-rich second jet 8 at an angle α to the geometric center axis 27 of the oxygen lance 12, which schematically first jet 7 meets with secondary fuel in a crossing region 9. This crossing region 9 has a distance E of less than 5 m, preferably less than 2 m, from the end of the oxygen lance 12. This is achieved in that the angle α of the angled nozzle 14 is between 5 and 25 °, preferably between 10 and 20 °.

In Fig. 4 is schematically shown in longitudinal section, the entire oxygen lance 12 with its connecting lines to an oxygen tank 21. In the rear region, the oxygen lance 12 has a position angle indicator 13, by means of which the operator can recognize in which direction the angled nozzle 14 in the interior of the rotary kiln 1 in the installed state. The oxygen lance 12 preferably has two inlet flanges 23 for the connection of tubular oxygen lines 22, which can supply the oxygen 11 from the oxygen tank 21 with only a slight pressure loss. It should be noted that the chemical purity of the oxygen in this process does not matter and also an oxygen-enriched gas, for example with an oxygen content of more than 50%, preferably more than 80%, can be used for the supply of the oxygen lance.

Fig. 5 illustrates once again the spatial situation at the outlet of the burner assembly 3. It can be seen that the first beam 7 from the supply tunnel 19 with secondary fuel obliquely and laterally from below is hit by the second oxygen-rich beam 8 in the crossing region 9. The oblique exit of the second jet 8 is achieved by the angled nozzle 14 on the oxygen lance 12, wherein the exact direction of the angled nozzle 14 by the attitude angle indicator 13 is also visible from the outside. Further supply tunnel 18 of the burner assembly 3 affect this process only slightly.

The present invention may be considered in new constructions of burner assemblies for rotary kilns, but mainly serves as well the retrofitting of existing burner assemblies, in which most supply tunnels, as required for the present invention for introducing an oxygen lance, are present. The targeted supply of oxygen or oxygen-enriched gas to a secondary fuel can significantly improve its combustion and thus significantly reduce pollutant emissions, in particular the emission of carbon monoxide.

LIST OF REFERENCE NUMBERS

1

Rotary kiln

2

cement

3

burner arrangement

4

Geometric center axis of the burner assembly

5

main burner

6

Primary flame

7

First ray

8th

Second ray

9

Intersection of first and second beam

10

Secondary fuel

11

oxygen

12

oxygen lance

13

Position angle display

14

Angled nozzle

15

supplemental

16

First feed tunnel

17

Second feed tunnel

18

Another feed tunnel

19

Feed tunnel for secondary fuel

20

Feed tunnel for oxygen lance

21

oxygen tank

22

oxygen line

23

inlet flange

24

exhaust hood

25

analyzer

26

insulation

27

Geometric center axis of the oxygen lance

α

nozzle angle

D

Diameter of the feed tunnel for the oxygen lance

d

Diameter of the oxygen lance

e

Removal of the crossing area from the burner assembly

Claims (15)

Method for improving the combustion of secondary fuel (10) supplied in a first jet (7) in a rotary kiln (1), wherein the rotary kiln (1) comprises a burner assembly (9) with a main burner (5) and with a plurality of feed tunnels ( 16, 17, 18, 19, 20) for various media, one of which (19) is designed for the supply of secondary fuel (10), in particular in the form of particles or chips in a stream of compressed air, characterized in that a tubular oxygen lance (12) for an oxygen-rich gas, in particular pure gaseous oxygen (11), with an angled nozzle (14) at its end in a supply tunnel (20) of the burner assembly (9) is arranged, wherein the oxygen lance (12) in a such that the oxygen (11) emerging from the nozzle (14) forms a second jet (8) which strikes the first jet (7). A method according to claim 1, characterized in that the proportion of undesirable components, in particular carbon monoxide (CO), measured in the exhaust gas of the rotary kiln (1) and the oxygen lance (12) is rotated and / or supplied with oxygen (11) that a minimum of the component in question or a minimum of the sum of various undesired fractions. A method according to claim 1 or 2, characterized in that the second beam (8) meets the first beam (7) within less than 5 m (meters) after exiting the burner assembly (9), preferably less than 2 m. Method according to one of the preceding claims, characterized in that the oxygen (11) supplied in such an amount is that in the rotary kiln (1) a total of a superstoichiometric ratio of fuels and oxygen (11) is formed. Apparatus for improving the combustion of secondary fuel (10) supplied in a first jet (7) in a rotary kiln (1), said rotary kiln (1) comprising a burner assembly (9) having a main burner (5) and a plurality of supply tunnels (Fig. 16, 17, 18, 19, 20) for various media, one of which is designed for the supply of secondary fuel (10), in particular in the form of particles or chips in a compressed air stream, characterized in that a tubular oxygen lance ( 12) for an oxygen-rich gas, in particular technically pure gaseous oxygen (11), with an angled nozzle (14) at its end in a supply tunnel (20) of the burner assembly (9) is arranged so that from the angled nozzle (14) escaping oxygen forms a second jet (8) which strikes the first jet (7). Apparatus according to claim 5, characterized in that the oxygen lance (12) in a rear, from the burner assembly (9) outstanding region means (13) for identifying the direction of the angled nozzle (14), in particular a position angle indicator (13). Apparatus according to claim 5 or 6, characterized in that the angled nozzle (14) by an angle (α) of 5 ° to 25 ° to a geometric center axis (27) of the oxygen lance (12) is angled, preferably 10 ° to 20 ° , Device according to one of claims 5 to 7, characterized in that the oxygen lance (12) has at its end a non-angled additional nozzle (15). Device according to one of claims 5 to 8, characterized in that the inner diameter (D) of the feed tunnel (20) for the oxygen lance (12) is considerably larger than the outer diameter (d), preferably at least 20% larger. Device according to one of claims 5 to 9, characterized in that the oxygen lance (12) is rotatably and slidably disposed in a supply tunnel (20) and its position is determined and fixed by its own weight. Device according to one of claims 5 to 10, characterized in that the oxygen lance (12) has two inlet flanges (23) for the connection of flexible hoses as oxygen line (22). Device according to one of claims 5 to 11, characterized in that the oxygen lance (12) and the angled nozzle (14) are dimensioned and connected to an oxygen supply (21, 22), that of the nozzle (14) exiting second beam (8) when in contact with the first beam (7) has approximately the same or a smaller beam diameter than the first beam (7). Device according to one of claims 8 to 12, characterized in that the additional nozzle (15) is designed for as large a range as possible of the oxygen (11) leaving it, preferably as a Laval nozzle. Device according to one of claims 5 to 13, characterized in that the supply tunnel (20), in which the oxygen lance (12) is arranged and the supply tunnel (19) for the first beam (7) of secondary fuel (10) are arranged in the burner assembly (9), that their connecting line does not intersect a geometric center axis (4) of the burner assembly (9). Device according to one of claims 5 to 14, characterized in that the secondary fuel (10) and oxygen lance (12) supply tunnels (19, 20) are arranged so that the first jet (7) is vertically higher than the second jet (8th) ) enters the rotary kiln (1).

Images