Lance for use during combustion

Abstract

A composite lance for use during the injection of gases during combustion, and a method for making such a lance. The lance has a channel through which gas flows, and it includes a core of a metallic material and a ceramic layer outside the core. The outer surface of the core includes a region having a smaller diameter bounded axially by regions each having larger diameters. The ceramic layer is positioned around the core with a gap between the outer surface of the core and the inner surface of the ceramic layer. The gap prevents the ceramic layer from cracking because of differences in thermal expansion between the core and the ceramic layer when temperature changes take place in the lance.

Description

FIELD OF THE INVENTION

The present invention relates to a lance that is used to inject gases into a combustion process at a high flow rate. The injected gases are intended to react with NO_x and thereby solve the emissions problem caused by NO_x gases generated during the combustion of fossil fuels.

DESCRIPTION OF THE RELATED ART

NO_x gases are formed during the combustion of fossil fuels, and it is desired to eliminate those gases from the combustion products. The elimination is carried out by injecting gases at a high flow rate into a combustion region. The gases are injected through lances that are located at a distance from each other and having nozzles placed directly adjacent to the high-temperature zone of the combustion region. As a result of the simplicity of the design, and also for reasons of economy, the nozzle is not cooled by any other method than the cooling that is obtained from the flow of the gases that are injected. Metal lances are currently used.

The gases are injected intermittently, that is, they are injected with an on/off-effect, and that causes problems because of varying temperatures of the lance and the nozzles—a high temperature exists when the gases are not flowing and a lower temperature exists when the gases flow through the lances and the nozzles. The complete unit of lances and nozzles is subjected to thermal stress, to high temperatures, and to hot, corrosive, and abrasive mixtures of gases and particles.

The problem of using metal lances is that thermal loading, exhaustion, and stress produce accelerated oxidation, as well as deformation that is induced by stress. One solution has been the use of ceramic lances.

The problems with ceramic lances are that they are difficult to manufacture with acceptable tolerances, and they are subject to the formation of cracks that can cause catastrophic failure of the unit. Furthermore, it can be difficult to manufacture accessories for the connection of the gas supply to such ceramic lances.

The present invention eliminates or significantly reduces those problems.

An object of the present invention is to join together a lance having a metallic core and a ceramic layer and in that way to form a composite lance.

SUMMARY OF THE INVENTION

The present invention thus relates to a lance to be used during the injection of gases into a combustion region. The lance includes an internal channel through which gas is to flow. The lance is a composite having a core of a metallic material and a ceramic layer outside of the core. The outer surface of the core is arranged with a region that has a smaller diameter bounded axially by regions that have larger diameters. The ceramic layer is arranged outside of the core with a gap between the outer surface of the core and the inner surface of the ceramic layer, whereby the gap prevents the ceramic layer from cracking because of the difference in thermal expansion between the core and the ceramic layer when subjected to changes of temperature.

The invention also relates to a method for the manufacture of such a lance.

BRIEF DESCRIPTION OF THE DRAWINGS

The structure, operation, and advantages of the present invention will become further apparent upon consideration of the following description, taken in conjunction with the accompanying drawings in which:

FIG. 1 a is a fragmentary, longitudinal cross-sectional view of a composite lance in which a ceramic layer has been sintered directly onto a metal core with a gap between the core and the ceramic layer;

FIG. 1 b is an enlarged view of region lb of FIG. 1a;

FIG. 2 a is a fragmentary, longitudinal cross-sectional view showing a preformed ceramic layer applied to a metal core by glue with a gap between them;

FIG. 2 b is an enlarged view of region 2b of FIG. 2a;

FIG. 3 a is fragmentary, longitudinal cross-sectional view of a composite lance having a thicker ceramic layer than those shown in FIGS. 1 and 2; and

FIG. 3 b is an enlarged view of region 3b of FIG. 3a.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 a shows an embodiment of a lance 1 for use in the injection of gases into a combustion region during a combustion process. The lance includes a channel 2 within the lance 1, through which channel gas is intended to flow.

In accordance with the invention, the lance 1 is a composite lance having a core 3 of metallic material and a ceramic layer 4 outside of the core 3. The outer surface of the core 3 has a region 7 of smaller diameter bounded axially by regions 6, 9 each having larger diameters. As shown in FIG. 1b, the ceramic layer 4 is arranged outside of the core 3 with a spacing or gap 5 between the outer surface of the core 3 and the inner surface of the ceramic layer 4. The gap 5 prevents the ceramic layer 4 from cracking because of differences in thermal expansion between the core 3 and the layer 4 when they are subjected to changes in temperature.

The metallic core 3 is manufactured from, for example, stainless steel or ODS (oxide dispersion strengthened) material. Both the region 7 having the smaller diameter and the region 6 having the larger diameter are surrounded by the ceramic layer 4. The ceramic layer 4 can advantageously be manufactured from SiC.

The present invention further relates to a method for the manufacture of a lance 1 to be used during the injection of gases during a combustion process and including a channel 2 within the lance 1 through which gas flows.

According to one preferred embodiment, the lance 1 is formed as a composite lance that includes a core 3 of a metallic material having a ceramic layer 4 outside of the core 3. The outer surface of the core 3 includes a region 7 with a smaller diameter bounded axially by regions 6, 9 having larger diameters. The ceramic layer 4 is arranged outside of the core 3 with a gap 5 between the outer surface of the core 3 and the inner surface of the ceramic layer 4, whereby the gap 5 prevents the ceramic layer 4 from cracking because of the difference in thermal expansion between the metallic core 3 and the ceramic layer 4 when temperature changes take place in the lance 1.

According to one preferred method, the gap 5 between the core 3 and the ceramic layer 4 is provided with the aid of an intermediate material that disintegrates in that it melts or burns and is vaporized at a temperature that is lower than the melting point of the metallic core 3.

According to a further preferred method, the intermediate material is polymer-based, or is a paper-based material, such as, for example, masking tape.

According to a preferred method, the ceramic layer 4 is applied outside of the intermediate material, which is applied outside of the core 3, after which the ceramic layer 4 is sintered.

According to a further preferred method, the ceramic layer 4 shown in FIG. 2a is sintered to its final form and is thereafter slid onto the core 3, as shown in FIG. 2b. Glue 8 is subsequently introduced between the metallic core 3 and the ceramic layer 4, with gap 5 positioned between the metallic core 3 and the glue 8.

According to a further preferred method, the glue 8 is a ceramic glue that is sintered after the ceramic layer 4 has been slid onto the metallic core 3.

FIG. 3 a shows a metallic core 3 with a ceramic layer 4 that is thicker than the ceramic layers shown in FIGS. 1 and 2. Thus the ceramic layer 4 can have a varying thickness without deviating from the aim of the invention. The thicker the layer 4 is, the better is the temperature stability provided for the metallic core 3.

According to one preferred method, an intermediate material, such as masking tape, is wound around the metallic core 3. The choice of the thickness of the tape and the choice of the number of times the tape is to be wound around the core 3 depend upon the thickness of the gap 5 that is desired for the completed composite lance 1. A ceramic powder, such as Al₂O₃ or SiO₂, is subsequently applied outside of the tape. The powder is pressed to form a green body and it is then sintered. During the rise in temperature that occurs in association with the sintering, the tape melts or burns. The tape melts or burns and is vaporized at a temperature that is lower than the sintering temperature of the ceramic material. The vapors from the tape find their way out at a point where the gap 5 between the core 3 and the layer 4 meets the surroundings (see reference numeral 10 in FIG. 1). Before the tape has vaporized, the green body has adopted its shape in the form of a porous layer 4, and it retains for that reason its shape when the tape has been vaporized, rather than being sintered such that it lies in contact with the core 3.

After the sintering process has been carried out, a metallic core 3 is obtained having a ceramic layer 4, between which a gap 5 has formed. The gap 5 ensures that the ceramic layer 4 is not sensitive to the difference in coefficient of thermal expansion between it and the metallic material that is used as the metallic core 3. Because there is a difference between the coefficient of thermal expansion of the metallic core 3 and that of the ceramic layer 4, cracks would otherwise develop in ceramic layer 4 when the core 3 expands, which takes place when the core 3 is subject to changes in temperature. The ceramic layer 4 is retained in place around the core 3 in that the core 3 is provided with a region 6 having a larger diameter, and thus the ceramic layer 4 cannot slide off the metallic core 3.

A further method is similar to the method describe above but with the difference that the ceramic layer 4 is sintered separately in its final form, and in the form of a hollow cylinder. The inner diameter of the ceramic layer 4 is adapted such that it can be slid onto a core 3 that is covered with tape. Ceramic glue 8 is applied to the tape before the layer 4 is slid onto the core 3. The layer 4 is subsequently slid onto the core 3, which is surrounded by the tape and the glue 8, and that is followed by sintering in order to form the glue 8 according to the outer surface of the tape and the inner surface of the ceramic layer 4, and in order to vaporize the tape. Gap 5 is thus formed also by that method, see FIG. 2b.

A number of embodiments and uses have been described above, However, the lance 1 including the channel 2, the core 3, the layer 4, the gap 5, and the glue 8 can be designed in another suitable manner without deviating from the fundamental idea of the invention. Thus the present invention is not limited to the embodiments described above: it can be varied within the framework specified by the attached patent claims.

Although particular embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that changes and modifications can be made without departing from the spirit of the present invention. Accordingly, it is intended to encompass within the appended claims all such changes and modifications that fall with the scope of the present invention.

Claims

1. A lance for use during the injection of gases into a combustion region, said lance comprising: a tubular member including a channel within which a gas can flow, wherein the tubular member is a composite lance structure including a tubular core formed from a metallic material and a ceramic layer outside of the core, wherein an outer surface of the core includes a first region having a first diameter, the first region bounded axially by respective second regions each having larger a larger diameter than that of the first region, wherein the ceramic layer is positioned outside of the core with a gap between the outer surface of the core and an inner surface of the ceramic layer, whereby the gap prevents the ceramic layer from cracking because of differences in thermal expansion between the core and the ceramic layer when temperature changes take place in the lance.

2. A lance in accordance with claim 1, wherein the ceramic layer overlies both the first and second regions of the core.

3. A method for the manufacture of a lance for use during the injection of gases into a combustion region, the lance including an inner channel within through which gases flow, wherein the lance is a composite lance, said method comprising the steps of: providing a tubular core of a metallic material, the core including a channel for gas flow, wherein the core has an outer surface that includes a first region having a first diameter and bounded axially by respective spaced second regions each having a larger diameter than that of the first region; positioning a ceramic layer in overlying relationship with the outer surface of the core; and providing a gap between the outer surface of the core and an inner surface of the ceramic layer, whereby the gap prevents the ceramic layer from cracking because of differences in thermal expansion between the core and the ceramic layer during changes of temperature in the lance.

4. A method in accordance with claim 3, wherein the gap between the core and the ceramic layer is formed by applying between the core and the ceramic layer an intermediate material that disintegrates at a temperature that is lower than the melting temperature of the metallic core.

5. A method in accordance with claim 4, wherein the intermediate material is a polymer-based material.

6. A method in accordance with claim 3, wherein the ceramic layer is sintered after it is positioned over the core.

7. A method in accordance with claim 3, including the steps of: sintering the ceramic layer to a final tubular form; sliding the sintered ceramic layer onto the core; and introducing a glue between the metallic core and the ceramic layer with the gap positioned between the metallic core and the glue.

8. A method in accordance with claim 7, wherein the glue is a ceramic glue, and including the step of sintering the glue after the ceramic layer has been slid onto the core.

9. A method in accordance with claim 4, wherein the intermediate material is a paper-based material.