Burner with a slurry coating, with high resistance to metal dusting

Abstract

At least a part of a burner for a catalytic reactor is coated with a silicate based nickel aluminide slurry diffusion coating.

Claims

1. Burner for a catalytic reactor comprising at least two concentric burner tubes for oxidizer and fuel supply, wherein the burner tubes are made of a Ni-based alloy, and at least a part of at least one of said burner tubes is coated with a silicate based nickel aluminide slurry diffusion coating, wherein a 10-1000 μm thick silicate based Al containing slurry is applied on at least one of the burner tubes by means of slurry spray, paint brush or immersion.

2. Burner for a catalytic reactor comprising at least two concentric burner tubes for oxidizer and fuel supply, wherein the burner tubes are made of a Ni-based alloy, and at least a part of at least one of said burner tubes is coated with a silicate based nickel aluminide slurry diffusion coating, wherein the silicate based nickel aluminide slurry diffusion coating is made by applying a 10-1000 μm thick silicate based Al containing slurry on at least one of the burner tubes, followed by heat treatment of the applied silicate based Al containing slurry.

3. Burner according to claim 2, wherein the heat treatment is a two step diffusion heat treatment in vacuum, first step is a ½-2 hour diffusion heat treatment at 600° C.-800° C., and the following second step is a 2-11 hour diffusion heat treatment at 900° C.

4. Burner according to claim 3, wherein the heat treatment is performed in a reducing atmosphere of 80-100% Argon and 0-20% Hydrogen.

5. Method for production of a silicate based nickel aluminide slurry diffusion coating on a burner tube for protection against high temperature corrosion caused by metal dusting, the burner tube being made of a Ni-based alloy, said method comprising the steps of: applying a 10-1000 μm thick silicate based Al containing slurry on the Ni-based alloy by means of slurry spray, paint brush or immersion; heat treating the Ni-based alloy with the applied silicate based Al containing slurry in a first step diffusion heat treatment in vacuum for ½-2 hour at 600° C. 800° C.; heat treating the Ni-based alloy with the applied silicate based Al containing slurry in a second step diffusion heat treatment in vacuum for 2-11 hour at 900° C.-1200° C.

6. Method according to claim 5, wherein said burner tube is a catalytic reactor burner tube.

7. A catalytic reactor burner tube made of a Ni-based alloy coated with a silicate based nickel aluminide coating, made by applying a 10-1000 μm thick silicate based Al containing slurry on the burner tube made of a Ni-based alloy, followed by heat treatment of the applied silicate based Al containing slurry.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a cross section of a sample after a five week metal dusting test.

(2) FIG. 2 is a magnification of FIG. 1.

(3) FIG. 3 is a magnification of the interface coating/base alloy.

(4) FIG. 4 shows the interdiffusion rate of six compositions.

(5) FIG. 5 is a magnification of FIG. 4 to compare five of the six compositions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(6) In an embodiment of the invention the Ni base burner for a catalytic reactor comprises at least two concentric burner tubes for oxidizer and fuel supply. According to this embodiment of the invention, at least a part of one or both the burner tubes is coated with an aluminide slurry diffusion coating. Although the invention advantageously is for use in large-scale burners with relative large burner tube diameters, the invention is not restricted to these large diameters, since an advantage of the invention is that the slurry diffusion coating may be applied inside relative small diameter burner tubes.

(7) In a further embodiment of the invention, the nickel aluminide slurry diffusion coating has a thickness of 10-1000 μm. Phase stability depends on coating thickness and exposed temperature. In a further embodiment the coating thickness is at least 100 μm. The burner tubes are in a further embodiment of the invention made of a Ni-based alloy. The invention is well suited for substrates with Ni-based alloys, as one of the advantages of the coating is that the interdiffusion of Ni in the coating and Al in the coated part of the burner is slower and to a much lower extent than the disclosed known art coatings.

(8) The burner is in a further embodiment coated with a silicate based nickel aluminide slurry diffusion coating by applying a 10-1000 μm thick silicate based Al containing slurry on at least one of the burner tubes or at least a part of the burner tube(s). The application of the slurry can be done by means of spraying, brushing or immersion. Further the coating must be done by a subsequent heat treatment of the applied silicate based Al containing slurry. The heat treatment may be performed in an oven where the coated burner parts are heated separately, or it may be performed locally on the assembled burner, for instance in situ in the catalytic reactor. This is especially advantageous for large-scale burners.

(9) In an embodiment of the invention, the heat treatment is performed in two steps as a diffusion heat treatment. The first heat treatment step is a ½-2 hour, preferably 1-hour diffusion heat treatment at 600° C. 800° C., preferably 700° C. The following second step is a 2 11 hour, preferably 10-hour diffusion heat treatment at 900° C.-1200° C., preferably 1050° C. The two step diffusion heat treatment may in another embodiment of the invention be performed in a reducing atmosphere containing 90% Argon and 10% Hydrogen. The controlled heat treatment prior to exposure to process conditions leads to formation of a uniform and protective metal coating.

(10) In a second aspect, the invention comprises a method for production of a silicate based nickel aluminide slurry coating on a Ni-based alloy for protection against high temperature corrosion caused by metal dusting, said method comprising the steps of applying a 10-1000 μm thick silicate based Al containing slurry on a Ni-based alloy heat treating the Ni-based alloy with the applied silicate based Al containing slurry in a first step diffusion heat treatment for ½-2 hour, preferably 1 hour at 600° C.-800° C., preferably 700° C. heat treating the Ni-based alloy with the applied silicate based Al containing slurry in a second step diffusion heat treatment for 2-11 hour, preferably 10 hours at 900° C.-1200° C., preferably 1050° C.

(11) In an embodiment of this aspect of the invention, the slurry is applied on Ni-based alloy by means of slurry spray, paint brush or immersion. The Ni-based alloy may in further embodiments of the invention be a catalytic reactor burner tube.

(12) More specifically, an aspect of the invention comprises the use of a silicate based nickel aluminide diffusion coating on a burner tube in a catalytic reactor burner in the temperature interval 400° C. to 900° C., at a carbon activity higher than 1.

(13) Summarizing, the advantages of the invention as described in the above aspects and embodiments comprise: the coating is produced from a water based slurry, free of Cr(VI) free and environmentally benign. It can be applied to large surfaces and inside thin burner tubes. Interdiffusion of Ni in the coating and Al in the substrate will be slower. Continuous diffusion of Ni into the coating and of Al into the metal alloy is a known problem, but the particular composition according to the invention shows the lowest interdiffusion in the relevant temperature interval. The controlled heat treatment prior to exposure to process conditions leads to formation of a uniform and protective metal coating.

FEATURES OF THE INVENTION

(14) 1. Burner for a catalytic reactor comprising at least two concentric burner tubes for oxidizer and fuel supply, wherein at least a part of at least one of said burner tubes is coated with a based nickel aluminide slurry diffusion coating.

(15) 2. Burner according to feature 1, coated with a silicate based nickel aluminide slurry diffusion coating.

(16) 3. Burner according to feature 2, wherein the silicate based nickel aluminide slurry diffusion coating has a thickness of between 10-1000 μm.

(17) 4. Burner according to any of the preceding features, wherein the burner tubes are made of a Ni-based alloy.

(18) 5. Burner according to feature 4, wherein the silicate based nickel aluminide slurry diffusion coating is made by applying a 10-1000 μm thick silicate based Al containing slurry on at least one of the burner tubes.

(19) 6. Burner according to feature 5, wherein the 10-1000 μm thick silicate based Al containing slurry is applied on at least one of the burner tubes by means of slurry spray, paint brush or immersion.

(20) 7. Burner according to feature 5 or 6, wherein the silicate based nickel aluminide slurry diffusion coating is made by a heat treatment of the applied silicate based Al containing slurry.

(21) 8. Burner according to feature 9, wherein the heat treatment is a two-step diffusion heat treatment in vacuum, first step is a ½-2 hour, preferably 1-hour diffusion heat treatment at 600° C.-800° C., preferably 700° C. and the following second step is a 2-11 hour, preferably 10-hour diffusion heat treatment at 900° C.-1200° C., preferably 1050° C.

(22) 9. Burner according to feature 8, wherein the heat treatment is performed in a reducing atmosphere of 80-100% Argon and 0-20% Hydrogen.

(23) 10. Method for production of a silicate based nickel aluminide slurry coating on a Ni-based alloy of a burner for protection against high temperature corrosion caused by metal dusting, said method comprising the steps of applying a 10-1000 μm thick silicate based Al containing slurry on the Ni-based alloy heat treating the Ni-based alloy with the applied silicate based Al containing slurry in a first step diffusion heat treatment in vacuum for ½-2 hour, preferably 1 hour at 600° C.-800° C., preferably 700° C. heat treating the Ni-based alloy with the applied silicate based Al containing slurry in a second step diffusion heat treatment in vacuum for 2-11 hour, preferably 10-hour at 900° C.-1200° C., preferably 1050° C.

(24) 11. Method according to feature 10, wherein the slurry is applied on Ni-based alloy of a burner by means of slurry spray, paint brush or immersion.

(25) 12. Method according to feature 10 or 11, wherein said Ni-based alloy is a catalytic reactor burner tube.

(26) 13. Use of a silicate based nickel aluminide diffusion coating on a burner tube in a catalytic reactor burner in the temperature interval 400° C. to 900° C., at a carbon activity higher than 1.

POSITION NUMBERS

(27) 01. Coating 02. Coating surface 03. Ni-based alloy

(28) FIG. 1 shows the cross section of a sample after 5 weeks' metal dusting test. Position 1 is the coating, and position 2 is oxides formed on the coating, whereas position 3 is the base alloy. No metal dusting is detected.

(29) FIG. 2 shows a magnification of FIG. 1. Position 1: coating, Position 2: oxides, and position 3: mounting material.

(30) FIG. 3 shows a magnification of FIG. 1 of the interface coating/base alloy. Position 1: coating, Position 2: base alloy.

(31) Interdiffusion is measured as changes in the Ni/Al ratio in the coating, compared to the original Ni/Al ratio. With time, Ni diffuses from the base metal into the coating and Al diffuses from the coating into the base metal alloy. Depending on the diffusion rate of Ni and Al, the ratio Ni/Al changes with time. If the Ni/Al increases significantly with time the resistance to metal dusting changes; experiments have shown that the coating becomes less resistant against metal dusting.

(32) The best coating is considered to be the one with most constant Ni/Al with time, because it will show the slowest interdiffusion.

(33) FIG. 4 shows that composition F has a high interdiffusion rate compared to the other five. FIG. 5 enlarges the scale to compare compositions A-E. Compositions B, D and E show linear growth with time and are therefore not as advantageous as compositions A and C, which show a slight increase in the beginning, but remain stable after that. Compositions close to A and C will be preferred.

EXAMPLE

(34) Metal dusting test of coated Ni-based alloy bars in the temperature range from 200 to 800° C. under very aggressive conditions with very low steam/carbon, under pressure 28.5 bar (g) for five weeks. The coating had been applied and heat treated in the range described in the invention. The thickness of the coating in the range 50-200 μm were tested. The coated Ni-based alloy bars did not show any metal dusting after 5 weeks, as compared to not-coated Inconel 601 bars which show metal dusting after less than one week.