Title of Invention

A DEVICE FOR PROTECTING A METAL SURFACE AGAINST METAL-DUSTING CORROSION

Abstract

The present invention relates to a device for protecting a metal surface against metal-dusting corrosion comprising an insulating layer of a gas-permeable, thermally insulating material, the side of the thermal insulating layer that is colder during operation being in direct vicinity of the metal surface, and the side of the insulating layer that is hotter during operation being heated by a gas stream containing carbon monoxide, which in addition contains atleast one of the reactants selected from hydrogen and steam and has a temperature in the range from 300 to 1700°C,characterized in that in the region between the metal surface to be protected and the hot side of the insulating layer a catalyst such as herein described is provided for reacting carbon monoxide with atleast one of the reactants selected from hydrogen and steam.

Full Text

This invention relates to a device for protecting a metal surface against metal-dusting corrosion. This invention relates to a metal surface protected against metal-dusting corrosion, which has an insulating layer of a gas-permeable, thermally insulatinq material, where the side of the thermal insulating layer that is colder during operation is in direct vicinity of the metal surface, and the side of the insulatinq layer that is hotter during operation is heated by a gas stream containing carbon monoxide, which additionally contains hydrogen and/or steam and has a temperature in the range from 300 to 1700°C. From DE-C-4327176 (to which corresponds US-Patent 5,490,974) it is known to protect metal surfaces against metal-dusting corrosion by introducing a largely CO-free, gaseous or vaporous protective medium into a region between the metal surface and the thermal insulating layer. The object underlying the invention is to perform the protection against metal-dusting corrosion in a simple and inexpensive way without supplying a protective gas from the outside. In accordance with the invention this is achieved in that in the region between the metal surface to be protected and the hot side of the insulating layer a catalyst is provided for reacting carbon monoxide with hydrogen and/or steam. 1A - 2 - Metal-dusting corrosion occurs under the influence of a hot, CO-containing gas when the gas cools on the metal surface, and the CO is decomposed to form C + C02 due to the Boudouard reaction. In the metal structure, carbides are formed which lead to the destruction of the structure of the material. Metal-dusting corrosion not only attacks steels, but for in-stance also nickel-based materials. The intensity of the corrosive attack increases with increasing partial pressure of CO and with increasing molar ratio between CO and CO2 on the metal surface. The phenomenon of the metal-dusting corrosion has not yet been clarified scientifically in all details, but it is known that the potential for the formation of free carbon from the decomposition of CO plays an important role. This decomposition of CO takes place below the Boudouard equilibrium temperature, with this temperature limit being briefly referred to as Boudouard temperature. The Boudouard temperature increases with increasing partial pressure of CO and with increasing molar ratio between CO and CO2. In accordance with the invention, the protection of the metal surface against metal-dusting corrosion is effected by the presence of a catalyst. This catalyst is disposed on the metal surface to be protected or in the region between the metal surface and the side of the insulating layer that is hotter during operation, and in particular in the region of the cold side of the insulating layer. By means of the catalyst, at least one of the reactions A or B (A) CO + 3 H2 —> CH4 + H2O (B) CO + H2O —> CO2 + H2 is promoted. Due to the local reduction of the CO concentration, the Boudouard temperature is reduced in the susceptible - 3 — region, so that the decomposition of CO is wholly or largely prevented. in the susceptible region, even small amounts of catalyst may be sufficient for protecting the metal surface, because usually only relatively small amounts of CO must be reacted. Usually, the thermal insulation consists of porous insulating concrete, porous bricks or a layer of ceramic fibers. Such thermal insulation can easily be provided with the required concentration of catalyst, e.g. through impregnation with a catalyst solution and subsequent drying- It is also possible to admix catalyst to the insulating concrete before the processing, or to the material for manufacturing the bricks. For promoting at least one of the above-mentioned reactions A or B, catalysts known per se may be used. These catalysts usually contain transition elements of the groups VIII, Ib and IVa of the Periodic Table. In particular, one or several of the metals nickel, copper, iron, cobalt, molybdenum, tungsten, chromium, platinum, palladium, rhodium or ruthenium are suited as catalyst components. Plant components susceptible to metal-dusting corrosion are, for instance, lines or conduits through which flows synthesis gas, whose main components are CO and H2 .Heat exchangers for cooling CO-containing gas, e.g. synthesis gas, must also be considered. The temperatures on the susceptible metal surface usually lie in the range from 300 to 1200°C, and the metal parts are exposed to pressures from 1 to 150 bar. The hot gas, which causes the corrosion, mostly has a CO content in the range from 2 to 80 vol-%. Embodiments for the protection against corrosion will now be explained with reference to the drawing. It represents a longitudinal section through lines carrying hot, CO-containing gas. - 4 - A collecting line 1 has an outer steel shell 2, which on the inside is lined with a porous, thermal insulating layer 3. In the interior of line 1 a hot, CO-containing gas flows, as is indicated by the arrows 5. Several individual lines 8, of which only one is represented in the drawing, open into the collecting line 1. The individual lines come, for instance, from a not represented tubular furnace for cracking hydrocarbons, in order to produce raw synthesis gas having a temperature in the range from e.g. 800 to 1000°C. In the orifice portion 8a of the individual line 8 the steel shell 2 has been shaped into a bell 9, whose upper portion 9a is welded with line 8. Between the bell 9 and the outside of line 8 there is likewise provided the porous thermal insulation, which fills this area. Since in particular the inside of the bell 9 is susceptible to metal-dusting corrosion, the insulating material has dispersed therein a catalytically active metal. The content of catalyst in the thermal insulation is indicated in the drawing by cross-hatched lines 4. As is furthermore shown in the drawing, not the entire thermal insulation is provided with catalyst, but only the susceptible portion inside the bell 9 and the portion directly adjacent thereto. Of course, the thermal insulation is only provided with a catalyst at those regions, of which it is known through calculation or from experience that the metal is attacked by metal-dusting corrosion. The type and concentration of the catalyst to be used is best found out by means of experiments. It was found out that the catalyst need only be present in relatively small concentrations in the vicinity of the susceptible points, in order to achieve the reguired reduction of the CO concentration in the gas produced there. In an example, an arrangement corresponding to the drawing was examined. The raw synthesis gas supplied through lines 1 -5- and 8 had a temperature of 870°C and the following composi-tion: CO2 5.0 vol-% CO 9.9 vol-% H2 50.1 vol-% CH4 5.0 vol-% H2O 30.0 vol-% The insulating layer 3 consisted of porous alumina, and within the area of the bell 9 it was impregnated with an aqueous nickel nitrate solution. The concentration of the Ni catalyst was 30 mg Ni per cm3. The gas composition directly on the inside of the bell 9 was determined by means of probes, and it was noted that the CO content of the synthesis gas was decreased to a residual content below 1 vol-% corresponding to reactions (A) and (B). At temperatures in this range of 400 - 600°C the risk of a metal-dusting corrosion did therefore not exist. Without the catalyst, the CO concentration on the inside of the bell virtually corresponded to the composition of the synthesis gas, so that a Boudouard equilibrium temperature of 785°C is obtained. In this case, metal-dusting corrosion therefore had to be anticipated. 6 WE CLAIM: 1. A device for protecting a metal surface against metal—dusting corrosion comprising an insulating layer of a gas-permeable, thermally insulating material, the side of the thermal insulating layer that is colder during operation being in direct vicinity of the metal surface, and the side of the insulating layer that is hotter during operation being heated by a gas stream containing carbon monoxide, which in addition contains atleast one of the reactants selected from hydrogen and steam and has a temperature in the range from 300 to 1700°C, characterized in that in the region between the metal surface to be protected and the hot side of the insulating layer a catalyst such as herein described is provided for reacting carbon monoxide with atleast one of the reactants selected from hydrogen and steam. 2. A device as claimed in claim 1, wherein the catalyst contains one or several of the metals nickel, copper, iron, cobalt, molybdenum, tungsten, chromium, platinum, palladium, rhodium or ruthenium. 3. A device as claimed in claim 1 or 2, wherein the thermal insulating layer consists of porous insulating concrete, porous bricks or a layer of ceramic fibers. 4. A device as claimed in claims 1 to 3, wherein the thermal insulating layer is provided with the catalyst adjacent the metal surface to be protected. - 7 - 5. A device as claimed in 1 or any of the preceeding claims, wherein the metal surface is designed for temperatures in the range from 300 to 1200°C. The present invention relates to a device for protecting a metal surface against metal-dusting corrosion comprising an insulating layer of a gas-permeable, thermally insulating material, the side of the thermal insulating layer that is colder during operation being in direct vicinity of the metal surface, and the side of the insulating layer that is hotter during operation being heated by a gas stream containing carbon monoxide, which in addition contains at least one of the reactants selected from hydrogen and steam and has a temperature in the range from 300 to 170° C, characterized in that in the region between the metal surface to be protected and the hot side of the insulating layer a catalyst such as herein described is provided for reacting carbon monoxide With at least one of the reactants selected from hydrogen and steam.

Documents:

01897-cal-1996 abstract.pdf

01897-cal-1996 claims.pdf

01897-cal-1996 correspondence.pdf

01897-cal-1996 description(complete).pdf

01897-cal-1996 drawings.pdf

01897-cal-1996 form-1.pdf

01897-cal-1996 form-13.pdf

01897-cal-1996 form-2.pdf

01897-cal-1996 form-3.pdf

01897-cal-1996 form-5.pdf

01897-cal-1996 form-9.pdf

01897-cal-1996 general power of attorney.pdf

01897-cal-1996 priority document.pdf

1897-CAL-1996-FORM 27.pdf

1897-CAL-1996-FORM-27-1.pdf

1897-CAL-1996-FORM-27.pdf

1897-cal-1996-granted-abstract.pdf

1897-cal-1996-granted-acceptance publication.pdf

1897-cal-1996-granted-claims.pdf

1897-cal-1996-granted-correspondence.pdf

1897-cal-1996-granted-description (complete).pdf

1897-cal-1996-granted-drawings.pdf

1897-cal-1996-granted-examination report.pdf

1897-cal-1996-granted-form 1.pdf

1897-cal-1996-granted-form 13.pdf

1897-cal-1996-granted-form 2.pdf

1897-cal-1996-granted-form 3.pdf

1897-cal-1996-granted-form 5.pdf

1897-cal-1996-granted-gpa.pdf

1897-cal-1996-granted-letter patent.pdf

1897-cal-1996-granted-priority document.pdf

1897-cal-1996-granted-reply to examination report.pdf

1897-cal-1996-granted-specification.pdf

1897-cal-1996-granted-translated copy of priority document.pdf