Alkali resistant refractories

Description

The United States Government has rights in this invention pursuant to contract no. DE-AC05-00OR22725 between the United States Department of Energy and UT-Battelle, LLC.

FIELD OF THE INVENTION

The present invention relates to refractory materials that are resistant to alkali attack, and more particularly to refractory materials having a lithium rich surface treatment that retards degradation of refractories upon exposure to alkali-rich molten salts particularly molten Na₂CO₃.

BACKGROUND OF THE INVENTION

Gasification of black liquor produced at paper mills during the pulping process is an attractive process of recovering inorganic materials while generating electrical power/steam/biofuels/hydrogen from the waste stream. The process has been delayed in development due to poor resistance of containment materials to alkali attack during long-term operations. Degradation of refractory and metallic containment materials in pilot-scale and demonstration-scale gasifiers presents a serious obstacle to the commercialization of black liquor gasifiers. Gasification vessel refractory linings degrade rapidly (6 months to a year), requiring replacement. Alkali resistant containment materials could extend the lifetime of refractory liners, making black liquor gasification a more attractive alternative to recovery boilers.

OBJECTS OF THE INVENTION

Accordingly, objectives of the present invention include provision of alkali resistant refractory containment materials for high-temperature vessels, and especially for black liquor gasification processes in order to make such processes more feasible. Further and other objects of the present invention will become apparent from the description contained herein.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, the foregoing and other objects are achieved by an article that includes a refractory material having a surface layer characterized by a greater concentration of lithium than the refractory material.

In accordance with another aspect of the present invention, a method of making an alkali-resistant material includes the steps of: applying to a refractory material at least one lithium-containing material; and heating the refractory material to a sufficient temperature so that the lithium-containing material forms an alkali-resistant surface layer on the refractory material.

In accordance with a further aspect of the present invention, a method of forming an alkali-resistant layer on a refractory vessel liner includes the steps of: providing a working material including lithium; and heating the working material in the vessel to a sufficient temperature so that the lithium forms an alkali-resistant surface layer on the vessel liner.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph of a test sample, after immersion testing in molten high alkali smelt, of refractory material having a lithium-rich layer in accordance with the present invention.

FIG. 2 is a photograph of a control sample, after immersion testing in molten high alkali smelt, of refractory material as received from the manufacturer and without a lithium-rich layer.

For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the above-described drawings.

DETAILED DESCRIPTION OF THE INVENTION

Any lithium-containing composition having a low melting point (less than 1300° C.), for example, LiOH and Li₂CO₃, is applied, either as a powder or as a paste formed from a mixture of powder and fluid, to the surface of alumina and alumino-silicate refractories. The lithium-containing composition is subsequently reacted at a temperature in the range of 700° C. to 1300° C. to produce an adherent, lithium-rich surface layer. The surface layer is generally characterized as having a higher concentration of lithium than the bulk refractory.

The surface layer is resistant to chemical attack by alkaline species, and protects the underlying bulk refractory material from chemical attack by alkaline species. The surface layer retards the degradation of refractory materials exposed to alkali-rich molten smelts, for example, molten Na₂CO₃/Na₂S. The surface layer generally comprises crystalline and/or glassy phases which may include at least one of the following classes of compounds: lithium aluminates, lithium silicates, and lithium alumina silicates, depending on composition of the starting refractory material. The surface layer can be altered during molten smelt exposure to form a layer material that appears to further retard sodium ion penetration.

EXAMPLE I

An approximately 2 mm thick layer of dry Li₂CO₃ was applied to the surfaces of mullite/SiO₂ refractory materials. The refractory and Li₂CO₃ layer was heated in air to a temperature of 900° C. for one hour to affect the desired reaction and formation of a lithium-rich surface layer on the refractory material. Subsequent x-ray examination of the surface revealed the formation of crystalline eucryptite (Li₂Al₂SiO₆) and LiAlO₂.

EXAMPLE II

A sample of refractory material prepared in accordance with Example I and an untreated control sample were immersed for 50 hours at 1000° C. in high alkali molten salt containing Na₂CO₃ and Na₂S. Cross sections were subsequently cut from the samples. An improvement in alkali resistance was observed for the sample having a lithium-rich surface layer, shown in FIG. 1, compared to the untreated control sample, shown in FIG. 2.

Other refractory materials such as: alumina, mixed α-β-alumina, and magnesium-alumina-spinel based refractories have shown some improved resistance to molten alkali salts after a lithium treatment though not to the extent observed for mullite-based refractories. As the lithium reacts with the alumina and/or silica minerals present in the refractory it forms a lithium-rich layer. On immersion in molten alkali salts, degradation of the refractory is retarded.

The present invention can be used to coat individual firebricks and/or high-temperature vessel liners. A damaged or worn lithium-rich layer can be repaired by re-application thereof by any of the processes described herein. The present invention can significantly extend the life of refractory materials.

In other embodiments of the present invention, a solution containing Li₂CO₃, LiOH and/or other lithium composition(s) can be infused via capillary action into the refractory body prior to heating between 700° and 1300° C. and subsequent formation of lithium-rich layer. Moreover, molten Li₂CO₃ or LiOH can be infused into the refractory with the subsequent formation of a lithium-rich layer.

EXAMPLE III

A solution containing Li₂CO₃ is applied to the surface of a mullite/SiO₂ refractory material and allowed to infuse thereinto. The Li₂CO₃-infused refractory is heated in air to a temperature of 900° C. for one hour to affect the desired reaction and formation of a lithium-rich layer on the refractory material.

Moreover, a slurry of Li₂CO₃ and/or LiOH or a lithium-containing composition could be applied to the refractory lining and heated in place to form lithium compounds on the surface.

EXAMPLE IV

An aqueous slurry of Li₂CO₃ is sprayed onto the surface of a mullite/SiO₂ refractory material. The Li₂CO₃-coated refractory is heated in air to a temperature of 900° C. for one hour to affect the desired reaction and formation of a lithium-rich layer on the refractory material.

Moreover, Li₂CO₃ and/or LiOH or a lithium-containing composition can be added to working material, for example, black liquor and/or biomass, and injected into the gasifier therewith so that during gasification, the formation (new, maintenance, and/or repair) of a lithium-rich layer occurs on the refractory liner during the biogasification process.

EXAMPLE V

Li₂CO₃ is added to a batch of black liquor prior to injection into a gasification vessel. The black liquor is then injected into the gasifier and the biogasification process is carried out therein. In the gasifier, the Li₂CO₃ is deposited on the refractory liner where it reacts with the refractory liner material, forming a lithium-rich layer thereon.

Refractory materials made in accordance with the present invention are suitable for use as containment materials or as containment liners for applications where high levels of alkali molten salts are present, for example, biogasification processes.

While there has been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications can be prepared therein without departing from the scope of the inventions defined by the appended claims.