MXPA00001469A - Cement-free refractory castable system for wet process pumping/spraying - Google Patents

Abstract

A method of applying a cement-free refractory castable to the surface of a refractory structure, comprising the steps of:a) preparing an intimately mixed refractory castable having alumina aggregate and a cement-free binder comprised of hydratable alumina;b) conveying the refractory castable under pressure through a delivery hose to a dispensing nozzle for applying the refractory castable;and c) adding a salt solution to the refractory castable prior to application by the nozzle at a rate wherein the salt solution comprises about 0.2%to 0.9%by weight of the refractory castable applied by the dispensing nozzle.

Description

REFRACTORY SYSTEM S¡ CEPTIBLI FREE OF CEMENT, FOR PF BOMBEQ / ASP FIELD OF INVENTION The present invention relates generally to installations and processes of shoccreting and, more particularly, to a system of wet process shotcreting, of refractory concrete that is free of cement.

BACKGROUND TO THE INVENTION Application by refractory shotcreting has become an important process for the repair and maintenance of refractory coatings in steel, non-ferrous, chemical, mineral and ceramic processing plants. In recent years, cement-free refractory concretes have been developed that are suitable for use in high temperature applications and have excellent resistance to slag corrosion produced during steel production. These refractories typically employ an alumina binder capable of hydration in substitution of calcium aluminate cement. Due to the suitability of these refractory concretes for high temperature applications in the steel production industry, it is highly desirable to be able to apply this material via a wet mix shotcreting process. Shooting is usually classified according to the process used, that is, wet mix spraying or dry mix spraying. A refractory wet mix shoccreíing process generally consists in the complete mixing of a refractory material and water to produce a mixture that is susceptible to pumping, then the mixture is introduced into an assortment hose and the mixture is pumped to a dispensing nozzle ( this is, sprinkling). A dry mix refractory shotcreting process generally involves transporting a dry refractory mixture through a supply hose by compressed air, then pressurized water is introduced into the nozzle before the application of the refractory to the target surface. In both processes, typically a setting modifier mixture can be added to the refractory concrete in the nozzle to initiate and accelerate the thickening and setting of the refractory concrete so that it does not collapse or sink when applied to vertical surfaces or ceilings. Because the mixture must be fluid for pumping in the wet mixing process, such mixtures are more critical in the wet mix compared to the dry mixing process. So far, refractory shotcreting has found limited application in high temperature and severe corrosion applications, such as, for example, in the steel production industry, where the refractory material may be exposed to temperatures in the 2700 ° range F at 2900 ° F and come into contact with corrosive slag matepals. A main reason why the refractory shooter is limited to such applications is due to the materials added to the refractory compositions in order to facilitate its application by a process of shotcreting by wet mixing or by dry mixing. In both processes a refractory concrete mixture is used as the basic refractory composition. The majority of dry process gun mixtures are based on refractory concrete mixtures that are modified to have finer aggregates (ie, smaller than refractory concrete) to reduce "bounce" when the refractory is applied to a surface. In addition, additives, usually clay, are added to the refractory to improve the stickiness characteristics (ie, non-collapsing) of the material when applied to vertical walls. These modifications make dry mixes for gun application less susceptible to use in severe corrosion and high temperatures, compared to refractory cements of similar base composition because the clay adds considerable silica to the refractory. The addition of silica to very pure alumina systems can have a particularly detrimental effect on the hot rupture moduli (MOR) of the material, in high temperature shrinkage and slag corrosion resistance of steel production. In this regard, such mixtures for gun application may have lower resistance to steel production temperatures in the range of 2700 ° F to 3000 ° F and exhibit a permanent linear change (ie, shrinkage) at certain temperatures, this is, above 2700 ° F. In addition, said mixtures for application with pisiole typically have high porosity, which is related to the addition of clay, altered grain size and poor inherent mixing in a dry gun application process. As a result, such mixtures for gun application are less than desirable in the repair of coatings of steel cauldrons or other surfaces where such coatings would be exposed to extremely high temperatures, that is, above 2700 ° F, and to highly scoria corrosive A shotcreying process of wet mix exceeds the less than desirable mixing inherent in a dry gun application process and generally does not require the addition of clay to the basic composition of the refractory concrete used. Accordingly, a refractory concrete suitable for use at high temperatures and at high corrosiveness can be advantageously applied in a wet mixing process, but only if an appropriate "accelerator" can be found for use with it. In this regard, to facilitate the wet mixing process, a setting modifying mixture, conventionally referred to as an "accelerator" can be added to the wet mix refractory just prior to spraying to accelerate the thickening and setting of the refractory concrete for the purpose of to avoid the collapse and collapse of the refractory when it is applied to a vertical surface. It is known that many accelerators have a negative effect on the properties of certain refractories that are typically used in environments of high temperature and high corrosivity. For example, sodium silicate is a well-known accelerator used in refractory shotcreting of wet mix and dry mix. However, even small additions of alkalis, such as sodium, can reduce the resistance to high temperature and its refractory quality in refractories with low cement content and high alumina. Therefore, it is important that an accelerant (ie, the "accelerator") used with a particular refractory concrete be capable of providing the thickening and set characteristics to the particular refractory concrete without adversely affecting the properties of the refractory concrete by inroduction of harmful material from refractory concrete. The present invention provides a wet mix shoccreying process for applying a cementless refractory material, of the type described above for use in high temperature applications.

In accordance with the present invention, a method is provided for the application of a refractory concrete, without cement, to the surface of a refractory structure, which comprises the steps of: a) preparing an intimately mixed refractory concrete, having aggregate of alumina and a cement-free binder composed of hydratable alumina; b) transferring the refractory concrete under pressure through a dispensing hose to a dispensing nozzle to apply said refractory concrete; and c) adding an acid or salt solution, wherein said solution is composed of a salt selected from the group consisting of soluble magnesium, and salts of aluminum, acid and acid salts, to the refractory concrete before its application by the nozzle in a proportion wherein said salt solution comprises about 0.2% to 0.9% by weight of the refractory concrete applied by the dispensing nozzle. According to another aspect of the present invention, there is provided a method for the application of a refractory concrete to the surface of a structure, which comprises the steps of: Mixing a refractory material composed primarily of alumina aggregate, calcined alumina and thermally reactive, magnesium oxide and a hydratable alumina cement; Transporting the refractory material under pressure through a dispensing hose to a dispensing nozzle to apply said refractory material; Y Adding a salt solution to the refractory material before application by the nozzle in a proportion wherein said salt solution comprises less than about 0.70% by weight of the refractory material applied by the dispensing nozzle, the refractory material having a corrosion resistance by slag near the same as a refractory poured with vibration (almost vibrational) of similar composition, and only slightly lower modulus of rupture at temperatures of use above 2500 ° F. It is an object of the present invention to provide a wet mixing process for the application of a refractory concrete material. Another object of the present invention is to provide a process like the one described above, to be used with refractory material without cement. Another object of the present invention is to provide a process as described above for the application of refractory material for use in high-temperature applications. Yet another object of the present invention is to provide a process as described above, wherein a concrete refractory without cement can be applied by gun firing (shoirecreed) and where the physical properties of the refractory applied by gunshot approach closely approximate. to the properties of a refractory poured with vibration. Still another object of the present invention is to provide an accelerator for a wet mix shorecreying process for the application of a refractory concrete, without cement, where the accelerator has a minimal impact on the physical properties of the mixture pumped and sprinkled , and the final material of the refractory concrete set. These and other objects and advantages will become clearer from the following description of a preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention relates to a refractory system for aliasing applications and to a method for the application of such a system by a wet mix shotcreying process. Specifically, the present invention relates to a wet mix shotcreting process for the application of a refractory concrete without cement. According to the present invention, a refractory system with a high content of alumina is provided and there is a hydrolyzable alumina agluinance and a setting modifying mixture to be used with said refractory in a wet mixing process. According to the present invention, the refractory mixture is preferably composed of about 80% to 86% aggregate, 6% to 11% fine and 4% to 8% hydratable alumina binder. The refractory material may also include small amounts of a dispersant to aid in the mixing of the refractory material and a small amount of fiber additives to create fine channels within the refractory to allow the vapor to escape during the initial heating of the refractory concrete. With respect to the aggregate, said aggregate may be alumina or bauxite and preferably has a particle size of less than 3 mesh and where approximately 60% of the aggregate has a particle size of 14 mesh or less. In accordance with the present invention, a hardening-modifying mixture component is used in the wet mixing shoicreiing process to provide tackiness and non-collapse characteristics to the refractory. It is important for the present invention that the accelerator does not contain silica or CaO, and preferably no alkali, such as Na20. According to the present invention, the setting modifying mixtures are composed of a solution composed of soluble alumina or magnesium salts, such as aluminum chloride hydrate (AIC * 6H20), aluminum ammonium sulfate, aluminum ammonium chloride, magnesium phosphate and magnesium gluconate, solutions of magnesium salts, for example, magnesium chloride hydrate (MgCl2 * 6H20), and magnesium sulfate (MgSO4). It was found that phosphoric acid is an effective accelerator and, therefore, it is expected that other acids will also provide adequate accelerated hardening of cement-free refractories. It is expected that the level of admixture added to a refractor will vary by 0.2% and 0.9% depending on the accelerator used. An addition of 0.5% by weight of accelerator to the refractory concrete is preferred. Efficacy accelerators for refractories that use cement-free, hydratable alumina binders include soluble magnesium or aluminum salts. Examples include magnesium or aluminum sulfate. Other effective accelerators include acids (eg, phosphoric acid) or acid salts (eg, ammonia acid phosphate).

Test 1 A test was carried out to examine the properties of the aforementioned setting modifying mixtures when they are added to a cement-free refractory concrete. The composition of the refractory concrete that was used is the following.

Various materials are tested with the preceding refractory material. The amount of setting modifier mixture that was added to each refractory was a batch of approximately 38 ml to 20 pounds (9.07 kg) of the refractory concrete. In percent weight, the addition varied (depending on the specific gravity of the solution) from 0.5% to 0.67%. The results of the test will show that the preceding refractory material is strongly accelerated by means of magnesium salts solutions (MgCl2 * 6H2O and MgSO). Aluminum sulfate was also effective. The majority of the solutions used were in 50% water, although MgSO4, which resembles gel at a 50% concentration, was also tested and found to be effective in a 33% solution. It was found that phosphoric acid (as received as a solution of (80% H3P04) was extremely strong in its acceleration effect and produced rapid hardening.The refractory hardening was so rapid that a more dilute solution was much preferable. of phosphoric acid Mixiure solutions vary widely in pH values, from very acidic (ie less than 2) to phosphoric acid to medium basic (approximately 8) for magnesium sulfate. It is believed that more than one mechanism of flow reduction influences the properties of the refractory concrete, in this sense, it is expected that the gelation and / or setting of the phase of the activated alumina cement will be accelerated by the presence of magnesium ions and generally In addition, it is expected that the acids will react with the magnesium oxide in the mixture, it is expected that the level of the mixture will fall Iro of the 0.2% interval 0. 9%, and more particularly, 0.3% - 0.5% weight addition of the refractory concrete.

Test 2 A second test was carried out to compare the physical properties of a cement-free and wet-sprayed refractory, with a comparable refractory material and pour with vibration (casi-vibrated). The composition of the respective materials was as follows.

Both refractories are refractory alumina (AI2? 3) / magnesium oxide (MgO), free of cement. Both refractories contain the same combined percentage by weight of white-fused alumina and iabular alumina. In this sense, both refractory materials contain 61% by weight of white fused alumina and iabular alumina. The particle sizes and proportions of these materials, however, are different. In the wet spray refractory, larger quantities of smaller particles were used to facilitate wet spraying of the material (i.e., producing a material capable of pumping with I Or a suitable consistency) and to reduce the "reboie" of the material sprayed from the surface to be coated. In addition, the wet-sprayed refractor included slightly more organic fibers to facilitate faster setting and curing of the refractory as a result of a setting-modifying mix that was added to the wet-spray refractory to prevent sinking and aging. crash The refractory poured with vibration (casí-vibraíed) is mixed with water and then poured and vibrated according to conventional techniques. The wet spray refractory is mixed with approximately 6.0% water and is wet sprayed using a conventional oscillating valve or pump. A solution of aluminum sulfate (AI2 (SO4) 3) was added to the hydrated mixture just before the spraying as a setting-modifying mixture. The solution was composed of 2 parts by weight of water to 1 part by weight of aluminum sulfate. The aluminum sulphate solution (AI2 (S04) 3) is added to the refractory at a rate of approximately 0.6 gallons per ton of refractory concrete., which is equivalent to approximately 0.3% by weight of the refractory material. The solution of aluminum sulphate (AI2 (SO) 3) is effective in preventing the subsidence and collapse of the refractory applied by shotcreying in a wet process. The properties of the respective materials such as poured with vibration and wet sprinkling, are as follows: The results show that the free cement and wet spray refractor provides a material that has adequate physical properties for application in corrosive environments. A test is carried out to determine the actual effect that the slag from the pouring cauldron has on the respective refractories. Said test is carried out by exposing samples of the respective refractories to slag from an induction furnace. The kiln slag has the following general composition, by weight: CaO 35% Fe2O3 25.3% AI2O3 14.8% MnO 10.1% Si02 9.9% MgO 4.8% Test samples of approximately 9"x 3" x 2"are exposed to slag at 2900 ° F lasts six hours on the wall of an induction furnace The effect of the slag on the samples is as follows: As can be seen in the previous results, the cement-free and wet-spray-free refractory is comparable to the cement-free refractory and poured with vibration, in corrosive slag resistance. The excellent corrosion resistance of the cement-free refractory is in this way obtained using a wet-mix shoccreying process. The present invention has been described with respect to a method of wet spraying refractory concrete. Modifications and alterations will be clear to those trained in the technique after reading the description. It is intended that all such modifications and alterations be included as they fall within the scope of the invention as claimed or in equivalents thereof.

Claims (8)

1. Novelty of Sa Invention 1. A method for the application of a refractory concrete, free of cement, to the surface of a refractory structure, comprising the steps of: a) preparing an intimately mixed refractory concrete and adding alumina and an aggregate cemenium free and composed of hydratable alumina; b) transporting the refractory concrete under pressure through a dispensing hose to a dispensing nozzle to apply said refractory concrete; and c) adding a chemical solution, wherein said solution is composed of water and a chemical selected from the group consisting of acid, salts of acid, soluble magnesium and aluminum salts to the refractory concrete before application by the nozzle in a proportion of wherein said solution comprises about 0.2% to 0.9% by weight of the refractory concrete applied by the dispensing nozzle; and d) sprinkling the aggregate of alumina, hydratable alumina and chemical solution on a surface.
2. 2. A method as defined in claim 1, wherein said acid is phosphoric acid.
3. 3. A method as defined in claim 1, wherein said acid salt is ammonium acid phosphate.
4. 4. A method for the application of a concrete refractory to the surface of a structure, comprising the steps of: mixing a refractory material mainly composed of aggregate of alumina, calcined and thermally reactive alumina; and a hydratable alumina binder; transfer the refractory material under pressure through a dispensing hose to a dispensing nozzle to apply the refractory material; adding a salt or acid solution to the refractory material before its application by the nozzle in a proportion wherein said salt or acid solution comprises less than about 0.90% by weight of the refractory material applied by the dispensing nozzle, the refractory having resistance to corrosion by slag, comparable to a concrete refractory of similar composition; and sprinkle the aggregate of alumina, calcined and thermally reactive alumina, hydratable alumina and acid or salt solution on a surface.
5. 5. A method as defined in claim 4, wherein said salt solution is an aluminum salt.
6. 6. A method as defined in claim 4, wherein said salt solution is an acid salt.
7. 7. A method for the application of a refractory concrete to the surface of a structure, the layers comprising: completely mixing a refractory material free of cement and composed mainly of alumina aggregate, calcined and reactive alumina and a hydratable alumina binder and magnesia; transporting the refractory material under pressure through a dispensing hose to a dispensing nozzle to apply the refractory material; adding a solution of soluble magnesium salt to the refractory material before application by the nozzle at a rate wherein said soluble magnesium salt solution comprises less than about 0.90% by weight of the refractory material applied by the dispensing nozzle; and sprinkle the aggregate of alumina, calcinated and thermally reactive alumina, hydratable alumina, magnesia and salt solution on a surface.
8. 8. A method for the application of a concrete refractory to the surface of a structure, comprising the steps of: completely mixing a refractory material consisting mainly of aggregate of alumina, calcined alumina and reactive thermally and a hydratable alumina agluinant and magnesia; transporting the refractory material under pressure through a dispensing hose to a dispensing nozzle to apply the refractory material; adding a solution of phosphoric acid to the refractory material upon application by the nozzle at a rate wherein said phosphoric acid solution comprises less than about 0.70% by weight of the refractory material applied by the dispensing nozzle; and sprinkling the aggregate of alumina, calcinated and thermally reactive alumina, hydratable alumina, magnesia and acid solution on a surface.