WO2011115352A1

WO2011115352A1 - Unshaped refractory composition added with alumina sol binder

Info

Publication number: WO2011115352A1
Application number: PCT/KR2010/008500
Authority: WO
Inventors: Kyoung Ran Han; Sang Whan Park; Chang Sam Kim; Jin Oh Yang
Original assignee: Korea Institute Of Science And Technology
Priority date: 2010-03-17
Filing date: 2010-11-30
Publication date: 2011-09-22
Also published as: KR20110104713A; KR101152656B1

Abstract

Provided is an unshaped refractory with an alumina sol binder added to a refractory mixture comprising Al₂O₃and SiC. The disclosed refractory is advantageous in that the alumina sol binder provides work flexibility to the refractory mixture, there is no erosion by CaO even at high temperature because CaO-containing cement is not used, shape is retained after drying, strength is enough for handling, contraction hardly occurs after heat treatment, porosity is low and strength is good. Thus, it is particularly useful for a gasifier.

Description

UNSHAPED REFRACTORY COMPOSITION ADDED WITH ALUMINA SOL BINDER

The present disclosure relates to an unshaped refractory for use as a lining of a gasifier with an alumina sol binder added thereto.

Unshaped refractories are preferred over refractory bricks where the gap between the bricks often becomes a problem. Thus, efforts have been made to improve high temperature durability, material properties and installations of the unshaped refractories. Although calcium aluminate cement has been predominantly used as an inorganic binder, low calcium aluminate cement is preferred for use in harsh environments such as high temperature and high pressure conditions.

Recently, there has been an attempt to use hydratable alumina containing trace calcium for unshaped refractories to improve their resistance to thermal wearing and corrosion. However, it also showed relatively low strength (flexural strength of 1.2-2.0 MPa) at a temperature of 800 to 1200 ºC, where water that maintains binding is dehydrated while ceramic bonding is not yet significantly formed. The sintered refractory has a flexural strength not greater than 20 MPa.

Recently, a gasifier used in an integrated gasification combined cycle (IGCC) of coal, which has been drawing public attention as an efficient, environment-friendly power generation system, which can be operated under a harsh condition. An unshaped refractory used in the lining of the gasifier must be firmly attached to a stainless steel pipe for the circulation of cooling water, have good thermal conductivity and readily allow formation of a slag layer on the surface.

In general, an unshaped refractory is prepared by binding metal oxides, carbides or a mixture thereof as a refractory material with aluminate cement. When the cement content is low, the density of the resulting refractory becomes low, and it becomes difficult to handle and control of drying time. Meanwhile, the low cement content improves corrosion resistance against slag and slows penetration. This is because calcium oxide (CaO) included in the cement reacts with the slag at high temperature and lowers the viscosity of the slag, thereby allowing the slag to easily penetrate and corrode the refractory. Further, cement is not advantageous in that it requires a lengthy time for drying at room temperature because of slow water evaporation

Search for a better refractory binder resulted in monoaluminum phosphate binder, where magnesium powder is used as a hardener. Aluminum phosphate-bonded refractories show high strength, high temperature stability, and abrasion resistance. It is used for a combustion furnace, but it is not suitable for the oxygen-deficient gasifier.

Besides, P₂O₅-MgO system produces problems that low-melting-point compounds are produced and the water-soluble monoaluminum phosphate migrates to the surface, resulting in non-uniform strength. In addition, P₂O₅ evaporates in a high temperature reducing environment, resulting in reduced and non-uniform strength. Accordingly, the aluminum phosphate-bonded unshaped refractory is not suitable for forming a refractory structure.

Recently, hydratable alumina has been used as an inorganic binder. For example, Alphabond 300, 500, etc., are, commercially available from Alcoa Industrial Chemicals. A refractory to which a hydratable alumina binder is added is not advantageous in that it requires a longer time for mixing until wet-out is achieved. Use of fine silica and colloidal alumina together with aluminate cement was reported. However, the flexural strength of the refractories heat treated at 1400 ºC is only about 5 to 17 MPa at room temperature.

Besides the strength, the conventional refractories also have deficiencies in adhesivity, thermal conductivity, drying time and corrosion resistance. Therefore, they are not suitable to be applied to gasifiers operated under high-temperature, high-pressure, and reduced conditions.

The inventors have made efforts to develop a refractory to be used for a gasifier operated under a harsh environment of high temperature and high pressure and succeeded in developing a refractory having superior adhesivity, strength, and corrosion resistance. The present disclosure is directed to providing the refractory.

In a general aspect, the present disclosure provides an unshaped refractory with an alumina sol binder added to a refractory mixture comprising Al₂O₃and SiC.

The refractory of the present disclosure has many advantages that the alumina sol binder provides work flexibility to the refractory mixture, there is no corrosion by CaO even at high temperature because CaO-containing cement is not used, shape is retained after drying, strength is enough for handling, contraction hardly occurs after heat treatment, porosity is low and high temperature strength is good. Thus, it is particularly useful for a gasifier. The alumina sol is mixed with fine alumina powder and acts like a glue, coating the surface of the aggregates and matrix and providing better contact among them. Unlike when cement is used, drying is fast because water is released as the sol transforms to gel. Since a thin film of alumina gel is formed even with a small amount of alumina sol, cracking does not occur during drying or fast heating. Further, since the sintering of the fine alumina powder is facilitated, a ceramic binding is formed between the aggregates and matrix, and hence a superior strength is attained.

The above and other objects, features and advantages of the present disclosure will become apparent from the following description of certain exemplary embodiments given in conjunction with the accompanying drawings, in which:

Fig. 1 is an optical microscopic image (×60) of an unshaped refractory prepared in Example 2.

Hereinafter, the embodiments of the present disclosure will be described in detail with reference to accompanying drawings.

The present disclosure provides an unshaped refractory with an alumina sol binder added to a refractory mixture comprising Al₂O₃and SiC. The refractory mixture may further comprise magnesium oxide, spinel, zirconia, chromia or hafnium oxide, without being limited thereto.

A sol is a suspension of particles in liquid, unlike a gel, showing fluidity. The particles move actively through Brownian motion. An alumina sol refers to alumina particles suspended in liquid. The alumina sol binder may be prepared by adding a small amount of acid (e.g., nitric acid, hydrochloric acid, acetic acid, formic acid, phosphoric acid, sulfuric acid, etc.) to a boehmite slurry, without being limited thereto. The alumina sol is mixed with fine alumina powder and acts like a glue, coating the surface of the refractories and providing better contact among them. Unlike when cement is used, drying proceeds fast because water is released as the sol transforms to gel. Since a thin film of alumina gel is formed even with a small amount of alumina sol, cracking does not occur during drying or fast heating. Further, since the sintering of the fine alumina powder is facilitated, a ceramic binding is formed between the aggregates and matrix, and hence a superior strength is attained.

The alumina sol binder may be included in the refractory in an amount of 0.2 to 4 parts by weight, more specifically 0.3 to 1.5 parts by weight, based on the alumina content of the refractory mixture. If the content of the alumina sol binder is smaller than 0.2 % by weight based on the alumina content of the refractory mixture, the role as a binder may be insufficient. In contrast, if it exceeds 4 % by weight, corrosion resistance and thermal conductivity may be degraded.

The refractory of the present invention has many advantages; the alumina sol binder provides work flexibility to the refractory mixture comprising Al₂O₃ and SiC, there is no risk of corrosion by CaO even at high temperature because of not using CaO-containing cement, can maintain shape after drying, retain strength sufficient for handling, contraction hardly occurs after heat treatment, low porosity, and good high temperature strength. For the above reasons, the refractory of the present invention is very useful for a gasifier.

In addition to the inorganic binder, i.e. the alumina sol binder, the unshaped refractory of the present disclosure may further comprise an organic binder such as hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose or latex. The organic binder may be included in an amount of 0.03 to 1.0 parts by weight, specifically 0.05 to 0.5 part by weight, based on the refractory mixture. Although the organic binder suppresses segregation of the refractory material during drying and improves strength, when degraded by heat treatment, it may generate pores and thus may be vulnerable to strength and thermal conductivity. Thus, it is used in as small an amount as possible.

The examples and experiments will now be described. The following examples and experiments are for illustrative purposes only and not intended to limit the scope of the present disclosure.

Preparation of aluminasol binder

Boehmite powder was suspended in distilled water to about 15 wt%. After slowly adding a small amount of nitric acid thereto while stirring at 70 to 80 ºC, the mixture was heated to prepare a semi-transparent sol with an alumina content of about 10 wt%. The sol was applied on a stainless steel substrate and dried at room temperature to produce a thin film. It was then put into a furnace heated to 500 ºC for about 20 minutes and then taken out to obtain a film with superior adhesivity and no crack.

Example 1

A refractory mixture was prepared in a polypropylene container as Composition 1 described in Table 1. About 50 g of the mixture was put into a paper cup and 5.2 parts (0.52 part by weight relative to the alumina content of the alumina sol) by weight of the alumina sol based on the mixture was added and mixed. Then, an unshaped refractory was prepared by tapping. After drying at room temperature for 2 hours and then in a 60 ºC dryer, the unshaped refractory was sintered at 1350 ºC for 2 hours in the air. Its flexural strength and density were measured and the result is given in Table 2.

Example 2

A refractory mixture was prepared in a polypropylene container as Composition 1 described in Table 1. About 50 g of the mixture was put in a paper cup and 6.4 parts (0.64 part by weight relative to the alumina content of the alumina sol) by weight of the alumina sol based on the mixture was added and mixed. Then, an unshaped refractory was prepared by tapping. After drying at room temperature for 2 hours and then in a 60 ºC dryer, the unshaped refractory was sintered at 1350 ºC for 2 hours in the air. Its flexural strength and density were measured and the result is given in Table 2.

Example 3

A refractory mixture was prepared in a polypropylene container as Composition 2 described in Table 1. About 50 g of the mixture was put in a paper cup and 6.55 parts (0.655 part by weight relative to the alumina content of the alumina sol) by weight of the alumina sol based on the mixture was added and mixed. Then, an unshaped refractory was prepared by tapping. After drying at room temperature for 2 hours and then in a 60 ºC dryer, the unshaped refractory was sintered at 1350 ºC for 2 hours in the air. Its flexural strength and density were measured and the result is result is given in Table 2.

Example 4

A refractory mixture was prepared in a polypropylene container as Composition 3 described in Table 1. About 50 g of the mixture was put in a paper cup and 7.3 parts (0.73 part by weight relative to the alumina content of the alumina sol) by weight of the alumina sol based on the mixture was added and mixed. Then, an unshaped refractory was prepared by tapping. After drying at room temperature for 2 hours and then in a 60 ºC dryer, the unshaped refractory was sintered at 1350 ºC for 2 hours in the air. Its flexural strength and density were measured and the result is given in Table 2.

Example 5

A refractory mixture was prepared in a polypropylene container as Composition 3 described in Table 1. About 50 g of the mixture was put in a paper cup and 9.8 parts (0.98 part by weight on the basis of the alumina content of the alumina sol) by weight of the alumina sol based on the mixture was added and mixed. Then, an unshaped material was prepared by tapping. After drying at room temperature for 2 hours and then in a 60 ºC dryer, the unshaped refractory was sintered at 1350 ºC for 2 hours in the air. Then, flexural strength and density were measured. The result is given in Table 2.

Example 6

A refractory mixture was prepared in a polypropylene container as Composition 3 described in Table 1. About 50 g of the mixture was put in a paper cup and 8.5 parts (0.85 part by weight relative to the alumina content of the alumina sol) by weight of the alumina sol and 0.03 part by weight of hydroxyethyl cellulose (HEC) based on the mixture were added and mixed. Then, an unshaped refractory was prepared by tapping. After drying at room temperature for 2 hours and then in a 60 ºC dryer, the unshaped refractory was sintered at 1350 ºC for 2 hours in the air. Its flexural strength and density were measured and the result is given in Table 2.

Comparative Example 1

A refractory mixture was prepared in a polypropylene container as Composition 1 described in Table 1. About 50 g of the mixture was put in a paper cup and 9.52 parts by weight of distilled water and 0.5 part by weight of HEC based on the mixture were added and mixed. Then, an unshaped refractory was prepared by tapping. After drying at room temperature for 2 hours and then in a 60 ºC dryer, the unshaped refractory was sintered at 1350 ºC for 2 hours in the air. Its flexural strength and density were measured and the result is given in Table 2.

Comparative Example 2

A refractory mixture was prepared in a polypropylene container as Composition 3 described in Table 1. About 50 g of the mixture was put in a paper cup and 8.24 part by weight of distilled water and 0.43 part by weight of HEC based on the mixture were added and mixed. Then, an unshaped refractory was prepared by tapping. After drying at room temperature for 2 hours and then in a 60 ºC dryer, the unshaped refractory was sintered at 1350 ºC for 2 hours in the air. Its flexural strength and density were measured and the result is given in Table 2.

	Al₂O₃(wt%)		SiC (wt%)					MgO (wt%)
Average particle size	3-5 mm	0.3 μm	1.25 mm	750 μm	90 μm	20 μm	5 μm	< 44 μm
Composition 1	7.0	7.6	38	23	3	20	1.4	0
Composition 2	7.0	7.6	38	23	3	19.6	1.4	0.4
Composition 3	0	7.6	45	23	3	20	1.4	0

Sample	Refractory composition	Additives (part by weight)			Density (g/cm³)	Flexural strength (MPa)
Sample	Refractory composition	Distilled water	10 wt% alumina sol	HEC	Density (g/cm³)	Flexural strength (MPa)
Ex. 1	Composition 1	0	5.2	0	2.69	45.45
Ex. 2	Composition 1	0	6.4	0	2.73	46.01
Ex. 3	Composition 2	0	6.55	0	2.65	55.70
Ex. 4	Composition 3	0	7.3	0	2.53	46.18
Ex. 5		0	9.8	0	2.66	53.24
Ex. 6		0	8.5	0.03	2.64	52.58
Comp. Ex. 1	Composition 1	9.52	0	0.5	2.46	< 5
Comp. Ex. 2	Composition 3	8.24	0	0.43	2.52	< 5

As shown in Table 2, when the alumina sol binder was added (Examples 1-6), the alumina sol facilitated the sintering of the fine alumina and improved the binding between the refractories. As a result, increased sintered density (decreased porosity) and improved flexural strength were achieved. When an organic binder (HEC) was used without addition of the alumina sol (Comparative Examples 1-2), the resulting strength was low because the fine alumina particles and the refractories were not sintered enough to produce bonding. Use of the alumina sol resulted in the increase of flexural strength by about 9 to 11 times as compared to when the alumina sol was not used.

The present application contains subject matter related to Korean Patent Application No. 10-2010-0023769, filed in the Korean Intellectual Property Office on March 17, 2010, the entire contents of which is incorporated herein by reference.

Those skilled in the art will appreciate that the conceptions and specific embodiments disclosed in the foregoing description may be readily utilized as a basis for modifying or designing other embodiments for carrying out the same purposes of the present disclosure. Those skilled in the art will also appreciate that such equivalent embodiments do not depart from the spirit and scope of the disclosure as set forth in the appended claims.

Claims

An unshaped refractory with an alumina sol binder added to a refractory mixture comprising Al₂O₃and SiC.
The unshaped refractory according to claim 1, wherein the alumina sol binder is prepared by adding an acid to a boehmite slurry.
The unshaped refractory according to claim 1, wherein the refractory mixture comprising Al₂O₃and SiC further comprises magnesium oxide, spinel, zirconia, chromia, hafnium oxide or a mixture thereof.
The unshaped refractory according to claim 1, wherein the alumina sol binder is included in an amount of 0.2 to 4.0 parts by weight based on the alumina content of the refractory mixture comprising Al₂O₃and SiC.
The unshaped refractory according to claim 1, which further comprises hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose or latex as a binder.
The unshaped refractory according to claim 5, wherein the hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose or latex is further included in an amount of 0.03 to 1.0 part by weight based on the refractory mixture comprising Al₂O₃and SiC.