GB2184111A - Refractory material - Google Patents

Abstract

A refractory material which contains iron is characterised in that it includes an additive which acts as an iron catalyst poison. e.g. elemental sulphur or a sulphur containing compound such as potassium sulphide or an organic sulphur containing compound which leads to the formation of iron sulphide, and good CO resistance.

Description

SPECIFICATION Refractory material This invention relates to refractory materials.

Refractory lining materials are often contaminated by metallic iron, iron oxides or other compounds containing iron, hereinafter simply referred to as "iron". Iron is well known as a catalyst for the reaction

which, depending on the CO gas concentration, takes place between 450" and 900"C.

Since any iron is contained throughout the refractory material, when the refractory lining contacts hot CO containing gas the carbon deposition takes place on the iron particles which act as catalyst sites inside the refractory lining. Continued carbon deposition gives rise to expansion, cracking and eventual complete disruption of otherwise mechanical sound refractory linings.

It will be appreciated that there are many industrial applications in which a furnace or reactor will contain carbon monoxide, either due to incomplete combustion of fuel or purposefully manufactured or added to the process to effect, for instance, reduction of metallic ores. Thus, CO occurs commonly in the petrochemical industry, coal conversion and coal gasification and in plasma arc and magnetohydrodynamic installations. Also, in the direct reduction of iron ore, hot ore is brought into contact with hot CO containing gases in shaft or rotary kilns. In many instances in direct reduction processes the CO gas is generated in external refractory lined generators, whilst in the more conventional blast furnace process the CO gas is generated internally by means of coke in contact with the ore.

The demand for relatively cheap CO resistant refractory materials is therefore considerable and tests have been developed namely BS1902-310:1981 and ASTM C288/78 to ascertain the resistance of a refractory material to CO disintegration.

On the other hand, most refractory raw materials contain iron as a contaminant in one form or another. All known methods of removing iron are either expensive, e.g. acid washing, or inefficient e.g. magnetting. Refractory materials can be prepared to stringent low iron specifications but these are generally expensive e.g. fused mullite, fused alumina and tubular alumina. It is common knowledge that even low iron materials will pick up iron during the preparation of the refractory mixes by contamination from steel crushing equipment and during ball milling with steel balls. The normal pick up of small amounts of abraded iron is sufficient to cause heavy carbon deposition in CO atmospheres. Furthermore, most aggregates e.g. calcined clay, andalusite, bauxite, high alumina, magnesia or chrome will normally include a proportion of iron oxide contaminant.

In some instances CO resistance can be imparted to refractory aggregates or to fired refractory brick by firing to high temperature, when all iron is oxidised to iron oxide and reacted to form an iron silicate (2FeO.SiO2) which is well known to be resistant to the carbon deposition mechanism. Again the high firing of aggregate is expensive and during the firing of a refractory brick at high temperature other properties, such as spalling resistance, may be impaired.

Many refractory linings are placed in an unfired form. These include refractory concretes, ramming masses and coating compounds where it is not possible to treat the composition to high temperature prior to installation. By their very nature the materials are placed at room temperature and heated to operating temperature through the 450 -900 C temperature range during which period CO attack may occur. In addition the establishment of a temperature gradient within the lining, when the lining reaches operating temperature, requires that much of the bulk of the refractory lining will be in the 450 -900 temperature range throughout the life of the lining.

It is an object of this invention to provide a refractory material which is protected against CO degradation.

According to the invention a refractory material which contains iron is characterised in that it includes an additive which acts as an iron catalyst poison.

Also according to the invention the additive is elemental sulphur, or a sulphur containing compound such as potassium sulphide or an organic sulphur containing compound which is reactive to iron and any iron compound which may be reduced to metallic iron in the presence of CO, to poison the iron catalyst by the formation of iron sulphide.

Thus the invention includes within its scope a refractory material, either as an aggregate or as a shaped body, containing iron and sulphur, the invention further embracing such refractory material in which iron and sulphur have already reacted to form the sulphide of iron.

In the preferred embodiment of the invention the iron catalyst poison material, preferably sulphur, is present in stoichiometric excess of the iron contained in the refractory material. More particularly, it is found that good CO resistance is achieved in unshaped refractory products if the sulphur is present in slightly stoichiometric excess of the metallic iron present in view of contamination from crushing and milling equipment.

The sulphur or reactive sulphur compound may be added to the unfired refractory composition as a solid or liquid component such that on heating to approximately 400"C in a kiln or in situ, the formation of iron sulphide occurs. Alternatively, a solution of soluble sulphide may be employed for impregnation of a preformed body which is subsequently fired or heated in situ.

The refractory material or composition of this invention may be used to produce refractory concretes or shaped bodies of high mechanical strength and abrasion resistance so that they are particularly useful for lining furnaces where the lining is in continual contact with large masses of burden. In these cases as also in the case of reactions in which hot gases are treated, the refractory of the invention is rendered resistant to attack by CO in the dangerous temperature range by inactivation of the iron content of the refractory material.

The invention also includes within its scope a method of forming an iron containing refractory material for use as a refractory body resistant to atmospheres containing CO including the step of adding an iron catalyst poison to such refractory material.

All refractory compositions produced in accordance with the invention pass the standard CO resistance tests.

The invention is illustrated by the following examples. In the examples the iron containing chamotte is used in the formation of two refractory concrete compositions "Mix A" and "Mix B" respectively excluding and including the iron catalyst poison of this invention. After casting according to conditions laid down in BS1902, samples were tested for CO resistance according to BS1902-310:1981 and ASTM C288/78.

Example 1 Naturally occuring clays are calcined or sintered to relatively high temperature to remove combined water and to densify the resulting chamotte such that it is suitable for manufacture of dense firebrick or dense refractory concretes. Iron compounds are common contaminants in the raw clay and in many instances the calcining temperature of the clay is insufficient to convert all the iron to inactive iron silicate. Addition of 0.3% of flowers of sulphur to react with the iron, forming iron sulphide, had a marked effect on the CO resistance of refractory bricks made from the chamotte.

Mix A Mix B Calcined chamotte - 12+5 mesh 30% by weight 30% by weight " " rr " " 45% " 45% 6" 5% 5% " " 5% alumina cement 20% " 20% sulphur +o +0.3% Chemical Analysis SiO2 42.1% by weight 42.1% by weight Al203 48.7% " 48.7% Fe203 0.6% " 0.6% TiO2 1.83% " 1.83% CaO 6.17% " 6.17% MgO 0.11% " 0.11% alkali 0.19% " 0.19% S - +0.3% CO test Carbon deposition 200 hours after 2 hours no carbon 40 hours complete deposition or disintegration. disintergration.

Example 2 During crushing and fine ball milling in conventional crushers and mills up to 0.25% Fe can be picked up by generally abrasive refractory materials. Andalusite incorporates natural iron containing minerals but generally has some degree of CO resistance.

Fine milling releases its iron minerals from the material but also contaminates the latter with metallic iron. Addition of 0.3%S provides full CO resistance to a refractory concrete mix.

Mix A Mix B Analusite -8+5 mesh 26% by weight 26% by weight 15 15 " 46% " 469/0 " 6 " 13% " 13% alumina cement 15% n 15% sulphur - +0.3% Chemical Analysis SiO2 29.5% by weight 29.5% by weight Al203 62.3% " 62.3% Fe2O3 0.7% " 0.7% TiO2 0.12% " 0.12% CaO 6.49% " 6.49% MgO 0.49% " 0.49% alkali 0.16% " 0.16% S - 0.3% CO Test Carbon deposition No carbon deposition after 2 hours No disintergration 100 hours complete after 200 hours.

disintergration.

Example It is well known that for maximum CO resistance in a refractory concrete the alumina cement must be low in total iron and particularly low in metallic iron. Many refractory alumina cements particularly for the lower temperature applications are high in iron e.g. the well known fondu cement contains approximately 16.0% Fe203. Thus even for low temperature applications where CO is present the more expensive white low iron high refractory alumina cement must be used.

In this example it is shown that the invention will allow the use of the less costly high iron cement in CO resistant mixes if at least a stoichiometric quantity of sulphur is added to the mix to allow poisoning of the iron as a catalyst for the CO reaction.

Mix A Mix B Chamotte - 12+5 mesh 30% by weight 30% by weight 5-0 " 45% " 45% 6 " 5% " 5% cement fondu 20% " 20% flowers of sulphur - +0.6% Chemical analysis SiO2 41.0% by weight 41.0% by weight Al203 42.0% " 42.0% Fe2Q 4.66% " 4.66% TiO2 1.55% " 1.55% CaO 10.30% " 10.30% MgO 0.3% " 0.3% alkali 0.4% " 0.4% S - +0.6% CO Test Carbon deposition Darkened but after 1 hour passed 200 hours 3 hours complete test.

disintergration.

While the invention has been exemplified with reference to clay, andalusite and alumina cement, it will be appreciated that any desired refractory material may benefit from the prevention of CO attack according to the invention.

Claims (17)

1. A refractory material which contains iron and which is characterised in that it includes an additive which acts as an iron catalyst poison.

2. The refractory material of claim 1 in which the additive is sulphur.

3. The refractory material of claim 2 in which the additive is elemental sulphur.

4. The refractory material of claim 2 in which the additive is a sulphur containing compound which is reactive to iron and any iron compound which may be reduced to metallic iron in the presence of CO, to form iron sulphide.

5. The refractory material of any one of claims 1 to 4 in which the additive is present at least in stoichiometric equivalence with the iron.

6. The refractory material of any one of claims 1 to 5 in which the additive has reacted with the iron to poison the latter as a catalyst.

7. A refractory body comprising a refractory material according to any one of claims 1 to 6.

8. The refractory body of claim 7, said body comprising a cast vessel lining.

9. The refractory body of claim 7, said body being shaped prior to use as a vessel lining element.

10. A method of forming an iron containing refractory material for use as a refractory body resistant to atmospheres containing CO including the step of adding an iron catalyst poison to such refractory material.

11. The method of claim 10 in which sulphur is added as an iron catalyst poison.

12. The method of claim 11 in which elemental sulphur is added to the refractory material.

13. The method of claim 11 in which a sulphur containing compound which is reactive to iron and any iron compound which may be reduced to metallic iron in the presence of CO, is added to the refractory material.

14. The method of any one of claims 10 to 13 in which at least the stoichiometric equivalent of the additive with iron is added to the refractory material.

15. The method of any one of claims 10 to 14 in which the refractory material is heated to allow the additive to react with the iron to poison the latter as a catalyst.

16. A refractory material containing an iron catalyst poison substantially as herein described with reference to any one of the examples.

17. A method of forming an iron containing refractory material for use as a refractory body resistant to CO attack substantially as herein described with reference to any one of the examples.