GB2234755A

GB2234755A - Method and composition for sealing a coking oven

Info

Publication number: GB2234755A
Application number: GB8916945A
Authority: GB
Inventors: Michael Anthony Roberts; Gerard Jacques Griffin-Appadoo
Original assignee: CASTOLUX Ltd
Current assignee: CASTOLUX Ltd
Priority date: 1989-07-25
Filing date: 1989-07-25
Publication date: 1991-02-13
Also published as: GB8916945D0

Abstract

A method of removably sealing a lid in to an aperture in a reaction vessel such as a coking oven, the method comprising employing as a refractory sealing compound a suspension of calcium sulphate in a carrier liquid comprising water and, as suspension stabilisers, a basic electrolyte, which is an alkali metal salt, and a suspension thickener. A dry mix and the suspension thereof in water of calcium sulphate and an alkali metal salt is also claimed per se.

Description

METHOD AND COMPOSITION FOR SEALING A COKING OVEN The present invention relates to a method of removably sealing a lid in to an aperture in a reaction vessel, such as a coking oven, by using a refractory sealing compound comprising calcium sulphate, and to a refreactory sealing compund containing calcium sulphate.

In the process of burning coal to form coke for metallurgical applications, the charge lid on top of the vessel (the "oven") in which the coal is burnt is normally sealed with a refractory cement or sealant, in order to prevent the escape of volatile substances into the atmosphere. A cement conventionally used is a clay-based cement and such a cement usually provides a good seal.

However, the clay-based cements have a tendency to sinter in the high temperatures generated during the coking process and consequently1 when the conversion from coal to coke has been completed, in up to 50% of cases the charge lid needs to be hammered out because of the strong bonding of the joint. The removal of the charge lid in this way is of course relatively time-consuming and may also lead to the adjacent brickwork on the oven being damaged. It is known that this problem can be overcome by employing a slurry or suspension of calcium sulphate as the sealant, since calcium sulphate sealants do not sinter under the conditions but remain relatively powdery thereby facilitating removal of the charge lid.However, a drawback encountered with calcium sulphate slurries is that at the high concentrations typically employed in a sealant, the calcium sulphate tends to deposit a hard sediment within a relatively short time. This sediment is often difficult, if not impossible, to resuspend and such suspensions consequently have a very limited useful life. Ideally, a suspension of calcium sulphate should remain stable (i.e.

relatively free from sedimentation) for at least 8 hours, which under current working practices corresponds approximately to the length of a working shift. Thus ideally it should be possible for an operative to prepare a slurry at the beginning of his working shift such that the slurry remains in a useable condition for the entire duration of the shift, thereby avoiding the need to undertake frequent and time consuming remixes during his shift.

It has now been found that by using a selected alkali metal salt as a basic electrolyte in combination with a suspension thickener, the formation of a hard sediment can be prevented.

In a first aspect, therefore, the present invention comprises a method of removably sealing a lid in to an aperture in a reaction vessel, such as a coking oven, by employing as a refractory sealant a suspension of calcium sulphate in a carrier liquid comprising water and, as suspension stablisers, a basic electrolyte which is an alkali metal salt, and a suspension thickener.

In a further aspect, the present invention provides a composition which is a suspension of calcium sulphate in a carrier liquid comprising water and a basic electrolyte, as defined hereinabove.

Calcium sulphate is available in various grades and degrees of hydration but, for the purposes of this invention the uncalcined dihydrate CaSO4, 2HzO is used.

Milled gypsum, which contains approximately 90-95% CaSO4, 2H20 and is commercially available in large quantities, is advantageously used in the sealing compound of the present invention.

Usually, the calcium sulphate will be present in the suspension in an amount corresponding to approximately 25% to approximately 75% (w/w) relative to the amount of water.

Typically the amount of calcium sulphate will approximate to 50% (w/w) relative to the amount of water.

The basic electrolyte suitably is a sodium or potassium salt for example sodium and potassium carbonates and silicates. A preferred electrolyte is sodium carbonate.

The electrolyte, for example sodium carbonate, will usually be present in an amount corresponding to between approximately 0.1%(w/w) and 1% (w/w) of the weight of the water. If an amount significantly less than 0.1% is employed, it is found that sedimentation still occurs to an appreciable extent. Conversely, if an amount significantly greater than 1% is employed, the resulting modified surface forces are high and solid flocculates form which drop out of suspension and cannot subsequently be resuspended.

A suspension thickener is also included in the liquid carrier. Such thickeners improve the stability of the suspension. Whereas when no thickener is used, a sediment of a soft flocculant nature can be formed which can be resuspended with mixing, the inclusion of an appropriate amount of thickener results in substantially no sedimentation of the calcium sulphate. Typical suspension thickeners are organic thickening agents such as methylcellulose, gums such as xanthan gums, glycols such as polyethylene glycols or any other organic thickening agents known in the art. The thickening agent is usually present in an amount corresponding to up to about 1% (w/w) relative to the amount of water. A particular thickening agent is xanthan gum, which is a polysaccharide gum of xanthic acid.

Such a gum can be obtained from Kelco Corporation, California, U.S.A., under the trade name Kelzan.

The invention is illustrated by, but is in no way limited to, the following examples of compositions containing calcium sulphate. In the examples, the compositions are defined by reference to the parts by weight of the various ingredients.

EXAMPLE 1: Calcium sulphate 100 parts Kelzan gum 1 part Sodium carbonate 0.1 part Water 200 parts The suspension was prepared by preblending the Kelzan gum and sodium carbonate with the bulk calcium sulphate powder. This dry blend was then added to the required volume of mixing water by feeding the powder blend slowly into the mixing water under agitation, preferably using a paddle mixer or mechanical stirrer. Manual stirring is also possible.

The following compositions were also prepared according to the method described in Example 1.

EXAMPLE 2: Calcium sulphate 100 parts Kelzan gum 0.5 part Sodium carbonate 0.1 parts Water 200 parts EXAMPLE 3: Calcium sulphate 100 parts Kelzan gum 0.25 parts Sodium carbonate 0.1 parts Water 200 parts In each of the compositions of Examples 1 to 3, the calcium sulphate remained in suspension for at least eight hours and substantially no sedimentation was observed during this period. In contrast, with compositions containing a similar concentration of calcium sulphate but containing neither sodium carbonate nor xanthan gum, sedimentation of the calcium sulphate took place after ten minutes.

Claims

CLAIMS:

1. A method of removably sealing a lid in to an aperture in a reaction vessel such as a coking oven, the method comprising employing as a refractory sealing compound a suspension of calcium sulphate in a carrier liquid comprising water and, as suspension stabilisers, a basic electrolyte, which is an alkali metal salt, and a suspension thickener.

2. A method according to claim 1 wherein the calcium sulphate is present in the suspension in an amount corresponding to approximately 25% to approximately 75% (w/w) relative to the amount of water.

3. A method according to either of claims 1 or 2 wherein the basic electrolyte is present in an amount corresponding to 0.1 to 1.0% (w/w) relative to the amount of water.

4. A method according to claim 3 wherein the basic electrolyte is sodium carbonate.

5. A method according to any one of claims 1 to 4 wherein the suspension thickener is present in the suspension in an amount corresponding to up to about 1% (w/w) relative to the amount of water.

6. A method according to any one of claims 1 tO 5 wherein the thickener is an organic thickener such as xanthan gum.

7. A composition which is a suspension containing calcium sulphate and a basic electrolyte as defined in any one of claims 1 to 6.

8. A dry mix, the addition of water to which provides a suspension as defined in claim 7.

9. A method of removably sealing a lid on to a reaction vessel, as defined in claim 1, substantially as described hereinbefore.

10. A composition for sealing a lid on to a reaction vessel,substantially as described hereinbefore with reference to the examples.