GB2226019A - Luting composition - Google Patents

Abstract

A luting composition for sealing gaps around the doors of heated chambers, especially coke ovens, comprises fly ash (25 to 55 wt%), clay binder (5 to 15 wt%), a lightweight carbonaceous, non-abrasive filler (10 to 40 wt%) and water (20 to 30 wt%). All the solid constituents are used in sufficiently finely divided form as to avoid the need for grinding, allowing a simple mixing procedure to be used in preparing the lute.

Description

LUTING COMPOSITION The present invention is concerned with a luting composition for sealing gaps around the doors or other closures of heated chambers, especially coke ovens, to prevent undesirable leakage leading to air pollution and structural damage.

Coke ovens are normally closed at both ends by removable doors of elongated metal construction. Well known designs of such doors include those of the so-called selfsealing types, with flexible sealing strips which bear against the metal door jamb. Others, however, with which this invention is more particularly concerned, but to which it is by no means limited, are still in use which possess no such sealing strip and require the application of a sealing material, otherwise known as a lute or daub, to plug the narrow gap remaining between the edge of the door and the jamb when the door is latched in position at the end of the oven.

The traditional form of lute in use has been a plastically workable mixture based essentially on clay and water, with coke breeze added as a filler to lighten the mix for ease of application and to provide bulk. A typical composition may incorporate 6 per cent by weight of coke breeze. Drawbacks to the use of such lutes include the following: their composition is not readily controllable; the mature must be prepared in a pan mill or other equipment to grind the coke breeze sufficiently finely; the grinding time is long and the process is labour-intensive; the abrasive nature of the breeze means that maintenance of the mill is expensive; and there is a tendency for the lute to catch fire around the doors towards the end of the coking period, thus thermally distorting the structure.

Other compositions have been proposed as an alternative to the type of lute just described. For example, DE 688821 claimed a mixture of coal dust or coke dust with tar for this purpose; however, the fumes evolved by the tar on heating would render such a mix clearly unacceptable today.

Intumescent lutes are claimed in GB 1 53 345 and GB 1 524 B91; the former consists of an aqueous finely ground mix of reclaimed lute, clay (e.g. coal flotation tailings) and about 1 per cent of an organic blowing agent, whereas the latter is composed of latex based on poly(vinyl alcohol), water, particulate filler (e.g. talc) and 5-15 per cent of inorganic fibre (e.g. amosite asbestos), plus a blowing agent as before, the proportion of filler being varied according to whether the mix was to be applied manually or by gunning. A gun for applying the lute described in GB 1 53 345 is described in GB 1 53 346.However, it is believed that these mixes have never found general acceptance in practice, and problems could be foreseen in accurately blending the small amound of blowing agent and the fibre, besides which, the blowing agent and the latex are relatively expensive.

US 4 425 191 covers the use of liquid silicate sealants for coke oven doors etc, the essential feature again being the ability to intumesce on heating; such sealants could be used either alone or in admixture with ground glass and clay. Drawbacks to these silicates are their alkalinity and their tendency to solidify in very cold weather; in addition, their main purpose appears to be to remedy deficiences in self-sealing doors and they would be very costly for sealing ordinary. luted doors. US 4 395 55 claims the use of various water-based pastes, curable by heat into a glassy form, for sealing joints and caps of coke oven ascension pipes.These pastes all contain boric acid and silica flour (or diatomite) as major constituents, with various other optional components to control rheology and softening temperatures; a filler could also be included.

Once again, these materials would be relatively costly for large scale use on coke oven doors and the proportions of the minor components could be difficult to control in practice.

Other proposals, less relevant to the present invention, are contained in US 3 875 018 (injection of a colloidal mixture into a channel at the edge of a coke oven door of a particular design), GB 2 145 184 (application of a lubricating adhesive silicate-polymer composition to coke oven doors and jambs), and GB 1 45 73 (a gasket with an asbestos core reinforced by steel wires and covered by neoprene and steel mesh, reminiscent of early types of dry seal for selfsealing doors using an asbestos strip, which is unacceptable nowadays on i?alth grounds).

According to the present invention there is provided a luting composition for sealing coke oven doors and the like comprising fly ash, a clay binder and a carbonaceous additive or filler, all in finely divided form, together with water.

The luting composition, or lute, in accordance with the invention is not only readily composable but also cheap, as fly ash, the basic component of the mixture, is readily available and produced by the combustion of pulverized fuels in the boilers of power stations and the like, and separated from the flue gases of such boilers by electrostatic precipitators. Its particle size is mostly below 158 Jum and it therefore requires no grinding before use in a luting composition. For the purposes of this invention, its chemical nature - within the range encountered in normal UK power station practice, at least - is of no consequence.

Preferably the fly ash is used in a conditioned, i.e. slightly damped, form to avoid dust problems in handling it. The nature of the clay, as long as it is sufficiently finely divided, is also immaterial. The carbonaceous additive or filler, like the coke breeze in the conventional lute, is intended to reduce the bulk density of the mix to a level at which it can be conveniently handled by the operator in sealing a door, and to improve the storage life of the mix.

This additive must therefore be of relatively low density, as well as of similar size to the fly ash, chemically inert with respect to the other components, non-volatile, and nonabrasive. It should also preferably possess some porosity, as an aid to retention of water and anchoring of the clay binder Partly graphitic materials are particularly suitable for this purpose, for example the fine solids collected in cyclones or other dust collectors from graphite or other carbon manufacturing processes, with a particle size mostly below 5 > Lm.

Suitable proportions by weight of the constituents of the lute according to the invention are as follows: per cent Fly ash 25 to 55 Clay 5 to 15 Filler 10 to 4 Water 2 to 3 Preferred quantities would be: Fly ash 35 to 45 Clay 8 to 12 Filler 15 to 3 Water 2 to 30 Such a lute requires no preliminary grinding of the constituents and may be prepared by any convenient blending equipment, including for example a ribbon mixer or a drum mixer. The advantages of this procedure compared with the preparation of a conventional lute are its rapidity and simplicity, the much reduced wear of equipment, the much lower power and labour requirements, and the possibility of closely controlling the proportions of the constituents, none of which is present in very small amount. Furthermore, a lute of this type resists ignition in situ.

As an example, a quantity in the region of 5 tonnes of lute of composition: fly ash 30 per cent, clay 12 per cent, carbonaceous filler 30 per cent, water 28 per cent (all percentages by weight), could be expected, used manually to seal more than 2 doors of the coke ovens charged during a whole shift at an industrial plant, while tests have indicated that sealing performance of the lute in accordance with the invention is superior to that of the conventional lute used under the same conditions, with very few leaks of tarry fumes observable, no disintegration of the lute, and no firing towards the end of the coking period.

Claims (12)

1. A luting composition for sealing coke oven doors and the like comprising fly ash, a cl dy binder and a carbonaceous additive or filler, all in finely divided form, together with water.

2. A luting composition as claimed in Claim 1, wherein the fly ash is of particle size mostly below 158 Sm.

3. A luting composition as claimed in Claim 1 or Claim 2, wherein the fly ash is used in a slightly damped condition.

4. A luting composition as claimed in any preceding Claim, wherein the carbonaceous additive or filler is of relatively low density.

5. A luting composition as claimed in any preceding Claim, wherein the carbonaceous additive or filler is of similar particle size to that of the fly ash.

6. A luting composition as claimed in any preceding Claim, wherein the carbonaceous additive or filler is chemically inert with respect to the other components.

7. A luting composition as claimed in any preceding Claim, wherein the carbonaceous additive or filler is nonvolatile.

8. A luting composition as claimed in any preceding Claim, wherein the carbonaceous additive or filler is nonabrasive.

9. A luting composition as claimed in any preceding Claim, wherein the carbonaceous additive or filler is a partly graphitic material.

10. A luting composition as claimed in any preceding Claim, wherein the carbonaceous additive or filler has a particle size mostly below 5 Am.

11. A luting composition as claimed in any preceding claim comprising: per cent Fly ash 25 to 55 Clay 5 to 15 Filler 1 to 40 Water 20 to 30

12. A luting composition as claimed in any preceding Claim, comprising: Fly ash 35 to 45 Clay 8 to 12 Filler 15 to 30 Water 20 to 30