GB1593161A - Refractory materials - Google Patents

Description

(54) REFRACTORY MATERIALS (71) We, STEETLEY REFRACTORIES LIMITED, a British Company, of Gateford Hill, Worksop, Nottinghamshire, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to pitch-impregnated basic refractory shapes and to a process for making such shapes.

Refractory linings for furnaces may be made using refractory shapes, for example fired bricks, which are either tar- or pitch-impregnated.

Tar- or pitch-impregnated shapes are usually made from dead burnt dolomite (doloma), dead burnt megnesite (magnesia), dead burnt lime, high alumina, aluminosilicate or mixtures of these materials of specifically graded fractions with a transient bond which services to make the brick or block suitable for handling after pressing to usually 6-10 tons per square inch. The pressed shapes are subsequently dried at 1000--3000 C for a period of approximately 24 hours and then fired to a high temperature usually in the range 140Q1800" C to develop a ceramic bond. The shapes are then impregnated with tar or pitch so that all or a major proportion of the open pores in the bricks are filled to give the so-called tar- or pitch-impregnated shape.

In service the tar or pitch carbonises and the residual carbon has a beneficial effect by restricting the ingress of slag.

A problem with coal tar or pitch impregnation is the formation of tar or pitch lumps on the surface of the refractory brick. This can be avoided by using a petroleum tar or pitch but unfortunately the use of such tars or pitches leads to a low residual carbon content when the tar or pitch is carbonised.

We have found that these disadvantages can be avoided using a heat-treated petroleum pitch.

Accordingly the present invention provides a process for the production of a pitchimpregnated basic refractory shape which comprises impregnating a basic refractory shape, with a heat-treated petroleum pitch.

Heat-treated petroleum pitches may be produced by heating a petroleum pitch to a temperature not less than 2500 C for a period of time sufficient to produce a quinoline-insoluble content of less than 2.5% by weight and a toluene-insoluble content greater than 11% by weight.

The invention includes a basic refractory shape impregnated with a heat-treated petroleum pitch.

Preferably, in making heat-treated pitch, petroleum pitch is heated at a temperature of 2500 C to 550" C. for up to 6 hours. The resulting heat-treated petroleum pitch is characterised by a quinoline-insoluble content of less than 2.5% by weight for example about 1% to 2% by weight, a toluene-insoluble content greater than 17% by weight for example, 21% to 25% by weight and a viscosity at 200 C of about 50 centipoise Carbon may be incorporated in the petroleum pitch by adding the carbon, as a finely divided solid or as a concentrated dispersion in a suitable liquid to the crude tar or by forming the carbon in situ in the tar (e.g. by adding an oxidising agent such as ammonium persulphate to the tar).The toluene-insoluble and quinolineinsoluble contents given for heat-treated pitches above, do not include such additional carbon. Suitable forms of carbon include graphite, carbon black, petroleum coke, anthracite coke and the like.

The amount of carbon-containing additive added to the pitch is preferably in the range 1 to 10% by weight based on the weight of the pitch.

The normal method of impregnating basic refractory shapes with tar or pitch is to heat the fired shape to a temperature in the range 100" to 300 C., dependent on the tar or pitch being used, then transfer the hot shape to a vacuum/pressure vessel and remove the air in the shapes by evacuation. Temperatures in the top part of this range, i.e. about 240 C, are suitable only for coal tar pitches. Tar or pitch preheated to a temperature such that its viscosity is suitable for impregnating the pores of the shape is then pumped into the evacuated vessel. Naturally the viscosity of the pitch will be such as to facilitate impregnation.After 1-4 hours the vessel is preferably pressurised to above atmospheric pressure eg. at 40-100 p.s.i. for a short time to complete the impregnation. The pressure in the vessel is then reduced to atmospheric pressure, the hot pitch is pumped out, the impregnated shape removed and cooled to room temperature. This method, or any other method, may be used to impregnate the fired shape with the heat-treated petroleum pitch.

After impregnation of fired shapes with the pitch, the shape may be subjected to one or several heat treatment and pitch-impregnation steps. The heat treatment may be effected by coking and/or stoving.

The term " coking " is used in respect of the process which takes place when the pitch-impregnated shape is heated in a reducing atmosphere, e.g. while embedded in carbon, to a temperature (usually in excess of 5000 C) such that the carbon content of the tar remaining after heating is greatly increased and very little volatile matter remains.

The term "stoving" is used in respect of the process which takes place when the pitch-impregnated shape is heated at elevated temperature usually lower than 5000 C in a substantially non-oxidising atmosphere. In this case although there is some increase in carbon content of the pitch and a decrease in the quantity of pitch volatiles, the effect is not so pronounced as with coking.

The following example is given to illustrate the process of the present invention.

In these examples the carbon retention of pitch-impregnated bricks was determmed as detailed in the British Ceramic Research Association Publication No. 52 (revised 1970).

Example.

Fired magnesia bricks of the following chemical analysis:- Constituents Wt. % SiO2 0.85 A1,0, 0.21 Fe2Os 0.15 CaO 1.80 TiO, 0.01 Mn,O 0.01 B2O, 0.02 MgO 96.95 were produced in the laboratory and the apparent porosity (i.e. the volume of open pores available for impregnation by the pitch) determined to be 16.0.

The bricks were impregnated by the vacuum-pressure process, described earlier in this specification with heat-treated aromatic pitch supplied by Croda Hydrocarbons Limited preheated to 220 C, having the following properties: Property Value Melting Point (Ring and Ball) "C 80 Specific Gravity at 15.50 C 1.21 Insolubles (a) In Toluene Wt.% (a) 22.0 (b) In Quinoline Wt.% (b) 2.0 Ash Content Wt.% 0.4% Coking Value (Alcan Method) Wt.% 45.7% Further bricks (B) of the same composition as those impregnated above were impregnated by the vacuum/pressure process with coal tar pitch having the following prcperties::-- Property Value Melting Point (Ring and Ball) C 70 Specific Gravity at 15.5 C. 1.27 Insolubles (a) In Toluene Wt.% 19.0 (b) In Quinoline Wt.% 2.8 Ash Content Wt.% 0.3 Coking Value (Alcan Method) Wt.% 45.5 The effect on the resultant retained carbon content of the bricks is shown in Table 1.

TABLE 1 Properties of Pitches and Bricks from Aromatic Pitch Trials

PITCH PROPERTIES PROPERTIES OF BRICKS Pitch Residual Ring and Ball Coking Value Bulk Loss on Impregnation Carbon Softening Point (%) by STPTIC Brick Dimensions Density Ignition Efficiency Content Surface ( C) Method (cm) (g.cm-3) (%) (%) (%) Finish 80 45.7 53 x 15.1./13.2 x 15.4 3.11 Edge:4.88 Edge: 82.4 1.50 Good (Aromatic pitch, Center: 4.76 Centre: 81.6 second trial) 70 45-46 53 x 15.1/13.2 x 15.4 3.09 - - 1.52 Fair (Coal tar pitch for comparison) WHAT WE CLAIM IS:1. A process for the production of a pitch-impregnated refractory shape which process comprises impregnating a basic refractory shape with a heat-treated petroleum pitch.

2. A process as claimed in claim 1 wherein the pitch has been heated to 250 to 550 C for a period of time up to 6 hours.

3. A process as claimed in claim 1 or claim 2 wherein the pitch has a quino-

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   Property Value Melting Point (Ring and Ball) C 70 Specific Gravity at 15.5 C. 1.27 Insolubles (a) In Toluene Wt.% 19.0 (b) In Quinoline Wt.% 2.8 Ash Content Wt.% 0.3 Coking Value (Alcan Method) Wt.% 45.5 The effect on the resultant retained carbon content of the bricks is shown in Table 1.

   TABLE 1 Properties of Pitches and Bricks from Aromatic Pitch Trials

   PITCH PROPERTIES PROPERTIES OF BRICKS Pitch Residual Ring and Ball Coking Value Bulk Loss on Impregnation Carbon Softening Point (%) by STPTIC Brick Dimensions Density Ignition Efficiency Content Surface ( C) Method (cm) (g.cm-3) (%) (%) (%) Finish 80 45.7 53 x 15.1./13.2 x 15.4 3.11 Edge:4.88 Edge: 82.4 1.50 Good (Aromatic pitch, Center: 4.76 Centre: 81.6 second trial) 70 45-46 53 x 15.1/13.2 x 15.4 3.09 - - 1.52 Fair (Coal tar pitch for comparison) WHAT WE CLAIM IS:1. A process for the production of a pitch-impregnated refractory shape which process comprises impregnating a basic refractory shape with a heat-treated petroleum pitch.
2. 2. A process as claimed in claim 1 wherein the pitch has been heated to 250 to 550 C for a period of time up to 6 hours.
3. 3. A process as claimed in claim 1 or claim 2 wherein the pitch has a quino-

   line-insoluble content of from 1 to 2%, a toluene-insoluble content of from 21 to 25% and a viscosity at 200 C of about 150 centipoise.
4. 4. A process as claimed in any one of the preceding claims wherein a carbon containing additive has been added to the heat-treated petroleum pitch.
5. 5. A process as claimed in claim 5 wherein 1 to 10% by weight of additive based on the weight of the pitch is added.
6. 6. A process as claimed in any preceding claim which process comprises subjecting the basic refractory heated to 100 to 300 C to reduced pressure, contracting the shape with hot-treated petroleum pitch, and raising the pressure.
7. 7. A process as claimed in claim 6 wherein the pressure is raised above atmospheric pressure.
8. 8. A process as claimed in claim 7 wherein the pressure is raised to from 40 to 100 psi.
9. 9. A process of impregnating a basic refractory shape as claimed in claim 6 substantially as hereinbefore described in the Example.
10. 10. A refractory shape when produced by a process as claimed in any one of claims 2 to 9.
11. 11. A refractory shape as claimed in claim 10 that is a refractory brick.
12. 12. A furnace lined with refractory shapes as claimed in claim 10 to claim 11.