CA1233840A

CA1233840A - High strength coke-oven mortar

Info

Publication number: CA1233840A
Application number: CA000487949A
Authority: CA
Inventors: Roger L. Rueckl
Original assignee: USS Engineers and Consultants Inc
Current assignee: USS Engineers and Consultants Inc
Priority date: 1984-12-03
Filing date: 1985-08-01
Publication date: 1988-03-08
Also published as: ES549500A0; CN1005109B; CN85109463A; ES8706586A1; ZA859264B

Abstract

ABSTRACT
A high strength mortar has been developed for use with silica brick, in the constructon of coke-oven heating walls. When fired to conventional coke oven temperatures of about 1100°C, the mortar develops a tensile strength within the mortar itself, and a tensile bond to the silica brick, which exceeds the tensile strength of the silica brick. The mortar is composed of three primary solid constituents: 25 to 88 percent SiO2, 6 to 65 percent A12O3 and 4 to 12 percent P2O5. To achieve such high tensile strength, the other solid constituents must be maintained at a minimum, desireably less than four percent and preferably less than two percent.

Description

HIGH STRENGTH COKE-OVEN MORTAR

Technical Field This invention relates to the construction of coke-oven heating walls and is more particularly related to the use of a mortar which provid s high tensile strength bonding with the silica brick utilized in the construction of coke oven heating walls.

Background Art In an attempt to increase the rate of the production of coke, the art has resorted to (i) the use of coke-ovens with heights exceeding 16 feet (~ 4.88 meters), (ii) the selection of coal blends which provide higher bulk densities and (iii) the use 15 of faster coking rates - all of which lead to increased coking pressures. Such increased coking pressures result in flexure of the coke-oven wall which, in turn, results in stress concentrations in the refractory shapes and ultimately the failure of the 20 refractories and loss of wall integrity. It has been found that the wall's inability to resist such increased pressure is, in large part, due to the fact that (a) existing mortars do not develop sufficient tensile bond strength to the brick and (b) such 25 existing mortars acquire, during service, high compression and shear strengths which decrease the ability of the mortar to yield and thereby relieve stresses caused by wall flexure. These limitations of such currently available materials of construction 30 (i.e. silica brick and silica coke-oven mortar) result in severe operating limits and reduced coke battery t throughput.

- 2 ~ 3 Disclosure of Invention A new high strength mortar has been develope~
for coke battery construction which; (1) develops a tensile bond strength within itself and to the surfaces of the silica brick to which it bonds, that is at least equivalent to the tensile strength of the silica brick itself under actual coking conditions, (~) as a result of its high strength bond, is resistant to deformation under load, but nevertheless is capable of yielding under stresses that exceed the normal static stress of the battery and (3~ is capable of being mixed to a consistency that permits its use in construction procedures conventionally used to install refractories in a coke oven heating walls.
Because of its enhanced tensile properties, it is estimated that use of the inventive mortar can provide productivity increases of from 10 to 15 percent, per coke oven. Tnus, while the new mortar composition is more costly to supply (than conventional coke-oven silica mortar) such increased purchase cost is more than offset by savings of: (a) the added capital cost for the construction of additional ovens (i.e. 10 to 15 percent additional ovens) required to match the capacity of a coke oven battery constructed with the inventive mortar and (b) future capital requirements res~lting from an anticipated service life of about 30 years, compared with the average service life of less than 15 years provided by silica coke-oven mortar.
These and other advantages of the instant invention will become more apparent from the following detailed description when read in conjunction with the appended claims.

_ 3 - ~3~8~

Modes for Carrying Out the Invention As previously noted, the principal design parameter for the instant mortar is that it develop a tensile bond strength, both within its mass and to the brick surfaces to which it is applied, which (at battery operating temperatures) approximately equals or exceeds that of the silica brick. Silica brick has a tensile strength of about 190 psi (134.39 kg/cm2) at 1100C and 90 psi (63.28 kg/cm ) at 1350C.
These criteria are provided by a silica base, aluminum bearing, phosphate-bonded mortar in which impurities are maintained at a minimum level, desireably below 4 percent and preferably below 2 percent. The primary constituent, for the production for the mortar, can be supplied by either the crystalline or amorphous form of silica. If the crystalline form is used, the high temperature forms crystobalite or tridymite are preferred over the lower temperature quartz form, so as to avoid the possibility of volume changes resulting from phase transformation. Since it is desired to maintain impurities to a minimum, amorphous or fused silica is preferred over the crystalline form, since the former is of generally of higher purity and is more readily commercially available.
The alumina can be supplied from any high purity source, such as tabular A12O3. The phosphate bond can be developed through the use of phosphoric acid, but the P2O5 is preferably provided by a commercially available bonding agent such as colloidal monoaluminum phosphate (MAP).
The sizing of the silica and alumina should be controlled so that: (1) the mortar has a workable and trowelable consistency, (2) the blend of the ~3~

constituents result in a homogenous mixing, and (3) the cured mortar has minimum apparent porosity and ~aximum bulk density. It is desirable that the granular materials be finer than 40 U.S. Standard ~esh (420,~) and preferably finer than 70 mesh (210~) for workability, and to gap size the granular ~aterial, that is use a coarser fraction, such as 70 - 100 ~esh (210~ - 149~L), and a finer fraction, such as finer than 200 mesh (~ 741L) to ~inimize apparent porosity and to l~axi~ize bulk density. The alumina will generally be of a size finer than the silica to achieve chemical homogeneity. If a MAP solution is used, the mortar would be supplied wet and ready to use; a dry phosphate binder such as ~1AP or hexaphos lS can be used, in which case the mortar would have to be ~ixed with water. This would generally be less desirable than premixed mortar, because of the potential for mixing errors which, in turn, could adversely affect mortar strength.
The co~position of the cured and dried mortar on a water-free basis will be within the range 25 to 88 percent SiO2, 6 to 65 percent A12O3, and 4 to 12 percent P2O5 with total other constituents being less than 4 percent. ~ithin this co~positional range, tensile strength is affected both by silica-alumina ratio and by phosphate content. In general, strength will increase with decreasing SiO2/A1203 ratios. For example, at a P205 content of 9.3%, a tensile strength greater than 200 30 psi (140.6 kg/c~2) at 1100C can be achieved when SiO2/A1203 ~ 4 - with strength further increasing until SiO2/A1203 is reduced to about 2. Further deGreases in the SiO2/A1~03 ratio cause a slight decrease in strength, although it - 5 ~

remained above 140.6 kg/cm2 (for a P205 content of 9.3%) at ratios as low as 0.4. Similarly, strength markedly increases as P205 content is decreased from 12% down to 8%. However, further decreases in P205 result in a rapid decrease in strength. To maximize tensile bond strength and resistance to deformation under load, the preferred range will therefore be (on a water-free basis) 60 to 70 percent SiO2, 25 to 35 percent A12O3, and 7 to 11 percent P2O5 (more preferably 8 to 10%) with total other solid constituents being less than 2 percent.
As a specific example of this invention, 52.5 percent by weight fused silica grain (31.5 percent minus 150 mesh and 21.0 percent minus 50, plus 100 mesh), 20.6 percent by weight minus 100-mesh tabular alumina, 23.1 percent by weight colloidal monoalu~inum phosphate (8.0 percent A12O3, and 30 percent P2O5), and 3.8 percent by weight water were blended into a workable mortar. When fired to 2000~F
(1093 C), this mortar develops a tensile bond to silica brick and within itself that exceeds the tensile strength of the silica brick. The apparent porosity of a trowelbed joint fired to 2000~F
(1093C) is less than 30 percent. The composition of the fired mortar is 64.1 percent SiO2, 27.4 percent A12O3, and 8.5 percent P2O5.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A pre-mix for the production of a mortar, consisting essentially of, on a dry basis, 25 to 88 percent SiO2, 6 to 65 percent Al2O3, 4 to 12 percent P2O5 and not more than 4 percent other solid constituents.

2. The pre-mix of claim 1, wherein SiO2 is 60 to 70 percent, Al2O3 is 25 to 35 percent, P2O5 is 7 to 11 percent and the other solid constituents not more than two percent.

3. The pre-mix of claim 2, wherein the P2O5 is 8 to 10 percent.

4. The pre-mix of claim 1, wherein at least a major portion of the P2O5 is provided in colloidal form.

5. The pre-mix of claim 2, wherein substantially all the solid constituents are finer than 420 microns.

6. In the construction of coke-oven walls wherein a monolithic heating wall is formed my the mortaring together of a multitude of silica bricks, characterized by a mortar for increasing the ability of such wall liners to withstand high coking pressures, wherein such mortar consists essentially of (a) on a dry basis, 25 to 88 percent SiO2, 6 to 65 percent Al2O3, 4 to 12 percent P2O5, not more than 4 percent other solid constituents and (b) sufficient liquid to provide the requisite workable consistency to such mortar.