JPS6340461B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermocatalytic reactor of the type used in radiant heating units.
and its manufacturing method. The reactor of the present invention is particularly suitable for use in flameless gas-fired radiant heaters. In such heaters, a thermal catalytic reaction is maintained on or near the outer surface of the thermal catalytic reactor cylinder, causing incandescence and the production of radiant energy output. An example of such a flameless radiant heater, including a thermal contact reactor, is given by Gerhart Weiss et al.
et al., US Patent No. 25, 1966, granted September 25, 1966
No. 3275497, the contents of which are specifically incorporated herein by reference.

In such radiant heaters, the thermal contact reactor typically comprises a refractory cylinder closed at one end. A plurality of individual, amorphous, inorganic ceramic fibers are typically arranged in a homogeneous porous wall structure of the reactor cylinder. The open end of this reactor cylinder is mounted on a hollow fitting that typically passes through a metal reflector.
The combustible air-gas mixture is passed through the center of the cylinder, and the holes in the reactor cylinder wall cause incandescence on the outer surface of the cylinder during combustion. Reactors of this type should normally remain thermally stable for long periods of time at relatively high operating temperatures.

Since the combustion reaction described above is flameless and the thermal conductivity of the reactor cylinder is relatively low, there is no flashback of this reaction into the interior of the reactor cylinder. A relatively high percentage of the heat output of this reactor cylinder is radiant energy.

Traditionally, combustion reactor cylinders of this type have been manufactured by methods that include the addition of filler or binder materials that are added during processing to chemically bond the reactants. For example, as described in US Pat. No. 3,275,496, the components of the cylinder, including alumina and colloidal silica, were mixed in a molding bath and then dispersed in water. An aqueous solution of aluminum nitrate was then added to form a gel, which was further diluted with water. Stripped fibers formed from a melt of alumina Al ₂ O ₃ and silica SiO ₂ were then added to form a slurry. A preferred fiber is derived from kaolin. A filler or binder, such as methyl methacrylate, was then added to chemically bond the alumina fibers and silica.

This slurry was then adhered around a screen mounted on a substrate that served as the inner tube of the reactor cylinder to form a reactor cylinder. The inner tube during cylinder formation is typically connected to the suction line of the pump and immersed in the gel molding bath for a sufficient period of time to deposit an appropriate amount of gel on the screen and form the molded reactor cylinder. do. After removal from the bath, the cylinder was dried at a temperature between about 60°C (140°) and about 66°C (150°) for a period between about 10 minutes and about 60 minutes. After drying, this reactor cylinder is heated at a relatively high temperature, i.e. above 593°C (1100°C), in order to sublimate the methyl methacrylate binder.
Fired in a kiln. In this conventional process, the binder had to be sublimed, so the kiln heating operation was a necessary processing step.
Heating to such temperatures, however, adversely affected the alumina fibers in the reactor cylinder. At temperatures below about 982°C (1800°C), alumina fibers were generally in either the gamma or theta phase or a combination of both. At temperatures above 982°C (1800°), however, the alumina fiber undergoes a further phase transformation to the alpha phase. As the alumina transformation progresses from gamma to theta to alpha, the alumina fiber develops a tendency to densify, which reduces the porosity and effective surface area of the resulting reactor cylinder.

No. 3,275,497 recognized that the alumina fiber phase in the reactor cylinder typically had little if any effect on its operational characteristics. However, I changed my point of view,
The gamma phase of alumina has been preferred because of its generally high surface-to-mass ratio, especially when catalytic agents are added to the bath for deposition onto the surface of fibers.

As previously mentioned, the reactor cylinder is preferably as porous as possible and has a large surface area for efficient use as a combustion source. Therefore, whenever possible, it is preferred that the alumina in this reactor cylinder initially be in the gamma or theta phase rather than in the denser alpha phase. 593°C which results in a reactor cylinder that is denser and less porous than the optimum binder.
This has hitherto been impossible due to the fact that sublimation has to be carried out at temperatures above (1100〓).

The method of the present invention attempts to provide a more suitable reactor cylinder that is formed without binder. 593 for binder sublimation, which produces a denser and less porous reactor than the optimum value.
The step of heating the cylinder in a kiln at temperatures above 1100 °C can be eliminated.
This was achieved by the addition of powdered talc. This binderless reactor cylinder produced at ambient temperature therefore contains less dense gamma phase alumina fibers. The reactor cylinder of the present invention is therefore more porous and has a greater surface to weight ratio than previously used reactor cylinders.

Accordingly, it is a primary object of the present invention to provide a binderless thermal contact reactor using a non-flame gas fired radiant heater.

Another object of the invention is to provide such a reactor cylinder containing powdered talc as a component thereof.

Yet another object of the present invention is to provide a reactor cylinder that is more porous and has a greater surface area than previously used binder-containing reactor cylinders.

Still another object of the present invention is to provide such a reactor cylinder initially containing alumina fibers in the gamma phase.

Still another object of the present invention is to provide a method for manufacturing such a reactor cylinder.

SUMMARY OF THE INVENTION In accomplishment of the foregoing objects and advantages, the present invention is summarized as follows: A reactor cylinder for use in a radiant heater comprising steps for the initial production of a liquid vehicle containing an alumina dispersion, magnesium sulfate, colloidal silica and powdered talc. Including manufacturing method. The alumina dispersion comprises an amount of dispersible alumina between about 1% and about 5% by weight, an amount of acid up to about 0.2%, and an amount between about 10% and about 30% by weight. Contains water. This dispersion is then diluted by the addition of water in an amount between about 40% and about 80% by weight. To this diluted alumina dispersion, approx.
Magnesium sulfate in an amount less than or equal to 10% by weight
The following amounts of colloidal silica and an amount of powdered talc between about 0.0001% and about 0.1% by weight are added, thus forming a liquid vehicle. Approximately 10 of Fiber per 3.79 (gallon) of vehicle
Solid aluminum and silica fiber composition are then added to the vehicle in a ratio of 1.5 g to the vehicle.
This mixture is then chopped, blended, and vacuum molded around a mandrel to form the reactor cylinder.

The thermal contact reactor of the present invention is intended for use as a combustion source in non-flame radiant heaters of the type described, for example, in U.S. Pat. Formed within the reactor cylinder.

The subject reactor cylinder consists of alumina dispersion,
It is produced by preparing a liquid vehicle containing magnesium sulfate, colloidal silica, water, powdered talc and preferably tributyl sulfate as an antifoaming agent. This vehicle is then mixed with a composition of alumina and silica fibers to form a slurry that is vacuum molded around a screen mandrel to form a reactor cylinder.

The alumina dispersion is first prepared by mixing dispersible alumina with water and acid. A preferred dispersible alumina is manufactured by Remet Corporation of Chadwicks, New York.
of Chadwicks, New York) under the trade name ``Dispal.'' The preferred acid is hydrochloric acid, most preferably at 37% strength.

In the production of alumina dispersions, water in an amount between about 10% and about 30% by weight, based on the weight of the total liquid vehicle, is sufficient to provide the desired PH in the resulting liquid vehicle. mixed with acid. The PH of the vehicle is between about 4 and about 6, preferably about 5.
It is preferable that For example, PH within this range
It has previously been found that 37% strength hydrochloric acid in an amount between about 0.1% and about 0.2% by weight, based on the weight of the total vehicle, can be added to water to produce a vehicle with a ing. A particularly preferred amount of 37% strength hydrochloric acid is between about 0.15% and 0.2% by weight.

To this water and acid mixture is then added dispersed alumina in an amount up to about 5% by weight, and preferably between about 1% and about 5% by weight, based on the weight of the total vehicle. . A particularly preferred amount of dispersible alumina is about 2%, which is sufficient to make a 10% alumina dispersion.

The alumina dispersion is then substantially diluted by adding between about 40% and about 80% water, based on the weight of the total vehicle. Preferably, the alumina dispersion is present in an amount between 60% and 70% by weight, most preferably between about 65% and about 70% by weight.
diluted in an amount of water between

After dilution of the alumina dispersion, magnesium sulfate is added in an amount up to about 4% by weight, based on the weight of the total vehicle. A preferred amount of magnesium sulfate is between about 1% and about 2% by weight, and a preferred amount is between about 1% and about 1.5% by weight.
It is between.

This mixture is then stabilized for an extended period of time, preferably overnight, during which time it becomes thixotropic.

After stabilization, colloidal silica is added to the mixture in an amount up to about 10% by weight, based on the weight of the total vehicle, followed by vigorous stirring.
A preferred colloidal silica is available from E.P., Wilmington, Delaware. Ai. It is commercially available under the trade name "Ludox AG" by DuPont. Preferably, the colloidal silica is added in an amount between about 5% and about 8% by weight, and more preferably between about 6% and about 7% by weight.

Sufficient powdered talc is then added to the mixture to cause the solid fiber sections to stick together. Preferably, powdered talc is added in an amount between about 0.0001% and about 0.1% by weight calculated based on the weight of the total vehicle. A particularly preferred amount of powdered talc is between about 0.0001% and about 0.0002%. It has been found that the addition of powdered talc in the above amounts allows the reactor cylinder to be formed without the addition of methyl methacrylate fillers or binders previously required. Furthermore, the exclusion of the filler or binder eliminates the need for sublimation or decomposition of the filler or binder at high temperatures to cause phase transformation of the alumina.

After introduction of powdered talc and vigorous stirring, the liquid vehicle may contain an undesirable amount of trapped air. Therefore, by adding an antifoam agent, such as tributyl phosphate, in an amount sufficient to remove this trapped air, typically no more than about 1 c.c. per gallon of liquid vehicle, It is desirable to degas the vehicle. The preferred amount of antifoam is about 2 c.c. per gallon. After adding the antifoam, the vehicle is further mixed until any remaining air bubbles are removed. The vehicle thus prepared to receive solid alumina and silica fibers has between about 4 and about 6
Preferably it should have a PH of about 5 and a specific gravity of greater than about 1.00.

The solid fiber portion consists of a mixture of alumina and silica fibers containing about 2% aluminum. A preferred source of the alumina and silica fibers is Johns Manville Co.
It is a commercial product sold under the trade name "Cerachrome" by Manville Corporation.

The solid fiber portion is added to a liquid vehicle and blended. This liquid vehicle has approx.
Add 2.52 (2/3 gallon) to approximately 10 g of alumina and silica solid fiber section. The mixture is then blended for a period of time, chopped, and then additional liquid vehicle is added to bring the total volume of the resulting slurry to about 1 gallon. Preferred ratios of solid fiber per gram to gallons of liquid vehicle are between about 8:1 and about 12:1 and preferably about 10:1.

A reactor cylinder is formed from the slurry produced as described above by a method similar to the vacuum molding process described in US Pat. No. 3,275,497. A vacuum tank and vacuum pump are required. The preferred vacuum pump is Garst, model
1022―103―G272X (Gast, Model 1022―103―
G272X) or equivalent, the preferred vacuum tank is equipped with a vacuum gauge to indicate 0-30 inches of mercury, a visible tube to indicate liquid level, a vacuum cut-off valve, and a drain valve. 37.9 (10 gallon) stainless steel model. A slurry molding tank is also required, preferably having a capacity of at least about 7 gallons, two lengths of vacuum hose, and a screen armature around which the reactor cylinder is molded. be.
The screen frame is closed at one end and has a gas/air feed tube attached to the other end. This screen is preferably approximately 1.59cm in diameter
(0.625″) and preferably stainless steel wire mesh 0.41cm
(0.16″), 20×20. This gas/air feed tube preferably has an outside diameter of 1.59cm (0.625″).
Made of stainless steel.

For process efficiency, one hose is used to connect the vacuum tank outlet to the vacuum pump inlet, and the other hose is used to connect the vacuum tank inlet to the gas/air feed tube at the screen temporary frame. use. Approximately 18.9
(5 gallons) of slurry is injected into the slurry molding tank. After starting the vacuum pump,
The screen frame is introduced into the tank in a nearly vertical position and placed within approximately 5 cm (2 inches) of the bottom of the tank. This temporary screen frame is maintained in position in the tank until the vacuum gauge reaches approximately 61 cm (24 inches) of mercury, at which point it is withdrawn while maintaining the vacuum. By this method, a slurry is formed around the temporary screen frame, thus creating a molded reactor cylinder.

The vacuum pump continues to operate until the vacuum gauge drops to approximately 10 cm (4 inches) of mercury, at which point it is stopped and the reactor cylinder is removed from the vacuum hose. This reactor cylinder is stored and
Also, the vacuum cutoff valve is opened and the remaining slurry is discharged. A new temporary screen is used for the next formation of the reactor cylinder.

While the reactor cylinder is still wet and relatively soft, its surface is divided into small regions for the purpose of disrupting thermal strain lines during combustion that lead to flaking of its surface. This can be achieved, for example, by a shaped press on the reactor cylinder surface. It also installs the reactor cylinder's gas/air feed tube into the chuck of the lathe and attaches ordinary sewing thread to it.
Wrap it in a continuous spiral with a pitch of 3.18 cm (0.125 inch) and pull it to approximately 0.076 cm.
(0.030 inch) notch. The free end of the thread can be secured in conventional manner, ie by tying or taping. The reactor cylinder is then removed from the lathe. The thread is burned away by the initial intense heat leaving its pattern permanently imprinted on the reactor cylinder surface.

The reactor cylinder is then placed on a support and dried, at which point it is ready for use. The kiln heating operations traditionally required are not required.

The following examples are intended to further illustrate the method of the invention and are not to be construed as limiting the scope of the invention.

Example 1 Continued by mixing 3500 g of water and 30 g of 37% hydrochloric acid
10 with the addition of 392g of Dispul dispersed alumina
% alumina dispersion was first prepared to form the reactor cylinder of the present invention. 4000 g of the resulting 10% alumina dispersion was then diluted with 12000 g of water and 200 g of magnesium sulfate was added. After overnight stabilization, a thixotropic gel resulted. 1200 g of Ludotux AG colloidal silica was added to this gel and mixed thoroughly, followed by rapid stirring.
0.3 grams of powdered talc was added per gallon of gel. 2 c.c. of tributyl phosphate was added as an antifoaming agent, thus forming a liquid vehicle.

approximately 2.52 (2/3) gallons of this liquid vehicle)
was placed in a Waring blender followed by the addition of 10 g of Cerachrome alumina and silica fiber. The mixture was chopped on low speed for 15 seconds and on high speed for 90 seconds. Additional liquid vehicle was added to bring the total volume to about 1 gallon, followed by vigorous stirring to form a slurry.

Approximately 18.9 (5 gallons) of this slurry is
(7 gallon) slurry molding tank. A reactor cylinder was built around a 0.041 cm (0.016"), 20 x 20 mesh stainless steel wire screen temporary frame with one end closed and a gas/air feed tube approximately 1.59 cm (0.625") outside diameter. A vacuum was drawn in the gas/air feed tube inserted into the slurry and maintained until the pressure reached approximately 25 inches. When this tube was pulled out, the vacuum was turned off and the reactor cylinder was removed from the vacuum pump. The completed reactor cylinder was then dried and ready for use. It had all the physical properties to be commercially acceptable for a reactor cylinder.

Example 2 The procedure of Example 1 was followed except that no powdered talc was added to the liquid vehicle. The resulting reactor cylinder was commercially unacceptable, ie, could not be molded around an air/gas mandrel.

Although the above examples illustrate distinct features of the novel products and methods of this invention, the teachings of this application are applicable to broader and different combinations than those set forth in this example. It is natural that it is evaluated as including the following.

Claims (1)

Claims: 1. A method of manufacturing a reactor cylinder for use in a radiant heater, the process comprising: (a) dispersible alumina in an amount between about 1% and about 5% by weight of the total vehicle; ; approximately 0.2 of the total vehicle
acid in an amount up to % by weight; and about 10% of the total vehicle.
(b) producing a liquid vehicle containing an alumina dispersion containing between about 40% and about 80% by weight of the total vehicle to make the vehicle; (c) about 4% by weight, based on the weight of the total vehicle;
magnesium sulfate; colloidal silica in an amount up to about 10% by weight; and the addition of powdered talc in an amount between about 0.0001% and about 0.1% by weight; (d) a combination of solid alumina and silica fiber; and the liquid vehicle in a ratio of grams of fiber to gallons of liquid vehicle of about 8:1.
(e) blending the solid fibers and liquid vehicle to form a slurry; and (f) blending the slurry around the mandrel to form the reactor cylinder. A method characterized in that it comprises vacuum molding. 2. The method of claim 1, wherein the alumina dispersion is about a 10% alumina dispersion. 3. The method of claim 2, wherein dispersed alumina is added in an amount between about 1% and about 3% by weight. 4. The method of claim 1, wherein the acid is hydrochloric acid added in an amount sufficient to reduce the pH of the liquid vehicle to between about 4 and about 6. 5. The method of claim 1, wherein magnesium sulfate is added in an amount between about 1% and about 1.5% by weight. 6. The method of claim 1, wherein powdered talc is added in an amount between about 0.0001% and about 0.0002% by weight. 7. The method of claim 1, wherein an antifoam agent is added to the liquid vehicle in an amount sufficient to remove any entrapped air. 8. In a reactor cylinder using a radiant heater, the cylinder comprises: (a) (i) dispersible alumina in an amount between about 1% and about 5% by weight of the total vehicle; about 0.2% by weight;
and an alumina dispersion comprising between about 10% and about 30% by weight water; (ii) between about 40% and about 80% by weight water; (iii) colloidal silica in an amount up to about 10% by weight;
and (iv) powdered talc in an amount between about 0.0001% and about 0.1% by weight; The ratio of number to gallons of liquid vehicle is approximately 8:
(c) blending the solid fibers and liquid vehicle to form a slurry; and (d) blending the slurry around a mandrel to form the reactor cylinder. A cylinder characterized in that it is formed by vacuum molding; 9. The reactor cylinder of claim 8, wherein the alumina dispersion is about 10% alumina dispersion. 10. The reactor cylinder of claim 9, wherein dispersed alumina is added in an amount between about 1% and about 3% by weight. 11. The reactor cylinder of claim 8, wherein the acid is hydrochloric acid added in an amount sufficient to reduce the pH of the liquid vehicle to between about 4 and about 6. 12. The reactor cylinder of claim 8, wherein magnesium sulfate is added in an amount between about 1% and about 1.5% by weight. 13. The reactor cylinder of claim 8, wherein powdered talc is added in an amount between about 0.0001% and about 0.0002% by weight. 14. The reactor cylinder of claim 8, wherein an antifoam agent is added to the liquid vehicle in an amount sufficient to remove any entrapped air.