US3223539A

US3223539A - Combustion chamber liner for well gas and air burner

Info

Publication number: US3223539A
Application number: US408609A
Authority: US
Inventors: Hyde Collin; Jr Herbert D Sheets
Original assignee: Chevron Research and Technology Co
Current assignee: Chevron USA Inc
Priority date: 1964-11-03
Filing date: 1964-11-03
Publication date: 1965-12-14
Anticipated expiration: 1982-12-14

Description

Dec. 14, 1965 c. HYDE ETAL COMBUSTION CHAMBER LINER FOR WELL GAS AND AIR BURNER Filed NOV. 3. 1964 United States Patent C) COMBUSTION CHAMBER LINER EUR WELL GAS AND AIR BURNER Collin Hyde, Titlin, and Herbert D. Sheets, Jr., Upper Arlington, Ohio, assignors, by mesne assignments, to Chevron Research Company, San Francisco, Calif., a corporation of Delaware Filed Nov. 3, 1964, Ser. No. 408,609 Claims. (Cl. 10o-64) This application is a continuation-impart of application Serial No. 165,675 filed January 11, 1962, by Collin Hyde and Herbert D. Sheets, Ir., and now abandoned.

This invention relates to downhole gas and air burners used in petroleum producing wells and the like to improve production therefrom and more particularly this invention relates to improved methods and materials for use in lining the combustion chamber of an oil well burner. This invention provides a combustion chamber for an oil well burner made from a castable materialv which will set to form a durable lining capable of withstanding very high temperatures and high gas velocities.

In the oil-producing art it is well known to stimulate oil production from a well by placing a down-hole gas and air burner in the well to improve the recovery characteristics of the oil in the well and the surrounding formation. The diameter of these burners must be small, usually in the 4range of about three inches to ve inches. The allowable heat transfer rate to the oil from the burner is limited by a value at which coking of the oil will occur. For many oils this value is in the range of 10,000 B.t.u. per hour per square foot of burner surface. Since the gas and air combusted in the burner cause temperatures in excess of 3000 F., the burner must beV supplied with a combustion chamber lining which will provide an acceptable heat transfer rate to the oil in the well. Further, the liner must be capable of withstanding very hard use both in surface handling by the operating crews and in placement in the Well. The liner is also subjected to high gas velocities during use and therefore it must be formed of a material and in a manner which will not erode during use. Since the burners are located in a well on the lower end of a long string of tubing, they must be capable of reliable operation over periods of a year or more of continuous operation without failure. Thus the combustion chamber line is an extremely critical part of a successful downhole burner.

Therefore, it is a principal object of the present invention to provide a method and material for forming a liner for the combustion chamber of a downhole burner which is capable of withstanding very high temperatures, which is strong enough to withstand rough use without fracturing, and which is durable enough to be of service over extended periods of use.

Briefly, the present invention provides a combustion chamber liner for a downhole burner formed of aluminum oxide and calcium aluminate cement. The aluminum oxide of the present invention comprises a special mixture of bubbled alumina and dense alumina. The bubbled alumina and dense alumina of the castable mixture have a particular grain sizedistribution. The bubbled alumina confers insulating qualities to the liner and the dense alumina provides strength to the liner. Desirable features of castability are also obtained from the mixture. Calcium aluminate cement is a cementing material useful with the aluminum oxide. The aluminum oxide and the calcium aluminate cement are mixed in a preferred ratio to form the liner of the invention. When a correct proportion of water is mixed with the aluminum oxide and calcium aluminate cement, the mixture may be formed into a variety of shapes which, when the 3,223,539 Patented Dec. 14, 1965 ice mixture dries, are capable of withstanding high temperatures and rough use.

Additional objectives and advantages of the present invention will become apparent from the following detailed description read in light of the accompanying drawing, which is a part of this specification and in which:

FIGURE 1 is a view, partially in section, and illustrates an arrangement of downhole burner apparatus and is useful in better understanding the present invention;

FIGURE 2 s a sectional View of a downhole gas and air burner.

FIGURE 3 is a sectional View taken at line 3-3 of FIGURE 2. y

In FIGURE l the general arrangement of a downhole burner and its supporting apparatus assembled for use in a well are shown. In this particular installation, for example, the downhole burner 20 is connected below producing pump 24 by means of a nipple 25. The oil well pump 24 is operated by means of sucker rod 19 and is used to pump oil to the surface. Combustible gas and' air from appropriate sources, such as gas source 26 and air source 27, are flowed to the combustion chamber of the burner through appropriate tubing. For example, a gas and air line 30 provides a passageway down the well to the combustion chamber of the burner.

Surface tubing

28 and 29 connect the gas and air sources to the downhole burner supply line 30. Valves 31, 32 and 33 are used to control the gas and air flow. Gas and air enter the interior of burner 20 through a side entry port 18.

The burner 20 may be provided with an exhaust tubing 3S, extending from the exhaust section of the burner to the surface. A valve 36 is used to adjust the back pres- Sure on the burner 20. The combustible mixture is ignited and is burned in the combustion chamber of the burner. Ignition may be accomplished by any suitable meansy such as, for example, by electrical means generally indicated by the numeral 34. The heat from the combustion in the combustion chamber of the downhole burner 20 serves to improve the production characteristics of the petroleumV product in well 21 and formation 22. As mentioned' above, the rate of heat flux to the oil must be controlled within acceptable limits or the oil will coke on the exterior of the burner. This can have serious consequences and can even tend to plug or damage the well. As is evident from the apparatus assembled in' the Well 21 in FIGURE 1, it is seen that the combustion chamber of the burner must have a relatively smallV diameter. This can be better realized when it is pointed out that the diameter of the well 21 inside the casing often' is lessy than 7 or 8 inches in diameter and all the tubing and equipment must be containedy in this relatively confined' space.

In FIGURE 2 and FIGURE 3 sectional views illustrate one form of a downhole burner in which the combustion chamber liner for the present invention is used. The burner, again represented generally by the numeral 20, has an ignition system, including a glow plug 40 having a suitable surface electrical connection such as wire 59; The combustible gas andl air mixture enters the burner through side entry port 18 and is directed into the combustion chamber 60 through

passageways

42 and 43. The pas sageways open into

ports

51 and 52 in the combustion chamber liner 62. The combustion chamber liner 62 serves to thermally insulate the wall 63' of burner 20 and to prevent the skin' temperature from becoming excesf sivel'y high'. In thisv regard it is usually desirableto limit the skin temperature of the burner to about 600 F. Since combustion temperatures' in the combustion chamber may reach as much as 3000lo F. or more, a high degree of insulation is required by a relatively thin liner. The liner 62 may be of any suitable length for a particular burner. Normally the liner 62 is cast inside the burner metal casing 63. After the liner has. been dried, it is held in place by suitable means, such as flange 64. Since the overall diameter of the burner must be kept to a minimum, it is apparent that the combustion chamber liner will be subjected to extreme gas velocity to obtain the desired rate of heat release. Heat releases of 100,000 to 200,000 B.t.u.s per hour are not uncommon in downhole burners of this type.

The present invention provides a castable mixture of aluminum oxide and calcium aluminate cement, which is used in forming the combustion chamber liner. Aluminum oxide has a chemical formula of A1203. The purity of Ya given mixture containing aluminum oxide may vary. For example, iron is often an impurity associated with aluminum oxide. The purity of A1203 in a mixture suitable for use in the invention should be above 95%. The aluminum oxide can be melted and formed into a variety of shapes. For example, the molten alumina can be formed into small bubbles or cooled and ground into hard dense grains. The castable of the present invention is comprised partly of dense alumina and bubbled alumina.

The dense alumina of the present invention is a generic term for fused alumina, sintered or calcined alumina, and crushed or broken bubbled alumina. Fused alumina is prepared by melting A1203 and cooling it into pigs. The pigs are crushed in Crushers resulting in a material having hard, dense grains. Sintered or calcined alumina is made by heating A1203 short of its melting point and crushing the resulting product. The hardness and the density of the grains formed by this process depend on the sintering temperature and on the purity of the A1203. As is well known in the art bubbled alumina is formed by blowing a stream of air through molten A1203. Hollow spheres usually in excess of 35 mesh size result when the heated A1203 cools. Crushed or broken bubbles made by this process may be further reduced in size to form dense alumina. Bubbled alumina has a relatively low thermal conductivity and is a good insulator.

The bonding agent for the castable of this invention is preferably a hydraulic setting cement. An example of a hydraulic setting cement particularly useful in the present invention is calcium aluminate cement. As is well known in the art, there are several compounds of CaO and A1203. A typical calcium aluminate cement often contains uncombined A1203 in quantities up to 50 percent. Any of the well-known calcium aluminate cements which serve to form a strong bond with the alumina are useful in the present invention. That is to say, the chemical formula of the cement is not critical to the castable of the present invention.

One example of a cement which is usable in the present invention is a cement of substantially 18% CaO by weight and 80% A1203 by weight with about 2% by Weight for impurities. The cement is prepared by sintering lime and alumina together as is well known in the cement manufacturing art.

Calcium aluminate cement will react with Water to produce a hard cementitious mass. It adheres strongly to alumina oxide and thus produces a strong concrete. In the present invention the percentage by weight of the cement in the castable should be in the range of 25 to 40% of the castable. A particularly desirable range of the cement in the castable is from 25 to 30% by Weight.

It has been found that grain size distribution of the dense alumina and bubble size of the bubbled alumina are critical to providing a combustion chamber liner having the required temperature resistance and strength qualities. Grain sizes may be measured by reference to mesh size. The mesh number gives the number of openings per linear inch of screen. Thus a 6 mesh size screen refers to a screen having six equal size openings per linear inch of screen; 10 mesh size screen to a screen having ten equal size openings per linear inch. This manner of referring to screen sizes is well known in the art. In designating the size in the present invention then, a designation of minus 14 mesh size refers to particles which pass a 14 mesh screen, hence particles having a size of smaller than 14 mesh. A designation herein of minus 12 mesh size refers to all the material which will pass through a 12 mesh screen. More simply stated, minus 12 mesh refers to material with the larger than 12 mesh size removed. A designation of 20 mesh size refers to particles having a size substantially equal to the 20 mesh screen openings.

Table I below is a standard sizing scale base on a standard 200 mesh screen.

T able I Size Mesh Example Millimeters Microns River gravel.

Pea gravel.

Beach sand.

Fine silt.

The alumina bubbles for the preferred castable mixture of the present invention should be relatively pure A1203. It has been discovered that the bubbles used in the castable mixture must be minus 12 mesh size in order to prevent pitting of the liner surface when the liner is cast and used in accordance with the invention. In other words, if the 12 mesh and larger portion of the alumina bubbles are left in the castable, the resulting liner surface will pit when subjected to high temperature and high [gas velocity. This will result in early failure of the liner. is lost when bubbles of larger than minus 12 mesh are used. Therefore, to provide a durable liner which will withstand very high temperatures, the alumina bubbles utilized should be minus 12 mesh size and 20 mesh size.

In order to retain good insulating qualities in the liner, such as are necessary to maintain the skin temperature of the outside of the combustion chamber at a level which will not cause the oil in the well to coke, the alumina bubbles which pass a 20 mesh screen are not used in the mixture. Since the insulating capacity of the bubble is largely a function of wall thickness and interior volume, a bubble size between minus 12 and 20 mesh size is a desirable size range. Clearly stated, this means the preferred size alumina bubbles are those which will pass a 12 mesh screen but not a 20 mesh screen. It has been found that an acceptable castable mixture may contain in the range of from 30 to 50% by weight of alumina bubbles of the size between minus 12 mesh and 20 mesh.

The dense alumina of the castable should be minus 14 mesh size and smaller. Thus, the dense alumina includes crushed fused alumina, crushed alumina bubbles and sintered or calcined alumina which pass a 14 mesh screen. A portion of the minus 14 mesh dense alumina should also pass a 48 mesh screen. Thus the size range of dense alumina for the castable mixture is desirably a combination of minus 14 mesh and minus 48 mesh. Extremely line material is not included in the minus 48 mesh size. There should be a substantial amount of the minus 14 mesh size in the mixture which does not pass Further, it has been found that strength the 48 mesh screen. Dense alumina of minus 14 mesh size should be in the castable mixture in an amount of between 20 and 30 percent by weight.

It has been discovered that if, in addition to the dense alumina of minus 14 mesh size, a substantial portion of the total dense alumina content of the castable mixture is minus 325 mesh size, casting of the liner is improved.

This is especially true where vibration is used during the I casting of liners having particularly delicate shapes to insure distribution of the castable mixture to all parts of the mold. The very fine grain size aids in retaining a uniform suspension of the larger sized grains and bubbles in the Wet mixture. It has been found that the castable mixture should contain between 5 and 15% by Weight of minus 325 mesh size dense alumina.

An example of a castable mixture which has given superior results when molded and used as a combustion chamber liner in downhole burners is set out below in Table II in percentage by Weight of each component.

Table II Percent by weight Alumina bubbles minus 12 mesh size About 36 Dense alumina minus 14 mesh size About 27 Dense alumina minus 325 mesh size About 9 Calcium aluminate cement 18% CaO, 80%

A1203 About A castable mixture of the formula of Table II mixed with an appropriate amount of water has set to form a liner having superior qualities of heat resistance and strength. The mixture was mixed in a propor ratio with Water and allowed to harden. A liner cast from this mixture and used to line a borehole heater has proven adequate in limiting heat transfer to the oil heated by the heater to an acceptable value of 10,000 B.t.u. per hour per square foot of surface.

A refractory liner was produced from a castable of the composition of Table II and was tested under oil well operating conditions. The refractory withstood high temperatures and high combustion gas velocities in a manner superior to all other refractories similarly tested. It is believed that limiting the alumina bubbles to minus 12 mesh size is a major factor in giving the refractory a surprising durability to hot high velocity gases. The refractory produced from the castable of the present invention was more durable than any other refractory tested. The refractory was also particularly resistant to both mechanical and thermal shock. This is an important feature for oil well use.

A castable according to Table II, when mixed in proper proportion with water, can be poured into molds of a wide variety of shapes and will harden to a concrete which makes an ideal combustion chamber lining. It has been found critical to use only alumina bubbles of minus 12 mesh in the castable when used to form the liner for downhole burner. When castables are prepared with bubbles larger than minus 12 mesh, the resulting liner pits when exposed to high temperatures and high volume gas flow across its surface. When this pitting occurs, the skin temperature of the burner can become dangerously high and coking of the oil in the Well can occur causing serious problems. As indicated above, since the burner is located at the end of a long tubing string, which may extend 5000 feet or more down a well, the liner cannot be inspected easily. It is critical, therefore, to have a liner which is sure to be in top shape for operation over long periods when inspection and repair or replacement cannot be done.

It is desirable to limit the largest size of the dense alumina to minus 14 mesh with a substantial portion passing a 325 mesh screen to give the liner mechanical and thermal strength. In a preferred embodiment, the dense alumina passing a 325 mesh screen should be about 9% by weight. The substantial portion of very tine dense alumina insures that phase separation between the water and the castable mixture will not occur during forming of the castable.

To prepare the liner of the present invention by molding, water should be added to the dry castable mixture. A preferred percentage of water to add to the castable to prepare it for molding is about 10% to 15 water by weight. A ratio of about 10% water by Weight has given very satisfactory results. A mixture of the castable and 10% water by weight will set up in about 24 hours at room temperature to form a liner having the special qualities of strength and heat resistance needed for use in well burners. The mixture should also be oven dried for an additional 24 hours at about 150 F. A further period of oven drying at 250 F. for 24 hours is also desirable to obtain a refractory with superior qualities.

As is obvious from the above discussion, a castable mixture useful in forming a combustion chamber liner having superior qualities is provided herein. A preferred embodiment of the invention having been described, we claim:

1. A method of forming the liner for the combustion chamber of a gas-and-air burner comprising the steps of preparing a dry castable mixture of alumina bubbles, between minus 12 mesh and 20 mesh size, about 30 to 50 percent by weight; dense alumina, minus 14 mesh size, about 20 to 30 percent by weight; dense alumina, minus 325 mesh size, about 5 to 15 percent by weight; and calcium aluminate cement, about 25 to 40 percent by Weight; mixing said castable mixture with water; molding the wet castable mixture into a predetermined shape to serve as a liner for the combustion chamber of a gas-andair burner; and drying said Wet mixture in said shape.

2. The method of forming a combustion chamber liner comprising the steps of forming a dry castable mixture of alumina bubbles, between minus 12 mesh and 20 mesh size, about 30 to 50 percent by Weight; dense alumina, minus 14 mesh size, about 20 to 30 percent by weight; dense alumina, minus 325 mesh size, about 5 to 15 percent by weight; and calcium aluminate cement, about 25 to 40 percent by Weight; mixing said castable mixture with water; forming the wet castable mixture in a predetermined shape to serve as a combustion chamber liner; and baking said mixture in said shape to solidify said mixture in said shape.

3. A new article of manufacture comprising a cornbustible chamber liner essentially consisting of alumina bubbles, between minus 12 mesh and 20 mesh size, about 30 to 50 percent by weight; dense alumina, minus 14 mesh size, about 20 to 30 percent by weight; dense alumina, minus 325 mesh size, about 5 to 15 percent by weight; and calcium aluminate cement, about 25 to 40 percent by weight.

4. A new article of manufacture comprising a combustion chamber liner for a downhole well burner consisting essentially of alumina bubbles, minus 12 mesh and 20 mesh size, about 36 percent by Weight; dense alumina, minus 14 mesh size and minus 325 mesh size, about 36 percent by weight; and calcium aluminate cement, about 28 percent by weight.

5. A combustion chamber liner comprising alumina bubbles, between minus 12 mesh and 20 mesh size, about 36 percent by weight; dense alumina, minus 14 mesh size, about 27 percent by weight; dense alumina, minus 325 mesh size, about 9 percent by weight; and calcium aluminate cement, about 28 percent by weight.

6. A castable mixture consisting essentially of alumina bubbles, between minus 12 mesh and 20 mesh size, about 30 to 50 percent by weight; dense alumina, minus 14 mesh size, about 20 to 30 percent by weight; dense alumina, minus 325 mesh size, about 5 to 15 percent by weight; and calcium aluminate cement, about 25 to 40 percent by weight.

7. A composition of matter consisting essentially of alumina bubbles, between minus l2 mesh and 20 mesh size, about 30 to 50 percent by Weight; dense alumina, minus 14 mesh size and minus 48 mesh size, a substantial portion of which does not pass a 48 mesh screen, about 20 to 30 percent by weight; dense alumina, minus 325 mesh size, about 5 to 15 percent by Weight; and calcium aluminate cement, about 25 to 30 percent by weight.

8. A castable mixture comprising alumina bubbles, between minus 12 mesh and 20 mesh size, about 36 percent by weight; dense alumina, minus 14 mesh size and minus 325 mesh size, a total of 36 percent by weight with at least about a 5 to 15 percent by weight portion passing a 325 mesh screen; and calcium aluminate cement, about 28 percent by Weight.

9. A castable mixture comprising alumina bubbles, beminus 12 mesh and 2O mesh size, about 36 percent by weight; dense alumina, minus 14 mesh size and minus 48 mesh size, a total of about 27 percent by weight;v

dense alumina, minus 325 mesh size, about 9 percent by Weight; and calcium aluminate cement, about 28 percent by weight.

10. A castable mixture comprising alumina bubbles, ybetween minus 12 mesh and 20 mesh size, about 36 percent by weight; dense alumina, minus 14 mesh size, about 27 percent by weight; dense alumina, minus 325 mesh size, about 9 percent by weight; and calcium aluminate cement, about 28 percent by weight.

References Cited by the Examiner UNITED STATES PATENTS 2,965,506 12/1960 Ueltz 106-64 TOBIAS E. LEVOW, Primary Examiner.

Claims

7. A COMPOSITION OF MATTER CONSISTING ESSENTIALLY OF ALUMINA BUBBLES, BETWEEN MINUS 12 MESH AND 20 MESH SIZE, ABOUT 30 TO 50 PERCENT BY WEIGHT; DENSE ALUMINA, MINUS 14 MESH SIZE AND MINUS 48 MESH SIZE, A SUBSTANTIAL PORTION OF WHICH DOES NOT PASS A 48 MESH SCREEN, ABOUT 20 TO 30 PERCENT BY WEIGHT; DENSE ALUMINA, MINUS 325 MESH SIZE, ABOUT 5 TO 15 PERCENT BY WEIGHT; AND CALCIUM ALUMINATE CEMENT, ABOUT 25 TO 30 PERCENT BY WEIGHT.