US 3630696 A
Description (OCR text may contain errors)
United States Patent  Inventors Maclin R. Mllner Clearwater; Frederick B. Johnston, Tampa, both of Fla.  Appl. No. 869,866  Filed Oct. 27, 1969  Patented Dec. 28, 1971  Assignee Trimex Corporation Clearwater, Fla. Continuation-impart of application Ser. No. 852,867, Aug. 25, 1969. This application Oct. 27, 1969, Ser. No. 869,866
 COMBUSTION ADJUVAN'I 12 Claims, No Drawings  U.S. Cl ..44/4, 44/51, 44/76  Int. Cl C1019/00, C101 1/32  Field of Search 44/4-6, 16, 41, 51,68 V, 76
1  References Cited UNITED STATES PATENTS 1,167,471 1/1916 Barba 44/4 2,139,398 12/1938 Allen 44/6 Primary Examiner-Daniel E. Wyman Assistant ExaminerC. F. Dees Attorney-Fidelman, Wolffe & Leitner ABSTRACT: An adjuvant for hydrocarbon fuels is provided comprising a calcium based montmorillonite clay, a phosphate, and a source of boron oxide. A preferred formulation comprises 85 weight percent calcium bentonite, 10 weight percent anhydrous trisodium phosphate, and 5 weight percent sodium borate. The adjuvant is combined with the hydrocarbon fuel or with combustion air in an amount of about 0.1 to 2.0 weight percent, based on the weight of the hydrocarbon fuel. Combustion efficiency is substantially improved and oxidation is substantially more complete, so that combustion products are produced in less noxious forms. In addition, the nature of slag or other deposits upon surfaces in a furnace or combustion chamber are substantially altered, so that corrosive conditions do not occur and the deposition of slag is prevented or materially reduced, and the ash is produced in a soft, friable form. 1
COMBUSTION ADJUVANT This application is a continuation-in-part of applicant's copending application, Ser. No. 852,867, filed Aug. 25, 1969.
This invention relates to an adjuvant for combustion processes, and to a method for increasing the efficiency thereof. Additionally, the utilization of the method and the product of this invention substantially reduces the relative amounts of undesirable, harmful and toxic components in the end products of hydrocarbon fuel combustion.
As is well known, the combustion of fuel oil, coaland natural gas produces a large number of byproducts, including dust, fly-ash, sulfur dioxide, etc. incomplete combustion results in the discharge of smoke, soot and carbon monoxide into the atmosphere. Anticipated industrial expansion threatens to increase the hazards of such air pollution appallingly in the relatively near future. Such pollution adversely affects vegetative plants and the health of animals and humans. Such effects range from petty annoyance to chronic illness and death.
Polluted air has been linked to irritation of nose, throat and eyes, aggravation of the respiratory tract, including bronchitis, emphysema, and cardiovascular ailments.
Whether coal, gas, oil or other organic material comprises the fuel, with even the most efficient furnace design and operating conditions, complete combustion is seldom if ever attained. Buildup of tar, coke, soot and mineral slag on boiler surfaces constitutes a serious problem, promoting chemical corrosion of metallic parts and greatly reducing efficiency of heat transfer. Burning of additional fuel to offset this reduced heat transfer merely increases the production of pollutants and adversely affects economy of operation. Furthermore, the procedures now commonly employed for removal of boiler deposits are costly, generally unsatisfactory, sometimes requiring shutdowns, and such practice as blowoff" of soot and fly-ash are increasingly prohibited by law.
Under conditions imposed by practical furnace construction, the formation of undesirable residues is a normal result of the combustion of fossil fuels. Except for the burning of the elemental carbon, the combustion comprises rapid chain reactions in the gas phase. Furnace operation can be described, in fact, as a controlled explosion." The type and predominance of the various chain reaction steps depends partly upon the type of fuel; but inasmuch as the principal ingredients are carbon and hydrogen, the process of burning is controlled more by external factors such as concentrations, initial gas temperature and manner of mixing of fuel with the combustion air.
Majority of combustion occurs in the flame front," which measures fractions of a millimeter in thickness. Whatever combustion occurs must be practically complete within this boundary between burned and unburned gases, wherein all locally available oxygen is consumed. Under conditions of rapid furnace firing, ignition and combustion occur almost simultaneously. Propagation of the flame front generally is a thermal process, in that the flame must transfer heat to the unburned gas to cause it to ignite.
ln oil burners the fuel is either vaporized or atomized before ignition. On heating and vaporization, a certain amount of decomposition of such oils occurs and some nonvolatile carbonaceous material forms. Droplets of heavy'oils are partly carbonized within the flame. The tendency to deposit carbon on and around the burner is a function of both molecular weight and molecular structure of the fuel. Tendency of fuel oils to smoke" increases with'their carbon/hydrogen ratio.
Pulverized coal is 50 percent combusted in 0.05 second after the particles leave the burner port. At 0.1 and 0.3 second, approximately 5 percent remains unburned. Further reduction of unburned fixed carbon proceeds very slowly; elementary carbon does not vaporize at ordinary flame'temperatures.
The combustion'flame front impinges on furnace walls and other heat absorbing surfaces, particularly under the conditions of hard firing. Although such surfaces may initiate some combustion 'stepsthrough production of free radical chain carriers, other combustion intermediates are destroyed by such contact. Additionally, in the presence of insufficient air for complete combustion, lighter fractions evaporate, but the more complex compounds decompose and form carbonaceous deposits. Other factors contributing to carbon deposition include insufficient secondary air, insufficient mixing of air with volatile matter, temperature of air and fuel falling below the critical temperature, insufficient time of contact between air and fuel, or impingementupon a cool" surface. lncomplete secondary combustion results in formation of tarry vapors, solid carbon, gaseous hydrocarbons, carbon monoxide and hydrogen. Finely divided carbon is swept away in suspension in the flue gases to cooler zones of the furnace or is discharged from the stack as smoke or soot.
Furnaces currently are constructed to provide for removal of deposits by blowers and scrapers (or lances). Out-of-service steam and water washing frequently is employed, although disposal of the wash water often becomes a problem. ln-service boiler water washing can result in damage and should never be used with high-alloy super heater tubes because of thermal shock damage. Also, chloride in the water can initiate cracking of austentitic tubing.
Contributing to inefficiency of furnace operations is deposition on the tubes of inorganic fuel ash. This slag not only creates resistance to transfer of heat energy, but is also generally acid in reaction, causing sulfuric acid corrosion of affected metal surfaces. Whereas coal ash tends to neutralize some of acid formed in the boiler, the vanadium contained in most oils increases the formation of sulfuric acid from sulfur dioxide. Consequently, the rapid removal of deposits on metal surfaces is extremely important.
In view of the problems arising from furnace operation there has been an increasingly urgent need for means to enhance completeness of combustion, minimize formation of tray and carbonaceous residues on boiler tubes and to prevent deposition of molten mineral slag on the metal surfaces.
It is accordingly an object of the present invention to provide an adjuvant for hydrocarbon fuels which increases the efficiency of combustion and alters the nature of the combustion products.
These and still other objects are realized by the-composition of the combustion adjuvant of the present invention, comprising a calcium-based montmorillonite, a phosphate, and a source of boron oxide. The calcium based montmorillonite constitutes at least about 75 weight percent of the adjuvant, while the phosphate makes up about 5 to l5 weight percent and the boron oxide source constitutes about 1 to 10 weight percent. In addition to the foregoing, the adjuvant can further include, if desired, an essentially inert diluent in amounts ranging from 0 up to several hundred, or even several thousand weight percent, based on the weight of the adjuvant. As an inert diluent, any material can be used which does not detrimentally hinder combustion or the functioning of the adjuvant. For example, the diluent can be a hydrocarbon fuel oil, a substantially inert solid, such as a diatomaceous earth, or even an excess of the calcium-based montmorillonite.
The calcium-based montmorillonite is preferably one of the naturally occuring montmorillonite based clays, such as bentonite. The material known as Southern Bentonite" is preferred, since it is readily available at low cost in aform which is directly usable in the combustion adjuvant of the present invention, i.e., it is a calcium-based montmorillonite. Other montmorillonite based clays can be used, but, since such materials are not ordinarily calcium based," it isnecessary that they be treated to replace at least part of another metal with calcium.
The term calcium based is used to indicate that a substantial proportion of the metallic ions replacing aluminum in the montmorillonite crystalline lattice are calcium. The montmorillonite clays are crystalline alumino-silicates of a specific, known composition, having a planar structure of alternating sheets" of silica and alumina layer bonded to two silica layers. In other clays, such as kaolinite and illite, the structure differs by bonding of each silica layer to two layers of alumina,
while the montmorillonite has each silica layer bonded to one alumina layer and one silica layer. Thus, designating silica as Si" and alumina by Al, the C-dimension" of the montmorillonite crystal lattice can be represented by the formula:
SiAl-SiSiAl-Si The adjacent "Si layers of the montmorillonite lattice gives the clay its distinctive properties.
Within the crystalline lattice of naturally occurring clays, a portion of the aluminum atoms are replaced by other metals in minor amounts, including iron, zinc, nickel, lithium, magnesium, calcium, potassium and sodium. In most montmorillonite clays of the bentonite variety, about 50 to 75 milliequivalents of exchangeable metallic bases occur per 100 grams of clay, and of this amount, sodium, calcium, magnesium and iron constitute the bulk. The relative amounts of sodium and calcium are of significance in the present invention, it being necessary to utilize a material having a predominant proportion of calcium and a relatively minor proportion of sodium. The material commonly known as Southern Bentonite" is suitable, having about 1.3 to 3.5 milliequivalents calcium and only about 0.3 to 0.45 milliequivalents sodium per 100 grams of clay. Other clays of the montmorillonite type ordinarily predominate in sodium, which is detrimental in the combustion adjuvant of the present invention, and such clays, if used, must be ion exchanged to remove sodium and add calcium. The sodium content should not exceed 1.0 weight percent. Since such manipulations add considerably to the cost of the product, it is preferred to use a calcium-based montmorillonite of a naturally occuring variety, e.g., "Southern Bentonite."
The phosphate component of the combustion adjuvant can be, insofar as is presently known, any phosphate functional material, although some will, of course, be preferred for reasons of availability cost, or efficiency. For example, while in some contexts it will be desirable to utilize organo phosphates, e.g., tricresyl phosphate and the like, to reduce dusting of the composition, in most circumstances, such materials will be prohibitively expensive in comparison with inorganic phosphates. Common phosphate rock might be effective but for the highly corrosive nature of the hydroflouric acid produced upon combustion. Preferred for economic considerations and effectiveness are the alkali metal phosphates, particularly anhydrous trisodium phosphate, which is inexpensive, readily available, and in a form conducive to ease of handling and formulation.
Similarly, the boron oxide can be supplied by any convenient source, so long as it does not further contain any constituent which is corrosive or detrimental to combustion. Boron oxide per se can be used, but a cheaper, more readily available, source is sodium borate or common borax, which is accordingly preferred. Other alkali and alkaline earth metal borates and boric acid are further examples, of suitable sources of the boron oxide.
The adjuvant composition is formed of the foregoing essential components as an intimate admixture in finely divided particulate form. The materials should be ground or pulverized to pass a ZOO-mesh, preferably a 325-mesh screen (to provide a maximum particle size of not more than about 44a). The finer particle sizes enhance dispersion in the hydrocarbon fuel and minimize atomizer wear. The materials in such finely divided form are often subject to dusting, which can be effectively prevent by including a minor amount of a light oil or other suitable oiling agent.
The composition is effective in rather broad relative proportions of the essential components, with at least about 75 weight percent of the calcium-based montmorillonite being used, preferably about 80 to 94 weight percent, while the phosphate is preferably about 5 to weight percent and the boron oxide source is l to 10 weight percent. When circumstances are appropriate, the essential components can be combined with varying amounts of an inert diluent. For example, when large scale furnaces are utilized, their operation is often automated, and the introduction ofthe adjuvant of the present invention is also desirably automated. Measurement, handling and distribution are often facilitated by increasing the bulk of the adjuvant. The inert diluent can be utilized in amounts ranging from 0 to several hundred, or even several thousand percent, e.g., 5,000 percent, based on the weight of the adjuvant. The nature of such an inert diluent is limited only to materials which do not detrimentally affect the operation of the furnace or of the adjuvant. Many such materials will be readily apparent to those or ordinary skill in the art, and can include, for example, both solid and liquid materials. For example, as illustrations of solid diluents which can be used, there can be mentioned coal, coke, carbon blacks,
diatomaceous earth, silceous materials, and the like. A particularly advantageous inert diluent is an excess of the calcium-based montmorillonite. Liquid diluents can include such materials as kerosene, fuel oil, cycle oil, residual oils or the like.
The amount of the combustion additive to be added to a furnace will vary with the size and type of furnace and with the nature of the fuel. The considerations vary greatly and no general rule can be given, although in most cases, about I to 3 pounds of the combustion adjuvant per l,000 square feet of furnace or boiler surface per day, not including any inert diluent, will be highly effective, although some operations require less, e.g., down to as little as 0.! pound per day per 1,000 square feet of surface, while in still other operations as much as 5 to even 10 pounds per day is required. Excessive amounts of the combustion adjuvant are not at all detrimental, but, of course, economic considerations ordinarily dictate that the minimum effective amount be used, which will ordinarily fall within the above ranges.
The combustion adjuvant can be introduced into the combustion zone directly or in combination with either the fuel or the combustion air. The addition can be either continuous or intermittent. About 0.] to 2.0 percent by weight of the adjuvant, based on the weight of the fuel is a convenient amount when the adjuvant is added combined with the fuel.
When the product ofthis invention, in finely ground form, is injected into the firing chamber, either independently, in intimate admixture with the fuel, or in the combustion air, completeness of combustion is greatly enhanced, indicated by composition of stack gases and lowering of stack temperature. Formation of smoke, soot and tars is greatly reduced, and the deposition of slag and other materials on tubes and refractive surfaces almost nullified. In fact, under proper firing conditions and without resort to mechanical cleaning methods, metal surfaces are maintained clean and bright. Accordingly, heat transfer is appreciably improved. Deposition of ash and slag is prevented almost entirely. Further, the slag removed from the ash pit is in a readily friable, powdery condition.
While the exact mode of operation of the composition is not clearly understood, the following explanation is offered, but it should be understood that applicants do not wish to be bound thereby. The minutely ground material, mixed with the fuel as it is sprayed or injected into the firing chamber, is broken into multitudinous finer particles at the flame front temperature. Heat energy absorbed by the crystalline material is surrended and exchanged to combustile products as flame front temperature decreases with flow though the furnace, thereby promoting more complete combustion. Whether added continuously or intermittently, the material of this invention, broken into particles by the extreme temperatures, provides a very thin but frequently renewed highly refractory surface, upon which unburned compounds impinge and thereby undergo further additional oxidative reaction.
EXAMPLE A heavy fuel oil was burned in a small, pilot scale furnace, and an analysis of the stack gases was conducted. The analysis was conducted after running the furnace for about 3 hours at fixed, equilibrium conditions. Then i percent by weight of the adjuvant of the present invention was combined with the fuel,
and a second analysis of the stack gases was conducted after l hour at the same conditions. The adjuvant of the example comprises 85 weight percent calcium based bentonite, 10 weight percent anhydrous trisodium phosphate, and 5 weight percent sodium borate.
A comparison of the analyses indicated a substantial reduction in the undesirable components of the stack gases, as shown in the table:
Stack Gas Component Weight Percent Reduction CO, (Increased) Formaldehyde 66% Forrnic Acid 75% Pyridines 66+% While the table indicates substantial benefits to be derived from the use of the adjuvant, still other benefits accrue. For example, during the period of operation, relatively substantial amounts of slag and ash were produced, and deposits formed upon the surfaces of the furnace components. After 1 hour of combustion with the adjuvant, slag and ash production was substantially reduced, and, additionally, the accumulated deposits were gradually eliminated.
As stated above, when bentonite is used as the silicate, it must be of low sodium content, not more than percent and preferably less than 1 percent as Na O. Likewise, in order to preclude slagging, the bentonite should possess not more than percent by weight of ion, calculated as Fe O Should either sodium or iron exceed the indicated maxima, these can be reduced in amount by partial proxying of the exchangeable bases with hydrogen ions, utilizing acid treatment. Such procedure is familiar to those skilled in the art.
What is claimed is:
1. An adjuvant for combustible hydrocarbons fuels comprising from about 80 to 93 weight percent calcium montmorillonite, 5 to weight percent an alkali metal phosphate, and l to 10 weight percent of a source of boron oxide, selected from the group consisting of boron oxide, boric acid, alkali metal borates, and alkaline earth borates.
2. The composition of claim 1, wherein said alkali metal phosphate is anhydrous trisodium phosphate.
3. The composition of claim 1, wherein said source of boron oxide is sodium borate.
4. The composition of claim 1, wherein said calcium montmorillonite is calcium-based bentonite.
5. An adjuvant for combustible hydrocarbon fuels comprising 85 weight percent calcium bentonite, 10 weight percent anhydrous trisodium phosphate, and 5 weight percent sodium borate.
6. A fuel having improved combustion properties comprising a combustible hydrocarbon and about l weight percent of the adjuvant of claim 2.
7. The fuel of claim 3, wherein said combustible hydrocarbon is a liquid petroleum oil.
8. The fuel of claim 3, wherein said combustible hydrocarbon is coal.
9. The method of promoting combustion efficiency of hydrocarbon fuels comprising burning said fuel in a combustion zone in combination with about 0.1 to 2.0 weight percent of the adjuvant of claim 1, base on the weight of the fuel.
10. The method of promoting combustion efficiency of hydrocarbon fuels comprising burning said fuel in a combustion zone in combination with about 0.1 to 2.0 weight percent of the adjuvant of claim 5, base on the weight of the fuel.
11. The method of promoting combustion efficiency of hydrocarbon fuels comprising burning said fuel in a combustion zone in combination with about 0.1 to 10 pounds per day of the adjuvant of claim 1 per 1,000 square feet of exposed surface area of said combustion zone.
12. The method of promoting combustion efficiency of hydrocarbon fuels comprising burning said fuel in a combustion zone in combination with about 0.1 to 10 pounds per day of the adjuvant of claim 5 per 1,000 square feet of exposed surface area of said cgmgust ion zone.