US3628925A - Combustion adjuvant - Google Patents

Abstract

A method of promoting combustion is provided by including an adjuvant for hydrocarbon fuels comprising a calcium based montmorillonite clay. The adjuvant is combined with the hydrocarbon fuel or with combustion air in an effective amount of about 2 X 10 5 to about 5 X 10 1 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 additions, 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.

Description

United States Patent [72] Inventor Maclin R. Milner Clearwater, Fla. [21] Appl. No. 11,827 [22] Filed Feb. 16, 1970 [45] Patented Dec. 21,1971 [73] Assignee Trirnex Corporation Clearwater, Fla.

[54] COMBUSTIQN ADJUVANT 7 Claims, No Drawings [52] U.S. Cl. 44/4, 44/51 [51] Int. Cl C101 9/00, C101 1/32 [50] Field of Search 44/46. 16, 51,68 V [56] References Citedv UNITED STATES PATENTS 1,167,471 1/1916 Barba 44/4 2,217,994 10/1940 Rick et al 44/16 Primary Examiner-Daniel E. Wyman Assistant ExaminerC. F. Dees e Att0rney-Fidelman, WoliTe & Leitner ABSTRACT: A method of promoting combustion is provided by including an adjuvant for hydrocarbon fuels comprising a calcium based montmorillonite clay. The adjuvant is combined with the hydrocarbon fuel or with combustion air in an effective amount of about 2X 1 0' to about 5X10 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 additions, 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 materiall reduced, and the ash is produced in a soft, friable form.

1 COMBUSTION ADJUVANT This invention relates to a method of promoting combustion processes, and for increasing the efficiency thereof. Additionally, the utilization of the method 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, coal and 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. Build up 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 practices as blow-off" 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 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.

In oil burners the fuel is either vaporized or atomized before ignition. n heating and vaporization, a certain amount of decomposition of such oils occurs and some nonvolatile carbonaceous materials 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 steps through 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 impingement upon a "cool" surface. Incomplete 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 inefiiciency 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 tarry 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 a method which increases the efficiency of combustion of hydrocarbon fuels and alters the nature of the combustion products.

These and still other objects are realized by the present invention, comprising the addition to the combustion zone of a calcium based montmorillonite.

The calcium based montmorillonite is preferably one of the naturally occurring montmorillonite based clays, such as bentonite. The material known as Southem Bentonite" is preferred, since it is readily available at low cost in a form which is directly useable 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 is necessary that they be treated to replace at least a 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:

Si-AlSiSi--Al-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 l00 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 preferable 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 ineffective in the method of the present invention, and such clays, if used, should 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 montmorillonitz of a natu rally occurring variety, eg. Southern Bentonite or Fuller's Earth.

The amount of the combustion additive to be added to a particular furnace will vary with the size and type of furnace and the with nature of the fuel. The considerations vary greatly and no general rule can be given, although in most cases, about 1 to 3 pounds of the combustion adjuvant per 1000 square feet of furnace or boiler surface per day will be highly effective, although some operations require less, e.g. down to as little as 0.1 pound per day per 1000 square feet of surface, while in still other operations as much as 5 to even 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.

It is preferred to determine the effective amount of the adjuvant for a particular hydrocarbon fuel. Fuels with high levels of pollution precursors, such as sulfur, and/or high levels of materials which affect the formation of slag or the corrosive ness of slag or ash, such as vanadium, require relatively large amounts of the adjuvant. Lower levels of such constituents permit lower proportions of the adjuvant. Generally, very small amounts based on the amount of the hydrocarbon fuel, are effective. Amounts as little as 2X10 weight percent have been found effective for relatively low-sulfur fuels, while amounts of about 5X l (1 weight percent are effective for even extreme high-sulfur levels. But, as has been mentioned above, excessive amounts are not at all detrimental, and no effective upper limit on proportions need be considered except con-- venience and economics.

When the product of this 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 condi tions 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.

Lil

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 frame front temperature. Heat energy absorbed by the crystalline material is surrendered and exchanged to combustile products as flame front temperature decreases with flow through 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 1 Bunker "C" fuel oil containing 340 p.p.m. vanadium and 2.67 wt. percent sulfur 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 1 percent by weight of sodium bentonite was analysis of the stack gases was conducted after 1 hour at the same conditions. The adjuvant of the present invention, calcium bentonite, was then combined with the furnace feed, combustion was equilibrated again, and a third analysis of the stack gases was conducted.

A comparison of the analysis indicated a substantial reduction in the undesirable components of the stack gases with the adjuvant of the present invention, as shown in Table 1:

TABLE 1 Fannie Acid 4.6 p.p.m.

Bunker C" fuel oil 56.0 p.p.m.

Bunker C fuel oil 1% sodium bentonite Bunker "C" fuel oil 1% calcium bcntonitc 46.0 ppm. 3.3 p.p.m.

EXAMPLE II An experimental testing of the method of the present invention was conducted in a steam electrical generating plant. The power plant utilized Bunker C" fuel oil as the primary fuel. A series of analyses were conducted on the fuel and stack gases on the 3 days preceding the addition of calcium bentonite in accordance with the present invention, in an amount cor responding to weight percent, based on the weight of the fuel. Additional analyses, of both fuel and stack gases were made 16 and 30 days after the initiation of the continuous additions. The results of the analyses appear in Table 11.

TABLE II Bunker C-Btec1r effluent Formal- Vanudlum, Sulfur, S03, C0, C02. dehyde, Formlc Day p.p.m. percent p.p.m. p.p.m. percent percent p.p.m acid The results of table ll show a clearreduction of pollutants in the stack gases for a fuel of substantially constant quality. In

addition a number of additional features were observed. Stack fallen off the tubes, leaving only minor random patches of slag rather than the continuous solid deposit at the beginning of th e test.

It is clear that substantial benefits are derived from ,the pracgreat importance; the increased heat exchange attained by virtue of the reduction or elimination of slag deposits on exchange surfaces is perhaps the greatest direct economic benef t to theuser.

tice of the method of the present invention. Increased heat} yield from and conversion of the fuels is dramatic, with the concomittent reduction of atmospheric pollutants, which is of What is claimed is: i a

1. The method of promoting combustion of hydrocarbon fuels comprising adding to a combustion zone about 2X10 to 5 l0weight percent, based on the weight of the hydrocarlaon fuel, of a calcium based montrnorillonite. ,1 2. The method of claim l wherein said calcium based montlmorillonite is added to said combustion zone mixed with said Minesathsnfusl- A m... z.

3. The method of claim 1 wherein said calcium based montmorillonite is added to said combustion zone mixed with the sussqiiwrs QFE P$E 3lL V 4. The method of claim l wherein said calcium based montmr q t M ua y ss it jss. H V. V 5. The method of claim 4 wherein said naturally occurring sntwsfillsqitss s'sismksntsnia.

6. The method of claim 1 wherein said calcium based montmorillgnite is not naturally occurring.

7. The method of claim 6 wherein said calcium montmorillonite is prepared by ion exchange.

i i 1 t

Claims (6)

1. 2. The method of claim 1 wherein said calcium based montmorillonite is added to said combustion zone mixed with said hydrocarbon fuel.
2. 3. The method of claim 1 wherein said calcium based montmorillonite is added to said combustion zone mixed with the oxygen source for combustion.
3. 4. The method of claim 1 wherein said calcium based montmorillonite is naturally occurring.
4. 5. The method of claim 4 wherein said naturally occurring montmorillonite is calcium bentonite.
5. 6. The method of claim 1 wherein said calcium based montmorillonite is not naturally occurring.
6. 7. The method of claim 6 wherein said calcium montmorillonite is prepared by ion exchange.