BACKGROUND OF THE INVENTION

This appl ication is a eontinuation-in-part of U. S .

Serial No . 763 ,942 , f iled August 8 , 1985 , the contents of which are hereby incorporated by reference into the present application .

Within this application several publications are refer¬ enced. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which this invention pertains.

This invention relates to the manufacture of coal bri¬ quettes from coal fines which are produced as a result of the mechanical breakage and crushing of coal which is concomitant with preparing the coal for consumption. The shape of the formed briquettes can be ovoid, cylin¬ drical, or honeycombed cylinder, although any size or shape would be possible. The briquetting process usu¬ ally requires mixing the coal with a binder to increase structural integrity. The typical range of binder addition is within the order of from about 5% to about 18% by weight. After mixing, the material goes to a vertical pug mill or "fluxer" where it is heated by direct steam injection which helps spread the binder evenly over the coal surface. On leaving the fluxer, the mixture is tempered before being briquetted. Bri¬ quetting pressures are generally high, frequently in excess of 6,000 pounds per square inch. After press¬ ing, the briquettes are cooled and removed. References exemplifying this general procedure include Dryden et al. United States Patent No. 2,652,318 and Braun et al. united States Patent No. 3,317,289.

Binders are used in order to provide for greater struc¬ tural integrity and stabilization of the briquettes formed. Structural integrity of the briquettes is crucial during weathering, storage, shipment and use. Without strong structural integrity the briquettes could easily be reduced to powder thereby eliminating the manifest benefits of briquette form such as ease of transport. Without increased stabilization the bri¬ quettes could lose much of their volatile matter there¬ by reducing the heating capacity of the briquettes.

The three most commonly used binders are petroleum asphalt, bitumen or coal tar pitch which is a residue from the distillation of coal tar. Coal tar pitch, also termed simply "pitch", is the most common binder in Europe. It is comprised of a relatively large num¬ ber of molecules having a high molecular weight. When heated, it becomes relatively soft and because of this physical property it is an acceptable binding agent. In the United States, asphalts and bitumens are most common.

The cost of manufacturing briquettes is sensitive to the cost of the binding material. Usually this cost represents about 15% to 30% of the total expenditure of manufacturing briquettes from coal. Besides the ex¬ pense, organic binding materials such as those above mentioned may give off smoke when combusted and may be carcinogenic to those handling them. It therefore is desirable to develop a process of briquetting which eliminates the need for organic binders.

Miller et al.. United States Patent No. 4,235,603, issued November 25, 1980, disclose binder additives.

which are eliminated by spraying coal fines with ace¬ tone, then removing the excess solvent by vacuum dry¬ ing. The pretreatment with acetone extracts organic material which becomes the binder. After the residual solvent is recovered through vacuum drying, the fines are then compressed to form briquettes. An obvious limitation of this process is that the coal being treated must have an adequate amount of extractable material which can act as a binder. "Coal Briquetting Without a Binder," Report No. IS-ICP-67, Iowa State University, Ames, Iowa (1979). Moreover, this process is expensive because it requires use of the solvent acetone and vacuum drying.

Gillstrap et al . , United States Patent No. 1,443,359, issued January 30, 1923, discloses pitch or' coal tar which is melted and then poured over crushed lignite, sub-bituminous coal, or other lignite matter. Ordinary clay, or clay containing pyrites is added along with ground commercial coke. The mixture is heated in a coke oven at between 500 and 1,000 °C, for 6 hours. An obvious limitation is that powder coke and charcoal are used along with dextrin. Coke and charcoal are pro¬ duced by carbonizing raw coal. An obvious limitation is that the mixture is heated at high temperatures for a significant period of time and pitch or coal tar along with ground commercial coke is used as the bind¬ er. Coke, of course, is prepared by carbonizing or pyrolyzing raw coal.

Hall et al.. United States Patent No. 3,026,189, issued March 20, 1962, disclose a method for th preparation of fuel briquettes which includes introducing crushed lignite into a heating chamber where volatile elements that would contaminate food in open fire cooking are

substantially removed from the lignite. An obvious limitation is that the mixture is heated at high tem¬ peratures to remove volatile elements.

Starr et al., United States Patent No. 3,402,033, is¬ sued September 17, 1968 disclose a solid fuel composi¬ tion comprising a major proportion of petroleum coke and minor proportions of wood-sawdust, charcoal, an oxidizing agent capable of supporting combustion, a binder and a non-hydratable clay. An obvious limita¬ tion is that coke and charcoal, both carbonized materi¬ al, are used as the major components of the mixture and the mixture is further dried at significant tempera¬ tures.

Onozawa, United States Patent No. 3,689,234, issued September 5, 1972 discloses a solid fuel composition comprising a perchlorate; a combustion-supporting sub¬ stance such as rice bran, oil meal, powdered bamboo or sodium oxalate; an adhesive such as dextrin; a composi¬ tion buffer substance such as clay, calcium hydroxide or foyaite; and a carbonaceous substance such as pow¬ dered charcoal, powdered anthracite coal or powdered coke. An obvious limitation is that powder coke and charcoal are used along with dextrin. Coke and char¬ coal are produced by carbonizing raw coal. All of these items are very costly to produce and will inter¬ fere with the adsorbent action of the clay and the sulfur trapping action of the lime.

Cass et al . , United States Patent No. 4,093,451, issued June 6, 1978, disclose a coke agglomerate consisting of a mixture of coke fines, hydraulic cement and a calcium material such as calcium hydroxide, calcium carbonate, and/or calcium fluoride. Water is added to

provide a plastic agglomerable mixture which is there¬ after agglomerated. An obvious limitation is that coke, a pyrolyzed material, and hydraulic cement are used.

Mitchell, British Patent No. 21,615, issued August 6, 1903, discloses a smokeless fuel formed by combining ground clay, small coal or coal dust, pulverised sodium sulfate, iron sulfate, a solution containing glucose, dextrin and oxalic acid, slacked lime and water to form a creamy material for forming blocks or briquettes. Obvious limitations are that sulfur containing com¬ pounds are used which will enhance the evolution of sulfur oxides; glucose and dextrin are used which are costly and will tend to cause smoke upon combustion; and the types of clay and coal used are not defined. We teach the use of specific types of clay defined as the result of a detailed study of the proximate and ultimate analysis of the coal, the particle size dis¬ tribution and moisture content of the raw coal, and the concentration and composition of the inorganic material within the coal that is usually referred to as ash.

Thus, the prior art discloses fuel compositions formed from carbonaceous material and methods for making such fuel compositions which are more complex and expensive than the non-pyrolyzed coal briquettes provided by the present invention.

Briquettes of the present invention can make use of raw high-sulfur, non-pyrolyzed non-carbonized lignite, lignite fines or any other type of coal and/or fines. These briquettes are made by using specific types of clay as a binder and calcium oxide, calcium carbonate or mixtures thereof to trap the sulfur without addition

of any external heat energy. The briquettes are smoke¬ less and odorless because the clay adsorbs the vola- tiles until their combustion temperature is attained, whereupon they combust to carbon oxides and water. The invention removes the need to beneficiate the coal and/or to desulfurize the flue gases since the sulfur is trapped in the ash.

Briquettes of the present invention are particularly beneficial to users requiring low-sulfur coal, who often pay a penalty of shipping low-sulfur coal long distances. The briquettes of this invention will enable these users to take advantage of large quanti¬ ties of high-sulfur coal material which may be located nearby.

Briquettes of the present invention also offer an inex¬ pensive means to minimize the health hazard resulting from the combusti_.. of high-sulfur coal. Combustion of high-sulfur coal often produces sulfur oxides which escape into the atmosphere. Scrubbing methods for removing sulfur compounds from the gases produced by coal combustion result in liquid waste material high in sulfur content. The high-sulfur ash material .which remains after burning briquettes of the present inven¬ tion can be used as road-bed, building or land-fill material. Maintaining sulfur in the solid residue provides a safe way to dispose of the sulfur present in high-sulfur coal.

Briquettes of the present invention require only stoi- chiometric amounts of calcium oxide, calcium carbonate or mixtures thereof to capture the sulfur. This is less costly and more efficient than the procedure used during fluidized bed combustion where three to five

times the stoichio etric amount of calcium oxide, cal¬ cium carbonate or mixtures thereof are fluidized along with raw coal in the fluidized bed combustion reactor to reduce the sulfur oxides in the stack gases by less than 80%.

SΠ ARY OF THE INVENTION

The object of the present invention is to provide a briquetting process for the manufacture of smokeless and odorless briquettes from coal. Another object is to provide a briquetting process which completely eliminates the use of carcinogenic compounds, organic binding materials, organic solvents, heating, vacuum drying, manufacturing steps requiring inordinate ex¬ pense and the need for coals having an adequate amount

¹⁰ of extractable binding material. This invention accom¬ plishes all these goals by exploiting the unexpected advantages resulting from the use of inorganic clay as a binding material. Further advantages are obtained from the use of calcium oxide, calcium carbonate or

¹⁵ mixtures thereof.

Moreover, the briquettes of this invention and their method of marvufacture can use common lignite coal as a starting material. Heretofore, this type of coal has or*. been unsuitable as a starting material for coal bri¬ quettes because of its high sulfur content, s okiness and bad odor when combusted. This invention also em¬ braces coal briquettes and a method for their produc¬ tion which uses lignite coal as the starting material ²⁵ while eliminating the detrimental properties heretofore associated with the use of lignite coal in coal bri¬ quetting.

A non-pyrolyzed coal briquette is described comprising

30 inorganic clay as a binder. Also described is a coal briquette comprising calcium oxide, calcium carbonate or mixtures thereof in a proportion effective to cap¬ ture the sulfur within the coal as a sulfur containing compound within the ash residue resulting from combus- 35 tion of the briquette. .

A process for manufacturing non-pyrolyzed coal bri¬ quettes is described which comprises contacting appro¬ priately sized coal fines with the proper amount of inorganic clay to create a blended mixture of inor¬ ganic clay and coal. The blended mixture is contacted with water so that the moisture content is sufficient to create a briquettable mixture. The briquettable mixture is compressed under conditions of ambient tem¬ perature and with appropriate pressure for a time suf¬ ficient to form briquettes. The briquettes are dried until the moisture content is at equilibrium with the atmosphere thereby creating non-pyrolyzed coal bri¬ quettes.

Another process for manufacturing non-pyrolyzed coal briquettes is described which comprises contacting appropriately sized coal fines with the proper amount and type of -inorganic clay to create a blended mixture of inorganic clay and coal. An appropriate amount of calcium oxide, calcium carbonate or mixtures thereof is added to the blended mixture to substantially elimi¬ nate the evolution of sulfur oxides in the blended mixture so that the moisture content is sufficient to create a briquettable mixture. The briquettable mix¬ ture is compressed under conditions of ambient tempera¬ ture and with appropriate pressure for a time suffi¬ cient to form briquettes. The briquettes are dried until the moisture content is at equilibrium with the atmosphere and, thereby, a non-pyrolyzed coal bri¬ quette is created.

nE ATT.BD DESCPTPTTON OF THE INVENTION

A non-pyrolyzed coal briquette comprising coal and inorganic clay as a binder is described. The briquette includes a major proportion of particulate coal and binder material comprising inorganic clay. The coal briquette may further comprise calcium oxide, calcium carbonate or mixtures thereof. To enhance combustion, the briquette may additionally comprise oxidizers such as sodium or potassium nitrate or nitrite. The per¬ centage of clay in the briquette is between about 5% and about 25% by weight of the briquette. The clay may be a clay having binding properties, such as bentonite, montmorillonite, attapulgite- anauxite, nacrite, halloysite, kaolinite or a mixture of these clays. Most preferably the clay is a kaolinite-type clay. If coal ash content is low, the percentage of clay required may be higher. If coal ash content is greater than--35% and if there is sufficient coal dust, it is possible to make the briquette without adding clay because the coal dust itself will act as a binder.

Combustion of a coal briquette at low temperature can often produce smoke and odor. The materials of the briquette which actually produce the smoke and odor at low temperature combust more fully (and therefore pro¬ duce less smoke and odor) at high temperature. The addition of clay preserves the smoke and odor producing materials for combustion at high temperatures by fill¬ ing the pores of the coal briquette. The clay swells upon contact with water and flows into the pores during drying and formation of the briquette.

Disclosed is another coal briquette containing calcium oxide, calcium carbonate or mixtures thereof. The

calcium oxide, calcium carbonate or mixtures thereof of the coal briquette is present in a proportion effective to reduce the evolution of sulfur containing compounds resulting from combustion of the briquette by capturing sulfur within the coal. Although the coal briquette may be pyrolyzed or non-pyrolyzed, it is preferably non-pyrolyzed. The calcium oxide, calcium carbonate or mixture thereof may be hydrated or not hydrated.

A process for manufacturing non-pyrolyzed coal bri¬ quettes is disclosed which comprises contacting appro¬ priately sized coal fines with the proper amount of inorganic clay to create a blended mixture of inor¬ ganic clay and coal. The blended mixture is contacted with water so that the moisture content is sufficient to create a briquettable mixture. The briquettable mixture is compressed under conditions of ambient tem¬ perature and with appropriate pressure for a sufficient time to form- briquettes. The briquettes are dried until the moisture content is at equilibrium with the atmosphere and, thereby, non-pyrolyzed coal briquettes are created. This process may be used with a variety of coals including anthracite, bituminous, subbitumi- nous, lignite or a combination of these coals. A. vari¬ ety of clays including kaolinite-type, montmorillonite, attapulgite, anauxite, nacrite, halloysite, or bentonite may be used. In the presently preferred embodiment the coal particle size should be not greater than about 3/8 inch in diameter, and should preferably be very predominantly within a range between about 3/8 inch and about 250 mesh (Tyler screen) . The drying process may be done with or without an artificial heat source. If done with artificial heat it should be from a low temperature oven. The creation of the briquettable mixture may be accomplished in one step

by contacting the coal, inorganic clay and water approximately simultaneously.

Another process for manufacturing non-pyrolyzed coal briquettes is disclosed which comprises contacting appropriately sized coal fines with the proper amount of inorganic clay to create a blended mixture of inor¬ ganic clay and coal. An appropriate amount of calcium oxide, calcium carbonate or mixtures thereof is added to the blended mixture to substantially eliminate sul- fur oxides. Water is mixed with the blended mixture so that the moisture content is sufficient to create a briquettable mixture. The briquettable mixture is compressed under conditions of ambient temperature and with appropriate pressure for a sufficient time to form briquettes. The briquettes are dried until the mois¬ ture content is at equilibrium with the atmosphere and, thereby, a non-pyrolyzed coal briquette is created. The same var-iations and limitations described for the previous process in which no calcium oxide was added are equally applicable to the just described process using calcium oxide, calcium carbonate or mixtures thereof.

EXAMPLE 1

Lignite coal particles from Thailand (two samples of which were analyzed as shown in Table 1) being prefer¬ ably predominantly within a range from about 3/8 inch and about 100 mesh (Tyler screen) were the starting material. Coal particles larger than this size were ground into the desired dimension. Inorganic kaoli- nite-type clay, as a powder, was added. The amount of clay added is a function of the proximate and ultimate analysis of the lignite and its particle size distribu-

tion; the greater the amount of clay added, the greater the briquette strength and stability. Increased clay content, however, may decrease the amount of heat evolved so a careful balancing must be achieved. A minimum of about 5% clay by weight of the lignite should be added. In general, high ash content requires less clay. On the basis of these considerations 10.4% clay was added to Sample A of Table 1 and 13.4% clay was added to Sample B of Table 1. The powdered lig¬ nite and powdered kaolinite-type clay were mixed to form a blended mixture.

Hydrated calcium oxide was added to the blended mix¬ ture. The amount of calcium oxide added was about three times the sulfur content in the lignite. The calcium oxide aids the binding capacity of the clay and acts as a desulfurizing agent, thereby preventing the emission of sulfur oxides. By acting as a desul¬ furizing agent pungent odors, especially common during early stages of ignition, are virtually eliminated and the amount of smoke resulting from combustion is re¬ duced.

I__£_£_1

ANALYSIS OF LIGNITE COAL SAMPLES

SAMPLE A SAMPLE B

Moisture , % 12 .05 13 .79

Ash , % 25 .18 15.67

Volatile matte r , % 32 . 47 35 .16

Fixed carbon, % 30 .30 35.38

H.V. (Cal/GM) 3 , 865 .00 4 ,330 .00

Sulfur , % 1 .02 1 .37

% RETAINED ON SIEVE NO. SAMPLE A SAMPLE B

4 1 .25 1.08

8 20.26 17.88

16 26 .28 26.15

30 9 .41 11.72

50 3 .67 5.45

100 0 .78 1.68

200 0 .20 1.15

Water was added to the clay, coal and calcium oxide mixture. The amount added was sufficient to generate a moisture content of at least 30% by weight. Less water is necessary if the lignite has a high ash content. The result of the addition of water was a briquettable mixture.

The briquettable mixture was compressed to form bri¬ quettes. This compression was done at ambient tempera¬ ture by a hand operated double ring roll machine and a hand operated hydraulic press machine. The pressure was approximately 500 to 1,000 pounds per square inch and the pressure was applied for approximately one second. In any case pressures less than 5,000 pounds per square inch would be sufficient to create bri¬ quettes. The shape of the formed briquettes was ovoid, cylindrical, or honeycombed cylinder, although any size or shape would be possible.

The briquettes were dried naturally in the, air or slow¬ ly in a low temperature drying oven. This drying step was conducted until the moisture content of the bri¬ quettes was at equilibrium with the moisture content of the atmosphere.

For the ovoid shape, the resultant non-pyrolyzed coal briquettes had a crushing strength of 22.5 kilo¬ grams/square centimeter for Sample A of Table 1 and 18.3 kilograms/square centimeter for Sample B of Table 1. For the cylindrical shape, the maufactured non- pyrolyzed coal briquettes had a compressive strength of 35.7 kilograms/square centimeter for Sample A of Table 1 and 31.6 kilograms/square centimeter for Sam¬ ple B of Table 1.

EXAMPLE 2

The coal briquettes produced in Example 1 were ana¬ lyzed. Procedures used for analyzing the briquettes are standard procedures followed by the American Soci¬ ety for Testing Materials. The results are shown in Table 2.

__2_B E 2

ANALYS IS OF COAL BRIOUETTES

Ash 34 .39%

Volatiles 40 . 09%

Fixed Carbon 25 .52%

Sulfur 1 .93 %

BTU/lb . 6 , 885

Burn tests were carried out with the briquettes pro¬ duced in Example 1. These tests were run in furnaces which provided temperature, pressure and atmosphere composition control. The amount of sulfur retained in the ash was calculated by measuring the amount of sul-

fur emitted in gaseous form after briquette burning and substracting that amount from the total amount of sul¬ fur present in the briquette prior to burning. Table 3 sets forth the results which show that sulfur-contain¬ ing compounds remain with the ash product under both oxygen and atmospheric burns.

L____I_E____

BURN TEST SAMPLES

CONDITIONS % SULFUR RETAINED IN ASH

1515 °F , at 78.5%

10 cubic feet/hour Nitrogen and 2 cubic feet/hour Oxygen

1800°F 88% at normal atmosphere