Title:
Process for treating coal with a magnetic gradient to reduce sulfur dioxide emissions
Kind Code:
A1


Abstract:
A process for treating high sulfur coal to reduce sulfur dioxide emissions when the coal is burned, which includes placing the coal in an aqueous basic soluble media saturated with a calcium salt which is pressurized with carbon dioxide. The pressure is then released to fracture the coal, and the aqueous fluids are substantially removed from the fractured coal by drying. A magnetic field is applied to the fractured coal to orient the calcium ions and to distribute the ions more uniformly on the fractured coal. The distributed calcium produces calcium sulfate when the coal is burned.



Inventors:
Farone, William A. (Irvine, CA, US)
Application Number:
11/236150
Publication Date:
03/30/2006
Filing Date:
09/27/2005
Primary Class:
International Classes:
C10L5/00
View Patent Images:
Related US Applications:
20080155887FUEL CONSUMING SYSTEMJuly, 2008Clark et al.
20090178330METHOD FOR OBTAINING A BIODIESEL FROM VEGETABLE OILS OF VARIABLE ACIDITY DEGREE IN A CONTINUOUS SYSTEM AND BIODIESEL FUEL OBTAINEDJuly, 2009Lebrón et al.
20090299109Renewable CompositionsDecember, 2009Gruber et al.
20020038064Colorless petroleum marker dyesMarch, 2002Asgaonkar
20090119980ABANDONED MINE DISCHARGE ALGAE CLEAN UPMay, 2009Walker
20020073612Artificial charcoalJune, 2002Motai et al.
20050016062Fire log made of recycled materials and a method and an apparatus for manufacturing the sameJanuary, 2005Bonnell-rickard et al.
20060021276Environmentally friendly fire logsFebruary, 2006Sonnier
20080295392Method for recycling and exploitation of the glycerin obtained in the production of biodieselDecember, 2008Rabello et al.
20050223632Cellular coal productsOctober, 2005Matviya et al.
20050005508Environmentally safe fire starterJanuary, 2005Hayden



Primary Examiner:
RINEHART, KENNETH
Attorney, Agent or Firm:
Cynthia H. O'Donohue (Anaheim, CA, US)
Claims:
We claim:

1. A process for treating coal to reduce sulfur dioxide emissions when the coal is burned, which comprises: a. placing the coal in an aqueous basic soluble media saturated with a calcium salt and then pressurizing the coal with carbon dioxide and then releasing the pressure to fracture the coal causing the calcium salt to penetrate the coal; b. removing some or substantially all of the aqueous fluids from the fractured coal by drying; c. applying a magnetic field to the fractured coal to orient the calcium ions and to distribute the ions more uniformly on the fractured coal; and d. wherein the distributed calcium produces calcium sulfate when the coal is burned.

2. The process of claim 1, wherein the pressure of the carbon dioxide is greater than 1 atm.

3. The process of claim 1, wherein prior to fracturing the coal, the coal is reduced to a size of less than about five centimeters (cm) maximum diameter.

4. The process of claim 3, wherein the coal is reduced to a size of less than about 3 cm maximum diameter.

5. The process of claim 4, wherein the coal is reduced to a size of about 3 microns to about 4 millimeters.

6. The process of claim 5, wherein the coal is reduced to a size of about 3 mm to about 4 mm.

7. The process of claim 1, wherein the releasing of the pressure of the carbon dioxide is between 10 seconds and 10 minutes.

8. The process of claim 7, wherein the releasing of the pressure of the carbon dioxide is between 10 seconds and 60 seconds.

9. The process of claim 1, wherein the carbon dioxide atmosphere is substantially pure carbon dioxide.

10. The process of claim 1, wherein the carbon dioxide atmosphere has a pressure of 10 at least 50 psi.

11. The process of claim 10, wherein pressure is about 100 psi to about 300 psi.

12. The process of claim 1, wherein the coal is immersed within the aqueous composition to form a slurry.

13. The process of claim 12, wherein the slurry is agitated.

14. The process of claim 1, wherein the aqueous composition is in contact with the coal by spraying the coal with the aqueous composition.

15. The process of claim 1I wherein the aqueous composition exhibits a pH of at least about 10.

16. The process of claim 15, wherein the aqueous composition exhibits a pH of at least about 13.8.

17. The process of claim 1, wherein the aqueous composition comprises a soluble basic salt.

18. The process of claim 17, wherein the aqueous composition comprises sodium hydroxide, calcium carbonate, and combinations thereof.

19. The process of claim 1, wherein the aqueous composition exhibits a pH of at least about 13.5 and comprises sodium hydroxide, calcium oxide, calcium carbonate, and combinations thereof.

20. The process of claim 1, wherein the coal comprises more than about 0.5 percent by weight of sulfur.

21. The process of claim 20, wherein the coal comprises more than about 0.8 percent by weight of sulfur.

22. The process of claim 1, wherein the coal resulting from the treatment of the process of claim 1 has sufficient calcium carbonate deposited within it to provide an amount sufficient to provide a molar ratio of Ca:S of at least 1.

23. The process of claim 19, wherein the resulting coal has about 1.0 percent by weight calcium carbonate associated therewith.

24. The process of claim 1, wherein the fractured coal is fully immersed in the aqueous solution.

25. The process of claim 1 wherein the coal is a high sulfur coal.

26. A process for producing energy from burning high sulfur coal while reducing the sulfur dioxide content of the emission from such burning, which process comprises depositing calcium salts within fractures in fractured coal and burning the resulting calcium salts-containing high sulfur coal at a high temperature.

27. The process of claim 26, wherein the coal comprises at least 0.5 percent by weight sulfur and calcium salts deposited within the fractures of the coal in an amount sufficient to provide a Ca:S molar ratio of at least 1.3:1.0.

28. The process of claim 27, wherein the coal has a particle size of less than about 5 cm.

29. The process of claim 28, wherein the coal has a particle size of about 50 mm to about 2 mm.

30. The process of claim 26, wherein the coal is powdered and is burned at a temperature of about 1600° F. to about 3500° F. by blowing it into a furnace, mixing it with a source of oxygen, and igniting the mixture.

31. A process for increasing the amount of calcium sulfate produced as a result of burning high sulfur coal, while at the same time reducing the sulfur dioxide emissions from such burning, which process comprises burning a vacuum fractured high sulfur coal having calcium salts deposited within fractures in the coal and recovering the calcium sulfate produced as a result of such burning.

32. The process of claim 31, wherein the coal comprises at least 0.5 percent by weight sulfur and further comprises a calcium salt deposited within the fractures in the coal in an amount sufficient to provide a Ca:S molar ratio of at least 1.0.

33. The process of claim 32, wherein the coal has a particle size of less than about 5 cm.

34. The process of claim 33, wherein the coal has a particle size of about 5 mm to about 2 mm.

35. The process of claim 31, wherein the coal has a particle size of less than 1 inch and is burned in a Stoker furnace at about 1600° F. to about 2600° F.

36. The process of claim 31, wherein the coal is powdered and is burned at about 3200° F. to about 3700° F. by blowing it into a furnace, mixing it with a source of oxygen, and igniting the mixture.

37. An apparatus for treating high sulfur coal with an aqueous composition under pressure, which apparatus comprises: a. a pressurizable container suitable for holding the coal to be treated; b. a first inlet to allow the aqueous composition to enter the pressurizable container and to make contact with the coal; c. a mechanism to remove the aqueous composition from the pressurizable container; d. a second inlet to allow carbon dioxide to enter the pressurizable container under a pressure higher than atmospheric pressure; e. a source of pressurized carbon dioxide connected to the second inlet; f. an outlet to remove the coal from the pressurizable container after the carbon dioxide pressure is released; and g. a magnetic gradient which the fractured coal is passed through.

Description:

This application claims the benefit of U.S. Provisional Application No. 60/613,625, filed Sep. 27, 2004.

FIELD OF THE INVENTION

The present embodiments relate generally to the treatment of coal to reduce emissions of sulfur dioxide from the coal combustion process. The present invention is directed towards a novel treatment of coal which reduces the sulfur dioxide emissions from the coal combustion process.

BACKGROUND OF THE INVENTION

The following description of the background of the invention is provided to aid in understanding the invention, but is not admitted to be, or to describe, prior art to the invention. All publications are incorporated by reference in their entirety.

Coal is one of the most bountiful sources of fuel in the world. Coal is typically found as dark brown to black graphite-like material that is formed from fossilized plant matter.

Coal generally comprises amorphous carbon combined with some organic and inorganic compounds. The quality and type of coal varies from high quality anthracite (i.e., a high carbon content with few volatile impurities and burns with a clean flame) to bituminous (i.e., a high percentage of volatile impurities and burns with a smoky flame) to lignite (i.e., softer than bituminous coal and comprising vegetable matter which does not fully convert to carbon and burns with a very smoky flame).

Coal is burned in coal-fired plants throughout the world to produce energy in the form of electricity. Over the years it has been recognized that certain impurities in coal can have a significant impact on the types of emissions produced during coal combustion. A particularly troublesome impurity is sulfur.

Sulfur can be present in coal from trace amounts up to several percentages by weight (e.g., organic sulfur, pyretic sulfur, or sulfate sulfur). When coal containing sulfur is burned, sulfur oxides, such as sulfur dioxide (SO2), are typically released into the atmosphere in the form of combustion gases. The presence of SO2 in the atmosphere has been linked to the formation of acid rain, which results from sulfuric or sulfurous acids that form from SO2 and water. Acid rain can damage the environment in a variety of ways, and in the United States, the Environment Protection Agency (EPA) has set standards for burning coal that restricts SO2 emissions from coal-fired plants. A need has existed to reduce sulfur emissions from burning coal.

It is against this background that a need arose to develop the present invention.

SUMMARY OF THE INVENTION

One aspect of this invention is a process for treating high sulfur coal to reduce sulfur dioxide emissions when the coal is burned. The process includes the steps of placing the coal in an aqueous basic soluble media saturated with a calcium salt. The coal in the aqueous basic soluble media saturated with a calcium salt is pressurized with carbon dioxide, and then the pressure is released to fracture the coal.

In addition, some or substantially all of the aqueous fluids are removed from the fractured coal by drying. A magnetic field is then applied to the fractured coal to orient the calcium ions and to uniformly distribute the ions on the fractured coal. The process comprises the use of a magnetic field either on slurry or on dried coal. When the fractured coal is burned, the distributed calcium produces calcium sulfate.

Another aspect of this invention is a process for producing energy from burning high sulfur coal while reducing the sulfur dioxide content of the emission from such burning, which includes depositing calcium salts within fractures in fractured coal and burning the resulting calcium salts-containing high sulfur coal at a high temperature.

A further aspect of this invention is a process for increasing the amount of calcium sulfate produced as a result of burning high sulfur coal, while at the same time reducing the sulfur dioxide emissions from such burning, which includes burning a vacuum-fractured high sulfur coal having calcium salts deposited within fractures in the coal and recovering the calcium sulfate produced as a result of such burning.

A further aspect of this invention is an apparatus for treating high sulfur coal with an aqueous composition under pressure, which includes a pressurizable container suitable for holding the coal, a first inlet to allow the aqueous composition to enter the container and to contact with the coal, a mechanism to remove the aqueous composition from the container, a first inlet to allow carbon dioxide to enter the container under a pressure higher than atmospheric pressure, a source of pressurized carbon dioxide connected to the first inlet, and an outlet to remove the coal from the container.

Other aspects of the invention may be apparent to one of skill in the art upon reading the detailed description of this invention.

DEFINITIONS

In accordance with the present invention and as used herein, the following terms are defined with the following meanings, unless explicitly stated otherwise.

The term ‘coal’ refers to any graphite-like material that is formed from fossilized plant matter. Coal is also known as anthracite, bituminous, or lignite. In one aspect coal refers to the fuel that contains a high sulfur content.

The term ‘% w/v of a substance’ denotes a concentration of the substance in a composition equivalent to 1 g of the substance per 100 ml of the composition.

The term ‘illegal level’ refers to concentration levels prohibited by law and are defined by various governmental agencies.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description will be better understood in conjunction with the accompanying drawings as follows:

FIG. 1 is a representation of a process of taking high sulfur bituminous coal from rail cars through pre-preparation and treatment according to an embodiment of the invention.

FIG. 2 is a representation of a steam plant that processes, burns and converts treated coal to heat energy, emissions, water and ash (including gypsum), according to an embodiment of the invention.

FIG. 3 is a representation of a high temperature generator where treated coal is burned to produce heat energy that can be used to generate power, according to an embodiment of the invention.

FIG. 4 depicts an apparatus for treating high sulfur coal using an aqueous solution.

The present invention is detailed below with reference to the listed Figures.

DETAILED DESCRIPTION OF THE INVENTION

Before explaining the present invention in detail, it is to be understood that the invention is not limited to the particular embodiments and that it can be practiced or carried out in various ways.

With reference to the Figures, FIG. 1, FIG. 2, FIG. 3, and FIG. 4 are representations of processes and an apparatus for treating high sulfur coal to reduce sulfur dioxide emissions when the coal is burned.

One of the benefits of this invention is that the invention provides an approach for reducing sulfur dioxide (SO2) and other polluting and harmful combustion gases by a unique pre-combustion treatment of coal.

One aspect of this invention is a process for treating high sulfur coal to reduce sulfur dioxide emissions when the coal is burned, which includes placing the coal in an aqueous basic soluble media saturated with a calcium salt, such as calcium carbonate. The aqueous solution can also include sodium hydroxide, calcium carbonate, and combinations thereof. The aqueous composition exhibits a pH of at least about 10. In another aspect the aqueous composition exhibits a pH of at least about 13.5 and comprises sodium hydroxide, calcium oxide and calcium carbonate.

The aqueous composition is prepared by dissolving a strong base in water to provide an aqueous solution that is highly basic (i.e., a pH of more than 10, preferably at least 12, and more preferably at least 13.5). The strong base typically will be an alkali metal hydroxide, such as sodium hydroxide or potassium hydroxide. In a further aspect the strong base is potassium hydroxide. A molar quantity of at least 3 will be used to prepare the alkaline solution with as much water as needed to maintain the pH at the desired level.

In particular, the aqueous composition may comprise about 15% w/v to 40% w/v calcium carbonate, and about 1.5% w/v to 4.0% w/v calcium oxide. As used herein, a 1% w/v of a substance denotes a concentration of the substance in a composition equivalent to 1 g of the substance per 100 ml of the composition.

The type of coal that can be treated is any coal that has an undesirable level of sulfur that will result in undesirable or illegal levels of SO2 if burned without treatment. For certain applications, a coal having a sulfur content of at least 0.5% by weight may be viewed as a high sulfur coal. The density of the coal often depends on the type of coal and typically varies from about 1.2 g/cm3 to 2.3 g/cm3 (e.g., apparent density as measured by liquid displacement).

The coal treated by the embodied process is more than about 0.5% by weight of sulfur, and can be more than about 0.8% by weight of sulfur.

The coal is contacted with the aqueous composition by spraying the coal with the aqueous composition, and is immersed within the aqueous composition to form a slurry, which can be agitated. In one aspect the fractured coal is fully immersed in the aqueous solution.

The coal is then pressurized with carbon dioxide. The carbon dioxide atmosphere is substantially pure carbon dioxide, and can have a pressure of at least 50 psi. The carbon dioxide atmosphere can have a pressure of about 100 psi to about 300 psi. In additional aspect the carbon dioxide has a pressure greater than 3 atm. The idea of fracturing here is not to break the coal into little pieces but to create fractures in the structure that allow the calcium salts to be better distributed in the coal.

The process also includes releasing the pressure of the carbon dioxide to fracture the coal. Releasing the pressure of the carbon dioxide can take between 1 minute and 10 minutes. The pressure can also be released between 10 seconds and 60 seconds. The releasing of the carbon dioxide fractures the coal making smaller sizes. The coal is then reduced to a size of less than about five centimeters (cm) maximum diameter. The coal can also be reduced to a size of less than about 3 cm maximum diameter; 3 microns to about 4 millimeters (mm) in diameter; or 3 mm to about 4 mm in diameter, and combinations thereof.

Releasing the pressure of the carbon dioxide will be sufficient to remove fluids, whether gaseous or liquid, entrapped in the coal. This is believed to result in fracturing the coal. Alternatively or in conjunction, releasing the pressure of the carbon dioxide may serve to remove fluids, whether gaseous or liquid, entrapped within pre-existing fractures in the coal. The fractures, whether created by depressurization or pre-existing, are typically elongated and may be inter-connected or may be spaced apart in a generally parallel manner. The fractures should be in adequate numbers and result in cross section sizes that allow a sufficient amount of the aqueous composition supersaturated with calcium carbonate to penetrate the fractures. For instance, releasing the pressure of the carbon dioxide may create numerous fractures in the coal that have cross section sizes in the range of 0.01 μm to 1 μm.

In addition, the process includes removing some or substantially all of the aqueous fluids from the fractured coal by drying. A magnetic field is applied to the fractured coal to orient and to uniformly distribute the calcium ions on the fractured coal. The coal resulting from the treatment is a high sulfur coal, with sufficient calcium carbonate deposited within it to provide an amount sufficient to provide a molar ratio of calcium (Ca): sulfur (S) of at least 1. The resulting coal can be about 1.0 percent by weight calcium carbonate associated therewith.

Finally, the fractured coal is burned to produce energy and then, the distributed calcium produces calcium sulfate. Sulfur is converted to CaSO4 and Na2SO4 as the coal burns at high temperatures by a chemical reaction between calcium carbonate, NaHCO3, and sulfur dioxide-sulfuric acid and/or sulfurous acid.

An advantage of the method of the invention is that the coal burns with low sulfur dioxide (SO2) emissions. In addition there is evidence for lower emissions of nitrogen oxides (NOx), mercury (Hg), carbon monoxide (CO), carbon dioxide (CO2) and hydrocarbons (HC). At the same time, by using this method, the quality of the combustion emissions is improved, and the solid by-products of the combustion process are modified to increase amounts of useful solids that can be collected. In particular, the ash provides a component (CaSO4) useful in the manufacture of cement.

Another aspect of the invention is a process for producing energy from burning high sulfur coal while reducing the sulfur dioxide content of the emission from such burning, which includes depositing calcium salts within fractures in fractured coal and burning the resulting calcium salts containing high sulfur coal at a high temperature.

The resultant fractured coal is at least 0.5% by weight sulfur and calcium salts deposited within the fractures of the coal in an amount sufficient to provide a Ca:S molar ratio of at least 1.3:1.0. Furthermore, the fractured coal has a particle size of less than 5 cm, and can have a particle size of about 2 mm to about 50 mm.

The coal is powdered and is preferably burned at a temperature of about 1600° F. to about 3500° F. by blowing it into a furnace, mixing it with a source of oxygen, and igniting the mixture.

A further aspect of the invention is a process for increasing the amount of calcium sulfate produced as a result of burning high sulfur coal, while at the same time reducing the sulfur dioxide emissions from such burning, which includes burning a vacuum fractured high sulfur coal having calcium salts deposited within fractures in the coal and recovering the calcium sulfate produced as a result of such burning.

In the above aspects, the coal is at least 0.5% by weight sulfur, and a calcium salt is deposited within the fractures in the coal in an amount sufficient to provide a Ca:S molar ratio of at least 1.0. Furthermore, the coal has a particle size of less than 5 cm. The coal also can have a particle size of about 2 mm to about 5 mm, or a particle size of less than 1 mm, which is burned in a Stoker furnace at about 1600° F. to about 2600° F.

The coal is powdered and is burned at about 3200° F. to about 3700° F. by blowing it into a furnace, mixing it with a source of oxygen, and igniting the mixture.

An additional aspect of this invention is an apparatus for treating high sulfur coal with an aqueous composition under pressure, which includes a pressurizable container suitable for holding the coal, a first inlet to allow the aqueous composition to enter the container and to contact with the coal, a mechanism to remove the aqueous composition from the container, a first inlet to allow carbon dioxide to enter the container under a pressure higher than atmospheric pressure, a source of pressurized carbon dioxide connected to the first inlet, and an outlet to remove the coal from the container.

The size of the coal that is treated at the depressurization stage may be the size that comes out of most mines, e.g., an irregular shape with a maximum cross sectional size of about 2 in. down to less than about ¼ in. The size that works for large Stoker burners is about ¾ in. to about 1 in., while the size that works for small Stoker burners is less than about ½ inch. Thus, the process may be used at a processing plant near where the coal is to be burned or right at the mining site.

If desired, the coal may be reduced in size prior to depressurization by, for example, crushing, grinding or pulverizing the coal into a powder of particles having sizes less than about 5 cm, e.g. less than 3 cm, with sizes in the range of about 50 μm to about 300 μm or from about 50 μm to about 100 μm being desirable for certain applications. This reduction in size of the coal may serve to increase surface area that can be exposed to depressurization and to the aqueous composition and may serve to reduce the amount of time required to process the coal.

If desired, the coal that has been reduced in size prior to depressurization may be mixed with a liquid (e.g., water) to form a slurry. For certain applications, it may be desirable to contact the coal with calcium oxide prior to depressurization by, for example, mixing the coal with calcium oxide in a powdered form. Contacting the coal with the calcium oxide may serve to further reduce SO2 emissions.

It should be additionally noted that once the coal has been depressurized, it is then contacted with an aqueous basic soluble composition saturated with a calcium salt for a time sufficient to infuse the fractures with the dissolved calcium salt, such as calcium carbonate. This results in intimately associating the calcium carbonate with the coal and further fracturing of the coal through crystallization of the calcium carbonate within the fractures. To enhance the fracturing of the coal, it may be desirable that the aqueous basic soluble composition also comprises calcium oxide.

The contacting step preferably takes place at ambient temperatures for ease of process, although elevated temperatures could be used. Generally the amount of the aqueous composition used will be from about 5 gal. to about 20 gal. or more per 100 lbs. of coal. For scales of economy about 10 gal. per 100 lbs. of coal in the container, and the coal may be immersed (e.g., fully immersed) in the aqueous composition. If desired, the coal can be stirred or agitated to intimately mix with the aqueous composition. Generally, only a few minutes will be needed to add the aqueous composition to the coal under ambient temperature and pressure. Further details regarding the aqueous composition will be discussed hereinafter.

Once the aqueous composition is in contact with the coal for a sufficient amount of time, the container in which the coal is located is pressurized with a gas, preferably carbon dioxide (CO2), for a time sufficient to force a portion of the aqueous composition into the fractures of the coal, to initiate crystallization of the dissolved calcium carbonate in the fractures, and to further fracture the coal. Preferably, the aqueous composition is removed from contact with the coal prior to the pressurizing step. In particular, a remaining portion (e.g., 70% to 90%) of the aqueous composition that has not penetrated the coal may be removed by a variety of methods, e.g., by filtering the coal or simply flowing the remaining portion of the aqueous composition out of the container through a mesh sieve.

Generally, the pressurization step will take place at ambient temperatures and at a pressure that will exceed 50 pounds per square inch (psi), and in another aspect at a pressure more than 100 psi. While the pressure may exceed 300 psi, the evidence suggests no more than 300 psi is needed for most applications. The pressurization typically will take place for no more than an hour, generally about 20 min. to 45 min.

Once the pressurization is complete, the coal may be burned or otherwise processed in accordance with any conventional method to extract energy from the coal. If desired, the coal may be reduced in size after treatment by, for example, crushing, grinding or pulverizing the coal into a powder of particles.

For certain applications, the coal may be retreated via the same process discussed above. In particular, the steps may be repeated two or more times, but generally no more than two cycles are needed for satisfactory results for the reduction in SO2 emissions. In one aspect the filtrate is reused for the next cycle, with fresh aqueous composition being added to provide the desired ratios of aqueous composition to coal, as discussed herein. It is thought that two cycles provide an adequate infusion of the coal with the calcium carbonate with respect to time and cost considerations.

The treated coal in accordance with the process will have calcium carbonate associated with it so that, when the coal is burned at a high temperature, emission of SO2 is reduced to a desired level. In particular, the treated coal may have a calcium carbonate content such that the molar ratio of Ca to S found in the treated coal is typically at least 0.5, with a ratio of at least 1 (e.g., 1-4) in a further aspect. This calcium carbonate content may reduce SO2 emissions by at least about 5% relative to an untreated coal, e.g., less than 20%, with a 60% to a 100% reduction being sometimes observed. It is thought that the sulfur contained in the coal reacts with the calcium carbonate to produce calcium sulfate, thus reducing or eliminating the formation of SO2. The calcium sulfate that is produced may be in the form of CaSO4.2H2O (Gypsum).

It should be recognized that the percent by weight of the calcium carbonate comprising the treated coal will typically vary depending on the percent by weight of sulfur in the untreated coal such that a desired molar ratio of Ca to S is achieved. Also, up to 50% of the sulfur in coal that is burned may remain in the fly ash and not released as SO2. Accordingly, a molar ratio of Ca to S less than 1 (e.g., 0.5) may be adequate for certain applications.

As discussed previously, the type of coal that can be treated by the process is any coal that has an undesirable level of sulfur that will result in undesirable or illegal levels of SO2 if burned without treatment and may have a sulfur content of about 0.2% by weight up to more than 7% by weight. The size of the coal that is treated may be about 2 in. down to less than about ¼ in. or may have rxeduced size by, for example, crushing, grinding or pulverizing the coal into a powder of particles having sizes less than about 5 cm, e.g., less than 3 cm, with sizes in the range of about 50 μm to about 100 μm being desirable for certain applications.

Still another aspect of this invention is a process for producing energy from the combustion of coal while reducing the sulfur dioxide content of the emission from such combustion. The process comprises depositing calcium carbonate within fractures in the coal and burning the resulting calcium carbonate-containing coal at a high temperature to produce energy. In particular, calcium carbonate may be deposited within fractures in the coal in accordance with the process discussed herein using the aqueous composition supersaturated with calcium carbonate, such that the calcium carbonate-containing coal comprises calcium carbonate deposited within fractures of the coal.

The calcium carbonate-containing coal may be burned in accordance with fixed bed combustion (e.g., underfeed stoker fired process, traveling grate stoker fired process, or spreader stoker fired process), suspension firing (e.g., pulverized fuel firing or particle injection process), fluidized bed combustion (e.g., circulating fluidized bed combustion or pressurized fluidized bed combustion), magnetohydrodynamic generation of electricity, and so forth. The particular technique and equipment selected to burn the calcium carbonate-containing coal may affect one or more of the following characteristics associated with the burning step: (1) temperature encountered during burning (e.g., from about 1800° F. to about 4000° F.; (2) whether the calcium carbonate-containing coal is used in a wet form following deposition of the calcium carbonate or is first dried; (3) size of the calcium carbonate-containing coal used; and (4) amount of energy that can be produced. For instance, the calcium carbonate-containing coal may have a particle size less than about 1 in. and is burned in a Stoker furnace at about 2400° F. to about 2600° F. As another example, the calcium carbonate-containing coal may be powdered to particle sizes less than about 300 μm and is burned at about 3200° F. to about 3700° F. (e.g., about 3500° F.) by blowing it into a furnace, mixing it with a source of oxygen, and igniting the mixture in accordance with suspension firing.

A further aspect of this invention is a process for increasing the amount of calcium sulfate produced as a result of burning high sulfur coal, while at the same time reducing the sulfur dioxide emissions from such burning. The process comprises burning coal having calcium carbonate deposited within fractures in the coal and recovering the calcium sulfate produced as a result of such burning. Calcium carbonate may be deposited within the fractures in accordance with the process discussed herein using an aqueous basic soluble media saturated with a calcium salt, and the coal may be burned in accordance with a variety of techniques as discussed herein.

Depending on the technique used for burning the coal, one or more of a variety of combustion products may be produced, e.g., fly ash, bottom ash, boiler slag, and flue gas desulfuriation material. Such combustion products may find use in a variety of applications, for example, for cement, concrete, ceramics, plastic fillers, metal matrix composites, and carbon absorbents. For instance, fly ash from the burning of the coal in accordance with the present invention may be used in the production of cement. In particular, sulfur contained in the coal reacts with the calcium carbonate deposited within the fractures to produce calcium sulfate. As discussed previously, the calcium sulfate that is produced is typically in the form of gypsum (CaSO4.2H2O) that remains in the fly ash. This fly ash may be used as is or one or more separation processes know in the art may be used to extract (CaSO4.2H2O) for use as a component of cement (e.g., Portland cement). Other forms of CaSO4 such as the anhydrous form (CaSO4) and the hemihydrate (CaSO4.H2O) are also usable in cement formulations and wall boards.

This aspect of the invention can be seen in the overall discussion of sequences shown in FIG. 1. Coal is brought to the steam generator plant via train cars 102 and dumped in the coal hoppers 103 underneath the control tower 100. Alternatively, the coal may be treated at the coal field instead of at the generator plant.

The coal is then fed onto conveyor belt 104 and transported to coal breaker 108 and coal breaker 109 via conduit 105. The low quality rejects and debris are transported to reject piles 111 and 112 via conduits 106 and 107. Coal is released from the breakers after being crushed to particles sized about 1 mm to about 2 mm in diameter. The coal falls on conveyor 110, which dumps it into conduit 114 then to conduits 113 and 114a. Conduit 114a carries the coal to hopper 115, which dumps the coal through a pressure hatch into pressure tank 16. The pressure hatch is closed under hopper 115 and at the junction of exit conduit 18 with the pressure tank 16.

As the coal is fed into the tank 16 through hopper 115, auger 17 pushes the coal to the distal portion of the tank 16 as the tank 16 is tilted up to about 45°. The tank 16 is sealed and a vacuum (about 26″ to 30″ of water) is applied for about 20 minutes by vacuum pump 23 housed in, and the tank 16 is lowered back in to neutral position. The aqueous composition of this invention, which may be synthesized in building 27, is pumped into storage tank 24 via conduit 35, then pumped via conduit 34 through conduit 21 and is drawn into tank 16 when valve is opened to the vacuum. The aqueous basic soluble media saturated with a calcium salt, such as ionized calcium carbonate and calcium oxide, and water is drawn into the evacuated pores of the coal.

After the system equilibrates, a remaining portion of the aqueous composition is removed, and valves are opened to allow CO2 from tank 26 to flow via conduit 36 through controller 23 and then through conduit 21. A pressure of about 100 psi to about 300 psi is maintained for up to an hour (e.g. 5 min. to 40 min.) and released. The CO2 pressure puts an increased bicarbonate ion load into the pores of the coal.

This increased availability of bicarbonate ion brings about crystallization of CaCO3 in the pores of the coal thereby fracturing it and making more and larger pores available for penetration of calcium carbonate and calcium oxide. At this point the process is preferable repeated once or twice to maximize the integration of the calcium ions into the coal. Once fully processed, the resulting coal is then pushed out through conduit 18 by auger 17 onto belt 30 which carries the treated coal to “Live Pile” 31.

The treated coal is released from “Live Pile” on belt 32 to conveyor 33. The treated coal may be burned as stoker coal in a stoker burner at temperatures of about 2400° F. to about 2600° F. or may be pulverized and burned in a blower furnace at temperatures of about 3200° F. to about 3700° F.

As seen in FIG. 2, a steam plant process burns and converts treated coal to heat energy, emissions, water and ash. Using a process to burn coal heats water to steam; the steam then drives turbines. The turbines in turn drive electric power generators that send power over the transmission lines.

Alternatively, as shown in FIG. 3, the treated coal is delivered to the coal bunkers 210 over conveyor 201, which communicates with conveyor 33 of FIG. 1. Coal is metered on demand through scale 209 into pulverizers 207 to produce powdered coal. This powdered coal is directed through coal dust air line 205 and into furnace 204 through fuel injections nozzles 203. This powdered coal is blown into the furnace 204, where it ignites into an intense, swirling fire that burns at about 3500° F. At the time of the burn, calcium carbonate, calcium oxide, water and sulfur dioxide react in the presence of intense heat to form greater quantities of gypsum (CaSO4.2H2O) and lime which remain in the ash. The increased gypsum makes the ash of increased value for cement and it is removed for this use from ash bin 206. Therefore, high sulfur coal may be burned with greatly reduced emissions along with improved quality of combustion products.

FIG. 4 depicts an apparatus for treating high sulfur coal with an aqueous composition under pressure, which includes a pressurizable container 300. The pressurizable container is used to hold the coal 302 to be treated. In addition, the apparatus includes a first inlet 304 to allow the aqueous composition to enter the pressurizable container 300 and to make contact with the coal. The aqueous composition is removed from the container, such as by drying with an integral heater (not shown). There is also a second inlet 306 to allow carbon dioxide to enter the pressurizable container 300 under a pressure higher than atmospheric pressure. A source of pressurized carbon dioxide 308 is connected to the second inlet 306. Lastly, there is an outlet 310 to remove the coal from the container after the carbon dioxide pressure is released. A valve 312 can be used to controllably release the carbon dioxide pressure. The fractured coal is passed through a magnetic field gradient 314.

The following examples describe specific aspects of the invention to illustrate and provide a description of the invention for those of ordinary skill in the art. The examples should not be construed as limiting the invention, as the examples merely provide specific methodology useful in understanding and practicing the invention.

EXAMPLE I

Slurry Version

This example describes a process for carrying out the process for treating coal prior to burning.

20 lbs. of ground coal are placed in a 5-gal. airtight container.

An aqueous basic solution with a pH of 13.5 is added into the container. The aqueous solution comprises a saturated calcium carbonate with sodium hydroxide. The aqueous solution is added in an amount sufficient to cover the coal.

Carbon dioxide gas is added to the airtight container. If the pore space in the coal and spaces between the coal in the container is 40% of the volume of the container and the temperature is 70° F., then 5.5 ft3 of CO2 or 0.7 lbs. is needed. The gas is pressurized up to 300 psi. The container is then pressurized for 20 minutes.

The carbon dioxide is then flashed off reducing the pressure from 300 psi to about 1 atm (14.7 psi).

The resultant material is then passed through a magnetic field gradient.

The magnetic field gradient is either at least one magnetic field gradient or a plurality of magnetic field gradients to orient the calcium ions and to distribute the calcium ions more uniformly on the fractured coal.

EXAMPLE II

Dry Version

This example describes another process for treating coal prior to burning.

20 lbs. of ground coal are placed in a 5-gal. container.

An aqueous basic solution with a pH of 13.5 is added into the container. The aqueous solution comprises a saturated calcium carbonate with sodium hydroxide. The aqueous solution is added in an amount sufficient to cover the coal.

Carbon dioxide gas is added to the airtight container. Preferably, 5.5 ft3 of CO2 or 0.7 lbs. is used. The gas is pressurized up to 300 psi. The container is then pressurized for 20 min.

The carbon dioxide is then flashed off reducing the pressure from 300 psi to about 1 atm (14.7 psi).

The resultant material is then dried until the material has less than 3 wt % aqueous solution.

The fractured coal is then passed through a magnetic field gradient.

The magnetic field gradient is either at least one magnetic field gradient or a plurality of magnetic field gradients to orient the calcium ions and distribute the calcium ions more uniformly on the fractured coal.

While this invention has been described with emphasis on selected aspects, it should be understood that within the scope of the appended claims, the invention might be practiced or carried out in various ways other than as specifically described herein.