US20110030271A1

US20110030271A1 - Method for removing impurities from coal in a reaction chamber

Info

Publication number: US20110030271A1
Application number: US12/538,341
Authority: US
Inventors: Chandrashekhar Sonwane; Samuel D. Draper; Lawrence B. Kool
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 2009-08-10
Filing date: 2009-08-10
Publication date: 2011-02-10
Also published as: CH701635B1; JP2011038098A; CH701635A2; CN101993754A; DE102010036871A1

Abstract

A method for removing at least one impurity from coal is described herein. The method includes providing coal comprising a plurality of impurities and contacting the coal with an acid solution in a reaction chamber. At least one of the impurities reacts with the acid solution to produce one or more first products soluble in the acid solution. The method further includes removing at least a portion of the acid solution including at least a portion of the first products from the reaction chamber and adding a nitrate composition to the reaction chamber to form a nitrate solution. At least one of the impurities, at least one of the first products, or combinations thereof react with the nitrate composition to produce one or more second products soluble in the nitrate solution. The method still further includes removing at least a portion of the nitrate solution including at least a portion of the second products from the reaction chamber.

Description

TECHNICAL FIELD

This disclosure generally relates to methods for producing ultra clean coal, and more particularly relates to producing ultra clean coal by removing impurities from coal.

BACKGROUND OF THE INVENTION

Clean coal, such as ultra clean coal, may be provided by treatment of coal including impurities to remove the impurities. For instance, coal including impurities may be treated with hydrofluoric acid in a first reactor to produce a first reaction slurry. The first reaction slurry may be transported to a filter (e.g., drum filter) to produce filtered, wet coal. The filtered, wet coal may then be transported to a second reactor for treatment with nitrates to produce a second reaction slurry. The second reaction slurry may then be transported to a filter for filtering. The resulting ultra clean coal may then be water washed and transported to a dryer for drying. Thus, this multi-step process requires multiple reactors, slurry pumps, and filters. The associated expense and space requirements for these various processing units may be quite large. Accordingly, there is a need for an improved process for removing impurities from coal which avoid one or more of the aforementioned disadvantages and deficiencies.

SUMMARY OF THE INVENTION

This disclosure provides a method for removing at least one impurity from coal. The method includes providing coal comprising a plurality of impurities and contacting the coal with an acid solution in a reaction chamber. At least one of the impurities reacts with the acid solution to produce one or more first products soluble in the acid solution. The method further includes removing at least a portion of the acid solution including at least a portion of the first products from the reaction chamber and adding a nitrate composition to the reaction chamber to form a nitrate solution. At least one of the impurities, at least one of the first products, or combinations thereof react with the nitrate composition to produce one or more second products soluble in the nitrate solution. The method still further includes removing at least a portion of the nitrate solution including at least a portion of the second products from the reaction chamber.
Other aspects, features, and advantages of this invention will be apparent from the following detailed description, drawings, and claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a flow diagram illustrating a method 10 for producing ultra clean coal in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

As summarized above, this disclosure encompasses a method removing at least one impurity from coal. Thus, embodiments of the method of the present disclosure provide ultra clean coal. As used herein, the term “ultra clean coal” refers to coal having a reduced ash content (e.g., below about 2%) and/or a substantially reduced sulfur content such that the coal may be fed directly into processes such as gas turbine processes and provide advantages such as improved thermal efficiency, for example. As used herein, “ash” refers to both the non-combustible components in the coal before combustion and the non-combustible byproducts resulting from combustion of the coal. An embodiment of the method for providing ultra clean coal is described below and illustrated in the flow diagram of FIG. 1. It should be understood that any system (e.g., gas turbine systems such as coal fired gas turbine systems, pulverized coal power plants, and integrated gasification combined cycle systems) may use the coal (e.g., ultra clean coal) provided by embodiments of the methods of the present disclosure.
FIG. 1 is a flow diagram illustrating an embodiment of the method 10 for removing at least one impurity from coal of the present disclosure. The method 10 includes providing coal comprising a plurality of impurities at step 12. Embodiments of method 10 may provide coal in the form of anthracite coal, bituminous coal, subbituminous coal, lignite coal, or combinations thereof In certain embodiments, the batches of coal treated by the method 10 are sufficient for a 24-hour feed to a turbine. In particular embodiments, the coal is provided in batches ranging from about 300 tons to about 10,00 tons in the reaction chamber. In other particular embodiments, the coal is provided in batches ranging from about 400 tons to about 600 tons in the reaction chamber. In still other particular embodiments, the coal is provided in batches ranging from about 400 tons to about 500 tons in the reaction chamber. It should be understood, however, that the amount of coal provided in batches may be scaled up or down depending on the use (e.g., different turbines, a different number of turbines, different uses such as converting coal to diesel, etc.)
In some embodiments, the impurities include, but are not limited to, oxides of aluminum, iron, potassium, calcium, sodium, and other metals, minerals, inorganic and organic sulfur compounds, alkalis, ash, or combinations thereof.
In certain embodiments, the impurities may be present in the coal in an amount ranging from about 2 wt. % to about 50 wt. %. In other embodiments, the impurities may be present in the coal in an amount ranging from about 3 wt. % to about 8 wt. %. In still other embodiments, the impurities may be present in the coal in an amount ranging from about 5 wt. % to about 7 wt. %.

TABLE 1

Examples of ranges of chemical composition for fly ash produced
from different coal types (expressed as percent by weight).

Component	Bituminous	Subbituminous	Lignite

SiO₂	20-60	40-60	15-45
Al₂O₃	5-35	20-30	10-25
Fe₂O₃	10-40	4-10	4-15
CaO	1-12	5-30	15-40
MgO	0-5	1-6	3-10
SO₃	0-4	0-2	0-10
Na₂O	0-4	0-2	0-6
K₂O	0-3	0-4	0-4
LOI	0-15	0-3	0-5

Source: http://www.tfhrc.gov

The method 10 also includes contacting the coal with an acid solution in a reaction chamber at the second step 14. At least one of the impurities reacts with the acid solution to produce one or more first products soluble in the acid solution. In some embodiments, the acid solution may include, but is not limited to, hydrofluoric acid solution, a nitric acid solution, a hydrochloric acid solution, a hydrofluorosilicic acid solution, a combination thereof, or other solutions of strong acids that dissolve oxides.
An example of an additional reaction of the nitrate solution 28 with at least one impurity is given below in Formula I.
SiO₂+4HF→SiF₄+2H₂O (I)
In certain embodiments, the acid solution has an acid concentration ranging from about 3 M to about 10 M. In other embodiments, the acid solution has an acid concentration ranging from about 3 M to about 6 M. In still other embodiments, the acid solution has an acid concentration ranging from about 4 M to about 6 M.
In particular embodiments, the weight ratio of acid solution to coal in step 14 ranges from about 10:1 to about 10:5. In other particular embodiments, the weight ratio of acid solution to coal in step 14 ranges from about 10:2 to about 10:4. In still other particular embodiments, the weight ratio of acid solution to coal in step 14 ranges from about 10:2.5 to about 10:3.5.
In certain embodiments, the acid solution comprises a hydrofluoric acid solution having a hydrofluoric acid concentration ranging from about 3 M to about 10 M. In other embodiments, the acid solution comprises a hydrofluoric acid solution having a hydrofluoric acid concentration ranging from about 3 M to about 6 M. In still other embodiments, the acid solution comprises a hydrofluoric acid solution having a hydrofluoric acid concentration ranging from about 4 M to about 6 M. In particular embodiments, the weight ratio of hydrofluoric acid solution to coal in step 14 ranges from about 10:1 to about 10:5. In other particular embodiments, the weight ratio of hydrofluoric acid solution to coal in step 14 ranges from about 10:2 to about 10:4. In still other particular embodiments, the weight ratio of hydrofluoric acid solution to coal in step 14 ranges from about 10:2.5 to about 10:3.5.
In particular embodiments, the second step 14 comprises contacting the coal with the acid solution for about 1 hour to about 10 hours. In other particular embodiments, the second step 14 comprises contacting the coal with the acid solution for about 3 hours to about 5 hours. In still other particular embodiments, the second step 14 comprises contacting the coal with the acid solution for about 4 hours to about 5 hours.
In particular embodiments, the second step 14 comprises contacting the coal with the acid solution at a temperature ranging from about 70° F. to about 200° F. In other particular embodiments, the second step 14 comprises contacting the coal with the acid solution at a temperature ranging from about 110° F. to about 170° F. In still other particular embodiments, the second step 14 comprises contacting the coal with the acid solution at a temperature ranging from about 140° F. to about 160° F.
In particular embodiments, the second step 14 comprises contacting the coal with the acid solution at a pressure ranging from about 14 psia to about 10 psia. In other particular embodiments, the second step 14 comprises contacting the coal with the acid solution at a pressure ranging from about 14 psia to about 42 psia. In still other particular embodiments, the second step 14 comprises contacting the coal with the acid solution at a pressure ranging from about 14 psia to about 20 psia.
In certain embodiments, the one or more first products comprises one or more fluorides, hydroxides, hydroxyfluorides, oxides, or combinations thereof. In embodiments where the first products comprise one or more fluorides, the fluorides may be selected from silicon fluoride, aluminum fluoride, iron fluoride, calcium fluoride, sodium fluoride, or combinations thereof.
The third step 16 of the method 10 comprises removing at least a portion of the acid solution including at least a portion of the first products from the reaction chamber. In particular embodiments, substantially all of the acid solution including substantially all of the first products may be removed from the reaction chamber in the third step 16.
In certain embodiments, the third step 16 may be carried out by opening a filter located proximate a bottom surface of the reaction chamber, thus allowing at least a portion of the acid solution including at least a portion of the first products to flow through the filter and out of the reaction chamber.
The fourth step 18 of the method 10 comprises adding a nitrate composition to the reaction chamber to form a nitrate solution such that at least one of the impurities, at least one of the first products, or combinations thereof react with the nitrate composition to produce one or more second products soluble in the nitrate solution. In certain embodiments, the nitrate composition comprises an aqueous nitrate solution, nitric acid, aluminum nitrate, ferric nitrate, fluoronitrate, other nitrates, hydroxide, hydroxyl fluoride, hydroxynitrate, ions thereof, or combinations thereof.
In some embodiments of the method, the one or more second products comprises nitrate ions, sulfate ions, iron ions, hydroxyfluorides, oxides, fluoro nitrates, or combinations thereof.
Examples of additional reactions of the nitrate solution 28 with at least one impurity are given below in Formula II and III.
FeS₂+14Fe(NO₃)₃+8H₂O→2SO₄ ²⁻+16H⁺+15Fe²⁺+42NO³⁻ (II)
SiF₄+2(Al,Fe)(NO₃)₃+2H₂O→SiO_2(s)+2(Al,Fe)F₂ ⁺+4H⁺+6NO₃ ⁻ (III)
In particular embodiments, the nitrate composition has a concentration ranging from about 0.1 M to about 5 M. In other particular embodiments, the nitrate composition has a concentration ranging from about 0.1 M to about 0.4 M. In still other particular embodiments, the nitrate composition has a concentration ranging from about 0.1 M to about 0.3 M.
In certain embodiments, the weight ratio of nitrate composition to coal in step 18 ranges from about 10:1 to about 10:5. In other embodiments, the weight ratio of nitrate composition to coal in step 18 ranges from about 10:2 to about 10:4. In still other embodiments, the weight ratio of nitrate composition to coal in step 18 ranges from about 10:2.5 to about 10:3.5.
In particular embodiments, the nitrate composition comprises a nitric acid solution having a nitric acid concentration ranging from about 0.1 M to about 5 M. In other particular embodiments, the nitrate composition comprises a nitric acid solution having a nitric acid concentration ranging from about 0.1 M to about 0.4 M. In still other particular embodiments, the nitrate composition comprises a nitric acid solution having a nitric acid concentration ranging from about 0.2 M to about 0.3 M. In certain embodiments, the weight ratio of nitric acid solution to coal in step 18 ranges from about 10:1 to about 10:5. In other embodiments, the weight ratio of nitric acid solution to coal in step 18 ranges from about 10:2 to about 10:4. In still other embodiments, the weight ratio of nitric acid solution to coal in step 18 ranges from about 10:2.5 to about 10:3.5.
According to certain embodiments of the present disclosure, the method 10 further comprises maintaining the nitrate solution in the reaction chamber for about 20 hours to about 30 hours. In other particular embodiments, method 10 further comprises, maintaining the nitrate solution in the reaction chamber for about 22 hours to about 26 hours.
In particular embodiments, the method 10 further comprises maintaining the nitrate solution in the reaction chamber at a temperature ranging from about 70° F. to about 190° F. In other particular embodiments, the method 10 further comprises maintaining the nitrate solution in the reaction chamber at a temperature ranging from about 150° F. to about 190° F. In still other particular embodiments, the method 10 further comprises maintaining the nitrate solution in the reaction chamber at a temperature ranging from about 140° F. to about 160° F.
In particular embodiments, the method 10 further comprises maintaining the nitrate solution in the reaction chamber at a pressure ranging from about 14.4 psia to about 100 psia. In other particular embodiments, the method 10 further comprises maintaining the nitrate solution in the reaction chamber at a pressure ranging from about 14.4 psia to about 43 psia. In still other particular embodiments, the method 10 further comprises maintaining the nitrate solution in the reaction chamber at a pressure ranging from about 14.4 psia to about 28 psia.
The fifth step 20 of the method 10 comprises removing at least a portion of the nitrate solution including at least a portion of the second products from the reaction chamber. In particular embodiments, substantially all of the nitrate solution including substantially all of the second products may be removed from the reaction chamber in the fifth step 20.
In certain embodiments, the fifth step 20 may be carried out by opening a filter located proximate a bottom surface of the reaction chamber, thus allowing at least a portion of the nitrate solution including at least a portion of the second products to flow through the filter and out of the reaction chamber.
After the fifth step 20, ash may be present in particular embodiments of the coal in an amount less than about 0.1% by weight. In certain embodiments of the method 10, after the fifth step 20, ash is present in the coal in an amount of about 0.1% by weight to about 1% by weight. In other embodiments of the method 10, after the fifth step 20, ash is present in the coal in an amount of about 0.1% by weight to about 0.3 % by weight.
In particular embodiments, the method further comprises agitating the acid solution in the reaction chamber, agitating the nitrate solution in the reaction chamber, or both. In some embodiments, the method 10 also comprises, after the fifth step 20, water washing the coal.
By processing coal in one reaction chamber in a “batch” process to remove at least one impurity from coal, multiple reactors, multiple filters, and conveying equipment (e.g., pumps and conveyer belts) may be eliminated and costs and space requirements may be reduced. In addition, exposure of coal outside of the reactor is reduced. In particular, one reaction chamber may be used to react both the first leaching solution with the coal and the second leaching solution with the coal. Thus, reducing coal losses and avoiding hazards associated with transfer of chemicals is realized.
It should be apparent that the foregoing relates only to the preferred embodiments of the present application and that numerous changes and modifications may be made herein by one of ordinary skill in the art without departing from the generally spirit and scope of the invention as defined by the following claims and the equivalents thereof.

Claims

1. A method for removing at least one impurity from coal, the method comprising:

providing coal comprising a plurality of impurities;

contacting the coal with an acid solution in a reaction chamber, wherein at least one of the impurities reacts with the acid solution to produce one or more first products soluble in the acid solution;

removing at least a portion of the acid solution including at least a portion of the one or more first products from the reaction chamber;

adding a nitrate composition to the reaction chamber to form a nitrate solution, wherein at least one of the impurities, at least one of the first products, or combinations thereof react with the nitrate composition to produce one or more second products soluble in the nitrate solution; and

removing at least a portion of the nitrate solution including at least a portion of the one or more second products from the reaction chamber.

2. The method of claim 1, wherein the acid solution comprises a hydrofluoric acid solution, a nitric acid solution, a hydrochloric acid solution, a hydrofluorosilicic acid solution, or combinations thereof.

3. The method of claim 1, wherein the acid solution comprises a hydrofluoric acid solution having a hydrofluoric acid concentration of about 3 M to about 10 M.

4. The method of claim 1, wherein the acid solution comprises a hydrofluoric acid solution, and wherein a weight ratio of hydrofluoric acid solution to coal in the step of contacting is about 10:1 to about 10:5.

5. The method of claim 1, wherein the one or more first products comprises one or more fluorides, hydroxides, hydroxyfluorides, oxides, or combinations thereof.

6. The method of claim 5, wherein the one or more first products comprises one or more fluorides selected from the group consisting of silicon fluoride, aluminum fluoride, iron fluoride, calcium fluoride, sodium fluoride, and combinations thereof.

7. The method of claim 1, wherein the step of contacting comprises contacting the coal with the acid solution for about 1 hour to about 10 hours.

8. The method of claim 1, wherein the step of contacting comprises contacting the coal with the acid solution at a temperature ranging from about 70° F. to about 200° F.

9. The method of claim 1, wherein the nitrate composition comprises nitric acid, ferric nitrate, fluoronitrate, hydroxide, hydroxyl fluoride, hydroxynitrate, ions thereof, or combinations thereof.

10. The method of claim 1, wherein the nitrate composition comprises a nitric acid solution having a nitric acid concentration of about 0.1 M to about 5 M.

11. The method of claim 1, wherein the nitrate composition comprises a nitric acid solution, and wherein the weight ratio of nitric acid solution to coal in the step of adding is about 10:1 to about 10:5.

12. The method of claim 1, wherein the one or more second products comprises nitrate ions, sulfate ions, iron ions, hydroxyfluorides, oxides, fluoro nitrates, or combinations thereof.

13. The method of claim 1, further comprising, before the step of removing the nitrate solution, maintaining the nitrate solution in the reaction chamber for about 20 hours to about 30 hours.

14. The method of claim 1, further comprising, before the step of removing the nitrate solution, maintaining the nitrate solution in the reaction chamber at a temperature ranging from about 70° F. to about 190° F.

15. The method of claim of 1, wherein the plurality of impurities comprise oxides of aluminum, iron, potassium, calcium, sodium, minerals, inorganic and organic sulfur compounds, alkalis, ash, or combinations thereof.

16. The method of claim 1, wherein, after the step of removing the nitrate solution, ash is present in the coal in an amount less than about 0.1% by weight.

17. The method of claim 1, wherein, after the step of removing the nitrate solution, ash is present in the coal in an amount of about 0.1% by weight to about 1% by weight.

18. The method of claim 1, further comprising agitating the acid solution in the reaction chamber, agitating the nitrate solution in the reaction chamber, or both.

19. The method of claim 1, further comprising, after the step of removing the nitrate solution, water washing the coal.

20. The method of claim 1, wherein the coal is provided in batches of about 300 tons to about 10,000 tons in the reaction chamber.