Patent Application
20110030270
This disclosure generally relates to methods for removing impurities from coal, and more particularly relates to methods for removing impurities from coal which include neutralization of a leaching solution.
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 a first leaching solution such as hydrofluoric acid (“HF”) 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 a second leaching solution such as a nitrate solution 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.
Typically, the moles of HF required for the first reaction are significantly lower than the moles of HF used. Thus, the unreacted HF remains in the liquid and may even remain in the coal (e.g., in the areas of pre-existing moisture and in etched pores in the coal created from the HF reacting with ash impurities) after the coal is filtered.
HF is known to be extremely toxic and to corrode glass. HF typically has an occupational exposure level of 2 ppm. The PPO's needed include rubber gloves, face mask or safety glasses, apron, and good ventilation. If HF is inhaled or ingested, the result may be fatal. HF is readily absorbed through the skin and skin contact may also be fatal. HF also acts as a systemic poison, causes severe burns, and is a possible mutigen. In addition, the reaction with HF may be delayed. Thus, any contact with HF, even if minor, requires immediate medical attention.
This disclosure provides a method for removing at least one impurity from coal. The method comprises providing coal having a plurality of impurities and contacting the coal with a first leaching solution. The first leaching solution reacts with at least one of the impurities to produce one or more first products soluble in the first leaching solution. The method further comprises adding a neutralizing composition to the first leaching solution. The neutralizing composition reacts with the first leaching solution to form a precipitate. The method further comprises separating at least a portion of the first leaching solution from the coal and the precipitate and contacting the coal and the precipitate with a second leaching solution. The second leaching solution reacts with at least one of the impurities and the precipitate to form one or more second products and one or more third products, respectively, the second products and the third products being soluble in the second leaching solution. The method further comprises separating at least a portion of the second leaching solution from the coal.
The present disclosure also provides another method for removing at least one impurity from coal. The method comprises providing coal having a plurality of impurities and contacting the coal with a first leaching solution. The first leaching solution reacts with at least one of the impurities to produce one or more first products soluble in the first leaching solution. The method further comprises separating at least a portion of the first leaching solution from the coal as an unreacted first leaching solution. The method further comprises adding a neutralizing composition to the unreacted first leaching solution. The neutralizing composition reacts with the unreacted first leaching solution to form a precipitate. The method further comprises separating at least a portion of the unreacted first leaching solution from the precipitate and contacting the coal and the precipitate with a second leaching solution. The second leaching solution reacts with at least one of the impurities and the precipitate to form one or more second products and one or more third products, respectively, the second products and the third products being soluble in the second leaching solution. The method further comprises separating at least a portion of the second leaching solution from the coal.
Other aspects, features, and advantages of this invention will be apparent from the following detailed description, drawings, and claims.
As summarized above, this disclosure encompasses methods for removing at least one impurity from coal. Thus, the method of the present disclosure may be used to produce ultra clean coal. As used herein, the term “ultra clean coal” refers to coal having a reduced ash content (e.g., below about 0.2%) 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. Embodiments of the method for removing at least one impurity from coal are described below and illustrated in
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 12 in an amount ranging from about 2 wt. % to about 50 wt. %. In other embodiments, the impurities may be present in the coal 12 in an amount ranging from about 3 wt. % to about 8 wt. %. In still other embodiments, the impurities may be present in the coal 12 in an amount ranging from about 5 wt. % to about 7 wt. %.
The method 10 contacts the coal 12 with a first leaching solution 14 in a first reactor 16. At least one of the impurities reacts with the first leaching solution 14 to produce one or more first products soluble in the first leaching solution. In certain embodiments, the first leaching solution 14 may comprise an acid solution. In some embodiments, the first leaching solution 14 may include, but is not limited to, first reactants such as a hydrofluoric acid, a nitric acid, a hydrochloric acid, a hydrofluorosilicic acid, a combination thereof, or other strong acids that dissolve oxides.
An example of a reaction of the first leaching solution 14 with at least one impurity is given below in Formula (I):
SiO2+4HF→SiF4+2H2O (I).
In certain embodiments, the first leaching solution 14 has a first reactant concentration ranging from about 3 M to about 10 M. In other embodiments, the first leaching solution 14 has a first reactant concentration ranging from about 3 M to about 6 M. In still other embodiments, the first leaching solution 14 has a first reactant concentration ranging from about 4 M to about 6 M.
In particular embodiments, the weight ratio of first leaching solution 14 to coal 12 added to the first reactor 16 ranges from about 10:1 to about 10:5. Unless otherwise indicated, all ratios are weight to weight ratios. In other particular embodiments, the weight ratio of first leaching solution 14 to coal 12 added to the first reactor 16 ranges from about 10:2 to about 10:4. In still other particular embodiments, the weight ratio of first leaching solution 14 to coal 12 added to the first reactor 16 ranges from about 10:2.5 to about 10:3.5.
In certain embodiments, the first leaching solution 14 comprises a hydrofluoric acid solution having a hydrofluoric acid concentration ranging from about 3 M to about 10 M. In other embodiments, the first leaching solution 14 comprises a hydrofluoric acid solution having a hydrofluoric acid concentration ranging from about 3 M to about 6 M. In still other embodiments, the first leaching solution 14 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 14 to coal 12 added to the first reactor 16 ranges from about 10:1 to about 10:5. In other particular embodiments, the weight ratio of hydrofluoric acid solution 14 to coal 12 added to the first reactor 16 ranges from about 10:2 to about 10:4. In still other particular embodiments, the weight ratio of hydrofluoric acid solution 14 to coal 12 added to the first reactor 16 ranges from about 10:2.5 to about 10:3.5.
In particular embodiments, the coal 12 is in contact with the first leaching solution 14 for about 1 hours to about 10 hours in the first reactor 16. In other particular embodiments, the coal 12 is in contact with the first leaching solution 14 for about 3 hours to about 5 hours in the first reactor 16. In still other particular embodiments, the coal 12 is in contact with the first leaching solution 14 for about 4 hours to about 5 hours in the first reactor 16.
In particular embodiments, the coal 12 is in contact with the first leaching solution 14 at a temperature ranging from about 70° F. to about 200° F. in the first reactor 16. In other particular embodiments, the coal 12 is in contact with the first leaching solution 14 at a temperature ranging from about 110° F. to about 170° F. in the first reactor 16. In still other particular embodiments, the coal 12 is in contact with the first leaching solution 14 at a temperature ranging from about 140° F. to about 160° F. in the first reactor 16.
In particular embodiments, the coal 12 is in contact with the first leaching solution 14 at a pressure ranging from about 14 psia to about 1000 psia in the first reactor 16. In other particular embodiments, the coal 12 is in contact with the first leaching solution 14 at a pressure ranging from about 14 psia to about 42 psia in the first reactor 16. In still other particular embodiments, the coal 12 is in contact with the first leaching solution 14 at a pressure ranging from about 14 psia to about 20 psia in the first reactor 16.
In certain embodiments, the one or more first products comprises one or more fluorides, hydroxyl fluorides, hydroxides, 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, potassium fluoride, or combinations thereof.
The method 10 further comprises adding a neutralizing composition 18 to the first leaching solution 14 such that neutralizing composition reacts with the first leaching solution to form a precipitate. By adding the neutralizing composition 18 to the first leaching solution 14, any unreacted first reactant (i.e. excess first reactant that has not reacted with at least one of the impurities) in the first leaching solution is neutralized.
In some embodiments, the neutralizing composition 18 comprises a neutralizing reactant including a calcium hydroxide, sodium hydroxide, any other alkali, or combinations thereof. In certain embodiments, the first leaching solution comprises a hydrofluoric acid solution, the neutralizing composition comprises calcium hydroxide, the precipitate comprises a calcium fluoride, and the one or more third products comprise calcium ions, nitrate ions, or combinations thereof.
In certain embodiments, the neutralizing composition 18 is added to the first leaching solution 14 after the coal 12 has been in contact with the first leaching solution for about 1 hours to about 10 hours in the first reactor 16. In other particular embodiments, the neutralizing composition 18 is added to the first leaching solution 14 after the coal 12 has been in contact with the first leaching solution for about 3 hours to about 5 hours in the first reactor 16. In still other particular embodiments, the neutralizing composition 18 is added to the first leaching solution 14 after the coal 12 has been in contact with the first leaching solution for about 4 hours to about 5 hours in the first reactor 16.
In certain embodiments, the neutralizing composition 18 has a neutralizing reactant concentration ranging from about 1 M to about 10 M. In other embodiments, the neutralizing composition 18 has a neutralizing reactant concentration ranging from about 1 M to about 4 M. In still other embodiments, the neutralizing composition 18 has a neutralizing reactant concentration ranging from about 2 M to about 3 M.
The method 10 further comprises separating at least a portion of the first leaching solution 14 from the coal 12 and the precipitate. By separating at least a portion of the first leaching solution 14 from the coal 12, at least a portion of the first products are also separated from the coal because they are soluble in the first leaching solution. Thus, in particular embodiments, substantially all of the first leaching solution 14 including substantially all of the first products may be separated from the coal 12 and the precipitate. In the method 10 illustrated in
The wet coal 26 is then fed to a second reactor 30 where the coal 12 and the precipitate are contacted with a second leaching solution 28. The second leaching solution 28 reacts with at least one of the impurities and the precipitate to form one or more second products and one or more third products, respectively. The second products and the third products are soluble in the second leaching solution 28. In certain embodiments, the second leaching solution 28 may comprise a nitrate solution.
Examples of reactions of the second leaching solution 28 with at least one impurity are given below in Formulas (II) and (III):
FeS2+14Fe(NO3)3+8H2O→2SO42−+16H++15Fe2++42NO3− (II)
SiF4+2(Al,Fe)(NO3)3+2H2O→SiO2(s)+2(Al,Fe)F2++4H++6NO3− (III).
In certain embodiments, the second leaching solution 28 comprises a second reactant including, but not limited to 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, fluoronitrate, or combinations thereof. In particular embodiments, the one or more third products comprise calcium ions or combination thereof.
In particular embodiments, the second leaching solution 28 has a second reactant concentration ranging from about 0.1 M to about 5 M. In other particular embodiments, the second leaching solution 28 has a second reactant concentration ranging from about 0.1 M to about 0.4 M. In still other particular embodiments, the second leaching solution 28 has a second reactant concentration ranging from about 0.3 M to about 0.4 M.
In certain embodiments, the weight ratio of second leaching solution 28 to wet coal 26 added to the second reactor 30 ranges from about 10:1 to about 10:5. In other embodiments, the weight ratio of second leaching solution 28 to wet coal 26 added to the second reactor 30 ranges from about 10:2 to about 10:4. In still other embodiments, the weight ratio of second leaching solution 28 to wet coal 26 added to the second reactant reactor 30 ranges from about 10:2.5 to about 10:3.5.
In particular embodiments, the second leaching solution 28 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 second leaching solution 28 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 second leaching solution 28 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 28 to wet coal 26 added to the second reactor 30 ranges from about 10:1 to about 10:5. In other embodiments, the weight ratio of nitric acid solution 28 to wet coal 26 added to the second reactor 30 ranges from about 10:2 to about 10:4. In still other embodiments, the weight ratio of nitric acid solution to 28 to wet coal 26 added to the second reactor 30 ranges from about 10:2.5 to about 10:3.5.
According to certain embodiments of the present disclosure, the second leaching solution 28 is in contact with the coal and the precipitate for about 20 hours to about 30 hours in the second reactor 30. In other particular embodiments, the second leaching solution 28 is in contact with the coal and the precipitate for about 22 hours to about 26 hours in the second reactor 30.
In particular embodiments, the second leaching solution 28 is in contact with the coal and precipitate at a temperature ranging from about 70° F. to about 190° F. in the second reactor 30. In other particular embodiments, the second leaching solution 28 is in contact with the coal and precipitate at a temperature ranging from about 150° F. to about 1.90° F. in the second reactor 30. In still other particular embodiments, the second leaching solution 28 is in contact with the coal and precipitate at a temperature ranging from about 140° F. to about 160° F. in the second reactor 30.
In particular embodiments, the second leaching solution 28 is in contact with the coal and precipitate at a pressure ranging from about 14.4 psia to about 100 psia in the second reactor 30. In other particular embodiments, the second leaching solution 28 is in contact with the coal and precipitate at a pressure ranging from about 14.4 psia to about 43 psia in the second reactor 30. In still other particular embodiments, the second leaching solution 28 is in contact with the coal and precipitate at a pressure ranging from about 14.4 psia to about 28 psia in the second reactor 30.
The method 10 further comprises separating at least a portion of the second leaching solution 28 from the coal. By separating at least a portion of the second leaching solution 28 from the coal, at least a portion of the second products and at least a portion of the third products are also separated from the coal because they are soluble in the second leaching solution. Thus, in particular embodiments, substantially all of the second leaching solution 28 including substantially all of the second products and substantially all of the third products may be separated from the coal. In the method 10 illustrated in
The method 10 may further comprise washing the wet coal 38 with water in a water wash apparatus 40 to remove any residual reactants or products from the coal. The water-washed coal 42 may be transferred to a coal dryer (not shown) over a conveyer belt (not shown), which will further act as a filter to remove water from the coal.
Ash may be present in particular embodiments of the water-washed coal 42 in an amount less than about 0.2% by weight. In certain embodiments of the method 10, ash is present in the water-washed coal 42 in an amount ranging from about 0.01% by weight to about 0.5% by weight. In other embodiments of the method 10, ash is present in the water-washed coal 42 in an amount ranging from about 0.01% by weight to about. 0.2% by weight.
In particular embodiments, the method further comprises agitating the first leaching solution in the first reactor, agitating the second leaching solution in the second reactor, or both.
As illustrated in
At least a portion of the unreacted first leaching solution 54 is separated by a filter apparatus 58 from the precipitate 60 as a neutralized first leaching solution 62. The precipitate 60 is then contacted with the second leaching solution 28 in the nitrate reactor, along with the wet coal 56. The second leaching solution 28 reacts with at least one of the impurities and the precipitate 60 to form one or more second products and one or more third products, respectively. The second products and the third products are soluble in the second leaching solution 28.
In alternate embodiments (not shown), the methods may be carried out in one reaction chamber in a batch process to avoid using multiple reactors, multiple filters, and conveying equipment (e.g., pumps and conveyer belts) an associated costs and space requirements. In addition, exposure of coal outside of the reactor is reduced, thus h
By adding a neutralizing composition to the first leaching solution either in the first reactor or into an unreacted first leaching solution separated from the coal and then contacting the produced precipitate with the second leaching solution, excess unreacted reactant, such as hydrofluoric acid, is reduced or eliminated from the remainder of the process and the resulting coal. Thus, the potential for exposure to hazardous chemicals, such as hydrofluoric acid or other acids used, as it is neutralized rather than transported to the second reactor along with the coal. In addition, the reactors volumes may be lower and the process can be carried out in a continuous manner instead of in a batch or semi-batch process.
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.
