WO1982002404A1

WO1982002404A1 - Removing sulfur and beneficiating coal

Info

Publication number: WO1982002404A1
Application number: PCT/US1982/000014
Authority: WO
Inventors: Co S Low; Anthony J Chinnici; Michael C Jaskowski
Original assignee: Co S Low
Priority date: 1981-01-08
Filing date: 1982-01-07
Publication date: 1982-07-22
Also published as: AU8145782A; EP0069148A1

Abstract

Processes for decreasing the sulfur content of coal and facilitating economic removal of sulfur contaminant from the treated coal. Desulfurization is undertaken by oxidizing sulfur values of coal under ambient conditions of temperature and pressure to produce sulfates. The sulfates are removed from the coal by chemical reaction while producing commercially usable by-products. Treatment in accordance with the invention also provides an increase in BTU content and a decrease in ash content of low-quality coal.

Description

REMOVING SULFUR AND BENEFICIATING COAL

This invention relates to decreasing the sulfur content of coal and facilitating removal of sulfur contaminant in preparing coal for combustion.

Many coals contain quantities of sulfur which generate unacceptable amounts of sulfur oxide upon burning.

Accordingly, technologies have developed for extracting sulfur bound within the coal. However, in order to reduce pollutants upon burning,- sulfur values must not only be extracted from the coal- but, in addition, the sulfur contaminant must be removed from the end product for burning.

Depending on the specific coal, the sulfur content may be bound in inorganic and/or organic sulfur compounds. Analysis of coals from Appalachia and the Eastern interior States reveals these coals to be rich in pyrite, an inorganic sulfur compound, as well as organic sulfur. In these coals, pyritic sulfur can range from about 25% to about 70% of the total sulfur content.

Prior art desulfurization technologies have generally concentrated on either the organic sulfur or inorganic sulfur compounds to the substantial exclusion of the other. Also, prior art desulfurization processes generally require elevated temperatures and pressures,- and, extended treatment times. The present invention substantially decreases both inorganic and organic sulfur content of coals. Further, that result is achieved in economically short treatment times by oxidizing sulfur values found in coals under ambient conditions of temperature and pressure. The sulfur values are converted to sulfates and, in accordance with an additional aspect of the invention, such sulfates are subjected to additional chemical reactions which facilitate removal of sulfur contaminants while producing useful by-products.

O PI In addition, the teachings of the invention significantly reduce the overall water volumes required when compared, for example, to desulfurization processes which convert the sulfur values of coal into compounds which must be dislodged from the desulfurized coal. In the present invention, desulfurization is facilitated by comminuting the coal to increase the surface area and, in turn, to increase the sulfur values available for reaction. Generally, coal can be ground to particle sizes ranging to about two hundred (200) mesh (U.S. screen) but, preferably, is ground to have maximum particle sizes from about thirty (30) to about sixty (60) mesh.

Sulfur values of the coal are oxidized to sulfates by treating the comminuted coal under ambient conditions of temperature and pressure with nascent oxygen. While heat can be generated in the process, reference herein to ambient conditions of temperature and pressure means without requiring external application of heat or external application of pressure. The source of nascent oxygen can be hydrogen peroxide, ozone, or mixtures of hydrogen peroxide and ozone.

During the oxidizing step, and in subsequent steps of the process, the coal is thoroughly wetted with water to facilitate functioning of the oxidizing agent within internal pores of the coal as well as on the surface of the coal. Another advantage is that the sulfate (SO,) ions are produced in solution in the water used to wet the coal and, are more readily subject to further reaction steps which contribute significantly to advantages of the invention. Also, the water helps to eliminate or diminish fire or explosion hazards.

Various stoichiometric equations are representative in the conversion of FeS- by H O or ozone into FeSO

2 2 2 4 depending upon the stage of oxidation of the iron ion (Fe++), such as FeO, Fe₂°3' ^pe O^ °^" Fe⁽OH^{) ;} e.g. 17(0) + FeS₂ > FeS0₄ + FeO + 3(S0₄)~

FeS 2- + 3.5 02_o + H2_0 FeSO4. + H2_SO4.

The oxidizing agent used in the oxidizing step supplies at least that amount of oxygen contained in the sulfate resulting from the stoichiometric oxidation of sulfur values of the coal being treated. Both dilute (as low as 3%) and high concentration (30%) hydrogen peroxide (H₂0₂) water solutions can be used, but, high concentrations are preferred when^'H₂0- is the primary source of nascent oxygen.

In a specific embodiment, dilute hydrogen peroxide is used to wet the coal and ozone (0₃) is used as the primary source of nascent oxygen. The water-wetted coal is treated in a reaction chamber into which the ozone is introduced; in a batch process, the ozone is continuously flowed through the reaction chamber; in a continuous process the coal is moved through the chamber. The flow rate of ozone is based on stoichiometric requirements. The sulfates resulting from the oxidation step are reacted with calcium hydroxide which can be provided as agricultural lime (about 71% CaO) or hydrated lime.^' The amount of calcium hydroxide is at least equal to, but preferably in excess of, the stoichiometric quantity required to insure complete reaction of the total sulfate produced. Preferably, for ease of lime addition and efficiency, the lime is added so as to be mixed with the comminuted coal or is^' communited with the coal. Reaction of the calcium hydroxide with the sulfates (in solution) results in the formation of calcium sulfate (CaS0₄). The following equation is representative of the neutralization occurring in the presence of Ca(OH)₂:

FeS0₄ + H₂S0₄ + 2Ca(OH₂) 2H₂0 + Fe(OH)₂ + 2CaS0₄

An important_, aspect of the invention involves chemically removing the oxidized sulfur values from the treated coal in a manner which avoids the dislodgement problems of the prior art. The sulfates produced upon

OMPI

' ^lPO oxidation react with the calcium hydroxide to produce calcium sulfate. Then, in a specific embodiment of the invention, the calcuim sulfate is reacted (in solution) with ammoniom hydroxide to regenerate the calcium hydroxide and to produce ammoniom sulfate, both of which can be readily isolated and usefully employed.

The reaction of calcium sulfate with ammonium hydroxide results in regeneration of Ca(OH)- which can be recycled in the process. A further significant contribution of the invention is that the undesired sulfur value of the coal is converted to ammonium sulfate which is commercially usable as a fertilizer.

The reaction equation for the ammonical treatment using ammonium hydroxide is represented as follows: 2C3S0, + 4NH-OH > 2(NH,) S0_y, + 2Ca(OH

4 4 4 2 4 2

Reaction of the ammonium hydroxide with the calcium sulfate may be undertaken in various ways but, preferably, the coal containing the calcium sulfate is subjected to a continuous spray of a dilute aqueous solution of ammonium hydroxide; for instance, a 2% solution of ammonium hydroxide. The amount of ammonium hydroxide used is generally at least equal to, but preferably in excess of, the calculated stoichiometric amount based on the sulfur values of the coal. The relatively insoluble calcium hydroxide (.077 grams/100ml. in hot water (100°C.)) is rinsed from the coal and separated as a precipitate which facilitates recovery of the ammonium sulfate solution. The coal is then ready for end product usage or can be dried for such usage. Results of a series of test runs employing hydrogen peroxide as the source of nascent oxygen are set forth in Table 1 and the results of test runs in which ozone is used as the source of nascent oxygen are set forth in Table 2. For both series, the wetted coal was ground in the presence of the Ca(OH)-. Note that, in certain test runs of Table 2, the coal, as indicated, was ground to a 1x0 size, which

OMPI is a standard used in the coal industry meaning one inch and smaller particles which will pass through one-inch screening.

In the series of both Tables 1 and 2, the weight ratio of Ca(OH)₂ to coal was 1:2, well over the stoichiometric amounts required to insure complete reaction of all sulfate ions with calcium ions. In both tests, a 2% ammonium hydroxide water solution was used to free the coal of the calcium sulfate; the amount of ammonium hydroxide used was in slight excess of the calculated stoichiometric amount, based on the original sulfur values of the unoxidized coal.

TABLE 1

SAMPLE Coal Ca(OH)₂ Hydrogen Sulfur

(gms) (gms) Peroxide Conten (gms) (%)

Ellwood City

Channel Cut ("C")

C-l (as is) 100 2.75

C-2 (3% H₂θ2) 100 50 50 2.46

C-3 (30% H2θ ) 100 50 50 1.23

C-4 (3% H₂0₂) 100 50 50 2.52

C-5 (30% H₂0₂) 100 50 50 1.25

C-6 (as is) 2.75

C-7 (3% H₂0₂) 100 50 50 2.60

C-8 (30% H₂0₂) 100 50 50 1.21

C-9 (as is) 2.86

New Kensington ^'

Stock ("B")

B-l (30% H₂0₂) 25 12 4 2.74

*B-2 (30% H₂0 ) 25 12 4 2.65

*B-3 (30% H₂0₂) 50 25 50 2.22

*B-4 (30% H 0₂) 50 25 50 2.39

B-5 (as is) 3.20

*B-6 (30% H₂0₂) 100 50 50 2.40

*B-7 (30% H₂0₂) 100 50 100 1.91

*NH₄θH rinse

The results of Table 1 indicate that increased concentrations of the H₂0₂ (C-3, C-5, and C-8) and increasing hydrogen peroxide (B-4, B-5, B-6, and B-7) result in more efficient oxidation of sulfur values contained in the coal. TABLE 2

SAMPLE Coal Sample Exposure time to Sulfur

Particle Wt. Ca(OH) Ozone at cone, of Conten Size (gms) (gms) 0.000009 gms/cm/min (%) or 0.00053#/ft/min (min)

Kensington Stock ("B")

B (as is) 30- -60 mesh 40 20 0 3 .20

B-0-5 π π R 5 1 .84

B-0-10 π R R 10 1 .76

B-0-15 R π H 15 2 .03

B-0-30 R H R 30 1 .95

B-0-45 R R R 45 2 .18

B-0-60 n R H 60 2, .41

B (as is) 1x0 53.3 26.7 0 3. ,45

BO-10-5 n R A 5 1. .28

BO-10-10 π R R 10 1. ,37

BO-10-15 R π R 15 1. ,64

BO-10-30 π R R 30 1. 32

BO-10-45 n H R 45 1. ,38

BO-10-60 R H H 60 2. ,98

The runs of Table 2 were conducted in a reaction chamber equipped with a gas (ozone) inlet tube and gas outlet. The reaction chamber was provided with a rack for perforated containers suitable for batch treatment of coal samples. Ozone was generated by a Griffin Ozone Generator Unit GTC-35 (modified with a diluting chamber) at a rate of 80 lb. ozone/day at 35 CFM. Because a dry ozone-air mixture was employed in the series of tests in Table 2, it was necessary to periodically re-wet the coal samples.

Using a laboratory generator in the runs of Table 2, the ozone concentration was only 0.000009 gms/cm /min. or

3 0.00053 lb/ft /min. Higher concentrations cause greater initial sulfur reductions reducing reaction time. In the series presented, optimum time exposures of coal samples to ozone entended to about 10 minutes. During such time interval with the above ozone concentration, the sulfur content of coal ground to 30x60 mesh was reduced from 3.20% to 1.76% while the sulfur content of coal crushed to 1x0

O PI

, s_λr VIPO A size was reduced from 3.45% to 1.28%. Exposure times exceeding 10 minutes did not significantly increase the amount of sulfur oxidized by the ozone. This effect, especially in batch processing, is deemed to be atributable to accumulation of the calcium sulfate which is formed within the first 10 minutes of ozone oxidation. Treatment times can be further decreased, e.g. to about 5 minutes, by increased concentrations of ozone.

Teachings of the invention are applicable to coals from any geographic region because the process results in the oxidation of sulfur values whether present as organic sulfur or inorganic sulfur compounds. Furthermore, it has been discovered that, as a result of the process of the invention, low-quality coals (high sulfur and ash contents) can be beneficiated by decreasing ash contents and increasing BTU levels. "Compliance coals" under most Federal and State regulatory agencies would require no more than about 1-1/2% sulfur; ash content is part of a disposal problem for a user. The increase in BTU level is deemed attributable to the oxidation of carbonaceous matter contained in the untreated low-quality coal. Such carbonaceous matter (referred to as bony material) is not readily combustible in ordinary burning of coal. The oxidation provided produces hydrocarbons which are readily combustible, providing additional fuel, and increases the overall BTU level of the treated coal. As noted in the following Examples A-H, in addition to increasing BTU level the ash content is decreased. In all the following examples, the sulfur content is substantially reduced. All percentages in Examples A-H are based on the weight of the coal sample; all analytical results are based on the "dry" basis sampling and BTU values are corrected for sulfur oxidation. Examples A-C

In Examples A-C, the following general procedure was employed:

Dry coal of 30. to 60 mesh or 1 x 0 was weighed out. The coal was then moistened with a 0.01% wetting agent solution, using commercially available wetting agent, and with a 6% solution of hydrogen peroxide. The coal was blended for two minutes with calcium hydroxide (300 grams of coal to about 25 grams of agricultural lime). Fifty (50) gram samples were placed in a reaction chamber in communication with a laboratory ozone generator (as described above in connection with the runs of Table 2 for various time intervals.; the output of the ozone generator

3 was 0.00053 lbs/ft /min. The reacted coal samples were washed and filtered four times with .200 ml. of 2% H₄OH solution, and then spray washed with about 200 ml. of a 2% to 4% NH₄C1 solution, which has a passivating effect in helping to inhibit reabsorption of organic materials. The coal samples were dried and ground to desired mesh for ensuing analytical procedures.

In Example A, a southwestern Pennsylvania coal, labeled "T" in the chart immediately following, with a 10.2% moisture content (as received) was subjected to the foregoing conditions with the following results: Minutes exposed BTU*s

Sample to ozone Sulfur (%) Ash(%) (corrected)

T-0 none (as received) 2.94 23.6 10,980

T-3 3 minutes 1.18 19.4 11,582

T-5 5 minutes 1.15 20.6 11,106

T-7 7 minutes 1.25 18.7 11,488

In Example B, a northern West Virginia coal with 6.3% moisture content, labeled "K" in the following chart, was subjected to the foregoing conditions with the following results: Minutes exposed BTϋ's

Sample to ozone Sulfur(%) Ash(%) (corrected)

K-0 none (as received) 3.04 16.4 12,604

K-3 3 minutes 2.59 16.0 12,595

K-5 5 minutes 1.32 16.7 - 12,706

K-7 7 minutes 1.69 16.2 12,914

K-10 10 minutes 1.99 16.8 12,634 In Example C, another sample of southwestern

Pennsylvania ("T" from Example A above) coal, designated

"TA" below, was subjected to the foregoing process conditions with the following results:

Minutes exposed BTU's

Sample to ozone Sulfur(%) Ash(%) (corrected)

TA-0 none (as received) 2.92 28.0 10,500

TA-1 1 minute 1.78 — —

TA-3 3 minutes 1.68 — — ^>

TA-5 5 minutes 0.99 18.0 11,980

TA-7 7 minutes 1.78 — —

TA-10 10 minutes 1.88 — —

TA-15 15 minutes 1.96 — —

Examples D and E

In Example D, southwestern Pennsylvania ("T" from Example A) coal, designated "TB" below, was treated under slightly different conditions than those of the preceding examples. One hundred grams of dry coal were pretreated with a wetting agent solution and 6% hydrogen peroxide. Then the wetted coal was blended with 5 grams of commercially available agricultural lime for two minutes. The sample was then subjected to reaction with 50 grams of 30% H₂0₂ for five minutes. The reacted coal samples were washed and filtered with 100 ml. of 2% NH₄OH. The coal was washed with about 100 ml. of water followed by a washing with 200 ml. of carbonic acid (saturated C0₂ solution) which has a passivating effect in inhibit reabsorption of organic materials. The sample was dried and ground to desired mesh for analysis of sulfur and

BTU values:

BTU values Sample "TB" Sulfur (%) (corrected) as received and dried 3.66 13,053

H₂0₂-treated 1.56 15,483

In Example E, 100 grams of the same southwestern Pennsylvania ("T" from Example A) coal, designated "TC" below, were pretreated as in Example D. Then 50 grams of

30% NH4.OH was blended with the coal for two minutes. The sample was then allowed to react with 50 grams of 30%

H₂0₂ for five minutes. After such reaction, the coal was washed with 100 ml. of water and then with 200 ml. of carbonic acid. The sample was ground for analysis of sulfur and BTU values:

BTU values Sample "TC" Sulfur (%) ^' (corrected) as received and dried 3.58 12,893

NH₄OH-treated 1.68 14,988

Examples F and G

In Example F, 100 grams of another southwestern Pennsylvania coal, designated "EC", were preteated as in the preceding Examples D a d E, followed by a step of blending with 50 grams of commercially available agricultural lime for two minutes. Then, the coal sample was allowed to react with 50 grams of 30% H₂0₂ for five minutes. The coal was then washed with 200 ml. of 2% NH₄OH and dried and prepared for analysis of sulfur content as in Examples D and E:

Sample "EC" Sulfur (%) as received and dried 2.75. hydrogen peroxide-treated 1.23 In Example G, another southwestern Pennsylvania coal, designated "ECA", was subjected to the same procedure as that followed in Example F, except that a further wash for the treated coal sample consisted of 200 ml. of water: Sample "ECA" Sulfer (%) as received and dried 2.86

^H2°2^{~treate ~}"^~*

Example H

In Example H, a northern West Virginia coal, labeled "K-l", with a 6.7% moisture, as received, was treated as follows: 100 grams of coal were weighed and pretreated with wetting agent and 6% hydrogen peroxide solutions, and 5 grams of reagent grade calcium hydroxide were blended for two minutes with the coal. The sample was then reacted with 50 grams of 30% hydrogen peroxide for three minutes. The reacted coal sample was washed with about 100 ml. of water. The coal sample was reacted again with an additional 50 grams of 15% hydrogen peroxide solution for three minutes. The reacted coal sample was washed and filtered with 100 ml. of 2% ammonium hydroxide and washed with about 100 ml. of water. The coal sample was dried and ground to desired mesh for the analysis of sulfur value. Sample "K-l" . Sulfur (%) as received and dried 3.88 after treatment 1.10

Ozone concentrations presented above are based on maximum ozone generated.

Treatment for the above data was undertaken at ambient conditions, i.e. atmospheric pressure and temperatures of ,60°F. to 80°F.

Procedures using other concentrations of ingredients can be utilized without departing from the scope of the invention; e.g. increasing the concentration of NH.OH in water can reduce the quantity of spray wash used. Other modifications will be available to those skilled in the art in the light of the above teachings; therefore, in determining the scope- of the present invention, reference should be made to the accompanying claims.

Claims

1. Process for decreasing sulfur values in coal, comprising the steps of comminuting untreated coal to increase the surface area of such coal available for reaction, adding calcium hydroxide to be mixed with such comminuted coal, contacting such mixture of comminuted coal and calcium hydroxide with nascent oxygen under ambient conditions of temperature and pressure, wherein the amount of nascent oxygen is at least that amount of oxygen stoichiometrically required for oxidation of sulfur values in the coal, adding water such that oxidation of such sulfur values produces sulfate ions in solution, such calcium hydroxide being at least that amount stoichiometrically necessary to react with such sulfate ions to form calmium sulfate, and recovering coal of decreased sulfur values.

2. The process of claim 1 in which such untreated coal is comminuted to particle sizes not substantially larger than thirty to sixty mesh.

3. The process of claim 1 in .which such calcium hydroxide is added for comminuting with such untreated coal.

4. The process of claim 1 in which water is added during such comminuting step.

5. The process of claim 1 in which a wetting agent is added to the coal.

6. The process of claim 1 in which at least a portion of the water is added as a solution of about 3% to about 6% hydrogen peroxide in water.

7. The process of claim 1 further including the steps of adding ammonium hydroxide to convert the calcium sulfate to calcium hydroxide, and separating the calcium hydroxide.

_ OMPI

8. The process of claim 1 including the steps of adding ammonium hydroxide to react with the calcium sulfate forming calcium hydroxide and ammonium sulfate, separating the calcium hydroxide, and recovering ammonium sulfate.

9. The process of claim 8 in which such ammonium hydroxide is added during such comminuting step.

10. The process of claims 1, 2, 3, 4, 5, 6, 7, 8, or 9 in which ozone is flowed in contact with such comminuted coal.

11. A process for desulfurizing coal by oxidizing sulfur values found in untreated coal comprising the steps of

(A) comminuting the untreated coal to increase the surface area available for reaction, such- comminuted coal being wetted with water for the following steps (B) through (D),

(B) oxidizing sulfur values in the untreated coal by contacting such coal with nascent oxygen under ambient conditions of temperature and pressure, wherein the nascent oxygen provided is at least that amount required for stoichiometric oxidation of such sulfur values to sulfate,

(C) adding calcium hydroxide to react such sulfate, the calcium hydroxide being added in an amount at least equivalent to the stoichiometric quantity necessary to convert such sulfate to calcium sulfate,

(D) adding ammonium hydroxide to react with such calcium sulfate, the ammonium hydroxide being added in an amount sufficient to convert calcium sulfate to ammonium sulfate and a calcium compound, and

(E) recovering the desulfurized coal.

12. The process of claim 11 wherein water is added in one or more of the steps (A) through (D) to carry out the steps of (B) through (D) in solution.

13. The process of claim 11 wherein the source of nascent oxygen is hydrogen peroxide.

14. The process of claim 11 wherein the source of nascent oxygen is ozone.

15. The process of claim 11 or 12 wherein the untreated coal is comminuted with the calcium hydroxide.

16. The process of claim 11 wherein the comminuted coal is treated with a wetting agent, wherein such coal is wetted at least in part with a solution of hydrogen peroxide in water, and wherein such wetted coal is then contacted with ozone.

17. The process of claim 11 in which step (D) is followed by spray-washing the coal with a solution containing about 2% to 4% NH-C1.

18. The process of claim 11 in which step (D) is followed by spray-washing the coal with carbonic acid.

19. The process of claim 11 in which step (E) is carried out by separating the ammonium sulfate and calcium compound from the desulfurized coal.

20. A process for desulfurizing coal by oxidizing sulfur values found in untreated coal and for increasing the BTU values of the desulfurized coal compared to the untreated coal, comprising the steps of

^' (A) providing untreated coal containing sulfur values and material which is substantially non-combustible during burning of coal,

(B) comminuting such coal in the presence of water and maintaining such coal in wetted condition during the following steps (C) through (E),

(C) oxidizing sulfur values found in the comminuted coal and converting at least a portion of such non-cumbustible material to a source of fuel by contacting such comminuted untreated coal with nascent oxygen under ambient conditions of temperature and pressure,

OMPI _ ^" - wherein the nascent oxygen provided is at least that amount required for stoichiometric oxidation of sulfur values to sulfate and converting at least a portion of such non-combustible material to a source of fuel,

(D) reacting such sulfate with calcium hydroxide in an amount at least equivalent to the stoichiometric quantity necessary to convert such sulfate to calcium sulfate,

(E) reacting such calcium sulfate with ammonium hydroxide to convert calcium sulfate to ammonium sulfate, and

(F) recovering desulfurized coal containing such additional source of fuel in which the BTU value of the desulfurized coal per unit weight is in excess of the BTU value per unit weight of the untreated coal.

21. The process of claim 20 wherein the source of nascent oxygen is hydrogen peroxide, ozone, or mixtures thereof.

22. The process of claim 20 in which the coal is wetted at least in part with a solution of H₂0₂ in water.

23. A process for decreasing the sulfur content of coal and converting such sulfur to ammonium sulfate for uses such as fertilizer, comprising the steps of

(A) comminuting untreated coal to increase the surface area of such coal available for reaction in accordance with steps (B) through (D),

(B) oxidizing sulfur values of such comminuted coal by contacting such coal with a source of nascent oxygen under ambient conditions of temperature and pressure, wherein the amount of nascent oxygen is at least that amount of oxygen contained in the sulfate resulting from the stoichiometric oxidation of such sulfur values to a sulfate.

-$ϊ £ ^ OMPI (C) reacting such sulfate with calcium hydroxide in an amount at least equivalent to the stoichiometric quantity necessary to convert such sulfate to calcium sulfate,

(D) reacting such calcium sulfate with ammonium hydroxide in an amount sufficient to convert calcium sulfate to ammonium sulfate and to regenerate calcium hydroxide,

(E) separating the calcium hydroxide, and

(F) recovering ammonium sulfate.

24. The process of claim 23 wherein the source of nascent oxygen is hydrogen peroxide, ozone, or mixtures thereof; wherein steps (B) through (D) are carried out in the presence of water; and wherein the ammonium sulfate of step (D) is dissolved in such water.