US3272721A

US3272721A - Process for desulfurizing and coking high sulfur content coal

Info

Publication number: US3272721A
Application number: US325450A
Authority: US
Inventors: Loevenstein Hirsch
Original assignee: Harvey Aluminum Inc
Current assignee: Harvey Aluminum Inc
Priority date: 1963-11-21
Filing date: 1963-11-21
Publication date: 1966-09-13
Anticipated expiration: 1983-09-13

Description

United States Patent 3,272,721 PROCES lFQR DESULFURIZING AND COKING Hli'GH 1ULFUR CUNTENT CQAL Hirsch lLoevenstein, Los Angeles, Calif., assignor to Harvey Aluminum Incorporated, Torrance, Califi, a corporation of California No Drawing. Filed Nov. 21, 1963, Ser. No. 325,450 Claims. (Cl. 20136) This application is a continuation-in-part of Serial No. 171,112, filed February 5, 1962, now abandoned, which application was a continuation-impart of Serial No. 76,585, filed February 19, 1960, now abandoned, which, in turn, was a continuation-in-part of Serial No. 810,821, filed May 4, 1959, now Patent No. 3,130,133; the disclosures of these earlier filed applications being expressly incorporated herein by reference.

The present invention relates to a process for making coke from coal. More particularly, the present invention relates to a coking process in which the coal from which the coke is produced is desulfurized as an integral part of the coking operation.

A large number of coals cannot be used for the production of coke because of their high sulfur content. Many attempts were made and many processes proposed, all aiming to reduce the sulfur content of the coals or of the coke produced from them. Some of these processes are concerned with the coal itself, trying to desulfurize it :as it is, others try to desulfurize the coal during the coking process, still others are trying to remove the sulfur from the already produced coke. As desulfurizing agents, different chemicals and gases with or Without catalyst were advanced. Some of the known processes are too expensive to be applied on an industrial scale, others do not sufficiently reduce the sulfur content of the coal or coke in order to be of practical value and still others have only laboratory value, as the conditions under which the desulfurization takes place cannot be applied on an industrial scale in the coke ovens used at the present time. The present invention obviates these difiiculties and permits the production of desulfurized coke which is particularly suitable for use in blast furnaces.

The main object of this invention is to provide a desulfurization process which can be applied on an industrial scale, using the existing degasification furnaces (coke ovens, gas retorts, etc.) and only changing the coking conditions.

It is a further object of the present invention to pro- Vide a coking process in which desulfurization may be performed such that the amount of sulfur removed from the coal may be accurately controlled within wide limits.

It is still another object of the present invention to provide a coking process according to which the coking coal is desulfurized by retarding the removal of the volatile matter from the coal.

Other objects and advantages of this invention, it is believed, will be readily apparent from the following detailed description of preferred embodiments thereof.

Briefly, the present invention comprehends within its scope a coking process in which the temperatures used in the process are such that the heating of the coal is retarded during the early stages of the process. More particularly, the process of the present invention comprises gradually heating the coal to be desulfurized and coked from a temperature of about 500 C. to a temperature of about 800 C. for two to five hours. It has been found that when this retarded heating procedure is used, a highly efficient desulfurization of the coal results. It may be theorized that this efiicient desulfurization of the coal occurs because the retarded heating of the coking process of the present invention does not remove the volatiles contained in the coal too rapidly. Surprisingly,

3,272,721 Patented Sept. 13, 1966 it would appear that retention of a substantial amount of volatiles in the coal during the desulfurization step substantially improves the efiiciency of this step. It would appear that the volatiles in the coal react with the sulfur, forming hydrogen sulfide which is driven off along with a portion of the volatiles, thus eliminating or greatly reducing the sulfur content. The coal ordinarily used for coking normally contains at least 10% volatiles. The coal used in the present invention should contain at least 3% volatiles. Thus, conventional coking coal is well suited for the present invention.

The rate of reaction between the volatiles and the sulfur increases as the temperature is increased, but the speed of removal of the volatiles is also increased with increases in temperature. Therefore, in conventional coking processes wherein the temperature of the coal is rapidly raised to temperatures on the order of 800 C. and higher, the sulfur content of the coal is not reduced by an appreciable amount. Furthermore, contrary to the widely accepted opinion of those skilled in the art, it is not necessary or desirable to rapidly heat the coal to the optimum desulfurization temperature and then attempt to keep it at that fixed temperature for the desired period of time. Rather, it is a significant contribution of the present invention that highly effective desulfurization can be obtained by slowly heating the coal in order to maintain a volatiles content which is sufiiciently high to effect removal of the desired or optimum amount of sulfur. This phenomenon permits desulfurization in the existing retorts which is quite difficult when operating for many hours at constant temperature and has not, as a practical matter, previously been possible.

Additional gases may be used to improve desulfurizat-ion. Hydrogen and hydrogen containing gases such as ammonia, coke oven gas, etc., which react with the sulfur in the coal thereby forming hydrogen sulfide may be used. In addition, neutral gases such as nitrogen which retard the degasification by lowering the partial pressure of the volatiles, thereby causing a more eflicient react-ion between the volatiles and the sulfur, may also be used. However, once the volatiles have been reduced below a minimum level, even the addition of hydrogen has little effect on sulfur removal. The volatiles contained in the coke are believed to be comprised mainly of hydrocarbons with, perhaps, some other organic compositions.

It is another contribution of the present invention that desulfurization of the coal may be performed without grinding it. In the past, it has been considered highly desirable, if not essential, that the coal be ground in order to obtain efiective desulfurization.

The following specific examples are illustrative of the process of the present invention, but it is to be understood that the invention is not to be limited to the details thereof. All proportions in these examples are set forth in parts by weight unless otherwise stated.

Example I Three 10 gram samples of a coal containing 0.63% sulfur and 17.83% volatiles were heated continuously to bring them to the temperatures indicated in Table 1. This heating was performed in the presence of hydrogen, the flow rate of the hydrogen being about 350* cc. per minute.

TAB LE 2 lfeati ng cycle, Time Sulfur Removed,

Percent Constant temperature method:

HH s e-w s" hr. 15 min 4 The constant temperature desulfurization of this example produced a coke having a final sulfur content of 0.4% while that produced by the retarded heating had a final sulfur content of 0.42%. Thus, this example clearly establishes that the retarded heating method of this example produces results comparable to desulfurization performed at a constant optimum temperature. This is highly significant because the retarded continuous heating method may be conducted on a commercial scale with standard coking equipment whereas the constant temperature method cannot be performed in existing industrial installations because it is impossible to keep all parts of the charge in an industrial retort at a constant temperature.

Example III Tests similar to those performed in Example II were conducted with a high sulfur coal which contained 1.71% sulfur and 33.10% volatiles. As in Examples I and II, 10 gram samples of this coal were heated in the presence of hydrogen which was supplied at a rate of about 350 cc. per minute. As in Example II, a constant temperature and a retarded continuous heating method were compared. The results of this comparison are set forth in Table 3.

The final sulfur content of the coke produced according to both the constant temperature and retarded heating methods of this example was 0.6%. Consistent with Example H, this example also establishes that the desulfurization obtained when the retarded continuous heating method is used is equally as efficient as that obtained when the constant temperature method is used. In fact, it is interesting to note that the slightly retarded heating from 500 C. to 800 C. in the constant temperature method of this example removed 64.7% of the total sulfur contained in the coal.

Example 1V When the coal is heated to 500 C. and this temperature maintained constant for a substantial amount of time, very little sulfur is removed. In the present example, samples of the high sulfur coal of Example III and the low sulfur coal of Example II were held at a constant temperature of 500 C. for four hours. The amounts of sulfur removed by this procedure are indicated in Table 4.

TAB LE 4 Sulfur Removed Time, hour Low Sulfur Coal, percent The amount of sulfur remaining in the high sulfur coal was 1.05% and the amount remaining in the low sulfur coal was 0.54%. Thus, this example establishes that it is not sufficient merely to hold the coal at a relatively low temperature in order to obtain efficient desulfurization, but that it is necessary to slowly and continuously heat the coal over a temperature range of 500800 C.

as shown in Examples II and III.

Example V It has been found that when additional hydrogen is supplied during desulfurization, the hydrogen flow need not be initiated until the temperature is in the range of from 500 C. to 700 C. This is of substantial importance since it eliminates the danger of explosion which is always present when hydrogen is introduced into a furnace atmosphere which still contains oxygen. At temperatures above 500 C., the furnace atmosphere consists essentially only of hydrocarbon vapors and hydrogen sulfide. If desired, heating may be initiated in an atmosphere of nitrogen and the atmosphere then converted to hydrogen when a temperature of about 500 C. to about 700 C. is reached. In general, it is preferred to convert the atmosphere to hydrogen since this will result in a more efiicient desulfurization.

In the present example, coal having a sulfur content of 1.71% and a volatiles content of 33.10% was slowly heated to 800 C. When no additional gas was introduced until the temperature reached 700 C., and then hydrogen introduced at a flow rate of 300 cc. per minute, the sulfur in the coal was reduced by 64.1%. When nitrogen at a flow rate of 300 cc. per minute was used until the temperature reached 700 C. and the atmosphere then converted to hydrogen at a flow rate of 300 cc. per minute, the total amount of sulfur removed was 76.3%. When only nitrogen at a flow rate of 300 cc. per minute was used throughout the process, the total amount of sulfur removed was 59.4%. The heating periods in this example were:

grams of the high sulfur (1.71%) coal having a particle size not larger than 1 mm. and 10 grams of the same coal consisting of particles having dimensions of 10 mm. x 10 mm. X 5 mm. were treated with hydrogen at a flow rate of 350 cc. per minute simultaneously in the same furnace. The temperature of this furnace was slowly raised from 500 C. to 800 C. over a period of 3 hr. 14 min. The large particles showed a final sulfur content of 0.92% and the smaller particles had a final sulfur content of 0.98%. Thus, when the present invention is used, the coal need not be ground to a very small size although such grinding has previously been considered desirable, if not essential for effective desulfurization.

Example VII 15 pounds of the low sulfur coal of Example II and 15 pounds of the high sulfur coal of Example III containing lumps up to 10 cm. in diameter were placed separately in steel retorts and heated without any additional gas in a furnace under the following conditions: 2 hours at 600 C.; 1 hour at 700 C.; 2.5 hours at 750 C.; 1.5 hours at 800 C.; 2.75 hours at 850 C. and 2 hours at 1000 C. The final sulfur content of the coke produced from the low sulfur coal was 0.54% which represents a reduction in sulfur of 29.6% and the final sulfur content of the coke produced from the high sulfur coal was 1.06% which represents a reduction in sulfur of 58.5%.

Example VIII As previously stated, it is believed that the improvement in desulfurization obtained according to the present invention is attributable, at least in substantial part, to the retention of volatiles by the coal during the desulfurization procedure. That this is so is believed to be readily apparent from the present example in which a coal having an initial sulfur content of 1.2% and an initial volatiles content of 39.4% and a coke produced from this coal having an initial sulfur content of 0.9% and an initial volatiles content of 2% were treated in hydrogen at twenty-three hours at 750 C. The coal was not ground and the coke produced from this coal was ground to 200 mesh.

After being so treated, the coal had a sulfur content of 0.15% which represented a reduction in sulfur of 87.5% while the coke had a sulfur content of 0.7% which represented a reduction in sulfur of only 22.3%.

It will be readily apparent to those skilled in the art from the foregoing examples that the retarded heating procedure of the present invention results in a vast increase in the efiiciency of desulfurization in the coking process. After the coal has been desul-furized according to the present invention, the coking process is then continued in the conventional manner to produce coke having the desired characteristics in addition to the desirably low sulfur content. Furthermore, when the desulfurization procedure of the present invention is used, the final amount of sulfur in the coke may be controlled within wide limits simply by varying the speed with which the coal is heated during the desulfurization procedure.

In general, it has been found desirable to continuously heat the coal from a temperature of about 500 C. to about 800 C. for a period of at least one hour and usually from about two to about five hours. However, these limits may be varied within reasonable bounds as long as the volatiles content of the coal is maintained sufiiciently high to enhance desulfurization to the desired degree. In this regard, it is, in general, believed that a minimum volatiles content of about 2% should be maintained during the desulfurization procedure. In most cases, the volatiles content should be maintained at at least 2% until the sulfur content has been reduced to 1% or lower.

Generally, it is not important to keep the coal at a given temperature [for any length of time as long as the heating is retarded such that the coal is continuously heated within the limits previously set forth. Furthermore, it is not necessary to cool the retort when a new charge is introduced. Only a small part of the coal is in direct contact with the hot retort walls and the remainder remains at a relatively low temperature because of the poor heat conductivity of coal, especially wet coal. Still further, the water vapors given off by wet coal also help in retarding the heating of the coal.

Although the use of additional gases such as hydrogen may be employed to still further increase the efficiency of the desulfurization procedure in the coking process of the present invention, it is an important feature of the present invention that the addition of such gases is not necessary. Rather, as shown in Example VII, substantial reductions in sulfur may be obtained according to the present invention without the addition of additional gases. Thus, the present invention makes possible the use of existing coking equipment which is not provided with means for introducing gases therein to desu-lfurize coal in a manner not previously considered possible. When additional gases are used, they may be stripped from the hydrogen sulfide in the efiiuent gases and reused in the coking process of the present invention.

After the desulfurization step of the coking process of the present invention has been completed, the desulfurized coal is calcined at temperatures of above 800 C., usually about 1000-1100 C., for a sufiicient length of time to reduce the volatiles content of the coke to a desired minimum. This time will vary depending on the temperature used, the thickness of the charge and other factors, but may easily be determined by routine eX- perimentation.

Having fully described the present invention, it is to be understood that it is not to be limited to the details set forth, but is of the full scope of the appended claims.

I claim:

1. A coking process comprising heating coal which contains a substantial amount of sulfur and at least 3% volatiles wherein said coal is continuously heated at gradually increasing temperature levels varying from about 500 C. to about 800 C., the coal not having been previously ground to a finely subdivided state and having a particle size of at least 5 millimeters, said heating being performed over a period of at least two hours during which time at least 2% volatiles are retained in the coal and whereby a substantial amount of sulfur is removed, and then heating said desulfurized coal at a temperature above about "800 C. for a time sufiicient to produce coke therefrom.

2. The process of claim 1 wherein said desulfurization time is from about two to about five hours.

3. A coking process comprising heating coal containing at least about 3% volatiles and a high sulfur content wherein at least 50% of said sulfur is removed by continuously heating said coal at gradually increasing temperature levels varying from a temperature of about 500 C. to about 800 C., the coal not having been previously ground to a finely subdivided state and having a particle size of at least 5 millimeters, said heating being performed over a period of least two hours during which time at least 2% volatiles are retained in the coal, and then heating said coal at a temperature above about 800 C. for a period of time sufiicient to form coke therefrom.

4. The process of claim 3 wherein said desulfurization time is about two to about five hours.

5. A coking process comprising heating coal containing a substantial amount of sulfur and at least 3% volatiles where-in said coal is substantially desulfurized by continuously heating said coal at gradually increasing temperature levels varying from a temperature of about 500 C. to about 800 C., the coal not having been previously ground to a finely subdivided state and having a particle size of at least 5 millimeters, said heating being performed over a period Of at least two hours during which time at least 2% volatiles are retained in the coal whereby a substantial amount of sulfur is removed, said coil being subjected during said heating to the action of additional desulfurizing gases, and then heating said coal at a temperature above about 800 C. for a period of time sufiicient to form coke therefrom.

6. The process of claim 5 wherein said additional gases comprise hydrogen.

7. The process of claim 5 wherein said additional gases comprise hydrogen producing gases.

8. The process of claim 6 wherein said hydrogen is first introduced when the temperature is at least about 500 C.

9. The process of claim 7 wherein said hydrogen producing gases are first introduced when the temperature is at least about 500 C.

10. A coking process comprising heating coal which contains a substantial amount of sulfur and at least about 3% volatiles, wherein said coal is desulfurized by continuously heating it at gradually increasing temperature levels varying from a temperature of about 500 C. to about 800 C., the coal not having been previously ground to a finely subdivided state and having a particle size of at least 5 millimeters, said heating being performed over a period of at least two hours during which time at least 2% volatiles are retained in the coal whereby a substantial amount of sulfur is removed, said volatiles being the sole source of desulfurizing agent used in the process, and then heating said coal at a temperature above about 800 C. for a period of time sufficient to form coke therefrom.

References Cited by the Examiner UNITED STATES PATENTS 12/1955 McKinley et al. 2023l OTHER REFERENCES MORRIS O. WOLK, Primary Examiner.

I. H. NEWSOME, Assistant Examiner.

Claims

1. A COKING PROCESS COMPRISING HEATING COAL WHICH CONTAINS A SUBSTANTIAL AMOUNT OF SULFUR AND AT LEAST 3% VOLATILES WHEREIN SAID COAL IS CONTINUOUSLY HEATED AT GRADUALLY INCREASING TEMPERATURE LEVELS VARYING FROM ABOUT 500*C. TO ABOUT 800*C., THE COAL NOT HAVING BEEN PREVIOUSLY GROUND TO A FINELY SUBDIVIDED STATE AND HAVING A PARTICLE SIZE OF A LEAST 5 MILLIMETERS, SAID HEATING BEING PERFORMED OVER A PERIOD OF AT LEAST TWO HOURS DURING WHICH TIME AT LEAST 2% VOLATILES ARE RETAINED IN THE COAL AND WHEREBY A SUBSTANTIAL AMOUNT OF SULFUR IS REMOVED, AND THEN HEATING SAID DESULFURIZED COAL AT A TEMPERATURE ABOVE ABOUT 800*C. FOR A TIME SUFFICIENT TO PREDUCE COKE THEREFROM.