US3076751A

US3076751A - Process for the low temperature carbonization of bituminous coal

Info

Publication number: US3076751A
Application number: US836524A
Authority: US
Inventors: Ronald G Minet
Original assignee: United Engineers and Constructors Inc
Current assignee: United Engineers and Constructors Inc
Priority date: 1959-08-27
Filing date: 1959-08-27
Publication date: 1963-02-05
Anticipated expiration: 1980-02-05

Description

Feb. 5, 1963 R. c. MINET {A 3,076,751 PROCESS FOR THE LOW TEMPERATURE CARBONIZATION OF BITUMINOUS COAL Filed Aug. 27, 1959 CHAR ' IN V EN TOR. flaw/u 0 6 M/A/U United States Patent "Ofilice 3,076,751 Patented Feb. 5, 1963 3,076,751 PROCESS FUR THE LBW TEMPERATURE CAR- BQNEZATIQN F BITUMINOUS COAL Ronaid Minet, Philadelphia, Pa., assignor to United Engineers & Constructors lno, Phiiadeiphia, Pa. Filed Aug. 27, 1059, Ser. No. 836,524 5 Claims. (Cl. 202-9) This invention relates to a process for the carbonizetion of bituminous coal at low temperature and particularly to a process whereby such carbonization can be carried out in a fluidized bed without a preoxidation step.

Many attempts have been made to develop an economical process for the carbonization of bituminous coal at temperatures below about 1000 F. In some countries, such processes are economically feasible and are in use. In the United States however, so far as is known, no such process is now in commercial operation.

In recent years a number of proposals have been made with a view toward adapting the fluidized bed technique to low temperature carbonization processes. In most of such proposals however, the coal having been reduced to finely divided form must first be preoxidized to keep it from agglomerating when heated to carbonization temperatures. This has required a minimum of two fluidized beds, one for preoxidation and another for carbonization.

This arrangement is inherently costly, since the gaseous stream removed overhead from the preoxidation bed consists very largely of products of combustion, which have little value. In no case is more than say 50% of the recoverable tar recovered during the preoxidation. Thus the major cost of building, maintaining and operat ing a fluidized bed preoxidizer is necessary simply to prepare the coal for car-bonization.

It is an object of the present invention to provide a process for the low temperature carbonization of certain bituminous coals in which no preoxidation step is necessary.

It is a further object of the present invention to provide a process for the low temperature carbonization of certain bituminous coals using the fluidized bed technique in which only one fluidized bed is necessary.

It is another object of the invention to provide a process for the carbonization of certain bituminous coals which will be more economical than existing processes.

According to the invention these and other objects are obtained by heating certain widely distributed types of bituminous coal at a carefully controlled temperature between about 800 F. and about 840 F. It has been found that by heating at this temperature the dry volatile content of the coal can be reduced to between about 18% and about 26% by weight, without danger of agglomeration, in a fluidized bed. Such treatment enables a mini mum of 70% by weight of the tars and oils which it is possible to derive from the coal by carbonization, to be recovered in a single step. If desired, the remaining tars and oils may be recovered 'by further heating in a second stage at say 860 to 1600 F.

It should be pointed out that the amount of volatile matter which can be recovered from a particular coal is a function of temperature, i.e. for any particular coal the volatile content which will remain in the coal after it has been heated to a given temperature is fixed. For most of the coals covered by the present process a minimum temperature of 800 F. is necessary in order to reduce the volatile content to 18-26% and recover a minimum of 70% of the tar.

Coals which can be treated according to the present invention are among those designated High Volatile B Bituminous (HVBB) and High Volatile C Bituminous (HVBC) according to the ASTM classification by rank. Such coals contain less than 69% dry fixed carbon and more than 31% dry volatile matter. They have a moist heating value between about 11,000 and about 14,000 B.t.u. per pound. For a description of the ASTM and other systems of classification, see Lowry, Chemistry of Coal Utilization (John Wiley and Sons, New York, 1945), chapter 2. HVBB and HVBC coals are widely distributed throughout the United States and are found in Pennsylvania, West Virginia, Kentucky, Ohio and Illinois. Such coals are particularly distinguished by the proportion of moisture and ash free oxygen present in the ultimate analysis. Coals which are amenable to treatment of the kind described contain at least 4 percent and preferably 6 to 12% by weight of oxygen on a moisture and ash free basis.

In carrying out the invention, the coal is preferably first reduced to a particle size to between about 4 mesh and about 325 mesh, usually between about 8 mesh and about 325 mesh. The imely divided coal is then suspended in a fluidized bed in a suitable reaction vessel equipped with a gas distributing device. Heat may be supplied to the bed by any convenient means, as for example by hot gases, which may also serve as a fluidizing medium. These gases may be entirely inert, such for example as steam or nitrogen, or they may contain quantities of oxygen or air. In the latter instance, the oxygen or air is used to burn a portion of the suspended coal to furnish at least part of the heat of carbonization.

The char resulting from the carbonization may be removed from the bed and further treated to recover the balance of the volatile matter remaining in it. This further recovery may be obtained by delivering the finely divided char to a second fluidized bed and heating it to above 860 F. and preferably not higher than 1600 F. to further reduce the volatile content.

The invention will be further described in the drawings in which FIG. 1 is a schematic flow diagram showing a preferred form of a carbonization system according to the invention, and

FIG. 2 is a schematic representation of another system according to the invention in which coal can be carbonized at a relatively low temperature and then further distilled at a higher temperature to remove residual volatile matter.

Referring first to FIG. 1, coal is fed into a mill 1 where it is reduced to a particle size in the range between about 10 mesh and about 325 mesh. Thus divided, it iscarried to a carbonization vessel 2 through a line 3. At the same time a fluidizing gas is fed into the vessel through a line 4 to form a fluidized bed 5, in the vessel 2. A grid 6 is provided at the bottom of the vessel to sustain the fluidized bed. The gas, introduced through line 4, may be an inert gas such for example as steam, or a mixture of an inert gas and an oxidizing gas, such for example as a mixture of steam and air. If steam is introduced alone, it should be at a temperature between about 1000 F. and about 1400 F. so that the temperature in the bed is maintained between about 800 F. and about 840 F. if a mixture of an inert gas and oxygen is introduced, it may be preheated, as for example to between about 600 F. and about 800 F., or it may be introduced at the ambient temperature. The proportion of oxygen present in the gas will depend on a number of factors, including the dimensions and design of the reactor, the size of the coal particles, the rate of coal processed and of course, the temperature to which the bed must be heated. When used, oxygen will generally comprise between about 10% and about 15% by volume of the fiuidizing gas.

At a temperature between about 800 F. and about 840 F., coal of the class described, containing over 31% dry volatile matter, distills, giving off a mixture of tars, oils and gases. The tars and oils are often referred to merely as tars. These volatile products pass out through a cyclone separator 7 and are removed from the system through line 8. They may then be separated into salable components by distillation or other means not shown. Char is removed through a line 9 at the bottom of the vessel 2.

As noted, the char removed from a carbonization vessel operated according to the invention contains a residue of between about 18% and about 26% by weight dry volatile matter. Whether it will be worthwhile to remove all or par-t of this residue depends on the composition of the particular coal and of the residue.

With certain HVBB and HVBC coals it may be economically justifiable to further carbonize at a temperature as high as 1600" F. in order to obtain a maximum yield of gaseous and liquid products.

A suitable system for carrying out the novel process where removal of the residual 18 to 26% volatile matter is desired, is shown in FIG. 2. Referring to FIG. 2, coal finely divided to a particle size between about inch and about 325 mesh, preferably to between about /8 inch and about 325 mesh, is introduced through a line 10 into a first carbonize-r 1.1. A fiuidizing gas is introduced at the bottom of the carbonizer 11 through a line 12. This creates a fluidized bed 13 which is supported on a grid 14 at the bottom of the vessel 11. The fiuidizing gas introduced through line 12 may be an inert gas, or a mixture of an inert gas and an oxidizing gas, as described in connection with FIG. 1 above. As in FIG. 1, the bed 13 is heated to between about 800 F. and about 840 At this temperature a large portion of the volatile material present in the coal passes overhead through cyclone separator 15 and line 16, and is thence removed from the system.

The solid residual char containing 18 to 26% volatile matter is removed from the vessel 11 through an overflow trap 17 into an inclined duct 13. Here it flows through a valve 19 into a second carbonizing vessel 20 where it is formed into a fluidized bed 21 supported on a grid 27, by means of a hot fluidizing gas introduced through a line 22.

The fiuidizing gas used in the bed 21, like that used in bed 13, and in the fluidized bed of FIG. 1, may be an inert gas, such as steam or a mixture of an inert gas and anoxidizing gas, such as a mixture of steam and air. In the latter case, the oxygen supports combustion of a portion of the char formed in the carbonizer 20 and thus serves to heat the bed 21.

When no oxygen is present in the gas introduced through line 22, the gas should be at a temperature between about 1240 F. and about 2000 F., so that the bed is maintained at a temperature between about 860 F. and about 1600 F., preferably between about 860 F. and about 1000 F.

When oxygen is used, the gas entering through line 22 may bepreheated, for example to a temperature between about 600 F. and about 900 F., or it may be introduced at ambient-temperature. The proportion of oxygen in the gas will, as explained above, be governed by many factors including the dimensions and design of the vessel 20, the size of the coal particles and the temperature desired in the bed 21. Generally it is between about 5% and about 10% by volume.

As pointed out, the temperature in the bed 21 is maintained between about 860 F. and about 1600* R, preferably between about 860 F. and about 1000 F. At these temperatures residual volatile matter is removed from the coal and passes overhead through cyclone separator 23 and line 24 through which it is removed from the system.

The char remaining, which now contains between 5 and about 20% by weight dry volatile matter, is removed through standpipe 25 and line 26. It may be used as a fuel, or for other purposes, such as for the production of metallurgical carbon.

The invention will be further described by means of the following specific examples, it being understood that these examples are given for purposes of illustration only and are not to be taken as in any way restricting the invention beyond the scope of the appended claims.

In the examples five different types of high volatile B bituminous coal were used. These types are designated A to E and are described in detail in Table I.

1 V111 =Volatile matter, percent by weight. 2 FO=Fixed carbon, percent by Weight.

Moist means that the coal contains natural bed moisture but not visible water on its surface.

Example I Two hundred pounds per hour of coal A were fed into a fluidized bed of the same material maintained at a temperature of 830 F. Steam was used as the fluidizing gas, with sufiicient air being introduced to provide the necessary heat for carbonization by combustion of the char. A superficial gas velocity of 1.2 feet per second was maintained at the bottom of the bed. The following products were recovered each hour from this operation:

Light oil 0.30 gallon. Tar 2.50 gallons. Gas 800 std. cu. it. at 350 B.t.u./c.f. Char 140 pounds.

The char remaining contained 20% by weight dry volatile matter. The proportion of total recoverable tar (tar and oil) actually recovered in the single carbonization stage was about 90%.

Examples 11 to V Examples II to V are tabulated below in Table II. In Example V, the residual char from the first carbonization step was further carbonized at the temperatures indicated using steam and air as the heating and fluidizing medium.

TABLE II Example II III IV V Coal treated B O D E Coal iced rate, lbs/hr... 200 200 200 200 1st carbonization stage:

Fluidizmg and heating medium. Bed temp, F 800 820 800 800 Overhead product, lbs/hr]- 44. 2 7 1. 2 42. O '13. 2 Analysis, weight percent:

\Vat 41. 8 31. O 28. 7 .3 11. 3 9. 5 8. 'J .1 4. 2 7. 2 8. 0 .1 42. 7 52. 3 53. 5 Char:

Obtained, lbs/hr 147. 115.8 151. 2 146. 3 Loss, lbs/hr S. 0 10.0 6. 8 8. 5 Weight percent dry volatile matter 23. 1 20.0 22. 8 22. 0 Percent total tar and light oil recovered 86. 0 81.0 71. 2 83. 0 2nd carbonization stage:

Fluidizing and heating mcdium Bed temp, F 950 Overhead product, lbs/hr 14. 0 Analysis, weight percent: 5

W" or 7. 3 Gas 43. 0 Light on 14. 6 Tar" 35.1 Char:

Obtained, lbs/hr 130.6 Loss, lbs/hr. 1. 3 Weight percent dry volatile matter 1'1. 1

1 Steam and air. 2 Steam. 8 All on air and steam free basis.

A consideration of the foregoing specification will make it clear that the present invention permits a number of common coals of the agglomerating type to be carbonized directly in a fluidized bed without oxidation pretreatment. It must be emphasized that the primary carbonization stage of the present invention (which in most cases will be the only carbonization stage) is a true carbonization step and not merely a pretreatment, since in every case at least 70% of the potentially recoverable tars and oils are distilled off in this step.

A distinction is therefore to be drawn between the present process and other carbonization processes using oxidation pretreatments. In such prior processes, the temperature of the pretreatment may occasionally be quite high, but for any specific coal, the temperature will not be sufiicient to recover more than at most 50% of the total recoverable tar and oils, and would therefore be considerably lower than the temperature which would be used if the present process were applied to that coal.

In the foregoing specification coal is described as being furnished directly to the carbonization vessel without preheating. It will be understood that if desired a certain amount of preheating may be carried out to remove surface water. Such preheating will be below 400 F. and will not in any way change the essential nature of the coal.

This patent application is a continuation-in-part of the Minet patent application, Serial No. 562,980, tiled February 2, 1956, now abandoned.

What is claimed is:

1. A method for the low temperature carbonization of a normally agglomerating coal which consists essentially of charging a feed stream consisting essentially of fresh finely divided coal having more than about 31% dry volatile matter and a moist heating value of between about 11,000 and about 14,00 B.t.u./lb., into a fluidized zone maintained at a temperature between about 800 F. and about 840 F., and educing hydrocarbona ceous matter from said coal in said zone until at least 70% by weight of the total tars and oils initially present in the coal are removed and the dry volatile content of said coal is reduced to between'about 18% and about 26% by weight without substantial agglomeration of said coal.

2. A method for the low temperature carbonization of a normally agglomerating bituminous coal having more than about 31% dry volatile matter and a moist heating value of between about 11,000 and 14,000 B.t.u./ 1b., which consists essentially of charging a feed stream consisting essentially of fresh coal to a fluidized carbonization zone at a temperature between about 800 F. and about 840 F. and maintaining said coal in said zone for a period sufficient to remove at least by weight of the total tars and oils initially present in the coal and to reduce the dry volatile content of said coal to between about 18% and about 26% by weight, there being substantially no agglomeration in said zone.

3. The method claimed in claim 2 and comprising burning a portion of the coal in the fluidized zone to furnish heat for the carbonization.

4. A method for the low temperature carbonization of a normally agglomerating bituminous coal having more than about 31% dry volatile matter and a moist heating value of between about 11,000 and about 14,000 B.t.u./lb., which consists essentially of charging a feed stream consisting essentially of fresh coal to a first fluidized carbonization zone maintained at a temperature between about 800 F. and about 840 F., maintaining said coal in said zone for a period suificient to remove at least 70% by weight of the tars and oils initially present in the coal and to reduce the dry volatile content of said coal to between about 18% and about 26% by weight, and then feeding said coal to a second fluidized carbonization zone at a temperature between about 860 F. and about 1600 F. but higher than the temperature in said first carbonization zone, there being substantially no agglomeration in either zone.

5. The method claimed in claim 4 wherein the coal in the second zone is heated to between about 860 F. and about 1000 F.

References Cited in the file of this patent UNITED STATES PATENTS Welinsky May 4, 1954 Welinsky Oct. 4, 1960 OTHER REFERENCES

Claims

1. A METHOD FOR THE LOW TEMPERATURE CARBONIZATION OF A NORMALLY AGGLOMERATING COAL WHICH CONSISTS ESSENTIALLY OF CHARGING A FEED STREM CONSISTING ESSENTIALLY OF FRESH FINELY DIVIDED COAL HAVING MORE THAN ABOUT 31% DRY VOLATILE MATTER AND A MOIST HEATING VALUE OF BETWEEN ABOUT 11,000 AND ABOUT 14,000 B.T.U./LB., INTO A FLUIDIZED ZONE MAINTAINED AT A TEMPERATURE BETWEEN ABOUT 800*F. AND ABOUT 840*F., AND EDUCING HYDROCARBONACEOUS MATTER FROM SAID COAL IN SAID ZONE UNTIL AT LEAST 70% BY WEIGHT OF THE TOTAL TARS AND OILS INTIALLY PRESENT IN THE COAL ARE REMOVED AND THE DRY VOLATILE CONTENT OF SAID COAL ARE REMOVED AND THE DRY VOLATILE CONTENT 26% BY WEIGHT WITHOUT SUBSTANTIAL AGGLOMERATION OF SAID COAL.