US3391076A - Single unit delayed coking and calcining process - Google Patents

Description

July 2, 1968 3,391,076

SINGLE UNIT DELAYED comm AND CALCINING PROCESS V. D. ALLRED Filed April 21, 1966 T0 ST$CK TO 4DISTILLATION y RECYCLE AIR COKABLE HYDROCARBONS COKING FURNACE INVENTOR.

BY VICTOR D. ALLED United States Patent 3,391,076 SHNGLE lUNiT DELAYED tCtllKiNG AND CALClNllNG PRUCEESS Victor Dean Alired, Littieton, Cola, assignor to Marathon Oil Company, Findlay, Ohio, a corporation of Ohio Filed Apr. 21, 1966, Ser. No. 544,189 tltairns. (Cl. Mid-131) AllidTRACT Uh THE DISCLOSURE The present invention comprises a process for the coking of petroleum hydrocarbons and the calcination of the resulting coke in situ in a single piece of apparatus comprising in combination the steps of conventionally delayedcoking cokable petroleum hydrocarbons in a delayedcoking drum, so designed as to be capable of withstanding the temperatures necessary to the calcining of the resulting delayed coke, and thereafter while said delayed coke remains in the drum in which it was coked, igniting said coke and introducing an oxygen containing gas into said coke at a point removed from the point at which said coke was ignited so as to cause the ignition of volatiles Within the coke in a relatively limited combustion zone, venting from the coke drum any combustion gases formed in said combustion zone, said venting occurring at a point on the opposite side of said combustion zone from the point of introduction of said oxygen containing gas, controlling the flow of said oxygen containing gas so as to cause coke contacting said combustion zone to be calcined to a predetermined desirable degree wtih minimal combustion of the fixed carbon present in said coke wherein the combustion zone is caused to pass through substantially the entire length of the coke drum so as to calcine substantially all of the cokes contained therein, and wherein the calcined coke is thereafter removed from the coke drum, and related apparatus. Calcined coke is used for a variety of purposes including the manufacture of electrodes for batteries, aluminum reduction, etc.

The present invention relates to new processes and apparatus for the combined coking and calcining of petroleum hydrocarbons in a single piece of apparatus.

The delayed coking process for the formation of coke from hydrocarbons is long established and well known. Briefly, the process consists of heating such hydrocarbons to temperatures sufiicient to cause them to coke and immediately and rapidly running the hot hydrocarbons into a relatively quiescent chamber generally known as a coking drum. Coking occurs in this drum with the noncokable volatilized hydrocarbons being evolved, generally from the top of the drum, and conveyed to other refining processes. After the coking is complete, the coke drum is usually unloaded by removing large manhole covers or doors from the top and bottom of the drum which is in most cases a vertical cylinder with conical or rounded ends. The delayed petroleum coke is a hard dense material which is removed from the drum only with difficulty. Probably the most common method of removal of the coke is the use of high pressure e.g., 800 to about 2000 p.s.i.g. water drills which cut out chunks of the coke and permit them to fall through the lower outlet of the drum. This process is continued until the drum is empty after which it is again refilled with hot cokable hydrocarbons.

The disadvantages of these processes include the difficulty in maneuvering the high pressure water drills in the relatively confined space of the coke drum, the time hfldlfl'lb Patented July 2, 1968 required to cut out chunks of relatively hard dense coke, and the need for handling the green or uncalcined coke and transporting it to a calciner.

Every one of these difiiculties is substantially overcome by the new process of the present invention and in addition, the need for a separate calciner is eliminated with a resulting saving in capital investment. The present process permits the in situ calcining of delayed coke in the same apparatus in which the coking occurs. In addition to saving capital investment and eliminating transporting of the green delayed coke, the present invention permits rapid removal of the calcined coke from the coke drum frequently without the need for any significant mechanical fragmentation of the coke. The invention particularly utilizes the fact that in most instances a major shrinkage e.g., in the range of 20%, occurs in coke during the calcining process. This shrinkage draws the calcined coke away from the walls of the coke drum, and causes some fracturing of the coke. In many instances merely removing the lower manhole will cause most of the coke to flow from the coke drum. Any bridging which occurs at the lower manhole can be avoided by providing a larger aperture or by conventionally rodding or otherwise agitating the calcined coke.

A basic aspect of the practice of the processes of the present invention is that the coke is calcined while it is still in the coke drum by igniting the coke preferably at a point near one end of the coke drum and directing an oxygen containing gas e.g., air through the body of coke so that the gas reaches the point of ignition, forming the relatively limited combustion zone and then passes out from the apparatus at a point on the other side of the combustion zone from the point of ignition.

Thus one principle of the present invention involves the oxygen-containing gas contacting the coke at a point where the coke is relatively cold (well below ignition temperature) because it has not yet passed through the combustion zone. The oxygen containing gas then passes up through this relatively cool coke until it meets the combustion zone where the volatiles are burned. The combustion gases from the combustion zone then continue on and exit through a point on the opposite side of the combustion zone from the point of injection of the oxygen. Preferably, the quantity of oxygen hydrogen containing gases injected is so controlled as to cause combustion gases evolved from the combustion zone to be oxygen-deficient This prevents any further oxidation of coke which has already been calcined. The hot combustion gases will in most instances, serve to remove further volatiles from the coke which has already passed through the combustion zone.

In short, the process of the present invention provides a process for the coking of petroleum hydrocarbons and the calcination of the resulting coke in situ in a single piece of apparatus comprising in combination the steps of conventionally delayed-coking cokable petroleum hydrocarbons in a delayed coking drum so designed as to be capable of withstanding the temperatures necessary to the calcining of the resulting delayed coke, and thereafter while the delayed coke remains in the drum in which it was coked, igniting the coke and introducing an oxygen containing gas into said coke at a point removed from the point at which said coke was ignited so as to cause the ignition of volatiles within the coke in a relatively limited combustion zone, venting from the coke drum any combustion gases formed in the combustion zone, said venting occurring at a point on the opposite side of said com- 3 bustion zone from the point of introduction of said oxygen-containing gas, controlling the flow of said oxygencontaining gas so as to cause coke contacting said combustion zone to be calcined to a predetermined desirable degree with minimal combustion of the fixed carbon present in said coke.

The drawing is a schematic diagram of typical apparatus for practice of the present invention.

Cokable hydrocarbons preferably the petroleum residual from a distillation of crude petroleum, are heated to a coking temperature in the general range of from 700 to 1200 and most preferably from about 880 to about 960 degrees F. in a coking furnace l. The hot hydrocarbons from this coking furnace pass through open valve 2 into a coke drum 3 until the coke drum is full. The vaporized portions of the hydrocarbons feed to the coke drum, pass out of the drum to the top outlet 10, and go on to a distillation or partial condensation in which they are separated into fractions which are recovered. At this time valve 7 is open and valves 8 and Ill are closed. After the coke drum is about full, valve 2 is closed and the coking hydrocarbons are allowed to remain quiescent. The coking takes from six to about thirty hours, more preferably from 12 to about 20 hours, during which time they cool substantially and solidify, forming delayed coke 4.

With valves 7 and 2 closed and valves 8 and 11 open, air is now forced by means of blower 9 into the coke drum for moving upward through the bed of coke. The coke bed is ignited near the top by use of an igniter 6 which may be a railroad flare, or a gas or electric powered ignition device.

The upward moving air meets the coke at the point of ignition then forms a relatively shallow combustion zone extending across the cross sectional area of the coke drum. Preferably, this combustion zone will be of a depth of from about A to about 4 feet and more preferably, from about /2 to about 2 feet as measured along the major axis of the coke drum.

Now valve 11 is operated to control the rate of air flow into the coke drum so that virtually all of the oxygen is consumed in the combustion zone and the area above the combustion zone is deficient in oxygen. This control is very much preferred in order to prevent unnecessary combustion of fixed carbon values from the coke after it has been calcined by contact with the combustion zone. The temperature in the combustion zone is maintained at above 1000 degrees F. and in most cases, lower than 2800 degrees F. While the temperature will vary somewhat according to whether full or partial calcination is desired and according to the percent volatile content of the coke prior to calcination (the green coke), the preferred temperature range in the combustion zone will generally be from about 1400 to about 2400 degrees F. Additional control of the temperature in the combustion zone and of the flow of oxygen into the coker can be achieved by recycling some of the exhaust gases which exit through upper outlet of the coke drum and through valve 8. By throttling valve 14 and opening valve 13 recycle of these exhaust gases can be controlled to decrease the oxygen content of the gases entering the coke drum through the bottom outlet 12.

In most cases it will be desirable that the combustion zone move downward at a rate of about /2 to about 6 feet/hour, and more preferably from about 1 to about 3 feet per hour. Various modifications, including the presence of two combustion zones e.g., by igniting the mass of coke in the coke drum at both the top and bottom surfaces and then introducing oxygen into the mid-point of the drum, can be employed.

Automatic control systems for the measurement of temperature within the coke drum and corresponding control of the oxygen content and the quantity of the oxygen-containing gases can be employed where desirable.

The materials of Construction of the coke drum 3 must be sufliciently temperature resistant to permit the attaining of the desired temperatures in the combustion zone. In most instances, a relatively conventional steel coke drum which has been specially lined with suflicient thickness of refractory materials e.g., castable refractories or firebrick masonry, will be utilized.

The products of the process of the present invention are of course, suitable for a wide variety of uses including use as fuels and as metallurgical additives.

After the combustion zone has traveled down the entire length of the coke drum as shown in the drawing, the drum will, in most instances, be filled with a mass of shattered coke and relatively large pieces. This mass of coke will, because of shrinkage due to devolatilization, have pulled away from the walls of the coke drum and be loose. Also, because the calcined coke is relatively friable, the larger chunks may be quickly and readily broken by rodding or similar agitation conducted either by a rod manipulated from the upper manhole 10, or by rod or other breaking device extending upward from the lower manhole 12.

It will be understood that the above described embodiment is merely illustrative and is not to be considered as limitative of the scope of the invention. The invention is subject to a wide variety of variations and modifications which will be apparent to persons skilled in the art, all of which are to be taken as being included within the claims appended hereto.

What is claimed is:

1. A process for the coking of petroleum hydrocarbons and the calcination of the resulting coke in situ in a single piece of apparatus comprising in combination the steps of conventionally delayed coking cokable petroleum hydrocarbons in a delayed coking drum which is substantially a vertical cylinder so designed as to be capable of withstanding the temperatures necessary to the calcining of the resulting delayed coke, and thereafter while said delayed coke remains in the drum in which it was coked, igniting said coke and introducing an oxygen containing gas into said coke at a point removed from the point at which said coke was ignited so as to cause the ignition of volatiles within the coke in a relatively limited combustion zone, venting from the coke drum any combustion gases formed in said combustion zone, said venting occurring at a point on the opposite side of said combustion zone from the point of introduction of said oxygen containing gas, controlling the fiow of said oxygen containing gas so as to cause coke contacting said combustion zone to be calcined to a predetermined desirable degree with minimal combustion of the fixed carbon present in said coke wherein the combustion zone is caused to pass through substantially the entire length of the coke drum so as to calcine substantially all of the cokes contained therein, and wherein the calcined coke is thereafter removed from the coke drum.

2. The process of claim 1 wherein the coke is ignited substantially a the top of the coke drum.

3. The process of claim 2 wherein the calcined coke is removed throuhg a closable aperture located near the bottom of the coke drum.

4. Apparatus for the coking and in situ calcining of cokable petroleum hydrocarbons comprising in combination a furnace for heating said hydrocarbons to at least their coking temperature, a coke drum having an inlet for said hydrocarbons connected to the outlet of said furnace, having an exhaust outlet for removing noncokable hydrocarbon vapors, having ignition means, having at least one inlet for the injection of oxygen containing gases, having an outlet for the venting of combustion products, and having at least one closable aperture located in its bottom portion for full removal of calcined petroleum coke, said apparatus being so constructed as to be capable of withstanding temperatures at least as high as those required to calcine the petroleum coke to a pre-determined desired degree.

5 5. The apparatus of claim 4 wherein the coke drum 3,116,231 comprises a steel outer jacket lined with a refractory 3 130 14 material.

References Cited 3173852 3,249,528 UNITED STATES PATENTS 5 2,732,332 l/1956 Geller 208-92 2,813,823 11/1957 Putnam 201-37 Adee 208-46 Plaster 208--106 Smith 20846 Allred 20846 HERBERT LEVINE, Primary Examiner.

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