US2716628A

US2716628A - Desulfurization of petroleum coke

Info

Publication number: US2716628A
Application number: US195185A
Authority: US
Inventors: Weikart John
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1950-11-13
Filing date: 1950-11-13
Publication date: 1955-08-30
Anticipated expiration: 1972-08-30

Description

1955 J. WEIKART 2,716,628

DESULFURIZATION OF PETROLEUM COKE Filed Nov. 13. 1950 OFF GAs AND LIQUID PRODUCT To REcovauLY C'LOKE Fzom ELEVATOR 1'2 H EATING i Sacnoru H 3 SOAKINC': 4 T 2 SECTION RADIATION 1O 9 a 3 L055 5 1: a j E E: COOLING ,5

1- SEQTIQN All {4 v FUEL. (Ms 7 (-0 Coma \lxAscaaw T METHANE QONVEYQL To t "VIBRATING Scum 'Qfohrz (J2 Llkori Urzvenbor .bg (9 Cltbo rneg United States Patent 2,716,628 DESULFURIZATION 0F PETROLEUM COKE John Weikart, Cranford, N. J., assignor to Esso Research and Engineering Company, a corporation of Delaware Application November 13, 1950, Serial No. 195,185 2 Claims. (Cl. 20231) The present invention is concerned with the removal of sulfur from petroleum coke. The invention is more specifically concerned with an improved process for the desulfurization of petroleum coke wherein the amount of coke consumed in the desulfurization operation is materially reduced. In accordance with the present invention, coke derived from petroleum is desulfurized by a process utilizing a top or upper preheating zone, an intermediate soaking zone and a bottom cooling zone. In accordance with the present process a fuel gas such as methane is introduced into the cooling zone wherein the coke is cooled to substantially atmospheric temperature. The fuel gas in the cooling zone is preheated to approximately the soaking zone temperature. Oxygen-containing gas is introduced into the soaking zone and the combustion controlled in order to heat the coke to the desired desulfurization tempera ture. The gas passing from this soaking zone to the heating zone serves to heat the incoming coke and to cool the effluent gas.

It is well known in the art to produce petroleum coke from various sources and by various processes. Usually the procedure comprises a coking operation wherein the desired fraction such as a heavy crude residua or similar stock is held at a temperature in the range from about 800 to 1100 F., preferably in the range from 900 to 1050 F. for a predetermined time period. Generally low pressures are employed, as from about atmospheric to 50 lbs. per sq. in. gauge.

The coke produced by these procedures contains sulfur in a concentration from about 1% to 5%, which sulfur is very undesirable and should be removed or substantially reduced. One operation for reducing the sulfur content is to soak the high sulfur coke. This operation comprises holding the coke at an elevated temperature for a predetermined time period. For instance, the sulfur content of coke by this method can be reduced from about 3 /2 to 1% or less by soaking the sulfur coke at a temperature of about 2700 F. for a time period of about 12 hours. It has also been proposed that the necessary heat be supplied by combustion of a portion of the coke. However, this method is relatively expensive as compared to supplying the necessary heat by a fuel gas or its equivalent. Thus, the present invention is concerned with a method for reducing coke consumption to a minimum while at the same time reducing the overall unit investment.

In accordance with the present invention, coke is desulfurized by employing a three-zone kiln. The threezone kiln of the present invention comprises an upper heating section into which coke from an elevator or equivalent means is introduced. The kiln comprises an intermediate soaking section wherein the coke being desulfurized is maintained at the desired temperature for the desired time period. Fuel gas is introduced into this middle or intermediate zone. The kiln of the present invention comprises a lower cooling section wherein the desulfurized coke countercurrently contacts a fuel gas, as for example methane for the purpose of effecting heat exchange between the two streams.

The present invention may be readily understood by reference to the drawing illustrating one embodiment of the same. Referring specifically to the drawing, coke from an elevator or equivalent means is introduced into the upper zone or heating section 1 of the kiln by means of feed line 2 at a temperature of about 60 F. The coke moves downwardly by any conventional moving bed technique into a soaking section 3 which is maintained at a temperature in the range from about 2500 F. to 3000 F. A preferred temperature is about 2700 F. From this zone a radiation loss occurs which is diagrammatically illustrated by means of line 4. The coke being desulfurized is maintained in soaking section 3 for the desired length of time which is usually from about 6 to 20 hours, generally from about 10 to 14 hours. A very desirable time period comprises about 12 hours at a temperature of about 2700 F. At the end of the prescribed time period the coke is moved downwardly from the soaking section or zone into a cooling section 5 and is finally removed from the cooling section by means of line 6 to a vibrating screen or other suitable conveyor.

In accordance with the present invention, fuel gas such as methane is introduced into the bottom of cooling section 5 by means of line 7. This gas flows upwardly through zone 5 and is preheated as it countercurrently contacts the down moving coke. The gas as it flows from zone 5 to zone 3 is mixed with oxygen, air or other oxygen-containing gas, which is introduced by means of line 8. In accordance with a preferred adaptation of the present invention, the oxygen, air or other oxygencontaining gas is preheated preferably to a temperature in the range from about 800 to 1500" F. before introducing the same to the fuel gas. A preferred temperature is about 1000 F. If this adaptation of the operation be conducted the air is introduced into a heating zone 9 by means of line 10. Under certain conditions in order to bring the coke to the desired coking temperature, it is desirable to introduce additional air into the system at a point intermediate the soaking section and the heating section by means of line 11.

The invention employs a single kiln comprising three sections or zones wherein lump coke moves from top to bottom in accordance with the well known moving bed technique. Natural gas, or other gaseous fiuid preferably, but not necessarily, having a high heat content temperature slope, is introduced at the bottom of the kiln near the cold desulfurized coke withdrawal point. Heat transfer between the hot coke and cold gas cools the coke for withdrawal and heats the gas prior to introduction into the soaking zone or middle section of the kiln. In this middle section the heated gas is contacted with suflicient air, either cold or preferably preheated, for combustion of a portion of the heat transfer medium natural gas or another gas diluted with sufficient natural gas equivalentin order to heat the heat transfer medium and coke to the desired temperature, preferably to about 2700 F., and to supply heat lost via radiation from the kiln. This air or other oxygen-containing gas will prefer entially burn the gaseous combustible rather than the solid coke and hence coke will not be consumed in the combustion step. However, some Water will be formed from the hydrogen, alone and in combination with carbon, in the fuel and this water will consume coke by means of the water gas reaction. This consumption, however, is small compared to that consumed by direct combustion of the coke with air. Since the greater the heating load, the greater the combustion and hence the higher yield of combustion Water for interaction and consumption of coke, the air is preferably preheated to reduce the heating These gases then pass out of the kiln to conventional gas handling equipment.

The present invention may be more fully understood by the following example illustrating the same:

Example 300 tons of petroleum coke having a sulfur content of about 3 /2% was introduced into the top of a heating section at a temperature of about 60 F. Gases were withdrawn from the top of the heating section and passed to a recovery zone at a temperature of about 600 F. The soaking section was maintained at about 2700 F. under these conditions about 1 /2 million B. t. u.s per hour were lost by radiation. The coke was withdrawn from the bottom of the cooling section at a temperature of about 120 F. The amount was about 21,200 pounds per hour which contained 51 tons per day of fines (less than /4 of an inch) and 203 tons per day of lumps (greater than /4 of an inch). Fuel gas comprising methane was introduced to the bottom of the cooling section at a rate of 225,000 pounds per day. Of this quantity 380 pounds per hour was for combustion and 9000 pounds per hour for a heat transfer medium.

The invention is broadly concerned with an improved process for removing sulfur from petroleum coke with a minimum of coke consumption. The invention comprises the utilization of a three-zone desulfurization unit comprising an upper heating section, an intermediate soaking section and a lower cooling section. The fuel gas is heated by heat exchange in the lower section, and is burned in the soaking section by the introduction of an oxygen-containing gas. In accordance with the preferred adaptation of the invention, a portion of the oxygencontaining gas contacts the coke as it flows from the heating section to the soaking section in order to bring the coke up to the desired soaking temperature.

Having described the invention it is claimed:

1. A process fordesulfurizing petroleum coke by heat soaking the coke at a temperature of about 2500" to 3000 F. including the steps of passing the coke through a heating zone, a heat soaking zone, and a cooling zone, in the said cooling zone contacting hot coke from the heat soaking zone with a fuel gas comprising principally methane, in the said heat soaking zone contacting coke from the said heating zone with the said fuel gas from the cooling zone in the presence of oxygen whereby oxidation of the coke is minimized by the preferential combustion of the fuel gas providing temperatures of 2500 to 3000 F., and maintaining the coke in the heat soaking zone for a period suflicient to decompose sulfur compounds, and in the heating zone contacting coke with hot efiiuent gases from the heat soaking Zone, said process further being characterized by use of an excess of fuel gas beyond that required for combustion to provide a heat transfer medium between said zones.

2. The process defined by claim 1 in which coke is maintained in saidheat soaking zone for a period of about six to twenty hours.

ReferencesCitcd in the file of this patent UNITED STATES PATENTS 1,789,380 Edwards etal Jan. 20, 1931 1,858,972 Snyder May 17, 1932 2,026,923 Warner Jan. 7, 1936 2,117,497 Owens May 17, 1938 2,445,327 Keith July 20, 1948 2,536,098 Royster Jan. 2, 1951 OTHER REFERENCES Snow: Ind. & Eng. Chem., vol. 24, No. 8 (1932) pgs. 903 to 909.

Claims

1. A PROCESS FOR DESULFURIZING PETROLEUM COKE BY HEAT SOAKING THE COKE AT A TEMPERATURE OF ABOUT 2500* TO 3000* F. INCLUDING THE STEPS OF PASSING THE COKE THROUGH A HEATING ZONE, A HEAT SOAKING ZONE, AND A COOLING ZONE, IN THE SAID COOLING ZONE CONTACTING HOT COKE FROM THE HEAT SOAKING ZONE WITH A FUEL GAS COMPRISING PRINCIPALLY METHANE, IN THE SAID HEAT SOAKING ZONE CONTATING COKE FROM THE SAID HEATING ZONE WITH THE SAID FUEL GAS FROM THE COOLING ZONE IN THE PRESENCE OF OXYGEN WHEREBY OXIDATION OF THE COKE IS MINIMIZED BY THE PREFERENTIAL COMBUSTION OF THE FUEL GAS PROVIDING TEMPERATURES OF 2500* TO 3000* F., AND MAINTAINING THE COKE IN THE HEAT SOAKING ZONE FOR A PERIOD SUFFICIENT TO DECOMPOSE SULFUR COMPOUNDS, AND IN THE HEATING ZONE CONTACTING COKE WITH HOT EFFLUENT GASES FROM THE HEAT SOAKING ZONE, SAID PROCESS FUTHER BEING CHARACTERIZED BY USE OF AN EXCESS OF FUEL GAS BEYOND THAT REQUIRED FOR COMBUSTION TO PROVIDE A HEAT TRANSFER MEDIUM BETWEEN SAID ZONES.