US2979388A

US2979388A - Method of heat hardening of fluid coke briquettes

Info

Publication number: US2979388A
Application number: US630057A
Authority: US
Inventors: James W Brown; Edward A Destremps
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1956-12-24
Filing date: 1956-12-24
Publication date: 1961-04-11
Anticipated expiration: 1978-04-11

Description

United States Patent METHOD or rtEA-T HARDENING or FLUID corn; nnrounrrns James W. Brown, Mountainside, and Edward A.

Destremps, Cranford, N.J., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed m n, 1956, Ser. No. 630,057 10' creams. (Cl.44--16) This invention relates to improvements in the heat hardening of fluid coke briquettes. I More particularly it relates to a process of this nature wherein a dehydrogenating chemical is incorporated during the briquetting of fluid coke so that the resulting briquettes can be better heat hardened in a one-stage treatment while in the form of a moving bed without any extraneous preliminary heating or pretreating step. V

There'has recently been developed an improved process known as the fluid coking process for the production of fluid coke and the thermal conversion of heavy hydrocarbon oils to lighter fractions, e.g., see US. Patents 2,725,349 and 2,721,169. For completeness the process is described in further detail below although it should be understood that the fluid coking process itself is no part of this invention.

The fluid coking unit consists basically of a reaction vessel or coker and a heater or burner vessel. In a typical operation the heavy oil to be processed is injected into the reaction vessel containing a dense, turbulent, fluidized bed of hot inert solid particles, preferably coke particles. A transfer line or staged reactors can be employed. Uniform temperature exists in the coking bed. Uniform mixing in the bed results in virtually isothermal conditions and effects instantaneous distribution of the feed stock. In the reaction zone the feed stock is partially vaporized and partially cracked. Effluent vapors are removed-from the coking veseel and sent to a fr'actionator for the recovery of gas and light distillates'therefrom. Any heavy bottoms is usually returned to the coking vessel. The coke produced in the process remains in the bed coated on the solid particles. Stripping steam is injected into the stripper to remove oil from the coke particles prior tothe passage of the coke to the burner.

The heat for carrying out the endothermic coking reaction is generated in the burner vessel, usually but not necessarily separate. A stream of coke is thus transferred from the reactor to the burner vessel, such as a transfer line or fluid bed burner, employing a standpipe and riser system; air being supplied to the riser for conveying the solids to the burner. Suflicient coke or added carbonaceous matter is burned in the burning vessel to bring the solids therein up to a temperature sufficient to maintain the system in heat balance. The burner solids are maintained at a higher temperature than the solids in the reactor. About 5% of coke, based on the feed, is burned for this purpose. This may amount to approximately 15 to 30 wt. percent of the coke made in the process. The net coke production, which represents the coke make less the coke burned, is withdrawn.

Heavy hydrocarbon oil feeds suitable for the coking process include heavy crudes, atmospheric and crude vacuum bottoms, pitch, asphalt, other heavy hydrocarbon etroleum residua or mixtures thereof. Typically such feeds can have an initial boiling point of about 700 F. or higher, an A.P.I. gravity of about to 20, and a Conradson carbon residue content of about to 40M.

ice

- 2 percent. (As to Conradson carbon residue see A.S.T.M. Test Dl894l.)- g Q A problem in the marketing of the fluid coke product is the small size of the particles, predominantly, i.e., about 60-90 wt. percent, in the range of 20 to 80 mesh'. The production of substantially larger particles is inconsistent with satisfactory operation of the fluid bed. On the otherhand industrial requirements for coke often necessitate particles having a diameter of about at least 4; inch to 2 inches. 1

These fluid coke particles have accordingly been contpacted into briquettes using various carbonaceous binder substances. The agglutinating carbonaceous binder sub.- 7

stances that'can be utilizedinclude suitable hydrocarbon binders, such as asphalt'and other heavy petroleum resie dues; aromatic tars, e .g. vacuum-reduced thermal tars, heavy'ends of coal tar, such as coal tar pitches having a softening point of about 100 to 250 F, heavy ends frointhe coking operation (coker bottoms) i.e. 1050'? V F.+material and mixtures thereof. Some specific'trade examples of the binders are Elk Basin residuum (160v F. softening point), Enjay 160 Asphaltand Hawkins coker bottoms. Lower softening point binders can be air blown to the 150 F. softening point desired. These substances are utilized in an amount of about 5 to wt. percent based on the coke charge and preferably 5 to 15 wt.

' percent. The binder can also be admixed with steam in an amount of 1 to 10 wt. percent to produce a finely atomized spray which makes for better mixing with the coke particles.

The fluid coke can be used as is to make briquettes, but the behavior of briquettes during heating and the strength of the final products are improved by grinding part or all of the coke to produce finer particles. The optimum temperature for binder mixing with the coke is one at which the binder has a viscosity in the range of 1000 to 5000 centipoises, for example 2500 centipoises. The briquetting should be done at a temperature slightly above the softening point of the binder or binders utilized, i.e.; conveniently at a temperature in the range of to 200 -F.,.for example F. The mixture is then briquetted by molding in apress at a pressure of about 2100 to 20,000 p.s.i. Roll presses such as those commonly em-.

ployed to make briquettes from coal and other materials can be used. Suchmachinesare described in the article Agglomeration in Chemical Engineering, October l, pages 161-165. The mixtures pass directly to the pressing rol s. a 1

These briquettes require heat hardening at a tempera,- ture of above 700 F. to decompose the binder to a carbonaceous residue, devolatilize the coke and'to produce adequate strength and cohesion. Treating at these temperatures, however, because ofthe melting of the binder material results in the deformation of the compactions and also fusion, i.e., adherence to each other.

Several methods have been proposed to overcome these difficulties. Some of them deal with particular ways of conducting a preliminary heat hardening step so as to avoid subsequent deformation in thehigher temperature carbonization treatment. Curing the briquettes by treat.- ,ment with an oxygen-containing gas at a low temperature has also been proposed. This latter operation' r'zequires special equipment.

This invention provides an improved method of thermally hardening compactions of fluid" coke which overcomes these difiiculties. The method comprises incorporating a dehydrogenating chemical with the fluid coke briquettes and then heating the briquettes while in the form ofa falling, moving bed to a temperature in the range of 1000 to 3000" F. by countercurrent contact with hot inert .gases. The gases leaving the top of the moviug'hed .(Whe're briquettes enter) are at a temperature in the range of 450 to 1500 F., preferably 800 to 1000 F. to allow reaction to occur before softening. The chemicals that can be utilized include chemicals such as sulfur, P H 80 MnO- and S Cl Sulfur and P 0 are particularly effective and desirable. The chemical'can be utilized in an amount of about to 60 wt. percent based on the agglutinating carbonaceous binder substance. The chemical is incorporated with the binder during the briquetting operation or after the briquettes have been made as by dipping in, e.g. 96% H 80 and no other modification in the latter is required. It is particularly surprising to find that the chemicals work in the manner indicated to rapidly impart strength to the briquettes so that they can be heated without falling apart or sticking to each other. An unduly high sulfur content in a briquette is normally undesirable. The utilization of sulfur as taught herein does not, however, increase its content in the final briquette product. It selectively goes to the binder material and is removed during the subsequent heat treatment as hydrogen sulfide. The briquettes as produced with the introduced chemical are then fed to a vertical elongated heat treatment zone conveniently ashaft furnace. They are there heated, first by contacting with the exit gases at 450 to 1500 F. as described before, then in the form of a downward moving bed to a temperature in the range of 1000 to 3000 F. for a total time interval of about /2 to 5 hours. The requisite temperature is provided by countercurrent contact with hot inert gases, which enter the heat treating zone at a lower portion thereof. The

gases leave the bed at a temperature in the range of 450 to 1500 F. to effect rapid chemical action. Lower exit temperatures would allow the briquettes to soften. The hot inert gases include materials like CO CO, N etc. Preferably the inert gases are flue gases from combustion systems. Combustible material can be fluid coke itself or an extraneous fuel such as fuel oil or natural gas. The combustion is supported by an oxygen containing gas such as air but preferably no oxygen contacts the briquettes. The superficial velocity of the inert gases is in the range of 0.1 to ft./sec. so that the briquettes flow downwardly in the form of a moving bed countercurrently thereto.

The advantages of this invention will be better understood by reference to the following examples.

EXAMPLE 1 Briquettes were prepared from fluid coke in the manner taught with the binder indicated below and various additives in the amounts indicated in the table. The briquettes were then first heat heardened at a temperature of 425 F. with nitrogen in the manner taught. The results are presented below on the compression strength of the briquettes prepared with various binders.

l 2.1 s.c.f.m. gas at 425 F. or 0.17 ft./sec. velocity.

2 Briquettes contained 7% Coker Bottoms plus indicated percentage of additive based on coker bottoms weight.

These results demonstrate the greatly improved compression strength of the briquettes prepared with P 0 as compared to those prepared with other additives or the control. These strentghs are still below the -30 lbs. required to prevent deformation because the temperature was below the range specified or insufficient for reaction.

EXAMPLE II A similar test was conducted as in Example 1 except that the temperature of first contacting with hot gases was 900 F.-to increase the rate of reaction. The results, presented below, show that strengths sufficient to withstand deformation were achieved.

1 2.1 s.c.f.m. gas or 0.17 ft./sec. gas velocity. 2 Briquettes contained 7% coker bottoms plus indicated percentage of additive based on coker bottoms weight.

The results again demonstrate the superiority obtained in strength by the use of this invention. The object is not to increase the final crushing strength of the product but rather to rapidly impart 20-30 lbs. crushing strength so that the briquettes can be retorted without squashing in the subsequent heating bed.

EXAMPLE 3 Briquettes were prepared in the same manner as Example 1 except that sulfur was incorporated as the additive in the amounts shown. The briquettes were first contacted while in the form of a fixed bed with nitrogen at 900 F. for the time interval indicated. are presented below.

The results Table III STRENGTH OF SULFUR BRIQUE'ITES HEATED AT 900 F. IN NITROGEN ATMOSPHERE Crushing Strength in Pounds After- N 2 Rate, SulInr Content c.f.m.

1 a 5 IIllD. 111111. 111171. 111111. mm. min.

1 No strength.

These results demonstrate how the crushing strength was rapidly increased through the addition of the sulfur without any preliminary heat hardening step allowing the briquettes to be retorted without deformation.

The conditions usually encountered in a fluid coker for fuels are also listed below so as to further illustrate how the fluid coke was prepared.

CONDITIONS IN FLUID (JOKER REACTOR Broad Preferred Range Range Temperature, "F 850-1, 200 900-1, 000 Pressure, Atmospheres 1-10 1. 5-2 Superficial Velocity of Fluidizing Gas, ft./sec 0. 2-10 0. 5-4 Coke Circulation (Solids/oil ratio) 2-30 7-15 The advantages of this invention will be apparent to those skilled in the art. Very strong briquettes are pre pared in an economic manner without the requirement of a preliminary, extraneous, heat treatment or curing step. I

If it is desired the fluid coke can be devolatilized, de-

allows the binder to be rapidly carbonized before the briquettes have a chance to deform or squash. This method, however, increases fuel cost because of the hot exit gas temperature required.

The techniques described are applicable to the heat hardening of other forms of agglomerates such as extrusions or pellets made by rolling or snowball pelletizing.

In the case of relatively expensive additives such as P it is possible to recover some of the value of this chemical by condensing the phosphorus which is evolved during heat treatment.

It is to be understood that this invention is not limited to the specific examples which have been offered merely as illustrations and that modifications may be made Without departing from the spirit of the invention.

What is claimed is:

1. In the heat hardening of briquettes of fluid coke containing about 5 to 25 Weight of an agglutinating carbonaceous binder substance at temperatures at which the briquettes normally tend to deform and fuse, the improvement which comprises incorporating a compound selected from the group consisting of sulfur and P 0 into the fluid coke briquettes during their preparation in an amount between about and 60 weight based on the agglutinating carbonaceous binder and heating the briquettes while in the form of a downwardly moving bed to a temperature in the range of 1000 to 3000 F. by countercurrent contacting with hot inert gases which first contact the briquettes at a temperature in the range of 800 F. to 1500 F. to cause rapid reaction before softening and heating for a total time in the range of A to 5 hours.

2. The process of claim 1 in which the hot inert gases are oxygen free.

3. The process of claim 2 in which the compound is sulfur.

4. The process of claim 2 in which the compound is P 0 5. In the method of heat hardening and retorting of briquettes prepared from coke particles produced in the fluid coking process and containing about 5 to 25% by weight of an agglutinating carbonaceous binder based on the weight of the fluid coke particles at a temperature at which the briquettes tend to deform and fuse together when the briquettes are heated in a downwardly moving bed to a temperature above about 700 F. to decompose the carbonaceous binder to a carbonaceous residue and to form the heat hardened fluid coke bn'quette product, the improvement which comprises incorporating a dehydrogenating chemical selected from the group consisting of sulfur and P 0 with the fluid coke particles during preparation of the briquettes in an amount between about 10 and 60 wt. percent based on said agglutinating carbonaceous binder and then heating the sotreated fluid coke briquettes while in the form of a downwardly moving bed to a temperature in the range of about 800 F. to 3000 F. by countercurrent contacting with hot inert gases which first contact the briquettes at a temperature of at least about 800 F. for at least about 15 minutes to effect reaction before softening of the briquettts occurs by rapidly carbonizing said binder and to rapidly impart a minimum crushing strength to said briquettes so that they can be retorted without squashing in the subsequent higher heat hardening temperature in said moving bed.

6. In the method of heat hardening and retorting of briquettes made from coke particles produced in the fluid coking process and containing about 5-25 wt. percent of an agglutinating carbonaceous binder at a temperature at which the briquettes tend to deform and fuse together when passing downwardly as a moving bed during the heat hardening step, the improvement which comprises rapidly improving the crushing strength of the briquettes by treating said briquettes to impart a minimum crushing strength to said briquettes by incorporating into said binder and into said fluid coke briquettes during preparation thereof about 10 to wt. percent based on said binder of a dehydrogenating material selected from the group consisting of sulfur and P 0 and then heating the so-treated briquettes in the presence of inert gas at a temperature above about 700 F. for a period of at least about A hour to cause rapid reaction and carbonization of said binder before any substantial softening occurs.

7. A process according to claim 5 wherein said compound is sulfur.

8. A process according to claim 5 wherein said compound is P 0 9. A process according to claim 5 wherein said compound is sulfur and said sulfur is substantially completely removed during said heating step.

10. The process of claim 5 in which the compound is sulfur and addition of sulfur to said briquettes does not increase the sulfur content of the final briquette product.

References Cited in the file of this patent UNITED STATES PATENTS 850,232 Kline Apr. 16, 1907 1,488,606 Love Apr. 1, 1924 2,479,561 Elkan Aug. 23, 1949 2,721,169 Mason et a1. Oct. 18, 1955 2,725,349 Cahn et al. Nov. 29, 1955 2,776,935 Jahnig et a1. Jan. 8, 1957

Claims

1. IN THE HEAT HARDENING OF BRIQUETTES OF FLUID COKE CONTAINING ABOUT 5 TO 25 WEIGHT % OF AN AGGLUTINATING CARBONACEOUS BINDER SUBSTANCE AT TEMPERATURES AT WHICH THE BRIQUETTES NORMALLY TEND TO DEFORM AND FUSE, THE IMPROVEMENT WHICH COMPRISES INCORPORATING A COMPOUND SELECTED FROM THE GROUP CONSISTING OF SULFUR AND P2O5 INTO THE FLUID COKE BRIQUETTES DURING THEIR PREPARATION IN AN AMOUNT BETWEEN ABOUT 10 AND 60 WEIGHT % BASED ON THE AGGLUTINATING CARBONACEOUS BINDER AND HEATING THE BRIQUETTES WHILE IN THE FORM OF A DOWNWARLY MOVING BED TO A TEMPERATURE IN THE RANGE OF 1000* TO 3000*F. BY COUNTERCURRENT CONTAINING WITH HOT INERT GASES WHICH FIRST CONTACT THE BRIQUETTES AT A TEMPERATURE IN THE RANGE OF 800*F. TO 1500*F. TO CAUSE RAPID REACTION BEFORE SOFTENING AND HEATING FOR A TOTAL TIME IN THE RANGE OF 1/4 TO 5 HOURS.