US3475323A - Process for the preparation of low sulfur fuel oil - Google Patents

Description

Oct. 28, 1969 A N, STUCKEY, JR, E'rAL 3,475,323

PROCESS FOR THE PREPARATION OF' LOW SULFUR FUEL OIL Filed May l, 196'? lmoOOw W4@ United States Patent O U.S. Cl. 208-97 10 Claims ABSTRACT F THE DISCLOSURE A low sulfur, low metals fuel oil is produced from a petroleum crude oil or distillation residue thereof by the steps of mild coking, distillation and hydrodesulfurization.

This invention relates to a process for the preparation of fuel oil of the type burned in industrial furnaces, particularly furnaces located at plants in or near metropolitan areas. More particularly, the invention relates to a process for upgrading high sulfur, high metals content petoleum crude or residual fractions for use as industrial Very large quantities of industrial fuel oils are burned daily in areas such as the eastern seaboard of the United States. Recently, statutes limiting the sulfur content of residual fuel have been enacted in eastern metropolitan areas. Sulfur contents of less than 3 wt. percent, preferably less than 1 wt. percent are being required to reduce air pollution.

A number of Latin American crude oils are favorably located for processing and shipping to the large eastern markets. However, in addition to a high sulfur content these oils -are characterized by a high content of metals such as iron, nickel and vanadium. These metals have an adverse effect upon the catalysts used in hydrodesulfurization of the resduum. In addition, if the metals are present in the fuel, they -attack the refractories used to line boilers and combustion chambers; cause slagging and buildup of deposits upon boiler tops, combustion chamber walls and the blades of gas turbines and they severely corrode high temperature metallic surfaces with which they come into contact.

The feedstocks of the present invention are also characterized by a high content of high molecular Weight hydrocarbons having complicated ring structures and a high carbon-to-hydrogen ratio. Asphaltenes and resins are representative of this type of hydrocarbon. These materials are the source of carbonaceous deposits laid down on the catalyst surfaces during the hydrodesulfurization reaction.

The buildup of metals and coke on the catalyst accelerates deactivation. Higher temperatures and higher hydrogen pressures must be employed to maintain hydrodesulfurization. Even with high hydrogen pressures it is not possible to obtain satisfactory catalyst activity maintenance with feeds containing large concentrations of metals and asphaltic components and as a result run lengths are short ad high catalyst replacement costs are incurred. Also high pressures and temperatures cause cracking and a reduction in the quantity of fuel oil product.

It is an object of this invention to provide an eilcient, economical method for obtaining low sulfur, low metals content residual fuel oil fractions and fuel oil blends by hydrodesulfurization. It is another object of the invention to carry out the hydrodesulfurization with a minimum conversion of fuel oil components to gas and light ends, and with a reduced deposition of carbonaceous and metal materials on the catalyst whereby the desired reduction in the sulfur content of the fuel oil is obtained over long periods at consistently high catalyst activity and life and at moderate conditions. Another object of the invention is to pretreat the fuel oil feedstock in the treating step which reduces the metals and coke precursor content of the oil and which provides a source material for making hydrogen which can be used in the process. Another object of the invention is to concentrate the metals in the feed in a form suitable for subsequent recovery of the metals.

In brief summary the objects of the invention are accomplished by subjecting a high sulfur, high metals content fuel oil feedstock to mild coking, taking the total coker overhead product boiling above about 600 F. or separating a fraction boiling in the gas oil boiling range from the coker overhead and subjecting either of the latter stocks to hydrodesulfurization.

In a preferred embodiment coke from the coking step is treated to produce hydrogen and a high metals coke concentrate is recovered.

The harmful effects of the organo-metallic components of the feed during the desulfurization step are shown in the following comparative runs. Feed A is a heavy Arabian (Safaniya) atmospheric residuum; Feed B is a topped Venezuelan (Bachaquero) crude. Feed A has 4.0% sulfur by weight and 84 p.p.m. V, 32 p.p.m. Ni, and 11 p.p.m. Fe by weight; Feed B has 2.65% sulfur by Weight and 316 p.p.m. V, 58 p.p.m. Ni, and 9 p.p.m. Fe by Weight. Processing conditions in the comparative desulfurization tests were 1500 p.s.i.g. pressure, 725 F. initial temperature, 1500 s.c.f./b. treat gas (97% H2, 3% CH4) and the tests were carried out over identical commercial CoMo/ A1203 catalyst. The tabulation vbelow compares the rate of loss of catalytic activity expressed as percent loss in kinetic activity (rate constant) per day; also shown are the temperatures required to achieve sulfur removal as a function of time for both feeds.

As shown by this comparison catalyst life is substantially shorter with the high metals Venezuelan feed (Feed B) as operations above 780-800 F. lead to substantial cracking and product degradation. By employing a coking step prior to the desulfurization step it is possible to convert a high metals feedstock to one with moderate or low metals.

The invention will be more fully described with reference to the attached drawing which is a fiow diagram of one embodiment of the process.

The process of this invention is specifically designed to prepare fuel oils from stocks having a high total content of sulfur compounds, metals compounds and coke formers. Typical feeds include heavy whole crude oils, atmospheric residuums, vacuum residuums, visbreaker bottoms, and crude oils topped by flashing or any other means. Generally speaking the from 30 to 90 wt. percent of the feed boils above 900 F. The preferred feedstocks are atmospheric residual bottoms having an initial boiling point ranging from 500 to 800 F. The characteristics of the feedstocks of the process are set forth below in Table Il.

TABLE II.-FEEDSTOCK CHARACTE RISTICS Particularly suitable fuel oil feedstocks have inspections like the Latin American fractions shown in the following table.

TABLE IIL-FEEDSTOCK INSPECTIONS Cil somewhat from the prior art in that coking conditions are carefully controlled to reduce a maximum quantity of oil for the subsequent hydrodesulfurization step which is low in metals and coke formers.

The effects of conversion, temperature and steam rate on product distribution and fuel oil metals content obtained by uid coking of a nominal Bacliaquero reduced crude (925 F.-l fraction, are shown by the data in the following table.

TABLE IV.FLUID SOLIDS DEASHING OF 50% BACllA QUERO REDUCED CRUDE Temperature, "F

Feed '937 Wt. percent steam GO. 1 55. 3 23. 4 1,015 F. conversion, vol. percent J. 1 55. 6 74. 5 Yields, on feed:

Coke, wt. percent 11.7 15.0 17.8 G3; wt. pereent. '5.1 l. 0 5. 0 C4, vol. percent 0.8 1.2 1.1 (l5/300 F., vol. percent. 9. 3 11.1 8.15 30o/600 F., vol. percent-.. S. 0 11.8 9. 8 600/1,025 F., vel. percent... 42. 1 27. 2 37. 0 300 F. plus, voi. percent 79. 2 73.6 72. 9 Conradson carbon, wt. percent 4. 6 12.2 8. 9 Nickel, p.p.m.... 93 16 20 5 Vanadium, p.p.1n. 601 100 143 lil These data show that fluid coking effectively reduces metals content and Conradson carbon when feeding residua. The data also show that reducing equivalent cut point in the coker by decreasing steam dilution is just as ef'iicient as decreasing actual coker temperature. The effect of the steam is to alter the effective distillation cut point in the reactor. Thus effective distillation cut point is felt to be the controlling factor in metals removal.

Coker products are removed from the coker in the vapor phase by line 8 and passed to any suitable separation means such as a flash distillation tower 9. Gas and light Tia Juana Medium At- Bacliaquero Bucliaquero mosplieric Vaccuuin Crude Rcsiduuni R esid Gravity, API 16.5 10.4 G. 7 Sulfur, wt. percent 2. 23 2. 16 3. 3 Carbon, Conradson, \vt pe1ce1 0. 8 10.9 18. 4 Metals, p.p.m.:

Vanadium 317 278 635 Nickel. 34 90 lron 34 t) Total 406 321 Total items 2-4, wt. percent. 12.03 13.06 C-H Analysis, C, wt. percent. 85. 93 CH Analysis, H, wt. percent. 11. 43 C/H atm. ratio. 0.63 Asphaltenes (MNI), wt. percent 10 Viscosity, S.S.F. at 122 F 77.5 226 Viscosity, S.S.F. at 250 F. 349 Pour point -5 22 softening point- 150 Quantity of feed 40 40 75 Referring to the drawing a Bachaquero reduced crude feed containing 601 p.p.m. V, 93 p.p.m. Ni, and 22 wt. percent Conradson carbon is passed by line 1 to fluid coker 2. Steam at a temperature of 900 to 1050 F. is passed by line 3 to the coker. The coke is maintained in a uidized state. Coking is carried out at a temperature in the range of 900 to 1100 F., a pressure ranging from atmospheric pressure to 70 p.s.i.a., in the presence of 5 to 100 wt. percent steam based on the feed. Small particles of petroleum coke, formed in the process itself circulate in a fluidized state between the coker 2 and the coke burner 4 and they serve as the heat transfer medium. Coke is passed by line 5 to the coke burner 4. A portion of the coke, i.e., 5 to 50 wt. percent is continuously burned in the presence of air supplied by line 6. Hot coke is returned to coker 2 by line 7. If the hydrogen production step described subsequently in this description is not employed part ofthe coke can be recovered from burner 4 as a cokemetals concentrate. The equipment and technology of fluid coking is available in the prior art and constitutes no part of the invention. The coking Step of the invention differs ends and liquids boiling up to 600 F. are removed overhead from the tower by line 10. In the preferred embodiment, all of the 600 F. plus material is passed by line 11 to the hydrodesulfurization reactor. The treatment of such a high boiling feed in a conventional hydrodesulfurization reaction is made possible by the metals and carbon reduction accomplished by the coking step. In another embodiment, not shown in the drawing, a vacuum distillation tower replaces the ash tower and a side cut boiling in the range of 600-1150 F. is recovered as the hydrodesulfurization feed and the bottoms from the vacuum tower, i.e., the 1150 R+ fraction is blended with desulfurized oil. Alternatively all or part of the 1150 F. can be recycled to the coker.

The coked hydrodesulfurization feedstock in line 11 has been reduced in metals content at least 50 wt. percent and more commonly iat least 75 wt. percent. Furthermore, the asphaltene content has also been reduced at least S0 wt. percent and more commonly at least 75 wt. percent. Similarly the Conradson carbon content of the oil `has been reduced at least The fraction is passed into hydrodesulfurization reactor 12. The reaction is carried out infa conventional reactor of the fixed bed, moving bed, or uidized bed type. The oil is preferably contacted in the liquid phase. Typical conditions are as follows:

TABLE V.-REACTION CONDITIONS Broad Range Preferred Range Temperature, F y 500-900 650-800 Pressure, p.s..g 500-3, 000 l, 000-2, 200 Space velocity, v./v. 0. 2-4. 0 0. 5-2. 0 Hydrogen rate, s.c.f.[b 500-10, 000 1,500 5, 000

Conventional hydrofining catalysts can be employed. Such catalysts include salts of metals of Groups VI and VIII of the Periodic Table supported on a suitable porous support material such as alumina, silica alumina, bauxite, magnesia and the like. Catalysts containing oxides or sulfides of cobalt, nickel, molybdenum and tungsten are preferred. Oxide catalysts are preferably sulfided prior to use or in situ. The most preferred catalyst is one containing 2 5 wt. percent cobalt oxide, 10i-25 wt. percent molybdenum oxide and the balance silica stabilized alumina. 'I'he preferred silica content of the base is 1.5 to 5 wt. percent. l

Hydrogen is fed to the reactor by lines 13l and 14. Hydrodesulfurization efiiuent is removed from the reactor by line 15 Iand passes to separator 16. Recycle gas passes overhead :by line 17 from the separator to gas purification system 18. Low sulfur fuel oil is recovered by line 19. If desired tHe oil in line 19 can be fractionated by any suitable means into a plurality of fuel oil cuts.

In gas purification system 18, hydrogen is separated from H28, NH3, CO, CO2 and other gases and light ends by known means such as cooling,water washing, amine scrubbers, the hot carbonate process or a combination of these gas purification techniques-Hydrogen is recycled by line 14. Gas impurities are purged by line 20.

In a preferred embodiment all or part of the hydrogen for hydrodesulfurization is prepared in the process. Referring to coke burner 4 in the drawing, coke is removed by line 21 from the burner at a temperature of 1300 to l500 F. after burning with air. The burning step tends to concentrate the metals in the coke. Coke is passed from line 21 into a water gas shift convertor 22 where it is contacted with steam from line 23. The hot coke and steam undergo the Well known water gas shift reaction, i.e.,

If desired, the CO and H2 product mixture may be further processed over a nickel catalyst to produce additional H2, i.e.,

The hydrogen containing gas from convertor 22 is passed by line 24 to gas purification system 18 for removal of impurities by known means.

Alternate processes for making H2 from coke include the partial oxidation process (Hydrocarbon Processing, September 1966, vol. 45, No. 9).

A part of the coke is recycled by line 25 from con vertor 22 to burner 4 for reheating and the remainder of the coke is recovered by line 26 iin the form of a cokemetals concentrate. The concentrate will contain from to 90 wt. percent vanadium, nickel and iron. The coking, coke burning and hydrogen making steps all serve to raise the metals concentration ofthe concentrate recovered by line 26. The metals can be recovered from coke by known means. A typical method is shown in U.S. Patent 3,226,316 issued Dec. 28, 1965.

The foregoing description and data show that the sequenc of mild coking and mild hydrodesulfurization provide an extremely effective means for preparing furnace oils from stocks having a very high content of sulfur, metals and coke formers. When the steps of hydrogen production and coke-metals concentrate recovery are integrated into the process, the combination provides an efficient, low overall cost solution to the production of furnace oils from highly contaminated feedstocks.

What is claimed is:

1. In a process for the preparation of low sulfur fuel oil by catalytic hydrodesulfurization, the improvement comprising the steps of (a) pretreating a fuel oil feed containing at least 1.0 wt. percent sulfur, at least p.p.m. metals, and at least 5 wt. percent asphaltenes in a fluid coking step at a temperature in the range of 900 to 1100 F. in the presence of 5 to 100 wt. percent steam and proportionally reducing the quantity of steam employed in said liuid coking stop as the temperature is increased over said range whereby the effective distillation cut point is controlled;

(b) recovering in toto all liquid fractions from the coking step, which fractions would contain no more than 50% of the metals and asphaltene content of the feed to the coking step; and

(c) contacting the total liquid effluent from the coking step with hydrogen and a hydrodesulfurization catalyst at hydrodesulfurization conditions and recovering low sulfur fuel oil.

2. Process according to claim 1 in which the catalyst is sulfided cobalt molybdate on silica alumina,

3. Process according to claim 1 in which from 30 to 90 wt. percent of the residual crude oil fraction boils above 900 F.

4. Process according to claim 1 in which the total sulfur, Conradson carbon and metals content of the residual crude oil fraction is in the range of 7-33 wt. percent.

S. Process according to claim 1 in which the total metals content of the residual crude oil is 22S-800 p.p.m.

6. A process for making an improved low sulfur content fuel oil from a high sulfur content, high metals content residual petroleum oil fraction comprising the steps of:

(a) coking said oil in a fluid coking step at a temperature in the range of 900 to 1100 F. in the presence 0f 5 to 100 wt. percent steam and proportionally reducing the quantity of steam employed in said fluid coking step as the temperature is increased over said range whereby the effective distillation cut point is controlled;

(b) recovering coker products;

(c) distilling lthe coker products to segregate a 600 F.}- bottoms fraction containing less than 50 to p.p.m. metals;

(d) subjecting said fraction to mild hydrodesulfurization at a temperature in the range of 500 to 900 F., a pressure in the range of 500 to 3000 p.s.i.g. in the presence of 500 to 10,000 s.c.f./b. of a hydrogen containing gas and a catalyst comprising a salt of a metal selected from Group VI-B or Group VIII-B of the Periodic Table and mixtures thereof on a suitable support material whereby the hydrodesulfurization reaction is carried out with a minimum deposition of carbonaceous and metal materials on the catalyst at a high rate of catalyst activity and sulfur removal; and

(e) recovering f-uel oil containing less than 50% of the sulfur present in the process feedstock.

7. Process according to claim 6 in which the cokemetals concentrate contains 10 to 90 metals.

8. Process according to claim 6 in which the cokemetals concentrate contains a major amount of vanadium.

9. Process according to claim 1 in which at least a portion of the hydrogen used in the process is produced by (d) recovering fluid petroleum coke from step (a);

(e) passing the coke to a coke burner;

(f) burning the coke;

(g) passing coke at a temperature of at least l400 F., to a water gas shift converter;

7 8 (h) reacting the coke with steam to produce a hydro- (l) passing the hydrogen to hydrodesulfurization step gen containing gas; (d); (i) separating hydrogen from the other product gases; (m) recovering fuel oil of reduced sulfur and metals (j) passing the hydrogen to hydrodesulfurization step content; and Y (c); 5 (n) recovering a coke-metals concentrate. (k) recovering fuel oil of reduced sulfur and metals content; and References Cited (l) recovering a coke-metals concentrate. UNITED STATES PATENTS 10. Process according to claim 6 lin which at least a (f) recovering uid petroleum coke from step (a); 2885350 5/1959 Brown et al 20S-127 2,894,897 7/1959 Post 208-127 (g) Passing the coke to a coke burner 2 901 417 8/1959 cook et a1 208-97 (h) bummgthe Coke; 3,226,316 12/1965 Metrailer et al. 20s- 251 (i) passing coke at a temperature of at least 1400" F., 15

t0 a Wafer gas Shlff CDIF/effen HERBERT LEVINE, Primary Examiner (1) reactmg the coke wlth steam to produce a hydrogen containing gas; U'S' C1' X'R' (k) separating hydrogen from the other product gases; 208-127, 130

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