US2976135A

US2976135A - Generation of carbon monoxide and hydrogen

Info

Publication number: US2976135A
Authority: US
Publication date: 1961-03-21
Anticipated expiration: 1978-03-21

Description

March 21, 1961 DU 501s EASTMAN 2,976,135

GENERATION OF CARBON MONOXIDE AND HYDROGEN FROM A LIQUID HYDROCARBON Filed Dec. 15, 1957 &

2,976,135 GENERATION OF CARBON MONOXIDE AND IgggROGEN FROM A LIQUID HYDROCAR- Du Bois Eastman, Whittier, Califl, assignor to Texaco Inc., a corporation of Delaware Filed Dec. 13, 1957, Ser. No. 702,661

3 Claims. (Cl. 48215) This invention relates to the production of a gas mixture containing carbon monoxide and hydrogen from a liquid hydrocarbon by partial combustion in a gas generator.

As the result of extensive research and numerous experiments I have found that it is beneficial to operate a gas generator under such conditions that a small critical amount of free carbon is deliberately produced along with the gases.

In the first place, I have found that the life of a gas generating combustion chamber is greatly lengthened when operating in such a way as to produce 0.5 to 10% of free carbon expressed as percent by Weight of the total carbon in the oil. notable when the oil happens to be one containing compounds of heavy metals which generally have a corrosive or erosive eilect on ordinarily refractory materials.

In the second place, within the broad range 0.5 to 10%, there is a narrower range of 0.5 to 5% Within which there is obtained the additional advantage of optimum thermal efliciency of the gas generating operation. The best thermal eificiency actually is obtained at a value of about 2% free carbon.

The single figure of the drawing is a graph showing the critical relationship between free carbon production and thermal efliciency in a gas generation process operating with partial combustion of fuel oil.

Petroleum commonly contains small quantities of heavy metals. The most common heavy metals contained in petroleurn are vanadium, nickel, iron, chromium and molybdenum. These heavy metals presumably occur in petroleum as compounds. The exact chemical compositions of the heavy metal compounds are somewhat in doubt. It is generally agreed that the metals are present, at least in part, in the form of oil-soluble metalloorganic compounds. Crude oils containing heavy metal constituents, and some heavy distillates from such crudes, have been found unsatisfactory for many purposes because of the nature of the ash from these fuels.

in particular, the naturally occurring compounds of vanadium and molybdenum contained in petroleum oils, upon oxidation, apparently yield very corrosive or erosive ash. The extent to which compounds of these metals are present in petroleum may vary from about 1 to about 1,000 parts per million by weight based upon the weight of the metal, per so. In general, petroleum oils containing even minor amounts of vanadium and nickel are troublesome when used as fuel. The ash from these fuels is corrosive or erosive to both refractories and to alloy metals. Of the heavy metal contaminants in petroleum fuels, vanadium and nickel appear to be the most detrimental to high temperature refractories, particularly aluminum oxide refractories.

A number of attempts have been made to treat ashcontaining liquid hydrocarbon fuels for removal or reduction of ash-forming constituents. These attempts hav been generally unsuccessful. The heavy metal con This advantage is particularly States Patent .may be employed in the process. 'tained by the rectification of air.

stituents of crude oils may be concentrated, to some extent, by means of distillation, the heavy metal constituents largely remaining in the distillation residues. Nevertheless, the metals of their compounds are also present in many distillate products, particularly in heavy fractions, such as products of vacuum distillation. The presence of the metals in the distillates may be due, either to actual vaporization of the metal compounds or to physical carryover or entrainment. These metals have also been found in such stocks as propane-deasphalted oil and solvent-refined distillate.

Recently, partial oxidation of hydrocarbons with oxygen to carbon monoxide and hydrogen has been developed commercially; the process is disclosed in US. 2,582,938 to du Bois Eastman and Leon P. Gaucher. In this process, a hydrocarbon, for example, fuel oil, is reacted with steam and air, oxygen, or oxygen-enriched air in a closed, compact reaction zone at a temperature in the range of about 2,000 to about 3,200 F. The reaction zone is free from packing and catalyst and has nearly minimum internal surface. The reaction may be conducted at atmospheric pressure or at an elevated pressure which may be as high as several hundred pounds per square inch. The reaction temperature, suitably about 2,600 E, is autogenously maintained. Preheating of the reactants is generally desirable. The amount of uncombined oxygen supplied to the reaction zone is limited so that near-maximum yields of carbon monoxide and hydrogen are obtained. The product consists essentially of carbon monoxide and hydrogen and contains relatively small amounts of unconverted hydrocarbon and carbon dioxide. l

Air, oxygen-enriched air, or substantially pure oxygen Oxygen may be ob- Commercial oxygen plants are available capable of delivering large amounts of high purity oxygen. Commercial oxygen, so pro- .duced, usually contains in excess of mol percent oxygen. Substantially pure oxygen, e.g., commercial oxygen, is generally preferred for generation of carbon monoxide and hydrogen.

The use of ash-forming hydrocarbons, particularly those containing vanadium and nickel, as fuels for the production of carbon monoxide and hydrogen by partial oxidation with oxygen has resulted in operational difiiculties. The reaction zone in which the partial oxidation takes place genera-11y comprises a steel pressure vessel provided with a high temperature refractory lining, for example, aluminum oxide. Ash from the fuel apparently combines with the refractory to form a composite having a lower melting point than that of the original refractory. The result of this combination is that the refractory melts away in a relatively short time (often a matter of a few hours) at usual operating temperatures of the order of 2,500 to 2,800 F. This results in overheating of the pressure vessel, a particularly dangerous condition when the gas generator is operated at elevated pressure. Since the low cost and the high B.t.u. content of heavy fuel oils and residua make them particularly attractive as fuels for the production of carbon monoxide and hydrogen by partial oxidation, it is desirable to devise a method for preventing attack on the refractories employed as linings for the gas generators. The present invention provides a method for the production of carbon monoxide and hydrogen from ash-containing hydrocarbons by partial oxidation with free oxygen in which the ash is sequestered with carbon, protecting the refractory lining of the gas generator.

In accordance with this invention, a hydrocarbon fuel containing mineral ash-forming constituents which are detrimental to the life of the refractory lining of the synthesis gas generator are introduced into the reaction Patented Mar. 21, 1961 zone of the gas generator together with sufiicient free oxygen to react exothermically with the fuel to autogenously maintain a temperature in the range of about 2,200 F. to about 3,200 F. and to convert not less than about 90 percent and not more than 99.5 percent of the carbon contained in the fuel to carbon oxides. The extent of conversion of the carbon may be varied within this range depending upon the amounts of heavy metals contained in the fuel. The quantity of unconverted carbon should be at least 50 times and preferably 100 times the combined weights of the nickel and vanadium contained in the fuels on the basis of the weight of the metal content of the metal-containing constituents present in the fuel. The unconverted carbon from the hydrocarbon is liberated as free carbon. Under these conditions of limited carbon conversion, the ash-forming constituents of the fuel, particularly the ash resulting from the heavy metal constituents, are associated with the carbon and the composite is liberated as a carbonaceous solid in particle form. The carbonaceous solid particles containing the heavy metals are substantially harmless to the refractory lining of the gas generator.

In a specific embodiment of the process of the present invention, oil containing mineral ash-forming constituents including nickel and vanadium is admixed with steam and fed into a compact, unpacked reaction zone. The reaction zone is free from packing and catalyst and has an internal surface area to volume of not more than 1.5 times the surface of a sphere equal in volume to the volume of the reaction zone. An oxygen-rich gas containing in excess of about 95 percent oxygen by volume is introduced into the reaction zone into intimate admixture with the oil and steam. The generator may be operated at atmospheric or superatmospheric pressure. Preferably the generator is operated at a pressure within the range of from about 100 to about 600 pounds per square inch gauge. The temperature within the gas generator is autogenously maintained within the range of 2,500 to 2,900 F.

The quantity of free oxygen supplied to the gas generator is limited so that the conversion of carbon to carbon oxides is limited to 95 to 99.5 percent of the carbon content of the oil feed to the gas generator. From about 1.8 to about 1.9 mols of free oxygen are supplied to the gas generator for each million B.t.u.s gross heating value of the oil feed to the gas generator.

The amount of unconverted carbon released as a carbonaceous solid in the generator is at least 50 times by weight the combined weights of the nickel and vanadium contained in the oil, based on the weight of the free metal content of the nickel and vanadium compounds in the fuel. Free carbon released in the gas generator is entrained in the gaseous products of reaction. Ash from the fuel, particularly the heavy metal constituents, is substantially completely retained in the carbonaceous residue. The hot gases from the generator containing entrained carbon are contacted with water in a gas scrubbing and quenching operation in which the gases are rapidly cooled to a temperature below the reaction temperature. The carbonaceous solid is removed from the gas stream in the scrubbing operation, and is then disposed of in a manner other than by burning it in the gas generator wherein its metal content would be released and damage the generator. The product gas is a mixture of carbon monoxide and hydrogen useful as 'feed gas for synthesis of hydrocarbons, methanol synthesis, or as a source of hydrogen for the synthesis of ammonia or for other purposes.

The following specific examples illustrate the effect of 'the limited carbon conversion on the life of a typical high temperature gas generator refractory. In each of the following examples the fuel oil was a San Ardo crude oil of the following composition and physical properties:

, Gravity API 12.s Viscosity S.F. at 122 F 650 4 Flash F 235 Pour point F 50 Conradson carbon 9.6 Gross heating value B.t.u./lb 18,450

Ultimate analysis:

Carbon Wt. percent..- 85.5 Hydrogen do 11.0 Nitrogen do 1.0 Sulfur do 1.9 Oxygen do 0.6 Ash:

Vanadium p.p.m 68 Nickel do 56 Iron do 57 The oil was atomized with steam and mixed with oxygen of 99.9 percent purity in a flow-type gas generator of the type disclosed in US. Patent 2,582,938. In each of the examples the generator was provided with 2 /2 inches of high purity alundum (aluminum oxide) lining surrounded by insulating firebrick.

Example l- Example 2 High Moderate Carbon Carbon Conversion Con version Feed Rates:

Oxygen e.t./l1r 186 12,187 Oil, lbs/hr--- 401. 5 954 Water, lbs/hr 224. 1 2.18 Dry Gas Production, c f /hr 20, 47, 915 Soot Production:

Lbs/hr l. 50 15.47 Weight percent of carbon i'etL 0. M 1. 8'.) Operating Conditions:

Temperature, F 2, 600 2, 850 Pressure, p.s.i.g 373 341 Preheat temp., F;

Oil-steam 710 7-50 Oxygen (i7 70 Mols O /MM Btu. oioil [ed 1.847 1 8:11

Product Gas Analysis:

Dry Basis, mol peroeut- CO 47. 0 40. 06 5 3. 71 0. 1 O. 44 0.02 47. 0 40. 51. 0. 3 O. 22 0.1 0. 04

Total 100.00 100. 00

After 186 hours of operation under operating conditions of high carbon conversion, representative data for which are shown in Example 1, the alundum lining of the generator was examined and was found to be so badly deteriorated as to preclude further operation of the generator. The lining was replaced and after about 673 hours of operation under conditions of moderate carbon conversion, some of the data for which are shown in Example 2, the lining was examined and was found to be in excellent condition. Operations continued with the same generator under similar conditions of moderate carbon conversion until a total operating time of about 3091 hours had been accumulated. During this period a number of heavy fuel oils were fed to the generator. Some of the fuel oils contained larger amounts of vanadium and nickel than the amounts contained in the San Ardo crude. At the end of this period, inspection of the lining of the generator showed that it was in excellent condition.

It will be evident from the foregoing that limiting the extent of carbon conversion in a synthesis gas generator wherein mineral ash-forming constituents are contained in the fuel so that sufiicient free carbon is released to sequester the ash, results in long life of the refractory lining of the generator and satisfactory operation over long periods of time.

The improved thermal efiiciency from operating with deliberate free carbon production is clearly demonstrated by the single figure of the drawing, which is a graph based on a large number of gas generation runs, the individual results of which actually lay on or close to the curve. Data for some of the runs are set forth in Table I below, the principal variable being the amount of carbon produced which varies inversely with the oxygen/oil ratio.

6 into said reaction zone in relative proportions such that a portion of the carbon contained in said hydrocarbon is uncombined and is liberated as a carbonaceous solid together with ash from said hydrocarbon and the weight All data were accumulated from runs. in the same mullite of the carbon liberated as a solid by said reaction is at lined autogenously heated synthesis gas generator using least 50 times the combined weights of the nickel and Bunker C fuel oil, oxygen and steam, and a generator vanadium contained in said liquid hydrocarbon supplied pressure of 400-450 p.s.i.g. to the reaction zone, and continuously removing from TABLE I B I o D i E I F G H Oxygen, Standard Cu. ft./hr 6,707 7, 6, 240 7, 612 5, 879 7, 520 35, 200 on, lbs/hr 504. 78 500. 8 510. 6 631. 67 492. s 030 2, 713 02/011, Mel/million Btu. 1. 024 1.88 1. 769 1. 745 1. 727 1. 704 1. 505 Water, lbs/hr 202.58 204. 27 320 208 310 198.86 320.5 2,288 CO+H2, Standard 011. ft/hr 23, 007 23, 510 26,169 24,186 29,754 23,305 29,935 118,874 Generator Temperature, F ,499 2, 363 2, 55 2, 163 2, 384 2,114 2, 603 2,200 Free Carbon in product gas, percent by weight of total carbon in oil .13 0. 24 1. 06 2. 2. 83 2. 84 4.18 4. 5 Thermal efficiency, percent 81.16 82.30 83.7 83.90 83- 39 84.04 82. 90 82.4

The important advantages of improved refractory life (particularly for ceramic materials) and improved thermal efiiciency discussed above increase the flexibility of the gas generation process. A wide variety of oils can be employed in the same generator, without having to analyze each oil carefully and make fine adjustments in the conditions of operation dependent upon the metals content or other composition variables.

This application is a continuation-in-part of my abandoned application Serial No. 487,451, filed February 10, 1955 'for Generation Of CO AND H From An Ashforming Hydrocarbon.

Obviously, many modifications and variations of the invention, as hereinbefiore set forth, may be made without departing from the spirit and scope thereof and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. In a process for the production of carbon monoxide and hydrogen from an ash-forming liquid hydrocarbon containing vanadium and nickel wherein said hydrocarbon is subjected to a partial combustion reaction with steam and free oxygen at a temperature above 2,000 F. in a reaction zone free from catalyst and packing, the improvement which comprises introducing said reactants the reaction zone gaseous products of reaction and said carbonaceous solid combined with ash from said hydro- References Cited in the file of this patent UNITED STATES PATENTS 1,078,304 Nix Nov. 11, 1913 2,558,760 Keith July 3, 1951 2,660,521 Teichmann Nov. 24, 1953 2,843,200 Rocchini July 15, 1958 OTHER REFERENCES Sachanan: Conversion of Petroleum, 2nd ed., 1948,

pp. 184-186 and 206-211.

Claims

1. IN A PROCESS FOR THE PRODUCTION OF CARBON MONOXIDE AND HYDROGEN FROM AN ASH-FORMING LIQUID HYDROCARBON CONTAINING VANADIUM AND NICKEL WHEREIN SAID HYDROCARBON IS SUBJECTED TO A PARTIAL COMBUSTION REACTION WITH STEAM AND FREE OXYGEN AT A TEMPERATURE ABOVE 2,000*F. IN A REACTION ZONE FREE FROM CATALYST AND PACKING, THE IMPROVEMENT WHICH COMPRISES INTRODUCING SAID REACTANTS INTO SAID REACTION ZONE IN RELATIVE PROPORTIONS SUCH THAT A PORTION OF THE CARBON CONTAINED IN SAID HYDROCARBON IS UNCOMBINED AND IS LIBERATED AS A CARBONACEOUS SOLID TOGETHER WITH ASH FROM SAID HYDROCARBON AND THE WEIGHT OF THE CARBON LIBERATED AS A SOLID BY SAID REACTION IS AT LEAST 50 TIMES THE COMBINED WEIGHTS OF THE NICKEL AND VANADIUM CONTAINED IN SAID LIQUID HYDROCARBON SUPPLIED TO THE REACTION ZONE, AND CONTINUOUSLY REMOVING FROM THE REACTION ZONE GASEOUS PRODUCTS OF REACTION AND SAID CARBONACEOUS SOLID COMBINED WITH ASH FROM SAID HYDROCARBON.