US2568351A - Process for making fuel gas from natural gasoline and straight run gasoline - Google Patents

Description

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Paocss Fon MAKING FUEL GAs mou NATURAL GASOLINE AND STRAIGHT RUN GASOLINE Filed Jan. 22, 1948 2 Sheets`Sheet 2 Patented Sept.. 18. 195?` PROCESS FOR MAKING FUEL GAS FROM NATURAL GASOLINE AND STRAIGHT RUN GASOLINE Charles Gordon Milboume, Toledo, Ohio, assignor to Surface Combustion Corporation, Toledo, Ohio, a corporation oi' Ohio Application January 22, 1948, Serial No. 3,716

3 Claims. 1

The increased use of manufactured andl natural fuel gas for seasonal heating in urban areas is now taxing the capacity of many utilities to meet the demand. Various expedients are being utilized such as mixing semi-gaseous petroleum products, also called liquid petroleum gases, such as propane and butane with air and feeding the mixture into distributing mains up to a proportion which will not adversely afl'ect the eiiiciency of the appliances burning these mixed fuels.

More recently there has come into use a process for partially oxidizing or cracking the raw propane or butane with air and steam to m-ake a gas which, when cold enriched with additional propane or butane, will yield a fuel gas which in most of its characteristics is comparable with city gas made by the older processes and which is substantially completely interchangeable therewith. The advantageof such a process is that a cracking plant may be located almost anywhere along a distribution system without in any way adversely aiecting the appliances fed by such system. However, propane and butane are true.

gases at normal temperature and pressure; hence when stored in large quantities they must be liquefied under high pressure necessitating a multiplicity of pressure vessels which are comparatively highly expensive. In point of fact the cost of providing storage for a whole winters supply may exceed the total cost of the cracking plant and its auxiliaries. Furthermore, the cost of these products themselves is greatly enhanced by havingto provide high pressure transportation facilities which precludes transportation in bulk.

The present invention has for its object to provide a gas making process which shall involve the use of a petroleum feedstock consisting of gasoline selected from the group consisting of natural gasoline and straight run gasoline.` Because of its relatively low vapor pressure straight run gasoline presents no particular shipping and storage problems such as the use of high pressure storage vessels; nor does natural gasoline provided its vapor pressure is not permitted to exceed 26` pounds RVP (Reids Vapor Pressure). See A. S. T. M. Speciiication D32343.

In the present invention the selected gasoline feedstock is ilrst subjected to fractional distillation to obtain a rst portion (hereinafter called the enriching portion or fraction) consisting essentially of hydrocarbons lighter than or not heavier than Ce for reasons presently appearing and to obtain a second fraction (hereinafter called the cracking portion or fraction) consisting essentially of hydrocarbons not heavier than Cs for a reason presently appearing. The rem-aining fraction is a still bottoms residue suitable for use as fuel oil or as a motor fuel.

The next step is to partially oxidize the cracking portion of the feedstock with air and/or steam in the presence of a catalyst to produce a product gas rich in hydrogen and carbon monoxide. The final step is to cold enrich the partially oxidized product gas with the enriching portion of the feedstock.

The enriching fraction of the feedstock should not contain any appreciable concentration of hydrocarbons heavier than Ce primarily because a heavier hydrocarbon is likely to condense in the gas distributing system. For example, la distribution system supplying a 540 B. t. u. gas of approximately 0.69 specific gravity normally requires an enriching vapor which will not condense in the gas mains at a ground temperature of 40 F.; hence, a C7 hydrocarbon, such as heptane. or any of the heavier hydrocarbons cannot be used for enriching purposes because with the proportionfof enriching vapor required, even at pressures close to atmospheric, condensation starts at temperatures of F. as compared to approximately 24 F. for a Cs hydrocarbon such as hexane.

The cracking portion of the feedstock should not contain lany appreciable concentration of a hydrocarbon heavier than C9 primarily because a heavier hydrocarbon tends to deposit excessive amounts of carbon under the conditions of partial oxidation with resultant fouling of the catalyst in the cracking tubes. Generally speaking, one of the objects of the invention is to maintain the activity of the catalyst at a high level for long periods of time, such as seven days or more, after which the initial activity can be restored in less than two hours by reactivation with air or mixtures of air and steam.

The B. t. u. and specific gravity of the partially oxidized product gas as it comes from the cracking operation are controlled to a predetermined value by adjusting the steam to air ratio in the mixture fed to the catalytic cracking tubes; the heating value can be varied over a range of to 370 B. t. u. and the specic gravity from 0.35 to 0.71 as compared to air. Cold enrichment of this product gas with the enriching portion of the feedstock results in a finished gas of the desired B. t. u. value and specic gravity as will now be readilyl understood.

(Air Gas from Pentane) 2C|Hu 5031+ 18.8Nz=10C0 12H2 18.8Nz 8 l' (Steam Gas from Pentane) C5Hi2+5HzO=5CO+11Hz A more complete understanding of the invention may be had from the following description of a typical plant for the practice of the process.

In the accompanying drawings forming part of this specification, Fig. l is a diagrammatic view of a plant for the practice of the present invention. Figs. 2 and 3 are explanatory charts.

A plant constructed in accordance with the present invention comprises a still or fractionating column I of any preferred type for dividing the selected gasoline feedstock into the fractions already mentioned, namely, an enriching portion, a cracking portion, and a still bottom residue suitable for use as fuel oil or motor fuel. The plant also comprises a catalytic cracking furnace II wherein the cracking portion of the feedstock is catalytically cracked i, e., partially oxidized with an oxidizing agent such as steam and/or air to produce a product gas rich in hydrogen and carbon monoxide.

A storage vessel for the gasoline feedstock to be processed is indicated at I2. The feed line I3 to the still I0 includes a pump I4, a control valve I 5, and a heat exchanger I6.

The still bottoms residue is withdrawn from the still IIJ by a pump Il which delivers to a line 20, 2l which leads through the heat exchanger I6 and thence by line 23, 24 to burners 22 which heat the catalytic cracking furnace I I. A branch 25 at the junction of lines 23 and 24 delivers the excess fuel to storage or for other uses.

Heat for the fractionating of the feedstock in the column I0 may be supplied in any preferred way as by continuously withdrawing and reheating a portion of the still bottoms residue in a reboiler 26 to which a. feed line 21 delivers and from which a return line 30 extends.

The distillate coming from the still I0 is conducted by an overhead line 3I to a water-cooled condenser 32 where the heavier hydrocarbons are condensed, the condensed portion constituting the cracking portion of the feedstock. The vapors which do not condense constitute the enriching portion of the feedstock. From the condenser the condensate and uncondensed vapors flow to an accumulator 33. From the accumulator, the uncondensed vapor iiows through line 34, 35 to a mixing chamber 36. the said line having a control valve 31.

The condensate in the accumulator 33 is drawn therefrom by a pump 40 which delivers to two separate lines 4I and 42. A portion of the condensate is or may be returned to the still as reflux through line 4I which includes a control valve 43. The setting of the valve 43 is controlled by a reflux ratio iiow controller 44 which in turn is controlled by the metering orifice 45 in the feedstock line between the storage vessel I2 and the still. The remaining portion of the condensate, the cracking portion, ows through line 42 to a heated vaporizer 46 and thence to a mixing chamber 41 by way of a line 50 having a control valve I. Steam and air supply lines 52 and 53, respectively, also deliver to said mixing chamber 41. The setting'of the control valve 5I is controlled by a controller 54 which in turn is con- 4 trolled by a metering orifice 65 in the finished gas line 56. In the mixing chamber 41 the cracking Portion of the feed stock is mixed with steam and/or air in controlled proportions preparatory to being catalytically cracked or oxidized. The cracking furnace I I comprises a plurality of vertically disposed cracking tubes 51 arranged in laterally spaced relation in a heating chamber heated by the burners 22 which fire directly thereinto. The cracking tubes will ordinarily be made of a heat-resisting alloy and will ordinarily contain a divided catalytic material such as broken pieces of flrebrick impregnated with nickel nitrate or any other suitable catalyst. Before entering the cracking tubes the mixture from the mixing chamber is preheated in a preheater 60. The cracking temperature is preferably above 1600 F.

From the cracking tubes the product gas iiows to a cooler 6| where it is cooled to atmospheric temperature and thence to the mixing chamber 36 where it is cold enriched with the enriching portion of the feed stock. The quantity of enriching vapor added at 36 is controlled by an instrument 62 known in the trade as a Calorimixer," this instrument controlling the setting of the valve 31 in the enriching vapor feed line 34, 35, the instrument itself being responsive to the B. t. u. value of the finished gas in the nished gas line 56.

A typical analysis of the partially oxidized product gas is: CO2, 4.6%; CO, 23.0%; H2, 44.6%; CH4, 6.8%; N2, 21.0%-B. t. u. 288 and specific gravity of 0.57 compared to air at 1.0.

A typical analysis of the enriched product gas which can be used in place of a typical city gas of 540 B. t. u. and 0.68 specific gravity is: CO2, 4.2%; CO, 21.2%; H2, 41.0%; CHi, 6.3%; CiHm, 8.1%; N2, 19.2%.

The pressure in the accumulator 33 and the still or fractionating column I0 is controlled by a pressure controller 63 which is responsive to the vapor pressure in line 34. This controller controls the setting of a valve 64 in the water outlet line 65 from the condenser 32 and controls the quantity of cooling water fed to the latter through line 66.

The composition of the product gas from the cracking tubes 51 can be varied by varying the steam to air ratio in the hydrocarbon-steam-air mixture fed to said tubes from 41. For the purpose of illustration the chart in Fig. 2 is included to show the typical variations in composition, heating value and specific gravity of these product gases produced from pentane without cold enrichment when going from steam-gas to 100% air-gas, i. e., from infinite steam-air ratio to zero steam-air ratio. For further illustration the chart in Fig. 3 is included to show the typical variations in heating value and specific gravity of chart Fig. 2 gases when cold enriched with butane. Chart Fig. 3 also illustrates the variations in composition of a 1000 B. t. u. finished gas produced from catalytically oxidized pentane enriched with butane when the steam-air ratio is varied from infinity to zero.

It will now be apparent that the method herein disclosed offers a solution to the heretofore very difficult problem of handling and transporting the light petroleum fractions usable for the production and enrichment of fuel gases. By dissolving these light petroleum fractions such as Ce and lighter into the heavier fractions Cn to Ce it is now possible to handle and transport the solvent and solute in the same manner as ordinary gasoline and when these components arev fractionated followed by partially oxidizing the heavier and enriching with the lighter a stable fuel gas is now obtainable comparable and interchangeable with city gas.

It is believed that from the foregoing the process will be clearly understood by those skilled in the art. It will also be understood that changes may be made in the details disclosed without departing from the spirit of the invention as set forth in the appended claims.

What is claimed as new is:

l. A process of making fuel gas, which comprises the steps of (A) passing through a distillation zone a. petroleum feedstock selected from the group consisting of straight run gasoline and natural gasoline whose vapor pressure does not exceed 26 pounds Reids vapor pressure so as to divide the feedstock into three portions by fractional distillation, said portions being portion (l) comprised essentially of hydrocarbons lighter 'than Ce, portion (2) comprised essentially of C to Ca hydrocarbons, and portion (3) comprised essentially of hydrocarbons heavier than Cn; (B) passing portion (2) directly from the distillation zone to and'through a catalytic cracking zone and reacting it therein with an oxidizing agent of the class consisting of air, steam and mixtures thereof so as to produce a. product gas rich in hydrogen and carbon monoxide; and (C) passing portion (1) directly from the distillation zone into said product gas at a point adjacent the outlet of the catalytic cracking zone so as to enrich the product gas of step (B) 2. A process of making fuel gas, which comprises the steps of (A) passing a petroleum feedstock selected from the group consisting of straight run gasoline and natural gasoline whose vapor pressure does not exceed 26 pounds Reids vapor pressure through a still so as to strip off a fraction comprised essentially of hydrocarbons at least as light as Cn; (B) passing the stripped fraction in vapor form directly to and through a condensing zone vso as to divide the stripped fraction into two portions, said portions being a vapor portion (l) comprised essentially of hydrocarbons lighter than Ca and a condensed portion (2) comprised essentially of Ca to Ca hy drocarbons; (C) passing portion (2) directly from the condensation zone to and through a catalytic cracking zone and reacting it therein with an oxidizing agent of the class comslsting of air, steam and mixtures thereof so as to produce a product gas rich in hydrogen and carbon monoxide; and (D) passing portion (l) directly from the condensation zone into said product gas at a point adjacent the outlet of the catalytic cracking zone so as to enrich the product gas of step (C).

3. A process `of handling light petroleum fractions for'use in the manufacture of fuel gas. which comprises the steps of (A) dissolving a petroleum fraction of hydrocarbons lighter than Cs in a petroleum fraction comprised essentially of C9 to Ca hydrocarbons, for purposes of storage and shipment; (B) passing the solution of petroleum fractions obtained in step (A) through a. distillation zone so as to divide the solution into two portions by fractional distillation, said portions being portion (1) comprised essentially of hydrocarbons lighter than Ce and portion (2) comprised essentially of C9 to Cs hydrocarbons: (C) passing portion (2) directly from the distillation zone to and through a catalytic cracking zone and reacting it therein with an oxidizing agent of the class consisting of air, steam and mixtures thereof so as to produce gas rich in hydrogen and carbon monoxide; and (D) passing portion (l) directly from the distillation zone into said product gas at a point adjacent the outlet of the catalytic cracking zone so as to enrich the product gas of step (C).

CHARLES GORDON MILBOURNE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,235,777 marea et a1 Aug. 7. 1917 1,967,669 Hickey' July 24, 1934

Claims (1)

1. A PROCESS OF MAKING FUEL GAS, WHICH COMPRISES THE STEPS OF (A) PASSING THROUGH A DISTILLATION ZONE A PETROLEUM FEEDSTOCK SELECTED FROM THE GROUP CONSISTING OF STRAIGHT RUN GASOLINE AND NATURAL GASOLINE WHOSE VAPOR PRESSURE DOES NOT EXCEED 26 POUNDS REIDHS VAPOR PRESSURE SO AS TO DIVIDE THE FEEDSTOCK INTO THREE PORTIONS BY FRACTIONAL DISTILLATION, SAID PORTIONS BEING PORTION (1) COMPRISES ESSENTIALLY OF HYDROCARBONS LIGHTER THAN C6, PORTION (2) COMPRISED ESSENTIALLY OF C9 TO C6 HYDROCARBONS, AND PORTION (3) COMPRISED ESSENTIALLY OF HYDROCARBONS HEAVIER THAN C9; (B) PASSING PORTION (2) DIRECTLY FROM THE DISTILLATION ZONE TO AND THROUGH A CATALYTIC CRACKING ZONE AND REACTING IT THEREIN WITH AN OXIDIZING AGENT OF THE CLASS CONSISTING OF AIR, STEAM AND MIXTURES THEREOF SO AS TO PRODUCE A PRODUCT GAS RICH IN HYDROGEN AND CARBON MONOXIDE; AND (C) PASSING PORTION (1) DIRECTLY FROM THE DISTILLATION ZONE INTO SAID PRODUCT GAS AT A POINT ADJACENT THE OUTLET OF THE CATALYTIC CRACKING ZONE SO AS TO ENRICH THE PRODUCT GAS OF STEP (B).

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