US2662051A - Conversion of heavy hydrocarbons - Google Patents

Description

Dec. 8, 1953 H. L. PELZER CONVERSION OF HEAVY HYDROCARBONS Filed Dec. 28. 1949 2 Sheets-Sheet lf EES:

. 8, 1953 H. 1 r-:| zERA 256325051 ACONVERSION OF HEAVY HYDROCARBONS.

Filed Dec. 28, 1949 2 Sheets-Sheet 2 Patented Dec. 8, T953 coNvEnsIoN on HEAVY HYDRocARBoNs Harry Louis Pelzer, Ogden Dunes, Ind., assigner to Sinclair Refining Company, New York, N. Y., a corporation of Maine Application December 2S, 19.4.9,l Serial No. 136,069

(Cl. 19H-51) 2y Claims.

This invention relates to improvements in the conversion of heavy hydrocarbon oils. More particularly, it relates to improvements in the economic utilization of heavy residua which to an undesired degree are the products of modern heavy oil distillation and cracking operations.

The disproportionate demand for light fuels as compared to heavy oils and fuels creates a severe disposal problem for the petroleum refinery. The heavy ends of crude oil contain substantial quantities of asphaltic and coke-forming materials which are left as end-products, in the form of asphalt, heavy residual fuel oil, or coke, of conventional operations such as vacuum distillation designed to strip out the maximum recoverable fraction of distillable hydrocarbons, cracking and Compared to the demand for ,gasoline and distillate fuels the market for heavy residual fuels and bituminous solids is smaller and less flexible. Hence the rei-incr has a major probleA in economic disposal. of residual materials, and this problem is aggravated asA the supply of residual materials is multiplied by increasing demand for the production of gasoline and distillate products.

I have now discovered an improved method for treating heavy oil stocks Which ,accomplishes a reduction in residuum produced and which effects an increase in the ultimate yield of gasoline produced from a given crude oil in over-all refinery operation. My method is especially practical in the sense that it is flexible and readily adapted to modern refinery practices. I have found that if heavy oils are heated to cracking temperatures in a fired heater so as to control residence 'time belovv that producing substantial cracking and if the preheated stock is flashed in a tower under conditions of reduced partial pressure and ininimum residence time, increased yields of gas oil useful as cracking feed stock and a surprisingly tially atmospheric conditions but with a partial 5 hydrocarbon pressure reduced by the presence of substantial quantities of steam.

I have found that when the so preheated stock is dashed under pressure conditionsof approximately atmospheric up toabout p. s. i. g. in the f y? presence Of steam in an amount approximating 10 t0 25 per cent by weight on the feed that the character of the conversion reaction is substantially shifted from conventional methods of treating heavy stocks. A higher yield of heavy gas oil is produced as distillate in comparison to vacuum distillation or to coking. The total quantity of overhead products isv increased compared to distillation methods, While the amount of thermally cracked gasoline and light gas is substantially reduced and the gas oil fraction increased compared to coking operations. The latter represents an ultimate economic advantage since the quality of thermal cracked gasoline produced by conventional conversion of heavy oils is usually low while my heavy gas oil product represents a useful charge stock to catalytic cracking operations sov that the. ultimate yield of good quality gasoline is increased. The gas oil product is less refractory than ordinary heavy cycle stocks as is shown by its U. O. P. characterization factor and ultimately produces gasoline of a quality beyond .that of the. incidental thermal gasoline produced in heavy oil conversion operations.

vThe nature of the .bottoms product produced according to my invention represents one of its important advantages. The material is a high melting point brittle pitch or asphalt like material buty may be. readily handled as a liquid at temperatures above its melting point as under processing conditions. Thus, the pitch `product is removed as liquid bottoms but upon cooling hardens to a brittle solid which can be readily pulverized Without coking. It can be easily iaked from Water cooled rolls and as flakes or lumps can be readily ground in a ball mill, burr mill, or the like. The pitch is pulverized readily in a hammer mill and is suitable for use as pulverized boiler fuel either alone or mixed with coal.

The invention will be better understood by reference to the accompanying drawings which represent conventionally and schematically a sirnplifed flow plan of' my process in Figure l and a combination process with a fluid catalyst cracking unit in Figure 2.

Aln Figure 1 a heavy feed stock is chargedv by means of line Hl and pump l! to vertical tube type heater I'2. 'In the heater the stock is raised vto a temperature aproximating 850 to 950 F. vand is held for a time sufficient to hold cracking below about 10 per cent, depending upon the nature of the pitch product desired While avoiding coking. The feed is introduced to pitching tower I3 through line I6, at a tower pressure of atmospheric or slightly above. If pressure is held on heater I2, a pressure reducing valve is provided in line I4. Saturated steam at about 212 to 300 F. is introduced to the bottom of tower I3 through line i5. Although have shown a straight sided pitching tower, the lower portion of the tower may have a smaller diameter than the upper. Steam is introduced in an amount approximating 10 to 25 per cent weight on the feed depending on the nature of the pitch product desired. Increasing the amount of steam or the flash temperature or the time factor in the heater increases the melting point of the pitch product while decreasing yield. The steam input cools the bottom of the tower and reduces the iiash temperature to about 790 to 850 F. At the same time the introduction of steam reduces the partial hydrocarbon pressure within the tower, minimizing tower Aresidence time. If desired, process steam or water may be introduced with the oil to the heater coils. I have found that process steam also reduces oil partial pressure in the iiash section and residence time in the coils, while increasing overhead gas oil and decreasing per cent crack.

The pitching tower as shown is advantageously divided hy plate i5 into a lower ilash section and an upper fractionating section. Bubble trays I? are 4provided in the upper portion of the tower to improve fractionation and a partial condenser Ii which may be a water condenser or a heat exchange handling feed stock for preheat may be provided at the tower top. Lighter products are drawn from the upper portion of tower i8 through line Se, through. condensing system 20 to receiving vessel 2l. f-is shown receiver 2l has a restricted bottom section for water drawoii through line 22 while gas is taken off through line 23 and gasoline through line 2li. A light gas oil fraction is advantageously taken from an upper tray of the tower as through line 25. A heavy gas oil fraction is taken from the bottom of the upper fractionating section of tower I3 as by line 20. hitch product is withdrawn as bottoms through line 2i at a rate maintaining a dry tower or minimum liquid level. ila-sh section of the tower may be advantageously baiiied so as to increase heat transfer between the charge oil and steam. We have found that it is important to maintain the boot of tower I3 below approximately 650 by steam introduction or other cooling means to prevent coking which would occur at higher temperatures in spite of operating with a dry tower. The maximum tower hoot temperature of course varies with the residence time of the oil upon the boot wall and thus with the size of the unit.

The principles underlying my invention will be illustrated in the following example representative of a series of pilot plant runs of 8 to 45 hours duration on a small unit of the type shown in Figure 1. rThe feed to the unit comprised a virgin reduced crude having the .following characteristics:

TABLE l' Gravity, /API 13.0 SUS, 210 F 424.5 Extraction sediment 0.041 ATM U. G, coke 13.5 Vacuum U. G. I. coke 5.3

K (U. O. P. characterization factor) 11.37

ri`his material was preheated to a temperature approximating 860 to 920 F. and was dashed into the pitching tower at a flash temperature ranging from about 810 to 850 F. The

The lower 4 tower top temperature range varied from 841 to 782 F. The quantity of process and stripping steam varied from 18.0 to 13.2 weight per cent on the feed. The tower bottom temperature maintained under these conditions varied between 597 and 670 F. The per cent crack in terms of weight per cent of 400 F. end-point material and lighter varied from 6.6 to 1.4 weight per cent on the feed. The yield of gas oil varied from 69.1 to 73.7 weight per cent while the yield of pitch varied from 19.7 to 27.4 weight per cent. The properties of the pitch produced varied with the yield obtained and the per cent crack on the feed stock. Pertinent data on six separate runs are tabulated below:

TABLE II Operating conditions:

Tower pressure, p. s. i. g.. 0 0 0 0 0 0 Ton tower temperature,

e 17.2 18.0 16.0 13.2 14.2 Percent crack, weight percent 400 F. and lighter 1.4 2.0 5.6 5.7 5.4 5.0 Yield:

Pitch,weightpcrcent 27.4 24.8 19.7 21.9 25.5 24.2 Gas oil (400 weight percent 71.2 73.2 73.7 72.4 69.1 70.8 Inspections:

Pitch- R.&B.M.P 194 212 280 230 220 243 Extraction sediment. 0.0 0.08 5.0 0.9 0.6 0.7 Gas oil API 18.4 18.6 18.9 18.7 18.5

I found that it was advisable to use a hot overhead receiver on this unit in order to minimize emulsion diiculties in handling the overhead. By operating the primary or hot overhead receiver at 400 F. approximately 85 per cent oi the heaviest hydrocarbons were condensed. The remaining 15 per cent of light hydrocarbons and the total water were readily separated in the secondary or cold overhead receiver.

I have found that pitch yield and quality is subject to exi-bility in control by control of the per cent crack or the feed stool-r, the per cent steam or the flash temperature. With higher per cent crack, the pitch melting point is higher and the yield is reduced. The pitch, however, diifers in quality from equivalent melting point pitch produced by increased steam quantities or flash temperatures in that the extraction sediment, for example, at the higher per cent crack is materially higher. A typical pitch produced according to the above example tested 265 F. (R Sz B) melting point and had a specic gravity of 1.1205 at 470 F. The molten pitch at this temperature was readily iiaked to it X 2-pieces of %"thickness on Water cooled rolls. The flakes were quite oi-ittle and could be ground to better than 50 per cent through 20D-mesh.

The light and heavy gas oil from the above runs were composited and evaluated as a thermal cracking feed stock. This material is a very vheavy long range gas oil which may be charged as such to a catalytic cracking unit. For thermal cracking the light and heavy gas oils should he handled separately or the composite material is advantageously rerun. The light gas oil produced in these runs was considered suitable as a TCC feed stock to a moving bed catalyst cracking unit such as the Thermofcr system although the sulfur content due to the crude source was rather high. The quality of the gasoline produced was typical of thermal gasoline produced from the crude type.

A heavy cracked residuum can be handled similarly according to my invention but in this event the gas oil recovered is most suitable as a fuel oil cutter stock. Where heavy oil disposal constitutes a serious economic problem, this method results in increased cracked cutter stock for blending oir heavy bottoms while releasing an equivalent amount of acceptable cracking charge stock to gas oil cracking.

In either event, the pitch product has high softening point above about 250 F. (R & B) and usually about 300 F. (R & B) or more and is susceptible to aking or pulverization in conventional equipment without caking or sticking. The heavy pitch is run as liquid from the unit to cooling belts or shaker drums for solidiiication and fragmentation. Slop pitch, melting below about 200 to 220 F. (R & B) is cut back with a cutter Istock and sent to tankage. Advantageously, the molten pitch run from the unit is directly injected into an agitated water bath from which the fragmented particles are collected.

In Figure 2 a pitching unit charging a reduced crude or heavy tar` and producing heavy gas oil cracking charge stock is illustrated in combination with a conventional fluid catalyst unit. The pitch feed comprises a heavy oil such as reduced crude or cracking still tar charged through line in which may be mixed some cycle oil from the fluid catalyst unit through line l0 The feed is preheated in heater |02 and ashed to pitching tower E03. Steam is intr-cduced to the boot of the tower through line |04 and overhead is removed by line |05. Pitch is removed from tower |03 by line I |0. A heavy gas oil cut is withdrawn through line |06 and is charged with the fresh feed to the fluid catalyst cracking unit through line |0'| to reactor riser |08. Regenerated catalyst is mixed with the fluid catalyst feed in line |08 from regenerator standpipe |09 and the mixture of charge oil and catalyst is discharged into reactor through grid ||2. A dense phase bed is maintained in reactor from which spent catalyst drops into stripping well ||3 where adherent oil is stripped from the catalyst by means oi steam introduced through steam stripping equipment ||'4. Cracked products pass overhead from reactor through nest of cyclones through line ||6 to fractionator Catalyst particles carried over with the vapors are knocked out in cyclone |5 and returned to the dense phase bed through dip leg H8. From fractionator gasoline and light gases are conventionally taken overhead by line I9. At least one cycle oil cut is withdrawn as through line 0| while heavy oil and catalyst sludge may be Withdrawn through line |20. The stripped spent catalyst descending through stripping well ||3 drops into reactor standpipe |2| and thus into the foot of regenerator riser |22. Regenerating air is conventionally utilized as a carrier and introduced at |23 to carry the spent catalyst into regenerator |24 where carbon deposited on the catalyst is burned off so that the regenerated catalyst may be returned to the reactor through standpipe |09. Flue gases'pass overhead through line |25 to a fines recovery system and stack (not shown).

My invention, therefore, provides a method for treating heavy hydrocarbon oils which is susceptible of eXible and continuous operation and which produces less residuum and that in a surprisingly attractive form. It produces more gas oil susceptible to cracking to valuable gasoline and light products in -conventional thermal or catalyst cracking systems, and may be advantageously combined with existing units as a feed stock preparation unit for handling oils too heavy to process economically in catalyst cracking systems inherently limited to a narrow range of clean stocks or limited by regenerator design capacities.

I claim:

1. A process for treating heavy hydrocarbon oils which comprises preheating the charge oil to .an incipient cracking temperature of about 850 F. to 950 F. for about 2 to 15 minutes and limiting the percent crack to below about 10 percent based on 400 F. and point gasoline and lighter materials, flashing the preheated charge in a tower maintained at a pressure of atmospheric to about 10 p. s. i. g., reducing the temperature within the ilash Zone to about 790,F. to 850 F. by introduction into the tower of about 10 to 25 weight percent of steam having a temperature from about 212 to 300 F., and removing vaporized materials and bottoms from the flash tower. 2. The method of claim 1 in which the as tower bottom temperature is maintained at less thanv about 650 F. by the introduction of the steam having a temperature from about 212 to 300 F. into the lower portion of the ash tower.

HARRY LOUIS PELZER.

References Cited in the ille of this patent UNITED STATES PATENTS

Claims (1)

1. A PROCESS FOR TREATING HEAVY HYDROCARBON OILS WHICH COMPRISES PREHEATING THE CHARGE OIL TO AN INCIPIENT CRACKING TEMPERATURE OF ABOUT 850* F. TO 950* F. FOR ABOUT 2 TO 15 MINUTES AND LIMITING THE PERCENT CRACK TO BELOW ABOUT 10 PERCENT BASED ON 400* F. AND POINT GASOLINE AND LIGHTER MATERIALS, FLASHING THE PREHEATED CHARGE IN A TOWER MAINTAINED AT A PRESSURE OF ATMOSPHERIC TO ABOUT 10 P.S.I.G., REDUCING THE TEMPERATURE WITHIN THE FLASH ZONE TO ABOUT 790* F. TO 850* F. BY INTRODUCTION INTO THE TOWER OF ABOUT 10 TO 25 WEIGHT PERCENT OF STEAM HAVING A TEMPEATURE FROM ABOUT 212* TO 300* F., AND REMOVING VAPORIZED MATERIALS AND BOTTOMS FROM THE FLASH TOWER.

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