US2896261A

US2896261A - Method of cooling and granulating petroleum pitch

Info

Publication number: US2896261A
Application number: US477795A
Authority: US
Inventors: Mcafee Jerry
Original assignee: Gulf Research and Development Co
Current assignee: Gulf Research and Development Co
Priority date: 1954-12-27
Filing date: 1954-12-27
Publication date: 1959-07-28
Anticipated expiration: 1976-07-28

Description

July 28, 1959 J. MCAFEE 2,896,261

METHOD OF COOLING AND GRANULATING PETROLEUM PITCH Filed Dec. 27, 1954 IN V EN TOR.

BY W

JrraeA/Ew- METHOD OF COOLING AND GRANULATING PETROLEUNI PITCH Jerry McAfee, Oakmont, Pa., assignor to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware Application December 27, 1954, Serial No. 477,795

3 Claims. (Cl. 18-471) This invention relates to a process for cooling and solidifying petroleum pitches and more particularly to a process for the preparation of granulated petroleum pitch particles from the liquid pitch.

The high rate of production of petroleum distillates during recent years has resulted in the production of large quantities of residual products of low value. A process that has recently been developed to reduce the amount of residual products produced in the refining of petroleum consists of preparing a solid petroleum pitch of low hydrogen to carbon ratio and thereby increasing the amount of distillate available as a charge stock to catalytic cracking processes. Processes in which the residual product is a pitch have an important advantage over coking processes, which also produce solid residual products, in that the pitches are liquid at high temperatures and may easily be removed from the equipment. The pitches can be prepared by an extremely deep vacuum reduction of certain types of crudes or by visbreaking of very heavy oils in combination with deep reduction of the visbroken material.

While the yield of pitch from most crudes may be relatively small, the extremely large crude oil runs in refineries will result in the production of large amounts of pitch. The principal use of the pitch is as a fuel. If the pitch can be used near its place of manufacture, it may be maintained and transported in the liquid form. However, the high softening point of the pitch, which generally ranges from 275 to 450 F ,makes its transportation as a liquid difficult, except for short distances. It is, therefore, desirable to solidify the pitch in a form which can be easily handled and transported to points of use.

According to this invention, a dispersion of liquid water and petroleum pitch is formed at temperatures sufficiently high above the softening point of the pitch to maintain it in a fluid condition and the dispersion is then flashed by a sudden reduction in the pressure to which it is subjected whereupon evaporation of the water cools and solidifies the pitch to form a finely divided solid product.

The single figure of the drawing is a schematic flowsheet illustrating apparatus suitable for use in the process of this invention.

The pitch to be treated according to this invention is ordinarily withdrawn from a distillation tower and used directly in this solidification process. The temperature of the dispersion of pitch and water must be below the critical temperature of water in order that there will be a rapid change in phase of the water upon flashing and the latent heat of vaporization of the water will be sufliciently large to extract substantial quantities of heat from the pitch. Hence, it may be necessary to cool the pitch prior to mixing with water. A pitch feed stock temperature in the range of 500 to 700 F. is preferred.

The water mixed with the pitch is preferably heated to approximately the same temperature as the pitch prior to mixing in order to facilitate the mixing. However, it is only necessary that a dispersion of pitch and water be made at a temperature high enough that the pitch-remains Patented July 28, 1959 fluid and easily handled as a liquid and at a pressure high enough to maintain enough water in the liquid phase that upon reduction of the pressure the extraction of the latent heat of vaporization of the liquid water from the pitch will solidify it; The temperature of the dispersion of pitch and water is preferably in therange of 500 to 600 F., and the pressure maintained on the dispersion when the temperature is in the preferred range is consequently in the range of approximately 700 to 1600 p.s.i.g. Cooling of the pitch or preheating of the water is not essential as long as a substantially uniform dispersion of water and pitch falling within the conditions defined above is obtained. A

A wide range of ratios of water to pitch may be employed. It is only essential that there be sufficient Water present as a liquid in the dispersion that vaporization of the water upon reduction of the pressure will extract sufficient heat from the pitch to solidify the pitch and cool it to a temperature at which it Will not cake nor agglomerate. Water in excess of that required is not a serious disadvantage since the excess water is readily drained from the solidified pitch. For instance, experimental runs have been made in which the ratio of water to pitch, on a volume to volume basis, has been varied from 0.38 to l to 1.4 to 1 without deleterious effects on the pitch.

It is important that the water and pitch be thoroughly mixed at the high temperature and pressure while the water is in the liquid phase. A substantially uniform dispersion, for example, an emulsion of the two liquids, is required to insure uniform cooling of all of the pitch by liberation of the heat of vaporization of the water. As a result, the pitch particles are substantially uniformly po rous, indicating flashing of water to steam uniformly throughout the pitch and large masses of partially cooled and solidified pitch, which might clog the separating equipment, are not formed.

The product of this invention is a particulate solid material. The pitch particles are porous and brittle and may easily be ground to finer sizes if desired as, for example, when the pitch is to be used as a powdered fuel. By adjustment of the conditions at @which the flashing of the water from the pitch occurs, particle sizes may be controlled in the range from fines having particle sizes below about one-sixteenth inch in diameter to particles one-half to three-fourths of an inch in diameter, or even larger. For example, by adjustment of the conditions during the flashing of the water from the pitch, particles of roughly cylindrical shape which swell to about one-half of an inch in diameter can be extruded continuously from a tube one-eighth inch in diameter. These large particles swell, become distorted, and break into segments as they are discharged from the tube, but like the finely divided particles, are porous and brittle. At other conditions, notably higher velocities in the tubing, fines of about one-sixteenth inch in diameter can be discharged as discrete particles from tubing of the same size.

Referring to the drawing, water for cooling the pitch is introduced through lines 10 and 12 to a pump 14 which pumps the water to a pressure sufficiently high to maintain a major portion of the water in the liquid phase during the subsequent heating and mixing opera tions. Pump 14 is of any type suitable for pumping the water to the high pressures in the range of about 700 to 3100 p.s.i. required to maintain the water in the liquid phase, and in the apparatus illustrated is of the piston type. The compressed water is discharged through a line 16 into a preheater 18, in which the water is raised to a temperature such that when mixed with molten pitch will form a mixture in the temperature range of about '450 to 700 F. and preferably 500 to 600 F. In the preferred mode of operation, the water is heated to substantially the same temperature as the pitch to facilitate mixing of the two liquids. The heated water is discharged from the preheater 18 through a line 20 to a mixer 22.

Pitch to be solidified is supplied through a line 24 to a pump 26 which is also illustrated as being of the piston type. The pitch is discharged from the pump 26 through a line 28 which delivers the pitch into line 20. The pitch feed stock in line 24 may be obtained directly from the bottom of a vacuum tower in which the pitch is formed. If the temperature of the pitch is too high, and will form a mixture of water and pitch having a temperature above the critical temperature of water, or higher than desired for other reasons, it may be passed through suitable heat exchanger apparatus, not shown, in which its temperature is reduced to the preferred range of about 500 to 700 F. For example, the pitch may be passed in indirect heat exchange with the water to supply at least a part of the heat required to raise the temperature of the water to the desired level prior to mixing.

The mixture of preheated water and pitch from line 20 passes through mixer 22 in which a substantially uniform dispersion of the pitch in water, such as an emulsion of the two liquids, is formed. The mixer 22 can be of any type suitable for the formation of the desired dispersion. In the apparatus illustrated in the drawings, the mixer is an elongated drum provided with a plurality of baffles 30 which create the turbulence necessary for the formation of the dispersion. A simple tube of a sufficiently small diameter to cause a highly turbulent flow within the tube and of suflicient length to accomplish thorough mixing is another example of apparatus that is suitable.

The conditions maintained within the mixer 22 are such that the major portion of the water is present in the liquid phase. Since the temperature of the mixture must be high enough to maintain the pitch in a fluid, easily pumped condition, the minimum temperature will be determined in part by the softening point of the pitch. Temperatures of at least about 450 F. and preferably in the range of approximately 500 to 600 F., and pressures ranging from about 700 pounds to as high as the critical pressure of water, and preferably from approximately 700 p.s.i. to approximately 1600 p.s.i., are maintained at the discharge end of the mixer 22.

The dispersion of water and pitch is throttled through a pressure control valve 32 in which the pressure on the mixture is rapidly reduced, thereby causing flashing of the liquid water. The mixture, at the greatly reduced pressure, is discharged through the control valve 32 and passes through line 34 into separator 36 maintained at substantially atmospheric pressure, for example, up to 50 p.s.i. absolute. Water vapor formed as a result of the flashing of the water in the dispersion is dischanged from the separator 36 overhead through a line 38 and preferably vented to the atmosphere through a line 40. The finely divided solid pitch particles are formed as a result of the extraction of heat from the pitch to supply the heat of vaporization of the water, fall to the bottom of the separator 36, and are discharged through a line 42. If water in excess of the amount required to cool the pitch is employed, the liquid water is collected at the bottom of the separator 36 and is removed with the pitch through line 42.

The size of the pitch particles can be controlled by regulation of the velocity of the mixture discharged from the control valve 32. At very high velocities the turbulence of the mixture is so great and the flashing of liquid Water upon reduction of the pressure is so violent that .the pitch mass is thoroughly broken up to form fines of a porous, brittle pitch in particles having a diameter of approximately one-sixteenth of an inch and smaller.

If the velocity of the material passing through the line 34 is reduced sufliciently, the mass of pitch in the line is not completely broken up and the pitch forms a substantially continuous highly, and uniformly, porous mass moving through the line 34 and discharged into the separator 36. The high degree of disperson of the pitch and water prior to flashing results in the pitch being uniformly cooled, even at relatively low velocities of discharge from the throttling valve into the separator, and prevents caking or agglomeration in the separator. The cooled pitch is brittle, and breaks up into short segments when discharged into the separator 36. The velocity through the line 34 can be controlled by the injection of an inert gas into the mixer 22, for example, through a line 37, by control of the diameter of the line 34, or by control of the heat supplied to the pitch and water to regulate the quantities of steam present in the mixer, as long as suflicient water is present in the liquid phase to supply the necessary cooling.

If desired, the water vapor flashed from the pitch can be recycled for further use by passing the steam from line 38 through line 44 to a condenser 46 in which the steam is condensed. A pump 48 returns the condensed steam through a line 50 to the inlet line 12 of pump 14.

The following examples illustrate specific applications of this invention for the production of pitch particles of different sizes.

Example] Water was heated to a temperature of 400 to 500 F. at a pressure that varied between 1100 and 1400 p.s.i.g. and introduced into a mixer at a rate of 5500 cc. per hour. Liquid petroleum pitch having a Ring and Ball softening point of 280 F. was introduced at a temperature of 550 F. into the mixer at the rate of 7200 cc. per hour. The mixer consisted of an elongated section of tubing in which the turbulent flow of the two liquids in the tubing produced a thorough dispersion of the two liquids. The resulting mixture at a temperature of approximately 500 F. was throttled through a valve and discharged through an ejector consisting of 6 inches of one-quarter inchpipe into a separator. The pitch was extruded as a continuous string from the outlet of the ejector and then quickly broken into particles of approximately three-quarter inch in diameter.

Example II The procedure described in Example I was repeated with the exception that the water was introduced into the mixer at a rate of 7200 cc. per hour and the thoroughly mixed Water and pitch after throttling through a pressure control valve were discharged through an ejector 4 inches long and one-eighth inch in diameter. The solid pitch wasin the form of fines of a size less than approximately one-eighth inch in diameter.

Example III Water was introduced into a mixer at the rate of 7200 cc. per hour for admixture with pitch which was introduced at the same rate to form a dispersion of two liquids at a temperature of 500 F. and a pressure varying between 1100 and 1400 p.s.i.g. Five hundred cubic feet of nitrogen per barrel of pitch were introduced into the mixer and the resulting mass discharged directly from a throttling valve into a separator. The pitch formed was primarily in particles one-eighth inch in diameter mixed with some smaller particles.

Example IV The process described in Example III was repeated with the exception that the nitrogen was introduced into the mixer at the rate of 1600 cubic feet per barrel of pitch instead of 500 cubic feet. The pitch particles formed in the separator were substantially all fines less than one-eighth inch in diameter.

The process of this invention provides an economical method of solidifying a petroleum pitch directly in particles of a size permitting easy subsequent handling. Large amounts of pitch may be solidified with a minimum of equipment occupying a small space. Throughout the process the pitch is either in a fluid condition or in the form of a highly dispersed solid which eliminates the formation of large solid masses which might plug the equipment.

I claim:

1. A process of solidifying hot liquid petroleum pitch having a softening point above about 275 F. comprising mixing the hot liquid pitch at a temperature of about SOD-700 F. with water to form a mixture having a temperature above about 450 F. and below the critical temperature of water, the mixing being performed at an elevated pressure at least high enough to maintain water in the liquid phase at the temperature of the mixture and below about 3100 p.s.i.g., the ratio of water to pitch being high enough that evaporation of the water on flashing at atmospheric pressure will extract suflicient heat to solidify the pitch, agitating the mixture of water and liquid petroleum pitch while at the elevated temperature and pressure to form a substantially uniform dispersion of water and pitch, and flashing the resulting mixture of pitch and water to substantially atmospheric pressure, whereby evaporation of the water cools the pitch to a atmperature below its softening point to form solid pitch particles.

2. A process as set forth in claim 1 in which an inert gas is mixed with the pitch and water at the elevated temperature and pressure before the flashing to atmospheric pressure.

3. A process as set forth in claim 1 in which the ratio of water to pitch is in the range of 0.38:1 to 1.4:1.

References Cited in the file of this patent UNITED STATES PATENTS 1,285,358 Perry Nov. 19, 1918 1,660,403 Turkington Feb. 28, 1928 1,911,860 Wahlgren May 30, 1933 2,136,208 Fehr Nov. '8: 1938 2,464,187 Seaton Mar. 8, 1949 2,551,452 Moss May 1, 1951 2,572,321 Deanesly Oct. 23, 1951 2,691,625 Clarke Oct. 12, 1954 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent NO. 2,896,261 July 28, 1959 Jerry McAfee It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5, line 13, for "process of" read process for line 23, for 'flashing at" read flashing to column 6, line 6, for "atmperature" read tempera-cure =0 Signed and sealed this 8th day of December 1959o (SEAL) Attest:

KARL Ho AXLINE ROBERT C. WATSON Attesting Ofiicer Commissioner of Patents