US3003943A - Asphalt manufacture - Google Patents

Description

D. M. LITTLE ASPHALT MANUFACTURE Filed March 28, 1958 Oct. 10, 1961 |Y om mm N. 5 m LM.. 95M* mv United States Patent C 3,003,943 ASPHALT MANUFACTURE Donald M. Little, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware Filed Mar. 28, 1958, Ser. No. 724,765 4 Claims. (Cl. 208-4) This invention relates to a process for manufacturing asphalt. In another aspect it relates to a process for making asphalt by vacuum distillation of hydrocarbon residuum. In still Aanother aspect it relates to a method of feed preparation for a vacuum distillation process. In another aspect this invention relates to a method of controlling the temperature of an asphalt manufacturing process which includes steam stripping of hydrocarbon residuum followed by vacuum distillation. In yet another aspect it relates to a control system in combination with steam stripping and vacuum distillation apparatus.

In the vacuum reduction of residual oils by a process which includes in sequence the steps of heating, steam stripping to remove light ends, and distillation under vacuum, the control of temperature is a difficult but critical problem. In vacuum distillations which `are most efliciently carried out under non-cracking conditions in the vacuum vessel at low pressures and high temperatures, it is desirable to attain the maximum temperature which does not produce furnace coking. This is ditlicult because there is ordinarily an appreciable temperature drop in the preliminary steam stripping operation. Since coking is a serious problem in `furnace operation, it is not feasible to attain a sufficiently high temperature in the preheating step to provide optimum conditions for vacuurn distillation. Atmospheric conditions can -add still another variable to the operations by affecting the amount of heat lost from the steam-stripped residuum as it passes to the vacuum distillation Vessel. With limitations thus imposed upon the process, a satisfactory asphalt could not be produced from several types of crude oil.

I have discovered a process by which the above problems are in large measure solved. By my process an asphalt can be produced from crude oils which have not heretofore been satisfactory charging stocks yfor this type of process. According to my invent-ion a hydrocarbon residuum, such as a topped crude or a cracked topped crude, is heated to a temperature safely below that temperature at which appreciable coking occurs, and the thusheated residuum is subjected to steam stripping as in conventional processes except that, in addition, air is introduced to the stripping column at a controlled rate to effect air blowing of the residuum. By employing the air as a heat trim agent the temperature is maintained at a desired value. The air blown-steam stripped residuum is then passed to a vacuum distillation vessel where it is liashed to form a satisfactory vacuum residuum or asphalt. As a further aspect of my invention the temperature of the process is controlled by sensing the temperature of the residuum leaving the stripping column and controlling the' rates at which air and steam are introduced into the column in response to this temperature. By increasing the air flow the temperature of the stripped residuum can be increased or by decreasing the air liow the temperature can be decreased and thereby maintained at a predetermined value. The `steam flow is also adjusted so that the total volume of stripping gases, air and steam, added per minute remains approximately constant. The temperature of the vacuum residuum is also sensed land employed to adjust the desired Value for the temperature of the residuum leaving the 'stripping column. The temperature V 3,003,943 Patented Oct-10, 1961 control system thus includes temperature control means regulating air and steam flow in response to stripped residuum temperature, and control reset means operating in response to the temperature of the asphalt in the vacuum distillation vessel.

It is -an object of my invention to provide an improved process for the manufacture of asphalt.

It is another object of my invention to enable lower furnace temperatures in `a vacuum distillation process and thereby reduce furnace coking.

It is still vanother object to provide a method of maintaining optimum conditions in a vacuum distillation process for the production of asphalt.

Still another object of my invention is to improve the treatment of stripped residuum which is fed to a vacuum distillation vessel in order to produce better asphalt.

Another object is in the provision of an improved system -for temperature control of such a process.

`Other objects, advantages, and features of my invention wi-ll be apparent to those skilled in the yart from the following description, claims, and drawing, which is a schematic representation of my process and control systern.

The process of my invention can best be understood by reference to the attached drawing. As shown in this drawing a crude oil charge 10 enters fractionator 11 and is fractionated into gases 12, gasoline 13, distillates 14, and gas-oil 16. A portion 17 of the gasfoil yield can be passed to catalytic cracking. The residual material or topped crude 1S fonrns the feed for the asphalt process. Other suitable feed materials include cracked topped crude or other heavy hydrocarbon residuums of similar nature. The hydrocarbon residuum is lthus passed to furnace 19 where it is heated by fuel 20 to a temperature in the range of `about 500 to 800 F., the temperature being less `than the temperature at which appreciable coking occurs. The heated residuum is then fed through line 21 to stripping column 22 wherein it is contacted in countercurrent How by steam from line 23, controlled by motor Valve 24, `and by air from line 26 controlled by motor valve 27. Stripping column 22 contains bubble trays or equivalent vapor-liquid contacting means. The steam ystripping can be carried out with about 0.5 to 1 pound of saturated steam (at about to 255 p.s.i.g.) per gallon of residuum fed.

The combined air and steam stripping gases enter the stripping column through line 28 and contact the downwar'dly flowing oil, stripping vapors therefrom. The air oxidizes 4a portion of the oil and thereby increases the temperature to offset thefnormal temperature reduction which would result from steam stripping and vaporization. As desired, the air can be cont-rolled to increase the temperature of the residuum in the stripping column, maintain the temperature substantially constant, or allow it to decrease slightly. In general the temperature of the residuum at the bottom of the col-umn is maintained in this manner in the range of about 700 to 770 F.

Oxidation products 'and stripped light vapors are res moved from the column through line 29 and pass through condenser 30 and line 31 -to settling vessel 32. The uncondensed vapors are withdrawn from separator 32 via line 33 while condensed hydrocarbon is withdrawn through line 34 and water is removed through line 36. The hydrocarbon product withdrawn through line 34 is known as stripper gas oil Iand is `a suitable feed for catalytic cracking.

The stripped and partially oxidized residuum is withdrawn from the stripping column through line 37 and passes through pressure reducing valve 38 to vacuum distillation vessel 39. `While a vertical vacuum distillation vessel is shown, it should be understood that any type vessel known as suitable in the art, such -as a horizontal vessel as described in U.S. Patent 2,774,723, issued December 18, 1956, to G. A. Moyer, can be employed. The residuurn enters the vacuum vessel 39 through sparger ring 40 and is flashed in the vessel to remove vaporizable components while the liquid residuum falls into the lower portion 41 of the vessel 39. Ejector 42 draws a vacuum of approximately 1 to 5 millimeters of mercury absolute pressure in the vessel and withdraws noncondensable materials. Suitable entrainment separators, as shown, are employed within the vessel. Gas oil sprays scrub the vapors, gas oil being withdrawn from the vessel by lines 43 and 46 and returned to the sprays via lines 44 and 47. The vacuum residuum is removed as asphalt through line 48.

The temperature employed in vacuum distillation vessel 39 is generally in the range of about 650 `to 750 F. and can be maintained at its maximum optimum value by the control system subsequently described. Temperature sensing element 49 positioned in line 37 at the exit of stripping column 22 senses the temperature of the stripped residuum. Lead Sti connects temperature sensing element 49 with temperature recorder-controller 51 which produces an output in response to the temperature of the stripped residuum. This signal is carried via leads 52 and 53 to motor valves 27 and 24 respectively controlling the rates of addition of air and steam to the stripping column. When operating on a crude oil charge of the approximate type described, about 1.32 standard cubic feet of air is required per barrel of oil fed to the stripping column for each degree Fahrenheit of temperature rise desired. As the temperature of the stripped residuum tends to increase, temperature recorder-controller 51 produces a signal which partially closes valve 27 and further opens valve 24. The change in the setting of valve 2d.- is made in order to maintain the combined volume of air and steam stripping gases added per minute approximately constant. While it is preferred that valves 27 and 24 act oppositely and in unison to keep the operation as smooth as possible, this is not absolutely necessary in order to practice my invention.

The temperature control is maintained primarily by varying the rate of air introduced to the column and the compensation in steam addition need be only approximate in order to maintain the total volume of stripping gases near the desired value. Thus, when controlling the air input to effect relatively small changes in temperature, the rate of steam addition can be allowed to remain unchanged.

Since it is quite possible that a xed temperature at the point of exit of the residuum from the stripping co1- umn will not mean a fixed temperature for the feed to the vacuum distillation vessel, additional control apparatus is supplied to compensate for such a variation. For example, line 37 generally covers a distance of several feet; and although the line may be insulated, atmospheric conditions such as sudden increases or decreases in ternperature will affect the temperature of the feed to the vacuum vessel if the temperature of the residuum from the stripper is constant. Therefore, temperature sensing element 54 in the lower section 41 of vacuum vessel 39 senses the temperature of the vacuum residuum. Lead 56 connects temperature sensitive element 54 with temperature recorder-controller 57 which generates a signal transmitted by line 58 to reset 59 which in turn communicates with temperature recorder-controller 51 through lead 60. Thus, when the temperature of the vacutun residuum in section 41 tends to decrease, this change is sensed by eiement 54, and -a signal is relayed by controller 57 to reset 59 which adjusts controller 51 to provide a new value for the temperature maintained in line 37 at the position of sensing element 49. The temperature of the stripped residuum is thereby increased, which in turn increases the temperature in the vacuum vessel to the desired value. Examples of suitable control instruments are shown in the Foxboro Bulletin 5A-10A, printed November 1955, by The Foxboro Company of Foxboro, Massachusetts. The Model 40 Single Action .Controller (A862) shown on page 11 can be used for temperature recorder controllers 51 and 57. The Model 40 Pneumaticset (A873) shown on page 14 can be used for reset 59. Controller 51 and reset 59 can be separate instruments or combined into one instrument. A single air supply from controller 51 can be used to actuate both valves 24 and 27 in opposite directions.

To further describe my invention, the following speciic example is given. The specic materials, quantities and conditions are presented as being typical only and should not be construed to limit my invention unduly.

A crude oil charge, Beggs crude, is charged to a fractionation column at a rate of 300 barrels per hour. Gas, gasoline, distillates and gas-oil are recovered as fractionation products leaving a bottoms product of topped crude having an API gravity of 15.0 degrees. The topped crude is passed continuously to a gas-fired furnace at a rate of about l0() barrels per hour. The topped crude is heated to 765 F. in the furnace and at this temperature substantially no coking occurs. The heated residuum is fed continuously to the upper portion of a stripping column equipped with bubble plates as the vapor-liquid contacting means. Saturated steam at a gage pressure of 200 pounds per square inch and air at 70 F. is fed continuously to the bottom of the column. The steam addition rate is 0.8 pound of steam per gallon of topped crude fed which is equivalent to 33.6 pounds of steam per barrel of oil. Air is fed at a rate of 1.32 standard cubic feet per barrel of topped crude fed per degree Fahrenheit of temperature increase required. The exit conditions of the stripped residuum are maintained at 750 F. and a pressure of 2 pounds per square inch gage. Therefore, a temperature decrease across the tower of 15 F. is allowed. Operating without the addition of air, the temperature drop across the tower would be approximately 25 F., so that suicient air is added to effect a temperature rise of 10 F. per barrel of oil fed to the column.

Light fractions and oxidation products are stripped from :the residuum and pass overhead to a condenser and separator from which uncondensed gases are vented and condensed hydrocarbon gas-oil is withdrawn after separation from the condensed water. This stripper gas-oil has an API gravity of 30 degrees and is produced at a rate of about 13 barrels per hour. Stripped and oxidized topped crude having an API gravity of 13.1 is withdrawn from the stripping column at a rate of barrels per hour. This product is fed continuously through a pressure reducing valve to a vacuum distillation vessel wherein gas-oil `and remaining light ends are ashed at an `absolute pressure of 2 millimeters of mercury and at a temperature of 725 F. Vacuum gas-oil having an API gravity of 2O is produced from the distillation vessel at a rate of 16 barrels per hour. Vacuum residuum is withdrawn from the vacuum vessel at a rate of 69 barrels per hour. This product has the following typical propcities:

When practicing my invention under the above-described conditions, which are presented as typical, an asphalt having physical characteristics comparable to those shown in the above table is obtained. When attempts were made to process Athe same crude oil charge Without the addition of lair to the stripping column, the vacuum residuum produced was not a satisfactory asphalt. Penetration, ring and ball softening point, and ductility values could not be obtained because the product was too soft. This product obtained by adding steam but not air to the stripping column had a typical API gravity of 17.3 degrees and Saybolt Furol viscosity of 1,950 seconds.

The improvement which is erected in the vacuum residuum by the addition of air to the stripping column is surprising in View of the fact that conventional air blowing processes in the production of asphalt are typically batch operations requiring several hours to complete. The continuous nature of the steam stripping process is, on the other hand, not altered by my invention.

In addition to an improved product, several advantages in control of the operation are realized by air blowing in the steam stripping column. Lower temperatures can be employed in the furnace and thereby reduce the pos sibility of coking where the hazard involved and cleaning problem is great. Any coking that occurs in the stripping column is considerably less troublesome since localized high temperatures are less likely to result. The oxidation and stripping function of the air succeeds in removing additional light ends from the topped crude and prevents overloading the jets in the vacuum distillation vessel. It is therefore easier to maintain a low and more stable pressure in the vacuum vessel. Also, as described above, the temperature control in the stripping column can be easily and accurately regulated by changing the amount of air introduced to the column. When the control system of my invention is employed, this feature enables an accurate temperature control in the vacuum vessel.

As an illustration of this control operation, let it be assumed that while operating according to the above example a sudden drop in atmospheric 4temperature occurs so that heat losses in the system increase and the temperature in the vacuum vessel drops to 720 F. The temperature controller 57, sensing this temperature drop through element 54, -signals the reset 59 which adjusts the setting of temperature controller 51 for the stripped residuum to 755 F. Since the temperature of the residuum leaving the stripping column is 750 F temperature recorder controller 51 activates the motor valve 27 in the air line 26 which opens to increase the air ow in suiicient amount to raise the temperature of the stripped residuum leaving the column to 755 F. The temperature of the vacuum residuum vessel 39 returns to 725 F.

These conditions are presented for exemplary purposes only and it should be understood that various modifications can be made from the above disclosure without departing from the spirit or scope of my invention. For example, While `air is used to oxidize and adjust the temperature of the crude oil in the stripping column, oxygen or other oxidizing gaseous mixtures can be employed. t e operating temperatures and pressures can be changed considerably and the control instruments can be adjusted to operate ou a highly sensitive basis to changes of a degree or less, or with an `appreciable lag, allowing temperature changes of several degrees before adjustments are made either in the reset or in the introduction of air and steam to the stripping column. Various other changes can be made within the broad aspect of my invention which is the air blowing of a hydrocarbon residuum during the steam stripping operation in the preparation of feed for vacuum reduction of heavy oil to asphalt.

I claim:

1. A method of producing asphalt which comprises fractionating crude oil to form a topped crude, heating said topped crude at a temperature suicient to produce asphalt but which is below the temperature which will produce' an appreciable amount of coking, passing the thus heated topped crude to a stripping zone, countercurrently contacting said topped crude in said stripping Zone with air and steam concomitantly, said yair being in suliicient amount to maintain the temperature of the topped crude leaving said stripping zone at a first predetermined Value in the range of Yabout 700 to 770 F., sensing the exit temperature of said topped crude leaving said stripping zone, producing a rst signal in response to said topped crude exit temperature, varying the Iamount of air in said contacting step in response to said rst signal to maintain said rst predetermined value by increasing the air ilow to increase said exit temperature and decreasing the -air flow to decrease said exit temperature, varying the amount of steam in said contacting step in response to said first signal to maintain the combined air and steam input at an approximately constant volume, passing the thus air blown and steam stripped topped crude toa vacuum distillation zone wherein a vacuum residuum of asphalt speciiication is produced, sensing the temperature of said vacuum residuum, producing a second signal in response to said residuum temperature, adjusting said first predetermined value -to maintain the temperature of said vacuum residuum at a second predetermined value in the range of about 650 to 750 F., and withdrawing `an asphalt product. Y

2. A method of producing asphalt which comprises fractionating crude oil to form `a topped crude, heating said topped crude at a temperature in the range of about 500 to 800 F. but which is below the temperature which `will produce an appreciable amount of coking, passing the thus heated topped crude 4to a stripping zone, countercurrently contacting said topped crude in said stripping zone with air `and steam concomitantly, said air being in sufficient amount to main-tain the temperature of the topped crude leaving said stripping zone at a first predetermined value in the range of about 700 to 770 F., said steam being saturated at gauge pressure of about to 225 pounds per square inch `and in an amount of about 0.5 to 1 pound of steam per gallon of topped crude Ifed, sensing the exit temperature of said topped crude leaving said stripping zone, producing Ia first signal in response to said topped crude exit temperature, varying the amount of air in said contacting step in response to said first sign-al to maintain said first predetermined value by increasing the :air ilow to increase said exit temperature and decreasing the -air now to decrease said exit temperature, varying the amount of steam in said contacting step in response to said first signal to maintain the combined air and steam input at an approximately constant volume, passing the thus air blown and steam stripped topped crude to a vacuum distillation zone operating at an absolute pres-sure of about 1 to 5 millimeters of mercury thereby producing a vacuum residuum of asphalt speciiication in said vacuum distillation zone, sensing the temperature of said vacuum residuum, producing a second signal in response to said residuum temperature, adjusting said first predetermined value -to maintain the temperature of said vacuum residuum at a second predetermined value in the range of about 650 to 750 F., and withdrawing an asphalt product.

3. In appartaus for processing -a hydrocarbon residuum to asphalt comprising a steam stripping column, la steam line for feeding steam to said column, a rst motor valve in said steam line, a vacuum distillation vessel, and a conduit connecting said stripping column and distillation vessel, the control system comprising, in combination, ya first temperature sensitive element positioned to sense the temperature of material at the bottom of said column, an airline yfor `feeding air to said column, `a second motor valve in said -air line, first control means connected to said iirst and second motor valves and communicating with said first temperature sensitive element to operate said Valves in response to column temperature, a second temperature sensitive element in said vessel, means for resetting said rst control means to `a desired temperature value, and second control means connected to said resetting means and communicating With said second ytemperature sensitive element to control said resetting means in response to vessel temperature` 4. Apparatus according to claim 3 wherein said rst and second valves are constructed and arranged to operate oppositely and in unison.

References Cited in the tile of this patent UNITED STATES PATENTS Rudigier June 12, 1928 Meigs July 9, 1935 Gutzwller Sept. 22, 1936 Batchelder Aug. 12, 1941 Boyd July 20, 1954 Goodwin Aug. 31, 1954 Irvine July 2, 1957

Claims (1)

1. A METHOD OF PRODUCING ASPHALT WHICH COMPRISES FRACTIONATING CRUDE OIL TO FORM A TOPPED CRUDE, HEATING SAID TOPPED CRUDE AT A TEMPERATURE SUFFICIENT TO PRODUCE ASPHALT BUT WHICH IS BELOW THE TEMPERATURE WHICH WILL PRODUCE AN APPRECIABLE AMOUNT OF COKING, PASSING THE THUS HEATED TOPPED CRUDE TO A STRIPPING ZONE, COUNTERCURRENTLY CONTACTING SAID TOPPED CURDE IN SAID STRIPPING ZONE WITH AIR AND STEAM CONCOMITANTLY, SAID AIR BEING IN SUFFICIENT AMOUNT TO MAINTAIN THE TEMPERATURE OF THE TOPPED CRUDE LEAVING SAID STRIPPING ZONE AT A FIRST PREDETERMINED VALUE IN THE RANGE OF ABOUT 700 TO 770*F., SENSING THE EXIT TEMPERATURE OF SAID TOPPED CRUDE LEAVING SAID STRIPPING ZONE, PRODUCING A FIRST SIGNAL IN RESPONSE TO SAID TOPPED CRUDE EXIT TEMPERATURE, VARYING THE AMOUNT OF AIR IN SAID CONTACTING STEP IN RESPONSE TO SAID FIRST SIGNAL TO MAINTAIN SAID FIRST PREDETERMINED VALUE BY INCREASING THE AIR FLOW TO INCREASE SAID EXIT TEMPERATURE AND DECREASING THE AIR FLOW TO DECREASE SAID EXIT TEMPERATURE, VARYING THE AMOUNT OF STEAM IN SAID CONTACTING STEP IN RESPONSE TO SAID FIRST SIGNAL TO MAINTAIN THE COMBINED AIR AND STEAM INPUT AT AN APPROXIMATELY CONSTANT VOLUME, PASSING THE THUS AIR BLOWN AND STEAM STRIPPED TOPPED CRUDE TO VACUUM DISTILLATION ZONE WHEREIN A VACUUM RESIDUUM OF ASPHALT SPECIFICATION IS PRODUCED, SENSING THE TEMPERATURE OF SAID VACUUM RESIDUUM, PRODUCING A SECOND SIGNAL IN RESPONSE TO SAID RESIDUUM TEMPERATURE, ADJUSTING SAID FIRST PREDETERMINED VALUE TO MAINTAIN THE TEMPERATURE OF SAID VACUUM RESIDUUM AT A SECOND PREDETERMINED VALUE IN THE RANGE OF ABOUT 650 TO 750*F., AND WITHDRAWING AN ASPHALT PRODUCT.

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