US2105874A

US2105874A - Process for preventing corrosion in the distillation of hydrocarbon oil

Info

Publication number: US2105874A
Application number: US734529A
Authority: US
Inventors: Blair G Aldridge; Edward G Ragatz
Original assignee: Union Oil Company of California
Current assignee: Union Oil Company of California
Priority date: 1934-07-10
Filing date: 1934-07-10
Publication date: 1938-01-18
Anticipated expiration: 1955-01-18

Description

Jan- 18, 1938- B. G. ALDRIDGE ET AL 2,105,874

HYDROCARBON OIL PROCESS FR PREVENTING CORROSION IN THE DISTILLATION OF Filed July 10, 1934 .QS m. 5N man @www a Bb @No Z gomme@ S JW R a 0 nn NNN W um mm V M m Q Euh m w r unbb M A iaz'r Aldridge 5 Y stantially increased by L fractionating system, whereby the caustic solu-` Patented Jan. 1,8, 1938 ilNlTED STATES iid-,874

PATENT OFFICE Blair G. Aldridge and Edward' G. Ragatz, Los

Angeles, Calif., assignors to Union Oil Company of California, Los Angeles,

Calif., a. corporation of California Application July 10, 1934, Serial No. 734,529

3 Claims.

'I'his invention relates to fractional distillation of oil, and particularly to vacuum distillation of hydrocarbon oils to-produce lubricating oil distillates.

It is -an object of this invention to provide a method of control which will automatically take care of variations in heat and feed input to a fractional distillation system.

It is another `object of this invention to eliminate thetroublesome tubular oil condenser ordinarily employed for condensation of the overhead fractionated vapors and to substitute therefor a means of condensing the overhead vapors by directly contacting them with cooled recycled oil 'in a heat exchange tray section in communication with the fractionating system.

It is another object of this invention to provide a method for initially establishing operating co-nditions within a system which utilizes a heat exchange section associated with the fractionating column in which condensation of the vapors is accomplished by direct contact with cooled oil.

It is another object pf this invention to increase the distillation capacity of the distillation system and to avoid undesirable decomposition of the heated feed oil by recirculation therewith through the heater of a quantity of unvaporlzed oil from the ash .section of the fractionating column. L

It is another object of this invention to reduce or substantially eliminate the corrosion in the heating system normally attendant upon the caustic solution treatment of the heated feed materials. l

This invention resides in a process and apparatus for the fractional distillation of hydrocarbon oils to produce lubricating oil distillatesl wherein the fractionated vapors are totally condensed by directly contacting them with a, cooled circulating oil, and wherein control of the fractionating system i maintained to allow for variations in quantity of heat and feed input by autcmatically returning to the fractionating column a quantity of reux suilicient to compensate for this variation, and wherein vthe distillation'capacity of the distillation system is subrecirculating through the heater with the feed a quantity of unvaporized oil from theflash section of the fractionating system, and wherein corrosion of the distillation system, and particularly the heater, is reduced or substantially eliminated by the introduction of caustic solution into the heated feed at a point between the heater and the ash section of the tion is permitted to iiash out of contact with the heater surfaces and whereby the thus flashed caustic is returned through the medium of the recirculating oil from the flash section of the fractionating column to the heater.

Figure 1 is an enlarged diagrammatic view of the connections for introducing caustic solution into the system.

Figure 2 comprises a. diagrammatic illustration of the preferred apparatus by which the process of this invention is carried on, in which H is a heater for providing a heated oil feed to the fractionating column, S, including plates I, 2, and 3, is the stripping section, F, including plates 4 to I3 is the fractionating section, E, including plates I4 and I5, is the heat exchange section, and the space between plates 3 and 4 into which the feed is introduced is the separating or ashsection. B illustrates a barometric condenser andv steam ejector system for maintaining a vacuum in the fractionating and strlpping system.4 T is a surge tank with a float control therein for accumulating and automatically regulating the return of reux to the fractionating system. SI, S2', and S3 are stripping columns in which intermediate distillate cuts received from the fractionating system are stripped of their light components to produce stripped lubricating oil distillates. C is a caustic storage tank from which caustic solution is withdrawn and introduced into the heated hydrocarbon feed to the fractionating column.

- The operation is as follows:

Preheated lubricating oil stock feed is introduced by means of pump 20 through lines 2l and 22 into the convection sectionl of thefheating tubes 23 of the heater H. The partially heated feed is nally heated -in the radiant tubular section 25 in the heater H and from there is introducedinto the flash section of the fractionating column through lines 26 and 2'1 and inlet 28. The thus heated oil falls upon and ows across plate 3 where it is intimately contacted with rising steam and hydrocarbon vapors from the stripping section S therebelow. Upon thus contacting the said steam and vapors the heated oil feed is partially flashed into vapors which in turn pass upward through the fractionating section F of the fractionating column in countercurrent contact with reux condensate resulting in the fractionation of the said vapors.

A portion of the unvaporlzed oil from the ash section of the fractionating columnis withdrawn at 30 and reintroduced by means of pump 3| and line 32 into the heating section 2i where it meets f and mixes with' the partially heated feed from heating section 23. The mixture of the new heated lubricating oil feed stock and the recirculated oil from the ash section of the column thus constitutes the feed introduced to the

said lines

26 and 21 and inlet 28.

'Ihe unvaporized oil not withdrawn through 30 from the Vflash section continues downward over trays 2 and of the stripping section S in counter current to steam to further strip light components therefrom, and the residual oil resulting therefrom is withdrawn through outlet 35, float control valve 36 line '31. A float control 38 serves to regulate valve 36 to maintain a constant residuum liquid level in the bottom of the stripping section S.

The fractionated vapors leaving the top trays I3 of the fractionating section F of the fractionating column pass into the heat exchange section E comprising plates' |4 and I5 where the said vapors are substantially totally condensed in contact with cooled recycled gas oil. The cooled recycled gas oil containing the commingled condensate formed in the heat exchange section E is withdrawn from plate |4 through outlet line 40, valve 4| and linel 42 to the surge tank T from which it is withdrawn through valve and forced by means of pump 46 through theV cooler 41. The flow vof the thus cooled gas oil is split in three ways, a predetermined quantity controlled by valve 50 being withdrawn to production through line 5|, a predetermined constant quantity determined by the setting of valve 52 being returned through line 53 to the heat exchange section E to contact and condense the vapors from the fractionating section of the column as here-

No

2, and 83 and 84 inbefore disclosed, and the balance of the gas oil being returned through

lines

55 and 51 as regulated by the oat control valve 56 for'reiiux to the top of the fractionating section F. l

The air, fixed gases and entrained oil vapors are withdrawn from the top of the fractionating column through line 60 to the condensing system B in which a barometric condenser 6| is provided for condensing the steam and entrained. vapors and a steam ejector 63 is provided for exhausting the said barometric condenser of the air and fixed gases. Water, preferably salt water, is supplied to the barometric condenser and the steam ejector through

lines

65 and 66. The water withdrawn from the barometric condenser leg, and the exhaust of the steam ejector is withdrawn from the tank 61 through outlet 68. Steam is supplied to the steam ejector through steam line` Intermediate side cuts of descending reux condensate are withdrawn from the fractionatng section F of the column through lines.15, 16, and 11 to stripping columns SI, S2 and S3 respectively. The trays from which the ,said Withdrawn side cuts are taken are regulated by the valves 19 and 80 for stripper No. 1, 8| and 82 for stripper for stripper No. 3'. Other connections may be provided so that side cuts may be taken from any of the trays in the column desired.l The thus Withdrawn side Acuts are stripped of their light constituents in countercurrent contact with'steam which is introduced at the bottoms o f the stripping columns as shown at in column SI. vapors and steam pass from the stripping columns through line 81 into the condenser 89 and the resulting condensate collected in receiver 90. The condensate from receiver 90, is returned by means of pump 92 through line 93 and returned and bottoms disposal The combined stripped `umn Sl is Withdrawn by means of pump 91 through outlet 98 through valve 99, cooler |00, and finally through line |0| to storage. The rates of withdrawal of the bottoms from the stripping columns are regulated by the bottoms valves to a predetermined constant quantity. Float controls |02, |04 and |06 act upon valves |03, |05, and |01 respectively to regulate the quantity of side cut withdrawn from the fractionating column to the stripping columns Sl, S2, and S3 respectively to maintain constant liquid levels in the bottoms of the said stripping columns.

In some cases where deep cuts of lubricating oil distillate are desired, the control of the with drawal of condensate from the column to the stripper S3 may be transferred from valve |01 to valve |08. Withthis arrangement valve |01l is maintained open and all of the descending reflux condensate is withdrawn v.from the lower end of late heavy oil through the heater with the feed material -to the extentof one'and one-half to three times the feed rate primarily, other conditions being established, to maintain the desired temperature of the flash tray. In recirculating the said unvaporized heavy oil through the heater it is advantageous to withdraw, for that purpose, the unvaporized oil from the flash tray in the bottom of the flash section of the column, which in' this case is the oil from the top tray 3 of the stripping section S. 'I'his oil from the flash tray is preferred to column bottoms or other bottoms material for the reasonthat it is very nearly the equilibrium liquid of the flash section vapors. When this condition obtains, the absorption oil effect of this oil recirculated with the f feed stock'through the heater is a minimum, permitting the distillation of the net overhead vapor cut at a lower temperature than would be possible where column bottoms or other oil less nearly in equilibrium with the vapors were employed.

When hydrocarbon oils are heated to high temperatures, especially in the hotter portions of the heater system, naphthenic acids, hydrogen sulphide and other materials are formed which are corrosive to the heater surfaces. In order to eliminate corrosion resulting from the formation of these corrosive substances in the heated oil, it has heretofore been the practice to introduce a quantity of a caustic solution into the feed material entering the heater. ered, however, that at the point in the heater where the excess waterin the said caustic solution flashes, an excessive amount of corrosion takes place. It has been found that this dificulty can be overcome by introducing the caustic solution into the heated feed a short distance It has been discov.

from the entrance to the fractionatingv column as shown at I I0. The feed line to the fractionating column at this point isa large one and it has been found p'racticable to introduce the small amount of caustic solution necessary by means of a special connectionas shown in Figure 2 into the central portion of the feed stream flowing therethrough. Apparently with this arrangement and due to the high velocity of the feed materials at this point and the sizeof the connection, the thus introduced caustic solution is able to flash entirely within the oil stream' without contacting any of the feed line or fractionating equipment surfaces.

A large percentage of this ashed caustic solution is retained in the unvaporized oil withdrawn from the ash section of the fractionating column and this material is then introduced into the heating system by way of the hereinbefore described recirculating oil which is withdrawn from the flash section and returned to the heater. 'I'hus only preflashed caustic solution is allowed to enter the heater tubes.

yThe caustic solution to be introduced into the heated feed is withdrawn from the caustic`supply tank C by means of pump Ill and delivered through line H2 to the point of introduction H0.

An auxiliary by-pass connection H3 is provided for introducing caustic solution directly into the heater by Way of line 32 if desired.

Normally, control of the distillation system is accomplished, as hereinbefore stated, by Withdrawing predetermined xed quantities of gas oil and side cuts to production, allowing the quantity of reflux returned to the column .and the quantity of bottoms withdrawn from the fractionating column to vary with variations of input of heat 'and quantity of feed to the fractionating system. For example, the valve 50 is manu lly regulated to allow a predetermined quantity of gas oil to be withdrawn to production and the valves corresponding to va'lve 99 on the strippers adjusted for the withdrawal of predetermined quantities of stripped side cuts, and the quantity of feed introduced into the heater through the feed line 2l and the temperature of the heated feed introduced into the fractionating system `through inlet 28 is maintained manually to approximately meet these arbitrarily set conditions. The quantity of recirculated cooled gas oil to the heat exchange trays is also regulated land fixed by means of valve 52. Any irregularity in the quantity and temperature of feed is then automatically compensated for by corresponding variations in the quantity of i'eux returned to the top of the fractionating section of the fractionating column and the quantity of bottoms Withdrawn from the stripping section o f the fractionating column. When, due to irregularity of firing of the heater, or for any other reason, the

temperature of the feed to the fractionating colg umn is increased, the attendant increase in overhead vapors will result in a greater quantityof fractionated vapors being condensed in the heat exchange section of the fractionating column. This increased quantity of condensate withdrawn from the heat exchange trays along with the recirculating cooling gas oil, will result in an increased accumulation. thereof in tank T, since the quantity of gas oil withdrawn to production and the quantity of gas nil recirculated to the heat exchange section of the column is a predetermined ixed quantity. This increase in quantity of` condensate accumulating in surge tank T will result in a rise in the liquid level and will act .The

through the iioat control therein to regulate valve 56 to allow, in turn, a correspondingly greater quantity of condensate to be returned for refluxing to the top of the fractionating section F of the fractionating column. 'I'hus 'variations of heat input to the column will automatically be compensated by z corresponding variations in quantities of heat absorbing reux.

'I'he .diiiiculties normally associated with an overhead tubular oil condenser for the condensation of fractionated vapors have been eliminated by the employment cf the set of heat interchanger trays as shown at Ui and i5 in the top of the column as hereinbefore described. In this section of the column substantially total condensation of the fractionated vapors occurs byl contacting them with cool recycled oil. This condensation is accomplished by the exchange of the latent heat of vaporization of the said fractionux returned to the top of the fractionating column. and the gas oil withdrawn to production are all of the same characteristics and quality.

In initiating operations of the fractionating system it is necessary that a cooling medium be supplied to the ,heat exchange section of the column in order to establish initial condensation of the vaporized feed material, otherwise the vapors may pass through and out of the column without condensation or fractionation. For this purpose a connection H5 with valve H6 is provided for making connection to an outside supply of gas oil, whereby a sufficient quantity may be introduced into the cooling oil circulating system to initially establish circulation of this condensing'medium through the heat exchange section E of the column and the cooler 47j Surge tank T may have suflicient gas oil storage capacity to provide for thus establishing operating conditions after shut-downs.

Variations in the quantities of feed,- other factors being constant, are taken care of by variations in the quantity of bottoms produced which are automatically withdrawn through ioat controlled valve 36 as controlled by oat control 38.

An example of operation is as follows:

A topped Santa Fe Springs residuum having a viscosity. of 348 sec. at 122 F. is introduced into the heater H at a preheated temperature of 350 F., at a rate of v1804 barrels per 24 hours. feed, after passing -through the heater,l is introduced into the flash section of the fractionating column at -28 at avtempera-ture of approximately 715 F. Unvaporized oil is withdrawn from `the flash tray atA 30 and recirculated through the radiant tubes of the heater and reintroduced lnto the fractionating Ycolumn with the feed at a rate of approximately 3500 barrels per 24 hours. Approximately 3750 barrels per 24 hours of gas oil at 115 F. is recycled to the heat exchange trays and approximately 604 barrels per 24 hours of reflux returned to the top of the fractionating section. The temperature of the coolest heat exchange tray is thus maintained at approximately 200 F. and the steam and xed gases are exhausted from the top of the column at approximately this same temperature and at a pressure of 29.1 in. vacuum. Approximately 2 gallons per hour of caustic solution is introduced into the heated feed to the fractionating system. Under these conditions 255 barrels of gas oil having a viscosity of 145 sec. at 100 F., 52.9 barrels per 24.ho'urs of lubricating oil distillate having a viscosity of 244 sec. at 130 F., 322 barrels per 24 hours'having a vis. cosity of 124 sec. at 210 F., 151 barrels per 24 hours of lubricating oil distillate having a viscosity of 355 sec. at 210" F. and 537` barrels per 24 hours of bottoms from thestripping section of the fractionating column are produced.

The foregoing described process and .apparatus is merely illustrative and the invention ,is not limited thereby, but may include any process and apparatus which accomplishes the same within the scope of the invention.

We claim: A

1. In a process for distilling oil, the steps comprising heating. the oil in a heating zone, withdrawing thei-heated oil from the heating zone and then commingling caustic alkali solution with the said heated oil, introducing the'heated oil together with the saidcommingled caustic alkali solution into a separating zone where vaporization'takes place and vapors and unvaporized oil are separated, withdrawing at least a portion of the unvaporized oil containing caustic alkali from said separating zone and commingling said withdrawn oil containing caustic alkali with oil being heated in said heating zone.

2. In a-process for distillng oil, the steps comprising heating the oil in a heating zone, withdrawing the heated oil from the heating zone and then commingling caustic alkali solution with the Asaid heated oil, 'ntroducing the heated oil together with the said commingled caustic alkali solution into a separating zone where vaporization takes place and vapors and unvaporized oil are separated, withdrawing at least a portion of the unvaporized oil containing caustic alkali from said separating zone and introducing a portion o .said withdrawn oil into an intermediate section of the heating zone.

3. A process according 4to claim 1 in which the introduced caustic solution is flashed in the center portion of the heated oil stream withdrawn fromthe heating zone whereby a minimum of contact of caustic solution vapors with the conduit leading to the separating zone is effected.

BLAIR G. ALDRIDGE. EDWARD G. RAGAIZ.