US1878845A - Apparatus for distilling hydrocarbon oils - Google Patents

Description

p W32 A. E. HARNSBERGER APPARATUS FOR DISTILLING HYDRQCARBON OILS Filed 001:. 26, 1928 a. b FF F a d L Patented Sept. 20, 1932 UNITED STATES PATENT OFFICE .AUIDLEY E. HARNSBERGER, OF CHICAGO, ILLINOIS, ASSIGNOR TO THE PURE OIL GOM- IEANY, OF CHICAGO, ILLINOIS, A CORPORATION OF OHIO V APPARATUS non DISTILLING HYDROCARBON OILS Application filed October 26, 1928. Serial No. 315,273.

This invention relates to an improved apparatus for distilling hydrocarbon oils, and has for its principal object the provision of an improved stilland method of operating the same by which the oil under treatment, which is continuously passed through the still," is heated to' distillation temperatures and in such manner that while the oil attains within the still the necessary temperature to effect its vaporization or distillation yet it is not overheated or raised to such temperatures wherein molecular decomposition of the oil or any substantial part thereof is effected.

With reference to its more specific aspects,

v the invention refers particularly to the contically across and through the banks of oil conducting tubesdispo'sed within the tube chamber. By this arrangement heat transfer takes place between the relatively colder fluids or' oil circulation through the. tube banks and the heated furnace gases, wherein the oil is raised to a required vaporization or distillation temperature, for example 7 50 F. when discharged from the outlet side of the tube bank, the furnace gases being cor respondingly lowered in temperature by the absorption, or partial absorption, of the heat units thereof, the furnace gases after passin through the tube banks being discharged usually to a posed off I In the operation of this customary type of tube still, the oil to be heated is introduced into the tube bank at a position where the furnace gases possess the lowest temperature and then is forced upwardly through the tube bank in counter-current flow to the descending furnace gases. Therefore when such oils or oil vapors are'about to be discharged from stack outlet or otherwise disi vlew taken on the plane lndicated by the line the tube bank the vapors encounter while at elevated temperatures the most highly heated surfaces of the tube bank. Due to the highly heated state of the oil and t0 the highlyheated condition of the tubes or pipes through which the oil flows, the oil body does not absorb heat with suflicient rapidity to prevent portions of the oil body from overheating, and this results in substantial cracking or conversion of the oil which is not desired in distillation processes, as distinguished from cracking or conversion processes.

To avoid this condition and to provide for improved distillatory methods the present invention resides chiefly in so regulating the vflow of oil or oil vapor through the pipe still that the temperature of the oil, when passing through the most highly heated tube pass of the still will be sufficiently low so that the oil will be in condition to readily absorb the heat in such highly heated pass without raising the temperature of the oil tolimits bordering on molecular decomposition, and to' then finally raise the oil body to the desired upper temperature limit by passing such oil through tube passes of the still which possess a lower temperature than said first named tubes, the oil being finally heated in the tubes of lower temperature so that the possibility of local overheating of the oil under treatment is removed.

For a further understanding of the principles and features of the present invention, reference is to be had to the following detailed description and to the accompanying drawing wherein Figure 1 illustrates a pipe still in vertical cross section formed in accordance with the present invention,

Figure 2 is a transverse vertical sectional 2-2 of Figure 1, t

Figure 3 is a modified form of the invention.

Referring more particularly to the dia grammatic showing of the specific form of pipe still illustrated in the accompanying drawing, the numeral 1 designates, the usual setting of the still, which is formed, as is customary, from fire brick or other refractory material capable of withstanding the internal temperatures developed within the setting. The exterior of the setting may be lagged or covered with suitable insulating materials to reduce heat losses through radiation and to improve the efiiciency of the unit. Interiorly the heater includes a vertical transversely extending bridge wall 2, formed from the same general material as the outer walls of the setting. The bridge wall terminates below the top or ceiling of thesetting and die vides the interior of'the still into combustion and tube chambers 3 and 4- respectively. lVithin the combustion chamber there may be located one or more burnerso by means of which combustion may take place within the still to produce the requisite temperatures necessary in the distillation of hydrocarbon oils. It is, of course, within the range of the invention to heat theinterior of the still by any other suitable method, such for example, as by passing the stack gases of a converter or cracking unit through the still, which would eliminate the necessity of. employing the burners 5, or the burners 5 maybe employed to supplement the heat of the waste gases received from another heating unit. The tube chamber 4 is providedwith a plurality of horizontally arranged parallel banks or passes of oil conducting pipes or tubes These pipes or tubes, indicated by the numeral 6, are suitably supported in connection w1th the walls of the setting 1 and are relatlvely spaced to permit of the circulation of the fur-- nace gasses therethrough, the tubes or adjacent banks'or passes being relatively staggered in their respective relationship so as to receive more efficiently the heat obtained from the furnace gases which sweep there'over. After passing through the tube banks the furnace gasesenter a stack outlet 7 and are led to the atmosphere or to any other sultable heat utilizing element. v

As stated in the foregoingpart of this specification, it has been customary in the operation of continuous pipe'stills of this type to introduce the oil to be heated into the tubes comprising the lower pass or bank of the heater. The oil is then permitted to flow upwardly through the tube bank and as t c rculates through the various banks 1t encounters progressively higher temperatures so that when the oil finally reaches the upper oroutlet bank of tubes it has attained its highest The rate of heat transfer is proportionate to the difference in temperature of the oil and flue gases and when the tube receives heat at a higher rate than the oil can carry the heat away, the tube overheats and the oil next to the tube wall is locally overheated or cracked if at a high temperature when it enters the g tube.

. Thiscondition is avoided by the arrangement of the tubes as'provided by the present invention. I have found it preferable to proyide for two stages of heating. In the primary stage the oil enters the lower bank of tubes. indicated at'a, and then circulates upwardly through the primary stage in countercurrent relationship to the descending furnace or flue gases. This is in accordance with theprevious practice of'introducing the oilinto the bottom ofthe tube bank. Instead. however, of permitting the oil to continue to travel upwardly through the tube bank the oil is then passed from the upper bank of tubes 6. comprising'the top pass of the primary stage. and is forced into the upper bank of tubes 0 found in the secondary stage. For example, the oil enters the lower bank a of the primary" stage at a temperature of, for

example. 300 F. and isldischarged from the tube bank I) and into the upper bank 0 of the secondary stage at a temperature of approximately 450 F. In the secondary stage of tube banks the oil flows parallel with the flue gases or. in other words. the flow of oil is toward the c'ooler zones of the still. Therefore. the highest rate of heat transfer occurs at the point where the oilenters the secondary stage and wherelocal overheating or decom osition of the oil is not likely to occur. As the oil'flows through the secondary stage of tube banks its temperature increases as the temperature of the flue or furnace gases. decreases. This presents a very desirable condition when destructive distillation of the oil is a not wanted. It will be seen that if the oil entering the hottest tube is 700 F. and local oyerheating can cause 100 F. difference some of the oil will reach a temperature of 800 F. in its passage through the tube, whereas if the oil enters the hottest tube at 400 F..'

as in the present case,,100 difference would have no damaging effect.

As a result. stills not oil-flue gas flow in the final heating stage mustoperate at lower furnace temperatures than that permitted with parallel flow. This causes consequent increase in fuel consump tion and first cost on account of the increased surface needed for the same work accomplished. f I 1 n actual practice the temperature of the flue gas at the point of the final heater outlet can be broughtto within 100 F; oflthe'temperature of the outlet oil which under normal conditions would give a heat transfer of 500 B. t. uyper' square foot. of heating surface,

designed for parallel which is an extremely mild condition as compared with the 20000 B. t. u. per square foot per hour and upwards obtained when tubes are exposed to the full radiant heat of a furnace.

If the tube still is operated under atmos pheric or superatmospheric pressures, as regards the oil or oil vapor passing through tubes thereof, the said tubes may be of constant cross sectional area. In the event, however, the tube still is operated under sub-atmospheric pressures, the tubes comprising the secondary or final heating stage are of progressively increasing diameter from the inlet to the outlet ends thereof for the purpose of permitting the vacuum to penetrate back to the inlet pass of the secondary stage. This is in accordance with the disclosures set forth in my prior Patent No. 1,666,597.

In view of the foregoing description it will be seen that the present invention provides for the distillation of hydrocarbon oils in a continuous process, through the use of a tube still, in such manner that the oil undergoing heat treatment will not be subjected to tem peratures inducive to molecular decomposition. By passing the preheated oil through the hottest tubes there is a sufficient temperature differential between the oil undergoing treatment and the furnace gas to effect an efficient absorption of heat on the part of the oil wherein local over-heating would have no injurious action on the oil. The oil following its flow in parallel relation with the flue gases is removed from the tube bank when the desired temperature is reached, and this outlet pass or tube bank is indicated by the letter d, from which the oil issues in vapor or liquid form at a temperature of approximately 750 F. Further circulation of the oil in a downward direction in the tube bank d would re sult in a decrease in the temperature of the oil vapor and thereby present undesirable conditions. For this reason, I place the preheating tubes in the zones of lower temperature and the final heating tubes in the zones of higher temperature. In the pre-heating tubes the oil flow is counter-current to the flow of the flue gases, whereas in the final heating zones the flow of oil is parallel and 7 concurrent with the flow of the flue gases, the

oil being then removed from the final heating zone when a desired high temperature on the part of the oil vapor has been attained, and

- this point of removal is always above the preheating zone. The system, of course, operates effectively when the oil vapor is circulated through the tube banks either under superatmospheric pressures or under sub-atmospheric pressures. As shown in Figure 3 when sub-atmospheric pressures are used the tubes comprising the final heating stage are of different cross sectional area. That is, the entrance tubes of the final heating stage possess the smallest area while the outlet tubes possess the largest area. This enables the vacuum on the system to penetrate back into the tube banks of the final heating stage and protect the oil from over-heating when subjected to high vaporizing temperatures.

What is claimed is:

In a tube still, a setting provided internally with a transversely extending bridge wall, said wall dividing the interior of the setting into combustion and tube chambers, burners arranged in said combustion chambers, means for passing furnace gases developed by said burners over said bridge wall substantially downwardly through the tube chamber, oil heating tubes arranged in said chamber, said tubes being arranged to provide a primary heating stage and a secondary heating stage, through which stages the oils are uninterruptedly and successively passed, said primary stage being arranged in the lower portion of said tube chamber in the zone of lower furnace gas temperature in said tube chamber, and the secondary stage of tubes being arranged in substantially the upper portions of said tube chamber in the zone of higher furnace gas temperature, means for passing oil through the tubes of the primary stage in substantially countercurrent relationship to the flow of furnace gases through the tube chamber, means for passing the oils through the secondary stage in substantially parallel concurrent relation to the flow of furnace gases through said tube chamber, the tubes of the primary heating stage being of constant internal cross sectional area from the oil inlet to the oil outlet ends thereof and the tubes of the secondary stage being arranged in rows possessing progressively increasing cross sectional area from the oil inlet to the oil outlet ends thereof, and said setting between said burners and said tubes being substantially devoid of heat absorbing structures to provide a high differential in temperature between thev furnace gases and the oil passing through the entrance or smaller tubes of the secondary stage.

In testimony whereof I affix my signature.

AUDLEY E. I-IARNSBERGER.

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