US1660856A - Art of cracking hydrocarbons - Google Patents

Description

. J. E. BELL ET AL ART OF CRACKING HYDROCARBONS Filed March 14, 1925 5 Sheets-Sheet 2 INVENTORS JMIEBELLfltTEAFFfl, 3r

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ATTORNEYS 'Feb. 28, 1928. 1,660,856

J. E. BELL ET AL ART OF CRACKING HYDROCARBONS Filed March 14, 1925 5 Sheets-Sheet 4 i it 1 I I I i INVENTORS ./4 50:14am; auzara rzcure/x 44w M [I Zwu Z M, M 91W ATTORNEYS Feb; 28, 1928.

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UNITED STATES PATENT OFFICE.

JOHN E'BELL, DECEASED, LATE OF BROOKLYN, NEW YORK, BY LOLA. R. BELL, EX- ECUTBIK, OH BROOKLYN, NEW YORK, AND EDWARD W. ISOM, OF LOO'UST VALLEY, NEW YORK, ASSIGNORS '10 SINCLAIR EEFINING COMPANY, OF NEW' YORK, 11'. Y.,

A CORPORATION OF MAINE.

ART OF CRACKING HYDROCARBONS.

. Application tiled Iarch 14, 1925. Serial No. 15,459.

This invention relates to improvements in cracking heavier hydrocarbon oils, such as gas oil, for the production of lighter hydrocarbon oils, such as gasoline or pressure a distillate, by distillation under pressure.

In cracklng hydrocarbon oils by distillation under pressure, the oil is heated to a cracking temperature under pressure and the heavier oil, or a ortion thereof, is broken to down or cracke with the formation of lighter oils which are vaporized and driven off. The cracking operation takes lace gradually and progressively, part the cracked constituents escaping as pressure M distillate and part of the heavier cracked constituents remaining and mixing with the charge of oil in the pressure still. A small amount of asphaltic, or pitch-like constituents, or heavy tar is also formed by the as cracking operation. This tar remains in the charge and gradually accumulates due to the vaporization of cracked constituents and to the progressiveformation of tar constituents. This tar accumulating in the oil at in the still tends to deposit on the heating surfaces of the still and in contact there with tends to form a carbonaceous dc osit thereon closely adhering thereto. i uch carbonaceous materials and the heavy tar 3o accumulating in the still charge are poor conductors of heat and when deposited on the heating surfaces of the still which are externally exposed to heating gases interfere with heat transfer and insulate the wall at from the protection afforded by the oil so that the walls of the still are apt to become overheated, the temperature of the metal of the heat transferring wall increasing over that of the oil to an extent dependent upon 4 the thickness of the deposit and the amount of heat externally delivered to the wall from the heating gases. As a consequence the pres sure still must frequently be shut down for cleaning or the temperature of the heating gases must be reduced below that which is most eflicient. There is also considerable danger involved due to possible bursting of the heat transferring walls at overheated oints. The heatin surfaces over which eating gases are rst circulated are exposed to the highest temperature of the heating gases and absorb the greatest amount of regulation of the character of the oil charge I is carried out to prevent or reduce the ac-' cumulation of tar in the oil in contact with the heating surfaces over which the heating gases are first circulated, that is the heating surfaces in contact with the hottest heating gases, and the regulation of the temperature of the heating gases is carried out without decreasing either the capacity or efiiciency of either the still or the heating furnace by returning part of the heating gases which have passed over the heating surfaces and admixing them with the fresh heating gases first circulating over the heating surfaces. This dual regulation, in accordance with the present invention, also provides two means of controlling the heating operation, and consequently the cracking operation. This dual regulation also enables an improved operation of the pressure still in the treatment of different charging stocks and for the production of products of varying characteristics.

By returning heating gases at approximately the temperature at which they are discharged from the heating surfaces and admixing them with fresh heating gases from the furnace, the fresh heating gases are tempered without however reducing the efficiency or capacity of the heating operation. The temperature of the heating gases first contacting with the heating surfaces can thus be reduced in an efiicient manner while at thesame time the furnace may be operated at high temperatures at which high fuel efficiency is secured. The reduction in temperature of the heating gases so effected reduces thetendency to overheating of the heating surfaces immediately adjacent the furnace with which the heating gases first contact and there is a decrease in the quantity of heat absorbed by these initial heating surfaces with an increase in the quantity of heat absorbed by the remaining heating surfaces. A. more uniform distribution of the heating action is thus accomplished while the increased volume of heating gases, due to the recycling of part of the heating gases, results in an increase of velocity which further promotes the rate and efficiency of heat absorption. An increase in both fuel economy and capacity may thus be secured. 1 v

In addition to this regulation of the temperature of the heating gases, and particularly of the temperature of the heating gases as they first contact with the heating surfaces of the still, fresh oil and reflux are also utilized to protect the initial heating surfaces and to promote the etficiency of the heating operation. The vapors from the cracking operation are subjected to a refluxing operation, and the reflux therefrom and fresh oil supplied to the cracking operation are first brought into heat exchange with the heating gases at their highest temperature, that is the fresh oil and reflux are brought into contactwith the initial heating surfaces with which the heating gases first contact and before the heating gases are passed over the more remote heating surfaces of the pressure still. As the light cracked constituents are vaporized, and as the oil loses its content of crackable hydrocarbons and as the concentration of tar constituents in the oil increases, the oil is brought into heat exchanging relation with the heating gases which have been tempered both by the return of part of the waste heating gases and by the abstraction of heat on the initial heating surfaces. The reflux is made up, of constituents which have been vaporized from the charge of oil in the still and is hence substantially free from tar constituents, and the reflux and fresh oil, which is also substantially tar free, are brought into heat exchange with the heating gases while at highest temperature, and, as tar tends to accumulate in the oil, the oil is passed over heating surfaces in contact with progressively cooler heating gases.

The heating surfaces of the pressure still most apt to suffer are thus protected by absorption of the heat transferred therethrough in heating and cracking the reflux and fresh oil, and thereduced concentration of tar constituents maintained in the oil in contact with these initial heating surfaces prevents or reduces the formation of carbonaceous deposits thereon. At the same time, the initial temperature of the heating gases as they first contact with the heating surfaces is also reduced by recycling part of the waste heating gases. The heat available in the heating gases, tempered bothby the recycling of part of the waste heating r eeaeae gases and the abstraction of heat through the initial heating surfaces by oil in which a relatively low concentration (if tar constituents is maintained, is then further employed to advantage in cracking the oil as tar constituents accumulate therein.

In carrying out the invention, the heating surfaces of the pressure still may be further protected and the heating of the pressure still charge equalized by providing progressively increased areas of heat transfer between the oil and the heating gases as the tar content of the oil increases and as the temperature of the heating gases decreases. The heating effect may thus be equalized by increasing the area of heat transfer as the temperature of the heating gases decreases while an increased area of heating surface is provided in contact with the oil containing an increased tar content where deposition is most likely to occur. The tar content of the pressure still charge may also be controlled and reduced by withdrawing tar from one or more portions of the still charge where the tar tends to accumulate.

The process of the invention may with advantage be carried out in a series of stages or cycles, with circulation of the oil in each stage or cycle from a body of the oil then in heat exchanging relation with the heating gases and back to the body, and transferring oil to successive stages or cycles as its tar content increases, circulating heating gases in heat exchanging relation with the oil in the stages or cycles successively in the order of increasing tar content, and supplying fresh oil and reflux to the stage or cycle in which the oil is subjected to heat exchange with the heating gases of highest temperature. Circulation of the oil in the successive stages or cycles may be maintained by convective action, or by mechanical forcing means such as a pump or pumps, or by the introduction of suitable gases. Circulation of the oil further assists in preventing or materially reducing the formation of carbonaceous deposits on the heating surfaces and assists in carrying tar constituents with the circulating oil. Circulation of the oil over the heating surfaces also promotes the heat transfer from the heating surfaces to the Oll and further protects the heating surfaces in this way.

The invention will be further described in connection with the accompanying drawings which illustrate in a diagrammatic way apparatus adapted for carrying out the process of the invention. The apparatus illustrated is described and claimed in applications filed January 17, 1921, Serial No. 437,662 and filed April 8, 1921, Serial No. 459,555, which have matured into Patents 1,547,993 and 1,547,994, respectively, and the process of the present invention is of special value and application in connection with pressure ltl iii

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stills of this general character. The process of the invention may, however, he carried out in other and different apparatus. In the accompanying drawings:

Fig. 1 represents a pressure still, in elevation and section with parts brolren away, adapted for carrying out the process of the invention, on line 1-1 of Fig. 2,

Fig. 2 is a section on line 22 of Fig. 1,

Fig. 3 represents a modified pressure still, in elevation and section with parts broken awa adapted for carrying out the process of t e invention, on line li -*3 of Fig. d,

Fig. i is a section on line l4c of Fig. 3, and

Fig. 5 is a section on line 5-5 of Fig. 3.

The pressure still illustrated in Figs. 1 and 2 comprises a drum 6 and a series of tubular heating elements communicating therewith arranged in the heating flue of the furnace 7. The heating flue comprises a series of vertical connecting flues 8, 9, 10 and 11, the line 8 also connecting with the furnace '1' and the flue 11 with a stack flue 12. The flues are arranged so that the heating gases from the furnace are passed successively therethrough to the stack. The still drum 6 is provided internally with a series of partitions 13, 14 and 15 dividing the drum into a series of compartments A, 15, G and D, and a corresponding series of heating elements separately communicating.

with each of these compartments are arranged in the heating flues. The heating element connected to compartment A, is arranged in line 8, that is the flue through which the heating gases are first passed, the heating element of the next compartment B in the flue 9, and so on, the heating element connected to the last compartment D being arranged in the last heating flue 11 through which the coolest heating gases are circulated. The partitions in the drum do not completely shut ofl the compartments from each other but extend a short distance above the normal liquid level therein leaving a common vapor space in the upper part of the drum. @ verflow pipes 16, 17 and 18 are arranged for progressively transferring oil to successive compartments in the series, and these pipes are provided with bell caps to prevent transfer of surface scum and froth to successive compartments. Arranged above the drum 6 is a reflux tower 19 adapted to receive vapors from the vapor space of the drum 6 and to discharge reflux, and an admixed oil, into the first compartment A. connection 20 is provided for introducing fresh oil. into the upper partof the reflux tower, and a connection 21 is provided for introducing fresh oil directly into the first compartment A. The vapors escape from the reflux tower through vapor line 22 to a condenser diagrammatically illustrated at 23. The pressure in the still tower and the still drum may, with ad vantage, be covered or protected with suitable heat insulation, such as an asbestos or mineral wool acket.

To the extent described above, the pressure still illustrated in l igs. 1 and 2 is of construction similar to that illustrated in Figs. 3, 4t and 5 and corresponding parts in Figs. 3, 4 and 5 are designated by the same reference characters with the letter a appended.

Again referring to the pressure still illustrated in Figs. 1 and 2, each of the heating elements connected to the respective compartments comprises three similar groups of heating tubes. Each of these groups comprises an outflow header 26, a series of upwardly inclined tubes .27 arranged through the heating fine for heat exchange with the heating gases therein, connecting headers 28, another series of upwardly inclined tubes arranged through the heating flue, and an inflow header 30. In order to facilitate cleaning and repair the headers are arranged outside of the heating lines and are formed with plugged hand holes in alignment with the heating tubes. In order to equalize the heating effect in the several heating elements and to provide an increased area of heat transfer as the tar content of the oil increases, the heat transferring area of the several headers is progressively increased as the temperature of the heating gases declines. lln the still illustrated, the header connected to the first compartment A has four tubes in each group, that connected to compartment ll eight tubes, that connected to compartment C twelve tubes, and that connected to the last compartment D sixteen tubes. Tn order to provide for drainage, and for withdrawal of tar during the cracking operation, the lower ends of the inflow headers in each heating element are connected to a manifold 31 having a valved outlet 32, the outletfrom the last compartment D being designated 32. A draft tube 33 is arranged for withdrawing waste heating gases from a point adjacent the exit of the heating fine 11, the fine in which the heating element connected to the last compartment D is arranged, and returning them to the flue 8 for tempering the heating gases fresh from the furnace in the fine 8. The draft tube may be operated by a steam jet or other suitable forcing means. By-passes 84 and 35 provided with regulating dampers 36 and 37 are provided for further controlling the distrilnition of heatin the several lines.

In the pressure still illustrated in Figs. 3, 4 and 5, the heating elements connected to the respective compartments also comprises three similar groups of heating tubes. Each till of these groups comprises a header 38, a series of upwardly inclined tubes 39 arranged through the heating flue, connecting headers 40, another series of upwardly inclined tubes 41 arranged through the'heating flue, and a header 42 discharging into the corresponding compartment in the drum 6. The headers 38 in each group are connected to a common horizontal header &3 which is in turn connected through pipe 44 to the discharge side of a circulating pump. A connection 45 is also provided between each compartment in the drum and the inlet side of the circulating pump discharging through the headeucoimeeted to that compartment. A separate pump may be employed for each of the compartments, or aseries of pumps may be arranged in a connnon casing and driven by a common driving means as shown in the drawings. The pumps shown in the drawings are of the rotary piston type, sometimes known as Connersville pumps-and areparticularly adapted for use in carrying out the process of the invention but it will be apparent that pumps of other suitable construction adapted to handle hot oil at the cracking temperature may be employed. The pumps shown are independent and the oil is separately circulated through each of them, partitions being arranged between the several pump chambers to confine the oil in each circulating stream to that stream. A valved outlet 46 is provided in the connection A to the last compartment for discharging tar from the pressure still during the cracking operation. A draft tube 47 is arranged for Withdrawing waste heating gases from a point adjacent the exit of the heating flue 11 and returning them to the flue 8 for temperin the heating gases fresh from the furnace in the flue 8. The draft tube may be operated by a steam jet or other suitable forcing means. By-passes provided with dampers may also be arranged between the heating flnes 8*, 9 and 10 as described in connection with the pres sure still illustrated in Figs. 1 and 2.

It will be apparent that, in each construction illustrated, the oil'supplied to the still is first brought in heat exchanging relation with the heating gases of highest tempera ture and as the tar concentration of the oil increases the oil is progressively brought in heat exchanging relation with heating gases of lower temperature and that, at the same time, the heating gases are tempered before first being brought in heat exchange with the oil'by recirculation of a part of the waste heating gases. The heating surfaces of the pressure still are thus protected in a dual manner, both by regulating the character-of oil charge in contact with the heating surfaces and by regulating the temperature of the heating gases. The area of heating surface of the heating elements may also be increased as the temperature of the heating gases declines and as the tar-concentra-. tion of the 011 increases, further protecting the heating surfaces of the pressure still.

In carrying out the process of the invention in the apparatus illustrated the still is initially charged with oil through conpressure employed may differ with different charging stocks and for the production of different pressure distillates. \Vith gas oil character charging stocks for the production of gasoline character distillates, pressures in the neighborhood of 90 to 125 lbs. per sq. in..or more may be employed. In cracking kerosene character charging stock to produce a gasoline character distillate, considerably higher pressures may be used, for example, pressures up to 300 lbs. per sq. in. or more may be employed.

After the still charge is brought to the cracking temperature and pressure, the cracked vapors rise from the several compartments and pass upwardly through the reflux tower 19, or 19 and the introduction of fresh oil into the reflux tower in direct contact with the vapors therein is begun. In the reflux tower, the fresh oil is intimately contacted with the vapors from the still, refluxing the heavier vapors and preheating the fresh oil, and the reflux and admixed fresh oil are returned to the first compartment A. Additional fresh oil may also be supplied through connection 21, or 2i. As reflux and fresh oil are supplied to compartment A, oil from this first compartment which has been deprived of part of its crackable constituents and contains some tar constituents overflows into the second compartment B where it is further cracked and a further part of its components are vaporized. In the same way oil is transferred from compartment B to compartment C and from compartment C to compartment D as the cracked constituents are vaporized and as the tar accumulates, the oil in the successive compartments containing less and less 'of the original oil constituents and more and more heavy tarry constituents. The supply of fresh oil and reflux to the first compartment A also assists in maintaining av low tar concentration in the oil therein. The introduction of fresh oil into the reflux tower may be controlled to regulate the refluxing operation; and where no tar, or only a relatively small amount of tar, is withdrawn the amount of fresh oil introduced into the reflux tower may correspond approximately to the amount of distillate taken off or may be somewhat in excess of this amount.

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Where larger amounts of tar are withdrawn, the still charge is maintained by the introduction of an increased amount of fresh oil, and the fresh oil supplied may be divided and introduced partly into the reflux tower and part1 into compartment A directly, or it may all be introduced directly into com partment A.

The heatin gases from the furnace 7, or 75, are passe successively over the heating elements connected to compartments A, B, C and D in order so that the oil in the first compartment A, including the reflux and fresh oil supplied to this compartment, is-

subjected to the highest temperature, that in the second compartment B to a somewhat lower temperature, and so on. However, before the heating gases fresh from the furnace are passed over the heating element connected to compartment A, they are temered by the admixture therewith of waste eating gases withdrawn from the last heating line and returned and admixed with the fresh products of combustion leaving the furnace. This tempering of the hottest heating gases assists in protecting the initial heating surfaces in the heating element connected to compartment A and these heating surfaces are further protected by the absorption of heat in the oil circulating thereover which oil contains a high proportion of rear and fresh oil constituents and a low proportion of tar constituents so that carbon deposition on these heating. surfaces 1S avoided or minimized. The heatmg gases passing over the heating elements connected to compartment 18 are thus tempered both by the recirculation of part of the circulating gases and by the absorption of heat in the heating elements connected to compartment A so that as the tar content of theoil increases the temperature of the heating gases declines, while theheating surfaces enposed to the hottest heating gases are protected by the circulation thercover of ml containing the least content of tar. ln all of the heating elements the absorption of heat by thev circulating oil protects the heating surfaces, and particularly in the first where the heating element 1s exposed to the hottest heating gases and where the circulat ing oil contains the reflux and the fresh oil and the least content of tar. [ls tar accumulates in the oil it is further craclred for the further recover of the desired pressure distillate hut by eat exchange with heating gases progressively declining in temperature as the tar content of the oil increases,

ft will thus he seen that the present invention provides an improved method of crashing hydrocarbon oils lay distillation under pressure 'in externally heated pressure stills in which the heating surfaces of the s ill are protected hoth lay recycling part of the Waste heating gases from the still and employing them to temper the fresh products of combustion from the furnace and by supplying fresh oil and reflux to that part of the oil charge circulating over the heating surfaces with which the heating gases first contact, that is the surfaces subjected to the hottest heating gases, so that the oil circulating over these initial heating surfaces contains a low content of tar. The heating gases cooled and tempered in this initial heating operation and by the tempering due to the recirculation of waste heating gases are then employed to further heat and crack the oil as carbon and tar constituents accumu late in it. The oil circulated over the initial heating surfaces thus contains the highest proportion of fresh oil and reflux constituents, and at the same time these heating surfaces are protected by the recycling of waste heating gases, while as the fresh oil and reflux constituents are cracked and vapbrized and as the circulating oil becomes heavier and carbon and tar constituents accumulate therein the oil is circulated over heating surfaces exposed to the cooler heating gases from the preceding heating of oil having a lower tar content. portant advantages of the present invention is that it enables the cracking operation to be'carried out over a long period without decreasing the rate of cracking. Another important advantage of the invention is that it enables an im roved application of the heating gases to t e cracking operation so that both the efficiency and capacity of the pressure still may be increased. A further important advantage of the present invention is the rotection which it affords to the heating sur aces of the pressure still, particularly to the heating surfaces which are exposed to the most intense heat and to the severest conditions.

We claim; I

1. lln improved method of cracking hydrocarbon oils, which comprises heating the oil to a cracking temperature under pressure in two stages, circulating oil from the first stage to the second sta e, supplying fresh oil to the first stage, su jecting the vapors from the cracking operation to a refluxing operation and returnm reflur. therefrom to the first stage, circulating heating gases for supplying the heat absorbed by the cracking operation in indirect contact heat enchang ing relation first with the oil in the first stage and then with the oil in the second stage, and recirculatin part of the heating gases from the secon stage and admiring them with the heating gases in the first stage.

2. An improved method of cracking hydrocarbon oils, which comprises heating the oil to a cracking temperature under pressure in two stages, circulating oil from the first Une of the in1- lltl llli

ltlli stage to the second stage, subjecting the vapors from the cracking operation to a refluxing operation in direct contact with fresh oil, returning the reflux and admixed fresh oil to the first stage, circulating heating gases for supplying the heat absorbed by the crack ing operation in indirect contact heat exchanging relation first with the oil in the first stage and then with the oil in the second stage, and recirculating part of the heating gases from the second stage and admixing them with the heating gases in the first stage.

3. An improved method of cracking hydrocarbon oils, which comprises heating the oil to a cracking temperature under ressure in two stages, subjecting the vapors fli'om the cracking operation to a refluxing operation, supplying to the first stage only fresh oil and reflux from the refluxing operation, circulating oil from the first stage to the second stage, circulating heating gases for supplying the heat absorbed by the cracking operation in indirect'contact heat exchanging relation first with the oil in'the first stage and then with the oil in the second *stage, and recirculating part of the heating gases from the second stage and admixing them with the heating gases in the first stge.

4. An improved method of cracking hydrocarbon oils, which comprises passing the oil successively-through a series of cycles, circulating the oil in each cycle and heating .the circulating oil therein to a' cracking temperature under pressure, subjecting the vapors from the several cycles to a refluxing operation, supplyin fresh oil and returning reflux from the re uxing operation to the first c cle in the series, circulating heating gases or supplying the heat absorbed by the cracking operation in indirect contact heat exchanging relation first with the oil in the cycle to w ich fresh oil and reflux are supplied and then with the oil in the successive cycles, and recirculating part of the heating gases from the last cycle and admixing them with the heating gases in the first cycle.

5. An improved method of cracking hydrocarbon. oils, which comprises passing the oil successively through aseries of c cles, circulating the oil in each cycle an heating the circulating oil therein to a cracking temperature under pressure, subjecting the vapors from the several cycles to a refluxing operation, supplyin rfresh oil and returning reflux from the re uxing operation to the first cycle in theseries, circulating heating gases for supplying the heat absorbed by the cracking operation in indirect contact heat exchanging relation first with the oil in the cycle to which fresh oil and reflux are supplied and then with the oil in the successive cycles, and recirculating part of the heating gases from a successive cycle and admixing them with the'heating gases in a preceding style.

6. An improved method of cracking hydrocarbon oils, which comprises heating a body of oil to a cracking temperature under pressure by circulating oil from the body in indirect contact heat exchange with heating gases and back to the body, subjecting the vapors from the body of oil to a refluxing operation, supplying fresh oiLto the body and returning reflux from the refluxing operation thereto, heating the fresh oil and reflux to a cracking temperature under pressure by indirect contact heat exchange with the heating gases before they are applied to the first mentioned heating operation, and recirculating part of the heating gases from the first mentioned heating operation and admixing them with the heating gases in the second mentioned heating operation.

7. An improved method of cracking hydrocarbon oils, which comprises passing the oil successively through a series of cycles, mechanically circulating the oil in each cycle and heating the circulating oil therein to a cracking temperature under pressure, subjecting the vapors from the several cycles to a refluxing operation, supplyin fresh oil and returning reflux from the re uxing operation to the first cycle in the series, circulating heating gases for supplying the heat absorbed by the cracking operation in mechanically circulating the oil in each cycle I and heating the circulating oil therein to a cracking temperature under pressure, subjecting the vapors from the several cycles to a refluxing operation, supplyin fresh oil and returning reflux from the re uxing operation to the first cycle in the series, circulating heating giises for supplying the heat absorbed by t e cracking operation in indirect contact heat exchangi relation first with the oil in the cycle to w ich fresh oil and reflux are supplied and then with the oil in the successive cycles, and recirculating part of the heating gases from a successive cycle and admixing them with the heating gases in a preceding cycle.

9. An improved method of cracking hydrocarbon oils, which comprises heating a body of oil to a cracking temperature under ressure by mechanically circulating oil rom the body in indirect contact heat exchange with heating gases and back to the body, subjecting the vapors from the body of oil to a refluxing operation, sup lying fresh refluxing o eration thereto, heating the fresh oil and re ux to a cracking temperature under pressure by indirect contact heat ex-' change with the heating gases before they are applied to the first mentioned heating operation, and recirculating part of the heating gases from the first mentioned heating operation and admixing them with the heating gases in the second mentioned heatmg operation.

In testimony whereof we aflix our signatures.

LOLA R. BELL, Ewecutm'm of the Last Will and Testz'ment of J 07m E. Bell, Deceased.

EDWARD W. ISOM.

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