US1617297A - Pressure still heating furnace - Google Patents

Description

J. E- BELL PRESSURE STILL HEATING FURNACE Feb. 8 1927. 1,617,297

Original Filed Jan. 28, 1922 s Sheets-Sheet 1 INVENTOR 70/777 EBGZZ ATTORNEYS Feb. 8, 1927.

J. E. BELL I PRESSURE STILL HEATING FURNACE Original Filed Jan. 28, 1922 5 Sheets-Sheet 2 QQQQ b @9000 @0@@ am, 0900 0 8 oooe INVENTOR .faim EBeZZ m Z144, *W

ATTORNEYJ Feb. 1927.

v J. E. BELL PRESSURE STILL HEATING FURNACE Original Filed Jan. 28, 1922 3 Sheets-Sheet 5 7/4 "win z w INVENTOR J07??? Z5, 36

M ATTORNEYS Patented Feb. 8, 1 927.

UNITED STATS JOHN E. BELL, OF BROOKLYN, NEW YORK, ASSIGNOR TO SINCLAIR REFINING COM- PANY, OF CHICAGO, ILLINOIS, A CORPORATION OF MAINE.

PRESSURE STILL Ena'rmo FURNACE.

Continuation of application Serial No. 532,482, filed January,28, 1922. This application filed April 1,

I 1924. Serial No. 703,340.- r

'This invention relates to an improved method and apparatus for cracking oil, and involves an improved method of'heating of oil cracking stills and improvements in cracking still heating apparatus whereby danger of overheating is avoided or mini.-

mized and a more uniform heating action is .obtained.

The invention relates particularly to improvements in the heating of pressure stills for cracking hydrocarbons of higher boiling points, such as crude petroleum, gas 011 and the like, to form more volatile or lighter hydrocarbons, such as those that constitute commercial gasoline or pressure distillate, and the apparatus therefor.

Among the objects of the invention are the protection of thetubes or oil heating surfaces of cracking stills from overheating or burning, the lengthening of the time of the runs between cleaning with a corresponding increase in the distillate produced, and a more uniform distribution of the heat throughout the heating chamber, and other advanta es which will appear from the following escription. I

Pressure stills and other stills for cracking oil are heated by furnaces in which coal,

'gas or oil isburned, and, for economy in fuel consumption, it is desirable that the fuel be burned in the furnace with the least amount of excess air and at maximum furnace temperature. Excessive temperatures are, however, objectionable in the heating chambers of oil craokin stills.

surface increases over the temperature of. the oil, the amount of this increase being proportional to the thickness of the carbon deposit and to the amount of heat delivered to the external surface heated by the fur: nacegases. The overheating of the still or of the tubes or heating elements of a cracking still,"'and the resulting increased-tendency of carbon formation, tend to give hot spots and involve aconsiderable element of Carbon is formed during the crac in operation and danger or hazard to life and propertydue to the possible bursting of a part of the heating surface which has become over-heated or burnt. In an oil cracking still the tubes heating surfaces most exposed to the heat of the furnace can be decreased by reducing the fuel consumption, but this in turn reduces the capacity of the still; while, if the still is driven hard to increase its capacity by. increasing fuel consumption, the danger of overheating is greatly increased.

According to the present invention, the heating of the still is modified and regulated to avoid or greatly reduce the danger of overheating and to secure a more uniform heating action.

According to the present invention, the products of combustion from the fire box are tempered. by admixture with hot gases at a lower temperature before the admixed heating gases are brought into contact with the tubes or other heating surfaces of the still, 'thereb reducing the temperature to which the rst tubes or surfaces are subjected and the amount of heat absorbed by them, and increasing the amount of heat absorbed by tubes or surfaces over which the gases pass before escaping from the heating chamber. This tempering ofthe products of combustion from .the furnace is nevertheless efi'ected without sacrificing either fuel economy or still capacity, and

may even result in a' considerable increase in still capacity.

Vith the ordinary furnace arrangement, such as commonly used under stills, a arge proportion of the heat in the fuel asses directly from the fuel bed where solid fuel is used, or' from the frame and hotter brick work when gaseous or oil fuel is'used directly to the heat absorbing surfaces by radiation. It has been shown by tests that the amount of heat absorbed by the surfaces next to the-fire may be and usually is "40 or 50 times as great as the average absorption of heat throughout the whole surface, and

this amount of heat is principally transshown that the amount of heat transferred in this way increases very rapidly with the furnace temperature, the process in general being controlled by Stcfans' law for radiation which makes the total amount of radiation propdrtional to the fourth power of the absolute temperature of the radiant. When the furnace is arranged so that the heat absorbing surfaces are shielded from direct radiation, the interposed shields and the connecting passages become secondary radiators and the total amount of heat transmitted by radiation is absorbed by the heating ases with the result that there is an actua increase in the temperature of the heating gas coming in contact with the heated surface of theboiler or still, although this increase in gas temperature doesnot compensate for the reduction in the radiant heat.

According to the present invention, the

' heat absorbing surface of the cracking still is protected from direct radiation from the furnace by the interposition of suitable passages or screens, such as a high bridge wallarrd a vertical flue with refractory walls, or by other suitable arrangement of the fire box and heating chamber.

Also, according to the present invention,

the products of combustion from the furnace are diluted and tempered with a heated gas before they are passed over the oil heating surfaces. For example, I may introduce a diluting body of air or gas into the connecting flue between the furnace and heating chamber at a point near the furnace. The addition of such a tempering body of hot air or gas reduces the gas temperature where the heating gases first contact with the heating surfaces of the still, and also the temperature of, the refractory walls. The heat absorbed by the surface or surfaces 'of the still with which the furnace gases first contact is thus reduced in two ways, namely, by.

the lower temperature of the heating gas, and by a reduction in the temperature of the refractory secondary radiating surfaces.

If the diluting air or gas is not heated, the result is a reduction in efficiency such as accompanies the burning offuel with an excessive amount of cold air. According to this invention, however, the diluting air or gas admixed with the products of combustion is heated, for example, to approximately the temperature of the waste heating gases leaving the heating chamber of the still. I have found that if the temperature of the diluting gas is approximately that of the waste heating gases leaving the still surface not only is there no reduction in the fuel economy and in the capacity of the still, but, on the other hand, there is a slight increase in both. 7

This application is a continuation of my prior application filed J anuary 28, 1922, Ser. ,No.v $32,482. In one method of operation described in said prior application, a pro-' portion of the hot waste heating gases at the temperature at which they leave the heating chamber of the still is drawn aside and returned for tempering the hot products of combustion from the furnace. The resent application relates more particular to an improved method and apparatus in w ich preheated air or gas is employed as the diluting and tempering medium.

According to this invention, air or gas is preheated by heat interchange with the escaping heating gases fromthe heating chamber and the heated air or gas admixed with the furnace gases. An air heater may be installed in'a flue leading from the heating chamber of the still and air forced through and preheated to the proper temperature in this heater and then introduced. into the furnace gases before the admixed furnace gases and preheated air are brought in contact with the tubes or other heatlng surfaces of the still.

Where a part of the hot waste heating gases from the still are employed as the heated diluent, as described in the above referred to prior application, and the same amount of fuel is burned in the furnace, a measure of the efficiency and capacity of the still can be made from the temperature and weight of the waste gases. The weight of the waste gases, however, is not changed by the continuous recycling of a part of the waste gases, and experience has shown that the temperature of the waste gases escaping from the still is reduced. As a result, the efficiency and capacity of the still are somewhat increased.

When preheated air orgas is used for the heated diluent, and at; approximately the tempcrature'of the exit gases leaving the still, as is the case where the tempering medium is heated by heat interchange with thehot waste .exit gases in a waste gas heater of sufficient proportions, the same considerations apply and the efficiency and capacity of the still are slightly increased. When the waste gas heater is somewhat smaller than will heat the tempering air orgas to approximately the temperature of the waste gases, there may be a slight reduction in efficiency and capacity.

The invention is of more or less general application fdr the heating of oil stills, and

' In a. tubular oil still the circulation of the.

heating gases is advantageously countercurrent, or in a general countercurrent direction, to that of the oil. Vhere, for example,

is of particular value for use with sucha tubular cracking still. In such a still, the oil is heated in its upward flow and is hottest in the upper tubes or in the upper por tions of the tubes. Where the high temperature products of combustion are introduced into the top of the heating chamber containing such tubes, the tubes containing the hottest oil are subjected'to the greatest'heat. According to the present invention, the excessive temperatures of combustion are moderated and the products of combustion are cooled before they are brought into contact with the tubes or portions of tubes containing the hottest oil. The more uniform dis tribution of the heating gases gives an increased heating effect in the lower tubes or in the lower portions of the tubes so that in general a more uniform heating of the oil flowing through the tubular heater is accomplished, as well as the avoiding of excessive over-heating of any portions of the tubes.

The invention will be further described in connection with an oil still such as that described and illustrated in Patent No. 1,285,200, granted to the Sinclair Refining Company, November 1.), 1918, on the application of Edward W. Isom; but-1t will be understood that the invention is of more general application, although it is of particular value with a tubular cracking still of the character referred to in said patent.

In the accompanying drawings I, have shown certain forms of apparatus embodying the invention and in which the process of the invention can be practiced, and the invention will be further described in connection therewith. It is to be understood ,however that these specific illustrations and description are for the purpose of exempllfication and that the scope of the invention is defined in the following claims, in which I have endeavored to distinguish it from the prior art so far as known to me, without, however, relinquishing or abandoning any portion or feature thereof. 1

In the oil cracking stills illustrated more or less diagrammatically in the drawings, the products of combustion coming from the tire box are tempered by an admixture of hot gas or air which has been preheated by heat ferent type of oil heating furnace in which the oil heating tubes are horizontal instead of vertical,

Fig. 3 is a transverse, vertical section on the line 33 of Fig. 2,

Fig. 4 is a horizontal section'on the line 44 of Fig. 2, and

Fig. 5 a fragmentary sectional View on the vertical plane of line 5-5 of Fig. 4.

It willbe understood that'only the heater portion of the cracking still is shown in the accompanying drawings. In connection with an oil cracking still of the general construction illustrated in Patent 1,285,200, the bulk supply tank containing the greater portion of the charge of the pressure still is arranged away from the furnace and the oil is circulated from the bulk supply tank through the heating tubes and b ck to the bulk supply tank. In its broader aspects, the invention is of general application to tubular cracking stills including single pass tubular cracking stills and other stills of various types and designs.

In the accompanying drawings, corresponding parts are designated by the same reference characters.

Referring to the drawings, the oil heating furnace illustrated in Fig. 1 comprises a fire-box 1, which may be of any usual or preferred form, communicating by an elongated throat 2 withthe upper end of the heating chamber 3 containing the oil heating tubes. The chamber 3 is of considerable vertical length and communicates at its lower end with a stack flue 4. The fire box is shown as equipped at 5 with a mechanical stoker and at, 5 with burners by means of which oil or gas may be used as fuel. The elongated throat 2 is separated from the heating chamber 3 by a lengthy bridge wall which overhangs at its top, as at 30, into the throat tubes extend. At their lower ends, the tubes 7 extend through a slab or slabs of refractory material 10 beneath which the header 12 is located. The slabs of refractory material may rest upon collars formed on the tubes, as shown in F ig.- 1, and the platesor slabs 10 may rest upon angle irons 13 at their edges. The entire battery of tubes is supported from the top header so as to be free to expand and contract with change of temperature.

The lower header 12 is connected to a" &

er 9 and thence through the upper manifold and pipe 11. When the heater is employed in a system of the type shown in the Isom patent, to which reference has been made, the pipes 11 and 12 are connected to the bulk supply tank (not shown) and preferably one or both of them is provided with means for accelerating the circulation as shown in said patent. The heating chamber is provided with baflles 14 and 15 which cause the hot gases to pass back and) forth among the tubes of the battery a number of times before reaching the flue 4, by which they make their exit from the heating chamber. By reason of this thorough circulation about and in contact with the oil heating tubes, heat is efliciently extracted from the products of combustion before they reach the flue 4. The efliciency is further increased due to the fact that the general directions of the flow of the heating gases and of the oil are opposed so that the relatively cool oil entering at the bottom of the tubes extracts the heat from the partially cooled gases and the temperature of the oil increases until it is at the maximum in the upper pass of the furnace where it is exposed to the gases fresh from the fire-box. The oil heatin tubes are, however, screened from direct ra iation from the fire-box, even at their upper ends, thus preventingoverheating with consequences to which reference has heretofore been made.

In order to reduce the temperature of the hot products of combustion coming from the fire-box before they strike the oil containing tubes, I provide means for tempering the fresh roducts of combustion from the firebox with preheated air at lower temperature. For this'purpose I provide a vertical flue 40 communicating at its lower end with the flue 4 and at its upper end with a horizontal flue 31 leading to a stack. A battery of vertical tubes 32 is arranged in this vertical flue and communicates at its upper end with a boxing or flue 33 through which the tubes 32 are supplied with air. The lower end of this tube battery communicates througha header 35 with a horizontal flue 34 leading to a transverse flue or boxing 18 extending across the throat of the fire box. This box is formed with a longitudinal opening or openings 19 communicating with the throat of furnace. The spent gases from the bottom of the heating chamber pass up through the vertical flue 40 and the battery of air heating tubes 32 therein. The air entering the flue 33 flows countercurrent to the hot waste heating ases from the heating chamber 3 through the battery of tubes 32 and into the flue 34 along which it flows to the outlet or outlets 19 where it intermingles'with and tempers the hot products of combustion from the fire-box.

In the oil heating furnace illustrated in Figs. 2 to 5 inclusive, the general arrangement of the furnace, including the fire box 1", the elongated vertical throat 2, and

downwardly extending heating chamber 3 hand side of the furnace, as shown in Fig.

3, is provided with a connection 42 to serve as an inlet for the oil, and the upper header on the same side is provided with a similar connection 43 to serve as an outlet for the oil. It will be noted that the uppermost and lowermost headers on the left hand side of the furnace, that is the headers to which the inlet and outlet are respectively connecte receive only two horizontal rows of pipes whereas the intermediate headers on the same side and all of the headers on the other side of the furnace receive four horizontal rows of pipes. This provides for a continuous circulation of the oil received through the inlet 42 back and forth across the heating chamber in its passage to the outlet 43 so that it is exposed many times in its passage through the furnace to the heat of the products of combustion circulating about the heating tubes as they pass back and forth across the tubes in passage from the top to the bottom of the heating chamber.

A stack'flue 4 communicates with a vertical flue 40 which at its upper end connects with a horizontal flue 41 returning to a stack. A battery of vertical tubes 32 is arlanged in this vertical flue and communicates at its upper end with a boxing or flue through which the tube battery 32 is supplied with air. .The lower ends of the tubes 32 communicate through a header 35 with a horizontal flue or flues 34 leadingto an outlet 34 in front of the bridge wall.

' The spent gases from the bottom of the heating chamber-3* pass up the vertical flue 40 and heat the tube battery therein. The air entering the flue 33 flows'countercurrent to the hot' waste heating gases from the heating chamber-.3 down the tubes 32 and into the flue or fines 34 along which it flows to the outlet 34 where it intermingles with and tempersthe hot products of combustion from the fire box.

It will be evident that the amount of hot preheated air or gas introduced into the hot gas, for example, to a temperature of about.

2000 F. before the admixed heating gases reach the tubes. In their passage through the first pass of the heating chamber the gases may be reduced from about 2000to 1300 F. at which temperature they enter the second pass, where they may be reduced to about 1 0'00 F. The gases finally leaving the lower pass may be reduced to about 800 F. at which temperature they enter the preheater for the tempering air or gas. The regulation of the introduction of the hot tempering diluent is independent of the rate of combustion in the fire box, and, with a suflicient introduction of the tempering mediumfthe rate of combustion may be somewhat increased Without objectionable overheating of the surfaces of the cracking still by the admixed heating gases.

It will thus be seen that the present invention provides for the reduction of the furnace temperature of the heating gases at the point where they first come in contact with the surfaces of the cracking still and that this reduction of temperature permits a milder condition of heat absorption in these tubes with resulting less coke formation, while the reduction of temperature in the furnace by recirculation of gases protects the brick work and prevents slagging of the same. The fast velocity of gases past the tubes tends to prevent the deposit of furnace slag and dust upon the tubes with resulting impairing of vision of the tubes and heat conductivity.

It will. further be seen that these and other advantages are obtained without sac rifice of the efliciency of the furnace but that the efliciency is somewhat increased, as well as giving .a more uniform application of heat to the oil heating surfaces. As a result, the life ofthe heating tubes or ele ments is greatly increased, while the danger of injury from overheating and burning 1s greatl reduced, and the apparatus can be operate for longer periods of time without requiring shutting down for cleaning). The furnace linings are also prolonged ecause of the lower temperature of the gases which are brought in contact therewith.

While the invention is of more or less general application to oil stills, and particularly to tubular stills, it is of special value in oil cracking stills operated ata high pressure where there is tendency for carbon deposits to form on the heating surfaces and where the failure of any part of The temperature in the the still is accompanied with great hazard to life and property. In a tubular. oil cracking still the invention makes the heating of the tubes more uniform, increases the efficiency of heat transfer, and decreases or removes altogether the danger of overheating; while nevertheless taking full advantage of the heat of the furnace gases utilized in heatingthe still.

I claim 1. An oil cracking still, having a heating chamber with oil heating surfaces therein, a fire box communicating with said chamber, meansv for preheating air with the hot gases leaving, the heating chamber, and means for tempering the hotproducts ofcombustion from the fire box with the preheated a r before the admixed air and combustion gases enter the heating chamber.

2. An oil cracking still, having a heating chamber with oil heating surfaces therein, a fire box communicating with said chamber, a stack flue communicating with said chamber, means in said stack flue for preheating air andmeans .for tempering the hot products of combustion from the furnace with the preheated air before the admixed gases enter the heating chamber.

3. A tubular oll cracking still having a heating chamber with oil heating tubes therein, a fire box communicating with said chamber, means for preventing direct radiation from the fire box against the tubes, means for preheating air with the hot gases leaving the heating chamber, and means for tempering the hot products of combustion from the fire box with the preheated air before the admixed gases enter the heating chamber.

4. A tubular oil cracking still having a heating chamber with oil heating tubes therein, a fire box communicating with said chamber, a stack flue communicating with said chamber, means in said stack flue for preheating air and means for tempering the hot products of combustion from the fire box with the preheated air before the admixed gases enter the heating chamber.

5. An oil cracking still having a heating chamber with oil heating surfaces therein, a fire box communicatin withsaid \hamber, means for preventing direct radiation from the fire box against the oil heating surfaces, means for'preheating air with the hot gases leaving the heating chamber, and means for tempering the hot products of combustion from the fire box with the preheated air before the admixed gases enter the heating chamber.

6. The improvement in the heatin of oil 1 cracking stills in which oil is heated to the cracking temperature by hot products of combustion from a fire box passing f externally over the oil heating surfaces of the still, which comprises preheating air by heat passing the resulting admixed heating gases over the oil cheating surfaces.

7. The improvement in the heating of oil cracking stills in which oil is heated to the cracking temperature by hot products of combustion from the fire box passing externally over the oil heating surfaces of the still which comprises preheating air to a temperature approximately equal to the temperature of the hot waste heating gases leaving the heating surfaces and passing the preheated air in admixture with the ot prodnets of combustion from the fire box over the heating surfaces.

8. The improvement in the heating of oil cracking stills in which oil is heated to the cracking temperature by hot products of combustion from a fire box passing externally over the oil heating surfaces of-the still, which comprises preheating air by heat exchange with hot waste heating gases which have passed over the heating surfaces, admixing the preheated air with the hot )roducts of combustion from the fire box before passin the admixed heating gases over the heating surfaces and passing the resulting admixed heating gases over the oil heating surfaces, and also preventing direct radiation'from the fire box to the oil heating surfaces. v

9. The improvement in the heating of tubular oil cracking stills in which oil is heated to the cracking ten'iperature by hot products of combustion from a fire box passmg externally over the oil heating tubes, which comprises preheating air by heat exchange with hot waste heating gases which have passed over the heating tubes, admix-' ing the preheated air with the hot products of combustion from the fire box, and passing the resulting admixed heating gases over the oil heatin tubes.

In testimony whereof I aflix my signa ture.

JOHN E. BELL.

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