US2080221A - Method and apparatus for heating fluids - Google Patents

Description

May 11, 1937. DE FLOREZ 2,080,221

METHOD AND APPARATUS .FOR HEAT ING FLUIDS Filed- Dec. 14, 1933 2 173 e ama $52 BY 45W fl/S' A TTORNE Y Patented May 11, 1937 UNITED STATES PATENT OFFICE Luis de Florez, Pomfret, Gonn., assignor to The Texas Company, New York, N. Y., a corporation of Delaware Application December 14. 1933, Serial No. 702,333

Claims.

This invention relates to a control for a fluid heating furnace of the type having a radiant heater section and a convection heater section. In one aspect, the invention is applicable to the 5 control of a tube still for the heating of petroleum oil, such as for the cracking of the oil to convert higher boiling constituents to lower boiling constituents, or for the distillation of the oil.

In a furnace of the type shown in my Patent No. 1,717,334 dated June 11, 1929, which is provided with a vertical radiant heating section and a convection heating section, and which is adapted to heat the oil or other fluid first by convection heat in the convection section, and then rapidly to a high temperature by radiant heat in the radiant heating section, it is desirable to use as little excess air as is practicable to obtain substantially complete combustion of the fuel supplied to the furnace. est combustion temperature in the radiant heating section with a comparatively lower velocity of combustion gases, which is conducive to greater heat input to the oil with consequent greater extraction of heat from the gases before they are discharged from the radiant section to the convection section. A smaller amount of heat is absorbed by the oil in the convection section under these conditions, giving substantially the maximum differential in temperature between the two sections of the furnace. An economical and highly eflicient heating of the oil or other fluid is thereby accomplished.

It is an object of the present invention to provide a control for a furnace of this type, which will automatically maintain the above-mentioned operating conditions. This is accomplished by regulating the fuel supply in accordance with the temperature of the oil at a selected point in its path of flow in the radiant heating zone; and by 40 regulating the air supply in accordance with the temperature of the oil at a selected point in its path of flow in the convection heating zone. In a preferred embodiment, the air supply is regulated in accordance with the variations in temperature of the oil from predetermined normals at selected points in its path of flow in both the convection and radiation zones. Regulation is effected at recurrent time intervals; and the amount of in" crease or decrease in air supply at any particular interval is proportional to the deviation in This provides the high- In the drawing, in which a preferred embodiment of the invention is illustrated,

Fig. 1 is a diagrammatic view of a tube still and associated control mechanism, with parts broken away and in section;

Fig. 2 is a detail view of a portion of the control mechanism; and

Fig. 3 is a view of a portion of a temperature recording chart of the continuous strip type.

Referring to the drawing, there is illustrated a furnace or tube still of the type shown in my mentioned Patent No. 1,717,334. This comprises a cylindrical furnace l0 built of brick work or other suitable material. It will be understood that the furnace may be made somewhat conical or chimney-like in shape, or rectangular or-polygonal in cross-section, although the cylindrical construction is preferred. Adjacent the upper end of the furnace is mounted a tube sheet II, which serves to suspend an annular ring of tubes I2 about the periphery of the radiant heating chamber I3. The tubes are connected at their upper endsby suitable headers l4, and at their lower ends by headers l5 located beneath a lower tube sheet l6.

Centrally arranged in the upper tube sheet H is an opening l8, through which ignited products are introduced into the combustion chamber from a mixing compartment l9 supplied by a fuel pipe 20 and an air pipe 2|. bustion chamber is an upwardly extending throat 23, through which the products of combustion escape into a flue 24. The air and fuel are projected downwardly into the central portion of the chamber l3 where active combustion takes place, and the products of combustion sweep out through the throat 23. Heat is transferred primarily by radiation from the combustion flame to the tubes [2, and contact of the highly heated products of combustion with the tubes is substantially avoided. As shown, the tubes may be arranged in several rows of concentric circles about the combustion chamber, the tubes of one circle preferably being staggered with respect to the tubes of another circle. They thus form a surface virtually lining the side 'wall of the furnace and shielding it from the intense heat. By reason of the vertical arrangement of the tubes, and their substantially uniform reception of radiant heat, sagging of the tubes and the attendant difiiculties of local overheating and ob- -j'ectionable coke deposition are effectively eliminated. The upper and lower ends of the tubes, including the headers, are shielded from At the base of the comthe radiant heat by being arranged within the end chambers and 26 respectively.

The combustion gases are introduced from flue 24 through opening 28 into a convection heater 29 formed of fire brick or the like, containing a horizontal tube bank 30 in the path of flow of the gases, which finally escape by flue 3| to stack 32. A by-pass 33 containing a pressure operated explosion damper 34 is arranged to establish direct communication between flue 24 and stack 32 in the event of an explosion or other abnormal pressure condition. Oil is supplied to pipe 35, such as from a pump or other suitable means, and thence to the tube bank 39, where it flows. from one horizontal row of tubes to a row beneath, thus passing generally countercurrent to the fiow of combustion gases. The partially heated oil then travels by pipe 36 to the tubes l2 in the radiant heating section, where it flows in series or in series-parallel through the tubes and finally is discharged by pipe 31 to a soaking or flashing chamber, or other treating device. The flow of oil is preferably maintained substantially constant by any suitable mechanism, such as by maintaining a substantially constant head upon the oil, or by a valve control. The furnace may be fired from the lower end of the combustion chamber as described in my Patent No. 1,717,334, so that the products sweep upwardly through the radiant heater instead of downwardly as shown in Fig. 1. It is also to be understood that any other suitable form of furnace or tube still, having convection and radiant heating sections in series, may be employed.

Located adjacent the outlet of coil I2 is a pyrometric thermocouple 40, which is connected in an electric circuit having leads 4| and 42. Located adjacent the outlet of tube bank 3|) is a second pyrometric thermocouple 43, which is connected by lead 4| in series with thermocouple 49. Lead 44 extends from thermocouple 43 to one pole of a galvanometer, shown diagrammatically by coil 46 and needle 48. Lead 42 connects by a movable point with the slide wire 41 of the main circuit of the potentiometer, indicated diagrammatically as also including battery 49 and battery adjusting resistance 45. The galvanometer circuit is completed by lead 42' connecting from one end of the slide wire 41 to the other pole of the galvanometer. A given temperature differential between thermocouples and 43 produces a given potential tending to induce current flow through the galvanometer circuit in one direction. For the predetermined temperature difierential which it is desired to maintain, the movable point is adjusted along slide wire 41 to give an equal counter potential from battery 49, to thereby maintain galvanometer needle 48 in neutral or central position, in the conventional manner of a potentiometer pyrometer. Thereafter, any change from the predetermined temperature difi'erential will produce a deflection of the needle to one side or the other of the central position, depending on whether the temperature differential has increased or decreased in amount. The extent of deflection of the needle is dependent on the amount of the increase or decrease from the normal or predetermined temperature difierential. Pivotally mounted so as to extend above the range of movement of the galvanometer needle 48, are bell cranks 50 and 5|. Below needle 48 is located a chopper 52, which is reciprocated by eccentric 53, to cause the chopper to be brought into contact with needle 48, and the needle in contact with one of the bell cranks 56 or 5|, depending upon the direction in which the needle is deflected. Power to move the bell cranks 56 and 5| is therefore taken from the mechanism 53 and not from the galvanometer needle; the galvanometer needle simply determines the selection of the bell cranks 50 and 5| and their extent of movement, since it will be obvious that a greater deflection of the needle for a given throw of the chopper will produce a greater movement of one or the other of the bell cranks.

Pivotally mounted at 55 is a bar 56, carrying studs 51 and 58 with which the depending arms of the bell cranks 50 and 5| respectively cooperate to cause tilting of the bar 56 from its normal position in which it is illustrated by solid lines, to inclined positions, one of which is indicated by dotted lines. It will be evident that the extent of tilting of bar 56 is dependent upon the extent of movement of one of the bell cranks 56 or 5|, x

which in turn depends upon the amount of defiection of galvanometer needle 46.

Located adjacent bar 56 is a restoring mechanism comprising a constantly rotating shaft 69 carrying cams 6| and 62, which have the general configuration shown in Fig. 2. Said cams are adapted in their rotation to strike the elevated ends of bar 56 and restore the bar to its normal horizontal position. Cams BI and 62 are insulated as at 63 from shaft 66, and electrical contact is obtained by brushes 64 and 65 bearing on the cams 6| and 62 respectively. Contact pieces 66 and 61, with which cams 6| and 62 respectively contact, are insulated at 68 from bar 56. Brush 64 is connected by lead 10 containing battery 1| to solenoid 12, the latter being connected by return lead 13 to contact piece 66. Brush 65 is similarly connected by lead 14 containing battery 15 to solenoid 16, return lead 11 connecting the solenoid with contact piece 61. The cores of solenoids 12 and 16 are interconnected by rod 18, which is pivotally connected to a link 19 pivoted at 80 on the stem of a throttle valve 8| positioned within air supply pipe 2|. The opposite end of link 19 is pivotally connected to a cross rod 82, carrying at its opposite ends suitable spring pressed plungers mounted within the casings 83 and 64. A second regulating mechanism similar to that shown herein, or in my Patent No..

1,806,597, dated May 26, 1931, is provided to control the supply of fuel through pipe 20, this not being shown for purposes of simplifying the drawing and inasmuch as the mechanism can be a substantial duplicate of that shown in said patent. This second mechanism is responsive to a thermocouple positioned at a selected point in the path of flow of the oil through the radiant heating coil l2, preferably adjacent the outlet of the coil. The thermocouple 40 may be connected by a parallel circuit to the galvanometer of this second regulating mechanism; or a separate thermocouple may be employed.

In operation, hydrocarbon oil is supplied to the heating coils of the pipe still at an adjusted rate which is maintained substantially constant. Fuel and air are admitted in suitably regulated proportions by pipes 20 and 2| to produce a combustion flame in the radiant heating section |3, the combustion gases passing through flue 24 into the convection heating section 29 where they flow over tube bank 30. The furnace is initially brought up to the desired temperatures, such as to give approximately the desired temperatures of the oil at the selected points in its path of flow.

The differential between the temperatures at the selected points in the radiant heater and convection heater sections depends upon the combustion conditions, and is indicated by the percentage of C02 in thecombustion gases. The sensitive regulators then serve to maintain these desired temperatures within a very few degrees of normal, likewise obviating hunting or periodic fluctuation from one side of normal to the other.

In a typical example in which oil is heated for cracking or flash distillation, fuel conditions are set to maintain a temperature at thermocouple 40 of substantially 810 F. and air supplied to the burners at a rate to maintain thermocouple 43 at substantially 640 F., as indicated by lines 85 and 86 on the chart of Fig. 3, or a difference of 150 F. between the two temperatures. Anyvariation in this predetermined difference will cause a corresponding deflection of the galvanometer needle 48 in a direction and to an extent depending on whether the difference is more or less and how much. As shown, a decrease in the temperature below normal at thermocouple 43 accompanied by no change (or by an increase) in temperature at thermocouple 40, and hence an increase in the difference between the two temperatures, will cause a deflection of needle 48 to the left as indicated in Fig. 1. bell crank 50 to raise the left-hand end of bar 56 to the dotted line position of Fig. 1. Cam 6|, in its constant rotation, will then be brought into engagement with contact 66. Due to the shape of the cam face, which progressively departs in a spiral path from the axis of shaft 60, a certain definite time of contact between cam SI and contact piece 66 will result, which depends upon the extent of deflection of bar 56 and in turn upon the extent ofdeflectionpf needle 48. Such contact closes the electrical circuit of solenoid 12 which swings link 19 tothe left from the full line to the dotted line position as shown in Fig. 1. This rocks valve ill a certain distance toward fully open position, consequently increasing the air supply to the furnace.

Continued rotation of cam 6| restores bar 56 to its normal position and then breaks contact as the outer end of the cam surface moves away from contact piece 66, whereupon the circuit of solenoid I2 is opened and the spring pressed plunger in casing 83 restores valve 8| to its original predetermined position. As stated, shaft 60 rotates at a constant rate, for example, three or four revolutions per minute; and chopper 52 is raised in timed relation therewith, generally shortly after contact has been broken between a cam and its associated contact piece. The increased charge of air admitted for a short period, will result in an increased velocity of flow of combustion gases, with the result that less heat is extracted from the gases in the radiation section, and more heat will be absorbed by the oil in the convection section. The control of the fuel supply will tend to keep the oil temperature at thermocouple'40 substantially constant, with the net result that the temperature of the oil at thermocouple 43 is increased. The galvanometer needle is thereby returned slightly toward its normal position. At the next cycle, the chopper 52 will accordingly swing bell crank 50 and bar 56 a lesser distance;- whereby the contact between cam iii and contact 66 is of decreased duration. The regulation is thereby accomplished by aseries of puffs of increased air supply, the amount of the increase at each periodic correction tending to Movement of chopper 52 will then cause constantly decrease as the oil temperature returns toward normal. Conversely, a decrease in the temperature diflerential between the thermocouples will cause a deflection of galvanometer needle 48 to the right, causing movement of bell crank 5| with consequent rocking of bar 56 to raise the righthand end of the bar into position to be engaged by cam 62. This closes circuit of solenoid 16, thereby rocking valve ill a predetermined distance toward closing position, spring pressed plunger 84 serving to return the valve to its normal preset position when contact is broken on each cycle. In this manner, a desired differential in temperature is maintained between the convection and radiation sections.

The amount of excess air employed for combustion is indicated by the proportion of CO2 in the combustion gases. For example, substantially the theoretical amount of air required for a given fuel supply, will produce combustion gases analyzing about 10% to 13% CO2, depending upon the character of the fuel. This is approximately the minimum amount of air used for most eflicient operation, and affords the highest flame temperature in the radiant section. A higher flame temperature causes greater transfer of radiant heat to the coil in the radiant section; consequently, there is less heat left in the combustion gases passing to the convection section.

By the use of approximately the minimum amount of air, the volume of gases is less, there is less friction of flow through the convection bank, and less heat transferred in the convection section. Increasing the air above the theoretical amount required for complete combustion, gives a lower flame temperature in the radiant section with a decreased heat transfer therein, and a greater volume of gases of higher temperature passing to the convection section, thereby increasing the heat in-Dut in the convection section. I have indicated this in the chart of Fig. 3, in which an increased air supply providing combustion gases analyzing 8% CO2, .has produced for the conditions illustrated an oil temperature of substantially 680 F. at the outlet of the tube bank of the convection' heater. Again, decreasing the air supply for a given fuel supply, has resulted in oil temperatures of approximately 660 F. and 640 F. with combustion gases testing about 9% and 10% C02 respectively.

The present invention takes advantage of these observed conditions, by making the air supply dependent upon the difference of oil temperatures at selected points in the radiant and convection heater sections respectively. The invention is particularly suitable for the heat treatment of oil, inasmuch as uniform radiant heat transfer to the'radiant heating coil is obtained, affording uniform cracking per pass, thereby enabling an accurate control and regulation to be effected. Thus, with the air supply initially adjusted somewhere within the range desired, for example, such as to give from 8% to 10% C02 in the combustion gases, a suitably high temperature flame can be produced in the radiant section with the control of the fuel supply, such as to give the predetermined high temperature of the oil at the outlet of the radiant heater. If the air supply is above the predetermined normal, which I have illustrated as being such as to produce substantially 10% CO2 in the combustion gases for a temperature of 640 F. at the outlet of the convection preheater, then the heat transfer to the oil in the convection heater will be greater than that desired, and the temperature of the oil adjacent the outlet of the convection heater will rise above the predetermined normal. This will produce a deflection of the galvanometer needle to the right, resulting in periodically recurring decreased charges of air, with consequent reduction in the oil temperature at the selected point in the convection section until the oil temperature at this point has returned to normal. Conversely, should the temperature of the oil at the outlet of the convection heater fall below the predetermined normal, indicating a further decrease in air for a given fuel supply, deflection of the galvanometer needle to the left will cause periodically recurring increases in the air supply which restores the oil temperature to normal.

While the above description presupposes that air is introduced by pipe 2| and liquid or fluid fuel by pipe 29, the valve 8! normally having an intermediate setting such as to give a predetermined air supply for combustion purposes, it is understood that a primary quantity of air can be introduced with the fuel through the pipe 20, and only an auxiliary or secondary supply of air introduced through pipe 2| under the control of valve 8|. It is, also, to be understood that any suitable control mechanism can be provided for the fuel supply through pipe 20, such, for example, as that illustrated in my mentioned Patent No. 1,806,597, in which a periodically recurring control is used to increase or decrease the fuel supply, the extent of the increase or decrease being proportional to the deviation from normal of the temperature of the oil at a selected point in the pipe still, for example, at the outlet of the radiant heater. This is indicated diagrammatically in Fig. '1 of the drawing, in which leads 88 and 89 responsive to thermostat 48 extend to a controller 90 of the type disclosed in the above mentioned patent. From this controller Bil, leads 9| and 92 pass to a valve mechanism 93 of any suitable conventional structure for regulating the supply of fuel passing through pipe 20. This mechanism 93 may be similar to that disclosed in my above mentioned. Patent No.

While the heat treatment of petroleum oil has been particularly described herein, it is to be understood that the invention is not so limited, and that it is adaptable for the heating of other liquids and fluids, such, for .example, as coal tar oils, hydrogenation products from coal, lignite or other materials, fatty oils, solvents or solvent mixtures, water or steam, hydrocarbon or other gases, and the like.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A tube still comprising a radiant heater section having a vertical combustion chamber, a burner chamber located at one end of said combustion chamber, anoutlet flue located at the other end thereof, said burner chamber and said outlet flue having cross-sectional areas less than the cross-sectional area of said combustion chamber, a continuous heating coil arranged in a series of vertically disposed interconnected tubes about said combustion chamber adjacent the wall thereof and outside the path of flow of the products of combustion, a convection heater section communicating with said outlet flue to receive products of combustion therefrom, a bank of tubes positioned within said convection heater sectiofr in the path of travel of said combustion gases, means for supplying a fluid to -be heated to said tube bank in the convection heater section and then to said interconnected tubes in the radiant heater section, means for supplying air to the radiant heater section, thermostatic elements responsive to the temperatures of the fluid at selected points in its path of flow, one adjacent the outlet of said tube bank in the convection heater section, and another adjacent the outlet of said interconnected tubes in the radiant heater section, mechanism actuated by said thermostatic elements for automatically controlling said air supplying means, means for supplying fuel to the radiant heater section, and means independent of the control of said air supplying means for controlling the said fuel supplying means in accordance with the temperature of the fluid adjacent the outlet of said interconnected tubes in the radiant heater section.

2. The method of treating a fluid which com prises passing such fluid in a confined stream through a convection heating zone and a radiant heating zone in series, introducing fuel and air into the radiant heating zone to produce an intense flame therein, passing combustion gases from the radiant heating zone to the convection heating zone, controlling the supply of fuel in accordance with the temperature of the fluid at a point in the radiant heating zone only which is responsive to combined heat input in the said convection and radiant heating zones, and increasing or decreasing at predetermined recurrent time intervals the quantity of air supplied, the extent of each increase or decrease being in proportion to the deviation from normal of the temperature differential of the fluid at points in both the radiant and convection heating zones, the said points being substantially spaced as regards the heating along the path of fluid flow and so positioned as to give an indication of heat input in the convection heating zone and combined heat input in the convection and radiant heating zones respectively.

3. A tube still comprising a vertical radiant heater section with a centrally arranged combustion chamber surrounded by a series of interconnected vertical tubes, and a separate convection heater section having a bank of interconnected tubes therein, means for passing a fluid to be heated through the said tube bank in the convection heater section and then through the interconnected tubes in the radiant heater section, means for supplying fuel and air to the centrally arranged combustion chamber of the radiant heater section to produce an intense flame therein, means for leading the products of combustion from the radiant heater section to the convection heater section, thermostatic elements responsive to the temperatures of the fluid passing through tubes in both the convection and radiant heater sections, one or more of said elements being so positioned as to be responsive to heat input in the convection heater section, and one or more of said elements being substantially spaced as regards the heating along the path of fluid flow from the first mentioned elements and so positioned as to be responsive to combined heat input in the radiant said convection and heater sections, mechanism actuated by a thermostatic element in the radiant heater section only for controlling said fuel supplying means, and mechanism actuated by thermostatic elements in both the radiant and convection heat- 2,oso,22i

er sections for controlling. said air supplying means.

4. The method of treating a hydrocarbon oil which comprises passing the oil at a substantially constant rate in a continuously flowing confined stream through a convection heating zone and a radiant heating zone in series, introducing fuel and air into the radiant heating zone to produce an intense flame therein, passing combustion gases from the radiant heating zone to the convection heating zone, controlling the supply of fuel in accordance with the temperature of the oil at a point in the radiant heating zone only which is responsive to combined heat input in the said convection and radiant heating zones, and increasing or decreasing at predetermined recurrent time intervals the quantity of air supplied, the extent of each increase or decrease being in proportion to the deviation above or below normal respectively of the temperature differential of the oil at selected points in its path of flow in both the convection and radiant heating zones, the said points being substantially spaced as regards the heating along the path of fluid flow and so positioned as to give an indication of heat input in the convection heating zone and combined heat input in the convection and radiant heating zones respectively.

5. The method of treating a fluid which comprises passing such fluid in a confined stream through a convection heating zone and a radiant heating zone in series, introducing fuel and air into the radiant heating zone to produce an intense flame therein, passing combustion gases from the radiant heating zone to the convection heating zone, controlling the supply of fuel in accordance with the temperature of the fluid at a point in the radiant heating zone only, which is responsive to combined heat input in the said convection and radiant heating zones, and increasing or decreasing the quantity of air supplied in proportion to the deviation from normal of the temperature difierential of the fluid at points in both the radiant and convection heating zones independently of the said fuel control, the said points being substantially spaced as regards the heating along the path of fluid flow and so positioned as to give an indication of heat input in the convection heating zone and combined heat input in the convection and radiant heating zones respectively.

LUIS DE FLOREZ.

Images