US2265959A - Method of heating fluids - Google Patents

Description

J. T. WARD METHOD OF HEATING FLUIDS Dec. 9, 1941.

Filed Feb. 10, 1938 BY! r2.

ATTORNEY 4 NM; .NJy mm Kim/$3M T @\&l@ M um o H HHH HHH H M .1 oxmxxxx M o k NW\ & a fix. V k W E muyw Q Patented Dec. 9, 1941 1' OFFICE METHOD OF HEATING FLUIDS John T. Ward, Westfield, N. J., assignor to Gasoline Products Company Inc., Newark, N. J., a corporation of Delaware Application February 10, 1938, Serial No. 189,756

4 Claims.

This invention relates to a method of heating fluids and more particularly heating hydrocarbon fluids to conversion temperatures.

In some present furnace designs certain of the heater tubes are shielded or protected to receive different amounts of heat from the radiant section of the furnace according to the degree of cracking desired. However, the control of the rate of heat transfer to the tubes is only approximate and better heat control is desired.

According to my invention the rate of heat transfer to the heater tubes is correlated with the cracks per pass carried on in the different sections of the heater tubes or heating coil. I accomplish this by using dummy tubes which are not used to convey the hydrocarbon fluids to be heated but which convey other heat absorbing medium or fluids. The dummy tubes are so positioned in the furnace with respect to the heater tubes as to control the rate of heat transfer to selected sections of heater tubes.

In one form of the invention a furnace is provided with a radiant section separated from a convection section by a bridge wall. Preheating tubes are positioned in the convection section for preheating the hydrocarbon fluids before passing them through heater tubes in the radiant section of the furnace. The preheated hydrocarbon fiuids are then passed through rows of heater tubes positioned along the side wall and bridge wall of the radiant section of the furnace wherein the hydrocarbon fluids under superatmospheric pressure are rapidly heated to a relatively high temperature. The highly heated hydrocarbon fluids are then passed through a single row of roof tubes positioned near the bridge wall and near the exit for the hot products of combustion leaving the radiant section of the furnace.

The hydrocarbon fluids are heated further in these roof tubes and then are passed to the lower row of a double row of roof tubes preferably arranged in staggered relation further away from the bridge wall than the first mentioned roof tubes. The hydrocarbon fluids are further heated to a higher temperature and are then passed through the upper row of the roof tubes which constitutes a soaking section. In order to prevent overheating of the hydrocarbon fluids passing through the double row of roof tubes, Iplace dummy tubes at the ends of the rows of roof tubes adjacent the side wall and roof of the radiant section of the furnace. A heat absorbing medium is passed through the dummy tubes and the dummy tubes are maintained at about the same temperature as the adjacent tubes of the double row of roof tubes. However, such dummy tubes may be located at other places in the furnace to prevent overheating of the hydrocarbon or other fluids passing through the heater tubes.

In this way heat which ordinarily would be absorbed by the upper portion of the side wall and the roof and reradiated to the roof tubes is absorbed by the dummy tubes to prevent overheating and coking of the hydrocarbon fluids passing through the double row of roof heater tubes. Water or steam may be passed through the dummy tubes to limit the amount of heat absorbed by the adjacent roof tubes. The wall temperature may be used as a means for controlling the amount of heat absorbing medium passed through the dummy tubes.

In another form of the invention wall heater tubes are omitted and the hydrocarbon fluids are passed through preheating tubes in the convection section of the furnace. The convection section is preferably separately fired to increase the amount of heat being transferred to the hydrocarbon fluids passing through the preheating tubes. The preheated hydrocarbon fluids are then passed through a single row of roof tubes positioned in the radiant section of the furnace adjacent the bridge wall wherein they are rapidly heated to a relatively high temperature.

The heated hydrocarbon fluids are then passed through a double row of roof tubes as above described in connection with the first form of the invention. The heating of the double row of roof tubes is controlled by using dummy tubes similar to those above described. Other forms of fur-' naoes may be used and provisions for other soaking sections may be made.

By the use of dummy tubes placed near certain tubes I am able to obtain very close control of the heat input to the stream of hydrocarbon fluids at various points in the heater tubes or coil and this is particularly important where single pass short time cracking is desirable. In addition the crack per pass can be increased because of the better control of heat input 'to the heater tubes.

In the drawing I have shown a vertical longitudinal cross section of one form ofa heater adapted for practicing my'invnetion, parts being diagrammatically shown to facilitate the disclosure.

Referring now to the drawing, the reference character Hi designates a'furnace or heater having a radiant section I2 and a convection section I separated by a bridge'walll6. Theconvection section has an extension I8 which leads to the flue 20. Positioned in the convection section 14 and extension l8 preferably in staggered relation are convection heating tubes 22.

The radiant section is heated by any suitable means, as, for example, by means of burners 24. Positioned in the radiant section l2 are horizontally disposed tubes in vertical rows disposed ad jacent the four boundary surfaces defining said section and, if desired, with suitable floor tubes connected to the other tubes.

For illustration;

however, there are only shown horizontally extending wall tubes 26 arranged in a vertical row along the side wall 28 of the furnace I .0 and horizontally extending wall tubes 30 arranged in a vertical row along the bridge wall I6. After bein heated in tubes 26 and 30 and similar tubes on the other two walls, the hydrocarbon fluids are passed through a single row of roof tubes indicated as 34 in the radiant section l2 then through a lower row of roof tubes indicated as 35 and finally through the upper row of roof tubes indicated as 38. Adjacent the side wall 28 of the furnace and the end tubes 40 of the lower row 36 of roof tubes and end tube 42 of the upper row 38 of roof tubes are dummy tubes 44 adapted to convey a h t a so bin m dium to p e o e heatin of the hydrocarbon flu ds in the roof tubes.

The furnace will now be more particularly described to set forth the method of heating fluids and the flow of the fluids throu h the heater tube A hydrocar on fluid or fluids. such as an oil stock to be cracked, is passed through line 48 by pump 50 under superatmospheric pressure thr ugh the heater tubes 22 in the convection section M to preheat the hydro arbon fluids. The preheated hydrocarbon fluids are then passed through line 52 to the lowest heater tube 54 in the row or heater tubes 30; along the bridge wall L6.

The hydr c r on fluids then pass to the lowest tube 58 of the row of heater tubes 25 along the side wall 23 of the furnace and then to heater tube 62 in row 30, etc passing from one row of heater tubes to the other to further heat the hydrocarbon fluids. The hydrocarbon fluids are then passed through line 66 to the single row of roof tubes 34 wherein they are further heated. The hydrocarbon fluids are then passed through line 08 and through the lower row of roof tubes 36 having its end tube 40 shielded by dummy tubes 4.4. The hydrocarbon fluids are then Passed through line Hi and through the upper row of roof tubes 38 having its end tube 42 shielded by the dummy tubes .44. The roof tubes 38 function as a soaking section. The heated and converted hydrocarbon fluids are then passed through line 12 and further treated to separate low boiling hydrocarbons as is well kn wn in the, art.

Th dummy tubes .44 are used to prevent overheating of the hydrocarbon fluids passing through roof tubes 36 and 38 by controlling the rate of heat transfer to the roof tubes. Such control is obtained by passing steam or the like through the dummy tubes 44 to maintain them at about the Same. temperature as the roof tubes 35 and 3.8. The dummy tubes absorb heat which would otherwise be absorbed by the wall 28 and roof I3 of the furnace l and reradiated tothe roof tubes. The amount of steam or other .medium. passing through the dummy tubes maybe controlled by means resp nsive t the t p st-- ture of the wall 2. adjacent the. roof tubes 36 and 3B. The steam or other heat absorbing medium is passed through line 14 by pump '16, through the tubes 44 and then. out through line 80.

A typical operation of one form of my invention will now be given. A hydrocarbon fluid such as a- Mid-Continent gas oil having a gravity of 35 A, B. I. is passed through the various tubes at, a, pressure of about 200 to 1000 pounds per square inch. The fluid is passed through the preheating tubes 22 and heated to a temperature of about 650 to 750 F. The preheated hydrocarbon fluid is then passed through the radiant coil including the rows of wall tubes 26 and 30 wherein it is heated to a temperature of about 750 to 865 F. The heated hydrocarbon fluid is then passed through the single row of roof tubes 34 and heated to a temperature of about 865 to 925 F.

The heated hydrocarbon fluid is then passed through the lower row of roof tubes 36 wherein it is heated to a temperature from about 925 to 950 F. The hydrocarbon fluid is then passed through the upper row of roof tubes 38 wherein further heat is added but without substantially raising the temperature of the hydrocarbon fluids. The dummy tubes 44 are maintained at a temperature of about 925 to 950 F. by circu'-- lating a heat absorbing medium such as steam therethrough.

In the above typical operation during the heating of the Mid-Continent gas oil in the radiant coil including the vertical rows of wall tubes 26 and 30, the heat input is about 40,000 B. t. u. per hour per square. foot and the per cent conversion to gasoline of the gas oil is about 30%. The heat input to the single row of roof tubes 34 is about 35,000 B. t. u. per hour per square foot of heater tube surface and the per cent conversion to gasoline of the gas oil is about 35%. The heat input to the lower row of roof tubes 36 is about 30,000 B. t. u. per hour per square foot of heater tube surface and the per cent conversion to gasoline of the gas oil is about 40%. The heat input to the upper row of roof tubes 38 is about 10,000 B. t. u. per hour per square foot of heater tube surface and the per cent conversion to gasoline of the gas oilis about 50%.

Where no wall tubes are used in the furnace and the preheater tubes 22 are separately fired, the Mid-Continent gas oil under superatmospheric pressure is preheated in the preheater tubes to about 800 F. and the heat input to the single row of roof tubes is about 40,000 B. t. u. per hour per square foot of heater tube surface and the per cent conversion to gasoline of the gas oil is about 30%. row of roof tubes is about 30,000 B. t. u. per hour per square foot of heater tube surface and the per cent conversion to gasoline of the gas oil is about 40%. The heat input to the upper row of roof tubes'is about 10,000 B. t. u. per hour per square foot of heater tube surface and the per cent conversion to gasoline of the gas oil is about 50%. The cracked products leave the radiant section l2 of the furnace through line 12 at a temperature of about 1000 to 1050 F.

It will be understood that the various tubes in the radiant section l2 are so disposed therein as to be substantially out of the path of the hot combustion gases and are heated mainly by radiant heat, while the tubes in the convection section are swept by the combustion gases and are heated mainly by convection heat. Moreover, while a specific flow of fluid tl nough the furnace tubes -has been described, various other flows well understood by those skilled in the art may be employed.

While I have shown several dummy tubes located in a particular part of the radiant section it is to be understood that the number of dummy tubes may be varied depending on the desired control ofheat input and further that the dummy tubes, may be located in that part of the radiant section where overheating may be experienced. For example, dummy tubes may be effectively The heat input to the lower employed in the bottom of the furnace and at one corner thereof when floor tubes are used in the radiant section [2. This may prove particularly advantageous when the oil leaves the radiant section through floor tubes which normally receive intense radiant heat and it is desired to avoid overheating. Dummy tubes may be also used to control the heating of hydrocarbon fluids passing through the top heater tubes adjacent the bridge wall.

While I have particularly referred to hydrocarbon fluids in describing my invention, it will be understood that my invention can be used in heating fluids generally where it is desired to closely control the rate of heat transfer to the fluids particularly to certain portions of the furnace or heater.

While'I have given examples of my invention it is to be understood that I am not restricted thereto as various changes and modifications may be made without departing from the spirit of the invention.

I claim:

1. In a process of heating hydrocarbon fluids wherein the hydrocarbon fluids are passed through heater tubes arranged in a radiant heating section of a furnace, the steps which comprise generating radiant heat in said radiant section, passing the hydrocarbon fluid through a single row of roof heater tubes to rapidly raise the temperature of the hydrocarbon fluid while cracking at a relatively low rate, then passing the heated hydrocarbon fluid through the exposed row of a double row of roof heater tubes to decrease the amount of heat being transferred to the hydrocarbon fluid in said heater tubes while increasing the crack per pass, then passing the heated hydrocarbon fluid through the shielded row of roof heater tubes in said double row to further decrease the amount of heat being transferred to the hydrocarbon fluid in said last mentioned heater tubes while further increasing the crack per pass and controlling the rate of heat transfer to end heater tubes in said double row of roof tubes to avoid overheating of the hydrocarbon fluid passing through said tubes by absorbing heat in said radiant section adjacent such tubes with a fluid heat absorbing medium passing through a separate conduit.

2. In a process of heating hydrocarbon fluids wherein the hydrocarbon fluids are passed through heater tubes arranged in a radiant heating section of a furnace, the steps which comprise generating radiant heat for said radiant section, passing the hydrocarbon fluid through a single row of roof radiant heater tubes to rapidly raise the temperature of the hydrocarbon fluid while cracking at a relatively low rate, then passing the heated hydrocarbon fluid through the exposed row of a double row of radiant heater tubes to decrease the amount of heat being transferred to the hydrocarbon fluid in said heater tubes while increasing the crack per pass, then passing the heated hydrocarbon fluid through the shielded row of radiant heater tubes in said double row to further decrease the amount of heat being transferred to the hydrocarbon fluid in said last mentioned heater tubes while further increasing the crack per pass and controlling the rate of heat transfer to the end heater tubes in said double row of radiant tubes to avoid overheating of the hydrocarbon fluid passing through said tubes by absorbing heat in said radiant section adjacent said tubes with a fluid heat absorbing medium passing through a separate conduit adjacent said end tubes.

3. In a process of heating hydrocarbon fluids wherein the hydrocarbon fluids are passed through heater tubes arranged in a radiant heating section of the furnace, the steps which comprise generating radiant heat for said radiant section, passing the hydrocarbon fluid through roof radiant heater tubes so disposed in said radiant heating section as to be subjected to the maximum heat densities to which the hydrocarbon fluid is subjected therein to rapidly raise the temperature of the hydrocarbon fluid while cracking at a relatively low rate, then passing the heated hydrocarbon fluid through the exposed row of a double row of radiant heater tubes to subject the hydrocarbon fluid to decreased heat densities while increasing the rate of cracking, then passing the heated hydrocarbon fluid through the shielded row of radiant heater tubes in said double row to thereby subject the hydrocarbon fluid to further decreased heat densities while further increasing the rate of cracking, and modifying the heat density applied to the end heater tubes in said double row of radiant tubes to avoid overheating of the hydrocarbon fluid passing through said tubes by absorbing heat in said radiant section adjacent such tubes with a fluid heat adsorbing medium passing through a separate conduit adjacent said tubes.

4. In a process of heating hydrocarbon fluids wherein hydrocarbon fluids are passed through heater tubes arranged in a radiant heating section of a furnace having a roof and side walls, the steps which comprise generating radiant heat in said radiant heating section, passing the hydrocarbon fluid through a single row of roof heater tubes adapted to receive direct radiant heat and reradiated heat from the roof of the furnace to rapidly raise the temperature of the hydrocarbon fluid while cracking at a relatively low rate, then directing the heated hydrocarbon fluid to a double row of roof heater tubes the end tubes of which double row are adjacent a side wall of the furnace, passing the heated hydrocarbon fluid first through the exposed row of said double row of roof heater tubes to decrease the amount of heat being transferred to the hydrocarbon fluid in said heater tubes while increasing the crack per pass, then passing the heated hydrocarbon fluid through the shielded row of roof heater tubes in said double row to further decrease the amount of heat being transferred to the hydrocarbon fluid in said last mentioned heater tubes while further increasing the crack per pass and controlling the rate of heat transfer to the end heater tubes in said double row of roof tubes to avoid overheating of the hydrocarbon fluid passing through said tubes by passing a separate stream of fluid through tubes positioned adjacent said side wall and roof and adapted to shield said end tubes of said double row of radiant tubes from reradiated heat from said side wall and to absorb radiant heat in the 201;? between said end tubes and roof and side wa JOHN T. WARD.

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