US2288366A - Furnace - Google Patents

Description

June so, 1942. w. M. PARSONS FURNACE Filed April 22, 1940 3 Sheets-Sheet l 5471M!!! f1 Farm/13 June 30, 1942.

w. M. PARSONS 2,288,366-

FURNACE Filed April 22, 1940 3 Sheets-Sheet 2 INVENTOR ORNEY June 30, 1942. w. M. PARSONS 2,288,366

' FURNACE Filed April 22, 1940 3 Sheets-Sheet 5 69 1& 15 15 15 g 59 s 2 Q9 3 1s 8 a 12 3 76 INVENTOR 12 o f 77 64mg Farm/1.;

12 I; ORNEY Patented June 30, 1942 UNITED STATES PATENT OFFICE FURNACE Winchell M. Parsons, Alhambra, Calif.

Application April 22, 1940, Serial No. 330,886

3 Claims.

This invention relates to tube stills and more particularly to furnaces suited to heat a fluid to the high temperatures required for the pyrolytic or catalytic conversion of hydrocarbons.

In certain processes of the above type it is necessary first to heat hydrocarbon oils to or above the vaporizing temperature, but below the temperature at which conversion takes place under the conditions of operation or, in the case of gases, to preheat the same to a suitable temperature below that at which conversion takes place, and subsequently to raise the gases or vapors rapidly and under controlled conditions to conversion temperature. The present invention provides a furnace for this purpose in which the conversion takes place in a split stream, utilizing banks of parallel connected tubes so arranged that all tubes are subjected to identical heating conditions, which may be accurately controlled as to total heat transfer and as to heat distribution along the tubes.

An object of the invention is to provide a furnace of the above type which is so constructed and arranged that rapid and eflicient heat transfer is obtained for heating the fluid to the high temperature required for conversion during its passage through the heating zone.

Another object is to provide a furnace of the above type in which a selected bank or banks of tubes may be periodically removed from stream for purposes of reactivation, regeneration, burning out the carbon deposited therein or repair while maintaining a substantially constant throughput and without materially altering the heat available for the preheating zone.

Another object is to provide a furnace of the above type which is suited to the commercial operation of various catalytic or pyrolytic conversion processes.

Various other objects and advantages will be apparent as the nature of the invention is more fully disclosed.

In one embodiment the furnace comprises a pair of side walls with an intermediate bridge wall extending upwardly from the floor, parallel to the side walls, to divide the furnace into an elongated combustion zone and an elongated convection zone. The converter tubes, which may contain a catalyst, are arranged vertically in a single row adjacent to but spaced from the side wall of the combustion zone. The converter burners are located in the floor and are inclined toward the bridge wall to direct the flame away from the converter tubes and over the bridge wall as a wall or sheet of flame and hot cornbustion gases, adapted to heat the face of the bridge wall to radiance.

The converter tubes are heated in part by direct radiation from the flame and hot combustion gases, in part by direct radiation from the bridge wall, in part by reflected radiation from the side wall and in part by convection. The arrangement of the burners and the draft causes the flames and hot combustion gases to hug the bridge wall and thereby prevent impingement thereof on the converter tubes. From the combustion zone the gases pass over the bridge wall and heat the tubes in the convection zone by convection and by radiation from the hot flue gases.

The combustion zone is divided into a plurality of individual combustion chambers by a set of transverse walls extending between the bridge wall and the side wall of the combustion zone. The tubes in each such combustion chamber are connected to headers to form an individual bank of parallel connected vertical tubes. The burners may also be connected in groups so that the flow of fluid through the individual banks of tubes and the combustion in the individual chambers may be controlled as desired. This provides for shutting down a bank of tubes together with the corresponding burners when desired without affecting the operation of the remaining banks.

In the embodiment shown the furnace is divided into four separate combustion chambers so arranged that any three tube banks may be operated at all times, one bank of tubes being placed on stream prior to the shutting down of a second bank. In this way the throughput is maintained substantially constant as distinguished from the so-called batch operation where a catalyst zone is first heated and then placed on stream until the temperature has fallen below a predetermined point.

A feature of the invention resides in the reduction of the percentage of the capacity of the furnace which is off stream for reactivation purposes at any one time, with a consequent increase in overall on stream efiiciency. In the embodiment above described it will be noted that of the total capacity may always remain in use, thereby making a substantially continuous operation possible in spiteof the necessity for pcriodic reactivation.

The convection zone extends along the entire length of the furnace. The tubes are arranged horizontally in this zone and also extend the entire length of the furnace to be heated by combustion gases received from each of the combustion chambers. Hence, if the same number of combustion chambers are operated at all times, the same total quantity of combustion gases will be available for heating the convection tubes regardless of which of the combustion chambers may be shut down at any instant.

For imparting additional heat to the convection tubes and for controlling the amount of preheating, a row of roof burners may be provided above the convection zone. These burners may be inclined toward the side wall of the convection zone so as to avoid direct impingement of the flame upon the convection tubes. The floor and roof burners may be controlled so as to maintain the desired heat distribution along the converter tubes as well as to obtain the total heat required for raising the fluid to the desired temperature in both the convection zone and the combustion zone.

Although the novel features which are believed to be characteristic of this invention are pointed out more particularly in the claims appended hereto, the nature of the invention will be better understood by referring to the following description, taken in connection with the accompanying drawings, in which a specific embodiment thereof has been set forth for purposes of illustration.

In the drawings:

Fig. 1 is a side elevation of a furnace embodying the present invention, with parts broken away to show the construction thereof;

Fig. 2 is a transverse section taken along the line 2-2 of Fig. 1; and

Fig. 3 is a horizontal section taken along the line 33 of Fig. 2.

Referring to the drawings more in detail, the furnace is shown as comprising a pair of side walls iii and II, end walls I2 and 13, a roof I l and a floor l5 forming an elongated rectangular furnace chamber. The side walls Ill and H are shown as comprising inner layers Illa and Ha and outer layers Nb and lib respectively, of suitable refractory material. The end walls I2 and I3 are similarly formed with inner layers 12a and Iiia and outer layers I21) and 13b, respectively. The arrangement is such that the inner layers Illa, Ha, 12a, and Mia may be made of a high grade refractory suited to withstand high temperatures. The outer layers of the furnace walls may be made of a lower grade refractory or red brick inasmuch as they are exposed to the atmosphere and are not required to Withstand as high a temperature as the inner layers. The furnace walls, however, may be constructed in any standard manner and a specific embodiment thereof has been shown only for purposes of illustration.

In the embodiment shown, the furnace is supported by buckstays it which are arranged along the outside of the walls and rest upon a suitable foundation i8. Cross girders i9 and longitudinal girders 20 form a frame on which the floor l5 of the furnace is supported. Cross girders 22, extending between the buckstays l6, are arranged to support the roof M. The buckstays 16 are shown as extended above the roof M of the furnace to support a roof truss 25 adapted to carry a covering 26 which protects the exposed piping, to be described, from the weather.

A bridge wall 30 extends longitudinally of the furnace between the side walls i0 and H to divide the furnace into a combustion zone SI and a convection zone 32. The bridge wall 30 may be supported by a pier 34 resting upon the foundation IS. The combustion zone 3! is shown as divided into a plurality of combustion chambers 3m, 3|b, 3lc and Md by a plurality of transverse walls 35 which extend between the bridge wall 30 and the side wall [0. The bridge wall 30 and the transverse walls 35 terminate short of the roof Id of the furnace so as to provide space for passage of combustion gases thereover into the convection zone 32.

A row of burners 36, having throats 3? in the floor i5, are inclined toward the bridge wall 35 so as to direct flame and combustion gases vertically against the face of the bridge wall for heating the same to a radiant condition. The burners are preferably closely spaced to provide a substantially continuous wall or sheet of flame and combustion gases over the face of the bridge wall 30 and may be controlled by individual valves 38 or the burners in each combustion chamber may be controlled as a group. The combustion gases, after passing over the bridge wall 35 and through the convection zone 32 are removed by a plurality of exhaust ducts ll communicating with a flue 42 which is connected through a pipe 33 to a stack 44. Individual dampers 45 are provided in the ducts 5| for controlling the flow of gases therethrough.

An additional row of burners 55, having control valves 5|, is shown as firing through the roof M of the furnace over the convection zone 32 for imparting additional heat to the gases passing therethrough. These burners may be inclined toward the wall II to direct flame and combustion gases against said wall so as to obtain surface combustion and to prevent direct impingement of the flame on the convection tubes.

A plurality of vertical converter tubes 55 are arranged in banks comprising a single row of ver tical tubes extending along but spaced from the side wall H). The tubes 55, in the case of a catalytic converter, may contain catalyst material with which the fluid is to be contacted. The tubes are shown as extending through an aperture 55 in the floor l5, which aperture may be filled with cement or other heat resisting and supporting material to effectively close the same after the tubes have been inserted. The tubes likewise extend through an aperture 57 in the roof I l and are shown as supported on brackets 58 bearing against collars 59 on the individual tubes and attached to beams 60 carried by the girders 22. The tubes of each bank may be connected by top and bottom elbows 62 and 63 respectively, to an inlet header G4 which is located above the furnace roof and an outlet header 65 which is located below the floor 5. The headers 64 and 65 of each bank of tubes are connected by pipes 55 and 6'! respectively to a supply line 68 and an outlet line 69. Valves l0 and H are arranged in each of the pipes 66 and El respectively to control the flow of fluid to the various banks of tubes.

A bank of serially connected horizontal convection tubes 15 is mounted in the convection zone 32. These tubes may be supported in a plurality of tube sheets 76 which are positioned between the bridge wall 30 and the side wall H and may be directly supported by said walls or from buckstays 16. The tubes 15 are shown as extending the entire length of the convection zone 32 and as serially connected by suitable headers ll located at the ends of the furnace. Fluid may be supplied to the tubes 15 by a supply line 80 and may be withdrawn through a line 8| which is shown as connected to the supply line 68 leading to the supply headers 64.

The pipes 6! leading to the outlet headers 65 are also connected by lines 85, controlled by individual valves 81, to a blow down line 85. The pipes 66 leading to the supply headers 64 are connected by lines 88, controlled by individual valves 90, to a supply line 89 through which steam and/or air may be supplied to the headers for purposes of reactivation, regeneration or cleaning as will be described. The line 8| may also be connected to a pair of lead-oil lines SI and 92 controlled by valves 93 and 94 respectively. A shut-oil valve 95 may be included in the line 3| between the lead-off lines 9| and 92 so that by closing the valve 95 and opening the valves 93 and 94, the preheated fluid from the convection tubes may be removed from the furnace for treatment prior to introduction into the converter tubes 55. Of course, the furnace may also be used to heat different fluids in the convection tubes and the converter tubes 55 by withdrawing one fluid through the line 91 and introducing a second fluid through the line 92.

In the operation of this furnace, the burners 35 are so adjusted as to maintain the bridge wall 35 in radiant condition whereby heat is transferred to the tubes 55 by radiation from the flame and hot combustion gases and from the surface of the bridge wall 39 and by reflection from the side wall l9. Heat is also transferred to the tubes 55 by convection from the combustion While the burners are inclined in such a way that the tubes 55 are out of the main path of the combustion gases, so as to prevent the tubes from burning out due to contact with the flame and highly heated gases, circulation of the combustion gases in the combustion zone 31 may cause some of the gases to contact with the tubes 55 so as to impart additional heat thereto. The heat distribution along the tubes 55 may be controlled by adjusting the burners 36 so as to vary the rate of combustion, the length of the luminous portion of the flame and the point or" contact of the flame with the bridge wall By firing longitudinally of the tubes 55, it is possible to maintain identical heating conditions for all of the tubes and also to control the distribution as desired.

The combustion gases from all of the individual combustion; chambers pass through the convection zone 32 in contact with the tubes therein, thereby preheating the fluid in the tubes 75 before the gases pass to the stack 44. It is usually preferable to connect the tubes 15 for the serial flow of fluid through the entire bank of tubes although the bank may be otherwise connected if desired. In certain instances there may not be suflicient heat available in the gases from the combustion zone to raise the fluid in the convection bank to the desired temperature. The burners 59 may accordingly be used to supply additional heat for this purpose. These burners 5%) are arranged to fire downwardly onto the upper part of the side wall H for obtaining surface combustion and also for preventing the flame fromimpinging directly on the tubes 15. The combustion gases from the combustion zone 3| also serve to shield the tubes 15 from direct contact with the flame from the burners 50 and thereby prevent overheating of the uppermost tubes.

By a suitable adjustment of the two sets of burners 3t and 50, the temperature gradient along the tubes 55 and between the combustion zone and the convection zone may be varied as desired.

The furnace is constructed in such a way that the individual banks of tubes 55 may be removed from stream and cleaned or reactivated when this is rendered necessary, for example, by reason of carbon deposition in the various tubes. This is particularly important in the case of a catalytic converter wherein frequent reactivation of the catalyst may be required. In accordance with the present invention, a selected bank of tubes is removed from stream by closing the appropriate valves 19 and H. The reactivation fluid, such, for example, as steam or a mixture of steam and air may then be supplied to the tubes by opening the appropriate valves 99 and the reactivation products may be passed directly to the blow-down line by opening the appro priate valve 81. During this reactivation the burners 36 in the combustion chamber containing the bank of tubes being reactivated may be shut down or the temperature thereof may be reduced as desired. The corresponding burners 53 may also be shut down or adjusted. Inasmuch as the reactivation usually involves an exothermic reaction, the temperature of the tubes may be maintained at the desired value without the introduction of additional heat from the burners. Preferably, superheated steam is first passed through the tubes to blow out any vapors which may be present therein and which would form an explosive mixture. Thereafter, air or a mixture of steam and air may be passed through the tubes to burn out the carbon deposit and to reactivate the catalyst. The quantity of air may be regulated so as to prevent overheating of the tubes. After reactivation superheated steam may again be passed through the tubes to purge the same of products of reactivation and air before the tubes are again placed on stream. By using the superheated steam at about the temperature of operation of the tubes, the reactivation may be accomplished without appreciable cooling of the tubes and without delay for again bringing the same up to temperature before they are return-ed to stream.

It will be noted that in the furnace shown three banks of tubes may be maintained on stream at all times while the 4th bank is being reactivated. Consequently, the combustion gases from three of the combustion chambers are always available for heating the tubes I5 in the convection zone. This results in a substantially uniform heat supply for the convection tubes, regardless of the particular combustion chamber which may be shut down at any instant. If desired, any substantial variation in heat supply may be avoided, by suitable regulation of the burners 59 so as to maintain the desired temperature in the convection zone, regardless of the condition of operation of the corresponding oombustion chambers. By increasing the number of separate combustion chambers, the ratio of useful capacity may be increased to any desired value.

The above described arrangement is such that the fluid, such, for example, as hydrocarbon fluid, may first be preheated in the convection zone to raise the same to a temperature below conversion temperature. The heated vapors may then be passed directly to the conversion tubes wherein they are rapidly heated to conversion temperatures and under conversion conditions. The arrangement is such that the rapid heat transfer may take place to the conversion tubes 55 without causing local overheating of the fluid. It is to be understood, of course, that the preheated fluid may be removed to a separate treating apparatus if desired before passage to the conversion tubes 55, valves 93, 94 and 95 being provided for this purpose.

The above described furnace is particularly applicable to certain catalytic and pyrolytic conversion processes for the treatment of hydrocarbons but is capable of various other uses, modifications and embodiments, as will readily appear to a person skilled in the art. The invention is only to be limited in accordance with the following claims.

What is claimed is:

1. A furnace for heating fluids comprising a pair of spaced side walls, a bridge wall parallel with said side walls dividing said furnace into a combustion zone and a convection zone, a row of burners disposed to direct a flame and hot combustion gases substantially vertically into the combustion zone in contact with and substantially parallel to said bridge wall to heat the same to radiance, a single row of parallel connected vertical converter tubes extending along but spaced from the side walls of said combustion zone out of the main path of the flame and hot combustion gases to receive radiant heat from the flame, the hot combustion gases and the bridge wall, reflected heat from the adjacent side wall, and convection heat from said combustion gases, whereby a rapid and eflicient heat transfer is obtained suited to quickly raise the fluid to a high temperature and a bank of serially connected horizontal convection tubes in said convection zone to receive heat by convection and radiation from said hot gases, and additional burners in said convection zone disposed to direct a flame and hot combustion gases vertically toward the bank of convection tubes and against the side wall of said convection zone, the tubes being shielded from direct contact with the flame from said last burners by the combustion gases received from the combustion zone.

2. A furnace for heating fluids comprising a pair of spaced side walls, a bridge wall parallel with said side walls dividing said furnace into a combustion zone and a convection zone, a row of burners disposed to direct a flame and hot combustion gases substantially vertically into the combustion zone in contact with and substantially parallel to said bridge wall to heat the same to radiance, a plurality of transverse walls extending between said bridge wall and the side wall of the combustion zone to divide the combustion zone into a plurality of separate combustion chambers, a bank of converter tubes in each of said combustion chambers, each bank comprising a single row of parallel-connected, vertical converter tubes extending along but spaced from the side walls of said combustion zone out of the main path of the flame and hot combustion gases to receive radiant heat from the flame, the hot combustion gases and the bridge wall, reflected heat from the adjacent side wall, and convection heat from said com-- bustion gases, whereby a rapid and efficient heat transfer is obtained suited to quickly raise the fluid to a high temperature, means for selectively removing each bank from stream, and a bank of serially connected horizontal convection tubes in said convection zone to receive heat by convection and radiation from the hot gases from all of said combustion chambers.

3. A furnace for heating fluids comprising a pair of spaced side walls, floor and roof forming a furnace chamber, a bridge wall parallel with said side walls extending upwardly from said floor to divide said furnace into a combustion zone and a convection zone, a row of burners in said floor disposed to direct a flame of hot combustion gases upwardly against said bridge wall to heat the same to radiance, a single row of parallel-connected vertical converter tubes extending along but spaced from the side walls of said combustion zone out of the main path of the flame and hot combustion gases to receive radiant heat from the flame, the hot combustion gases and the bridge wall, reflected heat from the adjacent side wall, and convection heat from said combustion gases, whereby a rapid and efficient heat transfer is obtained suited to quickly raise the fluid to a high temperature, and a bank of serially connected horizontal convection tubes in said convection zone to receive heat by convection and radiation from said hot gases, and additional burners in said roof disposed to direct a flame and combustion gases downwardly against the side wall of the convection zone, the tubes being shielded from direct contact with the flame from said last burner by the combustion gases received from the combustion zone.

WINCHELL M. PARSONS.

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