US3221711A - Ridge firing arrangement for process heaters - Google Patents

Description

3 Sheets-Sheet 1 ATTORNEY H. L. BEGGS RIDGE FIRING ARRANGEMENT FOR PROCESS HEATERS Filed May 28, 1964 5 7 6 MEX m NL IMJ mm; 0 0 o N O 0 O O O 0 0 O o O O 0 o m\ o o m o o o 0 01v 0 o o o o No 0 a o o o o o o 06 o o o o o o o o 0 of o o o o o 0 0 0 W0 m 1 1 m E INVENTOR Dec. 7, 1965 H. BEGGS RIDGE FIRING ARRANGEMENT FOR PROCESS HEATERS Filed May 28, 1964 3 Sheets-Sheet 2 HAROLD L. 856G S ATTORNEY H. L. BEGGS 3,221,711

.R IDGE FIRING ARRANGEMENT FOR PROCESS HEATERS Dec. 1, 1965 3 Sheets-Sheet 5 Filed May 28. 1964 ATTORNEY F/GE United States Patent 3,221,711 RIDGE FIRING ARRANGEMENT FOR PROCESS HEATERS Harold L. Beggs, St. Davids, Pa., assignor to Alcorn Combustion Company, New York, N.Y., a corporation of Delaware Filed May 28, 1964, Ser. No. 370,893 6 Claims. (Cl. 122-240) This disclosure relates to fired heaters used in the petroleum refining industry. The invention contemplates mounting at least one main burner on an elevated ridge above the floor. By this expedient critical tubes (those susceptible of high point film temperatures) can be positioned in troughs below the main flame burst so that film temperature can be controlled. Trim burners may also be mounted in the troughs for sensitive regulation of the heat input curve.

In fluid heaters such as those employed in vacuum service, it is desired to elevate the bulk temperature of the fluid to be heated to the level required for vaporization without subjecting the fluid to thermal cracking. Thermal cracking of the fluid wastes ingredients; but worse than this cracking usually deposits coke in the tubes. By impeding heat transfer to the fluid, coke deposits in the tubes hasten burning through of tube walls. In this regard hot spots on the interiors of tube walls raise point film temperatures and increase the tendency toward thermal crackmg.

The thermal cracking problem is aggravated by large tube sizes. In vacuum installations, with an increase in vapor pressure, larger tube sizes sometimes become neces sa'ry along the path of the fluid to keep fluid pressure drops within reasonable limits. The enlarged tubes avoid suppressing vaporization thereby obviating the superheating of the process fluid in its liquid state, but these larger tube sizes reduce the mass velocity through the tubes impairing the ability of the process stream to cool the tube metal. With reduced cooling the point temperature of process fluid at the tube wall elevates and the tendency toward thermal cracking becomes most critical. Toward the outlets of the tube banks, where tube sizes are largest, the thermal cracking problem is most acute.

The present teaching offers a heater design which avoids thermal cracking in vacuum installations. A radiant furnace chamber having a low floor level is provided. The floor is formed into at least one ridge projecting upward from this low floor level to describe an upper floor level. Main burners penetrate the floor upward through the ridge and are arranged to form a main flame burst above the upper floor level. The tube coil has a generally horizontal serpentine configuration with flow arranged to progress generally downward. Enlarged critical tubes, which are situated toward the downstream end of the path of the process fluid through the coil, are positioned in the trough so that heat input to these critical tubes from the main flame burst is relatively low. Trim burners can be mounted in the troughs where sensitive control of the heat input curve is desired.

Radiant tube coils are generally fired from either one side (single fired) or from opposite sides (double fired). Double firing evens out the heat input about the peripheries of tubes. With double firing, for a given heat input, the maximum point film temperature is less than that for single firing. The invention here disclosed is adaptable to both single and double fired designs, but double fired designs are preferred.

These and other features will appear more fully from the accompanying drawings wherein:

FIGURE I is an end view in section which depicts a fired heater including the present advance. This figure is taken along line II of FIGURE II.

3,221,711 Patented Dec. 7, 1965 FIGURE II is a side view in section taken along line IIII of FIGURE I.

FIGURE III is an end view in section which shows a single fired embodiment of this invention.

Basically, these designs call upon known design principles and market-available components. Setting 1 with end walls 2, roof arch 3, floor 4, and side walls 5, define furnace chamber 6 therein. Steel frame 7 transmits loads to foundations 8.

Main flame bursts 9 are elevated vis-a-vis tube coils 11. Floor 4 defines ridges 12 whose upper extremities 13 project upward to form high floor level 14 above low floor level 16. Main burners 17 as well as small trim burners 18 penetrate floor 4 via ridges 12 and low levels 16. Burners 17 and 18 communicate with furnace chamber 6 to introduce fuel and air therein. Burners 17 an 18 are operatively associated with setting 1 so that main flame bursts 9 and trim flame bursts 19 are formed and combustion gases are generated. The combustion gases exit furnace chamber 6 via convection section 21' and stack 22.

Process fluid (supplied from a source not shown) after being preheated in convection coils 23, is coursed in flow series through upright tube coils 11. Coils 11 define substantially horizontal serpentine tube configurations arranged for generally downward flow. In the embodiment of FIGURES I and II radiant tube coils 11 are disposed between main flame bursts 9 for double firing. In the embodiment of FIGURE III radiant tube coils 11 are arranged against side walls 5 for single firing. The process fluid is introduced into radiant coils 11 at their upper ends 24, and passes generally downward therethrough for exit via lower ends 26.

As the process fluid courses downward through radiant coils 11, it is usually necessary to increase tube diameters so that vapor suppression is avoided and so that pressure drop through radiant coil 11 is kept within reasonable limits. Downstream tubes such as 27 have diameters suificiently large that film temperature control becomes extremely difficult. These are the critical tubes.

The primary consideration in this design in to keep point film temperatures in these critical tubes 27 within acceptable limits. Towards this objective floor 4 defines troughs 28 below the levels of main flame bursts 9. In the embodiment of FIGURES I and II troughs 28 are between adjacent ridges 12. In the embodiment of FIG- URE III lateral troughs 28 are between side walls 5 and ridge 12. Critical tubes 27 .are disposed in troughs 28 so that the effect of main flame bursts 9 on these tubes is reduced.

Where sensitive control of the heat input curve is called for, trim burners 18 can be arranged in troughs 28. Adjustment of trim burners 18 as well as adjustment of main burners 17 is well known to furnace designers and operators.

It will be apparent to those skilled in furnace design that Wide deviations in the detail of this disclosure can be made without departing from the main theme of invention set forth in the claims.

What is claimed is:

1. A fired heater comprising a setting which includes a roof arch and a floor as well as walls all cooperating to define a furnace chamber therein,

the floor defining a low floor level,

the floor having at least one ridge projecting upward from the low floor level,

the ridge having an upper extremity which defines a high floor level,

the floor defining at least one trough below the high floor level,

at least one main burner penetrating the floor via the upper extremity of the ridge and communicating with the furnace chamber to introduce fuel and air therein and arranged so that a main flame burst is formed above the high floor level,

means in the vicinity of the roof arch for exhausting combustion gases from the furnace chamber,

at least one tube coil arranged to form a generally horizontal configuration in the furnace chamber,

the tube coil having an upper end communicating in flow series with a source of process fluid so that the fluid courses generally downward therethrough,

the tube coil having a lower end communicating in flow series with means for exhausting the process fluid therefrom,

the tube coil including at least one enlarged critical tube situated downstream in the path of process fluid flow,

the critical tube positioned in the trough so that heat input to the critical tube from the main flame burst is reduced.

2. The heater of claim 1 with at least one trim burnermounted in the trough,

means for adjusting the heat output of the trim burner.

3. A fired heater comprising a setting which includes a roof arch and a floor as Well as opposed end walls and opposed side walls all cooperating to define a furnace chamber therein,

the floor having a low floor level,

the floor corrugated to define a raised ridge projecting upward from the low floor level and disposed between the side walls,

the ridge having an upper extremity which defines a high floor level,

the ridge spaced from each of the side walls to define lateral troughs between the ridge and the side walls,

at least one main burner penetrating the floor via the ridge and communicating with the furnace chamber to introduce fuel and air therein and arranged so that a ,main flame burst is formed above the high floor level,

means in the vicinity of the roofvarch for exhausting combustion gases from the furnace chamber,

two tube coils describing vertical planes in the furnace chamber with each of the coils adjacent one of the side walls and with each of the coils arranged to form a generally horizontalserpentine configuration,

each of the tube coils mounted longitudinally relative the ridge and having an upper end communicating in flow series with a source of process fluid so that the fluid courses generally downward therethrough,

each of the tube coils having a lower end communicating in flow series with means for exhausting the process fluid therefrom,

at least one ofthe tube coils including an enlarged critical tube situated downstream in the path of process fluid flow,

the critical tube positioned in one of the troughs so that heat input to the critical tube from the main flame burst is reduced.

4. The heater of claim 3 with at least one trim burner mounted in the same lateral trough as the critical tube,

means for adjusting the heat output of the trim burner.

5. A fired heater comprising a setting which includes a roof arch and a floor as well as opposed end walls and opposed side walls all defining a furnace chamber therein,

the floor having a low floor level,

the floor corrugated to define at least two raised elongated ridges each projecting upward from the low floor level,

The ridges each having an upper extremity which extremities define a high floor level,

the floor defining a depressed elongated trough between the ridges,

at least one main burner penetrating the floor through each of the ridges and communicating with the furnace chamber to introduce fuel and air therein and arranged so that main flame bursts are formed above the high floor level,

means in the vicinity of the roof arch for exhausting combustion gases from the furnace chamber,

atleast one tube coil describing a vertical plane in the furnace chamber and arranged to form a generally horizontal serpentine configuration,

the tube coil having an upper end communicating in flow series with a source of process fluid so that the process fluid courses generally downward therethrough,

the coil having a lower end communicating in flow series with means for exhausting the process fluid therefrom,

the tube coil mounted longitudinally relative the ridges and disposed between the flame bursts for double firthe tube coil including at least one critical tube situated downstream in the path of process fluid flow and having a diameter substantially larger than that of the rest of the tube coil,

the critical tube positioned in the trough so that heat input to the critical tube from the main flame bursts is reduced.

6. The heater of claimS with at least one trim burner mounted in the trough,

means for adjusting the heat output of the trim burner.

References Cited by the Examiner UNITED STATES PATENTS 10/1935 Gibson 122-356 1/1954 Mekler 122356 X

Claims (1)

1. A FIRED HEATER COMPRISING A SETTING WHICH INCLUDES A ROOF ARCH AND A FLOOR AS WELL AS WALLS ALL COOPERATING TO DEFINE A FURANCE CHAMBER THEREIN, THE FLOOR DEFINING A LOW FLOOR LEVEL, THE FLOOR HAVING AT LEAST ONE RIDGE PROJECTING UPWARD FROM THE LOW FLOOR LEVEL, THE RIDGE HAVING AN UPPER EXTREMITY WHICH DEFINES A HIGH FLOOR LEVEL, THE FLOOR DEFINING AT LEAST ONE TROUGH BELOW THE HIGH FLOOR LEVEL, AT LEAST ONE MAIN BURNER PENETRATING THE FLOOR VIA THE UPPER EXTREMITY OF THE RIDGE AND COMMUNICATING WITH THE FURNACE CHAMBER TO INTRODUCE FUEL AND AIR THEREIN AND ARRANGED SO THAT A MAIN FLAME BURST IS FORMED ABOVE THE HIGH FLOOR LEVEL, MEANS IN THE VICINITY OF THE ROOF ARCH FOR EXHAUSTING COMBUSTION GASES FROM THE FURNACE CHAMBER, AT LEAST ONE TUBE COIL ARRANGED TO FORM A GENERALLY HORIZONTAL CONFIGURATION IN THE FURNACE CHAMBER, THE TUBE COIL HAVING AN UPPER END COMMUNICATING IN FLOW SERIES WITH A SOURCE OF PROCESS FLUID SO THAT THE FLUID COURSES GENERALLY DOWNWARD THERETHROUGH, THE TUBE COIL HAVING A LOWER END COMMUNICATING IN FLOW SERIES WITH MEANS FOR EXHAUSTING THE PROCESS FLUID THEREFROM, THE TUBE COIL INCLUDING AT LEAST ONE ENLARGED CRITICAL TUBE SITUATED DOWNSTREAM IN THE PATH OF PROCESS FLUID FLOW, THE CRITICAL TUBE POSITIONED IN THE TROUGH SO THAT HEAT INPUT TO THE CRITICAL TUBE FROM THE MAIN FLAME BURST IS REDUCED.

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