US3276436A

US3276436A - Process heater

Info

Publication number: US3276436A
Application number: US384707A
Authority: US
Inventors: Salvatore A Guerrieri
Original assignee: Lummus Co
Current assignee: CB&I Technology Inc
Priority date: 1964-07-23
Filing date: 1964-07-23
Publication date: 1966-10-04
Anticipated expiration: 1983-10-04
Also published as: FR1441214A; NL6509503A; DE1501558A1; GB1077387A

Description

Oct. 4, 1966 Filed July 23, 1964 s. A. GUERRxERl 3,276,435

PROCESS HEATER C3 Sheecs-Sheet l Ail* INVENTOR. SALVATORE A. GUERR/ER/ ATTORNEY OC- 4, 1965 s. A. GUERRxER 3,276,436

PROCESS HEATER Filed July 23. 1964 5 Sheets-Sheet :2

F'IG. 2

FLUX

RELAT/VE 0.5 c ,l z c DEGREES FROM PO//VT 48 ON TUBE 30 INVENTOR. SLVATORE A. GUERR/ER/ A T TOR/VEV Oct- 4, 1966 s. A. GUERRIERI 3,276,436

PROCESS HEATER Filed July 25, 1964 5 Sheets-Sheet 5 United States Patent O 3,276,436 PROCESS HEATER Salvatore A. Guerrieri, Rowayton, Conn., assignor to The Luinmus Company, New York, NEI., a corporation of Delaware Filed .Iuly 23, 1964, Ser. No. 384,707 12 Claims. (Cl. 122-356) This invention relates in general to a new and improved process heater and reradiators therefore, and more particularly, to a process heater utilizing tubes through which process fluid passes while being heated within a chamber, the heater being capable of achieving more uniform heating around the tubes. Heaters according to the invention are further capable of increasing the heat iiux around the process Itubes without increasing the maximum local heat flux or, conversely, providing the same average flux to the tubes with a lower maximum local heat flux.

In process heaters, it is common practice to arrange the tubes in a line in the center of the furnace and to heat Athe tubes by burning fuel along walls parallel to the tubes. This is done in order to satisfy, as nearly as possible, the design criteria of achieving uniform heat flux around the tube circumference. Despite this arrangement, the heat flux around a tube varies from a maximum along lines directly opposite the firing walls to a minimum along lines ninety degrees therefrom. The arrangement of the tubes in the center with the burning of fuel along the walls parallel to the tubes minimizes the difference in heat ux at diametrically opposite spots on the tubes immediately opposite the ame because these spots see essentially the radiant heat sources directly. On the other hand, this arrangement does not materially help the flux variation between a spot on the tube directly opposite the flame and a spot ninety degrees away from it.

Therefore, it is the general object of this invention to reduce the foregoing and other difficulties of prior art practices by the provision of a new and improved process heater which is better in operation and less expensive to manufacture.

Another object of this invention is the provision of a new and better process heater in which more uniform heat flux is achieved about the circumference of the process tubes in the furnace chamber.

Still another object of this invention is the provision of a new and better process heater in which the process tubes have a higher average heat liux thereabout with a lower total heat transfer surface, without the necessity of increasing the temperature in the heater.

Other objects and advantages of the present invention will be made clear in the course of the following description of several embodiments thereof, and the novel features will be particularly pointed out in connection with the appended claims.

A better understanding of the invention will be gained by referring to the following detailed description, in conjunction with the drawings, and wherein:

FIGURE l is a cross sectional elevation of a rectangular process heater built in accordance with the principles of the present invention;

FIGURE 2 is a partial horizontal cross sectional plan view of the process heater of FIGURE l, taken along lines 2-2 thereof;

FIGURE 3 is a curve of the heat flux computed about one quadrant of the process tube of FIGURE 2, with and without the reradiating surfaces of the present invention;

FIGURE 4 is a cross sectional elevation of an annular pyrolysis heater built in accordance with the principles of the present invention; and

ICG

FIGURE 5 is a partial cross sectional plan view of the apparatus of FIGURE 4.

In FIGURE l, there is shown a process heater built in accordance with the principles of the present invention and generally designated by the numeral 10. Process heater 10 is rectangular in shape, has a top wall 12, a bottom wall 14, and

side walls

16 and 18 which define a refractory-lined heating chamber 20. The side walls I6 and 1S have

burners

22 and 24 mounted therein and extending the length and width thereof. The purpose of having a plurality of burners is to enable

side walls

16 and 18 to approach, as nearly as possible, a uniform radiating plane. The

burners

22 and 24 are supplied with fuel through

conduits

26 and 28, respectively, provided with suitable valves (not shown).

As shown in FIGURE 1, vertically extending process tubes 3ft are placed in the center of the chamber 20, equidistant from side walls 16 and I8. Process tubes 30 are supplied with a reactant mixture through an inlet conduit 32. The inlet conduit 32 feeds a common manifold 34 which supplies the reactants to all of the tubes Si). The manifold 34 is conne-cted through a coupler 36 to the tube 30 with each of the tubes having their own individual coupler. After passing through the tube 30, the reaction products are removed through a manifold 38 which is coupled to the .tube 30 through a coupler 46. The manifold 38 is connected to an outlet conduit 42.

It will be easily seen that the present invention can be utilized with a variety of types of process heaters, for example, such as a steam reformer or a pyrolysis heater. In some embodiments it may be desirable to have the tubes 3i) at one side or the other of chamber 2t), rather than centrally located as in FIGURE 1.

The tubes 30 and 31] are manufactured of a material suitable for the operating conditions (i.e., reactants, furnace atmosphere, pressure, temperature, etc.). As shown in FIGURE 2, the tubes 30 and 3G are spaced one from another a distance of approximately two diameters from center to center. Between adjacent tubes there is placed a vertically extending rod 44 extending the length of the tubes 36 and .30 and in line with the centers of the

tubes

30 and 30. Rods 44 shall hereinafter be called reradiators, and may be manufactured of any metal, alloy, ceramic, or combination of such materials, which will give a high emissivity, strength and low cost. In the embodiment of FIGURE 2, the reradiator is square in cross section with a thickness one quarter the tube diameter. Instead of square cross section, however, reradiators of rectangular cross section may be used, and they may be arranged with either their wide or narrow sides facing the tubes. The range of useful sizes for the reradiator lies between about one eighth and one half of a tube diameter, any combination of these dimensions for width and thickness and any orientation of the reradiators which may be desirable being useable for any given case.

The reradiators should be made of materials having an emissivity as near unity as possible, or of materials coacting with a substance which will give emissivity of near unity. The reradiators can 'be hollow in shape, but a solid reradiator will generally perform better, as it has `a lower temperature gradient between the sides facing the radiator sources and the sides facing the tubes. It is evident that since the reradiators are not subjected to any internal or external pressures, they may be made out of the lowest cost material available which is capable of withstanding the atmosphere and temperature within the chamber.

In operation, a reactant mixture such as, for example, a steam-methane mixture, is fed through process tubes 39 and subjected to the high temperature (1400-2200 'F.) maintained within chamber 20 by

burners

22, 24. In the instance described, that of steam reforming, a nickel oxide catalyst within the tubes 30 catalyzes the steam reforming reaction, resulting in the production of hydrogen together with some CO, CO2 and other reaction products. It will easily be understood that the

points

48 and 50 on the tube 30, which are closest to the radiating

side walls

16 and 18, are points of maximum heat linx. These

points

48 and 50 are perpendicular to the common center line of the

tubes

30 and 30. The

side walls

16 and 18 provide radiant heat directly through the

burners

22 and 24, respectively, and additionally, reradiate heat rellected thereon so that the points 48 and S0 nearest the

side walls

16 and 18 receive the maximum heat flux.

In `FIGURE 3, the results of calculations of the heat flux about one quadrant of the tube 30 are shown from maximum point 48 closest to radiant Wall 16, to minimum point 52 ninety degrees from point 48. The calculations indicate the changes in relative radiant heat llux as a function of the position on the periphery of the tube 30. The point 48 is thus indicated as a 0 point and point 52 is the 90 point. In FIGURE 3, curve AB has been provided to indicate the relative radiant heat llux about the tube 30 without the reradiators 44. Curve AB thus shows that the point 48 directly opposite the radiant walls 16 receives radiant heat at an equivalent rate equal to unity. Point 48 has been chosen as a relative point as it is known to receive the maximum heat flux. A point on the tube 30 which is thirty degrees from the point 48 receives radiant heat at a relative rate of only 0.92. Fortyfive degrees from the maximum point 48 there is a relative radiant heat flux of only 0.82. Sixty degrees from the maximum point 48 there is only a relative heat flux of 0.72. Finally, at ninety degree point 52 there is only 0.65 relative heat flux.

A second curve AC, is shown in FIGURE 3, which shows the relative heat flux of the tube 30 with the reradiators 44 in place. A portion of curve AC is shown as a broken line 'because its position and shape has not been exactly calculated, but it is considered to lbe substantially correct. It will be noted that the curve AC shows that with the reradiators 44 in place, the relative heat llux at the ninety degree position 52 is now 0.83. Even at a point seventy-tive degrees from the maximum point 48 of the tube 30, the relative heat flux is approximately 0.80. Thus, the difference between the maximum heat flux and the minimum heat llux has been changed from 0.35 when the reradiators 44 are not utilized -to 0.17 when the reradiators 44 are in place. It should further be noted that in addition to the above advantage, the average heat flux about the tube 30 has also been increased significantly by the reradiators 44. The average heat ux to the tube 30 without the reradiators 44 is approximately 0.82 in varbitrary units, whereas the average heat flux to the tube 30 with the reradiators 44 in place is approximately 0.87. This represents an increase in capacity of at least tive percent for the tube, making no allowance for the expected improve-ment due lto a more uniform wall temperature due to the reradiators 44.

It is to be observed that the use of the reradiators along the center line of the tubes does not affect the radiant flux to any appreciable extent up to a position of approximately sixty degrees away from the reference point 48. It is only in the region of the ninety degree position that -a marked increase in heat flux is obained. This is especially advantageous, as it is only about the ninety degree position that it is essential to increase the radiant heat flux so as to avoid the great difference between the maximum and minimum radiant heat flux about the periphery of the tube.

It is obvious that reradiators having other shapes than those disclosed can be utilized, and that the shape of the lreradiator would have an eifect on the redistribution of the radiant heat llux. For example, under certain conditions it may be desirable for reradiators 44 to have convex A' or concave surfaces facing either the tubes or the burners. All such configurations are to be included in the terms reradiators elongated reradiators and rod-shaped reradiators, as deiined herein.

In FIGURE 4, there is shown the present invention as embodied in a process heater having an annular chamber. The pyrolysis heater 74 has a cylindrical outer wall 76 with a refractory lining 78, and a cylindrical inner vwall with a refractory liner 82. The outer wall 76 and the inner wall 80 define, together with top and bottom walls, an annular chamber 84 therebetween. The outer wall 76 is supported on suitable structural steel members 85. Centrally disposed within the inner wall 88 there is a convection section 86 and a stack 88. Suitable ducts 90 provide a passage for combustion fumes from the annular chamber 84 into the convection section 86 and stack 88. The operation of the annular furnace 74 is more fully described in my copending patent application Ser. N-o. 384,706, tiled July 23, 1964, and entitled Apparatus The inner wall 80 has a plurality of burners 92 along the length and width thereof. Also, the outer wall 76 has outer wall burners 94 along the length and width thereof. The

burners

92 and 94 are intended to heat vertically extending process tubes 96 centrally disposed in a circular path within the annular chamber 84. The tubes 96 are spaced equidistant the inner wall 80 and the `outer wall 76, but this is not a critical limitation. As shown, the process tubes 96 may be used as a pyrolysis heater in the production of ethylene. The fuel for the process is supplied through an input conduit 98 and removed through an outlet conduit 100. The pyrolysis heater has reverse bends 102 for permitting a plurality of passes of the process fluid through the process tubes 96.

Between adjacent process tubes 96, there are positioned vertically extending reradiating rods 104 extending the length of tubes 96. The rods 104 are similar to the rods 44 associated with the tubes .30 of FIGURE 2. The rods 104 perform the same function described with respect to the rectangular furnace l0 in that they achieve a more uniform heat flux about the circumference of the process tubes 96 and also increase the average heat ilux to the process tubes. The rods 104 are placed equidistant adjacent tubes 96 along the circular path of the center lines of the tubes 96, which circular path is coaxial with the inner and

outer walls

80 and 76 forming the annular chamber 84.

It will be understood that the embodiment of the invention set forth hereinabove are illustrative only and that various changes in the steps, materials and arrangements `of parts may be made by those skilled in the art Within the scope of the invention as defined in the appended claims.

I claim as my invention:

1. A process heater comprising:

a housing dening :a heater chamber therein;

means capable of heating said chamber;

said housing including two spaced radiating surfaces in said chamber;

a plurality of process tubes arranged in :a single row -in said chamber in spaced relation to `one another and to said radiating surfaces;

inlet means for supplying process liuid to said tubes and outlet means for removing said fluid after passing through said tubes in said chamber; and

a plurality of rod-shaped reradiators equidistant be1 tween adjacent tubes and presenting heat absorbing surfaces to said heating means and reradiating sur- -faces to said tubes.

2. The process heater as claimed in claim 1, wherein said reradiator surfaces have -a high emissivity.

3. The process heater as claimed in claim 1 wherein said reradiators are rectangular in cross section `and have a width and lthickness between one eighth and one half of the tube diameter.

4. The process heater as claimed in claim 1, wherein said reradiator is solid throughout so as to provide a low temperature gradient and is capable `of withstanding the temperature and atmosphere `of said heater.

5. The process heater as claimed in claim 1, wherein said radiating surfaces are planar.

6. The process heater as claimed in claim 1, wherein said radiating surfaces `are cylindrical, said cylindrical surfaces being coaxial to form an annular chamber, said tubes being arranged in a circular path coaxial with said surfaces, said reradiators being arranged in the circular path of said tubes.

7. A process heater comprising:

a housing Vdening a heating chamber therein;

burner means in said chamber;

said housing including two spaced radiating surfaces in said chamber with said burner means mounted therein;

a plurality of process t-ubes in said chamber between said radiating surfaces :and spaced in relation to one another, said process tubes being -in a single plane;

reradiators spaced between adjacent process tubes in said plane, said reradiators having a high emissivity;

inlet means for supplying process fluid to said tubes;

and

'outlet means for removing said fluid after passing through said tubes in said chamber.

8. The process heater as claimed in claim 7, wherein said reradi-ators extend the length of said tubes, said reradiators being smaller in `cross section than said tubes,

said reradiators being shaped to absorb heat from said burner means and reradiate heat toward the portions of said tubes closest to said reradiators.

9. The process hea-ter as claimed in claim 8, wherein the `diameter of each `of said tubes is equal, said reradiators are rectangular in cross section, and said reradiators have a width and thickness between one eighth and one half of a tube diameter.

10. The process heater as -claimed in claim 9, wherein said reradiators are solid.

11. The process heater `as claimed in claim 9, wherein said reradiators are hollow.

12. In the construction of process heaters having process tubes disposed in a single row between heat-radiating surfaces, the improvement which comprises elongated reradiators disposed equidistant between :adjacent tubes, said reradiators being shaped to absorb heat from said heatradiating surfaces and reradiate 'heat towards the portion of said tubes closest thereto.

References Cited by the Examiner UNITED STATES PATENTS 559,021 4/1896 Baker 110-98 2,081,971 6/1937 Alther 122-356 2,274,256 2/ 1942 Praeger 122-356 2,326,492 8/ 1943 Praeger 122-356 2,625,918 1/1953 Lumly 122-356 2,638,879 5/1953 Hess 122-356 CHARLES I. MYHRE, Primary Examiner.

Claims

1. A PROCESS HEATER COMPRISING: A HOUSING DEFINING A HEATER CHAMBER THEREIN; MEASN CAPABLE OF HEATING SAID CHAMBER; SAID HOUSING INCLUDING TWO SPACED RADIATING SURFACES IN SAID CHAMBER; A PLURALITY OF PROCESS TUBES ARRANGED IN A SINGLE ROW IN A SAID CHAMBER IN SPACED RELATION TO ONE ANOTHER AND TO SAID RADIATING SURFACES; INLET MEANS FOR SUPPLYING PROCESS FLUID TO SAID TUBES AND OUTLET MEANS FOR REMOVING SAID FLUID AFTER PASSING THROUGH SAID TUBES IN SAID CHAMBER; AND