Furnace radiant sections with vertical heat exchanger tubing, and convection section

The method of combining two furnaces into one, each furnace having a lower radiant section that includes upright walls and horizontal heat exchanger tubes, and an upper convection section, the lower section having associated fuel burners, including removing the horizontal heat exchanger tubes from the lower section; extending the lower section upright walls vertically upwardly, and providing space between the vertically extended lower sections; providing top walls over the vertically extended lower sections, and providing vertically extending heat exchanger tubing and suspending the tubing vertically within the vertically extended lower radiant sections, to be heated by hot gases produced by combustion of fuel supplied via the burners; and providing and locating an upright convection section of the furnace in flow receiving communication with the lower sections via lateral passages therefrom.

BACKGROUND OF THE INVENTION 
This invention relates generally to heaters or furnaces, and more 
particularly concerns improvements to furnaces of the type containing heat 
transfer tubing that extends horizontally in both "radiant" lower furnace 
sections and "convective" upper furnace sections. 
In the above type furnace, which is conventional, complex support 
arrangements are required for the banks of horizontally extending tubing. 
Removal and replacement of such complex supports is required in order to 
periodically remove and clean the tubing, all of which is time consuming 
and expensive. There is need for a furnace construction which overcomes 
these problems, and particularly a reconstructed furnace which employs 
original furnace materials, to reduce capital cost and to reduce cost of 
periodic horizontal tubing removal and repair. 
SUMMARY OF THE INVENTION 
It is a major object of the invention to provide a method of furnace 
re-construction, and a reconstructed furnace unit itself, which meets the 
above need. Basically, the invention contemplates re-constructing two 
furnaces of conventional type to provide one improved furnace, in which 
tubing structure may be suspended vertically in lower "radiant" furnace 
sections, thereby eliminating need for complex supports for horizontal 
tubing structures. 
Accordingly, the invention is directed to a method of combining two 
furnaces into one, each furnace having a lower radiant section that 
includes upright walls and horizontal heat exchanger tubes, and an upper 
convection section, the lower section having associated fuel burners, that 
includes: 
(a) removing the horizontal heat exchanger tubes from the lower sections, 
(b) extending the lower section upright walls vertically upwardly, and 
providing space between the vertically extended lower sections, 
(c) providing top walls over the vertically extended lower sections, and 
providing vertically extending heat exchanger tubing and suspending that 
tubing vertically within said vertically extended lower radiant sections, 
to be heated by hot gases produced by combustion of fuel supplied via the 
fuel burners, 
(d) and providing and locating an upright furnace convection section in 
flow receiving communication with the lower sections, via lateral passages 
therefrom. 
As will appear, the method of step (b) above typically may include 
supplying additional vertical walls and locating said walls above the 
vertical walls of lower sections of said two furnaces; and also removing 
the upper convection sections from the lower sections of the two furnaces, 
prior to said (c) step. 
Additional steps may include locating said convection section above the 
space between said two lower sections; providing the lateral passages in 
upper side walls of said two lower sections; and providing a top wall over 
the space between the two lower sections and beneath the lateral passages. 
Operation of the furnace includes passing combustion gases upwardly on the 
two lower radiant sections, to transfer heat to the vertical tubing 
therein; laterally combining the hot gases from the two lower sections, 
and flowing the combined hot gas stream through the single upper 
convection sections of the furnace to subsequently exit the furnace. 
Furnace apparatus embodying the invention includes: 
(a) two lower radiant furnace sections extending in close side-by-side 
relation, and having interiors, 
(b) upper walls over the respective interiors, and heat transfer tubing 
suspended to extend vertically in said interiors, below said upper walls, 
(c) a single upper convective furnace section having a lower entrance, 
(d) and means on the lower section to receive hot combustion gases 
therefrom and to transfer the gases laterally and upwardly from the lower 
sections to the upper section, via said entrance. 
As will be seen, the upper section typically contains heat transfer tubing. 
These and other objects and advantages of the invention, as well as the 
details of an illustrative embodiment, will be more fully understood from 
the following specification and drawings, in which:

DETAILED DESCRIPTION 
In FIG. 1, conventional furnace or heater apparatus 10 is shown, and may 
comprise a reactor or oil heater as usable in a refinery. Upright housing 
11 includes a lower section 11a, associated with hydrocarbon fuel burners 
and windboxes designated at 12. The latter receive air and hydrocarbon 
fluid, as via lines 13 and 14 to produce burner flames at 15. Concrete 
piers 16 support the housing. 
Located within the radiant section 11a of the housing are horizontal heat 
transfer tubes 17, to which process fluids are fed from a source 18 and 
via a valve 19 and heat transfer tubing 126 discussed below. The fluid is 
heated within the tubes 17, as by the hot combustion gases flowing 
upwardly at 20. Hot process fluid leaves the tubes and the housing at 21. 
The tubes 17 typically extend horizontally in open reaction zone 22 for 
heat absorption by radiation from hot gases flowing upwardly through the 
length of the housing. 
The hot gases flow upwardly in the housing to and through a narrowed 
section 125 at the top 11d of the housing. The lower "convective" extent 
125a of the stack contains additional heat transfer tubing 126 extending 
as seen in FIGS. 1 or 2. Thus, the horizontal tubes 126 may be connected 
in series to deliver hot fluid to the tubes 17, via junction 117. The 
tubes 126 are spaced, and/or staggered, to be contacted by the hot gases 
entering and flowing upwardly in the stack lower extent 125a. Hot gases 
leave the stack 27 at 127. 
In FIG. 3, two of the furnace housings 11 have been moved into proximity to 
one another, but are separated by space 90. Lower radiant sections 11a 
remain the same, as do associated burners in boxes 12. Thus upright walls 
11b and 11c are the same. The horizontal tubes 17, however, are removed. 
The lower section upright walls on three sides of each furnace are 
extended upwardly, as by installing two auxiliary upright walls 11d above 
walls 11b, and two upright walls 11e and 11f that extend above front and 
rear lower walls 11g and 11h. Plates 92 may be welded to the lower and 
upper walls, to bridge the joint 93 therebetween. This also ties the two 
furnaces together. A narrow top wall 94 is provided to extend over space 
90, and is welded to the tops of walls 11c, as at 95. This also ties the 
two furnaces together. In this construction process, two lateral openings 
are provided at 96, at the junctions of the interior vertical spaces 97 
and 98 with the common interior space 99 above top wall 94, for purposes 
as will be made clear in FIG. 4. 
Referring to FIG. 4, the construction is now completed. Top walls 101 are 
provided to extend over the vertically extended lower sections, and 
interiors 97 and 98. An upright convection section 125, as retrieved from 
one or two of the furnaces in FIG. 1, for example, (or provided new), is 
now installed in the position shown, above space 99, so as to be in flow 
receiving communication with the interiors 97 and 98 of the two vertically 
extended lower radiant sections 11a. Hot combustion gases may now flow 
upwardly within interiors 97 and 98, then laterally through the openings 
96 above walls 11c, and then upwardly to enter the narrower convection 
section 125, as before. Support framing may be provided as at 110. 
The above now makes it possible to suspend vertically elongated heat 
transfer tubing 117 in the interiors 97 and 98, as for example is shown, 
without complex supports between the vertical tubes. Suspension of the 
tubes may be in any convenient manner, as for example by hanger structures 
118 including uprights 118a connected to walls 101, brackets 118b, and 
pins 118c. Upper manifolds may be provided at 119, and connected to tubes 
117 and at 120 to tubes 126, as shown. Lower manifolds 122 may be 
connected to the lower ends of tubes 117, and may deliver heated process 
fluid at 121 to the exterior, as via valves 124. 
Removal and cleaning or servicing of the vertical tubes 117 is much easier 
than removal and repair of tubes 17, in FIG. 1.