Free-floating combustion chamber and stack

A burner-stack-furnace system comprising a stack of selected diameter and height, which is supported on a circular base ring, which is, itself, supported on a plurality of circularly positioned upright columns. The columns are supported on grade and are spaced equally circumferentially. The furnace or combustion section of the system is of the same diameter as the stack, and has a plurality of re-entrant vertical channels in its outer wall, spaced to surround each of the columns, with a selected air space between them. The combustion section thus hangs partly within the circle of the columns or piers, and partly between the piers. A shallow excavation is made below grade within and between the columns, and the combustion section extends downwardly into the excavation, which is deep enough that the bottom edge of the wall is above the base of the excavation. The combustion section is open on the bottom, but is filled with a porous fill of heat-resisting material, to a selected level. One or a plurality of circumferentially spaced openings in the wall of the combustion section are provided for combustion air and for gaseous or liquid fuel burners. In addition to the pipes which supply fuel to the burners, there are other pipes which supply either water or steam. The water is supplied through an atomizing nozzle, so that the droplets flow directly into the path of the fuel and into the flame.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention lies in the field of fluid fuel combustion systems. More 
particularly, it is concerned with furnace systems, which have a stack of 
substantial height and weight, and provides means for supporting the stack 
independently of the combustion section. 
2. Description of the Prior Art 
In the prior art, the stacks and combustion sections were generally of the 
same diameter, and the stack was supported integrally with the combustion 
section, which was, itself, supported on grade. 
In view of the need for large areas of openings in the combustion section 
for the supply of combustion air, the structural strength of the 
combustion section wall is reduced to the point where there is danger of 
collapsing under the weight of the stack. To prevent collapse, extensive 
reinforcement of the wall of the combustion section is required. Thus, as 
a practical matter, the combustion section must be designed as a 
structural system rather than a combustion system. 
SUMMARY OF THE INVENTION 
It is a primary object of this invention to provide a structural support 
for a furnace that has a stack and a combustion section, by erecting a 
circle of spaced columns or piers standing on grade, and adapted to carry 
a circular support ring, on top of which is placed the stack, with the 
combustion section hung penduously from the support ring, inside of, and 
between the columns. 
These and other objects are realized, and the limitations of the prior art 
are overcome in this invention by supporting the stack on a circular base 
ring, which is itself supported on a plurality of vertical piers or 
columns, positioned in a circular ring. The columns are set on grade, and 
can be constructed of concrete or steel, or in any desired manner. 
The height of the columns which support the support ring, on which the 
stack is carried, is limited in relation to the total height of the 
columns plus the stack. Therefore, the vertical extent or height and 
volume of the combustion section is dependent on the height of the column. 
The combustion chamber is nominally of the same diameter as the stack and 
has a plurality of reentrant vertical channels in the outer wall, which 
are spaced to correspond to the spacing of the columns. Thus, the 
combustion chamber hangs partly between the columns and partly inside the 
columns. These segments between the columns add a large cross-sectional 
area to the combustion zone over that of the prior art, where the 
combustion section hangs entirely within the piers. 
It is desirable also to increase the height of the combustion section to a 
value greater than that of the columns. But, since it hangs from the 
support ring, the only way the height can be increased is by creating a 
shallow excavation between the inside of the piers, so that the combustion 
section can hang down inside of the excavation. 
The combustion section, or furnace, does not have a closed bottom and the 
space inside the wall is filled to a selected depth, with a fill of heat 
resistant material, such as sand, gravel, or porous ceramic material, for 
example. The diameter of the excavation is greater than that of the 
furnace so that there will be sufficient clearance for the wall to expand 
and contract in accordance with the temperature inside the furnace. The 
outer wall also hangs so that its bottom edge is above the base of the 
excavation, so that combustion air can be drawn down outside of, and under 
the bottom edge of the wall, and up into the combustion chamber through 
the porous fill. This serves to provide additional combustion air, as well 
as to keep the fill material cool. 
There are a plurality of circumferential openings in the outer wall of the 
combustion section, which are positioned symmetrically with regard to the 
columns. These openings are for the entry of combustion air, and also for 
fuel pipes and burners. Also, additional pipes may be provided for waste 
or steam to be injected into the flame for the purpose of improving the 
complete combustion of the gases. The water pipes have nozzles which 
provide a very fine spray of water droplets into the flame. If desired, 
the water spray can be injected into the fuel line. Alternatively, steam 
can be injected into the flame or into the fuel line to mix with the fuel 
prior to issuance into the combustion chamber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings and, in particular, to FIGS. 1 and 2, there 
is shown the prior art type of construction, in which the combustion 
section, or furnace 21 is supported penduously from a support ring 14 and 
hangs entirely within the inner perimeter of the ring of columsn, or 
piers, 16A, 16B, 16C, and 16D. The combustion chamber 21 is suspended 
entirely within the circle of the piers, and is of lesser diameter 22 than 
that 20 of the stack 12. Also, because of the limitation in the height of 
the piers 16, which is dependent upon the total height of the piers plus 
the stack, additional combustion space 26 is required for the combustion 
chamber. This is provided in two ways, which are illustrated in FIGS. 3 
and 4. 
FIG. 3 is a vertical cross-section taken along the plane 3--3 of FIG. 4 and 
identifies the structure by the general numeral 40. The construction 
comprises a group of piers or columns 16A, 16B, 16C, and 16D, which are 
arranged in a circle of such diameter that they can support a circular 
base ring 14 which rests on the top of the columns. The base ring is of 
such diameter as to fully support the weight and provide stability for the 
stack 12. The stack is of conventional construction, which provides a 
circular cylindrical outer wall 21 and has ceramic insulation material 
inside, suitable to the temperatures that will be provided in the space 28 
inside of the stack, as the hot gases from the furnace rise to be expelled 
at the top of the stack into the atmosphere. 
The colums 16 rest on grade 18 and are limited in their height in relation 
to the overall height of the columns, plus the support ring, plus the 
stack. The combustion chamber indicated generally by the numeral 21 hangs 
penduously from the base ring 14, which supports the stack. Thus, the 
stability of the stack depends only on the columns and is independent of 
the combustion section. This is contrary to the normal construction, in 
which the stack rests entirely on the combustion section. As more and more 
openings 34 are provided in the wall of the combustion section, the 
structural strength of the combustion section becomes less and less, and 
the design of the combustion section becomes more structural than thermal. 
The improved construction of our invention separates the structural 
requirement from the thermal requirements of the combustion section. 
As shown in FIG. 4, the cross-section of the combustion section 21 has an 
outer nominal diameter which is equal to that of the cross-section of the 
stack, with a plurality of reentrant vertical channels in the wall of the 
combustion section, identified by the numerals 60. These channels are 
spaced such as to be symmetrical with respect to the columns, and to 
provide a suitable air space 30 between the columns and the wall of the 
combustion section, for the purpose of cooling the structural columns. Air 
circulation through the spaces 30 will be provided by the heating of the 
air in the spaces 30, which consequently rises to be replaced by cool air 
entering the channels in the lower region and moving upwardly. 
A comparison of FIGS. 2 and 4 will indicate the particular advantage of the 
construction of FIG. 4 over that of FIG. 2, namely, that the diameter of 
the combustion chamber is not limited to the dimension 22 but has sectors 
having a larger diameter of dimension 20. Thus, a much larger 
cross-sectional area of a combustion zone is provided by the design of 
FIGS. 3 and 4 over those of FIGS. 1 and 2. 
The volume of the combustion zone is increased in another way as shown in 
FIGS. 3 and 5. This is by means of an increase in vertical height of the 
combustion zone. In FIG. 1 and in the priot art, while the combustion 
section hangs entirely within the ring of columns, the bottom has been 
shown as being closed, with suitable ceramic insulation, and is supported 
a suitable distance 32 above grade. 
In FIG. 3 the improvement of this invention is shown as a shallow 
excavation of depth 56 below grade, and of outer contour which is somewhat 
larger than the outer contour of the combustion section as shown in FIG. 
4. The purpose of the excavation is to permit a design in which the 
combustion chamber height 24 is considerably greater than that of the 
prior art installations. The bottom of the combustion chamber is open and 
the internal space is filled with porous material 49 to a height 44. The 
porous material can be sand, gravel, ceramic, etc. 
FIG. 5 shows a detail of the construction of the excavation. The vertical 
extent of the excavation is indicated by dimension 56. The outer steel 
wall 50 of the combustion zone and the internal insulation covering 52, 
are somwhat shorter, and hang a suitable distance 48 above the base 47 of 
the excavation. This provides an air space 48 so that cool air can flow in 
accordance with arrow 54 down through the space 46 outside of the 
combustion chamber wall, and under the wall 50 through space 48, and up 
through the porous material 49 in accordance with arrows 55. This flow of 
cool air upwardly through the fill 49 inside of the combustion chamber 
serves not only to provide additional combustion air, but also to provide 
cooling for the porous material. Thus, as indicated in FIGS. 3, 4, and 5, 
the improved construction of this invention serves to provide a 
considerably larger volume of combustion space 26 inside of the combustion 
chamber. 
Most of the combustible waste gases or liquids which are to be burned in 
the flare are smoke-prone, and smoky burning is environmentally 
unacceptable, if any smoke escapes, visibly, to the atmosphere. Smoke is 
carbon particles which have escaped from the combustion zone where carbon, 
hydrogen, and other elements provide the composition of the waste matter. 
In most cases it is possible to secure complete burning of waste--that is, 
the avoidance of smoke, through retention of carbon within the combustion 
chamber-stack structure, at sufficiently high temperature, long enough for 
the carbon to oxidize. In that case, no visible smoke emerges to the 
atmosphere. 
Since waste matter for disposal by burning can vary widely, as to smoking 
tendency, a system which is satisfactory for smokeless operations with a 
great majority of waste materials, may still deliver visible smoke when a 
very few smoke-prone materials are being burned. This would require the 
elimination of smoke even for these very few materials which are only 
burned on rare occasions. 
At temperature above ignition temperature, carbon can oxidize in a number 
of ways, such as: 
EQU C+1/2O.sub.2 =CO 
EQU C+O.sub.2 =CO.sub.2 
EQU C+H.sub.2 O=CO+H.sub.2 
EQU C+2H.sub.2 O=CO.sub.2 +2H.sub.2 
The first two reactions shown are typical of oxidation of carbon, at 
adequate temperature level, by oxygen alone. The second two represent the 
attack of water-vapor and are typical "water-gas shift" reactions which 
are well-known in industry. Greater partial-pressure of water vapor in an 
atmosphere greatly accelerates the water-gas shift reactions when the 
temperature is adequate, as it is in a combustion zone. Also, when 
water-spray is introduced to a combustion zone it immediately is 
evaporated to become water vapor, rather than droplets of water liquid, to 
add to water vapor partial-pressure in the combustion zone. The water 
vapor effect is to greatly accelerate carbon oxidation. The CO and H.sub.2 
produced burn by direct oxidation with tremendous speed, and in an 
assured manner, and cannot be seen. 
When it is necessary for avoidance of smoke emission, we take advantage of 
the water-gas chemistries through injection of water spray from at least 
one water spray nozzle to the combustion zone. It is clear that the spray 
is not constantly required but is used for smoke-prone wastes normally. 
However, use of water spray with all burning will allow a smaller (less 
expensive) combustion chamber-stack system, to provide satisfactorily 
smokeless operation constantly in many waste disposal problems. The total 
internal volume of the combustion chamber-stack can be less because of the 
greatly accelerated carbon oxidation as discussed. Of course, steam can be 
used in place of water for injection into the flames. However, because of 
its cost, steam would be a second choice. 
Referring now to FIG. 6, one example is shown of the possible arrangement 
of fuel pipes and water and/or steam pipes, inserted into an opening 34 in 
the wall of the combustion section. Although any type of fuel burner can 
be used, the illustration shows a gas burner 62, having a nozzle with 
ports 64. Gas is supplied in accordance with arrow 68 from a suitable 
source through the pipe 62 and issues as high speed jets 66 from the ports 
64. The pipe 70 is illustrated as a possible water pipe, which has a 
nozzle 71, and water supplied in accordance with arrow 72. Water will 
issue through the orifices as jets of tiny droplets of water which would 
be injected into the flow of gas issuing from the ports 64 in accordance 
with the spray 66. 
Alternatively, pipe 74 is shown which has a suitable flow of steam in 
accordance with arrow 76, and has a nozzle 75 with suitable ports that 
provide a series of jets 78 of steam, which are injected into the flow of 
gas 66. For gaseous fuel, the water droplets or the steam can be injected 
alternatively in accordance with the pipe 74 with suitable nozzles and 
ports to provide spray 78 into the main flow of gas, so that initimate 
mixing of the water droplets with the fuel will provide intimate contact 
with the water vapor resulting from evaporation of the droplets as the gas 
and water are injected into the flame. Thus, the suitable burning 
chemistry is provided. The openings 34 are much larger than would be 
needed simply for the piping, so that there is adequate area for flow of 
combustion air, as shown by arrows 80 in FIG. 6. Also, openings can be 
provided solely for air, as needed. 
In further clarification of the combustion chamber-stack volumetric 
relationship, both the stack 28 and the combustion chamber 26 volumes 
combine to provide a total volume, within which there is to be complete 
burning of waste matter. But the chemical reactions of combustion are 
almost infinitely more rapid in the high temperature turbulent combustion 
chamber than they are in the diffusive (unturbulent) lower temperature 
stack gas flow. For this reason, and if emission of smoke is to be 
avoided, a vast majority of the combustion chemical reactions must have 
been completed before emergence of continued burning from the combustion 
chamber internal volume 26 to the stack internal volume 28. The combustion 
chamber turbulence is burner-created, and the internal volume of the 
combustion-chamber determines how soon, or how rapidly, the burning will 
depart from the combustion chamber, and enter the non-turbulent stack. 
Thus, there is need for all the combustion chamber volume which is 
possible within structural limits. 
While this invention has been described with a certain degree of 
particularity, it is manifest that many changes may be made in the details 
of construction and the arrangement of components without departing from 
the spirit and scope of this disclosure. It is understood that the 
invention is not limited to the embodiments set forth herein for purposes 
of exemplification, but is to be limited only by the scope of the attached 
claims, including the full range of equivalency to which each element or 
step thereof is entitled.