Combustion – Process of combustion or burner operation – Heating feed
Reexamination Certificate
2001-07-17
2004-11-09
Price, Carl D. (Department: 3749)
Combustion
Process of combustion or burner operation
Heating feed
C431S161000, C431S243000, C431S247000
Reexamination Certificate
active
06814568
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method of and an apparatus for combusting lean concentrations of a burnable gas at superatmospheric pressure, and more particularly to such a combustion arrangement having a heat sink/pressure equalization chamber for protecting the combustor from back pressure generated during the combustion process.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 3,229,746 (the '746 patent), which is incorporated by reference herein in its entirety, shows a heat recovery apparatus and a method suitable for combusting lean concentrations of a burnable gas. That patent, by way of example, is directed to the burning of lean gases such as, but not limited to, catalytic cracking off gas containing carbon monoxide concentrations of less than 8%. The invention in that patent permits the stabilizing of carbon monoxide ignition at a temperature in the range of from 1200° F. to 1500° F. After start-up, this temperature can be maintained in most cases by the combustion of the carbon monoxide alone. In the remaining cases, there is a minimal auxiliary fuel requirement to assure safe ignition and/or to maintain the desired amount of heat recovery.
FIG. 1
of this application shows the heat recovery apparatus of the '746 patent. In
FIG. 1
, a setting generally designated by reference numeral
1
defines a combustion zone
2
and a heat recovery zone
3
horizontally disposed at grade level. Gas is communicated to the combustion zone
2
via gas chamber
4
and gas ports
6
. Air is introduced via air chamber
7
. The air enters the combustion chamber
2
through air ports
8
. Secondary air to support the combustion of auxiliary fuel is admitted to the combustion chamber through conduits
9
. The gas and air are intermittently commingled by opposing vortexes indicated by directing arrows
11
and
12
created by an aiming device shown as inclined conduits
13
, which conduct the gas mixture from the gas chamber
4
to the gas ports
6
and short air pipes
14
. Auxiliary burners
16
are provided to initially heat the gases in the combustion zone
2
to a suitable kindling temperature. Refractory material
17
lines the combustion zone
2
to re-radiate heat to the gases therein.
By the arrangement shown in
FIG. 1
, lean gas such as carbon monoxide in concentrations of less than 8%, such as catalytic cracking off gas, can be burned. Higher concentrations, of course, can be combusted more easily. An outstanding feature of the design shown in
FIG. 1
is that it requires less than 1% of excess oxygen as measured in the products of combustion.
In the combustion chamber
2
, a temperature in the range of from 1200° F. to 1500° F. can conveniently be maintained so that after light-off, carbon monoxide will usually be able to burn without the need for auxiliary fuel. Heat is liberated by the burning of carbon monoxide in the combustion zone
2
. Intrinsically, there is a heat liberating system operating in the combustion chamber
2
. In an extrinsic sense, the combustion zone
2
has been designed so that there is practically no heat input or heat removal to the combustion zone
2
vis-a-vis its surroundings. In particular, no cooling devices, such as heat exchange tubes, are associated with the combustion zone
2
.
An end wall
18
is defined by a partition
19
. Air ports
8
and gas ports
6
penetrate the partition
19
to define substantially concentric angular groups in the end wall
18
.
FIG. 1
shows an open checker brick wall
21
as a canalizing device, which causes the combustion gases to flow through restricted canals
22
to thereby increase commingling. The heat recovery zone
3
is defined by the setting
1
downstream of the combustion zone
2
. An appropriate heat recovery apparatus, such as steam tubes, an economizer, a superheater, other fluid streams, and the like, can be provided in the heat recovery zone
3
.
The setting
1
defines an enclosure for the combustion zone
2
having end walls and side walls extending between the end walls. All of the walls are arranged to re-radiate heat to the combustion zone via the refractory material
17
. The exhaust port by which the hot gases are transmitted to the heat recovery zone
3
is at an end of the setting
1
, opposite from the gas ports
6
and air ports
8
, and constitutes a sufficiently small portion of one of the side walls to maintain re-radiation of heat from all walls of the enclosure at the highest level possible.
In addition, as shown in
FIG. 1
, the heat recovery zone
3
, which is the only heat sink structure of the apparatus, is completely removed from exposure to the combustion zone
2
. This is in comparison to conventional carbon monoxide boiler installations where a heat sink in the form of water tubes either is in the combustion zone or is exposed to radiant heat of the burning gases. Such an internal heat sink increases the requirement for auxiliary fuel and reduces to a marked extent flame stability and reliability of carbon monoxide gas conversion.
The apparatus shown in
FIG. 1
typically operates at high temperatures. For example, the typical lean gas is fed to the apparatus at 600° F. to 1100° F. or higher. As a result of the combustion process, the combusted gases exiting the combustion zone can be in the range of 1200° F. to 1800° F. or higher.
FIGS. 2 and 3
show prior art apparatuses that adequately avoid overheating of the external casing plates thereof, which are respectively insulated on the lean gas chamber and the combusted gas chamber, by using a flow of pressurized ambient (“cold”) air to an air chamber, which is formed and contained by these chambers. In such arrangements, the pressurized ambient air is utilized as the oxidant source to combust both the lean gas and an auxiliary fuel stream in the apparatus.
FIG. 2
shows a conventional combustion device
200
, which includes a lean gas chamber
212
, a combustor
230
, a heat recovery zone
240
, and an exhaust
250
. Ambient air is pressurized and fed by an air pump
220
through a supply line
221
to the combustor
230
. Lean gas
210
is supplied through a supply line
211
to the lean gas chamber
212
.
FIG. 3
shows in more detail a combustion device
300
. The combustion device
300
includes a lean gas chamber
312
and a combustor
330
. Lean gas from lean gas chamber
312
enters the combustor
330
through a gas port
317
. Pressurized ambient air
320
enters the combustor
330
through an air port
327
. The combustion device
300
is insulated by a refractory lining
301
. Combustion products exit the combustor
330
and are sent to a heat recovery section
340
, typically through a heat exchanger (not shown).
One having ordinary skill in the art will appreciate that a suitable number of auxiliary burners
16
(shown in
FIG. 1
) may be provided as start-up means to initially heat the gases in the combustor
230
(
FIG. 2
) or
330
(
FIG. 3
) to a desired kindling temperature, or as a means to provide a level of heat input for the desired heat recovery.
As discussed above, such apparatuses are most typically used in processes where the lean gas is delivered to the apparatus at some pressure above atmospheric pressure (for example, 0.1 psig to 5.0 psig or higher), and the combusted gases typically are discharged to the atmosphere after heat recovery and, in some instances, after exhaust gas clean-up systems. This, however, results in a back pressure within the combustion zone. As noted in
FIG. 2
, air is supplied to the apparatus with a pump to meet the pressure requirements. The apparatus, of course, is designed to contain and withstand these internal pressures. The advantage of the configuration of such an apparatus is the economics of its construction for the pressure containment discussed above, resulting from integration of the gas chamber and air chamber within the overall pressure container. Thus, only nominal pressure differentials exist between the respective chambers.
We have found, however, that a problem arises in the conventional arrangement shown in FIG.
3
. In that e
Jacobsen Eric
Jacobsen John G.
Jacobsen Krista
McEvoy Lawrence J.
Fitzpatrick ,Cella, Harper & Scinto
Foster Wheeler USA Corporation
Jacobsen Eric
Jacobsen Krista
Price Carl D.
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