Combustion – Process of combustion or burner operation – Controlling or proportioning feed
Reexamination Certificate
2003-08-08
2004-11-30
Basichas, Alfred (Department: 3749)
Combustion
Process of combustion or burner operation
Controlling or proportioning feed
C431S033000, C110S190000
Reexamination Certificate
active
06824383
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a furnace combustion system.
BACKGROUND OF THE INVENTION
A furnace may provide heat by burning fuel gas in a combustible mixture with oxidant gas. Such a furnace includes one or more burners, and has a reactant supply system with lines and valves that direct streams of the fuel and oxidant gases to the burners. In some furnaces the fuel and oxidant gases are provided to the burners in separate streams that form combustible mixtures within the burners. In other furnaces the fuel and oxidant gases are provided to the burners in a combustible mixture known as premix. In each case, the furnace has a control system that controls the reactant supply system so that combustion of the fuel will occur in a manner appropriate for the heating process to be performed by the furnace. The control system includes instruments such as temperature sensors, igniters, and flame detectors, and controls the valves in the reactant supply system with reference to combustion parameters indicated by those instruments.
Parts of a known furnace apparatus
10
are shown schematically in
FIGS. 1 and 2
. These include a burner assembly
12
mounted in a furnace wall structure
14
. The wall structure
14
defines a combustion chamber
15
, which may be referred to as a process chamber, with a flue gas outlet
16
. A reactant supply system
20
provides reactants to the burner assembly
12
under the direction of a control system
22
. This enables the burner assembly
12
to provide a controlled amount of heat for a heating process to be carried out in the combustion chamber
15
.
The reactant supply system
20
includes fuel and oxidant supply lines
24
and
26
that convey fuel and oxidant from respective sources
28
and
30
to the burner assembly
12
. The oxidant is typically the oxygen in a stream of air, and the fuel is typically natural gas. A motorized oxidant valve
32
controls the stream of air in the oxidant supply line
26
. A pair of motorized fuel valves
34
and
36
control the stream of fuel in the fuel supply line
24
. The oxidant valve
32
and the first fuel valve
34
are modulating valves. The second fuel valve
36
is a shut-off valve. Each valve motor is operated by the control system
22
to open, shift, and close the respective valve
32
,
34
or
36
as directed by the control system
22
.
The burner assembly
10
has two major portions
40
and
42
that are shown schematically in FIG.
1
. The first portion
40
is a burner tile with an internal reaction zone
43
. A generally cylindrical inner surface
44
of the burner tile
40
is centered on an axis
45
, and defines the peripheral boundaries of the reaction zone
43
. An outer end surface
46
of the burner tile
40
defines an outlet
47
that communicates the reaction zone
43
with the combustion chamber
15
. The outlet
47
is circular and also is centered on the axis
45
. An end portion
48
of the inner surface
44
is tapered radially inward so that the outlet
47
is constricted relative to the generally cylindrical configuration of the reaction zone
43
.
The second major portion
42
of the burner assembly
10
comprises a burner with a fuel inlet
50
and an oxidant inlet
52
. Passages within the burner
42
receive the streams of fuel and oxidant from the inlets
50
and
52
to form a combustible mixture, and the burner
42
is oriented to fire a flame into the reaction zone
43
in a direction extending into the combustion chamber
15
through the outlet
47
.
The control system
22
includes a controller
60
. The control system
22
further includes a temperature sensor
62
which is operative in the combustion chamber
15
. Additional parts of the control system
22
that are shown schematically in
FIG. 1
include an igniter
64
and a flame detector
66
. These are conventional devices that are operatively mounted in the burner assembly
10
in a known manner.
Other parts of the burner assembly
12
, the furnace wall structure
14
, the reactant supply system
20
and the control system
22
are known to a person of ordinary skill in the art. Those parts, such as a flame stabilizer within the burner assembly
12
, are omitted from the drawings for clarity of the schematic illustrations.
As indicated in
FIG. 1
, the controller
60
includes flame supervisory controls in the form of hardware and/or software
70
for operation of the furnace apparatus
10
with flame supervision, and further has a flame supervision bypass function, including hardware and/or software
72
for bypassing flame supervision. As the controller
60
carries out those instructions, it first actuates the valves
32
,
34
and
36
to provide streams of fuel and oxidant along the supply lines
24
and
26
, and actuates the igniter
64
to initiate combustion of those reactants in a flame that projects from the burner
42
.
As the streams of fuel and oxidant continue to flow to the burner
42
, the controller
60
provides flame supervision in accordance with the corresponding flame supervisory controls
70
. Flame supervision is one of several supervisory functions the controller
60
performs by monitoring sensors that can indicate system malfunctions. If a malfunction occurs, the controller
60
can respond by closing the shut-off valve
36
as a safety precaution. However, if a malfunction does not present an unsafe condition, the controller
60
can bypass the supervisory function for the corresponding sensor, and can allow combustion to continue. The controller
60
thus monitors the flame detector
66
in readiness to close the shut-off valve
36
if the flame detector
66
indicates the absence of a flame. This would occur if the flame were inadvertently extinguished by a system malfunction. However, the controller
60
monitors the temperature sensor
62
also, and is operative to compare the sensed combustion chamber temperature to a predetermined auto-ignition temperature of the fuel supplied to the burner
42
. If the sensed combustion chamber temperature is not less than the auto-ignition temperature, and if the flame supervision bypass function
72
is enabled, the flame supervisory controls
70
are bypassed. With the flame supervisory controls
70
bypassed, indication by the flame detector
66
of the absence of a flame projecting from the burner
42
will not result in the controller
60
closing the shut-off valve
36
. Rather, the controller
60
then holds the shut-off valve
36
open so that the fuel can continue to flow through the burner
42
and onward through the reaction zone
43
to enter the combustion chamber
15
through the outlet
47
. This results in diffuse combustion of the fuel upon auto-ignition in the combustion chamber
15
in the absence of a flame at the burner
42
, as shown in FIG.
2
.
SUMMARY OF THE INVENTION
The invention provides a method and apparatus for inducing a diffuse combustion mode of operation in a furnace, whereas the diffuse combustion described above is an unpredictable default condition that occurs when the flame is inadvertently extinguished.
The method includes the step of extinguishing a flame fired from a burner in a reaction zone upon determining that a sensed combustion chamber temperature is not below a predetermined auto-ignition temperature of a fuel. A subsequent step is performed before the sensed combustion chamber temperature drops below the auto-ignition temperature. The subsequent step provides a flow of the fuel through the burner and into the combustion chamber through a reaction zone outlet. This initiates diffuse combustion of the fuel by auto-ignition in the combustion chamber in the absence of a flame fired from the burner in the reaction zone.
The flame is can be extinguished in any one or more of a number of different ways including, for example, interrupting a flow of fuel to the burner, applying a gas pulse, or providing reactants to the burner in a fuel/oxidant ratio that does not sustain the flame. A delay may be imposed to ensure that the flame is fully extinguished before the flow of fu
Basichas Alfred
Jones Day
North American Manufacturing Company
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