This technology relates to the operation of a burner for a furnace.
Regenerative burners may be used to heat a process chamber in a furnace. Each regenerative burner has a bed of heat-regenerative material, and is arranged in a pair with another regenerative burner. The two burners are cycled alternately such that one burner is actuated while the other is not. When a burner is actuated, it discharges fuel and combustion air into the process chamber for combustion to proceed in the process chamber. Much of the combustion air is pre-heated by driving it through the regenerative bed. Alternately, when a burner is not actuated, exhaust gases from the process chamber are drawn outward through the regenerative bed at that burner. The exhaust gases heat the regenerative bed to provide the thermal energy that pre-heats the combustion air when the burner is again actuated to fire into the process chamber.
A reactant supply and control system supplies a regenerative burner assembly with streams of pilot fuel and pilot air. The system can maintain a pilot flame continuously throughout consecutive regenerative cycles in which a main flame is turned on and off, and can supply either or both of the pilot streams with flow rates that differ between a regenerative exhaust condition and a regenerative firing condition. This can help to ensure that the pilot flame ignites a main flame for each regenerative firing condition. Lower flow rates of pilot reactants in the regenerative exhaust conditions can reduce fuel consumption and exhaust emissions.
The furnace 10 shown in the drawings has parts that are examples of the elements recited in the claims. The following description thus includes examples of how a person of ordinary skill in the art can make and use the claimed invention. It is presented here to meet the statutory requirements of written description, enablement, and best mode without imposing limitations that are not recited in the claims.
As shown partially in the schematic view of
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A main fuel conduit 50 surrounds the pilot air conduit 40. A primary air conduit 52 surrounds the main fuel conduit 50. These conduits 50 and 52 have inlets 54 and 56 at their rear ends and outlets 58 and 60 at their front ends, respectively. This provides a main burner that is configured to provide a main flame that projects axially forward from the outlets 58 and 60. In the illustrated example, the concentric outlets 44, 58 and 60 are coplanar and radially adjacent. More specifically, the pilot burner outlet 44 is the circular space bounded by the surrounding edge of the pilot air conduit 40. It is spaced radially inward from the main fuel outlet 58 by only the thickness of the conduit 40 that is interposed radially between those two outlets 44 and 58. The main fuel outlet 58 is the annular space bounded by the concentric edges of the pilot air conduit 40 and the main fuel conduit 50. That outlet 58 is spaced radially inward from the surrounding outlet 60 by only the thickness of the main fuel conduit 50. The primary air outlet 60 likewise has an annular configuration defined by and between the concentric edges of the main fuel conduit 50 and the primary air conduit 52.
The cylindrical body 20 in the illustrated example has three major portions. These include a rear portion 70, a central portion 72, and a front portion 74. The rear portion 70 includes a refractory structure 80 within a steel shell 82. Lower portions of those parts 80 and 82 define the base 28 at which the burner assembly 16 is mounted over a regenerative bed. The refractory structure 80 within the steel shell 82 defines a plenum 85 extending upward from a port 87 at the lower end of the base 28. The refractory structure 80 further defines a generally conical pocket 89 (
As shown separately in
The secondary ports 27 also are located on the circular front surface 98 of the baffle 90. Two pairs 104 and 106 of air flow passages extend from the rear of the baffle 90 to the secondary ports 27 at the front surface 98. As shown in
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Referring again to
The controller 146 has hardware, software, or a combination of hardware and software that is configured to control the valve assembly 148. The controller 146 may thus comprise any suitable programmable logic controller or other control device, or combination of control devices, that is programmed or otherwise configured to perform as recited in the claims. As the controller 146 carries out those instructions, it actuates the valve assembly 148 to initiate, modulate, and terminate independent flows of reactant streams through the burner assembly 16.
In one particular example of a start-up sequence, the controller 146 first directs the valve assembly 148 to supply the reactant delivery structure 26 with streams of pilot fuel, pilot air, and primary air, and also actuates an igniter (not shown). This causes a pilot flame to project axially forward toward the primary port 25 (
The streams of main fuel and primary air begin to mix as they flow together through the tapered bore 101 toward the primary port 25, and continue to mix as they flow outward from the port 25 into the process chamber 15. The mixture surrounds, ignites and begins to combust over the pilot flame. As shown schematically in
Secondary combustion air flows through the secondary air line 170 to the regenerative bed 18. The plenum 85 (
A main flame supervisory device 186 monitors combustion in the primary reaction zone 185. If the main flame supervisory device 186 fails to confirm combustion of the main fuel and primary air, the controller 146 directs the valve assembly 148 to terminate the main fuel stream. If combustion of the main fuel and primary air is confirmed, the controller 146 directs the valve assembly 148 to continue supplying those reactant streams to maintain a regenerative firing condition until the burner assembly 16 is switched to a regenerative exhaust condition.
The flame supervisory devices 180 and 186, which may be UV or other sensors for detecting a flame, are configured in a known manner for the pilot sensor 180 to sense the pilot flame, or optionally to sense both the pilot flame and the main flame, and for the main sensor 186 to sense the main flame but not the pilot flame. This prevents the pilot frame from being mistaken for a main flame, which permits the pilot flame to be maintained continuously throughout consecutive cycles in which the main flame is turned on and off for regenerative operation of the burner assembly 16. The reactant supply and control system 140 is configured accordingly. Specifically, when the burner assembly 16 is in the regenerative exhaust condition, the pilot sensor 180 senses the pilot flame but the main sensor 186 does not sense a main flame. The controller 146 directs the valve assembly 148 to supply the reactant delivery structure 26 with first streams of pilot fuel and pilot air in that condition. Since there is no stream of main fuel and no need for a main flame, either or both of the first streams of pilot fuel and pilot air can have a flow rate that is lower than the flow rate ordinarily provided for the pilot flame to ignite a main flame.
The system 140 is further configured to continue supplying pilot fuel and pilot air to the reactant delivery structure 26 to maintain the pilot flame, but to shift from the first streams to second streams that differ from the first streams when the burner assembly 16 is being shifted from a regenerative exhaust condition to a regenerative firing condition. The controller 146 then directs the valve assembly 148 to supply a main fuel stream, and also to provide either or both of the second streams of pilot fuel and pilot air with a flow rate that exceeds the corresponding first stream flow rate sufficiently to ensure that the pilot flame ignites a main flame. The increased pilot flow rate or rates can be shifted back to a lower level during the regenerative firing condition, when shifting to the next subsequent regenerative exhaust condition, or during the next subsequent regenerative exhaust condition. In each case lower pilot flow rates can reduce both fuel consumption and exhaust emissions as the pilot streams are continued without interruption but are shifted back and forth between the first and second flow rates throughout multiple cycles of shifting back and forth between the regenerative exhaust condition and the regenerative firing condition.
The patentable scope of the invention is defined by the claims, and may include other examples of how the invention can be made and used. Such other examples, which may be available either before or after the application filing date, are intended to be within the scope of the claims if they have elements that do not differ from the literal language of the claims, or if they have equivalent elements with insubstantial differences from the literal language of the claims.