Patent Application
20080081301
The furnaces illustrated schematically in
The furnace 100 of
Although a nozzle mix burner could be used, this burner 116 is a premix burner with a mixer tube 140 and a burner tile 142. The burner tile 142 defines a reaction zone 145 between the mixer tube 140 and a port 147 leading to the process chamber 115. The burner 116 also includes a flame stabilizer 148. The flame stabilizer 148 could be configured in any suitable manner known in the art, but is preferably the same as the flame stabilizer 30 described above with reference to
As further shown schematically in
The reactant supply system 120 has fuel and oxidant supply lines 170 and 172. It also has a plurality of branch lines with flow control valves. A first branch line 174 extends from the fuel supply line 170 to the fuel coupling 164 at the burner 116. A first valve 176 controls the flow of fuel through the first branch line 174. A second branch line 178 extends from the oxidant supply line 172 to the oxidant coupling 162 at the burner 116. A second valve 180 controls the flow of oxidant through the second branch line 178. Third and fourth branch lines 184 and 186 likewise have third and fourth valves 188 and 190. Those branch lines 184 and 186 extend from the fuel and oxidant supply lines 170 and 172 to the bypass apparatus 126.
Unlike the burner 116, the bypass apparatus 126 does not include a flame stabilizer. It is instead configured to inject unignited premix into the process chamber 115 without the influence of a flame stabilizer, whereby the resulting ignition and combustion of the premix proceeds without flame stabilization. In this particular example, the bypass apparatus 126 includes a mixer body 200 and a premix injector tube 204. A mixing chamber 205 is defined within the mixer body 200. The mixing chamber 205 communicates with the third branch line 184 through a fuel coupling 206, and communicates with the fourth branch line 186 through an oxidant coupling 208. The premix injector tube 204 has an open inner end 210 at the mixing chamber 205 and an open outer end 212 at the process chamber 115. There is no structure in the bypass apparatus 126 for slowing the flow of premix at a location between the inner end 210 of the injector tube 204 and the region of the process chamber 115 where the premix emerges from the open outer end 112 of the injector tube 204. Nor is there any structure for inducing upstream recirculation toward or within the injector tube 204. Instead, the bypass apparatus 126 is free of any structure configured for the purpose of inhibiting flashback or blow off of a flame propagating in a direction inwardly of the premix injector tube 204.
The controller 130 has hardware and/or software configured to control combustion in the process chamber 115 by selective use of the burner 116 and the bypass apparatus 126. The controller 130 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 130 carries out those instructions it actuates the valves 176, 180, 188 and 190 to initiate, regulate and terminate flows of reactant streams through the reactant supply system 120.
In a startup mode of operation, the controller 130 actuates an igniter 220 in the reaction zone 145, and opens the first and second valves 176 and 180 while maintaining the third and fourth valves 188 and 190 in closed conditions. This transmits streams of fuel and oxidant to the mixer body 160 at the burner 116 while blocking transmission of fuel and oxidant to the process chamber 115 through the bypass apparatus 126. The reactant streams transmitted to the burner 116 form premix as they mix and flow together through the mixer tube 140 toward the reaction zone 145. The premix is ignited upon emerging form the mixer tube 140 to form a flame that projects through the reaction zone 145 and into the process chamber 115 through the port 147 under the influence of the flame stabilizing structure 148. As a safety precaution the flame is monitored by the controller 130 and a flame sensor 222. The flame sensor 222 may comprise any suitable device that is operative to detect the presence of a flame stabilized at a burner. Such devices that are known in the art include, for example, a flame rod, a UV (ultraviolet) flame detector, an IR (infrared) flame detector, a thermopile, and an acoustic flame sensor.
When a temperature sensor 224 indicates that the temperature in the process chamber 115 has risen to a level at or above the autoignition temperature of the premix, the controller 130 responds by shifting from the startup mode of operation to a diffuse combustion mode of operation. The controller 130 shifts to the diffuse combustion mode by closing the first and second valves 176 and 178 to block the transmission of fuel and oxidant to the burner 116, and by opening the third and fourth valves 188 and 190 to transmit fuel and oxidant to the bypass apparatus 126. The fuel and oxidant then mix together in the chamber 205 to form unignited premix that is transmitted through the injector tube 204 for injection into the process chamber 115. Importantly, the premix emerging from the open outer end 212 of the injector tube 204 flows into the process chamber 115 without the influence of a flame stabilizer. This enables autoignition of the premix to result in diffuse combustion more uniformly throughout the process chamber 115. Since the bypass apparatus 126 does not produce a stabilized flame, the furnace 100 does not have a flame sensor in operative association with the bypass apparatus 126, but instead employs the temperature sensor 224 as a safety device to monitor diffuse combustion in the process chamber 115.
The furnace 300 of
As shown in the drawing, the furnace 300 differs from the furnace 100 by including a bypass apparatus 340 that is structurally combined with the burner 306 rather than structurally separate from the burner 306. Specifically, the bypass apparatus 340 includes a premix injector tube 342 that extends through the burner tile 344. The outer end 346 of the injector tube 342 is open to the process chamber 305. The inner end 348 of the injector tube 342 is open to an oxidant plenum 349 within a bypass mixer body 350 that is joined with the mixer body 352 at the burner 306.
An oxidant branch line 360 with a flow control valve 362 extends from an oxidant supply line 364 to an oxidant coupling 366 at the bypass mixer body 350. A fuel branch line 370 with a flow control valve 372 extends from a fuel supply line 374 to a fuel coupling 376 at the bypass mixer body 350. The flow path of fuel from the source 332 to the injector tube 342 is completed by an internal fuel line 380 that extends from the fuel coupling 376 into the inner end 348 of the injector tube 342.
The controller 320 initiates a startup mode of operation by actuating the igniter 308 and opening the fuel and oxidant flow control valves 390 and 392 that serve the burner 306. The resulting flame is stabilized by a flame stabilizer 394 and monitored by a flame sensor 396 throughout the startup mode. The flow control valves 362 and 372 that serve the bypass apparatus 340 are maintained in closed conditions throughout the startup mode.
When the temperature in the process chamber 305 reaches a level at or above the autoignition temperature of the premix, as indicated by a temperature sensor 398 in the process chamber 305, the controller 320 responds by shifting from the startup mode of operation to a diffuse combustion mode of operation. This is accomplished by closing the valves 390 and 392 that serve the burner 306, and by opening the valves 362 and 372 that serve the burner bypass apparatus 340. Streams of fuel and oxidant then flow into the open inner end 346 of the injector tube 342 and form premix as they flow together along the length of the tube 342 toward the process chamber 305.
As shown in the drawing, there is no flame stabilizer in the premix flow path that extends through the injector tube 342 and into the process chamber 305 from the open outer end 348 of the injector tube 342. There is no flame sensor operatively associated with the bypass apparatus 340. Therefore, in operation of the bypass apparatus 340, an unignited stream of premix flows through the open outer end 348 of the injector tube 342 and into the process chamber 305 without the influence of a flame stabilizer. Diffuse combustion in the process chamber 305 proceeds accordingly, and is monitored for safety by the temperature sensor 398.
The claimed invention further provides other operational modes in addition to the startup and diffuse combustion modes described above. For example, furnace startup is not the only time at which the burner can be on while the bypass apparatus is off. That flame stabilization mode can be continued after startup, and can be alternated with the non-stabilization mode in which the burner is off and the bypass apparatus is on. It may also be appropriate to operate in a mode in which the burner and the bypass apparatus are on simultaneously. Overall target rates of fuel and oxidant injection could then be provided in partial rates at the burner and the bypass apparatus. In this regard,
This written description sets forth the best mode of carrying out the invention, and describes the invention to enable a person of ordinary skill in the art to make and use the invention, by presenting examples of the elements recited in the claims. The patentable scope of the invention is defined by the claims and may include other examples that occur to those skilled in the art. 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 structural or method elements that do not differ from the literal language of the claims, or if they have equivalent structural or method elements with insubstantial differences from the literal language of the claims.
