Patent Publication Number: US-2021163821-A1

Title: Automatic draft control system for coke plants

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a divisional of U.S. patent application Ser. No. 13/589,009, filed Aug. 17, 2012, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     The present invention relates generally to the field of coke plants for producing coke from coal. Coke is an important raw material used to make steel. Coke is produced by driving off the volatile fraction of coal, which is typically about 25% of the mass. Hot exhaust gases generated by the coke making process are ideally recaptured and used to generate electricity. One style of coke oven which is suited to recover these hot exhaust gases are Horizontal Heat Recovery (HHR) ovens which have a unique environmental advantage over chemical byproduct ovens based upon the relative operating atmospheric pressure conditions inside the oven. HHR ovens operate under negative pressure whereas chemical byproduct ovens operate at a slightly positive atmospheric pressure. Both oven types are typically constructed of refractory bricks and other materials in which creating a substantially airtight environment can be a challenge because small cracks can form in these structures during day-to-day operation. Chemical byproduct ovens are kept at a positive pressure to avoid oxidizing recoverable products and overheating the ovens. Conversely, HHR ovens are kept at a negative pressure, drawing in air from outside the oven to oxidize the coal volatiles and to release the heat of combustion within the oven. These opposite operating pressure conditions and combustion systems are important design differences between HHR ovens and chemical byproduct ovens. It is important to minimize the loss of volatile gases to the environment so the combination of positive atmospheric conditions and small openings or cracks in chemical byproduct ovens allow raw coke oven gas (“COG”) and hazardous pollutants to leak into the atmosphere. Conversely, the negative atmospheric conditions and small openings or cracks in the HHR ovens or locations elsewhere in the coke plant simply allow additional air to be drawn into the oven or other locations in the coke plant so that the negative atmospheric conditions resist the loss of COG to the atmosphere. 
     SUMMARY 
     One embodiment of the invention relates to a coke oven including an oven chamber, an uptake duct in fluid communication with the oven chamber, the uptake duct being configured to receive exhaust gases from the oven chamber, an uptake damper in fluid communication with the uptake duct, the uptake damper being positioned at any one of multiple positions including fully opened and fully closed, the uptake damper configured to control an oven draft, an actuator configured to alter the position of the uptake damper between the positions in response to a position instruction, a sensor configured to detect an operating condition of the coke oven, wherein the sensor includes one of a draft sensor configured to detect the oven draft, a temperature sensor configured to detect an uptake duct temperature or a sole flue temperature, and an oxygen sensor configured to detect an uptake duct oxygen concentration in the uptake duct, and a controller in communication with the actuator and with the sensor, the controller being configured to provide the position instruction to the actuator in response to the operating condition detected by the sensor. 
     Another embodiment of the invention relates to a method of operating a coke plant including the steps of operating multiple coke ovens to produce coke and exhaust gases, wherein each coke oven includes an uptake damper adapted to control an oven draft in the coke oven, directing the exhaust gases from each coke oven to a common tunnel, fluidly connecting multiple heat recovery steam generators to the common tunnel, operating all of the heat recovery steam generators and dividing the exhaust gases such that a portion of the exhaust gases flows to each of the heat recovery steam generators, and automatically controlling the uptake damper of each coke oven to maintain the oven draft of each coke oven at or above a targeted oven draft. 
     Another embodiment of the invention relates to a method of operating a coke plant including the steps of operating multiple coke ovens to produce coke and exhaust gases, wherein each coke oven includes an uptake damper adapted to control a flow of exhaust gases exiting the coke oven, directing the exhaust gases from each coke oven to a common tunnel, fluidly connecting multiple heat recovery steam generators to the common tunnel via multiple crossover ducts, wherein each heat recovery steam generator includes a heat recovery steam generator damper adapted to control a flow of exhaust gases through the heat recovery steam generator and wherein each crossover duct is connected to one of the heat recovery steam generators and connected to the common tunnel at an intersection, fluidly connecting a draft fan to the heat recovery steam generators, wherein the draft fan is located downstream of the heat recovery steam generators, operating all of the heat recovery steam generators and dividing the exhaust gases such that a portion of the exhaust gases flows to each of the heat recovery steam generators, exhausting the exhaust gases from the coke plant through a main stack, wherein the main stack is located downstream of the draft fan, detecting an operating condition downstream of the coke ovens with a sensor, and automatically controlling at least one of the uptake dampers, the heat recovery steam generator dampers, and the draft fan in response to the detected operating condition. 
     Another embodiment of the invention relates to a method of operating a coke oven including the steps of operating a coke oven to produce coke and exhaust gases, detecting an oven draft in the coke oven, adjusting a position of a first uptake damper fluidly connected to a first sole flue labyrinth and a position of a second uptake damper fluidly connected to a second sole flue labyrinth to maintain the detected oven draft at least at a targeted oven draft, detecting a first sole flue temperature in the first sole flue labyrinth, detecting a second sole flue temperature in the second sole flue labyrinth, comparing the first sole flue temperature to the second sole flue temperature, and biasing the position of the first uptake damper relative to the position of the second uptake damper in response to the comparison of the first sole flue temperature to the second sole flue temperature to maintain the first sole flue temperature and the second sole flue temperature within a specified temperature range. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic drawing of a horizontal heat recovery (HHR) coke plant, shown according to an exemplary embodiment. 
         FIG. 2  is a perspective view of portion of the HHR coke plant of  FIG. 1 , with several sections cut away. 
         FIG. 3  is a schematic drawing of a HHR coke plant, shown according to an exemplary embodiment. 
         FIG. 4  is a schematic drawing of a HHR coke plant, shown according to an exemplary embodiment. 
         FIG. 5  is a schematic drawing of a HHR coke plant, shown according to an exemplary embodiment. 
         FIG. 6  is a schematic drawing of a HHR coke plant, shown according to an exemplary embodiment. 
         FIG. 7  is a schematic view of a portion of the coke plant of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a HHR coke plant  100  is illustrated which produces coke from coal in a reducing environment. In general, the HHR coke plant  100  comprises at least one oven  105 , along with heat recovery steam generators (HRSGs)  120  and an air quality control system  130  (e.g., an exhaust or flue gas desulfurization (FGD) system) both of which are positioned fluidly downstream from the ovens and both of which are fluidly connected to the ovens by suitable ducts. The HHR coke plant  100  preferably includes a plurality of ovens  105  and a common tunnel  110  fluidly connecting each of the ovens  105  to a plurality of HRSGs  120 . One or more crossover ducts  115  fluidly connects the common tunnel  110  to the HRSGs  120 . A cooled gas duct  125  transports the cooled gas from the HRSG to the flue gas desulfurization (FGD) system  130 . Fluidly connected and further downstream are a baghouse  135  for collecting particulates, at least one draft fan  140  for controlling air pressure within the system, and a main gas stack  145  for exhausting cooled, treated exhaust to the environment. Steam lines  150  interconnect the HRSG and a cogeneration plant  155  so that the recovered heat can be utilized. As illustrated in  FIG. 1 , each “oven” shown represents ten actual ovens. 
     More structural detail of each oven  105  is shown in  FIG. 2  wherein various portions of four coke ovens  105  are illustrated with sections cut away for clarity. Each oven  105  comprises an open cavity preferably defined by a floor  160 , a front door  165  forming substantially the entirety of one side of the oven, a rear door  170  preferably opposite the front door  165  forming substantially the entirety of the side of the oven opposite the front door, two sidewalls  175  extending upwardly from the floor  160  intermediate the front  165  and rear  170  doors, and a crown  180  which forms the top surface of the open cavity of an oven chamber  185 . Controlling air flow and pressure inside the oven chamber  185  can be critical to the efficient operation of the coking cycle and therefore the front door  165  includes one or more primary air inlets  190  that allow primary combustion air into the oven chamber  185 . Each primary air inlet  190  includes a primary air damper  195  which can be positioned at any of a number of positions between fully open and fully closed to vary the amount of primary air flow into the oven chamber  185 . Alternatively, the one or more primary air inlets  190  are formed through the crown  180 . In operation, volatile gases emitted from the coal positioned inside the oven chamber  185  collect in the crown and are drawn downstream in the overall system into downcomer channels  200  formed in one or both sidewalls  175 . The downcomer channels fluidly connect the oven chamber  185  with a sole flue  205  positioned beneath the over floor  160 . The sole flue  205  forms a circuitous path beneath the oven floor  160 . Volatile gases emitted from the coal can be combusted in the sole flue  205  thereby generating heat to support the reduction of coal into coke. The downcomer channels  200  are fluidly connected to uptake channels  210  formed in one or both sidewalls  175 . A secondary air inlet  215  is provided between the sole flue  205  and atmosphere and the secondary air inlet  215  includes a secondary air damper  220  that can be positioned at any of a number of positions between fully open and fully closed to vary the amount of secondary air flow into the sole flue  205 . The uptake channels  210  are fluidly connected to the common tunnel  110  by one or more uptake ducts  225 . A tertiary air inlet  227  is provided between the uptake duct  225  and atmosphere. The tertiary air inlet  227  includes a tertiary air damper  229  which can be positioned at any of a number of positions between fully open and fully closed to vary the amount of tertiary air flow into the uptake duct  225 . 
     In order to provide the ability to control gas flow through the uptake ducts  225  and within ovens  105 , each uptake duct  225  also includes an uptake damper  230 . The uptake damper  230  can be positioned at number of positions between fully open and fully closed to vary the amount of oven draft in the oven  105 . As used herein, “draft” indicates a negative pressure relative to atmosphere. For example a draft of 0.1 inches of water indicates a pressure 0.1 inches of water below atmospheric pressure. Inches of water is a non-SI unit for pressure and is conventionally used to describe the draft at various locations in a coke plant. If a draft is increased or otherwise made larger, the pressure moves further below atmospheric pressure. If a draft is decreased, drops, or is otherwise made smaller or lower, the pressure moves towards atmospheric pressure. By controlling the oven draft with the uptake damper  230 , the air flow into the oven from the air inlets  190 ,  215 ,  227  as well as air leaks into the oven  105  can be controlled. Typically, an oven  105  includes two uptake ducts  225  and two uptake dampers  230 , but the use of two uptake ducts and two uptake dampers is not a necessity, a system can be designed to use just one or more than two uptake ducts and two uptake dampers. 
     In operation, coke is produced in the ovens  105  by first loading coal into the oven chamber  185 , heating the coal in an oxygen depleted environment, driving off the volatile fraction of coal and then oxidizing the volatiles within the oven  105  to capture and utilize the heat given off. The coal volatiles are oxidized within the ovens over a 48-hour coking cycle, and release heat to regeneratively drive the carbonization of the coal to coke. The coking cycle begins when the front door  165  is opened and coal is charged onto the oven floor  160 . The coal on the oven floor  160  is known as the coal bed. Heat from the oven (due to the previous coking cycle) starts the carbonization cycle. Preferably, no additional fuel other than that produced by the coking process is used. Roughly half of the total heat transfer to the coal bed is radiated down onto the top surface of the coal bed from the luminous flame and radiant oven crown  180 . The remaining half of the heat is transferred to the coal bed by conduction from the oven floor  160  which is convectively heated from the volatilization of gases in the sole flue  205 . In this way, a carbonization process “wave” of plastic flow of the coal particles and formation of high strength cohesive coke proceeds from both the top and bottom boundaries of the coal bed at the same rate, preferably meeting at the center of the coal bed after about 45-48 hours. 
     Accurately controlling the system pressure, oven pressure, flow of air into the ovens, flow of air into the system, and flow of gases within the system is important for a wide range of reasons including to ensure that the coal is fully coked, effectively extract all heat of combustion from the volatile gases, effectively controlling the level of oxygen within the oven chamber  185  and elsewhere in the coke plant  100 , controlling the particulates and other potential pollutants, and converting the latent heat in the exhaust gases to steam which can be harnessed for generation of steam and/or electricity. Preferably, each oven  105  is operated at negative pressure so air is drawn into the oven during the reduction process due to the pressure differential between the oven  105  and atmosphere. Primary air for combustion is added to the oven chamber  185  to partially oxidize the coal volatiles, but the amount of this primary air is preferably controlled so that only a portion of the volatiles released from the coal are combusted in the oven chamber  185  thereby releasing only a fraction of their enthalpy of combustion within the oven chamber  185 . The primary air is introduced into the oven chamber  185  above the coal bed through the primary air inlets  190  with the amount of primary air controlled by the primary air dampers  195 . The primary air dampers  195  can be used to maintain the desired operating temperature inside the oven chamber  185 . The partially combusted gases pass from the oven chamber  185  through the downcomer channels  200  into the sole flue  205  where secondary air is added to the partially combusted gases. The secondary air is introduced through the secondary air inlet  215  with the amount of secondary air controlled by the secondary air damper  220 . As the secondary air is introduced, the partially combusted gases are more fully combusted in the sole flue  205  extracting the remaining enthalpy of combustion which is conveyed through the oven floor  160  to add heat to the oven chamber  185 . The nearly fully combusted exhaust gases exit the sole flue  205  through the uptake channels  210  and then flow into the uptake duct  225 . Tertiary air is added to the exhaust gases via the tertiary air inlet  227  with the amount of tertiary air controlled by the tertiary air damper  229  so that any remaining fraction of uncombusted gases in the exhaust gases are oxidized downstream of the tertiary air inlet  227 . 
     At the end of the coking cycle, the coal has carbonized to produce coke. The coke is preferably removed from the oven:  105  through the rear door  170  utilizing a mechanical extraction system. Finally, the coke is quenched (e.g., wet or dry quenched) and sized before delivery to a user. 
     As shown in  FIG. 1 , a sample H.HR coke plant  100  includes a number of ovens  105  that are grouped into oven blocks  235 . The illustrated HHR coke plant  100  includes five oven blocks  235  of twenty ovens each, for a total of one hundred ovens. All of the ovens  105  are fluidly connected by at least one uptake duct  225  to the common tunnel  110  which is in turn fluidly connected to each HRSG  120  by a crossover duct  115 . Each oven block  235  is associated with a particular crossover duct  115 . Under normal operating conditions, the exhaust gases from each oven  105  in an oven block  235  flow through the common tunnel  110  to the crossover duct  115  associated with each respective oven block  235 . Half of the ovens in an oven block  235  are located on one side of an intersection  245  of the common tunnel  110  and a crossover duct  115  and the other half of the ovens in the oven block  235  are located on the other side of the intersection  245 . Under normal operating conditions there will be little or no net flow along the length of the common tunnel  110 ; instead, the exhaust gases from each oven block  235  will typically flow through the crossover duct  115  associated with that oven block  235  to the related HRSG  120 . 
     In the HRSG  120 , the latent heat from the exhaust gases expelled from the ovens  105  is recaptured and preferably used to generate steam. The steam produced in the HRSGs  120  is routed via steam lines  150  to the cogeneration plant  155 , where the steam is used to generate electricity. After the latent heat from the exhaust gases has been extracted and collected, the cooled exhaust gases exit the HRSG  0 . 120  and enter the cooled gas duct  125 . All of the HRSGs  120  are fluidly connected to the cooled gas duct  125 . With this structure, all of the components between the ovens  105  and the cooled gas duct  125  including the uptake ducts  225 , the common tunnel  110 , the crossover duct  115   s , and the HRSGs  120  form the hot exhaust system. The combined cooled exhaust gases from all of the HRSGs  120  flow to the FGD system  130 , where sulfur oxides (SOO are removed from the cooled exhaust gases the cooled, desulfurized exhaust gases flow from the FGD system  130  to the baghouse  135 , where particulates are removed, resulting in cleaned exhaust gases. The cleaned exhaust gases exit the baghouse  135  through the draft fan  140  and are dispersed to the atmosphere via the main gas stack  145 . The draft fan  140  creates the draft required to cause the described flow of exhaust gases and depending upon the size and operation of the system, one or more draft fans  140  can be used. Preferably, the draft fan  140  is an induced draft fan. The draft fan  140  can be controlled to vary the draft through the coke plant  100 . Alternatively, no draft fan  140  is included and the necessary draft is produced due to the size of the main gas stack  145 . 
     Under normal operating conditions, the entire system upstream of the draft fan  140  is maintained at a draft. Therefore, during operation, there is a slight bias of airflow from the ovens  105  through the entire system to the draft fan  140 . For emergency situations, a bypass exhaust stack  240  is provided for each oven block  235 . Each bypass exhaust stack  240  is located at an intersection  245  between the common tunnel  110  and a crossover duct  115 . Under emergency situations, hot exhaust gases emanating from the oven block  235  associated with a crossover duct  115  can be vented to atmosphere via the related bypass exhaust stack  240 . The release of hot exhaust gas through the bypass exhaust stack  240  is undesirable for many reasons including environmental concerns and energy consumption. Additionally, the output of the cogeneration plant  155  is reduced because the offline H.RSG  120  is not producing steam. 
     In a conventional HHR coke plant when a HRSG is offline due to scheduled maintenance, an unexpected emergency, or other reason, the exhaust gases from the associated oven block can be vented to atmosphere through the associated bypass exhaust stack because there is nowhere else for the exhaust gases to go due to gas flow limitations imposed by the common tunnel design and draft. If the exhaust gases were not vented to atmosphere through the bypass exhaust stack, they would cause undesired outcomes (e.g., positive pressure relative to atmosphere in an oven or ovens, damage to the offline HRSG) at other locations in the coke plant. 
     In the HHR coke plant  100  described herein, it is possible to avoid the undesirable loss of untreated exhaust gases to the environment by directing the hot exhaust gases that would normally flow to an offline HRSG to one or more of the online HRSGs  120 . In other words, it is possible to share the exhaust or flue gases of each oven block  235  along the common tunnel  110  and among multiple HRSGs  120  rather than a conventional coke plant where the vast majority of exhaust gases from an oven block flow to the single HRSG associated with that oven block. While some amount of exhaust gases may flow along the common tunnel of a conventional coke plant (e.g., from a first oven block to the HRSG associated with the adjacent oven block), a conventional coke plant cannot be operated to transfer all of the exhaust gases from an oven block associated with an offline HRSG to one or more online HRSGs. In other words, it is not possible in a conventional coke plant for all of the exhaust gases that would typically flow to a first offline HRSG to be transferred or gas shared along the common tunnel to one or more different online HRSGs. “Gas sharing” is possible by implementing an increased effective flow area of the common tunnel  110 , an increased draft in the common tunnel  110 , the addition of at least one redundant HR.SG  120 R, as compared to a conventional HHR coke plant, and by connecting all of the HRSGs  120  (standard and redundant) in parallel with each other. With gas sharing, it is possible to eliminate the undesirable expulsion of hot gases through the bypass exhaust stacks  240 . In an example of a conventional HHR coke plant, an oven block of twenty coke ovens and a single HRSG are fluidly connected via a first common tunnel, two oven blocks totaling forty coke ovens and two HRSGs are connected by a second common tunnel, and two oven blocks totaling forty coke ovens and two HRSGs are connected by a third common tunnel, but gas sharing of all of the exhaust gases along the second common tunnel and along the third common tunnel from an oven block associated with an offline HRSG to the remaining online HRSG is not possible. 
     Maintaining drafts having certain minimum levels or targets with the hot exhaust gas sharing system is necessary for effective gas sharing without adversely impacting the performance of the ovens  105 . The values recited for various draft targets are measured under normal steady-state operating conditions and do not include momentary, intermittent, or transient fluctuations in the draft at the specified location. Each oven  105  must maintain a draft (“oven draft”), that is, a negative pressure relative to atmosphere. Typically, the targeted oven draft is at least 0.1 inches of water. In some embodiments, the oven draft is measured in the oven chamber  185 . During gas sharing along the common tunnel  110 , the “intersection draft” at one or more of the intersections  245  between the common tunnel.  110  and the crossover ducts  115  and/or the “common tunnel draft” at one or more locations along the common tunnel  110  must be above a targeted draft (e.g., at least 0.7 inches of water) to ensure proper operation of the system. The common tunnel draft is measured upstream of the intersection draft (i.e., between an intersection  245  and the coke ovens  105 ) and is therefore typically lower than the intersection draft. In some embodiments the targeted intersection draft and/or the targeted common tunnel draft during gas sharing can be at least 1.0 inches of water and in other embodiments the targeted intersection draft and/or the targeted common tunnel draft during gas sharing can be at least 2.0 inches of water. Hot exhaust gas sharing eliminates the discharge of hot exhaust gases to atmosphere and increases the efficiency of the cogeneration plant  155 . It is important to note that a hot exhaust gas sharing HHR coke plant  100  as described herein can be newly constructed or an existing, conventional HHR coke plant can be retrofitted according to the innovations described herein. 
     In an exhaust gas sharing system in which one or more HRSG  120  is offline, the hot exhaust gases ordinarily sent to the offline: HRSGs  120  are not vented to atmosphere through the related bypass exhaust stack  240 , but are instead routed through the common tunnel  110  to one or more different HRSGs  120 . To accommodate the increased volume of gas flow through the common tunnel  110  during gas sharing, the effective flow area of the common tunnel  110  is greater than that of the common tunnel in a conventional HHR coke plant. This increased effective flow area can be achieved by increasing the inner diameter of the common tunnel  110  or by adding one or more additional common tunnels  110  to the hot exhaust system in parallel with the existing common tunnel  110  (as shown in  FIG. 3 ). In one embodiment, the single common tunnel  110  has an effective flow inner diameter of nine feet. In another embodiment, the single common tunnel  110  has an effective flow inner diameter of eleven feet. Alternatively, a dual common tunnel configuration, a multiple common tunnel configuration, or a hybrid dual/multiple tunnel configuration can be used. In a dual common tunnel configuration, the hot exhaust gasses from all of the ovens are directly distributed to two parallel, or almost parallel, common tunnels, which can be fluidly connected to each other at different points along the tunnels&#39; length. In a multiple common tunnel configuration, the hot exhaust gasses from all of the ovens are directly distributed to two or more parallel, or almost parallel common hot tunnels, which can be fluidly connected to each other at different points along the tunnels&#39; length. In a hybrid dual/multiple common tunnel, the hot exhaust gasses from all of the ovens are directly distributed to two or more parallel, or almost parallel, hot tunnels, which can be fluidly connected to each other at different points along the tunnels&#39; length. However, one, two, or more of the hot tunnels may not be a true common tunnel. For example, one or both of the hot tunnels may have partitions or be separated along the length of its run. 
     Hot exhaust gas sharing also requires that during gas sharing the common tunnel  110  be maintained at a higher draft than the common tunnel of a conventional HHR coke plant. In a conventional HHR coke plant, the intersection draft and the common tunnel draft are below 0.7 inches of water under normal steady-state operating conditions. A conventional HHR coke plant has never been operated such that the common tunnel operates at a high intersection draft or a high common tunnel draft (at or above 0.7 inches of water) because of concerns that the high intersection draft and the high common tunnel draft would result in excess air in the oven chambers. To allow for gas sharing along the common tunnel  110 , the intersection draft at one or more intersections  245  must be maintained at least at 0.7 inches of water. In some embodiments, the intersection draft at one or more intersections  245  is maintained at least at 1.0 inches of water or at least at 2.0 inches of water. Alternatively or additionally, to allow for gas sharing along the common tunnel  110 , the common tunnel draft at one or more locations along the common tunnel  110  must be maintained at least at 0.7 inches of water. In some embodiments, the common tunnel draft at one or more locations along the common tunnel  110  is maintained at least at 1.0 inches of water or at least at 2.0 inches of water. Maintaining such a high draft at one or more intersections  245  or at one or more locations along the common tunnel  110  ensures that the oven draft in all of the ovens  105  will be at least 0.1 inches of water when a single HSRG  120  is offline and provides sufficient draft for the exhaust gases from the oven block  235  associated with the offline HRSG  120  to flow to an online HSRG  120 . While in the gas sharing operating mode (i.e., when at least one HRSG  120  is offline), the draft along the common tunnel  110  and at the different intersections  245  will vary. For example, if the HRSG  120  closest to one end of the common tunnel  110  is offline, the common tunnel draft at the proximal end of the common tunnel  110  will be around 0.1 inches of water and the common tunnel draft at the opposite, distal end of the common tunnel  11 . 0  will be around 1.0 inches of water. Similarly, the intersection draft at the intersection  245  furthest from the offline HRSG  120  will be relatively high (i.e., at least 0.7 inches of water) and the intersection draft at the intersection  245  associated with the offline HRSG  120  will be relatively low (i.e., lower than the intersection draft at the previously-mentioned intersection  245  and typically below 0.7 inches of water). 
     Alternatively, the HHR coke plant  100  can be operated in two operating modes: a normal operating mode for when all of the HRSGs  120  are online and a gas sharing operating mode for when at least one of the HRSGs  120  is offline. In the normal operating mode, the common tunnel  110  is maintained at a common tunnel draft and intersection drafts similar to those of a conventional HHR coke plant (typically, the intersection draft is between 0.5 and 0.6 inches of water and the common tunnel draft at a location near the intersection is between 0.4 and 0.5 inches of water). The common tunnel draft and the intersection draft can vary during the normal operating mode and during the gas sharing mode. In most situations, when a HRSG  120  goes offline, the gas sharing mode begins and the intersection draft at one or more intersections  245  and/or the common tunnel draft at one or more locations along the common tunnel  110  is raised. In some situations, for example, when the HRSG  120  furthest from the redundant HRSG  120 R is offline, the gas sharing mode will begin and will require an intersection draft and/or a common tunnel draft of at least 0.7 inches of water (in some embodiments, between 1.2 and 1.3 inches of water) to allow for gas sharing along the common tunnel  110 . In other situations, for example, when a HRSG  120  positioned next to the redundant HRSG  120 R which is offline, the gas sharing mode may not be necessary, that is gas sharing may be possible in the normal operating mode with the same operating conditions prior to the HRSG  120  going offline, or the gas sharing mode will begin and will require only a slight increase in the intersection draft and/or a common tunnel draft. In general, the need to go to a higher draft in the gas sharing mode will depend on where the redundant HRSG  120 R is located relative to the offline HRSG  120 . The further away the redundant HRSG  1120 R fluidly is form the tripped HRSG  120 , the higher the likelihood that a higher draft will be needed in the gas sharing mode. 
     Increasing the effective flow area and the intersection draft and/or the common tunnel draft to the levels described above also allows for more ovens  105  to be added to an oven block  235 . In some embodiments, up to one hundred ovens form an oven block (i.e., are associated with a crossover duct). 
     The HR.SGs  120  found in a conventional HHR coke plant at a ratio of twenty ovens to one HRSG are referred to as the “standard HRSGs.” The addition of one or more redundant HRSGs  120 R results in an overall oven to HRSG ratio of less than 20:1. Under normal operating conditions, the standard HRSGs  120  and the redundant HRSG  120 R are all in operation. It is impractical to bring the redundant HRSG  120 R online and offline as needed because the start-up time for a HRSG would result in the redundant HRSG  120 R only being available on a scheduled basis and not for emergency purposes. An alternative to installing one or more redundant HRSGs would be to increase the capacity of the standard FIRSGs to accommodate the increased exhaust gas flow during gas sharing. Under normal operating conditions with all of the high capacity HRSGs online, the exhaust gases from each oven block are conveyed to the associated high capacity HRSGs. In the event that one of the high capacity HRSGs goes offline, the other high capacity HRSGs would be able to accommodate the increased flow of exhaust gases. 
     In a gas sharing system as described herein, when one of the HRSGs  120  is offline the exhaust gases emanating from the various ovens  105  are shared and distributed among the remaining online HRSGs  120  such that a portion of the total exhaust gases are routed through the common tunnel  110  to each of the online HRSGs  120  and no exhaust gas is vented to atmosphere. The exhaust gases are routed amongst the various HRSGs  120  by adjusting a HRSG valve  250  associated with each HRSG  120  (shown in  FIG. 1 ). The HRSG valve  250  can be positioned on the upstream or hot side of the HRSG  120 , but is preferably positioned on the downstream or cold side of the HRSG  120 . The HRSG valves  250  are variable to a number of positions between fully opened and fully closed and the flow of exhaust gases through the HRSGs  120  is controlled by adjusting the relative position of the HRSG valves  250 . When gas is shared, some or all of the operating HRSGs  120  will receive additional loads. Because of the resulting different flow distributions when a HRSG  120  is offline, the common tunnel draft along the common tunnel  110  will change. The common tunnel  110  helps to better distribute the flow among the HRSGs  120  to minimize the pressure differences throughout the common tunnel  110 . The common tunnel  110  is sized to help minimize peak flow velocities (e.g., below 120 ft/s) and to reduce potential erosion and acoustic concerns (e.g., noise levels below 85 dB at 3 ft). When an HRSG  120  is offline, there can be higher than normal peak mass flow rates in the common tunnel, depending on which HRSG  120  is offline. During such gas sharing periods, the common tunnel draft may need to be increased to maintain the targeted oven drafts, intersection drafts, and common tunnel draft. 
     In general, a larger common tunnel  110  can correlate to larger allowable mass flow rates relative to a conventional common tunnel for the same given desired pressure difference along the length of the common tunnel  110 . The converse is also true, the larger common tunnel  110  can correlate to smaller pressure differences relative to a conventional common tunnel for the same given desired mass flow rate along the length of the common tunnel  110 . Larger means larger effective flow area and not necessarily larger geometric cross sectional area. Higher common tunnel drafts can accommodate larger mass flow rates through the common tunnel  110 . In general, higher temperatures can correlate to lower allowable mass flow rates for the same given desired pressure difference along the length of the tunnel. Higher exhaust gas temperatures should result in volumetric expansion of the gases. Since the total pressure losses can be approximately proportional to density and proportional to the square of the velocity, the total pressure losses can be higher for volumetric expansion because of higher temperatures. For example, an increase in temperature can result in a proportional decrease in density. However, an increase in temperature can result in an accompanying proportional increase in velocity which affects the total pressure losses more severely than the decrease in density. Since the effect of velocity on total pressure can be more of a squared effect while the density effect can be more of a linear one, there should be losses in total pressure associated with an increase in temperature for the flow in the common tunnel  110 . Multiple, parallel, fluidly connected common tunnels (dual, multiple, or hybrid dual/multiple configurations) may be preferred for retrofitting existing conventional HHR coke plants into the gas sharing HHR coke plants described herein. 
     Although the sample gas-sharing HHR coke plant  100  illustrated in  FIG. 1  includes one hundred ovens and six HRSGs (five standard HRSGs and one redundant HRSG), other configurations of gas-sharing HHR coke plants  100  are possible. For example, a gas-sharing HHR coke plant similar to the one illustrated in  FIG. 1  could include one hundred ovens, and seven HRSGs (five standard HRSGs sized to handle the exhaust gases from up to twenty ovens and two redundant HRSGs sized to handle the exhaust gases from up to ten ovens (i.e., smaller capacity than the single redundant HRSG used in the coke plant  100  illustrated in  FIG. 1 )). 
     As shown in  FIG. 3 , in HHR coke plant  255 , an existing conventional HHR coke plant has been retrofitted to a gas-sharing coke plant. Existing partial common tunnels  110 A,  110 B, and  110 C each connect a bank of forty ovens  105 . An additional common tunnel  260  fluidly connected to all of the ovens  105  has been added to the existing partial common tunnels  110 A,  110 B, and  110 C. The additional common tunnel  260  is connected to each of the crossover ducts  115  extending between the existing partial common tunnels  110 A,  110 B, and  110 C and the standard HRSGs  120 . The redundant HRSG  120 R is connected to the additional common tunnel  260  by a crossover duct  265  extending to the additional common tunnel  260 . To allow for gas sharing, the intersection draft at one or more intersections  245  between the existing partial common tunnels  11 . 0 A,  110 B,  110 C and the crossover ducts  115  and/or the common tunnel draft at one or more location along each of the partial common tunnels  110 A,  110 B,  110 C must be maintained at least at 0.7 inches of water. The draft at one or more of the intersections  270  between the additional common tunnel  260  and the crossover ducts  115  and  265  will be higher than 0.7 inches of water (e.g., 1.5 inches of water). In some embodiments, the inner effective flow diameter of the additional common tunnel  260  can be as small as eight feet or as large as eleven feet. In one embodiment, the inner effective flow diameter of the additional common tunnel  260  is nine feet. Alternatively, as a further retrofit, the partial common tunnels  110 A,  110 B, and  110 C are fluidly connected to one another, effectively creating two common tunnels (i.e., the combination of common tunnels  110 A,  110 B, and HOC and the additional common tunnel  260 ). 
     As shown in  FIG. 4 , in HHR coke plant  275 , a single crossover duct  115  fluidly connects three high capacity HRSGs  120  to two partial common tunnels  110 A and  110 B. The single crossover duct  115  essentially functions as a header for the HRSGs  120 . The first partial common tunnel  110 A services an oven block of sixty ovens  105  with thirty ovens  105  on one side of the intersection  245  between the partial common tunnel  110 A and the crossover duct  115  and thirty ovens  105  on the opposite side of the intersection  245 . The ovens  105  serviced by the second partial common tunnel  110 B are similarly arranged. The three high capacity HRSGs are sized so that only two HRSGs are needed to handle the exhaust gases from all one hundred twenty ovens  105 , enabling one HRSG to be taken offline without having to vent exhaust gases through a bypass exhaust stack  240 . The HHR coke plant  275  can be viewed as having one hundred twenty ovens and three HRSGs (two standard HRSGs and one redundant HRSG) for an oven to standard HRSG ratio of 60:1. Alternatively, as shown in  FIG. 5 , in the HHR coke plant  280 , a redundant HRSG  120 R is added to six standard HRSGs  120  instead of using the three high capacity HRSGs  120  shown in  FIG. 4 . The HHR coke plant  280  can be viewed as having one hundred twenty ovens and seven HRSGs (six standard HRSGs and one redundant HRSG) for an oven to standard HRSG ratio of 20:1). In some embodiments, coke plants  275  and  280  are operated at least during periods of maximum mass flow rates through the intersections  245  to maintain a target intersection draft at one or more of the intersections  245  and/or a target common tunnel draft at one or more locations along each of the common tunnels  110 A and  110 B of at least 0.7 inches of water. In one embodiment, the target intersection draft at one or more of the intersections  245  and/or the target common tunnel draft at one or more locations along each of the common tunnels  110 A and  110 B is 0.8 inches of water. In another embodiment, the target intersection draft at one or more of the intersections  245  and/or the common tunnel draft at one or more locations along each of the common tunnels  110 A and  110 B is 1.0 inches of water. In other embodiments, the target intersection draft at one or more of the intersections  245  and/or the target common tunnel draft at one or more locations along each of the common tunnels  110 A and  110 B is greater than 1.0 inches of water and can be 2.0 inches of water or higher. 
     As shown in  FIG. 6 , in HHR coke plant  285 , a first crossover duct  290  connects a first partial common tunnel  110 A to three high capacity HRSGs  120  arranged in parallel and a second crossover duct  295  connects a second partial common tunnel  110 B to the three high capacity HRSGs  120 . The first partial common tunnel  110 A services an oven block of sixty ovens  105  with thirty ovens  105  on one side of the intersection  245  between the first partial common tunnel  110 A and the first crossover duct  290  and thirty ovens  105  on the opposite side of the intersection  245 . The second partial common tunnel  110 B services an oven block of sixty ovens  105  with thirty ovens  105  on one side of the intersection  245  between the second common tunnel HOB and the second crossover duct  295  and thirty ovens  105  on the opposite side of the intersection  245 . The three high capacity HRSGs are sized so that only two HRSGs are needed to handle the exhaust gases from all one hundred twenty ovens  105 , enabling one HRSG to be taken offline without having to vent exhaust gases through a bypass exhaust stack  240 . The HHR coke plant  285  can be viewed as having one hundred twenty ovens and three HRSGs (two standard HRSGs and one redundant HRSG) for an oven to standard HRSG ratio of 60:1 In some embodiments, coke plant  285  is operated at least during periods of maximum mass flow rates through the intersections  245  to maintain a target intersection draft at one or more of the intersections  245  and/or a target common tunnel draft at one or more locations along each of the common tunnels  110 A and  110 B of at least 0.7 inches of water. In one embodiment, the target intersection draft at one or more of the intersections  245  and/or the target common tunnel draft at one or more locations along each of the common tunnels  110 A and  110 B is 0.8 inches of water. In another embodiment, the target intersection draft at one or more of the intersections  245  and/or the common tunnel draft at one or more locations along each of the common tunnels  110 A and  110 B is 1.0 inches of water. In other embodiments, the target intersection draft at one or more of the intersections  245  and/or the target common tunnel draft at one or more locations along each of the common tunnels  110 A and  110 B is greater than 1.0 inches of water and can be 2.0 inches of water or higher. 
       FIG. 7  illustrates a portion of the coke plant  100  including an automatic draft control system  300 . The automatic draft control system  300  includes an automatic uptake damper  305  that can be positioned at any one of a number of positions between fully open and fully closed to vary the amount of oven draft in the oven  105 . The automatic uptake damper  305  is controlled in response to operating conditions (e.g., pressure or draft, temperature, oxygen concentration, gas flow rate) detected by at least one sensor. The automatic control system  300  can include one or more of the sensors discussed below or other sensors configured to detect operating conditions relevant to the operation of the coke plant  100 . 
     An oven draft sensor or oven pressure sensor  310  detects a pressure that is indicative of the oven draft and the oven draft sensor  310  can be located in the oven crown  180  or elsewhere in the oven chamber  185 . Alternatively, the oven draft sensor  310  can be located at either of the automatic uptake dampers  305 , in the sole flue  205 , at either oven door  165  or  170 , or in the common tunnel  110  near above the coke oven  105 . In one embodiment, the oven draft sensor  310  is located in the top of the oven crown  180 . The oven draft sensor  310  can be located flush with the refractory brick lining of the oven crown  180  or could extend into the oven chamber  185  from the oven crown  180 . A bypass exhaust stack draft sensor  315  detects a pressure that is indicative of the draft at the bypass exhaust stack  240  (e.g., at the base of the bypass exhaust stack  240 ). In some embodiments, the bypass exhaust stack draft sensor  315  is located at the intersection  245 . Additional draft sensors can be positioned at other locations in the coke plant  100 . For example, a draft sensor in the common tunnel could be used to detect a common tunnel draft indicative of the oven draft in multiple ovens proximate the draft sensor. An intersection draft sensor  317  detects a pressure that is indicative of the draft at one of the intersections  245 . 
     An oven temperature sensor  320  detects the oven temperature and can be located in the oven crown  180  or elsewhere in the oven chamber  185 . A sole flue temperature sensor  325  detects the sole flue temperature and is located in the sole flue  205 . In some embodiments, the sole flue  205  is divided into two labyrinths  205 A and  205 B with each labyrinth in fluid communication with one of the oven&#39;s two uptake ducts  225 . A flue temperature sensor  325  is located in each of the sole flue labyrinths so that the sole flue temperature can be detected in each labyrinth. An uptake duct temperature sensor  330  detects the uptake duct temperature and is located in the uptake duct  225 . A common tunnel temperature sensor  335  detects the common tunnel temperature and is located in the common tunnel  110 . A HRSG inlet temperature sensor  340  detects the HR.SG inlet temperature and is located at or near the inlet of the HRSG  120 . Additional temperature sensors can be positioned at other locations in the coke plant  100 . 
     An uptake duct oxygen sensor  345  is positioned to detect the oxygen concentration of the exhaust gases in the uptake duct  225 . An HRSG inlet oxygen sensor  350  is positioned to detect the oxygen concentration of the exhaust gases at the inlet of the HRSG  120 . A main stack oxygen sensor  360  is positioned to detect the oxygen concentration of the exhaust gases in the main stack  145  and additional oxygen sensors can be positioned at other locations in the coke plant  100  to provide information on the relative oxygen concentration at various locations in the system. 
     A flow sensor detects the gas flow rate of the exhaust gases. For example, a flow sensor can be located downstream of each of the HRSGs  120  to detect the flow rate of the exhaust gases exiting each HRSG  120 . This information can be used to balance the flow of exhaust gases through each HRSG  120  by adjusting the HRSG dampers  250  and thereby optimize gas sharing among the HRSGs  120 . Additional flow sensors can be positioned at other locations in the coke plant  100  to provide information on the gas flow rate at various locations in the system. 
     Additionally, one or more draft or pressure sensors, temperature sensors, oxygen sensors, flow sensors, and/or other sensors may be used at the air quality control system  130  or other locations downstream of the HRSGs  120 . 
     It can be important to keep the sensors clean. One method of keeping a sensor clean is to periodically remove the sensor and manually clean it. Alternatively, the sensor can be periodically subjected to a burst, blast, or flow of a high pressure gas to remove build up at the sensor. As a further alternatively, a small continuous gas flow can be provided to continually clean the sensor. 
     The automatic uptake damper  305  includes the uptake damper  230  and an actuator  365  configured to open and close the uptake damper  230 . For example, the actuator  365  can be a linear actuator or a rotational actuator. The actuator  365  allows the uptake damper  230  to be infinitely controlled between the fully open and the fully closed positions. The actuator  365  moves the uptake damper  230  amongst these positions in response to the operating condition or operating conditions detected by the sensor or sensors included in the automatic draft control system  300 . This provides much greater control than a conventional uptake damper. A conventional uptake damper has a limited number of fixed positions between fully open and fully closed and must be manually adjusted amongst these positions by an operator. 
     The uptake dampers  230  are periodically adjusted to maintain the appropriate oven draft (e.g., at least 0.1 inches of water) which changes in response to many different factors within the ovens or the hot exhaust system. When the common tunnel  110  has a relatively low common tunnel draft (i.e., closer to atmospheric pressure than a relatively high draft), the uptake damper  230  can be opened to increase the oven draft to ensure the oven draft remains at or above 0.1 inches of water. When the common tunnel  110  has a relatively high common tunnel draft, the uptake damper  230  can be closed to decrease the oven draft, thereby reducing the amount of air drawn into the oven chamber  185 . 
     With conventional uptake dampers, the uptake dampers are manually adjusted and therefore optimizing the oven draft is part art and part science, a product of operator experience and awareness. The automatic draft control system  300  described herein automates control of the uptake dampers  230  and allows for continuous optimization of the position of the uptake dampers  230  thereby replacing at least some of the necessary operator experience and awareness. The automatic draft control system  300  can be used to maintain an oven draft at a targeted oven draft (e.g., at least 0.1 inches of water), control the amount of excess air in the oven  105 , or achieve other desirable effects by automatically adjusting the position of the uptake damper  230 . The automatic draft control system  300  makes it easier to achieve the gas sharing described above by allowing for a high intersection draft at one or more of the intersections  245  and/or a high common tunnel draft at one or more locations along the common tunnel  110  while maintaining oven drafts low enough to prevent excess air leaks into the ovens  105 . Without automatic control, it would be difficult if not impossible to manually adjust the uptake dampers  230  as frequently as would be required to maintain the oven draft of at least 0.1 inches of water without allowing the pressure in the oven to drift to positive. Typically, with manual control, the target oven draft is greater than 0.1 inches of water, which leads to more air leakage into the coke oven  105 . For a conventional uptake damper, an operator monitors various oven temperatures and visually observes the coking process in the coke oven to determine when to and how much to adjust the uptake damper. The operator has no specific information about the draft (pressure) within the coke oven. 
     The actuator  365  positions the uptake damper  230  based on position instructions received from a controller  370 . The position instructions can be generated in response to the draft, temperature, oxygen concentration, or gas flow rate detected by one or more of the sensors discussed above, control algorithms that include one or more sensor inputs, or other control algorithms. The controller  370  can be a discrete controller associated with a single automatic uptake damper  305  or multiple automatic uptake dampers  305 , a centralized controller (e.g., a distributed control system or a programmable logic control system), or a combination of the two. In some embodiments, the controller  370  utilizes proportional-integral-derivative (“PID”) control. 
     The automatic draft control system  300  can, for example, control the automatic uptake damper  305  of an oven  105  in response to the oven draft detected by the oven draft sensor  310 . The oven draft sensor  310  detects the oven draft and outputs a signal indicative of the oven draft to the controller  370 . The controller  370  generates a position instruction in response to this sensor input and the actuator  365  moves the uptake damper  230  to the position required by the position instruction. In this way, the automatic control system  300  can be used to maintain a targeted oven draft (e.g., at least 0.1 inches of water). Similarly, the automatic draft control system  300  can control the automatic uptake dampers  305 , the HRSG dampers  250 , and the draft fan  140 , as needed, to maintain targeted drafts at other locations within the coke plant  100  (e.g., a targeted intersection draft or a targeted common tunnel draft). For example, for gas sharing as described above, the intersection draft at one or more intersections  245  and/or the common tunnel draft at one or more locations along the common tunnel  110  needs to be maintained at least at 0.7 inches of water. The automatic draft control system  300  can be placed into a manual mode to allow for manual adjustment of the automatic uptake dampers  305 , the HRSG dampers, and/or the draft fan  140 , as needed. Preferably, the automatic draft control system  300  includes a manual mode timer and upon expiration of the manual mode timer, the automatic draft control system  300  returns to automatic mode. 
     In some embodiments, the signal generated by the oven draft sensor  310  that is indicative of the detected pressure or draft is time averaged to achieve a stable pressure control in the coke oven  105 . The time averaging of the signal can be accomplished by the controller  370 . Time averaging the pressure signal helps to filter out normal fluctuations in the pressure signal and to filter out noise. Typically, the signal could be averaged over 30 seconds, I minute, 5 minutes, or over at least 10 minutes. In one embodiment, a rolling time average of the pressure signal is generated by taking 200 scans of the detected pressure at 50 milliseconds per scan. The larger the difference in the time-averaged pressure signal and the target oven draft, the automatic draft control system  300  enacts a larger change in the damper position to achieve the desired target draft. In some embodiments, the position instructions provided by the controller  370  to the automatic uptake damper  305  are linearly proportional to the difference in the time-averaged pressure signal and the target oven draft. In other embodiments, the position instructions provided by the controller  370  to the automatic uptake damper  305  are non-linearly proportional to the difference in the time-averaged pressure signal and the target oven draft. The other sensors previously discussed can similarly have time-averaged signals. 
     The automatic draft control system  300  can be operated to maintain a constant time-averaged oven draft within a specific tolerance of the target oven draft throughout the coking cycle. This tolerance can be, for example, +/−0.05 inches of water, +/−0.02 inches of water, or +/−0.01 inches of water. 
     The automatic draft control system  300  can also be operated to create a variable draft at the coke oven by adjusting the target oven draft over the course of the coking cycle. The target oven draft can be stepwise reduced as a function of the elapsed time of the coking cycle. In this manner, using a 48-hour coking cycle as an example, the target draft starts out relatively high (e.g., 0.2 inches of water) and is reduced every 12 hours by 0.05 inches of water so that the target oven draft is 0.2 inches of water for hours 1-12 of the coking cycle, 0.15 inches of water for hours 12-24 of the coking cycle, 0.01 inches of water for hours 24-36 of the coking cycle, and 0.05 inches of water for hours 36-48 of the coking cycle. Alternatively, the target draft can be linearly decreased throughout the coking cycle to a new, smaller value proportional to the elapsed time of the coking cycle. 
     As an example, if the oven draft of an oven  105  drops below the targeted oven draft (e.g., 0.1 inches of water) and the uptake damper  230  is fully open, the automatic draft control system  300  would increase the draft by opening at least one HRSG damper  250  to increase the oven draft. Because this increase in draft downstream of the oven  105  affects more than one oven  105 , some ovens  105  might need to have their uptake dampers  230  adjusted (e.g., moved towards the fully closed position) to maintain the targeted oven draft (i.e., regulate the oven draft to prevent it from becoming too high). If the IMSG damper  250  was already fully open, the automatic damper control system  300  would need to have the draft fan  140  provide a larger draft. This increased draft downstream of all the HRSGs  120  would affect all the HRSG  120  and might require adjustment of the HRSG dampers  250  and the uptake dampers  230  to maintain target drafts throughout the coke plant  100 . 
     As another example, the common tunnel draft can be minimized by requiring that at least one uptake damper  230  is fully open and that all the ovens  105  are at least at the targeted oven draft (e.g., 0.1 inches of water) with the HRSG dampers  250  and/or the draft fan  140  adjusted as needed to maintain these operating requirements. 
     As another example, the coke plant  100  can be run at variable draft for the intersection draft and/or the common tunnel draft to stabilize the air leakage rate, the mass flow, and the temperature and composition of the exhaust gases (e.g., oxygen levels), among other desirable benefits. This is accomplished by varying the intersection draft and/or the common tunnel draft from a relatively high draft (e.g., 0.8 inches of water) when the coke ovens  105  are pushed and reducing gradually to a relatively low draft (e.g., 0.4 inches of water), that is, running at relatively high draft in the early part of the coking cycle and at relatively low draft in the late part of the coking cycle. The draft can be varied continuously or in a step-wise fashion. 
     As another example, if the common tunnel draft decreases too much, the HRSG damper  250  would open to raise the common tunnel draft to meet the target common tunnel draft at one or more locations along the common tunnel  110  (e.g., 0.7 inches water) to allow gas sharing. After increasing the common tunnel draft by adjusting the HRSG damper  250 , the uptake dampers  230  in the affected ovens  105  might be adjusted (e.g., moved towards the fully closed position) to maintain the targeted oven draft in the affected ovens  105  (i.e., regulate the oven draft to prevent it from becoming too high). 
     As another example, the automatic draft control system  300  can control the automatic uptake damper  305  of an oven  105  in response to the oven temperature detected by the oven temperature sensor  320  and/or the sole flue temperature detected by the sole flue temperature sensor or sensors  325 . Adjusting the automatic uptake damper  305  in response to the oven temperature and or the sole flue temperature can optimize coke production or other desirable outcomes based on specified oven temperatures. When the sole flue  205  includes two labyrinths  205 A and  205 B, the temperature balance between the two labyrinths  205 A and  205 B can be controlled by the automatic draft control system  300 . The automatic uptake damper  305  for each of the oven&#39;s two uptake ducts  225  is controlled in response to the sole flue temperature detected by the sole flue temperature sensor  325  located in labyrinth  205 A or  205 B associated with that uptake duct  225 . The controller  370  compares the sole flue temperature detected in each of the labyrinths  205 A and  205 B and generates positional instructions for each of the two automatic uptake dampers  305  so that the sole flue temperature in each of the labyrinths  205 A and  205 B remains within a specified temperature range. 
     In some embodiments, the two automatic uptake dampers  305  are moved together to the same positions or synchronized. The automatic uptake damper  305  closest to the front door  165  is known as the “push-side” damper and the automatic uptake damper closet to the rear door  170  is known as the “coke-side” damper. In this manner, a single oven draft pressure sensor  310  provides signals and is used to adjust both the push- and coke-side automatic uptake dampers  305  identically. For example, if the position instruction from the controller to the automatic uptake dampers  305  is at 60% open, both push- and coke-side automatic uptake dampers  305  are positioned at 60% open. If the position instruction from the controller to the automatic uptake dampers  305  is 8 inches open, both push- and coke-side automatic uptake dampers  305  are 8 inches open. Alternatively, the two automatic uptake dampers  305  are moved to different positions to create a bias. For example, for a bias of 1 inch, if the position instruction for synchronized automatic uptake dampers  305  would be 8 inches open, for biased automatic uptake dampers  305 , one of the automatic uptake dampers  305  would be 9 inches open and the other automatic uptake damper  305  would be 7 inches open. The total open area and pressure drop across the biased automatic uptake dampers  305  remains constant when compared to the synchronized automatic uptake dampers  305 . The automatic uptake dampers  305  can be operated in synchronized or biased manners as needed. The bias can be used to try to maintain equal temperatures in the push-side and the coke-side of the coke oven  105 . For example, the sole flue temperatures measured in each of the sole flue labyrinths  205 A and  205 B (one on the coke-side and the other on the push-side) can be measured and then corresponding automatic uptake damper  305  can be adjusted to achieve the target oven draft, while simultaneously using the difference in the coke- and push-side sole flue temperatures to introduce a bias proportional to the difference in sole flue temperatures between the coke-side sole flue and push-side sole flue temperatures. In this way, the push- and coke-side sole flue temperatures can be made to be equal within a certain tolerance. The tolerance (difference between coke- and push-side sole flue temperatures) can be 250° Fahrenheit, 1000 Fahrenheit, 50° Fahrenheit, or, preferably 250 Fahrenheit or smaller. Using state-of-the-art control methodologies and techniques, the coke-side sole flue and the push-side sole flue temperatures can be brought within the tolerance value of each other over the course of one or more hours (e.g., 1-3 hours), while simultaneously controlling the oven draft to the target oven draft within a specified tolerance (e.g., +1-0.01 inches of water). Biasing the automatic uptake dampers  305  based on the sole flue temperatures measured in each of the sole flue labyrinths  205 A and  205 B, allows heat to be transferred between the push side and coke side of the coke oven  105 . Typically, because the push side and the coke side of the coke bed coke at different rates, there is a need to move heat from the push side to the coke side. Also, biasing the automatic uptake dampers  305  based on the sole flue temperatures measured in each of the sole flue labyrinths  205 A and  205 B, helps to maintain the oven floor at a relatively even temperature across the entire floor. 
     The oven temperature sensor  320 , the sole flue temperature sensor  325 , the uptake duct temperature sensor  330 , the common tunnel temperature sensor  335 , and the HRSG inlet temperature sensor  340  can be used to detect overheat conditions at each of their respective locations. These detected temperatures can generate position instructions to allow excess air into one or more ovens  105  by opening one or more automatic uptake dampers  305 . Excess air (i.e., where the oxygen present is above the stoichiometric ratio for combustion) results in uncombusted oxygen and uncombusted nitrogen in the oven  105  and in the exhaust gases. This excess air has a lower temperature than the other exhaust gases and provides a cooling effect that eliminates overheat conditions elsewhere in the coke plant  100 . 
     As another example, the automatic draft control system  300  can control the automatic uptake damper  305  of an oven  105  in response to uptake duct oxygen concentration detected by the uptake duct oxygen sensor  345 . Adjusting the automatic uptake damper  305  in response to the uptake duct oxygen concentration can be done to ensure that the exhaust gases exiting the oven  105  are fully combusted and/or that the exhaust gases exiting the oven  105  do not contain too much excess air or oxygen. Similarly, the automatic uptake damper  305  can be adjusted in response to the HRSG inlet oxygen concentration detected by the HRSG inlet oxygen sensor  350  to keep the HRSG inlet oxygen concentration above a threshold concentration that protects the HRSG  120  from unwanted combustion of the exhaust gases occurring at the HRSG  120 . The HRSG inlet oxygen sensor  350  detects a minimum oxygen concentration to ensure that all of the combustibles have combusted before entering the HRSG  120 . Also, the automatic uptake damper  305  can be adjusted in response to the main stack oxygen concentration detected by the main stack oxygen sensor  360  to reduce the effect of air leaks into the coke plant  100 . Such air leaks can be detected based on the oxygen concentration in the main stack  145 . 
     The automatic draft control system  300  can also control the automatic uptake dampers  305  based on elapsed time within the coking cycle. This allows for automatic control without having to install an oven draft sensor  310  or other sensor in each oven  105 . For example, the position instructions for the automatic uptake dampers  305  could be based on historical actuator position data or damper position data from previous coking cycles for one or more coke ovens  105  such that the automatic uptake damper  305  is controlled based on the historical positioning data in relation to the elapsed time in the current coking cycle. 
     The automatic draft control system  300  can also control the automatic uptake dampers  305  in response to sensor inputs from one or more of the sensors discussed above. Inferential control allows each coke oven  105  to be controlled based on anticipated changes in the oven&#39;s or coke plant&#39;s operating conditions (e.g., draft/pressure, temperature, oxygen concentration at various locations in the oven  105  or the coke plant  100 ) rather than reacting to the actual detected operating condition or conditions. For example, using inferential control, a change in the detected oven draft that shows that the oven draft is dropping towards the targeted oven draft (e.g., at least 0.1 inches of water) based on multiple readings from the oven draft sensor  310  over a period of time, can be used to anticipate a predicted oven draft below the targeted oven draft to anticipate the actual oven draft dropping below the targeted oven draft and generate a position instruction based on the predicted oven draft to change the position of the automatic uptake damper  305  in response to the anticipated oven draft, rather than waiting for the actual oven draft to drop below the targeted oven draft before generating the position instruction. Inferential control can be used to take into account the interplay between the various operating conditions at various locations in the coke plant  100 . For example, inferential control taking into account a requirement to always keep the oven under negative pressure, controlling to the required optimal oven temperature, sole flue temperature, and maximum common tunnel temperature while minimizing the oven draft is used to position the automatic uptake damper  305 . Inferential control allows the controller  370  to make predictions based on known coking cycle characteristics and the operating condition inputs provided by the various sensors described above. Another example of inferential control allows the automatic uptake dampers  305  of each oven  105  to be adjusted to maximize a control algorithm that results in an optimal balance among coke yield, coke quality, and power generation. Alternatively, the uptake dampers  305  could be adjusted to maximize one of coke yield, coke quality, and power generation. 
     Alternatively, similar automatic draft control systems could be used to automate the primary air dampers  195 , the secondary air dampers  220 , and/or the tertiary air dampers  229  in order to control the rate and location of combustion at various locations within an oven  105 . For example, air could be added via an automatic secondary air damper in response to one or more of draft, temperature, and oxygen concentration detected by an appropriate sensor positioned in the sole flue  205  or appropriate sensors positioned in each of the sole flue labyrinths  205 A and  205 B. 
     As utilized herein, the terms “approximately,” “about,” “substantially,” and similar terms are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. It should be understood by those of skill in the art who review this disclosure that these terms are intended to allow a description of certain features described and claimed without restricting the scope of these features to the precise numerical ranges provided. Accordingly, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations of the subject matter described and are considered to be within the scope of the disclosure. 
     It should be noted that the term “exemplary” as used herein to describe various embodiments is intended to indicate that such embodiments are possible examples, representations, and/or illustrations of possible embodiments (and such term is not intended to connote that such embodiments are necessarily extraordinary or superlative examples). 
     It should be noted that the orientation of various elements may differ according to other exemplary embodiments, and that such variations are intended to be encompassed by the present disclosure. 
     It is also important to note that the constructions and arrangements of the apparatus, systems, and methods as described and shown in the various exemplary embodiments are illustrative only. Although only a few embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. For example, elements shown as integrally formed may be constructed of multiple parts or elements, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes and omissions may also be made in the design, operating conditions and arrangement of the various exemplary embodiments without departing from the scope of the present disclosure. 
     The present disclosure contemplates methods, systems and program products on any machine-readable media for accomplishing various operations. The embodiments of the present disclosure may be implemented using existing computer processors, or by a special purpose computer processor for an appropriate system, incorporated for this or another purpose, or by a hardwired system. Embodiments within the scope of the present disclosure include program products comprising machine-readable media for carrying or having machine-executable instructions or data structures stored thereon. Such machine-readable media can be any available media that can be accessed by a general purpose or special purpose computer or other machine with a processor. By way of example, such machine-readable media can comprise RAM, ROM, EPROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to carry or store desired program code in the form of machine-executable instructions or data structures and which can be accessed by a general purpose or special purpose computer or other machine with a processor. When information is transferred or provided over a network or another communications connection (either hardwired, wireless, or a combination of hardwired or wireless) to a machine, the machine properly views the connection as a machine-readable medium. Thus, any such connection is properly termed a machine-readable medium. Combinations of the above are also included within the scope of machine-readable media. Machine-executable instructions include, for example, instructions and data which cause a general purpose computer, special purpose computer, or special purpose processing machines to perform a certain function or group of functions.