Patent Application
20160319198
The present technology is generally directed to integrated control of coke ovens in a coke plant in order to optimize coking rate, product recovery, byproducts and/or unit lime consumption.
Iron and steel are vital parts of the global economy. The World Steel Association reported that 1.1 billion tons of raw iron was produced globally by blast furnaces in 2013. This process uses coke and iron ore as its main raw materials. Coke is a solid carbon fuel and carbon source used to melt and reduce iron ore in the production of steel. Coke is produced by exposing properly selected and prepared blend of bituminous coals to the high temperatures of a coke oven for an adequate period of time in the absence of air. During the entire conversion, volatile gases, vapors and tars are being expelled from the charge. As the temperatures of the charge increases in the reducing coke oven atmosphere, the coking coals pass through a plastic or softening stage, gasses and tars are evolved, coal particles swell and shrink and then bond or adhere together re-solidifying into a semi coke and finally a coke at about 1830 degrees Fahrenheit. Coking coals are unique with respect to this unusual behavior when heated. The coals are solid when charged, become fluid to varying degrees, then with further increase in temperature, become the solid, hard porous substance, known as coke. Coke is porous black to silver gray substance. It is high in carbon content, low in non-carbon impurities such as sulfur and ash. Physically, the coke produced is strong, resistant to abrasion, and sized to span a narrow size range.
The melting and fusion process undergone by the coal particles during the heating process is an important part of coking. The degree of melting and degree of assimilation of the coal particles into the molten mass determine the characteristics of the coke produced. In order to produce the strongest coke from a particular coal or coal blend, there is an optimum ratio of reactive to inert entities in the coal. The porosity and strength of the coke are important for the ore refining process and are determined by the coal source and/or method of coking.
Coal particles or a blend of coal particles are charged into hot ovens, and the coal is heated in the ovens in order to remove volatile matter (“VM”) from the resulting coke. The coking process is highly dependent on the oven design, the type of coal, and the conversion temperature used. Typically, ovens are adjusted during the coking process so that each charge of coal is coked out in approximately the same amount of time. Once the coal is “coked out” or fully coked, the coke is removed from the oven and quenched with water to cool it below its ignition temperature. Alternatively, the coke is dry quenched with an inert gas. The quenching operation must also be carefully controlled so that the coke does not absorb too much moisture. Once it is quenched, the coke is screened and loaded into rail cars, trucks, or onto belt conveyors, for shipment.
As the source of coal suitable for forming metallurgical coal (“coking coal”) has decreased, attempts have been made to blend weak or lower quality coals (“non-coking coal”) with coking coals to provide a suitable coal charge for the ovens. One way to combine non-coking and coking coals is to use compacted or stamp-charged coal. The coal may be compacted before or after it is in the oven. In some embodiments, a mixture of non-coking and coking coals is compacted to greater than 50 pounds per cubic foot in order to use non-coking coal in the coke making process. As the percentage of non-coking coal in the coal mixture is increased, higher levels of coal compaction are required (e.g., up to about 65 to 75 pounds per cubic foot). Commercially, coal is typically compacted to about 1.15 to 1.2 specific gravity (sg) or about 70-75 pounds per cubic foot.
The manner in which coals are selected, prepared and combined greatly effects the properties of the coke produced. Coals must be reduced in size by grinding to optimal levels and then thoroughly mixed to ensure good distribution of coal particles that will promote the maximum coke quality achievable form the available coals. In North America, coke makers generally pulverize their coals or blends to 75% to 95% minus ⅛″ size. The size the coal is crushed is expressed as % minus ⅛″ is commonly referred to as the pulverization level. In addition to size control, bulk density must be controlled. High bulk density can cause hard-pushing and damage coke oven walls in a byproduct coke oven. Low bulk density can reduce the strength of the coke produced.
Two coke oven technologies dominate the industry: by-product coke ovens and heat recovery coke ovens. The majority of the coke produced in the United States comes from by-product oven batteries. This technology charges coal into a number of slot type ovens wherein each oven shares a common heating flue with the adjacent oven. Natural gas and other fuels are used to provide heat to the ovens. Coal is carbonized in the reducing atmosphere, under positive (higher than atmospheric) pressure and the gasses and tars that evolve (off-gases) are collected and sent to a by-product plant where various by-products are recovered. Coal to coke transformation in a by-product oven takes place when the heat is transferred from the heated brick walls into the coal charge. The coal decomposes to form plastic layers near each wall and these layers progress toward the center of the oven. Once the plastic layers have met in the center of the oven, the entire mass is carbonized.
Alternatively, using heat-recovery, non-recovery, or beehive oven technology, coal is charged to large oven chambers operated under negative (lower than atmospheric) pressure. The carbonization process takes place from the top by radiant heat transfer and from the bottom by conduction of heat through the sole floor. Primary combustion air is introduced into the oven chamber through several ports located above the charge level. The evolving gasses and tar are combusted in the top chamber and soles of the oven and provide the heat for the coking process. In heat recovery ovens, excess thermal energy from the combusted gases is recovered in the waste heat recovery boiler and converted to steam or power. Coal to coke transformation in a heat-recovery, non-recovery and beehive oven takes place when the heat is transferred from the heated brick floor or radiant heat from the top of the coal bed into the coal charge. The coal decomposes to form plastic layers near the wall and the top of the bed and these layers progress toward the center of the oven. Once the plastic layers have met in the center of the oven, the entire mass is carbonized.
The rate of movement of the plastic layer to the center of the coal bed in both by-product and heat-recovery ovens is limited by the conductive heat transfer rate of the coal bed. Coal chemistry and bed density have a major impact on the heat transfer rate which ultimately sets the oven cycle time and battery production capacity. By-product ovens generally have cycle times between 17 to 24 hours per charge. Heat-recovery ovens generally have cycle times between 24 and 48 hours per charge.
The common method to increase bulk density of the coal charge to the oven is to compact the coal bed prior to or after it is charged by mechanical means known as stamp charging. While a stamp charge method can successfully increase the overall bulk density of the coal charge, it requires expensive equipment to perform the compaction. In heat recovery ovens, it results in a longer coking cycle because the closely packed particles release volatile matter slower than a loosely packed bed. At the same time, stamp charging's higher density leads to improved coke quality. This allows attaining a higher coke quality and the option to substitute lower cost, lower quality coals. In the United States, there is an abundance of high quality low cost coal. The abundance of low cost, high quality coal and the high cost of installing a stamp charger has led to stamp chargers not being employed in the United States. Any low cost method to improve coal density without stamp charging would have application in the United States to improve coke quality and possibly use some lower cost coals or coal substitutes.
The present technology is generally directed to integrated control of coke ovens in a coke plant, including horizontal heat recovery (HHR) coke plants, beehive coke plants, and by-product coke plants, in order to optimize coking rate, product recovery, byproducts and unit lime consumption. Coking rate is defined as tons of coal coked out/hr, energy efficiency defined as net energy production (total heat produced−heat consumed for coke making−heat losses). Product recovery is defined as amount of coke produced (tons) per amount of coal consumed (tons) on a wet or dry basis. Byproducts are defined by power or steam. Unit lime consumption is defined as tons of lime consumed per ton of coal charged to the ovens.
According to one exemplary embodiment of the disclosure, horizontal heat recovery coke plants consist of several systems including a series of coke ovens connected to each other with a single or multiple hot flue gas ducts, multiple heat recovery steam generator (HRSG) units to generate steam from waste heat of flue gas from ovens. In alternative embodiments, the coke plant may include a steam turbine generator generates power from steam. In still further embodiments, the coke plan may include flue gas desulphurization units to remove sulfur from flue gas and/or a bag house to remove particulate matter. A schematic diagram is shown in
According to aspects of one embodiment, more than a hundred coke oven may be included in a single coke plant. Coke ovens are typically divided in to several batteries. Several of these coke ovens in each battery share heat recovery steam generators. For example, in accordance with one embodiment, a hundred oven coke plant there could be three batteries and there could be one heat recovery steam generator for every 20 ovens. According to additional embodiments, there could be fewer or more ovens affiliated with each heat recovery steam generator. Each of the coke ovens are built the same and behave similarly, although each coke oven has some differences caused by carbon formation, oven leaks, charge, etc. In operation, coke ovens may be charged on a 48 hour cycle. Odd ovens are charged one day and even ovens the next day. Blended coal with a particular set of properties such as moisture content, volatile matter (VM), fluidity, etc. is charged in the oven and coked for 48 hours. Heat for coking in horizontal heat recovery coke ovens is provided by the volatile matter that is released from coal. Volatile matter consists of tar, hydrocarbon, hydrogen, carbon-monoxide and other gases that are burnt in the oven. In horizontal heat recovery ovens, the gases are burnt in the crown section at the top of the coal as well as under the floor in sole flue. Thus coking of the coal happens from both top of the coke cake and the bottom of the coke cake. The air needed for burning the volatile matter is provided in the crown by using air holes in the door, at the ceiling of the crown (top air) or from a different non-movable surface in the oven crown. The air needed for burning the volatile matter in the sole flue is provided from the holes in the end walls. One horizontal heat recovery oven configuration with door holes is shown in
One aspect of the disclosure is the formulation of the different control schemes for integrated oven control to optimize coking rate, product, byproduct recovery and unit lime consumption. This is described in further detail below.
One optimization objective of the coke oven is to maximize throughput (defined as amount of coal that can be charged and coked out in one batch), yield (defined as tons of coke made per ton of coal charged) and coke quality (stability, coke strength after reaction (CSR) and mean size). Coke chemistry, coke size, and coke strength (stability) have been considered the most important factors for evaluating coke for use in a blast furnace. However, coke reactivity index (CRI) and CSR are increasing in importance as their impact on blast furnace performance is better understood. For example, a decrease in coke consumption during hot metal production can be linked to increases in CSR values. The magnitude of coke rate reduction varies with changes in blast furnaces size and operating parameters. However, it is estimated that 2 to 5 lbs. of coke are saved per net ton of hot metal produced for every point that CSR increases.
Throughput is maximized by maximizing the coking rate (defined as tons of coal converted to coke per hour). Coking rate can be optimized by optimizing the temperature profiles in crown and sole flue. Yield can be maximized by minimizing the burn loss in the oven (defined as amount of coke burnt out in a batch). Again, yield can be optimized by optimizing the temperature profiles in crown and sole flue. The temperature profiles in crown and sole flue affect the size of the coke (bottom vs top coke), stability and CSR. Optimization objectives are achieved through controlling certain variables (called control variables) by manipulating available handles (called manipulated variables) subject to constraints and system disturbances that affect the controlled variables. These different variables are explained in further detail below.
Controlled Variables (CVs): CVs are defined as variables that are controlled to desired user set-points to meet the optimization objectives. From above, optimization of coke oven involves defining the optimal set-point temperature profile trajectories and controlling the temperature profiles to the optimal set point profiles in both the crown and sole flues. Temperatures are affected by the amount of oxygen in the oven i.e combustion control. If the oxygen intake in the oven is matched to the fuel (in volatile matter) release rate then temperature can be maximized (in other words controlling the fuel/air ratio). However, neither the gas evolution rate (and also composition) nor the air flow in to the oven is measured. Hence a direct control of fuel/air (or oxygen) is not possible. However, one can try a feedback control by measuring the temperatures and adjusting the oxygen to maximize the temperature (or controlling to a desired set-point). Alternatively one can also use an inferential control by indirectly inferring the amount of gas (air (at a particular density)+volatile matter) by using the draft (or pressure) in the oven and controlling the temperature by controlling the draft in the oven by moving the door hole dampers, sole flue (SF) dampers or uptake dampers (which controls the amount of air).
Thus the controlled variables include temperatures in the crown (center, push side (PS) and coke side (CS)), temperatures in the sole (PS and CS) and/or draft within the oven system that would include the crown, sole flue, downcomers, upcomers and uptakes to the damper blocks. Controlled variables can be controlled to a set point profile (like temperatures) or maintained in a deadband (i.e. draft). According to further embodiments, an additional controlled variable may be the delta T between the coke side and push side temperatures.
Manipulated Variables (MVs): MVs are defined as variables that can be moved independently by the controller in order to control the controlled variables. The main variables that can be manipulated to control the ovens are the oven uptakes, the sole flue dampers and the door hole or top air hole dampers on the push side and coke side.
Disturbance Variables (DVs) and Feed Forward (FF) Variables: DVs are variables that cause the controlled variables to change, but may not be available for the controller to move them.
Feedforward (FF) Variables are a special class of DVs which can be measured. This measurement can be used to predict future controlled variable changes which can be accounted for with compensating manipulated variable changes. Some examples of disturbances are given below.
Emergency Vent Stack (EVS) Draft: As shown in
Door holes: Door holes are used as a main source for providing primary air or secondary source in addition to top air holes. If the door holes are controlled manually then they can be treated as disturbances to the automatic control scheme. In other words if an operator opens the door holes and let in more air the controller will treat it as a disturbances affecting the controlled variables (such as temperatures or draft) and take an action with the other manipulated variables available (such as uptakes or top air hole dampers) to keep the controlled variables within their limits.
Sole Flue (SF) Dampers: Similar to door holes if the sole flue dampers are not automated.
Ambient conditions: If the ambient conditions change it will affect the properties of the air intake. For example, the density, temperature or humidity changes of the air could affect the controlled variables.
Coal property changes: Properties of the coal charged in to the oven can change from day to day. For example, the moisture content, volatile matter, fluidity, bulk density, etc. could vary from one day to the other. These act as disturbances affecting the controlled variables.
Coal Charging: Coal is charged by using a pusher charger machine (PCM) by an operator. The machine settings and charging speed could affect shape and level of the coal bed in the oven. For example, uneven speed of charging could result in more coal in the push side compared to coke side or vice versa. Similarly there could be side to side variations. Uneven coal bed loading leads to uneven volatile matter evolution in the oven and hence would act as disturbances to the control system affecting the controlled variables.
Constraints: Constraints are limits for the variables that need to be honored by the control system and cannot be violated. Constraints arising from safety, environmental, equipment limitations or efficiency need to be incorporated in to the control system. These could be temperature limits (for example, high limit to prevent melting of oven bricks), draft limits (for example, to prevent the oven pressure from going positive leading to outgassing), or oxygen limits (for example, high limit to prevent the oven from cooling off due to excess air). Control systems are designed to handle these constraints in a prioritized fashion.
As discussed above, coke ovens have several controlled and manipulated variables and are subject to various disturbances and constraints. Depending on the level of complexity and desired response several control schemes can be configured.
As shown in
For control of coke ovens, several control schemes starting from simple single loop control to advanced multi-loop cascade control is then discussed. The use of state of the art multivariable matrix based Model Predictive Control (MPC) is then described.
EVS Draft Control Schemes—Decoupling Oven Control from Downstream Operations:
Plant without Gas Sharing Tunnel:
Coke Plant with Gas Sharing (GS) Tunnel:
EVS Draft Control During Normal Operation with all HRSGs Running
Control Scheme H1: EVS Draft PIC with #11 Under Inlet PIC
In this scheme, the individual emergency vent stack pressure, before the tie-in point to the new tunnel, are controlled using the corresponding pressure control valve downstream of that heat recovery steam generator as shown in
Control Scheme H2: EVS Draft PIC with HRSG 11 Under FIC
In order to overcome the first challenge mentioned in scheme H1, one can control the mass flow (or steam flow) form the heat recovery steam generator. A mass flow meter can be used to measure the flue gas flow through the heat recovery steam generator. Having the heat recovery steam generator under flow control ensures a fixed flow through the heat recovery steam generator at all times (production and non-production times). This is like isolating the heat recovery steam generator and removing the interactions caused by heat recovery steam generator flow changes to the other heat recovery steam generators.
Control Scheme H3: HRSG Inlet PIC with HRSG 11 Under Inlet PIC
In order to overcome the second challenge mentioned in control scheme H1, the heat recovery steam generator inlet pressure, after the tie-in point, can be controlled. This series as a direct PIC scheme and a model between pressure control valve and heat recovery steam generator inlet pressure can be readily obtained by step test data collection methods. A better model for controller enables one to tune the PIC much tighter ensuring a superior control (model uncertainties typically result in bad controller tuning and hence poor pressure control). It is extremely important to have good and tight control of the individual heat recovery steam generator pressure in order to prevent and minimize the interaction between different heat recovery steam generators caused by the common gas sharing tunnel. For example, if the PICs are tuned slowly, when there is excess gas causing increase in pressure, the pressure control valve will react slowly to let the excess gas go through the heat recovery steam generator. Now, the excess gas will start going to the other heat recovery steam generators through the new gas sharing tunnel. This will hence affect the other heat recovery steam generator PICs. Similarly, if one PIC swings other PIC will start swinging. Hence, to have good operation with gas sharing tunnel it is important to have the PICs working in concert.
Control Scheme H4: HRSG Inlet PIC with HRSG 11 Under FIC
To overcome both challenges described in control scheme H1, we can use HSRG inlet PICs and FIC on #11.
EVS Draft Control During GS Operation with One HRSG Down
When one of the heat recovery steam generator goes down, depending on which heat recovery steam generator, the draft set points (SP) for the heat recovery steam generators and flow set point for #11 (if control schemes H2 or H4 is used) have to be changed so that the flue gas from the heat recovery steam generator that is down can be sent to other heat recovery steam generators. The draft and flow set point have to be chosen carefully in order to have a smooth transition, minimize the interactions, stabilize the system quickly and prevent any emergency vent stack from opening during the transition. The draft and flow set point for control scheme H4 for different scenarios is shown in Table 1.
Transition responses using control scheme H4 during other heat recovery steam generator trips are show below.
The Haverhill plant Phase II Ovens have been modified in order to automatically control the pressure within each oven while maintaining similar pusher and coke side sole flue temperatures. This is done using a pressure sensor in the crown of each oven, the existing sole flue temperature probes and radar systems. The radar systems replace the proximity switches and perform the same function of monitoring damper position.
The oven pressure sensor reading is used by a programmable logic controller (PLC) which sends a signal to the oven uptake dampers in order to keep the oven pressure at a pre-determined set point. The oven pressure is controlled by moving the coke side and pusher side dampers in the same direction.
The sole flue temperatures are used by a separate PLC controller which sends a signal to the oven uptake dampers in order to keep the oven sole flue temperatures within 100 degrees of each other. This action, called temperature biasing, is accomplished by moving the coke side and pusher side dampers in the opposite directions. This movement forces more hot gas from the side whose damper is closing to the side whose damper is opening.
Although the outlet dampers are automatically controlled, the sole flue dampers and the door dampers may continue to be manually controlled by the burner or operator. Rules for adjustment of the sole flue dampers and the door dampers will not change due to this modification.
HMI Screen for Damper Controller
Each oven screen (Exemplary Screen Shot 1) has been modified. The proximity indicators have been replaced with radar position indicators. The radar position indicators show the actual coke side and pusher side damper openings and the set points that the system wants. Above each set of readings there is a button which opens the damper controller (Exemplary screen shot 2).
H. The CLOSE button will remove the dialog box from the screen.
Each oven screen has also been modified to include an oven pressure set point button. When the button is clicked, the oven pressure controller dialog box will appear (Exemplary screen shot 4).
The dialog box shows the current oven pressure set point. To input a new set point, the SET button is clicked. This will open the set point keypad (Exemplary screen shot 6).
The set point must be a negative number and be within the range of −0.1 to −1.5. The new set point is entered in the New Value window and the OK button is clicked. The new set point will appear in the oven pressure controller dialog box. Clicking CLOSE will remove the dialog box from the screen.
Information concerning oven pressure, damper operating mode (automatic or manual), damper drift (enabled or disabled) and temperature bias (active or inactive) is available on the individual oven screen (Exemplary screen shot 1) and the oven overview screen (Exemplary screen shot 7). The percentage of ovens that are in automatic pressure control is indicated at the top of the oven overview screen. A yellow triangle over the overview screen's damper position indicates that there is a sensor or damper position fault.
Once the downstream heat recovery steam generator control can stabilize the emergency vent stack pressures the ovens are practically decoupled from downstream operations and hence can be independently controlled using different control schemes discussed below. Disturbances do occur when one of the heat recovery steam generator goes down since the emergency vent stack stacks have to operate at a different draft. This will be handled in the oven control scheme by using a feedforward variable control action that will be discussed below (at the end of the oven control schemes).
These are independent one-to-one controllers where each controlled variable is controlled by a corresponding manipulated variable.
Control Scheme 1:
In this scheme, the coke side crown temperature is controlled using coke side door or top air holes or holes that are in any non-movable surface on the coke side of crown, the push side crown temperature is controlled using push side door or top air holes or holes that are in any normally non-movable surface on the push side of crown, sole flue (SF) coke side temp is controlled by the coke side sole flue damper, sole flue (SF) push side temp is controlled by the push side sole flue damper and the draft in the oven measured by the crown pressure cell is controlled by the uptakes. A schematic diagram of the control scheme is shown in
The set point (SP) for the temperature and draft controllers as a function of time is supplied by the user.
In this scheme, the temperature controllers try to maintain the temperatures in crown and sole flue, respectively. The draft controller is a knob that can be used effectively to distribute the heat to the crown or sole flue as desired. For example, a higher crown draft would mean that more gas would be burnt in the crown relative to sole flue and a lower draft would mean the opposite. Thus care should be taken while defining the optimum set point trajectories for the crown, sole flue and draft so that the controllers wouldn't fight each other.
One variable to control for in this control scheme is the changing relationship over time between the damper and the temperature changes. This makes single loop controller (especially PID type controller) tuning very challenging. This can be better explained by the excess oxygen (surrogate for damper opening) vs temperature relationship.
The most popular controller type for single loop controller is a proportional integral derivative (PID) controller. Other types of single controller that could be used include fuzzy logic controller, other variants of PID control or user defined algorithm relating the controlled variables to manipulated variables.
Control Scheme 1A:
If the door holes and sole flue dampers are not automated then the oven can be controlled by using just the pressure controller to control the crown pressure. The pressure set point trajectory profile can be developed offline by using previous historical data from the ovens to correspond to a desired oven temperature profile. One can also configure some over-ride controller such as temperature bias controller to control the temperature difference between sole flue coke side and push side temperatures to ensure uniform sole flue temperature. This scheme is shown in
Control Scheme 1B:
If the door holes and sole flue dampers are not automated, control scheme 1 can be modified such that the temperature controller can be cascaded to crown pressure controller. The temperature controller can be configured as a crown temperature controller with a set point trajectory defined for the crown temperature or it can be an average sole flue temperature (average of push and sole flue temperatures) controller. The temperature controller will be the master controller writing its output to the set point of the underlying crown pressure controller. The pressure controller will try to maintain the setpoint required by the temperature controller by using the uptakes. These schemes are shown in
It should be noted all the above oven control schemes can be implemented without the crown draft PICs. Also the temperature controller can use any combination of the PID elements namely proportional, integral or derivative actions along with a combination of sole flue bias controller. One such scheme is shown in Control Scheme 1C.
Control Scheme 1C:
This scheme represents an advanced control scheme consisting of a combination of crown temperature control, sole flue temperature control and a feed-forward scheme to offset the effect of stack draft variations during gas sharing scenario. It is basically a combination of control schemes 1A and 1B without the cascaded pressure controller and the addition of feed forward component. Details of the control scheme are shown herein.
Control Scheme 2:
This is similar to control scheme 1 except that the oxygen analyzer is used to detect the transition from fuel-rich to fuel-lean regime and the controller parameters are changed to handle the switch. This scheme is shown in
Control Scheme 3: Multivariable Control
Instead of using several single loop controllers that interact with each other one could use a pure multivariable controller such as Model Predictive Control (MPC). This methodology consists of developing empirical dynamic models between the manipulated variables and disturbance feed forward (FF) variables, and controlled variables using data from the ovens. Data can be obtained either from past historical data or from controlled set of experiments by perturbing the manipulated variables and feed forward disturbance variables around a nominal operating trajectory and collecting the response of the controlled variables. Alternatively, if one has a fundamental theoretical nonlinear model of the process then it can be used to get the linear dynamic models around the nominal trajectory by either linearizing the nonlinear model around the nominal trajectory or by perturbing the nonlinear model in a simulation and getting the responses. A matrix is developed representing the relationship between manipulated variables, feedforward variables and controlled variables. Model Predictive Control uses the relationship matrix and the past data within a time horizon, at every instant of time “k”, to predict the controlled variable profiles for a future prediction time horizon. The predicted deviation from the set point profile is then minimized by using an optimization program by calculating a set of manipulated variable moves for a future time horizon (could be the end of the batch or a reduced horizon). The first set of manipulated variable moves is implemented.
In Model Predictive Control framework, the process model change between air (door holes, sole flue damper, uptakes) and temperature can be handled by switching the model in the matrix or by using a variable gain equation within the controller. Again, the switching time can be decided by using any of the methods described previously in the single loop control schemes.
During the first three hours of the coking cycle the uptake dampers are held fully open at 14 inches. After the first three hours the uptake dampers are automatically controlled by the oven pressure. The pressure set point is dependent on the time that has elapsed since the oven was charged. A sample schedule of set points:
If the difference between the set point and the actual pressure value indicates that the uptake dampers must be adjusted, the PLC calculates the distance that the dampers must be moved and repositions the uptake dampers. The PLC will wait 10 minutes to allow the oven to stabilize before another move is made (if necessary). The minimum move is ½ inch. The maximum move is 3 inches.
The uptake damper opening is limited during automatic pressure control and this limit is dependent on the time that has elapsed since the oven charge. The PLC will not open the uptake damper beyond this point even if the calculated distance would do so. A sample of uptake limits are:
Temperature biasing uses the difference between the coke side and push side sole flue temperatures. If the difference in temperatures exceeds 100 degrees, the PLC calculates the distance that the uptake dampers must be moved and repositions the uptake dampers. The uptake dampers are moved in opposite directions. This movement forces more hot gas from the hotter side (whose damper is closing) to the cooler side (whose damper is opening). The PLC will wait 60 minutes to allow the oven to stabilize before another move is made (if necessary). The minimum move is ½ inch. The maximum move is 3 inches. The PLC will not open the uptake damper beyond the damper opening limit.
The sole flue dampers and the door dampers will continue to be manually controlled by the burner or the operator. After the coal charge the crown temperature should be 1900-2,100° F. and the sole flue temperature should be 2000-2700° F. The guideline for door dampers during the first 20 hours of the coking cycle is:
At 20 hours the crown temperature should be 2500° F. or more and all door dampers closed. Crown temperatures should be periodically checked and controlled to normal operating range since any incomplete combustion in the crown will result in higher sole flue temperatures. At push the crown temperature should be 2400-2,600° F. and the sole flue temperatures 2100-2,300° F.
The maximum crown temperature and the maximum sole flue temperature are 2,800° F. If the crown temperature reaches 2750° F. and continues to climb, decrease the draft to slow down the temperature rise. The draft can be decreased by increasing the oven pressure set point. The burner or operator can override the pre-determined pressure set point by following the instructions stated in HMI SCREEN FOR PRESSURE CONTROL SET POINT.
Example of Overriding Pressure Set Point:
The burner or operator can open one oven damper more than the other oven damper. This may be necessary to control sole flue temperatures. This can be done by following the instructions stated in item C of HMI SCREEN FOR DAMPER CONTROLLER.
Example of Biasing Oven Dampers:
The maximum temperature difference between the coke side sole flue temperature and the push side sole flue temperature is 200° F. The sole flue temperatures must be rebalanced to avoid this condition. If rebalancing is required, the following steps should be taken:
First Action:
Adjust oven pressure set point to the actual oven pressure reading. This can be done by following the instructions stated in HMI SCREEN FOR PRESSURE CONTROL SET POINT. Check and adjust door and sole flue dampers as necessary to aid in balancing the temperature.
Second Action:
Wait 20 minutes. If temperature begins rebalancing, DO NOTHING. When sole flue temperatures are within 100 begin stepping oven pressure set point back to where it was before the NTE condition occurred. Report action taken and results to the Turn Manager.
Third Action:
If the temperature does not begin balancing within 20 minutes or if the sole flue temperature difference reaches 350 degrees before 20 minutes have elapsed, place both damper controls in manual mode. The burner or operator must manually adjust uptake dampers using the instructions stated in item C of HMI SCREEN FOR DAMPER CONTROLLER. The burner or operator must also adjust door and sole flue dampers as required. When the temperature difference reduces to 100° F., both damper controls can be placed back in automatic and the oven pressure set point returned to where it was before the NTE condition occurred. It may be necessary to bias the uptake dampers in order to maintain balanced sole flue temperatures. This can be done by following the above Example of Biasing Oven Dampers. The burner or operator should monitor the oven and adjust door and sole flue dampers as necessary. The burner or operator should report all actions taken and the results to the Turn Manager.
The alarms listed in item G of HMI SCREEN FOR DAMPER CONTROLLER require the following responses from the burner or operator.
First Action:
Adjust oven pressure set point to the actual oven pressure reading. This can be done by following the instructions stated in HMI SCREEN FOR PRESSURE CONTROL SET POINT. Check and adjust door and sole flue dampers as necessary to aid in balancing the temperature.
Second Action:
Wait 20 minutes. If temperature begins rebalancing, DO NOTHING. When sole flue temperatures are within 100° F., begin stepping oven pressure set point back to where it was before the NTE condition occurred. Report action taken and results to the Turn Manager.
Third Action:
If the temperature does not begin balancing within 20 minutes or if the sole flue temperature difference reaches 350 degrees before 20 minutes have elapsed, place both damper controls in manual mode. The burner or operator must manually adjust uptake dampers using the instructions stated in item C of HMI SCREEN FOR DAMPER CONTROLLER. The burner or operator must also adjust door and sole flue dampers as required. When the temperature difference reduces to 100° F., both damper controls can be placed back in automatic and the oven pressure set point returned to where it was before the NTE condition occurred. It may be necessary to bias the uptake dampers in order to maintain balanced sole flue temperatures. This can be done by following the above Example of Biasing Oven Dampers. The burner or operator should monitor the oven and adjust door and sole flue dampers as necessary. The burner or operator should report all actions taken and the results to the Turn Manager.
The alarms listed in item G of HMI SCREEN FOR DAMPER CONTROLLER require the following responses from the burner or operator.
Sensor Fault/Bad Value will cause the damper controller to switch to manual with the damper staying at its last position. The burner or operator may manually control the damper using the instructions stated in item C of HMI SCREEN FOR DAMPER CONTROLLER. The burner or operator must enter an emergency work order to repair the pressure sensor.
DMPR POS FLT (Damper Position Fault) will cause the damper controller to switch to manual with the damper staying at its last position. The burner or operator or operator may manually control the damper using the instructions stated in item C of HMI SCREEN FOR DAMPER CONTROLLER. The burner or operator must enter an emergency work order to repair the radar positioning system.
DMPR Drift (Damper Drift) has no effect on the control system. The burner or operator should enter a work order to inspect and repair the damper linkage.
As mentioned before, even though the heat recovery steam generator control decouples the oven controller from downstream operations, when one of the heat recovery steam generator goes down the emergency vent stack stack draft set point has to be changed for the new mode of operation. This could induce a disturbance to the ovens which would make the crown and sole flue temperatures change. Feedback control as shown in oven control schemes may be too slow to react since the oven temperatures may take long time to respond due to thermal inertia. When the temperatures do respond it may be too late for the feedback control to move the uptakes to compensate (for example, ovens may have already cooled down and one may have lost all the flue gas required to keep it warm). In order to effectively counteract this disturbance, we could add a feed-forward control action where the operator can start closing the uptakes when the draft set point is increased in anticipation of oven cooling down. This is shown in
In operation, the optimal oven operation is to implement a fully automated oven using all the crown, sole flue and uptake dampers to control the temperature profiles of crown and sole flues to the desired profiles. Use of single loop or multivariable control scheme would depend on the amount of interaction, ability to reject different disturbances and the performance of the controller to maintain the controlled variable to its trajectory.
If all the manipulated variables are not available to control then an alternative scheme with reduced set of manipulated variables may be used. For example, any of the control schemes 1, 1A, 1B, 2 or 3 could be used with reduced set of manipulated variables. If certain variables are not used as manipulated variables they can be treated as disturbances when they are moved manually.
Instead of having one heat recovery steam generator under flow control and all other heat recovery steam generators under pressure control as show in in control system H4, one could reverse it and have one heat recovery steam generator under pressure control and all other heat recovery steam generator under flow control. This alternate scheme will help distribute the flow between the heat recovery steam generator to user specified values and allow one heat recovery steam generator to act as a floater to absorb pressure variations. This scheme will be useful when the emergency vent stack is separated from the heat recovery steam generator as shown in
The location of the holes in the crown and sole flue could vary. For example, if the door design is a two piece design with the top portion being fixed and the bottom removable, then door holes for the primary air could be placed in the top section of the fixed door and hence the damper automation hardware could be easily mounted to control the primary air flow. Alternatively instead of the crown the primary air holes can also be located in the lintels at the top close to the door holes. Similarly, for secondary air, the location of holes in sole flue could be different. For example, one could have the holes at the bottom of the sole flue instead of the end walls. A combination of different locations is also possible. The holes will typically be on any non-removable surface but can it is also possible to have them on removable surfaces and automate them. Irrespective of where the holes are the control scheme described above applies.
Control scheme combinations: The control schemes described above could be combined in different ways. For example, one could have a combination of single loop and multivariable controllers or multivariable controllers at the top layer cascaded to single loop controllers at the bottom layers. Moreover, the transition from fuel rich to fuel lean occurs both in crown and sole flue. Hence the detection scheme for transition applies to both crown and sole flue temperature control.
Also, in the oven control schemes with the top air configurations one can use individual TICs to vary each of the top air hole independently or use a common manifold to control the hole positions the same on each side (as shown in
Exemplary Control Data Readings from the Oven:
Expert Advisory System:
An operator can use the information from the temperature trends and uptake positions to create an expert advisory system for the operators to use in taking manual actions either in the current batch or in future batches. This will especially be useful if oven control schemes 1A, 1B or 1C is used. For example, an expert advisory page could look like the one shown below in Table 3.
Table 3 illustrates an exemplary expert advisory system to assist burners or operators in making changes to current and future batch based on temperature responses with auto control of uptakes. Optimal control of coke ovens to will allow the operator to minimize the batch to batch quality variations, improve product yield & throughput and maximize the steam/power generation using the flue gas.
In horizontal heat recovery coke ovens with manual control, operators must go out to the coke ovens and manually look at the coke and adjust the door and sole flue dampers. They also take a look at the temperature profile of the crown and sole flues to make some adjustments to the dampers. Uptakes are set to a specific fixed position based on the time in the cycle. This is based on experience to control the draft and temperature profile. However, automatic control removes the inconsistencies caused by burner to burner operations. Moreover automating enables the system to make changes at a higher frequency (for example every minute or so) than it is humanly impossible for operators to make. Additionally when there is interaction between systems (for example, between the ovens and the heat recovery steam generator) it is difficult for operators to calculate the optimal set of moves to make. It is easier for a computerized program to calculate and suggest the optimal moves.
Automatic control further enables operations close to constraints. Operating on the constraint boundary enables increased profitability by having better efficiencies. It also helps improve environmental control. For example, one can easily program variable draft set points for the control system depending on the production cycle to eliminate outgassing caused by positive pressure at a particular point in the cycle.
In accordance with aspects of the disclosure, a coke plant could operate in various modes, for example, an initial mode without a gas sharing system installed, with a normal low draft operation, and using the temperature profile system to optimize the system. Alternatively the coke plant could run in a gas sharing system mode with normal low draft operation wherein the heat recovery steam generator control system is used to balance the draft and the temperature profile system is used to optimize the system. In still further embodiments, the coke plant could operate in gas sharing transition mode wherein the system transitions to high draft gas sharing and has a control system that automatically changes the uptake position. In accordance with this mode, the system kicks in when transitions to gas sharing mode occur, for example in the event of an unplanned loss of a heat recovery steam generator. In still further embodiments, the coke plant could operate in use the gas sharing system to operate in a gas sharing high draft mode using the heat recovery steam generator to balance the draft and using the temperature control system to optimize the temperature.
Experimental results confirm the control effects described herein. The compensation of integrated component control of the sole flue temperature, the crown temperature and the feed forward control on the stack draft combine to yield an optimized system with higher yield, faster throughput and increased by-product.
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.
The following Examples are illustrative of several embodiments of the present technology.
1. A system for integrating control of a coking oven, the system comprising:
2. The system of example 1 wherein the oven chamber includes a crown and sole flues and the controlled variable includes controlling temperature in the crown, in the sole flues, and/or draft in the crown.
3. The system of example 2 wherein the oven chamber and/or the sole flue includes a push side and a coke side and wherein the controlled variable includes controlling to a temperature differential between the push side and the coke side.
4. The system of example 1 wherein the air openings are at least one of a sole flue damper, door hole damper, or top air hole damper in the crown, wherein the manipulated variables include opening or closing the uptake, sole flue damper, door hole damper or top air hole damper in response to the temperature profile trajectories in the oven chamber.
5. The system of example 1 further comprising a common tunnel, heat recovery steam generators and an emergency vent stack in fluid communication with the oven, the heat recovery steam generators includes a pressure control valve configured to maintain a draft in the system.
6. The system of example 1 further comprising a common tunnel, a gas sharing tunnel, a plurality of heat recovery steam generators and an emergency vent stack in fluid communication with the oven, the plurality of heat recovery steam generators are configured to balance draft in the gas sharing tunnel.
7. The system of example 6 wherein at least one of the heat recovery steam generators include a mass flow meter to measure exhaust gas flow through the heat recovery steam generators.
8. A method of optimizing operation of a coke plant, comprising:
9. The method of example 8, further comprising:
10. The method of example 8, further comprising:
11. The method of example 10, further comprising:
12. The method of example 8, further comprising:
13. The method of example 8, further comprising:
14. The method of example 8, further comprising:
15. The method of example 8, further comprising:
16. The method of example 15, further comprising:
17. The method of example 16, further comprising:
18. The method of example 15, further comprising:
19. The method of example 15, further comprising:
20. The method of example 15, further comprising:
21. The method of example 15, further comprising:
22. The method of example 21, further comprising:
23. The method of example 22, further comprising:
24. The method of example 15, further comprising:
25. The method of example 15, further comprising:
26. A coke oven, comprising:
27. The coke oven of example 26, wherein the sensor comprises a temperature sensor configured to detect the oven temperature.
28. The coke oven of example 27, wherein the sensor is positioned in the oven chamber.
29. The coke oven of example 28, wherein the position instruction is configured to allow excess air into the oven in response to an overheat condition detected by the sensor.
30. The coke oven of example 26, wherein the sensor comprises an oxygen sensor configured to detect the uptake duct oxygen concentration in the uptake duct.
31. The coke oven of example 30, wherein the position instruction is configured to maintain the uptake duct oxygen concentration within an oxygen concentration range.
32. The coke oven of example 26, wherein the sensor comprises a temperature sensor configured to detect the sole flue temperature.
33. The coke oven of example 32, wherein the position instruction is configured to allow excess air into the oven in response to an overheat condition detected by the sensor.
34. The coke oven of example 33, further comprising:
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.
Further, although the technology has been described in language that is specific to certain structures, materials, and methodological steps, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific structures, materials, and/or steps described. Rather, the specific aspects and steps are described as forms of implementing the claimed invention. Further, certain aspects of the new technology described in the context of particular embodiments may be combined or eliminated in other embodiments. Moreover, while advantages associated with certain embodiments of the technology have been described in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages to fall within the scope of the technology. Accordingly, the disclosure and associated technology can encompass other embodiments not expressly shown or described herein. Thus, the disclosure is not limited except as by the appended claims. Unless otherwise indicated, all numbers or expressions, such as those expressing dimensions, physical characteristics, etc. used in the specification (other than the claims) are understood as modified in all instances by the term “approximately.” At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the claims, each numerical parameter recited in the specification or claims which is modified by the term “approximately” should at least be construed in light of the number of recited significant digits and by applying ordinary rounding techniques. Moreover, all ranges disclosed herein are to be understood to encompass and provide support for claims that recite any and all subranges or any and all individual values subsumed therein. For example, a stated range of 1 to 10 should be considered to include and provide support for claims that recite any and all subranges or individual values that are between and/or inclusive of the minimum value of 1 and the maximum value of 10; that s, all subranges beginning with a minimum value of 1 or more and ending with a maximum value of 10 or less (e.g., 5.5 to 10, 2.34 to 3.56, and so forth) or any values from 1 to 10 (e.g., 3, 5.8, 9.9994, and so forth). From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may he made without deviating from the scope of the invention. Accordingly, the invention is not limited except as by the appended claims.
This application claims the benefit of priority to U.S. Provisional Patent Application No. 63/099,383, filed Jan. 2, 2015, the disclosure of which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62099383 | Jan 2015 | US |
