Title of Invention

AUTOMATIC HEAT CONTROL OF COKE OVEN BATTERY .

Abstract

An automatic heat control system for coke oven battery, comprising, means for estimating the thermal state of the coke oven battery, means for calculating heat flow-to the coke oven battery, a control unit for processing said coke oven battery temperature and said heat flow to the battery and for generating set point for fuel flow for the next heating cycle and outputting said set points for automatic heat control of said coke oven battery.

Full Text

-2- FIELD OF APPLICATION The present invention relates to an automatic heat control system for coke oven battery. BACKGROUND OF THE INVENTION Coke ovens heating practice is based on the operator's expertise, judgement and experience. The operators are guided by flue temperature measurement obtained through hand-held pyrometer. The flue temperatures thus obtained, for each oven, are validated against a predetermined temperature - prescribed for uniformity in coke exit temperature. In absence of a reliable model the operator controls the fuel flow based on his judgment and thus varies from operator to operator and causes non-optimal fuel consumption. The existing heating control system for coke oven battery depends on operator's view of battery wide process variables, recorded in circular chart recorders. The overall heating control function is based on heuristic judgements of operators and corresponding manual actions. There was therefore, a need for the development of a model for automatic heating control of the coke oven battery. SUMMARY OF THE INVENTION The main object of the present invention therefore, is to provide a system for automatic heat control of coke oven battery for optimizing fuel consumption and ensuring uniform coke exit temperature. -3- The module developed in the present invention which has been implemented and tested and can generate and display set point for heating control in advisory mode to the operators, who in turn accordingly changes the fuel flow and pause time i.e. the ideal time between the fuel reversals. This results not only in optimization of fuel consumption but also ensures uniform coke exit temperature. A typical coke oven battery consists of 54 numbers Otto twin flue compound under jet 4.5-meter ovens arranged in two sub-batteries of 27 ovens each. Measurements of battery heating conditions are to be enhanced by introducing new temperature probes. As a first and necessary step towards level II, the emphasis has been on migrating from the conventional, analog mode of integrating data obtained from sensors, to the PLC-computer combination based digital realm. This results in tapping signals from the recorder panel to PLC via signal isolators, programming the PLC to handle all data inputs and outputs, and interfacing two computers with the PLC to enable human interfaces to the real time database, using a sophisticated SCADA (supervisory control and data acquisition) package, called Intellution FIXDMACS. Apart from process data management this phase also includes a few critical new features, such as computer-generated cascade PID controller for MGCV/CO injection, mechanism for level II set point downloads to the PLC, process signal state detection etc. -4- The data acquisition and level I control system is designed and implemented at control room to fulfill the following objectives. • A computer based information and reporting system for operations and maintenance. • Demonstration of level I control functions using computers. • A platform for implementing advanced model based (level ZZ) heating control. In the present invention the computer uses regenerator thermocouple temperature for the identification of the overall-heating regime of the battery at any point of time. At selected regenerator positions gives the most important feedback about the combustion efficiency of the battery. The air / LG preheating process, the flue duct combustion processes, the overall battery heat up-take level all these are represented very accurately by the regenerator dynamics. When a fuel flow set point change is made, the regenerators reflect the effects of the change the fastest among the battery's measured variables. Fuel and draught will be adjusted to correct for minor deviations occurring in the thermal state of the thermal state of the battery, while pause control will be utilized for effecting major modulations and corrections tn heat input. In the system of the present invention same controller hardware of level I are utilized. During a parallel run phase, the level II system only generates set point advice to the operators, who can then execute the adjustments manually. After the system stabilizes for three months the model will take care for the control variable. -5- Optimum efficiency of the heating system depends on a design, which is consistent with the physical laws and on maintaining optimum flow distribution and pressure under alt operating conditions. The battery is adjusted to the shortest possible coking time, i.e. maximum possible heat requirement and required possible amounts of gas, air and waste gas per unit of time. Under these conditions the battery will be heated continuously during the regenerator half period without a pause. If the heat requirement has to be reduced for longer coking times, the amounts of air and gas entering the system and the amount of waste gas leaving the system per unit time, are kept constant and the reduced heat requirements are achieved by a pause between regenerator half periods, that means the total reversal time remains constant. The heated period plus the not heated period (pause) is in the present case 30 minutes. As a necessary step towards level II the conventional and analog mode of integrating data obtained from sensors are converted to PLC-computer combination based digital realm. This results in tapping signals from the recorder panel to the PLC via signal isolators, programming the PLC to handle all digital inputs and outputs, and interfacing two computers with the PLC to enable human interfaces to the real-time database, using a sophisticated SCADA package called Intellution FIXDMACS. -6- The thermocouples, which were placed in the regenerators, are utilized for identification of the overall heating regime of the battery at any point of time by the computer. Fuel and draught controls will be adjusted to correct for minor deviation occurring' in the thermal state of the battery, while pause control will be utilized for effecting major modulations and corrections in the heat input. The level II system is generating set point advices for the operators who can then execute the adjustments manually. The data acquisition and control functions are broadly spread over three hardware units: the PLC panel, level I machine and a second PC, which serves as the site of mainly level II functions. All inputs signals and outputs set points are handled via PLC. Human interfaces to the real-time database is enabled using SCADA (supervisory control and data acquisition) package, called Intellution FIZDMACS, which is run on PC. The PLC is used for interfacing all existing field signals as inputs, and also for issuing set point signals as outputs. A pair of personal computers has been used for monitoring process status and downloading set points. The software and user interface required for these are development using Intellution's FIXDMACS package. Thus the present invention provides an automatic heat control system for coke oven battery, comprising: means for estimating the thermal state of the coke oven battery; means for calculating heat flow to the coke oven battery; a control unit for processing said coke oven battery temperature and said heat flow to the battery and for generating set point for fuel flow for the next heating cycle and outputting said set points for automatic heat control of said coke oven battery. -7- BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The invention will now be described in detail with reference to figures of the accompanying drawings where Figure i shows overall system interconnection diagram for coke oven battery heating control system. Figure 2 shows input / output details of the coke oven battery heating control system. Figure 3 shows FIX screen for operator interface. Figure 4 shows heating control flow-chart for the coke oven battery (every reversing 30 min). The various components of the hardware in the overall system interconnection diagram shown in Figure 1 are described as follows: All existing field signals are tapped from the recorder panel. Each signal is tapped through a signal isolator 1. Outputs of the isolators are connected to a programmable logic controller 2. Signals from the thermocouples are directly connected to a programmable logic controller (PLC) 2. -8- The programmable loop-cum-logic controller (PLC) 2 used can be a Tata Honeywell 620-16 logic controller series PLC with universal analog input handling capability. It is used as an interface for the computers (PC) 3, 4 for data acquisition and control. The 620-60 MS-DOS LOADER is the utility package for programming the PLC 2. This software is available In FIX 2 PC 4 where the serial THL configuration interface card is also installed and connected to the programmable logic controller (PLC) 2 using a cable. The programmable logic controller (PLC) 2 program includes a cascaded - PID block for CV/CO inject loops, sequencing and timing logic path for pause-reversal signalling, mechanisms for accepting operator entered data from FIX, a few analog outputs and many analog inputs. The data collected from the PLC 2 is transmitted to the process monitoring computer 3 (named "FDC1" or "Level I PC" or PC 1) via TCP / IP protocol. An Advantech Industrial PC, 64 MB Ram, 2 GB hard disk can be used for PC-1 and PC-2. An EIM (ethernet interface module) has been used to connect the Level -1 PC to the supervisory control computer 4 (named "FIX2 or "LEVEL-II PC" OR PC-2) and a printer. The operating system is MS-WINDOWS NT workstation with service pack 4.0. SCADA package is an Intellution FIXDMACS 7.0 (R+N) + FIXTOOLS, Y2K compliance. The users can monitor the status of the process, migrating through sub-system in a hierarchical, tree like fashion. The VIEW screen has also been programmed to accept commands ultimately meant for the PLC from the users such as downloading set points. Users can migrate to all levels of the heating control application-using simple one-click or two-click mouse operators. -9- In order to get regenerator temperature trend over a period of time the operators can choose from the displays in the oven identification screen. There are two nodes running FIX software. SYS-I is mainly responsible for communications with the PLC handling level 1 functions. SYS II is responsible for handling intensive tasks such as level II functions. Application specific code written in Visual C++ Version 5.0. Driver PLC: Ethernet Interface Module (EIM). The heating control strategy illustrated in Figure 2 is explained as below: The regenerator thermocouple temperatures serve as the basis for the estimation of battery temperature and means 10 are provided for this estimation. The battery temperatures of the previous two cycles are also taken into consideration. This is the input for the calculation of the net change in the heat to be corrected for the next reversal cycle This is used for the calculation of the target heat for the next cycle. The procedure for calculating the target heat has been illustrated in the heat control strategy of Figure 2. The heat inflow to the battery is calculated depending on the fuel flow and the calorific value using means 20. {(Fuel Flow*calorific value) / 1000000 gives net heat rate in Gcal / hr.)}. The battery temperature and heat flow to the battery are the inputs to a control model 30. The outputs of the model 30 are set point for the fuel flow for the next cycle. Means 40, 50, 60 are provided for controlling fuel flow, pause and draught set points for the next cycle. The heated period plus the not heated period (pause) is known as one heating cycle. -10- A brief description of the control model 30 is given below: The required input data coming from the plant is read using FIX. The program reads the data from the FIX database. A flag is generated by FIX database to indicate whether the battery is operating on rich gas or on mixed gas. The validity of each data is checked via a utility program built into FIX. The validity is done for the calorific value, fuel flow rate and all the regenerator thermocouple temperature. The implies that the data is checked for its value lying between the maximum and minimum value of the range. Case 1 (Mixed Gas Firing): In this case the calorific value will be Cvc_201 taken form ths FIX database. If this is out of range, then the program takes a constant value of 900 instead of the value read from the database. The actual fuel flow rate in the battery is Fy_102 + Fy_201 where Fy_102 is CO gas injection flow and Fy_201 is BFgas flow. Validation is done only for Fy_201. If this value is out of range, then the data has to be discarded. Case II (Rich Gas Firing) : No validation check is done for the calorific value and the value taken from the FIX database corresponds to the tag Cvr_201. The operator enters this value. The actual fuel going into the battery is CO gas and the corresponding tag value is Fy_101 in the database. If this is out of range then the data is discarded. -11- Case III (Half of the battery is running on rich gas firing and the remaining half on mixed gas firing): If Cg_901 = 0 and Fy_101>l000, then it is ensured that the battery is running in the above said condition. In such a case there will not be any control calculation or control action for the next cycle. The program skips until the battery comes to the normal condition (i.e. either rich gas firing or mixed gas firing). There will be no control action for the first one-hour. The program takes the data and stores it for 1 hour and gives the control calculation at the end of 1 hour (at the end of the 2nd Cycle). The program is designed with a basic idea of each cycle of 30 minutes. The cycles are defined as ODD and EVEN. In between each odd and even cycle there will be a pause of 20-60 second. During the pause there will be no flow of gas through the regenerators. The program actually stores the data during the cycle and gives me control output only after the start of the reversal i.e at the end of the cycle. The variable Rev_start denotes the reversal start and end. Rev_start=0,1 implies the start and end of the reversal. The operator enters the required data in the view screen of the FIX. The operator entries include the mode of firing, the set point for the heat rate, the heat allowance, the set point for the generator thermocouple temperature and the control flag. -12- Figure 3 is the FIX screen for operator interface.The FIX screen consists of three types of variables. Process Variables: These are the on-line process variables. RS_904: This is the FIX tag for the reversal start and reversal end. RS_904= 0,1 implies the start and end of the reversal. CG_901: This tag represents the mode for firing. If this is equal to 0, it means that the battery is running on mixed gas, if it is 1 then it is running on rich gas. CVC_201: calorific value of the mixed gas. FY_201: CO gas injection Flow FY_102: BFgasFlow CVR_201: calorific value of the rich gas FY_101: CO gas flow for rich gas firing. Operator Set points : These are the variables, which can be changed by the operator if required. AUT_MANUAL: This tag actually indicates an abnormality in the process. This has to be equal to 1 in order to run the model smoothly. HEREQD: This is the actual heat required by the battery. HEAT_ALLOW: The heat allowance required by the battery. REGTMP_SP: The set point of the regenerator thermocouple temperature. Calculated Variables: These are the model-calculated parameters. These are calculated once in every heating cycle. -13- P_TIME: The total time elapsed between RS-904=0 to RS = 1. P_TIME_SP: The set point of the pause calculated for the next reversal cycle. DRAFT_CORR_A: This is the suggested draft correction for Block A. DRAFT_CORR_B: This is the suggested draft correction for Block B VALID_TC: Number of valid regenerator thermocouples (in which the regenerator thermocouple temperature is within the range). FLOW_SP: Set point of the fuel flow for the next reversal cycle. HEAT_SP: Set point of the heat rate for the next reversal cycle. When the Rev_start=0, the program gives the calculated controlled ouput variables. This includes net heat gone to the battery during the cycle, heat rate set point, set point for the Fuelflow, Draft correction and the set point of the pause. All these program outputs are advices to the Operators who in turn execute the adjustments manually. In the control flow chart for heating module; to start with the program requires the following data values. Target regenerator temperature for the current cycle given by the operator (T*b), target regen-temp of the previous cycle set by the operator (T*B_L), measured or actual average regen-temp calculated by the program (Tb), average regen.temp of the last cycle (Tb_L), measured regen.temp of the last but one cycle (Tb_L-l), measured heat rate of the current cycle (H), target heat rate of the last cycle set by the Operator (H_L), The flow chart of Figure 4 is explained as below: The change value of the heat is calculated as follows: A = {(T*b-Tb)-T*b-L-Tb_l)} B = {(T*b-Tb)} C = {(Tb-Tb_L)} D = {(Tb-Tb_L)-(Tb,L-Tb_L_l)} Change value of heat {(C_heat)= (K1*A) + (K2B) - (K3C) - (K4*D)} The C_heat is compared with the heat allowance given by the operator, If the C_heat is greater than or equal to the heat allowance, then C_heat takes the value of the heat allowance. Then it checks for the status of the control flag. If the control flag is off, then target heat rate = measured heat (H) + CJieat. If the control flag is on, then target input heat rate = H J_ + C_ heat. The target heat is compared with its high and low limits. If it is less than its lower limit or more than its higher limit, then the corresponding limit is set for the target heat. If it is within the range then it takes the same value. This will be the heat set point for the current cycle. The program reads operator set points from the view screen. The operator can give the set point at any point of time during the cycle and the program reads it every minute. -15- Based on the calorific value and the fuel flow rate, the program calculate the actual heat rate in the battery, Heat_net = (fuelflow x calorific value) / 1000000. This gives heat rate in Gcal / hr. Average temperature of the valid regenerator thermocouples is calculated every minute and the cumulative average is obtained at the end of the cycle. Delta Heat is calculated based on the heat set point and the calculated heat from the input data. There exists three condition i.e. delheat less than 0, delheat greater than zero, and delheat equal to zero. Delheat > 0 and the pause time are within the range. In that case the pause set point for the next cycle will be equal to the minimum value of the pause. Delheat > 0 and the current pause is equal to the maximum value of the pause time. In such a case the pause set point of the next cycle will be equal to the average of the maximum and minimum values of the pause. Deltime is the difference between the current pause and the pause set point. Having the deltime, the residual delheat of the net delheat for correcting the fuel flow is calculated as follows. Res_deLheat=deltime X Calorific value X Fuelflow. -16- Delheat Delheat The delflow is calculated depending on the residual delheat. The difference between the delheat and the residual delheat divided by the calorific value gives the difference of flow to be corrected. Delflow divided by 1000 give correction to be made in the draft. Delflow added to the actual flow gives the set point of the fuel flow for the next cycle. The salient features of the automatic heat control system of the present invention are as follows: Real time process visualization through SCADA software (FIX 32 from intellution). -17- Interface with Level I system (Honeywell PLC). Historical trending of data Real time trending of the process parameters • BF Gas Flow • CO Gas Injection Flow • CO Gas Flow for Rich firing • Mixed Gas Flow Scanning and managing of alarms Average battery temperature: estimation from continuous on-line measurements of flue top temperatures at selected flue ducts. Heat demand and heat input computation: from (on-line) fuel gas flow, CV. Heat input control: scheme which includes fuel pressure / flow control, and pause control. Computerized process control: process parameter and process data tracking, process data storage and analysis to have a better control of the process. The benefits accrued from the heating control system is as follows: Uniform battery temperature. Uniform coke exit temperature (the range of the coke exit temperature is narrowed). -18- The fuel consumption is optimized. This is done through model generated set points, which are displayed in advisory mode to the operators who in turn can do the adjustment manually. This control can also be made automatic. The following are the controlled output variables given by the module which are to be implemented on the next reversal cycle. • The set point of the fuel flow • The set point of the pause time • Draft correction set point • Heat set point -19- WE CLAIM 1. An automatic heat control system for coke oven battery, comprising: means for estimating the thermal state of the coke oven battery; means for calculating heat flow to the coke oven battery; a control unit for processing said coke oven battery temperature and said heat flow to the battery and for generating set point for fuel flow for the next heating cycle and outputting said set points for automatic heat control of said coke oven battery. 2. The system as claimed in claim 1, wherein the thermal state of the coke oven battery estimated by said means is based on the temperature of thermocouples placed in regenerators of said coke oven battery. 3. The system as claimed in claim 2, wherein, said regenerator thermocouple temperature signals are directly fed to a programmable loop-cum logic controller (PLC). 4. The system as claimed in claim 3, wherein said PLC is a Tate Honeywell 620 - 16 logic controller with analog input handling capability. -20- 5. The system as claimed in claim 1, wherein said system is provided with means for controlling fuel flow, means for controlling pause and means for controlling draught, using said set points generated by said control module. 6. The system as claimed in claim 1, wherein a display unit is provided for displaying set point advices for heating control in advisory mode for use of the operator. 7. An automatic heat control system for coke oven battery substantially as herein described and illustrated in the accompanying drawings. An automatic heat control system for coke oven battery, comprising, means for estimating the thermal state of the coke oven battery, means for calculating heat flow-to the coke oven battery, a control unit for processing said coke oven battery temperature and said heat flow to the battery and for generating set point for fuel flow for the next heating cycle and outputting said set points for automatic heat control of said coke oven battery.

Documents:

00020-kol-2005-abstract.pdf

00020-kol-2005-claims.pdf

00020-kol-2005-correspondence-1.1.pdf

00020-kol-2005-correspondence-1.2.pdf

00020-kol-2005-correspondence-1.3.pdf

00020-kol-2005-correspondence.pdf

00020-kol-2005-description(complete).pdf

00020-kol-2005-description(provisional).pdf

00020-kol-2005-drawings.pdf

00020-kol-2005-form-1.pdf

00020-kol-2005-form-13.pdf

00020-kol-2005-form-18.pdf

00020-kol-2005-form-2-1.1.pdf

00020-kol-2005-form-2.pdf

00020-kol-2005-form-3.pdf

00020-kol-2005-form-5.pdf

00020-kol-2005-g.p.a.pdf

00020-kol-2005-others document.pdf

20-kol-2005-granted-abstract.pdf

20-kol-2005-granted-claims.pdf

20-kol-2005-granted-correspondence.pdf

20-kol-2005-granted-description (complete).pdf

20-kol-2005-granted-drawings.pdf

20-kol-2005-granted-examination report.pdf

20-kol-2005-granted-form 1.pdf

20-kol-2005-granted-form 13.pdf

20-kol-2005-granted-form 18.pdf

20-kol-2005-granted-form 2.pdf

20-kol-2005-granted-form 3.pdf

20-kol-2005-granted-form 5.pdf

20-kol-2005-granted-gpa.pdf

20-kol-2005-granted-reply to examination report.pdf

20-kol-2005-granted-specification.pdf