FIELD OF INVENTION
The present invention relates to an improved control system for blast furnace stoves. More particularly, the invention relates to a control system for predicting thermal status with suitable control strategy increasing the thermal efficacy of blast furnace stoves at desired time intervals.
The invention also relates to a method for prediction of thermal status and controlling the stove operation with improvisation of the thermal efficacy of the blast furnace stoves.
BACKGROUND AND PRIOR ART
A blast furnace is provided with three or four stoves to preheat cold blast to a higher temperature before sending to blast furnace. The stove consists of two parts - combustion chamber and checker work both made of refractory. Stove is a regenerator consisting of two alternate cycles - heating and cooling cycle. During the heating cycle, the stove is heated by the combustion of fuel gas in the combustion chamber. The combustion products leaving the combustion chamber enter the dome of the stove and then flow downward through checkers to heat them up. During cooling cycle, cold blast air enters the bottom of the checker and travels upward through the checkers, where it is heated, enters the dome and then exits the stove. The temperature of the blast air leaving the stove is controlled by mixing with cold blast using the mixer valve.
Typical stoves of blast furnace are considered, which have a blast rate of 2,000-2,200 Nm3/min. The fuel fired is BF gas enriched with BOF gas (CV = 750-780 kcal/Nm3) and throughput capacity of 35,000 Nm3/hr per stove. Blast furnaces are provided with distributed control system (Toshiba make CIE 1200) for Level-I control.
JP2005325446 discloses improvement in thermal efficiency in the operation of a hot blast stove, as regards the control method of the hot blast stove for supplying hot blast into a
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blast furnace, a controller, a control system, a computer program, and a computer readable recoding medium. The blast furnace stove is controlled using control parameters as gas flow rate and combustion gas temperature so as to improve the thermal efficiency.
US 5 3 56220 describes a method and apparatus for monitoring temperature of blast furnace and temperature control system using temperature monitoring apparatus. Temperature distribution is measured based on the intensity of Raman back scattering light by using an optical fiber. The temperature distribution is displayed on a display screen to monitor the temperature distribution of the whole area of the iron skin of the hot-air oven to detect an abnormal condition thereof.
The existing system comprises of distributed control system (Level-1 control) which suffers from the following drawbacks / disadvantages:
A. No knowledge of on-line thermal status of stoves
B. No cycle wise performance data of stoves
C. No audio-visual signal for the heater with the event of stove changeover
D. No prediction of hot blast temperature in forthcoming cycle
E. No storage of performance data of stoves
F. Thermal imbalance in stoves leading to poor compaign life, spalling of stove
refractory and more fluctuations in HBT
Thus there is a need to provide for a control system and method for predicting thermal status with suitable control strategy increasing the thermal efficacy of blast furnace stoves at desired time intervals.
The present inventors have now found that a control system comprising of supervisory control module being provided with an on-line mathematical model having some desired functionalities can predict thermal status at desired level of residual heat for desired hot blast temperature (HBT) and current blast rate providing suitable control strategy increasing the thermal efficacy of blast furnace stoves at desired time intervals. The model may also be used to predict cycle-wise performance parameters of each stove for
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analysis of stove performance leading to poor thermal efficiency, so that corrective action can be taken by the operator to improve the thermal efficiency.
OBJECTS OF INVENTION
Thus one object of the present invention is to provide a supervisory control module.
Another object of the present invention is to develop dome temperature input based on-line mathematical model of stove to predict thermal status of each stove at desired interval of time.
Yet another object of the present invention is to provide a suitable control strategy for efficient running of stoves with improved thermal efficiency.
Yet another object of the present invention is to provide a method for controlling the thermal status with improvisation of the thermal efficacy of the blast furnace stoves.
SUMMARY OF INVENTION
Thus according to one aspect of the present invention there is provided a control system for predicting thermal status with suitable control strategy increasing the thermal efficacy of blast furnace stoves, said system comprising:
a supervisory control module operatively interfaced with a data acquisition system; wherein said supervisory control module comprises on-line mathematical model adapted to predict residual heat for desired hot blast temperature of stoves.
Another aspect of the present invention is to provide a control system for predicting thermal status with suitable control strategy increasing the thermal efficacy of blast furnace stoves, said system comprising:
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a supervisory control system provided with main model program module and stove status program module, characterized in that the main program model comprises plurality of input sections and output sections wherein said input sections being adapted to receive predetermined parametrical data on-line and/or off-line; and wherein said output section generates data as required by the operator.
Yet another aspect of the present invention is to provide a method for controlling the thermal status with improvisation of the thermal efficacy of blast furnace stoves, said method comprising steps of:
execution of main program model in a desired background and establishing a relationship with the stove status program model such that stove performance of all stoves are calculated at a predetermined interval of time;
execution of stove status program model in the foreground adapted to view predetermined parameters of stoves.
DETAILED DESCRIPTION OF PRESENT INVENTION
The control system of the present invention consists of the following components
(i) Existing data acquisition hardware and software (hereinafter referred to as
"Level -1 control")
(ii) Interfacing hardware and software with switch (iii) Supervisory control module (iv) Application software (v) On-line mathematical model
EXISTING DATA ACQUISITION HARDWARE AND SOFTWARE:
Broad specification for data acquisition system (DAS) installed for level-I control is given in Table-1.
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Table-1: Specification of DAS (Existing)
1. Distributed control Toshiba (CIE 1200)
system
2. PLC Consists of Central Processing Unit (CPU), having the following
specifications; i
User memory : 72 KB for program and 72 KB for data
Flash EPROM (micro memory) : 2 MB
Execution time for bit operation: 2 µ sec
Counters: 256
Timers : 256
Capacity to handle Analog Inputs: 128
Capacity to handle Digital inputs : 512
3. Thermo-couples K type & R type
4. Transmitters Air, Gas & steam flows, pressure, temperature transmitters
5. Orifices/venturies Primary flow elements
6. Gas analyser Waste gas O2 analyser
7. Controllers Toshiba make (EC311 /EC 321)
INTERFACING HARDWARE & SOFTWARE WITH SWITCH
Broad specification for interfacing hardware and software is given in Table-2.
Table-2 : Specification of interfacing hardware and software
1. Network interface card 10/100 Mbps
2. Ethernet cable CAT 5 type
3.Ethernet switch 8 port
4. FIX32 Version 7.0 (600 I/O, Development+Network)
5. Interface Library software FIX integration toolkit to interface VC++/VB programs with FIX32 (version 7.0)
SUPERVISORY CONTROL MODULE: Supervisory control module of the present invention comprises on-line mathematical model and control of stoves using model run in a computer. The specification of the PC is as given in Table-3.
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Table-3: Specification of PC
Processor Intel P-IV Processor with HT technology , 3.0 GHz
Cache memory 1 MB, integrated L2
RAM 512 MB RAM, 400 MHz
HDD 40GB at 7200 RPM
CD drive CD ROM
Monitor 19" CRT monitor, 24 bit color, 1280X1024 max resolution
OS Window 2000 Professional (service pack 4)
APPLICATION SOFTWARE
Broad specification of application software is given in Table-4.
Table-4: Specification of application software
1. Macromedia Flash Studio MX 2004
2. MS office Professional edition 2003
3. MS VB/VC++ Visual studio 6.0
SUPERVISORY COMPUTER SYSTEM AND METHOD OF CONTROL
The functionalities and the modules of the supervisory control system are described in greater details below:
1. On-line prediction of thermal status of stove
2. Cycle wise performance data of stoves
3. Audio-visual signal for heater with the event of stove changeover
4. Prediction of HBT in forthcoming cycle
5. Storage of performance data of stoves
6. Trending of process parameters
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On line prediction of thermal status is accompanied by a mathematical module. One dimensional model of BF stove by assuming all channels identical and neglecting conduction in the checker work has been developed.
At any moment, rate of heat absorbed or given out by the checker equals rate of heat
transfer from the gas or to the gas represented by the following equation:
mscs Ts/t =hA(Tg -Ts) - (1)
At any moment, amount of heat convection in the gas or out from the gas in the direction of flow equals heat transfer from checker or to the checker represented by the following governing equation:
Vg cg L Tg/y = h A (TS - Tg) (2)
Vg is the flowrate of gas
Cg is the specific heat of gas
L is the height of checker
Tg/y is the gas temperature gradient
h is the overall heat transfer gradient
A is the surface area surrounding checker hole
Ts is temperature of checker
Tg is temperature of gas
The above governing equations alongwith boundary and initial conditions were discretized using finite difference technique and program in "C" was written to solve the same. Tuning of model was done by comparing with measured waste gas temperature during heating period and comparing hot blast temperature with measured ones during cooling period.
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HEAT BALANCE CALCULATION Heat input
Sources of heat in the stoves are potential heat of fuel, sensible heat of combustion air and sensible heat of fuel in the heating cycle.
Qin = [Qp + Qa +Qr].Tg (3)
QP = VfFcv (4)
Qa = Vacata (5)
Qf=Vfcitf (6)
Heat output
Assuming dynamic equilibrium, output part has three components - heat given to blast, heat taken by flue gas and losses.
Qout = Qb tb + Qfl tg + Qloss [tg + tb + Dt] (7)
Qb = Vb(cb2T2-Cb,T1) (8)
Qfi = VflCfltfl (9)
Qloss = 0.085 Qin ifTc<=1200°C
= 0.090 Qin if Tc>1200°C (10)
Efficiency of stove
r| = Heat supplied to the blast in a cycle/ Total heat input in the cycle
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= Vb (cb2 T2- Cb. T, ) tb / { Vf Fcv + Va ca Ta + Vr crTr) tg ]
(11)
where, Vb is the flowrate of the blast; Cb2 is the specific heat of hot blast; T2 is temperature of hot blast; Vf is the flowrate of gaseous fuel; Cf is the specific heat of gaseous fuel; Tf is the temperature of gaseous fuel; Fev is the calorific value of gaseous fuel; Va is the flowrate of combustion air; Ca is the specific heat of combustion air; Ta is the temperature of combustion air; tg is heating duration of gaseous fuel.
The method of prediction of the thermal status of the blast furnace stoves and providing
control strategies to the user comprises:
i. Main program model
ii. Stove status program model
MAIN PROGRAM MODEL
This program has been developed in VC++ to run in the background. Whenever computer is switched on, this program is loaded automatically. Input and output sections are as follows:
Input Section
Inputs to the model are off-line as well as on-line.
Off-line inputs are:
i. Thickness and thermal properties of insulation layer in the wall
ii. No. of checker holes
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iii. Size of checker hole and their spacing On-line inputs are:
i. Dome temperature
ii. Cold blast temperature
iii. Blast rate
iv. %of mixer valve opening
Output Section
Main parameters calculated from the model are:
i. Exit waste gas temperature
ii. Hot blast temperature
iii. Temperature distribution of checker work across the height
iv. Gas temperature across the height of checker hole
v. Total and residual heat content of checker work
vi. Cyclewise heat balance and stove efficiency
This program is responsible for calculation of control parameters, generation of report
files and data files for historical trends.
STOVE STATUS PROGRAM MODEL
This program has been developed in VB to run in the foreground. Whenever computer is
switched on, a welcome screen with a button named "stove program" appears. Clicking this button loads stove status program in the computer. This program has been provided with following features:
Main screen:
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All important parameters for monitoring three stoves are captured in the main screen as shown in Fig. 2 with a refresh rate of 10 seconds. Actual heat contents of stoves as calculated by background model program and desired residual heat content for stove on blast predicted by stove status program are displayed in this screen.
A visual pop-up blinking screen appears in the middle of main screen, whenever model predicts for stove change over to alert the heater. This screen guides the heater to change over with proper identification of stoves. The screen disappears as soon as heater initiates some action for the same.
Animation program:
After clicking button "stove show" in the main screen animation program is activated. A new screen appears showing the status of each stove in animated form. Flows of gas and blast are simulated with different colors and stove on gas, on blast or on isolation can be easily recognized from distance.
Graphics Section
By clicking button "Graphics", historical trends of stove important parameters are displayed. Historical trends of following parameters are provided:
(i) Dome temperature
(ii) Waste gas temperature
(iii) HB temperature
(iv) Gas flow rate
(v) CA flow rate
(vi) CB flow rate
(vii) Checker temperatures at top, middle and bottom locations
Graphics are user friendly and following features are incorporated :
i. Multiple selection of parameters to see the simultaneous trends of two or
more parameters is provided
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ii. Trends are displayed shiftwise by pressing "Previous Shift"' or ''Next Shift" buttons.
iii. Trends can be seen for other stoves by pressing "Next Stove" button
iv. Movement of cursor line by pressing PgUp or PgDn keys allows display values of all graphic parameters and status of stove with time (time resolution - 1 min.).
Report viewing
By clicking button "Report" we can view all model and MIS reports as described later. Updation of CV and Air/Gas ratio
By double clicking button "Calorific value", a prompt screen appears to enter % CO and % H2 of BF gas. It calculates current CV and corresponding Air/Gas ratio and displays them in the main screen.
Updation of duration
This is required first time after computer restart. Duration of stove on gas or on blast needs to be entered by clicking button "Duration" for each stove.
Stove change over control
Clicking this button enables heater to change over stove from this terminal itself.
Automatic/manual stove change over control
Clicking this button enables heater to switch over from manual stove change over to automatic stove change over and vise-versa. This button prompts for an encrypted
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password screen to prevent un-authorized entry or to check against accidental click of this button.
Audio signal stoppage
Whenever model predicts stove readiness for changeover, in addition to visual signal, audio signal for duration of 2 minutes is generated. The heater can stop this audio signal prematurely by clicking this button.
System Shutdown
By clicking button "Login" it prompts for encrypted password, which enables system shutdown by authorized person.
MODEL REPORTS AND MIS
Following reports and MIS are generated -
i. Event Log Report - logs computer start/restart date with time, predicted stove changeover ready time with stove numbers and actual stove changeover time. This report is saved monthwise with backup of 12 months.
ii. Stove Daily Report - contains daily average (6 AM to 6 AM basis) values of HBT, RAFT, Gas flow rate, CA flow rate and CB flow rate. This report is saved monthwise with backup of 12 months.
iii. Cycle parameters (stovewise) - contains cyclewise on-gas start time, on-blast start time, gas duration, blast duration, average gas flow rate, average HBT, average CB flow, cycle efficiency and total checker heat contents at end of gas and blast periods respectively. This report is saved stovewise and monthwise with backup of 12 months.
iv. Model output Report (stovewise) - contains at frequency of 5 minutes parameters like checker heat content; top, middle and bottom layer checker temperatures; top, middle and bottom layer gas temperatures; measured waste gas temperature; calculated as well as measured HBT; dome temperature; dome temperature rise rate; Gas flow rate and air/gas ratio and BFG pressure. This report is saved stovewise and datewise with backup of 12 months.
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v. Stove parameters at a glance (stovewise) - contains at frequency of 5 minutes parameters like dome temperatures at two locations, waste gas temperatures at two points, gas flow rate, CA flow rate, combustion chamber temperature. CA temperature and gas temperature. This report is saved stovewise and datewise with backup of 12 months.
vi. Common stove parameters at a glance - contains at frequency of 5 minutes common parameters like HB temperatures at two locations, % opening of mixer valve, CB flow rate, CB temperature, CB pressure, HB pressure, steam flow rate, BF gas line pressure, CA line pressure and RAFT. This report is saved datewise with backup of 12 months.
PROCESS CONTROL SCHEME
The model considers input like dome temperature, cold blast temperature, blast rate, blast humidity, stove changeover events, mixer valve opening, etc. The output of the model is checker temperature, hot blast temperature, Exit flue gas temperature, stove efficiency, actual heat content of checkerwork, etc with time. It also evaluates desired level of residual heat for desired HBT and current blast rate. It checks for the maximum achievable HBT for a given condition and informs the operator for the same. It keeps comparing actual and desired residual heats. The moment actual heat becomes less than desired residual one, stove changeover moment for the current cycle is predicted. This prediction is to be in tune with existing practice incorporating safety features.
The details of the invention, its objects and advantages are explained in great detail in relation to non limiting exemplary embodiments of the improved method of blast furnace stoves control system of the invention in relation to the accompanying figures.
BRIEF DESCRIPTION OF ACCOMPANYING FIGURES
Figure 1 shows the scheme for supervisory control system in blast furnace stoves.
Figure 2 shows the main screen for stoves control.
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Figure 3 shows flowchart inter-connection among various control block of the system of the present invention.
DETAILED DESCRIPTION OF ACCOMPANYING FIGURES
Reference is invited to figure 3 where transducer/transmitters (10) is adapted to convert field signals into supervisory control module signal. Main four program modules (100,200,300;400) are required to be executed in the supervisory module. Processing block (100) comprising SCADA programming block along with I/O driver (110) brings field signals into processor (100).
Model program block (200) running in the background accepts input block (20). Input block (20) represents off-line section containing off-line data like design parameters of stoves, etc. Block (200) is adapted to calculate stove performance of all the stoves in turn and repeatedly at regular interval of time which can be varied between 30 seconds and 120 seconds considering input from block (20) and on-line data from block (120). Calculated parameters are fed in block (210) and block (120) for further processing by other program blocks. Block (120) collects mainly on-line data from field signals via block (100) and (110) at regular interval of scanning. This block is also being updated by program blocks (200) and (400). This is responsible to download data to master control station and micro-processor based controllers identified as block (1200).
Animation program block (300) is event driven program. This consists a set of animated programs, each set simulating a particular condition of all stoves together, eg condition of stoves #1 & #2 on-Gas and stove #3 on-blast, etc. This block interacts with program block (400), where decision is taken about a particular block of animated program and fresh execution of another set of animated program is also decided by block (400).
Stove status program block (400) is the main computer screen running in the Foreground. This is responsible for interaction with operator shown as block (410). Input from
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operator block (410) is passed to this block to take further action and similarly some actions/decisions taken in block (400) are passed on to the operator (block 410). Various actions/decisions taken in block (400) are executed in four main blocks namely (420), (430), (440) and (450).
Block 420 represents screen display consisting of important stove performance and control data. Fig.2 gives elaborate list of data display stove-wise. Block (430) consists of various reports, whose detail description is provided section "'Model reports and MIS". Block (430) gives historical trends of some of important parameters for stove control, which are required for critical monitoring. Block (440) represents event-based system detected audio-visual signals, which are meant for operators" guidance to change-over stoves.
The system of the invention is thus a cost effective solution for an improved method of blast furnace stoves control system in a Blast Furnace.
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WE CLAIM
1. A control system for predicting thermal status with suitable control strategy
increasing the thermal efficacy of blast furnace stoves, said system comprising:
a supervisory control module operatively interfaced with a data acquisition system; wherein said supervisory control module comprises on-line mathematical model adapted to predict residual heat for desired hot blast temperature of stoves.
2. A control system for predicting thermal status with suitable control strategy
increasing the thermal efficacy of blast furnace stoves, said system comprising:
a supervisory control system provided with main model program module and stove status program module, characterized in that
the main program model comprises plurality of input sections and output sections wherein said input sections being adapted to receive predetermined parametrical data on-line and/or off-line; and wherein said output section generates data as required by the operator.
3. System as claimed in claim 1, wherein on-line mathematical model is adapted to
predict amount of heat convection in or out of gas at any moment represented by
equation

where, Vg is the flowrate of gas
Cg is the specific heat of gas
L is the height of checker
Tg/y is the gas temperature gradient
h is the overall heat transfer gradient
A is the surface area surrounding checker hole
Ts is temperature of checker

Tg is temperature of gas
4. System as claimed in claims 1 to 3, wherein efficiency of the stove is given by
r\ = Vb (cb2 T2 - cbi Ti )tb / { Vf Fcv + Va ca Ta + V,- cfTf) tg }
where Vb is the flowrate of the blast;
Cb2 is the specific heat of hot blast; T2 is temperature of hot blast; Vf is the flowrate of gaseous fuel; Cf is the specific heat of gaseous fuel; Tf is the temperature of gaseous fuel; . Fcv is the calorific value of gaseous fuel; Va is the flowrate of combustion air; Ca is the specific heat of combustion air; Ta is the temperature of combustion air; tg is heating duration of gaseous fuel.
5. A method for controlling the thermal status with improvisation of the thermal
efficacy of blast furnace stoves, said method comprising steps of:
execution of main program model in a desired background and establishing a relationship with the stove status program model such that stove performance of all stoves are calculated at a predetermined interval of time;
execution of stove status program model in the foreground adapted to view predetermined parameters of stoves.
6. Method as claimed in claim 5, wherein the time for calculation ranges from 30
seconds to 120 seconds.

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7. Method as claimed in claims 5 and 6, wherein stove status program model
adapted to provide parametrical values- of dome temperature, waste gas
temperature, HBT, gas flow rate, calorific value and air/gas ratio.
8. Method as claimed in claims 5 to 7, wherein stove status program model
comprises graphic section wherein multiples parameters are selected and are
displayed shift wise by pressing means.
The present invention relates to a control system and method for predicting thermal status with suitable control strategy increasing the thermal efficacy of blast furnace stoves.The system comprises a supervisory control module operatively interfaced with a data acquisition system.Supervisory control module comprises on-line mathematical model adapted to predict residual heat for desired hot blast temperature of stoves.The supervisory control is provided with main model program module(100,200,300,400)and stove status program module.The main program model (100,200,300,400) comprises plurality of input sections and output sections (410) receiving and generating parametrical data.The method comprises execution of main program model in a desired background and establishing a relationship with the stove status program model such that stove performance of all stoves are calculated at a predetermined interval of time;execution of stoves status program model in the foreground adapted to view predetermined parameters of stoves.