Contribution of Control Systems to Energy Savings in Steel Works

Copyright C IFAC AUlOmation in Mining. Mineral and Meta l P rocess ing. Helsinki . Fin land. 1983

CONTRIBUTION OF CONTROL SYSTEMS TO ENERGY SAVINGS IN STEEL WORKS Y. Yoshitani Professor of Cont rol Engineering, Technological University of Nagaoka , Kamitomiokacho Nagaoka, 949-54, J apan

Abst r act. The Japanese stee l i ndustry succeeded 1 0 % of energy savings and 70% r eductions of pet roleum fue l within t h e past ten years even in the prolonged market stagnat i ons . Th is paper reviews how the in str ume n tat i on an d con t rol s ystems has cont r ibuted fo r the success of energy savings. Keywords. I n strumentat i o n, Process contro l, Computer control , computersystem app l ication , microprocessors , stee l industry .

I ntrod uction

yield imp r ovements. Proportional energy savings could be possib l e by t h e yie l d improvements . One of the characteristics of energy structure of i ntegrated iron and ste el wo r ks is that near l y half of the energy are cor.sumed in the ironmaking area. About 70 % of energy are intro duced in the form of coal . The r efo r e , the cont r ibutions of blast furnaces to the energy consumption are very heavy . Even the thermal efficiency of blast fu r naces are said h i ghest among the chemical reactors , the energy con sumptions of blast furnaces acount for 54% of the total energy consumed i n the works. Stab l e operation wi th l ow fuel rate of the blast fu r naces are essential for t h e energy saving of the integrated iron and steel wo r ks . Advent of oxygen steelmaking that has became popular since 1960 had made re markable energy savings by the effective use of latent heat of hot meta l and reaction heats . Al so the applicat ions of continuous cast i ng process has promoted t h e energy savings i n t h e stee l making area . As the results , the energy consumption i n steelmaking area became very small percentages. Useful energy in the integrated stee l works are relative l y hig h among the ind u stries . Recoverable energy from the waste heats are abou t 30% as s h owen in the Table.2. However , they r eq uire relatively high investiment cost for t h e recove r y .

Th e steel industry has been consider ed a s a huge energy consuming indust r y . Actually 15 %of energy were consum ed by t h e steel industry alone in 1980 in Japan . ( 17% in 1970 ) Energy saving has been always a serious problems in t h e industries s i nce she depended on h eavily wit h imported energy . Needs of energy savings h ad became stronger since t h e oil crisis . Also the oil c ri s i s tr i ggered wo r ld wide econom i c s t agnations. Many stee l works has been s uffered with low product i ons and in c r ease of cost . Various activities on energy sav i ngs has been started since 1973 , such as the promotions of bette r combustion and developments of new heat recovery systems. There are five princple routes for the energy savings as the followings . 1. Improving yield

2 . Improving productivity 3 . Imp r oving process efficency 4 . Improved energy management 5 . Heat recovery from wasted heats I ns trumentation , process control , and computer contro l system are al l vital t ools fo r those routes . Me n u sed to thi nk di r ect l y about fue l saving s when they co n cern about energy savings . Howeve r, t h e first essen tial app r och f o r t h e reduction of energy cons umpt ions is a improvement of product yie l d. Ha l f of t h e energy sav i ngs that has been s aved by the stee l ind u stry in the pas t decade were contributed by 25

Y. Yoshitani

26

Table.l. Percentage energy consumptions in integrated steel works in the N.S.C. in 1979. process coke oven sintering blast furnace Steelmaking Continuous Casting Bloomig and Slabbing Hot rolling Cold rol l ing Power plant

percentage 6.8 12.3 54.0 0.4 0.8 2.7 10.5 5.1 6.6

Various form of energy are used in the integrated steel works. About 70% of energy are introduced in the form of coal. Three types of byproduct gases are available,namely, COG, BFG,and LDG. Since their supply are limited, effective utilization of those gases are important for the energy savings. Main flow of various energies in the integrated steel works is illustrated in the Fig.l. Electric power are mainly consumed in the rolling mills, blast blowers, and oxygen plant. The power cost are relatively high in the Japan. Previously, power consumption per ton of crude steel was around 250 kwh per ton. However, it had been increased to 600kwh due to the increase of finishing degree and the environmential protections. Introduction of new process such as the continuous casting and continous rolling and treatment has been contributed greatly for both improvements of yields and energy consumptions. However, those new processes are somewhat inflexible for change of size and grade of steel products. Increase of products variety are common trends of modern industries. The steel industry has been requested more product mix similar to other industries. The steel industry has to meet such market requrements. Quick change of the production from one products to another is important for the better productivity. Thus the production scheduling system and production information system becomes more vital for the coordination of related processes and frequent change of the productions. Of cource, the better instrumentation are essential for the energy savings for both tight control of the process and production managements. Especially, temparature,flow, and weight measurments are the basis of energy savings. Equal cares should be taken to all the problems from tracerability of the instrumentations and to the maintenance of many systems in the works.

Table 2. Percentage energy consumptions in integrated steel works ( NSC 1975 ) Useful energy 56.5% Metallurgical reaction heat 29.0 Rolling and tranceport energy 16.3 Latent heat of rolled semi-finish products 11. 2 Recoverable heat Latent heat of products 13.0 Cooling water 9.0 Combustior. heat loss 8.0 Non recoverable Furnace wall loss 8.5

2. Production control system First integrated production control system (PCS )was started in 1968,1n the Japanese steel industry. ]1owever the appriciation )f the PCS was not so good due to its ambiguous economic returns except man power savings. There are many benefits of the PCS which are difficult to estimate quantitatively,such as stable production by better scheduling and a benefits gained by quick actions during a miII delay. As I mentioned previously, the application of new processes require more tight sychronious operations. The Japanese steel industry concentrated for the adaptation of contino us casting since it was a only solutions which expected big energy savings and yield improvements. However, the problems of continous casting are inflexibility of size and grade changes and low productivity. One of the solution for this is good communication between the steelmaking and rolling mills. Introduction of continous casting has been accerated since the oil crisis. Ratio of continuously casted semi-finished products had been increased from 20% in 1973 to 74.2% in 1981. The high operating practices and proper machine adjustments are the basis of this high dependance with the con tinuous castings/however, the sound PCS is vital for the success of such new process. Energy center has been installed for better distribution of energy and efficient use of energy since 1960. However, because of the complex structure of energy in the integrated steel works, the extent of demand and supply control were somewhat restricted in the individual control, such as electric power,byproduct gas; water, and etc. Review of energy dis-

Contribution of Control Systems

tribution had been done in monthly bases. Big power cost savings would be anticipated through the proper adjustment of rolling mill schedule for the reduction of peak load. Also better utilization of byproduct gas will be expected by the adjustment of production schedule and maintenance program. It is not a easy task to develope an optimum energy distribution model due to the complex energy structure of the steel works. It require various basic datas such as individual energy consumptions for the estimation of energy demands. It is possible to h ave such data gethering system within the computer system of energy center, howe ver , it is costly. If the data bank of production control system is available, it will be easy to introduce optimum distribution system in the energy center. Also the pes needs energy informations from energy center if they wish to introduce actions for total energy savings. Fortunately, the integrated steel works in the Japan already prepaired on -line production systems when the oil crisis had happened, although the degree of computerization differ from works to works. Also the computer control of individual processes had been developed in relatively resonable level. Number of process computers in the Japanese steel industry had 280 sets in 1973 and the inst e llations has been increased steadily to 946 sets by 1983 even in the prolong market stagnation. By the progress of data trans mission, it became easier to exchange processed informations between the various computer centor and the shopes. Thus the introduction of integrated energy managment system became feasible with far less investiment cost than before. 3. Energy management system The steel works consume huge amount of water,steam,oxygen, and compressed air They equally consume energy for their generations and supplies. They should treated as a kind of energy in the total energy management, which is the basic idea of energy center. Another aim of energy center is the integration of operation of various stations scattered inside the works for the man power savings. Principle aim was naturally the energy savings through better distribution and efficient generations of power, oxygen, and etc. However, the adjustment of production schedule in view of supplies had been reviewed only in long term basis. Daily decisions for the energy management had been left to the engineers and operators decisions in the energy center. Yet the benefit of energy center in the 60's were 1. man power savings by the integration 0f operation of stations.

2. 3.

27

Better utilization of byproduct gases. Quick actions for emerge ncies

After the pollution problems bec ame serious issue in the industries since 1965, the energy center were effectively used as the monitoring and control center of pollution. The atmospheric pollution has direct relati on with the fuel consumptions. 30metimes it require to switch from high sulpher fuel to low sulpher fuel depend on total sulpher dioxide emission . The energy center was a best instellation for the control of both quality of water and atmospher. By the progress of computer systems in the steel works, the application of optimal distribution system became feasible since 1975. Trend of energy management system is summerized in the Table 3. Hard ware configuration of recent energycenter useing optical data highway is showen in the Fig.2. Various optimalizing techniques are now avariable such as the liner pro graming. The energy management model are different from works to works . However , the princple of models are based on the objective of reduction of purchased energy minimum. A exsam ple of the energy distribution model structure is showen in the Fig.3. One works reported that about 1% of energy has been saved, and another reported that they saved 0.4 million dollors per year by the application of optimal distribution system . 4. Iron-making area Over half of the energy has been con sumed in the iron making area. Stable operation of the blast furnaces is a first task for the energy savings. Their operation will also influence downstream operations and the generation of byproduct gases. Stable comp osition of byproduct gases wil l pro mote better combustion in the heating facilities. Studies of the blast fur nace has a long history since the begining of the computer control . It took considerable time and efforts to achieve effective control system due their complexities of the process and a lack of reliabl e sensors. Variouse instruments for both monitoring and control of the furnaces has been actively developed by many steel works and the institutes of the world . Present instruments and sensors installed in the furnace are listed in the Table 4. Avariable control means in the common blast furnaces are

28

1.

2. 3. 4

Y. Yoshitani

Materlal prcperties (physical and chemical properties) Material charging conditions (stock line level,coke base, ore/coke ratio) Blase conditons (wind distribution, flame temp., fuel injection) Others (tuyer size, tapping condi tions)

It was difficult to control desired burden profil and also the instrumentation on top of the furnace was poor with a conventional bell type chargl~g system in the past. Along with the developments of new charging control system such as a rotating shute charging device, active studies on the developments of instruments for measurment of top gas flow and temperatue distribution, and burden proflle,has been done in many steel works. Control of the P-W type charglng system itself require delicate control, however, it will be worthl~ss without a relieable burden prof11e meter. A mechanical type, a m1crowave type, and a leaser type had been tried. Among them, the leaser profile meter seems promissing. By the fast progress of image processing, they applied for many pattern measurments in the steel industry. Fro~ ITv,image through the tuyers, var10US 1nformations such as the coke size and flame luminosity were obtained by the image processing. Those informations has been used for the monitoring of the blast conditions. Two flow measurments by correlation method had been developed for the slag flow and the pulvalized coal injection flow. Flow control of slag water quench became possible by the development of slag flow meter. It was reported that 30% of power had been reduced by the application of slag water flow ratio control, and the quality of quenched slag has been 1mproved. Studies of computer control of the blast furnaces had started since the begining of the computer control. However, it took considerable time and efforts to achieve acceptable control system due to their complexity of the process and the lack of reliable sensors. Studies of the mathematical models of the blast furnace has been contributed greatly for the understanding of the process and operations, and used for both for the determination of short and long range policies of the furnace operations. Failure of early application was due to the use,of few variables. The process are h1ghly complex multi-variable system, and the operating policy

has to decide from more informations. In the early 70's,the total decision model had been proposed by the combination of permeability model of the shaft and heat model of the lower zone of the furnace. Application of dynamic model which was concerned both reactions, heat transfer, and gas flow had been started since 1975. Recent trends of the computer control system are, 1. development of integrated control system, 2. two dementional dynamic model, and 3. conversational data analysis and display. Recent concepts of blast furnace control system is illustrated in the Fig.4. Man-machine interface of the funace control pulpit has been revolutionary 1mproved by the use of CRT display and m1croprocessor based instrumentation. Operators can call far more informations from the data bank with far better display. They can able to call previous performance of the furnace if they wish to compair present furnace conditions. It is difficult to estimate benefits of those instruments and control system, however, the stable opera ton of furnace with low fuel rate are only poss1ble through those instruments and control systems. 5. Steelmaking area The success of the computer control of BOF process has been presented in various papers,therefore, I will mention here few topics in relation to the energy savings. Previously the recovery of BOF off gas was around 70 Nm'per ton of crude steel with conventional hood presure control. With precise control of recovery cycle by the estimation of off gas generation, 100 Nm~ton of recoveryhas been achieved in the OG system. Hot metal are transported by either torpido car or open ladles. One of the works introduced trucking system for the torpido transportation, and succeeded the reduction of hot metal tempareture drop during the transport within less than 130·C by the efficient transport of torpido cars. This is a,exsample of energy savings by the 1mprovement of handling procedure between the two processes by the tracking and information system. The soaking pits operation are the typical of such case. Major energy savings has been brought from the application of continuous casting and direct rolling from hot slabs and blooms. Development of CC instrumentation had been delaied due to the sevier emvironment of the process. Various sensors had been requ-

29

Contribution of Control Systems

ested for the control of CC process as showen in the Fig.5. Many types of sensors had been tried for mould level alone. It took considerable time and efforts for the developments of those sensors. Various control systems were required for the stable operation of CC-process. Also the adjustments of machine before the casting such as pinch roll adusthlents are very important. Breakout has been a big problem, therefore, breakout monitoring are also requested. By the progress of those instrumentation and control systems, the CC process became acceptable, and the applications had steadily increased sinc e 1970. Several integrated works now depend on 100% CC operations. Mould level control which is one of the key control of CC process will influence by various disturbances such as variation of casting speed tundish level, flow characteristics change of nozzle,and mechanical backlash of sliding nozzle actuator. Those factors should be consider in the design of level control. Some works are introduced auto-start up and stop for the stable startup and shutdown. Several breakout monitoring system h as been developed based on either change of friction between the mould and the shell, or the change of mould surface temperature. Prev iously, the casted slabs were fully cooled down for the surface inspection and conditionings. However, because of the energy savings, many works started direct rolling from hot slabs. It is better to keep as much slab heat as possible for the direct rolling. Two problems arised in the application of direct rolling. More precise control of secondary cooling and on-line hot surface inspection are required. The secondary cooling control were al ready solved by the application of cooling model and actual surface temperature feedback. Howe ver , the hot surface inspection are not standarized yet. Various approaches has been tried in many steel works. Some works use inspector with remote viewer, and some has automatic inspection system with automatic slab marking devices. The Fig.6. shows control system of one of the typical CC-OR process. This steel works succeeded 90% of OR in 1982. A electro-magnetic ultrasonic transducer has been de v eloped, and are applied for the measurment of solidified shell thickness.

6.

Control of heating combustion

and

Process control were first applied for the combustion control in the steel industry. They were successful in the early technical levels, however, there were many basic problems in the instrumentations and control, such as temperature and flow measurements. Fuel-air ratio control has been improved by the feedback of wast gas oxygen content due to the progress of zirconia oxygen sensors. Thermal efficency was improved 0.3 % over the conventional feedback control by the combination of waste gas oxygen control and feed forward control in the blast hot stoves. Because of inaccuracy in the low flow rate in the orifice flowmeter, it is difficult to keep accuracy of fuelair ratio in low flow rate, such as the case of soaking period of sorking pits. Waste gas low oxygen control solved this problems. Many soaking pits and feheating furnaces are now using this low oxygen control. Generally speaking, a rolling mill had less heating capacity than the rolling capacity. Previously, frequent mill delay were common due to low tchnical level. Rollers wish to produce more, and thus the rolling pitch often exceeds over the reheating capacity when the rolling were in good conditions. As the results, mill delay will happen due to drop of furnace temperature. Then the furnace start storeing heats during the delay. It is important to have good coordination between the reheat furnaces and rolling mill operations for the stable operation of the furnaces. The rolling pitch should be kept within the heating capacity. Computer can calculate proper rolling pitch according to the types of products and heating capacity. This is a important function of the computer control of hot rolling. Previously, the steel were rolled at relatively high temperature, between 1250 C to 1350 C. Power consumption of hot rolling naturally increase with the decrease of bar temperature. However, the total energy consumption will be increase with a increase of discharge bar temperature as showen in the Fig.7. Many steel works decided to reduce discharge temperature of the reheating furnaces after the oil crisis. However, there are several problems along with a adoption of low temperature practice. 1. Charging of the furnace should be such a order as to allow proper temperature setting of the furnaces.

30 2.

3. 4.

Y. Yoshitani

How to solve the increase of skid marks. How to keep the finishing temperature by the low discharge temperature. How to overcome from the surface defects due to the hard scale.

First three items had been solved by the application of improved control systems. Proper discharge temperature of the slabs were calculated with the following conditions, 1. 2.

3.

discharge temperature should be above the permissible temperature of each steel grade. discharge temperature should be above the finishing temperature plus the total temperature drop in the rolling. discharge temperature should be above the limits to allow roughing and finishing mill operations.

The computer will calculate minimum allowable discharge temperature of the slabes and select the code for each grade of slabes and assign the heating practice to the furnaces. Also the computer will program charging program of the furnaces according to the rolling order. By the application of automatic setting of rolling order,a works reported that they succeeded the reduction of 131 10~kcal/ton of fuel consumptions, 25 c C lower exsit temperature of roughing mill, and 0.13% reductions of scale loss. Increase of skid markes had been solved by the improvement of AGC system and the application of width control in the roughing mill. The improvements of AGC systems in the hot strip mills had been done by the replacement of electric screw down to faster hydraulic screw dowen, and the adoption of feed forward control. One works reported that the feed forward control with optimal control theory was effective for the reduction of skid markes. Third problem had been solved by the review of pass schedule and the use of overhead hood for the protection of temperature drop on the runout tables. Computer control of reheat furnaces were started in relatively early, and few works had succeeded the modern optimal control theory. However, because of the difficulties of understanding of complex heat transfer models and the modern control theory, they were not so successful. By the improvements of surrounding conditions such as the adoption of automatic mill pacing, the computer control of reheat furnace became practical since late 70's. One of the typical exsample of the system is showen in the Fig.B. Over 10)( 10'kcal/ton of fuel consumptions

has been reduced by the application of the system. 7. Energy recovery system 33 blast furnace top pressure recovry turbines has been installed among the 40 blast furnaces now operating in the Japan by 19B2. 34 hot stove waste heat recovery, 21 coke dry quench systems (CDQ) , and 14 sinter waste heat recovery has been in operation by 1982. Total power recovered by the TRT reached about two billion kwh in 1982 which is equal to 6% of total power consumed in the integrated steel works of Japan. Introduction of those recovery system always added another nuisance to the processes. Thus the requests for the instellation of recovery system are no disturbance to the main process and without additional man power for the operation of the system. Control system solved those problems. The blast furnace top pressure is controlled by the valve installed before the recovery turbine inlet. In order to keep high recovery rate, a priority has been set to the front pressue control aganist the conventional septum valve pressure control by setting few difference between the two pressure controllers. The CDQ is a heat recovery system from discharged hot coke from the coke ovens. The discharged hot coke are charged into a cooling chamber, and the heat of coke are exchenged by nitrogen injected from the bottom of the chamber. The heated nitrogen are then introduced to the boiler and generat steam. About 1000·C hot coke are cooled down to 200·C in the cooling chamber. The nitrogen will heat up from lSO'C to 800 c C and will recover 300,000 kcal/ coke ton. About 35,000 ton of steam had been recovered from CDQ unit by the processing of 70,000 ton of coke per month. Amount of coke produced from coke ovens are vary with time according to the pushing program. On the other hands, the CDQ prefer stable constant charging, pre-chamber was used as the buffer for the variation of coke supplies. Level control of pre-chamber is very important for the stable operation of the CDQ. Gamma rey and capacitance levelmeter has been used for the monitoring and microprocessor has been use for the estimation of exact level of the coke. Negative pressure zone are exist in the CDQ system due to the recirculation of nitrogen. Combustible gas that are released from the coke, are contained in the nitrogen gas. Two oxygen analyzer has been used for the safty.

Contribution of Control Systems

8.

Conclusion

I did not mention here about the improvements of yield by various shape control systems in the rolling mill area, since they are presented in the papers. Especially, the MAS plate mill control system developed by the Kawasaki Steel has been achieved rearkable plate yield of 93%. However, it will not apply to a conventional plate mill. It is omly possible for a mill which has fast hydraulic screwdown and computer control systems. This fact shows clearly how the instrumentation and control system are vital for the better performance of the process. In conclusion, 1. Better instrumentation are the basis of energy savings as the supply of basic informations. 2. Stable operation of processes are the key for the energy savings. The control systems are vital for the stable production. Therefore, the maintenance and tracerability of the systems should not be forgotten. 3. Stable operation of blast furnaces are essential for the energy savings of integrated steel works. Raw material, charge distribution, blast furnace, and hot stove control systems are especially important. 4. Integrated production control system are necessary for the energy savings by the introduction of new process such as the continuous castings. 5 Energy center has working successfully for both functions of energy savings and pollution control. 6. Development of reliable sensors are the key for the success of new control systems and process. 7. Education and training are important for the adoption of advanced control system. 8. Fast progress of information and control devices and theory expanded the field of applications with less investiment cost. 9. It will be difficult for the Japanese steel industry to achieve further energy savings since they nearly reached the theoretical limits of energy consumptions. Few savings left are further integration of information and control system and the introduction of new process.

31

REFERENCES Toyoda,S. (1983) Change in the use of energy in Japanese steel industry. Trans. ISIJ. vol.23, No. 1. (1) Iki,T. (1983) Production and technology of iron and steel in Japan during 1982. Trans. JISI. vol 23, No.4. ( 361) Ishi.O. (1982) Energy management system in integrated steel works. The energy consrevation. Vol.34 No.lO. Kihara. H. (1981) Computer control of energy center. Fuji electric Jour. Vol. 54. No.12. (821) Yashima. T. (1982) Trend of energy center instellation. Fuji electric Jour. Vol.55. No.l1. (727) Shibuya.T. (1982) Current situation and future prospect of blast furnace measurment and control Techniques. Trans. ISIJ. Vo1.22. No.lO. Iwamura.T. (1982) Sensor and signal quantification for blast furnace gas distribution control. Trans. ISIJ. Vol.22. No.lO. Sakamoto. Y. (1982) Development and improvement of the measurment method for blast furnace computer control. Trans. ISIJ. Vol.22. No.lO. Tanaka.A. (1979) Man machine system design for blast furnace instrumentation. Jour. SICE. Vol. 18. No.8. (689) Tamiya. T. (1981) Instrumentation and control for energy saving. Nishiyama Memo. Lecture. No.76. Fuji.K. (1980) Instrumentation and control for continuous casting. Jour.SICE.Vol,19. No.12. Tamura.Y. (1982) Radiation Pyrometory in iron and steel process. Jour.SICE. Vol.2l.No.ll. Tsuboi.K. (1981) Development of surface inspection for continuous casted hot slab. Instrumentation (Japanese) Vol. 24.No.12. Oshima.M. (1977) Automation of plat production. Jour,SICE. Vo1.l6. No.6. (505)

32

Y. Yoshitan i

Ta bl e 3 .

Tr e n d o f e n ergy ma n a gemen t sy stem

Previo us System

. . 1P l anningk ___ ~....

Basic Co n cep t

IMon it o ri ng and Contro l

- --

-- ~ perforemancel An a l ysis

Stab l e Distrib u tion Independent process computer Hard Ware

No di r ect linkage wit h production scheduling system. Planni n g (yearly, quarterly and monthly)

System P l ann inq

Static energy supply plan ning from monthly production schedule and energy consumptions .

Pre s en t Syste m ~ P l an n i n~

I

Mon itoring I a nd Co n tro lj

J

p erfo r e man ceJ

'L An a l ysis

Total Cos t Mi nimum Direct l inkage with proce ss compute r s a n d ce n t r a l computers . Inc r ease of mo n itering items . Added weekly . dai l y , and shift base p l anning . Time ser i e s p l anning became poss ib l e from hour l y base ene r gy con sumpt i ons and p r od uction datas . Cost minimum energy s u pply p l an by on -l ine simu l ation.

Simulation of monthly cons umptions by batch calculation. Monitor i ng and contro l

Perfor mance An a l ys i s

Unexpected loss were inevit ab l e due to manual trend contro l . Bo il er control and emergen cy act i on were executed by t h e operators decision.

Consumption analysis had been done in monthly by manua ll y. Estimation of individual energy consumptions were inaccurate due to the lack of suffic i ent data.

Low l oss monitori ng contro l are poss i ble from the demand fore cast. Hi g h efficiency boilor co n t r ol are possible by computer co n trol . Eme r gency control becomes possible for powe r and e n ergy distribution. On-l ine performance analysis are possible. Various statistical analys i s are possible by the use of data bank .

Contr ibution of Control Systems

33

Tab l e 4. Bl a s t fur nace I n strumentation s ensor c h arge l eve l charged burdeb profile

measurement i t e ms

contro l ite ms

c h a r ging and d ece nt

c h arg in g

profile of cha r ged b urd en - -'» c h arge d istri b u t ion furnace h eat

top pressure top gas temperature gas conposit ion cross sonde shaft sonde

permeab i li t y of shaft top temperature a n d horizontial and vertical "temperature dist r ib u tion ~ shaft ga s f l ow d i stribu t i on - ~ top gas conposition es t imat i on of coh esive ~ zone distribution of temp . ./" flow, and composition of tQP_ qas distribution of temp. , flow , and composi t ion of gas in shaft

shaft pressure

pressure distrib u tion

wa l l tempera tnre

furnace lining temper ture

tuyor tipe temp.

thermal condition of race way

bottom temp .

/

-

V

b l ast conditions

i njection

injection conditions

'v tota l integrated control sy s tem I'

I"

permeab ili ty contro l

~

furnace l ining maintenance --

~

furnace heat contro l

monitoring of erosion of the bottom l ining

b l ast temp . pressure f l ow humidity

r--

operation policy heat l eve l contro l permeability control

I'

I'

34

Y. Yoshitani

Fuel oil _ _ _ _ _ _ _-; LPG,LNG

Fuels for heating facilities

Coal----------~~~~~--~

Heat recovery system CDQ

"""-==~~===:...-------€-~~~~ Electr ic Power Purchased

powe!:r:....:===d--1[!;~~;~~~

(400 - 550 kwh/t) Steam

L:~~~~~~r------------~

Oxygen (60 -7 0 Nrrf/t)

Water pump us~t~a~t~1~·o~n~____-t----------------~ Water (100-200 t i t) Air compressor!-----------~ Compressed Air station

Fig.l.

Energy supply system in the integrated iron and steel works.

Energy

center

[Core merrory. I28 kbitJ

off-line

_ - - - - - - - - . . . , E.C

P o r t f - - - - - - - - - - - - -__ Optical Data Highway - - ~

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Fig. 3. Flow diagram of optimum energy rnanagerrent system

w V1

Y. Yoshitani

36

r--- - - - - - - - - - - - - - - - - - - -------------,

External

disturbance~Integrated r- - - -

production control system

I

1 1 I

l.

1

Iphenomenas I inside furnace \

I 1

2.

.ISensors

I

3. 4.

I I

rI I

I

1

I

I

1 1 1

Mathematical Model

Estimation~

I

5.

- - - - - ______ 1

Items for overall decision makinq Furnace heat level Gas permeability and burden descending Tapping of iron and slag Gas efficiency Furnace wall heat load burden distribution, gas flow distribution. cohesive zone profile and position Circumferential balance

I I

~-Optimal

action'

1

\1Control measures l.

2

3 4

j

l.-

I I I 1

I I I I I

Material properties (physical and chemical properties) Material charging conditions (mover able armor, bell-less charging, stock line level, coke base, and ore/coke) Blast condition (blast volume,blast temperature, blast humidity, and injected fuel rate. ) Others (Tuyor size, and tapping conditions) Fig. 4.

Integrated control system of blast furnace.

bubbling control

steel weight in ladle

steel temperature measurment

slag detection

tundish preheat control auto-start-stop

tundish temperature mould width adj. tundish weight control casing speed control

mould powder charging control

mould oscillation measurment roll alignment

mould level control

slab tracking

coolin control (mould)

surface inspection of casted slabs optimal cutting control

control

roll gape measurement

slab marking

shell thickness measurement ----i~1

slab weight handling control

o

0

o

I

o

Fig.5. Instrumentation and control system of continuous casting

00

I

'I Cen t ral compute r M- 1B Or

IChemica l

r

~f

1

,

l ab }-1

1

J J

r

BOF

RH degas

CC / DR

computer

computer

computer

H- BO

U- 1SOO

U- 1SOO

Blooming mill

I~

computer H- BOE ~

"

S l a bb ing mi ll computer

Hot strip mill comput er

H-1 OO

T-7 000

n

o

;:l

et

". . . eT C

....o et

Centra l computer

IQua l ity

~oducts assiqnment Sy~t~

classifica t ion systeITJ

;:l

o

H>

n

Slab/ bloom information i

I

I slab/ bloom

o

specificatio ns

I

;:l

et

".....o (fl

~ Ul

cooling I

Reject instruction

1

caster

F i g . 6.

et

Temperature model

ro

S

Ul

Furnace t e mperature control Charge order

L--h olding

Extractor v

..___---..

~nace

)

Compute r sys t em o f CC/ DR process. w

"

Y. Yoshitani

38

350 '-..

ra U .>::

~ ~

o

consum~ion

of rolling, 300

~

0

\

power

.-I

0 0 0 .-I

600

Total energy consumption

-I.l

' r!

-I.l

0..

E

__ ':::
Ul ~

....

O-l.l

u'-.. .-I >,ra iJ'U ... .>::

x ~

0..0 .r!

'O-I.l ~

::l

550

0..

250


5DJ

fuel

~o


ra E

.-I

.-I Ul

-I.l

ra

::l

0

::l 0

~

-I.l

U

1100

1000

Fig.7.

1200

13'10

Temp. C

Total energy consumptions vs. Extract temperature of slab (hot strip mill)

IDischarge pitch

forecast

Slab trackingl

1 Slab temperature model

Heuristic Model

j ( - (heat balance model emmisivity)

Optimal fuel distribution model Heat balance model

I

IiJ •

.J,

Fuel flow setting

I

Perforemance data furnace temperature

'v , flow rate Reheat-Furnace'" ~ fuel

..

slab temperature after roughing mill

Fig. 8 . Model structure of Reheat furnace comput~r control

"i.