3. MRPII Paso a paso
3.2 Planeación de la Administración de operaciones
Suresh Prasad, P. Kumar, M Sen, T S Reddy and D Mukerjee [email protected]
Abstract
The iron and steel industry is constantly striving to reduce its energy consumption and thereby minimize its overall costs. In the present scenario of global cost competitiveness, the challenge could be met by finding solutions to reduce energy consumption, which is one of the major cost factors. Research & Development Centre for Iron & Steel (RDCIS) is a corporate research centre for Steel Authority of India Ltd (SAIL) and nodal agency for working out measures for reduction of energy consumption in its steel plants. RDCIS has made immense contribution towards reduction in energy consumption & GHG emission by implementing supervisory computer control based on in-housed developed mathematical model for BF stoves operation, Blast Furnace Gas burners in boilers, in-house developed energy efficient combustion system like curtain flame burners for ignition hood of sinter machines, etc. RDCIS also plays a major role in suggesting measures for reducing energy consumption by conducting energy audit.
1.0 Introduction
Present global energy consumption level is around 120 trillion Gcal (120 x 109 Gcal), which has increased in last 30 years by 66 %. Major source of global energy is from fossil fuels constituting 86%. Global energy demand mostly by developing countries is expected to rise by 40-50% by 2030, which will reduce sustainability of fossil fuels further.
The iron & steel industry accounts 3 to 4% of world’s total energy consumption, which is mainly from fossil fuels. The use of renewable sources of energy in steel industry is still to be explored. On an average 4.3 Gcal energy is consumed for every tonne of steel produced in the world. Energy consumption in Indian steel industry is considerably higher and consumes more than 6 Gcal/tcs. Energy consumption in Indian steel plant varies from 5.0 to 8.0 Gcal/tcs depending upon the level of technology and process route adopted. In the present scenario of global cost competitiveness in steel industry, the challenge could be met by finding solutions to reduce energy consumption, which is one of the major cost factors. RDCIS have made immense contribution towards energy conservation and improvement in furnace productivity and product quality in SAIL plants by implementing innovative ideas, introducing in-house developed energy efficient combustion systems and optimisation of thermal regimes. RDCIS has been playing a lead role in identifying energy conservation schemes for modernisation of SAIL plants. In SAIL, RDCIS has been in the forefront for development and commercialisation of energy efficient burners using by-product fuels available in integrated steel plants. SAIL
Energy Conservation & Management 119 plants have decreased energy consumption and GHG emission considerably over the years after successful implementation of various innovative RDCIS projects on energy conservation.
2.0 Efforts towards Energy conservation
SAIL has been formulating to introduce energy efficient technologies from time to time by modernization programs. Some of the important energy efficient technologies introduced and under implementation are:
• Phasing out in-efficient processes like twin hearth furnaces by BOF
• Continuous casting in place of ingot casting
• Walking beam furnaces in place of pusher type furnaces
• Coke dry quenching to generate steam/power in new coke oven batteries recovering sensible heat of hot coke
• Introduction of auxiliary fuels like pulverized coal & tar in blast furnaces
• Top recovery turbines to generate power utilizing blast furnace top gas pressure
• Up-gradation of blast furnace stoves using improved stove design and computerized control for stove change-over
• Waste heat recovery system to preheat combustion air in ignition hood of sinter machine utilizing sensible heat of hot sinter
RDCIS has also been/will be contributing for reduction of specific energy consumption and GHG emission by:
• Introduction of supervisory computer control system in BF stove operation
• Introduction of BF gas burner in Boiler#6 of PBS to utilize surplus BF gas at BSP
• Introduction of Curtain Flame burners in sinter plants of SAIL
• Modification of combustion system in reheating furnaces of R & S Mill, BSP
• Introduction of efficient ladle heating systems in SAIL plants
• Improvement in furnace efficiency of heavy structural mill by regulation of gas and air at ISP
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• Waste heat recovery system in sinter plant to generate hot water for preheating sinter mix under RDCIS project
There has been a steady improvement in the specific energy consumption (SEC) per tonne of crude steel in SAIL (Fig. 1). SEC reduced from 7.76 to 6.73 Gcal/tcs during the period from 2001-02 to 2009-10. During the last decade the energy intensive open hearth furnaces have been replaced with twin-hearth or basic oxygen furnaces (BOF). Continuous casting has been introduced in all the steel plants. In addition to the above major modernisation programs, various medium and low capital investment schemes and indigenous technologies have been introduced.
3.0 R & D Innovations towards Reduction in Energy Consumption in SAIL Plants
3.1 Supervisory computer control in BF stove operationSupervisory computer control system was introduced in BF stove operation in Blast Furnace No. 3 of Durgapur Steel Plant. Stoves of BF#3 is designed for hot blast temperature of 1050OC. The stoves have a blast rate of around 1,700-2,000 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. The designed maximum dome temperature of the stoves is 1250 OC. Distributed control system (Toshiba make CIE 1200) is provided for I control. Over this Level-II supervisory control using mathematical model was introduced under R & D project.
Energy Conservation & Management 121 An on-line mathematical model for BF Stoves operation was developed considering input parameters like dome temperature, blast rate, cold blast temperature, duration of on-gas and on-blast periods. The model computes checker and gas/blast temperature as function of time and height of checker work. During on-gas period, waste gas temperatures and during on-blast period, hot blast temperatures are predicted by the model. Model predicts on-line thermal status of individual stoves in different conditions.
The checker temperature distribution along the height predicted by model is utilized to calculate actual residual heat of checker, which is dependent on blast rate and on the history of heating rate during “On Gas” period.
Evaluation of desired residual heat is done based on desired HBT and blast rate. Stove changeover for the current cycle is predicted based on comparison of actual and desired residual heats.
Model generates audio-visual signal for the heater whenever stove changeover condition is met. Implementation of the same resulted in lower coke rate due to consistency and increase in HBT. The trial results showed that HBT and coke rate were 945OC and 535 kg/thm respectively as against 919OC and 553 kg/thm before innovation as shown in Fig 2 & 3 below:
FIG. 2: VARIATION OF HBT & CB FLOW BEFORE INNOVATION (15-11- 2005)
900
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FIG. 3: VARIATION OF HBT & CB FLOW AFTER INNOVATION (19- 01- 2006)
900
The similar project is being implemented in Blast Furnace No. 4 of Bhilai Steel Plant.
3.2 Design, Development and Introduction of High Capacity Blast Furnace Gas Burner
This unique burner design for firing Blast Furnace Gas (BFG) at high rate (10,000Nm3/hr) was developed for boiler no. 6 of Power Plant-I of Bhilai Steel Plant (BSP) to use surplus BFG and replace purchased coal. BFG being a lean gas (calorific value ~ 800 Kcal/Nm3) has low flame temperature and poor in-flammability etc. for which pure BFG is used mainly in blast furnace stoves and boilers. BFG burners used in boilers are normally fired along with other rich fuels like furnace oil, coke oven gas (COG) or pulverized coal. To generate desired bushy type stable flame within the width of the firing chamber of the boiler, high rate of mixing of the out-coming BFG and air streams has been achieved by increasing interfacial surface area between gas and air streams (Fig. 4). The introduction of burners has resulted in:
i) Reduction in fly ash and green house gas emissions by 15,000 and 100,000 ton/year respectively due to utilization of surplus by-product gases generated in the steel plant.
ii) Annual benefit of Rs 1,080 Lakh due to elimination of purchased coal.
Energy Conservation & Management 123 Fig. 4: Burner Nozzle
3.3 Design, Development &Introduction of Curtain Flame Ignition System
Curtain type flame based ignition system was developed to improve the ignition of top layer of sinter mix and to reduce the specific gas consumption. The concept involves mounting several small capacity burners close to one another on the roof across the sinter bed to generate curtain shaped continuous flame across the sinter bed, which ignites the top layer of the sinter bed. All the burners are mounted in a single row perpendicular to the direction of strand movement. In the conventional system, side burners are used on both the side walls of sinter hood and this has an inherent problem of slow and uneven heat distribution across the sinter bed. To avoid this, several side burners are used, which requires large furnace (ignition hood) length and consumes higher quantity of heat
In the curtain flame burner, primary air is sent through swirls for better mixing of gas and air and secondary air slots are provided in the burner module to obtain curtain flame configuration (Figs. 5). In this system higher quantity of heat transfer to the top layer of sinter bed takes place by convection instead of radiation as in case with conventional side burner. The curtain flame ignition system were installed in sinter machines of RSP, Rourkela, BSL, Bokaro, BSP, Bhilai and presently being implemented at DSP, Durgapur. It has resulted in reduction in specific fuel consumption and also furnace volume by more than 80%, thereby reducing the cost towards refractory consumption and increase in productivity by extra furnace length available for sintering process.
Benefits:
Reduction in specific fuel consumption by 30 to 40% (from 0.042 to 0.027 Gcal/t). Annual saving of Rs 1000 Lakh Reduction in GHG emission by 1,87,000 t/year.
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Fig.5: Curtain flame Ignition Hood
4.0 Conclusion
RDCIS is a nodal agency for working out measures for reduction of energy consumption in SAIL’s steel plants.
RDCIS have made immense contribution towards energy conservation and improvement in furnace productivity and product quality in SAIL plants by implementing innovative ideas, introducing in-house developed energy efficient combustion systems and optimisation of thermal regimes. RDCIS has been playing a lead role in identifying energy conservation schemes for reduction in energy consumption in SAIL plants. Joint efforts of RDCIS and SAIL plants have resulted in reduction of specific energy consumption to a level of 6.73 Gcal/tcs.
Potential exists for further reduction of specific energy consumption in SAIL by maintaining technological discipline, regular energy audits, beneficiation of raw material to improve its quality, phasing out obsolete technologies like twin hearth, ingot route etc. and adopting newer technologies like CDQ, TRT, alternate fuel injection in BF, Continuous casting etc.
Acknowledgement
The authors are thankful to the concerned officials and staff of different shops of SAIL Steel Plants at Bhilai, Bokaro, Rourkela & Durgapur for their co-operation during the investigation and implementation of energy efficient combustion systems. The authors are grateful to the Management of RDCIS for granting permission to present the paper.
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References:
• Achievement of higher HBT in BF#3 by incorporating supervisory computer control system based on mathematical model, Durgapur Steel Plant, Report No. R & D: 81.02.3516.01.2006, January’06
• Introduction of blast furnace gas firing in boiler No. 6, PP – I, Bhilai Steel Plant, Report No. R & D:
81.02.3423.01.2005, March’05
• Introduction of curtain type flame for ignition of sinter-mix in Band # 2 & 3 of Sinter Plant at Bokaro Steel Plant, Report No. R & D: 81.02.3371.01.2004, Dec’04