Energy Conservation in High Energy Intensity Industry
Published on : Sunday 09-05-2021
Suresh Babu Chigurupalli documents a reduction of plant incident trends through low cost automation mechanisation.
Energy conservation is the effort made to reduce the consumption of energy by using less of an energy service. This can be achieved in two ways. One is by using energy more efficiently (using less energy for a constant service). On the other hand, energy can be conserved by reducing wastage and losses, improving efficiency through technological upgrades and improved operation and maintenance.
Background and context
Ferro chrome manufacturing is a high energy intensity industry because smelting processes need more energy to produce the ferro chrome through Submerged Arc Furnace (SAF). AC arc furnace harmonics were traditionally compensated by passive filter banks on the medium voltage 11 kV/33 kV side. Unfortunately passive filtering cannot take care of the sub harmonic flicker frequency of the furnace currents and traditionally static VAR compensation using the phase controlled switching and line commutation was employed for fast power factor control and voltage drop compensation to reduce voltage flicker at intervening high voltage nodes in the power supply system.
Submerged Arc Furnaces are defined as AC or DC power furnaces which use Soderberg electrodes to melt briquettes (raw material – chrome ore), flux and redundant (coal and coke). Heat is supplied from electricity that produces metal baths and through a tapping process tap the material. The SAF comprises a refractory shell which holds the charge and the three electrodes one each connected to the three phases of the AC electric power supply and held in special clamps on swing support structure which can be swung aside for charging and which can allow each electrode to be raised or lowered with hydraulic actuators. The furnace specific power consumption depends on the raw materials moisture content (%), grade of ore fines, high MgO and SiO2%, raw material properties (coke, coal and flux), refractory material and heat losses flue gas heat losses (400 to 500°C), electrode management, load management, cooling effect in the transformer area, ambient temperature, load fluctuations and quality power. Balasore Alloys Ltd (BAL), Balasore, Odisha has 5 furnaces with a total capacity of 72 MVA to produce 1, 44,000 MT bulk ferro alloys per annum. The BAL has entrusted the power quality and equipment efficiency study of the plant in the year 2018-19.
Scope of the Study
1. Conducting power quality & harmonic analysis by data logging with power & harmonic analyser to find out existing harmonic levels, power quality disturbances like inrush current/transients at the selected transformers and suggesting suitable solutions to the problems identified.
2. Performance evaluation of compressed air system by measuring inlet air temperature/humidity of various compressors comparing vis-à-vis benchmarks for efficiency.
3. Performance assessment by measurement of flow, velocity and evaluate the efficiency of the pump and the pumping system. Suggesting suitable improvements to improve the efficiency and reduce the power consumption.
4. Performance assessment of fans by measurement of flow, velocity, static pressure and evaluating static efficiency of the fans and suggested suitable improvements to reduce the power consumption.
Why do we require power quality analysis?
1. To improve power factor and system efficiency.
2. To avoid break-downs and production interruptions
3. To avoid excess energy consumption.
4. To remove harmonics, surges and transients from the electrical network.
5. To avoid voltage/frequency fluctuations and PLC hang-up.
6. To avoid transformer overheat, capacitor burst, trip, etc.
7. Savings in energy bills due to reduced losses and kVA demands.
8. Accurate measurements by installed meter.
9. Better production rate and quality due to reduced interruption.
10. Enhanced life cycle of electrical network and component.
11. Maximise plant distribution capacity.
Energy audits and implementation of the recommendations
The power quality issues are to be addressed on LT transformers as the distortions generated by the furnace transformers are creating disturbances throughout the grid and affecting the other auxiliary loads. It is observed that the auxiliary LT transformers are running under low load conditions. Transformers efficiency will be optimal at 50-60 % loading. In view of this it is suggested to check the possibility of shifting of auxiliary loads from lowly loaded to other moderately loaded transformers and completely shut off the low loaded transformers so that the transformer losses can be avoided.
Install capacitor banks on the LT side of the transformers (auxiliary) major load centres to reduce the line losses on account of low PF. At locations where the harmonic presence is high and above tolerable limit it is suggested to install LT capacitor banks along with series reactors. The plant installed capacitor banks on HT side, 11 kV bus to maintain power factor close to unity. However this will not compensate for the line losses on the LT side. The harmonic distortion is also causing the RMS power factor to drop. It is suggested to install suitable series reactors in place of existing damping reactors to suppress harmonics on the 11 kV side. The low power factor on 11 kV bus for auxiliary transformers indicates inadequate power factor correction on LT side, it is suggested to install APFC panels on LT side of auxiliary transformers which reduces the line losses and improves PF on both LT and HT.
It is also learned the harmonic problems generated by the submerged arc furnaces cause a short duration voltage drop affecting the auxiliary loads of the furnaces, viz., pump house. To mitigate this problem it is suggested to install a STATCOM, which will reduce the harmonic problem and regulate the voltage to overcome the tripping due to voltage sags. The voltage drops causing the pump house motors to trip if suggested prime mover is installed as per the manufacturer specification; this forced the plant to install higher capacity motors. After the installation of STATCOM for pump house loads, it will be possible to either down size or retrofit the pump motors with VFD as the voltage regulation will become better. It is observed that the ID fans are running with good efficiency except a couple of fans and it is suggested to replace these fans with high efficiency fans. The loss in efficiency is converted to heating of the air. It is also observed during the study the short term flicker generated by the furnace transformers is reaching alarming levels at some of the locations and it is suggested to reduce the flicker by installation of STATCOM.
Install the EnMS Software to closely monitor the power consumption data on a daily basis and quality of the power, PF, MD, etc. It is also observed that the heat generated in the VFD room of GCP ID fans is not effectively removed though ACs are installed. This calls for rechecking the location of AC units installed or reassessing the heat load to be removed and installing AC units accordingly. The briquetting plant/pan mixers/pressers are running with low PF and high distortion, to improve this it is suggested to install PF improvement capacitors along with harmonic block reactors.
Summary of the results
After conducting the audit and followed by recommendations, a cross-functional team (CFT) formed to execute the action plan. The following are the significant implementations:
1. The existing damping reactors with a 0.2% reactance (Xl/Xc) replaced by a series reactor with a 6% reactance rate installed to suppress the harmonics and inrush currents.
2. In phase wise, we have upgraded the fans to improve the efficiency to 85% and above.
3. To eliminate the manual intervention and errors, we have installed EnMs software to track and monitor the real-time data and auto time stamping.
4. Installed APFC (automatic power factor correction) to reduce the line losses and improve the power factor.
5. Optimised the loads on the transformers to reduce the iron losses and improve the efficiency.
Challenges identified during the implementation:
a. In time procurement of energy saving equipment like sensors, reactors, VFDs, etc.
b. Installation on running plant and arranging shutdown.
c. Release of fund for ordered equipment.
d. Dependence on external service engineers during installation.
Conclusion
Smelting in ferro chrome manufacturing requires high energy. Energy audits at regular intervals help the industry to capture the gaps. Mitigation plans on the gaps, significantly improved the energy efficiency and quality of the power. By implementing the audit recommendations there was a significant drop in voltage surge and inrush currents and eliminated the manual errors of data collection. The impact indirectly helped reduce the maintenance cost and optimised the specific energy consumption per ton of ferrochrome.
Sureshbabu Chigurupalli is on the Board of Directors/Operations & Maintenance/Keynote Speaker/Lean Practitioner/Production Management/TPM Practitioner with 26+ years of experience. He is Director (Operations) at Balasore Alloys Limited, Balasore, Odisha. He did his B.Tech.in Instrumentation from Andhra University (1994). He is an enterprising leader & planner with a strong record of contributions in streamlining operations, invigorating businesses, heightening productivity, systems & procedures.
Sureshbabu has achievement-driven professional experience in spearheading entire unit/ plant operations to maintain continuity and match organisational goals through supervising Operations, Quality Control, Production Goals, Automation, Maintenance, Process Improvements, Safety Guidelines, Manpower Development, New Policy/Procedure Guidelines, Resource Allocation and Cost Optimisations. He is leading and managing all plant operations with effective utilisation of all resources and implementing industry best practices such as TPM, Six Sigma, Lean Management & others Business Excellence initiatives that contribute to improve productivity and efficiency. He has exhibited leadership in closely collaborating with numerous Japanese Consultants for implementing TPM to enhance overall plant effectiveness.
