The article deals with the energy conservation achieved by adapting various energy-efficient technologies and incorporating energy-efficient operation.
Energy is one of the major inputs for the economic development of our country, more so with depleting fuel reserves. Energy consumption in industrial sector is accounting for about 50 per cent of the commercial energy available in our country. Among the industrial sector, nine sectors have been identified as highly energy-intensive. These include: power, fertilizer, iron and steel, cement, pulp and paper, aluminium, chlor-alkali, textile and railways.
In this scenario of energy shortage, increasing energy demands and price, particularly for developing countries like India, it may be difficult to pursue the present rate of development and will be forced to retard its development/industrialisation programmes for want of sufficient energy reserves, unless focused measures are taken. In this background, the imperative need for every citizen and the industry in particular is to contribute towards energy conservation and environmental sustainability.
This paper deals with the energy conservation achieved by adapting various energy-efficient technologies and incorporating energy-efficient operation. Various activities implemented to reduce power consumption are as enumerated below:
- Compressor power optimisation
- Pressure drop reduction in cyclone
- Single raw meal silo operation instead of two
- Star feeder instead of 3KS system
- SPRS for process mil fans
- Operated Turbo blowers instead of PD blowers
- Optimisation of air conditioner consumption
- Provided VFDs to potential equipment
- Installation of occupancy sensors in load centres
- Cogged belts in place of V belts & FRP blades in place of aluminium/CI blades
- Monitoring of special power on a daily basis and controlling of idle power consumption
Lets see the above energy conservative activities in more details:
Energy conservation activity – 1 – Compressor power optimisation
An air compressor is a device that converts power in to potential energy, stored in pressurised vessel. Compressor plays a major role in utility power consumption, Various energy efficient technologies adopted in our unit to optimise compressor power are as below:
Upgradation of old with energy efficient compressor
Background: In line 2 Pyro section, 1 No of 965CFM, Double stage, water cooled screw compressor, rated shaft power of 132kW (SF – 1.2) was in operation (24×7) for past 14 years, at an operating efficiency of 76 per cent and it consumes around 143 to 145 KW/hour as input power to deliver the specified volume at an pressure of 5.2 to 5.7 bar.
Action taken: Upgradation with latest energy efficient model (925CFM, air cooled, oil flooded double stage screw compressor of shaft power 110KW (SF – 1.1)
Benefits and savings:
- Power consumption reduced (17 KW/Hr)
- As this is an air cooled compressor, intangible benefit of reduction in cooling tower operation for 240 LPM (5 KW/Hr)
Installation of VFD in compressor
Background: For our packing plant operation, double stage air cooled, 535CFM screw compressor was in operation and it consumes around 0.32 to 0.35 units/tonne of cement packing. The loading and unloading pattern of compressor is not uniform. Since the inward movement of cement truck is at different timing and to maintain the truck TAT compressor need to operate on continuous basis, hence ideal running is more.
Action taken: Operating this compressor through VFD, which enabled speed variation of the motor according the pressure setting and constant pressure is maintained in line and ideal running avoided.
Benefits: Compressor power consumption reduced to 0.24 units/tonne of cement packing and for 0.1 units/tonne reduction in cement.
Total savings (units/tonne)Power cost (Rs/unit)Packing in line -2 FY (18-19)Annual savings, (Rs lakh/year) 0.14.8516192587.85
Installation of additional receiver tanks
Background: The compressor air generated in compressor room is directly fed to the receiver tank of CVRM-2 Building, fourth floor. Due to line layout and cement bag house operation, line header pressure is reduced by 0.8 bar and frequent loading/unloading is happening.
Action taken: One more buffer tank of 6,000 liter capacity is installed nearer to the compressor station at ground floor.
Benefits:
Pressure drop in common header line reduced around 0.5 bar
Generation pressure reduced from 6.2 to 5.7 bar
Savings:
Power savings – 0.1 units/tonne of cement grinding
Total savings (units/tonne)Power cost (Rs/unit) Cement grinding in CVRM-2 FY (18-19)Annual savings,
(Rs lakh)Investment cost (Rs lakh)ROI (months)v 0.14.8516152937.830.50.77
Optimisation of pressure settings and vigilant monitoring
Background: Compressors required for plant operation are connected in common header and tappings are taken from common header irrespective of pressure requirements. Also the pressure drop between the compressor end and load end is on higher side because of various piping sizes. Hence generation pressure setting is maintained more.
Action taken:
Higher volume requirement are taken from common header
High pressure and lower volume requirements at load end are compensated through booster
Operation of standby 950 CFM compressor during peak demand is compensated with smaller capacity compressors connected in the header and pressure settings are optimised
Also by vigilant monitoring and reviewing of compressor consumption on a daily
basis, leakages are arrested and minimised in the initial stage itself
Benefits:
Pressure drop reduced around 0.4 bar
Generation pressure reduced from 6 to 5.5 bar
Energy Conservation Activity – 2
Cyclones in modern cement plant: Modern cement production relies on conservation and efficient use of natural resources viz., raw materials and fuels. Kiln gases are used efficiently to preheat and dry raw materials before they enter the kiln. During design of cement plant pre heater, stages are added to the tower to reduce the pre heater exist temperature, as more heat is transferred to the fresh raw meal. Background: In our line-2 preheater system, it was observed that pressure drop across cyclone 1 was on higher side (i.e., around 250 mmwc instead of recommended range 90-120 mmwc), which affected the heat transfer in the system.
Action taken: For reducing pressure drop, it was decided to widen the gas inlet area. In first phase, the inlet area opening was increased to 250 mm and pressure drop got reduced to 220 mmwc. In second phase, it was further increased to 400 mm and the pressure drop got reduced to 180 mmwc
Benefits:
- Pressure drop across cyclone-1 reduced from 250 to 180 mmwc (i.e., 70 mmwc)
- PH fan power consumption reduced around 50 units/hour
- Improvement of flow in PH cyclones
- Collection efficiency improvement in PH cyclones
Savings: PH fan power consumption reduced around 150 units/hour
Total Savings (Units /Hr)Power Cost (Rs. / Unit)Running Hrs in FY (18-19)
Annual Savings, (Rs. Lakhs/year)Investment Cost (Rs. Lakhs)ROI (Months)
504.856560.215.912.31.73
Energy conservation activity – 3
Optimisation of raw meal silo operation – blending and extraction: In a cement plant, raw meal silo is meant for storing of raw-meal powder and for homogeneous process for better quality of cement. In Line 1 – 2 numbers of raw meal silo?s are there for this application.
Background: Our L1 kiln is producing clinker for all special cements like OWC, SLS , SRPC, etc. for OWC production, single silo is used, whereas for OPC clinker production two silos are simultaneously operated during feeding and extraction.
Due to this:
- Auxiliary power consumption was higher
- All the drives in the circuit were running and standby equipment are not available for operation during failure
- Hence, planned to optimise raw meal silo operation to save energy
Action taken: For OPC production, single silo operation logic was implemented without affecting product quality.
Benefits:
- Six drives were stopped in the circuit
- Ready standby circuit available to avoid breakdowns
- Reduction in spares and maintenance cost
Savings:
By stopping these equipment, power consumption reduction – 40 kW/hour
Total savings (Units/hour)Power cost (Rs/unit)Running hours in FY (18-19)Annual savings, (Rs Lakh/year)Investment cost (Rs lakh)
404.85592111.49Nil
Energy Conservation Activity – 4
Star feeder instead of 3KS system in cement mill feed: 3KS is an hydraulic system with three flaps, one flap gets open at a time and balance two flaps remains closed in-order to restrict false air entry inside the mill. Star feeder is a rotating feeder consisting of a horizontal shaft fitted with radial blades running within a close-fitting cylindrical chamber provided with an inlet and an outlet.
Background: CVRM-1 Mill – Materials fed through 3KS system and its drawbacks are:
- 40Frequent gate struck-up due to foreign materials entry
- Side liner worn out and leads to false air entry (around 23 per cent in CVRM-1 mill circuit)
- Periodic flap jamming due to moisture in materials
Action taken: For reducing the false air entry and other nuisance – 3KS upgraded with star feeder. In this activity, we eliminated one feeding belt (531BC3) from the circuit and its feeding belt 531-BC2 is extended to fed the mill through star feeder. Star feeder motor capacity and hydraulic pump motor capacities are same.
Benefits:
- Maintenance cost is reduced on account of one belt conveyor is eliminated
- False air is reduced to 13 per cent across the mill
- Elimination of 3KS hydraulic system maintenance
Savings:
Reduction in mill fan power consumption – 70 units/hour
Total savings (KW/hour)Power cost (Rs/ unit)Running hours in FY (18-19)
Annual savings, (Rs lakh)Investment cost (Rs lakh)ROI (Months)
704.855614.519.061710.70
Energy Conservation Activity – 5
SPRS for process mill fans: Slip energy recovery is one of the methods of controlling the speed of an slip ring induction motor. This method is also known as Static Scherbius Drive. In the rotor resistance control method, the slip power in the rotor circuit is wasted as I2R losses during the low-speed operation. The efficiency is also reduced. The slip power from the rotor circuit can be recovered and fed back to the AC source so as to utilise it outside the motor. Thus, the overall efficiency of the drive system can be increased. In a wound-field induction motor the slip rings allow easy recovery of the slip power, which can be electronically controlled to control the speed of the motor. The oldest and simplest technique to invoke this slip power recovery induction motor speed control is to mechanically vary the rotor resistance.
Background: The old SPRS system for CVRM-1 mill fan was installed in 1996 and it was served around 22 years. This SPRS system was outdated, spares are obsolete in the market and due to aging the reliability of this SPRS system is very poor. In last FY around eight months, it was not in operation because of non availability of spares. The speed range is 70 to 99 per cent.
Action taken: New SPRS system installed with wide speed range of 60 to 99 per cent. Also in the new system, the auto transformer is eliminated.
Savings:
- Operating speed range is wider (i.e. 60 to 99 per cent)
- Reliability of this new system is very high
- Spare available in market and maintenance cost is very cheap
- Auto transformer (575 to 1641 KVA) is eliminated in new system and the rating of recovery transformer also optimised to 450KVA from 837KVA. Hence transformer losses are reduced.
- Because of reliable system the recovery power/hour is around 150 units.
Total savings (units/hour)Power cost (Rs/ unit)Running hours in FY (18-19)Annual savings (Rs lakh/year)Investment cost (Rs lakh)ROI (Months)
1504.855614.540.854212.3
Energy Conservation Activity – 6
Operated turbo blowers instead of PD blowers: The PD blower is also known as positive displacement blower and it is used to move gas or air for a variety of applications. To be precise, these devices utilise positive displacement technology by trapping a certain volume of air then discharging or forcing it out against the system pressure. The air is usually forced in to some type of pipe or hose to propel materials or gas to a destination. PD blower efficiency will be around 45 to 65 per cent. Turbo blower is the latest technology – energy efficient blower and its efficiency will be around 82 per cent.
Background: PD blowers are used for PC and kiln coal pumping application and it consumes more power for pumping. It occupies more space and generates more heat and noise (requires big silencers) during operation. Also it needs more maintenance. Efficiency of PD blower is very low.
Action taken: Because of efficiency, turbo blowers are operated instead of PD blower for kiln and PC coal pumping application. It occupies less space, operation is very quiet. It has few moving parts hence low maintenance is required and no complex oil cooling system is required for turbo blowers.
Savings: Energy efficient blower and operating at an efficiency of > 82 per cent
Power saving – 95 units/hour (by operating turbo blower for kiln coal pumping – 40 units/hour and by operating turbo blower for PC coal pumping – 55 units/hour)
Energy Conservation Activity – 7
Optimisation of air conditioner power consumption: In line 2 around 222.5 TR of package ACs are installed and operated for maintaining the temperature in PLC, MVAC and VFD rooms, training centre and CCR as listed below:
Sr. NoLocationCapacity (TR)
1Load center 159.5
2Load center 251
3Bag House Load center34
4CVRM Load center22
5RTC22
6CCR34
Total222.5
In CCR & VFD -Load Center the AC’s are operated by 24×7 and in training centre based on need basis. Various energy-efficient technologies were adopted to optimise.
Air conditioner power as below:
Water cooled condenser in place of air cooled condenser Depending on the type of the cooling system the packaged air conditioners are divided as water cooled and air cooled condensers. In water cooled packaged air conditions, the condenser is cooled by the water. The condenser is of shell and tube type, with refrigerant flowing along the tube side and the cooling water flowing along the shell side. The water has to be supplied continuously in these systems to maintain functioning of the air conditioning system. In air cooled packaged air conditioners, the condenser of the refrigeration system is cooled by the atmospheric air. The packaged AC with the air cooled condensers are used more commonly than the ones with water cooled condensers since air is freely available
Background: In L 2, all the package ACs are deigned as air cooled and after five years of use full lifecycle, the cooling efficiency is not effective because of lesser heat transfer in condenser coils. (The thin aluminum fins in coils are choked completely, air is not passing through the fins and getting damaged during cleaning within five years of lifecycle). Hence to maintain the temperature additional AC?s were operated continuously in addition to the regular units.
Action taken: Replaced the air cooled condenser coils with water cooled condensers in phased manner and without operating separate water pumps for water supply, tappings taken from water tanks feed lines and return water line laid to cooling tower.
Benefits:
- Thus cooling efficiency of package AC’s improved
- Operation of additional units stopped and standby unit available in all locations to meet the demand during breakdowns
- Power saving achieved
- Maintenance reduced
Savings:
Power savings around – 90 units/hour
LocationPower consumption (units/hour) before installation of WC condenser
Power consumption (units/hour) after installation of WC condenser
Load center 15740
Load center 24832
Bag House Load center3216
CVRM Load center2613
RTC2613
CCR3216
Total221130
Optimisation of air condition space
By optimising the room space, air conditioner power consumption reduced and room temperature maintained effectively.
Background: In bag house, the room size is larger and drive panels are accommodated within 3/4th of the room. Similarly in CVRM 2 Load center, the the false ceiling height is on higher elevated level and cooling duct is passing above 2 meters height over the panels. Hence cooling of more areas in done unnecessarily in both load the centers leads to power wastage and requires additional unit operation for effective cooling.
Action taken: In bag house, the cooling area partition modified along with the cooling duct modification to the required space and all other opening outside the new partition were closed. Similarly in CVRM-2 load centre, false ceiling and duct height reduced in such a way that the duct passes at 0.5 meter height over the panels. Thus effective cooling of load centres and panels ensured and additional unit operation is completely stopped.
Benefits:
Standby unit available in both locations to meet the demand during breakdowns
Power saving achieved
AC plant operation based on room temperature instead of return air Background: Package AC’s operation and cutoff is based on return air temperature. Due to leakage/improper flow of return air to the machine room, the AC unit is operated continuously and the room temperature is below the set point. This leads to unnecessary more cooling of load centres, CCR and wastage of power.
Action taken: Temperature controllers installed in all load centres, CCR and interlocked the control circuit of package AC’s with temperature controllers. Nowadays based on room temperature package AC’s are getting one or off. Thus power saving achieved.
Benefits: Power saving achieved. Other projects In addition to the above, various other Encon measures implemented as required, including VFDs for all process cooler fans and key auxilliary bag filter fans, occupancy sensors for the load centres and office building, cogged V belts in-place of V belt for blower and AHU’s. Further, for sustenance and continual improvements, daily energy monitoring of the specific power consumption is done through a structured format, capturing the drive wise power along with key operational parameters and accordingly brainstorming done, corrective actions taken and power optimised.
ABOUT THE AUTHOR: The article is authored by R. Rajamohan, Sr. General Manager( IE, Environment, PH) from Dalmia Cement Bharat Ltd., Dalmiapurum, Trichy.