The production of cement has an energy-intensive process. Energy is a global matter and the highest input in cement cost.
Cement producers face an increasingly competitive global business environment, they seek opportunities to reduce production costs without negatively affecting product yield or quality.
Energy efficiency is an important component of a company’s production and environmental strategy and energy efficiency projects contribute to reduce the emission of carbon dioxide during the production of cement.

Energy Efficiency=Useful Output/Energy Driven
Energy Efficiency: Minimizing the energy consumption without to reduce the amount and the quality of production and without to stop the economical development and
social prosperity.
Energy efficiency might be investigated under three main title;

• The Main Principles for the Design of Electrical Supply and Distribution Systems in the plants,
• Electrical  Motors,
• Transformers,
• Frequency Converters,
• Energy Quality,

The Main Principles for Electrical Systems Design in the Plants
 Established power for the plants should be well determined.
 High Voltage feeders for the plant substation should be preferred.
 Power transformers should be located just near process units instead in main substation building,
 Medium  Voltage should be preferred for electricity distribution from substations to local MCCs,
 The coordination and selectivity of the protection relays should be fulfilled.
 THD(Total Harmonic Distortion) for voltage and current is advised to be achieved as appr. %2 and %5 respectively.
 Cable cross-sections should be well calculated.
 The underground cable channels with sufficient ventilation should be designed in the plants.
 The metal-clad, vacuum insulated and withdrawable type circuit breakers should be preferred for MV and LV swithcgears.

 Cable placements on the trays and in the conduits should comply with the regulations considering the natural ventilation.
 Electricity buildings should be well air-conditioned.
 The use of day light should be taken into consideration for architectural design of buildings and civil structures.
 The bus bar within the boxes should be preferred for short distance energy transfer inside the electricity buildings.
 Computer based energy measuring and monitoring systems are needed.

- Running characteristics for mechanical equipment to be drived,
- Power, speed and voltage,
- Method of starting,
- Frequency of subsequent startings,
- Determination of motor type(running class,efficiency, protection class, cooling method, erection type etc.),
- Climatic conditions,
- Type of motor case(Compressed or normal)

                                   Energy losses for motors

- Energy losses in motors are heat energy which appears during the running of motors.
- Motor losses are iron loss, friction &wind loss, stator loss, rotor aliminum loss and stray loss.
- The efficiency of EFF1 motors is %1-%10 higher than EFF2 motors and %10-%20 higher than EFF3 motors.
- Energy loss for EFF1 motors is %7-%45 lower than EFF2 motors.
- EFF1 motors have higher over loading capability for continuous running.(SF 1.15)


                                                          Capability for Motor Loading


- Preventive, Predictive or Proactive maintenance have to be applied.
- The maintenance of motors with 3000 rpm speed have to be performed once a year by dismantling.
- The maintenance of motors with speed of 1500 rpm have to be performed in every 2-3 years by dismantling.
- The predictive maintenance is preferred for  the motors with speed of 750 rpm and lower by dismantling.
- Motor bearings  have to be lubricated periodically.
- Mechanical and electrical measurement datas for bigger motors are saved in PCs.
- Daily visual inspections have to be carried out especially for slip rings and DC motors.
- Visual inspection should be made for critical motors in process by thermal camera.
- Efficiency for transformers is quite important because of the presence of at least five transformers in order to transmit electricity from the power plants to the consumers.
- So, efficiency for transformers should be higher than %99. 
- Efficiency for transformers is investigated separately as power and energy efficiency.
Efficiency Parameters for Transformers;
- Loading ratio,
- Power factor,
- Temperature,
- Quality of network,
Efficiency of Transformers;
- Optimum range for loading ratio is between %70-%100 because of the low losses and low harmonics.
- Maintenance of transformers should be well made.
- Physical and chemical oil tests should be made yearly.
- Primary and secondary protection relays should be tested periodically.

The great energy saving is achieved by means of variable speed AC motors instead constant speed motors where flow is controlled by valve and  gate. 
         A Typical Comparison Variable and Constant Speed Motors


Aim based management should be applied for the process management. Some of the aims;
- Energy intensity,
- Spesific energy(kWh/ton, kCal/ton, etc.)
- Amount of production,
- Breakdown periods, etc.
Energy management system is one of the main methods for the efficiency of a plant. Some items are as follows;
- Presence of PC based energy monitoring system,
- Using the most proper electricity tariff ,
- Minimum operation during the peak time,

- Cogeneration units are suitable for the plants where steam, hot gas and/or hot water together with electricity are used.
- Processes should be operated by automation systems.
- Heat recovery units should be available.
- The systems with the lowest specific energy consumptions should be preferred at new investment projects.
- Waste materials at maximum amount should be burnt in the kilns as well as possible.
- The processes should be measurable and open at maximum level.
- Mechanical conveying systems should be preferred comparing with pneumatic ones.
- Distributing the compressors in large plants are more efficient due to the pressure losses.
- Energy consumption is appr. 7-8kWh to produce 1 M³ pressurized air.
- Insulatings for process pipings, fittings etc. should be well made.
- The burning optimization in the kilns and burners and cooler optimization
 must be ensured.
- The exhaust heat should be used.
- Mill optimisation should be ensured due to the filling levels of the mills and other parameters.
- Specific energy consumption for cement mill process with roller press is %20 lower than cement mill without roller press.
- Specific energy consumption for Horomill type cement production process is %20-25 lower than cement mill with roller press.
- Specific energy consumption of vertical mill is %40 lower than ball mill for raw meal.
- Optimum material handling should be fulfilled in all steps from quarry to product delivery to customer.
- Energy Consumptions for the Vertical Conveying Systems
 Fuller Pump           1.20kWh/Ton/100M
 Airlift             1.10  “
 Intensified Phase Pumps       0.59 “
 Elevator             0.41 “

   Steps of Energy Efficiency Survey
• Establishing a survey team with members from the groups of process, mechanics, electricity and environment,
• Constituting detailed action plan to determine the potential,
• Application of action plan,
• Energy balancing studies,
• Comparison for actual and established energy consumptions  of systems and equipments,
• Inspecting and examining the processes and control logic, 
• Evaluation of all datas obtained in acc. with action plan,
• Studies on the use & cost analysises and feasibilities,
• Classifying the job items based on their priority due to the pay back time,
• Using the consultant if required,
• Execution the items,
• Studies for efficiency survey is a circle required continuity.

A Summary for Energy Efficiency Applications and Technologies in Cement Production

Raw Materials Preparation
• Efficient transport systems
• Raw meal blending systems
• High-efficiency roller mills
• High-efficiency classifiers
Clinker Production (Dry)
• Energy management and  process control with automation
• Seal replacement
• Kiln combustion system improvements
• Kiln shell heat loss reduction
• Use of waste fuels
• Conversion to modern grate cooler
• Refractories
• Heat recovery for power generation
• Low pressure drop cyclones for suspension pre-heaters
• Optimize grate coolers
• Addition of pre-calciner to pre-heater kiln
• Long dry kiln conversion to multi-stage pre-heater kiln
• Long dry kiln conversion to multi-stage pre-heater, precalciner kiln
• Efficient kiln drives
• Oxygen enrichment
Finish Grinding
• Energy management and process control with automation
• Improved grinding media (ball mills)
• High-pressure roller press
• High efficiency classifiers
General Measures
• Preventative maintenance (insulation, compressed air system, maintenance)
• High efficiency motors
• Efficient fans with variable speed drives
• Optimization of compressed air systems
• Efficient lighting
Product  Changes
• Blended cements                                                                      
• Limestone cement
• Low Alkali cement
• Use of steel slag in cement
• Reducing fineness of cement for selected uses

Although technological changes in equipment can help to reduce energy use, changes in staff behavior and attitude may have a greater impact. Staff should be trained in both skills and the company’s general approach to energy efficiency in their day-to-day practices. Personnel at all levels should be aware of energy use and objectives for energy efficiency improvement.
                                                                                                                                                              Mahmut SELEKOĞLU - 2008


- International Energy Agency, Key World Energy Statistics, OECD/IEA, Paris, 2005, s.48,52,56.
- An Energy Star Guide for Energy and Plant Managers, Ernest Orlando Lawrence Berkeley National Lab., January 2004
- Cement Review Handbook
- ABB and Siemens Motor and Drive Publications