Cement and Energy

Energy Efficient Technologies Various state-of-the-art equipment are available for reduci ng the electrical and thermal energy consumption levels in cement manufacture. A cement plant with the latest technology is expected to achieve specific electrical and thermal energy consumptions of 80-85 kWh/t of OPC and 680-700 kcal/kg clinker respectively against the rresent industry average for dry process cement rlants or about 104 kWh/t of OPC and 780 kcal/kg clinker. Technological developments in cement manufacture for reduction of energy consumption are main ly in the following areas: Crushing and grinding systems Mobile crushers, horizontal impact crushers Jm rrovement in ball mill internals High efficiency separators Vertical Ro ller mill or Ro ller Press Horo Mill Pvro-processing : Low pre.ssure cyclones Contro l Flow Grate (CFG) coolers Multi channel burners 5/6 stage Pre heater systems Short rotary kilns Material handling systems : Improved mechanical conveying systems Pipe conveyors Instrumentation and Process Control: Refractory management system Kiln/Mill expert control system On line Bulk Material analysers X-ray analysers (XRF) X-ray Diffractometer (XRD) Electrical drives/fans : General : High efficiency fans Vari able speed drives Sli p power recovery systems(SPRS) Variable voltage frequency control systems(VVFC) Use of alternati ve fuels Waste heat recovery systems Production of blended cements Even though there are many technologies as mentioned above for energy conservation, it is of paramount importance to identify the specific measures suitable for a plant based on techno-economic considerations. Operational Aud it of a cement plant is an effecti ve means for this. Holtec's Experiences Holtec has recently carried out Oper ational Audit study in a cement plant having three uni ts, namely, U - I , II and III of 2200tld, 3000 tid and 3500 tid capacity kilns with a view to study the plant operations, assess the present systems, energy utilisation effectiveness and identify the areas and causes for high energy consumption and suggest measures for increasing production and reducing energy consumption. A multi-discipl inary team visited the plants to carry out the studies. Prior to the visit, detailed plant data and operational data were collected th rough a questionnaire. The team had extensive discussions wi th the plant personnel and carried out process measurements and observed the oper ations of the individual sections for identilication of the potential areas for reducing energy consumption. Based on the study the following areas were identified for reducing energy consumption : • Reduction of preheater exhaust gas volume by optimising kiln operation • Reduction of oxygen level in the preheater outlet • Arresting of false air entry into the systems • Adjustment of cooler grate speed and ratio • Optimisation of cooling air distribution in cooler • Switch-over from pneumatic to mechanical conveying • Modification/retrofitting of conventional cooler into high efficiency coo ler • Installation of dip tubes in lower stage cyclones • Replacement of oversized motors by swapping • Providing software interlocks to avoid idle running of auxiliary equipment • Replacement of top stage cyclones with low pressure cyclones • Installation of multi-channel burner • Introduction of VVFC and SPRS on fans 6