Finish Grinding

In the finish grinding, clinker is mixed with gypsum and other minerals, such as blast furnace slag, according to the specifications of desired end products and are ground, or milled, to achieve required particle fineness.  Finish grinding accounts for nearly 40% of the electricity use in cement production. (ECRA, 2009) 

Ball mills continue to be the dominating choice for finish grinding, although their share has decreased from 59% in 2000 to 49% in 2007.  On the other hand, vertical roller mills (VRM) are increasingly used for finish grinding (having a share or 39% in 2007).  Combined share ofroller presses and horizontal rollers for finish grinding is 12% (ZKG, 2010).   A significant reduction of the specific energy demand for cement grinding can be achieved either by combining VRMs or high pressure grinding rolls (HPGR) with existing ball mills or by a complete replacement of ball mills by these technologies. Saving potentials are, however, limited by the quality requirements of the final product and the specific system layout as well as auxiliary equipment installed. Whereas required grain sizes up to 4500 to 5500 Blaine can be achieved in VRM and HPGR, the resulting particle size distribution of the cement and thus cement performance can vary in the different systems raising the need for product quality control plans. (ECRA, 2009)

In contrast, combined grinding layouts, being the most common systems installed, set the standard for product quality and do not have to face quality problems. These multi-stage configurations are, however, more complex to operate. Their saving potentials approach to 30% with an additional 80% increase in throughput as compared to single-stage grinding in ball mills. Despite such savings, it has to be taken into account that the application of VRM and HPGR is connected to higher capital costs and requires additional maintenance efforts. (ECRA, 2009)

Finish GrindingTechnologies & Measures

Technology or MeasureEnergy Savings PotentialCO2 Emission Reduction Potential Based on LiteratureCostsDevelopment Status
Vertical Roller Mills for Finish Grinding

Energy savings enabled by replacing ball mills with VRMs can be 20 to 30% and is primarily a function of the product fineness. 

Electricity consumption can be reduced by 10-24 kWh/ton of cement.

Indian flag Savings in the range of 20-24 kWh/t clinker are reported from India, depending on clinker  grindiability and product blaine.

Indian flag It is reported that vertical pregrinder can typical increse the capacity by 30%, and provide power saving in the range of 15-25% in the Indian context. 

Chinese flag  In China, replacement of ball mills with vertical roller mills in finish grinding can reduce energy consumption by 10 to 15 kWh/t-cement, representing a saving between 30 to 40% (MIIT, 2012. p. 26).

Chinese flag Using VRM in finish grinding, Hubei Yadong Cement Co, Ltd. achieved capacities and unit energy consumption values of 217.5 t/h and 30 kWh/t in producing of Grade P.O 42.5 cement and, 199.7 t/h and 34 kWh/t in producing grade P.C 32.5 cement (MIIT, 2012. p.27).

Chinese flag The electricity consumption of the main engine, the separator, and the fan of TRM45.4 finish vertical roller grinding system developed by Tianjin cement industry Design and Research Institute is reported to be between 18 ~ 22kWh/t-cement, 0.3 kWh/t-cement, and 9 kWh/t-cement respectively. Power consumption of this system is reported to be 4~6 kWh/t lower than that of combined grinding system with roller press and ball mill, and 10~15 kWh/t lower than that of ball mill system. This technology was successfully applied in Fukuyama Cement Corporation in Vietnam, producing better quality products and eliminating the need to use water and grinding aids (MIIT, 2012. p. 27).

Chinese flag In the Chinese context, CO2 emissions can be reduced by 7.9 to 19 kg/t-cement with the use  of this technology. 

Indian flag In the Indian context, CO2 emissions can be reduced by 8.1 to 19.4 kg/t-cement with the use  of this technology. 

Investment costs are estimated to be between US $2.5 - 8 per annual ton cement capacity. 

Indian flag For India invesments in the range of $10-15 million, or US  $40-$65 per ton of hourly capacity are reported. 

Commercial
High-Efficiency Separators/Classifiers for Finish Grinding

Electricity savings between 0 to 7 kWh/t cement are reported dependent on the plant and cement type and fineness required.

Chinese flagAs compared to a conventional separator or a ball mill with open circuit, third generation separator/classifier can reduce power consumption by 5 kWh/t-cement (NDRC, 2009. p.46).

Chinese flag Zhejiang Hushan Group Co.Limited installed a high efficiency separator/classifier in its 5000 tpd plant and reduced specific energy consumption in finish grinding from 36 kWh/t-cement to less than 31 kWh/t-cement. Annual electricity savings of 10 GWh (3500 tce) are realized - corresponding to annual production of 2 million t-cement (NDRC, 2009. p.47).

Chinese flag By installing a high efficiency separator/classifier in their 3700 tpd production line, Huaihai China United Cement Company Limited reduced specific energy consumption in finish grinding by 2 – 3 kWh/t-cement, resulting in annual electricity savings of around 4.2 GWh (1470 tce) (NDRC, 2009. p.47).

Investment costs were estimated to be US $2/annual ton of finished material.

Indian flag For India, the investment costs are reported to vary between US $0.2-0.4 million, or around US $2 000 per ton or hourly capacity. 

Chinese flagInstallation of a high efficiency separator/classifier for a 5000 tpd production line in Zhejiang Hushan Group Co.Limited required an investment of 2 million RMB and took three months to complete. For annual output of 2 million tons of cement, the investment resulted in a payback time of less than one year (NDRC, 2009. p.47).

Chinese flagInstallation of a high efficiency separator/classifier for a 3700 tpd production line in Huaihai China United Cement Company Limited required an investment of 2.4 million RMB and took one month to complete. The system helped improve the product quality, increased output by 10%, allowed for increased use of cement additives by 5 to 10%, and reduced dust emissions. The payback time for the investment was less than one year (NDRC, 2009. p.47).

Commercial
Closed circuit systems for ball mills

Reductions in the range of 4-6 kwh/t cement are reported from India, depending upon the product type

Chinese flag In China, for 5000t/d cement production line using a ball mill with closed circuit system, power consumption index is reported to range between 38 ~ 42kWh/t (NDRC, 2008. p.48).

Investments in the range of US $455 million are reported for a 3000 kW mill.  (1 US$=¥ 110)

For India invesments are reported to range  $5 -10 million depending upon the capacity.

Commercial
Process Control and Management in Finish Grinding

Electricity savings can be in the range of 3.8-4.2 kWh/t cement. 

Estimated payback periods are typically between 6 and 8 months

Commercial
Optimizing the operation of the cement mill

Electricity use can be decreased by up to 2 kWh/t cement

CO2 emissions can be reduced by 1 to 2 kg per ton of cement

Investment cost for retrofit is estimated to be € 10 thousand  (US $14 thousand), based on a clinker capacity of 2 million ton per annum. Operational costs are expected to decrease by up to €0.15  (US $0.21) per ton of cement. 

Commercial
High Efficiency Fans for Finish Grinding

Savings will depend on the efficiency of existing fans

 Indian flag0.13 kWh/t-clinker is reported. (UNFCC, 2008, p.9)

 Indian flagFor India, the implementation costs of this measure are reported to be between $0.05 - 0.15 million depending upon the capacity, or around $400 per tph mill capacity. 

Commercial
High-Pressure Roller Press

Power consumption can be reduced by 10 - 24 kWh/t-cement. 

Savings in the range of  7 - 15 kWh/t cement are reported from India. 

Chinese flag Energy consumption of a single-set high-pressure roller mill with 200 t/h capacity is reported to be less than 30 kWh/t-cement (NDRC, 2008. p. 48).

Chinese flag In China, a 5000t/d cement grinding plant reduced electricity consumption by more than 30% (approximately 8~ 10kWh/t cement) by using high-pressure roller mills, instead of ball mills (NDRC, 2008. p. 48)

Chinese flag In another plant with 2500t/d cement grinding capacity, switching over to high-pressure roller mills has reduced electricity consumption by more than 30% (approximately 8~ 10kWh/t cement) (NDRC, 2008. p. 48. )

In the Chinese context, CO2 emissions can be reduced by 7.9 to 19 kg/t-cement with the use  of this technology.

In the Indian context, CO2 emissions can be reduced by 8.1 to 19.4 kg/t-cement with the use  of this technology.

Investment costs are estimated to be between US $2.5 - 8 /annual ton cement capacity, 

For India investments are reported to ranege between uS $10-15 million, or US $40-65 per ton of hourly capacity. 

Chinese flag For China investments are reported to range between 12~20 million RMB, and payback period may be between 3 and 4 years (NDRC, 2008. pp.48-49).

Commercial
Emerging Grinding Technologies

Not available

Not available

Not available

Research
Cement grinding with Horomill

Power consumption can be reduced by 10-25 kWh/ton of cement  based on  clinker  grindability and product blaine. 

In the Chinese context, emissions can be reduced 7.9 to 19.8 kg of CO2/t-cement with this technology.

In the Indian context, emissions can be reduced 8.1 to 20.3 kg of CO2/t-cement with this technology.

Not available

Commercial
Grinding Aids for Ball Mills

Not available

The cost of diethylene glycol is reported to be between US $1,360 to 1,820 per m3. [1US$=¥110]

Commercial
Improved Grinding Media for Ball Mills

This practice can reduce the grinding energy use by 5-10% in some mills, which is equivalent to estimated savings of 3-5 kWh/t cement. 

CO2 emissions can be reduced by 0.7 - 1.2 kg/t-cement with this technology. 

Payback times of eight years are estimated, based solely on energy savings. 

Commercial
Vertical roller mill as pre-grinding to ball mill

Specific power consumption can be decreased by about 10 - 20%.

 

Japanese flagImpplementation costs for a 100 ton per hour system in Japan are reported to be US $6.4~9.1 million, including cost of ancillary facilities and construction [1US$=¥110]. 

Indian flag In India, there are no references for VRMs being used for pre-grinding. 

Commercial
High pressure roller press as pre-grinding to ball mill

Specific power consumption decreases by about 10%.

Reductions in specific energy consumption in the range of 7-24 kWh/t-cement are reported (LBNL, 2008)

Chinese flag Power consumption per ton of cement can be reduced by 8 ~ 12 kWh, representing 15% to 30% saving over a traditional ball mill system. System output can be increased by more than 100%. Specific energy consumption is around 30 kWh/t-cement for grade 32.5 and around 33 kWh/t-cement for grade 42.5 (MIIT, 2012. p.25)

.

Chinese flag For a 5000 tpd plant, annual energy savings can reach 20 TWh (MIIT, 2012. p.25)

Chinese flag Hefei Donghua building materials Co., Ltd. installed a combined open-circuit roller press (HFCG160-140), SF650/140 dispersing classifier and a φ4.2 × 13.0m ball mill, and reached a capacity of 180t/h, with specific grinding power consumption of 27kWh/t-cement, and overall grinding station consumption of less than 32kWh/t-cement – saving 12kWh/t-cement as compared to a traditional ball mill system (MIIT, 2012. p. 25)

Chinese flag  By installing a combined roller press and ball mill grinding system in a 2400tpd cement production line, Tianjin Zhenxing Cement Co, Ltd. reduced specific energy consumption by 7.0 kWh/t-cement. For an annual production of 900 000 tons, this provides a saving of around 6.3 TWh/y (MIIT, 2012. p.25).

CO2 emissions can be reduced by 6 - 19 kg/t-cement. 

For a 100 ton per hour mill in Japan, the installation costs are reported to be about US $2.7 million (1 US$=¥110), including auxiliary and construction. 

Indian flag For India installation costs are reported to be between $10 - 20 million, or between  $55 000-$65 000 per tph system capacity. 

Chinese flag For a 5000 tpd plant, annual electricity savings can amount to 10 million RMB (MIIIT, 2012. p.25).

Chinese flag By installing a combined roller press and ball mils system, Hefei Donghua building materials Co., Ltd. realized annual savings for more than 6 million RMB, due to reduced electricity consumption (MIIT, 2012. p.25)

Chinese flag  By installing a combined roller press and ball mill grinding system for a 2400tpd cement production line, Tianjin Zhenxing Cement Co, Ltd. realized annual savings of more than 3 million RMB due to reduced power consumption (MIIT, 2012. p.25).

Commercial
High efficiency grinding of blast furnace slag

Power consumption can be reduced by around 30 kWh/t-slag (for a slag blain value of 4000 cm2/g)

In Japan, the cost for the installation of a 40 ton per hour unit is reported to be around US $7.3 million, including cost of supplemental facilities and construction fees. [1US$=¥110]

Commercial
Classification liner for the second chamber of the ball mill

The power consumption of the ball mill can be decreased by 1 - 2 kWh/t-cement. 

Implementatoin costs, for a 3000 kW mill, were reported to be US  $682 thousand (1US$=¥110). 

Commercial
Clinker flow rate regulator for the tube mill

Power consumption can be reduced by 2 - 3 kWh/t-cement. 

In japan, implementation costs for of a 1000 kW and 3m diameter mill were reported to be US $320 thousand (1US$=¥110)

Commercial