High-Efficiency Roller Mills

Traditionally, ball mills are used in cement industry for raw material, fuel and product grinding. Ball mills use an established technology and offer certain advantages. However, they have higher energy demands. By using an appropriate kind of the more efficient roller mill technologies – either as a replacement or in combination with ball mills – considerable energy savings can be achieved without compromising product quality. The following roller mill concepts are applicable to cement manufacturing:

Vertical roller mills: In these mills materials are crushed between a rotating grinding table and 2 to 6 grinding rollers positioned slightly less than 90 degrees from the table surface and pressed hydraulically against it. Main advantages of vertical roller mills include:

  • relatively low power consumption (less than 10 kWh/t – for medium raw material hardness and medium fineness);
  • ability to combine grinding, drying (using waste heat from kiln system) and separation;
  • ability to manage larger variations in mass flow rate (30 to 100% of mill capacity).

Vertical roller mills are available in a wide range of capacities – 5 to 1200 t/h. 

Chinese flag According to National Development Reform Commission of China, VRMs have the following generic power consumption values when used for different purposes in a cement plant:

  • for raw material grinding, power consumption may range between 14 ~ 17kWh/t-material;
  • for coal grinding, power consumption may range between 20 ~ 22kWh/t-coal;
  • slag grinding, electricity consumption may range between 39 ~ 45kWh/t-slag.

The life-time of the wear resistant material is reported to vary between 8000 to 12000 hours. (NDRC,2008. p.50).

In China, market penetration of VRMs within the building materials sector was expected to reach 50% during the eleventh five-year development period, requiring an investment of around 1.08 billion RMB, and holding a potential to reduce energy consumption by 500 GWh (NDRC, p.51). 

VRMs are installed in new cement plants with dry systems, and also often replace ball mills during plant modernization, where the raw material moisture content is less than 25%. As of 2010, VRMs for raw material preparation had a penetration rate of 45% in Chinese market. During the twelfth five-year period, the market penetration of the technology is expected to reach 80% (MIIT, 2012. p.20)

Horizontal roller mills: Here materials are crushed inside of a rotating mill tube which also contains a grinding roller that is hydraulically pressed against the inside surface of the tube. Horizontal roller mills use 65-70% of the energy used in ball mills.

Roller press (high-pressure grinding rolls): In this technology materials are crushed between two counter-rotating rollers. These rollers are up to 2 m in diameter and 1.4 m long. Roller presses use 50-65% of the energy used in ball mills.

Development Status Products
Commercial
clinker, Cement

High-Efficiency Roller MillsCosts & Benefits

Parent Process: Raw Material Preparation
Energy Savings Potential

By replacing ball mills with vertical or horizontal roller mills in raw material preparation, energy savings of 6-10 kWh/t-raw materials (depending on grindability of raw material) can be achieved.

CO2 Emission Reduction Potential

Chinese flag For Chinese context, reductions are estimated to be 4.7 to 5.5 kg-CO2/t-raw material (assuming 0.79 kg CO2/kWh electricity)
Indian flag For Indian context, reductions are estimated to be 4.9 to 5.7 kg-CO2/t-raw material (assuming 0.81 kg CO2/kWh electricity)

Costs

Chinese flag Investments are estimated to be US $5.5/t annual raw material processed.

Indian flag For India investment costs are reported to be $10 - 20 million (or $25 000 to $30 000 per t/h capacity) depending upon the type & size. 

Chinese flag In a 2500t/d clinker production line, installation of a VRM costed 14 million RMB and took eight months to complete. The technology provided annual savings of 4 million RMB in electricity costs and resulted in a payback period of 3-4 years (NDRC, 2008. p.51).

Chinese flag In China, installation of a vertical mill for raw material grinding in a plant with with 5000t/d production is reported to require an investment of around 50 million RMB, and has operating and maintenance expenses of approximately 17 million RMB /year. When working with raw material with medium grindability, a saving of about 10kwh per ton of raw material can be achieved. If material consumption factor is 1.55 and production days are 300 days per year, the technology can save 22.5 million kWh per year and result in a payback period between 3 and 5 years, based only on savings on electricity costs (MIIT, 2012. p.19).

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High-Efficiency Roller MillsSchematic

High-Efficiency Roller Mills Publications

Energy Efficiency Improvement Opportunities for the Cement Industry

The U.S. Environmental Protection Agency’s (EPA) energy guide, Energy Efficiency Improvement and Cost Saving Opportunities for Cement Making, discusses energy efficiency practices and technologies that can be implemented in cement manufacturing plants. This ENERGY STAR guide provides current real world examples of cement plants saving energy and reducing cost and carbon dioxide emissions.

Page Number: 

3

Energy Efficiency and Resource Saving Technologies in Cement Industry

 

This Cement technologies booklet was compiled by the APP Cement Task Force (CTF) through one of its activities to help its member countries share information on all available energy efficient technologies generally used in the world’s cement industry. The document offers a comprehensive compilation of commercially-available energy efficient technologies used in the cement industry.

Page Number: 

67

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49

Advanced and Applicable Technology Guide for Energy Saving and Emission Reduction in Building Materials Industry (first batch)

Published jointly by the Chinese Ministry of Industry and Information Technology, Ministry of Science and Technology, and Ministry of Finance, this guide describes information on currently available as well as developing technologies that can help reduce energy consumption and emissions in building materials industries. The guide aims to inform decision makers involved with designing new plants and/or implementing energy efficiency and emission reduction projects in existing plants.

Page Number: 

20

High-Efficiency Roller Mills Reference Documents

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51