Geneva, Switzerland - The manufacturing process for cement is both electrical and thermal energy-intensive. The environmental considerations and cost factors accompanying both sources of energy are driving companies to reduce energy use at their cement plants. This case study, published by the World Business Council for Sustainable Development (WBCSD), looks at how one such facility managed to reduce its thermal energy requirements per ton of cement produced between 2003 and 2004.

About one tonne of carbon dioxide gas is released in the production process for one tonne of cement. Concrete, the most commonly used building material worldwide, is a mix of water, air, cement, and an aggregate such as sand or gravel. Cement is used as a bonding agent, usually making up about 10-15% of the mix.

The Vancouver-based EcoSmart Foundation works to reduce energy consumption and greenhouse gas emissions from concrete by replacing up to 80% of this cement with supplementary materials, such as fly-ash or other industrial by-products. The result is a more environmentally friendly concrete that can be cheaper and stronger than conventional cement-based concrete. However, there is still a need to reduce the energy consumption of cement production worldwide. Holcim (South Africa) (Pty) Limited is one of the largest suppliers of construction-related materials in Southern Africa. Holcim has been producing high quality A1 cement in South Africa since 1934. From the company’s base factories at Ulco in the Northern Cape and Dudfield in the North West Province, the product is transported to depots across the country, and thence distributed in bulk and bags to a large and wide-ranging customer base.

Holcim’s Dudfield plant managed to reduce its thermal energy requirements per ton of cement produced between 2003 and 2004. The project was triggered by the need for significant repair work at the plant.

After 24 years of service, the Dudfield cement kiln line number 3 had reached a mechanical condition that required a major overhaul to ensure continued reliable and safe operation. The kiln shell and the drive train were among some of the larger items needing capital-intensive attention.

Klean Industries is also creating a sustainable advantage and a green opportunity to reduce energy consumption in cement industry with its integrated pyrolysis and gasification systems that produce extremely clean fuels which are injected directly into the cement plants calciners and or pre-heat towers. These clean fuels can be generated from almost any common waste stream, whether liquid, solid, mixed or unmixed (including whole tires, all types of plastics, e-waste, shredder residues, sewage sludge, animal wastes, biomass, ligneous and infectious biohazard medical waste) and represent an environmentally friendly and commercially viable alternative to traditional methods of processing waste. Klean Industries is also producing high quality asphalt modifiers from carbon char derived from tires which increases asphalt tensile strength and rut resistance in high traffic areas by approximately 400%.

More information about this application can be found by clicking here.

Targets

A project was conceptualized to transform maintenance requirements into an opportunity not only to repair existing equipment, but also to entirely replace older sections of the plant.

A task team was assembled and key areas of equipment that had become technologically obsolete were identified. This was followed by proposals for the installation of state-of-the-art equipment.

The following objectives were identified:

• Achieving optimal environmental performance;
  
• Achieving optimal economic performance in a number of areas, among which was the usage of thermal power; and
  
• Compliance with performance standards within Holcim that includes but is not limited to equipment efficiency and safety. Activities
  
• Installing a state-of-the-art heat recovery system (clinker cooler). Modern coolers are rated to obtain heat recovery efficiencies of above 75%.
  
• Replacing the main burner to allow for tighter control of combustion air introduced to the coal flame and to swirl the air as it leaves the tip of the burner, enabling the kiln operator to manipulate the shape of the flame to maintain optimal burning conditions. Dudfield investigated various options of new burner technology on the market and based its choice on the flexibility of flame control and the reduction of combustion inefficiencies.
  
• Identifying the possibility of installing new and more modern cyclones in the preheater tower to allow for the more efficient transfer of heat.
  
• Keeping “false” air from entering the kiln system via cracks and other openings. The more “false” air enters, the more heat is required to heat up the whole system and the harder all the equipment has to work to produce the same amount of clinker. The Dudfield kiln was shut down for an extended period, allowing unwarranted apertures to be identified and repaired.
  
• Replacing the air lift (transport of fine powdered material in a stream of fast-blowing air) with a bucket elevator, thereby realizing further savings in kiln system fuel consumption.
  

Results

After the implementation and successful commissioning of the project in 2003 and 2004, the thermal heat consumption of the cement kiln decreased dramatically as expected. A “before-and-after” analysis of the amount of thermal energy needed to produce one ton of cement was performed.

Lessons Learned / Conclusion

A focused technical approach and specialized expertise enabled Holcim to identify sections of the old manufacturing system that could be modernized at costs that would ultimately be rationalized by the resultant savings.

Aside from a 15% decrease in the thermal energy consumption of Dudfield kiln 3, the following benefits were accrued:

• The use of less coal for every ton of cement produced, thereby decreasing the amount of CO2 emitted per ton of cement;
  
• An increase in the reliability of the kiln line, resulting in greater productivity, which consequently enhances the company’s reputation for dependable delivery in the minds of its large customer base;
  
• The technology installed in this plant in South Africa is at the leading edge of cement manufacturing systems worldwide.
  

The entire case study can be downloaded here.