Low energy cement production
Researchers in Germany have developed a high-performance mineral binder, which, they say, can help reduce the energy consumption and CO2 emissions associated with cement production.
Celitement, the material’s trade name, is based on hydraulic calcium hydrosilicates.
It is made by forming calcium silicate hydrates in a hydrothermal reaction at temperatures between 150 and 200ºC. In a second step the autoclaved material is co-milled with a SiO2-rich material, such as quartz-sand.
‘Production of Ordinary Portland Cement (OPC) at temperatures of up to 1,450°C is a highly energy-consuming process,’ explains Dr Hanns-Günther Mayer, Managing Director of Celitement, a spin-out of the Karlsruhe Institute of Technology (KIT). ‘In addition, cement plants emit more than two billion tonnes of CO2 annually. In comparison to OPC Celitement has the potential to reduce both energy use and CO2 by up to 50%.’
‘During hydration, Celitement transforms to calcium silicate hydrate gel. This material is the cement hydrate, which defines the mechanical strength and stability of traditional concrete. Thus material properties of test samples made with Celitement, such as strength development and final compressive strength (up to 80 MPa) resemble those of samples made with OPC,’ adds Mayer.
Strength can be regulated by varying the mixing and processingparameters. ‘One big advantage of Celitement is the fact that it can be used just like any other cement.’
Celitement and its production is proprietary, but Mayer says that all necessary mechanical components have been used for decades in industry for production of OPC or autoclaved aerated concrete.
In spring 2011, a small pilot with a production rate of 100kg/day will start operation at KIT to perform extensive material tests and prepare scale-up.
‘The integration of a Celitement production line in an existing cement plant is one of the first milestones on the way to the mass market,’ Mayer notes. ‘By 2014/2015 the first industrial plant with an annual capacityof 30,000-50,000t per year will be commissioned.’
Concrete and cement science specialist Dr Charles Fentiman of Fentiman Consulting, based in Horsham, UK, says, ‘The claim of low energy usage and reduced CO2 will have to be substantiated because if lime calcium oxide or calcium hydroxide is used the energy to produce the lime and
CO2 released in that process will need to be taken into account as a Life Cycle Assessment.
‘Also energy usage in autoclaving and milling will be part of this evaluation. If the claims of lower CO2 emissions and lower energy consumption are true, this will indeed represent a very important development that could have a big impact on how cements are manufactured in the future.’
Further information: Celitement