Grinding ultra-fine cement at industrial level
A cementitious minerals processing technology could provide an alternative to ball mills, for producing ultra-fine-particles for industrial applications.
The technology, designed at New Jersey Institute of Technology, USA, involves a dry stirred media mill operating in a proprietary ‘confined bed mode’. In this phase, the grinding media is confined so that when stirred in the mill, the volume does not change and remains in direct contact within a continuous closed circuit.
The raw feed, is introduced into the circuit at a predetermined calibrated rate. The feed is processed in the mill and the output from it passes to an air classifier, where the product fines are recovered in a cyclone and/orbaghouse. The oversize is returned to the mill for additional processing.
Brandon Williams, Managing Member at Flyanic LLC in Newark, USA, who are licensees and developers of the technology, explains, ‘Cementitious materials ground to ultra-fine particle sizes have significant benefits in a range of industrial applications, including specialized grouts for oil and gas exploration. Fly ash and slag, finer than 10µm, are high reactivity super-pozzolans for building products such as high performance structural concrete and pre-cast concrete.’
He adds, ‘An ultra-fine cementitious material has greater surface area and therefore a greater rate of reaction. Ultrafine pozzolans prepared in this way can compete with silica fume and metakaolin currently selling at prices of US$500t or higher. A one micrometre median fly ash product has not been previously available on an affordable industrial scale’.
According to Williams, the technology, which is ongoing patent application, will improve energy and cost efficiency due to improved grinding and the ability to produce ultra-fine comminution products at quicker rates. The team has demonstrated the technology at a truckload scale, with a production rate of over one tonne per hour.
He says, ‘Operating in a “compressed bed mode” produces a consistently in-specification ASTM C-618 quality fly ash. Also, energy input per tonne of output was a small fraction of the conventional expanded bed mode and balls mills’. However, results achieved in comparison studies cannot be disclosed.
Dr Leon Black, Senior Lecturer on Civil Engineering Materials at Leeds University, UK, adds, ‘Grinding is very energy intensive, and any new process would need to be energy efficient. If the process could offer considerable energy savings then it would be, an attractive proposition.
Yet, the company quotes a grinding price of US$30-75t, and with cement costing approximately US$90t, this might not leave much room for manoeuvre’.
The technology is also said to be suitable for industries handling pumice, calcium carbonate, talc, nepheline syenite, clays, ceramics, zeolites and graphite.