Automatic control of cement quality using on-line XRD

Today, automatic control of cement quality is possible by the use of a continuous on-line X-ray diffraction (XRD) machine. Continuous on-line XRD analysis at the cement mill outlet has been tested to directly control calcite addition, SO₃ content, gypsum hemihydrate and pozzolan addition. Furthermore, the information that XRD provides is used to generate models that predict strength. As such automatic control of cement strength may be achievable in the near future. XRD is a common analytical technique used to directly measure the mineral content of cement, such as C3S, C2S and gypsum. The technique is highly developed and able to detect most cement minerals, even distinguish between the different phases of aluminates, belite and gypsum for example. While XRD is often carried out in a laboratory, a number of plants have installed a field instrument, which analyzes a continuous stream of material in real time. The field instrument employs a special patented position sensitive detector that allows for a full mineral analysis of a moving stream of material to be trended in real time continuously, giving the information needed for real time automated plant control. In contrast, laboratory units analyze a small sample specimen over a finite time to give an analysis. The principles used to determine mineral composition in an on-line XRD machine are no different to those used in laboratory machines. However, the volume and timeliness of the data from an on-line instrument allow for the control of certain quality parameters in real time. An on-line XRD can avoid sample preparation problems by examining a vast number of crystals in a continuous sample presentation system. This article describes a technology for on-line XRD analysis, and how it can provide benefits to cement and clinker production.