Application and Operational Benefits
| QCX/OnStream® combines high frequency sampling and energy dispersive X-ray fluorescence analysis (EDXRF) techniques to provide tight on-line chemical quality control of cement raw mix or other powder process streams. Elements from Mg and upwards in the periodic system can be analyzed with adequate analytical performance. Thus, in a cement application all the 4 key elements (Al, Si, Ca, Fe) can be analyzed for. Analysis of Mg and/or S are available options. The basic operation principle is that a sampler extracts a small bypass sample stream from the powder process stream. Every approx 6-7 minutes a sample dosing device extracs a small sample portion from this bypass sample stream. The sample portion is delivered to a cavity in a revolving circular tray. After dosing, next step is low pressure pressing followed by sample presentation to the analyzer head, mounted in a fixed position over the revolving tray. The sample is analyzed for typically 2-3 minutes, whereafter the last step in the handling cycle is reject of the sample portion or collection of same into an optional composite sample mixing container. 
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Operational Benefits
For the typical raw mix quality control application, the combination of QCX/OnStream’s high analysis frequency and the powerful control facilities offered by the QCX/BlendExpert-Mill software will result in: - a significant reduction in variation of key chemical parameters in the mill product
- a significant reduction in manpower requirements for sampling, preparation and analysis activities for the key sampling point
The much tighter quality control compared to conventional control schemes will potentially allow for smaller design capacities of homogenizing facilities before and after the raw mill department. Thus, for new production lines, QCX/OnStream may help save capital investment in otherwise larger stock piles and/or homogenizing silos. Likewise, the concept can be used to ‘repair’ the overall control performance of existing poorly functioning raw meal homogenizing silo systems.
Operational specifications
For optimal performance of the QCX/OnStream system, the
following specifications apply:
Ambient temperature (inside shack)
Operating temperature: 15-30 deg. C
Max temp gradient: max 3 deg. C/hour
Material
Moisture: < 0.5 %
Particle size: 90 % < 100 micron
Temperature (entering cabinet): < 100 deg C
The sampling point should preferably be placed before kiln dust is returned to the raw meal process flow. Process delays in form of surge bins between raw material feeders and raw mill inlet or long transport times and alike may affect the overall control performance.
Feed additives such as slag, fly ash etc may likewise affect the analytical performance. If such materials are present in the feed, a set of samples should be forwarded to FLSmidth for further evaluations. |
Brochure:
Options for Kiln feed & Cement analysis
Although designed for on-line raw mix control by sampling at the raw mill outlet, QCX/OnStream can be applied also for:
Kiln feed: If the horizontal distance between the raw mix
(mill output) and kiln feed (silo output) sampling points is limited (normally max 15-20 m), it will with an extra sampler, some extra piping and optionally a horizontal belt sample transport device be possible to have one QCX/OnStream system analyze both raw mix and kiln feed. In such a set-up, one could as an example
analyze 3-5 raw mix sample portions for every kiln feed portion being analyzed. The result for the latter could as an example be passed on to a high level kiln control systems and enhance the automatic kiln control by providing fast info on changes in kiln feed chemistry.
Cement: Installed in the cement mill department QCX/OnStream can monitor the sulphur contents and other elements of interest, and on this basis control the amount of gypsum /or other
additives. The same sampling point may also supportRaw mix control
In a ‘traditional’ raw mix control loop based on a laboratory WDXRF instrument (e.g. QCX/Laboratory + QCX/BlendExpert-Mill), a new control sample is typically analyzed every ½ to 1 hour. QCX/OnStream typically increases the control frequency to once every 6-7 minutes. With this high frequency – also referred to as the fast inner control loop - optimization of the raw mix blending is looked after by applying all control features of
QCX/BlendExpert-Mill, except for feed estimation and updating of silo balances for accumulated deviations. At a lower frequency, typically once per 1 hour (user defined), the QCX/OnStream software calculates an average composition over the period, and this analysis is used as the basis for feed estimation and updating of accumulated deviations in the silo system(s). Please refer to the QCX/BlendExpert-Mill Product Profile for more details of the comprehensive control features. New set points are sent to the feeder controllers via the interface to the general plant control system. While not a mandatory requirement, FLSmidth Automation recommends to include laboratory XRF analysis of a representative composite sample in the control scenario. This implies: with a low frequency, typically once/twice per shift or per 24 hours and pending the requirements to monitor elements not analyzed by the QCX/OnStream analyzer, an average composite sample is brought to the laboratory and analyzed by a conventional laboratory XRF analyzer (WDXRF) monitoring all releven elements. This analysis is mainly used to check the analytical results from the on-line XRF analyzer, and compensate for possible bias. And in the case of equipment maintenance or malfunction, a simple switching can activate the laboratory XRF based control loop to take over responsibility for the mix control, but in this case based on conventional sampling. This setup defines a robust structure, which is tolerant to errors in any of the two analysis instruments.