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SPECTRAFLOW CROSSBELT ANALYZER - TECHNICAL SPECIFICATION
The SpectraFlow Crossbelt Analyzer is an online measurement system for the cement and minerals industries. When used on a belt conveyor behind the crusher in the cement plant, it provides the chemical analysis of the bulk material. This analysis is the base for the Stockpile blending.
The SpectraFlow system consists of two major hardware components:
a. The illumination head including the spectrometer, and
b. The control unit containing the industrial PC, heating and cooling system, and the power supply.
Requirements of the belt conveyor:
a. The space above the belt conveyor has to be in minimum 2000mm.
b. The gradient of the belt conveyor should not to be bigger than 10%
Near Infrared (NIR) technology utilizes the full wide range of Near infrared spectra which are provided by light lamps. Their emitted NIR radiation hits the target raw material to be analyzed as it passes underneath on the conveyor belt. This NIR radiation excites oscillations of the molecular bonds in the monitored material, which results in reflection respectively absorption spectra that are characteristic for the analyzed constituents. Figure 1 shows a typical set of absorbance spectra, received from limestone after the crusher.
Figure 1: A typical wide range infrared spectrum
The complete NIR spectrum, which is needed to perform the online chemical analysis, is supplied by a set of light sources. These lights emit the NIR radiation, which is used for the analysis. The infrared light reflected by the moving bulk material gets collected by a Fourier Transform Infrared (FTIR) Spectrometer in the center of the illumination system (Figure 2).
Figure 2: Basic Principle of the SpectraFlow illumination system
The FTIR spectrometer is used to generate the absorbance spectra output because it defines each single spectrum in one step. This also means it is extremely stable and calibration models can be easily transferred from one spectrometer to the other in case of spectrometer maintenance.
The FTIR spectrometer used can utilize much more of the reflected NIR radiation than a standard dispersive NIR Spectrometer and it is mechanically extremely robust. The FTIR spectrometer does not need any electric motor. A periodically excited electromagnet is sufficient. This feature ascertains an extremely stable measurement performance and reduces the referencing on an external white reference to maximum four times a year, which is only necessary because the aging of the light spots has to be compensated.
Figure 2 and 3 show the dust and light shield for the conveyor belt application.
Figure 3: Bottom view (left) and top view (right) of the illumination system
Inside the control unit, a dual core Industrial PC (IPC) is running: On one core runs a soft PLC, which controls and supervises the complete analyzer. On the other core runs the basic spectral data handling software. The SpectraFlow Client Software with the Graphical User Interface (GUI) is installed on a second PC either in the control room or in the laboratory that is connected to the same network. On this PC the concentration of the constituents is actually determined. Figure 5 shows some the SpectraFlow GUI screenshots.
Figure 5 Examples of SpectraFlow GUI screenshots
A maximum benefit of a SpectraFlow analyzer can be gained when the analyzer is used together with a Raw Mix Proportioning (RMP) control software. The software package can be provided from any supplier as long as this control software is installed either on the same network, in this case the analysis results are transferred as ASCII text files via TCP/IP, or the SpectraFlow Analyzer is connected to the Profibus-DP bus of the plant and the control software has access to these values over e.g. OPC.
In order to get accurate measurement results about the chemical composition of the analyzed bulk material, a calibration model is needed, which performs the transformation of the received spectra into chemical concentrations (see Figure 4).
The SpectraFlow analyzer system is delivered with a customized calibration models for the appropriate application. To build the calibration model well analyzed samples have to be provided to SpectraFlow Analytics approximately 8 weeks before the intended shipping date.
Depending on the application and the ranges for the different components 20 to 50 samples are needed. The samples should cover the range for each component that should be analyzed. SFA requires approximately 2.5 – 5 kg of well analyzed sample material.
The samples must be representative of the material, which is on the belt conveyor. They must be sent with their chemical analysis i. e. with the concentration of the constituents of interest. In addition the samples must contain minimum one with the minimum concentration of each constituent, which shall be measured and one with the respective maximum concentration
After the installation of the SpectraFlow analyzer system the online results are compared with the laboratory XRF results and the calibration model is optimized for the specific customer ranges. This crosschecks and improves the accuracy of the reported analyzed components.
Figure 4: Example for a Calibration Model for CaO
The installation of the SpectraFlow system is quick and easy. The client installs a frame over the conveyor belt that supports the illumination system. A separate support is needed for the electronics cabinet containing the stabilized power supply for the lamps, the communication electronics and an industrial PC, which does the control of the system and the evaluation of the concentrations.
The SpectraFlow illumination head does not need to be installed perpendicular to the conveyor belt.
The total weight of all components delivered is approximately 180 kg.
Figure 6: Example of the structure for the analyzer
For weather protection in an outdoor installation, the analyzer shall be enclosed all around to avoid stray light.
Figure 7 shows an installed analyzer above a belt conveyor
Figure 7: Picture of an installed belt conveyor analyzer