Chlorine analysis in refuse-derived fuels (RDF)
The NIR spectrometers uniSPEC2.2MPL, uniSPEC1.9HSI, uniSPEC2.2HSI as well as the fiberoptic hyperspectral cameras uniSPEC1.9FOM and uniSPEC2.2FOM are utilised in quality control of refuse-derived fuels.
The RDF material (fluff) is monitored by process controlled NIR devices. The determination of the weight distribution is achieved by applying statistical methods.
At known total weight, the relative mass contents are calculated by applying the specific weight of the material types. The material composition of the RDF stream is given in weight percent. Identification and
evaluation of the material sorts in the material stream
are the basis for the evaluation of the chlorine value,
humidity and caloric value.
A reliable statistical evaluation of the chlorine content requires a large sample size. Thee realive content of PVC/PVDC related to the total weight can be concluded by the relative mass content and the weight distribution of the total mass. For both material sorts (PVC/PVDC) an average chlorine content is presumed. The method can be used for material streams with different material compositions.
Comparison of RFA and NIR method for chlorine analysis
|RFA-laboratory measurements||NIR in-line measurements|
|Chlorine value analysis||Direct||Indirect|
|Analysis time||A few days between sample drawing and availability of the analysis results||Analysis results are immediately available|
|Analysis mass||From heterogeneous solid RDF material mixes a truly representative sample cannot be drawn. Only samples of a few kilogram can be drawn with a justable effort. Usually, the analysed material amount is only about 50 to 150 ‰ of total mass, which is not a representative sample for the total chlorine contents.||The NIR in-line methods continuously analyses about 7 to 12 % of total mass assuming an average material layer thickness on the conveyor belt of 15 cm. For this amount the chlorine content, resulting from PVC and PVDC impurities, can be determined.|
|Example||Based on a RDF delivery of 25 tons, the analysed material amount is about 10 – 40 kg.||Based on a RDF delivery of 25 tons, the analysed material amount is about 1750 – 3000 kg.|
Humidity analysis of the RDF material stream is performed for paper, wood and identified plastic composites. The humidity stored in unipolar plastics is small and therefore neglectable. The humidity content is calculated for the polar plastics. The analysis result is given in weight percent.
Determination calorific value
For each identified material type, statistic calorific values are stored in the NIR measurement system. These statistic calorific values are applied to the weight percent of the determined material sorts. The total calorific value is calculated in MJ/kg and provided to the process control. The known total weight of the material stream is a prerequisite for the calculation of the calorific value.
|Measurement method||Near Infrared, identification and analysis by monitoring, scanning of the material surface and application of statistical methods|
|Input material||RDF material streams (no agglomerate pellets)|
|Sorting width||400 – 3000 mm|
|Grain size||> 10 mm|
|Sorting speed||Max. 3 m/s|
Analytical evaluation of granulates and agglomerates
Determination of material composition
The devices uniSPEC1.9QC and uniSPEC2.2QC are small, automatic conveyor belts combined with a multiplexed NIR process spectrometer or a hyperspectral camera. With these devices, plastic granulates (>= 3 mm particle size) can be spectrally identified and the percentage distribution of the material sorts can be evaluated statistically and recorded. The devices are suitable for random sample tests in manufacturing processes and can be used for the identification of all kinds of plastic granulates.
The device consists of an optical unit (spectrometer with multiplex unit or hyperspectral camera), controlled by an electronic unit. The electronic control units for conveyor belt and spectrometer are installed in the closed and ventilated chassis of the conveyor belt device. A probe line, consisting of illumination and measurement optics, is mounted above the conveyor belt. The control of the device is performed via a 19“ touch screen. A hopper including a vibrating plate is used for material supply onto the conveyor belt. The material is measured while passing below the probe line. At the end of the conveyor belt, the material is collected by a detachable case. The percentage distribution of the identified material types is shown on the screen and is saved in a protocol file. The result can be transferred to a separate process control.
Input materials are non black plastic granulates and agglomerates with a particle size of 3 mm minimum. Black particles will be evaluated as „black“ in % of the total mass. The following plastics are identified:
|Plastics||PP, PE, PVC, PET, PS, EPS, ABS, PC, PA, PUR, PBT, POM, PMMA|
|Blends||PC + ABS, PVC + ABS, PPE + SB, PC + PBT|
|Flame retardants||ABS + TBBPA, ABS + TBBAep, PS + TBBPA, PS + TBBAep|
|Remains without identification||Black plastics|
Error rate of identification
|Granulate||0,7 % - 1 % Identification error related to the overall material stream|
|Agglmerate||0,7 % - 1 % Identification error related to the overall material stream
2 % - 4 % Evaluation error based on inhomogeneity