Online Monitoring of Ash and Moisture in Washed Coal
Introduction
Coal from mining operations is typically extracted, crushed, screened and then washed and stored or loaded onto trucks for distribution. The quality of the final product depends on precise control of ash content and moisture level.
Excessive ash reduces the calorific value of the coal, while uncontrolled moisture can affect both logistics and combustion efficiency. Traditionally, these values are verified through laboratory-based coal analysis, which provides accurate but delayed results. In contrast, online NIR spectroscopy enables real-time monitoring of these critical parameters directly on the production line.
By integrating contactless NIR sensors within the process, operators gain immediate insight into coal quality, transforming control from reactive to proactive and ensuring each batch meets specification before delivery.
Application
At a coal washery site, raw coal presents strong variability depending on the mine of origin and extraction conditions. This heterogeneity affects both washing performance and product uniformity.
To overcome this, a Polispec NIR Contactless analyzer was installed for continuous, non-destructive measurement of key parameters:
Moisture (5–18%)
Ash content (30–40%)
Calibrated with laboratory reference data, the inline NIR provides the same accuracy as traditional lab testing, reaching analytical-grade precision, while offering a continuous flow of information, real-time coal quality monitoring that supports immediate process adjustment, improving consistency and throughput in the washery.
Installation
The Polispec NIR was mounted above the conveyor belt, at strategic points of the coal washing process, between the washing stage and final loading area.
The configuration includes:
- A contactless optical probe performing online coal analysis without touching the material.
- Mechanical protection and air purge, maintaining a clean optical window even in dusty and humid environments.
- Direct PLC integration, enabling real-time data transmission for automatic process control.
- A local display, giving operators direct access to real-time readings of ash and moisture.
This non-contact NIR system operates seamlessly with plant automation, providing direct insight for
coal washery quality control in demanding industrial environments.
Results
During the monitoring campaign, continuous NIR data was collected and validated with laboratory results. The correlation confirmed excellent accuracy and stability across variable feed conditions.
Performance summary:
- Moisture: values ranging from 5 to 18%, closely matching laboratory references.
- Ash content: values between 30–40%, in excellent agreement with analytical results.
Trend analysis charts showed how the real-time NIR monitoring system tracked fluctuations in coal composition and process parameters. Operators were able to adjust washing intensity and drying times instantly, maintaining consistent product quality output and improving process efficiency.
Conclusions
The integration of Polispec NIR spectroscopy in coal washing plants for online monitoring demonstrates the tangible benefits of real-time process control:
- Continuous and non-destructive quality monitoring of moisture and ash.
- Reduced dependence on laboratory-only analysis, minimizing delays.
- Enhanced process optimization, thanks to live analytical data.
- Improved product consistency, ensuring compliance with market specifications.
By combining precision with continuity, Polispec NIR analyzers help coal washery operators achieve stable quality, optimized performance, and a measurable reduction in reprocessing costs: a decisive step toward data-driven process automation and competitiveness in the mining industry.
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