Coal Preparation » Dewatering
Dewatering of fine coal tailings becomes more and more challenging due to the variation of tailings composition, and the complex surface properties and gelation. Among dewatering methods, solid bowl centrifugation has proven superior owing to an efficient combination between chemical reagents and their mechanical forces. However, the dewatering effectiveness of a solid bowl centrifuge (SBC) evaluated via the cake moisture content and the centrate quality is dependent on many factors such as the plant feed characteristics, chemicals, and their dosages, not to mention operational parameters like the feed flowrate, speeds of main and back drives, particle residence time, and pool depth. This project aims to deliver a control system for the SBC to provide flexibility and adaptability to the plant conditions and product quality requirements.
The project completed the following:
- Preparing and characterising coal tailings samples. Installing a sensor to evaluate the centrate quality and a peristaltic pump that can control the flocculant dosage;
- Fully automating the solid bowl centrifuge via a wireless connection to a laptop computer;
- Developing a real-time data-based model for the solid bowl centrifuge. Correlating the centrate quality, cake moisture content, and cake yield stress with the chemical dosages;
- Developing a closed-loop control system based on the real-time data-based model;
- Implementing, testing, and validating the designed control system.
The composition of coal tailings and process water is significantly varied from mine to mine and significantly affects the dewatering efficiency. A light sensor measuring the light transmittance is installed to determine the quality of water and centrate discharged from the SBC. A peristaltic pump is installed to control the chemical dosage, while all parts of the SBC are automated. The light sensor, pump, and SBC are connected to a computer and controlled by a LABVIEW graphical user interface (GUI). Particularly, a real-time data-based model is developed and successfully applied to accurately describe the dynamic relationship between the flocculant dosage (input variable) and the centrate quality (output variable). A closed-loop control system with controlling parameters optimised using the real-time data-based model is developed and applied to control the output water quality of a mixer and the SBC centrate. Specifically, the control system can maintain the light transmittance of the output water of a mixer which homogeneously mixes wastewater (0.04 or 0.12 g/L solid content) and fresh water. The control system can also effectively maintain the light transmittance of the centrate from the SBC by automatically altering the flocculant dosage. The project introduces an appropriate model and a control system that can be applied to effectively and accurately control the operation of solid bowl centrifuges. The control system developed in this project can be applied to other dewatering devices such as belt-press filters or high-pressure disc filters to enhance their flexibility and adaptability to plant conditions and output quality requirements.