Exploring the complexities of coal washing, this article studies the transformation of run-of-mine coal into a cleaner, high-quality resource for power generators and other industries. The primary objective is to elevate coal quality and calorific value while mitigating sulfur and ash content, aiming for a cleaner, more sustainable and efficient energy source.
https://www.lzzgchina.com/news/coal-sand-cleaning-equipment.html
Coal Washing Techniques:
Surveying diverse methods such as flotation, dense medium separation, and magnetic separation, this section highlights the diverse techniques available for coal washing in both theory and current commercial practices. The significance of complete coal-washing plants is emphasized as pivotal contributors to achieving higher-grade coal.
Dense Medium Cycle:
Dense medium separation (DMS) stands out as a widely employed technique in coal washing, renowned for its efficacy in removing impurities and enhancing coal quality. In this process, coal particles are separated based on their density differences by creating a medium with a specific density. The suspension, typically made from magnetite, plays a critical role, and the quality of the final coal depends on the density of the medium.
The dense medium cycle, used worldwide, is a key method for effective separation. Specifically, it’s important to note that sub-bituminous coals with 30-40% ash content could see their ash content reduced by up to 5%. Also, it’s easier to clean coarse coal compared to finer particles, which have a higher concentration of ash.
Jigging:
Jigging, a gravity separation technique in coal washing, produces the separation of coal particles based on their density. It entails the pulsating motion of water within a jigging bed, leading to the stratification of coal particles. Heavier coal particles settle faster, while lighter impurities are carried away by the water, facilitating the separation process.
Frothation in Coal Washing:
Frothation, or froth flotation, emerges as a separation process employed in coal washing to selectively isolate hydrophobic coal particles from hydrophilic impurities. The technique leverages certain chemicals, known as collectors, to selectively adhere to coal particle surfaces, creating a froth layer separable from the bulk solution.
Cost/Benefit Analysis and Coal Preparation Plants:
The economic viability of coal washing should be meticulously evaluated through a cost/benefit analysis, underscoring the indispensable role of coal preparation plants. These plants, integral for the success of coal washing, crush and stockpile graded coal, preparing it for market transport. The analysis considers coal quality parameters such as ultimate and proximate analysis, ash mineral analysis, sulfur content, and calorific value.
The washability test, specifically ASTM D4371, is highlighted as a crucial step in assessing cleaning effectiveness and impurity characterization before selecting any washing procedure or technology. Neglecting washability testing can lead to pitfalls such as selecting the wrong technology, incurring high operating costs, and making misguided investments.
Dense medium, often accompanied by technologies like dense medium separators, centrifuges, and dewatering screens, ensures effective solid/liquid separation, culminating in a clean coal product balanced for the market.
It’s worth noting that while not all coals are easily washed, coal washing offers numerous benefits, including reduced ash and sulfur content and an increased calorific value. Improved coal quality translates to reduced emissions during combustion, easier handling and storage due to lower ash content, and enhanced efficiency in usage with fewer slagging and fouling issues. However, the coal washing process isn’t without drawbacks, encompassing higher energy production costs, the necessity for wastewater treatment, and potential environmental concerns stemming from slurry.
Some references
https://www.researchgate.net/publication/228013236_Minerals_Recovery_and_Processing
https://publications.gc.ca/collections/collection_2019/rncan-nrcan/m38-13/M38-13-85-2-eng.pdf