DINGLI GROUP

Lignite is a typical low-rank coal characterized by a highly porous structure, high volatile matter content, and a relatively low ignition point. Many clients attempt to achieve rapid dewatering by simply raising the hot air temperature, often overlooking the material’s inherent properties. High-temperature drying can trigger a chain of problems, including the risk of spontaneous combustion, degradation of coal quality, and moisture re-absorption in the finished product.

1. High temperatures significantly increase the risk of spontaneous combustion and dust explosions

Due to its high volatile matter content, lignite begins to release significant amounts of volatiles at temperatures above 200°C, and its ignition point is only around 270°C. If the temperature inside the drying drum becomes excessively high in certain areas, the material particles overheat and volatiles accumulate. This creates a dual risk: the particles themselves may ignite, and the mixture of coal dust and volatile gases heightens the danger of dust explosions, posing a major safety threat to the entire production line. Even if no fire breaks out inside the equipment, the intense heat increases the internal reactivity of the lignite. Once discharged and stockpiled, the coal continues to oxidize and generate heat upon contact with air, drastically increasing the likelihood of spontaneous combustion in the stockpile later on.

2. High temperatures degrade coal quality and result in a loss of calorific value

Excessive heat causes mild pyrolysis, leading to the loss of valuable volatile matter and a direct reduction in the coal’s calorific value. This creates an awkward situation where “moisture drops, but heating value drops along with it”—meaning the drying process, intended to upgrade quality, actually devalues ​​the product and fails to achieve the goal of quality and efficiency improvement. Furthermore, high temperatures can cause localized charring and fragmentation, significantly increasing the proportion of coal fines; this generates large amounts of fine dust, exacerbating dust-related issues during subsequent storage and transportation.

3. High temperatures aggravate the phenomenon of moisture re-absorption

Lignite features an abundant microporous structure, much like a sponge. Rapid, high-temperature drying expands these internal pores too quickly, preventing the formation of a dense surface structure. Upon discharge, the lignite rapidly absorbs atmospheric moisture; within just a few days, its moisture content rebounds, severely undermining the drying results. This leads to a common industry dilemma: the product meets specifications immediately after drying but fails to do so after being stockpiled for a few days.

4. It leads to wasted energy and increased operating costs

Most of the free moisture in lignite can be effectively removed within the 100–150°C range; simply raising the hot air temperature results in excess heat being lost rather than utilized for dehydration, thereby driving up fuel consumption and operational costs.

To address these challenges, Dingli’s lignite dryer moves away from the conventional approach of rapid, high-temperature drying in favor of a zoned, gradient temperature control process. By matching appropriate temperature ranges to specific drying stages—applying moderate heat exchange during the high-moisture phase and strictly capping temperatures during the drying phase—the system ensures efficient dehydration while inhibiting excessive volatile matter release and reducing the risk of spontaneous combustion. Additionally, the equipment optimizes material lifting and airflow distribution to improve material porosity and mitigate moisture re-absorption in the finished product. This balanced approach—addressing safety, coal quality, and energy efficiency—provides a reliable equipment solution for lignite upgrading.