Coal is an important fossil fuel. When it burns, it releases a large amount of heat energy and is widely used in many key industries, such as power generation, metallurgy, the chemical industry, and building materials.
However, industrial production often encounters wet coals such as anthracite, lignite, coke, and coal slime. They have low calorific value and cause resource waste. How do you effectively dry the wet coal to improve its combustion efficiency?
4 types of coal
Natural coal is formed by the carbonization process of plants under geological action. Initially, plant debris gradually accumulated in a moist, oxygen-deficient environment to form a soft organic substance—peat coal.
Over time, peat evolves into coal under high temperatures and pressures generated by crustal movement. This process is called coalification. It is worth mentioning that peat can also be used for burning after drying, so it is still used as energy in some areas.
There are four types of coal, depending on the degree of coalification. Each type of coal has a unique carbon content, calorific value, and use.
1. Anthracite
Anthracite is the best quality of coal, also known as "hard coal". It is hard, brittle, black in color, and has a smooth, metallic luster. This type of coal is very rare, accounting for only about 1% of the total coal.
The carbon content of anthracite is as high as over 86%. This coal burning produces almost no smoke and has a high calorific value, but its price is also relatively high. It is mainly used in the metallurgical industry and high-end civilian heating.
2. Bituminous coal
Bituminous coal is one of the most common types of coal. It is a medium-rank coal with a higher degree of coalification than subbituminous coal but lower than anthracite.
It has a high calorific value. It is the main fuel for power plants and steel mills around the world. Bituminous coal has a certain cohesiveness and can be used for coking. The surface often presents a striped structure with alternating light and dark colors.
3. Sub bituminous coal
Sub bituminous coal is a coal with a coalification degree between bituminous coal and lignite. It is black and dull. Most of the coal mined in mines belongs to subbituminous coal.
It has a higher moisture content, lower carbon content than bituminous coal, lower to medium calorific value, stable combustion, and is mainly used for power generation. It is a mid-range fuel widely used in the power industry.
4. Lignite
Lignite, also known as brown coal, is usually shallowly buried and easily mined in open pits. It is the least coalified type of coal, with a low carbon content (25% to 35%), high water content (20% to 70%), and low calorific value.
Lignite is highly volatile. It tends to spontaneously combust, and has a short storage life, so it needs to be carefully monitored. This type of coal is mainly used in thermal power plants.
In addition, there are many types of coal and by-products derived from coal processing, such as coal gangue, coke (such as petroleum coke), lean coal, long flame coal, semi-coke, clean coal, gas coal, etc.
Why do you dry coal?
Raw coal often has high moisture, especially lignite with over 30%, which reduces the calorific value and combustion efficiency, and leads to incomplete combustion in the boiler and energy waste.
Moreover, coal beneficiation and coal washing will produce industrial waste residues such as coal slime and coal slurry. They also have high water content and low calorific value, hard to use directly. The coal drying process can turn them into combustible materials to improve resource utilization efficiency.
Secondly, wet coal is heavy and bulky, which not only increases transportation and storage costs, but also easily agglomerates and adheres to equipment, causing blockage and wear.
Dried coal has a high density and a small volume, which is not only convenient for transportation and stacking, but also reduces the failure rate, improves system stability, and prolongs equipment life.
Therefore, coal drying is very important! Dried coal is widely used in steel making plants, power plant boilers, and building materials plants.
How do you effectively dry coal?
The traditional coal dryer has problems such as high drying cost, high energy consumption, uneven drying, and complex operation.
The FTM Machinery single-drum coal drying line is tailored to different coal types (e.g., coke abrasiveness, lignite flammability), greatly improving the drying efficiency and safety, and increasing calorific value by over 30%.
Coal drying line
The entire coal drying line usually includes the following core links:
- 1 Feed trough: Wet coal enters the coal drying machine through this entrance.
- 2 Rotating drum: The cylindrical drum rotates slowly, so that the coal is fully exposed to the heat source in the drum, and is evenly heated and dried.
- 3 Burner and hot air furnace: provide the heat source for the drying of raw coal, generate hot air blown into the drum, and provide necessary heat. The heat source can be natural gas, coal gas, diesel or other fuels.
- 4 Lifting plate device: The lifting plate in the drum lifts and disperses the coal evenly when rotating, effectively increasing the heating area of the coal, thereby achieving efficient drying.
- 5 Exhaust and dust collection system: Exhaust the evaporated water during the drying process and collect coal dust, which is environmentally friendly and energy-saving.
- 6 Intelligent control system: Including sensors, monitors and control panels, which are used to automatically control parameters such as drying time, drying temperature, humidity, speed, etc. to ensure drying quality.
Single drum dryer is the core equipment for coal drying
The coal dryer often uses a single drum dryer, which is in the shape of a drum. It rotates around its axis, so it is also called the rotary drum dryer or the roller dryer machine.
It solves the maintenance issues of triple pass dryers and offers high efficiency, large capacity, full automation, and low drying costs. The single drum dryer can reduce coal moisture to below 13% and has been a market bestseller for years.
Five advantages of single drum dryer:
1. Strong drying capacity
The direct heating method can efficiently dry wet coal, coal slime, and coke material within 50 mm.
The capacity is 1.9–76 tons/hour, which is suitable for large-scale production. The drum speed and drying temperature can be adjusted to meet various coal types and moisture needs.
2. Good drying effect, no adhesion
The drying drum is welded with a lifting plate made of stainless steel, set at flexbile angles (90°/135°/150°) to improve drying uniformity and speed. Bolt connections are available for easy replacement.
During drying, the lifting plate crushes, cleans, and disperses wet coal, preventing coal slime from sticking to the drum and enhancing the drying efficiency.
3. Strong sealing performance
The closed feed cover and feed end, combined with the sealing sheet, adapt well to cylinder movement. It ensures effective sealing, reduces heat loss and air backflow, and improves thermal efficiency.
There are about 200 sealing sheets, all made of stainless steel with good elasticity and heat resistance.
4. Adaptable to multiple heat sources
The heat source burns to provide hot air to the dryer. There are three common heat sources:
Solid fuels (coal, biomass pellets, rice husks, wood), gas fuels (natural gas, biogas, coal gas, liquefied petroleum gas, waste heat flue gas), and liquid fuels (diesel, heavy oil, biomass oil)
The specific heat source used by the coal dryer is based on your production needs, fuel source, environmental assessment requirements, equipment investment cost, and production cost.
5. Stable operation and easy maintenance
The single drum dryer can achieve 24-hour continuous coal drying and maintenance every three to six months.
It only needs regular lubrication to reduce operating costs.
Conclusion
As environmental regulations tighten, efficient coal drying plays a vital role in coal processing. FTM Machinery's single drum dryers improve coal quality and cut production costs. We offer a customized, one-stop coal drying process. Contact us for equipment details and project plans to support efficient, safe, and low-carbon coal uses.
