Coal Drying

Background
There are three major forms of fossil fuels: coal, oil and natural gas. All three were formed many hundreds of millions of years ago before the time of the dinosaurs – hence the name fossil fuels.
Throughout history, coal has been used as an energy resource, primarily burned for the production of electricity and heat.

Coal Drying Improves Performance
Coal is a hard, black or brown coloured rock-like substance. It is made up of carbon, hydrogen, oxygen, nitrogen and varying amounts of sulphur. Coal comes in four main types or ranks: lignite or brown coal, bituminous coal or black coal, anthracite and graphite. Each type of coal has a certain set of physical parameters which are mostly controlled by moisture, volatile content (in terms of aliphatic or aromatic hydrocarbons) and carbon content.
Low-rank, high-moisture coals constitute 50% of the coal reserves worldwide. Studies have shown that power plants which are fuelled by high-moisture coals use about 7% of the fuel heat input to evaporate and super-heat the moisture in the fuel. Furthermore, high-moisture, low-heating value coals result in higher fuel and flue gas flow rates, higher power requirements in milling operations and ID fans and increased mill and burner maintenance costs.
A reduction in coal moisture through thermal drying improves boiler and unit efficiency, plant operation, and economics while reducing CO2 and criteria emissions.
Studies worldwide show that coal drying can result in significant improvement in the following areas:
• Increase in heat value of the fuel
• Increase in combustion efficiency and nett power production
• Less load on coal transportation systems
• Decrease in mass flow of flue gas
• Savings in electrical consumption in ID fans
• Less corrosion in boiler
• Less maintenance costs in mills, pulverisers and boiler
• Better emission quality in flue gas
• Lower CO2 footprint

Thermal Dryers for Coal Drying
Type of drying technology for coal applications is mainly determined by the size of coal particles, location and purpose of drying process.
If coal is considered as a commodity, the unit price of coal is directly affected by its heat value per mass. Furthermore, decreasing moisture content decreases cost of shipping per heat value transported and this provided huge savings either on supplier or end user side. Therefore, coal miners investigate options in investing in a thermal drying system.
If a power plant operation plans an investment on a coal drying facility, then the combustion technology of the plant, technology of milling and pulverising, availability of waste heat for drying and the distance of coal mine to the plant are the main criteria in deciding such an investment.
The most economical way of drying coal within a power plant operation would be using any sort of waste heat available in the plant. In most of the cases, heat energy in exhaust gases would be used as heat source for drying. If there are no waste heat available in the plant, then the second most economical way would be using the coal itself as a heat source for drying. Some portion of the dried coal could be circulated back into a combustion unit to generate hot air and this hot air could be used for drying process.
Drying process could be utilized either for lump coal (particle size may vary from 0.5 mm to 70 mm) or powdered coal (<4 mm).
Fluid bed dryers are considered as the most efficient drying equipment for powdered coal. With the ability of utilizing waste heat, fluid bed dryers provide a fast, safe and efficient solution for coal drying needs.
Rotary dryers or belt dryers would be more applicable where the particle size are bigger and it is not possible to create a fluidised bed.

Use of A Belt Dryer for Coal Drying
Our client is a coal mining company who sells coal products in various particle size and calorific values. After investigating the available drying technologies, our client decided to invest in a lump coal drying plant in order to increase the heat value of coal and also cut down the cost of transportation to its clients.
Particle size distribution of coal to be dried was from 20 to 60 mm and the type of coal was lignite.
Our client did not have any available heat source on site for drying process and therefore, it was decided that the coal itself would be used as heat source.
As per our client’s request, we have designed and delivered a low temperature, long retention time belt drying plant and successfully commissioned the plant in 2014.

The plant comprises of a hot air generator, a drying tunnel, a drying belt, moist coal feeding conveyors, air blowers for process air and exhaust gas, recirculation air fans, exhaust gas cleaning units, the stack and complete instrumentation and PLC/MCC package.

Type of Coal : Lignite
Feed Capacity : 20 Tonnes/Hour
Particle Size : 20 – 60 mm
Inlet Water Content : 50% w/w
Outlet Water Content: 30% w/w
Heat Source : Hot Air Generated by Coal Combustion

Side view – Belt Drying Plant with Coal Fuelled Hot Air Generator – 20 t/h
Top view – Belt Drying Plant with Coal Fuelled Hot Air Generator – 20 t/h
3D Design – Belt Drying Plant with Coal Fuelled Hot Air Generator – 20 t/h
Belt Drying Plant with Coal Fuelled Hot Air Generator – 20 t/h

All dryer projects require technical support which we will be pleased to offer without charge.
So, if you would like to know more, simply follow the contact link below and we will get back to you straight away. We will be pleased to talk through your issues, and of course there is no obligation to buy.