Coal Dryer

Coal-Drying-System

KILBURN manufactures thermal drying system for various types and sizes of coal. These include:

  1. Rotary Dryer
  2. Swirl Flash Dryer
  3. Fluid Bed Dryer with inbuilt Heat Exchangers.
  4. Static Fluid Bed Dryer
  5. Vibrating Fluid Bed Dryer
  6. Paddle Dryer

These dryers are suitable for handling different types of coals such as bituminous, sub-bituminous, anthracite, lignite etc. with various particle size distribution.



“KILBURN, in more than 39 YEARS, has DESIGNED, MANUFACTURED, SUPPLIED & INSTALLED more than 20 CUSTOMIZED COAL DRYER SYSTEMS  in VARIOUS INDUSTRIES “

WORKING OF COAL DRYER

The hot gases required for drying are generated in the hot gas generator by firing fuel such as oil, natural gas, coal or any waste gas available in the plant. The hot gas is introduced in the Fluid Bed Dryer at the bottom of vibrating bed through a perforated plate. The coal is conveyed from feed end to discharge end by vibrations and comes in contact with hot gas resulting in drying the coal. The combined action of vibrations and fluidization ensures uniform drying and product moisture.

The exhaust gas from the dryer is passed through a bag filter for removing the fines carried over before releasing it to the atmosphere. It is also possible to re-circulate part of the flue gas from bag filter outlet to dryer. This minimizes chances of explosion by reducing oxygen content in flue gas and also provides heat recovery.

ADVANTAGES
AND SPECIAL FEATURES

• Completely dust proof construction with explosion vents
• Uniform drying and product moisture
• Compact and sturdy design
• Minimum fines generation compared to rotary dryers
• More efficient compared to rotary dryers
• Minimum capital expenditure
• Easy to install
• Easy to operate and maintain

THE KILBURN
COAL DRYING SYSTEM

KILBURN Coal Drying System comprises of following sub-systems :
• Heat Source (Hot Gas Generator).
• Coal Feeding System.
• Vibrating Fluid Bed Dryer (VFBD)
• Bag Filter
• Screw Conveyor with rotary valve
• Recirculation Fan
• Instrumentation & Control System
Details & layouts of a Coal Drying System vary with the application (viz. steel, coal or power plant industry) and the heat source (viz. coal, flue gas, etc.). Two typical flow schemes are given below.

SPECIAL DESIGNS

Coal Drying Systems

The flow scheme of a Coal Drying System with exhaust gas recirculation is shown here (Fig. CDS-HGG-RECIR-1)

Coal Drying System for Steel Plant

The following flow scheme ( CDS-HGG-2-SP) illustrates a typical coal drying system for a steel plant. It is a complete system with hot gas generator using blast furnace / waste gas but without re-circulation (which can be included)

TYPES OF
DRYING SYSTEMS

Vibrating Fluid Bed Dryer for Coal

Rotary Dryer – A rotary dryer can be used, however, the generation of fines is high. These are vey low RPM dryers and hence the drying is inconsistent i.e. the dried coal does not have uniform moisture.
Tornesh or Flash Dryer – Maximum particle size limited to 6 mm. Though dryers are cheap, the crushing of coal to lower sizes cannot be avoided.
Static Fluid Bed Dryer – Steam or hot water is used as convective heat source in the thermally imbedded tubes. Though the design is thermally efficient, the dryer is suitable for particle sizes of < 6 mm and hence the problem of crushing of wet coal cannot be avoided.
Vibrating Fluid Bed Dryer (VFBD) – VFBD coal drying system is the best possible design. This can handle upto 60 mm of particle size with max. of 5% over size upto 80 mm. This technology works on the principle of vibrations. Coal is fed on to a vibrating fluidized bed having a height of 100 to 500 mm. It gets dried while travelling from one end to the other.
Thus, VFBD Technology for drying coal is far superior to other systems in respect of :
• Wide particle size variations (no need to crush wet coal)
• Uniform Drying of coal
• High throughputs
• No generation of fines
• High thermal efficiency
Paddle Dryer– Heat transfer from heating medium to the material is by conduction. Efficient drying of powdery/crystalline/granular coal particle is achieved by bringing them in direct contact with revolving cuniform hollow paddles without using gas as heating medium. The trough is uniformly heated by passing heating medium through the jacket this ensures that the entire coal in the dryer is in full contact with the total heat transfer area during its passage through the dryer.

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HEAT SOURCE

There are several advantages of drying coal but the efficiency of system largely depends on economics & availability of drying medium. Space is another constraint. Following heat sources are normally recommended :
Boiler Flue Gas – Boiler flue gas at 140 Deg.C can be used as a heat source in direct contact with coal and the exit gas kept at 70 Deg.C. This gas will be carried through ducting to a bag filter and to exhaust through a ID fan. Since coal has sulphur, the flue gas will have SO2 of around 0.02% by volume and hence there is possibility of acid corrosion.

Proper preventive measures are taken in selection of materials of construction of the equipment & its components against acidic corrosion..
Independent Hot Gas Generator – In case, layout is a constraint or sulphur percentage is very high, a independent hot gas generator fired by pulverized coal can be used. Flue gas temperature upto 400 Deg.C is generated for drying of coal. The exhaust temperature will be limited to 140 Deg.C and hence there is no necessity of prevention of acid due point corrosion.

As flue gas is not available in mines, an independent hot gas generator is used as a heat source.

TECHNICAL SPECIFICATION

The specifications vary from case to case. The drying system is tailor made for specific applications. However broad specifications are as under (Higher Capacity on Request):

Capacity Upto 150 Tons/hr
Inlet Moisture Upto 40%
Outlet Moisture 4 to 5 %
Particle Size 0.5mm to 75mm
Drying Temprature 300 to 400ºC