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COAL DRYING SYSTEMS |
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| Kilburn undertakes design and manufacture of Vibratory Fluid Bed Coal Dryer in collaboration with Carrier Vibrating Equipment Inc., USA. Kilburn Coal Drying System has several advantages compared to the conventional systems used for such applications. |
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| These dryers are suitable for handling different types of coals such as bituminous, sub bituminous, anthracite, lignite etc. with various particle size distribution. |
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BENEFITS OF DRYING COAL |
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There are several benefits of drying coal viz.,
- Coal can be sourced at a lower cost.
- Crushing, screening & conveying of coal becomes easier.
- Thermal efficiency of boiler increases.
- Power consumption decreases.
- Transportation cost of coal is saved if drying is done in mines.
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| The moisture level needs to be reduced to a level of 5 to 7% higher than the inlet moisture of the coal. The initial moisture varies with variety of coal from 25 to 35%. The drying system needs to be designed to suit specific requirements of a plant |
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TECHNOLOGIES USED |
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Several technologies have been developed for drying coal using varying types of drying systems. These are :
- 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.
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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
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THE PRINCIPLE OF WORKING
OF VFBD SYSTEM OF DRYING COAL |
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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. |
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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. |
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VIBRATING FLUID BED DRYER |
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HEAT SOURCE |
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| 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. |
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THE KILBURN COAL DRYING SYSTEM |
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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
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| 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. |
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TYPICAL FLOW SCHEMES |
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| The flow scheme of a Coal Drying System with exhaust gas recirculation is shown here ( Fig. CDS-HGG-RECIR-1) |
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| 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) |
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GENERAL SPECIFICATIONS OF A COAL DRYING SYSTEM |
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The specifications vary from case to case. The drying system is tailor made for specific applications. However broad specifications are as under: |
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| 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 |
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| VFBD FOR DRYING COAL |
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SPECIAL FEATURES & ADVANTAGES |
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Completely dust proof construction with explosion vents. |
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Minimum capital expenditure. |
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More efficient compared to rotary dryers. |
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Minimum fines generation compared to rotary dryers. |
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Uniform drying and product moisture. |
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Compact and sturdy design. |
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Easy to install, operate and maintain. |
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LIST OF CUSTOMERS |
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Job No. |
Party |
Type of requirement |
Product handled |
Capacity |
Year |
| CVD-011 |
Essar Construction (I) Limited |
Vibrating Fluid Bed Dryer |
Coal |
50 T/hr |
2008 |
| CVD-012 |
Essar Construction (I) Limited |
Vibrating Fluid Bed Dryer |
Coal |
50 T/hr |
2008 |
| CVD-013 |
Essar Construction (I) Limited |
Vibrating Fluid Bed Dryer |
Coal |
50 T/hr |
2008 |
| KSD-223 |
GHCL Limited |
Vibrating Fluid Bed Dryer |
Coke Breeze |
8.5 T/hr |
2009 |
| CVD-019-020 |
First Carbon Technologies Pvt. Ltd. |
Vibrating Fluid Bed Dryer |
Coal |
50 T/hr |
2010 |
| CVD-022 |
Yasin Briquettes Energy Pvt. Ltd. |
Vibrating Fluid Bed Dryer |
Coal |
10 T/hr |
2010 |
| CVD-023 |
JSW Steel |
Vibrating Fluid Bed Dryer |
Coke |
150 T/hr |
Under Execution |
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