GENERAL WORKING AND DESCRIPTION OF COAL HANDLING PLANT
In thermal power station, Coal is a principal fuel and hence a careful thought is given to the design and layout of the coal handling plant. As the consumption of coal is very large, the design and layout of a coal handling plant should be simple but robust with a view to reduce the maintenance and running cost to the lowest possible figure consistent to reliability. Mode of Coal Transportation : Coal is brought to the power station by three modes of transportation : 1. Roadways : Coal is carried in trucks and a truck can carry about 8-10 tons of coal. But due to low capacity, low unloading rate and time consuming, this mode is not in much use for large thermal power stations. 2. Railways : coal is brought by railway wagons. One rack consists of 58 wagons. Each wagon contains 58 MT of coal. Locos bring the wagons from the marshalling yard and place them on wagon tippler. These wagons are then unloaded with the help of wagon tippler. If these wagons are not unloaded in stipulated time period (generally 7 hrs.), demurrage charges are lavied by railway department. There are two types of wagon tipplers. a) Side Wagon Tippler : Wagon is unloaded into a hopper which at the side of the railway track. The max. angle of tilt is generally set between 140 to 150°. The rate of unloading is 13 wagons per hour. The time required for one cycle of operation of this wagon tippler is as below. 1. Weighing Wagon + coal before tippling 2. Tippling of Wagon to hopper 3. Pause 4. Tippling of Wagon back to home position 5. Weighing Wagon after tippling 15 sec. 90 sec. 5 sec. 90 see. 15 sec.
The weighing machines are integral with tippler mechanism and are fitted with a ticket printing recorder and totaliser. b) Ring type (Rotary) Wagon Tippler : In rotary tipplers the wagon is fixed between the two large rings which are fastened to form a cage like structure. The cage is rotated and discharged coal falls into the hopper right below the rail track. Angle of tippling is 140 - 160°. The rate of unloading is 25 wagons per hour. The time required for one cycle of operation of this wagon tippler is 60 sec. only. 84
For easy and speedy movement of wagons, mechanized bettle chargers are provided before and after wagon tippler i.e. inhaul and outhaul bettle chargers. These wagon tipplers are provided with photocell protection to avoid the entry of other wagons when tippling cycle is in progress. Track hopper system : This system is provided at Chandrapur thermal power station. BOBR (bottom opening wagons) wagons are unloaded in track hoppers. The holding capacity of track hoppers is 4500 MT. MGR Railway system : This system is provided where coal mines are located near the power station. Railway wagons are used to transport the coal from coal mines to power station and unloaded wagons are returned to coal mines for refeeding. So this forms a ring type system. Wagons alongwith railway tracks being the MSEB property, this becomes the most economical way of coal transportation having a very low maintenance time and cost as compared to the ropeway system. 3. Ropeways : This mode of coal transportation is used where coal mines are located near the power stations. Coal is brought by hanging buckets/trolleys travelling on track ropes, which are pulled by a haulage rope with a driving mechanism. The payload of each bucket varies from 1 to 3 tons. Automatic loading and unloading mechanisms are provided at loading and unloading stations. Rate of unloading varies from 75 to 275 MT/Hr depending on the type of ropeways used. This type of coal transportation is very economical compared to road or rail transportation and gives assured supply of coal, being the MSEB property. The only disadvantage of this system is long time for maintenance works. There are mainly two types of ropeway systems used in power stations. 1. Mono Cable Ropeway : This ropeway operates on one single endless haulage rope. This...
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