The coal feeding process under the coal handling plant in where the coal is taken from the yard crushed and screened and then fed to the coal bunkers.
The coal that is present in the yard at a pre-defined ratio between Indian and Imported coal is moved to the reclaim hopper 261.10 using dozers. These reclaim hoppers have a rack and pinion gate (RPG), which allows a controlled flow of the coal. The coal is passed on to the electro magnetic vibrating feeder, which is of hanging type. This feeder is connected to the conveyor 261.05, which has a suspension magnet situated in the middle to the conveyor to eliminate iron particles. This is then passed on to the next conveyor 261.40, which also has asuspension magnet. The coal then moves on to a flap gate 261.62, before the installation of the impactors the crushers were used. The coal was crushed and screened and then sent to the boiler bunkers. But the new fluidized bed combustion type (FBC) boiler needs the coal particles not to be more than 8 mm in size. This is the reason why the crushers were changed to impactors, and hence a flap gate arrangement with a bypass directly to the conveyor 261. ISA.
From the conveyor 261. ISA the coal is taken to the two way chute and towards the two impactors. The crushed coal from the impactor in sent for screening to the filter, here coal particles of size till 8 mm in passed on to the conveyor C1. The uncrushed coal from the filter is carried by the conveyor C2 to the oversize coal conveyor C4. This C4 conveyor takes the uncrushed coal back to the impactor thus reducing wastage. The impacted and screened coal is carried on the conveyor 261.12 and passed on to the conveyor 261.13. Here a dust fan 261.44 in placed. The last conveyor in the feeding process is the flight conveyor 261.14, which is also called a plate conveyor. This one fills the boiler bunkers through the RPG, thus each bunker in filled with the same amount of coal.
The over-size coal conveyor C4, also known as the reject conveyor is used for the transfer of uncrushed coal back to the impactor. We observed that this conveyor could be used for feeding coal, there by making the process less complex and more effective.
By extending the C4 conveyor on its tail-end and there by reducing its height and then installing a new feeding system we can directly feed coal using a front loader. The new feeding system is a mechanically vibrating one, so that it doesn't obstruct the front loader while feeding coal. By installing this system, we can save a considerable amount of energy and cost.
DETAILS OF MODIFICATION
The modification on the C4 conveyor was carried out mainly for energy conservation and for reducing the chute maintenance. The conveyor system in the coal feeding process is made simpler and more effective, by-passing two conveyor systems on the coal feeding process.
The conveyor is extended to around 3 meters from the middle of the existing end column. This is for reducing the height of the feeding system that is being installed at the tail-end. The height is a major criterion when we use a front loader for loading coal. For better strength an ISMC 150 is used from the middle of the existing column, this is because it will be dealing with a much bigger load than the earlier one. Four new 400x400 columns are constructed; this would be the platform for the conveyor roller and its driving arrangements.
The side view of the conveyer modification shows the existing and proposed columns with the roller in position. The idlers are also clearly shown in here. Another detailed view shows the tail end side that gives us an idea of the specifications of the roller, the idlers, and the channel sections used in here. The different bolts are also specified. The plan of the modification gives us an idea of the channel sections. The column can be seen with its MS plate on top. Another important view is the front view, or elevation. Here we have specified the channel sections that are not visible on the side view and elevation. A sectional view of the idler shows us the way the impact idlers are supported on the conveyor belt and the way the return idlers are supported. The way impact idlersare kept in an inclined manner is also clearly shown.
The new system is installed at the right side of the conveyer C4. The system is mounted on 3 ISMC columns. On the top of the columns, a support plate is placed. A conical slide is placed on the support plate by means of four open coiled springs. The arrangement is such a way that the slide is free to vibrate on the springs in the longitudinal direction. The springs are strong enough to carry the entire load. The detailed dimensions of the springs are given in the design section. The vibrating motion to the slide is given from the back portion of the slide by means of two cams. These cams are mounted on a shaft which is driven by a motor. This shaft is mounted on two ball bearings. The power is transferred from the motor to the shaft is by means of belt - pulley arrangements. The forward motion is given by the cams and backward motion is given by means of two closed coiled springs. One end of the springs is fitted on a rigid plate which is placed at certain distance from the back portion of the slide and the other end is on the slide itself. The coal feeding rate is 8 ton per hour. The stroke given by the cam is 8 mm. The speed of rotation of the shaft can change according to the need by means of stepped pulleys. The slide is made up of cast iron with 10mm thickness and also has a mild steel liner with thickness 6mm. The liner is fitted on the slide by using screws. The advantage of liner is that, wearing is takes place on this liner and thus the slide is safe from the damage. We can easily change the liner with lower cost. The area of cross section of the slide is continuously decreasing when move towards the front. The slide is placed at an angle 12o from the horizontal level to the downward direction for the smooth flow of the coal through the slide. The detailed design of shaft, cams, springs, motor etc. are given in the design section. The entire arrangements are covered for avoiding the damage due to the dusts during the loading. The coal is loaded from the back portion of the slide by means of a front loader. The slide is continuously vibrating along the longitudinal direction at a constant speed. Due to this vibration the coal is directed to the conveyer. By installing this system we can save the energy required for the working of two extra conveyers.
RESULTS
In our project, we designed a new coal feeding system. Our views and the design procedures are shown in following pages. The working model of the advanced coal feeder mechanism was also developed to get a better perspective of the same.
ADVANTAGES OF THE NEW COAL FEEDER MECHANISM.
Ø If there is any break down in any of the conveyors 261.05, 261.40 we can by pass all of them by feeding coal on the new installed coal feeding mechanism.
Ø No complicated mechanisms.
Ø Coal is directly loaded the feeder by using a front loader.
Ø Only one motor is required for the system instead of using two large motors in the case of existing feeder.
Ø Can have a considerable saving of energy and man power.
Ø There is a cost benefit on this new modification, as we need to run only the C4 conveyor instead of the other 2 conveyors.
Ø The chute maintenance on the conveyor 261.40 is considerably high, so this can be brought down.
Ø Parts are of less cost and can be changed easily.
