Power Plant Engineering
Download 3.45 Mb. Pdf ko'rish
|
Power-Plant-Engineering
- Bu sahifa navigatsiya:
- 4.8 PULVERISED COAL FIRING
- Bin or Central System.
|
4.7.3 SHAFT MILL
Fig. 4.24 shows fuel pulverization with a shaft mill. The fuel from bunker is moved to feeder via automatic balance. Then from duct fuel goes to mill where it is crushed by beaters secured on the spindle of the mill rotor. Bunker Automatic balance Feeder Duct Shaft Mill Air duct Hole Fig. 4.24. Pulverization with a Shaft Mill. The pulverised fuel is dried up and then blown into shaft by hot air. Secondary air is delivered into the furnace through holes to burn the fuel completely. 4.8 PULVERISED COAL FIRING Pulverised coal firing is done by two system : (i) Unit System or Direct System. (ii) Bin or Central System. Unit System. In this system (Fig. 4.25) the raw coal from the coal bunker drops on to the feeder. Raw Coal Banker Feeder Hot Air Fan Pulverising Mill Burner Secondary Air Primary Air Coal Furnace Fig. 4.25. Unit or Direct System. 162 POWER PLANT ENGINEERING Hot air is passed through coal in the feeder to dry the coal. The coal is then transferred to the pulverising mill where it is pulverised. Primary air is supplied to the mill, by the fan. The mixture of pulverised coal and primary air then flows to burner where secondary air is added. The unit system is so called from the fact that each burner or a burner group and pulveriser constitute a unit. Advantages (i) The system is simple and cheaper than the central system. (ii) There is direct control of combustion from the pulverising mill. (iii) Coal transportation system is simple. Bin or Central System. It is shown in Fig. 4.26. Crushed coal from the raw coal bunker is fed by gravity to a dryer where hot air is passed through the coal to dry it. The dryer may use waste flue gases, preheated air or bleeder steam as drying agent. The dry coal is then transferred to the pulverising mill. The pulverised coal obtained is transferred to the pulverised coal bunker (bin). The transporting air is separated from the coal in the cyclone separator. The primary air is mixed with the coal at the feeder and the mixture is supplied to the burner. Raw Coal Burner Vent Fan Hot Air For Coal Drying Exhaust Fan Mill Dryer Primary Air Fan Conveyor Burner Secondary Air Feeder Pulverised Coal Burner Cyclone separator Return AIr Download 3.45 Mb. Do'stlaringiz bilan baham: 
|