| OCR Text |
Show It is safe to choose 3000°F as the design temperature which is slightly higher than the required melting point of F e ^ . Many methods may be used to bring up the temperature of slag to 3000°F. Three methods have been considered. They are electrical resistance heating, additional gas burner heating and modified coal combustion. There are advantages and disadvantages to each method. After the discussion with the engineering staffs in Tampa Electric Co., a general conclusion has been reached that the modified coal combustion is the best method among them. The temperature of 3000°F can be easily reached with a minimum change. The following is the detail consideration of the modified coal combustion method. (A) Estimate the Additional Amount of Coal to be Burned on the Furnace Floor The easiest way to raise the slag temperature is to burn more coal particles on the furnace floor. However, how much additional coal is needed has to be estimated. The following conditions are assumed for estimation: Burning rate of coal is The ash content (deposited on the floor) in coal is The temperature of slag to raised is The specific heat of the slag is The heating value of coal is The heat absorbed by slag is 25% of the heating value of coal. It is found that the additional amount of coal to be burned on the furnace floor is 0.736 lbm/min, i.e. .736%. The additional coal particles can reach the floor with the following possible modifications: 1. Increase the downward momentum of coal particles by modifying the coal feeder as shown in Fig. 2 100 lbm/min 7.5% 1000°F 0.3 Btu/lbm-°F 12227 Btu/lbm Additional part Fig. 2 Modified Coal Feeder for Additional Downward Momentum Existing nozzle 2. Change the coal particles to a larger size, or add 0.736% of coal with a larger size to the present coal particles. |
