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Show The height of the boiler from the distributor plate to the top of the steam drum is about 21 ft. Again, a 15-ft freeboard has been incorporated beyond the anticipated height of the expanded bed. An additional 7.5-ft wide convection section is located along the full length of the back wall and extends the overall boiler width to about 23 ft. The boiler is waterwalled with supplementary evaporator tubes located in-bed along with the superheater. The fluidizing air is provided by a forced draft fan with a capac-city of 270,000 lbm/h. The air is blown into a gas-to-air tubular preheater. The air enters at about 85°F and exits at about 600°F. The gas enters at roughly 765°F and exits at about 300CF. From the base of the preheater, the heated airflow will split into two main side ducts that run the length of the bed at plenum level. From each side duct there are four equally sized and spaced feeder ducts into the plenum (total of eight ducts). They are sized at 1.5 ft by 2 ft to accommodate a 70-ft/sec inlet air velocity when undampered. The plenum is sectioned by dampers underneath the cell separating wall. In a similar arrangement to the PFB boiler system, coal and limestone are delivered to and stored in separate large storage bins. The bins are roughly the same size as their PFB system counterparts, and coal preparation is identical. The two feed streams are mixed and elevated to a five-minute storage bin. The feed is split into 32 pneumatic conveying lines. These lines vary in length from 6 to 17 ft and turn sharply upward underneath the bed, penetrating the plenum and distributor plate. The flue gases exit the boiler through four vents at the end of the convection passes. There is an ash dump located below the tube bundles in this section to collect the flyash that drops from the gas stream. Through the four vents the gas is ducted through four single stage cyclones to the air heater. Without pressurization the gas stream volumetric flow rate is considerably larger than the PFB, thus the cyclones are large and serve only as primary particulate collectors. Each one handles about 35,000 ACFM (at T ^_ 800°F) and is sized at about 7.3 ft in body diameter, 14.7 ft in body height, and about 26 ft in overall height. The air heater also has an ash dump to collect knockout ash. The gas leaves the heater at the top and is pulled through the 21-11 |
