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Show used to two ends: increasing the steaming rate for a given size bed, or decreasing the size of the bed for a given steaming rate. The latter is desirable for size reduction (smaller cross-sectional area) to make the system packageable. The PFB boiler is designed for an 8-ft static bed depth and 8 ft/sec superficial velocity. The bed temperature will be 1600°F, and the desired freeboard pressure is 3.5 atm, about the limit for commercial industrial turbochargers. The boiler shell is an upright cylinder with flanged "deep dish" drumheads (Fig. 3). The cylindrical body portion is 25-ft high and 12-ft outer diameter. The tall height is due to the deep bed coupled with a freeboard of approximately 15 ft. The diameter of the bed is limited because of rail shipping size constraints. Fluidizing/combustion air is introduced through a distributor tuyere plate sandwiched between the cylindrical section and the bottom drumhead. The bottom drumhead cavity acts as a plenum and is fed by four ducts from the two turbochargers. The turbochargers are each capable of handling 23,000 to 30,000 CFM of air and producing a maximum boost of about 3.5 atm. It has been estimated that no air preheat will be necessary since the compressor work should raise the air temperature from 80°F to 410°F. It should be noted that, unlike its counterpart that is being developed for utility applications, the industrial PFBC concept produces no net electrical power. Delivered coal and dolomite are stored in separate bins sized to hold eight hours of material. The coal bin discharges into a ring crusher to produce 1/4-in. top size feed. The limestone bin receives its material already sized and screened from the supplier. The two streams (18,463 lb/h of coal, 6,154 lb/h of dolomite) are metered, mixed, and fed to a storage hopper with a five-minute residence time to minimize segregation. Material is metered from this vessel through /Jo' a rotary feeder into a Fuller-Kinyon (F-K) pump. This pump is sized to handle approximately 400 ft3/h of crushed or sized material. With some pneumatic assistance, the discharge from the F-K pump spills into a pressurized riffle box assembly. The feed system splits the mixture into eight equivalent streams that are transported pneumatically into the bed. The pressure vessel contains approximately 375 boiler tubes that run the length of the 21-8 |
