OCR Text |
Show The potential consequences of the short freeboard are not clear at this time, but data forthcoming from the demonstration unit should verify whether this design is feasible. Economic calculations indicate that if the carbon combustion efficiency drops below 85%, the cost savings achieved by shop fabrication will have been eroded severely. If the 15-ft freeboard is indeed necessary, then it is unlikely that the AFB boiler could be made rail shippable even with the windbox detached. In contrast, with the cyclones detached, the PFB boiler module could be shipped on its side. The auxiliary equipment space requirements tend to overshadow that for the boiler modules even for the FBC units, but both AFB and PFB boiler assemblies are less "sprawling" than conventional systems as evidenced by Fig. 6. Much of the auxiliary flue gas and solids handling equipment will require field assembly even though the items are shop fabricated to a high degree. The field assembly costs could be reduced through innovative development of new cyclone configurations and solids feeding, distribution, and metering equipment. The costs associated with the two fluid bed systems were estimated. The capital cost for a 150,000 lb/h field-erected AFB and a shop-fabricated PFB are shown in Table 3. The primary difference in cost lies in two areas. First, the shop fabrication of the boiler module makes that PFB component about half the cost of the AFB. Secondly, the construction time and the construction facilities are estimated to be less for the PFB since it is packaged. The overall cost difference between the two systems is about 34%. It should be noted that these costs are somewhat conservative in nature in that they include a substantial coal handling system capable of unloading multiple car shipments. The actual size and type of coal unloading facility will depend in part on the location of the steam plant site relative to the coal supply. Plants located distant from coal mines will probably select large rail shipments while those that are close may choose truck delivery. The choice can make a substantial difference in cost as shown in Table 4 and would make the packageability look more attractive. The cost advantage of the PFB packaged system also should hold true when compared to a 21-15 |