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   ABCO Boilers : Completely Water cooled Furnace designs  V.Ganapathy
Steam generators to 300,000 lb/h capacity 
Steam pressure up to 1500 psig 
Steam temperatures from saturation to 1000 F 
Oil and gas fired applications 
Custom designed boilers with low operating         costs and high efficiency 
Convective superheaters with longer life and higher reliability 

Pictures show ABCO Packaged steam generators with front,rear and side walls of completely water cooled membrane walled design.The advantages of this design /construction feature are discussed below.  
Advantages of ABCO Water cooled Furnaces 
One of the recent improvements in packaged boiler design is the water cooled furnace that offers several advantages over refractory lined furnaces. The furnace side walls,front and rear walls and floor are of membrane wall construction.This results in a leak proof enclosure,eliminating gas leakage and corrosion of casing as seen in boilers with refractory. 
Refractory maintenance concerns are eliminated. Plant engineers are familiar with the annual cost of refractory maintenance and the associated downtime.  
Startup rates can be faster without concern for refractory limited heat up rates and hence fuel cost per startup is also reduced.The entire furnace expands and contracts as a unit. This eliminates relative expansion problems that occur between water cooled walls and refractory lined casings. 
For a given volume,the ABCO design has lower heat release rates on area basis due to the larger furnace effective projected area; hence heat fluxes are lower. Depending on the furnace dimensions,the improvement can be 5 to 15 %.The furnace exit gas temperature is also lower.  
Cooling of the flame and reradiation from refractory impact local combustion temperatures and hence NOx formation.The contribution to NOx from the front refractory lined wall is signifcant .A cool environment at the flame front due to the water cooled front wall design,on the other hand, helps to lower the emissions. 
Refractory on the floor is another design feature which has been carried over from the last generation of boiler designs.There is no need for it.The effective furnace projected area is reduced,increasing the furnace exit gas temperature,thereby causing problems for the superheater if present,in addition to increasing the redradiation from the floor which increases the NOx.There are hundreds of boilers designed without floor refractory,which are working fine.The problems in oil fired furnaces due to higher furnace exit gas temperature can be more severe,such as possible slagging and corrosion of superheaters.
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