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Indiana University Studies 



on the proper thickness, judgment must be exercised. If the 

 draft is weak, a thin fire will be in order, but if strong, a thicker 

 fire should be carried. 



9. Regulate the draft by the bottom or ash pit doors and not 

 by the stack dampers, because, when the stack damper is used it 

 tends to produce a smoky chimnej^ since it reduces the draft, 

 while the closing of the ash pit door diminishes the capacity to 

 burn coal. If strict attention is given to firing according to the 

 demand for steam, there will be no occasion to have recourse 

 to the dampers except when there is a sudden interruption in the 

 amount of steam being used. 



10. A good general rule is to fire little and often, according 

 to steam demands, rather than heav}^ and seldom. The former 

 means economj^ in fuel and a clean chimney, while the latter 

 signifies extravagance in fuel and a smoky stack. 



The part of the heat of the fuel that can be utilized in the 

 boiler varies with the care given the firing, and engineers state 

 that the boiler that can utilize 80 per cent of the heat is exceptional 

 and 75 per cent represents very good practice. The only boiler 

 plants in the district that reach anywhere near this figure are the 

 larger plants in the better mills of the district. Many of the 

 plants in the older mills and quarries are probably not utilizing 

 over 50 per cent of the heat in the fuel consumed. The losses of 

 heat from a boiler furnace are summed up hy Gebhardt in Steam 

 Power Plant Engineering (p. 45), as follows: 



1 Loss in dry chimney gases. 



2. Loss due to incomplete combustion. 



3. Loss of fuel through the grate. 



4. Superheating the hygroscopic moistm-e in the air. 



5. Moisture in the fuel. 



6. Loss due to the presence of hydrogen in the fuel. 



7. Unburned fuel carried beyond the combustion chamber in the form 

 of soot or smoke. 



8. Radiation and minor losses. 



These losses refer only to boilers in continuous operation. In 

 most plants where the load is such that additional boiler equip- 

 ment must be held in reserve to handle peak loads the loss is 

 much greater. 



As a steam plant increases in size, the question of draft always 

 arises, and the relative value of mechanical draft and natural 

 draft has to be considered. There is no question but that with 

 a larger boiler equipment the steaming power of the plant to meet 

 varying loads is increased by mechanical draft. ^Mechanical 



