INCREASED CAPACITY OF COAL BURNING PLANTS WHEN USING OIL FUEL No exact formulae for the height of stacks for oil burning furnaces are available, but general experience has proven that for a given installation about 6o% of the height of a stack for a coal burning furnace will give satisfactory results when burning oil.
The reason for this is obvious, as the air supporting combustion in a coal burning furnace is retarded by the bed of coals and clinkers, necessitating a greater draft than is necessary for oil. Hence the stack capacity for a coal burning installation will be materially increased if oil fuel be used.
This increased capacity applies not alone to the stack, but to the boilers as well. The absence of soot on the boiler shell and tubes, — decreased losses in the flue gas, as well as a material reduction in stand-by losses all tend to increase the capacity of the plant as a whole when burning oil.
The sum total of these savings often amounts to 20% to 30%, and should be given careful consideration by those wishing to increase their plant capacity without providing additional boilers, stack or space.
Effect of an Excessive Draft when Using Oil Fuel.
In general a draft pressure of .15" to 2" of water gives the best results when using oil fuel. When greater differences of pressure exist between the fur nace and boiler room it is difficult to so design the furnace as to prevent some of the air supporting combustion from passing by the fire, thus doing no good as far as the combustion is concerned, but tend ing to cool the gases, lower the CO2, and increase the per cent. of excess air, all of which will lower the efficiency of the boiler and furnace.