7800 Horse-power Installation of Babcock & Wilcox Boilers, Equipped with Babcock & Wilcox Chain Grate Stokers at the Metropolitan West Side Elevated Ry. Co., Chicago, Ill.
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It becomes evident, therefore, that the question of stack height for oil-fired boilers is one which must be considered with the greatest of care. The designer, on the one hand, must guard against the evils of excessive draft with the view to plant economy, and, on the other, against the evils of lack of draft from the viewpoint of upkeep cost. Stacks for this work should be proportioned to give ample draft for the maximum overload that a plant will be called upon to carry, all conditions of overload carefully considered. At the same time, where this maximum overload is figured liberally enough to insure a draft suction within the setting under all conditions, care must be taken against the installation of a stack which would give more than this maximum draft.
Figures represent nominal rated horse power. Sizes as given good for 50 per cent overloads.
Based on centrally located stacks, short direct flues and ordinary operating efficiencies.
[Table 56] gives the sizes of stacks, and horse power which they will serve for oil fuel. [This table] is, in modified form, one calculated by Mr. C. R. Weymouth after an exhaustive study of data pertaining to the subject, and will ordinarily give satisfactory results.
Stacks for Blast Furnace Gas Work—For boilers burning blast furnace gas, as in the case of oil-fired boilers, stack sizes as suited for coal firing will have to be modified. The diameter of stacks for this work should be approximately the same as for coal-fired boilers. The volume of gases would be slightly greater than from a coal fire and would decrease the draft with a given stack, but such a decrease due to volume is about offset by an increase due to somewhat higher temperatures in the case of the blast furnace gases.
Records show that with this class of fuel 175 per cent of the rated capacity of a boiler can be developed with a draft at the boiler damper of from 0.75 inch to 1.0 inch, and it is well to limit the height of stacks to one which will give this draft as a maximum. A stack of proper diameter, 130 feet high above the ground, will produce such a draft and this height should ordinarily not be exceeded. Until recently the question of economy in boilers fired with blast furnace gas has not been considered, but, aside from the economical standpoint, excessive draft should be guarded against in order to lower the upkeep cost.