Walke, Earl W.

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 The Knowledge Bank at The Ohio State University Ohio State Engineer   Title:  Chimneys and their Construction Creators:  Walke, Earl W. Issue Date:  Nov-1925 Publisher:  Ohio State University, College of Engineering Citation:  Ohio State Engineer, vol. 9, no. 1 (November, 1925), 7-8. URI:  http://hdl.handle.net/1811/33729  Appears in Collections: Ohio State Engineer: Volume 9, no. 1 (November, 1925)     THE OHIO STATE ENGINEERCHIMNEYS AND THEIR CONSTRUCTIONBy EARL W. WALKE, Chemical Engineering, '28HE subject of chimneys and chimney constructionis an extremely diversified one, requiring notonly a knowledge of the mechanical and mathe-matical features, but a knowledge of chemistry,thermodynamics, ceramics and subjects dealing not alonewith the flow of gases, but also the effects of differentgases under various conditions of temperature and moist-ure content.The steaming rate of a boiler depends on the rate atwhich coal can be burned. This in turn depends uponthe difference of pressure available to produce flow ofair through the fuel bed on the grate to the chimney.This difference in pressure is known as draft and is re-quired to overcome various obstaclees which retard theflow of air. There are two types of draft: natural draft,produced by chimneys, and mechanical draft, producedby fans.Draft as produced by a chimney is caused by the dif-ference in weight between a column of hot gases insidethe chimney and the weight of a column of gases ofequal height outside the chimney. Chimney draft varieswith climatic conditions and is less when the outsidetemperature is high. Other influencing factors are theheight of the chimney, its diameter and height abovesea level.A chimney is called upon to perform various dutiesin addition to producing draft for steam boilers. It isthis multiplicity of duties that presents the many chim-ney problems. Many chimneys are connected directlyto roasting kilns, furnaces used in the production ofchemicals, etc.The material used in chimneys is usually brick, steelor concrete, the former being used most extensively.Brick chimneys consist of an outer and an inner wallwith an air space between them. The outer wall is madeof hard, well burned brick and varies in thickness by aseries of steps from top to bottom, the minimum thick-ness at the top being usually the length of a single brick.The taper of the outer walls is about one quarter of aninch per foot. The inner wall or lining is made of firebrick, and the inner diameter is usually uniform withthe offsets on the outside. At the top of the chimneythe outer wall is drawn in over the opening between thetwo walls. A cast iron cap or grating is usually placedon the top as a protection against the action of weather-ing. The use of two walls eliminates the trouble thatwould be caused by the unequal expansion of a singlewall of such a thickness. The air chamber is an excel-lent insulation against loss of heat by radiation. Aclean-out door is provided near the base of the stack.The chimneys used at the Ohio State University powerhouses are typical examples of brick chimneys. Thestack at the new power house furnishes natural draftfor seven large steam boilers. It is 230 feet high andhas a base approximately 20 feet square. The stack atthe old plant has a height of 205 feet.A chimney to handle acid gases is generally made ofbrick and must be designed and built not only for ade-quate capacity and draft but also to resist the destruc-tive effect of the particular acid gas. A damp acidsmoke in contact with ordinary mortars of cement, limeand sand produces a swelling and puffing of the joints,the change taking place on the surface. The mortar be-comes soft and of the consistency of mud, and as timepasses the softening works entirely through the walls,causing the brick work to bulge and crack. If the brickis not highly impervious the exposed surfaces will alsosoften and flake off. It is therefore necessary to use ahighly vitrified brick and an acid-proof mortar for thechimney lining. An acid resisting cap of lead or monelmetal is generally used.Steel chimneys are either self supporting or guyed,and are usually composed of a series of steel cylinderswith single riveted lap joints. The steel plate variesfrom three-sixteenths to one-half of an inch in thick-ness, depending upon the size of the stack. The cylin-drical rings may be of two different diameters in thesame chimney, alternating the two, or all the rings maybe the same diameter but slightly conical in shape sothat the tapered end of one may fit into the next ring.The various rings are fastened together by a single rowof rivets. The bottom ring is flared to form a baseThe Tallest Chimney in the WorldA 57 0-foot stack of the Saganoseki Copper Co., Sagano-seki, Japan. Has withstood several violent earthquakes.78 THE OHIO STATE ENGINEERwhich is held to the foundation by anchor bolts. Thesteel structure above the boiler is often used to supportthe stack in order to reduce the ground space required.This type of chimney depends for its stability uponthe anchor bolts and the foundation. It is usually linedto prevent excessive radiation and to protect the steelfrom the corrosive action of gases. Beginning at thebottom a good portion of this lining is tire brick, butthe upper part is common brick.Steel chimneys are often guyed to insure stability bythree steel cables, the upper ends of which are fastenedto a band about two-thirds of the way to the chimneytop. The bottom ends are securely anchored on theground at such a position that the cable makes abouta 60° angle with the vertical.Concrete chimneys which have been used only in thelast few years can be either straight or tapered. Whentapered the thickness of the wall at the top is about fourinches and when straight, about six inches. The con-crete must be reinforced in order to resist the tensilestrains resulting from wind pressure. Concrete chim-neys are ordinarily lined to about one-third of theirheight since acid smoke rapidly disintegrates the cementcontent.For all types of stacks a suitable foundation must beprovided to prevent the chimney from tipping or settling.It is usually constructed of concrete and distributed overa sufficient area to prevent settling. Bases over a hun-dred feet square are not uncommon.The life of brick and concrete is longer than that ofsteel chimneys, the former types retaining their useful-ness for about fifty years and steel chimneys for fromfive to fifteen years, depending on the care taken to pre-vent erosion. Because of cracks due to faulty bricklaying, a brick stack may have considerable air leakage,which is seldom found in the other two types.The concrete chimney is comparatively light in weight,requires a smaller space than either the steel or brickchimneys, has great resisting power and can be rapidlyconstructed. If unlined it is apt to have an excessiveloss due to radiation, which will lower the draft pro-duced.The steel chimney can be constructed at a more rapidrate and has less weight than either brick or concrete.It requires frequent painting to prevent corrosion, whichis rapid in air that contains salt water.The cost of the brick chimney is the highest and thatof the steel stack is the lowest. The cost of concretechimneys varies from about $2,000 for a chimney havingan inside diameter of four feet and height of 105 feet,to about $18,000 for a stack with an inside diameter of16 feet and height of 258 feet. These figures give someidea of the variance of cost in chimney construction.In order to reduce the necessary height of chimneysand at the same time to maintain a draft which is suffi-cient regardless of weather conditions, fans and blowersare often used. This is known as mechanical draft, butsince its study covers a large field not within the limitsof this paper, it will not be discussed here.

Chimneys and their Construction

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Chimneys and their Construction

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