Show THE SMOKE NUISANCE IN SALT LAKE by 0 W OTT at the he pres present elit time there is a noticeable awakening of the public conscience to the necessity for concerted action on questions affecting the general welfare of the people the present a agitation i tation for the abatement of the smoke ni in salt lake city anny m axy be considered in part due to this general movement and in part due to the appreciable increase of the nuisance during daring recent years there are two principal causes for the existence of the cloud of smoke which hangs over the city during the winter months one set of conditions is responsible for the cloud effect and another set is responsible for the addition of the blank soot under certain atmospheric conditions a large amount of smoke can be ejected without causing a nuisance while under other conditions a small amount of soot and smoke will produce very objectionable results this article artcle deals exclusively with the reasons for excessive coal smoke production and the possibility of reducing it to a minimum the combustion of fuel consists of the oxidation of the various combustible elements in in the fuel or in other words the chemical combination of these elements with the oxygen of the air if this oxidation is complete the products of combustion are principally carbon dioxide and water vapor with a small percentage of sulphur dioxide and contain no opaque substances in order to get complete combustion it is necessary that the oxygen of the air have free access to every particle of fuel and that the temperature pera ture be maintained high enough to insure chemical combination to obtain these conditions is the fundamental problem of combustion and the secondary problem is to avoid passing an unnecessary amount of air through the fuel because such surplus air has to be heated to the temperature of the escaping products of combustion and the heat thus used is entirely wasted the coal that is used in salt lake city is a high class bituminous coal and contains from forty per cent to fifty per cent fixed carbon about forty per cent to afif fifty ty per cent hydrocarbon hydro carbon four per cent to eight per cent moisture four per cent to ten per cent of ash and a trace of sulphur the hydrocarbons hydro carbons of the coal are volatile compounds which distill at a low temperature producing principally a gas commonly called methane or marsh gas which is composed of one part of carbon and four parts of hydrogen As the principle combus combustible tibe materials in coal are carbon either in corn com wils wilson on ott consulting engineers salt lake city bained or uncombined form and hydrogen the products of combustion will consist ot ol oxygen compounds or these thee the e elements namely carbon dioxide carbon monoxide and water vapor together with a trace or of sulphur dioxide and other impurities with these products of combustion will be associated a large volume of that unavoidable evil inert nitrogen which after being heated up in the furnace is expelled through the stack the process of combustion may be described briefly as follows the first heat volatilizes a portion of the hydrocarbons hydro carbons at a comparatively low temperature if the temperature of the fire is sufficiently high the hydrocarbons hydro carbons are completely gas gasified fled and ignited and assist in bringing the fixed carbon portion of the coal to a state of incandescence the burning of the hydro car bon gases simply means their combination with oxygen to form new compounds if the temperature of the fire is not sufficient the hydrocarbons hydro carbons are neither ignited nor completely gasi gasified fled and pass out of the stack in the form of poisonous gasses mixed with solid particles of coal tar and free carbon producing what is known as smoke gradually the fire attains sufficient tem grature to distill off all the viol atile portion of the coal and we then obtain a bed of incandescent fuel which is composed principally of the fixed carbon content of the coal this incandescent carbon is now in a state to combine with the oxygen of the air and form an oxygen compound of carbon if the combustion is complete the resultant compound is composed of two atoms of oxygen and one of carbon and is known as carbon dioxide if the incandescent coal has not been provided with sufficient air the product of combustion will consist of one atom of oxygen and one atom of carbon which is known as carbon ide this gas in turn will burn to carbon dioxide if at any further point in its passage it meets with sufficient air at the same time however this additional air must come into contact with the carbon ide at sufficiently high temperature to bring about IgIni J ignition tion otherwise the a additional air will simply dilute the monoxide and the air and gas will pass out of the stack together ether unconsumed even after part of the fuel has been completely oxidized to car bon dioxide the gas as thus formed may while passing through the remainder of the fuel bed take up an additional atom of carbon thus being reduced to a monoxide form which ch in turn vill require additional ali ail for its combustion the ca complete combustion of one pound of coal requires theoretically about three pounds of oxygen and this amount of oxygen is contained in thirteen pounds of air by reason of the large proportion of inert nitrogen in air eighty per cent by volume it is impossible to obtain intimate contact between the oxygen and the fuel and therefore an excess of air has to be furnished the exact amount of excess air required over and above the theoretical 13 pounds will vary greatly according to the condition of the fire boiler setting and various other factors in ordinary hand firing with natural draft approximately per cent excess of air will be required with some stoker settings and forced draft the excess of air may be reduced i considerably below this amount any excess of air above that which is theoretically required for combustion simply causes a waste of heat the amount of which depends on the quantity in excess and the temperature at which it is finally discharged from the chimney chhn ney it has been shown that in order to obtain complete combustion a large amount of air is required and therefore means must be devised for forcing the necessary air through the fire and then removing the products of combustion this is accomplished by either natural draft as exemplified by the ordinary chimney or by artificial draft as referred to later draft braf t might be defined as the ability of a chimney under given temperature conditions to set in motion a column of air this air being drawn in at the bottom and discharged at the top the move movement meat of air up through a chimney is due entirely to the lower density sita y of the air inside the chimney compared with the density of the surrounding atmosphere the reduced density of the air in the stack is the direct result of its temperature and therefore in starting a furnace there is no appreciable draft until there is some heat and as the fire increases the draft increases until normal conditions are attained the actual value of the draft is equal to the difference between the weight of heated gases in the stack and the weight of a similar ilar volume of air from outside and is therefore dependent on the height of the stack as well as the difference in temperature of the t gases ases and the external air in a chimney feet high with an outside temperature of 30 de deg F and a temperature pera ture inside the stack at the bottom of leg deg IF a draft will be produced equiha lent to approximately 12 ib of water pressure or ii I 1 ri other words a pressure of 14 oz per sq inch tending to force the gases up and out of tiie th the e L gases ga s e s irk in passing through the furnace flues and stack encounter a certain frictional resistance which depends on the character chai acter of the fuel bed and the prea area and len length ath of the flues and smoke stack as well as on th the velocity of the gases it will bo be seen therefore that the draft required dep depends ands on these conditions 1 the proportion of the be total draft which is used up in overcoming friction in the ahe smoke stack should be small pro provided aided vided that the smoke stack is properly designed it i is s therefore seen that not only must the height of the chimney be sufficient to produce the velocity required but the area of the chimney must be sufficient to accommodate the volume of I 1 bases ases given off by the combustion of the fuel in the furnace an example of improper chimney design which recently came to the notice of the writer and in which this matter of sufficient area to handle the volume of gas was overlooked is as follows A certain heating plant having a chimney approximately 32 inches square inside and 60 f feet h high I 1 gh originally nalty served one boiler of 80 HP two additional boilers of HP each were then installed without making any change in the chimney the boilers were vere equipped with automatic stok ers and forced draft fans falls and it was expected that this would remedy any trouble due to insufficient area of the chimney the actual result was that the friction of the gases in the chimney was excessive and formed a large proportion of the total pressure required to force the gases from the boiler room to the top of the stack this meant that the pressure in the fire box was considerably above atmospheric pressure and there was waa a tendency for the flames and hot gases to heat up the boiler front instead of being taken directly through the flues and tubes to the stack in addition to this the fan being driven at a high speed to give the necessary draft consumed an excessive amount of power the insufficient size of the chimney in this case was not necessarily productive of smoke because the fan was of sufficient size to supply the necessary air for ordinary loads however at certain times the load would increase so that the fan was hi incapable capable of furnishing the air required for the proper consumption of the additional amount of coal and there was more or less smoke the ability of a chimney to create a movement of air depends upon the heating of the air in the chimney whereas the economy of the boiler plant depends largely on abstracting all the heat from the flue gases before they are turned into the stack under certain condi conditions tons the temperature of the flue gases which will give the most economical operation is insufficient for producing the proper amount of draft except by the use of an ex excessive hi hii high I sil si l thereto TOM 0 in such cases artifice daf 11 ift has been made use of as a means of supplying the air required for combustion artificial draft as it is called may be produced by various methods in the giocomo locomotive the action of a jet of steam as it rushes up the stack produces considerable suction or vacuum which in turn pulls air up through the grates and fire and out of the flues comparable to the locomotive is 18 the ahe vacuum fan or induced draft system where the furnace and a fan is placed between 1 the chimney and the products 11 ets of combustion withdrawn from the furnace by the fan and with this method forced up the chimney of producing draft the effect of the chimney itself in producing a movement of the conditions in the gases has no bearing on firebox but simply enables the plant to operate with a smaller fan or conversely the fan enables the plant to operate with a smaller chimney where a fan blowing engine air compressor or other blast apparatus is used to force air through the fire the chimney however is a very necessary adjunct in removing the gases or products of combustion and in preventing the maintenance of any pressure above the fire as has been noted previously where it is impossible to provide stacks which have draft creating value and it is desired to use a pressure fan the closed fire room system is sometimes used in this system the entire boiler room is under air pressure the only outlet being through the furnace and out of the stack so as to insure the required amount of air passing through the fire enough has been said relative to the value of draft and the necessity for bblain obtaining the proper amount of air for combustion anid and we now come to the question of feeding the coal on to the grate in such a way that the temperature of the fire is maintained if a large amount of fuel be added at one time to a fire which is in good condition the immediate effect is to increase the resistance si to the air passing through the fire and thus cut down the supply of air and also to lower the temperature of the fire if this same coal instead of being 0 fed fn an one large amount were fed in several small amounts at more frequent intervals there would be a much better chance of maintaining the proper air supply and fire temperature for perfect combustion in fact proper feeding of a fire with fresh coal consists solely in applying it in sufficiently small quantities and at sufficiently frequent intervals to avoid too much interference with the temperature and draft conditions this can be accomplished entirely satisfactorily by hand firing with the constant attention of the fireman but such attention is very difficult to secure and hence the stoker has come into vogue the automatic stoker in a properly designed boiler setting furnishes the most satisfactory method of obtain obtaining ng proper combustion with the absence of smoke stokers smokers can be divided broadly into two classes the underfeed and the overfeed types in the underfeed stoker the coal is forced up through the fire and consequently consequent lyp the gas is is induced to distill off before the coal reaches the surface of the fire and thus passes through the upper layers of incan dese cent luel fuel and thereby attains a temperature pera ture well above the i ignition point this type of stoker seems to be particularly well adapted to the bituminous coal used in this vicinity smoke however can easily be pro deuced when it is attempted to force the fire unless the air supplied by the fan fail is ilo r creased in proportion to the increase in coal smoke will vill result simply from the inability of the fan to force sufficient air through the fire to maintain proper combustion this was the case in one of the heating plants I 1 in the downtown district where the demand for steam was ext extremely remey fluctuating it was found necessary in this instance to increase considerably the ratio of the increment of 0 fan speed over that of stoker feed speed in a heating plant with stokers smokers sto kers where th the load is practically uniform it should be possible to burn the coal without any smoke whatever however as some of the heating plants shut down about 1100 at night and start up early in the morning the danger comes in of building up the fire too rapidly with fresh coal with the result that considerable smoke is often produced as is demonstrated daily by some 0 of f the down dow ni to town wn plants in the overfeed type of stokers smokers the fresh coal is fed to the tops of the fire or is gradually moved forward into the area of combustion it would take too much time to describe in detail the various types of stok ers in this class and it must suffice to mention the two principal ones in the chain grate stoker the fresh coal is fed through a hopper at the front of the boiler on to a traveling grate composed of chainlike chain like links which is suspended on sprocket wheels at the front and back ends of the fire box in this way the fresh coal is gradually carr carried le d 1 nto into the furnace where it is ignited by the burning coal immediately ahead of it and the unconsumed ashes are dropped of off into a suitable hopper as the grate surface passes over the rear sprocket wheels 1 in the step down or rocking grate stoker the grates are set |