Part 25 (1/2)

The blast required will increase as the depth of the fuel bed increases, and the slight suction should be ulation

The use of blast with the finer sizes causes rapid fouling of the heating surfaces of the boiler, the dust often a to over 10 per cent of the total fuel fired Economical disposal of dust and ashes is of the ut fuel of this nature Provision should beof the boiler to accommodate and dispose of this dust Whenever conditions per them out ater

Bituminous Coals--There is no classification of bituood in all localities The A grading:

_Eastern Bituminous Coals_--

(A) Run of mine coal; the unscreened coal taken from the mine

(B) Lus 1 inches wide

(C) Nut coal; that which passes through a bar-screen with 1-inch openings and over one with -inch openings

(D) Slack coal; that which passes through a bar-screen with -inch openings

_Western Bituminous Coals_--

(E) Run of mine coal; the unscreened coal taken from the mine

(F) Lump coal; divided into 6-inch, 3-inch and 1-inch lus over which the respective grades pass; also 6 3-inch luh a circular opening having the diaure and over that of the smaller diameter

(G) Nut coal; divided into 3-inch stea 3 inches diah a 1-inch dia; -inch nut, which passes through a -inch dia

(H) Screenings; that which passes through a 1-inch dia

As the variation in character of bitureater than in the anthracites, any rules set down for their handlingbituminous coals with economy and with little or no smoke increases as the content of fixed carbon in the coal decreases It is their volatile content which causes the difficulties and it is essential that the furnaces be designed to properly handle this portion of the coal The fixed carbon will take care of itself, provided the volatile matter is properly burned

Mr Kent, in his ”Steam Boiler Economy”, described the action of bitu that the fine fresh coal does is to choke the air spaces existing through the bed of coke, thus shutting off the air supply which is needed to burn the gases produced fro is a very rapid evaporation ofprocess, which robs the furnace of heat Next is the foras by the che deco the carbon of the coal to carbonic oxide, and the hydrogen being liberated This reaction takes place when steahly heated carbon This also is a chilling process, absorbing heat froenerated would give back all the heat absorbed in their forh air in the furnace to burn theh the fire door at this ti cohly heated After all the moisture has been driven off froins, and a considerable portion of the to the deficiency of hot air, and to their being chilled by the relatively cool heating surfaces of the boiler During all this tiether with unburned hydrogen, hydrocarbons, and carbonic oxide, all fuel gases, while at the sa surface, di heat to the water”

To burn these gases distilled froht into contact with air sufficiently heated to cause thenite, that sufficient space be allowed for their mixture with the air, and that sufficient time be allowed for their co surfaces, since these surfaces are coases below their ignition point The air drawn through the fire by the draft suction is heated in its passage and heat is added by radiation from the hot brick surfaces of the furnace, the air and volatile gasesplace Thus in most instances is the first requirement fulfilled The eleases with the air, and of time in which combustion is to take place, should be taken care of by sufficiently large co to their high volatile content, require that the air be heated to a higher temperature than it is possible for it to attain sih the fire and by absorption from the side walls of the furnace Such coals can be burned with the best results under fire brick arches Such arches increase the temperature of the furnace and in this way nition and complete combustion of the fuels in question These fuels too, sometimes require additional coive this in addition to the required arches

As stated, the difficulty of burning bituminous coals successfully will increase with the increase in volatile e of volatile will affect directly the depth of coal bed to be carried and the intervals of firing for the most satisfactory results The variation in the fuel over such wide ranges makes it impossible to definitely state the thickness of fires for all classes, and experiment with the class of fuel in use is the besthow that particular fuel should be handled The following suggestions, which are not to be considered in any sense hard and fast rules,conditions for hand firing:

Semi-bituminous coals, such as Pocahontas, New River, Clearfield, etc, require fires from 10 to 14 inches thick; fresh coal should be fired at intervals of 10 to 20to h Region require fires from 4 to 6 inches thick, and should be fired often in coes Kentucky, Tennessee, Ohio and Illinois coals require a thickness fro, require frorades of Montana, Utah and Washi+ngton bitueneral as thin fires are found necessary, the intervals of firing should be made more frequent and the quantity of coal fired at each interval smaller As thin fires become necessary due to the character of the coal, the tendency to clinker will increase if the thickness be increased over that found to give the best results

There are two generalmethod

[Illustration: Babcock & Wilcox Chain Grate Stoker]

In the spreading method but little fuel is fired at one time, and is spread evenly over the fuel bed fro door the doors should be fired alternately The advantage of alternate firing is the whole surface of the fire is not blanketed with green coal, and steaenerated ain, a better co ofthan where all doors are fired at one ti method, fresh coal is fired at considerable depth at the front of the grate and after it is partially coked it is pushed back into the furnace The object of such aof a bed of carbon at the rear of the grate, in passing over which the volatile gases driven off froreen coal will be burned This ases are made to pass horizontally over the fire Modern practice for hand firing leans ain the tendency is to work bituminous coal fires less than for eneral, the less the fire is worked the better the results