The colliery manager's handbook; a comprehensive treatise on the laying-out and working of collieries, designed as a book of reference for colliery managers and for the use of coal by Pamely Caleb

Author:Pamely, Caleb
Language: eng
Format: epub
Tags: Coal mines and mining
Publisher: London, C. Lockwood and Son
Published: 1904-03-25T05:00:00+00:00

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Fig. 422,— Water-gauge tlacku in a Door ok Stopping.

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It will be well here to consider some of the rules for working out problems connected with furnaces and fans as used for motive powers.

The power obtained by furnace ventilation is measured by the difference between the weight of the air in the downcast and upcast shafts. The length of column in the downcast, which would be equal in weight to the difference of the weight of the air in the two shafts, is called the motive column, to find which use the following formula:—

Let M = Motive column in feet.

„ T = Average temperature of air in the upcast.

/ = Temperature of the air in the downcast.

D = Depth of the downcast in feet.

T-/ Then M = D rp—-—•

If the depth of upcast and downcast were each 300 feet and were 12 feet in diameter, or had 113 feet superficial area, the temperature of the downcast 60° F. and the average of that in the upcast 150° F., the motive column would be 3CX) x

—§—; = 44'^^ feet, that is, the jur in the downcast would balance the air in

150+459 ^^•>'> ' '

the upcast with a column 44*33 feet shorter than that in the upcast.

From the formula already given to find the weight of a cubic foot of air at any temperature, and under any pressure, if the barometer read 30 inches, to find the

weight of a. cubic foot in the downcast, ~^ "V^q = '0766 lb., and this multiplied by the depth in feet and by the area thus, '0766 x 300 x 113 = 2,596*74 lbs.

the total weight in the downcast. For the upcast, coXTtJ' = '06529 lb.,

the weight of a cubic foot and multiplied by 300 and by i I3 = 2,2i3'34 lbs. as the

total weight in the upcast. 2,59674—2, 2i3'34 = 383*4 lbs. as the difference in

weight in the two shafts. Therefore to find the motive column, as 2,59674 : 300

• • 383'4 : 44*3, as given before. If the quantity of air circulating were 150,000

cubic feet per minute, proceed to find the horse-power exercised by the furnace

thus :—The weight of a cubic foot of air in the downcast being '0766 lb. at the

bottom of the pit, there would be a pressure of '0766 x 300 = 2298 lbs. due to

its mere weight. In the upcast the weight would be 06529 x 300 = 19*587 lbs. and

22*98 — i9'587 = 3'393 lbs. as the difference of pressure on each square foot of

^, ^ 150,000 X3"303 area. Therefore ';•''' = 15*4227 horse-power.

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Some authorities use the formula M = D x which gives the length

^ -f 459 of motive column in feet of air of the temperature in the upcast, and this formula

T — / will give the same pressure in pounds per square foot as M = D x ,=

T -h 459 which gives the length of motive column in feet of air of the temperature of the

air in the downcast, but the former gives also the theoretical velocity, viz.

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