| Show the ventilation venti lation of mines BY THOMAS CHESTER continued from last issue the point of paramount impo importance artance in designing a fan for ventilating a mine is to ascertain as nearly as possible the resistance si which the mine will offer to the required volume of air As mentioned previously sly this required volume is calculated by making suitable allowance for the number of men and animals in the mine and by additional allowances for removing gas coal is mined in the majority of cases from seams at some distance below the surface and it is necessary to bore shafts to get to the coal in mines of this type which form about 90 per cent of those operated in the country the resistance will vary ary from 1 in to 6 or 7 in according to the sizes of downcast and shafts and airways air ways in west virginia a large amount of the country has been eroded by the action of water and the coal is sometimes several hundred feet above the river valleys and above the railroad tracks which are in the valleys what is known as drift mining is employed to get out the coal under such conditions and horizontal drifts or adits adias are run into the coal seam it is possible to use as many inlets and outlets as necessary with a mine of this kind and in consequence disc fans can be used as the resistance usually is only from 12 to 1 in of water reversibility most mine fans are made reversible so that air can be either blown into or exhausted from the mine by the fan so that changing over the latter changes the entire circulation in the mine this thi s is made use of to thaw out ice formed in cold weather it is usually found best to have the downcast shaft or the place where the air enters the mine employed for getting out the coal as this keeps the gangways down below in a fairly safe condition as clean air passes through them when this is the case electric lights can bo used without danger as short circuiting oi of wires or breaking of lamps would not cause any harm and with good illumination the output of coal can be considerably increased the cold air entering the shaft will in winter sometimes freeze the water which is cont continually dropping down and tend to cho choke ke the shaft and als also 0 block the gangways below by reversing the fan at night occasionally the warm air of the mine can be caused to flow back through the hoisting shaft and thaw out the accumulated ice A mine fan operating as an exhauster abstract of paper presented before new york chanter of the american society of heating and ventilating r engineers I 1 creates a depression of head or pressure within its impeller and this causes the adjacent air in the fan s side ide drifts to flow in to take the place of the air removed by the fan in this manner air is forced out of the shaft by the higher 0 atmos pharic pressure producing a downward flow through the dow downcast shaft and air currents through the mine to the shaft shaf t some ventilating engineers speak of fan exhausters exha usters as pulling out the air but of course this is entirely incorrect as there is no cohesion between air molecules and a gas cannot be pulled in the same way as a solid bar some ventilating engineers have a preference either for fans operated as ex usters haasters ha or as blowers but there is not much difference in the results with a mine operated under the exhaust system the pressure in the mine generally is less than that of the atmosphere outside so that when the fan is shut down the pressure within the mine is increased slightly and tends to hold back the 1 flow 0 or gas this is not of any 6 great consequence however as the pressure of the pent up or occluded gas in the strata overlying the coal seam seam is very high frequently amounting to several atmospheres there is not much need of emphasizing the value of proper ventilation in mines both from a humanitarian standpoint and as accident pre prevention bention ven tion there is however another side to the question which is is sometimes overlooked ventilation has a very decided influence on the mines production and profits men who are in good physical condition can get out more coal than those who are reduced in efficiency due to the presence of noxious gases JJ J J walsh a prominent mine inspector of pennsylvania has estimated that 10 per cent more coal could be produced than is at present taken out if all mines were thoroughly ventilated and this is a conservative estimate in some well authenticated cases the increase has amounted to 30 per cent metal mines in metal mines the volume of air handled per minute is very much less and as a consequence the humidity is very much higher as the moisture carried per cubic foot is increased due to compression in the case of a mine or feet deep in one case where fans were installed in a mine in brazil the production per man was about doubled owing to reduction in temperature pera ture caused by improving the ventilation the increase of air temperature due to air becoming more dense as it passes down a mine is about I 1 deg fahr for every ft while the increase ture is in rock approximately i 1 11 deg for f f ft t the rock temperature ti keeping up a current of cold fresh f in metal mines it was satisfactory to once 0 oud 81 allow the miners mine to use of the air which escapes drills this being afroz about from 80 to 1 ft per drill per minute A consi change has taken place in the haq i years and most metal mines of any anys 8 now equipped with regular fan system ventilation testing mine fans all shaft mines are provided tin ti shaft sunk from the surface to the etu or gangways below called an air sh this may be either a separate ope obenia op enia the sole purpose of conveying air or i of the main hoisting shaft partitions for that purpose at the foot ottil ot the shaft two or more separate channel airways branch off in different diredo these channels are termed splits air shaft passes through solid cases and is generally lined with ted concrete and as the splits are channel in the solid coal there is no chance chan fe leakage so that test readings can be led at any point where the flow is fairi fa form if required readings can ie be s simultaneously in the splits near alif tie I 1 of the air shaft and the total volume I 1 led by the fan can be calculated bya by the volumes passed by the different the places for taking test readings be chosen with a view to getting gett ms I 1 average unbroken stream of air in a i case and this of course I 1 is only where the airway air way surfaces area are re smooth and not broken up by JW sections and indentations where splits or main airways air ways nea Reg s ah I 1 foot of the air sh shaft aft are of large frequently possible to get reliable reli alle of afan anal as to air velocities by means this W of ter indications as in cases I 1 velocity is often around 1000 0 it per F tube readings are more is only n it however and dolmer y hect the impact tube to the t na of 0 sid side the open water gauge as the SO strument ment is subjected to of the airway air way reading during a test simultaneous speed of oi made of the or the 1110 tor developed by power the side the static wat water er gauge in grf the leading to the fan and erred to I 1 minute as ret ref handled per is of course cours e d the volume are dal multiplying the cross section tel the average av airways air ways or splits by ori fic equivalent no mine should be equipped equip inel style of fan having a niini 0 1 less than twice the equia equiv equi 15 d effi efficiency anything like good this holds true whether the fan is to be used as a blower or as an exhauster as at the point of highest efficiency there is a definite ratio between the fan inlet area and the mine equivalent orifice in the majority of good installations the mine inlet t area are is about 25 times the equivalent ori orifice of the mine the equivalent orifice varies directly as the volume of air passed per minute and inversely as the square root of the resistance so that with the same mine conditions prevailing the equivalent orifice remains the same with the fan speeded altered and the volume increased or decreased |
