Show the ventilation venti lati on of mi mines e nes BY THOMAS CliST CHESTER JRR the total coal production of the united states is about tons per annum about of this being bituminous coal and the remainder anthracite if this volume of coal were to be arranged in the form of a long block 3 ft square it would extend about miles or twelve times around the earth at the equator in order to obtain the production of tons of coal per annum about men are employed including the men required outside as well as inside the mines one fifth of the total amount of coal mined is used as fuel on the railroads the remaining four fifths being burned at power plants and in residences in transporting this latter 80 per cent around the country there is a great deal of lost energy as the freight cars weigh about 25 per cent of the weight of coal carried these cars return empty to the mines so that the deadweight represents 50 per cent of the weight of the coal transported scientists have recommended that coal be burned at power plants located close to the mine shafts and electrical energy delivered f ll to the surrounding cities over high tension wires in the same manner as power is transmitted from generating stations at niagara falls and other water power plants the production of power from coal at the mines for distribution to surrounding cities is now being made use of to a limited extent one plant of considerable size is located at hauto cauto pa which is owned by the lehigh valley coal navigation co the thermal efficiency of the best power plants in the country however does not exceed 17 per cent which is a very low amount and in the majority of cases this efficiency is only 5 to 10 per cent of course the energy obtained from the turning burning of coal is that which was given to it 11 in the carboniferous period over years ears ago the trees and plants used the heat float energy of the sun to dissociate the carbon and an oxygen in carbon dioxide build 1119 DS up the cellular tissue of leaves and brurs from brorn the carbon in combination with hydrogen taken from water thus the olver nver ivsich ch furnishes us with all modern ven fen ces was taken from sunlight of agai ago the great improvement in liv conditions during ring the last two centuries call ca be directly atly attributed to the use of coal ag a fuel oata obtained as the tremendous ous amount of power froin coal enables the varied prod acts ts 0 of ana manufacture facture to be produced at corn lively Wat ively small expense regard to power production how ever i it is unquestionable f conable that in af after ter ages agea people will make more use 0 of f water or ork astra chapter t of paper P presented before new I 1 ar felting ng of the american society of and arl 0 r ventilating engineers power than at present as in the case of new york state for instance the annual rainfall amounts to in and this is equal to tons of water on each square mile of surface this energy also is of course obtained from the sun due to the heating of the atmosphere causing winds and the evaporation of water which is transported in the form of a gas and descends as rain possibly the total number of men employed in the electrical industries is around so that it will readily be seen the electrical production of the country could be vastly increased if the men now employed underground were changed over to electrical work no doubt at some future time the internal heat of the earth will be made use of for heating factories and residences and it seems absurd to keep such a large army of men at work digging out coal when a few shafts in each city driven down from five to ten miles would furnish all the heat necessary by allowing wat water er to descend to the heated interior to be turned into steam natural ventilation both coal and metal mines will to a considerable extent ventilate themselves by natural means due to the different temperatures pera tures of the air outside and within the mine this of course is caused by the light air ascending and the heavy air descending sc the impression is held to a considerable sid erable extent that the draft of a stack is caused by suction in some manner but the principle involved is the eff effect act of gravity on the heavier air causing same to flow under the lighter air similarly a balloon rises for the reason that it is thrust upwards by the heavier air around its exterior the air current in mines usually reverses itself twice a year it is easier for it to descend down one shaft and ascend through the other than to have upward and downward currents in the same shafts it will be seen that with the motion through a mine in one direction in the winter the downcast shaft will be considerably cooled due to the cold air entering same when warm weather arrives this cold shaft is gradually warmed up by reason of the war warm air and as spring advances the entering air becomes warmer than the air leaving the mine at the shaft this causes a retarding influence and eventually the current will reverse itself so that the upward motion will be through the warm shaft which was the downa downcast ast shaft during winter natural ventilation cannot be relied upon to give satisfactory results in mines as there is not sufficient difference in ead available for any regulation to be made artificially so as to compel fresh air to travel around the mine generally the air tends to take the path of least resistance and if regulators or doors are used to choke the air path so as to cause air to flow around the workings generally the ventilating current is considerably reduced fan ventilation the majority of mines are equipped with fans which either deliver air to or exhaust it from the workings most mine fans are made reversible so that they can operate in either manner as will be described later on the amount of air used to ventilate a coal mine is usually from two to three times as great in weight as that of the coal taken out in a given time A mine producing say 2000 tons of coal a day will therefore require the movement of about tons of air state laws usually call for cu ft of air per minute per man in nongaseous mines and cu ft per man in mines producing a good deal of gas the allowance for mules is usually cu ft per minute per animal it is found this allowance will produce the necessary dilution to keep the dangerous gases down to a safe amount the gases to be removed consist principally of methane carbon dioxide and carbon monoxide methane is lighter than air and therefore stratifies near the roof surface in regions where there is not much air movement it is found that if the air velocity is not allowed to fall below ft per minute this stratification cannot take place the amount of methane produced in a mine is usually very large as in some pennsylvania mines in the anthracite region it reaches cu ft in twenty four hours and sufficient fresh air has to be taken through the workings to keep the dilution down to a safe amount if the amount of methane in gas laden air is less than 5 per cent it will be below the danger point but the amount of air drawn through the workings should be sufficient to keep the gas down dow n below 2 per cent as a maximum explosions in mines are produced by ignition of methane in most cases and this is greatly intensified by the subsequent immediate combustion of the dust which is found in practically all mines especially during the winter months during this season of the year the entering air carries only a small amount of moisture in suspension and upon being warmed up within the mine its relative humidity is made very low so that it readily picks up moisture from the coal and dust leaving the latter in a very burnable form explosions are generally caused by miners using open lights in dangerous places by windy shots where where the tamping blows out of the holes and flames issue for considerable distances by electrical short circuits in the wires transmitting power and by sparks produced when the roof falls occasionally the friction of the descending rocks setting fire to any gases in their vicinity effect of fall in barometric pressure A drop in the barometric pressure of 12 in of mercury will cause the gas in the old workings to expand 16 per cent in volume and this means that this amount will flow out from the old workings into the gangways and entries this air having been stagnant for a long time is likely to tie be heavily charged with methane and carbon monoxide the former obtained from the strata overlying the coal seam and the latter from oxidation of coal dust and mine timbers it is customary to use stop pings to close off old workings but these are not always made as tight as they should be thus with loosely constructed stop pings the air in the old workings will flow out into the mine generally as a drop in pressure of 12 1 in of mercury represents 68 in water gauge and the difference in head of 68 in on two sides of a stopping will produce a velocity of ft per minute carbon monoxide this gas is highly explosive and also is a highly poisonous gas much more so than carbon dioxide it is produced by explosives used in getting out coal the slow oxidation of coal in the workings and it is also given off from the strata overlying the coal numbers of people are killed every year in garages as a result of automobile engines giving off this gas when running slowly as a very slight percentage is sufficient to cause death it has an affinity for the red corpuscles corpus cles in the blood and a cut producing a flow of blood will not be stopped as in the ordinary manner by clotting as the blood of a person who has inhaled carbon monoxide remains fluid and of a bright scarlet instead of turning to brown the poison is especially insidious a man never realizes there is anything wrong until he finds himself too weak to move all mines have carbon monoxide in them it seeps out of the cracks in the rock in metal mines and out of both coal and overlying rocks in coal mines in gaseous mines the miners occasionally make use of canaries or mice as these creatures succumb very readily to the gas and a miner is made aware it is time to go when he sees a canary or mouse collapse or die even with as small an amount of carbon monoxide as 1 per cent a man will succumb to the influence of this poisonous gas as his blood will gradually absorb it charged to saturation point the blood of a alman human being will pick up about two pints of this gas to be continued |