| Show MINING department USES OF compressed AIR IN MINING A california engineer tells why it ita Is superior to electricity in many M a ny ways ya ys the fOll follo wlm 1 is 14 4 part of a lecture upon the of compressed air for mining purposes which was recently delivered at leland stanford jr university ver sity by A itla it Is not my purpose e to belittle the service which is rendered by that incomparable power which wo we call electricity although I 1 imly claim that it lias his u usurped the legitimate place of 0 compressed air in ili many instances there Is no coull conflict let between two tiro great agencies agen cles each has its proper aud legitimate field of usefulness ful ness independent of tit the other anil and it is easy for tin an intelligent eng engineer to recognize these iso ep parate arate lights light and in proportion as lie he does docs so 40 will his work be successful A small portion of 0 the territory of these powers seems to overlap and it is there that wo we hoar hear tile the nuie noise and of disputed title and many in III the midst of this turmoil lose sight of the lie great in depend out domain of 0 each which requires development and which will yield rich return to tho the earnest student and ili worker compressed air Is the only power w which lich is alone sufficient to supply all the power needs 0 of an average wine mine por for lighting purposes from froin five to ten per cent may inny it if required be converted into electricity for that purpose where steam or water power is used litty fifty per cent or more Is converted into compressed air and five to ten per cent into electricity for lighting where electricity I 1 ia used from fifty per cent to ninety per cent is 14 converted into compressed nir air the remainder being directly used tor for light in atlie alie reason for so great a conversion of other powers powel into compressed sed air lie lies in the lie fact ti that it generally one halt half the entire power is absorbed by pumps underground hoists and rock drills drilla the two former in ili nineteen cases out olit of twenty are actuated actuate il by compressed air and the latter always it is true that both tile hoists and ami pumps way be ruu run by electricity economically but aa yet there has not been produced a rock drill actuated actuate I by electricity which has been a success and Inas inasmuch as nir la Is required for rock drills and ns as they consume more than the pil pumps lills anti and lioi hoist t as a rule the mine manal management gement generally concludes to use air for all three kinds hinds of work rk rather than introduce two kinds ot of po pow er sen ice underground 1 I ant am perfectly aware that my statement regarding tile failure of 0 electric rock drills may be disputed by manufacturers rs of the so called article or by electrical enthusiasts enthusiast but notwithstanding all that shall hall maintain my statement true and it will receive the Eup support port of the larger electrical concerns it is true that electric drills have been made by two or throe three firms firm and on OIL the shop floor they drill very nicely at the rate of two inches per minute in ili medium granite for the first two feet from that point on to four and one half feet the average depth of a blasting hole their drilling capacity deteriorates very rapidly the air drill does from three to four time the work easily tho the claim for the electric drill is that it consumes but one third the power pomer this is true truc but if it takes three of them to do the i w ork ot of otic one air drill tile lie wages of six men will have to be balanced against tile wag wages es of two men and extra power consumption the later equals perhaps the pay of one man mail so that to do the same saine work with t the e electric drill v N cost coa twice moro more than for the air hill there are other considerations consideration however independent of this which militate against the electric c ira dria viz that it will N ill not stand the dust mud water hammer boating and general rough aage usage and again it would be ner necessary cs to introduce a ventilating system for fresh air as well as to expel smoke where electric drills are used while etli with the air machines their exhaust furnishes all necessary fresh air and ventilation it needs no great tant to see therefore that the lie simplest and in most desirable proposition and I 1 hie lie one involving the least machinery machine y and transformation of one power into 1 ilo the other is compressed air which ox changes from live five to ten per cent ot of itself for lighting purposes only while any of the others must make exel exchange iange for at least fifty per cent of air and the lighting be beside stile 1 I have assumed of course that the c cost st of any of these powers delivered to the mine anine was eual equal and the motors which absorbed them were the most efficient for the purpose se I 1 kii all things bein epla equal then I 1 assume a e from what I 1 have seen of the various requirements of a mine for power purposes and tor for the reasons reason given before that compressed air Is the ideal with varying conditions condition however it Ss Is simply a matter of combining and comparing the cost of fuel or water repairs interest on oil the plant insurance und and taxes in order to select the proper general power and should com iari pari hons bo be nearly equal then general utility simplicity ind and safety should decide the choice when the preponderance of evidence is for one of these the forms of power it requires no skill to make a 1 selection but when all things are equal na as to cost and maintenance or nearly so KO in bringing any ally of the powers to the mine then I 1 wish to show why k fly compressed air should be the choice N w ith out ont lie and after the choice Is thus abu cluade how to use it so as to justify tho the choice compressed air lias has been abused in ili its use most shamefully and until to ie evently none of its friends have h ive been able to be seen or heard so intensely lias has the interest of the world been con lored upon the marv marvelous elou results of the investigation in the electrical phenomena tile the mysterious has hai such a for tin the ordinary mind nud and vie uie meteoric moU oric developments of electrical li science vience have followed so thick and fast stud nail in ili so many fields of usefulness ihal the average lu individual could ve be stampeded into the electrical camp bi b a mere inere mention of the name of tits thia most elusive fluid now there giai b as conle come a breathing spell and ami tile the advocates of compressed cd nil air ire are callina attention to the fact that compressed air properly generated and applied owns a 1 place in ili the economics of the day ami this they poopoo io to maint maintain aill compressed air has generally been understood to be a most expensive furn form of 0 power nud and has been riven given sul suf ft rance only because of its utility since for underground work it really has ila 8 no it 0 alval at any price because the laws of compression and expansion n of permanent gases belong to the rellin realm of higher mathematics few understood what they i were ere dealing iv with I 1 ill a and nd many of 0 those these unable to overcome the fri freezing cz of their motors did as th the public generally did viz used the air at practically full stroke and throw threw away ail the lie intrinsic energy of theair the air which m e ca can n develop liy I 1 ay iy expansion theoretically they thus threw away two thirds of their power and practically about obice fourths Ordin ordinary iry direct acting pumps and rock drills no do not have hare an efficiency of 2 25 per cent no small wonder rider then that the wood woodpiles piles havo lave dwindled rapidly away and small power results been produced everything was sacrificed to utility and air did riot not take its proper rank until bosan began to realize that it must be used expansively to use air in fit till nn ordinary direct pump Is equivalent to throttling a head ot of water to one fourth of its spouting spout ine velocity to accommodate the speed of 0 a I 1 wrongly geared water wheel 1 I amicy that most of 0 the trouble on oil the whole subject ila has arisen from it a misconception of what COW compressed pressed air is in I a sense many boileve that the power of 0 the engler which compresses the air ila has been stored in ill the compressed air and the wore more steam they give giro the engine and the harder it worries and flur rici the tit more york work the air should finally yield up they cannot understand that a pound ot of compressed air at the same temperature contains the same intrinsic energy no matter what the pressure is ig and till this is originally contained in fit the atmosphere before it is compressed at all this being the he ease case no matter what power was expended to compress one pound of air to say ninety pound gauge pressure it will have at the same temperature but one intrinsic potential stored within it temperature is the head if I 1 may use the term applied to water from it conbes the power if by reason of a il condition viz pressure one pound of air is allowed to fall from a height represented by a 1 temperature sixty to one lower represented by say GO that one pound will generate toot foot pounds of work through every degree it falls and so ui or until it roaches reaches the absolute 0 which Is if the bottom where in theory air has baa neither pressure nor volume and its work is done one tile the total intrinsic energy is always multiplied by the number of degrees decrees the one pound of air Is distant from degrees fahrenheit tills this IS is simply the which represents the foot pounds of work in one british thermal unit multiplied by which is the specific heat of air at constant vo volume lunie that 1 is 13 3 to say it is the fraction of a british thermal unit necessary noc ebsary to raise one pound of air one deg degree ace the quantity of heat therefore necessary to raise the temperature pera ture of one pound of air from absolute zero to sixty degrees fahrenheit which ie represents presenta a distance of degrees will lie be 93 multiplied by which would bo be foot pounds which represents tho the intrinsic energy of one pound of air at sixty degrees fahrenheit this of course presumes pres that no heat will be either lost or gained by radiation or otherwise V so during the expansion of niland this sort of expansion is calad called adl abadic the center of the earth 1 Is 13 3 the absolute 0 of water power for there water has 1113 no weight this corresponds to the absolute 0 ot of air and every pound of water at the same di distance tance measured in fit pressure from tho the center or of the earth has the same potential and independent of its temperature just its as one pound of air has the same potential at tile tho same distance men measured in temperature from its absolute 0 independent of its pressure the sea level for mater tt ator corresponds to the line for air for at points neither will manifest motion or power suppose the land and water to lie on a level wo ire could not then use any of the potential in ili the mater unless by sonie some mechanical levice device we continually created a shaft whose depth xie we would call pressure below the sen sea level for the water to fall into and gen generate crate power find and it matters riot not how much power it requires to maintain maint aln this shaft haft at any depth one pound of vat water dropping into it will always yield up lip the same fraction frn etlou of its total intrinsic potential the same wi thair at tile the atmospheric live lire we cannot avail ourselves of its potential so we use a mechanical df device ak e called a compressor to prepare a 1 shaft as it acie which aich we also call pressure ghose depoli we measure in degrees of temperature and no matter how much power it takes to mail maintain etain tins this condition of affairs one pound of air dropping into this shaft haft will always waa s give out tile the same fraction of its total intrinsic energy I 1 hope I 1 have hare made the idea clear that I 1 wished to convey 1 viz that in neither case ila did tile resultant power depend for its measure me aure upon the mechanical inc means ans which caused its activity shining and scientific review |
