March 15, 1918. 546 THE COLLIERY GUARDIAN. own plant and he heard they were doing even better. In connection with super-power stations he thought the coal cost was small in proportion to the total cost of current. The subject of by-product recovery was tremendously involved. The question was well worth investigation, and experiments might be made on a small scale. There was a lot to learn in connection with exchange stations. The great difficulty was finance, but in modern stations an enterprising man had the opportunity of experimenting and finding out what by-product recovery really would do. Mr Allcock said the report promised a saving of 55,000,000 tons of coal, a saving of a corresponding amount of transport, concurrent economies aggregating 100,000,000 per annum. Such a report would make an impression on the Reconstruction Committee unless an antidote like Mr. Pearce’s address was administered. They were in agreement that the municipal boundary should no longer be the boundary of electrical supply. Another point of agreement was on the question of linking up. Those were great assets for the Recon- struction Committee which was considering the future of the electric power industry. ____________________________ ELECTRICITY v. STEAM POWER AT COLLIERIES.* By R. E. Hobart. The development of the Hauto power plant and the claims made by various engineers that electricity was more economical than steam for power purposes in and about the mines, led the Lehigh Coal and Navigation Company, in 1911, to conduct a test to ascertain the consumption of power used by a large steam hoisting engine. The question being one onwhich.no reliable information could be found, and the opinion of various engineers differing to such an extent, it was decided that a test under actual operating conditions was necessary. This was arranged for at one of the collieries. The engine selected was a 30 by 60 in. piston-valve engine of modern type, and comparatively new. The boiler plant from which the hoist received its power was about 600 ft. from the engine, the latter being fed by a 10 in. steam line insulated with magnesia pipe covering. Two batteries of the boiler plant, aggregating 1,200 horse-power, were cut off and fed into a separate steam line leading direct to the hoist engine. Steam auxiliaries, consisting of feed-water pump and blowers, were fed by the boilers in test, and their con- sumption charged against the hoist. A barrel weighing device was installed, as it was felt that this would be the most accurate way of determining the consumption of water. The fuel, No. 3 buckwheat, was carefully weighed, and every precaution was taken to make the test accurate in every particular. The test was run for one week, or a total of 168 hours. A record was kept of the number of trips hoisted or lowered, and continuous indicator cards were taken. One particular set of cards was taken with the hoist operating balanced, and also with the hoist operating with no counterweight other than the empty cage, the coal in the car being weighed. The speed of the hoist was taken by means of a graphic recording instrument which registered the number of revolutions every 5 sec. From this record, speed-time curves were plotted. The test was divided into two periods : working times and idle time. The hoist did not operate between the hours of 5 30 p.m. and 6.30 a.m., nor from 3.30 p.m. Saturday until 6.30 a.m. Monday morning. The actual working time, therefore, was 64 hours, and the idle time 104 hours for the week. The total weight of coal used in idle time was 108,075 lb., while the coal used in working time was 119.950 1b. From these figures, the amount of coal consumed per hour to cover stand-by losses would be 108,075 4-104 = 1,038 lb. of coal per hour. During the week, 1,705 cars of coal were hoisted from a depth of 581 ft. A tabulation of test results is shown in Table 1. Table I.—Hoisting by Steam. Depth of shaft, ft............................. 581 Weight of coal per car, lb...................... 8,960 Coal used during 104 idle hours, lb. ........... 108,075 ........................ Coal per hour idle, lb.......................... 1,038 Trips during week............................ 1,705 Actual time used in hoisting, sec., 1,705 x 25... 42,625 Actual hours hoisting, 42,625 4- (60 x 60) ....... 11’82 Seconds during week ........................ 604,800 .................................... Seconds idle during week .................... 562 175 Idle hours....................................... 156’2 Coal used during idle time, lb., 156’2 x 1,038 ... 162,135 ........... Coal used during hoisting, lb., 228,025 — 162,135... 65,890 Coal used per trip, lb., 65,890 4- 1,705.......... 38’6 581 x 8,960 Horse-power hours per trip, 33^00 x 60......... 2’63 88‘6 Coalperhorse-powerhour, lb.,.........................14’70 From these results, it will be noted that to the 104 idle hours, representing the period when the hoist was not operating, must be added the idle time occurring between hoists during the operating period, which makes a total of 156’2 hours, the actual hoisting time being only 11 82 hours in the week. The Lehigh Coal and Navigation Company felt, therefore, that it would be advisable to use electric power at the new operation to be developed at No. 11 shaft. Conditions for Electric Hoisting*. It is a well-known fact, in the anthracite region, that the working time of a coal hoist is only from eight to nine hours in a day, the night hoist being intermittent. At the time the test was made very few electric hoists of this capacity were in operation, and most of the larger ones had either the Ward-Leonard or Ilgner system of control, the only large induction hoists being in South Africa. Various hoist engineers were consulted on the different types of hoists using alternating current. Propositions were submitted on the Ward-Leonard and Ilgner systems, as well as on the induction motor type. All these hoists have their good and bad features. * Paper read before the American Institute of Mining Engineers. The Ward-Leonard system consists of a motor-generator set in which an alternating-current motor is directly connected to a direct-current generator, which generator furnishes power to a direct-current hoist motor. The Ilgner system also consists of a motor-generator set, which drives a direct-current hoist motor, the generator being separately excited. By means of a flywheel and slip regulator, the load peak on the power system is practically eliminated. The other type of hoist is driven with an induction motor, with a polar-wound rotor to permit of the addition of external resistance to the rotor direct. TheliftatNo.il shaft was 266ft.,and the desired number of cars to be hoisted per hour was 120. This short lift and the number of cars per hour would mean numerous peaks, which from the brief description given of the different systems might make it appear that the Ilgner system would have been the better one to use. However, when it was considered that the working day at that time consisted of nine hours, with occasional hoisting during the remaining 15 hours of the day, and with frequent stoppages for various reasons during the working time, it will readily be seen that the generator set would be operating continuously, whereas the actual work done by the hoist would be very little. The other disadvantage of the Ilgner system is its high first cost, the hoist costing about 60 per cent, more than an induction hoist. 1.'or these reasons, it was decided to use a slip-ring induction-motor system. Its disadvantages of poor efficiency, low-power factor, and high-load peaks in starting were offset by the fact that when the hoist is not working, no current is used for the hoisting system excepting the small amount necessary to run the pump for the liquid rheostat, which may be shut off at the will of the operator. At all the company’s operations, synchronous con- verters are used in connection with the mine haulage. It was found that there was sufficient converter capacity connected to the supply line to permit of a great deal of power-factor correction. The next important feature connected with this hoist was to design and make a proper control system. The usual control for electric hoists up to that time consisted of a slow-down device at a predetermined point in the travel, or a device that would automatically operate the controller and apply the brake at a predetermined point. The overwind features were also included. From experience with steam hoists, it was felt that type of control would not do for electric hoists, on account of fluctuating loads. Many times loaded cars are hoisted without balance, and loaded cars are lowered at various times, and, what is more important, from 75 to 100 trips a day are made for raising or lower- ing men. To meet these varied conditions, the company insisted that the following features should be embodied in the control of this hoist: - 1. Hoist must not over-travel in either direction. 2. It must be impossible for the operator to start hoist in the wrong direction at either limit of travel. 3. Hoist must not back away, due to failure of power or overload. 4. Protection must be provided against overspeed, due to any cause whatever in any position of travel. 5. Emergency brake must set and power be inter- rupted if operator fails to retard hoist approaching landings. This value to be graduated and to be adjust- able to meet conditions. 6. Hoist must not start return of power if operator has carelessly left lever in “on” position. 7. If control circuits become grounded, hoist must stop. 8. If operator fails to keep power brake in proper adjustment, emergency brakes must set and power must be interrupted, to remain so until operator has readjusted brake. 9. Hoist must be brought to rest and brake applied on loose drum before clutch can be disengaged. 10. It must be impossible to release brake on loose drum while clutch is disengaged. 11. Pawl must be provided, interlocking with clutch engine lock, this pawl to engage in loose drum before clutch can be released. 12. It must be impossible to operate hoist unless clutch is full “ in ” and locked. 13. Air reservoir must not be drained by emergency stopping of hoist. 14. There must be no delay in operation of hoist due to emergency stopping. 15. It must not be necessary for operator to call assist- ance in case of emergency stop, over-travel, or otherwise. 16. For operating hoist, multiplicity of levers must be avoided; two will be allowed, viz., brake and control. 17. Hoist operator must not be endangered by flying levers in emergency stopping of hoist. 18. No safety features must be dependent on the will of the operator. 19. Switch must be provided on operator’s platform for an emergency stop, if necessary. 20. Travel limits and speed range must be easily adjustable. 21. Current input and acceleration of hoist motor must be governed automatically. 22. Hoist must start from rest gradually without excessive jerks and come to rest smoothly, and must be under control of the operator at all times. 23. The speed of the hoist must be varied by cutting the resistance into or out of the rotor circuit. The rheostat must be of the liquid type and of ample capacity to meet all operative conditions All the foregoing features were met in every par- ticular, and it will be found that this type of control for slip ring induction motor hoists has been made standard by the larger hoist manufacturers. The hoist was placed in operation on April 16, 1915. and has operated with no delays and very little upkeep. During two and a-half years, the only repairs necessary to keep the hoist in operation have been a few contact tips for the reversing switches, and packing for the brakes and rheostat pump. The average power used for hoisting a car of coal 266 ft., including line and transformer losses, is 2’59 kilowatt-hours, which at __________________________________________ 8 mills per kilowatt-hour amounts to 0’0207 dol. a year, the average weight of coal in the car being 8,960 lb. In connection with the electrification of the hoist, it was decided to electrify both inside and outside the mines. The electric haulage system was already installed inside, but the fans, pumps, and air compressor were steam driven. The fan, which was situated on Sharpe Mountain, was about 100,000 cu. ft. per minute capacity, being driven by an 18 by 36 in. slide valve engine. The hoisting engine and air compressor were situated near the fan and close to the boiler plant. The development of the new No. 11 shaft allowed the abandonment of the 30 by 60 hoisting engine, as the new electric hoist would operate from the same level as the steam hoist. The 900 cu. ft. per minute steam-driven air com- pressor has been replaced by one of 1,500 cu. ft. per minute, electrically driven by a 250 horse-power syn- chronous motor. A 200.000 cu. ft. per minute fan, driven by 150 horse-power slip ring induction motor, was installed to take the place of the steam fan, and a small steam plant was built for heating purposes. Electric Pumping* Installation. The steam pumps were located in a pump house south of the bottom of the old No. 11 shaft. The old pumping plant consisted of one 42 by 20 by 72 in. duplex pump, and two 16 by 48 in. single pumps. At various times, in flood seasons, it was necessary to instal water tanks in the coal shaft either to prevent drown- outs or to hoist the water from the mine in case of a drown-out. The sump for the old pump house was situated about 50 ft. south of the old shaft, so it was decided to drive a small sump tunnel from the old sump into the shaft sump. The old sump was also extended westward about 300 ft., making the opening into the sump on a pitch, so that a car could be run into the main sump for cleaning purposes. One 1,500 gals, per minute triplex, one 1,500 gals., and two 3,000 gals, all bronze centrifugal pumps were ordered for this pump house. The triplex and the 1,500 gals, centrifugal pumps were placed south of the shaft, and the two 3,000 gals, centrifugal pumps were placed north of the shaft. The tail pipes of the 1,500 gals, and the two 3.000 gals, centrifugal pumps were run into the shaft sump, while the tail pipe of the triplex pump was run into the main sump. A ditch of large capacity was made on the west side of the pump house, entering into the main sump. Gates were installed to allow the water to be diverted into the shaft sump if necessary, and a gate was installed in the sump tunnel, which dammed off the main sump from the shaft sump. By this method it is always possible to clean either sump, and it is not necessary to wait for a dry season, with the added expense of installing dams for this necessary cleaning. All the centrifugal pumps are horizontally split, being all bronze, with a full load speed cf 725 r.p.m. The reason for specifying this low speed was that the mine water is acidulous and gritty. All pumps are hydraulically balanced, none of them depending upon thrust bearings. A very important thing to consider in the specifica- tion for a centrifugal pump is to have a proper metal for acidulous water. The specification for the bronze in these pumps was 75 per cent, copper, 15 per cent, lead and 10 per cent. tin. All screws, washers and dowel pins should be eliminated from the seal rings and diffusion vanes. In fact, it is believed better to buy pumps without diffusion vanes,.as this part of the pump is very apt to give trouble; and there are objections to labyrinth rings for mine pumps. The seal rings should be wide, straight rings, the one on the impeller being shrunk on, the stationary ring being held from turning by a tongue resting on the bottom split of the casing. It is a question whether the hydraulically balanced pump will operate und^r all acid conditions, However, the 8 in. six stage pumps operating in No. 11 shaft have not given any trouble in this respect since they were placed in operation. The cost for operating these pumps, including transmission line and transformer losses, on a 266 ft. lift, is 1’545 kilowatt hour per 1,000 gals., which, at a rate of 8 mills per kw.-hr., amounts to 0 012 per 1,000 gals. Total Savinggby Electrification. When operating the old boiler plant at No. 11, which furnished steam for the No. 11 shaft hoisting engine, one steam fan, one 900 cu. ft. air compressor, the inside pumps and steam heat, the cost of the boiler plant for the year April 1914 to April 1915 was 46,992 dols. This figure included the cost of fuel and handling, wages of firemen and ashmen, maintenance of boilers and pumping of water for the boilers. During the same time, the shaft produced 343,665 tons of coal, or a steam cost of 0’137 dol. per ton. For the year November 1916 to November 1917 the electric power cost was as follows :— Dois. Hoist............................ 3,300’16 Fan............................. 3,270’63 Air compressor ................. 8,845’39 Pumps ......................... 6,174’08 Total......................... 21,590’26 To this figure should be added the cost of the heating plant, making a total power cost of 30.290’26 dols. During this period the shaft produced 435,073 tons, with a power cost of 0 0696 dol. per ton. This shows an actual saving per annum of 16,702 dols., but as the use of electricity permitted more efficient work and less loss of time from repairs, drown-outs, etc., the tonnage hoisted increased from 343,665 to 435,073, and the cost of power per ton produced decreased from 0137 dol. to 0’0696 dol., a saving of 0’0674 dol. per ton, which, for the output of 435,073 tons, amounts to 29,149 dols. per annum. _______________________________ Manchester Geological and Mining Society.—A paper on “Wastes, Shales, Lower Grades of Small Coal: their Nature, Recovery and Use for Oil and Power Pur- poses,” by Mr. J. Drummond Paton, was read at the meeting of the society on Tuesday evening. A report will appear in our next issue.