38 



THE CUBA REVIEW 



ADVANTAGES OF THE ELECTRIFICATION OF 



CANE SUGAR FACTORIES 



By G. Lobo 



After several years of experience with rane 

 sugar factories which are operated by elec- 

 tricity to a greater or less extent, opinions can 

 now be safely expressed as to the many ad- 

 vantages to be obtained l)y this method of 

 drive. The first and greatest is the lower 

 initial cost of the plant, and the lower cost of 

 operation; but this great saving can only be 

 entirely realizetl in the case of a new factory, 

 designed in advance for complete electric 

 drive. Up to the j)resent time no such factory 

 has been erected, to the writer's knowledge, 

 although one or two have been completely 

 designed to be so equipped. 



When there is a complete installation, the 

 main place must be given to those of the elec- 

 trically driven grinding mills which are driven 

 independently, each one by its own motor. 



The list of advantages found in actual prac- 

 tice are as follows: 



(1) It is possible to vary the speed of each 

 set of rolls relatively to the others and inde- 

 pendently of them, in accordance with the 

 percentage of fibre in the cane and the quan- 

 tity of maceration water. 



(2) It is possible to stop or start or handle 

 in any desired way any one of the various 

 mills, should it slide or get l)locked, without 

 affecting at all the operation of the others. 



(3) It is possible to continue to work with 

 the rest of the plant, should bj' accident one 

 of the mills be broken or otherwise disabled. 



(4) There is less danger of breakage, as 

 neither the inertia of the moving parts nor 

 the power of the motor, which is only of suffi- 

 cient size for one mill, will be enough to cause 

 breakage should a sudden resistance be ac- 

 cidentally encountered. The inertia of the 

 moving parts is considerably decreased, as in 

 the case of motor drive no heavy flywheel is 

 necessary. 



(5) There is a large saving in the quantity 

 of men required to look after the engines — to 

 start, to stop them, etc. — as the motors re- 

 quire no attention whatsoever and the occa- 

 sional starting and stopping can be attended 

 to by a few men, and if the controlling ap- 

 paratus is installed in a convenient platform 

 perhaps only one man need l)e used for the 

 complete control of the grinding mills. 



(6) The gear wheels and pinions are all the 

 same size, making the keeping of spares 

 cheaper and the repairs and replacements 

 much easier and more economical. 



(7) Only one motor of moderate size need 

 be kept as a spare for the rei:)lacement of any 

 one of the driving motors in case of accident. 



(8) There is greater reliabilitj" of operation, 

 as it has been found that with electric motor 

 drive there are fewer stoppages by reason of 

 hot bearings, leaky valves, worn or defective 

 eccentrics, and the many other weaknesses of 

 the engines. 



(9) The consumption of lubricating oils and 

 greases is decreased. 



(10) The exhaust steam is free from oil. 



(11) The cost of operation is decreased, as 

 will be shown later at more length. 



(12) There is complete freedom from large 

 steam mains, exhaust pipes, drain pipes, etc. 



(13) There is considerable economy in the 

 amount of live steam required, and conse- 

 quently redu(!ed consumption of fuel. This 

 statement has l^een douljted by some of our 

 colleagues, and we will endeavour to show its 

 correctness. 



With 70 to 80 lbs. initial steam pressure 

 and about 8 lbs. exhaust, as is usually the case 

 in Cuba, and with other conditions as are met 

 there, the best mill engines used at the present 

 time consvmie about 45 lbs. of steam per 

 brake H. P. per hour. A steam turbine of 

 the type installed in the Central Amistad con- 

 sumes about 29 Itjs. per brake H. P., per hour 

 under the same conditions. By actual test 

 it has been found at this Central, in spite of 

 the temporary and inefficient nature of the 

 installation, that the actual loss between the 

 turbine and the motor was only 1(3 per cent., 

 thus giving an efficiency of 84 per cent. This 

 statement we can confirm as follows: Effi- 

 ciency of generator, 94 per cent.; efficiency of 

 transmission, 97 per cent. ; efficiency of motor, 

 92 per cent, and combined efficiency equals 

 0.94x0.97x0.92 equals 0.8388. 



If it is assumed that there is an additional 

 loss of 4 per cent, in the initial or extra set of 

 gears, the total loss will be 20 per cent — that 

 is, an efficiency of 80 per cent. 



The total steam consumption, therefore, 

 required for the development of one H.P. on 

 the shaft of the first mill pinion; that is, on 

 the shaft of the gear wheel to which is geared 

 the motor shatt, 29-8 equals 36.25 lbs., thus 

 showing a saving of 9 lbs., or 20 per cent, 

 over the former method. 



This additional amount of high pressure 

 steam is rendered available for heating pur- 

 poses, and there is a consequent reduction in 

 the total amoiuit of fuel consumed. 



In other jjarts of the jjlant, the advantages 

 may be summarized by the statement that in- 

 creased efficiency, greater cleanliness, besides 

 greater ease of operation, of control, and of 

 supervision are everywhere obtained. These 

 advantages are especially realized in the case 

 of the many pumping units operated through- 

 out the factory where there are now installed 

 electrically driven centrifugal and triplex 

 pumps, which raise a water horse-power with 

 a steam consumption of 40 to 50 lbs. per 

 H.P. hour, whereas with the steam pumps 

 used hitherto a consumption of 150 to 200 lbs. 

 of steam for each horse-power of water raised 

 is everywhere considered the normal. 



In regard to the comparative cost of opera- 

 tion it may be said that considerable saving 

 is shown in the following items: Cost of 

 manufacture; maintenance; depreciation and 

 interest. 



At the Amistad factory, Cuba, electrifica- 

 tion has been carried out almost completely, 

 although the equipment has been gradually 

 and tentatively installed. The last step, that 

 fo the electrification of the grinding mills, was 

 only attempted for the last season, and so 



