Oct., 1922
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
By this means, it will be seen that we have a very definite means of separating the 100 per cent unit coal into its two constituents, fixed carbon and volatile matter, thus fulfilling the preliminary argument that a ratio to be of value must exclude all extraneous matter. These two unit values may be expressed either as a ratio or a percentage, since together they equal 100 per cent, but the percentage values are employed for plotting in diagrammatic form, so as to indicate the comparison to better advantage. Numerous additional illustrations of the practical value of the unit coal formula and the factors that accompany it might be given. For example, in Table IV, a certain area in Illinois is shown wherein the unit heat value for the coal produced averages 14,300 B. t. u. Assuming certain values for moisture, ash, and sulfur in the coal as marketed, a heat value for a number of average commercial conditions for the coal as delivered has been derived by reversing the calculation, starting from the accepted unit coal value. If the output from any specific mine in that region is known to have a unit coal value of 14300 B. t. u., the calculated values for the various assumed amounts of impurities will be accurate to
923
within 0.5 per cent of the calorimetric indications, entirely comparable to duplicate results by the same operator on the same sample. Many methods for utilizing such a table or other values deducible by the same formula will readily suggest themselves-such as checking guaranties on coal bids, verifying the samples submitted as to their agreement with the gross shipment, detecting errors in calorimetric results, calculating calorific values in the absence of an instrument, obtaining the variable in heat value for each unit of ash, being exactly 154 units in this particular tabulation, etc. One other table is submitted as having possible value in matters of every-day concern. In Table V, Column A, are listed the values for the unit coal in per cent of the coal as received. These vnlues are derived simply by application of the unit coal formula incorporating, of course, “W” for t,he moisture present. Column B gives simply the reciprocal of the values under A and represents the number of pounds of each sample which would be required to furnish 100 lbs. of actual combustible or pure coal substance.
The Electric Steam Generator’ By Horace Drever ELECTRIC FURNACE CONSTRUCTION CO., 908 CHESTNUT ST., PHILADELPHIA, PA.
Electric generation of steam has been developed i n principle and practice to a definite place i n engineering work. Its main features are settled. It has been proved simple, reliable, and safe in daily operation. It may be profitably utilized i n localities where fuel cost is high and hydroelectric power is availabie on a low firm-power rate. This device m a y weli be used by central stations to consume their surplus power, and by others who have surplus power under a f i r m power contract. Among the advantages inherent in the electric steam generator are the elimination of f u e l transportation, storage, and handling: elimination of ashes, smoke, or dirt; its ready adaptability to the use of surplus power; and its constant readinessfor service without large standby losses. It can be located where it is most desirable and requires a minimum of attention. Long pipe lines are unnecessary when this apparatus is used.
LARGE number of small-capacity units of various types of the electric steam generator have been in use for several years in Europe, where the high cost of fuel and the availability of hydroelectric energy offer extremely favorable conditions for fiuch equipment. The large-capacity units, producing up to 2500 boiler h. p., such as are now in successful operat,ion on this continent, however, are entirely due to the independent development of Mr. F. T. Kaelin, of Montreal. While the late business depression made available a large surplus of hydroelectric power in many localities and gave cause for the installation of many large units, the actual operation of these units has proved that even where power is available only part of the day, the installation of an electric steain generator may prove a paying investment. In fact,, it is quite likely that users of hydroelectric power who are operating a t less than 90 per cent load factor, and who are burning coal for steam purposes, upon investigation
A
1
Received April 5, 1922.
will find that a definite saving may be made by the conversion of their off-peak power into steam. The principles underlying the electric generation of steam are simple and are quite well known, but for a complete exposition of them the reader is referred to a recent paper by I?. T. K a e l h 2 It will be sufficient for the purpose of this short article to recapitulate them here. Steam is generated by passing alternating current directly through the water, which is heated because of its resistance to the current. Usually high-tension power i8 employed. The amount of heat generated by the passage of 1 kw. hr. of electric energy is equal to 3412 R.t. u. The heat content of 1 lb. of steam at, say, a pressure of 135lbs. per sq. in., is 1193 €3. t. u., and, if we assume a feed-water temperature of 150” F., the total heat to be supplied will be 1193-((150-32) or 1075 B. t a u . One kw. hr., will therefore produce 3412/1075, or 3.17 lbs. of steam, no heat loss considered. On large units the heat loss is very small and the thermal efficiency can safely be taken as 98 per cent. On this basis, one kw. hr. will produce 3.10 lbs. of steam. Under average conditions, 1 lb. of coal of about 12,000 B. t. u. evaporates 8 lbs. of water, and 1 ton, 16,000 lbr. of water. The electric energy required to evaporate the same amount of water is equal to 16,000/3.10=5161 kw. hr.=215 kw. days=0.59 kw. yrs. =0.8 h. p. year. In short, 215 kw. in an electric steam generator are equal to 1 ton of coal per clay, burned under average conditions of boiler efficiency. Since the boiler horse power is defined as the evaporation of 34.5 lbs. of water from and a t 212” I?. per hr. and represents 33,479 B. t. u. per hr., one kw. hr. being 3412 B. t. u. and at an average efficiency of 98 per cent equal to 3344, the relation of b. h. p. to kw. hr. is almost exactly 10 : 1. or an electric steam generator of 1000-kw. capacity is equal to a boiler of 100 b. h. p.
* “Generation of Steam by Electricity,” J . Eng. Insf. Calzada, January 19, 1922; see also F. A. Lidbury and F. A. Stamps, “An Electric Steam Generator for Low Voltage.” Trans. A m . Electvochem. Sac., 40 (1921).77.
924
THE .IO URA'AL OF I N D USTHIAL AND ENGINEERING CHEMISTRY
E:luAric itcam generators have been huilt recmtly in sizes up to 25,000 Lw., or 2500 b. h. p. The photographs shoa7 sevrral vesy sucressful installations. The installation ir inex
Vol. 14, No. 10
the other, but onc of saving good dollars and cents that are being paid out when there is already a means at hand to accompliih the purpose, even though ;lie latter is the more expensive method under normal conditions. Instances are on hand to prove tlist very often the electric steam generator can pay for itself in a few months and thereafter save the coal bill when conditions are such as outlined in the preceding paragraph. One installation saved its cost in about 2 mo., and is now helping the owner to meet the competitive conditions of the period hy the saving it effects in the coal hili.
As m OFF-PEAKLOAD The importance of good load-factor to power stations is undisputed and fundamental. That this is well recognized is shown by the lower rates granted by many central stat.ions for night loads. By installing the electric steam generator to run on off-peak power, weekend power, etc., the loadfactor of the system can he boosted, a very favorahle rate can be made, and all parties to the contract will be benefited. In this case the steam generator will be used as auxiliary to the exkt.ing boiler capacity of the plant. There seems to be a very bright future for such applications in many hydroelectric systems. AS A REPLACEMENT OB EXISTINQ PLANT, OR AS ALTEHN.4TNE TO
NEWPUNT
In the preceding discussion, the generator bas been considered without regard to the absolute relative costs of steam
Ill0 1--20.000 Kw.- 2000 B. H. P. E~.rcnrcSTSAMCINBBAIOX AT Pnrm MlLL Power SuppIr-RMlO volis-3 pharr; pressure-185 Ibs.
pensive and econiisnicnl of space. About 100,000 kw. have been installed or are being built for various plants in Canada and the United States. While the electric steam generator is of too recent development to enable u s to make an authoritative forecast of its future, we can indicate certain uses and ascertain tho outlines of its economic field. European practice applies this type of apparatus to the paper and pulp industries in Scandinavia, where parallel conditions with our northern states and Canada exist; to the chemical and other industries of the Rhone valley and the territory contiguous to the Alpine water powers. Briefly, wherever abundance of hydroelectric power and high-cost fuel go hand-in-hand, tho generation of steam by electricity is probably economical. Such conditions are found in the tcrritories mentioned above and in the western United States, Brazil, Chilc, and Japan. A TEAIPERATORE EXPEDIENT D U ~ I N C Psnrons Imosmr~r,SLACKNESS
OF
The world is passing through a period of subnormal husincss activity. With demaod for their output below the capacity of the plant, many mills are forced to e.ut costs to the last cent t,o survive at all. As hydroelectric power bought under a firm rate is usually contraeted for in amount to take care of the plant's normal requirements, some of this is being paid for but not used when the mill is running below capacity. If coal is being burned to provide steam for drying or heating while firm power is going to waqte, although paid for, the electric steam generator can be installed to use the excess power and save the cost of an equivalent amount of coal. Here it is not a question of the one method being cheaper than
FIG BAILBY BY M m n CRART BROU GSNBRATO~ Saowri XN F'ro 1, ssowI N 0 U T * 0s Sn3*U n o w bND PPBSSOXB
produced by the two methods, but under this heading these will be included. Whenever steam is used for any purpose other than power, the fuel-burning boiler can be replaced by the electnc steam generator, provided the relatiom of cost are in favor of the latter. The quality of steam, its pressure, and the amount are exactly thc same for both methods, with the one exception that the electric generator does not deliver superheated steam. At ftrst sight it might appear that electric power would have to be extremely cheap and coal very high indeed before serious consideration could be given to the replacehent of an installation of coal boilers. On a strictly B. t. u. basis, 1 lb. of coal is equal to about 4 kw. hr., but when the relative efficiencies of application are
Oct., l!m
THE J ~ I U R ~ V : iOI" L 1N.DUSTRIAL A N D ENGINEERING CHEMISTRY
925
on the cm at the plant, on a basis of fuel cost only, electric power would have to be as cheap as 2 mills per kw. hr. The element of fuel cost is not the only one entering into the problem, hovever. Labor, interest on investment, and fixed cbarges generally will be much greater for the coal plant than for the electric generator, and in fact, aside from power cost, every item will be greater for coal plants than for the electric generator. One man can easily do all the work connected Wrth the latter, except major repairs, for units totaling BS muoh as 5ooo b. h. p., and where the load is fairly constant, one attendant can operate a plant of twice this size. I-co*L-P'meD
FlANV
cost Of plant: 8 - 4 0 h.D. stoker-fired bofler;-$GW
(0)
........... Buildings and shck.. ...................... ram, I ~ V B S M H N T . . ....................
(a) Labor:.
No. of
TOl*L8 $192,000.00 40,000.00 $232,oo0.00
Hourly Total Cost PEI Dag
Number of men and duties Men Hours Rata 1 boiler house foieman on ihiit 1 watc 1 foiemnn of coal handling. Zcoal handlersoneaChshift.. I ash handler on each shift. ..
..
2 helpersoneachshift..
Yearly cost, 385 days R e . 3-5OOO Kw.-500 B . II. P . ELICTWIC S r m x G n ' h - E n ~ l o ~ I ' yilppiy--.2znn ~ ~ ~ voitr--3 ~ phase: presssui-isn ibs.
considered the difference is not so marked. If the average efficiencyof small or medium-sized boiler plants is taken as 65 per and that ofthe electric generator as 98 per cent, we find that 1 lb. of coal of 12,000 H. t. u. is equivalent to 2'/a kw. hr. Thus, to compete with con1 at $10.00 per ton
x
24 9
0.90 0.66 0.65
121.~0 15.80 5.85
48
0.55
26.40
24
0.65
72 48
0.66
13.20 48.80
24
.....
-
1155.85..
.
249
2R."
0.55
....
1155.86 $56,885.25
(c) Fvel coat: At an average boiler and furnsce emciency of 65 per cent. the plant will bum about 80,000 tons of coal per year. Assuming thii coal
coets $10 per ton io the plant, the snnual coal bill will be $800.000.00. (d) Fired charges (interest, depreciation. t ~ x e and ~ , inruraocc) will approximate 14 per cent,, 01a tots1 yeearly charge of $32,480.00. Combining the vsliious items and making allowances for maintenance sod suppIies:
I. 56,885.25 eno,ow.oo
Maintenance and supplies estimated TO~A ANNUAL L Cosr
.
32,480.00 8.WO.W
1 8 ~ ~ ~ 5 . z 5
zag machinery should lesitimately be charged against the eost of cosl, but zm account will be takes of it here.
II-ELBcTR~~ GBN&RATOR (0)
Cost 01 pianf including oecesery feed pump. hot
.. 12,000.00
( b ) Labor:
$53.000.00
1;man per shift - 60-24
man hin.=$14.40 per
day Annual Ltbor cost, 365 X 14.40.. (r) Fower:
..............
B
5,256.00
iovesiment,BE in thc case of the coil boiler plant Labor..
............. ..........
Tor& A N N V UCosr.. ...........
$657,875.00
The savingin favor ofthe electricgenerator will be $69~.365.25-$657,876. or 637,489.25, which sum will amortize the plant in less than 2 Y ~ E .
Fre. C 1 3 0 0 Kw.--i30 B. Ii. P. E~ncrarcSTa~arG ~ N B R A T O R Power supply-2200 volts-3 phase: preseure--125 fbr.
___
I Fernaid and Orrok, "Bogineeiiug of Power Plants,.' p. 158; Henry Kreisingei. "Saving Coal in Boiler Plants,.' Unimrsnl En#.,1919.
I Compsrison of 8 coal-flred boiler installatioo sad an electric steam generator in a typical p ~ p e mill. r The coal plant will conrist of eight 400h.p. boilers equipped with nstvral draft stoken and mal and ash handling apparatus. The figures given sre assumed to m ~ e ran average plant. neither the worst nor the best. Coal will be assumed to cost 510 per ton and electric power $15 per e. h. p. year. s Does not iodude piping, since this item will be appmximately the same for both types ofplnnf. 8 Loren E. Iiibbard, Tech. Arsoc. PePnr, 4th series. P. 19. x Fernald and Orrok,Loc. &it,, 255; "Stsndard Handbook for Electrical
EngiCtCerS.l'
