Document pppvqj5Z10v3YNqXVxrXwBgDk

m Ten Years' Experience BurniJ y 1 i 1 'I To SUPPLV STEAM ANO POWW whf they sre needed, plant engineer ha* to figure out many answers. Here's how we did just that (at ten yean at the 17,500-kw steam-electric plant of the Granby Consolidated Mining, Smelling & Power Co, Ltd. This plant, which serves the company's copper mine at Copper Mountain and its concentrator at AUenby, U os the SimUkameen Hirer neat Princeton In soothers British Columbia, about 200 miles east o( Van* couver. Mato equipment. The three boilers in the plant are: One 40,000-lb-per-hr chain-grate stoker* fired Stirling holler. Two 80,000-lb-per-hr Combustion Engl* neering boilers, pulverited-coil-fired as follows: No. 2, by two Raymond impact mills No. 3 by two Raymond bow) mills. In the power-generating plant are four steam turbine-generaiort: No. 1: SOO-kw Allis-Chalmers No. 2: 2000-kw Frazer-Chalmers ----------- -- wifi COAL BURNCRS: Wlndbex ond pulverited-cool burners of-No. 3 boiler ore in center background with No. 4 turbine on right. No woll divides boiler end turbine rooms | AllNlso-C. h3aalmnedr4a.: SOOO-itw end 10,000-kw I Steam conditions ar$ 250 psi, super* Out plant normally burn, lignite and iubbituniilnoui with high- heated to 600 F. Al) boilers are equipped with forced* and Induced* ash, high-mofiture content, but to lick a fuel shortage and draft fans, and Bailey manually oper* eted combustion control. Feed pumps high prices we bought a huge culm dump. This coal, with 36.2% are lurbine-drin-n 2-stage centrifugals. ash and 6600 Btu, Is pulverized and burned under our boilers Three circulating pumpa, of 10,000-gpm capacity each, provide cooling water for the condensers, one being enough In winter end two in July and August. One service and two fire pumps supply By A K EAirCOTT, Power Plant Superintendent Granby Coitfo/Jdoted Mining, Smelting A Power Co. water to service and fire lines. All pumps are motor driven, installed, in a pumphouse near the intake pond on the river bank. loco! Cool Sappty. When erected in 1937, the plant contained No. 1 and 2 ponded the plant by adding No- 3 boiler and No- 4 turbine. This boiler U a Combustion Engineering VU type larger than bituminous co&ls require, but pooi"grlndsbility and high ash sod boilers, and No. 1, 2 and 3 turbines. of 80,000-lb-per-hr steaming capacity, moisture content of local coals dictated Coal in tha area Is lignite and subbitu* similar to No. 2; the turbine is t 10,- ample mill capacity. minous, of high ash and moisture con* 000-kw Aliis*Chafmers unit. Experience at Cranby has proved that teat and 7300 to 9000 Bin per lb. Experience with the high-moisture subbituminoua and lignite coals can ha Experience with the origins! two lignite dictated a high mill temperature. burned successfully in suspension by pulverbed-coal-fired boilers taught (bat Therefore, the new boiler was equipped either the bowl- or Impact-mill pulver the coal's high Inherent moisture re* with a tubular heater for primary air iser. But ample mill capacity is re quired more drying than the plate-typo In Its first pass in odditlon to the plate quired along with a primary air heater preheater provided. A tubular primary preheater at the boiler outlet. Combus to supply 600'F air to the mil! btleta air heater was subsequently installed tion-air temperature Is raised to 375 F In spits of this coal's poor grindablllty in the second pats of No. 2 boiler to )a the plate preheater, which la ade mill wear need not be excessive. Bo supply high-temperature air to Its Im quate for secondary air. Primary air cause of high volatiles end low fixed pact mills. from this source U raised in the tubular carbon this coal Is readily Ignited; From 1937 to 1940, we purchased heater to 600 F; st this temperature it therefore, It is not necessary to pay too soma power from the public utility serving the district, fn 1940, we ex- gees to the pulverising mills. Two 4.8-ton-per-hr Raymond bow! mills fire the new boiler. These are much attention to fineness. We obtain a somewhat higher efi* cieney from No. 3 boiler, equipped 74 f?76) with bowl mills, then from No- 0 'OWE* M.y Ignite and Discarded Slack Coal tations precluded installing standard precipitators ahead of the induced- draft fans, s problem solved by install- ing wstcr-spray gas scrubbers between f&ns and stacks. Discharge from the scrubbers is pumped to e series of set tling ponds from which nothing but clear water returns to the river. The pulverited-coal-fired boiler furnaces have hopper bottoms, os in cross sec tion, p 78, to take care of the large quantity of ashes, which are removed '7- to -a hopper .outside the plant from which they are trucked away. Operating straight condensing with no process * steam requirements, the plant has no serious feedwater prob^ ferns, 'raw makeup water being only about 3% of total evaporation. The HaU system of internal treatment is adequate. Boiler water is tested dally for phosphate, alkalinity, sulphite and KjjiviBatNQ MtLU: Cool-puivarUlng mills thot too 600-f pilmory air are In base* I below burners. Bowl mills In foreground; Impoct mills in right background sulphate. An excess of phosphate is maintained to combat calcium car bonate hardneu and to prevent precipi tation of sulphates. An excess of sul phite Is maintained to scavenge .oxygen ftfeteh has impact mills. At first we at- Hboted this difference to the'mills, bat ttperience over s number of years leads ! (he conclusion thst for this class of Iinti one mill has practically no adru(t| over the other, i'No. 3.boiler, with four burners in* i of two, with a better primary air and a variable-speed hydraulic coupling on the induced-draft fan, cm be expected to show slightly higher efficiency than No. 2. U No. 2 had four toraen and impact mills of a larger die, we believe the difference In the two boilers' efficiency would be neg ligible. Where bituminous coals are burned, rhaescu remains constant over a longer 'period In a bowl mill, with one adjusttaest of the classifiers, than la an im* intelligently. We completely overhaul the bow! mills every 10,000 hr of oper ation or every 22,000 tons of coal, .whichever comes sooner. This over haul includes new liners, bull rings and grinding rolls. The Imped mills do not have as definite overhaul periods. The hammers are turned et 1200 to 1500 tons, and renewed at 2300 to 2500 tons. At each hammer renewal, liners are inspected and renewed where necessary. Cool Handling. Coal supplied by truek from local mines and by nil from outside Is delivered by elevator and screw conveyor to the boiler bunkers. Under normal load conditions from 1&5 to 200 tons ore burned dally. From 15,000 to 20,000 tons are usually stored In the ysrd adjacent to the plant This coal Is handled by dragline scraper. (torn the water. Caustic eoda controls desired alkalinity. We use dispersive tannin as on embrittlement Inhibitor end as a mechanical means of prevent ing scale. Amount of blowdown Is de termined by the sulphate reading* No. 2 and 3 boilers are taken out of service every four months for washing. On the first outago of the year, drum internals are removed to turbine firstpass and roof tubes. On the second out age, wsterwal! tubes ore turbined, and on the third outage, floor tubes. Thus, every tube in contact with radiant heat is turbined once a year. The downcom ers in the rear pau ere never turbined because washing them at each washout period is sufficient During each outage the induced-draft fen end other auxili aries are inspected and repaired. iptet mill. This Is an advantage (or the Ibowl mill, but with high-volatile low* cfiied-csrbon coala, fineness la not ol Jf paramount importance. On the other .'hand, impact mills here the advantage 1 simpler construction. Our experience > ha been that outages for an impact t' talll are more frequent, but of shorter l dorados than for a bowl mill, rl When burning pulverized coal the I'Sperattag staff keeps so accurate log *"*>1 hours' operation and tonnage I through the pulverizers. Without such t records, repairs could not be scheduled We have had some trouble with spon taneous combustion in the stockpile. Certain local costs cannot, be .stored deeper thao 6 ft Others give no trou ble when properly spread and com pacted by a bulldozer, even when piled to a depth of 15 to 20 ft When coarse and fines segregate in the stockpile, spontaneous combustion Invariably follows. As originally built the boilers were not equipped with flyssh precipitators. We soon found, however, that we had to reduce the fljrosh nuisance. Space Uml* Beilor Plont Operation. The table gives e fair-picture of the boiler avail ability, steam production and tons of coal burned by each boiler during the 10-year period, 193746. No. 1 boiler has become a standby since No. 3 was. installed. Us long outage in 1943 was due to renewal of the mud dram. In the boiler plant's operation we have had to Iron out the usual bugs. Slagging of the first-pass tubes was one of our most serious difficulties. Some improvement resulted from lowering the lirat-psss baffle to reduee gas ve- r. H. * ! i ir i |.r f i r i i i.; i. i:' :l < Oow I* May 1949 UT7| 71