SMOKE AND DUST ABATEMENT COTTRELL. 677 



a considerable portion of the time the sulphur dioxide in the gases 

 could be brought low enough without interference with the draft, 

 and during these periods the fans were stopped entirely, although the 

 gases still passed through them. 



At the rectifier building the current was received from the com- 

 pany's three-phase power circuit at 2,300 volts, 60 cycles, and after 

 being transformed up to from 25,000 to 30,000 volts under the con- 

 trol of the operator through variable resistance and induction regu- 

 lators was rectified into an intermittent direct current, as already ex- 

 plained, and distributed to the individual precipitating units. 



Figure 26 shows a cross section through one of these units or pre- 

 cipitating flues as first installed, and although forms of construction 

 have been greatly modified and improved in later installations, this 

 view still clearly illustrates the fundamentals of the method. The 

 double vertical lines represent the collecting or grounded electrodes, 

 each 6 inches wide by 10 feet high, made of No. 10 sheet iron. The 

 dotted lines represent the discharge electrodes, consisting of two 

 iron-wire strands between which was twisted the discharge mate- 

 rial, for which both asbestos and mica preparations were at various 

 times used in this plant. Each unit contained 24 rows of 24 elec- 

 trodes of each type. The collecting electrodes were carried by bars 

 connected directly to the frame of the chambers themselves, while 

 the discharge electrodes were spanned by springs between a system 

 of buss bars carried on externally placed insulators, as shown in the 

 figure. To the auxiliary chambers surrounding these insidators a 

 small regulated amoimt of air was admitted to prevent conductive 

 dust or fume from working back and settling on the insulators. 



The cam and shaker rod extending across the middle of the unit 

 was originally designed for the purpose of vigorously shaking the 

 electrodes, as it was greatly feared that the removal of precipitate 

 from the electrodes in units of this size might be one of the most 

 serious problems. In actual operation it was found, however, that 

 the electrodes could easily be shaken by hand from the top entirely 

 free from dust, the whole operation including cutting the unit in 

 and out of the system and the removal and replacement of its covers, 

 requiring only about 10 minutes, this having to be repeated everj'^ 

 six or eight hours, depending on the dust content of the gases. The 

 precipitated dust and fume as it fell from the electrodes was carried 

 by the conveyor in each unit to a common longitudinal conveyor, 

 which in turn discharged into cars carrying it away for treatment 

 and recovery of its values. 



Figure 27 is the interior of the rectifier house or control station, 

 showing the general arrangement of the apparatus and wiring. 

 Figure 28 shows the precipitation units in course of construction, 

 while figure 29 is a view over the tops of six out of the nine units 



