A Practical Manual On Sea Water Distillation
With A Description Of The Necessary Machinery For The Process

MULTIPLE DISTILLATION. 193 Never be niggardly in the size of the boiler. It is far better for the boiler to be too large than too small. A liberal margin will always be gratefully remembered by the attendant in charge of the apparatus. 47. Therefore, in settling upon the size of the boiler, one must be guided by precedent as to former plants supplied. The following instance will show how the size of a boiler is arrived at for a treble distilling apparatus producing, say, 40 tons of water per day (24 hours), which is (approximately) 400 gallons per hour. In treble distillation it has been shown that the ratio of water produced is as follows :— 10 of primary water = 41 per cent. 8 of secondary water = 32’8 ,, 6’4 of tertiary water = 26 2 ,, 24*4 total . . . - 100-0 So that the primary water (i.e., the evaporation from the boiler) will be theoretically 41 per cent, of 400 gallons per hour, which equals 164 gallons ; this divided by 6’24 = 26 (nearly) cubic feet or H.P. It is, however, better to avoid H.P. estimates, and to base the calcula- tion on the number of pounds of water to be evaporated per hour. In the present case this would be 1,640 lbs., and the working pressure be, say, 80 to 100 lbs., but in settling the boiler for other types the working pressure would be somewhat different. 48. As a salt-water feed is under consideration, allow- ance must be made for (1) extra feed, to allow a proper blow off of brine ; and (2) loss of power due to scaling of heating surfaces. 13