THE DRY PURIFICATION OF COAL GAS
599>
D = depth (in feet) of oxide in the whole set of purifiers. Thus, if depth of oxide in eacli box is 4 feet and there are four boxes, then D = 16.
C = a factor dependent upon the number of boxes in the set. Thus for two-box series C = 4, three-box series C = 8, four-box series C = 10.
The value of S is determined from the following table :—
Grains H»S per 100 c. ft. unpurified gas. Factor S.
1,000 or more .......... 720
900 ............... 700
800 ............... 675
700 ............... 640
600 ............... 600
500 ............... 560
400 ............... 525
300 ............... 500
200 or less .......... 480
The above formula, it will be noted, gives the necessary capacity as much smaller than that commonly worked to in this country. For instance, if consideration is given to a works with. a make of 1,800,000 cubic feet per maximum day, the following resiilts are obtained :—
(«) By the author’s formula (page 21) 900 square feet area for each box.
(b) By the Steere formula 600 „ „ „
General Construction
The body of a purifier is invariably constructed from cast-iron plates, bolted together, the joints being made in the usual manner from borings, or faced and red-leaded (see page 523). On the other hånd, it is essential that the lid of the vessel should be liglit, to which. end it is built up from steel or wrought-iron plates (usually J inch thick) and suitably braced with rolied steel sections. Owing to the necessity of maintaining a clear passage for the cover in the water-lute, the flanges of purifier plates are frequently arranged ina somewhat uncon-ventional manner. The construction of the lute, showing the way in which the flange changes over from the exterior to the interior, and the method of bolting on the separate lute plate and the base plate, will be followed from Fig. 360. It should be noted that in the case of a ground-level vessel the flanges would be internal, and not external. In this way the joints and bolts, being inaccessible from below, can be attended to from the interior. So far as the
thickness of the cast-iron plates employed is con-cerned, the following figures may be taken as satis-fying all requirements :— '
K3lgaiEaiE3IEgl»1
Fig. 360.—Purifier Side Plate (Cast-iron).