FIG. 25.
Of late years great improvements in the form of the boiler have been introduced. Fig. 25 is an illustration of Roeckner’s Patent Boiler. The vomit pipe is outside the boiler. Steam entering by the cock D, forces the liquor up the vertical vomit pipe and distributes it over the grass. The pipe K is used for heating the liquor at the commencement of the operation by means of waste steam. F F are gauges for indicating the height of the liquor. The grass is put in by the opening G. The pipes A B and C are for the supply of {94} steam, strong lye and water. The boiled grass is discharged by the circular door E.
The boiler holds three tons of grass and the boiling is completed in about 2 1⁄2 hours, the pressure being about 35–40 lb. per square inch. It is claimed that by its use a saving both of time and soda is effected.
FIG. 26.
Sinclair’s Patent Boiler is shown in Fig. 26. The vomit pipes, of which there are two, are made of thin steel plates {95} riveted to opposite sides of the boiler. The liquor drains through the perforated false bottom, and is then forced up the vomit pipes above the perforated plates through which it is distributed over the grass in a number of fine jets. The boiler is charged by the door e and emptied by j. The small cock a is used as a blow-through cock; the opening b is used for blowing-off steam when emptying the boiler; c for letting in caustic soda lye; d for water. Steam enters by the small branch of the T pipe at the bottom of the boiler, the other, g being used for running off the waste liquor. A boiler holds from two to three tons of grass, and a boiling is completed in about two hours at a pressure of 40–50 lb. per square inch.
The two forms of boiler above described possess the obvious advantage of having the whole or nearly the whole of the interior available for holding grass; the boilers can therefore be made to hold more, and the boiling is moreover much more evenly accomplished.
Washing.—The boiling being completed, the steam is allowed to escape and the liquor to collect at the bottom of the boiler where it is run away by the pipes placed at the bottom for the purpose. Water is then run in and steam turned on for a short time; this is also run off, and the grass drained as completely as possible. The boiled grass is then emptied into trucks and taken away to the washing engines. These resemble those already described under rags.
During the process of washing, a certain amount of the shorter fibres find their way through the meshes of the wire-cloth. In addition to this a large proportion of the cellular tissue surrounding the fibro-vascular bundles (see Fig. 12, p. [57]) is carried away. If the wash-water be examined under the microscope, it will be seen to consist largely of this cellular matter. Though this entails a certain loss of cellulose, its removal is in other respects advantageous, as it is possessed of hardly any “felting” properties, and it is moreover exceedingly difficult to bleach.
The amount of fibre actually obtained in practice is but little below that contained in the grass. A certain loss is {96} inevitable, but this probably does not exceed 1 or 2 per cent.