Preliminary Treatment.—Picking.—Willowing Esparto.—Boiling Esparto.—Sinclair's Esparto Boiler.—Roeckner's Boiler.—Mallary's Process.—Carbonell's Process.—Washing Boiled Esparto.—Young's Process.—Bleaching the Esparto.
Preliminary Treatment: Picking.—Esparto is imported in bales or trusses, tightly compressed by hydraulic presses, and bound with twisted bands of the same material, much in the same manner as hay, except that which comes from Tripoli, which is bound with iron bands. The bands being cut, the loosened material is then spread out upon tables, partly covered with iron, or galvanised-iron, netting, to allow earthy matter or sand to pass through to a receptacle beneath. Here it is carefully picked by women and girls, who remove all roots, other kinds of grass, weeds, and heather. The material thus cleansed from impurities is transferred to the boiling-room. This careful preliminary treatment has been found necessary, since pieces of root and other vegetable matters which may be present are liable to resist the action of the bleaching liquor to a greater extent than the grass itself, and therefore produce specks, or "sheave" as they are termed at the mill, in the manufactured paper.
At some mills, however, as at the Horton Kirby Mills of Messrs. Spalding and Hodge, at South Darenth, for example, the cleaning of esparto is admirably effected by means of a willow, or esparto-cleaner, constructed by Messrs. Masson, Scott, and Bertram, which entirely supersedes the system of hand-picking. Having recently visited the mill referred to, we were enabled, through the courtesy of Mr. Sydney Spalding, to witness the action of this willow, which appeared to perform its functions with perfect uniformity, and to clean the grass most effectually. The rationale of the operation of willowing esparto may be thus described:—
Willowing Esparto.—A bale of the grass is unbound at a short distance from the machine, and the grass, which is in the form of small bundles or sheaves, tied with bands of the same material, is thrown by a woman on to a table or platform placed by the side of the willow, and a second woman, standing near the hopper of the machine, takes the bundles, a few at a time, and drops them into the hopper. The machine being in motion, in a few moments the grass, freed from its bands and dirty matters, appears in a perfectly loose condition at the wider end of the drum, and passes upward along a travelling-table to a room above, in the floor of which are the man-holes of a series of esparto boilers. During the passage of the loosened fibre, women standing on steps or platforms at the sides of the travelling-table are enabled to examine the material, and to remove any objectionable matters that may be present. Beneath the drum of the machine is a pipe, through which the dust and dirty matters are drawn away by means of a fan.
Boiling Esparto.—In the boiling-room at the mill referred to is a series of vertical stationary boilers, each about twenty feet high, and capable of holding about three tons of grass. The man-holes of these boilers pass through the floor of a room above, being nearly level with it, into which the cleaned esparto is conveyed, as described, by the travelling-table of the willowing machine. In this room is a series of compartments in which the willowed esparto is stored until required for boiling, when it is fed into the boilers by means of two-pronged forks provided for the purpose. The boiler being partially charged with caustic ley at 14° Twad., the esparto is introduced, and steam also, by which the esparto becomes softened, and thus a larger quantity of the fibre can be charged into the vessel. When the full charge of ley and esparto have been introduced the head of the boiler is securely fixed by means of its bolts, and steam then turned on until a pressure of about 20 lbs. to the square inch has been reached, which pressure is kept up for about three hours, when the steam is shut off and the blow-off tap opened. When the steam is blown off, the spent liquor is run off, and hot water then run into the boiler, steam again turned on, and the boiling kept up for about twenty minutes to half an hour, at the end of which time the steam is shut off and the blow-pipe opened. As soon as the steam has blown off, the washing water is run off by the bottom pipe, and the grass allowed to drain as thoroughly as possible. A door at the lower end of the boiler is then opened, and the grass emptied into trucks and conveyed to the washing-engines.
Fig. 15.
Fig. 16.
Sinclair's Esparto Boiler.—Another form of boiler, known as Sinclair's boiler, of the vertical cylindrical type, is shown in Figs. 15 and 16. It is constructed on what is termed the "vomiting" principle, but without the central vomiting-pipes generally used, and is fitted with one or more vomiting-pipes close to the side, two diametrically opposite pipes being used by preference. Steam jet pipes, with upwardly-directed nozzles, are fitted into the vomiting-pipes at points a little above the bends, between the vertical and horizontal parts. The liquid or ley thrown up the vomiting-pipes by the action of the steam is delivered from the upper ends of the pipes over a diaphragm or plate fixed near the top of the boiler, and the liquid is retained at a certain depth on the diaphragm by a number of small tubes fixed in it, and the liquid becomes well heated by the steam before overflowing down the tubes, which tubes also serve to distribute it uniformly over the fibrous materials in the boiler. A casing is formed at the bottom of the boiler, and in some cases extended more or less up the sides, and is supplied with steam, which should be superheated, or of high pressure. With this arrangement the heat in the boiler is maintained without the excessive condensation of steam and consequent dilution and weakening of the liquors which occurs in ordinary boilers. Figs. 15 and 16 are horizontal and vertical sections of one form of this boiler. The boiler is made with a vertical cylindrical shell, 1; with a flat top, 2; and flat bottom, 3; and there is an inner or second bottom, 4; the space between it and the bottom, 3, being for steam to assist in heating the contents of the boiler. At a little distance above the inner bottom, 4, there is the usual perforated horizontal diaphragm, 5, down through which the liquid or ley drains from the fibre. Two diametrically opposite vertical vomiting-pipes, 6, are formed by the attachment of curved plates to the cylindrical shell, 1, and these vomiting-pipes, 6, have their upper ends above a horizontal diaphragm, 7, attached by stays to the boiler top, 2. This diaphragm is perforated, and short tubes, 8, are fixed in the perforations so as to project upwards, by which arrangement the liquid, rising up the vomiting-pipes, 6, lies on the diaphragm to the depth of the tubes, 8, and overflows down through them all equally, so as to be uniformly distributed over the materials in the boiler. Steam jet nozzles, 9, are fitted in the lower parts of the vomiting-pipes, being supplied with steam by pipes, 10, from one of which a branch, 11, supplies steam to the double bottom, 3, 4. The steam jets cause the liquid to be drawn from under the perforated diaphragm, 5, and thrown up the pipes, 6, whereby a constant circulation of the liquid through the fibre is maintained. The liquors are drawn off by the pipe, 15. In another form of boiler Mr. Sinclair employs vomit-pipes formed of thin steel plates riveted to opposite sides of the boiler, and the liquid which drains through the perforated double bottom is forced upward through the vomit-pipes to the perforated plates above, through which it distributes over the material in fine jets. The boiler is capable of holding from 2 to 3 tons of esparto, and under a pressure of from 40 to 50 lbs. the boiling occupies about two hours.