double-effect 20 ℔, a triple-effect 30 ℔, and so on.[1] The
liquor to be concentrated is pumped from the storage tanks to the top or first effect of the Yaryan apparatus through a series of
multiple-effect heaters, corresponding to the number of effects in the machine, by means of which the liquor is heated to as near the boiling point as possible of the liquor in the tubes of the first effect.
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| The Mirrlees Watson Co., Ltd. |
| Fig. 7.—The Yaryan Patent Multiple Effect Evaporator. |
Live steam is introduced into the chamber surrounding the tubes of the first effect, and from the separator of the last effect the concentrated liquor is pumped to the incinerator.
Any form of incinerating hearth can be used in conjunction with the multiple-effect evaporator, but one very suitable to the continuous work of, and the high degree of concentration produced by, the Yaryan machine is that known as the Warren rotary furnace. This consists of a revolving iron cylinder lined with brick, about 12 ft. long by 10 ft. in diameter. The lining being 6 in. thicker at the inlet[2] than at the discharge, the interior of the furnace is conical in form so that the ash gradually works forward and is eventually discharged fully burnt into trucks for storage, or on a travelling band, and so carried automatically to the dissolving or lixiviating tanks. The strong liquor runs in at one end in a slow continuous stream; by the rotation of the hearth the burning mass is carried up the sides and drops through the flame again to the bottom, much in the same manner as rags do in a revolving duster. In this way all the labour required to stir the ash of the ordinary hearth is dispensed with, and the burning material comes continuously in close contact with the flame, a complete and thorough combustion being the result. The fire-box is situated at the delivery end of the furnace, and is mounted on trucks[3] so that it can be run back when cleaning or repairing the brickwork. The waste heat is utilized in raising steam in a steam boiler set behind the furnace, and often in keeping the thick liquor hot after leaving the evaporator and before entering the rotary furnace.
Paper-making proper from prepared pulp, whether of rags, esparto, wood or other raw material, may be said to begin with the operation technically known as “beating” which is carried out in one of the various forms of beating engine or “Hollander.” The object of the beater is to reduce the fibres to suitable lengths and also to beat or bruise themBeating. into a stiff pulp of sufficient consistency to absorb and carry the water necessary to felt them together on the wire cloth of the paper-machine. This operation is one of the most important and most delicate processes in the manufacture, requiring experience, skill and careful manipulation. Not only does every class of fibre demand its own special treatment, but this treatment has to be modified and varied in each case to suit the qualities and substances of the papers to be made from it.
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| Masson, Scott & Co., Ltd. |
| Fig. 8.—Taylor’s Patent Beater. |
Although there are now in use a great many forms of beating engine, they are all, more or less, modifications of the original Hollander, which in its essential details differs little from the breaking engine already described. There are usually more bars in the roll and plate than in the breaker; the bars of the plate are set at a slight angle to the fly-bars of the roll to act as shears in a similar manner to a pair of scissors. Bars and plates of bronze are frequently used for the higher grades of paper to avoid rust and dirt and to produce a softer and less violent action on the fibres. The time required for the beating process varies from 3 to 4 hours up to 10 and 12 and even more. Beating engines fitted with mechanical circulation by pumps or otherwise have been extensively adopted, more particularly for working esparto and the other substitutes for rags. Fig. 8 shows one of these beaters, known as the Taylor beater; the roll and plate are fixed above the trough of the beater, which has no partition or mid-feather, and from the lower end a powerful circulator or pump circulates the pulp through the beater and discharges it through a pipe in a continuous stream in front of the roll. In the pipe is fixed a two-way valve, so that when the beating operation is complete the finished pulp can be run into the stuff-chests of the paper machine. The advantages of this form of beater are that a quicker and more thorough circulation of the pulp takes place than when the roll has to do the double duty of making the pulp travel and beating it up at the same time, and thus tends to reduce the time of the operation. Also more bars can be fixed in the roll, increasing its effect on the pulp, and less power is required than when the roll revolves in the middle of the stuff as in the ordinary form of beater.
Beating engines of quite a different construction are now largely used in American mills, and also to some extent in Great Britain, These are known as “refiners,” and the most important forms are the Jordan and Kingsland beaters (so called from the names of the inventors), or modifications of them.
The first (fig. 9) consists of a conical plug or roll fixed on a shaft and revolving at a high rate of speed within an outer casing of corresponding shape; both the plug and the casing are furnished with steel bars parallel with the shaft, but set at slightly different angles, taking the place of the bars in the roll and plate of the ordinary beater. This conical plug or roll can be moved in either direction parallel to its axis and by this means the cutting action
- ↑ The figures given here are theoretical rather than actual. In practice a double effect is not capable of evaporating twice as much with 1 ℔ of coal as a single-effect, owing to loss of efficiency through radiation, &c.
- ↑ This was the original Warren principle, but has largely been abandoned in favour of a parallel brick lining throughout; the ash gradually works forward and is discharged as described.
- ↑ A later method is to build the fire-box on the descending side of the rotary furnace, while a specially constructed door and ash discharge shoot are provided at the ascending side, which gives access to the inside of the furnace and provides all the other essentials without the loss of heat which resulted from the portable fire-box, due to leakage between the box and the rotary furnace proper.
