PAPER MILL MACHINERY
In the case of common printings and writings, which form the great
bulk of the paper made, the possibility of one mill competing against
another, apart from the important factor of the cost of freight, coal,
and labour, is almost entirely determined by the economy resulting from
the introduction of modern machinery.
The equipment of an up-to-date paper mill, therefore, comprises all
the latest devices for the efficient handling of large quantities of
raw material, the economical production of steam, and the minimum
consumption of coal, matters which are of course common to most
industrial operations, together with the special machinery peculiar to
the manufacture of paper.
The amount of material to be handled may be seen from the table on page
215, which gives the approximate quantities for the weekly output of a
common news and a good printing paper.
_Economy in Coal Consumption._--The reduction to a minimum of the
amount of coal required for a ton of paper has been brought about by
the use of appliances for the better and more regular combustion of
the coal, such as mechanical stokers, forced and induced draught, the
introduction of methods for utilising waste heat in flue gases by
economisers, and the waste heat in exhaust steam and condensed water
by feed-water heaters, the adoption of machines for securing the whole
energy of the live steam by means of superheaters, adequate insulation
of steam mains and pipes, high pressure boilers, and engines of most
recent design.
The firing of steam boilers is now conducted on scientific principles,
the coal being submitted regularly to proper analysis for calorific
value, the evaporative power of the boilers being determined at
intervals by adequate trials, the condition of the waste flue gases
being automatically
TABLE SHOWING THE MATERIALS REQUIRED FOR NEWS AND PRINTINGS.
-----------------------------+--------------+------------------
-- | Common News.| Good Printings.
-----------------------------+---------------+-----------------
Weekly output of paper, say | 600 tons | 250 tons
Mechanical wood pulp, moist, | |
50 per cent. dry | 800 " | Nil.
Chemical wood pulp, dry | 200 " | 150 tons
Esparto | Nil. | 200 "
Soda ash | Nil. | 16 "
Coal | 600 tons | 800 "
Lime | Nil. | 45 "
China clay | 60 tons | 25 "
Bleach | Nil. | 30 "
Alum, rosin, and chemicals | 20 tons | 20 "
Water, per ton paper | 8,000 gallons| 40,000 gallons
-----------------------------+---------------+-----------------
_The Sarco Combustion Recorder._--This instrument is a device which
automatically records the percentage of carbonic acid gas in the waste
gases from boiler furnaces. The flue gases are analysed at frequent
and regular intervals, and the results of the analysis can be seen on
a chart immediately, so that it is possible to determine the effect of
an alteration in the firing of the boilers within two minutes of its
taking place. The apparatus is rather complicated, but the principle
upon which it is based is simple.
Measured quantities of the flue gases are drawn into graduated glass
tubes and brought into contact with strong caustic soda solution, which
absorbs all the carbonic acid gas. The remaining gases not absorbed
by the caustic soda are automatically measured and the percentage of
carbonic acid gas registered on the chart.
The use of suitable boiler feed-water is also an important factor in
modern steam-raising plant. The hot condensed water from the paper
machine drying cylinders, and exhaust steam from the engines and
steam-pipes, is returned to the stoke-hole to be utilised in heating up
the cold water which has been previously softened by chemical treatment.
[Illustration: FIG. 55.--Conventional Diagram of a Water Softening
Plant.
A. Water supply.
B. Regulating tank.
C. Lime mixer.
D. Soda tank.
E. Settling tank and filter.
F. Outlet for softened water.
]
_Water Softening._--The water softeners available on the market are
numerous, and as each possesses special advantages of its own, it would
be almost invidious to select any one for particular notice.
They are based upon the principle of mixing chemicals with the water
to be treated, so as to precipitate the matters in solution and
give a boiler feed-water free from carbonates and sulphates of lime
and magnesia. The chemicals are added in the form of solutions of
carefully regulated strength to the water, which flow in a continuous
stream into a tank. The flow of the water and chemical reagent is
adjusted by previous analysis.
The various machines differ in details of construction, and in the
methods by which the mixing of the water and reagents is effected. The
object to be achieved is the complete precipitation of the dissolved
salts and the production of a clear water, free from sediment, in an
apparatus that will treat a maximum quantity of water at a cheap rate
per 1,000 gallons.
The process needs proper attention. The addition of reagents in
wrong proportions will do more harm than good, and possibly result
in hardening the water instead of softening it. The following may be
quoted as an example:--
----------------------+-----------+-----------+------------
Composition of Water. | Before | After | Change.
| Treatment.| Treatment.|
----------------------+-----------+-----------+------------
Calcium carbonate | 13·863 | 38·920 | 25·057 gain
Calcium oxide (lime) | 0·0 | 14·300 | 14·300 "
Calcium silicate | 2·062 | 3·591 | 1·529 "
Calcium sulphate | 1·625 | 2·121 | 0·496 "
Magnesia | 0·0 | 0·266 | 0·266 "
Ferric oxide, etc. | 0·447 | 0·987 | 0·540 "
+-----------+-----------+------------
Scale forming mineral| 17·997 | 60·185 | 42·188 gain
+-----------+-----------+------------
Calcium chloride | 1·331 | 2·114 | 0·783 gain
Magnesium chloride | 0·672 | 0·0 | 0·672 loss
Sodium chloride | 0·478 | 0·476 | 0·003 "
+-----------+-----------+------------
Soluble salts | 2·482 | 2·590 | 0·108 gain
+-----------+-----------+------------
Total mineral matter | 20·479 | 62·776 | 42·297 gain
+-----------+-----------+------------
Carbonic acid gas | 9·71 | 0·0 | 9·71 loss
Oxygen gas | 0·66 | 0·66 | 0·0 "
----------------------+-----------+-----------+------------
Treatment required: 1·8 lbs. of lime, 0·2 lbs. soda ash per 1,000
gallons. Apparently 5·5 lbs. of lime were being used and no soda
(Stromeyer).
_Superheated Steam._--The effective application of the energy of the
high pressure steam is probably one of the most important problems in
paper mill economy. The use of superheated steam is being extended
in every direction, and, in addition to the advantages obtained in
the steam engine itself, its wider possibilities for the boiling of
esparto, wood, and fibres generally have been noted. The following case
may be quoted as the result of a trial at a paper mill, showing for
stated conditions the advantages of superheated steam:--
--------------------------+-------------+----------
-- | Superheated | Ordinary
| Steam. | Steam.
--------------------------+-------------+----------
Duration of test hours | 26 | 34
| |
Coal consumed (lbs.)-- | |
Per hour | 610·5 | 661·5
Per 1 h.-p. hour | 1·83 | 2·08
| |
Water evaporated (lbs.)-- | |
Per hour | 4,832 | 5,679
Per 1 h.-p. hour | 14·55 | 17·8
From and at 212° F. | 8·7 | 8·94
| |
Steam, temperature F. | 464 | 334
Pressure | 90·3 | 90·8
| |
Steam engine-- | |
1 h.-p. total | 331·5 | 323·2
Temperature F. | 381·8 | 333·8
| |
Coal used per 1 h.-p.-- | |
Per hour at boiler | 1·83 | 2·08
--------------------------+-------------+----------
This appears to show a saving of 12 per cent.
_Gas Producers._--The substitution of gas for steam in the paper mill
has not yet proved a success. The fact that heat is required for the
drying cylinders of a paper machine, and that the heat is most cheaply
and readily obtained in the form of exhaust steam from the engines
driving the paper machine, militates considerably against economies
which might otherwise be possible. The difficulties of heating such
cylinders, or rather of properly controlling and regulating the
temperature by any other means than steam, may easily be surmised.
Gas engines of over 200 h.-p. seem to give considerable trouble at
present, but no doubt in course of time the required improvements will
be effected.
It is generally supposed that gas producers can only be economical
when utilised for the production of gas on a large scale, and for
distribution to engines of smaller capacity than the main steam engine
required in a paper mill. The peculiar conditions of the manufacture
of paper do not appear to be favourable to the adoption of the gas
producer system in its present form.
_Motive Power._--The paper-maker has taken advantage of every modern
improvement in steam engines for the purpose of reducing the cost of
motive power. Amongst other alterations in this direction the use of
a high speed enclosed engine and the employment of the modern steam
turbine may be noted.
In the enclosed engine the working parts are boxed in by a casing
fitted with oil-tight doors. The cranks and connecting rods splash into
the oil, which is thus thrown about in all directions, so as to ensure
sufficient lubrication. Another feature of this engine is the variable
speed, and it is possible to run the paper machine at speeds varying
from 100 to 500 ft. per minute without the use of change wheels.
_Electrical Driving._--The application of electricity for motive power
has made steady advances in the paper mill. At first it was limited
to the driving of machinery in which variations of speed or load were
not required to any large extent, but of recent years beating engines,
calenders, and paper machines have all been fitted with electrical
drives.
[Illustration: FIG. 56.--An "enclosed" Steam Engine.]
The following details relate to the installation at the Linwood Paper
Mills:--
The installation consists of 250-K.W. steam dynamos. The engines are
Willan's high speed triple expansion, working with a boiler pressure of
250 lbs. per square inch at the stop valve, the steam being superheated
to give a temperature of 500° Fahr. at the engine. By means of jet
condensers a vacuum of 25 to 25½ inches is obtained on the engines.
The two boilers are of the Babcock type, and have 3,580 square feet of
heating surface each. The furnaces have chain grate stokers, and the
boilers are arranged with their own superheaters. The motor equipment
consists of eight 80, two 50, and ten 25 B.H.P. motors.
Six of the 80 B.H.P. drive the beating engines, and it has been found
that the motors readily respond to an overload of 50 per cent. without
beating or other trouble. To remedy the excessive and sudden variation
a belt drive was adopted. An 80 motor drives the pulp refining engine.
The two paper-making machines have each two motors, one a 25 and a 50
and the other two 25 B.H.P. motors. The speed can be regulated with
exactitude. The auxiliary plant of the paper-making machine, pumps,
agitators, etc., is worked from lines of shafting driven by motors.
Calender motors are of the variable speed type, being designed to
run from 100 revolutions per minute to 600 revolutions per minute.
Variations from 300 to 600 revolutions per minute can be regulated by
the shunts, the loss being negligible. Several of the motors are geared
up to the various machines, as is the case with the calender.
As regards cost, the capital outlay on the 500-K.W. generating plant,
including engines, dynamos, boilers, condensers, steam pipes, filters,
etc., and all engine room accessories, was £9,500.
[Illustration: FIG. 57.--An Electrically Driven Paper Machine.]
In addition to the above, the plant also contains a Parson's steam
turbine of 1,000 K.W., driving two continuous current dynamos.
[Illustration: FIG. 58.--Diagram of the "Eibel" Process.]
_The Eibel Patent._--One of the most important improvements in
connection with the manufacture of newspaper is the Eibel process,
designed to increase the speed of the machine and to reduce the amount
of suction at the vacuum box. In the ordinary machine the wire has
usually been arranged to move in a horizontal plane. In some machines
means have been provided for adjusting the breast-roll end of the wire
to different elevations to provide for dealing with different grades
of stock, but the wire has never hitherto been so inclined as to cause
the paper stock to travel at a speed, under the action of gravity, to
equal or approximate the speed of the wire. In all previous methods
of working, the wire has for a considerable portion of its length,
starting from the breast-roll, drawn the stock along in consequence of
the wire moving much faster than the stock, and the stock has waved, or
rippled, badly near the breast-roll end of the wire. This has gradually
diminished until an equilibrium has been established and an even
surface obtained, but not until the waving or rippling has ceased at
some considerable distance from the breast-roll have the fibres become
laid uniformly, and the machines have therefore necessarily been run
slowly to give ample time for the water to escape and for the fibres
to lie down so as to make them a uniform sheet. In many cases the
breast-roll has been raised 14 or 15 inches, and the stock rushes, as
it were, downhill.
As, during the formation of the paper, the stock and the wire
practically do not move relatively to each other, there is no drag
of the stock upon the wire; consequently there is a more rapid and
uniform drainage of the water from the stock, the full influence of the
"shake" is made effective to secure uniformity in the distribution and
interlocking of the fibres, and the regularity of the formation of the
paper is not disturbed by waves or currents, which would otherwise be
caused by pull of the wire upon the stock.
This ingenious device is now working successfully in many paper mills.
_Machinery._--In setting out the plant necessary for a paper mill
which is designed to produce a given quantity of finished paper, the
manufacturer takes into consideration the class of paper to be made
and the raw material to be employed. The following schedule has been
prepared on such a basis:--
PLANT AND MACHINERY FOR HIGH-CLASS PRINTINGS.
_Paper._
High-class printings made of wood pulp and esparto, used alone or
blended in varying proportions as required. Quantity, 250 tons
weekly.
_Raw Material._
Esparto; chemical wood pulp.
Quantity: esparto, about 200 tons; wood pulp, 150 to 160.
China clay and usual chemicals.
In the estimation of materials required for the production of about
250 tons of paper, it is assumed that the 200 tons of esparto fibre
will yield 90 tons bleached esparto fibre, and that the mechanical
losses which take place during manufacture are counterbalanced by the
weight of china clay added to the pulp. These conditions naturally vary
in different mills, but such variations do not affect the schedule of
machinery.
_Unloading Sheds._
2 steam or electric cranes for handling fibre, clay, alum, bleach,
rosin, coal, and finished paper.
1 3-ton weighbridge.
1 5-cwt. platform scales.
_Steam Plant._
6 8-ft. by 30-ft. Lancashire boilers.
Fuel economiser.
Feed-water pump and tank.
Water softening apparatus.
1 500-h.-p. main steam engine, for fibre departments and beater
floor.
_Chemical Department._
Hoist for clay, alum, bleach, lime, &c.
4 causticising pans, 9 ft. diameter, 9 ft. deep.
2 storage tanks.
2 chalk sludge filter presses.
2 clay-mixing vats, 6 ft. diameter, 6 ft. deep.
1 starch mixer, 6 ft. diameter, 6 ft. deep.
1 size boiler, 8 ft. diameter, 8 ft. deep.
3 size storage tanks, 1,000 gallons each.
3 bleach-mixing vats.
3 bleach liquor settling tanks.
2 clear bleach liquor storage tanks.
1 alum dissolving tank.
_Recovery Department_:--
_Soda._
1 multiple effect evaporating plant.
1 rotary furnace.
4 lixiviating tanks, 2,000 gallons each.
2 storage tanks for clear liquor from lixiviating tanks, 20,000
gallons capacity.
_Fibre._
2 tanks for receiving machine backwater.
2 Fullner's stuff catchers, or some other system of treating
backwater.
2 filter presses.
_Esparto Department._
1 esparto duster.
Travelling conveyer for cleaned esparto.
6 Sinclair vomiting boilers, each of 3 tons capacity.
2 measuring tanks for caustic liquor.
4 washing engines, 15 cwt. capacity.
6 Tower bleaching engines.
1 presse-pâte.
10 galvanised iron trucks.
_Wood Pulp Department._
4 pulp disintegrators and pumps.
4 Tower bleaching engines.
4 washing tanks or drainers.
6 galvanised iron trucks.
_Beater Floor._
8 1,200-lbs. beating engines.
2 Marshall refiners.
6 galvanised iron trucks.
_Paper Machine Room._
2 paper machines, 106 in. wide, with stuff chests, strainers, and
engines complete.
1 paper machine, 120 in. wide, with stuff chests, strainers, and
engines complete.
Patent dampers for each machine.
_Calendering Room._
2 110-in. supercalenders.
2 100-in. supercalenders.
2 6-reel cutters.
1 200-h.-p. main steam engine.
_Finishing Room._
Sorting tables.
Packing press.
Weighing machine.
_Repairs Department._
Usual repair outfit, such as lathes, planing machine, drilling
tools, etc.
Blacksmith's shop outfit.
Carpenter's shop outfit.
Calender roll grinder.
_Water Supply._
Main storage tank, 50,000 gallons capacity.
Water pumps.
Piping and connections to various departments.
Bell's patent filters (if necessary).