One of the most interesting of the modern applications of electricity
to the manufacture of chemicals is to be found in the recently
perfected process known as the Readman-Parker process, after the
inventors Dr. J.B. Readman, F.R.S.E., etc., of Edinburgh, and Mr.
Thomas Parker; the well known practical electrician, of Wolverhampton.
Before giving an account of this process, which has advanced beyond
the experimental to the industrial stage, it may be well to recall the
fact that for several years past Dr. Readman has been devoting an
enormous expenditure of labor, time and money to the perfection of a
process which shall cheapen the production of phosphorus by dispensing
altogether with the use of sulphuric acid for decomposing the
phosphate of lime which forms the raw material of the phosphorus
manufacturer, and also with the employment of fire clay retorts for
distilling the desiccated mixture of phosphoric acid and carbon which
usually forms the second stage of the operation.
The success of the recent applications of electricity in the
production of certain metals and alloys led Dr. Readman to try this
source of energy in the manufacture of phosphorus, and the results of
the first series of experiments were so encouraging that he took out
provisional protection on October 18, 1888, for preparing this
valuable substance by its means.
The experiments were carried on at this time on a very small scale,
the power at disposal being very limited in amount. Yet the elements
of success appeared to be so great, and the decomposition of the raw
material was so complete, that the process was very soon prosecuted on
the large scale.
After a good deal of negotiation with several firms that were in a
position to supply the electric energy required, Dr. Readman finally
made arrangements with the directors of the Cowles Company, limited,
of Milton, near Stoke-on-Trent, the well known manufacturers of alloys
of aluminum, for a lease of a portion of their works and for the use
of the entire electrical energy they produced for certain portions of
the day.
The experiments on the large scale had not advanced very far before
Dr. Readman became aware that another application for letters patent
for producing phosphorus had been made by Mr. Thomas Parker, of
Wolverhampton, and his chemist, Mr. A.E. Robinson. Their joint patent
is dated December 5, 1888, and was thus applied for only seven weeks
after Dr. Readman's application had been lodged.
It appeared that Mr. Parker had conducted a number of experiments
simultaneously but quite independently of those carried on by Dr.
Readman, and that he was quite unaware--as the latter was unaware--of
any other worker in this field. It was no small surprise, therefore,
to find during an interview which took place between these rival
inventors some time after the date referred to, that the two patents
were on practically the same lines, namely, the production of
phosphorus by electricity.
Their interests lay so much together that, after some delay, they
arranged to jointly work out the process, and the result has been the
formation of a preliminary company and the erection on a large scale
of experimental plant in the neighborhood of Wolverhampton to prove
the commercial success of the new system of manufacturing phosphorus.
Before describing these experimental works it may be as well to see
with what plant Dr. Readman has been working at the Cowles Company's
works. And here we may remark that we are indebted to a paper read by
Dr. Readman at the Philosophical Institution, Edinburgh, a short time
ago; this paper being the third of a series which during the last year
or two have been read by the same scientist on this branch of chemical
industry. Here is an abstract giving a description of the plant. The
works are near the Milton Station, on the North Staffordshire Railway.
The boilers for generating the steam required are of the
Babcock-Wilcox type, and are provided with "mechanical stokers;" the
steam engine is of 600 horse power, and is a compound condensing
horizontal tandem, made by Messrs. Pollitt & Wigzel, of Sowerby
Bridge. The fly wheel of this engine is 20 feet in diameter, and
weighs 30 tons, and is geared to the pulley of the dynamo, so that the
latter makes five revolutions for each revolution of the engine by
rope driving gear, consisting of eighteen ropes. The engine is an
extremely fine specimen of a modern steam engine; it works so silently
that a visitor standing with his back to the engine railings, at the
time the engine is being started, cannot tell whether it is in motion
or not.
With regard to the dynamo, the spindle is of steel, 18 feet long, with
three bearings, one being placed on either side of the driving pulley.
The diameter is 7 inches in the bearings and 10 inches in the part
within the core. This part in the original forgings was 14 inches in
diameter, and was planed longitudinally, so as to leave four
projecting ribs or radial bars on which the core disks are driven,
each disk having four key ways corresponding to these ribs. There are
about 900 of these disks, the external diameter being 20 inches and
the total length of the core 36 inches.
The armature winding consists of 128 copper bars, each 7/8 in. deep,
measured radially, by 3/8 in. wide. These bars are coupled up so as to
form thirty-two conductors only; this arrangement has been adopted to
avoid the heating from the Foucault currents, which, with 1½ in.
conductors, would have been very considerable. The bars are coupled at
the ends of the core across a certain chord and are insulated.
The commutator is 20 inches long, and has sixty-four parts. The
current is collected by eight brushes mounted on a separate ring,
placed concentric to the commutator; and the current is led away from
these brushes by a large number of thin bands of sheet copper strapped
together into convenient groups. The field magnets are of the
horizontal double type.
As this machine is virtually a series wound machine, the magnet coils
each consist of a few turns only of forged copper bars, 1½ in. wide by
1 in. thick, forged to fit the magnet cores.
There is no insulation other than mica wedges to keep the bars from
touching the core.
The dynamo furnishes a current of about 5,000 amperes, with an E.M.F.
of 50 to 60 volts, and three years ago was claimed to be the largest
machine, at least as regards quantity of current, in the world.
The current from the dynamos is led by copper bars to an enormous "cut
out," calculated to fuse at 8,000 amperes. This is probably one of the
largest ever designed, and consists of a framework carrying twelve
lead plates, each 3½ in. × 1/16th in. thick. A current indicator is
inserted in the circuit consisting of a solenoid of nine turns. The
range of this indicator is such that the center circle of 360°=8,000
amperes.
The electrodes consisted of a bundle of nine carbons, each 2½ in. in
diameter, attached by casting into a head of cast iron. Each carbon
weighs 20 lb, and, when new, is about 48 inches long.
The head of the electrode is screwed to the copper rods or "leads,"
which can be readily connected with the flexible cable supplying the
current.
The electric furnaces are rectangular troughs built of fire brick,
their internal dimensions being 60 in. × 20 in. × 36 in. deep. Into
each end is built a cast iron tube, through which the carbon
electrodes enter the furnace.
The electrodes are so arranged that it is possible by means of
screwing to advance or withdraw them from the furnace.
The whole current generated by the great dynamo of the Cowles Company
was passed through the furnace.
In the experiments raw materials only were used, for it was evident
that it was only by the direct production of phosphorus from the
native minerals which contain it, such as the phosphates of lime,
magnesia, or alumina that there was any hope of superseding, in point
of economy, the existing process of manufacture.
In the furnaces as used at Milton much difficulty was experienced in
distributing the heat over a sufficiently wide area. So locally
intense indeed was the heat within a certain zone, that all the oxygen
contained in the mixture was expelled and alloys of iron, aluminum,
and calcium combined with more or less silicon, and phosphorus were
produced. Some of these were of an extremely interesting nature.
We now turn to a short account of the works and plant which have been
erected near Wolverhampton to prove the commercial success of the new
system of manufacturing phosphorus.
The ground is situated on the banks of a canal and extends to about 10
acres, which are wholly without buildings except those which have been
erected for the purposes of these industrial experiments. These
consist of boiler and engine houses, and large furnace sheds.
There are three Babcock & Wilcox steam boilers of 160 horse power
each, and each capable of evaporating 5,000 lb. of water per hour. The
water tubes are 18 ft. long × 4 inches diameter, and the steam and
water drums 43 in. in diameter and 23½ ft. long, of steel 7/16 ths.
in. thick, provided with a double dead head safety valve, stop valves,
blow-off cock, water gauges, and steam gauge.
The total heating surface on each boiler is 1,619 square feet and the
total grate surface is 30 square feet.
The boilers are worked at 160 lb. pressure.
The engine is a triple compound one of the type supplied for torpedo
boats, and built by the Yarrow Shipbuilding Company. It is fitted with
a Pickering governor for constant speed. The engine is capable of
delivering (with condenser) 1,200 indicated horse power, and without
condenser 250 indicated horse power less.
With steam at 170 lb. pressure the engine worked at 350 revolutions
per minute, but it has been rearranged so as to deliver 700 indicated
horse power with 160 lb. steam pressure without condenser, and at 300
revolutions per minute:
The high pressure cylinder is 14½ inches diameter.
" intermediate " " 25 " "
" low pressure " " 32 " "
" stroke is 16 inches.
The dynamo for producing the requisite amount of electric current
supplied to the furnaces is one of the well known Elwell-Parker type
of alternating current dynamos, designed to give 400 units of
electrical energy, equivalent to 536 indicated horse power.
The armature in the machine is stationary, with double insulation
between the armature coils and the core, and also between the core and
the frame, and is so arranged that its two halves may be readily
connected in series or in parallel in accordance with the requirements
of the furnaces, e.g., at an electromotive force of 80 volts it will
give 5,000 amperes, and at 160 volts, 2,500 amperes when running at
300 revolutions per minute.
The exciting current of the alternator is produced by an Elwell-Parker
shunt wound machine, driven direct from a pulley on the alternator
shaft, and so arranged as to give 90 amperes at 250 volts when running
at a speed of 800 revolutions per minute. From 60 to 70 amperes are
utilized in the alternator, the remainder being available for lighting
purposes (which is done through accumulators) and general experimental
purposes.
The process is carried out in the following way: The raw materials,
all intimately and carefully mixed together, are introduced into the
furnace and the current is then turned on. Shortly afterward,
indications of phosphorus make their appearance.
The vapors and gases from the furnace pass away to large copper
condensers--the first of which contains hot and the second cold
water--and finally pass away into the air.
As the phosphorus forms, it distills off from the mixture, and the
residue forms a liquid slag at the bottom of the furnace. Fresh
phosphorus yielding material is then introduced at the top. In this
way the operation is a continuous one, and may be continued for days
without intermission.
The charges for the furnace are made up with raw material, i.e.,
native phosphates without any previous chemical treatment, and the
only manufactured material necessary--if such it may be called--is the
carbon to effect the reduction of the ores.
The crude phosphorus obtained in the condensers is tolerably pure, and
is readily refined in the usual way.
Dr. Readman and Mr. Parker have found that it is more advantageous to
use a series of furnaces instead of sending the entire current through
one furnace. These furnaces will each yield about 1½ cwt. of
phosphorus per day.
Analyses of the slag show that the decomposition of the raw phosphates
is very perfect, for the percentage of phosphorus left in the slag
seldom exceeds 1 per cent.--_Chemical Trade Journal_.
* * * * *