THE SCOTTISH SHALE-OIL INDUSTRY
In view of the great interest which is now being centred in the
production of petroleum in the British Isles--thus making this country
to a large extent less dependent upon foreign sources of supply--the
Shale-oil Industry of Scotland is assuming a new importance, for the
reason that it is in the direction of the development of new oil-shale
areas in several parts of the country that experts look with a great
amount of confidence.
It is specially interesting, therefore, to deal at some length with
the growth of the industry, the methods by which the oil shales are
operated, and the prospects for its extension.
The name of Dr. James Young, of Renfrewshire, will ever be associated
with the commercial exploitation of the oil-bearing shales in the
Midlothians, for it was due to his enterprise that the Scottish
shale-oil industry really owed its birth and much of its later
development. It was while Young was managing a chemical works at
Liverpool that his attention was drawn to small flows of oil which
came from a coal seam at Alfreton, in Derbyshire. This was in 1847,
and after experimenting with the liquid, Young succeeded in extracting
therefrom on a commercial scale both a light burning oil and a
lubricant, as well as wax. When the supply became exhausted, Dr. Young
had an idea to imitate the natural processes by which he believed the
oil had been formed. The outcome of this was the well-known Young
patent for obtaining paraffin oil and other products from bituminous
coals at slow distillation.
The Young process was utilized with much success in the United States
until such time as it became unprofitable owing to the largely
increasing production in America of liquid oils obtained direct from
the earth. It was about this time that a bituminous mineral known as
Boghead coal, and existing in the Midlothians, was discovered, and
from this Young secured upwards of 100 gallons of oil from each ton
treated, but soon this mineral was, in a practical sense, exhausted,
and so the bituminous shales, now known as oil-shales, came in for
attention. Before passing away from Dr. Young’s services in connection
with the establishment of the Scottish shale-oil industry, it should be
mentioned that he figures very largely in more than one of the earlier
Scottish shale concerns. He founded the Bathgate Oil Company, which, in
the zenith of its operations, treated 1,000 tons of shale daily, this
Company being later merged into the Young’s Paraffin Light and Mineral
Oil Company, Ltd., one of the large Scottish shale-oil undertakings and
well known throughout the world to-day.
The Scottish shale-oil fields, as exploited to-day, cover a belt of
territory which is about 6 miles broad and stretches from Dalmeny
and Abercorn, on the Firth of Forth, southwards across the fertile
tract between the River Almond and the Bathgate Hills to the moorland
district of Cobbinshaw and Tarbrax. Throughout this region there are
various important mining centres, such as Broxburn, Uphall, East
Calder, Mid-Calder, West Calder, and Addiwell; and in connection with
the shale-oil industry, upwards of 25,000 persons now find regular
employment.
The shale measures on which the shale-oil industry depends, form part
of the calciferous sandstone series of Mid and West Lothian and the
southern coast of Fife. The carboniferous system of Scotland may be
arranged in descending order in four divisions, as under--
4. Coal measures, comprising red sandstone, shales, and marls with no
workable coals, underlaid by white and grey sandstones and shales with
numerous valuable coal seams and ironstones.
3. Millstone grit, consisting of coarse sandstones, with beds of
fireclay, a few thin coals, ironstones, and thin limestones.
2. Carboniferous limestone series, embracing three subdivisions, the
highest of which contains three or more limestones with thick beds of
sandstone and some coals, the middle includes several valuable seams of
coal and ironstone, and the lowest is characterized by several beds of
marine limestone with sandstone, shales, some coals, and ironstones.
1. Calciferous sandstone series, forming two subdivisions. The upper
is known as the oil-shale group, and is over 3,000 feet in thickness,
and contains, in its highest part, beds of coal, usually of inferior
quality, and, farther down, about six main seams of oil-shale,
inter-stratified with beds of sandstone, shale, fire-clay, marl, and
estuarine limestones.
Although the calciferous sandstone series is well developed in other
parts of Scotland, it has not hitherto yielded any oil-shale of
economic importance beyond the limits of West Lothian, Mid Lothian,
and Fife. Thin seams of oil-shale do occur in various places in the
counties of Haddington and Berwick, but, generally speaking, the
quantity is not sufficient to be practically worked.
A word or two as to the oil-shales themselves. The shales, as known
in the Lothians, are fine black or brownish clay shales, with certain
special features which enable them to be easily distinguished in the
field. Miners draw a distinction between “plain” and “curly” shale,
the former variety being flat and smooth, and the latter contorted or
“curled,” and polished or glossy on the squeezed faces. In internal
structure, oil-shale is minutely laminated, which is apparent in the
“spent” shale after distillation, when it is thrown out in fragments,
composed of extremely thin sheets like the leaves of a book.
Before touching upon the methods employed in mining the shale and the
treatment it receives during distillation, it is interesting to note
that the industry in Scotland has passed through many vicissitudes
since its establishment. At that time, the American oil industry was
but in its infancy, and the production in the States was utilized
mainly on the American markets. Consequently, there was a great
demand for the Scottish oils in this country, and in 1870 there were
no fewer than ninety small oil-works in the Lothians, the majority
of which were operating the shales. It was about this time that the
American illuminating oil came over to this country, and a very
sorry blow was dealt the Scottish industry. So disastrous was the
resulting competition between the Scottish products on the one hand,
and the American and Russian petroleums on the other, that one by
one the Scottish companies closed down, and, after less than eight
years of competition, the number of operating companies had fallen to
twenty-six. The decay continued until the number of active concerns in
the Scottish shale-oil industry could be counted on one’s fingers.
The industry exists to-day simply as a result of the great improvements
which have been made in the retorting of the shale, by which larger
quantities of products are produced--including ammonia. It is thus able
to withstand foreign competition.
To-day, it is estimated that nearly 4,000,000 tons of the Scottish
shales are treated every twelve months by the several operating oil
companies. The most important of these concerns--the Pumpherston Oil
Company--has been regularly operating since 1883, and, inasmuch as it
deals with by far the largest quantities of shale treated, a brief
account of its operations will be of advantage in enabling the reader
to understand the methods by which a total of nearly 400,000 tons of
oil are produced each year in Scotland.
The operations of the Pumpherston Oil Company are upon a scale of
considerable magnitude, for the Company’s works comprise the crude oil
plant, the sulphate of ammonia plant, oil and wax refineries, etc. The
Seafield and Deans works, 7 and 4 miles distant respectively, possess
only crude-oil and sulphate-producing plants, the refining plants being
confined to Pumpherston. The Company’s works cover 100 acres, while
the shale fields extend over many thousands of acres in and around the
district of Pumpherston.
As has already been mentioned, the shale fields so far operated
lie, in the main, in the Lothians, and, as one motors by road from
Edinburgh to Glasgow, the shale country is passed through. Before
the commercial development of a shale field, trial borings are sunk,
now more generally by means of a diamond bore, for by its revolving
action a solid core is obtained which readily shows the character and
inclination of the strata passed through. When a seam of shale has been
found by boring operations, and the exact position and depth of outcrop
determined, it is necessary, before sinking a mine, to put down a trial
shaft for the purpose of making sure as to the true gradient at which
the shale is lying, and the thickness as well as the quality of the
same.
In the shales in the Pumpherston district there are five distinct
seams, dipping from 29 degrees to 38 degrees, and the mine is driven in
the middle seam, the other seams being entered by level cross-cut mines
driven from one to another. Each of these seams is worked separately,
the cross-cut shown in the sketch serving the purposes of communication
and transit. In some cases, where the inclination of the shales is at
a different angle, it is necessary to sink a vertical shaft, and this
method is applied to the series known as the Mid-Calder.
The usual dimensions of the inclined shaft are a width of from 10
to 12 feet, and the height is from 6 to 8 feet. If the sides of the
shaft prove to be of a soft nature, as is generally the case with the
shale at the crop, walls are run up and the roof is supported by larch
crowns, but, where the shale is hard and the roof good, then the less
costly method of timbering is adopted.
The supports to the roof in many cases are fixed “centre” fashion,
dividing the shaft into two unequal parts. The smaller division has
generally a width of just over 3 feet, and is used for haulage ropes
and water pipes, while the larger division is utilized for winding.
During the progress of sinking, levels are broken away in the seam at
regular distances, and driven so as to get communication with, and
drive headings to form, the outer mine. These headings are driven in
the same direction as the sinking mine to the levels above, until
they connect with the outer mine or shaft. The outer mine is then
used for winding the shale up to the surface, and the other is kept
for sinking purposes, and by this means winding and sinking can go on
simultaneously.
[Illustration: GENERAL VIEW OF THE PUMPHERSTON WORKS]
The seams of shale in the Midlothian fields vary generally from 4 to
10 feet in thickness, say 7 feet as an average, and, on the whole,
they are comparatively free from ribs of unproductive rock. With a
thickness of 7 feet, experience has shown that the method best adapted
for the efficient working of the shale is “stoop and room,” but in the
case of two seams of shale, separated by a bed of foreign material
of sufficient thickness for packing, the long wall method proves the
more suitable. The “stoop and room” method, however, is more generally
used throughout the Scottish shale district than any other, its chief
characteristics being the (1) “whole” or first working, and (2) the
broken or second working. The whole working consists of a series of
excavations made in the shale, whereby it is divided into rectangular
blocks or pillars. These excavations are called rooms, one set being
driven at right angles to the dip of the shale and at regular distances
from one another, and commonly called “levels”; another set, driven to
the rise of these levels and at right angles to them, being usually
known as “ends” or “upsets.” The latter are broken off the levels at
regular intervals and driven upwards to meet the levels above.
The shale miner holes as far as he can reach--probably three or more
feet--and brings down the shale by blasting, the process being repeated
until he penetrates a distance of from 9 to 12 feet from the face at
road-head. The shale, being loosened from its natural bed, is then
placed in “hutches,” which are taken to the bottom of the shaft by
either horse or chain haulage (much as with coal), and then the journey
to the mouth is commenced. Before leaving the question of shale mining,
it should be explained that the shale miner is subject to dangers much
as his colleague in the coal-pit, but the volume of gases found in the
shale seams is not so great as in the coal measures. These, however,
are of an explosive nature, the most common being fire-damp.
Once above ground, the shale is conveyed to breaking machines by
endless wire-rope haulage. Passing through the machines, it is broken
into suitable sizes for distillation, and drops into hopper-shaped
hutches. These hutches have a capacity of about a ton, and each in turn
is conveyed to the top of the retorts on an inclined scaffold by an
endless chain. The shale then falls by the operation of a lever into a
hopper or magazine communicating directly with the retorts, one hopper
with a storage capacity of 24 hours’ supply of shale being connected to
each retort of the Pumpherston Company.
This Company’s retorts--they are patented--are in use at the various
works of the Pumpherston Company, and are an interesting feature to
visitors. The shale is fed by gravitation into cylindrical-shaped
retorts, and built vertically in ovens of four, each oven having four
chambers. The upper portion is of cast-iron, 11 feet long by 2 feet
in diameter at the top, and slightly enlarged toward the bottom. Heat
is applied externally from the incondensable gases obtained from the
distillation of the shale, and this heat is made to circulate round
the retort. In the case of the poorer qualities of the shale, however,
the heat is assisted by producer-gas. The heating gas enters near
the bottom portion of the retort, which is of fire-brick, along with
a certain quantity of air, and a high temperature--from 1,200°F. to
1,600°F.--is maintained, in this portion converting the nitrogen of the
shale into ammonia, which is preserved by a continuous supply of steam
delivered at a slight pressure at the bottom of the hopper.
The oil gases are distilled from the shale in the cast-iron portion
of the retort at a temperature of about 900° F., and, along with the
ammonia gas, are drawn off by the exhausters through a branch pipe
at the top of the retort, through the atmospheric condensers, from
which the condensed liquid oil and water containing ammonia flow into
a small separator tank. It is here that, owing to their different
specific gravities--for one is lighter than the other--they assume
different levels, and are thus drawn off into separate tanks. The
gases then pass through ammonia scrubbers, in which they are washed
for ammonia, and then through the naphtha scrubbers, where the lighter
gases, which could not be caught in the atmospheric condensers,
are washed with oil and a good quality of light oil or naphtha is
recovered. The incondensable portion passing from these scrubbers is
burned in the retorts as previously mentioned. With a shale of average
yield, the retort can be heated by these incondensable gases from the
distillation, and a surplus obtained for burning under steam boilers.
What is doubtless a very unique feature of the Pumpherston retort
is the mechanical arrangement for withdrawing the spent shale
continuously, and thus keeping the whole mass inside the retorts in
constant movement. Below each pair of retorts is fixed a hopper made
of cast-iron, and fixed to girders supported on the brick piers or
columns between the ovens. At the top of each hopper, and immediately
underneath the bottom of the retorts, is fixed a cast-iron disc or
table, with a space left between its edge and the sides of the hopper.
The whole mass of shale in the retort rests upon the table, the space
permitting some to pass over the edge. Through the centre of the table
a steel spindle projects, on the upper end of which is fixed a curved
arm, and this, when rotated, pushes some of the shale off, causing it
to fall over the edge of the table into the hopper below. The shaft
carrying the curved arm passes through a stuffing-box on the hopper,
and has a ratchet and lever fitted to the lower end, actuated by a
rod of T-iron which is made to travel horizontally, and is driven by
a small electric motor. The motion is comparatively slow, the arm
making but one revolution in about 20 minutes, but the action is most
satisfactory, the through-put of shale being regulated at will.
The ammonia water got from the atmospheric condensers is pumped through
a heater, in which it is raised in temperature by the waste water
flowing from the still, and passes into the top of the still, which is
circular in shape, about 30 feet high, and has a series of cast-iron
shelves or trays fixed horizontally every 2 feet or thereabouts from
the top to near the bottom. Steam is put into the bottom of the still
at a pressure of 40 lb., and passes to the top through a series of
conical arrangements on the shelves carrying with it the volatile
ammonia, while the water, after traversing the whole area of each tray,
passes out into a concrete tank containing a cast-iron worm, which is
the heater already referred to, for the ammonia water on its way to the
still. During its progress from the top to the bottom of the still, the
water is diverted into a chamber containing milk of lime, setting free
the fixed ammonia which cannot be got by steaming.
The steam and ammonia gas liberated in the still pass over into a
large lead-lined tub or saturator, and bubbles through holes in a
lead worm placed round the circumference at the bottom of the vessel.
Sulphuric acid is at the same time run into the saturator, and, at
a certain temperature, sulphate of ammonia is formed. The sulphate
falls into a well, formed in the centre of the bottom of the vessel,
in which are placed two steam ejectors, and these blow it out along
with some liquor. This mixture is delivered into hutches having
perforated bottoms, through which the ammonia liquor drains off, the
solid sulphate being left in the hutch. This is now run by an overhead
railway to the drying or storage stalls, and from these it is packed
up and dispatched to the market. The exhaust steam and waste gases
from the saturator are passed into the retorts, and utilized for the
formation of ammonia from the shale, while the spent water is pumped to
the spent shale bing, and thoroughly filtered before being allowed to
escape from the works.
For dealing with the weak acid water recovered from the refinery, the
Pumpherston plant consists of lead-lined tubs or crackers, into which
a quantity of the acid water is run, and saturated with ammonia gas
until it is near the salting point, when it gravitates into settling
vessels in order to separate any tar carried over with the acid water.
The clear liquid is then drawn into the saturator, where it is quickly
converted into sulphate and blown out in the manner already described.
So up to date is the whole of the system governing the treatment of the
shales and the resulting products, that the pumping of water from the
mines, the haulage of the shale to the refineries, as well as driving
of machinery in the works, is performed by electric power, the exhaust
steam from the engines driving the generators, as in the case of the
sulphate of ammonia exhaust, being sent to the retorts for use in the
production of ammonia.
The process of refining the crude oil obtained from the shale into
the various products is somewhat complicated and perplexing to those
unassociated with the industry on account of the many distillations
and treatments which have to be carried out before a good marketable
article is produced. The following outline, however, will give a fair
idea of the process adopted throughout Scotland.
The crude oil is delivered at the refinery into large tanks, which
are placed at a sufficient height to feed the stills by gravitation.
The crude oil is allowed to settle for twelve or more hours at a
temperature sufficiently high to separate any water that may have
passed the test at the retorts, and after this water has been run
off, the oil is fed into the centre boiler of a battery of oil
boilers. The lightest fraction of the oil--ultimately motor spirit and
illuminating oils--is distilled off the feeding boiler and condensed
in a coil of cast-iron pipes immersed in water in a tank, cold water
being continuously run into the tank, while heated water is run off.
The boilers on each side of the feed vessel receive their oil by a
pipe connecting with the bottom of the latter, and they also distil
over the lighter portion of oil with which they have been fed, the
heavier portions passing on to a third boiler, where the process of
distillation is repeated.
The oil now left is delivered into a cast-iron pot-still, in which
it is ultimately distilled to dryness, the residue left in the still
forming oil coke, which is valuable as a fuel on account of its high
percentage of fixed carbon and low yield of ash. Steam is admitted to
the still in large quantities at all distillations. The various stages
of distillation are carried through in almost identically the same
manner as that of crude oil, and, therefore, need not be described in
detail.
The treatment or washing of the oil to remove the impurities that
cannot be eliminated by distillation, consists in stirring the oil
by compressed air for a given time in an iron vessel, with a fixed
quantity of sulphuric acid, allowing it to settle, and running off the
heavy mixture of tar and acid which separates. The acid-treated oil
is then run into another similar vessel, treated with a solution of
caustic soda, settles, and the soda tar which separates is run off.
The acid tars are steamed and washed, the resulting acid water being
sent to the sulphate of ammonia house for the manufacture of sulphate
of ammonia, whilst the tar is mixed with that from the soda treatments
and burned under the stills as liquid oil. As there is more than
sufficient of this tar to distil all the oil at the various stages,
the distillation is carried out without cost for fuel, excepting that
necessary for steam-raising purposes.
A portion of the oil distilled at the second distillation, or green
oil stage, is sent from the stills to the paraffin sheds to be cooled
and the scale extracted, this eventually being made into paraffin wax.
Stored in tanks until brought down to atmospheric temperature, the
oil is pumped into the inner chamber of a cooler, which consists of a
series of four vessels having inner and outer compartments. At the same
time, anhydrous ammonia is forced into the outer compartment or jacket,
and absorbs heat from the cooler, freezing the oil in the inner jacket
into a pasty mixture of liquid oil and solid crystals of wax.
This mixture is then pumped into filter-presses, where a portion of
the oil flows away through the cloth, while the wax is left behind
in solid cakes, still containing a quantity of oil. These cakes are
delivered by conveyors to the back of the hydraulic presses, where
they are wrapped in cloth and placed on shelves between iron frames in
the presses, most of the remaining oils being thus squeezed out. The
material obtained from the hydraulic presses is known to the trade as
paraffin scale, and as it is discoloured by the small quantity of oil
which cannot be removed by pressing, a process of sweating by steaming
in large brick compartments is adopted, in order to remove the oil.
The scale, consequent upon the removal of the oil therefrom, becomes
whiter and of higher melting point, and after further treatment is
finally passed through filter paper and run into moulding trays. When
cooled, this product is known as paraffin wax, of which there are many
grades. One cannot enter into the technical arrangements involved, for
obvious reasons, the chief one of which is that these cannot interest
the reader; but sufficient has already been written in this chapter to
suggest to the reader the perfection which has now been reached in the
treatment of the shales of the Midlothians.
As to the future, it is full of promise. There is no doubt that for
many years to come the full force of foreign competition, as it has
existed in previous times, will not be felt. There is a free field
for Scottish enterprise in connection with the distillation of its
oil-bearing shales. Nor is the region for development limited to its
present area. Reports point to the fact that much area of commercial
ground exists, not only on the eastern side of Scotland, but also in
the north and north-west, while it is already an open secret that
those responsible for the conduct of Government operations are viewing
with favour even the liquid extraction of oil from certain areas not
far distant from the zone of the present operations. The Scottish
shale-oil industry has, so far, managed to defy competition from abroad
to an extent which is reflected in the balance sheets of the several
operating companies, whose yearly dividends have been from 50 per cent.
downward during recent years.
One thing is certain, and that is, the Government is well aware that
there are great possibilities associated with the shale-oil industry
of Scotland, and it is not only watching developments with direct
interest, but is doing all in its power to foster the industry, and
by all means possible encourage the exploitation of areas so far
not commercially developed. At some future date there is a great
possibility that the present area for developments will be largely
extended, and as this is written, there is much evidence forthcoming to
suggest that this commercial development of new lands will not long be
delayed.