Albert Lidgett

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.

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.