Page:Encyclopædia Britannica, Ninth Edition, v. 18.djvu/259

 241 Manufacturing Operations. The manufacture divides itself into two distinct sections : (1) the crude works, dealing with the preparation and distillation of the shale and with the production of crude oil and the collateral products illuminating gas, gasoline, and ammonia ; and (2) the refinery, in which the crude oil is purified and separated or split up into the considerable range of commercial products obtainable from it. The following table shows the stages through which the various pro ducts are derived from shale : f Illuminating gas, partly burned and ) ) Al Gasoline. partly condensed to form gasoline, j &quot; . Naphtha f A 2. Solvent naphtha. f B 1. Naphtha ) A 3. liurning naphtha. A 4. Burning oil. Crude oil. Ammoniacal liquor. f 0:.ce-run oil. 1 Coke. ( With sulphuric acid ( =Sulphate of ammonia. B. Burning portion. B 2. Burning fraction. Burning oil of various den sities. oil with soft) ~ Intermediate ( scale. 1. Intermediate oi?. 2. Soft scale. B 3. Heavy oil with soft 1. Lubricating oils, various scale. densities. 3. Heavy oil with hard f C JJ*&quot;* M with suft j 2 Soft SCllle Sca1u 1 C -2. Hard scale. = Paraffin of high meltin Crude, Works. Bituminous shale as brought from the pits is passed through powerful toothed cylinder machinery, reducing it to fragments not larger than a man s fist. In this state it is conveyed in hutches to the retorts, iu which it undergoes destruc tive distillation the distinctive operation under Mr Young s patent. The retorts used have undergone many and important modifications. Originally, as was natural, horizontal retorts arranged in benches, in all respects like gas retorts, were employed, but these in the Scottish trade very quickly gave way to the verti cal retort. The form of vertical retort originally in general use consisted of a cast-iron cylinder, circular or oval in cross section, 8 or 10 feet in height and about 2 feet in diameter, or equivalent thereto. It tapered at the top, where it was provided with a hopper for charging the material to be distilled and a valve for closing the retort mouth. The bottom end dipped into a trough of water, forming an efficient lute, and effectually preventing the escape downwards of any of the gaseous products of distillation. These retorts were arranged in linear benches of six, three on each side of a furnace fed with coal, the heat from which passed to each side into the chamber or oven in which the retort stood. The distilled vapours passed away by a pipe at the upper end of the retort, their emission being aided by a jet of superheated steam injected at the bottom. The distillation in these retorts was continuous, a portion of spent shale being withdrawn through the water in the trough every hour or thereby, and a corresponding amount of fresh shale being added by the hopper. As competition with American petroleum increased, the efforts of manufacturers were directed to cheapening the distilling process, by utilizing the spent shale from the retorts in its hot condition as fuel for distilling the succeeding charge. The difficulties in the way of accomplishing this were very great, chiefly on account of the large proportion of ash in the coked residue, amounting to from 85 to 90 per cent, of the whole. To use spent shale so poor in carbon it was essential that it should be dropped into the fur nace direct from the retort without exposure to the air, and this was first successfully accomplished by the improved retorts and furnace patented by Mr Norman M. Henderson in 1873. According to the Henderson system, which has been adopted in the more important Scottish oil works a scries of four vertical retorts are arranged in quadrangular order over a common fire-chamber or furnace ; the bottom ends of the retorts are provided with doors capable of being closed gas-tight ; and immediately below each door there is a valve which, in one position, and while the charge is being distilled, entirely cuts otf the retort bottom from the furnace or fire-chamber, leaving the retort bottom exposed to the external air, but when the retort charge has been exhausted of oil, and is about to be passed into the furnace as fuel, the valve can be turned over outwards, in which position it forms an inclined shoot contiguous to the bottom of the retort and the fire-chamber. The door-closing at the bottom of the retort having been first withdrawn, and the valve drawn back, the contents of the retort pass freely into the furnace, where their combustion is at first assisted by a jet of the incondensible inflammable gas given off by the retorts themselves. Each Henderson retort can contain about 18 cwt. of shale. The four retorts forming a set are being cleared in rotation at intervals of five hours, so that each charge suffers distillation for twenty hours. The temperature is kept at about 800 F., this giving the best results. The vapour produced in the retort is led off by a pipe issuing from near the bottom, and, in order to avoid unnecessarily prolonged sojourn of the vapour in the hot vessel, a jet of superheated steam is constantly made to stream in above and guide the vapour downwards. The vapour, which amounts to about 3000 cubic feet per ton of shale distilled, is passed through a system of condensing pipes, communicating below through a pro perly divided horizontal chest, like that used in gas works for the condensation of the tar. From the last compartment of the con denser the still uncondensed gas is diavn away by a fan or other &quot;exhaust&quot; through a set of &quot;scrubbers.&quot; In the first of these the point. gas is washed with water and thus stripped of what it still contains of ammonia ; in the succeeding ones it is washed with heavy oil, which withdraws a considerable portion of the vapours of the more highly volatile hydrocarbons which are diffused throughout it. From this heavy-oil solution the absorbed hydrocarbons are extracted by distillation as &quot;naphtha.&quot; The gas, after having thus been freed from its more readily condensible parts, is either led away into gas holders to be utilized as illuminating gas or used directly as a fuel (see above). The product which collects in the condenser chests consists of crude oil (about one-fourth of it) and a weak aqueous solution of ammonia and volatile ammonia salts, containing from 2 to 5 per cent, of real ammonia, NH 3, which, however, in all cases represents only a small percentage of the potential ammonia which was contained in the original shale in the form of nitrogenous carbon compounds. In the golden days of paraffin oil making this ammonia liquor was simply allowed to go to waste ; but when the American petroleum began to depress the prices of the oils the manufacturer saw the propriety of working up the liquors for sulphate of ammonia by the same methods as are employed in connexion with the coal-gas industry (see NITROGEN, vol. xvii. p. 519). And as, during the last decade or two, the demand for ammonia has been steadily increasing, the ammonia in the shale industry by and by rose from the rank of a minor collateral to that of one of the principal products, and a number of attempts have been made to recover that part of the nitrogen which, in the ordinary process, is lost as a com ponent of the coke. Dr H. Grouven proved (1875-77) that all nitrogenous organic or organoid matter when exposed to a current of steam at about 1000 C. burns into carbon oxides, hydrogen, and ammonia, the last-named including all the nitrogen. Messrs G. T. Beilby and William Young have worked out and patented a process for discounting this fact in the shale industry for a more exhaustive extraction of the ammonia. In one of the later forms of the process the shale is being distilled in retorts standing over a fire brick chamber surrounded by flues and kept at a far higher tem perature than the retorts themselves. The coke from the retorts is discharged straight into this chamber, and therein exposed to a mixed current of steam and air, which burns away the carbonaceous part into carbonic acid, carbonic oxide, hydrogen, and ammonia. The large mass of hot gas thus produced passes next through the retorts above to aid in the distillation, and conjointly with the retort vapour is subjected to systematic successive condensation. The incondensible gas which is ultimately obtained includes all that the gas from the ordinary process contains, and also a large pro portion of hydrogen and carbonic oxide from the hot-chamber process. It serves as a fuel for heating the chamber and the retorts ; but, as it does not furnish quite enough of heat for all this, a combined retort and gas-producer is built into the bench with the shale retorts. This supplementary apparatus is charged with coal, which, in it, is first distilled, then converted partiallv into gas by steam and at last completely by a regulated cur rent of air. The gas from the first and second stages is scrubbed to strip it of its ammonia and tar, and then, conjointly with the gas from the third, used as a fuel for the retorts. In this wa the advantages of gas-firing are secured at little expense, as the condensed products are nearly equivalent in money value to the coal consumed. In the Young-Beilby process, which is extensively used in Scottish works, the yield of ammonia is on the average double, and in special cases five times, that obtained in the ordin ary process of distillation. The Working of the Oil. The composition of the crude oil is very variable (see above). It generally forms a very dark green, almost black, liquid, somewhat tarry in appearance, and endowed with a highly unpleasant empyreumatic odour. The specific gravity ranges from S62 to 895. Each ton of shale distilled yields on an average 30 gallons of crude oil (about 260 ft&amp;gt;), 700 lb of coke, gas, and loss, and 1270 lb of cinders. The crude oil on refining yields 38 to 44 per cent, of oils available as &quot; spirit &quot; or for burning, 1 5 to 20 per cent, of lubricating oil, and 9 to 12 per cent, of solid paraffin. XVIII. - - 31