Page:EB1911 - Volume 20.djvu/810

Rh retort is provided with a disk or table to support the material within the retort. Above the table there is a revolving arm or scraper, by the action of which a portion of the material is continuously swept off the table and discharged into the hopper below. The column of material within the retort is thus caused to move downwards, and the tendency of the material to flux or dander is thereby prevented or reduced. In order to pulverize the material before reaching the hopper, teeth may be formed upon the lower part of the retort and upon the table, and the revolving scraper may be similarly toothed. A short revolving worm or screw may be substituted for the table or scraper. As a modification, the table may be made convex and provided on each side with rocking-arms connected together above the table by a cross-arm or scraper.

The principal object of the invention for which patent No. 71 13 of 1895 was granted to the same applicants is stated to be such arrangement of the parts of the retort as results in the retort, after being heated and started, requiring " practically no fuel to keep it going, owing to the great amount of heat generated in the retort by means of the effectual decomposition of the carbon contained in the waste material by means of one or more jets of steam (which may be superheated) being passed into the retort as near the outlet or discharge-door of the retort as possible, thus utilizing all, or nearly all, the heat contained in the waste material within the retort, thus saving labour, time and expense, as well as wear and tear of the retort."

The object of the invention for which patent No. 4249 of 1897 was granted to Bryson is stated to be " to so construct the hoppers of the retorts that one or more retorts can be drawn or discharged through one door, and also to provide simple and efficient means for operating the said door."

Patent No. 13,665 of 1897 was granted to William Young and John Fyfe for an invention the objects of which are described in the specification in the following words: "To reduce labour, save fuel, and increase the products, and to enable existing but wornout retorts that have been erected in accordance with the above invention to be economically replaced upon existing foundations by similar retorts, provided with improved and enlarged multiple hoppers for the reception of the shale to pass through the retorts, and also enlarged chambers for the reception of the ash or exhausted shale; the retorts being provided with mechanical arrangements for the continuous passage of the fresh shale into them from the multiple hopper, and the continuous discharge of the ash or spent shale into the receiving chamber. Those improved mechanical alterations in the structure of the retorts greatly reduce the manual labour, enabling most of the work to be done during the day, the multiple hopper and spent-shale chamber being of such dimensions as will supply fresh shale and receive the spent shale during the night-shift, the only labour then required being the supervision, regulating temperature of the retorts, and seeing that the mechanical arrangements are working properly."

The multiple hoppers are constructed of mild steel plates with flat bottoms to which the retorts are bolted by flanges, the steel bottoms admitting of the differential expansion, to which the retorts are subject, taking place without damage to the retorts or hoppers. To ensure the shale regularly passing from the hoppers to the retorts, each hopper is provided with a rocking-shaft to which are attached rods or chains hanging into the mouths of the retorts, these rods or chains being thus made to rise or fall. The spent shale receiving chambers at the lower end of each retort are of greatly enlarged size, and the lower end of each retort is provided with a mechanical device for the continuous discharge of the spent shale into these chambers. The improvements are stated to be specially applicable to retorts of the Young and Beilby (Pentland) type.

Patent No. 15,238 of 1899 was obtained by the same inventors for improvements designed to obviate objections found to attach to retorts constructed on the ordinary Young and Beilby system. In the use of such retorts, composed of an upper metalHc section and a lower fire-brick section, with chambers or hoppers at their upper ends, these upper ends became gradually filled up with hard carbonaceous matter, and this necessitated the periodical stopping of the working to have such matter removed. Moreover, the shale residues became fluxed and fixed to the walls of the lower section of the retorts. The residues were further liable to pass through the retort in an imperfectly exhausted condition, and to pass more quickly down the front or side of the retort next the discharging door. It was also found that when air and steam were used difficulties arose in regulating the quantities and proportions of stearri and air used to burn the carbon out of the shale residues while preventing obstructions due to fluxing of the residues. To overcome these drawbacks each retort is composed of four sections, viz. a hopper re distillation chamber at the top, a metallic section, a fire-brick chamber, and a combustion chamljer of large capacity at the bottom. The combustion chamber is not externally heated, but receives the spent shale from the retort in a red-hot condition, and the further supply of heat in this chamber is wholly due to the burning of the carbon by the introduced air and steam, the danger of the fluxing and fixing of the shale residue to the walls of the chamber being thus minimized. To successfully burn the carbon remaining in the shale residue when it reaches the combustion chamber, so as to obtain the maximum yield of ammonia, careful regulation of the quantity and

proportions of the air and steam is necessary, and a special device is provided for this.

The important construction of retorts for which patent No. 26,647 of 1901 was granted to N. M. Henderson of the Broxburn Oil Works, relates to such retorts as are described in the same inventor's previous patent, No. 6726 of 1889. The patentee dispenses with the chamber or space between the upper and lower retorts, the upper cast-iron retorts being carried direct on the upper end of the lower brick retorts, thus forming practically one continuous retort from top to bottom; and instead of one toothed roller being employed for the purpose of withdrawing the exhausted residue, a pair of toothed rollers is used for each retort, This improved construction is stated to give " better and larger results with less labour and expense in working and for repairs."

The vapour from these retorts, amounting to about 3000 cub. ft. per ton, is partially condensed by being passed through 70 to 100 vertical 4-in. pipes, whose lower ends fit into a chest. About one-third of the vapour is condensed, the liquid, consisting of about 75% of ammonia cal liquor and 25% of crude oil, flowing into a separating tank, whence the two products are separately withdrawn for further treatment. Part of the uncondensed gas is sometimes purified and used for illuminating purposes, when it gives a light of about 25 candlepower. The remainder is used as fuel, usually after compression or scrubbing to remove all con dens able vapours.

Crude shale-oil is of dark green colour, has a specific gravity o-860 to 0-890, and as at present manufactured, with the newer forms of retorts, has a setting point of about 90° F. It contains from 70 to 80% of members of the paraffin and define series, together with bases of the pyridine series, and some cresols and phenols. Beilby states that average Scotch shale-oil contains from i-i6 to 1-45% of nitrogen, mainly removable by sulphuric acid of specific gravity 1-220, and mostly remaining in the pitchy residues left on distillation. The lightest distillate, known as naphtha, contains from 60 to 70% of defines and other hydrocarbons acted upon by fuming nitric acid, and the lubricating oils consist mainly of olefines. The paraffin wax chiefly distils over with the oil of specific gravity above 0-840.

In the refining of crude shale-oil, the greatest care is exercised to prevent dissociation of the paraffin, large volumes of superheated steam being passed into the still, through a perforated pipe, at a pressure of from 10 to 40 lb, to facilitate distillation at the lowest possible temperature. The original system of intermittent distillation is now employed only at the works of Young's Company. The stills have cast-iron bottoms and malleable-iron upper parts, their former capacity being 1200 to 1400 gallons, but those now made usually holding 2000 to 2500 gallons. Each still has its own water-condenser, the flow of water being regulated according to the nature of the distillate. The usual condensing surface is 230 ft. of 4-in. pipe. The process now in general practice is, with slight variations, the Henderson system of continuous distillation (patent No. 13,014 of 1885). It consists of a primary wagon-still, connected with two side-stills, which are further connected with pot-shaped coking-stills. The oil is heated in feed-heaters by the gases evolved from the hottest still before passing into the first still, where the temperature is so regulated as to drive off only naphtha up to about 0-760 specific gravity. The heavier portion of the oil passes to the other stills, the outermost receiving the heaviest only.

In both these systems the naphtha is collected separately, while the remainder of the distillate, known as " once-run oil, " is condensed without fractionation. This " once-run oil " is treated with sulphuric acid and alkali at a temperature of 100° F. in agitators of varying construction — some being horizontal cylinders with a shaft carrying paddles, while others take the form of vertical cylindrical tanks with egg-shaped bottoms — in which agitation is produced by means of compressed air. The loss of oil during the agitation is estimated at 1-5 to 2-0 %.

The oil is next fractionated, either by the intermittent or the continuous system. After the most volatile fractions have distilled off, steam is blown in through a pipe at the bottom of the still. In many cases the distillate, with a density up to