September 25, 1914. THE COLLIERY GUARDIAN. 665 and was distilled with milk of lime. The ammonia gas liberated from the liquor passed into the sulphuric acid, when sulphate of ammonia was formed. Obviously this process is a roundabout one, as the ammonia is first dissolved in water, and then expelled therefrom. In the Journal of the Iron and Steel Insti- tute for 1883 there is an abstract of a paper by R. Tervet, in which he predicted the ultimate abolition of this system, and forecast what is known throughout the world as the direct recovery process. It was not until about 1905, however, that the direct recovery process was satisfactorily operated on a commercial scale. In this process the gas is passed directly into sulphuric acid, thus obviating the necessity of washing out the ammonia by means of water. Several types of direct recovery process are now in operation, and the first to meet with commercial success was that designed by Mr. Koppers. This process has since been largely adopted, and at the present time deals with the gas from upwards of 20,000,000 tons of coal per annum. Strange to say, in spite of the marked advantages which this process offers over the old system, and the fact that it has been largely adopted on coke oven plants in Great Britain, not a single gas works of any size in this country has yet discarded the old system in favour of the new on$. A start has, however, been made on the Continent, and at the new works of the city of Budapest the Koppers’ process is in operation, dealing with the make of 9,500,000 cu. ft. of gas per day. The accompanying illustration (fig. 2) shows a dia- grammatic representation of the Koppers’ system. The hot gas direct from the ovens enters the coolers B, where its temperature is reduced to about 25 degs. Cent. The gas is then drawn by an exhauster C, by which it is delivered to the tar extractor B. After having been freed from the tar, the gas is led into the reheater M, where it becomes heated to a temperature of about 50 to 60 degs. Cent. The heated gas is then conducted along the main F, to the saturator E, in which the ammonia gas is extracted by direct absorption in sul- phuric acid, and is recovered in the form of sulphate. The saturator is of the totally enclosed type, and the sulphate is continuously removed therefrom by means of an ejector working either with steam or compressed air. The salt is delivered on to a collecting table, and thence into a centrifugal dryer L, where it is completely freed from mother liquor. The products of condensa- tion which are extracted in the cooling and tar eliminated operations are drawn off from the condensers, tar extractors, etc., and are conveyed into a separating tank H, where the tar and ammoniacal liquor separate owing to their different densities. The tar flows into the storage tank I, and the liquor into the storage tank J. The liquor is pumped to the ammonia still G, where the ammonia is driven off by steam and lime in the usual way. The vapours of distillation are conducted from the still, and are delivered into the main F, where they mix with the heated gas, and the whole then passes into the saturator. It is important to note that no live steam is required in the process, either for distilling the liquor to liberate the ammonia, or to reheat the gas after cooling and tar extracting.' For both these pur- poses the exhaust steam from the engines driving the exhausters is more than sufficient. The gas passes out of the saturator by the main K, by which it is conducted back to the ovens and other points where required. In cases where benzol is required to be recovered, it is necessary for the gas to be cooled down after leaving the saturator, after which it is sub- jected to the scrubbing operation described below. The sulphate produced by the above process is far superior to that obtained by the old system, and owing to the fact that the gas is thoroughly free from tar before entering the saturator, a perfectly white salt is invari- ably produced. This portion of the paper would not, however, be complete without reference to the latest type of ammonia recovery systems of Burkheiser and Feld. Crude coal gas, as it leaves the ovens, contains sulphur in the form of sulphuretted hydrogen. Now sulphur is the basis of sulphuric acid, and the ideal process is therefore one which will utilise the sulphur in the gas to combine with the ammonia, instead of having first to convert it into acid and then neutralise it by the ammonia to form sulphate of ammonia. It is this shortening of the process which is the object of both the Feld and Burkheiser systems. At present both these systems seem to be somewhat too complicated for general adoption, but the author believes that ultimately such a process will obtain. The recovery of benzol has received much attention of late, owing to the fact that a large quantity of refined benzol is now being used in place of petrol as fuel for motor engines. , The majority of coke oven plants now have benzol recovery plants, but very few produce refined spirit—what is known as “ crude ” or “65 per cent.’’ benzol being generally made. The benzol can be extracted from the gas without affecting the amount of energy obtained from it when used for boiler firing purposes, or for combustion in gas engines by more than about 5 to 10 per cent. The quantity of benzol obtainable differs, of course, accord-' ing to the nature of the coal. In South Yorkshire, Derbyshire, the Midlands, and Cumberland, the yield is about 2| to 3 galls, of crude spirit per ton of coal; in Durham it is about 2 to 2| galls.; whilst in South Wales it is usually only about 1 to galls. The recovery of benzol from coke oven gas is now universally effected by means of absorption in creosote oil—a product obtained in the distillation of coal tar— and the difference between the various systems on the market lies principally in the internal arrangement of the apparatus employed, and the temperature and steam pressure at which the various parts are worked. In some cases rotary washers are substituted for the tower scrubbers mentioned in the following description. The method employed for the recovery of benzol con- sists of the following stages. After passing through the saturators the ammonia-free gas is conducted to final coolers, where the temperature is reduced to the degree required for the efficient extraction of benzol. The cooled gas then enters a series of tower scrubbers, inside of which are a number of boards, in order to ensure an even distribution of the scrubbing oil and complete extraction of the benzol. The oil is calculated by means of pumps, and is fed into the scrubbers at the top through sprays. The oil flowTs in counter-stream to the gas, and by the time the gas has passed through all the scrubbers, the benzol is completely extracted from it. The enriched oil containing the benzol passes to a storage tank, whence it is pumped into a preliminary heater, where its temperature is raised to about 60 degs. Cent. It then goes to the superheater, where it is heated to a temperature of about 135 degs. Cent., after which it runs over into the still. By means of live steam the whole of the benzol is driven off, the deben- zolised oil then flowing out at the bottom of the still. This weak oil is cooled and used again for scrubbing purposes. The benzol vapours, together with some water vapour, leave the still and enter a heat exchanger. In this apparatus the heat contained in the vapours is transmitted to rich oil, and the vapours are thereby cooled down considerably, led into a final cooler, and condensed to the liquid form. The benzol and water thus obtained pass to a separator, where, by reason of the difference in specific gravity, the two are entirely dissociated. The benzol so obtained is known as crude spirit, and is usually of about 65 per cent, strength. When a refinery is available the crude benzol is not produced higher than 50 to 60 per cent. Up to this point the process is continuous, and can proceed with- out interruption for any length of time, a little fresh scrubbing oil being added occasionally and some of the old oil removed. If it is desired to produce a refined spirit, it is neces- sary to submit the crude benzol to processes of redis- tillation and purification. The crude spirit runs from the separator into a storage tank, and from there is pumped into a still of large capacity. This is heated by means of steam coils. The benzol vapours pass into a dephlegmator, in which separation of the various con- stituents takes place owing to the different temperatures at which they boil. In order to produce the higher boiling homologues of benzol, further distillation under a partial vacuum by means of live steam is resorted to. The vapours leaving the dephlegmator are condensed, and run into the various tanks. The products so obtained are benzol, toluol, xylol, etc., and each of these is now heated separately in order to produce a refined spirit. A pump delivers the spirit to an agitator, where it is washed with sulphuric acid. After allowing an interval for separation the acid is run off, and the spirit is treated with caustic soda, and finally with water. By finer dephlegmation and slower distillation in another still, the washed spirit is fractionated, and the products known as 90 per cent, benzol, 90 per cent, toluol, sol- vent naphtha, etc., are obtained. In order to produce pure benzol, toluol, etc., for chemical purposes, further fractional distillation is necessary, but these products are seldom, if ever, manufactured in coke oven plants. In the stills from which the crude benzol is first redistilled a certain quantity of hydrocarbons, consist- ing mainly of naphthalene, settles out and is brought to a centrifugal machine and dried. The oily matter remaining is run back into the scrubbing oil and used for scrubbing purposes. The sulphuric acid used for washing the crude spirit can, after a time, no longer be used for that purpose. It is run into lead-lmed pots and heated by live steam, thereby being freed from hydrocarbons. The cleaned acid is then used in the saturator for the manufacture of sulphate of ammonia. Use of Coke Oven Gas in Iron and Steel Works. Coke oven gas is now very largely used as a fuel in iron and steel works, but the author prefers to leave detailed statements with regard to the suitability of coke oven gas for this purpose to those engaged in its employment. There is no doubt, however, that the use of coke oven gas is increasing very rapidly indeed, and the tendency is becoming more and more pronounced for iron and steel works to manufacture their own coke and utilise their own coke oven gas in the steel works. Coke oven gas has been used in open hearth furnaces with great success, in some instances practically replacing the whole of the coal formerly used. At the Hubertushutte in Germany, figures quoted by Mr. Amende show that although the durability of bulkheads and roofs decreases 8 to 10 per cent, when using coke oven gas, that of the chequers increases about 50 per cent. This is in general accord with the experience at other installations, and in an appendix to the paper reference is made to the effect of the coke oven gas on the life of the furnace at Friedrich Wilhelmshutte. At the Hubertushutte the quality of the steel was not affected at all; a point which is particularly emphasised in the statement of the working results at Friedrich Wilhelmshutte. The consumption of coke oven gas was about 2,000,000 cu. ft. per 24 hours, and the coal con- sumption per ton of steel was reduced from 31*8 per cent, to 14-9 per cent, by the use of coke oven gas. In this instance the coking coal was only of poor quality, no more than 45 per cent, of surplus gas being avail- able. According to another authority, coke oven gas, with a calorific value of 500 British thermal units per cubic foot, will displace coal as a fuel for various fur- naces in the following ratios :—In billet heating furnaces 1,000 cu. ft. of gas displace 64 lb. of coal used in gas producers; in rod mill heating furnaces 1,000 cu. ft. of gas displace 58-9 lb. of coal used in gas producers: in bolt rod heating furnaces 1,000 cu. ft. of gas displace 67 lb. of coal fired direct. In the foregoing ratios the coal displaced contained 8-5 per cent, of moisture, and evaporated 5*8 lb. of water per lb. of coal when fired under boilers. In a communication from the Dominion Iron and Steel Company Limited, of Canada, the author is informed that the surplus gas from the coke ovens of the company is used entirely in the steel department. One hundred tons of lime per day for use in basic Bes- semer and open hearth furnaces is burnt, and the mixer into which all the iron from the blastfurnaces is put before going to the steel plant is entirely heated by coke oven gas. The dolomite for open hearth and Bessemer work is calcined by coke oven gas, and all ladle drying is done by the same means. Coke oven gas is also used to a certain extent in reheating ingots before rolling, but this is not constant practice. Any surplus gas not required for the above purposes is used in the open hearth furnaces for steel melting. The calorific value of the gas is about 525 British thermal units, per cubic foot, benzol not being extracted. The communication further states : “ There is no question but that the greatest economy possible in steel works practice is through the general adoption of by-product coke ovens, and not the least of these is in the proper utilisation of the large quantities of surplus gas.’’ In this connection it will be remembered that the president of the institute, Mr. Adolph Greiner, emphasised particularly, in his presidential address at the May meeting, the enormous economics possible through by-product coke ovens, and the great opportunities for the development of the by-product industry. Tests on a Battery of Combination Ovens. At the Friedrich Wilhelmshutte Dr. Rudolph Bier- mann has carried out a number of experiments on a battery of combination ovens, part of which was being heated by coke oven gas and part by blastfurnace gas. The capacity of the ovens is about 8-05 tons of dry coal; uncompressed coal is used, charged into the ovens from above, and it has been found that with coke oven gas COKE SIDE MACHINE SIDE CHIMNEY 8 Hours io U 12 2 3 * s 360r- 360 - 320 <~ 300- 280 - 260 260- Fig. 3.—Temperatures at the Regenerator Outlets. 360 COKE SIDE VINE SIDE Fig. noo 1080 1060 1060 1020 1000 1200 HOC 5 6 7 8 HOWS Regenerators. 3 IQ U 12 I 2 4.—Temperatures q 200 no S 900 £ 900 700 600 SOO TEMPERATURE IN TOP HORIZONTAL FLUE • H30*C Moisture in Corl.................12 Her Cent Fig. 5. 6 9 n n 12 13 N IS K!7 R 0 20 2/22 23262S2S2329 Hour of Carbonization. Temperature in top horizontal pure.. IO6O-IQ7O*C Moisture in Coal............IS Per Cent Fig. 6. 1200 noo tooo 900 800 700 600 500 600 ! 300 ! 200 TOO 9 M // 12 !3 N ISI6I7N N 290 22 23M2S2S27& Hour of Carbonization the time of carbonisation per charge is 29 hours, and with blastfurnace gas 27 hours. Dr. Biermann explains this in the following way. To produce 1,000 calories, 0-24 cu. m. of coke oven gas is required, or 1-007 cu. m. of blastfurnace gas; the volumes of the waste gases respectively produced are 1-28 and 1-88 times these volumes. The greater volume effects a better distri- bution of the heat, and therefore gives more even heating of the oven. Further, although producer gas gives a greater amount of waste gas reckoned per 1,000 calories, on account of its specific heat, 0-58 less heat is lost through the chimney than is the case with coke oven gas with a specific heat of 1-75. A complete account of Dr. Biermann’s investigation appeared in the Gas World (coking section), June 6, 1914, and the accom- panying tables are taken from this publication.