November 15, 1918. THE COLLIERY GUARDIAN. 1021 from sinking further, and we had to resort again to ordinary methods of sinking when sinking resumed. There still existed 12 to 13 ft. before touching the rock head, and as the mud was tough it was considered safe nough to sink a few feet under the crib and then build it up. Accordingly it was decided to sink 3 ft., but before proceeding far it became evident that the sides of the shaft were not going to stand, and it was found necessary to build up the exposed parts in segments, and then cut out the remaining segments and build them up to complete the circle. (See fig. 6.) This completed a 3 ft. length of brickwork below the crib. On sinking further it was found that the mud was becoming much tougher, so it was decided to attempt a 4 ft. length in segments as before. The circle of the shaft was accordingly divided into eight equal parts or segments, and two opposite segments at a time were cut out and built up. These formed pillars of brickwork which were extended round the shaft until the circle was completed. As the mud continued to improve, it was found possible to reach the rock head with the next lift, and this was accomplished in the manner of the preceding lifts. From the rock head downward no difficulty was expe- rienced beyond ordinary sinking troubles, and it may be truly said that thus ended one of the most trying experiences of its kind in the history of Scottish coal mining. It has, however, been fruitful of many good lessons, which if properly learned and timeously applied should make similar sinkings of the future easier, safer, more efficient, and less costly. MIDLAND INSTITUTE OF MINING, CIVIL AND MECHANICAL ENGINEERS. A general meeting of the Midland Institute of Mining, Civil and Mechanical Engineers was held at the Danum Hotel, Doncaster, on Saturday, November 9, the President (Mr. W. D. Lloyd, of Altofts) in the chair. Economic Considerations in Coke Oven Practice. Mr. W. Colquhoun, A.M.Inst.C.E., of Sheffield, read a paper on “ Some Economic Considerations in Coke Oven Practice.” (See p. 1022.) Discussion. Mr. J. W. Porteous (Bishop Auckland), in a written contribution to the discussion, said there were one or two points in the paper that he would like to supplement. He was pleased to find that Mr. Colquhoun had dealt with the mixing of coals. This, in his opinion, was greatly neglected on the majority of coking plants. A firm that he worked for during his earlier career made this a speciality, and as a result their cokes, produced in beehive and by-product ovens, held for many years a premier place in the north and west of England, and in these days, when coal of an inferior quality was being dealt with, it was more necessary than ever that Mr. Colquhoun’s remarks should be seriously considered. Indifferent mixing led not only to a lack of uniformity in the build of the coke, but also to serious losses in percentage yield owing to excessive quantities of ballast being produced. One other detail which was often overlooked was the crushing of the coal. The general practice was to crush coals, whether high or low in volatile matter, to the same degree of fineness, which method failed to bring about the rigidity and compactness in the coke which could be obtained by crushing the coals to different degrees of fineness according to their percentages of volatile hydro- carbons. In other words, if a coal low in volatile were crushed to the same degree of fineness as a coal high in volatiles, the aggregate of surfaces of the former coal might be such that the combining proper- ties of the highly volatile coal would not be sufficient in quantity to bring about true coherence. He agreed that too little attention was paid to moisture. If the moisture in the coal was kept within a reasonable per- centage there would be fewer queries regarding steam at the boilers. On the majority of coke oven plants water was converted into steam in the wrong place. Mr. Colquhoun had dealt very effectively with its influence on the condensing of the gases, and there was much that he could have said regarding its influence on the lining of the coking chamber and the large quantities of unnecessary weak ammoniacal liquor produced through high percentages of moisture. After watching its effects on various types of ovens dealing with different classes of coal, his (Mr. Porteous’) opinion was that it should never be allowed to exceed 10 per cent., and even at that amount it had a deteriorating effect upon the percentage yield of coke produced, owing to its action, when converted into steam, upon the carbon in the coke. On a plant of 50 ovens producing, say, 1,500 tons of coke per week, it was possible, apart from other losses, to lose nearly 20 tons of coke by converting it into gaseous matter through neglecting to keep the moisture in the coal within reasonable limits. But the trouble did not end there; the walls of the cells of coke were weakened, the ash content was proportionately in- creased, and also the quantity of breeze. The destruc- tion of fuel through this item alone had caused much misunderstanding. As an instance of effect of such moisture on carbonisation, and its ultimate effect on steam raising, Mr. Porteous pointed out that the late Mr. G. S. Cooper published two charts showing its effect upon two charges at the end of a 28 hours coking period. He stated that, with 12 per cent, of moisture in the coal, at the end of 28 hours the temperature 1-17 in. from the wall was 1,100 degs. Cent. ; at 6-24 in. from the wall it was again 1,100 degs., and at the centre of the charge it was 1,050 degs. With 15 per cent, of moisture in the coal the following results were obtained: At 1-17 in. from the wall the temperature was 1,000 degs. Cent. ; at 6-24 in., 850 degs. ; and at the centre of the charge, 800 degs. When it was remembered that practically 520 cu. ft. of gas was required to drive off each 1 per cent, of moisture in the charge above 8 per cent., it would be understood how desirable it was, from a tempera- ture and fuel standpoint, for the moisture to be kept under control. Dealing with its effect upon the yield of by-products, Mr. Porteous said it was well known that, up to a certain percentage, moisture protected the ammonia compounds, and the protection continued until 9 to 10 per cent, had been reached; but if the amount exceeded 10 per cent., working practice proved that the amount of recoverable ammonia de- creased, and it had been shown by Mr. Fox we J that, with a coal yielding 31 lb. of ammonium sulphate per ton of coal with 9 per cent, of moisture present, only 27 lb. of ammonium sulphate were obtained with a moisture content of 15 per cent. Up to a certain point, as the moisture increased the tar yields in- creased, but when this took place the yields of benzol decreased. Analytical results indicated that when the moisture content exceeded 6 per cent., the benzol decreased for every 1 per cent, increase of moisture, and over 16 per cent, of moisture caused a rapid decline in the benzol yield. With regard to compress- ing, great improvements were obtained in the coke by correctly stamping the coal charges, and also in the output of coke per oven, but he (the writer) thought that one thing ought to be remembered, namely, that where stamping was in operation it always necessi- tated a certain amount of moisture being present in the coal, and owing to the repressed character of the cells in the coke, brought about by stamping, the percentage yield of coke was decreased througn the escaping steam acting more vigorously than if the coke were less den^e. During the early days of stamping, on one battery of ovens 14 ovens were loaded with stamped charges, and 14 with unstamped charges. In both cases the coal contained the same amount of moisture, and was obtained from the same source. The percentage yield of coke, including breeze, was: Unstamped charges, 76-08 per cent.; stamped charges, 74-78 per cent. ; or 1-9 per cent, less with stamped charges. Having had charge of tapered and un- tapeied ovens for a number of years, he quite agreed with ail Mr. Colquhoun had said, and he might add that on the batteries of Bernet-Solvay ovens with which he was connected, built at three different codieries and aggregating 290 ovens, they had never experienced any ctimculty in pushing the charge from the untapered ovens. M ith regard to horizontal flues, it might also be stated that with the horizontal flue it was possible to have a solid middle wall. With reference to the radiation of heat through the lengthening of the battery, he had found that, where the middle wall had existed, normal conditions had been attained earlier and with considerably less trouble and anxiety, and, when it had been neces- sary to stop charging through labour troubles, or to maue extensive repairs to gas mains, the middle wall had been a great benefit. On all tlieir Bernet-Solvay ovens the middle wall was 18 in. thick, and this made it possible to put one oven off for repairs and re-line it completely from end to end without interfering with the adjoining ovens; whereas with the vertical flue ovens, when an oven was laid off for repairs the output of five ovens was effected, unless the oven to be repaired was near the ends of the battery. Further, the horizontal flue oven, with the middle wail present, was less influenced by a high moisture content of the coal than was the vertical flue oven. He was familiar with two batteries of ovens, one of which had been in operation for 10 years, and the other about 8J years, both of which were Semet-Solvay ovens with 18 in. walls, and when only one oven had been out for repairs and the moisture in the coal had been kept within reasonable limits, the output of coke per battery had not been interfered with. Mr. G. E. Foxwell (of the Koppers’ Coke Oven and By-Product Company, Sheffield) wrote that Mr. Colquhoun referred to the “ combined water ” in coal. This was presumably a slip, as, if they were entitled to say that the water evolved from coal on distilla- tion was combined water in the same sense as that obtained similarly from, say, kaolin, it would be a valuable step towards the elucidation of the constitu- tion of coal. He asked if Mr. Colquhoun had any positive evidence on this point. With regard to the retarding influence on output due to the taper in an oven, published figures of oven temperature confirmed the author’s statement. Prof. Simmersbach had found that up to the end of the period in which the moisture was being evaporated, the temperature of the coal at points equidistant from each oven wall at the narrow and wide ends of the oven was the same. After this, however, the temperature at the narrow end rapidly increased, and by the time it approached its maximum this temperature was 280 degs. Cent, above that of a similar point at the wider end. At the same time he (Mr. Foxwell) feared the wear and tear on the oven walls would be too great to consider building ovens without a taper. This would be especially noticeable with regard to bricks inclined to spall, or which had been attacked by salt. He could not subscribe to Mr. Colquhoun’s statement that there was a reversion of opinion in favour of horizontal fuel ovens. In a recent issue of Iron Age, details of the coke oven plants in the United States were given. From this and other information he found that the plants now under construction in the United States were as follow: — Koppers ........ 2,677 ovens ... Vertical-flued Semat-SMvay ... 324 ,, ... Horizon ta'-flued Wilputte .......... 85 „ ... Vertical-flued He regretted that at short notice he could not obtain similar information with regard to this country. The author was on very debatable ground when he stated that the distribution of heat in horizontal flue ovens was uniform. On purely theoretical grounds it seemed impossible to have a flame 32 ft. long which should heat a given area equally at any point along its length. It must inevitably happen that the few feet along which combustion commenced was a zone of much more intense combustion than the other end of the flue. It could not be wholly true to say that the products of combustion carried the heat to the cooler end and so equalised the temperature, for these products were required to give up a notable propor- tion of their heat, m order to carbonise the coal, as tfiey passed along the flue. The whole question was very debatable, and had apparently never been dealt with adequately and experimentally by an absolutely un- biassed authority. Anotner point was the formation of ammonia. The author stated that “ the thermal decomposition of the gases that are evolved is in- appreciable below 870-9uU degs. Cent., and this fixes the temperature of operation at the top of the oven chamber.” This was surely not quite accurate, since if coal gas containing no tar was passed through a tube containing firebrick at 500-buU degs. Cent, a plentiful deposit cf carbon was formed. Tar consisted of bodies still more easily decomposable. Moreover, the products obtained by distilling coal at lower temperatures were of a paraifinoid nature, and these bodies were converted into aromatic compounds at a higher temperature. As regarded the tar, the temperature of 900 degs. Cent, was that below which the tar would be contaminated with paraffin, and above which too much decomposition occurred. The thermal decomposition of ammonia took place at quite a low temperature, but might be partly prevented by adding excess of nitrogen or oxygen, in accordance with the law of mass action. The same effect, though not so marked, was observable on dilution with other gases. Undoubtedly decomposition of ammonia took place at 900 degs. Cent. They must not, however, overlook the temperature of formation of ammonia from coal. The amount increased with the tempera- ture, as vide the formation of ammonia by direct combination of its elements on passing through the electric arc. The time spent by any given molecule of ammonia in the coke oven was, however, relatively so much longer than that spent by a molecule in the electric arc that decomposition robbed them of a portion of the ammonia. Tne optimum temperature of 900 degs. Cent, was that at which the two reactions so balanced as to give the highest yield. He could not resist the conclusion that higher yields of ammonia would be obtained by drawing the gases out of the coke oven rapidly by high suction, and at the same time using higner temperatures. He could bear out all Mr. Colquhoun’s statements with regard to the hot direct process. Mr. J. Marr (Sheffield) also forwarded a contri- bution, in which he said that it would be of interest to coke oven builders to know whether our Govern- ment, even after the war, would permit them to follow the American practice of coking in 16 hours, if it involved a loss of 20 per cent, on tar and benzol, and 10 per cent, on sulphate. A ruling on this point would indicate in what direction developments should proceed. He agreed with the author’s statement that “ regenerative ovens per se are not more economical than waste heat ovens,” but the surplus energy balances, as stated under headings 1, 2 and 3, did not in his opinion, bring this point out very clearly. The apparent balance in favour of the regenerative oven was entirely due to the higher efficiency of gas engines compared with steam turbines. A true com- parison could only be made when the surplus energy for each case was stated in similar units. If they selected surplus gas or its equivalent in steam per ton of dry coal they had surplus energy for: Case 1— 5,500 cu. ft. of gas; Case 2—(a) 7,000 cu. ft. of gas (i.e., the equivalent of 2,000 lb. of steam raised in Lancashire boilers; (b) 5,200 cu. ft. of gas (i.e., the equivalent of 2,000 lb. of steam raised in Bonecourt boilers; Case 3—(a) 7,100 cu. ft. of gas (i.e., the equivalent of 1,400 lb. of steam raised in Lancashire boilers, plus 2,200 cu. ft. of surplus gas); (b) 5,840 cu. ft. of gas (i.e., the equivalent of 1,400 lb. of steam raised in Bonecourt boilers, plus 2,200 cu. ft. of surplus gas). From these figures it would appear that the waste heat oven per se was at least equal in economy to the regenerative oven. This was true for horizontal flue ovens when the excess air was admitted into the top flue. Under such conditions the excess air in the burnt products leaving the ovens might be reduced to 5 per cent, in the waste heat ovens and 80 per cent, in the regenerative ovens. In practice the figures had been known to be lower. A study of coke oven gas of 450 B.Th.U. per cu. ft. would show the following temperatures of combustion for gas at 0 deg. Cent, with varying proportions of excess air of different temperatures : — Excess Temperature Temperature air. of air. of combustion. No. Per cent. Degs. Cent. Degs. Cent. 1 . 5 0 1,840 2 . 25 0 1,680 3 80 900 1,880 4 130 900 1,700 Nos. 1 and 3 were permissible in horizontal flue ovens, as previously explained. Nos. 2 and 4 were of necessity practised in vertical flue ovens in order to keep below the fusing point of the brickwork, which was about 1,700 degs. Cent. No. 2 for waste heat, and No. 4 for regenerative ovens. Assuming the products of combustion in all four cases passed up the stack at 300 degs. C., it could be shown that the amount of heat lost per molecular volume of gas burned was: For Case 1, 11-3 calories; Case 2, 13-0 calories. Case 3, 17-7 calories; and Case 4, 21-9 calories. Taking the amount of gas burned in the flues as 78 per cent, in the waste heat oven and 50 per cent, in the regenerative, they could compare the losses in the stack thus: — Waste heat horizontal flues 0’78 x 113 = 8‘82 cal. Do. vertical ,, 0’78 x 13’0 = 10T5 ,, Regenerative horizontal ,, 0’50 x 17 7 = 8*85 ,, Do. vertical ,, 0’50 x 21’9 = 10’95 „ From these figures it would be readily realised that the losses in the stack in waste heat and regenerative ovens were about equal, and that the losses in either type of horizontal flued ovens were appreciably less than in vertical flued ovens. Mr. Colquhoun had remarked that multiple ascension pipes would increase the yield of ammonia, and he (Mr. Marr) suggested that their adoption would prove advantageous in other directions. For instance, the increased pressure