114 July 21, 1916. THE COLLIERY GUARDIAN. _______________________________________________________________________________ been planed down by denudation almost to the same level as the surrounding country, except where, as at Rowley Regis, dolerite sills had resisted the levelling action to some extent. At about the same time that the horst had been formed, the visible field was folded, crumpled, and faulted. Several short folds were initiated in various directions, such as the Salt wells-Netherton anticline (Malvernoid), the Dudley-Sedgeley fold (Charnoid), and others. None of these flexures were, in the author’s opinion, primary features of the field. They were all secondary embellishments or later ornaments, added, for the most part, after the deposition of the entire carboniferous series, though perhaps, to some extent, initiated in inter-carboniferous times. As to the somewhat difficult question as to when this modification of the original syncline took place, Dr. Arber was inclined to agree with the current view that it was before the trias was deposited. The fact that in the north of the Cannock Chase district the trias rested directly on the productive measures, was very significant in this respect. This horst appeared to have risen as an island above the area over which the triassic deposits accumulated. They, however, occurred all along its flanks, especially in the south, in which direc- tion the horst appeared to have sunk gradually to the level of the surrounding plain. The northern part of the field, despite the depression by the great Bentley fault of 350 ft. or more, appeared to have been more rapidly denuded than the southern extremity, for in the Cannock Chase district the whole of the unproductives seemed to have disappeared, whereas in the south they still covered a large area. From the visible field, so called, the unproductives had been since denuded down to the red clay group (Old Hill marls), while in many places even these had disappeared, and the highest beds of the productives also in the subsequent planing down of the horst. The explanation which the author had to offer of the history and nature of this field differed in toto from the continuous-sheet theory, as regards the productive measures, which it was impossible to reconcile with the evidence. Dr. Arber had also shown elsewhere, in the case of the Welsh borderland fields, that this theory also failed to explain the facts. The theory .adopted here did not demand an anticline in South Staffordshire, where none existed. It did not assume immense overlaps of the various stages of the measures from the Pennine regions southward to the Birmingham district. Nor did it ignore the very wide differences which existed between the grey productives of the Pennine and South Midland fields, which on the author’s view were far too great to be accounted for as simple lateral variations. It was obvious that our notions of the extent of the concealed areas would depend, in no. small degree, on ouir interpretation of the history of this field. On the continuous-sheet (anticline) theory, the South Stafford- shire productives would sink deeper and deeper under the concealed ground to the east and west of the boundary faults, until they began to rise up again in the visible Warwickshire and Wyre Forest-Coalbrookdale fields. The author’s interpretation of the concealed field, on the syncline theory, was that the productives would rise (except where the rocks are disturbed by minor folds and faults) from the boundary faults to their natural outcrops against the original barriers to the east and west. On the anticlinal view, productives existed under the whole of the concealed ground, on the syncline theory, only under portions of it. From the practical standpoint, the first stage should be to locate the barriers and the original outcrops of the productives systematically, and then to explore towards the boundary faults. The few attempts which had been already made, such as the Claverley boring already mentioned, had failed from their very isolation. In all other cases, such as Hams lead and Sand well Park, on the concealed ground to the east, and at Baggeridge and Four Ashes, on the west, and in the concealed part of Cannock Chase, exploration had been going on from the known to the unknown, and not as it should be, from the known to the known. Further, these explorations were confined to what we may call the nearer portions of the concealed areas, the real extent and concealed resources of which had remained as yet unproved. _______________________________ Immingham Coal Exports. — The coal exported from Imminsfham during the week ended July 14 consisted of 2,342 tons to Porto Vecchio. The totals for the correspond- ing period of last year were 2,865 tons foreign and 970 tons coastwise. Indian Coal.—In a paper contributed to the Royal Society of Arts, Prof. Wyndham Dunstan stated that a large number of Indian minerals had been investigated at the Imperial Institute in order to ascertain their suitability and value for various industrial purposes. These included coal, lignite, clays, mica, metallic ores, rare earth minerals, etc., etc. The composition and quality of the various coals of India formed the subject of several extensive and important reports. Some of the difficulties with which a rapidly expanding industry had to contend were still encountered. The war served to emphasise the importance of many industrial positions, and among them the coal supply of India and its capacity to supply the markets of the East. In Egypt, where coal was not known to occur, increasing quantities were being used in con- nection with the extension of irrigation schemes. The present transport difficulties stood seriously in the way of Indian enter- prise, and the admitted fact that most Indian coal was inferior to Welsh coal constituted an objection which every engineer would press so long as supplies of Welsh coal could be secured at a reasonable cost. Prof. Dunstan referred to the great possibilities which Indian coal offered as a factor of industrial importance to India itself, not only as a source of power, but in connection with the adoption of improved methods of car- bonisation and the production of liquid fuel, as well as of power gas. Economical Production and Utilisation of Power at Collieries.* By F. F. MAI RET. All collieries require great quantities of power. The coal has to be raised from the depths of the earth; it has to be conveyed great distances underground; a powerful ventilation has to be produced; water has to be pumped; coal-cutting machines may have to be driven; and on the surface a great mass of machinery is employed in con- nection with the preparation of the coal for the market, and in the workshops auxiliary to- the mine. Mines have in the past been wasteful producers of power. A superfluity of small coal, which was until recently an almost valueless asset, made the wasteful use of boiler fuel a matter of indifference. As the market value of boiler fuel (slack) was so small its waste was not thought a serious matter. A colliery consuming 10 per cent, of its output was 30 years ago rather economical than otherwise. A majority of collieries must have con- sumed very much more, but with the advent of coking and modern stoking appliances the value of small coal has ceased to be negligible, and the coal burnt at a colliery represents a substantial sum in hard cash. A comparison between the heat units utilised at an average colliery with those utilised at an economical modern steam plant, such as a generating station, shows in a striking manner the possibilities of economy in colliery steam production and utilisation. The writer, from data in his possession, puts the colliery result at 1-7 per cent, of the heat units produced from the fuel burnt, while at the generating station 8 to 9 per cent, are converted into work. The one result is less than one-fourth of the other. The conditions are so different that it is impos- sible that the same result can be attained -at the colliery as -at the modern steam plant, but some considerable lee- way may be made up, and it is very largely to pointing out the losses which now occur in colliery plants that the writer has devoted the present paper. With the doubling of the wage bill the cost of all coal has more than doubled. It has, therefore, become urgent to turn this coal, hitherto lavishly burnt, into profit. Take, for example, a colliery with an output of 500,000 tons a year and con- suming 10 per cent, thereof, that is, 50,000 tons; if 3 per cent, can be made to do the work, 15,000 tons only are required, and 35,000 tons are saved, which at 5s. a ton represent £'8,750. This is the subject to be dealt with, under the following heads : (1) Steam generation and distribution; (2) engines, economical and otherwise; (3) scope for condensation and compounding, including turbines; (4) utilisation of electricity as a means of dis- tribution; and (5) gas power from coke ovens and gas engines. The type of boiler adopted, the steam pressure used, and the positions of the boilers relatively „o the engines to be supplied have an important bearing on results. At modern collieries large boilers worked at pressures of 120 to 1501b. per -square inch are now usually installed, and are either mechanically stoked or heated with waste gas, and occasionally with gas producer. The engines are placed as close as possible to the boilers, and the steam pipe lines are short. Where good water is avail- able water tube boilers are sometimes installed. An endeavour is made to -approach as nearly as possible to the best central-station practice, but it is seldom results so good as are attained at the latter are realised at collieries—even the best. The reason is obvious. The colliery conditions are more complicated, the load-factor is generally low, and there is not the same necessity for the engineer to watch his coal bill. It is seldom possible to take advantage of superheating steam at collieries. Still, very good economical results are often secured in well-laid-out modern plants. A consumption of 3 lb. of coal per indicated horse-power (non-condensing) may be regarded as the best practically obtainable. At older collieries, 8, 10, or 20 lb. of coal are consumed to produce 1 horse-power hour, owing to bad boilers at low pressure, antiquated steam engines, long ranges of pipes, and bad conditions generally. Such wasteful appliances should be gradually discarded, and more efficient power users substituted, one remedy being to introduce electricity, as far as practicable, to minimise distribution losses. Without discussing the heat losses incidental to using low-pressure saturated steam, it will suffice to say that, to get economical results from steam, it is necessary to approximate to central station practice, and to make use, where possible, of condensing and superheating, converting the power into electricity and using this as far as possible for the distribution of power, steam being confined to winding and perhaps one or two other purposes. Steam Generation and Distribution. At collieries in the past, and indeed till very recent times, steam raising was performed with very inefficient and wasteful boiler plant. In some cases ordinary cylin- drical egg-ended boilers were used, especially where the feed water was bad. More generally double-tube boilers of the “ Lancashire ” type were installed, but not always with sufficient regard to good setting, and the exclusion of cold air, and the analysis of chimney gases, generally showed a low percentage of CO2. Speaking generally from the purely boiler standpoint, the steam was gene- rated under most uneconomical conditions. The writer’s experience confirms the results given by Dr. Schultze, viz., that of the heat produced in colliery boilers only about 50 per cent, is absorbed in the water. This low efficiency is in part due to causes which would obtain under the most favourable conditions, but there are other losses which are attributable to^special bad conditions, which frequently exist at collieries. With the best regu- lated boiler plants loss may occur due to : (1) Heat carried away by products of combustion; (2) heat carried away by excess air; (3). heat lost in evaporating and * From a paper read before the Midland Institute of Mining, Civil and Mechanical Engineers. superheating moisture in fuel; (4) heat lost by incomplete combustion; (5) radiation; (6) priming; (7) hot ashes, etc. In a test from a battery of six Lancashire boilers, hand fired with fuel of 11,840 British thermal units per lb., the following balance was arrived at :— 1 lb. of fired, value B.T.U. P.c. coal as lower 11,840 ...100*0 B.T.U. Heat lost in the products of com- bustion 1,575 .. Heat lost due to excess air 1,960 .. Heat lost in superheating & evaporating m istureinfuel 65 .. Incomplete com- bustion — .. U nburnt combus- tible in ashes ... 365 .. Radiation—h o t ashes. Moisture in air & unburnt hydrocarbons 1,323 .. Heat transferred to water 6,550 .. P.c. . 13*3 . 16*6 . 0*5 . 3*1 . 11*2 . 55*3 11,840 ...100*0 11,840 .. .100*0 3,580 B.T.U. Deductions. Heat transmitted per square foot of heating surface, per hour ......................... Weight of fuel fired per square foot of grate, per hour ................................. Water evaporated per lb. of fuel as fired ... Equivalent from and at 212 degs. Fahr....... Air used per ]b. of fuel as fired .. *___________ Air theoretically necessary for complete com- bustion ................................... A test taken from a similar set of five boilers supplied with the same feed water and working under the same draught, but fired with fuel of a lower calorific value, gave results as under :— B.T.U. P.c. lib. of coal ...10,370 ...100*0 15*1 lb. 6 06 „ 6 75 ,, 22-6 ,, 9’4 _______ 10,370 ...100*0 B.T.U. P.c. Heat lost in the products of com- bustion....... 1,092 ... 10’6 Heat lost by ex- cess air....... 2,847 ... 27‘4 Evaporating and super-heating moisture in fuel 2 6 .... 2‘0 Incomplete com- bustion....... — ... — Unburnt com- bustible in ashes 881 ... 8’5 Radiation — hot ashes. Moisture in air and un- burnt hydro- carbon ....... 1,147 ... 11*1 Heat transferred to water ..... 4,132 ... 40*4 10,370 ...100*0 Deductions. Heat transmitted per square foot of heating surface, per hour ...................... 1,834 B.T.U. Coal consumed per square foot of firegrate per hour ................................... 12*1 lb. Water evaporated per lb. of coal as fired ... 3*88 „ Equivalent evaporation from and at 212° Fahr. 4*32 „ Air used per lb. of coal as fired ............. 29’8 „ Air theoretically necessary ..........:____ 8*2 ,, From the above it will be seen that with lower classes of fuel there is a tendency to increase the excess air— no doubt to force combustion. This could be attained by using heated air, preferably as dry as possible. An examination of the figures in the last table show that the loss due to excess of air is nearly three times as much as by reason of the chimney gases not being sufficiently cooled. If there is enough heat to make economisers (fitted in the uptake) profitable, it would pay still better to apply a good system of forced and heated draught to the furnaces. A test made at Messrs. Davy Brothers, of Sheffield, on a 9 ft. by 28 ft. Lanca- shire boiler, fitted with the Atlas system of balanced draught and hot air economisers, with Green’s feed water economiser, showed that the excess air was materially decreased, presumably by the heating of the draught. Flue covers have been tried with a varying amount of success, with the idea of preventing both the leakage of cold air and the radiation of heat. One of the best of these covers is the Lyddon pattern, shown in fig. 1, having high non-conducting properties to air and heat, and being practically impervious to moisture. It is provided with a lip to receive the covering from the crown of the boiler, which ensures an airtight joint between the two. Fig. 2 gives the loss in British thermal units per square foot of surface per hour for steam at 180 lb. pressure. It is sufficient that one pressure should be given from which a chart can be made by converging lines to a given point. On such a chart it is easy to calculate the exact loss at any steam pressure and temperature. A plain statement of the actual loss in British thermal units does not always appeal to the steam user to the same extent as the actual loss in pounds of steam, coal, or £s. d. In one case known to the writer, a range of 8 in. internal diameter naked steam pipes conveys steam from the boilers to an engine 294 ft. distant : with the temperature of 307 degs. Fahr., which corresponds to the steam pressure, the actual loss due to condensation is 1*5 lb. per foot- run of pipe, or 492 lb. of steam condensed in transit. With such boilers as obtain in the average colliery, viz., 50 per cent, efficiency, this represents 90 lb. of coal per hour. To verify the above results, the writer gauged the condensate at the end of the steam range, and obtained figures identical with the above. The ideal material