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shot-pouch. It is also quite obvious how easy it is to “draw” such a retort : in fact, when the lower door is opened, the coke will almost fall out of itself, whereas with the horizontal setting the “ drawing " is a far more laborious task even than the “charging.” With these retorts, called “slopers” in the gas world, I have seen six men “charge," " draw," and throw all the coke back (a distance of about twenty feet), from thirty twenty-foot retorts in one hour and a half. This meant 93 tons of coal “charged” and six tons of coke “ drawn," and “thrown back.” And this was done by unskilled labour : men despised by the trained stokers, and by them facetiously called “ Ally Slopers." There is perhaps some wit and appropriateness in the appellation. Now, with the horizontal settings of equal size, it would be excellent work for nine men to“ charge,” “ draw," and throw back the coke from twenty retorts in the same time-in fact, I doubt if they could do it.

At some convenient spot in the large pipe that conveys the gas from the “retort-house," preferably where it ascends abruptly to the top of the “condenser," there must be a pipe running downwards to allow the tar to fall away from the gas simply by gravitation. Also there is a good deal of “ ammoniacal liquor,” and these two products are valuable. They are separated from one another by a simple gravitation "separator," and pass into different underground tanks for future reference.

The gas, still drawn on by the exhauster which is straining to create a vacuum, now enters the condenser. There are many different kinds, but perhaps the most simple and efficient is the twisting of the pipe backwards and forwards into a series of immense zigzags, through the middle of which a water pipe is passed. The cold water coming in at the opposite end to the gas, and running throughout the series in contradiction to it, acts as a simple refrigerator. This same water may also be passed, after serving this purpose, into the "scrubbers ” or “washers,” there to take up most of the remaining ammonia that the gas contains, and finally to pass away into the “liquor” tank. But whatever the construction of the condenser may be, it has but one use ; and that is, to cool the gas down to a temperature of about 60 to 65 degrees before it is passed into the scrubbers. And this, simple as it may appear, is of the utmost moment : in fact, the importance of correct temperatures and pressures throughout the different processes cannot be too highly rated.

The gas now, at a temperature of (say) 62 degrees, passes through the exhauster, and then, instead of being impelled as heretofore by “vacuum," it is expelled and propelled through all the remaining plant by “pressure.” This will easily be understood; and as we have not time to go into the details of construction, and even if we had, there are many different kinds of exhausters that are perhaps equally good, it would not be fair to describe one without the other.

The same remarks apply to the scrubbers and washers through which the gas is now passed, and the object of which is to extract from it all the remaining ammonia. But probably the simplest and best process is a series of large upright cylinders filled with broken and unbroken brushwood (birch), so that as the gas passes upwards it is obliged to find its way in a very eccentric manner. At the same time a revolving jet of water is playing in from the top, and as this has naturally to pass through the brushwood in its descent in every conceivable direction (just as the gas must do in ascending), it has every chance of taking up all the ammonia that the gas contains, and also of washing out much of the cyanogen, carbonic acid, and sulphur in its various forms. In its passage through the series of scrubbers, this water of course becomes “ammoniacal liquor," and falls into the tank as a valuable product.

After leaving the scrubbers, the gas passes along and into the “purifiers," and this "purification,” apart from the expense of plant, is a costly and important process. Again, in this there are several methods ; but I will take what is probably the best. First, I must describe the construction of a purifier. It is a large square tank, having a water-sealed lid (which is easily removable by special gearing), made to withstand a good pressure, and being fitted across at equal distances with a series of skeleton “shelves," upon which “grids” may be fitted to form an entire “tray.” For convenience sake we will say that there are four such in each purifier. Now, to make these ready for use each tray is overlaid with lime or oxide of iron (prepared) to a thickness of about six inches. In the former case we have what is called a “lime purifier,” in the latter an "oxide purifier." Of course the “grids” are so constructed (as the word itself almost explains) that, although the apertures are close enough together to hold up the lime or oxide, yet the passage of the gas is little impeded; and in its ascent through the trays of these purifying substances it is very evenly distributed. The purifiers extract several very objectionable products. The lime acts chiefly upon the carbonic acid gas and the bi-sulphide of carbon. This latter seems as a kind of red rag to the “Referee” bull : though the fuss that is made about it appears to me to be a hurricane in the smallest of tea-kettles. Gas works are allowed an average of 22 grains in 100 cubic feet in the summer months, and a trifle less in winter-quod erat absurdum. At the first

casual glance, perhaps, you would imagine that the above figures mean 22 per cent. ; but in reality they represent 22 in 21,500. Now, as nearly as we can estimate, the coal itself would have contained about 33 grains of this bi-sulphide of carbon ; so when the law has stepped in and extracted 11 grains, probably no one on earth but a Referee is the wiser—or the better off. The oxide of iron absorbs the sulphuretted hydrogen, and some other matter that is quite insignificant, so the gas is passed first through a series of "lime purifiers," and then through several "oxide purifiers.” But, as a matter of fact, these objectionable products may be extracted by other methods than I have here briefly described—though perhaps none are so practicable.

The lime must be continually renewed, and this is a large expense ; whereas the oxide of iron may be used over and over again, and will produce almost equally good results until it becomes impregnated with 40 to 45 per cent. of sulphur. But in works where room is no object it is possible to "purify” gas by oxide of iron only; and the process would have the advantage of being less objectionable—for although the smell of “foul lime ” may be healthy enough, I would sooner be very much farther afield when the purifier is “taken out.”

At the present time this foul lime (as a matter of argument) is valueless. Buit, to my mind, this waste product might by enterprise become a staple article of manufacture. As I suggested in connection with the coke trade, it should not be procured direct from the gas works, but should pass through the hands of another company (or private enterprise) in whose hands it might be pulverised, an apportionate percentage of guano added, and sold as an invaluable manure for gardens, and as a dressing for lands where roots “ club” and insects congregate.

From the purifiers our gas now passes through the “s'ation meter” into the “holders.” The station meter merely registers the quantity manufactured. When the holder is full—ihat is, when it has risen to the top of the girders which form the frame in which it works—the work of the exhauster is accomplished (and good work indeed you must admit that it has been), and its current must be turned into a fresh holder. Now, to supply the district, the valve of the pipe connected with the works being closed, the “governor” of the district is opened. The weight of the holder itself is now our pressure and motive power ; and the governor (a pearshaped valve working in connection with a cunningly-devised balance) determines the pressure at which the gas is supplied to the consumer. These governors are in a "governor-house," and “pressure men” must be in constant attendance.' The pressure so put on each district, of course varying greatly for day and night, is recorded by gravitation floats holding a pencil with which they write automatically upon “pressure papers” that are revolved by clock-work. The casual observer in passing through London and seeing these immense gasholders dotted here and there in clusters, would not be likely to realise their enormous capacity ; nor would he be likely to think that there is as much underground work to each holder as there is in the way of the foundations and tank : foundations adequate to carry the structure ; and the enormous tank that forms the "waterseal,” and into which the holder must sink as it belches forth its vast store of light and heat to each separate consumer. Nor would a casual observer be likely to guess to what extent such a mass of gas may be contracted or expanded by any marked difference in temperature.

Now, all the processes that I have here described so brieiy could be carried out at the pit's mouth, and I should not then advise the driving of the gas direct from the manufacturing plant into the existing holders in London, but that it be “exhausted " into holders at the pit's mouth and from them supplied to the various London stations for distribution. In this way the two would be connected (figuratively speaking) by direct balance, although many miles apart; and the heavier holder being at the manufactory it would naturally sink down, and in so doing force up the lighter one in any given district in London; and acting upon it as it would by a direct continual pressure, and the gas forming the connection (as it were) between the two being lighter than our atmosphere, the expenditure of force per mile drive would be a mere bagatelle.

I should also advise that all the holders supplying London in the various districts should be in direct connection one with the other, so that in case of need they could supply one another.

I have, naturally, here been obliged to entirely pass over the sulphur tests, and many other most interesting and intricate techni. calities in gas manufacture ; and here let me say that the purity of all gas is carefully tested before it passes into the holders. The blackening of ceilings is, I believe, not due so much to any fumes arising from the incomplete combustion of an impure article, as to a cause that few, perhaps, would think of. In the iron pipes that supply our houses a great deal of condensation is, of course, continually taking place; consequently, especially in a climate subject to very sudden changes of temperature, our gas always arrives at the burner, to a certain extent, impregnated with water-the combustion

VOL. CCLXXIII. NO. 1939.

of hydrogen and oxygen also produces a water moisture. So when ever our gas is alight there must be an imperceptible and perfectly insignificant current of steam ascending swiftly to the ceiling; bu, of course, in the rush of hot air, all the blacks and minute particles of dust that come within the vortex are thrown upwards, and the remotest suggestion of a vapour is sufficient to make them adhere to the ceiling, until in the course of time it becomes much discoloured. This same effect may be seen over any steam or hot-water pipe. But although I have passed over the “sulphur test” with so much indifference, I must say a word or two about the “illuminating power” test. Of course, the illuminating power of gas must be kept up to a certain standard, and this, goodness only knows why, is determined by candles. All gas sent out to the consumer must be above a certain “candle power’”; this is under Government regulation and control, and varies slightly in different districts. But the mode that is imposed by law of such testings is a simple absurdity. Although very elaborate and expensive machinery must be used, there is no law regulating the sperm candles against which the gas is being tested, as far as their quality or manufacture is concerned. To do any good, it seems to me that the County Council should supply (or at least control) properly tested candles, stamped with the magic C. C. Not only would this simplify matters for the gas companies, but it would be in the interests of all consumers. The quality of gas is easily made up when necessary by the addition of “cannel” coal or oil when changing the retorts. But if my idea were fully carried out, all this misunderstanding and unravelling of red tape would be avoided. For the supply of London at the present time four mains forty-eight inches in diameter, inside, would probably be found quite sufficient. What would be easier than to place a little Government testing station upon each of these, to tap the main, and to test the gas with a vigilant and unrestful eye before its arrival into London 2 I do not think, honestly, that any arrangement for the “exhausting” of smoke away from our great cities, or the annihilation of “town-fogs” by explosions of electricity after the nuisance has been wantonly committed, is worthy of consideration. The thing to aim at is the prevention of the evil by the means which I have tried to demonstrate : for “prevention is better than cure.” If I have, in this short article, seemed to take the part of existing gas companies, in the face of the generally adverse public sentiment, it is merely with the idea of giving “the Devil his due.” LYNN CYRIL D'OYLE.

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