Popular Science Monthly/Volume 16/March 1880/Water as Fuel
|WATER AS FUEL.|
By WM. C. CONANT.
THE satyr in the fable was not more scandalized at the man who blew hot and cold with the same breath, to warm his fingers and to cool his porridge, than the old acquaintances of water as the natural cooler and refresher of the world have been to find it artificially asserted as supreme in the opposite office of heating. It may well seem the extreme of paradox that the same element which tempers the excess of both solar and animal heat should also become the great source of supply for their deficiency. And yet why should not the universal absorbent of this power be made to restore it? We have long known that water is but the fuel of the universe as transformed by combustion—a cold residual of a cosmic conflagration that still rages in the central mass of our system, and has hardly subsided as yet in its principal fragments.
Hydrogen—the "water-parent," or distinctive element of water, as its name imports—may be regarded, metaphorically at least, as a metal, which no degree of cold in nature, or where life exists, can reduce to the density of a liquid. It oxidizes so eagerly, and in such infinite abundance, as to be the only combustible comparatively worth mentioning: nowhere to be found, in fact, but in vehement combustion or in its cold result as water, unless where locked in the embrace of its secondary affinity, carbon, in the various oily products of organic life. In the latter condition—the hydrocarbons—hydrogen is protected from the all-devourer, oxygen, and enters into innumerable uses. As the inflammable ingredient of wood, of bituminous coal, of petroleum and other vegetable and animal oils, we have it sealed up by Providence, as it were, for a temporary and portable fuel, pending the full development of man's proper authority over the elements—temporary, for it has long been a source of anxiety to economists that the resources of forests and coal-fields are so finite and their prospect of exhaustion so definite. It is evident from the coal "measures" that man was never intended to remain dependent on what he could pick up ready made for his needs, in respect of fuel any more than of other things; albeit this provisional supply for his infancy was made ample and accessible above all others. Even the novel service of carbon (which we shall observe more particularly further on) in smelting hydrogen "ore" from the vast mines of lake and ocean—as it does also the oxides of other metals from telluric mines—bids fair to be divided with some more unlimited artificial agency in due time. To the present time carbon, diffused and heated to intense brilliancy in burning hydrogen, has been our only artificial illuminant on a practical scale. And yet it now seems likely enough to be superseded in this office also, at no distant day, by fixed illuminators excited by the combustion of hydrogen or the force of electricity.
The better hydrogen becomes known, therefore, the more interesting and important to us it is found beyond all other elements, oxygen scarce excepted. To all the vital and delightful uses of water, as we have seen, it adds also those of light and heat. For, although scarcely luminous in itself, hydrogen is a principal source of the heat which makes other substances luminous, and is thus a chief condition of illumination. Terrestrial flame is generally hydrogen gas in the act of combustion, colored and made brilliant with white-hot carbon also oxidizing. Carbon may therefore be called a diffused illuminant, and the only one of any importance available at a living temperature, although in the terrific conflagration of the sun all things, even the most stable, are diffused in gaseous incandescence. The more stable substances that maintain their solid form in the comparatively moderate terrestrial heat of burning hydrogen until they become intensely bright are called fixed illuminators. Progressive examples may be cited: in platinum, the most non-fusible of metals, which endures and emits in light the intensity of hydrogen burning in air; and in lime, a still more refractory substance, which glows with dazzling power in the fierce combustion of hydrogen with pure oxygen, commonly known under the name of calcium light.
If Mr. Lockyer should succeed in verifying his startling hypothesis that hydrogen may be in fact the only thing in the material universe—not the water-parent only, but the all-parent—our present celebration of this great element would prove neither inopportune nor inordinate!
After all that has been said of it, the nineteenth century furnishes an ever-fresh and amazing retrospect. Within the memory of the living these now common facts—too vast and sublime, however, to be called familiar—were hid, with the great bulk of modern science, indeed, from the sages of the world. Oxygen had but just been discovered, a hundred years ago; hydrogen was unknown; water was supposed to be an elementary substance; fire and flame were mysteries; what the sun might be, and the nature of its light and heat, nobody could guess. After hydrogen had been found elsewhere, it was discovered (in 1781) that water is the result of its combustion with oxygen, and in 1805 that two parts in three of the vast volume of that element pervading and covering the earth are contributed by this ethereal ingredient. Several ways to dissociate the two gases were found, but the common and practical method was and is the contact of steam with red-hot carbon. This, in the absence of free oxygen, results in a transfer of the water oxygen to the carbon fuel in combustion, leaving the water hydrogen free. Red-hot iron answers a similar purpose, forming an oxide of iron (rust) in place of carbonic acid; but the consumption of so valuable an article as iron in the process has hitherto excluded this method from practical use, although there is now some prospect that by deoxidizing the iron-rust it may become available over and over for the elimination of hydrogen at a minimum of cost.
Until a recent date it has been quite generally taken for granted that, since to separate the two gases of water must cost as much heat as they will evolve by reuniting in combustion, there could be no possible profit in forcing the separation for the sake of fuel. Hence, the application of water hydrogen to practical purposes has been regarded as visionary. But there are some considerations on the other side also that seem to have been overlooked. The unavoidable waste in burning-solid fuel has been found to range from fifty per cent, as a minimum in the arts up to ninety-five per cent, as a common proportion in stoves, and thus to exceed by several volumes the whole cost of obtaining from water a gaseous fuel which can be used with but insignificant waste. Besides this, the doubted possibility of economizing the carbonic acid has also been realized, and that hitherto worthless incumbrance has been incidentally recarbonized in the process and utilized as carbonic oxide, to an economic success. Direct economies in the process have also been achieved, preventing great waste of heat in various ways, including that of a large amount hitherto lost in cooling off the finished gas. These recent—and American—improvements have suddenly given a practical character to the manufacture of water-gas, and a practical purpose to the elucidation of the subject.
Notwithstanding an unbroken succession of failures in the economic sense for more than half a century, the unlimited and ubiquitous stores of hydrogen "ore" have mightily stimulated inventors to the task of extracting treasure from these mines of fuel. Few objects have engaged the ingenuity of the nineteenth century in so extensive and indefatigable researches, with (prior to 1874) so little result. Scores of patents have been taken out, mostly by French and English inventors, for different methods of obtaining and employing water hydrogen for illuminating purposes; and a number of minor towns and manufactories in Europe have been and are to this day supplied, by as many different methods, with water-gas. Want of space forbids us to review these methods as to their successes or defects. The common inherent obstacle to their progress is the lack of a sufficient margin of economy to overcome the immense vested interests that oppose any departure from the use of bituminous coal. Such a margin can never be attained under the waste inseparable from the use of retorts, heated externally, to which all the European inventors have adhered. One of the best of their efforts is that of Tessié du Motay, adopted and modified by the Municipal Gaslight Company of New York, and lately purchased of the latter for the down-town district held by the old New York Gaslight Company. Its advantages, however, are subjected to an obvious drawback, in addition to others before mentioned, in a necessity for reheating the gas to give it a fixed character.
In short, the test of successful propagation had never been met by any system, in any measure, on either side the Atlantic, until the introduction of the recent American process, which has proved both in theory and practice a consummation and a contrast to the whole previous history of invention in its line.
But illuminating gas, and the struggles of half a century to cheapen it by water hydrogen, have interested us but incidentally as leading up to a later and still more important result—the practical availability of water-gas as fuel. In fact, the rapid progress and generally anticipated success of the electric light have given pause to all present enterprise in illuminating gas. New movements are almost suspended, and shares in the oldest and most profitable works are no longer the favorite investment. A probability has suddenly appeared that the uncounted millions of irrecoverable capital invested in gas mains, pipes, holders, etc., may eventually find no other employment but to supply fuel-gas to the households that have hitherto depended on them for light. In view of such a prospect the feeling of the gas interest toward water hydrogen must become seriously modified. The lately dreaded process begins to look like a friend in need—the only hope of rescuing much capital from total loss in the not improbable event of a satisfactory and economical diffusion of the too concentrated electric light.
Our remaining space, then, will be dedicated mainly to fuel-gas, and the process as modified for that product; first, briefly describing the apparatus, and the distinctive processes for producing by it illuminating and non-illuminating or fuel-gas.
Disregarding details, the apparatus consists, substantially, of a strong brick cupola-furnace with an iron shell, as gas-generator; this connected by a flue with a secondary chamber as superheater, filled with loose fire-brick nearly to the top. The gases generated from an anthracite fire in the furnace are driven by the air-blast through the connecting flue into the secondary or superheating chamber, at the bottom; here they meet a second air-blast, which urges them to a blaze of intense and complete combustion; and in this superheated condition they are forced up through the labyrinthine interstices of the firebrick with which the interior of the chamber is piled.
So effective are these simple arrangements that, in the few minutes required to kindle the mass of coals in the furnace to a cherry-red, the mass of fire-brick in the superheater becomes white-hot and ready for use. This result is the work of carbonic oxide and other products of imperfect combustion usually passed off in the smoke of our domestic chimneys, and finely illustrates the main point of advantage in gaseous fuel—its more complete utilization. If any of us could see the regular gaseous waste from our kitchen-stoves kindled up in the chimney to a pitch of heat sufficient to melt iron there, it would be a convincing proof of the estimated loss of ninety-five per cent, of our fuel, and would resemble faintly what is done outside the fire-chamber of the Lowe or Strong furnace, and in what answers to the chimneys of our dwellings.
At this point (to return) the air-blast is shut off; the outlet of the chimney is tightly closed; and a cock is turned which lets a jet of steam from a boiler into the bottom of the furnace and up through the mass of glowing coals. Instantly the process of combustion ceases (as between the coal and atmospheric oxygen), and the generation of water-gas begins; in other words, the coal now takes oxygen in combustion from the steam which has been substituted for air, and leaves the water hydrogen free. The hydrogen, lightest and thinnest of gases, which had been pent in the form and consistency of water, is now itself again, expanding to vast volume, like the ethereal génie let out of the casket by the Arabian fisherman, and ready to do the bidding of its liberator. At the same time a valve is opened in the upper part of the furnace, which lets fall a steady shower of crude petroleum on the fire. The pungent and fuliginous vapor in which the oil rebounds from the burning coals is a heavy solution, so to speak, of carbon in hydrogen. Into this thick mixture the free water hydrogen, rushing up from the decomposition of steam below, freely enters, diluting it to proper proportions for burning completely and cleanly, without smoke, in the open air. Another ingredient, rolling up from the fiery laboratory, also mingles in the tempest of hot gases, and still further heightens the calorific and consuming powers of the compound. This is carbonic oxide, the great value of which, either in a fuel or illuminating gas, and its spontaneous development in place of incombustible carbonic acid, are among the advantages which have given to the American method the first decisive success in supplying the public with water-gas.
The oxygen of the steam, as we have seen, on entering the burning coals at the bottom of the furnace, instantly unites in full proportions with the first carbon it encounters, forming carbonic acid. But this carbonic acid, as fast as formed, is driven upward through the fire, and, before it reaches the other gases, its greedy oxygen has gorged itself with a double portion of carbon from the coals, and it is now carbonic oxide—a gas rich with carbon, which is ready to unite in combustion with a further proportion of oxygen wherever it can find it. But it finds no oxygen among the gases to which it is introduced, for the air-blast was shut off when the steam was let on. Consequently, it enters into the compound, and remains as a third combustible.
Meanwhile, the mingled gases are rushing from the furnace, under high pressure, through the flue into the secondary chamber or superheater, and up through the white-hot mass of fire-brick which it contains. Struggling through the hot crevices in attenuated streams, the gases reach a temperature of nearly 2,000°, at which all the elements present are perfectly released and enabled to form such recombinations as their stronger affinities dictate. As the oxygen here finds itself in a hopeless minority, and remains dominated by the superabundant carbon with which it is associated in carbonic oxide, there is no rival to forbid the bans between the king and queen of combustibles—Hydrogen and Carbon.
The charge of coal in the generator makes from five to seven thousand cubic feet of gas: the process of generation taking thirty minutes. The steam is then shut off, and the generation of gas ceases. The lid is raised, the air blast readmitted, and ordinary combustion is resumed. The stoker approaches the fiery pit on a floor level with its mouth and pours in another charge—a barrel of anthracite—fastens down the lid, and for fifteen or twenty minutes the air-blast again urges combustion until the mass in the generator is of a lively red, and the fire-bricks in the superheater are once more white-hot for a second run of gas. At every sixth charge the ashes are raked out, and two barrels of coal, instead of one, are put on.
When the eight sets of apparatus in the Baltimore works are in operation, the actual product per twenty-four hours, with all delays, amounts not unusually to 600,000 cubic feet; and it has been practically demonstrated that 1,000,000 cubic feet could be made by the same apparatus in the same time. Provision is also made for as many more sets of apparatus as may be required by the future extension of the business.
We are now prepared to understand clearly the later and more important process of making pure fuel-gas; which commends itself to us as the next great economic stride of the arts, and therefore as the true "objective point" of this article.
The first stage of the process invented by Mr. Strong is so nearly the same with that already described that a repetition is unnecessary, the furnace being fired up until the loose brick contents of the secondary chamber or superheater are at a white-heat, when, as before, gas-making is commenced. But here the current of the process, so to speak, is reversed. Instead of letting the jet of steam in at the bottom of the furnace, we let on steam at the other end of the system, i. e., at the top of the superheater, and pass it directly downward through the mass of white-hot fire-brick. This raises the steam to a perfectly invisible gas, hotter than devouring flame, as it rushes from the superheater, through an extra flue, into the upper part of the furnace. There it meets a shower of anthracite coal-dust instead of petroleum, sifted down into the furnace from above, and literally burns it up with intense combustion—precisely as coal-dust would be devoured in the fierce flame of the blast-furnace seven times heated, except that the oxygen of this combustion is supplied entirely by a steam-instead of an air-blast. In other words, the steam furnishes both heat and oxygen for the instant conversion of the coal-dust to carbonic acid, with the consequent release of its own prodigious volume of hydrogen. Under their own increased pressure, the gases continue without pausing, down though the mass of glowing coals. In making this passage, the carbonic acid takes up a double portion of carbon from the hot coals and becomes carbonic oxide—the powerful heating gas so often seen burning in a lambent violet flame on the surface of anthracite fires when the air is let in on them. As there is no access of atmospheric oxygen to the furnace, there is no opportunity for the combustion either of this gas or of the freed hydrogen, and accordingly both pass out together at the bottom of the furnace, through a pipe which conducts to the gas-holder.
The product of this process, before purification, has been rigorously analyzed by the several methods, by Professor Gideon E. Moore, Ph. D., and proves to be 52·76 per cent, pure hydrogen, 35·88 per cent, carbonic oxide, and 4·11 per cent, marsh-gas, making nearly ninety-three per cent, of the whole volume in these powerful calorific agents, leaving only six to seven per cent, of incombustible waste (carbonic acid and nitrogen). Wurtz also gives substantially the same proportions, in Johnson's "Cyclopædia."
The purity of this fuel is a consideration nearly sufficient of itself to revolutionize the manufacture of iron, and especially of steel, for which, in its perfection, few if any mineral coals are sufficiently free from such troublesome ingredients as sulphur, phosphorus, etc.; but of this further on.
With respect to comparative calorific values, Professor Moore's report shows, by rigorous calculation, that the Strong fuel-gas will produce 2·78 times the practical effect of the amount of coal consumed in its manufacture, supposing the same coal were burned directly by the most perfect methods of combustion and utilization known in the arts. But in these methods, according to standard authorities, at least five times as much of the fuel is utilized as in the average of stoves. The practical heating value of our domestic fuel may therefore be multiplied fourteen times (5 X 2·78) by using it to make water-gas.
But, again, the material actually used at Mount Vernon in making the water-gas analyzed by Professor Moore, instead of being our domestic fuel, worth from four to six dollars per ton in New York, was mostly nothing but waste coal-dust, dug up from an old "fill," where it had been used in grading the street; and when the gas product itself is reapplied to making and superheating the steam—as, of course, it will be—the use of merchantable coal may be entirely dispensed with. Of the refuse dust we have literal mountains accumulated at our coalmines and depots, as well as constant deposits at every coal-yard, which the proprietors would now be glad to have taken away gratis. Making ample allowance for the expense of appropriating these supplies of coal-dust, and allowing only the lowest price of chestnut coal for the article consumed in our stoves and furnaces, we can multiply the present equivalent for our domestic coal bill at least three times more by the gas process—less the charges for invention and organization, capital and interest, manufacturing management, and distribution. The proprietors propose to have the fuel-gas delivered at fifty cents per one thousand feet, with a good margin of profit, as it can even now be made for ten cents. Compared with illuminating coal-gas by volume, its heating power is found to be about as three to five. Hence, coal-gas at eighty-five cents would be as cheap fuel as water-gas at fifty. But, in point of profit to the maker, the difference at these prices would be greatly in favor of the water-gas; while, in another controlling matter, on the side of the consumer, it is not malapropos to say that comparisons are "odorous." The mysterious but not agreeable smell raised by a coal-gas jet of the best air-mixing or total-combustion burner, when impinging on the surface of any cooking utensil (thought by Professor Wurtz to arise perhaps from a synthetic re-formation of gas) is a serious objection to coal-gas cooking, from which water-gas is absolutely free. Its combustion is perfect, without air mixture, and without smell, "synthetic" or whatever. So far as the hydrogen is concerned, the product of combustion is pure aqueous vapor, in a quantity not likely to overcharge with moisture the atmosphere of the house. The other principal ingredient, thirty-six per cent, of carbonic oxide, becomes, of course, carbonic acid in burning, and must be conducted away.
Using a Goodwin's gas-stove to its full capacity at once as baker, broiler, and boiler—simultaneously baking bread and potatoes, boiling other vegetables and coffee, and broiling steaks and chops, sufficient for a dinner-party of "experts"—Mr. Strong found the time thirty minutes, and the consumption of gas thirty-two and a half feet, or sixty-five per hour. This (at fifty cents per one thousand feet) was three and a quarter cents per hour for the full running of the cooking apparatus or one and five eighths cent for cooking the entire dinner.
Turning from the domestic to the business arts, we encounter a prodigious revolution on the threshold with the incoming fuel. The gas-engine already referred to, as recently improved and extensively introduced under the German patents of Otto, supplants the steam-engine completely, on the small scale, even at the present high cost of coal-gas, and with certain other drawbacks peculiar to that somewhat tarry article. It is already available up to thirty horse-power, and at fifteen and under it is universally found a much cheaper source of power than steam, and with gas of five times the cost and much less adaptability than the American water-gas. Thousands of these engines are used in England, and in London it is expected that steam-boilers with their smoke and danger will ere long be prohibited where the gas engine is available. The "silent" gas-engines are also selling rapidly in America on the lines of rural and minor manufactures. What new stride this important substitution may take with gas at fifty cents and free of tarry ingredients, one hardly dares conjecture. But its absolute safety, automatic operation, and slight displacement, open to the gas-engine a vast sphere of common and household uses for which no motor had before been adapted. On the large scale, moreover, we may perhaps live to see such things as gas-locomotives, unburdened with coal or water, rid of their boilers, their annoying smoke, and their destructive sparks, and satisfied with picking up at intervals a plate-iron tender-car full of compressed water-gas.
In hope of closing with a sustained interest, the first actual and one of the greatest possible applications of the new gas-fuel has been left to be last mentioned—that of the manufacture of iron and steel, lately commenced in Sweden, under the American patents and the personal superintendence of a gentleman to whose inexhaustible energy and tact the American water-gas is largely indebted for its difficult yet brilliant progress—Mr. George S. Dwight, of Montclair, New Jersey.
Siemens's gas—a product saved from the combustion of coal in a furnace invented by that distinguished metallurgist—has long been used with admitted advantage in various branches of iron-working. With this well-known and standard form of gaseous fuel, Professor Moore's report, already quoted, minutely compares the American water-gas, showing that the former is many times more expensive and less efficient than the latter. In fact, water-gas made under all the old disadvantages of method is said to have been in use twenty years ago at the Oldbury furnaces near Birmingham, England, and was introduced nearly as long ago in the Yorkshire blast-furnaces. It has also been used with marked preference in France, by workers in the finer metals particularly. Of the American water-gas, Dr. Moore says that its special advantages in metallurgy are, besides its great economy in cost and consumption, the high and easily regulated temperature it affords beyond all other fuel, and the relatively small volume of products of combustion evolved—being, in short, the most concentrated form of gaseous fuel hitherto available for such purposes. To which he might have added (if he had not been at the moment confining his comparisons to gases) that its freedom from the impurities rife in mineral coals, and that greatly restrict the supply of iron fit for refining, seems alone sufficient to insure its substitution for all other fuel in the manufacture of iron and steel.
That Sweden has been first to move in this direction was natural, from peculiar circumstances. This preëminence of "Swedes iron" has been sustained under a singular disadvantage as to fuel. The country is destitute of coal, and pays a monstrous tax on that grand factor of its leading industry in the expense of importing it from England. On the other hand, it possesses inexhaustible stores of peat, which is well adapted to the manufacture of water-gas by the American process, and will henceforward supply the Swedes with that perfected form of fuel at a cost that will seem to them as nothing.
The operations now going on in Stockholm under the superintendence of Mr. Dwight were initiated by a semi-official body styled the Jernkontoret (or Metallurgical Association), which, under the patronage of the Government, pursues whatever investigations and experiments promise advantage to the grand interest of that country. Its voluminous published researches and reports are of standard authority in metallurgy all over the world. Water-gas making was commenced with American apparatus erected in the Atlas Works, Stockholm, in 1879, and the product applied to the treatment of iron ores and the manufacture of steel. An official certificate of unqualified strength has been published under the signatures of leading Swedish and Russian metallurgists, and new works on a practical scale are now being established. The subject excited extraordinary interest throughout the intelligent classes of the nation. Preparations were also made to conduct the gas into various establishments and mansions for the purposes of warming and cooking. Orders have reached New York for fuel-gas works of the same kind in St. Petersburg, Russia, and preparations were making at the latest advices for similar movements in Austria and Bohemia, as well as to press forward organizations for the supply of American cities with both domestic fuel and manufacturing power in this form. The introduction of a ubiquitous motor (for the Otto silent gas-engine) as handy, cheap, and common as the ordinary gaslight, will mark a new era in industry, and prove an important new factor in political economy.