Of the Economy of Fuel
The Coal Question: Of the Economy of Fuel
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Historical E-Book: The Coal Question: An Inquiry Concerning the Progress of the Nation, and the Probable Exhaustion of Our Coal-Mines
Author: William Stanley Jevons
Edition Used: London: Macmillan and Co., 1866. (Second edition, revised)
First Published: 1865
Chapter VII
IT is very commonly urged, that the failing supply of coal (The Coal Question: Of the Economy of Fuel) will be met by new modes of using it efficiently and economically. The amount of useful work got out of coal may be made to increase manifold, while the amount of coal consumed is stationary or diminishing. We have thus, it is supposed, the means of completely neutralizing the evils of scarce and costly fuel.[1] It is shown, in fact, by the mechanical theory of heat, that the work done by coal, in a good engine of the present day, does not exceed about one-sixth part of what the coal is capable of doing. In furnaces, too, the portion of heat actually used is a small and often infinitesimal fraction of the heat wasted; and in the domestic use of coal, in open grates, at least four-fifths of the heat escapes up the chimney unheeded.
I speak not here of the domestic consumption of coal. This is undoubtedly capable of being cut down without other harm than curtailing our home comforts, and somewhat altering our confirmed national habits. The coal thus saved would be, for the most part, laid up for the use of posterity. But even if our population could be induced to abstain from the enjoyment of a good fire, the saving effected would not extend over more than about one-third of the total consumption of coal; the domestic consumption being, on an average, about one ton per annum, per head of the population. Of the other two-thirds, nearly one-third is used in our iron manufactures; and the remainder in our factories, furnaces, and machine shops generally.
But the economy of coal in manufactures is a different matter. It is wholly a confusion of ideas to suppose that the economical use of fuel is equivalent to a diminished consumption. The very contrary is the truth.
As a rule, new modes of economy will lead to an increase of consumption according to a principle recognised in many parallel instances. The economy of labour effected by the introduction of new machinery throws labourers out of employment for the moment. But such is the increased demand for the cheapened products, that eventually the sphere of employment is greatly widened. Often the very labourers whose labour is saved find their more efficient labour more demanded than before. Seamstresses, for instance, have perhaps in no case been injured, but have often gained wages before unthought of, by the use of the sewing-machine, for which we are so much indebted to American inventors.
So it is a familiar rule of finance that the reduction of taxes and tolls leads to increased gross and sometimes even nett revenues; and it is a maxim of trade, that a low rate of profits, with the multiplied business it begets, is more profitable than a small business at a high rate of profit.
Now the same principles apply, with even greater force and distinctness, to the use of such a general agent as coal. It is the very economy of its use which leads to its extensive consumption. It has been so in the past, and it will be so in the future. Nor is it difficult to see how this paradox arises.
The number of tons of coal used in any branch of industry is the product of the number of separate works, and the average number of tons consumed in each. Now, if the quantity of coal used in a blast-furnace, for instance, be diminished in comparison with the yield, the profits of the trade will increase, new capital will be attracted, the price of pig-iron will fall, but the demand for it increase; and eventually the greater number of furnaces will more than make up for the diminished consumption of each. And if such is not always the result within a single branch, it must be remembered that the progress of any branch of manufacture excites a new activity in most other branches, and leads indirectly, if not directly, to increased inroads upon our seams of coal.
It needs but little reflection to see that the whole of our present vast industrial system, and its consequent consumption of coal, has chiefly arisen from successive measures of economy.
Civilization, says Baron Liebig, is the economy of power, and our power is coal. It is the very economy of the use of coal that makes our industry what it is; and the more we render it efficient and economical, the more will our industry thrive, and our works of civilization grow.
The engine is the motive power of this country, and its history is a history of successive steps of economy. Savery recommended his engine for its cheap drawing of water and small charge of coals. But as he allowed the steam to act straight upon the water, without the intervention of a piston, the loss of heat was tremendous. Practically, the cost of working kept it from coming into use; it consumed no coal, because its rate of consumption was too high.[2] Newcomen made the first step towards the future use of the engine, by interposing a piston, rod, beam, and pump, between the steam and water. It was asserted that mines formerly drowned out and abandoned might sometimes, when coal was very cheap, be profitably drained by his rude atmospheric engine. But when Brindley went to Wolverhampton, to inspect one of these engines, he formed the opinion "that, unless the consumption of coal could be reduced, the extended use of this steam-engine was not practicable, by reason of its dearness, as compared with the power of horses, wind, or air."[3]
Smeaton, the most philosophical of engineers, after a careful study of the atmospheric engine, succeeded in nearly doubling its efficiency. The engine had long been hanging on the verge of commercial possibility; he brought it into successful use, and made it both possible and profitable. But in this branch of his art he willingly gave place to that even greater man, who, after long continued scientific and practical labours, made the steam-engine the agent of civilization. I need hardly say that Watt (Watt, James)'s two chief inventions of the condenser and the expansive mode of working are simply two modes of economising heat. The double cylinder of Woolf, the method of surface-condensing, of super-heating, &c. are other inventions, directed to economy of coal. To save the loss of heat in the boiler, and the loss of power by friction, are two other points of economy, to which numberless inventions are directed. And with the exception of contrivances, such as the crank, the governor, and the minor mechanism of an engine, necessary for regulating, transmitting, or modifying its power, it may be said that the whole history of the steam-engine is one of economy.
"The economy of fuel is the secret of the economy of the steam-engine; it is the fountain of its power, and the adopted measure of its effects. Whatever, therefore, conduces to increase the efficiency of coal, and to diminish the cost of its use, directly tends to augment the value of the steam-engine, and to enlarge the field of its operations."[4]
The result of these efforts at economy is clearly exhibited in a table of the duty done by engines at different periods. This work or duty is expressed by the number of pounds of water raised one foot high by the expenditure of a bushel (84 lbs.) of coal.[5]
| Duty in lbs | |
|---|---|
| 1769. Average of old atmospheric engines... | 5,590,000 |
| 1772. Smeaton's atmospheric engine... | 9,450,000 |
| 1776. Watt's improved engine... | 21,600,000 |
| 1779-1788. Watt's engine working expansively... | 26,600,000 |
| 1820. Engine improved by Cornish engineers... | 28,000,000 |
| 1830. Average duty of Cornish engines... | 43,350,000 |
| 1859. Average duty of Cornish engines (per 112 lbs.?)... | 54,000,000 |
| 1859. Extreme duty of best engine (per 112 lbs.?)... | 80,000,000 |
In less than one hundred years, then, the efficiency of the engine has been increased at least ten-fold; and it need hardly be said that it is the cheapness of the power it affords that allows us to draw rivers from our mines, to drive our coal-pits in spite of floods and quicksands, to drain our towns and lowlands, and to supply with water our highest places; and, finally, to put in motion the great system of our machine labour, which may be said, as far as any comparison is possible, to enable us to do as much as all the other inhabitants of the world with their unaided labours.
Future improvements of the engine can only have the same result, of extending the use of such a powerful agent. It is usual with a certain class of writers to depreciate science in regard to the steam-engine, and to treat this as a pure creation of practical sagacity. But just as the origin of the engine may be traced to a scientific work, so it is now theory and experiment in their highest and latest developments, which give us a sure notion how great will be the future improvement of the engine, and through what means it is to be aimed at.
"A well constructed and properly working ordinary double-acting steam-engine," of the present time, consumes about 4.00 lbs. of bituminous coal per horse-power per hour. "A double-acting steam-engine, improved to the utmost probable extent, would use 2.50 lbs. of the same coal;" while a theoretically perfect engine, working between such limits of temperature as are usual in steam-engines, "would require only 1.86 lbs."[6]
But theory further points out, what practice has partially confirmed, that the work done by an engine for a certain expenditure of fuel is proportional to the difference of the temperatures at which steam enters and leaves the engine. From this principle arises the economy of using high-pressure and super-heated steam; for we have, as it were, all the old force of the low-pressure and less-heated steam, with a great addition from the initial high pressure and the increased store of useful heat in the steam. The economy already effected in this manner is wonderful. The very engines which had burned 12 or 14 lbs. of coal per hour, when worked with steam at 4, 6, or 8 lbs. pressure, have been found to burn only 3½ or 4 lbs. of coal when supplied with stronger [[boiler]s], and worked at steam-pressures from 30 to 70 lbs. per square inch.[7]
Such simple changes as the shortening of the steam supply, the addition of a second cylinder, the felting of the boiler and steam-vessels, the enlarging of the boiler, the raising of the pressure, or the acceleration of the speed of travelling of an engine, are the simple means by which the self-same engine has often been made to give a manifold result.
It is true that, as we go on improving, the margin of improvement becomes narrower, and its attainment more difficult and costly. The improvement of the boiler mainly depends upon the amount of capital expenditure against current expenditure. For the efficiency of a boiler grows with the surface of water we can expose to absorb the heat of the fire; but the more we extend this surface, the less additional economy will an equal extension effect.
So the accomplishment of a new steam-engine, with much increased limits of temperature and economy, will probably require a wholly new set of mechanical expedients, because heated steam destroys the lubricating oil which is an essential part of all machinery, and is even said to attack the iron itself. Many of the difficulties inherent in the steam-engine are, however, absent in the air-engine, which presents a wide prospect of economy, as seen in the following numbers:—
| Actual consumption of Coal per horse-power, per hour. |
Consumption of theoretically perfect engine. | |
|---|---|---|
| Sterling's air-engine... | 2.20lb. | 0.73lb. |
| Ericsson's engine of 1852... | 2.80 | 0.82 |
"Sterling's engine," it is said, "as finally improved, was compact in its dimensions, easily worked, not liable to get out of order, and consumed less oil, and required fewer repairs, than any steam-engine; still, the advantages shown by that engine over steam-engines were not so great as to induce practical men to overcome their natural repugnance to exchange a long-tried method for a new one."[8]
Still, the fact is established, that an engine has worked at about one-half the expenditure of an ordinary good engine of the present day.[9] The ultimate improvement of the air-engine will probably reduce the consumption to less than one-third of the present consumption. The gradual progress of mechanical workmanship, and long continued efforts incited by the extraordinary profits of success, can alone lead to such an advance. The inventor who can bring a new and economical air-engine into use will reap a fortune to be counted by millions, and will gain the rank of a second Watt (Watt, James).
But such an improvement of the engine, when effected, will only accelerate anew the consumption of coal. Every branch of manufacture will receive a fresh impulse—hand labour will be still further replaced by mechanical labour, and greatly extended works will be undertaken by aid of the cheap air-power, which were not commercially possible by the use of the costly steam-power. At least three great employments of the steam-engine are now in their germ, or scarcely beyond it, which would grow beyond conception by a great improvement of the engine. The pumping of liquid sewage out of our great towns, and its distribution over the country, is one mode which would return a clear profit of many millions a year. The steam-plough is a second instance. Its efficiency is beyond question, and the soil is said to be quickened by its irresistible tillage, as a fire is quickened by the poker. But it yet hangs upon the verge of commercial possibility, as did Stephenson's locomotive-engine, when he had got it to draw, but scarcely cheaper than horses. Taking the first and current costs into account, it is yet doubtful whether the steam-plough works as cheaply as the old horse-plough; but James Watt, to the surprise of his contemporaries, asserted that steam-ploughing was possible;[10] and Mr. Fairbairn, at the British Association in 1861, confessed his belief that many of those present would live to see the steam-plough in operation over the length and breadth of the land. Now, an improvement in the engine, reducing the cost of fuel, will turn the balance in favour of coal-power, and its common use in agriculture will be a certainty.
But it is in steam navigation that the improvement of the engine will have most marked effects. Any extensive saving of fuel, saving its stowage-room as well as its cost, will still more completely turn the balance in favour of steam, and sailing-vessels will soon sink into a subordinate rank.
What is true of economy in the engine is true of several other important, and many less important instances of economy. The extraordinary increase of the iron trade is a trite example. "This rapid and great increase, shown in the last few years, has been, in some part, caused by the economy introduced through the use of the hot blast in smelting, a process which has materially lowered the cost of iron, and, therefore, has led to its employment for many purposes in which its use was previously unknown."[11] In fact, as shown in a subsequent chapter,[12] the reduction of the consumption of coal, per ton of iron, to less than one-third of its former amount, has been followed, in Scotland, by a ten-fold total consumption, not to speak of the indirect effect of cheap iron in accelerating other coal-consuming branches of industry.
Siemens' regenerative furnace is a very good example of economy, now coming into use. It is somewhat on the principle of the hot blast. The current is passed alternately in opposite directions through two brick chambers, between which lies the furnace. Much of the waste heat, on its way to the chimney, is absorbed by the bricks, and again given out, when the current is reversed, to the cool air on its way to the furnace. Much less fuel is required, in such a furnace, to maintain a given temperature, than if cold air were allowed to flow directly into the fire. The general application of such regenerative chambers to furnaces would require the investment of a large amount of capital; and the question in such improvements, as in the case of the boiler, lies between a large initial investment and large current expenses.
The utilization of spare heat from a puddling or reheating furnace, by passing it through a steam-boiler; the saving of the waste gases of a blast-furnace, to heat the blast, or work the engines; the employment of spare heat in salt pans; the use of small gas flames, or gas furnaces, where large coal fires were before used: such are a few of the very many modes in which coal may be greatly saved. In fact, there is hardly a single use of fuel in which a little care, ingenuity, or expenditure of capital may not make a considerable saving.
But no one must suppose that coal thus saved is spared—it is only saved from one use to be employed in others, and the profits gained soon lead to extended employment in many new forms. The several branches of industry are closely interdependent, and the progress of any one leads to the progress of nearly all.
And if economy in the past has been the main source of our progress and growing consumption of coal, the same effect will follow from the same cause in the future. Economy multiplies the value and efficiency of our chief material; it indefinitely increases our wealth and means of subsistence, and leads to an extension of our population, works, and commerce, which is gratifying in the present, but must lead to an earlier end. Economical inventions are what I should look forward to as likely to continue our rate of increasing consumption. Could we keep them to ourselves, indeed, they would enable us, for a time, to neutralize the evils of dearness when coal begins to get scarce, to keep up our accustomed efficiency, and push down our coal-shafts as before. But the end would only thus be hastened—the exhaustion of our seams more rapidly carried out.
Let us remember that we are dependent on the comparative cheapness of fuel and motive power. Now comparative cheapness of fuel cannot be procured or retained by inventions and modes of economy which are as open to our commercial competitors as to ourselves, which have in many cases been introduced by them, and are more readily adopted by versatile foreigners than by English manufacturers bound by custom and routine. Even our superior capital will not avail us against dear fuel, because nothing more readily flows abroad in search of profitable employment than capital. And if we are to uphold a worldwide freedom of intercourse, let us not deceive ourselves as to its natural results upon the material basis of our prosperity.
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