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For the same value of the ratio m, the carbon burned in the zone of reduction increases when, by increasing the temperature of the blast, the total consumption, as well as that near the twyres, tends to decrease; and yet the caloric developed in the zone of reduction is so much the less as the blast temperature is higher. If we compare the three Tables with each other, we see that to ascertain the caloric necessary in the furnace, the blast temperature must be so much the higher as m is less. But it is evident that, all other things being equal, it will be more economical to get this necessary caloric by a good design of the furnace than by an overheated blast. In any case, the maximum of economy will be attained by the combination of high temperature of blast and a high value of the But this high value of m corresponds with

ratio m =

CO2
CO

a certain mean height of furnace, as shown in the preceding paragraphs, and presupposes that the working is slower in proportion to the greater capacity of the furnace—that is, from the moment a certain limit is overstepped.

And now to answer the question proposed at the commencement of this paragraph-whether there is advantage to heat the blast to 800°, 900°, or 1000°. We can boldly answer, Yes. For each rise in temperature of the blast there is increased economy, abstraction being made of course of the cost of maintaining and firing stoves for heating the blast. At the same time this economy decreases rapidly with the rise in temperature. The economy arising from each accession of 100° to temperature of blast is much less from 800° upwards than from 500° to 700°, and still less than between 400° and 500°, and thus in practice it is almost useless to exceed 700° to 800°.

$ 26. Conclusions.-It is now time to state the conclusions to which we have been successively led by the preceding study of the blast furnaces of Cleveland.

1. The production of blast furnaces beyond the capacity of 7000 cubic feet does not increase in proportion to that capacity (§ 1).

2. To appreciate rightly the working of blast furnaces, it CO2 is important to determine by experiment the ratio in the CO

escaping gases. By help of this ratio we can not only calculate the true composition of the gases, but also the weights of blast necessary for the furnace.

3. To determine exactly the ratio it is not sufficient to

CO2
CO

draw off a certain number of samples taken from time to time instantaneously. The gases must be drawn off for several hours, and for this purpose it will be well to have recourse to an apparatus analogous to that used by Mr. Scheurer-Kestner

in his analysis of the products of combustion of coal under steam boilers (§ 9; Plate, Fig. 13).

4. Once the composition of the gases is known, if we would render an exact account of the working of the blast furnace, we must establish a balance between the caloric received and the caloric expended, and estimate separately the caloric developed in the zone of the twyres, and that which is produced in the zone of reduction (§§ 10 to 15).

5. In the application of these principles to several blast furnaces of Cleveland, we have found that the advantages of very high furnaces over low furnaces, result simply from the lower temperature of the upper parts of the body of the furnace. Reduction goes on more perfectly and completely by the action of CO alone, without intervention of solid carbon. We approach the ideal working, which supposes the solid carbon burned exclusively by the oxygen of the blast. An additional advantage, and more direct, is the less amount of sensible heat in the escaping gases (§ 21).

6. The consumption of blast furnaces depends partly on their yield. The minimum consumption corresponds to a mean speed of descent of the charges, and this varies besides with the height and absolute capacity of the furnaces (§§ 22 and 23).

7. By reason of the dissociation of the CO in the upper region of blast furnaces, the temperature of the escaping gases cannot descend below a certain limit, and on this account there is no advantage from the time this limit is attained in enlarging either the capacity or height of the furnaces (§ 24). A very slow rate of working and an excess of capacity are prejudicial.

8. The caloric carried in by the hot blast replaces advan

tageously what is developed in the zone of the twyres. The relative economy due to hot blast decreases as the temperature is made higher. In practice there seems to be no real economy after the limit of 700° to 800° has been reached.

CO2 The hot blast tends to raise the ratio and by cooling the CO

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upper regions of the furnace it favors reduction without consumption of solid carbon; that is, the ideal working of the apparatus.

APPLICATION OF THE NEW METHOD OF ANALYSIS TO A FRENCH BLAST FURNACE.

§ 27. The investigation of which I have just summed up the principal conclusions is composed of two parts:

I first showed how, with help of a simple apparatus, we can obtain samples, small in volume, it is true, but representing the exact mean composition of the escaping gases of a blast furnace, and how, by merely determining the ratio of CO2 we can, quite sufficiently for practice, approximate not CO only to the complete composition of these gases, but in a more rigorous way than by any other method, the weight of the blast consumed in the furnace.

I then showed how, with help of the elements thus determined, we can make up the calorific balance of blast furnaces, and thus render a complete account of all the details of its working.

By applying these principles to some English blast furnaces, and making use of the analysis made by Mr. Lowthian Bell, I endeavored to solve the important question of the

maximum height and limit of capacity, and also that of the use of superheated blast.

It is quite unnecessary that I should insist on the advantages of such an analytic study of the working of blast furnaces. It is time to quit empirical methods for rational investigation.

Up to the present time the difficulties and complication of processes have stayed progress. The mode of analysis which I propose is simple, and available in every industrial laboratory. Until this mode can be applied by myself and others in France I desire to show by one example how it is possible to ascertain, even without chemical analysis, how nearly the working of a blast furnace approaches or falls short of the ideal working, that is, of the minimum consumption possible.

We have seen above how far the old 46 to 56 feet furnaces of Cleveland were from realizing the ideal workings; the gases escaped at a high temperature, and the proportion of

CO2

carbonic acid in them is small. The ratio rarely attained

CO

0-40. The progressive increase in the height of the furnaces overcame this double disadvantage; but it is quite evident that in cases where the gases are cool, and the ratio of CO2 to CO approaches unity, the progressive increase of height is useless, and hence the great importance of determining the CO2

ratio in each particular case. We could then determine CO

a priori whether there would be or not an advantage in modifying the dimensions of the furnaces. By these studies abortive trials, such as are alluded to in § 2, may be avoided— blast furnaces raised to great heights, and then decapitated and reduced to the old dimensions.

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