IMPROVEMENT IN HOT-BLAST OVENS.* " On the Practical Results obtained from Blast-Furnaces by the Use of Hot Blast of a very High Temperature." One of the most valuable papers read before the British Association at its meeting this year was one by E. A. Cowper, on the subject above stated. It will be seen that the blast is heated by a cellular mass of brick-work, on the principle of Siemens's furnace.
This plan of obtaining an intense heat is destined to play a great part in the arts, and we wonder that it has not attracted greater attention in this country.
" It is not proposed to detain the meeting with a history of the numerous attempts which have been made to raise the blast for blast-furnaces to a very high temperature, nor will the author occupy much time in the description of the means by which the desired result has been obtained, as a full account of the apparatus was given at the meeting of this Association held at Oxford, though the paper on the subject was not printed in the Transactions.
"In 1861, experimental stoves only, on the new plan, had been erected and worked for heating the blast for one tweer out of the five used for one blast-furnace. Such satisfactory results were, however, obtained, that it was clear that the difficulty of pro curing blast of a very high temperature had been overcome, and Messrs. Cochrane & Co., of Woodside Iron-Works, Dudley, and Ormesby Iron-Works, near Middlesboro'-on Tees, forthwith erected large stoves on the new plan for a complete blast-furnace, and it is now proposed, with your permission, to lay before the section the results obtained during upwards of four years' practical working with these stoves.
"The effect of heating air on the new plan was that a temperature of blast of 1150° Fah. was obtained, instead of only 600° or 700°, as with cast-iron pipes in the common stoves. There was no loss of blast from leakage owing to cracked or damaged cast iron pipes. The iron produced was of rather better quality; twenty per cent. more iron was made from the same furnace, and fully 5 cwt. of coke was saved in the blast-furnace
per ton of iron made.
" The details of the construction of the new stoves will be readily understood by reference to the drawings.
"First. There are two stoves, which are heated alternately and used alternately in heating the cold air: these are filled with brick-work 'set open,' or with small spaces between the bricks, and form regenerators, on the principle of Mr. Siemens's 'regene rator furnaces,' as now so largely used in glass-houses, gas-works, iron-works, he., both for obtaining great heat and economizing fuel.
"The outside of the stoves is of thin wrought-iron plate lined with fire-brick, the iron skin being necessary to retain the blast under pressure, while the fire-brick resists the heat.
"Second. There are provided for the purpose of heating the stove's valves, for the admission of gas and air into a central flue, where combustion takes place when a stove is being heated, the products of combustion passing up the flue and down through the mass of fire-bricks forming the regenerator, and escaping at the bottom to the chimney after the whole of the heat has been abstracted by the fire-bricks, the temperature of the chimney being from 212° to 250°, or thereabouts, during the time a stove is being heated, viz.: for a period of four hours. Then, when a stove is hot, the gas and air are turned off, the chimney-valve shut, and the cold blast is turned on at the bottom of the regenerator, and passes up through the bottom courses of brick-work in the regenerator, thus very quickly becoming heated; and passing in the heated state up through the remaining courses of brick-work, and down the central flue through the hot-blast valve to the blast-furnace, the process of absorption of heat by the air being so perfect that, as long as a few of the top-courses of the brick-work remain hot, the blast is well heated, the va riation in the temperature of the blast being only about 100° Fah. with four-hour changes.