BLAST FURNACE PRACTICE, Modern. The first requisite for the conduct of blast furnace practice is equipment.
The construction of the Duquesne blast fur naces in 1902 and 1903 marked a great advance in the evolution of the modern blast furnace, for the labor of filling the furnaces,. formerly done by hand, was performed mechanically and their size far exceeded any previously built. The capacity of 600 tons per day was fully 50 per cent greater than any other furnace produc tion at that time. These furnaces were 100 feet high and were equipped with powerful blowing engines of large capacity.
The ore was handled in and of stock pile mechanically by means of a large gantry crane equipped with a scraper bucket spanning the ore yard. The stock house was equipped with steel bins for ore, stone and coke, and the furnaces were filled by an inclined hoist, op erating a cylindrical bucket, which was depos ited in the stock house on a low car and trans ferred to the bin chutes for filling.
This bucket was closed by a bell, to the rod of which the hoist rope was hooked, when the tub was hoisted, and this bell when lowered on top discharged the contents automatically into the receiving hopper, thus forming a complete ring in layers of material in this hopper each time a tub was hoisted.
The success of these stacks was followed rapidly by the construction in different parts of the country of stacks of similar dimensions but differing somewhat in equipment, particularly in the charging mechanism. These furnaces for a while gave good results but later were a grave disappointment, owing to the almost universal failure of their linings after a few months' op eration, while the Duquesne furnaces made over 1,000,000 tons on their first lining, a result due to the good distribution obtained by the me chanical charging apparatus installed at the Duquesne Works. As a result, charging mech anisms have been generally improved, and still larger furnaces are being erected.
The hoist and distributing mechanism in stalled at Duquesne seemed to engineers, when built, more complicated and expensive than was necessary, and at the same time they aimed to make a still greater reduction in the labor em ployed, but some failed to appreciate the im portance of good stock distribution on top of the furnace and how it was accomplished by the Duquesne design.
The usual construction now adopted for charging the furnace is mechanical stock hand ling, storage bins and skip hoists equipped with single or double skips. These dumping skips are responsible for the short life of the fur nace linings, for in discharging their load on top of the furnace they cause a sorting of the stock, the finer parts dropping down near the dumping point of the skip and the lumps going farthest away. It is quite possible to obtain a uniform layer in the furnace of coke, lime stone and ore, but the fact that more of the lumps went to the side of the furnace farthest from the skip made the gases channel on that side and thus cut the inwall by concentrating the smelting action to that side of the furnace. Good stock distribution may be obtained by mechanically filled furnaces provided with any kind of skip hoists by the use of the rotary dis tributor, of which there are three distinct types.
From the bins,.a larry should weigh and deliver the stock to the skip at the foot of the inclined furnace hoist.
When the•plant is located on navigable water and receives its ore that way, the unloading machines operating grab buckets are arranged to deliver the material into the stock piles, from whence it is recovered by another grab bucket, operated by a crane spanning the ore yard and delivering its load into an elec trically driven transfer car serving the stock bins. When two or more large furnaces are located away from navigable water, and hence receiving all the stock by rail, a mechanical car dumper is an economy.
Considering next the power equipment, the water tube boiler gives the best results with waste gas as a fuel, but, for more than two furnaces, much greater economy is obtained by burning the gas direct in the cylinder of the gas engine and thus furnishing the electric power required to drive auxiliary machinery about the plant, and in the gas-driven blowing engine the blast required for the furnace. In plants where the water-tube boiler is still in use, the steam engines are compounded and the exhaust steam condensed in a central condenser of large capacity.