This is a reverberatory furnace to which is connected a regenerative system of heating. A longitudinal section of a furnace, lined for the basic process, is shown in Fig. 26, and the diagram below the furnace is a simplified arrangement to show plainly the connections and passages for air and fuel gas in the regenerative system.
Fig. 26. - Open-Hearth Steel-Furnace.
The hearth or basin, built on flat steel plates FF which are supported by I-beams, is composed of brick and magnesite as shown. The charging doors D are on the side of the furnace next to the charging platform (about 12 feet above ground level) and the tapping hole is on the opposite side of the furnace. The roof of the furnace is made of silica bricks arched across the furnace.
The lower sides of the air ports RR' and the gas ports GG' are covered with a layer of chrome brick, a basic material, as these bricks may become loosened and fall into the metal in the hearth. Above the level of the molten charge, where no chemical reaction will result, the furnace is built of silica bricks to save expense of basic materials.
Opening into each end of the furnace are two ports (R and G on one side and R'G' on the other) which convey air and fuel gas into the space above the charge where they mix and the gas burns, causing a long flame of intense heat which sweeps across the length of the basin or hearth. The regenerative system operates as follows: A supply of producer or natural gas from the gas main, marked in the diagram, passes along the conduit A, through the highly heated checker-brick work in the gas regenerator C, and enters the furnace through the port G. Air drawn from the atmosphere passes through the air inlet, along the conduit B, through the checker-brick work of the air regenerator, and enters the furnace by its port R. Both gas and air are highly heated by passing through the incandescent checker-brick work of their respective regenerators, and as soon as they come into contact they unite in a flame of intense heat. The draft of the chimney causes the products of combustion to pass into the gas and air ports G' and R' at the opposite end of the furnace, through the two regenerators below (to which they give up much heat) and along the conduits K and L into the culvert T which leads into a tall chimney.
At intervals of about half an hour, the valves M and N are reversed, this causing a reversal of the path of air and gas through the furnace and regenerative systems. In this way the regenerators at the opposite ends of the furnace act alternately as heaters of gas and air as they pass to the furnace, and absorbers of heat from the burned gases after they leave the furnace. This system makes possible the maintenance of the high heat which the open-hearth process requires.
The hearth is so supported as to leave a large space underneath open to the air. This allows a radiation of heat and prevents overheating of the materials composing the hearth. The entire brick work of the furnace is rigidly braced by vertical steel beams joined above and below the brick work by tie rods as shown in Fig. 27.