[TRANSACTIONS OF THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS.]

REGENERATING METALLURGIC FURNACES.

BY JACOB REESE..

Read at the Annual Meeting, 1880.

The regenerating principle as applied to heating furnaces was patented and made known by Robert Sterling in the year 1817. His invention relates to heating air, gases and fluids by the agency of air, gases or fluids passing through passages formed of brick, metal, stone or any other material adapted to the degree of heat required, and he describes his invention as applicable to the manufacture of glass, pottery and any other case where great heat is required.

This principle has been embodied in improved apparatus, and practically utilized for metallurgical operations by Charles W. Siemens and Frederick Siemens, and is now in general use in the open-hearth process. The advantages of the system are: 1. A more perfect and uniform combustion of the fuel; 2. The utilization of slack or other cheap material; 3. The recovery and return to the furnace of a large percentage of the caloric of the waste gases; 4. Greater facility for securing and maintaining a high and uniform temperature; 5. Readily securing an oxidizing or a carbonizing flame during treatment of the metal.

In the construction of these regenerative furnaces, the regenerators have been placed below ground, and generally beneath the ground. This arrangement I believe to be objectionable on account of the following reasons: 1. the arrangement renders it inconvenient to secure a sufficient length of heating surfaces for the passage of the incoming and outgoing air and gases; 2. the ground is generally damp and wet, and considerable heat is lost by radiation and absorbtion; 3. the regenerators are very difficult to get at for cleaning and repairs; 4. the continual changing of the temperature causes their walls to crack, and their alternate expansion and contraction is liable to destroy the solidity of the furnace, or to crack the bottom and allow the molten metal to run down into the regenerators; 5. the metal is liable to boil over and run down as in the preceding case. In order to overcome these objectionable features, I have designed a new arrangement and construction of the regenerators, in which

the stoves are made of a cylindrical form, encased in wrought-iron shells, placed entirely above ground, and are connected with opposite ends of the furnace by combustion chambers, as is shown in the plates connected herewith, in which:

Fig. 1 in Plate I., indicates a front elevation of the improved regenerative open-hearth furnace.

Fig. 2, Plate II., indicates a sectional elevation of the same.

Fig. 3, Plate III., indicates a cross sectional plan view of the same. Fig. 4 indicates a cross sectional elevation of the upper portion of one of the stoves.

Fig. 5 indicates a top view of one of the stoves.

Fig. 6, Plate IV., indicates a front sectional elevation of the improved regenerative open hearth, provided with an oblong revolving bottom, such as is shown and described in English Letters-Patent No. 1,223, granted in 1853 to Walker & Warren for improvements in the manufacture of iron.

Fig. 7 indicates a cross sectional view of the same.

Fig. 8, Plate V., indicates a front elevation of an improved regenerative heating furnace.

Fig. 9, Plate VI., indicates a cross sectional view of same.

The construction and arrangement of the regenerators, as applied to the ordinary open hearth may be readily understood by reference to Figs. 1 and 2, which indicate the arrangement, and Figs. 3, 4 and 5, which disclose details of construction. It will be observed that the stoves are of a cylindrical form; that they are provided with iron shells and are placed entirely above the ground, one being at each end of the furnace, and connected thereto by means of a combination chamber at one side of its base.

Each stove is divided into two distinct and separate compartments, by means of a division wall, which extends from its base up to the top of the dome, as is indicated in the sectional view of the top shown in Fig. 4. This division wall is placed somewhat to one side of the center of the stove, so that the compartment for the air may have a larger area than the compartment for the gas. Both these compartments are subdivided into two sections, which communicate together at the dome, by means of vertical division walls, which extend from the bottom of the compartments upward to that point, and each of the subdivisions are filled with fire brick in lattice arrangement, which extends up to the top of the subdivision walls, so that the air and gas may ascend in one subdivision and turn in the dome, and return downward in the other subdivision of their respective compartments. The bottom of these compartments, upon which the lattice work rests is formed by the perforated arched roofs of the distributing and combustion chambers at the base of the stove.

The distributing chambers are provided with a central double-valve chamber, to admit the outward passage of the waste gases into the stack, and to regulate the same; and they are also provided with an air-inlet chamber open to the atmosphere, and with a gas-inlet chamber communicating with the producers, for the admission of the air and the gas into their respective distributing chambers and compartments.

The stoves are provided with manholes in the tops of the dome, in order to admit of entrances for repairing, and to allow the insertion of mechanism for cleaning. The man-holes are closed when the stoves are in use, by caps, as shown in Fig. 5. The stoves are also provided with cleaning doors, which open into the distributing chambers, and the combustion chambers in order to allow the removal of the dust, slag, and other matters which may collect therein during the cleaning of the regenerator or working of the furnace.

Figs. 6 and 7 indicate my improved arrangement and construction of regenerators, in connection with a Walker & Warren oblique revolving hearth. In this case, the only difference in construction is that of the furnace proper, which is fully set forth in their English Letters-Patent, No. 1,223, of 1853.

Figs. 8 and 9 indicate my arrangement and construction of regenerators as applied to heating furnaces.

In the construction of a ten-ton plant, such as is shown in Figs. 1 and 3, I propose to make the stoves about ten feet in diameter by thirty-five in height, which will require thirty thousand four hundred and fifty brick for the outer walls, ten thousand one hundred and seventy-four for the division walls and arches, and twenty thousand five hundred and eighty for the lattice work. This construction will give a passage way of seventy feet for the air and gases through each regenerator, and twelve thousand seven hundred and twenty square feet of heating surface to each pair of stoves, being seven thousand five hundred square feet more than that of the ordinary form of regenerators applied to such furnaces, and consequently, in practice, the temperature of the outgoing waste gases will be reduced to a much lower, and the temperature of the incoming air and gases will be raised to a much higher point than has been secured by the use of the ordinary plant, and an exceedingly high temperature may be easily and economically maintained in the furnace.

One of the reasons for constructing the stoves with so great a length of passage-way for the air and gases, and with so great an area of heating surface, is that they are designed to be used in cases where a very high and constantly uniform temperature is required. It is well known that iron and steel are more fluid at any given temperature when they possess the most carbon, and that the molten

metal containing the least carbon, requires the greatest heat to keep it in the fluid condition. Now, in designing these stoves, I had in view the production of ingot iron, very low in carbon, by desdiconizing and decarburizing the metal in a silicious-lined converter, and then running it into an open hearth, excluding the slag, for further treatment either by the acid or by the basic process. This decarburized metal requires a very high and continuous temperature to keep it in a fluid condition, and, as it is run into the open hearth without the slag, it must be protected from oxidation. Therefore, to secure these conditions as far as possible, the area of the heating surfaces and the lengths of their passages have been greatly increased, and a combustion chamber is formed at the base of each stove, so that combustion will take place previous to the entrance of the gases into the metal chamber.

The operation of the regenerators is as follows: Gas is admitted from the producers into the gas-distributing chamber, and air into the air-distributing chamber of one of the stoves, and its double outlet chamber is closed. The double outlet chamber of the opposite stove is opened to create a draft from the stack, and its air and gas inlet valve chambers are closed. The draft from the stack draws the air and gas through the perforated arched roofs of their respective chambers, up through the lattice work into the dome, where they turn and pass downward through the lattice work of the other division of their respective compartments into the combustion chamber, where they commingle, are consumed, and the products of combustion pass into the furnace, over the metal chamber, into the combustion chamber of the opposite stove, upward through the lattice work into the dome, and then pass downward through the lattice work of the other subdivisions, into the distributing chambers, and from there, through their double outlet chamber, into the stack.

When the lattice work of the stove has been sufficiently heated, the currents are reversed by opening and closing the proper valves, and the cold air and gas, in passing upward and downward through its lattice work, absorb the heat which has been deposited there by the outgoing waste products of combustion,and when they commingle in the combustion chamber, an intense and vivid combustion takes place, and an exceedingly high temperature is produced. After this operation has continued for about half an hour, the currents should be again reversed, and the stoves alternately subjected to the action of the outgoing waste gases and to the action of the incoming air and gases as described.

In the operation just described, the outgoing waste gases will enter the stove at a temperature of about four thousand degrees, Fahrenheit, and, on account of their long passage and the great heating

area of the stove, they escape into the stack at a temperature of about four hundred degrees, so that a saving is effected of ninetenths of the caloric, which, in ordinary non-regenerative furnaces, escapes into the air.

The cost of these regenerative stoves will be about three thousand five hundred dollars for a pair of the size specified, which is greater than that of the ordinary underground brick work, but as their heating surface and capacity is so much greater, and as I believe they possess a construction and arrangement which obviates the objectionable features which characterize the ordinary construction and arrangement, I hope to find their use very advantageous in the refining of ordinary open-hearth steels, as well for the production of low ingot irons by the method to which I have referred.

This construction and arrangement will also be applicable to steam boilers and to all furnaces where it is desirable to use cheap fuel, to avoid smoke, and to maintain a high, constant and uniform pressure.

DISCUSSION.

Mr. Holley-It seems to me that Mr. Reese has done a good thing, applicable under certain circumstances, in introducing this form of stove. It is quite true, as he says, that under some conditions the regenerator cannot be well put under the hearth of the furnace. In most cases where a regenerator is likely to be deranged from a rise of water, it is very important to have it placed above such a possibility. In adopting the Siemens-Cochrane system substantially, that is the tall stove with the up-and-down chambers, he seems to have got the regenerators into the least ground space, and the room occupied above is not wanted for anything else. But the best open-hearth plant now, I believe, is a furnace set so high that the regenerator can be put underneath without going down much below the general level, so that it is unnecessary in those cases to take up the little room that Mr. Reese does take up with those outside generators. With the charging floor of the furnace twelve or fifteen feet above the level of the pit, there is quite room enough for them underneath the floor. Mr. Reese's system of a regenerator, provided it is to be used for heating furnaces which must stand on the general level, seems a good one where the water is likely to give trouble. But, I may say in passing, that the continuous regenerator, used by Mr. Sellers in one form, and as is used by Mr. Swinell in Pittsburg, possesses some advantages over the more complex form of an alternating regenerator for merely heating purposes. The objection Mr. Reese made to the pos