Open hearth furnace

The open-hearth furnace is used for the purification of pig iron for the purpose of recovery of steel and is one of the so-called open-hearth process. The term goes back to the name of Friedrich Wilhelm and Siemens, as well as Pierre -Émile Martin and his father Émile Martin.

• 2.1 The last open-hearth furnace in Western Europe 2.1.1 design features and key changes

Procedure

The Siemens - Martin process is a technical development of the hitherto known methods of production of steel in crucible furnaces. The essential difference is that the temperature in the furnace increased to 1800 ° C and molten steel is produced. The fuel used generator gas or oil. The original capacity of the open-hearth furnaces of 10 t Abstichmasse was increased to over 600 tonnes in the course of development for liquid use in the USA and Russia.

To produce steel from the recovered blast furnace pig iron, accompanying elements included (so-called " iron companions " ) such as carbon, manganese, silicon, phosphorus and others must be removed. This is done by so-called refining. The impurities are oxidized and escape either gaseous (such as CO2) or swim as slag from solid oxides on the molten steel.

In the Siemens - Martin process, the oxidative effect is achieved by the addition of a certain proportion of scrap, pig iron ores and lime that give off oxygen to the melt. This solid insert is introduced into wells by means of charging machines in the hearth oven. In the liquid application, the pig iron through a channel in the hearth furnace is tilted.

Usually the hearth furnace is usually combined with Siemens 's regenerative firing, which is housed in an underlying chamber. In regenerativ in regeneration chambers, the gaseous fuel is preheated by the exhaust gases from the furnace to achieve the necessary temperature of 1800 ° C. Also, the hot flame gases have oxidative effect and are absorbed directly into the melt.

The technological process

The melting process is divided into several sections that are not strictly separated:

Total time 8 h

Immediately after tapping the molten steel is poured into ingot molds. After solidification, the blocks / slabs are transported for further processing to the rolling mill.

Construction of an open-hearth furnace

The open-hearth furnace consists of upper and lower oven.

The upper oven is the melting or stove space in which the metallic charge (scrap) is melted. Individual parts of the upper furnace are the hearth, the vault, the front and rear walls, heads, and the runner. In addition to the steel structure of the furnace consists primarily of a refractory material. Burner heads with gas and air trains are used for heating / melting the raw material. Feeding is by a charging crane on the furnace platform.

In the lower furnace are the slag and regenerative chambers. In the slag and dust chambers the slag particles are added. In the regenerative chambers is preheated by the use of exhaust heat, the combustion air or the gas generator. The chambers are lined with a checker of refractory material.

Advantage: the regenerativ the energy contained in the exhaust gases to preheat the fuel gases and the air is used for this purpose, a periodic switching of the chambers 8 and 20 minute intervals is necessary. The control / switching occurs from the wheelhouse. Lower furnace and fireplace are connected by channels.

History

In 1856, Friedrich Siemens had applied for a patent on his invention of the regenerative furnace. This new furnace based on a system for generating high- temperature preheating of the gas and air. Wilhelm Siemens experimented with for several years. So important is this invention was, it initially failed the Siemens brothers to produce liquid steel because at the temperatures reached 1600 ° C, the lining of the furnace melted. Friedrich Siemens applied the method of regenerative furnace successfully in the manufacture of glass, and thus became the largest glass manufacturers in Europe.

In France, the experts were aware of smelting Émile Martin and Pierre -Émile Martin (father and son) on the great advantages of the regenerative furnace and acquired by Wilhelm Siemens drawing and license to operate the furnace. The Martins made ​​a breakthrough in the application, because they used temperature-resistant bricks for furnace lining. The process for the production of steel in an acidic, regenerative -fired reverberatory furnace was born.

1867 at the World Expo received the Martins for their excellent steel and the Siemens brothers for the stove top honors.

The Siemens - Martin process was over 100 years one of the most important technologies for the production of steel. The economic importance of the open-hearth process is the special feature of the high scrap use.

The era of open-hearth steel production began on 8 April 1864 in the French resort Sireuil. The first open-hearth furnace in the German-speaking area was built in 1868 in the Austrian Kapfenberg. In Germany, the first open-hearth furnaces in 1869 went to dinner at Alfred Krupp and in Berlin in operation; about the same time in England, Sweden, Italy, and also in North America. At the beginning of the 20th century, the development and initial difficulties were overcome.

In 1915, the proportion of open-hearth steel in Germany rose to over 50%: end of the 40s there were already 75 % worldwide. In 1965, the highest production on a world scale was achieved with 278 million tons. Thereafter, production numbers fell sharply.

In 1985, the proportion of open-hearth steel in Western Europe was no longer significant and important only in Eastern Europe and China.

In Western Europe, the Siemens - Martin process since the 1960s has largely been replaced by the basic oxygen, and since the late 1980s through the electric steel process. In the United States, China and Russia, the method is applied sporadically.

The last open-hearth furnace in Western Europe

The last open-hearth furnace in western Europe is located in the Industrial Museum of Brandenburg an der Havel.

He was taken as the open-hearth furnace XII on October 12, 1967 by VEB steel and rolling mill Brandenburg in operation. Originally conceived as a test furnace, should be achieved with it top results. The research contract for this project was " to test the new design elements and technologies to production and to achieve optimal performance and outcome indicators that correspond to the world standards with fully oil-fired open-hearth furnaces under the terms of the fixed deployment and use of oxygen ." The results should be used for the modernization of all Brandenburg -hearth furnaces. A special feature from the outset was that the furnace was operated with a plate XII fireplace. 1968, the furnace was used, however, as No. XII to fulfill the plan tasks and thus will interfere with his job as a research furnace. It became apparent that the oven would not achieve the planned parameters especially in the furnace power, heat consumption in the oven shelf and the repair times; in the development of the furnace was therefore continued. As the required state plan requirements for the steel mill were not achieved, began in 1970 a comprehensive reconstruction. This began with the furnace XII. 1975 were rebuilt every twelve furnaces in the steel and rolling mill.

In the autumn of 1990 began with the demolition of the open-hearth furnaces in the steel plant Brandenburg before the plant was shut down with the last tap on 13 December 1993.

Design features and key changes

• Upper furnace with wall support structure in segments after Maerz Boehlens principle
• Introduction of large, two-piece slag cars
• Air guide for the upper furnace cooling in the steel construction
• Enlargement of the hearth area to 83 m²
• When developing a stove series
• Installation of adjacent two-stage regenerative chambers
• Modern waste gate
• Full oil heating