This vacuum system, with an effective pumping speed of almost 600,000 m³/h, is the largest vacuum system built by Leybold in its 164-year history to date. The Siemens VAI customer Altos Hornos de Mexico (AHMSA) extended the product range of its No. 2 converter steel mill to steel grades for oil and gas industries. The treatment capacity of the 150-ton double-RH vacuum degassing should be around 2 million metric tons of liquid steel per year, approximately 50 batches per day.
 
With this new plant, AHMSA will be able to produce special steel grades with a very low hydrogen content, as they are required for applications in the oil and gas industries. The commissioning of the new RH plant is planned for October 2015.
 
The required vacuum technology is covered by systems of Oerlikon Leybold Vacuum. Essential functions of RH degassing systems include the removal of hydrogen, the forced decarburization and the chemical heating of the liquid steel. The treatment of the molten steel is carried out under vacuum conditions, reducing the carbon content by means of oxygen injection in a first step. Afterwards the pressure is further lowered and the dissolved hydrogen content in the steel is lowered to the target value. A low hydrogen content is the essential prerequisite for the production of these high-strength steel grades.
 
Energetic balance of mechanical vacuum systems
The increasing demand for higher-quality steels triggers the need for innovative and efficient steel degassing. The traditional steam ejector systems have a number of disadvantages such as high energy consumption and significant CO₂emissions. In addition, the metallurgical processes see increased cost due to a very complex wastewater treatment and sometimes also by the expensive operation of steam boilers. Therefore, modern, mechanical vacuum systems are a real alternative, functionally as well as economically.
 
Especially in comparison with steam ejectors and liquid ring vacuum pumps, innovative, mechanical vacuum pump system for steel degassing offer a rugged, reliable and powerful vacuum supply with a stable vacuum level independent of external disturbances such as the water temperature. This is particularly important with regard to the ever increasing demands on cost of ownership and CO₂ reductions.
 
Using modern, robust, dry compressing screw type vacuum pumps and Roots pumps such systems are nowadays used even for the most demanding degassing processes.
 
Modular system design
The delivery of Oerlikon Leybold for AHMSA includes 10 standardized steel degassing modules in an "8-2-3 variant". The 10 modules provide a nominal pumping speed of 784,000 m³ / h. They are thus able to handle all gas flows released at the various operating points, and to evacuate the degassing vessel in the required time of <5 min. The modules provide a high pumping speed with an extremely small system footprint and thus enable the customer to have a space-saving plant set up.
 
“The future lies in handling not only the manufacturing aspects of the industrial processes in question, but also in managing the increasing environmental demands. The energy balance and the intelligence of the components used to build up systems will drive future markets,” explained Dr. Martin Fuellenbach, CEO of Oerlikon Leybold Vacuum, “The chance to control and monitor systems facilitates the optimization and maintenance of the production process. This certainly represents a cost advantage.”
 
Highest security
As the plant operator partially expect the existence of potentially flammable gases during the oxygen injection process, he defined an explosion zone 1 for the interior of the vacuum pumping system, which in turn necessitates the use of components, which are qualified in accordance with the ATEX directives. Oerlikon Leybold Vacuum is an ATEX-certified provider of vacuum systems and supplies systems which are performing according to the criteria of Category 2.
 
Steel degassing plant
For AHMSA's twin RH plant in Monclova, in the state of Coahuila, Siemens also supplies the vessel, the structural steel work and a combined vessel ladle lifting system (CVL). This solution requires little space, enabling vessels to be lifted in places inaccessible to cranes. The scope of supply from Siemens also includes the electrical and automation equipment for the RH plant. The compact and extremely versatile adjustable vacuum technology delivered by Oerlikon Leybold Vacuum is an essential part in the performance of the overall system.