Ejectors pump hot dirty gases out of the molten steel and evacuate them through the ejector stages and interondensers.
Ejectors are the established pumping systems for vacuum degassing of steel because of high gas handling capacities at low pressures. Nash provides the right solution and system for your steel degassing requirements. Learn more by reviewing our portfolio of ejector vacuum systems.
Solutions for Vacuum Degassing of Steel
The Steel Degassing Process
Vacuum degassing of steel takes place after the molten steel has left the furnace and before the steel is poured into ingots or processed through a caster. The main objectives of steel degassing are:
- Reduction or elimination of dissolved gases, especially hydrogen and nitrogen
- Reduction of dissolved carbon for more ductile steel
- Preferential oxidation of dissolved carbon over chromium when refining stainless steel grades
After leaving the furnace, molten steel is moved in a ladle to the degassing area and positioned inside the degasser. The ladle is covered with a layer of slag that is penetrated approximately 18” deep by the snorkels.
As the snorkels are inserted, the NASH steam ejectors create a vacuum of 0.5 mm HgA and draw the steel into the chamber. The lower partial pressure within the vacuum chamber removes both hydrogen and nitrogen gases from the liquid steel, which are both vented as the steel is continuously circulated. The evacuation time is usually five minutes or less.
Types of Steel Degassing
There are three basic types of vacuum degassers: steam, recirculation, and ladle. The system choice is determined by many factors, including the primary objective of the degassing capital investment costs, operating costs, temperature losses, tonnage, throughput, space availability, and turnaround time.
All types of systems take place in a vacuum chamber, and the vacuum is created by multis-stage NASH steam jet ejectors, often in combination with a NASH liquid ring vacuum pump.
Steam jets work on a constant mass flow basis, while liquid ring vacuum pumps work on a constant volume basis. Used together, an economic break-even point may be reached to take advantage of the best characteristics of each. Our degassing system is designed to meet specific requirements and your Nash engineer can help you determine the optimal solution. The steel degassing process requires:
- Rapid evacuation of the vacuum tank
- Maintenance of vacuum while at the same time removing a heavy flow of inert gas
- Immediate availability
- Dust resistance
- Safe operation under harsh conditions
Designing the Vacuum Pumping System for Steel Degassing
In order to design your degassing system, you will need the following information:
- The number of dissolved gases to be removed. Absolute pressure, steel chemistry, and argon flow rate will all affect the rates at which the gases will be removed.
- The load at system design pressure in dry air equivalent.
- The load the system needs to meet at different pressures (if required by outgassing system).
- The system volume.
- The processing time required to go from atmosphere to deep vacuum.
- The final absolute pressure of the system to help determine how many stages are needed.
- The quantity of argon required to determine the agitation energy and the rate of dissolved gas removal.
- The in-leakage rate of air into the system.
- The steam pressure and temperature.
- The cooling water temperature.
- The cost of steam and electricity.
Global Provider
With over 110 years of liquid ring vacuum pumps and steam jet ejector design experience, Nash is the premier provider for your systems and solutions.
Backed by our NASH CERTIFIED™ Service offering, as well as a full range of OEM parts, spare, and aftermarket services, we can act as your trusted partner; protecting your investment and providing you with total peace of mind.
