Metallurgical and Glass Industry.
The use of pure oxygen in the melting of ferrous and non-ferrous metals is a well-established technology for rotary furnaces. Recent developments in the field of ladle preheating and steel heating furnaces have brought back interest in pure oxygen technology.
Melting of ferrous and non-ferrous metals
Generally speaking, for the fusion of various ferrous and non-ferrous metals, such as steel, cast iron, aluminum, copper, etc., various types of melting furnaces are used, such as rotary or chamber furnaces. For many years now, the most widespread and consolidated fusion technique has been Oxy-combustion with pure oxygen, which has replaced the old air systems. Below we will see some applications and related application advantages.
Cast Iron (Oxy-Fuel burner)
Oxygen combustion systems guarantee:
- reduced specific fuel consumption
- reduced emission factors
- better combustion control
- great operating flexibility
- increased thermal efficiency of the process
- reduction of operating and management costs
- excellent results in terms of metallurgy
- reduction of refractory consumption with consequent lengthening of the furnace campaign
Aluminium
In the same way as cast iron, the same criteria for the applicability of pure oxygen combustion also apply to aluminium, which can be summarised in the following main advantages:
- Reduction of methane consumption varying between -50% and -60% compared to air combustion systems
- Reduction of the quantity of slag during the melting process due to the oxidation of the metal; taking into account the value of aluminium, the 1% reduction in slag translates into a significant saving of raw metal.
- Increase in the melting capacity of the furnace up to +50%
- Reduction of V.O.C emissions generally due to the gasification process of organic materials present on aluminum scrap
- Reduction of NOx emissions up to 90%
- Reduction of CO2 emissions up to 50%
Heat treatments
In most heat treatment processes, furnaces must operate in a neutral or reducing atmosphere to avoid changes in the surface composition of the metal due to oxidation phenomena that would cause a deterioration of the surface appearance and the modification of the tribo logical properties. In other words, the atmosphere must not react with the surface of the metal in cases of annealing or tempering. The only exception is the cementation or nitriding processes where the atmosphere serves to transfer carbon or nitrogen respectively, forming carbides or nitrides, to confer greater hardness and resistance to mechanical wear.
In the following table we can see the most common heat treatments of metals and the related technical gases used.
|
Quenching/Carburizing |
Case-hardening / Hardening | Nitrogen – Methanol |
| Low-pressure carburizing and high-pressure gas quenching | Acetylene for cementation; Nitrogen – Helium Hydrogen for quenching | |
| Carbonitriding | Nitrogen – Methanol – Ammonia | |
| Nitriding | Ammonia – Nitrogen – Nitrous oxide | |
| Nitrocarburization | Ammonia – Nitrogen – Carbon dioxide | |
| Cryogenic hardening | Liquid Nitrogen | |
| Annealing | Annealing/tempering | Nitrogen – Hydrogen – Hydrocarbons |
| Endothermic generator with nitrogen dilution | ||
| Brazing/Sintering | Brazing/Sintering | Nitrogen – hydrogen |
| Endothermic generator with nitrogen dilution |
Technical industrial glass
The general advantages of fusion by oxygen combustion also apply to the glass sector. However, we must consider that glass melting furnaces are of considerable size and for this reason they operate continuously for several years until the refractory bricks containing the molten glass need to be replaced. Due to this particularity, oxygen combustion applications normally require the application of different combustion systems for each furnace and generate an oxygen requirement that often reaches up to 3,000 mch for each furnace; consequently, the methane requirement is also very high and this translates into a very low price of the methane consumed and the consequent need for a very low price of oxygen. Usually, a large glassworks is supplied via pipes or with on-site systems of the VPSA type which require very high investments.
Sometimes, while waiting for the application of a pure oxygen system, the customer may request a temporary enhancement of systems for enriching the combustion air in order to temporarily increase productivity.
Main advantages of oxygen conversion of a glass furnace
|
ADVANTAGES |
Technical glass 200 tpd borosilicate |
Hollow Glass 400 tpd soda lime |
|
Air furnace with regenerators |
Air furnace with recuperators |
|
|
NOx emissions |
-80% |
-75% |
|
CO2 emissions |
-40% |
-38% |
|
Fuel Economy |
-35% |
-33% |
|
Operational cost savings |
-5% |
-5% |
Fusion, technologies, pure oxygen
