Heating

Heating technologies

Drever International has acquired a wide experience in the heating technologies for more than 50 years.

The most common technologies for continuous heat treatment of steel strips are:

• Direct flame
• Radiant tubes
• Combustion Technology
• Induction
• Electrical heating elements
  
  

Continuous annealing and pickling line (CAPL for stainless steel). 

Vertical direct flame furnace

Direct flame

In direct flame furnaces the flame created by the combustion of natural gas radiates freely in the furnace. The fumes travel in counter flow with the strip to allow a preheating of the strip before the heating section. At the entry of the preheating section, the fumes are collected and sent to a global recuperator to preheat the combustion air used by the burners.

This technology allows fast reaction of the furnace and high efficiency thanks to the combination of high combustion air temperature and a preheating section.

When it is necessary to avoid the oxidation of the strip in the furnace, the combustion is under-stoichiometric, so the furnace atmosphere is reducing. The residue of the combustion contains therefore unburnt radicals (mainly hydrogen and carbon monoxide) that are burnt in the post-combustion taking place in the preheating section.

For the heating of stainless steels, there is no risk of strip oxidation so the combustion can be achieved directly with an excess of oxygen (oxidizing atmosphere).

Radiant tubes

In radiant tubes furnaces the combustion of the gas takes place within a tube, so there is no contact between the strip and the fumes. The fuel can be natural gas, but also coke oven gas, blast furnace gas or a mixture of different gas.

Radiant tubes must be used in a protective atmosphere furnace of HN_x, a mixture of nitrogen and hydrogen. There are several shapes: I, P, double P and W. I, P and double P are used together with recuperative or regenerative burners while W shapes are only available with a high performance recuperator. These tubes can be made of cast steel, welded steel sheets or, for I tubes, ceramic material.

Combustion technology

The combustion of gas generates mainly 2 pollutants: CO₂ and NO_x.

• The energy consumption and thus the quantity of CO₂ generated can be reduced by recovering the heat in the fumes and preheating the combustion air thanks to a central recuperator, individual regenerators or individual recuperators. The remaining heat in the fumes can be used to produce steam or hot water in waste heat boilers. 
• NO_x production can be reduced with specific combustion technologies aiming at reducing the maximum flame temperature and / or the level of oxygen within the flame. Fumes can be also treated by De-Nox system including some catalysts before release in the atmosphere.