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Processes - Ferrous (Iron / Steel): Reheat

The purpose of a reheat furnace is to heat and deliver a well-soaked (uniform temperature) slab, billet or bar with limited decarburization to the rolling or forming mill for the drawing and forming processes to follow.

Since the 1980s advanced controls, recuperation, and new more efficient (and low emission) combustion systems have reduced the average fuel consumption to a range of 1.5 - 2.0 MMBtu/ton when heating cold billets.

In 1984 heating and annealing furnaces accounted for 58%, 228 Bcf, of all natural gas used by the steel industry. Roughly half of the consumption, 135 Bcf, was used to reheat steel for rolling. Continuous furnaces reheated 71.5 million tons while batch furnaces processed 11.2 million tons. In the mid-1980s, reheat furnaces consumed between 2.2 - 2.6 MMBtu / ton.

Technological changes in the steel industry, such as hot charging, direct rolling, and thin steel casting, are propelling the industry toward more continuous processes, many of which reduce or eliminate the need for the traditional reheat step.

Hot Charging
Currently, investments are being made to locate the reheat furnaces closer to the continuous caster. This type of facility is known as a Direct Hot Charging Process (DHC). These reheat facilities lower fuel use and also increase productivity.

Example of DHC Impact on Energy Use and Productivity
Walking beam reheat furnace directly linked to the caster:

  • 70% of caster production was charged directly
    - Average charge temperature: 1400°F
    - Average 210 tons per hour
  • 10% warm charge
    - Average charge temperature: 1000°F
  • 20% cold charge
    - Average 170 tons/hr
  • For this installation 0.69 MMBtu/ton was achieved