Institute for Energy Process Engineering and Fuel Technology > Research > Minimization of the energy consumption and decrease of the pollutant emission in continuous annealing furnaces

Minimization of the energy consumption and decrease of the pollutant emission in continuous annealing furnaces

There still exist many possibilities for improving the efficiency of most industrial furnaces, for example by recovering heat from the exhaust gases or from the hot charge when energy is supplied by combustion. This recovered energy can then be circulated back into the furnace as physical enthalpy of the combustion air stream. Often it is possible to preheat the combustion air to a temperature approaching 1300~°C. Figure 2.1.1. shows the potential fuel savings as a function of the preheated combustion air temperature. 

 

 

 

Figure 2.1.1: Potential fuel savings as a function of the preheated combustion air temperature. The furnace exit temperatures (i.e. 773 K, 973 K, etc.) are shown on the chart. The recuperater, or regenerator, efficiency is represented by w.


However, due to the high combustion air temperatures, nitric oxide emissions rapidly increase. Thus, we need to develop methods to keep these emissions under control. The technology that makes this possible is called Moderate or Intense Low-oxygen Dilution, or MILD combustion. It is here the subject of investigation. Figure 2.1.2 shows a comparison between the specific energy consumption between conventional technology and MILD-combustion applied to a reheating furnace with a throughput of 300 tons of steel per hour.

 

 

Figure 2.1.2: Potential fuel savings when replacing conventional combustion technology with MILD-combustion technology.

 

Figure 2.1.2 shows the reaction zone of a natural gas-fired burner operating under MILD configuration. Due to the physical separation of the gas jets and the air inlet nozzles, the incoming air and gas streams are mixed with a large amount of exhaust gas before they mix and react with one another. This has the effect of a "mild" combustion characterized by a moderate increase in oven temperature and a considerable reduction in temperature peaks and fluctuations. Low emissions of NOx and CO2 (due to the energy savings), low-noise emissions, and a homogeneous heat flux profile are also characteristic of MILD combustion. Flameless combustion is very similar to MILD combustion because both are associated, in practice, with the disappearance of visible flames.

The primary technical objectives of the project are:

  •  To determine the relevant properties for MILD combustion, to apply them in furnaces, and to develop strategies for controlling these targeted properties.
  • To investigate the influence of MILD combustion on product quality.
  • To establish extensive experimental data sets of flow fields, concentration profiles, heat transfer, etc. for validation of mathematical models in development (see research topic 2.6)

 

 

 

 

Figure 2.1.3: MILD combustion (0.5 MW thermal power) (1. Natural gas nozzle, 2. Air nozzle, 3. Combustion area)

 

Contact:Dr.-Ing. M. Mancini

 

 

 

 

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