Christian Schwotzer

Numerical Investigation for the Design of a Central Recuperator with Hybrid Air Preheating

Abstract Industrial furnaces, especially in steel industry but also in non-ferrous, ceramic or chemical industry, are often fired with fossil fuels like natural gas, oil or coke. Considering the transition to green energy, it is necessary to enable the use of renewable energies like wind and solar energy in fossil-fueled furnaces. Resulting from this motivation, a hybrid recuperator for combustion air preheating with off-gas heat and electric energy is being developed in a public research and development project. The hybrid recuperator consists of a conventional tube bundle module and an electric heating module. The design of the prototype is based on numerical investigations to determine pressure loss, increase in temperature and heat transfer. This article introduces the concept of the new hybrid recuperator and initial results of numerical investigations for a small-scale hybrid recuperator geometry.

Development of an Energy-Efficient Burner for Heat Treatment Furnaces with a Reducing Gas Atmosphere*

Abstract One of the main reasons for metal loss of semi-finished metal products during heating in reheating and heat treatment furnaces is scale formation. In the presented project a burner is developed which produces a low oxidizing / reducing atmosphere in the furnace. The concept is realized by a recuperative burner, which generates a reducing furnace atmosphere due to fuel rich combustion of natural gas and air. The complete combustion of the furnace atmosphere is ensured by the injection of additional air and takes places in an open radiant tube resulting in a high energy efficiency. In this paper numerical and experimental results are presented and discussed. The numerical results showed the huge impact of the secondary air swirl on the post-combustion in the annular gap which is formed between the open radiant tube and the burner. Mixing phenomena in the annular gap results in a nearly complete post-combustion at low and high swirl angles of the additional combustion air (ω = 0°, ω = 90°). Instead of that, at a swirl angle of ω = 45° the entire reaction from CO to CO2 was not ensured within the boundaries of the numerical model. The quality of the post-combustion was experimentally evaluated by measuring the CO-emissions in the off-gas channel. These were lower than 50 mg/m3 in a wide range of operation. The NOx-emissions are lower than 121 mg/m3 at all tested cases.