The European Green Deal aims at a 90 to 95 % reduction of CO2-emissions within the year 2050 compared to 1990 and identified different solutions to reach these goals. For process heating purposes, direct use of electricity and use of hydrogen produced from renewable energies are mainly discussed. Hydrogen can be used in various applications to substitute fossil energy carriers, especially in high temperature applications. Within steel heat treatment furnaces, natural-gas-fired and electrically heated radiant tubes are industrially well-established. Prominent examples are carburizing furnaces for case-hardening of gear parts.
Case-hardening is a process to harden the surface of parts while the core remains soft. The process includes carburizing of the parts, i.e. infusing carbon atoms into the surface layer, and hardening. The process is controlled by the furnace atmosphere which contains carbon monoxide as the main carbon carrier. It is therefore essential to separate furnace atmosphere and burner off-gas. In carburizing furnaces like pusher type or chamber furnaces, natural-gas-fired I-type radiant tubes are widely used for process heating. Electrical heating is state of the art in carburizing furnaces but is in many countries economically less feasible. Hydrogen-fired radiant tubes are not industrially implemented and further investigations are needed to examine various mechanisms, e.g. pollutant emission and damage mechanisms.
First results of the experimental investigation of a 40 kW self-recuperative burner fired with hydrogen-air inside an I-type radiant tube are presented and discussed. Within the ecological analysis, different process heating technologies for carburizing furnaces are discussed by a quantitative approach. A state-of-the-art carburizing natural-gas-fired furnace is used as reference case, while electrical and hydrogen heating are the alternatives investigated. Energy balances, primary energy consumption and resulting CO2-emissions are compared for the different cases. For this purpose, different scenarios of the energy mix and CO2-emissions development until 2050 are considered.
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