Method and configuration for the recovery of thermal energy in the heat treatment of cold-rolled steel strip in a hood-type annealing furnace

A method for recovering thermal energy in a thermal treatment of a cold-rolled steel strip in a hood-type annealing furnace, where the cold-rolled steel strip is heated up in a protective gas atmosphere to a temperature above a recrystallization temperature, being subjected in a subsequent first, slow cooling phase and a second, fast cooling phase, following the first, slow cooling phase, to a protective gas and having a temperature reduced in a course of the first, slow cooling phase down to an intermediate temperature and in the second, fast cooling phase from the intermediate temperature to a final temperature, which comprises the steps of:

• providing a first heat exchanger being flowed through by the protective gas exclusively in the first, slow cooling phase, the first heat exchanger transferring the thermal energy of the protective gas by way of a closed oil circuit and a second heat exchanger to a working medium, the working medium under standard pressure having a boiling temperature of less than 80° C., and evaporates in the second heat exchanger;
• feeding the working medium to a steam motor, the steam motor converting a part of the thermal energy contained in the working medium into at least one of mechanical or electrical energy;
• coupling the steam motor in driving terms to an electrical generator, the electrical generator feeding generated electrical energy into at least one of a power storage unit, a public power supply or a power supply of its own;
• and
• providing a further heat exchanger being flowed through by the protective gas exclusively in the second, fast cooling phase and in the further heat exchanger the thermal energy contained in the protective gas is transferred to a further heat transfer medium for heating up service water.