(57) In an iron- or steel-making plant comprising a metallurgical processing vessel (1)
from which, in operation of the plant, there issues a stream of waste gas at superatmospheric
pressure and elevated temperature, there is provided means for recovering energy from
the waste gas stream. This energy recovering means comprises means (6, 12) for supplying
the gas stream to the inlet of a gas expander (16) which includes a rotor (18) drivable
by the gas stream and comprising an output drive shaft (22), an alternating current
generator (28) arranged to be driven by the shaft (22), and a voltage and frequency
converter (32) having its input side connected to the electrical output of the generator
(28) and its output side connected to an electrical power network (5). The converter
(32) is of the kind which, over a predetermined range of the speed of rotation of
the generator (28), delivers at its output side electric power at a voltage and frequency
which at all times conform to the voltage and frequency of the network (5).
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