5  EP 2 100 011 B1 6  23 for supply of the compressed siderurgical gases from the compression unit 14 to a regulation device24, i n which also the natural gas converges through a duct 25. The regulation device 24 is connected by a duct 26 to the combustion chamber 5 and is able to dose the per- centage of siderurgical gas and natural gas supplied to the combustion chamber 5 and to exclude selectively supply both of siderurgical gas and of natural gas. [0030] The gases,whether siderurgicalgases, natural gases ora mixture ofthe two,are burntinthe combustion chamber 5, traverse the turbine 6, and are conveyed through a duct 27 to the boiler 12 in which a recovery of heat is carried out for heating the condensed steam. [0031] Thesiderurgicalgases are supplied tothe com- pression unit 14, in particular to the compressor through a duct 28 by the steel plant 2. The compression unit14 comprises:arecirculation duct29,which extends between the outlet of the compressor 16 and the inlet of the compressor 16 itself to re-introduce the siderurgical gases compressed by the compressor 16 to the com- pressor 16 itself; a duct 30 for supplying the siderurgical gases compressed by the compressor 16 to the second compressor17;a duct31 forconnectingdirectlythe outlet ofthe compressor16 tothe duct23;avalve 32,setalong the recirculation duct 29 for partializing or excluding the flow of siderurgical gases; and a valve 33 set along the duct31 forpartializing orexcluding theflowofsiderurgical gases along said duct 31. [0032] The plant 1 comprises a heat- exchange unit 34 for transferring the heat generated by the compression unit 14 to the steam that has undergone condensation upstream of the degasser 11 in the steam- turbine unit 9. The heat-exchange unit 34 comprises: a closed circuit 35 in which a fluid circulates, in the case in point water; a pump 36, designed to carry out a forced circulation of the water in the circuit 35 in the direction indicated in the annexed figure; a heat- exchanger 37 for transferring the heat of the oil of the hydraulic circuit 19 to the water; a heat-exchanger38 fortransferring the heatgenerated in the oil of the lubrication circuit 22 to the water; a heat- exchanger 39 for transferring the heat of the siderurgical gases compressed by the compressor 16 and conveyed along the recirculation duct 29 to the water; a heat- ex- changer 40 for transferring the heat of the siderurgical gases compressed by the compressor 16 and conveyed along the duct30 to the compressor 17 to the water; and a heat-exchanger 41 for transferring the heat accumu- lated during the passage through the heat exchangers 37 to40 tothe vapourthathas undergone condensation. [0033] In other words, the pump 36 and the heat ex- changers 37 to 41 are arranged along the closed- loop circuit 35, in which the heat exchangers 37 to 40 are provided for transferring the heat generated by the com- pression unit 14 to the water of the circuit 35, whilst the heat-exchanger 41 is provided for transferring the heat from the water of the circuit 35 to the vapour that has undergone condensation of the circuit 13. [0034] As pointed out previously, the advantages of the present invention are multiple, both from the stand- point of recovery of energy and productivity of the com- bined-cycle plant 1 and from the standpoint of the im- provement of the running conditions of the boiler 12. Claims 1. A combined-cycle plant for the production of electri- cal energy, the combined-cycle plant comprising: a gas-turbine unit(3)providedwitha combustion chamber (5); a steam-turbine unit (9) provided with a degas- ser(11),aboiler(12)and a circuit(13)forsupply of the condensed steam to the degasser (11) and, subsequently, to the boiler (12); a unit(14)forcompression ofsiderurgicalgases for supplying the combustion chamber (5); and a duct (27) for conveying the siderurgical gases burnt in the the combustion chamber (5) to the boiler (12) in which a recovery of heat is carried out for heating the condensed steam; the combined-cycle plant (1) being  character- ized by  comprising a heat-exchange unit (34) for transferring the heat generated by the com- pression unit (14) to the condensed steam up- streamofthe degasser(11)inthe steam- turbine unit (9). 2. The combined-cycle plant according to Claim 1, characterized in that  the heat-exchange unit (34) comprises a circuit (35) for circulating a heat- ex- change fluid. 3. The combined-cycle plant according to Claim 2, characterized inthat  the circuit (35) is a closed cir- cuit. 4. The combined-cycle plant according to Claim 2 or Claim 3,  characterized in that  the heat-exchange unit (34) comprises a pump (36) for feeling the heat- exchange fluid into the circuit (35). 5. The combined-cycle plant according to any one of Claims 2 to 4,  characterized in that  the compres- sion unit (14) comprises a hydraulic converter (18) for connecting the gas-turbine unit (3) kinematically tothe compression unit(14);the heat- exchange unit (34)comprising a firstheat- exchanger(37)fortrans- ferring theheatgeneratedby thehydraulicconverter (18) to the heat-exchange fluid. 6. The combined-cycle plant according to any one of Claims 2 to 5,  characterized in that  the compres- sion unit(14)comprises alubrication circuit(22);the heat-exchange unit (34) comprising a second heat- exchanger (38) for transferring the heat from the lu- 4