Combined cycle units achieve the highest efficiency values. Major elements of such units include gas turbine, heat recovery steam generator and steam turbine. The combustion of gas takes place in a gas turbine, which powers the generator. Turbine exhaust gas is directed to heat recovery steam generator. Steam generated by HRSG powers the steam turbine, which is also coupled with the generator. Such a system enables the achievement of thermal efficiency amounting to 50% which, combined with almost emission-free gaseous fuel makes combined cycle units the most environment friendly among thermal power plants. Within the field of design of heat recovery steam generators RAFAKO is a licensee of Nooter Eriksen.