Ways of TPP Power Units Modernization During Their Conversion to Ultra-Supercritical Steam Parameters

The approach to solving the applied problem of modernization of the 300 MW series power units produced by JSC "Ukrainian Energy Machines" by converting them from supercritical to ultra-supercritical steam parameters, provided that regenerative feed water heating system is preserved as much as possible, which will lead to an increase in the energy efficiency of the TPP with minimal conversion, is analyzed in the paper. The conversion of the K-300-240-2 power unit to the parameters of fresh steam 650 °C/30 MPa and intermediate superheated steam 650 °C/7 MPa, determined as optimal as a result of previous studies, can be carried out by completely replacing the high-pressure cylinder of the existing unit for a new high-pressure cylinder with ultra-supercritical steam parameters and superstructure with an additional intermediate-pressure cylinder while fully preserving the parameters and designs of the intermediate- and low-pressure output parts. Two options for modernization of the 300 MW series power unit thermal circuit structure were considered, and the scale of conversion of the regenerative feed water heating system was evaluated. In the first option of the thermal scheme, the 1st steam selection is organized from the cold threads of the modernized high-pressure cylinder with ultra-supercritical steam parameters, and the 2nd one – from the cold threads of the additional intermediate-pressure cylinder. In this case, two high-pressure heaters and a turbo drive of the feed pump are subject to replacement. The disadvantage of this option is that due to a significant increase in steam parameters, it is impossible to choose high-pressure heaters from the existing model range, and a new design must be developed. The electrical efficiency for this modernization option increases from 36.5% (the initial thermal circuit of the K-300-240-2 turbine) to 42.5%. In the second option, it is proposed to install an additional turbine with a capacity of 3 MW, to the input of which a steam from cold threads of the high-pressure cylinder with ultra-supercritical steam parameters is supplied with a loss equal to the sum of the 1st and 2nd selections of the original version of the turbine, on the same shaft with a turbo drive of the feed pump for the sake of preserving the existing high-pressure heater. The steam from the additional turbine selections goes to high-pressure heaters HPH9 and HPH8 with parameters corresponding to the output data of the existing turbine. Taking this into account, high-pressure heaters will not be replaceable. In addition, the power of the additional turbine is sufficient to ensure the operation of the feed pump together with the turbo drive of the feed pump to obtain a water pressure of 34 MPa. In view of this, the turbo drive of the feed pump also remains unchanged, except for the additional turbine installation. The electrical efficiency for the second option of the modernization scheme of the K-300-240-2 power unit is 42.4%. It was determined that the payback period of the modernization according to the first option is 5 years, taking into account the modernization of the boiler unit, and according to the second one – 4.5 years. It is proposed to choose the option of the thermal scheme with an additional turbine, since in this case it is possible to modernize the K-300-240-2 power unit with the maximum possible preservation of the regenerative feed water heating system while increasing its energy efficiency by almost 14%.