Exergy-economic modelling of the integration of two black start diesel engines into the combined cycle gas turbine for rapid-cold start-up

Abstract

Exergy-economic modelling of the integration of two black start diesel engines (BSDEs) into the combined cycle gas turbine (CCGT) provides an analysis of the potential of utilizing the heat from exhaust gases and cooling water released by the operation of the two BSDEs, which is currently being wasted into environment. In the case of non-voltage for the CCGT rapid-cold start-up, two BSDEs can provide not only electricity, but also thermal energy for heating the high-pressure drum (HPD) of the heat recovery steam generator (HRSG), which is essential for a rapid-cold start-up of the plant. This is exactly where the originality and innovation of this study are shown as so far this type of analysis has not been carried out. However, for a rapid-cold start-up of the system, it must be preheated to at least 393 K as per instructions of the HRSG manufacturer. In addition to using the heat of the exhaust gases to preheat the HPD, the heat of the cooling water of both BSDEs is also used for the purposes of heating buildings. The advantage of using the heat from the exhaust gas and cooling water of the BSDE is, therefore, reflected in increased energy and exergy efficiency allowing the use of the BSDE also in other cases of increased demand for electricity. A vital aspect of the optimisation is the secure supply of heat to the HPD, which cannot be provided by the existing auxiliary sources in the event of a power grid failure. The exergy-economic modelling of BSDE integration into a combined cycle gas turbine (CCGT) has shown that it is possible to maintain the temperature in the high-pressure drum (HPD) needed for rapid-cold starting the CCGT installation by installing an additional heat transfer system in the BSDE exhaust system. The results of the model show that the two BSDEs can use their exhaust gases to preheat the HPD of the HRSG to the temperature of 393 K in as little as 16 min. The heating time, however, depends on the load of both BSDEs. The use of heat from both BSDEs also increases the energy and efficiency.