Cogenerative performance of a wind-gas turbine-organic rankine cycle integrated system for offshore applications

Gas Turbines (GT) are widely used for power generation in offshore oil and gas facilities, due to their high reliability, compactness and dynamic response capabilities. Small heavy duty and aeroderivative units in multiple arrangements are typically used to offer larger load flexibility, but limited efficiency of such machines is the main drawback. A solution to enhance the system performance, also in Combined Heat and Power (CHP) arrangement, is the implementation of Organic Rankine Cycle (ORC) systems at the bottom of the gas turbines. Moreover, the resulting GT-ORC combined cycle could be further integrated with additional renewable sources. Offshore wind technology is rapidly developing and floating wind turbines could be combined with offshore GT-ORC based power plants to satisfy the platform load. The pioneering stand alone power system, for an oil and gas platform, examined in this paper comprises a 10MW offshore wind farm and three gas turbines rated for 16:5MW, each one coupled with an 4:5MW ORC module. The ORC main parameters are observed under different wind power fluctuations. Due to the non-programmable availability of wind and power demand, the part-load and dynamic characteristics of the system should be investigated. A dynamic model of the power system based on first principles is used, developed in the Modelica language. The model is integrated with a time series-based model of two offshore wind mills. Various thermodynamic indexes, available in the literature, are identified and evaluated to compare the actual combined heat and power performances of single components and of the overall integrated system in the considered wind scenarios.