Semi–Closed Hat (SC-HAT) Power Cycle

This new power cycle is derived from a simplified HAT cycle, with a partial recirculation of the exhaust gases added with respect to the traditional HAT configuration. The basic idea of applying recirculation to the HAT cycle stems from the interesting performance levels and general environmental advantages obtainable applying this technique to combined-cycle (SCGT/CC) and regenerative GT solutions (SCGT/RE); these power plants all share the integration with CO2 chemical scrubbing of the exhaust stack in order to reduce greenhouse effects.A relevant advantage of the proposed configuration over the original HAT solution is the possibility of complete water recovery from the separator before the recirculation node; here the temperature level is necessarily very low, allowing thus condensation of water produced by the natural-gas combustion process. This allows the self–sustainement of the HAT cycle, from the water consumption point of view, without any external supply. For the water separator, two thermodynamic models were developed (respectively simulating a single- and a multiple temperature condensation process), which have provided similar results.The whole cycle is modeled using a modular code, thoroughly tested against the performance of a large set of existing GTs. The layout is derived from an existing HAT configuration, with suppression of the economizer section in the regenerator and the possible practice of external (non-recuperative) intercooling between the two compressors. The first choice is imposed by the presence of an additional low-temperature heat load for the CO2 removal plant, while the second is sometimes necessary depending on the compressor pressure ratios and the possibility of including inside the cycle low-temperature internal cycle regeneration.The expected performance of the plant is relatively high and close to those typical of HAT, SCGT/RE and SCGT/CC cycles: a LHV-based efficiency level exceeding 50% inclusive of CO2 separation and delivery at ambient pressure and temperature; the specific work levels — in the range of 680 kJ/kg for the basic configuration — are lower than those of the HAT cycle but larger than for SCGT/CC and SCGT/RE solutions; the cycle requires relatively high overall pressure ratios (35–40). A notable improvement in specific work can be obtained with reheat.Copyright © 2000 by ASME