Thermoeconomic evaluation of the SCGT cycle

The analysis of the SCGT (Semi-Closed Gas Turbine cycle) is extended to the treatment of acid condensation (sulphur compounds) at the exit of the sepa rator (SEP), with reference to different possible configurations already st udied from the thermodynamic and environmental points of view. This detaile d analysis was considered necessary because the natural gas fuel can contai n a small amount of H2S which, reacting with air, can form SO2 and finally sulphuric acid. This can represent a problem (mainly from the economic poin t of view) because of the possibility of sulphuric acid condensation at the exit of the separator, where the temperature can reach values below the ac id dew point of the mixture. The data obtained from ENI publications were used for the natural gas compo sition, and a 0.005% H2S molar fraction was additionally hypothesized. With these assumptions, about 0.1% SO2 can be found in the exhaust gases at the separator inlet. Aspen Plus was used in order to evaluate the chemical effects of the acidit y of the condensate produced in the separator. An evaluation about costs of the devices to be used for condensation of the recirculated flue gas humid ity has been performed, considering use of the special materials necessary for reducing the aggressive effects of acid water condensation. A final evaluation of the overall conversion system plant is also produced, showing the economic balance in terms of resulting cost of the unit of ele ctrical energy produced and of inlet power in terms of fuel. The results are also evaluated in terms of CO2 emissions, considering the r atio between the global cost of the power generation plant and the global c arbon dioxide emissions, compared to other types of energy conversion open cycle solutions. (C) 1999 Elsevier Science Ltd. All rights reserved.