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Description of the BIO_MGT system


The BIO_MGT system matches an externally fired cycle with an open MGT (100kWe) cycle. Hot flue gases generated by the bio-furnace flow into a high temperature heat exchanger, which transfers the heat to the air from the compressor before the GT combustion chamber. A significant share of the total energy input (40-60%) is given by solid biomass: the remaining is provided by CH4 internal combustion. The flue gas stream at the MGT outlet is mixed with the hot flow from the bio-burner: the mixed gases supply the HE hot side. The plant than delivers power, heat and (through an absorption chiller) cold to the end-user.

General description of the BIO_MGT system
The general layout of the system is based on the well know configuration named EFGT (externally fired gas turbine) or also HAGT (hot air gas turbine). Contrarily to these schemes, the BIO_MGT system maintains a share of internal combustion performed in the gas turbine combustor. By this way the BIO_MGT becomes a dual combustion gas turbine (DCGT).
The indirectly fired gas turbine uses clean air as working fluid. The GT compressor increases both pressure and temperature of the working fluid, which is then further heated in the high temperature heat exchanger (HT-HE) by the hot flue gases from a biomass furnace. The compressed hot air reaches the maximum cycle temperature thanks to the natural gas internal combustion, and then expands through the gas turbine. In the BIO_MGT scheme, around 50% of direct (natural gas) combustion is maintained, with the aim to keep the MGT running at good thermodynamic efficiencies and to keep thermal and corrosive stresses on the HT-HE low. The maximum inlet temperature in the HT HE is 850░C. Previous works which have focused on this issue concluded that this working condition should be possible with high quality steel. A major part of the energy still available from the hot-side exhaust of the HT-HE (at 350-400░C) can be utilised for heat generation by a gas-water heat exchanger.

Project supported by the European Community under the Sixth Framework Programme.

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  CREAR - Centro Interdipartimentale di Ricerca per le Energie Alternative e Rinnovabili Università di Firenze

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