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1. Introduction - Firenze University Press

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The CO2 emission factor which indicates the net CO2 emission per 1 GJ of produced heat has also<br />

been calculated in accordance with (4). Considering dual product situation (heat and electricity) it<br />

has been assumed that the main product is heat and the emission assigned to heat is calculated as<br />

difference between total emission from the CHP unit and emission avoided in other power stations<br />

due to production of specified amount of electricity in considered CHP unit. The scheme for<br />

avoided emission calculus has been illustrated in Fig. 3. The equivalent power plant is assumed to<br />

be coal-fired, non-CCS, supercritical unit of net electric efficiency equal to 44%.<br />

m<br />

CO 2 m<br />

CO 2 _avoid<br />

Q<br />

<br />

<br />

(4)<br />

dh<br />

Fig. 3. Scheme for calculus of avoided CO2 emission<br />

4. Simulation model<br />

All analyzed CHP systems have been modelled using the Thermoflex software [9]. Thermoflex<br />

contains models of typical energy conversion devices like compressors, turbines or heat exchangers,<br />

as well as, agglomerated multi-device models such as steam boiler or gasifier islands. The modeling<br />

approach combines the physical and empirical modeling.<br />

The flow sheets of analyzed IGCC, CFB and CFB reference systems used for simulation purposes<br />

are presented in Figs A.1, A.2 and A.3 in appendix A.<br />

Main assumptions taken for the simulation process for all considered systems are as follows:<br />

the same district heat power (ca. 110MWth),<br />

the same parameters of district water 62,6C/37C (annual average),<br />

the same feedstock (hard coal),<br />

CO2 stream compressed to 13 MPa for both CO2 capture installations,<br />

the same temperature of cooling water at battery limits (20C).<br />

122

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