1. Introduction - Firenze University Press

Figure 2. Idea for heat recovery from the flue gas compression train to steam cycle (case 3)
Comparing to the reference case, the additional flue gas coolers located behind appropriate
compression stages have been added. The cooling media within these new coolers is steam
cycle condensate. The flue gas is finally cooled to the required, possible lowest temperature
before following compression stage by cooling water as for the reference case.
2.4 Lignite drying by ASU-waste nitrogen (Case 4)
The idea for lignite drying by ASU-waste nitrogen (case 4) is presented in Fig. 3. The plant
structure includes fluidized-bed lignite dryer fed by dry nitrogen taken from ASU exhaust.
Additionally, the heat exchanger is located inside the bed to enhance the heat transfer to the
fuel being dried. Such a technology has been tuned for utilization of low-temperature waste
heat and follows the commercially proved idea presented in [6]. The coal dryer applied within
power system presented in [6] uses however air as drying agent and assumes integration with
conventional air-firing boiler.
It has been assumed, that the dry nitrogen and water for the in-bed heat exchanger are
preheated by the compressed air from the ASU air compression line. The detailed flow sheet
of Case 4 has been presented in Fig. A4 in appendix A. The steam cycle is the same as for the
reference case, so the Fig. A1b in appendix A refers also to Case 4. Detailed information
about streams entering fuel drier has been shown in Table 2.
Table 2. Detailed information about streams entering fuel dryer
Stream (No at Fig.3) Temperature, 0 C Mass flow, kg/s
Nitrogen entering preheater (158) 30 566,9
Nitrogen entering fuel dryer (161) 70 566,9
Nitrogen leaving fuel dryer (155) 35 575,3
Lignite entering fuel dryer (159) 25 219,2
Lignite leaving fuel dryer (2) 30 204,5
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