16.06.2013 Views

1. Introduction - Firenze University Press

1. Introduction - Firenze University Press

1. Introduction - Firenze University Press

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

points efficiency increase related to the reference plant. This increase is however lower than<br />

sum of efficiency changes obtained for cases 2, 3 and 4.<br />

5. Conclusions<br />

The proposed improvements based on waste heat recovery within the oxy-fuel power unit<br />

may bring substantial rise of the net electric efficiency. The reference, not thermally<br />

integrated plant, achieves the efficiency of 29.55%, while in case of highly integrated plant<br />

(almost all waste heat is utilized) the efficiency increases to 32,98%.<br />

As results from the temperature profiles in heat exchangers where waste heat is recovered,<br />

there is still some potential for increase of waste energy use by e.g. replacing also part of the<br />

high-pressure steam regeneration.<br />

Comparing to literature studies, the conclusion drawn in [2] on better results obtained by<br />

preheating the steam cycle condensate comparing to preheating of oxidizer has been<br />

confirmed within the current research.<br />

The proposed lignite drying by ASU-waste nitrogen is promising technology from the energy<br />

efficiency and exploitation safety (explosion risk) points of view. Considering practical<br />

aspects presented in [6] for similar air-fed dryers, the verification of dryer dimensions and<br />

capital cost will be crucial for final assessment of this technology.<br />

It is important to mention, that the efficiency increase in case no. 5 (relative to the reference<br />

plant – case no 1) which simultaneously cumulates all improvements introduced in cases 2, 3,<br />

and 4 is less than the sum of efficiency increases obtained in cases 2, 3 and 4. The reason is<br />

that each single improvement causes decrease of waste heat production. Moreover, single<br />

cases are partially using the same waste heat of the flue gas which is not possible within the<br />

cumulated case no 5.<br />

Acknowledgments<br />

This work has been prepared in framework of the task of research: "Development of oxycombustion<br />

technologies for pulverized-coal and fluidized bed boilers integrated with carbon<br />

dioxide capture” funded by the Polish National Centre for Research and Development within<br />

the strategic program of research and development: "Advanced energy generation<br />

technologies".<br />

Nomenclature<br />

ASU air separation unit<br />

CCS carbon capture and storage<br />

E<br />

chfuel chemical energy of lignite, calculated on LHV basis, MW<br />

HP high pressure<br />

LHV lower heating value, kJ/kg<br />

MP medium pressure<br />

LP low pressure<br />

N elN net electric power of the system, MW<br />

ST steam turbine<br />

53

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!