MODERN THERMAL POWER PLANTS

Abstract
The European Union (EU) has laid down very clear objectives for the reduction of
greenhouse gases in the hope that it will prevent or mitigate climate change. Political
incentives are used to make the power industry adopt changes in order to reach
these EU targets. In this thesis, some solutions that could help power companies
meet the EU objectives are evaluated. Thermodynamic models have been developed
to evaluate the proposed methods. A description of the models and the way in
which they are used to model power plant cycles in off-design mode is included in
this thesis.
The focus was on combined-cycle power plants, which have the highest
efficiency among commercial power plants today. Three ways of adapting power
plants so as to meet the EU targets were formulated:
• reduced CO 2 emissions
• increased use of biofuels
• improved part-load abilities
A new method based on using low-grade heat when implementing carbon capture
in a combined cycle power plant is presented. The results show that the method can
increase the total efficiency and reduce the initial cost of the power plant. The
method is applicable for both retrofitting to existing plants and for new plants. The
effect of using low-calorific bio-fuels in a combined-cycle power plant was
investigated. The results show that below a heating value of about 20-25 MJ/kg the
plant quickly departs from its design point. The supply of power to the national grid
is expected to be fluctuate more in the future due to the uneven availability of wind
and solar power. Therefore, two part-load operation strategies were evaluated. The
first involves a strategy that entails less wear on the gas turbine, which could extend
the maintenance interval of the unit. The second method combines two wellestablished
part-load strategies for part-load operation of steam-cycle power plants.
The combination of the two methods will increase the part-load efficiency of the
power plant.
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