87299 - Energy Systems T

Learning outcomes

Study of the Brayton cycle gas turbine plant. Optimization of efficiency and specific work as a function of compression ratio and maximum temperature. Steam power plants with reheat and regeneration. Thermodynamic optimization of efficiency and work ad a function of main operating quantities. Gas-steam combined cycle power plants. Steam turbines.

Course contents

MODULE I

Ideal gas and real gas: step-by-step compression. Enthalpy and specific heat as function of the temperature: calculation codes. Step-by-step expansion. Enthalpy and specific heat of a gas mixture. Lower heating value and higher heating value experimentally evaluated and by means of standard enthalpies of formation.

Analytic determination of the energy balance within a non-adiabatic combustion chamber. Combustion effectiveness and combustion chamber efficiency. combustion: theory air, real air and air excess. Nm3and Sm3.

Brayton cycle gas turbine plant. Layout of a Brayton cycle gas turbine plant. Operating principle of compressor, turbine and combustion chamber. Work and efficiency trend as a function of compression ratio, polytropic efficiency and TIT (cp=constant). T,s diagram. Thermodynamic optimization of gas turbine performance under hypothesis of ideal fluid. Equations governing the operation of a gas turbine in case of real gas. Comparison between ideal and real performances of a Brayton cycle gas turbine plant. Influence of TIT, polytropic efficiency and compression ratio on real performance.

Steam power plants. Basic layout an operating principle. Heat exchange diagram for the condenser and criticisms related to the decrease in condenser pressure. Acid dewpoint. T-s and h-s diagrams. Compression work of a liquid. Effect of the condenser pressure decrease on the thermodynamic efficiency. Layout of a steam plant with reheat, T-s diagram. Optimization of the reheating pressure of a steam group. Quality trend at the outlet of the steam turbine as function of the reheating pressure. Layout of a steam plant with one regeneration level, operating principle and T-s diagram. Thermodynamic optimization following the adoption of one regeneration level in a steam group (degree of regeneration). Mixing and surface heat exchangers: architectural and performance differences. Layout of a steam plant with three regeneration levels. T-s diagram. Energy balances at the regenerative heat exchangers. Produced power and efficiency.

The steam generator. Layout and operating principle. Water side and gas side lines. The problem of boiler bank temperature. The Ljungstrom exchanger and link with regeneration. Burners disposition. The combustion temperature (graphic determination). The heat load. Efficiency of the steam generator (direct and indirect evaluation). The degree of shielding and its increase with the potential of the steam generator.

Gas-steam combined cycle power plants. One pressure level combined cycle: T,s diagram and operating principle. Heat exchange diagram T,Q and T,q. Energy balances for the combined cycle heat exchangers. Analytical expression of the conversion efficiency. Recovery efficiency as a function of the ratio between the low pressure mass flow and flow to the condenser.

The condenser. One and multiple pass tube and shell side layout. Speed of cooling water in pipes and its influence on global heat transfer coefficient and pressure drop. Constructive measures to increase the performance of a condenser by increasing the global heat transfer coefficient.

Turbomachines. Equations of fluid motion in fixed channels. Static and total quantities. The speed of sound and flow regimes. Compressible fluid flow equations. The chocking. Maximum flow rate and flow parameter. Link between transversal area and flow in a channel depending on the regime of motion: Hugoniot equation. Converging channel and converging-diverging channel. Stator losses and g,s diagram. Enthalpy diagram for converging channel and converging-diverging channel. Euler equation and equation with the differences of kinetic energy for a rotor row. Degree of reaction. Total to total and total to static efficiencies.

The physical states of a reaction stage, h,s diagram. Rotor losses. The axial turbines reaction stage; velocity triangles. Normal stage. Maximum work and velocity triangles. Total to total efficiency definition and maximum point.

The impulse stage: the velocity triangles, the maximum work, physical states on the enthalpy diagram. Total to static efficiency. comparison between reaction stage and impulse stage losses.

The De Laval Turbinescheme and operating principle. De Laval Turbine limitations on the enthalpy change.

Two velocity stages turbine: scheme and operating principle. The velocity triangles. Work and maximum work evaluation for a two velocity stages turbine. Total to static efficiency. Comparison with the impulse turbine efficiency.

The multiple impulse stage turbine, scheme and operating principle. Total to static efficiency and recovery factor.

The reaction turbine, scheme and operating principle. The role of balancing drum. Limits on input and output volumetric flow of a reaction turbine. Analytic expression of the input and output volumetric flow. The mixed and double flow turbines.  

Readings/Bibliography

"Sistemi Energetici" 1 – MACCHINE A FLUIDO, G: Negri di Montenegro, M. Bianchi A. Peretto – Pitagora Editore

Teaching methods

Two modules will be developed in parallel during the first period. Topics explained during the lessons are strictly close to those present in the book written by the Professors.

Assessment methods

The assessment consists of an oral examination, generally composed by three questions about the lessons program.

Required diagrams(the student must know how to draw the diagram in a realistic manner):

• T,s diagram of air with isochoric and isobaric curves
• T,s diagram of water with isobaric curves inside and outside of the liquid-vapor region
• H,s diagram of water with isobaric and isothermal curves inside and outside of the liquid-vapor region
  

  Required layouts

• Turbo-gas, steam plants, combined cycles and cogeneration plants. All the schemes shown during the lessons.

  Required drawings:

• impulse turbine
• Curtis Wheel turbine
• multiple impulse stage
• reaction turbine
• Steam Generator
• Steam Condenser

Teaching tools

Parts of Machines given and explained to the students in the classroom during the lesson.

Office hours

See the website of Antonio Peretto