31399 - Energy Systems T

Learning outcomes

Gas turbine, steam power plant and combinaed cycle power plant basic concepts. Introduction to the study of turbomachinery.

Course contents

- Basic concepts. Compression and expansion processing. Internal and polytropic efficiency for a compression and expansion. Isentropic efficiency as a function of compression ratio and polytropic efficiency.

- Brayton cycle gas turbine plant. Lay-out of a Brayton cycle gas turbine plant. Thermodynamic optimization of gas turbine performance under hypothesis of ideal fluid. Work and efficiency trend as a function of compression ratio, polytropic efficiency and TIT. Equations governing the operation of a gas turbine in case of real gas.

- Heat exchangers. Global heat transfer coefficient. Wall temperature. Fair and countercurrent heat exchangers. Temperature, thermal power diagram and definition of heat exchanger efficiency. Heat capacity per hour. Graphical evaluation of heat exchanger efficiency in the T-Q diagram. Logarithmic average DT and the e-NTU method.

- S team power plants. Basic lay-out. T-s and h-s diagrams. Compression work of a liquid. Analytical evaluation of the convenience of changing thermodynamic parameters of a steam plant (dh / ds <h / s). Variation of Rankine cycle maximum pressure and its maximization. Variation of maximum pressure and temperature of a cycle Hirn and their maximization. Influence of lowering condensing pressure of a steam group. Optimization of the reheating pressure of a steam group. Thermodynamic optimization following the adoption of n regeneration levels in a steam group (degree of regeneration). Lay-out of a steam plant with three regeneration levels. T-s and Mollier diagram for water. Equations governing the operation of a steam group. Regulation of steam groups.

- The condenser. One and multiple pass tube and shell side lay-out. 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 capacitor by increasing the global heat transfer coefficient.

- The steam generator. Lay-out and operating principle. Water side and gas side lines. The problem of boiler bank temperature. The Ljungstrom exchanger. The heat load. The combustion temperature and efficiency of the steam generator. 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: diagram and operating principle. Influence on the adoption reheating and regeneration levels efficiency. Combined cycle with post-combustion, analytical evaluation of the efficiency and powers ratio, maximum gas turbine work and maximum efficiency in the case of post-combustion. Lay-out of a two pressure level plant. T-s diagram. 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. Optimal criterion for the distribution of flow and exhaust temperature of the heat recovery steam generator. General criteria for design and optimization.

- Compressible flow turbomachines. Static and total quantities. Equations of fluid motion in moving channels. The speed of sound and flow regimes. Compressible fluid flow equations. The chocking. Link between transversal area and flow in a channel depending on the regime of motion: Hugoniot equation. Euler equation and equation with the differences of kinetic energy for a rotor row. The impulse stage: the velocity triangles, the maximum work, physical states on the enthalpy diagram. The axial turbines reaction stage; velocity triangles, degree of reaction, maximum work, total to total efficiency, total to static efficiency, representation of physical states in the enthalpy diagram.

- The De Laval Turbine and limitations on the enthalpy change.Curtis wheel and its velocity triangles. Efficiency evaluation for one, two and three velocity stages. The pressure stage turbine and the recovery factor. The reaction turbine. Limits on input and output volumetric flow of a reaction turbine. The mixed and double flow turbines.

Readings/Bibliography

SISTEMI ENERGETICI 1– Macchine a fluido – G. Negri di Montenegro, M. Bianchi, A. Peretto – Ed. Pitagora

Teaching methods

The examination at the end of the course aims to assess the achievement of learning objectives, verifying the knowledge that the students have acquired about design aspects, structural, functional and management about the environmental impact from energy system
The final grade is defined by a single oral exam, testing the student's knowledge in all topics covered in the 9 CFU

Assessment methods

The course consists of 6 credits (CFU) in two modules.

The modules provides some lessons presenting numerical examples.

Teaching tools

Teaching materials: teaching material presented in class will be made available to the student in electronic format via internet.

Office hours

See the website of Francesco Melino

See the website of Gian Marco Bianchi