88247 - Turbomachines and Offshore Generation

Learning outcomes

The course is aimed at providing basic principles for design and operation of typical fluid machines used for “island” application in off-shore installations.

Course contents

INTRODUCTION: overview on primary energy source and on energy demand and supply.- Definition and overall classification of fluid machines.

SIMPLE CYCLE GAS TURBINES: layout and working principle. Brayton cycle thermodynamic analysis: temperature-specific entropy diagram, isentropic and polytropic compression and expansion, specific work, introduced heat, thermal efficiency. Thermodynamic optimization of Brayton cycle: cycle limits, net work, heat and thermal efficiency as functions of pressure ratio for the real cycle. Thermal efficiency as function of net work, varying pressure ratio and polytropic efficiency. Gas turbine types: aeroderivative vs heavy duty. Gas turbine configuration: compressor, combustion chamber and turbine. Architecture of standard GT combustion chamber: casing, liner, diffuser, swirler, primary and dilution air flows.

GAS TURBINES WITH HEAT RECOVERY: layout and thermodynamic diagram, working principle. Limit conditions on compressor and turbine outlet temperatures and on pressure ratio: calculation of beta limit. Effect of the increment of beta. Heat transfer analysis on the recuperator (assuming counter-flow configuration, no thermal and pressure losses, same fluid and same flow rate on both sides of the heat exchanger): thermal balance, heat transfer diagram. Definition of the heat transfer effectiveness. Efficiency improvement due to heat recovery: ratio of the efficiencies with and without the recuperator. Micro-gas turbine: main features, sizes and applications. Micro-GT in combined heat and power (CHP) applications: layout and working principle, electrical and thermal efficiency, fuel utilization factor. Micro-GT architecture examples.

SINGLE PRESSURE LEVEL COMBINED CYCLE POWER PLANT: Introduction to combined cycle concept. Overview of steam turbine power plant: T-s diagram of water (saturation curves, critical point, isobaric curves).

Steam turbine cycle: layout, working principle, T-s diagram of Rankine and Hirn cycles. Specific work, introduced heat and thermal efficiency. Total power output and total efficiency. Minimum quality at turbine outlet. Effect of vaporization and condensation pressure. Heat transfer diagram for the condenser (condensation temperature and pressure).

Combined cycle power plant: layout, T-s, working principle, heat transfer diagram of the HRSG. Total power and total efficiency, heat recovery factor. Power allocation in combined cycle (Ratio of gas turbine power and steam turbine power). Thermal balance in the heat recovery steam generator.

ORGANIC RANKINE CYCLE: overview; heat sources and applications. Comparison of ORC and steam cycle: differences depending on fluid properties (critical point, slope of saturation curve, heat of vaporization); dry, isentropic and wet fluids. Dry and wet expansion. Working fluid selection criteria: thermodynamic properties, environmental and safety properties. Definition of ozone depletion potential (ODP) and global warming potential (GWP). Expander types. Layout and T-s diagram of simple ORC. Layout and T-s diagram of recuperated ORC. Specific work, introduced heat and thermal efficiency.

TURBOMACHINERY STAGE:

Fluid flowing in a channel with constant mass flow rate: determination of the channel geometry (Hugoniot equations). Axial turbomachinery stage: definition of stage (stator + rotor). Compressor stage and turbine stage. Axial turbine stage: impulse vs reaction stage; degree of reaction. Geometry of the turbine nozzle: converging vs converging-diverging. De Laval turbine (simple impulse steam turbine): layout description, working principle and main features. Curtis turbine. Multi-stage reaction turbine: layout description, working principle and main features (axial force balance, steam bleeding). Mixed turbine (impulse + reaction).

OFF DESIGN GAS TURBINE OPERATION: Definition of mass flow function and corrected speed. Characteristic curves of compressor. Compressor instability phenomena: surge, stall and chocking. Characteristic curves of turbine. Coupling of compressor and turbine in gas turbine power system. Coupling constraints (equivalence of rotational speed, continuity of mass flow rate, continuity of pressure, constant mass flow function at turbine inlet). Gas turbine stacking maps. Regulation of gas turbine in off-design conditions: single shaft GT with fixed geometry; Single shaft GT with variable inlet guide vanes (VIGV); Double shaft GT with fixed geometry; Double shaft GT with variable nozzle guide vanes (VNGV).

Readings/Bibliography

Energy systems
J. H. Horlock, Combined Power Plants.
Macchi, E., 2017. Organic Rankine Cycle (ORC) Power Systems. Elsevier.
Negri di Montenegro G., Bianchi M., Peretto A., Sistemi energetici e macchine a fluido, Pitagora 2009 (in
italian).

Turbomachinery
Dixon, S. L., et al. Fluid Mechanics and Thermodynamics of Turbomachinery, Elsevier Science & Technology,
2013. ProQuest Ebook Central, https://ebookcentral.proquest.com/lib/unibo/detail.action?docID=5754462.
H. I. H. Saravanamuttoo, Gordon Frederick Crichton Rogers, Henry Cohen, Gas Turbine Theory, Pearson
Education, 2001. ISBN: 013015847X, 9780130158475.
Bianchi M., Melino F., Peretto A., Sistemi energetici: complementi, Pitagora 2008 (in italian).

Teaching methods

Theoretical lectures + exercises (tutored and self-directed).

Assessment methods

The knowledge acquired by the student will be assessed through an oral exam consisting of theory and exercises.

Teaching tools

Course materials, tutorials, files, videos, etc. will be available on the interactive course website:
Virtuale (unibo.it) [https://virtuale.unibo.it/]

Office hours

See the website of Saverio Ottaviano