Gas Turbine Modules 11-12 Quick Notes

Modules 11 and 12: control system, instrumentation, operation & maintenance, installation requirements; Module 12 focuses on gas turbine overhauls.

Pressure ratio: ext{PR} = \frac{p{t}}{p{i}} (turbine exit pressure to intake pressure)
Firing/ turbine inlet temperature: higher TIT improves work output and plant efficiency
Result: higher TIT and PR lead to higher efficiency and output

Applications: aircraft propulsion, power generation, mechanical drives, marine propulsion
Aircraft engines: turbojet, turbofan, turboprop

Inlet/intake accelerates air via first-stage compressor blades
Stators (fixed blades) convert velocity into pressure
Example progressions: Stage 1 pressure rises from ~1 bar to ~4 bar; temperature ~胎 15–180°C
Second stage: pressure rises to ~10 bar; temperature up to ~300°C; air enters combustor
Overall: multiple stages increase pressure; diameter narrows per stage

Lubrication system: pumps, scouring pumps, filters (dual-sided)
Gearing and bearings: thrust and general bearings; multiple bearings in assembly
Seals: various seal types used throughout
Fuel system: fuel supply, nozzles, heaters (air/fuel and oil/fuel heaters)
Noise control: acoustic liners; spacing/number of rotor/stator blades affect output and noise
Start and testing: performance and mechanical test codes (ASME, API)

Functions: start sequence, shutdown, operation control, protection
Open loop vs closed loop:
- Open loop: no process feedback; manipulated variable set manually or by program
- Closed loop: measured variables feed back to correct error toward setpoint
Modern turbines: distributed control systems (DCS), condition monitoring, optimization systems
Feedforward vs feedback:
- Feedback: uses measured errors to adjust
- Feedforward: preemptive adjustments based on expected changes

Start sequence usually automatic; measurements must be correct before start
Starter assists until self‑sustaining speed; ignition must light off
Hold fuel for a short period during fast starts for purge
Ready-to-start lamp indicates unit readiness; local control buttons initiate start modes

Load control via fuel input modulation based on:
- Turbine firing temperature, inlet guide vane position, and airflow
TIT control uses inputs: EGT, compressor pressure ratio, compressor exit temp, air mass flow
Pyrometers/probes increasingly used for direct TIT measurement (noncontact)

Parameters monitored: speed, pressure, temperature, vibration, thrust-related temps
Temperature transducers:
- Thermocouples: range ~200–2760°C
- RTDs: range ~270–1000°C
- Pyrometers: noncontact temperature measurement
Pressure devices: Bourdon tubes, manometers, Pitot tubes, pressure transducers, barometers
Vibration: displacement, velocity, acceleration
Position sensing: eddy current proximity probes (shaft position, bearing health)
- Advantages: works in hostile conditions; inexpensive
Velocity sensors: self‑generating transducers; placement sensitive; 10 Hz–1 kHz typical
Acceleration sensors: piezoelectric crystals; limited low-frequency response

Plots natural blade/flexible part frequencies vs RPM
Prohibited (resonant) speed ranges shown; avoiding excitation at natural frequencies
Used for blade/rotor dynamic assessment and test on shaker table

To ensure even combustion and normal operation, use flame detection and monitoring

Failure-based (breakdown) vs scheduled preventative vs predictive vs proactive vs condition-based vs reliability-centered vs TPM
TPM focuses on overall product/process quality and equipment reliability
Lifecycle costs depend on component efficiency and operating efficiency
Typical lifecycle cost mix: initial cost 7–10%, maintenance 15%, operating energy largely dominates
Example: improving motor efficiency (ABB synchronous motor) by 0.25% yielded ~\$500k savings over 20 years

Effective conditioning reduces underutilization and downtime; improves availability and cost
Life cycle economics depend on fuel costs, efficiency, and maintenance strategy
Parameters affecting hot-section life: fuel type, firing temperature, material properties, cooling efficiency, number of starts

Overhaul = major inspection/renewal conducted at fixed intervals (Time Between Overhauls, TBO)
Typical TO intervals: modern gas turbines ~6k–8k hours
Work scope planning guides: reliability considerations, service bulletins, modifications, on-condition items, fleet experience
Goals: reduce shutdowns, optimize maintenance, improve spare parts planning and training

Heavy industrial vs aeroderivative:
- Aeroderivative: higher reliability/availability, faster startup, lighter, more frequent maintenance
- Heavy industrial: higher inertia, longer inspection intervals but slower startup; larger, heavier
Availability typically expressed as days/year; inspection intervals evolve over time with fleet experience

Assignment 1: CAD/drawing of energy-limited starting system including gas accumulator, check valve, start valve, starter, main engine starter pump, APU relief valve, hind pump, reservoir
Assignment 2: Health monitoring program for gas turbine components:
- List components, likely failure modes, available health monitoring methods
- Assess cost-effectiveness for each method
- Evolve fault diagnosis procedures with maintenance capabilities
- Establish feedback mechanism to update program