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The Inner-Workings of a General Gas Turbine

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Kathryn Everett

on 5 August 2014

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Transcript of The Inner-Workings of a General Gas Turbine

Single shaft connects turbine to the compressor as well as the generator
First and second generation gas turbines were of a hot end drive while most third generation's are cold
Equipment accessibility
Inlet duct must be configured to accommodate cold end drive
LM6000 exhaust duct

General Information
Illustration of the complex composition of the fuel in gas turbines.
The Inner-Workings of a General Gas Turbine
Selective Catalytic Reduction (SCR) is a postcombustion NOx emission reduction system.
Anhydrous or aqueous ammonia (NH3) injected in the flue gas stream reacts with NOx to form nitrogen and water in the following reactions:

8(NH3) + 6(NO2) --------> 7(N2) + 12(H2O)
4(NH3) + 4(NO) + O2 --------> 4(N2) + 6(H2O)
2(NH3) + NO + NO2 --------> 2(N2) + 3(H2O)

Catalyst: base metals, zeolites or precious metals; honeycomb or plate design.
Reduces NOx emissions up to 95%.
SCR allows the LMS100 to meet the EPA's below 25 ppm requirement, while maintaining best-in-class performance.
Selective Noncatalytic Reduction (SNCR) lessens NOx emissions by injecting either ammonia or urea into the steam generator with the flue gas. The following reaction demonstrates this process:

4(NO) + 4(NH3) + O2→4(N2)+6(H2O) + heat

Achieves maximum NOx reduction (70-80%) between 1,500 to 2,200 F.
SNCR is very site specific and varies with fuel type, size, and steam generator heat transfer characteristics.
Achieves 20% NOx reduction when qualifications aren't met.
When qualifications are met, it has an economical advantage over SCR because SNCR doesn't require the purchase of a catalyst.
Combustion Turbine
Expanding high pressure gas released from the combustion section spins the blades creating useful energy.
Work done on the turbine is the exact work that is done by the compressor.
Shaft also turn the rotor inside a generator.

Combustion Reaction
Chemistry principles: proper stoichiometric ratios, equivalent masses in reactants and products, fixed weight relationships in chemical compounds, and the release or consumption of heat during the reaction itself.
Exothermic reaction.
The following equation represents the general combustion of methane:

CH4 + 2(O2N2)→2(N2) + CO2 + 2(H2O) + heat
Gas turbine operation at high temperatures allows for higher efficiencies.
Cooling techniques were able to advance with technology improvements.
Without cooling technology, firing temperatures would have leveled off and would be limited to metal alloys and coatings.
Improvements have have increased rotor life by reducing turbine damage
Air flows through at a higher pressure than the surrounding gas.

Example LMS100
The material of the Blades in Stage 1 are cooled by Compressor Discharge Air
The Blades in Stage 2 are simply cooled by convection

HPT Air Cooling Blades and Vanes
Dry Low Emission (DLE)
The Dry Low Emission (DLE) control erases the need of water injection for NOx emission control in the LMS100.
Helps the plant reach full rate power in under 10 minutes.
Fast start capability and flexible operation.
Particulate Matter
PM10 - particulate matter with a nominal aerodynamic diameter of 10 microns.
These could be smoke, dirt, mold, pollen etc.
Have severe health effects.
PM2.5 has a diameter of 2.5 microns.
Finer particles caused by fires and metal smelting.
The U.S. EPA is developing a method to measure PM2.5.
History of Turbines

This specific Turbine consists of three components.
High Pressure Turbine
Intermediate Pressure Turbine
Power Turbine
The High Pressure Turbine drives the High Pressure Compressor.
Intermediate Pressure Turbine drives the Low Pressure Compressor.
The shafts are concentric.
Power Turbine is aerodynamically connected to the IPT and it's shaft drives the generator and is completely separate from the rest of the Combustion Turbine.
Max RPM: 3,600

Blades and Angle of Attack
Each stage of a turbine consists of a row of stationary vanes followed by rotating blades (opposite of the compressor)
The vanes, or nozzles, "turn" the flow to direct it into the rotor blades at the optimum angle
Efficiency of the turbine is determined by how well the turbine extracts mechanical energy from the hot, high-pressure gasses

The turbine engine is of constant volume and its power output is directly proportional to and limited by its air mass flow rate.

Components of a Combustor
slows the high speed, highly compressed, air for the combustor.
withstands high/low pressure differences.
Fuel injector
introduces fuel and mixes it with air. Types: pressure-atomizing, air blast, vaporizing and premix/prevaporizing injectors.
Causes of Emission
Fast start ups/ ramp rates
Water injection for NOx control
Start up limitations/ exemptions
Steady state or low loads
DLN (dry low NOx burner)
ULN (ultra low NOx burner)
These are combustors that minimize air and flame temperature
All gas turbines follow the Brayton Cycle.
The hot exhaust is passed through the power turbine and work is done by the flow from station 4 to station 5.
The nozzle (specific to turbojet combustion turbines) then brings the flow isentropically back to free stream pressure from station 5 to station 8.
Overall Process of Combustion
Compressed fuel and are are mixed then ignited.
Ignitors turn off once combustion is self-sustaining.
Flame is contained in the small combustor.
Wide range of operation.
Low pressure loss with uniform exit temperature profile.
The products of the combustion reaction flow to the turbines after emission control systems.
Water Injection System
Demineralized water is injected through the water injection manifold.
The water or steam mixes in the flame with the combustion by-products.
Results in a lower flame temperature and, thus, reduced formation of thermal NOx.
Can increase CO emissions.
is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work.

an engine actuated by the reaction or impulse or both of a current of fluid (as water, steam, or air) subject to pressure
The first known turbine is the steam turbine. It was developed around 100 BC by egyptian scientist, Hero. Hero is said to have used this invention to pull-open temple doors.
1930 an Englishman, Frank Whittle, submitted a patent application for a gas turbine for jet propulsion. It was not accepted until 1939. And in 1941, the the engine made its first flight.
The first electricity-generating wind turbine was a battery charging machine installed in 1887 by Scottish academic James Blyth to light his holiday lights in Marykirk, Scotland.
The first water turbines date to the late 3rd or early 4th century AD at a Roman turbine mill in Chemtou, Tunisia. The tangential water inflow of the millrace made the submerged horizontal wheel in the shaft turn like a true turbine.
The word "turbine" was coined in 1822 by the French mining engineer Claude Burdin from the Latin word turbo, or vortex.
Carbon Monoxide Reduction (COR) reduces CO emissions by an oxidation catalyst located in the exhaust duct.

2(CO) + O2→2(CO2)

Natural gas does not create a lot of CO emissions but the rate is large enough for environmental concern.
Oxidation catalyst can also reduce VOCs produced from combustion.
Specified Combustion Equation
Ratio of oxygen to nitrogen in the air, (1 : 3.76), gives us the following equation:

CH4 + 2(O2) + 7.52(N2)→7.52(N2) + CO2 + 2(H2O) + heat

Compared to the original:

CH4 + 2(O2N2)→2(N2) + CO2 + 2(H2O) + heat

The more specified the reaction, the more accurate our calculations are for fuel and emissions.
Natural gas inherently has low PM10 emissions.
Wet scrubbers, electrostatic precipitators, fabric filters, absolute filters, and ceramic filters can further reduce PM10.
Volatile Organic Compounds (VOC)
Turbine Components
Turbine Blades and Vanes

The stator NGVs form convergent ducts.
Convert the gaseous heat and pressure energy into higher velocity gas flow.
In addition to accelerating the gas, the vanes "turn" the flow to direct it into the rotor blades at the optimum angle.
NGVs are shaped to swirl the gas flow.
Static components mounted into the casings

or for a perfect gas with Cp = constant
Turbine Disks
Each section of the turbine (HPT, IPT, LPT) has a set of disks that connect to the shaft.

Locate and retain the rotating blades enabling the circumferential force to be transmitted through the central shaft

Every turbine varies in the amount of disks present.

Each row of blades is retained in the rim of a disk via a root fixing, commonly of fir-tree design, designed to withstand the enormous centrifugal loads.

The vanes and blades are airfoils that work together to provide for a smooth flow of the gases.

As the airstream enters the turbine section from the combustion section, it is accelerated through the first stage stator vanes.
Casing and Structure
The outer structure of the turbine
Forged steel or nickel alloys strong enough to contain the internal gas pressure
Contain any debris if a component should fail

Connect casings to internal shaft bearing supports,
Transmit the bearing loads into the case and stiffening the assembly
A typical turbine assembly may be broken up into five main component types:

1) Casings and Structures
2) Shafts
3) Disks
4) NGVs (Nozzle Guide Vanes)
5) Blades
Turbine Shafts
The turbine shafts have three main functions:
1. transmitting torque
2. transmitting axial loads to the compressor and generator rotor
3. supporting the discs and blade assemblies

Oil-cooled and lubricated bearings mounted within the structure
Frame/Heavyweight have single shafts
Multi-spool engines' shafts each rotate concentrically and dependent of each other.

Calculation of Shaft Power

The Euler turbine equation relates the power added to or removed from the flow, to characteristics of a rotating blade row. The equation is based on the concepts of conservation of angular momentum and conservation of energy.
It relates the temperature ratio (and hence the pressure ratio) across a turbine or compressor to the rotational speed and the change in momentum per unit mass.
Blade Equations
This section of the Brayton Cycle is an adiabatic (no heat transferred), Isentropic (no change in entropy), quasi-static (or reversible) expansion in the turbine with which
1. Some work is used to drive the compressor
2. The remaining can be used as acceleration for jet propulsion, or to turn a generator for electrical power generation

Increase of entropy due to friction
Real turbines are not reversible.
Hot exhaust is passed through the power turbine and work is done by the flow

General Information
Ambient Air Conditions
Filter House


Relative Humidity
Climate Conditions

Ambient Air

Filter House




Filter House

Filter specific sizes generally medium

Smaller than 0.5 um

Larger than 1 um

Filter House

Filter House

Percentage Loss 0.35% ISO

Percentage Loss 0.74% ISO

Constant Volume Mass Flow Device
Air is working fluid
Air is compressible

Centrifugal and Axial Flow
Inlet Guide Vanes
Variable Bleed Valves


Aero-Derivative Compressor

Lower pressure ratio
More mass per blade
Larger power capability
More Air Flow
Larger Stronger Components

Frame Compressor


What does the compressor efficiency depend on?
Compression ratios
Isentropic efficiencies
Air conditions


Importance of the compressor pressure ratio
Ideal Brayton cycle

Importance of the Compressor Isentropic Efficiency
Back Work (40-80%)
Rapid decrease in overall efficiency (60%=0)


How to improve efficiency?
Reduce the work of the compressor
Increase the mass flow


Intercooler will reduce compressor work



Air to Water Intercooler
Air to Air Intercooler
GE LMS 100

Inlet Chilling
Vapor Compression (Mechanical Chiller)

Inlet Conditioning

Evaporative Cooling Methods
Wetted Media
Wet Compression

Inlet Conditioning

Inlet Chilling
Vapor Compression (Mechanical Chiller)
Lithium Bromide (LiBr)
Ammonia (NH3)

Inlet Conditioning

Inlet Chilling
Vapor Compression (Mechanical Chiller)

Inlet Conditioning

Inlet Chilling

Inlet Conditioning

Simple Psychrometric Model

Inlet Conditioning

Ideal Inlet Temperature

Inlet Conditioning

General Ideal Heating and Cooling Options

Inlet Conditioning


Filters will depend on ambient air conditions
Protects the critical components of CT
High pressure ratio
Smaller footprint
Derived from jet engines
Higher efficiencies
Faster start sequence

Evaporative Cooling
Wetted Media
Wet Compression

All hydrocarbons except methane.
Make up 20-50% Unburned Hydrocarbon (UHC) emissions.
Diameter < 100 microns.
Includes Particulate Matter molecules.
High vapor pressure, low boiling point.
Emissions are low due to proper combustion controls.
Further reduced by CO oxidation catalyst.
Brayton Cycle
Saudi Electric Company
30 GW
42% CT
24% decrease T=120 F
Inlet Guide Vane Ice Buildup
AFC First Stage Tip Failure
AFC Tip Failure
Seligman Arizona
2003 - $11,907
2004 - $191,321
+ atmosphere =
acid rain

free radicals

free radicals
repeat the cycle until the
's are not photo reactive.
UHCs also react with sunlight to form ozone.
is the main component of photochemical smog.

Without emissions control, acid rain and smog would be an even bigger issue, along with the greenhouse gases - water vapor, CO2, CH4, NOx, O3.
High temperature from heat of compression
Inverse exponential curve
Compressor Efficiency Trends
NOx in Combustion
Opportunities for Nitrogen Oxide (NOx) formation during combustion:
Thermal NOx - gas turbines; controlled with nitrogen and oxygen concentrations and temperature of combustion.
Fuel NOx - coal plants; the ionized nitrogen in the fuel is oxidized to create NOx.
Prompt NOx - gas or coal; nitrogen in air oxidizes along with fuel and becomes NOx during combustion.
NOx Control Methods
Reducing peak temperature
(70-85% efficiency)
i.e. Inject Water or Steam
Reducing residence time at peak temperature
i.e. Inject Air, Inject Fuel, Inject Steam
Chemical reduction of NOx

i.e. Selective Catalytic Reduction, Selective Non-Catalytic Reduction
Oxidation of NOx with subsequent absorption
(No Data)
i.e. Inject Oxidant
Removal of Nitrogen
(No Data)
i.e. Ultra-Low Nitrogen Fuel
Using a sorbent
i.e. Sorbent in Combustion Chambers, Sorbent in Ducts
contains the process and introduces various airflows.
Superalloy withstands high temperature cycles.
Cooled by:
Film cooling
Transpiration cooling r
separates primary and secondary air.
adds turbulence to minimize pressure loss while mixing the fuel and air through swirler stabilization.
- after the fuel and air are mixed, before the actual combustion reaction. Most are electrical spark igniters, similar to automotive spark plugs.
Major Applications
Jet engines
Turboprop engines
Power generation
Mechanical Drive
Heather Ferry
Kaleb Hutchens
Kathryn Everett

Prepared For:
Mechanical Engineering Department
Non-Ammonia Selective Catalytic Reduction (NASCR) is the same process of SCR but with the injection of urea instead of ammonia.


CO(NH2)2 + H2O --------> 2(NH3) + CO2 + H2O
2(NH3) + NO + NO2 --------> 2(N2) + 3(H2O)

Urea is the preferred reactor when there is a high ammonia consumption rate.
Lowest number of risk and regulatory issues.
Still a developing technology.
Ammonia Slip
Some ammonia (NH3) can pass through SCR un-reacted, called ammonia slip.
Causes of slip: temp too low, over-injection, catalyst has degraded.
An oxidation catalyst is used to convert the ammonia to nitric oxide and water.

4(NH3) + 5(O2)→4(NO) + 6(H2O)

Temp. below 392 F can cause reaction to form explosive ammonium nitrate that can back up the catalyst.
Stresses between the blade and rotor disk
Provide large areas of contact between he blade and disk
Multiple "branches" ensure stability
Better stress distribution
Easier maintenance

NOx Data
GE J85
Small single-shaft turbojet engine
Max RPM: 16,550
The single-shaft connects the turbine to the compressor
Turbine Section

Incomplete Combustion
Ideal products: CO2, N2, and H2O.

Additional by-products:Nitrogen Oxides (NOx), Sulfur Oxides (SOx), Carbon Monoxide (CO), Unburned Hydrocarbons (UHCs), Volatile Organic Compounds (VOCs), and Particulate Matter (PM).

There are various ways to reduce these emissions in order to meet EPA standards.
Air to Fuel Ratio
Combustion process completes in 4-5 milliseconds at an engine speed of 6,000 rpm.
High air-fuel ratio preferable in gas turbine.
GE LM6000
SO2 and SO3
SO3 + water vapor = sulfuric acid mist.
0.002% of natural gas.
Much bigger issue in coal plants.
Use of low sulfur fuels reduces emissions.
Unburned Hydrocarbons
All hydrocarbons except methane and ethane.
Occurs when fuel molecules do not burn or burn only partially.
Includes Volatile Organic Compounds which have emission control systems in the gas turbine.
Spray RCVR
Ammonia RCVR
Pg < 0
Types of Combustors
Can Cannular Annular
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