Team Global

Advancement in Turbine Technology

The important point of turbine system is turbine expansion process (working fluid’s high T energy gas is converted into mechanical energy to drive the compressor and the electric generator). One of the ways to increase the efficiency of turbine expansion process is raising the temperature. But there has limit to maintain the materials shape of turbine system. So, we need to improve an effective thermal barrier to shield the spar from the hot combustion gases. How we enhance the strength of materials of turbine? We associated the way to enhance the strength of materials with process of materials in material science and engineering.

New Materials

Materials with High Thermal Resistance

Types of high temperature materials for gas turbines

Ni-base Super Alloys Used for high temperature components

Single Crystal Super Alloys High temperature capabilities

Third-generation SC Alloys Increase inlet gas temperature to increase thermal efficiency (in land-based gas turbines)

Fourth-generation SC Alloys With platinum group metals; next generation Jet engines

New Materials

Oxide Dispersion-strengthened Super Alloys Excellent creep strengths at high temperature, ultra-high thermal efficiency

Intermetallic Alloys Disadvantage: poor room-temperature ductility

e.g.: Ti-Al alloy: light weight and high specific strength, certain level room-temperature ductility

Refractory Alloys High melting points (uncooled turbine blades)

Platinum-group Metals based Refractory Super Alloys: “refractory super alloys” composed of the γ / γ’ structure observed in Ni-base super alloys in Platinum

group metals with high melting points

New Materials

Ceramics Long creep rupture life at high temperature, high toughness, long-time oxidation & corrosion resistance

At extremely low temperature, some ceramics exhibit superconductivity

E.g. Silicon Nitride (Si3N4)

Composite Materials Ceramic matrix composites (CMC): great fracture resistance ,lightweight, can tolerate ultra-high

temperatures

(excellent candidates for combustor liners, high-pressure turbine vanes and shrouds)

Ceramic fiber reinforced ceramic (CFRC) material: elongation to rupture up to 1%, strongly increased

fracture toughness, extreme thermal shock resistance, improved dynamical load capability,

anisotropic properties following the orientation of fibers

New Materials

Composite Materials Carbon-Carbon (C/C) composites: lightweight, high strength at high temperature

Notes: • It is essential to improve the properties of high temperature

materials so that higher inlet gas temperatures can be reached.

• Ni-base super alloys will be playing a major role in near future although new materials are being materialized.

Processing of Materials

Manufacturing Processes to Maximize Resistance

Heat treatment techniques

Heat treatment involves the use of heating or chilling, normally to extreme temperatures, to achieve a desired result such as hardening or softening of a material. Heat treatment techniques include annealing, case hardening, precipitation strengthening, tempering and quenching. There are many purposes of heat treatment. • Improving resistance to strength and tensile force (Tempering) • Making grains finer and less directional (Normalizing) • Stabilization and homogenization of structure (Annealing) • Improvement of surface strength (Surface Hardening) and so on...

Directional solidification

Having many grains at high temperature reduces material property because of grain boundary sliding. Grain boundary sliding also creates surface cracks. Directional solidification technique enhances properties of the materials at high temperature by avoiding grain boundary sliding. Directional solidification also helps to match to alloy composition by reducing creep strength of certain super alloys.

Directional and progressive solidification describe types of solidifications within castings. Directional solidification occurs from farthest end of the casting and works its way towards the sprue. Progressive (or Parallel) solidification starts at the walls of the casting and progresses perpendicularly from that surface.

Note: The [100] growth direction offers the best overall mechanical properties.

Single crystal solids A single crystal or monocrystalline solid is a material in which the crystal lattice of the entire sample is continuous and unbroken to the edges of the sample, with no grain boundaries. The absence of the defects associated with grain boundaries can give monocrystals unique properties, particularly mechanical, which can also be anisotropic depending on the type of crystallographic structure.

Single crystals has no grain boundaries so they are expected to endure high temperatures. But it is difficult to manufacture single crystals in the shape of a blade so we need to study about casting.

Design and Testing

Configurations and Component Testing Methods

Focus Power plants today focus mainly on the

Cost Efficient Production of Energy.

Imposes requirements of:

• Low overall life cycle costs

• High reliability and availability

• Operating flexibility

Types of Power Plants

Steam Power Plants (SPP) Standard steam power plants.

Operated at sub-critical conditions.

These have efficiencies of about

30-35%

Types of Power Plants

Combined Cycle Power Plants (CCPP) A combined cycle is an assembly of heat engines that work in tandem from the same source of heat, converting it into mechanical energy, which in turn usually drives electrical generators.

Principle:

Exhaust of one heat engine is used as the heat source for another, thus extracting more useful energy from the heat, increasing the system's overall efficiency.

Example: Integrated Gasification Combined Cycle (IGCC) The waste heat produced from the reaction to create the syngas is then recovered to create steam that is used to drive a steam turbine creating more electricity.

Source: http://www.instructables.com/id/Top-Tips-for-a-Power-Station-to-increase-its-effic/step4/Integrated-Gasification-Combined-Cycle-IGCC/

Improving Efficiency Technologies that can be used to increase efficiency:

Fluidised Bed Combustion Supercritical & Ultra supercritical Technology

Integrated Gasification Technology Advantage: If implemented across all power plants up to 25% reduction in C02 emissions from coal which would equate to a 6% reduction in global CO2 emissions.

Fluidised Bed Combustion The process of fluidised bed combustion involves suspending solid fuels in upwards jets of air during the combustion process. The advantage that FBC has is it makes it easier to burn fuels that are hard to ignite such as coal mine wastes and petroleum coke.

Source: http://www.instructables.com/id/Top-Tips-for-a-Power-Station-to-increase-its-effic/step3/Fluidised-Bed-Combustion-FBC/

Supercritical & Ultra-supercritical Technology

Supercritical Steam Generator In contrast to a "subcritical boiler", a operates at such a high pressure (over 22 MPa) that actual boiling ceases to occur, the boiler has no liquid water - steam separation.

Efficiency 42-46%

Ultra-supercritical Steam temperatures above 600 degrees Celsius and pressures around 27 MPa.

Efficiency 45-48%

Testing

Laboratory testing • Destructive

• Non-destructive: ultrasonic, liquid penetrant, magnetic particle and X-ray examination (For critical rotating components)

Field testing Example: Rainbow tests Materials for evaluation are installed in customers’ machines for side-by-side comparison with current baseline material.

Syngas as a Fuel

High Temperature Combustion

The fuel gas generated by gasification of coal consists primarily of H2 and CO, along with smaller amounts of CH2 and higher-order hydrocarbons, CO2 , and H2O;

The level of N2 in syngas can vary from low to high,

depending on whether the gasifier is oxygen- or air-blown.

Advantages:

High Temperature Combustion (700 degrees)Higher Efficiency

Renewable Source (if biomass is used)

Reduced or even zero emissions coupling of a gas turbine

combined-cycle system with coal gasification

Major Challenges • CV of syngas = 1/3 of natural gas;

CV of hydrogen = 0.3 times that of methane

Leads to differences in the relative gas flows in the turbine when compared on the basis of constant power; implications for combustor design, flame stability and increased heat transfer to the combustor can and airfoils.

• Need for better long-term data to characterize creep and fatigue performance of materials as a basis for improved design and reliable operation, as well as better definition of the actual conditions, especially temperature and temperature range, experienced by the key components in the hot gas path.

Major Challenges • Syngas (and hydrogen) have significantly higher laminar flame speeds than

natural gas, giving rise to flame stability issues.

• High levels of water in changes heat transfer properties of the flame and ability to maintain adequate cooling of key components; high water vapor levels also may have detrimental effects on component durability.

• Greater corrosion potential based on its increased water vapor content, and presence of alkali and sulfur levels near the maximum typically allowed.

Hig

her

Effic

ienc

y

Combustion at Higher Temperatures

High Temperature Fuel

Materials with high thermal resistance

Material Behavior for Design

Testing and Sensing Techniques

Better Coatings Better cooling

techniques Combined Cycle

Power Plants (CCPP)

Thank You