121

What are the benefits of undertaking retrofit, in a power plant?

v Power plant retrofit improves power plant efficiency, increases output & reduces emissions

v  Saving on capex while benefiting from new technologies

v  Optimization of existing plant components

v  Adaptation of the plant for new or changed products

v  Increase in piece number and cycle time

v  Guaranteed spare parts availability, as new parts are retrofitted

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What is Creep?

In materials science, creep (sometimes called cold flow) is the tendency of a solid material, to move slowly or deform permanently under the influence of mechanical stresses.

Creep may be defined as a time-dependent deformation, at elevated temperature and constant stress.

The end of useful service life of the high-temperature components in a boiler (the superheater and reheater tubes and headers, for example) is usually a failure by creep.

It can occur as a result of long-term exposure to high levels of stress that are still below the yield strength of the material.

Creep is more severe in materials that are subjected to heat for long periods, and generally increases as they near their melting point.

The rate of deformation is a function of the material properties, exposure time, exposure temperature and the applied structural load.

Depending on the magnitude of the applied stress and its duration, the deformation may become so large that a component can no longer perform its function — for example creep of a turbine blade will cause the blade to contact the casing, resulting in the failure of the blade.

Creep is usually of concern to engineers and metallurgists when evaluating components that operate under high stresses or high temperatures.

123

What is Fatigue?

In materials science, fatigue is the weakening of a material caused by repeatedly applied loads.

It is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading.

Fatigue occurs when a material is subjected to repeated loading and unloading.

The nominal maximum stress values that cause such damage may be much less than the ultimate tensile stress limit, or the yield stress limit.

If the loads are above a certain threshold, microscopic cracks will begin to form at the stress concentrators such as the surface, persistent slip bands, and grain interfaces. Eventually a crack will reach a critical size, the crack will propagate suddenly, and the structure will fracture.

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What are the factors affecting fatigue-life of an equipment/ component?

v  The state of cyclic stress

v  Geometry of the component

v  Surface quality

v  Material type

v  Residual stresses

v  Size and distribution of internal defects

v  Direction of loading

v  Grain size

v  Environment

v  Temperature

v  Crack closure

125

What is center of gravity?

The center of gravity is a geometric property of any object.

The center of gravity is the average location of the weight of an object.

Center of gravity is the point in a body around which the resultant torque due to gravity forces vanishes.

126

What is center of mass?

The center of mass of a distribution of mass in space, is the unique point where the weighted relative position of the distributed mass sums to zero.

127

What is CFD analysis?

Computational fluid dynamics, usually abbreviated as CFD, is a branch of fluid mechanics that uses numerical methods and algorithms to solve and analyze problems that involve fluid flows.

Computers are used to perform the calculations required to simulate the interaction of liquids and gases with surfaces, defined by boundary conditions.

The fundamental basis of almost all CFD problems are the Navier–Stokes equations.

128

What is Coal blending?

Uniform mixing of different grades of coal in predetermined proportion to achieve desired GCV/ properties, is called Coal blending.

129

List some of the advantages of Coal blending.

v  GCV of as-fired coal can be enhanced

v  Reduction in ash content

v  Reduction in Soot blowing frequency

v  Decrease in Maintenance cost

130

What are the various methods of Coal blending?

v  Blending by mixing two streams of coal on conveyor belt 

o    Imported coal reclaimed from Reclaimer and domestic coal from track hopper/ Wagon Tipplers

o    Both coals reclaimed by Reclaimers

v  Blending by Ground Hopper

v  Blending in Stockyard 

v  Blending on conveyor by Silos

v  Blending of Imported Coal by Installing additional low capacity Reclaimer on existing stock yard