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Limiting Factors for Steam Parameters

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Presentation on theme: "Limiting Factors for Steam Parameters"— Presentation transcript:

1 Limiting Factors for Steam Parameters
Presented by, Nithin Seenivasan, FH Aachen, Jülich, 15th December, 2011

2 Contents of the Presentation
Introduction Main Steam Parameters Various Limiting Factors for Steam Parameters Corrosion Material Limitations High Steam Velocity Limitations Impure Feedwater Fuel Heating Value Limitations References

3 What is Steam?! Technical term for water vapor, the gaseous phase of water, which is formed when water boils.

4 What is Steam?! Source: Alliance Knowledge, 2011 Source: Petaflop Blog
Water Steam Steam + Water Droplets Source: Alliance Knowledge, 2011 Source: Petaflop Blog Heat Water Vapor Water Droplets + Vapor Condensation Condensation

5 What is Steam?! Technical term for water vapor, the gaseous phase of water, which is formed when water boils. Dry Steam is INVISIBLE

6 Main Steam Parameters Pressure Temperature 40 Mpa (400 Bar)
Mass Flow of Steam 40 Mpa (400 Bar) 900 °C (1173 K) 600 Kg/s Example of an Exploded Chemical plant in Nevada, USA Source: Exponent Consultants

7 Limiting Factors of Steam Parameters
Oxidation Corrosion Fuel Ash Corrosion Carburization Hydrogen Damage Creep Fatigue Erosion Increased Losses Water Hammer Impure Feed Water Fuel Heating Values Corrosion Material Properties

8 Limiting Factors of Steam Parameters

9 Corrosion Source: Checkthishouse Inc

10 Oxidation Corrosion Oxidation rates of metals increases with Temperature Typical Value for tubes mm / Year Parts built below Oxidation Limit A high magnification optical microscope view of a cross-section through a failed Aluminum Tube reveals that a localized area of the coating on the ID surface has been replaced by oxide scale (arrow) Source: Metallurgical Technologies Inc.

11 Hydrogen Damage Caused by Excessive Deposition and low pH of feedwater
Increases at higher Temperature and Pressure Hydrogen ions from water are adsorbed into Metal Matrix causing Hydrogen Embrittlement Brittle failure in a pipe due to hydrogen damage Source: Babcock and Wilcox – Boiler Tube Analysis

12 Fuel Ash Corrosion Wastage of tubing caused by chemical reactions with the fuel ash Chlorides, Sulfur corrode Oxidation resistant surfaces Ash forms a corrosive liquid layer on surface Fuel Ash Corrosion of OD of a Superheater. Very thick scale was observed on the OD, with a significant amount of chlorine detected in the deposit Source:

13 Carburization Occurs due to incomplete combustion, giving rise to CO and un-burnt fuel in Flue Gas Chromium from surface of steel reacts with C to form Chromium Carbides Causes severe Embrittlement and reduced Corrosion resistance Excessive temperature in combination with high carbon activity in the Furnace caused changes in microstructure of the tube, which resulted in severe embrittlement and premature failure. Source: Lifechem

14 Limiting Factors due to Material Properties
Source: Infograph

15 Creep Creep is the tendency of a solid material to deform permanently under the influence of stresses for a prolonged period of time Stresses may be lower than Yield Strength Creep always increases with Temperature Even if no other failure occurs in the tube metal, creep will definitely occur Plastic Paper Clip Metal Paper Clip

16 Fatigue Fatigue is the progressive and localized structural damage (crack propagation) that occurs when a material is subjected to cyclic loading In Steam generation, stresses due to Temperature differences in Startup and Shutdown cause fatigue. (larger the temperature, larger the chance of fatigue failure) Versailles train crash! Fatigue failure in a Train axle Source: Wikipedia

17 Increased Losses High-pressure steam leaks from piping, components, and pressure reducing valves High-pressure radiation loss for steam piping and components High Pressure Steam Leak being repaired by a technician Source: Super Shakti Sealing Services

18 Erosion Erosion is a function of Ash content in Fuel, Ash Composition and Gas velocity Coupled with Stresses, can result failure Source: INSA Lyon Source: Pair O Docs LLC

19 Melting! Source:

20 Limiting Factor due to High Steam Velocity
Source: CWLP, Illinois

21 Steam Hammer Steam hammer is a pressure surge or wave resulting when Steam in motion is forced to stop or change direction suddenly. Can cause noise, vibration or Pipe Collapse Due to high Fluid Velocities resulting from high pressure Steam Expansion joints destroyed due to a Steam Hammer (magnitude up to tune of 5000 Psi = MPa) Source: Wikipedia

22 Limiting Factors due to Impure Feedwater
Source: Water Rhapsody

23 Effects of Impure Feedwater
Scaling (Deposition of impurities on boiler walls) Hinders Heat Transfer and Steam Production Higher Temperature and Pressure increases rate of scaling Internal deposits resulting from poor boiler water treatment. These deposits, besides hindering heat transfer, allowed boiler water salts to concentrate, causing corrosion. Source: Steam – The Babcock & Wilcox Company

24 Effects of Impure Feedwater- Scaling
Power Output- 450 MW Boiler- Natural Circulation Boiler Steam Production- 378 kilograms per second Feedwater Hardness – 1 ppm (minerals and oxides) Deposits in Boiler - 11,340 Kg per year!! Source: Steam – The Babcock & Wilcox Company

25 Effects of Impure Feedwater
Corrosion Oxygen Pitting Corrosion (DO – Dissolved Oxygen) Acid Corrosion An Economiser showing the effects of Pitting corrosion, caused due to Feedwater impurities. The tube was damaged by oxygen pitting and poor feed water chemistry. Source: Power Corrosion (Consultants) LTD

26 Limiting Factor due to Fuel Heating Values
Source: Texas Tribune

27 Heating value of Fuels Used for Steam Generation
Source: Steam – The Babcock & Wilcox Company

28 More Fuels Compared Source: BioMass Energy Center

29 Conclusion A huge number of Limiting Factors exist for Steam Parameters All the Limiting Factors have to be taken into consideration while designing a plant Careful maintenance has to be done to avoid preventable breakdowns due to a few Limiting Factors

30 Book References Steam/its generation and use, Edition 41 by The Babcock & Wilcox Company Standard Handbook of Powerplant Engineering, 2nd Edition by Thomas C. Eliott, Kao Chen and Robert C. Swanekamp

31 Internet References (Hydrogen Embrittlement)

32 Thank you!

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