Скачать презентацию Cycling HRSGs Jeffrey Phillips Jphillips Fern Engineering com Скачать презентацию Cycling HRSGs Jeffrey Phillips Jphillips Fern Engineering com

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Cycling HRSGs Jeffrey Phillips Jphillips@Fern. Engineering. com Cycling HRSGs Jeffrey Phillips [email protected] Engineering. com

CTC 2 HRSG Cycling Study • In 2001, Fern conducted a study for the CTC 2 HRSG Cycling Study • In 2001, Fern conducted a study for the Combustion Turbine Combined Cycle Users Group (CTC 2) • Issued CTC 2 Report HSRG 20 -14 • On CTC 2 “best seller list” (www. ctc 2. org)

Study Goals • Review problems encountered when operating an HRSG in cycling mode • Study Goals • Review problems encountered when operating an HRSG in cycling mode • Identify “best practices” that are employed to avoid or minimize these problems • Results should be applicable to both existing plants and new units

Major Cycling-Related Problems • Four General Categories – Thermal stress – related – Water-related Major Cycling-Related Problems • Four General Categories – Thermal stress – related – Water-related – Exhaust gas side – Other • Will focus on first two categories – Report covers all four

Best Practices for Existing Units • The Two Most Important Actions to Take: – Best Practices for Existing Units • The Two Most Important Actions to Take: – Conduct a design review of the HRSG • Determine cyclic design conditions • Assess remaining fatigue life • Define ramping limits – Implement effective water lay-up procedures • Wet lay-up should use nitrogen or steam cap • Dry lay-up: drain hot & use nitrogen cap

Other Actions • Use slower ramps • Gradually reduce superheated steam T at shutdown Other Actions • Use slower ramps • Gradually reduce superheated steam T at shutdown – Moderates impact of CT purge on SH • Avoid or closely monitor Spin Cooling • Add motor-operated drain valves on superheater and automate drain sequence

Other Actions • Keep HP drum P as high as possible during shutdowns – Other Actions • Keep HP drum P as high as possible during shutdowns – close all valves including blowdown – import steam from another unit or aux. Boiler – Add a stack damper or inlet “garage door”

Stack Damper Stack Damper

“Garage Door” on Inlet “Garage Door” on Inlet

Other Actions • For long-term shutdowns, add and circulate a octadecyl amine (ODA) to Other Actions • For long-term shutdowns, add and circulate a octadecyl amine (ODA) to BFW – Forms a protective film on metal surfaces – Then place unit in dry lay-up – Film resists corrosion even if surfaces get wet • Add on-line water quality analyzers – p. H of drum and conductivity of condensate

Summary: Remember 2 Things • Know what your HRSG is capable of withstanding! – Summary: Remember 2 Things • Know what your HRSG is capable of withstanding! – Conduct a design review (or life cycle analysis for new units) • Implement good water lay-up practices – Hint: buy nitrogen • The rest is details – I. e. , read the report!

Background Information Causes of Thermal Stress During Cycling – See “notes” portion of Powerpoint Background Information Causes of Thermal Stress During Cycling – See “notes” portion of Powerpoint presentation for narrative

Thermal Stress • All metals expand when heated • Amount of expansion is directly Thermal Stress • All metals expand when heated • Amount of expansion is directly proportional to the change in temperature • Unconstrained expansion does not generate stress, but… – Constrained parts will be stressed – Non-uniform temperatures also create stress

Steel Stress-Strain Curve Steel Stress-Strain Curve

Yield Strength vs T Yield Strength vs T

Cyclic Stresses => Fatigue • Fatigue is damage caused by repeated application of cyclical Cyclic Stresses => Fatigue • Fatigue is damage caused by repeated application of cyclical stresses • Fatigue will also cause a material to fail at stress levels below the yield strength • The effects of fatigue are cumulative • Fatigue is a function of the number of stress cycles and the magnitude of the cyclic stress

Fatigue Curves for Steel Fatigue Curves for Steel

Fatigue-driven Life Expenditure Fatigue-driven Life Expenditure

Thermal Stress-Related Problems • Fatigue damage from rapid ramping – HP Steam Drum is Thermal Stress-Related Problems • Fatigue damage from rapid ramping – HP Steam Drum is the most vulnerable – Ramp downs cause more damage to drum than ramp ups – Less of a concern for steam systems <1500 psig (103 barg) – Warm and hot starts can be faster due to smaller overall temperature change