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Risk management during start up and commissioning of super critical once through units
 

Risk management during start up and commissioning of super critical once through units

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The Allowable Water and Steam Chemistry Regimes for Supercritical Units have been identified along with maximum deviations during start up and commissioning. This presentation gives guidelines for ...

The Allowable Water and Steam Chemistry Regimes for Supercritical Units have been identified along with maximum deviations during start up and commissioning. This presentation gives guidelines for contracting norms to avoid damages.It is for the EPC Contractors in charge of construction of these units to understand the risks associated and design organizational skills both in technical and commercial areas to avoid major delays and damages.

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    Risk management during start up and commissioning of super critical once through units Risk management during start up and commissioning of super critical once through units Presentation Transcript

    • EPC Risk Management Paradigm Start Up Chemistry In Supercritical Power Generating Units PRESENTED BY DR. HIMADRI BANERJI EX CEO RELIANCE ENERGY MD ECOURJA TRUEVENTUS Engineering, Procurement & Construction (EPC) Senate Date: September 23 - 24, 2013 Venue: Sofitel Bangkok Sukhumvit, Bangkok Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 1
    • EPC Risk Management Paradigm & Start Up Chemistry In Supercritical Power Generating Units 1. INTRODUCTION Most power stations today are going super critical due to the immense advantages of efficiency and their potential of lowering emissions of carbon dioxide. However it is now being recognized that supercritical units pose significant chemistry challenges during the start up and commissioning regime with consequent financial risks to EPC Contractors, who hitherto not aware or exposed to these risks have now to adapt quickly to a new Risk Management paradigm 2. OBJECTIVE: To understand the risks and challenges in start up and commissioning of supercritical power generating units and take up proper risk management and control measures Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 2
    • Supercritical Units: Efficiency Advantage Improvements in the efficiency of pulverized coal (P.C.) fired boiler/steam turbine power plants have been pursued since the introduction of P.C. fired boilers in the 1920’s. This led eventually in the late 1960’s to the introduction of supercritical boilers operating at about 570 Deg C (1060qF) superheat/reheat temperatures and 24 MPa (3400 psi) pressure for the steam. Presently boilers with 300bar and 700 Deg C are being adopted for many of the recent power plants. Since at these pressures and temperatures there is no distinct differences between the water and steam phases, no drums are required in the same. Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 3
    • SUPERCRITICAL UNITS: CONSTRUCTION FEATURES Conventional steam power plants operate at a steam pressures in the range of 170 bar and 565 Deg C. These are Subcritical power plants. The new generation of power plants operate at pressures higher than the critical pressure. These are Supercritical power plants. The operating pressures are in the range of 230 to 265 bar. And 565 Deg C The next generation of power plants will operate with Steam Pressures in the range of 300 bar and 630Temperatures 630700 Deg Centigrade. These are the Ultra Super Critical Power Plants. Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 4
    • SUPERCRITICAL UNITS: CONSTRUCTION FEATURES The lower part of the boiler furnace is arranged in a spiral configuration such that the fluid path wraps around the boiler as it travels up the furnace. Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 5
    • SUPERCRITICAL UNITS: MATERIALS OF CONSTRUCTION Comparison of Allowable Stresses between Conventional and Advanced Stainless Steel Tubes, Advanced CrMo Steel Pipes Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 6
    • 3.LEARNING 3.LEARNING THROUGH A CASE STUDY SUPERCRITICAL UNITS: EPC CONTRACTOR’S CHEMISTRY CHALLENGES Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 7
    • SUPERCRITICAL UNITS: EPC CONTRACTOR’S CHEMISTRY CHALLENGES Oxygenated Treatment OT of Supercritical Boilers onceThe benefits from a once-through supercritical boiler on OT include: doubleLowering overall corrosion rates by forming a protective, double-oxide layer with a controlled amount of oxygen present in the condensate [This protective layer is considered to be more stable than the oxide layer formed using AVT(O) or AVT (R)] Decreasing boiler chemical cleaning frequency due to reduced amounts of iron transport and deposition Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 8
    • SUPERCRITICAL UNITS: EPC CONTRACTOR’S CHEMISTRY CHALLENGES Oxygenated Treatment OT of Supercritical Boilers • Allowing quicker, cleaner start ups and reduced corrosion product transport rates during cold and hot start ups • Allowing boiler operation at lower pH with overall objective of minimizing chemical costs • Eliminating feeding, handling, and storage of oxygen scavenger products Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 9
    • SUPERCRITICAL UNITS: EPC CONTRACTOR’S CHEMISTRY CHALLENGES Oxygenated Treatment OT of Supercritical Boilers coalShows the pressure drop history of a coal-fired supercritical plant in Japan that changed the water chemistry from AVT to OT in 1996. After 7 years operation since the change, there has been no significant increase in pressure drop. This plant has not required acid cleaning since the change, and no future cleaning is planned. Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 10
    • SUPERCRITICAL UNITS: EPC CONTRACTOR’S CHEMISTRY CHALLENGES all-ferrous metallurgy...no copper please onceMost once-through supercritical boilers have been converted from previously predominant AVT to OT, with new facilities almost exclusively using OT. allThis chemistry change requires all-ferrous metallurgy in the feed water train, copperand precludes copper or copper-based alloy feed water heat exchangers in system design and bronze impellers in condensate pumps and valve trims in the condensate system. The other chemistry challenge requires that there be very high level of cleanliness during construction of the entire piping and boiler tube system to avoid silica from dust, iron from rust and other contaminants Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 11
    • SUPERCRITICAL UNITS: EPC CONTRACTOR’S CHEMISTRY CHALLENGES all-ferrous metallurgy...no copper please This is primarily the challenge to the engineering group of the EPC contractor to ensure that this is strictly adhered.. Risk of contamination with copper and zinc in steels is very high. The procurement group has to be aware and must use proper risk mitigation. Risks of contamination during fabrication and erection have to be recognized by the construction teams. Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 12
    • SUPERCRITICAL UNITS: EPC CONTRACTOR’S CHEMISTRY CHALLENGES & RISKS STARTUP CHALLENGE In order to avoid corrosion in the ferrous materials in the water circuit, a minimum alkalinity is to be maintained in the feed water (as measured by pH). cycle, The startup and commissioning cycle, therefore include startup on All Volatile Treatment(AVT) with quick conversion to OT( Oxygenated Treatment) and this is the EPC turnkey contractor’s responsibility. onceTo ensure efficient startup and commissioning of once-through supercritical boilers, the EPC turnkey contractor must address these chemistry issues and develop a practical approach to achieving steam feedpurity and specified feed-water chemistry requirements. Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 13
    • SUPERCRITICAL UNITS: EPC CONTRACTOR’S CHEMISTRY CHALLENGES & RISKS STARTUP CHALLENGE The reducing environment (negative oxidation reduction potential [ORP] present when operating on AVT(R) ESPECIALLY DURING STARTUP may contribute to increased iron transport, subsequently increasing the pressure drop through the boiler. onceHence some once-through supercritical boiler manufacturers have instituted penalties against the allowable pressure drop during initial boiler performance testing, an additional complication that may impact start up and commissioning activities including causing delays These penalties are based on extended operation on all volatile treatment reducing (AVT[R]) during start up and commissioning. Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 14
    • SUPERCRITICAL UNITS: EPC CONTRACTOR CHEMISTRY CHALLENGES & RISKS STARTUP CHALLENGE The major problem with this is however that we still do not have a standard on penalties against pressure drop during startstart-up based on models or analytics (risk management principles) Besides each unit is different from the other As a result these pressure drop correction penalties will be fervently debated by the EPC contractor during commissioning and challenged by both owners and plant operators Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 15
    • SUPERCRITICAL UNITS: EPC CONTRACTOR’S CHEMISTRY CHALLENGES WARRANTY IMPLICATIONS Steam turbine suppliers are also setting limits, in the equipment contract, on the number of hours a turbine out-ofcan be operated with out-of-specification chemistry. actionThese limits are typically listed in an action-level format where minor chemistry excursions are allowable for predetermined time periods without violating the equipment warranty. up— Steam Purity Limits During Start up— EPC OnceContractor Recommendation for Once-Through Boilers...usually one week Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 16
    • SUPERCRITICAL UNITS: EPC CONTRACTOR’S CHEMISTRY CHALLENGES During steam-side start up and commissioning, the EPC contractor is mostly interested in main and reheat steam chemistry. Table below lists EPRI recommendations for once-through boilers operating under OT, including normal target value and action levels 1, 2, and 3. Although recommendations listed in Table are acceptable for targeted chemistry limits during operation, EPC contractors would like to see the following two columns added to this table: • Allowable chemistry excursions during hot start up • Allowable chemistry excursions during cold start up Feed Water Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 17
    • What Are Action Levels 1, 2, 3 Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 18
    • SUPERCRITICAL UNITS: EPC CONTRACTOR’S CHEMISTRY CHALLENGES Start up chemistry guidelines should primarily focus on main steam chemistry targets, including cation conductivity: it warns of salts and acids that may cause turbine corrosion silica : silicate scaling may contribute to turbine capacity and efficiency losses. sodium: critical for avoiding corrosion because uncontrolled sodium hydroxide concentrations are known to cause corrosion damage failures in boiler tubes. Targets for chlorides, sulphates, and organic compounds should be deferred until the end of the commissioning cycle. Degassed cation conductivity is the preferred conductivity to be measured during commissioning since system air leaks are still being discovered and sealed during the start up and commissioning phase. The measurement of degassed cation conductivity will aid in differentiating between air leaks and other contamination sources Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 19
    • SUPERCRITICAL UNITS: EPC CONTRACTOR’S CHEMISTRY CHALLENGES The two most important parameters in Table are feed water cation conductivity and pH. Cation conductivity should be maintained below 0.15 µS/cm during operation on OT. Normal pH range for feed water under OT is 8.0 to 8.5. The EPC contractor is challenged with controlling pH when feed water cation conductivity increases to concentration levels listed in Table , action levels 1, 2, and 3 (≤0.3 µS/cm, ≤0.6 µS/cm, >0.6 µS/cm, respectively). Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 20
    • SUPERCRITICAL UNITS: EPC CONTRACTOR’S CHEMISTRY CHALLENGES onceThe pH/conductivity relationship is crucial for oncethrough cycles on OT; thus, the EPC contractor implements the chemistry control at its own risk. Important issues to be addressed when implementing OT include: • At what point during the start up and commissioning process should the chemistry regime be switched from AVT to OT to prevent frequent switching back and forth between a reducing and an oxidizing environment? • What would be the “detrimental effects” of going from an oxidizing atmosphere to a reducing (or close to reducing) atmosphere, for temporary periods? • How can these “detrimental effects” be quantified and addressed during design and equipment procurement? Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 21
    • SUPERCRITICAL UNITS: EPC CONTRACTOR’S CHEMISTRY CHALLENGES Stringent steam quality limits implemented by steam turbine suppliers, boiler manufacturers have tightened limits on feed water chemistry. Yet EPC contractor requires standards to be relaxed during commissioning to permit timely unit start up. The challenge also is in determining the appropriate time to switch from AVT to OT Once cation conductivity levels are stable below 0.15 µS/cm, EPRI recommends operation on OT with oxygen injection in a pH range of 8.0 to 8.5. EPRI guidelines also state that oxygen injection into feed water may continue with pH controlled between 9.2 and 9.6 and cation conductivity between 0.15 µS/cm and 0.3 µS/cm. However, at cation conductivity levels greater than 0.3 µS/cm, EPRI recommends that oxygen injection be terminated and AVT resumed. Upsets in cation conductivity may lead to serious corrosion problems if oxygen is continuously fed during upset conditions. Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 22
    • Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 23
    • SUPERCRITICAL UNITS: EPC CONTRACTOR’S CHEMISTRY CHALLENGES Startup Start up Steam Chemistry Limits Guidelines on Feed Water Chemistry Turbine Rolling Continued AVT(O) Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 24
    • SUPERCRITICAL UNITS: EPC CONTRACTOR’S CHEMISTRY CHALLENGES Turbine Rolling Continued Balance of Commissioning Period Chemistry Limits Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 25
    • SUPERCRITICAL UNITS: EPC CONTRACTOR’S CHEMISTRY CHALLENGES Operation Guidelines with AVT R and AVT O AVT(R) Feed water Chemistry Control Guidelines AVT(O) Feed water Chemistry Control Guidelines Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 26
    • SUPERCRITICAL UNITS: EPC CONTRACTOR’S CHEMISTRY CHALLENGES Suggested Start up Feed water Chemistry OnceGuidelines for Once-Through Cycles Without Deaerators Practical start up chemistry guidelines should be established by consensus among the turbine manufacturer, boiler manufacturer, and EPC contractor early on in project development and outlined in equipment contracts. Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 27
    • SUPERCRITICAL UNITS: EPC CONTRACTOR’S CHEMISTRY CHALLENGES ROLE OF CONDENSATE POLISHERS DURING COMMISSIONING Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 28
    • SUPERCRITICAL UNITS: EPC CONTRACTOR’S CHEMISTRY CHALLENGES & RISKS STARTUP CHALLENGE It must be recognized that no blowing down and adding fresh water periodically during start up to flush off dirt and corrosion product and dilute concentration of impurities carried into the system from the feed water circuit is available as an operating intervention as in conventional boilers to supercritical once through units. Removal of such impurities during start up and commissioning of supercritical units is done by full flow condensate polishers placed in the feed water circuit which continuously keep removing the impurities. These polishers however need to be periodically taken off line as their filtering ability get exhausted and need to be chemically regenerated thus contributing significantly to increasing in the start up and commissioning time and costs leading to major financial risks to the EPC contractors. Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 29
    • SUPERCRITICAL UNITS: EPC CONTRACTOR’S CHEMISTRY CHALLENGES Impurities shaken loose during start up may cause a chemistry hold, where plant load increases are temporarily halted until these impurities are removed from the system. onceFor a once-through supercritical boiler, impurities are removed exclusively by condensate polishers subsequent to chemical cleaning and boiler flush. Once impurities are removed, the chemistry hold is lifted and the plant is allowed to continue to ramp up to full load without exceeding allowable boiler or turbine chemistry limits. Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 30
    • SUMMARY EPC Contractor Risk Management Responsibilities include that onceChemistry limits are before, during and after once-through supercritical boilers commissioning & besides, • Control system component cleanliness during shop fabrication • Control system component cleanliness during construction start• Flush system components prior to start-up • Implement stringent water quality requirements for hydro testing • Perform boiler and feed water system chemical cleaning • Flush system components thoroughly following chemical cleaning • Perform steam blows to obtain steam cycle cleanliness time• Implement time-based, progressively improving feed water and steam chemistry targets Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 31
    • SUMMARY EPC Contractor Risk Management Responsibilities Before awarding a contract (boiler or turbine), the EPC contractor as a turbine), measure of contract risk mitigation should negotiate startup and feedcommissioning feed-water quality and steam purity guidelines with the boiler and turbine suppliers to ensure that long-term warranties are not voided longduring startup and commissioning activities and opportunities of speeding up commissioning activities are not missed. In addition, industry standard steam purity guidelines for steam turbine operation should be relaxed to the most practical limits commissioning, longfeasible during commissioning, while considering the owner’s longterm warranty interests. Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 32
    • SUMMARY EPC Contractor Risk Management Responsibilities Cycle chemistry-related equipment is operational and in good condition, personnel are properly trained, and procedures are in place for sampling, analysis and control of cycle chemistry parameters, Ensuring that all of the steps which must be taken to ensure the entire cycle is as clean as possible so that the cycle chemistry can quickly be brought within recommended limits Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 33
    • SUPERCRITICAL UNITS: EPC CONTRACTOR’S CHEMISTRY CHALLENGES Steam and Water Analysis System (SWAS) shall be furnished for continuous monitoring and control of water and steam purity in the plant cycle Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 34
    • THANK YOU QUESTIONS PLEASE Dr. Himadri Banerji:Conference on EPC Risk Management Bangkok 23-24 Sept 2013 35