Modeling & Testing Low Pressure Turbine Replacements at DCPP 1

Transcription

1 Mdeling & Testing Lw Pressure Turbine Replacements at DCPP 1 Summary Diabl Canyn Pwer Plant (DCPP), a dual unit nuclear plant rated at 1165MWe/hr each, replaced the Lw Pressure Turbines (LPT s) n bth f the units. A small part f the LPT warranty was imprved efficiency measured by increased electrical generatin f 35MWe/hr n each unit. Since the ratings f the units were 1165 MWe/hr when new, an upper end value f 1200 MWe/hr wuld be theretically pssible, but nt prbable as these units are 20+ years ld and have been perated with capacity factrs upwards f 90%. Unit 1 pre LPT replacement warranty test actual utput was MWe/hr and the crrected utput was MWe/hr. Unit 2 pre LPT replacement warranty test actual utput was MWe/hr and the crrected utput was MWe/hr. Pst LPT replacement fr Unit 1 LPT indicated MWe/hr uncrrected and MWe/hr crrected. Unit 2 LPT replacement indicated 1201MWe/hr uncrrected and a crrected utput f 1202MWe/hr. The LP turbines n bth units met the utput imprvement prtin f the warranty. Intrductin Diabl Canyn Pwer Plant unit specific PEPSE mdels were develped utilizing Valves Wide Open (VWO), Westinghuse riginal turbines and misture separatr reheaters, and OEM supplied feedwater heaters. Prir t perating, the cndenser tubes were changed frm admiralty brass t titanium, and the misture separatr reheaters were changed frm tw pass t fur pass. Minr changes t the PEPSE mdel needed t be incrprated as a result f this which the heat balance diagram did nt reflect. Full PTC 6 testing was perfrmed at initial start ups fr the unit and gd baseline data was btained. Over the perating histry, all feedwater heaters were replaced which included a tube material change frm cpper nickel t stainless steel, misture separatr reheaters tube bundles were changed frm cpper nickel t stainless steel and ptimized hur glass shaped bundles were incrprated. In additin a blw dwn recvery system was installed. PEPSE mdels fr each unit were mdified t prperly represent the plant changes as they ccurred. Next the LPT s were replaced. Again the PEPSE prgram was mdified t represent replaced Lw Pressure Turbines while using the riginal vendrs High Pressure Turbines (HPT), mdified steam plant and reduced steam pressure that the units are currently frced t perate at preserving the life f the steam generatrs until they are replaced. Detailed Discussin PEPSE mdels f DCPP have existed fr many years as the PEPSE license was issued in abut In the 20+ years DCPP has wned and used PEPSE, albeit the mainframe versin was difficult t use, many mdels f the pwer plant were built. Alng in abut the mid 90 s, well after PEPSE ran n desktp cmputers and had a decent graphical users interface, detailed PEPSE diagrams began t 1 Slide 1 PwerPint

2 be built. Three reasns drve this. One is that DCPP s management was never pleased with simple ne line diagrams nt representing the reactr in the drawing. Secndly, the identical cmpnents were behaving differently as the equipment aged requiring different mdeling techniques. And three, the identical units are nt identical in sme steam pipe ruting, and HP turbine first stage blades. Additinally, tubes in a feed water heaters became plugged, seal and shaft damage t a main feed water pump turbine ccurred requiring it t draw a significant amunt mre steam t run prperly, etc. Thus the need fr additinal details in a gd mdel fr each unit became apparent. With a Westinghuse plant, Westinghuse turbines, data was relatively easy t gather and build detailed PEPSE mdels 2. The Westinghuse LPT s were 44 Last Stage Blades (LSB). One f these detailed PEPSE mdels became the Heat Balance Diagram (HBD) layut utilized by Alstm and supplied t DCPP 3. Once the HBD s were received frm Alstm, the existing PEPSE mdels were changed t reflect the Alstm Lw pressure rtrs. This required changing extractin stage turbine grup pressures, enthalpy, grup efficiencies, misture remval and the exhaust area went frm127.4ft² t ft² per end. Als, if the mdeler uses the Misture Remval Effectiveness (MRE) curve supplied with the thermal kit, nthing makes sense in the resulting PEPSE runs. The Bgie diagrams d nt use the MRE curve, and when prgrammed in via a schedule, each extractin stage results did nt agree with the HBD. That initially was perplexing because bviusly PEPSE was prgrammed wrng via Mr. Minner. Nw hw culd that be? Maybe PEPSE cannt handle schedules, but wait PEPSE uses schedules all f the time. Lking at the MRE curve supplied by Alstm, it was nticed hw similar the curve seemed t be t ther curves. Opening KC s bk t the crrect page, there was the identical MRE curve. Alstm just supplied a representative curve, nt a DCPP turbine MRE curve 4. Nte, the fist rtating blade set exhaust pressure in the Bgie is ~84 psia 5. Als, nt n the drawings, the new Alstm LPT s are 57 LSB which were the first and the largest LSB turbines built by this vendr t date, but there are nw thers being prpsed r built. And these are lw speed rtrs, i.e rpm. Alstm s heat balance diagrams indicate full pwer t be MWe/hr fr Unit 1 and MWe fr Unit 2. The installed OEM HP turbines were designed t perate at ¾ arc admissin and less than VWO. DCPP Unit 1 was intended t run at abut 1165 MWe/hr after a cmpany perfrmed unit uprate. The abslute best it ran was 1161 MWe/hr uncrrected, and it was never subjected t PTC-6 testing. Unit 2, als an 1165 MWe/hr rated unit during testing t warranty cnditins was crrected t 1167 MWe/hr after PTC-6 testing. It ran at 1160 MWe/hr fr a brief perid ver the past 18 years. Due t turbine issues such as, aging, frequent expensive verhauls, inspectins (every 1 ½ years a LP rtr was remved and replaced with a refurbished spare rtr), a LP turbine replacement prject was implemented. Five bidders submitted prpsals and bid n the replacement rtrs. The winning bidder, Alstm, was chsen based upn a matrix f items such as ease f verhaul, generatin reliability, length f time between verhaul, cst, and service reputatin t name but a few. The rtrs were replaced first n Unit 1 late 2005 and then in May f 2006 n Unit 2. Bth unit s rtrs met the vendrs warranty cnditins using a mdified PTC-6 test prcedure. Mixing vendr data t create the mdels created a lt f questins. As an example, Westinghuse srt f uses 5% turbine extractin flange pressure drp and abut the same lss in the extractin lines. Well, nt s Alstm HBD s. Lk at this example. Once again nte the stage pressure in LPA turbine 2 Slide 2 PwerPint PEPSE Mdel 3 Slide 3 PwerPint U-1 VWO 4 Slide 4 MRE Curve 5 Slide 5 84 psia stage pressure

3 as psia. This is the same pressure shwn in the extractin line all the way t feedwater heater 3A. Well, we all knw that aint right. Nw use that pressure and establish the saturatin temperature fr that pressure as F. Then cmpute the TTD and it cmes ut 8.9 F. But Bgie is shwing a TTD f 3.8 F. What, dn t thse Eurpeans knw hw t calculate TTD s? Well, nt shwn in the HBD is this pressure drp 6. Thus there is additinal hidden infrmatin n the Bgie that ne must be aware f. Nw mdeling 4 pass MSR s was als a challenge. Frm the Alstm HBD 7, it is near impssible t determine what they are representing. Breaking this dwn, i.e. the vendr supplied additinal infrmatin 8, line ruting and mdeling became pssible. Next, the agreement was reached n using grup A PTC-6 crrectins, and that these crrectin curves nw needed t be generated. With 2 units being verhauled apprximately 6 mnths apart, turbines being replaced in 40 day utages, the units being refueled, replacement steam generatr prject demanding time and PMAX being implemented, time t cmplete all f these tasks was just nt available. Scientech was engaged t generate the crrectin curves based upn the DCPP PEPSE mdels, DCPP U1 Current R mdl set 1. Since bth units are near identical, it was agreed that the crrectin curves generated frm the Unit 1 PEPSE mdel wuld be used fr Unit 2. Als, the PEPSE mdel fr Unit 2 was nt finished. Since Scientech was hired t d the wrk, fine tuning the mdels and training als ccurred during this sessin. The end result was that the mdel t the HBD had a 0.1MWe/hr discrepancy. The next Unit 1 mdel PEPSE set 2 was created fr 100% pwer peratins t Bgie. It implies full pwer generatin t be while Alstm s bgie implies Thus a deviatin f 0.8 MWe/hr exists and insufficient time was, and still is nt available t find and remve the discrepancy. It will mst likely never be crrected as gd test data fr base line cnditins nw exist. The imprtant mdel is DCPP U1 Current R mdl set 3 (DCPP U2 R mdl set 3) which is the near 100% pwer mdel with PTC-6 test data input int PEPSE mdel. Sme f the key parameters fr Unit 1 were, but nt limited t: pwer Final feed water temp F Turbine Exhaust Pressure f HgA Per cntract agreed, crrectins Unit 1 was crrected t MWe/hr Autmatic data input culd have been used, but nce again, time t learn this was nt available due t ther nging prjects. PEPSE was then run using the data input int set 3 as set 4 with nly the feed water flw adjusted t generate 100% thermal pwer. PEPSE utput results indicate MWe/hr. Thus between as crrected test data and PEPSE the difference was 2.3 MWe/hr. Thus the Unit 1 PEPSE mdel fr 100% pwer has essentially been validated by testing. Next, the mdel has t be independently reviewed t assure the mdel and input data is crrect and it will then be used fr baseline data and unit rating. 6 Slide 6 FWH schematic representatin 7 Slide 7 HBD 8 Slide 8 MSR schematic

4 Althugh Unit 2 testing has been cmpleted, the PEPSE mdels fr the as tested cnditin has nt been cmpleted due t time cnstraints. Warranty Testing and Issues Althugh the crrected generatin was ~1200 MWE, this was a brand new lw pressure turbine set. Since the amunt f time t prperly align the turbines was nt taken due t excessive ff line time, it is my speculatin that nminal full pwer generatin will be abut 1195 t 1198 MWe/ hr fr each unit. Why wuld anyne be cncerned as t the full pwer ratings? One f the reprting requirements t the state and federal agencies is the rated full pwer f the units. Since the LP rtr vendr did nt rate the T/G set and the previus ratings are n lnger where the unit runs, pssible re-rating shuld be accmplished. Recall, additinal generatin was nt the reasn fr replacement f the turbines, but frequency f verhaul is. Als if ne uprates by 50 MWe/hr there is sme mandated threshld reached requiring additinal smething. Since the pre-rtr replacement ratings were 1165 MWe/hr, clearly the 50 MWe/hr uprate was nt exceeded fr either unit. A tremendus amunt f time was spent negtiating hw crrectins wuld be determined and made It was finally agreed upn that PEPSE mdels wuld be used t establish the ff nrmal crrectin curves. This was accmplished by first verifying gd fidelity t the Alstm bgie, then varying a single parameter and nting the change. This was dne fr thrttle pressure, pwer factr, feedwater temp and reactr pwer, etc. Feed water flw instrumentatin and accuracy was f curse a majr tpic and tk cnsiderable effrt t wrk thrugh t acceptable by bth parties. Special test instrumentatin was purchased and installed by DCPP, and Alstm riginally insisted that their check instruments were t be installed in parallel with the test instrumentatin. Of curse ne can understand the vendr s psitin as there is a lt f mney at stake if the turbine did nt meet warranty. In additin, DCPP is nt paid fr generatin, but a flat daily rate whether n line r nt. Rephrasing that, the same amunt f revenue is generated when the plant is shutdwn as when perating at 100% pwer. Therefre any additinal generatin abve the warranty is f n value t the utility and thus n reward r incentive was ffered r agreed upn. The Califrnia Public Utility Cmmissin (CPUC) sets the electric rates and this was the agreement reached as the cmpany became slvent again. Nw, n ne can predict the future, but it is my cntentin that DCPP is being paid fr generatin. The cmpany, Pacific Gas & Electric Cmpany is in the business f selling electricity t the cnsumers. If cmpany generated electricity is nt available, then higher priced electricity must be purchased n the pen market. Als, the CPUC rate cases are rutinely reviewed and reset. It is my speculatin that in the future DCPP will nce again be prviding electricity and being paid fr generatin. There was a significant discrepancy between the vendrs HBD s fr 100% pwer and what was the actual generatin. Part was the cnservative nature f Alstm since this was the first 57 LSB turbine they had ever built. Secnd, the exhaust lss curve is simply the exhaust velcity with n turning lsses included. Since the LPT hds were supplied by the OEM, little t n data was available and f curse Alstm was cncerned additinal lsses might be incurred here. The last interesting pint is the first extractin LPT stage pressure. Alstm s design indicated 20 psi higher than what measured during testing. Why this ccurred is a mystery t the end users, but I suspect Alstm is clsely lking at the data and is wrking n, r has understd this issue. It is als my belief that Alstm will fine

5 tune future prpsals and market their successful DCPP LPT replacement prject and then glean additinal revenue frm this substantial increase in generatin Cnclusins Future wrk remains as a result f this LP steam path replacement: Creatin f new heat balance diagrams as the HBD s are nt crrect S/G replacement that will raise the perating pressure at the TV s t abut 850 psia Future HP turbine replacement.