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Upgraded Steam Turbine Produces Less Output
After upgrading steam turbine's output is 5 to 6 mw less than other steam turbine.

Dear Sir,

Our plant configuration is two blocks. Each block consists two 9fa Gas turbines and one GE D-11 steam turbine. we are facing the problem with one block steam turbine whose output is around 5 to 6 mw less than other steam turbine.

The steam turbine which is giving less output is connected to upgraded 9fa turbines. Recently pkg 4 upgradation done for one block 2 9fa turbines means some R zero and R 11 blades changed. so these upgraded turbines can able to produce 180 MW at lesser IGV around 5 deg compared to other 9fA's which are not upgraded.

Initially it was thought less steam turbine output is because of the less heat input as IGV opening is less for upgraded units. less heat energy is available to produce steam as there is change in exhaust mass flow of around 5 to 6 kg/sec.

at base load operation upgraded GT's giving more load around 8 MW more than non upgraded GT's. however even at baseload the steam turbine output is around 5 to 7 MW less for the upgraded GT's block.

Not much difference in condenser pressure variation with other steam turbine is around 0.010 bar. and High pressure steam header flow is around 20 ton/hr less than other steam turbine.

and steam turbine with less output was feed with around the HP steam at 5 bar less than the Other non upgraded steam turbine.

than this we felt all other parameters seems same for both steam turbines.

What can be the reasons for drop in HP steam pressure inlet pressure to turbine around 5 bar compared to other?

what can be the possible reasons for reduced steam turbine power output?

I mean can you please suggest what are the main factors influencing steam turbine power output. and also suggest me the best way to troubleshoot. so that i can come up with solution. please guide me how to troubleshoot, and what parameters i must be mainly looking. so that i can make trends for various parameters. almost we are running both blocks on same load I mean all GT's are at same load.

Please some one help us in troubleshooting the loss in steam turbine output. I will follow up with you till the problem solved. one can contact me on suryavine@yahoo.com

2 out of 3 members thought this post was helpful...

suryavine,

What has the provider of the Package 4 upgrade told you about the expected heat rate output of the gas turbine exhaust after the upgrade?

Have you compared the exhaust temperature of the upgraded units at the same loads as the exhaust temperature of the non-upgraded units? Are they the same? Higher? Lower?

Have you looked at the air flow calculations of the upgraded versus the non-upgraded units at the same loads to compare the change in air flow? (The usual signal name for air flow on a Speedtronic turbine control system is AFQ, and AFQD (for dry air flow, presuming the humidity/dew point sensor is working correctly).)

Most steam turbines are "slaves" to the gas turbines in combined cycle power plants--especially if the HRSGs are unfired (do not have auxiliary duct burners). The gas turbine exhaust temperature and flow-rates greatly affect the steam produced by the HRSGs--and if changes in axial compressor airflow are the result of the Package 4 upgrade, then it's very safe to assume there will be changes in the gas turbine exhaust temperature and flow-rates. Hotter exhaust makes more steam; more air flow can sometimes reduce steam production. Heavy duty gas turbines with higher air flow flow-rates (and therefore higher exhaust flow-rates) can also experience lower exhaust temperatures (because of the cooling effects of the additional air flow).

It really seems that NO upgrade was performed to the steam turbine, but that an assumption has been made that the steam turbines would produce the same or even possibly more than before the gas turbines were upgraded. And, it's never safe to make assumptions of this kind. Use the data you have--you have upgraded machines and non-upgraded machines, you don't even have to look at past, historical data--and use it to understand what is happening.

You should also work with the Package 4 upgrade provider to understand the expected knock-on effects of the upgrade to other combined cycle power plant equipment. They are likely in the best position to help with understanding what should be happening, and if it's not--they are also in the best position to be able to help understand how to correct the problem.

But, it's not a safe assumption that just because the gas turbine output was increased the steam turbine output would increase, or even remain the same. Changes in air flow-rates (which change exhaust flow-rates) and exhaust temperatures (which are also affected by changes in air flow rates) will affect the steam production, and not always in the manner expected.

Hopefully otised will add to this discussion and add some clarification. Or, to correct me--I have been wrong before, and will be in the future, too.

2 out of 2 members thought this post was helpful...

CSA & suryavine,

I don't know exactly what a Package 4 upgrade is, or who the provider is. However, if the gas turbines were upgraded to provide a higher output, it would stand to reason that at base load condition there would be a greater heat input (increased air flow and/or gas temperature) to the HRSG which should produce a greater steam output IF the HRSG is capable of the increased output. Was any documentation provided with this upgrade showing the thermodynamic effects of the upgrade? You should have received new Heat Balance data that would provide the expected steam and water flows, pressures & temperatures for the HRSG and steam turbine. Gas turbine air (inlet and exhaust) flows, temperatures and pressures, and fuel flows (mass and heat energy) are also shown on heat balance diagrams and data sheets. These should be compared to the heat balance data from the plant prior to the upgrade.

Can the steam turbine take additional steam flow? The HP and Reheat steam temperature at the steam turbine inlet are likely not increased -- every 9FA I worked on needed to attemperate the HP and RH steam due to pipe and turbine metallurgy limits. However, the uprate would likely have a higher water flow into the attemperators which would further add to the steam flow to the steam turbine.

Are the HP and RH (IP) bypass valves fully closed? (If the steam turbine cannot handle the higher steam flow, the bypasses would have to open to bleed off the excess.)

Is the steam turbine in Inlet Pressure Control mode?

You absolutely need to study the "before" and "after" Heat Balances to understand what the upgrade is supposed to accomplish.

By sandeep on 4 May, 2017 - 6:19 am

Dear Sir,

GE does not provide any new heat balance sheets. in package 4 upgradation they have changed the compressor 1 stage and last stage blades with some other type. this is provided by GE only (OEM).

How to confirm the steam turbine can't able to take extra steam flow. I noticed the steam flow was increased around 5 to 6 tons more after the upgradation. but the steam pressure was reduced around 2 to 3 bar and temperature also reduced 10 bar. I understand the enthropy of the steam reduced because of the reduced pressure and temperature. but when you calculated the heat energy (enthropy * mass flow) the heat energy input to the steam turbine was increased but still the steam turbine output was less?

does the steam turbine take extra flow to produce same amount of output when the steam pressure and temperature reduced?

how to troubleshoot, i was confused.

1 out of 1 members thought this post was helpful...

When the governor valves on a ST are wide open (e.g. as in a CCGT plant like yours), there as a close to linear relationship (especially at high loads) between steam pressure, steam flow and output power. Therefore the fact that the ST inlet pressure is down 5 bar (assuming steam pressure is around 150 - 160 bar), the steam flow is down 20 ton/hr and output power is down 5 - 6 MW all seems completely reasonable and consistent to me.

Everything points to reduced steam generation from the HRSG. The steam generation from the HRSG is purely a function (unless you have duct burners) of the residual energy in the GT exhaust. The residual heat in the GT exhaust is related to exhaust gas mass flow and the exhaust gas temperature. I suspect that either or both of these have reduced as a result of the GT upgrade.

From your description the only changes that have been made in the upgrade are compressor blade changes? Are you sure no changes have been made to the control system tuning such that the total GT flow has been reduced? Similarly, have any changes been made to the maximum TIT / TET (e.g. in order to increase blade life / reduce EOH). Have you compared the GT exhaust gas temperature entering the HSRG between the two blocks?

By suryavine on 3 April, 2017 - 7:37 am

Dear all, Please excuse for a long time late reply.

HGPI & compressor Pkg 4 upgradation completed recently on 2 units. I am giving a list of parameters comparison at base load operation before upgradation and after upgradation. note: the ambient conditions are almost close at these two sets of data.

It was noticed the exhaust mass flow from gas turbine was increased and exhaust temperature was decreased at the base load conditions after upgradation. however overall heat energy (mass flow*enthalpy of exhaust gas) was increased after upgradation. The HRSG steaming output also increased but steam temperature was less and steam pressure was 1 to 1.5 bar less as well. however the steam energy input to the steam turbine was more than to the previous condition (note: no modifications or upgradations done to steam turbine) but steam turbine output is less after applying the correction factors. my understanding with less pressure and less enthalpy the turbine would consume more steam flow to produce same amount of output. But what making the enthalpy of steam reducing though heat energy input to the HRSgG is increased.

Please look the below parameters.


Upgradation
Before After Before After
GT21 GT22
dp AirFilter mmH2O 74.48 58.38 63.59 64.98
M Comp Inlet kg/s 599 628.1 599.2 622.1
P CompInlet bar(a) 0.997 1.005 1.002 1.001
T CompInlet °C 24.8 18.38 25.08 17.97
M CompOutlet kg/s 571 609.1 595.2 644.8
P CompOutlet bar(a) 15.18 16.14 15.21 16.33
T Comp Disch max °C 397.1 394.2 396.2 395.7
M FuelGas kg/s 13.44 14.24 13.75 14.73
T FuelGas °C 105.2 96.68 105.4 97.14
M ExpInlet kg/s 584.5 623.3 608.9 659.5
P ExpInlet bar(a) 15.18 16.14 15.21 16.33
T Comb Ref °C 1334 1328 1332 1323
P Exhaust mmH2O 402.3 402.9 415 430.3
T Exhaust median °C 623.5 609.6 621.1 605.3
M Exhaust kg/s 612.4 642.3 613 636.8
M FuelGas FGQ kg/s 13.44 14.24 13.75 14.73
FSR Fuel % 79.83 83.14 80.38 84.23
Pe Gross Power MW 227.4 247.4 227.7 249.9
Gen Term Voltage kV 16.2 16.49 16.2 16.49
Gen Phase Current kA 8.144 8.969 8.128 9.019
Gen Field Volt V 219.7 258.3 217.5 256.6
Gen Field Curr A 1299 1505 1293 1498
Gen H2 Purity % 96.25 96.75 96.66 95.85

ST 20 (Before upgradation) ST 20 (After upgradation)
HP FW Flow ST kg/h 562017 574470
IP FW Flow ST kg/h 78900 84625
RH Spray Flow ST kg/h 3118 4826
LP Adm Steam ST kg/h 70209 78741
Crossovr Steam ST kg/h 712080 741600
LP Exh Steam ST kg/h 713520 741600
IP Adm+RHSpray ST kg/h 82018 89452
M HP MainStm ST kg/h 561960 574560
P HP MainStm ST Bar(a) 122.6 121.6
T HP MainStm ST °C 554.1 542.3
H HP MainStm ST kJ/kg 3490 3460
Q HP MainStm ST kJ 544805 552126
V HP MainStm ST m3/kg 0.0288 0.0285
M HP ExhSteam ST kg/hr 559080 574560
P HP ExhSteam ST bar(a) 27.91 27.95
T HP ExhSteam ST °C 341.6 332.4
H HP ExhSteam ST kJ/kg 3101 3079
Q HP ExhSteam ST kJ 481621 491360
H.isentro HP ExhSteam ST kJ/kgK 3043 3024
M HRH Steam ST kg/hr 643680 662760
P HRH Steam ST bar(a) 25.41 25.44
T HRH Steam ST °C 556.2 543
H HRH Steam ST kJ/kg 3588 3558
Q HRH Steam ST kJ 641522 655187
RH PressDrop ST % 8.961 8.969
M IP Adm Steam ST kg/hr 78912 84636
M LP AdmStm ST kg/hr 70200 78732
P LP AdmStm ST bar(a) 5.163 5.426
T LP AdmStm ST °C 314.3 314.8
H LP AdmStm ST kJ/kg 3094 3094
Q LP AdmStm ST kJ 60336 67677
M Crossover Stm ST kg/hr 712080 741600
P Crossover Stm ST bar(a) 4.98 4.987
T Crossover Stm ST °C 310.7 301.5
H Crossover Stm ST kJ/kg 3087 3068
Q Crossover Stm ST kJ 610411 631985
H.isntr CrossoverStm ST kJ/kgK 3071 3050
M LP ExhSteam ST kg/hr 713520 741600
P LP ExhSteam ST bar(a) 0.116 0.103
T LP ExhSteam ST °C 45.69 43.28
H LP ExhSteam ST kJ/kg 2562 2546
Q LP ExhSteam ST kJ 507783 524527
H.isntro LP ExhSteam ST kJ/kg 2398 2371
P HRH Steam ST bar(a) 25.41 25.44
P CRH Steam ST bar(a) 27.91 27.95
LP ExhSteam P mbar ST mbar 116.1 103.4
Thermal Eff ST % 33.41 32.83
IsentroEff HPT ST % 87.03 87.36
IsentroEff IPT ST % 96.92 96.56
IsentroEff LPT ST % 76.13 74.92
Shaft Power ST kW 257258 259103
kW Loss PF ST kW 1729 1869
Energy Input ST kW 765041 783630
P Condenser ST mbar 116.06 103.41
Tsat Condenser ST °C 48.75 46.46
TTD Condenser ST °C 5.77 6.6
LMTD Condenser ST °C 9.64 10.45
U+ Coeff Condenser ST kW/m²K 3.03 2.9
subcooling Condenser ST °C 2.63 2.51
CW Flow Cond ST m3/h 44361 47064
Q Heatload CT kW 469214 486427
Cooling Range CT °C 9.182 8.969
Approach T CT °C 10.46 14.35
Effectiveness CT % 46.75 38.46
Cond. Vacuum ST mmHg 87.05 77.56
Q Cond HotWell ST kJ 38273 37916


Before After Before After
HRSG 21 HRSG 22
M LPECN inlet kg/s 0.0 0.0 0.0 0.0
P LPECN inlet bar(a) 25.0 24.8 25.0 24.8
T LPECN inlet °C 56.7 55.8 59.7 57.5
H LPECN inlet kJ/kg 239.4 235.8 252.1 242.9
Q LPECN inlet kJ 0.0 0.0 0.0 0.0
M LPECN out kg/s 98.5 104.1 99.1 100.8
P LPECN out bar(a) 17.0 16.3 15.4 14.1
T LPECN out °C 153.4 153.4 152.7 154.4
H LPECN out kJ/kg 647.6 647.8 644.7 651.6
Q LPECN out kJ 63751.0 67443.0 63884.0 65709.0
LPECN Approach °C 6.7 8.2 5.6 5.4
M LP SatStm kg/s 0.0 0.0 0.0 0.0
P LP SatStm bar(a) 6.2 6.4 5.9 6.1
T LP SatStm °C 160.1 161.6 158.4 159.8
H LP SatStm kJ/kg 2758.0 2759.0 2756.0 2757.0
Q LP SatStm kJ 0.0 0.0 0.0 0.0
M LPSH Stm kg/s 9.7 10.9 9.8 10.9
P LPSH Stm bar(a) 5.9 6.2 6.0 6.2
T LPSH Stm °C 316.1 316.1 316.1 316.9
H LPSH Stm kJ/kg 3096.0 3095.0 3096.0 3097.0
Q LPSH Stm kJ 30083.0 33854.0 30292.0 33861.0
M IPECN inlet kg/s 11.0 11.4 10.9 12.1
P IPECN inlet bar(a) 57.2 56.8 57.8 57.1
T IPECN inlet °C 159.2 160.8 161.4 162.8
H IPECN inlet kJ/kg 675.1 681.9 684.8 690.5
Q IPECN inlet kJ 7424.0 7750.0 7477.0 8384.0
M IPECN outlet kg/s 11.0 11.4 10.9 12.1
P IPECN outlet bar(a) 53.3 52.9 52.6 52.0
T IPECN outlet °C 222.7 223.2 226.1 227.5
H IPECN outlet kJ/kg 956.8 959.1 972.4 978.9
Q IPECN outlet kJ 10523.0 10901.0 0.0 0.0
IPECN Approach °C 6.6 6.3 2.9 2.1
M IP SatStm kg/s 0.0 0.0 0.0 0.0
P IP SatStm bar(a) 27.6 27.7 27.5 27.8
T IP SatStm °C 229.3 229.5 229.0 229.6
H IP SatStm kJ/kg 2803.0 2803.0 2803.0 2803.0
Q IP SatStm kJ 0.0 0.0 0.0 0.0
M IPSH Stm kg/s 11.0 11.4 10.9 12.1
P IPSH Stm bar(a) 27.6 27.7 27.7 28.0
T IPSH Stm °C 317.5 317.0 317.5 317.4
H IPSH Stm kJ/kg 3045.0 3043.0 3044.0 3043.0
Q IPSH Stm kJ 33483.0 34587.0 33241.0 36950.0
M CRH Stm kg/s 77.3 81.8 78.0 77.8
P CRH Stm bar(a) 27.9 28.0 27.9 28.0
T CRH Stm °C 341.6 332.4 341.6 332.4
H CRH Stm kJ/kg 3101.0 3079.0 3101.0 3079.0
Q CRH Stm kJ 239806.0 251909.0 241815.0 239451.0
M RH1 inletStm kg/s 0.0 0.0 0.0 0.0
P RH1 inletStm bar(a) 27.9 28.0 27.9 28.0
T RH1 inletStm °C 343.3 334.4 342.9 333.9
H RH1 inletStm kJ/kg 3105.0 3084.0 3104.0 3083.0
Q RH1 inletStm kJ 0.0 0.0 0.0 0.0
M RH1 outletStm HRGS11 kg/s 88.3 93.2 88.9 89.9
P RH1 outletStm HRGS11 bar(a) 26.2 26.2 26.2 26.3
T RH1 outletStm HRGS11 °C 488.9 479.9 487.2 477.8
H RH1 outletStm HRGS11 kJ/kg 3437.0 3416.0 3433.0 3412.0
Q RH1 outletStm HRGS11 kJ 0.0 0.0 0.0 0.0
M RH SprayWtr kg/s 0.5 1.1 0.7 0.0
P RH SprayWtr bar(a) 57.2 56.8 58.0 3.8
T RH SprayWtr °C 159.2 160.8 161.4 162.8
H RH SprayWtr kJ/kg 675.1 681.9 684.8 2783.0
Q RH SprayWtr kJ 319.8 716.5 493.3 0.0
M RH2 inletStm kg/s 88.8 94.2 89.6 89.9
P RH2 inletStm bar(a) 26.2 26.2 26.2 26.3
T RH2 inletStm °C 482.3 466.2 477.3 477.8
H RH2 inletStm kJ/kg 3422.0 3386.0 3411.0 3412.0
Q RH2 inletStm kJ 0.0 0.0 0.0 0.0
M HRH Stm kg/s 88.3 93.2 88.9 89.9
P HRH Stm bar(a) 26.0 26.0 25.9 26.0
T HRH Stm °C 559.2 544.9 557.9 545.3
H HRH Stm kJ/kg 3594.0 3562.0 3591.0 3563.0
Q HRH Stm kJ 317442.0 331892.0 319241.0 320328.0
P LP Drum bar(a) 6.2 6.4 5.9 6.1
T LPSH Stm °C 316.1 316.1 316.1 316.9
P IP Drum bar(a) 27.6 27.7 27.5 27.8
T HRH Stm °C 559.2 544.9 557.9 545.3
P HP Drum bar(a) 128.8 127.8 128.6 127.7
T HP Stm °C 556.2 545.1 550.3 535.1
M HPECN inlet kg/s 77.7 81.8 78.4 77.8
P HPECN inlet bar(a) 144.3 141.9 144.5 139.9
T HPECN inlet °C 165.6 167.0 163.1 164.8
H HPECN inlet kJ/kg 708.0 713.9 696.9 704.2
Q HPECN inlet kJ 55031.0 58405.0 54628.0 54759.0
M HPECN outlet kg/s 77.3 81.3 78.0 77.5
P HPECN outlet bar(a) 138.8 137.8 138.6 137.7
T HPECN outlet °C 327.0 326.4 327.1 328.1
H HPECN outlet kJ/kg 1502.0 1498.0 1502.0 1510.0
Q HPECN outlet kJ 116087.0 121828.0 117219.0 116935.0
HPECN Approach °C 3.1 3.1 2.9 1.3
M HP SatStm kg/s 77.3 81.3 78.0 77.4
P HP SatStm bar(a) 128.8 127.8 128.6 127.7
T HP SatStm °C 330.1 329.5 330.0 329.5
H HP SatStm kJ/kg 2666.0 2668.0 2666.0 2668.0
dQ HPSH1 outlet kJ 256813.9 0.0 259473.0 0.0
M HPSH1,2 outlet kg/s 77.3 81.3 78.0 77.4
P HPSH1,2 outlet bar(a) 128.8 127.8 128.6 127.7
T HPSH1,2 outlet °C 494.1 486.3 494.9 485.7
H HPSH1,2 outlet kJ/kg 3322.0 3302.0 3325.0 3300.0
M HP SprayWtr kg/s 0.4 0.5 0.3 0.3
P HP SprayWtr bar(a) 144.3 141.9 144.5 139.9
T HP SprayWtr °C 165.6 167.0 0.0 0.0
H HP SprayWtr kJ/kg 708.0 713.9 696.9 704.2
Q HP SprayWtr kJ 299.6 342.1 239.2 218.7
M HPSH3 inlet kg/s 77.7 81.8 78.4 77.8
P HPSH3 inlet bar(a) 125.6 124.5 125.8 124.8
T HPSH3 inlet °C 486.1 478.4 489.8 481.2
H HPSH3 inlet kJ/kg 3305.0 3284.0 3315.0 3292.0
Q HPSH3 inlet kJ 256897.7 268664.0 259829.7 255985.9
M HPSH3 outlet kg/s 77.7 81.8 78.4 77.8
P HPSH3 outlet bar(a) 0.0 0.0 125.8 124.8
T HPSH3 outlet °C 557.1 546.0 558.1 545.0
H HPSH3 outlet kJ/kg 3613.0 3589.0 3497.0 3464.0
Q HPSH3 outlet kJ 23945.0 24895.0 14296.0 13369.0
M HP Steam kg/s 77.7 81.8 78.4 77.8
P HP Steam bar(a) 123.6 122.6 123.4 122.6
T HP Steam °C 556.2 545.1 550.3 535.1
H HP Steam kJ/kg 3494.0 3466.0 3479.0 3440.0
Q HP Steam kJ 271598 283581 272685 267519

A long list of parameters posted! A difference of 3-5 MW, when there is no undesirable leak/bypass in STG system can likely be the result of either lower vacuum (which obviously isn't the case here) or lesser condensate preheat.

As HP and IP feedwater flows have been mentioned but not LP feedflow although LP economizer (which must be Condensate PreHeater "CPH" rather) has been mentioned , it can be gathered that the flow through this LP Eco or CPH is effected by the Condensate pump, and must reach dearator consequent to the heat exchange.

Condensate Preheat Re-circulation Pump "CPHRCP" recirculates the CEP discharge, after Gland Steam Condenser, within the boiler. Temperature at the outlet of CPH is controlled by mixing the streams of CPHRCP outlet and CEP outlet.As soon as flow through CPH is reduced by increasing bypass, less heat is extracted from the outgoing flue gas, dearator temp drops and you have to increase pegging steam.

So just look at the historical data for inlet and outlet temp at CPH, the position of CPH bypass valve, the position of pegging steam supply valve as well as the "Stack Temp" before and after upgrade. After all, useful heat must be getting wasted somewhere and stack is the only way out in the absence of leaks and insufficient vacuum .Please don't forget to give the feedback even if you don't come across any related surprise.

By suryavine on 17 April, 2017 - 4:09 am

Thank you very much for your time Mr.Mechop.

we don't have integral deaerator with LP drum. Deaeration takes place in the condenser itself.

The flow through CPH is automatic based on stack set point to protect from ADC (acidic dew point corrosion). Usually the max possible heat absorption takes from flue gas to the CPH depends on the 3 way valve opening and seldom during startup we use pegging steam. During normal operation we never used pegging steam (from IP drum to LP drum through a pegging control valve).

I will look at the historical data for inlet and outlet temp at CPH, the position of CPH bypass valve, the position of pegging steam supply valve, as well as the "Stack Temp" before and after upgrade. However I think it does not make any difference I think so. any how let me check and update you sir.