Optimisation of Pumps in Thermal Power Stations

.B.H.E.L HYDERABAD

OPTIMISATION of PUMPSinThermal Power Stations

J. Gopichand AGM(PED), BHEL, Hyd.Date : 24.11.2006

Pump is a device which converts mechanical energy into pressure energy due to which the fluid moves from one point to another.

(A) CENTRIFUGAL PUMPS : Energy is generated through the centrifugal force of the vortex.(B) POSITIVE DISPLACEMENT PUMPS : Energy is generated by the direct displacement of the fluid.

TYPES OF CENTRIFUGAL PUMPS VOLUTE CASING PUMP

DIFFUSER VANE PUMPBased on type of casing, Centrifugal Pumps are classified as :

TYPES OF IMPELLERSRADIAL FLOW IMPELLER

AXIAL FLOW IMPELLER

MIXED FLOW IMPELLERBased on the major direction of flow with reference to the axis of rotation, Impellers are classified as :

TYPES OF IMPELLERSSINGLE-SUCTION IMPELLER

DOUBLE-SUCTION IMPELLERBased on the flow into the suction edges of the vanes, Impellers are classified as : TYPES OF IMPELLERS

TYPES OF IMPELLERSOPEN IMPELLER

SEMI-CLOSED IMPELLER

CLOSED IMPELLERBased on the mechanical design, Impellers are classified as :

TYPES OF CASINGSAXIALLY-SPLIT CASING

RADIALLY-SPLIT CASINGBased on the Casing splitting type, Pump Casings are classified as : TYPES OF CASINGS

SPECIFIC SPEED :- It is the speed of a geometrically similar Pump which delivers one unit of Capacity against one unit of total Head.-It is generally used for comparison between various types of Centrifugal Pumps.-It is expressed asNS = ( N Q ) / H3/4where N is the Speed of the Pump, rpm.-It determines the type of Impeller.-Its value varies from 30 to 1000 for Centrifugal Pumps.Radial Flow Impeller = 30-290Mixed Flow Impeller = 290-440Axial Flow Impeller =440-1000

PUMP CHARACTERISTICS :- It is the relationship between Capacity, Head, Power and Efficiency.-The graphs, showing the inter-relationship between Capacity, Head, Power and Efficiency, are called Pump Characteristic Curves.Capacity :-It is the quantity of fluid flowing through the Pump for a given time ofperiod.-It is expressed in m3/hr.-It is measured by weight method, volumetric method, orifice plate or by weirs.Head :-It is the measure of energy to move the fluid from one point to another.-It is expressed in metres of liquid column.

Power :-The horse power produced by the liquid is called as Water Horse Power (WHP) or Liquid Horse Power which is expressed asWHP = ( Q H) / 75where Q = m3/sec , H = mlc & = kg/m3-The power required to drive the pump is called as Brake HorsePower (BHP) which is expressed asBHP = ( Q H) / 75 where is the efficiency of Pump.Efficiency :-It is the measure of the Pump performance.-It is the ratio of WHP to BHP.

CHARACTERISTIC CURVE OF A PUMP

NET POSITIVE SUCTION HEAD (NPSH) :Available (NPSHA) :- NPSHA is the total Suction Head of liquid (absolute), determined at the first stage Impeller datum, less the absolute vapour pressure of the liquid at a specified Capacity. NPSHA = hsa - hvpwherehsa = Total Suction Head (abs) = hatm + hshatm = Suction Pressurehs = Static Water level at reference datumhvp = Absolute Vapour Pressure of liquid at pumping Temperature-NPSH is the parameter used to evaluate the suction conditions of the system.

Required (NPSHR) :- It is a parameter of the selected Pump.-It is the amount of Suction Head, over Vapour Pressure, required to prevent more than 3% loss in total Head from the first stage of the Pump at a specified Capacity.-It is an important parameter in the pumping system to ensure that the NPSHA (which is determined by the system) is at least equal to the NPSHR by the Pump (which is a function of Impeller design & Pump Speed).-It is required to ensure adequate margin between NPSHA & NPSHR.-It is therefore essential that the Pump manufacturer is given adequate information on NPSHA, operating Flow range, transient conditions, etc., so that the best Pump selection can be put forward.

COMPARISION BETWEEN NPSHA & NPSHR :

AFFINITY LAWS :

- All Centrifugal Pumps follow the Affinity Laws which are given below :

Q NQ DH N2 andH D2P N3P D3

where N is the Speed of the Pump (rpm) & D is the Diameter of the Impeller

SYSTEM HEAD :- It is the total head of a system against which a pump must operate.-For a given capacity, it is expressed asSystem Head = Total Static Head from supplying level to discharge level + Discharge Pressure - Suction Pressure - Friction losses - entrance and exit losses

OPERATING CONDITIONS :

PARALLEL OPERATION :

Major pumps in a power station :-BOILER FEED PUMPSBOILER FEED BOOSTER PUMPSCONDENSATE EXTRACTION PUMPSCIRCULATING WATER PUMPSAUX COOLING WATER PUMPSPump is a device which converts Mechanical energy into Pressure energy due to which the fluid moves from one point to another.

Typical arrangement of Pumps in a thermal power station

Function of Pumps in a thermal power station BFPs are used to feed water from deaerator feed storage tank to the boiler

Booster pumps are provided ahead of BFPs to ensure adequate NPSH to BFP for its cavitation free performance

CEPs are used to transfer condensate from condenser hotwell to deaerator

CWPs are used to circulate cooling water through condenser for condensing steam and ACWPs to supply cooling water to various auxiliary coolers

BOILER FEED PUMP

BFP BARREL & CARTRIDGEBarrelCartridge

BOILER FEED PUMP

Boiler Feed BOOSTER PUMP

BOOSTER PUMP

BOILER FEED PUMP TRAIN

CONDENSATE EXTRACTION PUMP

CIRCULATING WATER PUMP

CIRCULATING WATER PUMPSDRY WELL WET WELL

DESIGN OPTIONS FOR CWPs

Wet well / Dry wellPull out / Non pull outSingle / Double foundationWith / Without thrust block at discharge elbowWith / Without non reversible ratchetWith/ Without shaft inclosing tube

SUMP MODEL STUDIES

Improper sump design results in :

Vortex formation, swirl and poor flow distributionLoss of hydraulic performanceNoise and vibrationAccelerated wear of componentsMechanical failures

Multiple CW Pumps installationsSump Dimensions - Plan view

Multiple CW Pumps installationsSump Dimensions- Elevation view

Sump Dimensions versus Flow

Multiple CW Pumps installations RECOMMENDEDNOT RECOMMENDED

Turbine Auxiliaries (~30% of total power consumption)

CEP, BFP and TG integral auxiliaries like vacuum pump, GSC exhauster, oil purifier, oil vapour exhauster etc.Power consumption for TG Auxiliaries for 500 MW shall be ~4% of total power consumption with TD BFPs in operation

Boiler Auxiliaries (~30% of total power consumption)

Mills, ESP, ID / FD / PA fans and LT drivesBoiler Circulating Water Pumps for 500 MW unit

CLASSIFICATION OF AUXILIARIES

CLASSIFICATION OF AUXILIARIES (contd..)Plant auxiliaries (~ 40% of aux. power )

CW, ACW, DMCW & Plant Water System DM plant & pre-treatment plantHP/ LP dosing & chlorination plantHydrogen generation plantCoal and Ash handling plantCompressed air systemAir conditioning & ventilation systemFuel oil system / Electric tracing Electrical system: GT, UAT, ST losses & lighting load

AUXILIARY POWERAuxiliary power consumption along with heat rate are the two important technical parameters used by the power utilities to assess the performance of power plants

AUXILIARY POWER (contd..)Auxiliary power consumption can be defined as the difference between gross electric power generated at generator terminals and net exportable power to grid

Power plant itself consumes nearly 8 10% of energy generated

Optimisation Areas in PumpsSizing and design margins

Mechanical design

Materials of construction

Quality / Inspection checks

Performance testing

OPTIMISATION OF AUXILIARY POWERAux. power can be brought down by proper sizing of pumps, selection of technology and equipments

The following factors having impact on auxiliary power consumption need to be considered during design stage of the project:

Optimisation of sizing & design margins

Proper selection of equipments

Layout options

Optimisation of sizing & design marginsDesign margins are provided on equipment / systems to cater for ageing, wear & tear, uncertainties etcConservative designs with large margins ( e.g. on flow and head of pumps) and specifying suitability for abnormal operating conditions result in lower efficiency and higher auxiliary power consumptionProper standby philosophy based on efficiency of operation, availability & reliability, like 1x100% Working + 1x100% Standby or 1x100% Working + 1x30% Startup or 2x50% Working + 1x50% Standby etc.

OPTIMUM DESIGN MARGINS COMPARISON OF 500 MW CEP PARAMETERS * FOR VINDHYACHAL CEP PARAMETERS WERE WORKED OUT BY NTPC

Sheet1

ParametersSimhadri (Rs in Lacs)Talcher (In $)Rihand (In $)Ramagundam (Rs in Lacs)Kahalgaon Phase - I / II (In $)Sipat (In $)

Auxiliary Power Consumption per KW

100% MCR0.95$1,555$1,8271.01$1370 / $1347$1,151

80% MCR$490 / $465$335

60% MCR$163 / $155$112

50% MCR$163 / $155$112

Total0.95$1,555$1,8271.01$2186 / $2122$1,710

CW Pumping Power per KW

At Design CW Flow0.95$1,555$1,8271.01$2186 / $2121$1,709

ParametersMaithon (Rs in Lacs)Parli (Rs in Lacs)Paras (Rs in Lacs)Raigarh (Rs in Lacs)

Auxiliary Power Consumption per KW

100% MCR1,62,0001,63,0001,63,0001,30,000

ParametersSimhadri (KW)Talcher (KW)Rihand / Ramagundam (KW)Kahalgaon Phase - I / II (KW)Sipat (KW)

CEP'S1484137014641450 / 13451345

MDBFP (15% )11551215112011201120

Vacuum Pump115115115115115

Lube Oil System of Main Turbine & BFPT & Control Fluid System310310310295295

ParametersSimhadriTalcher

BHELMITSUIBHELABB

Auxiliary Power Consumption (KW)

At 100% TMCR *170251854639503597

CW Pumping Power (KW)

At Design CW Flow between TP1115-891577

ParametersKahalgaon Phase-I

BHELSKODASEC, China

TG Package Auxiliary Power Consumption (KW)

At 100% TMCR422039754627

At 80% TMCR300027174187

At 60% TMCR24302638.63787

At 50% TMCR23902569.83327

CW Pumping Power (KW)

At Design CW Flow between TP9609951500

ParametersRosa

BHELAlstomCNMEG, ChinaSEC, China

Rating (MW)250270283.5283.5

MS Pressure (ata)150150170170

Power Consumption21700 KW22250 KW26900 KW25230 KW

8.68%8.24%9.49%8.90%

ParametersJindal Raigarh

BHELDEC, China

Rating (MW)250300


Power Consumption13700 KW19800 KW

5.48%6.60%

ParametersMaithon

BHELSEC, China

Rating (MW)4X2503X350


Power Consumption for the Station (with Bowl Mills)67940 KW76060 KW

6.80%7.24%

Power Consumption for the Station (with Tube Mills)76432 KW81952 KW

7.64%7.80%

ParametersUnitMD BFPTD BFPLoading (In Crores)Remarks

Arrangement-2x100%1x100% TDBFP & 2X50% MDBFP--

Rated OutputMW250250--

Turbine Cycle Heat RateKcal / kwh1936.31980.3--

Differential Power ConsumptionKW(+) 6500Base--

Net Turbine Cycle Heat RateKcal / kwh19881980.3--

Differential Net Turbine Cycle Heat RateKcal / kwhBase(-) 7.7(-) 5.24@ 68.1 Lacs

Equipment CostCroresBase(+) 7.9(+) 7.9-

Net EffectCroresBase-(+) 2.66-

ParametersDahanuKothagudemMaithonKorbaRosaRaigarhParli / ParasSantaldih

CEP'S (KW)550565542550515515

BFP (KW)677568507152684068906552

Vacuum Pump (KW)8393939397-

Turbine Lube Oil Purification unit (KW)65606065115 *60

ParametersCEP

Vindhyachal Stage-II *Simhadri

Design Parameters

Capacity (M3/Hr)835800

Head (MLC)350275

Power at Pump Input (KW)971731

Efficiency (%)8181

Parameters at 100% Load



Efficiency (%)79.580

ParametersMotor Driven BFP

Vindhyachal Stage-IISimhadri

Maximum Condition Parameters


Head (MLC) ( Incl. BP)26722482



Speed (RPM)59005770

Parameters at 100% Load


Head (MLC)21882165



Speed (RPM)52805255

Sheet2

Sheet3

CEP SIZING CRITERIA (Typical)

BOILERGEN.CEP/ BFP Sizing during turbine bypass condition

BFP SIZING CRITERIA (Typical)

CWP SIZING CRITERIA (Typical)

PROPER SELECTION OF EQUIPMENTPumps are selected based on Parameters :- pump flow rate- total dynamic head- operating temperature- suction pressure / NPSH availableDevelopments in design & technology have made available reliable & efficient products & systems aimed to reduce auxiliary power consumptionThe best efficiency shall preferably be between design and normal point. Design capacity shall be within 80-110% of the best efficiency capacityPumps shall have stable Q-H characteristicsContinuous head rise to shut off of atleast 10% preferred for parallel operation

VARIABLE SPEED DRIVESBoiler Feed Pumps (BFPs), Forced Draft (FD) fans and ID Fans are large consumersConstant speed drives use throttling elements incurring energy losses in the systemVariable speed drives are being increasingly used due to several advantages they have over the conventional fixed speed drivesUse of hydraulic coupling reduces the losses to some extent as efficiency of coupling itself is very low at lower speedVFD enables operation over a wide range of load at high efficiency with low energy consumption at lower speeds

Optimisation of Mechanical DesignMechanical design parameters like the design pressure of pump casings etc. are specified corresponding to the most severe possible scenario such as ;- over frequency of operation at 51.5 Hz- highest operating speed of the pump- shut off head at zero flow

The above criteria results in higher values for design pressures thereby increasing the pump component costs. In actual site operation, eventuality of pump subjected to all the above severe operating conditions simultaneously is remote.

Optimisation of Materials of constructionBronzeCast ironCast steel400 series Stainless steel300 series Stainless steel etc.

Selection criteria for materials :corrosion resistanceabrasive wear resistancecavitation resistancecasting & machining propertiesendurance limitnotch sensitivitygalling characteristicscost

Optimisation of Quality / Inspection checksToo much ambitious quality checks like LPI, MPI, UT and Radiography for 100% quantity & 100% area would add to cost of product as well as increased cycle time in view of the CHPs involved

Too much ambitious special/type tests like NPSH test on all the contracted pumps would add to cost of product as well as increased cycle time in view of the CHPs involvedRoutine test is ok

PERFORMANCE TESTING Routine tests on all pumps

Mechanical performance to check :

- Vibrations- Temperatures- Leakages

Hydraulic performance to check :

- Flow Vs Head Characteristic - Flow Vs Power Characteristic- Flow Vs Efficiency Characteristic

Type tests as optional HOT WATER PERFORMANCE TEST COMBINED STRING TEST AXIAL THRUST MEASUREMENTS PRESSURE PULSATION TEST DRY RUN TEST THERMAL SHOCK TEST VISUAL CAVITATION TESTSpecial tests on Boiler feed pumps : NPSH TEST

PERFORMANCE TESTING

Conclusion Optimisation of sizing, selection, mechanical design, quality/inspection checks and performance testing results in :lower auxiliary powerlower cost &lower cycle time

Hence utmost attention is to be given for the optimisation of the above

Thank You

Documents

Optimisation of Pumps in Thermal Power Stations