Optimisation of Auxiliary Equipment System-Condensate Extraction Pump Design in Thermal

Power Stations

* G.Sekar **J.Subbiah ***Dr.R.Senthil

*PhD scholar Dr MGR university,No.3 First street,Rukmani nagar,Poonamallee,Chennai,India **DCE/Turbine(O&A)/TSII/NLC/Neyveli-607807/TN/India ***Associate Prof. /Villupuram campus/Anna university/Chennai/India.

Abstract

Inspite of a phenomenal growth in the energy sector in the recentyears, the energy availability is consistently falling short of the energyrequirement. Unless new ways and means are employed like efficiencyimprovement, energy optimisation, availability improvement measures andemploying various energy conservation techniques, the deficit cannot be met.

While designing high capacity machines, design optimisation of variouselements in the thermal cycle is to be given top priority. For optimum designvarious factors are to be considered including site conditions, type of fueletc. The parameters required for the design of equipment should be preparedonly after thorough study and analysis. Oversized equipments will result inloss in efficiency, high capital cost and operating cost. While going forexpansion projects, available infrastructure and potentials should be very wellexploited to reduce project funding.

This paper focuses on the oversized Condensate Extraction Pump in ThermalPower station II, NLC Ltd and Energy optimisation in Condensate ExtractionPump by fitting pump curve with the system curve as a case study.

This paper brings out very useful feedbacks with relevant details forthe generating companies, designers and consultants for optimisation of designof auxiliary equipments in general and Condensate Extraction Pump inparticular.

Introduction

Energy efficiency losses through oversizing of pump and electric motorsare commonplace and, if the pump and motor specification far exceeds theapplication, it could be costing industry crores of rupees in wasted energy.

Industry figures suggest that around 80% of pump & motors could be theincorrect size.The majority are overspecified by as much as 10 or 15% asdesigners wanting to be "on the safe side".As pumps typically account foraround 30% of an industrial country's energy usage, this represents a seriousloss of energy.This takes no account of the extra cost of a larger motor withall the associated equipment, drives, cabling etc.

Electric motor manufacturers are forever striving to increase energyefficiency by one or two percentage points, but incorrect specification by anapplication engineer can mean that is wasted effort.Where a single percentage

point increase in energy efficiency can save the equivalent of the purchaseprice of an electric motor over its design life, it seems ludicrous to wasteenergy through poor specification.

Undersizing is also relatively common and should not be ignored.Anelectric motor can operate above its rated output thus allowing for temporaryoverloads.However, the motor will run hotter as a result and if this statecontinues, for example, where the pump continues to stop and start in itsduties or a higher specific gravity liquid is pumped than originally specified,overheating will cause damage.

Two points where this can directly affect the motor life are thebearings, which influence the motor reliability, and the coilinsulation.Overheating degrades the insulation more rapidly and encouragesdischarges which further degrade the insulation, thus shortening the motor'slife.Specification of motor size should, therefore, include starting conditionas well as running torque.

Method of starting is also important; direct online starting methods willcreate high torque that also impose mechanical stresses on the pump andhydraulic components, whereas star delta starting delivers lower torque andcurrent.Including a variable speed drive or soft starter in the systemspecification, matched to the requirements of motor and pump will easilyovercome these problems.Variable speed drives also improve energy efficiency inthe long term by matching application requirements with the correct motor speedand thus avoid energy wasted by, for example, belt drives, clutches and gears.

This paper focuses on the oversized Condensate Extraction Pump in ThermalPower station II, NLC Ltd/Tamil nadu/India and Energy optimisation inCondensate Extraction Pump by fitting pump curve with the system curve as acase study.

Energy optimisation in Condensate Extraction Pump:

It is essential to define required pump parameters viz. flow, head withas mush clarity as possible. It would be ideal if the actual pump operationoccurs as close to design point as possible. Too much of safety margin willresult in improper selection e.g. too much of buffer in the parameters willresult in a pump which is over designed for the purpose. A complete band withinwhich pump is likely to operate most of the time should be defined so that pumpselection can be optimized to suit the band. System characteristic (Resistance)curve should be properly prepared.

Operation of the pump away from best efficiency point (BEP) means lowerpump efficiency, more vibration and noise levels. We require a flow rate of540m3/hr to de-aerator at 210MW MCR condition. But, CEP capacity is 678m3/hr @225m Head.

Hence, the required flow is fed to de-aerator by throttling the levelcontrol valve CD-14. At this required flow, valve CD-14 opening is about 55%only. So, excess throttling is taking place in the control valve. This resultsin energy loss. 1.1Control Valves

The control valves are functioning as a variable orifice at variousopening of valve plug from the seat ring. The complexity of control valvedesign increases as the process parameters become more and more stringent.1.2 Flow Coefficient (Cv)

The flow coefficient (Cv) is the number of US GPM of water at 60ºF thatwill pass through flow restriction at maximum drop of 1 PSI.

Q = Cv √ ΔP/G

Q = Flow rate in GPM or kg/hr.ΔP = Pressure difference across control valve in PSI or kg/cm2

G = Specific Gravity at referred temperature.1.3 Control Valve CD-14

It is a modified Equal % valve. Ref. Fig. 1,2,3. Equal Percentage (= %)flow characteristics valve provides equal percentage increase in rate of flowfor equal increments of plug lift. The change of flow rate with respect tovalve travel will be relatively small when the valve plug is near its seat andrelatively high when the valve plug is nearly wide open. From the fig., it isseen that 70% of valve opening is required for passing a 30% flow of themedium.

CEP – Technical Specification Model - EN 6J 40 D (6 stages) Rated Flow (Q) - 678 m3/hr. Total Head - 225 mwc Pump shaft power - 507 kW. Efficiency - 81%

Motor – Technical Specification. Type - Induction motor. Rating - 600 kW. Voltage - 6600 V. Current - 67.2 A.

Valve CD-14 excess throtling can be avoided by removing one stage impeller(Blinding one stage) in the pump. This would reduce the head in step. For this6 stages pump, blinding one stage will reduce head by 16.66%.

This can prove to be very cost effective. Hence, this 6 stages pumpmodified to house only 5 stage will generate a head down by 16.66% and resultsin power saving by 16.66%.

1.4 Power Calculations

1.4.1 Model CEP EN 6J 40 (6 stages)Pump Hydraulic Power

Ph (kW) = (hd – hs) x ρ x g

1000

Ph = Hydraulic Power in kWQ = Flow in m3/sec.hd = Discharge head in mwchs = Suction head in mwc ρ = Density of liquid in kg/m3.g = Acceleration due to gravity m/sec2.

Pump Shaft Power

Ps = Ph / ףpump

Ps = Pump Shaft Power in kW.Ph = Hydraulic Power in kW.

p ף = Pump Efficiency in %Electric Motor Input Power

M input = Ps/ף motorM input = Motor Input Power in kW.Ps Pump Shat Power in kW.

motor ף = Motor Efficiency in %.

Operating Condition540 m3/hr @ 264 mwc

Hydralic power = 384.2 kWPump shaft power = 384.2 / 0.795

= 483.27 kW.

p ף = 79.5%Motor Input power = 483.27 / 0.93

= 520 kW.

motor = 93% ף

1.4.2 CEP EN 6J 40 (Modified) (5 stages)Q = 678 m3/H = 187.5 m3/hrPump Shaft Power = 423 kWPump efficiency = 81%

Operating Condition540 m3/hr @ 220 mwc

Hydralic power = 320.16 kW.Pump shaft power = 320.16 / 0.795

= 402.71 kW.

p = 79.5% ףMotor input power = 402.71 / 0.93

= 433 kW.

motor = 93% ףPower Saving = 520 – 433 kW

= 87 kW.Assume running hours in a year to be 85%

= 7446 hrs.Power saved per annum = 87 x 7446 = 6,47,802 kWhr.

1.5 Analysis

Modified CEP EN 6J 40 will be similar to CEP EN 5J 40 available at TTPS,Tuticorin.

In Stage-I (3 x 210 MW), we have CEP motor rating of 515 kW . Hence,motor rating of 600 kW shall be replced by motor rating of 515 kW forstandardisation .

CEP power consumption gets reduced by 16.6%. Unit auxiliary power consumption comes down by 0.044%. CEP EN 6J 40 modification results in a energy saving of 6,47,802 kWhr per

annum at operating condition.

1.6.Conclusion

System specification preparation should be preceded by proper system study,analysis by competent persons.

Equipment capacity should be based on optimum safety margin. While going for expansion projects, the existing station auxiliary system

capacity should be studied for utilizing in the expansion projects. Number of equipments and capacity should be optimised to reduce capital cost

and O&M cost. Energy efficient equipments should be selected to reduce the energy cost.

We hope this paper brought out very useful feedbacks with relevantdetails for the generating companies, designers and consultants foroptimisation of design of auxiliary equipments.

Reference:

1. IEEE Recommended practices for Energy Management in Industrial andCommercial Facilities,IEEE Std,739-1995

2. NEPA 70-1996 ,National Electric Code,(NEC)3. NEPA MG 1-1993,Motors and generators.4. Andrew Glover - Product Manager for WEG Motors.

Annexure:

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