Download - 005 energy saving tips

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Anil Palamwar [email protected]

Energy Saving methods with typical examples and exercises for power

stations

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General • Undertake regular Energy Audits. • Plug all Oil Leakages. • Leakage of one drop of oil per second amounts

to a loss of over 2000 liters/year. • Filter Fuel oil in stages.• Impurities in Fuel oil affect combustion. • Pre-heat the oil. (Reduces viscocity)• For proper combustion, oil should be at right

viscosity at the burner tip.Better atomisation.

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General • Provide adequate Pre-heat capacity for fuel oil.• Incomplete combustion leads to wastage of fuel.• Observe the colour of smoke emitted from

chimney. • Black smoke indicates improper combustion and

fuel wastage. • White smoke indicates excess air & hence loss of

heat. • Hazy brown smoke indicates proper combustion.• Use of Low air pressure “film burners” helps save

oil up-to 15% in furnaces.

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Furnace• Recover & utilize waste heat from furnace flue gas

for preheating of combustion air. (Air-pre-heater)• Every 21°C rise in combustion air temperature results

in 1% fuel oil savings. • Control excess air in furnaces. • A 10% drop in excess air amounts to 1% saving of fuel

in furnaces. • For an annual consumption of 3000 kl. of furnace oil.• This means a saving of Rs 3 Lacs. (Cost of furnace oil-

Rs. 10 per litre).

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Furnace• Reduce heat losses through furnace openings.• Observations show that a furnace operating at a

temperature of 1000°C having an open door (1500mm*750mm) results in a fuel loss of 10 lit/hr.

• For a 4000 hrs. furnace operation this translates into a loss of approx. Rs. 4 Lacs per year.

• Improve insulation if the surface temperature exceeds 20°C above ambient.

• Studies have revealed that heat loss form a furnace wall 115mm thick at 650°C amounting to 2650 Kcal/m2/hr can be cut down to 850 kcal/m2/he by using 65 mm thick insulation on the 115 mm wall.

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Boiler• Remove soot deposits when flue gas

temperature rises 40°C above the normal.• A coating of 3mm thick soot on the heat

transfer surface can cause an increase in fuel consumption of as much as 2.5%.

• Recover heat from steam condense.• For every 6°C rise in boiler feed water

temperature through condensate return, there is 1% saving in fuel.

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• Improve boiler efficiency.• Boilers should be monitored for flue gas losses,

radiation losses, incomplete combustion, blow down losses, excess air etc.

• Proper control can decrease the consumption up-to 20%.

• Use only treated water in boilers.• A scale formation of 1mm thickness on the waterside

would increase fuel consumption by 5-8%.

• Stop steam leakage. • Steam leakage from a 3 mm-diameter hole on a

pipeline carrying steam at 7kg/cm2 would waste 32 kl of fuel oil per year amounting to a loss of Rs. 3 Lacs.

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• Maintain steam pipe insulation.• It has been estimated that a bare steam pipe,

150 mm in diameter and 100m in length, carrying saturated steam at 8kg/cm2 would waste 25 kl of furnace oil in a year amounting to an annual loss of Rs. 2.5 Lacs.

• Frequently, insulation is not restored after maintenance work.

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D.G. Sets• Maintain diesel engines regularly. • A poorly maintained injection pump increases fuel

consumption by 4Gms/KWH. • A faulty nozzle increases fuel consumption by

2Gms/KWH. • Blocked filters increase fuel consumption by 2Gms/KWH. • A continuously running DG set can generate 0.5 Ton/Hr

of steam at 10 to 12 bars from the residual heat of the engine exhaust per MW of the generator capacity.

• Measure fuel consumption per KWH of electricity generated regularly.

• Take corrective action in case this shows a rising trend.

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Electrical Energy Conservation

• Improve power factor by installing capacitors to reduce KVA demand charges and also line losses.

• Improvement of power factor from 0.85 to 0.96 will give 11.5% reduction of peak KVA.

• And 21.6% reduction in peak losses.• This corresponds to 14.5% reduction in

average losses for a load factor of 0.8.

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• Avoid repeated rewinding of motors.• Observations show that rewound motors

practically have an efficiency loss of up-to 5%. • This is mainly due to increase in no load

losses.• Hence use such rewound motors on low duty

cycle applications only. • Use variable frequency drives, and fluid

couplings for variable speed applications such as fans, pumps etc.

• This helps in minimizing consumption.

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Illumination• Electronic ballast in place of conventional choke

saves energy up-to 20%. • CFL lamp in place of GLS lamp can save energy up-

to 70%.• Clean the lamps & fixtures regularly. • Illumination levels fall by 20-30% due to collection

of dust. • Use of 36W tube-light instead of 40 W tube-light

saves electricity by 8 to 10%. • Use of sodium vapour lamps for area lighting in

place of Mercury vapour lamps saves electricity up-to 40%.

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Compressed Air

• Compressed air is very energy intensive.• Only 5% of electrical energy are converted to useful

energy. • Use of compressed air for cleaning is rarely justified. • Ensure low temperature of inlet air.• Increase in inlet air temperature by 3°C increases

power consumption by 1%. • It should be examined whether air at lower

pressure can be used in the process. • Reduction in discharge pressure by 10% saves

energy consumption up-to 5%.

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• A leakage from a ½” diameter hole from a compressed air line working at a pressure of 7kg/cm2 can drain almost Rs. 2500 per day.

• Air output of compressors per unit of electricity input must be measured at regular intervals.

• Efficiency of compressors tends to deteriorate with time.

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Refrigeration & Air Conditioning• Double doors, automatic door closers, air

curtains, double glazed windows, polyester sun films etc. reduce heat ingress and air-conditioning load of buildings.

• Maintain condensers for proper heat exchange. • A 5°C decrease in evaporator temperature

increases the specific power consumption by 15%.

• Utilisation of air-conditioned/refrigerated space should be examined and efforts made to reduce cooling load as far as possible.

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• Utillise waste heat of excess steam or flue gases to change over from gas compression systems to absorption chilling systems and save energy costs in the range of 50-70%.

• Specific power consumption of compressors should be measured at regular intervals.

• The most efficient compressors to be used for continuous duty and others on standby.

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Cooling Towers

• Replacement of inefficient aluminium or fabricated steel fans by moulded FRP fans with aerofoil designs results in electricity savings in the range of 15%.

• A study on a typical 20ft. diameter fan revealed that replacing wooden blade drift eliminators with newly developed cellular PVC drift eliminators reduces the drift losses from 0.01-0.02% with a fan power energy saving of 10%.

• Install automatic ON-OFF switching of cooling tower fans and save up-to 40% on electricity costs.

• Use of PVC fills in place of wooden bars results in a saving in pumping power of up-to 20%.

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Pumps• Improper selection of pumps can lead to large

wastage of energy. • A pump with 85% efficiency at rated flow may have

only 65% efficiency at half the flow. • Use of throttling valves instead of variable speed

drives to change flow of fluids is a wasteful practice.• Throttling can cause wastage of power to the tune

of 50 to 60%. • It is advisable to use a number of pumps in series

and parallel to cope with variations in operating conditions by switching on or off pumps rather than running one large pump with partial load.

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• Drive transmission between pumps & motors is very .

• important. Loose belts can cause energy loss up-to 1-20%.

• Modern synthetic flat belts in place of conventional V-belts can save 5% to 10% of energy.

• Properly organized maintenance is very important. Efficiency of worn out pumps can drop by 10-15% unless maintained properly.

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HEAT RATE AND

AUXILIARY POWER CONSUMPTION IMPROVEMENT

REDUCTION OF APC

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Gross TG Heat Rate = {(Main Steam Flow X MS Enthalpy)

- (FW Enthalpy at Eco I/L X Feedwater flow at I/L)+ CRH Steam Flow X (HRH Enthalpy - CRH Enthalpy)

+ RH Spray X (HRH St Enthalpy - FW Enthalpy at Eco I/L)}Gross Generation

xxxxxxxxxxxxxxxxxxxGross Unit Heat Rate =

Gross TG Heat Rate / Boiler Efficiency

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Heat Rate in Short

• Therefore the heat rate in K.Cal / KWh• =

• Net heat used by the System in K.Cal/ Electrical output in KWh.

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HEAT INPUT TO TURBINE AND HEAT RETURN

HOT R/H

LIVE STEAM

COLD R/H

TO ECONOMISER

HPT IPT

HPH

RH

LPHDEA

LPTLPT

C

Maximum effort is made to return as much heat as possible to the Boiler, But latent heat is lost in the

Condenser.

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THERMAL POWER PROCESS – INPUT & OUTPUT

C.W.OUTLET

C.W.INLET

253.03 MW

FEEDWATER

CONDENSATE

HEAT INPUT BY FUEL FIRING=585.28 MW

(2397K.Cal/KWH)

BOILER EFFICIENCY = 86.17 %

STEAM OUTPUT FROM BOILER &

INPUT TO TURBINE =504.34 MW

2065 K.Cal / KWH EFFICIENCY =92.41 %

GENERATOR EFFICIENCY

=98.58%

LP & HP HEATERS

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Heat Energy To Electrical Energy• Conversion Factor :- 860 Kcal = 1 Kwh• TG Heat Rate = 2065 Kcal / Kwh At 33 deg. C.W. Inlet• Gross TG Efficiency (860/2065) = 41.65 %• Boiler Efficiency = 86.17 %• Gross Unit Heat Rate (2065 / 0.8617) = 2397 Kcal / Kwh• Gross Unit Efficiency (860 / 2397 ) =

35.88 %

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WHY A.P.C.Reduction ????

• A TPS is like any other factory.• A TPS has to handle the INPUTS and discharge the

OUTPUTS of its process of power generation.• COAL – AIR – WATER are the inputs .• FLUE GASES – ASH – are the outputs.• Fans – Pumps –Crushers –Conveyors – Feeders etc.

are needed to handle these.• These auxiliaries use a motor as the prime mover.• The motors consume part of the electricity produced.• The export of power is reduced by Auxy. Consmn.

Boiler Auxiliaries - Schematic

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FD Fan-A

FD Fan-B

W I

ND

B OX

FD Fan / Secondary Air Circuit

Scanner Air Fan

Igniter Fan

APH-B

APH-A

SCAPH-A

SCAPH-B

FLUE GAS

FLUE GAS

PRDS

PRDS

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PA Fan-A

PA Fan-B

Filter

Filter

SA Fan-B

SA Fan-A Hot A

ir To M

ills

Cold

Air To

Mills

CO

LD

PA

HEA

DER

Primary Air Circuit

To Mills

A/HAA/HA

A/HBA/HB

SCAPH

SCAPH

Hot P

A H

ead

er

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Flue gas

PA SA

Flue gas

SAPA

AIR

SIDE

GAS

SIDE

Regenerative Air HeaterRegenerative Air Heater

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Air CircuitAir Circuit

Cold Secondary Air Hot Secondary Air to Wind

Box

Cold Primary Air

Hot Primary Air to Bowl Mills

Tem

perin

g

Air

Bowl Mill

Pulverized Coal & Air Mixture to Burners

Atmos Air

Atmos Air

Seal Air Fan

Scanner Air Fan

To scanners

To Mills

PA Sector

SA Sector

F/Gas Sector

Hot Flue

GasCold Flue Gas

Tri-sector Air Pre-Heater

Wind box – Secondary Air Dampers-Coal & Oil Burners –Igniters.

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Secondary Air Dampers – (S.A.D.)

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Louvres & Drift Eliminators

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Efficiency – Loading of the Plant

• If the auxiliaries do not work efficiently, they will consume more power.

• This will reduce the export and the Efficiency of the plant as a whole.

• Proper maintenance of the auxiliaries will reduce APC.• Every auxiliary has a no-load power consumption.• When it runs at less capacity than design, then %

consumption will be high.• Hence the need to run the PLANT at OPTIMUM

capacity.

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Reasons for inefficiency

• Auxiliary not running as designed.• Due to wear and tear in operation.(Neck Rings)• Worn Grinding elements, fan blades.• Dampers not functioning properly• Inadequate Loading on the TG Set.• Deposition of soot / ash on heat transfer surfaces.• Water side deposition on tubes of Boiler / Condensor.• Poor D.M. water chemistry.• Poor Cooling water chemistry and Poor C.W. system.• Poor vacuum condition.

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Boiler Efficiency by Loss Method• Boiler Losses Design Value %1. Un-burnt Carbon (In B/A & F/A) 0.3312. Dry Gas Loss 4.9183. Moisture in Fuel 1.2434. Hydrogen In Fuel 5.2175. Moisture in Air 0.0746. Radiation Losses (Fixed) 0.2007. Sensible Heat in Bottom Ash 0.0718. Sensible Heat in Fly Ash 0.1029. Unmeasured Losses[1.5+(7)+(8)] 1.67310. TOTAL 13.8311. Design Blr.Effi. (100-13.83) = 86.17

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Turbine Losses• Internal Losses• A] Friction Losses • Nozzle Friction • Blade Friction • Disc Friction• B] Diaphragm Gland & Blade Tip Friction• C] Partial Admission (Throttling)• D] Wetness• E] Exhaust (Leaving Loss)

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• External Losses• – A] Shaft Gland Leakage• – B] Journal & Thrust Bearing.• – C] Governor & Oil Pump

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Turbine Cycle Heat Rate Deviations

• Due to • 1]] Main Steam Pressure• 2]] Main Steam Temp..• 3]] HRH Steam Temp..• 4]] Pressure Drop Across Re-Heater• 5]] Condenser Vacuum• 6]] F.W..Temp at Economiser Inlet

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Loading of HPT – IPT -LPT

• Design Turbine Cylinder Efficiency & Load Sharing of 210 MW LMZ M//C—

Load -%- Load MW Cylender ῇ• HPT : 24.76 % 52 MW 88.11%• IPT : 45.24 % 95 MW 89.93%• LPT : 30.00 % 63 MW 85% • TOTAL: 100 % 210 MW

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Cylinder LoadingsHPT - IPT - LPT LOADING

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Generator Losses

Losses MW %% of Total

LossesIron Loss (Core

Loss)0.436 0.208 14.63

Windage & Friction Loss (Core Loss)

0.720 0.343 24.16

Stator Copper Loss 1.010 0.481 33.89

Rotor Copper Loss 0.814 0.388 27.32

Total Losses 2.980 1.420 100.00

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Iron Loss (Core Loss)

Windage & Friction Loss (Core Loss)

Stator Copper

Loss

Rotor Copper

Loss

0.000

0.200

0.400

0.600

0.800

1.000

1.200

GENERATOR LOSSES - MW

MW

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WHY ENERGY EFFICIENCY IS IMPORTANT ?

• Depleting fossil fuel-Resources are scarce • Optimum plant utilization-Competitiveness• Global warming-Carbon Credit• Designated consumer-E.A. made it Mandatory.• Generate more energy with same fuel

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PERIOD STEAM PRESSURE&

TEMPERATURE

UNIT SIZE(MW)

TURBINEHeat Rate(Kcal/kWh)

Unit Heat Rate(Kcal/kWh)/Efficiency

1951-60 60 kg/cm2, 482oC 30 – 57.5 2470

1961-75 70 kg/cm2, 496oC to 90 ata 538oC

60 – 100 2370

1961-75 130 ata 535/535oC 110 – 120 2170 – 2060 2552-2423

1977-82 130 ata 535/535oC 210 (Russian) 2060 2423/35.4%

1983+ 150 ata 535/535oC 210 (Siemens)

2024 233536.8%

1984+ 170 ata 535/535oC 500 1950 (TDBFP) 229437.4%

1990+ 150 ata 535/535oC 170 ata 538/538 oC

210/ 250250/ 500

1950 (MDBFP)1950 (TDBFP)

22942294

*Above are best design values (design rates of individual unit varies based on

reference ambient, coal quality, design and supply dates)

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EFFICIENCY IMPROVEMENT CAN GIVE YOU For an average increase of 1 % in the Efficiency

would result in:-

Coal savings of approx. 11 million tons per annum worth Rs.13,000 Million

CO2 reduction about 13.5 million tons per annum Lower generation cost per kWh- as more efficient

the unit works, the more economical it is 1% increase in efficiency for 210 Mw unit with

heat rate 2335 kcal/kwh means heat rate improvement to 2275 kcal/kwh

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MAJOR CAUSE OF INEFFICENCY IN POWER PLANT

• High Flue gas exit Temp• Excessive amount of excess air(O2)• Poor Mill/Burners performance causing high

unburnt carbon in fly and bottom ash• Poor insulation• Poor house Keeping• Poor instrumentation and automation

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MAJOR CAUSE OF INEFFICENCY IN POWER PLANT (Cont…)

• Not running the units on design parameter• Heaters not in service or poor performance of

regenerative system• Poor condenser vacuum• Excessive DM water consumption- passing and

leakages• Use of Reheat spray to control Reheat

Temperature• Poor Cylinder Efficiency of turbine

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CONTROLLABLE PLANT PARAMETERS

• M.S. & R.H. Steam Temperatures• M.S. Steam Pressure• Condenser Vacuum• Final Feed Water Temperature• DP Across Feed Regulation Station• Auxiliary Power Consumption• Make Up Water Consumption

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SYNERGIZE OPERATIONOF UNIT

Need to clearly understand the relation between performance & fuel, operation and design parameters

Operational behavior and performanceImpacts of operating efficiency of Boiler, Turbine and

their auxiliaries on Net Unit Heat RateMaximum Achievable Load, Maintenance &Availability

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SOME CRITICAL FACTORS AFFECTING BOILER PERFORMANCE

• Fuel:- Heating Value, Moisture Contents, Ash Composition, Ash Contents,& Volatile Matter.

• Operational Parameter:- Level of Excess Air, & operating Condition of Burner Tilt Mechanism.

• Design:- Heating input per plan area, Height of Boiler, Platens & pendants heat transfer Surfaces, Burner & wind Box design.

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BEHAVIOURAL IMPACTS• Low heat value results in over firing of fuel causing more heat availability

for super heater and re-heater thus more attempration spray requirement. Hence increase in THR, overloading of ash handling system, fans and increased soot blowing

• Moisture content increase causes increase in heat transfer to S.H, and R.H. Hence again increase in attempration spray and THR (Turbine Heat Rate)

• Ash composition and contents increases damage to pressure parts surfaces because of melting behavior of low fusion ash temperature of blended coal in particular

• In consistency in fired fuel characteristics results in variation in excess air requirement thereby increasing stack loss and hence boiler efficiency reduction, overloading of ID Fan and ultimately unit load limitation

• High heat value causes excessive radiant heat transfer to water walls thereby leaving lesser heat for super heater and re-heater

• .

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Normally excess air ranges from 15% to 30% of stoichiometric air.

• High O2 % and presence of CO at ID Fan outlet are indicator of air in leakages and improper combustion in furnace

• Poorly effective damper control also is the cause of higher SEC of fans both primary and secondary

• The quality and purity of feed water and make up water is

also required to be maintained in a meticulous way by limiting blow down losses to nearly 1% and by checking the passing and leakages of valves. However, maximum 3% of flow can be taken as make up for these causes including soot blowing requirements

• Soot blowing is dependent on ash contents and is unit specific. Intelligently devised soot blowing can result in saving the fuel

BEHAVIOURAL IMPACTS

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• Cascading effects on efficiency, loading and availability because of following systems and equipments performance also needed to be looked into. The systems are:-Fuel receiving, preparation and handling systems.Pulverizing systemAir HeaterFansElectrostatic PrecipitatorFly ash handling systemBottom ash handling systemWaste disposal system

BEHAVIOURAL IMPACTS

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PERFORMANCE IMPACTS ON STEAM CYCLE , UNIT HEAT RATE & OUTPUT

• Various design & operating parameters of a unit are responsible for its cycle performance, heat rate,& out put

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CRITICAL FACTORS AFFECTING CYCLE PERFORMANCE

1. Re-heater & its system pressure drop2. Extraction line pressure drop3. Make up4. Turbine exhaust pressure5. Air preheat6. Condensate sub-cooling7. S/H & R/H spray flows8. Wet Bulb Temp9. Top Heaters out of service10. H.P. heater drain pump11. Type of BFP drives & method of flow control

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RH & ITS SYSTEM PRESSURE DROP….

• Every one 1% decrease in drop can improve THR and output by 0.1% & 0.3% respectively

• Normally designed for pressure drop equivalent to 10% of HP exhaust pressure

• Causes are Feed Heater abnormalities R/H safety valve passing

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EXTRACTION LINE PRESSURE DROP…

• Permissible pressure drop between stage pressure & Shell pressure is maximum 6%

• For every 2% increase in this pressure drop, THR would be poorer by 0.09%

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CYCLE MAKE-UP….

• Acceptable value of make up water is 3% to offset cycle water losses

• For every 1% increase in make up 0.4% increase in THR & 0.2% reduction on output is there

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EXHAUST PRESSURE…

• Increase & decrease in exhaust pressure do affect the THR.

• Though no valid thumb rule has been devised so far, however last stage blade design & exhaust area of turbine do affect the impact of changing exhaust pressure.

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AIR PRE-HEAT….

• Air preheating of combustion air before entry to regenerative air heater is done with either steam coil air pre - heater or hot water pre heating coil to maintain Average Cold End Temperature (ACET) to escape dew point temperature complications

• Condensate retrieval is necessary to avoid deterioration to THR depending upon unit load and combustion pre heating duty

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CONDENSATE SUB-COOLING…

• For 30% total flow and 2.5 deg C sub-cooling ,an increase of 0.001% in THR can be there for every subsequent 10% increase in flow

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R.H & S.H. SPRAY FLOW…

• Spray water whether drawn from BFP or after the final heater, it is always less the generative and less productive as well

• Every 1% spray flow, correction need to be done in THR & load computed from the curves supplied with the machine

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TOP HEATER OUT OF SERVICE….

• Extraction steam flow meant for top heater is required to pass through turbine thereby increasing the output.

• But at the same time final feed water temp. Is lowered resulting in poor THR.

• The % loss increases from lowest stage (.5 to .6 ) to highest stage (1.2 to 1.5%)

• Roughly each Deg C in TTD will result in a loss of 0.25% efficiency.

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PERFORMANCE MONITORING

• Analyze the poor efficiency areas from previous record

• Go down to specific system and then to component• Carry out performance/diagnostic study as suggested

in the Auditing Manual & operating manual• Devise a unit specific efficiency control sheet for few

terminal conditions (Act vs Des)• Monitor once per shift to know the operating

efficiency and check any deterioration

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Coal Handling Plant• Coal Crushers-• If significant quantity of coal >20 mm size is observed

on down side of crusher then it may led to substantial decrease in mill performance.

• Identification of combination of various least power consuming equipmen and recommending merit order operation.

• Use of natural daylight through conveyor galleries and use of fire resistant translucent sheet.

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Soft Starters- V.F.D.

• Explore Installation of power saver device in major LT motors. (Conveyor belt etc.):

• Major HT /LT motors i.e. conveyors, crushers etc. are often partially loaded & also there is frequent starts /stops.

• Explore the possibility of providing power saver devices (soft starters) in major motors.

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Power Factor of Motors.

• Power factor correction possibility: Induction motors may have vey low power factor, leading to lower overall efficiency. Capacitors connected in parallel with the motor are used to improve the power factor. The PF correction reduces KVA demand, reduced I2R losses in cable upstream of capacitor, reduced voltage drop in cables (leading to improved voltage regulation), and an increase in the overall efficiency of the plant electrical system.

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Chemicals for Dust Suppression

• Explore the possibility of using chemicals for reduced water spray:

• Mixing of chemical compounds in water provides much better atomization of water spray, by reduction in surface tension of water.

• Thus for the given application of dust suppression, lesser quantity of water is sprayed which also results into lesser wastage of latent heat in the steam generator.

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Use of Bull Dozers ?

• Maximum Mechanical Handling: Minimum Bulldozing: Receipt, unloading, stacking and reclaiming and the selection of machinery should be such that all the handling operations are accomplished without the use of semi mechanized means like bulldozers which are more energy intensive equipment.

• When coal is stocked in yard for more than incubation period (duration between coal mined and getting self ignited), special precautions like compacting water spraying must be taken.

•

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Bunkering Frequency

• Reduced Number of Fillings:• Live storage capacity of raw coal bunkers and the

filling pattern of bunkers is so planned that,• 24 hours coal requirement of the generating units is

met by not more than two fillings per day. • This will eliminate frequent starting and stopping of

the CHP system.

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Electric Motors

1. Induction Motors. (Wound Rotor, Squirrel Cage Rotor)2. Direct Current Motors.3. Synchronous Motors.

Motor Speed (RPM) = 120 x Frequency /No.of Poles.If f=50 c/s, Then motors speeds will be 2 pole = 3000 rpm; 6 pole = 1000 rpm4 pole = 1500 rpm; 8 pole = 750 rpm.10 pole =600 rpm; 12 pole = 500 rpm.

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Slip

Actual motor speed of an Induction Motor is less than the synchronous speed.The difference is called slip.Slip (%) = (S.S.-F.L.S) x 100 / S.S.S.S. = Synchronous Speed F.L.S.= Full Load Speed.Power Factor = KW / KVA = Cos. ФIf SS = 1500; and FLS = 1440; then ,Slip (%) = (1500 – 1440) x 100 / 1500= 4 %.

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Motor Efficiency and p.f.

Efficiency = Mech. Power Output / Electrical InputPower factor – like in inductive loads , is less than one.So for same real power the current drawn will be more for the lower power factor.High efficiency and p.f. close to unity for efficient overall plant operation.Squirrel Cage motors are more efficient.Similarly, higher speed, higher rating, and better cooling result in better efficiency.

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LossesIntrinsic losses depend on the design.Fixed losses = magnetic core loss + Friction + Windage.Variable losses depend upon load =Cu.Loss in Stator +Cu.Loss in Rotor + Stray losses.Part load performance also depends upon design.Efficiency and p.f. are low at lower loads.No load test – Rated voltage is applied and motor is brought to full speed. Note the following:- (i)Input power,(ii)Current ,(iii) frequency,(iv)Voltage.Input Power at No-Load = Stator Cu.loss +[Friction

+Windage]

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Friction & Windage (F & W)losses

If we plot No-load input versus Input voltage, the intercept will be F&W (Friction & Windage)component.Also,F&W and Core loss = Input Power – Stator Cu.Loss.Stator & Rotor Cu.Loss –Stator resistance measured by bridge or Volt-Amp method.Resistance must be corrected for temperature.R2/R1 = (235+t2)/ (235 + t1)*t1 – Ambient temperature in deg.C.*t2 –Operating temperature in deg.C.

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Rotor Resistance & Cu.Loss

Rotor resistance can be determined by Locked Rotor test at reduced frequency.However Rotor Cu.Loss is measured from measurement of slip, by Stroboscope or Tachometer.Rotor Cu.Loss = Slip x (Stator Input – Stator Cu.Loss –

Core loss )Stray Load Losses IS & IEC take it as 0.5% of output.IEEE Table-for stray losses-1 - 125 HP –1.8% 125 – 500 HP – 1.5%500 – 2500 HP –1.2 % Above 2500 HP – 0.9%

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Example

Motor Specifications-Rated power =34 KW / 45 HP. Voltage =415 VoltsCurrent =57 Amps Speed = 1475 rpm.Insulation class =F; Frame = LD 200 L; Connection = DeltaNo load test data –Voltage = 415 V; Current = 16.1 Amps; Frequency = 50 Hzs.Stator phase resistance at 30 deg.C.= 0.264 Ohms.No-Load –Power (PnL) = 1063.74 Watts.Calculate (a)Core +F&W loss; (b) Stator resistance at 120 deg.C.(c) Stator Cu.Loss at 120 deg.C.; (d)Full load slip and rotor input.assume Rotor losses = slip x rotor input.(e)Motor Input (assume 0.5% stray loss of motor rated power)(f) Motor full load Efficiency and Power factor.

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SOLUTION(a)Let Pi = Core (Iron)loss and Fw = Friction + Windage loss.No load power =PnL = 1063.74 Watts (given)Stator Cu.Loss at 30 deg.C. = 3 x (16.2/cube root 3)x (16.2/cube root 3) x 0.264=68.43 Watts.Pi + Fw = PnL – Stator Cu.Loss = 1063.74 – 68.43 = 995.3 Watts.(b) Stator resistance at 120 deg.C.R120 = 0.264 x (120 + 235 )/(30 + 235 ) = 0.354 Ohms per phase.(c) Stator Cu.Loss at Full load =Pst Cu.120 =

3 x (57/cube root 3)x (57/cube root 3)x 0.354 = 1150.1 Watts.(d) Full load slip = S = (1500 – 1475 ) / 1500 = 0.0167Rotor Input = Pr = Poutput /(1-S) = 34000 /(1-0.0167) = 34577.4 Watts.(e) Motor Full load Input power = P input =Pr + P st Cu 120 + (Pi +Fw)+P stray

=34577.4+1150.1+995.3 + (0.005* x 34000) = 36892.8 Watts.•Stray losses =0.5 % of rated output.(assumed)(f) Motor Efficiency at Full Load =100 x ( P output / P input)

=100x(34000/36892.8) = 92.2 %

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Full Load P.F.

Full Load P.F. = P input / Cube root 3 x V x I fl=36892.8 / (1.732 x415 x 57 )=0.90

Comments –Measurement of stray losses is very difficult. Actual stray losses for motors below 200 HP may be 1% - 3 %.Slip from name plate data is not accurate.Actual speed should be measured.When a motor is rewound, resistance per phase may increase due to material quality.Losses will increase.Calculate losses if winding resistance increases by 10% per phase.

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Energy Efficient Motors (EEM)To improve Efficiency, the Losses must be reduced.Stator & Rotor Cu.Loss – 55% to 60% 0f total losses.Suitable cross section of conductors will reduce resistance.To reduce motor current, the flux density has to be lowered.For this the air gap has to be minimum permissible.Rotor Cu.Loss can be reduced by selecting Copper bars in stead of Aluminum bars.Reducing the Slip will also reduce Rotor Cu.Loss as it is a function of Slip.Motor running closer to Synchronous speed will be more efficient. Core Loss due to hysterisis and eddy currents.These are independent of load. And are about 2-025% of total losses.Use of thinner laminations for core reduces this loss.

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Loss reduction . . . . . Friction & windage loss –8-12 % of total losses.These are also independent of load.When Cu. Losses in Stator & Rotor are reduced, less heat is generated. Then Smaller cooling fans can be used to reduce windage.Proper bearings and lubrication reduces friction loss.Stray load losses. – Are proportional to Square of load current.These are caused by LEAKAGE FLUX induced by the load current in the laminations and are 4-5 % of total losses.Careful selection of slot numbers, tooth / slot geometry and air-gap reduce these losses.

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Factors affecting Efficiency

Quality of Input Power.Actual voltage and Frequency.B.I.S. specifies voltage variation of +/- 6% and frequency variation of +/- 3% in which the motor should deliver its rated output.Greater fluctuations are observed in our system and badly affect the motor performance.Voltage un-balance i.e. voltages in 3 phases not being equal are more detrimental to motor performance and its life.Any single phase loads must be distributed equally among all three phases. OR,Single phase loads should be fed from a separate line/transformer.

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MOTOR LOADING

Input Power drawn by Motor (KW) x 100% Loading =

% Loading =Input Power drawn by Motor (KW) x 100

Name Plate 3 x KV x I x Cos Phi.

(Name plate KW / Name plate efficiency)

•Never assume Power Factor.•Loading should not be estimated as the

ratio of Currents.

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Questions1. A 4-pole induction motor operates with 5% slip at full load.

Calculate the full load RPM of motor when the frequency is 50 c/s ; 40 c/s ; 45 c/s ; and 35 c/s.

2. List the losses and their approximate % in Induction Motors.3. List the factors affecting efficiency of motors.4. The p.f. of an Induction Motor – i)Increases with load ii) falls

with load, iii) Remains constant with load iv) Is not related to load.

5. List methods of speed control of Induction Motors.6. A 50 KW motor of 86 % efficiency is replaced by a motor of

89% efficiency.Calculate Annual savings for 6000 Hrs operation and tariff Rs.4.50/KWH.

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Steam for Heating

Use steam at lowest possible pressure for indirect heat exchange.LATENT HEAT is more at lower pressure.Steam at 3 bar will release 134 KJ/Kg heat than at 10 bar.

Latent & Sensible Heat in Steam

0200

400600

800

0.1 0.15 0.2 0.25 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 2 5 10

Sensible Heat Latent Heat in K.Cal

90

Chimney smoke colour

BLACK SMOKE – Low air to fuel ratio.Oxygen deficient combustion, Incomplete combustion,High un-burnt losses.WHITE(or Invisible) SMOKE – High air to fuel ratio, Oxygen rich systemComplete combustion but heat loss by excess air.Excess fuel consumption due to higher stack loss.GREY SMOKE – Optimum air to fuel ratio.Complete combustion with least losses.Optimum fuel consumption.

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Recover Condensate

Condensate holds about 20% fuel energy.

Latent & Sensible Heat in Steam

0200

400600

800

0.1 0.15 0.2 0.25 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 2 5 10

Sensible Heat Latent Heat in K.Cal

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Distribute steam at highest possible pressure

Steam volume is less at higher pressure.This reduces piping cost.

Specific Volume M3/Kg

0

5

10

15

20

0.1

0.15 0.

2

0.25 0.

3

0.4

0.5

0.6

0.7

0.8

0.9

1.01

3 2 5 10

Absolute Pressure Bars

Vo

lum

e in

Cu

bic

M

eter

s

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Steam Traps remove condensate from steam line,Condensate film reduces heat transfer

160

120

80

40

0

STEAM AT 3 BARS

AIR 0.2 MM

CONDENSATE FILM1 MM

PIPE WALL 6 MM

TEMPERATURE DROP THROUGH AIR AND CONDENSATE FILM

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INSULATION

Keep the insulation DRY.Heat loss through wet insulation can be 30 times more.Conductivity of wet insulation is much higher than that of dry insulation.

95

Steam Tapping must be from the top of the pipe.Otherwise condensate may also flow out with the steam and affect the process.

96

Condensate in steam line can accumulate and cause hammering.It also erodes the bends.

Erosion seen in secondary condensate lines.Not in Steam or Water lines.

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Recover Heat in FLASH Steam

Flash steam may be only 10-15%

but it holds nearly 50 % heat.

This heat must be recovered to

improve efficiency.

98

Drain size must be properly selectedIn adequate sized pipe will not drain drain away the condensate fully.This will affect the process.Drain pockets are useful for effective draining.

99

Avoid group tapping of Dains

High pressure drain may block the draining of other drains.

100

Convert Group Tapping To Individual Tapping

101

Problem in Group Tapping

102

Steam Heating V/s Thermic Fluid

1 Kg of steam is equal to 27 Kg of thermic fluid for

the same amount of heat transfer.

Steam carries latent heat which is a major part of

total heat in the steam.

Thermic Fluids carry only sensible heat.

Smaller heat exchangers are possible with steam.

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SATURATED V/S SUPERHEATED STEAM

Superheated steam has to first cool to saturation temperature and

then it can give up its latent heat by condensing.

Thus the heat transfer coefficient of superheated steam is lower than of saturated steam which does not have to lose any sensible heat before condensing.

Thus use of saturated steam is preferable.

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Enthalpy components of STEAM at 10 Bar & 300 deg.C.

Latent Heat66%

Superheat9%

Enthalpy of Water

25%

/mydocuments/adp/npti/auxyConsmn. 105

Generation & Auxiliary Consumption

Sr.No. GenerationAuxy

Consmn.% Auxy. Consmn.

1 5.04 0.425 8.43

2 4.536 0.425 9.37

3 4.0824 0.404 9.89

4 3.67416 0.384 10.44

Generation reduced by 10 %Auxy. Consumption reduces by 5 %% Auxy Consumption rapidly rises.


AUXY CONSUMPTION

Factors-•Plant Layout-• C.H.P. , A.H.P. , W.T.P. ETC.•Bhusawal TPS has two stage pumping of ash slurry.•Parli TPS water is pumped in two stages from 20 Km. Distance.


• WTP for Koradi & Khaperkheda TPS is situated at opposite side from the water source.

• Some TPS have two stage coal crushing in CHP.


Condition of Auxy.

Similar P.A. Fans draw different current for same load.(Air flow)Boiler feed pumps are not opened until a pump fails.Coal mills loading is different for same coal feeding.These indicate loss of efficiency.Maintenance spares must be selected wisely.Cheap spares may prove costly in the long run.Purpose of maintenance should be restoring original efficiency of the auxy and not just restoring it back in service.


Availability of Key auxy.s

•Oil Burners-•Coal Mills•Hot P.A. fans.

Availability of above auxiliaries greatly affects

GENERATIONand hence % auxy consumption.


Use of Design capacity•C.H.P.- Loading of conveyor belts. •Poor loading will result in more running time of CHP.•Inadequate belt maintenance –More power consumption.•A.H.P. – Wet slurry disposal- •If slurry concentration is poor, running hours will increase.•Boiler & Gas ducts – Excessive air ingress will overload I.D.Fans and finally reduce generation.•Filters – Choking affects power consumption/Output.•Condenser cleanliness- Higher D.P. Power loss.


Coal Mills - Pulverisers

Performance depends upon air flow.Air flow may be less due to 1. Blocked air inlet. This may be due to i) Broken scrapper. Accumulation of coal in air path.ii) Incorrect throat gap.iii) Incorrect gap at inverted cone2. Clogged classifier.Close attention to these is necessary.

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THANK YOU

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