ENERGY EFFICIENCY ENERGY EFFICIENCY IN ELECTRICAL UtilitiesIN ELECTRICAL Utilities

D.PAWAN KUMARD.PAWAN KUMAR

ENERGY EFFICIENCY IN ENERGY EFFICIENCY IN COMPRESSED AIR SYSTEMCOMPRESSED AIR SYSTEM

Air Is Free !!!

Compressed Air Is Free !!!

Not

Compressed Air Efficiency:60 to 80% of the power of the prime mover is converted into

an unusable form of energy (HEAT)And to a lesser extent, into friction, misuse and noise

Approximately 10% gets to the point

of use!!

A TYPICAL COMPRESSED A TYPICAL COMPRESSED AIR SYSTEMAIR SYSTEM

COMPRESSOR FAMILY TREECOMPRESSOR FAMILY TREE

TYPES OF AIR COMPRESSORSTYPES OF AIR COMPRESSORS

There are three basic types of air compressors:Reciprocating (Recip)Rotary Screw (Screw) Rotary Centrifugal (Centrifugal)

These types are further defined by:the number of compression stages method of cooling (air, water, oil) drive method (motor, engine, steam, other) how they are lubricated (oil, oil-free) packaged or custom-built

RECIPROCATING COMPRESSORRECIPROCATING COMPRESSOR

STAGES OF RECIPROCATING COMPRESSORSTAGES OF RECIPROCATING COMPRESSOR

STAGES OF RECIPROCATING COMPRESSORSTAGES OF RECIPROCATING COMPRESSOR

SCREW COMPRESSORSCREW COMPRESSOR

CENTRIFUGAL COMPRESSORCENTRIFUGAL COMPRESSOR

GENERAL SELECTION GENERAL SELECTION CRITERIA FOR COMPRESSORSCRITERIA FOR COMPRESSORS

Capacity (m3/h) Pressure (bar) Type of Compressor

From To From To

Roots power compressor single stage

100 30000 0.1 1

Reciprocating

- Single / Two stage 100 12000 0.8 12

- Multi stage 100 12000 12.0 700

Screw

- Single stage 100 2400 0.8 13

- Two stage 100 2200 0.8 24

Centrifugal 600 300000 0.1 450

SYSTEM COMPONENTSSYSTEM COMPONENTS Intake Air Filters : Prevent dust and atmospheric impurities from entering compressor. Dust causes sticking valves, scored cylinders, excessive wear etc.

Inter-stage Coolers : Reduce the temperature of the air (gas) before it enters the next stage to reduce the work of compression and increase efficiency. They can be water-or air-cooled.

After Coolers : Reduce the temperature of the discharge air, and thereby reduce the moisture carrying capacity of air.

Air-dryers : Air dryers are used to remove moisture, as air for instrument and pneumatic equipment needs to be relatively free of any moisture. The moisture is removed by suing adsorbents or refrigerant dryers, or state of the art heatless dryers.

Moisture Traps : Air traps are used for removal of moisture in the compressed air distribution lines. They resemble steam traps wherein the air is trapped and moisture is removed.

Receivers : Depending on the system requirements, one or more air receivers are generally provided to reduce output pulsations and pressure variations.

AIR DISTRIBUTION SYSTEMSAIR DISTRIBUTION SYSTEMS The air distribution system links the various components of the compressed air system to deliver air to the points of use with minimal pressure loss. The specific configuration of a distribution system depends on the needs of the individual plant, but frequently consists of an extended network of main lines, branch lines, valves, and air hoses. The length of the network should be kept to a minimum to reduce pressure drop. Air distribution piping should be large enough in diameter to minimize pressure drop. A loop system is generally recommended, with all piping sloped to accessible drop legs and drain pointsWhen designing an air distribution system layout, it is best to place the air compressor and its related accessories where temperature inside the plant is the lowest. A projection of future demands and tie-ins to the existing distribution system should also be considered.

COMPRESSOR EFFICIENCYCOMPRESSOR EFFICIENCY

1 -

PP 0.612 / P Q 1-KNK / NK

1-K

s

ds

N =No. of stagesK =Ratio of specific heats (1.35 for air)Ps =suction pressure in kg/cm2Pd =Discharge pressure in kg/cm2Q =Actual air flow (m3/min.)Actual kW = 3 V I PF as measured

Efficiency of compressor and motor combination = kW Actual

kW lTheoretica100

Theoretical kW =

EFFECT OF INTAKE AIR TEMPERATURE EFFECT OF INTAKE AIR TEMPERATURE ON POWER CONSUMPTIONON POWER CONSUMPTION

Inlet Temperature (0C)

Relative Air Delivery (%)

Power Saved (%)

10.0 102.0 + 1.4

15.5 100.0 Nil

21.1 98.1 - 1.3

26.6 96.3 - 2.5

32.2 94.1 - 4.0

37.7 92.8 - 5.0

43.3 91.2 - 5.8

Every 40C rise in inlet air temperature results in a higher energy consumption by 1 % to achieve equivalent output. Hence, cool air intake leads to a more efficient compression.

EFFECT OF PRESSURE DROP ACROSS AIR EFFECT OF PRESSURE DROP ACROSS AIR

INLET FILTER ON POWER CONSUMPTIONINLET FILTER ON POWER CONSUMPTION Pressure Drop

Across air filter (mmWC)

Increase in Power Consumption (%)

0 0

200 1.6

400 3.2

600 4.7

800 7.0

For every 25 mbar pressure lost at the inlet due to choked filters, the compressor performance is reduced by about 2 percent.

ELEVATIONELEVATION

Percentage Relative Volumetric Efficiency

Compared with Sea Level Altitude Meters

Barometric Pressure

Mbar At 4 bar At 7 bar

Sea level 1013 100.0 100.0

500 945 98.7 97.7

1000 894 97.0 95.2

1500 840 95.5 92.7

2000 789 93.9 90.0

2500 737 92.1 87.0

It is evident that compressors located at higher altitudes consume more power to achieve a particular delivery pressure than those at sea level, as the compression ratio is higher.

EFFICACY OF EFFICACY OF INTER AND AFTER COOLERSINTER AND AFTER COOLERS

Details Imperfect Cooling

Perfect Cooling

Chilled Water Cooling

1 Stage inlet temperature 0C 21.1 21.1 21.1 2 Stage inlet temperature 0C 26.6 21.1 15.5 Capacity (m3/min) 15.5 15.6 15.7 Shaft Power (kW) 76.3 75.3 74.2 Specific energy consumption kW (m3/min)

4.9 4.8 4.7

Percent Change + 2.1 - - 2.1

It can be seen from the table that an increase of 5.50C in the inlet to the second stage results in a 2 % increase in the specific energy consumption. Use of cold water reduces power consumption

COOLING WATER REQUIREMENTCOOLING WATER REQUIREMENT

Compressor Type

Minimum quantity of Cooling Water required

for 2.85 m3/min. FAD at 7 bar (lpm)

Single-stage 3.8 Two-stage 7.6 Single-stage with after-cooler 15.1 Two-stage with after-cooler 18.9

POWER REDUCTION THROUGH POWER REDUCTION THROUGH

PRESSURE REDUCTIONPRESSURE REDUCTION

Pressure Reduction

Power Reduction (%)

From (bar)

To (bar)

Single-stage

Water-cooled

Two-stage Water-cooled

Two-stage Air-

cooled

6.8 6.1 4 4 2.6

6.8 5.5 9 11 6.5

A reduction in the delivery pressure of a compressor would reduce the power consumption.

EXPECTED SPECIFIC POWER CONSUMPTION EXPECTED SPECIFIC POWER CONSUMPTION OF RECIPROCATING COMPRESSORS OF RECIPROCATING COMPRESSORS

(BASED ON MOTOR INPUT)(BASED ON MOTOR INPUT)

Pressure bar No. of Stages Specific Power kW/170 CMH

1 1 6.29

2 1 9.64

3 1 13.04

4 2 14.57

7 2 18.34

8 2 19.16

10 2 21.74

15 2 26.22

ENERGY WASTAGE DUE TO ENERGY WASTAGE DUE TO SMALLER PIPE DIAMETERSMALLER PIPE DIAMETER

Pipe Nominal

Bore (mm)

Pressure drop (bar) per 100 meters

Equivalent power losses (kW)

40 1.80 9.5

50 0.65 3.4

65 0.22 1.2

80 0.04 0.2

100 0.02 0.1

Typical acceptable pressure drop in industrial practice is 0.3 bar in mains header at the farthest point and 0.5 bar in distribution system

DISCHARGE OF AIR THROUGH DISCHARGE OF AIR THROUGH ORIFICEORIFICE

Gauge Pressure

Bar 0.5 mm 1 mm 2 mm 3 mm 5 mm 10 mm 12.5 mm

0.5 0.06 0.22 0.92 2.1 5.7 22.8 35.5

1.0 0.08 0.33 1.33 3.0 8.4 33.6 52.5

2.5 0.14 0.58 2.33 5.5 14.6 58.6 91.4

5.0 0.25 0.97 3.92 8.8 24.4 97.5 152.0

7.0 0.33 1.31 5.19 11.6 32.5 129.0 202.0

COST OF AIR LEAKAGECOST OF AIR LEAKAGE

Orifice Size mm

KW Wasted

* Energy Waste (Rs/Year)

0.8 0.2 8000

1.6 0.8 32000

3.1 3.0 120000

6.4 12.0 480000

Based on Rs. 5 / kWh ; 8000 operating hours; air at 7.0 bar

HEAT RECOVERYHEAT RECOVERYAs noted earlier, compressing air generates heat. In fact, industrial-sized air compressors generate a substantial amount of heat that can be recovered and put to useful work. More than 80% of the electrical energy going to a compressor becomes heat. Much of this heat can be recovered and used for producing hot water or hot air.

Typical uses for recovered heat include supplemental space heating, industrial process heating, water heating, makeup air heating, and boiler makeup water preheating. Recoverable heat from a compressed air system is not, however, normally hot enough to be used to produce steam directly. 

As much as 80-93% of the electrical energy used by an industrial air compressor is converted into heat. In many cases, a properly designed heat recovery unit can recover anywhere from 50-90% of this available thermal energy and put it to useful work heating air or water

HEAT RECOVERY WITH AIR-COOLED HEAT RECOVERY WITH AIR-COOLED ROTARY SCREW COMPRESSORSROTARY SCREW COMPRESSORS

Air-cooled packaged rotary screw compressors are very amenable to heat recovery for space heating or other hot air uses. Ambient atmospheric air is heated by passing it across the system's aftercooler and lubricant cooler, where it extracts heat from both the compressed air and the lubricant that is used to lubricate and cool the compressor

  Since packaged compressors are typically enclosed in cabinets and already include heat exchangers and fans, the only system modifications needed are the addition of ducting and another fan to handle the duct loading and to eliminate any back pressure on the compressor cooling fan. These heat recovery systems can be modulated with a simple thermostatically-controlled hinged vent. When heating is not required -- such as in the summer months -- the hot air can be ducted outside the building. The vent can also be thermostatically regulated to provide a constant temperature for a heated area.

Hot air can be used for space heating, industrial drying, preheating aspirated air for oil burners, or any other application requiring warm air. As a rule of thumb, approximately 50,000 Btu/hour of energy is available for each 100 cfm of capacity (at full-load). Air temperatures of 30 to 40oF above the cooling air inlet temperature can be obtained. Recovery efficiencies of 80-90% are common

AIR AMPLIFIERSAIR AMPLIFIERS

Compressed air flows through the inlet (1) into an annular chamber(2). It is then throttled through a small ring nozzle (3) at highvelocity. This primary air stream adheres to the coanda profile (4),which directs it toward the outlet. A low pressure area is createdat the center (5) inducing a high volume flow of surrounding airinto the primary air stream. The combined flow of primary andsurrounding air exhausts from the Air Amplifier in a high volume,high velocity flow.

STEPS IN SIMPLE SHOP-FLOOR METHOD FOR STEPS IN SIMPLE SHOP-FLOOR METHOD FOR LEAK QUANTIFICATIONLEAK QUANTIFICATION

Shut off compressed air operated equipments (or conduct test when no equipment is using compressed air).Run the compressor to charge the system to set pressure of operationNote the sub-sequent time taken for ‘on load’ and ‘off load’ cycles of the compressors. For accuracy, take ON & OFF times for 8 – 10 cycles continuously. Then calculate total ‘ON’ Time (T) and Total ‘OFF’ time (t).The system leakage is calculated as System leakage (cmm) = Q T / (T + t)

Where, Q = Actual free air being supplied during trial,

in cubic meters per minute T = Time on load in minutes t = Time unload in minutes

LEAK TEST: EXAMPLELEAK TEST: EXAMPLECompressor capacity (CMM) = 35Cut in pressure kg/SQCMG = 6.8Cut out pressure kg/SQCMG = 7.5On load kW drawn = 188 kWUnload kW drawn = 54 kWAverage ‘On-load’ time = 1.5 minutesAverage ‘Unload’ time = 10.5 minutes

Comment on leakage quantity and avoidable loss of power due to air leakages.

a)      Leakage quantity (CMM) =

= 4.375 CMMb) Leakage per day = 6300 CM/dayc) Specific power for compressed air generation=

= 0.0895 kwh/m3

d) Power lost due to leakages/day = 563.85 kWh

35

5.105.1

1.5

CMH6035

kWh 188

CAPACITY ASSESSMENT IN SHOP-FLOORCAPACITY ASSESSMENT IN SHOP-FLOOR Isolate the compressor along with its individual receiver being taken for test from main compressed air system by tightly closing the isolation valve or blanking it, thus closing the receiver outlet.Open water drain valve and drain out water fully and empty the receiver and the pipe line. Make sure that water trap line is tightly closed once again to start the test.Start the compressor and activate the stop watch.

Note the time taken to attain the normal operational pressure P2 (in the receiver) from initial pressure P1.Calculate the capacity as per the formulae given below :

Actual Free air discharge Min./NM T

V

P

PP Q 3

0

12

Where

P2 = Final pressure after filling (kg/cm2 a)

P1 = Initial pressure (kg/cm2a) after bleeding

P0 = Atmospheric Pressure (kg/cm2 a)

V = Storage volume in m3 which includes receiver, after cooler, and delivery piping

T = Time take to build up pressure to P2 in minutes

EXAMPLEEXAMPLEPiston displacement : 16.88 CMMTheoretical compressor capacity : 14.75 CMM @ 7 kg/SQCMG Compressor rated rpm 750 : Motor rated rpm : 1445Receiver Volume : 7.79 CMAdditional hold up volume, i.e., pipe / water cooler, etc., is : 0.4974 CMTotal volume : 8.322 CM

Initial pressure P1 : 0.5 Kgf / SQCMG

Final pressure P2 : 7.03 Kgf / SQCMGAtmospheric pressure : 1.026 Kgf/cm2A

Compressor output CMM :

2 1P P Total Volume

Atm. Pressure Pumpup time

4.021 .0261

8.322 5.003.7

= 13.17 CMM

ENERGY EFFICIENCY IN ENERGY EFFICIENCY IN REFRIGERATION SYSTEMREFRIGERATION SYSTEM

INTRODUCTIONINTRODUCTION

Refrigeration deals with the transfer of heat from a low temperature level at the heat source to a high temperature level at the heat sink.

Air conditioning for comfortRefrigeration for process

TON OF REFRIGERATIONTON OF REFRIGERATION

1 ton of refrigeration = 3024 kCal/hr heat

rejected.

The cooling effect produced is quantified as tons of refrigeration.

VAPOUR-COMPRESSION REFRIGERATION SYSTEM VAPOUR-COMPRESSION REFRIGERATION SYSTEM (R-22)(R-22)

VAPOUR – ABSORPTION REFRIGERATION SYSTEMVAPOUR – ABSORPTION REFRIGERATION SYSTEM

EVAPORATOR

CONDENSOR

PUMP

GENERATOR

ABSORBER

STRONG

SOLUTION

WEAK

SOLUTION

COOLING WATER IN

HOT WATER OUT

THROTTLING VALVE

Regulating Valve

Waste Heat/

Direct Fired

Heat load In

PERFORMANCE ASSESSMENTPERFORMANCE ASSESSMENT

The specific power consumption kW/TR is a useful indicator of the performance of refrigeration system. By messing refrigeration duty performed in TR and the Kilo Watt inputs measured, kW/TR is used as a reference energy performance indicator.

The refrigeration TR is assessed as TR = Q Cp (Ti – To) /

3024

Where TR is cooling TR duty Q is mass flow rate of coolant in kg/hr Cp is coolant specific heat in kCal /kg / 0C Ti is inlet. Temperature of coolant to evaporator (chiller) in 0C.To is outlet temperature of coolant from evaporator (chiller) in 0C.

OVERALL ENERGY CONSUMPTIONOVERALL ENERGY CONSUMPTION

Compressor kWChilled water pump kWCondenser water pump kWCooling tower fan kW

Overall kW/TR = sum of all above kW/ TR

EFFECT OF VARIATION IN EVAPORATOR TEMPERATURE EFFECT OF VARIATION IN EVAPORATOR TEMPERATURE

ON COMPRESSOR POWER CONSUMPTIONON COMPRESSOR POWER CONSUMPTION

Evaporator Temperature

(0C)

Refrigeration Capacity

(tons)

Specific Power

Consumption

Increase in kW/ton (%)

5.0 67.58 0.81 -

0.0 56.07 0.94 16.0

-5.0 45.98 1.08 33.0

-10.0 37.20 1.25 54.0

-20.0 23.12 1.67 106.0

A 10C raise in evaporator temperature can help to save almost 3 % on power consumption.

EFFECT OF VARIATION IN CONDENSER TEMPERATURE EFFECT OF VARIATION IN CONDENSER TEMPERATURE ON COMPRESSOR ON COMPRESSOR

POWER CONSUMPTIONPOWER CONSUMPTION

Condensing Temperature

(0C)

Refrigeration Capacity

(tons)

Specific Power

Consumption

Increase in kW/TR

(%)

26.7 31.5 1.17 -

35.0 21.4 1.27 8.5

40.0 20.0 1.41 20.5

EFFECT OF POOR MAINTENANCE EFFECT OF POOR MAINTENANCE

ON COMPRESSOR POWER CONSUMPTIONON COMPRESSOR POWER CONSUMPTION

Condition Evap. Temp (0C)

Cond. Temp (0C)

Refrigeration Capacity

(tons)

Specific Power

Consumption (kW/ton)

Increase in

kW/Ton (%)

Normal 7.2 40.5 17.0 0.69 - Dirty condenser

7.2 46.1 15.6 0.84 20.4

Dirty evaporator

1.7 40.5 13.8 0.82 18.3

Dirty condenser and evaporator

1.7 46.1 12.7 0.96 38.7

ENERGY SAVINGS OPPORTUNITIESENERGY SAVINGS OPPORTUNITIES

Cold Insulation Process Heat Loads Minimisation

Flow optimization and Heat transfer area increase to accept higher temperature coolantAvoiding wastages like heat gains, loss of chilled water, idle flowsFrequent cleaning / de-scaling of all heat exchangers

.

AT THE REFRIGERATION PLANT AREAAT THE REFRIGERATION PLANT AREA Ensure adequacy of chilled water and cooling water flows, avoidance of bypass flows by valving off the idle equipment.Minimize part load operations by matching loads and plant capacity on line, adopting variable speed drives for varying process load. Ensure efforts to continuously optimize condenser and evaporator parameters for minimizing specific energy consumption and maximizing capacity.Adopt VAR system where economics permit as a non CFC solution

SELECT THE RIGHT COOLING MEDIUMSELECT THE RIGHT COOLING MEDIUM

Type of cooling Power Consumption

1. Cooling tower water 0.1 KW/TR2. Chilled water System at 10oC 0.7 KW/TR3. Brine System at -20oC 1.8 KW/TR

Order of preferenceCooling water ChilledWater

Brine

ENERGY SAVINGS IN REFRIGERATION SYSTEMSENERGY SAVINGS IN REFRIGERATION SYSTEMS

There are two broad ways by which energy can be conserved

1.By decreasing the load

2.By optimising the refrigeration system

CALCULATING THE OPERATING LOAD OF A CALCULATING THE OPERATING LOAD OF A CHILLER PLANTCHILLER PLANT

Refrigeration plant

Refrigeration plant

Hot well12OC

Cold well8OC

Process

Chilled water flow – 100 m3/hr

Refrigeration TR - 100,000 kg/hr x 1 x 4

3000

- 133.33 TR

Efficiency -Power drawn by compressor, kW

TR

m Cp

120

133.33- = 0.9

DT

EFFICIENT OPERATION & MAINTENANCEEFFICIENT OPERATION & MAINTENANCEThe suction temperature, pressure delivery pressure of

compressors should be kept at optimum level

Ensure all indicators are working properly

Keep record of oil consumption

Condensers

Remove scale and algae and adopt suitable water treatment

Give periodic purging of non-condensable gases

Lesser the water temperature more the COP

Routine defrosting of Cooling coils

Stop condenser water pump when compressor not working

5OC rise in condensing temperature increases 10 % power consumption

5OC rise in evaporating temperature increases 10 % power consumption

ENERGY SAVING MEASURES IN REFRIGERATIONENERGY SAVING MEASURES IN REFRIGERATION

Look for process modifications to reduce the cooling load

Use cooling water to remove the maximum heat before using chilled water

Provide VSD for condenser water pumps

to vary the cooling water flow to maintain 4oC difference across the condensers

Avoid primary pump operation

Normally two pumps are operation

(Chilled water supply pump from cold well and return water pump from hot well)

Modify to operate only return water pump

Provide VSD for efficient part load operation

Explore ‘Ice-bank’ system for Maximum demand reduction

Explore application of vapour absorption with cost economics

Replace old systems with modern energy efficient systems

COLD INSULATIONCOLD INSULATION

Thumb rules for cold InsulationChilled water pipe insulation (Provide 2 to 3 inch thickness) Duct insulation (Provide 1 to 2 inch thickness) Suction line refrigerant pipe insulation(Provide 2 to3 inch thickness)

Difference in temperature

between ambient and surface

Heat ingress

kCal/m2/hr

Exposed area per tonne of refrigeration

5 35 86

10 73 41

15 113 27

20 154 19

Basis: Ambient temperature - 35OC, emissivity – 0.8, still air conditionsAllowable heat ingress – 10 –15 Kcal/m2/hr