1

Energy Conservationin

Air Compressors & Compressed Air System

Confederation Of Indian IndustryEnergy Management Cell

Life Cycle Cost For A Compressor

Energy Cost90%

Initial Cost5%

Maintenance Cost5%

2

Air Compressors

Positive Displacement Type Centrifugal Type

Reciprocating

Vertical Type

(100-500 cfm)

Horizontal Balance Opposed

(200-5000 cfm)

Rotary

Screw(high speed)

Advantage: Intake air can also have some

moisture

Disadvantage: Oil carry over

Radial Flow

Axial Flow

> 12000 cfm

Single Acting, Two Stage Reciprocating Compressor

Trap (Drain)

Receiver

After cooler

Val

v e

Relief valve

Trap (Drain)

Trap (Drain)

Pressure switch

Motor starter Inlet filter

Inter cooler

Motor

*Filter Dryer

3

Why Inter-cooler?

! Compressed air leaves cylinder at high temperature

" Density is lower

" Volumetric η decreases

! Inter cooling reduces temperature & volume

! Mass of air delivered increases

! Inter-cooler generally saves 7 %

Why After-Cooler?How much is the energy savings?

A) Savings same as inter cooler - 7 %

b) Higher than inter cooler

c) Lesser than inter cooler

4

Why After-Cooler?How much is the energy savings?! At higher temperature moisture carry

over very high

! Condensed water moves with same velocity of air

" Damage to instrument valves

" Makes instruments sluggish

! After-cooler saves energy – higher when air dryers are installed

Methodology for Energy Audit

# Is the correct type and size of compressor being used?

# Is the system efficient?

# What is the required operating pressure?

# What is pressure drop between user and compressor?

# Is correct type of dryer used?

5

# Is compressor cooling water monitored?

# Are auto drain valves provided?

# Can compressed air be substituted?

# Are valves provided at the user points?

Methodology for Energy Audit

Optimal Utilisation of CompressorsBackground

37 kW compressor in operation

At present loading - 30%

Unloading - 70%

Power consumption

Unload - 9 kW

Loading - 27 kW

6

Install 15 kW ON/OFF Air Compressor and Use Existing 37 kW Air Compressor as Standby

Action

! Install 15 KW package air compressor

! Saves no-load power

! Use existing compressor as stand-by

Savings - Rs.59,000Investment - Rs.50,000

Payback - 11 monthsRs.

Rs.

# Air requirement - 100 cfm normal running

# In case of yarn breakage, sudden demand of 600 cfm

! Compressor : Screw type

! Capacity : 600 cfm

! Avg. loading : 17%(during normal running)

Optimal Utilisation of Compressors

7

Action

# Installed new air compressor of 125 cfm capacity for normal operation

# When pressure falls in receiver, screw compressor to start automatically

Optimal Utilisation of Compressors

Annual Savings : Rs. 5.99 lakhsInvestment : Rs. 1.50 lakhsPayback period : 3 months

Instrument Air Compressor

(6.5 bar, 570 cfm)Receiver

Refrigerated

type

dryer

Brine Air Compressor

(6.5 bar, 210 cfm) Receiver

Average loading: 60%Load power : 85.2 kWUnload power : 43.5 kW

Average loading: 55%Load power : 33.7 kWUnload power : 15.3 kW

Manage Available Facility Optimally

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# Interconnect the two receivers

# Stop Brine compressor

Manage Available Facility Optimally

Annual Savings : Rs.4.28 lakhsInvestment : Rs.0.02Payback period : < 1 month

Utilise the Correct Type of Compressor

# Battery of screw & reciprocating compressors – 200 kW capacity! 2 Screw Compressors

" One 100% Load " Second 40% Load

! Reciprocating compressor stand by

# Screw compressor operation! Load power = 180 kW (40%)! Unload power = 60 kW (60 %)

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# Reciprocating Compressor Operation

! Load power = 165 kW (40%)

! Unload power = 25 kW (60%)

# Operate Reciprocating Compressor on continuous basis

! Keep Screw as stand by

Utilise the Correct Type of Compressor

Annual Savings = Rs. 4.90 Lakhs

Capacity Test (Pumping Method)

Average Compressor Delivery = . VR .

P1 = Initial pressure in receiver

P2 = Final pressure in receiver

P = Atmospheric pressure

VR = Volume of air receiver

∆t = Time taken for charging the receiver from P1 to P2

P2 - P1 1

P ∆t

10

Comparison of Specific Power Consumption

Reciprocating Centrifugal Screw

FAD

KW 549 521 650Specific Power (kW/m3/min)

4.9 4.65 5.8

112 m3/min (3950 cfm)

Replacement of Inefficient Compressors

# Compressor – Pneumatic Conveying

# Design Specifications! Capacity (FAD) = 20 m3/min

! Pressure = 7.0 kg/cm2

! Motor = 120 kW

# 10 year Old Compressor ! Re-boring carried out

! Overhauling done

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# Capacity Test Conducted

! Actual volume (FAD) = 14.6 m3/min

! Volumetric Efficiency = 73%

! Operating Pressure = 7.0 ksc

! Specific Power = 6.56 kW per m3/min

# Specific Power Norm - 4.9 kW/m3/min for 7.0 ksc

Replacement of Inefficient Compressors

# Energy Saving potential : 25%

# Replaced with New Reciprocating Compressor

Replacement of Inefficient Compressors

Annual savings = Rs. 4.03 LakhsInvestment = Rs.8.00 LakhsPayback period = 24 months

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Segregate High-Pressure & Low-Pressure Compressed Air Users

# Reciprocating Compressors

! 2700 m3/h x 5 nos.

# Compressed Air Generation ! 7000 m3/h @ 7.4 ksc at generation

! Pressure at Receiver – 6.0 ksc

# Major users – Interlacers & Instrumentation

# Requirement! 4400 m3/h @ 4.5 ksc for interlacer

! 2600 m3/h @ 6.5 ksc for instrumentation

Segregate High-Pressure & Low-Pressure Compressed Air Users

# At interlacers – PRV’s installed

! After PRV pressure 2.2 ksc

# Higher volume required at lower pressure

! Total volume at higher pressure

# Energy Inefficient Method - loss due to PRV’s

# Power Consumption α Operating Pressure

# Excellent Potential to Segregate Generation

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Segregate High-Pressure & Low-Pressure Compressed Air Users

# Dedicate 2 compressors for interlacer reqmt.! Operate at 4.5 ksc

! About 34% pressure reduction

# Dedicate 1 compressor for instrumentation

! Operate at the same existing pressure

# Separate lines laid with PLC control system

Annual Savings : Rs.31.86 lakhsInvestment : Rs.8.25 lakhsPayback period : 4 months

VFD - A New Concept

Advantages

# Operates at Lower Avg. Pressure ! Proportional Savings

# No Unloading

# Less Leakages! Lower Pressure

# Better Motor Efficiency

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Concept - Conventional Control

Time

Upper Limit

Lower Limit - Reqd. Pr.

Average Pr.

Pressure

Ksc

6.5

6.0

7.0

Concept - VFD Control

Time

Reqd. Pr.

Pressure

Ksc

{

Savings Due to Pressure Reduction

6.16.0

With VFD6.5

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Savings in Unload Power

# Compressors Designed to meet Fluctuating Load

# Fluctuating Load Leads to Load / Unload

# Lean Time - Unload

# Unload power 15 - 40%

# No useful work

# VSD Avoids Unloading of Compressors

1100

0

1200

1300

1400

1500

12 24

Time

CFM

Reqd

Compressor 4

ReceiverUsers

M

M

M

Compressor 1

Compressor 2

Compressor 3

M

Power In

VSD

PIC6.0 KSC to 7.0 KSC

Case Study

4 Compressors in Operation

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Install VFD for One Compressor

# VFD For One Compressor

# Constant Pressure of 6.0 ksc

# 4% Savings in all compressors

Annual Savings = Rs.12.00 LakhsInvestment = Rs. 12.00 LakhsPayback period = 12 Months

Precautions Reciprocating Compressors

# Lubrication Oil Pump Connected to the same shaft

# Lubrication Pump Output Depends on the Speed

# More than 30% Speed Reduction Leads to Mechanical Problems

Alternative# Install Separate Lubrication Pump# Complicated# Details to be Studied

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Compressed Air Utilisation in a Conventional System

Artificial Demand, 20%

Production, 50%

Poor Practices, 10%

System Losses, 20%

Compressed Air System

Base Demand (kW)

Time

C

F

MArtificial Demand

(rkVA)

Total Demand (kVA)

Reduce Artificial Demand to reduce Total Demand

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606264666870727476788082

PSIG

Compressed Air Pressure Real Time Data

11:05 12:15 13:37 14:36 15:58Time

2

The problem with fluctuating Air Pressure

$ Higher Energy Consumption

$ Increased maintenance costs

$ Higher operating costs

$ Interruptions in production schedules

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Air In Air Out

On Load On Load

C/A BypassedC/A Bypassed

Air Out

PSI

G

Air In

Air In Air Out

On Load Unloaded

Air OutAir In

C/A OnlineC/A Online

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Before Control System

$ Energy Consumed =11,760 kWh/day

$ Main Header Pressure Variances = +/- 13 psig

After Control System

$ Energy Consumed =10,329 kWh/day

$ Main Header Pressure Variances = +/- 1.5 psig

! Total Project Cost = 20 Lakhs! Energy Cost Savings = Rs. 29 Lakhs per annum.! Energy Savings = 2392 kWh/day ( ~ 19 % )! Simple Payback period = Less than 9 months

Case Study: Manufacturing Industry

Install Smart Controller for Air Compressors

160 kW

160 kW

160 kW

Before1768 kW/Day average consumption

95

105

85

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Install Smart Controller for Air Compressors

95

105

85

1429 kW/Day average consumption

AfterSMART

CONTROLLER

160 kW

160 kW

160 kW

Install Smart Controller for Air Compressors

# Energy Savings of @340 kWh/day

# Optimized Pressure of 82 +/-2psig supplied

to the plant

# Full automation of the present Compressor

System

# 18% Energy Savings Achieved

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Install Smart Controller for Air compressors

Advantages

" Steady operating pressure – low bandwidth

" Lesser leakages

" No standby compressor for peak requirement

Annual savings - Rs 12.58 LakhsInvestment - Rs 15.0 LakhsPayback period - 14 Months

Install Smart Controller for Air compressors

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Minimise Leakages

! Common in all industries

! Tricky

! Quantification

God has given abundant air, which is free!!

But … compressed air is not free!!

! Allow compressor to run normally

! Allow compressed air to flow in the system

! Close all the user points

! Measure the loading and unloading time

! Percentage of loading time is percentage of leakages

Quantification

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Leakage Test# Close all user points

# Charge the lines

# Note: On-load time of compressor (T)Off-load time of compressor (t)

# Q : Capacity of compressor

Air leakage : L = . Q

% air leakage = x 100

T

T + t

Air leakage

Compressor capacity

Cost Of Leakage At 7kg/cm2

Orifice dia (mm)

Air Leakage (cfm)

Power Wasted

(kW)

Annual Savings @ Rs.3.50/kWh.

1.6 6.5 1.26 Rs.35,0003.2 26.0 5.04 Rs.1,40,0006.4 104.0 20.19 Rs.4,25,000

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# Calendar - Maintain at Uniform Temp.

! Cool Air (Chilled Water Cooled) Blown

! Additionally, Compressed Air Used

# Compressed Air - Header at 6.0 kg/cm2

! 8 nozzles of ½” size

! Estimated Quantity - 2000 cfm

# Compressor Rating - 1040 cfm x 2 nos.

! Power Drawn - 140 kW each

Compressed Air for Calendar Cooling

Compressed Air for Calendar Cooling

Calendar

8 Points each of ½” dia hoseCompressed air from Mill air header at 6.0 ksc

Cool AIr

Blower AIr

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# For cooling operation

! Volume is the Criteria

! Not Operating Pressure!!

# Compressed air – Energy Intensive

# Specific Power Comparison

! Compressed air = 15 kW/100 cfm

! Blower air = 4 kW/100 cfm

Compressed Air for Calendar Cooling

# Replaced Compd. Air with Blower Air

! New Blower

" Rating - 6000 cfm, 600 mm WC, 15 kW

! Increase Nozzle Size – ½’ to 2”

! Increase Number of Nozzles – 8 to 16

Compressed Air for Calendar Cooling

Annual Savings= Rs.80.00 LakhsInvestment = Rs.2.00 Lakhs

Simple Payback= 1 month

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Replace Compressed Air with Blower Air for Agitation in ETP

# ETP – Agitation Very Important

# Compressed air used in several industries

! Highly energy intensive

# 7 ksc pressure utilised for 8’ depth tank

! Required pressure 0.5 ksc only

! Quantity consumed – 120 cfm

# For Agitation - Quantity is Criteria, Not Pressure!!

# Specific Power Comparison! Compd. air : 15 kW per 100 cfm

! Blower air : 5 kW per 100 cfm

# Replaced with 7.5 kW blower! Capacity - 150 cfm

! Head - 0.5 ksc

Annual Savings : Rs.3.36 lakhsInvestment : Rs.0.50 lakhsPayback period : 2 months

Replace Compressed Air with Blower Air for Agitation in ETP

Compressed Air Line

ETP

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Replace Pneumatic Tools With Electric Tools

Background# Compressed air costlier

! Theoretically - 25% more# In practice much more than that# 40 pneumatic grinders in a plant

Action# Replaced 40 pneumatic grinders

Annual Savings - Rs. 6.50 lakhsInvestment - Rs. 11.00 lakhsPayback period - 21 months

Use Transvector Nozzle In Air Hose

# Sucks atmospheric air along with air jet

# Reduces air consumption by 50%

# Compressed air used for cleaning the burrs

# Provided transvector nozzles at the end users

Compressed Air @ 7.0 KSC

Atmospheric Air

Atmospheric Air

Annual Savings - Rs. 0.48 LakhsInvestment - Rs.0.25 LakhsPayback period - 6 months

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Background

$Compressed air used for cleaning$After every 2 minutes operator has to walk 10 to 15 feet to close

valveAction$Provide a ball valve at the end of the pipe

Savings - Rs. 3.6 lakhs

Install Ball Valves At The User Point To Avoid Compressed Air Wastage

Nozzle pipe

New ball valve to be provided

Compressed air header

Existing ball valve

Compressed Air Dryers

Why Air Dryer?! Water carryover damaging instruments! Possible corrosion of receiver and air lines

Adsorption Type Refrigeration Type

DessicantHeatless Type

DessicantHeated Type

Dessicant Heat of Compression Type

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Heat of Compression (HOC) -Air Dryer

A B

AC1

AC2

100%

Saturated Air Heating

Dry Air (-40oC atmospheric dew point)

Service

After-filter

Heat Of Compression (HOC) -Air Dryer

A

AC1

AC2

100%

Saturated Air Cooling

Dry air (-40oC atmospheric dew point)

After-filter

Service B

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Comparison of Air Dryers

Type of Dryer (cfm) Capital Cost Running Cost

Atmospheric Dew Point oC

Pressure Drop

Best Suitable for

Dessicant Heatless Low High -40 Medium 150Dessicant Heated High Medium -40 High 100-750Dessicant HOC High Very Low -40 High >500Refrigeration Dryer Medium Low -20 Low 100

Replace Dessicant Heater Dryer With HOC Dryer

# Plant had 5 Reciprocating Compressors

!Used for Instrumentation

# Drying by Dessicant Heater dryer

# Dry air requirement - 50 m3/min

# Heater capacity - 32 kW

# Purge air loss - 10% ~ 5m3/min

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Replace Dessicant Heater Dryer With HOC Dryer

Benefits of Replacement

# Heaters eliminated

# No purge air losses

# Required dew point achieved

Annual Savings : Rs. 7.20 lakhsInvestment : Rs. 14.75 lakhsPayback period : 25 months

List Of Energy Saving Ideas In Compressed Air System

! Select correct size air compressor! Operate compressor at required

pressure! Install VFD! Minimise system losses - Proper line

sizing! Replace compressed air with blower air

for agitation ! Replace pneumatic tools with electric

tools

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List Of Energy Saving Ideas In Compressed Air System

! Provide ball valves at the user point to avoid compressed air wastage

! Use transvector nozzles in air hoses

! Cool inlet air to the compressor

! Provide sensors to sense unloading and switch off

! Replace inefficient compressors

! Install high efficiency dryers

Confederation Of Indian IndustryEnergy Management Cell

34

Compressor Layout

Loop header most efficient

! Pressure losses are lesser

! Easier to add/delete user points

Compressor Layout

Loop

Unit loop

35

Compressor Layout..Grid

Unit grid

Factors in Distribution System

Pipe NormalBore (mm)

Pressure Drop(Bar) per 100m

Equivalentpower loss

(kw)

40

50

65

85

100

1.80

0.65

0.22

0.04

0.02

9.5

3.4

1.2

0.2

0.1

Pressure drop in supply line

Air velocity : 6-9 m/s and same flow

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Factors In Distribution System

# Type of valve

! Globe Valves - Very high pressure drop

! Butterfly valve, Gate, Ball valves - Low

pressure drop

# Number of bends & joints to be minimal

© Confederation of Indian Industry

Compressed Air Dryers

Why Air Dryer?$Water carryover damaging instruments$Possible corrosion of receiver and air lines

Adsorption Type Refrigeration Type

DessicantHeatless Type

DessicantHeated Type

Dessicant Heat of Compression Type

37

Air Dryer - Dessicant Heatless Type

A B

100% saturated air(from compressor)

Dry air (to process)

inRegeneration

inService

Purge air (12-15%)(to atmosphere)

Air Dryer - Dessicant Heated Type

HeaterBlower

100% saturated air(from compressor)

Dry air (to process)

Purge

inRegeneration

inService

Purge air (2%)(to atmosphere)

BA

38

Refrigeration Dryer

2oC

17oCAir, 100%

saturated 7 kg/cm2,

28oC

Drain

15oC

Dry air

Refrigeration Unit

Heat of Compression (HOC) -Air Dryer

A B

AC1

AC2

100%

Saturated Air Heating

Dry Air (-40oC atmospheric dew point)

Service

After-filter

39

Heat Of Compression (HOC) -Air Dryer

A

AC1

AC2

100%

Saturated Air Cooling

Dry air (-40oC atmospheric dew point)

After-filter

Service B

© Confederation of Indian Industry

Comparison of Air Dryers

Type of Dryer (cfm) Capital Cost Running Cost Atmospheric Dew Point oC Pressure Drop Best Suitable for

Dessicant Heatless Low High -40 Medium 150Dessicant Heated High Medium -40 High 100-750Dessicant HOC High Very Low -40 High >500Refrigeration Dryer Medium Low -20 Low 100