Air Compressors

Energy Conservation

in

Air Compressors & Compressed Air System

© Confederation of Indian Industry

Life Cycle Cost For A Compressor

Energy Cost 90%

Initial Cost 5% Maintenance cost 5%


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, 2-Stage Reciprocating Compressor

Trap (Drain)

Receiver

After cooler

Valv

e

Relief valve

Trap (Drain)

Trap (Drain)

Pressure switch

Motor starter Inlet filter

Inter cooler

Motor

*Filter Dryer


Why Inter-cooler?

Compressed air leaves at high temp.

Density is lower

Volumetric 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?

Savings same as inter cooler - 7 %

Higher than inter cooler

Lesser than inter cooler


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 only 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?


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 Compressors

Background

37 kW compressor in operation

At present loading - 30%

Unloading - 70%

Power consumption

Unload - 9 kW

Loading - 27 kW


Action

Install 15 kW package air compressor

Saves no-load power

Use existing compressor as stand-by

Annual Savings - Rs.59,000Investment - Rs.50,000Payback period - 11 months

Rs.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)



Action

Installed new air compressor of 125 cfm

capacity for normal operation

When pressure falls in receiver, screw

compressor to start automatically


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


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 in receiver

t = Time taken for charging receiver from P1 to P2

P2 - P1 1

P t


Comparison of Specific Power Consumption

Reciprocating Centrifugal Screw

FAD

KW 549 521 650

Specific Power (kW/ m3/ min)

4.9 4.65 5.8

112 m3/ min (3950 cfm)


Replacement of Inefficient Compressors

Compressor - Conveying Blended Cement Design Specifications

Capacity (FAD) = 34.32 m3/min Pressure = 5.5 kg/cm2 Motor = 180 kW

Compressor Operated at Lower Pressure Optimized by plant team @ 4.2 ksc (avg.)

5 year Old Compressor Regular Maintenance Conducted Overhauling done


Capacity Test Conducted

Actual volume (FAD) = 31.80 m3/min

Volumetric Efficiency = 92%

Operating Pressure = 4.2 ksc

Specific Power = 5.471 kW per m3/min

Lower Operating Pressure – Lower Specific

Power



Specific Power Norm

4.90 kW/m3/min for 7.0 ksc

3.185 kW/m3/min for 4.2 ksc

Energy Saving potential : 40%

Replaced with New Reciprocating Compressor


Annual savings = Rs. 10.59 LakhsInvestment = Rs.10.00 LakhsPayback period = 12 months


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



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 Operating Pressure

Excellent Potential to Segregate Generation



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 lakhs

Investment : Rs.8.25 lakhs

Payback period : 4 months


Centrifugal Compressor

Energy Efficient

Higher than Reciprocating and Screw

Behavior different from Reciprocating and Screw

Ideal if user demand = Compressor Capacity

Efficient at 60-90% flow range


Centrifugal Compressor – Performance Curve

Volumetric Flow

Dis

ch

arg

e P

ressu

re

Stall/ Choke

Natural Surge Point

Throttled Surge

Natural Curve

Rise to Surge

Surge Line


Capacity Selection

Capacity Sizing – Very Crucial

If Actual Capacity Required < Rated

Capacity

Could end-up in “Surge”

Might lead to Blow-off

Alternatives

Impeller Reduction

Variable Speed Drive


Operating Pressure Operating Pressure – Process Related

If Actual Press. Reqd. < Operating pressure

Could Lead to “Stall or Choke”

Compressor Delivers More Air

Lead to Operation with Recirculation/ Venting

Alternatives

Impeller Reduction

Variable Speed Drive


Conversion of 2-stage Centrifugal Air Compressor to 3-stage

Earlier System

Battery of Compressors

Centrifugal Compressors - 700 HP x 3 nos.

Reciprocating Compressors - 250 HP x 2 nos.

All Compressors in Operation

Centrifugal Compressor – 2-stage



Modified System

Converted All Centrifugal Compressors

2-stage to 3-stage

Same Motor Retained

Only Air end changed

Air end comes along with Inter stage Cooler



Benefits

8 % Savings Achieved Compressor Operation

(3 x 700 HP) - Centrifugal

Stopped Reciprocating Compressors

Annual Savings : Rs. 80.00 Lakhs

Investment : Rs.150.00 Lakhs

Simple Payback: 23 months

Optimising compressed air system

Cooper-12050 cfm

IR-3 (C-15)1520 cfm

IR-2 (C-21) 2160 cfm

IR-1 (C-25)2391 cfm

Cooper-22050 cfm

To receiver

ON OFF ON OFF ON

Typical operation Cooper –1 : 100% load IR-1 (C-25) : 100% load IR-2 (C-15) : Varying load

orIR-3 (C-21)

Majority of time IR-2 (C-15) in operation


Loading of compressors Normal operation times (full load)

C-15/ C-21 on variable load Off peak times

C-15/ C-21 – Unloads Other IR also unloads

Variable load of C-21 Loading - 40% Unloading - 40% Vent - 10% Part load - 10%

Potential to save


Pressure in the common header Normal times : 108-120 psi (Avg. 114 psi) Off-peak times : 118-132 psi (Avg. 125 psi)

Tremendous potential to save power Recommendation

Install new screw (oil free) compressor 1000 cfm capacity with VFD

Benefits Reduction in system pressure (4%)

In all compressors Unloading/ venting totally avoided Stable inlet pressure to intermediate controller


Annual savings = S$ 61000

Est. Investment= s$ 120000

Simple payback = 24 months


606264666870727476788082

PS

IGCompressed Air Pressure

Real Time Data

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

Time

2


The problem with fluctuating Air Pressure

Higher Energy Consumption. Increased maintenance costs. Higher operating costs. Interruptions in production schedules.


Air In Air Out

On Load On Load

C/A BypassedC/A Bypassed

Air Out

PS

IG

Air In


Air In Air Out

On Load Unloaded

Air OutAir In

Control System Control System


Before Control System :Energy Consumed =

11,760 kWh/day

Main Header Pressure Variances = +/- 10 psig

After Control System :

Energy Consumed =10,329 kWh/day

Main Header Pressure Variances = +/- 1.0 psig

Energy Saving = Rs. 29 lakhs

Total Project Cost = Rs. 20 Lakhs

Simple Payback period = 9 months.

Case Study: Automobile Industry


Minimise Leakages

Common in all industries

Tricky

Quantification


Allow compressor to run normally

Allow compressed air to flow in the

system

Close all the user points

Measure the loading and unloading

time

% of loading time is % of leakages

Quantification


Leakage Test

Close all the user points & Charge all the lines

Note the Load time of compressor (T)

and

Unload time of compressor (t)

% air leakage (L) = [T/ (T + t)] x 100 Qty. of leakages = L x Compressor Capacity (Q)


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


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


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


Background

Compressed air used for cleaning Every 2 mins. operator walks 10 to 15 feet to close

valveAction Provide a ball valve at the end of the pipe

Annual Savings - Rs. 3.60 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

Dessicant Heatless

Type

Dessicant Heated Type

Dessicant Heat of Compression

Type


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


Refrigeration Dryer

2oC

17oCAir, 100%

saturated 7 kg/cm2,

28oC

Drain

15oC

Dry air

Refrigeration Unit


Heat of Compression (HOC) Dryer

A B

AC1

AC2

100%

Saturated Air Heating

Dry Air (-40oC atmospheric dew point)

Service

After-filter


Heat Of Compression (HOC) Dryer

A

AC1

AC2

100%

Saturated Air Cooling

Dry air (-40oC atmospheric dew point)

After-filter

Service B


Comparison of Air Dryers

Type of Dryer (cfm) Capital CostRunning

CostAtmospheric 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


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 lakhs

Investment : Rs. 14.75 lakhs

Payback 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


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


Thank you

Documents

Air Compressors