energy efficiency of industrial utilities

Research Paper

on

Presented by:

Pratap Jung Rai

(065/BIE/047)

Symbol No: 39792

Thapathali Campus, Nepal

11/5/20141

What is Energy Efficiency?An Energy Efficiency/Audit is an inspection, survey and analysis of energy for energy conservation in

an industry, building, process or system to reduce the amount of energy input to the system without

negatively affect the output.

Objectives of Energy Efficiency of Industrial Utilities

To minimize energy waste/costs.

To achieve and maintain optimum energy procurement and

utilization.

Enhance environmental performance and minimize GHG

emissions.

Improve reputation with costumer, public and government

Energy Generation

Industrial Utilities:1) Boiler

2) Furnace

3) Electric Motor

4) Pump

5) Compressor

6) HVAC System

11/5/2014Pratap Jung Rai 2

Types of Energy Audit1) Preliminary Energy Audit

Shortly, called Walk-Through Audit. Its name implies, is a

tour of the facility to visually inspect each of the energy using

systems.

2) Targeted Energy Audit

It often results from preliminary audits. They provide data and

detailed analysis on specified target projects. For example,

industries may target its lighting system or boiler system.

3) Detailed Energy Audit

It is a comprehensive audit and results in a detailed energy

project implementation plan for a facility, since it accounts for

the energy use of all major equipment. Detailed energy

auditing is carried out in three phases

a) Pre-audit Phase

b) Audit Phase

c) Post-Audit

Methodology of Energy Efficiency

Pratap Jung Rai 4 Source: UNEP

1)Boiler

What is a Boiler?

• Enclosed vessel that heats water to become hot water or

steam

• At atmospheric pressure water volume increases 1,600

times

• Hot water or steam used to transfer heat to a process

BURN

ERWATER

SOURCE

Brine

SOFTENERSCHEMICAL

FEED

FUELBLOW DOWN

SEPARATOR

VENT

VENT

EXHAUST GASSTEAM TO

PROCESS

STACK

PUMPS

BOILER

ECO-

NOMI-

ZER

-Poor combustion

-Heat transfer surface fouling

-Poor operation and maintenance

-Deteriorating fuel and water quality

Causes of poor boiler performance


Heat in Steam

BOILER

Heat loss due to dry flue gas

Heat loss due to steam in fuel

gas

Heat loss due to moisture in fuel

Heat loss due to unburnts in residue

Heat loss due to moisture in air

Heat loss due to radiation & other unaccounted loss

12.7 %

8.1 %

1.7 %

0.3 %

1.0 %

100.0 %

Fuel

73.8 %

2.4 %

Heat Balance

Balancing total energy entering a boiler against the energy

that leaves the boiler in different forms

Heat Balance

How energy is transformed from fuel into useful energy,

heat and losses

Avoidable losses include: Stoichiometric

Excess Air

Un burnt

FUEL INPUTSTEAM OUTPUT

Stack Gas

Ash and Un-burnt

parts of Fuel in Ash

Blow

Down

Convection &

Radiation


Energy flow diagram

Boiler Flue gas

Steam Output

Efficiency = 100 – (i + ii + iii + iv + v + vi + vii)

Air

Fuel Input, 100%

i. Dry Flue gas loss

ii. H2 loss

iii. Moisture in fuel

iv. Moisture in air

v. Fly ash loss

vii. Surface loss

vi. Unborn fuel loss

Boiler efficiency () =Heat Input

Heat Output

x 100Q x (hg – hf)

Q x GCVx 100=

Where,Q- Quantity of steam generated kg/hr

hg - Enthalpy of saturated steam in kcal/kg of steam

hf - Enthalpy of feed water in kcal/kg of water

GCV- Gross calorific value kcal/kg

Boiler Efficiency

a) Direct Method (Input output Method)b) Indirect Method

Advantages

• Complete mass and energy balance for each individual

stream

• Makes it easier to identify options to improve boiler

efficiency

Disadvantages• Time consuming

• Requires lab facilities for analysis

Advantages• Quick evaluation

• Few parameters for computation

• Few monitoring instruments

Disadvantages• No explanation of low efficiency

• Various losses not calculated

Efficiency of boiler () = 100 – (i+ii+iii+iv+v+vi+vii)Pratap Jung Rai 7

1.Stack (flue) temperature control• Keep as low as possible

• If >200°C then recover waste heat

2. Feed water preheating using economizers

• Proper economizer can reduce 15-20% fuel

consumption

3. Combustion air pre-heating

• If combustion air raised by 20°C = 1% improve

thermal efficiency

4. Incomplete combustion minimization

• Air shortage, fuel surplus, poor fuel distribution

• Poor mixing of fuel and air

Energy Efficiency Opportunities

5. Excess air control

• 1% excess air reduction = 0.6% efficiency rise

6. Avoid radiation and convection heat loss

• Fixed heat loss from boiler shell, regardless of

boiler output

• Repairing insulation can reduce loss

7. Automatic blow down control

• Sense and respond to boiler water conductivity

and pH

8. Reduction of scaling and soot losses

• Every 22oC increase in stack temperature = 1%

efficiency loss

• 3 mm of soot = 2.5% fuel increase


2) Furnace

What is a Furnace?

Equipment to melt metals

• Casting

• Change shape

• Change properties

Low efficiencies due to

• High operating temperature

• Emission of hot exhaust gases

Furnace Components

Furnace chamber:

constructed of

insulating materials

Hearth: support

or carry the steel.

Consists of

refractory

materials

Burners: raise or

maintain chamber

temperature

Chimney: remove

combustion gases

Charging & discharging doors for

loading & unloading stock

Charging & discharging doors for

loading & unloading stock

Materials that• Withstand high temperatures and sudden changes• Withstand action of molten slag, glass, hot gases• Withstand load at service conditions• Withstand abrasive forces• Conserve heat• Have low coefficient of thermal expansion• Will not contaminate the load

What are Refractories:


Assessment of Furnaces

Fuel Input 100%

Useful heat in

stock

(30-50%)

Wall lo

ss (3 -10%

)

Flue

loss

(20-50

%)

Op

en

ing

loss (1-2

%)

Co

olin

g lo

ss (5-10%

)

Sto

red

he

at (2 -5 %)

Oth

er lo

ss

Recycled heat (10-30%)

Furnace

Parameters

to be

measur

ed

Location of

measurement

Instrument

required

Required

Value

Furnace soaking

zone temperature

(reheating furnaces)

Soaking zone and

side wall

Pt/Pt-Rh thermocouple

with indicator and

recorder

1200-1300oC

Flue gas

temperature

In duct near the

discharge end, and

entry to recuperate

Chromel Alummel

Thermocouple with

indicator

700oC max.

Flue gas

temperature

After recuperate Hg in steel thermometer 300oC (max)

Furnace hearth

pressure in

the heating

zone

Near charging end

and side wall over the

hearth

Low pressure ring gauge +0.1 mm of

Wc

Oxygen in flue gas In duct near the

discharge end

Fuel efficiency monitor for

oxygen and temperature

5% O2

Billet temperature Portable Infrared pyrometer or

optical pyrometer

-

Instruments to Assess Furnace Performance


Energy Losses Areas

Furnace Efficiency

a) Direct Method

Thermal efficiency of furnace = Heat in the stock / Heat in fuel consumed for heating the stockHeat in the stock Q:

Q = m x Cp (t1 – t2) Where,

Q = Quantity of heat of stock in kCal

m = Weight of the stock in kg

Cp= Mean specific heat of stock in kCal/kg ℃t1 = Final temperature of stock in ℃t2 = Initial temperature of the stock before it enters the

furnace in ℃

b) Indirect Method

It is similar to the Boiler indirect efficiency Method

Example:Heat lossesa) Flue gas loss = 57.29 %b) Loss due to moisture in fuel = 1.36 %c) Loss due to H2 in fuel = 9.13 %d) Loss due to openings in furnace = 5.56 %e) Loss through furnace skin = 2.64 %

Total losses = 75.98 %

Furnace efficiency =Heat supply minus total heat loss

Furnace Efficiency = 100% – 76% = 24%


1. Complete combustion with minimum excess air

2. Proper heat distribution

3. Operation at the optimum furnace temperature

4. Reducing heat losses from furnace openings

5. Maintaining correct amount of furnace draft

6. Optimum capacity utilization

7. Waste heat recovery from the flue gases

8. Minimize furnace skin losses

9. Use of ceramic coatings

10. Selecting the right refractories



What is an Electric Motor?

• Electromechanical device that converts

electrical energy to mechanical energy

• Mechanical energy used to e.g.

• Rotate pump impeller, fan, blower

• Drive compressors

• Lift materials

• Motors in industry: 70% of electrical load

3) Electric Motor

Motors loose energy when serving a load

Factors that influence efficiency

Age

Temperature

Load

Rewinding

Capacity

Speed

Type

Efficiency of Electric Motors

11/5/2014Pratap Jung Rai 13 Load

Eff

icie

ncy

Assessment of electric motors

Efficiency of Electric Motors

Motor load is indicator of efficiency

Input power measurement

Ratio input power and rate power at 100% loading

• Three steps for three-phase motors

Step 1. Determine the input power:

Pi = Three Phase power in kW

V = RMS Voltage, mean line to

line of 3 Phases

I = RMS Current, mean of 3

phases

PF = Power factor as Decimal

1000

3xPFxIxVPi

Step 2. Determine the rated power:

• Compare slip at operation with slip at full load

r

r xhpP

7457.0

Where,

Pr = Input Power at Full Rated load

hp = Name plate Rated Horse Power

r = Efficiency at Full Rated Load

Step 3. Determine the percentage load:

• Compare measured amperage with rated

amperage

Where,

Load = Output Power as a % of Rated Power

Pi = Measured Three Phase power in kW

Pr = Input Power at Full Rated load in kW

%100xP

PiLoad

r



1. Use energy efficient motors Efficiency 3-7% higher

Wide range of ratings

More expensive but rapid payback

2. Reduce under-loading (and avoid

over-sized motors)

If motor operates at <50%

Not if motor operates at 60-70%

3. Improve power quality

too high fluctuations in voltage and

frequency

4. Rewinding

sometimes 50% of motors

5. Power factor correction by capacitors Benefits of improved PF

•Reduced kVA

•Improved voltage regulation

Capacitor size not >90% of no-load kVAR of motor

6. Improve maintenance Inspect motors regularly for wear, dirt/dust

Checking motor loads for over/under loading

Lubricate appropriately

Check alignment of motor and equipment

Provide adequate ventilation

7. Speed control of induction motor Variable speed drives (VSDs)

•Reduce electricity by >50% in fans and pumps

•Convert 50Hz incoming power to variable

frequency and voltage: change speed


Assessment of compressors and compressed air systems

Simple Capacity Assessment Method

Where, P2 = Final pressure after filling (kg/cm2a)

P1 = Initial pressure (kg/cm2a) after bleeding)

P0 = Atmospheric pressure (kg/cm2a)

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

delivery piping

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

Compressor Efficiency

Isothermal efficiency

Where,P1 = Absolute intake pressure kg / cm2

Q1 = Free air delivered m3 / hr

r = Pressure ratio P2/P1

Isothermal power (kW) = P1 x Q1 x loge r / 36.7

Isothermal efficiency =

Actual measured input power / Isothermal power

Volumetric efficiency

D = Cylinder bore, meter

L = Cylinder stroke, meter

S = Compressor speed rpm

χ = 1 for single acting and 2 for double acting cylinders

n = No. of cylinders

Volumetric efficiency

= Free air delivered m3/min / Compressor displacement

Compressor displacement = Π x D2/4 x L x S x χ x n


1. Location• Significant influence on energy use

2. Elevation• Higher altitude = lower volumetric efficiency

3. Air Intake• Keep intake air temperature low

• Every 4 oC rise in inlet air temperature = 1%

higher energy consumption

4. Pressure Drops in Air Filter• Install filter in cool location or draw air from cool

location

• Keep pressure drop across intake air filter to a

minimum

Every 250 mm WC pressure drop = 2% higher

energy consumption

5. Use Inter and After Coolers• Inter coolers: heat exchangers that remove heat

between stages

• After coolers: reduce air temperature after final

stage

6. Pressure Settingsa) Reducing delivery pressure

Operating a compressor at 120 PSIG instead of 100

PSIG: 10% less energy and reduced leakage rate

7. Minimizing Leakage• Tighten joints and connections

One pinpoint of compressed air = 60000 IC

8. Condensate Removal• Condensate formed as after-cooler reduces

discharge air temperature

• Install condensate separator trap to remove

condensate



5) HAVC System

High Temperature

Reservoir

Low Temperature

Reservoir

R Work Input

Heat Absorbed

Heat Rejected

Condenser

Evaporator

High

Pressure

Side

Low

Pressure

Side

CompressorExpansion

Device

1 2

3

4

Choice of compressor, design of condenser,

evaporator determined by•Refrigerant

•Required cooling

•Load

•Ease of maintenance

•Physical space requirements

•Availability of utilities (water, power) COP increases with

rising evaporator

temperature (Te)

COP increases with

decreasing condensing

temperature (Tc) 11/5/2014Pratap Jung Rai 18

Assessment of Refrigeration and AC

Assessment of Refrigeration

TR = Q xCp x (Ti – To) / 3024

Q = mass flow rate of coolant in kg/hr

Cp = is coolant specific heat in kCal /kg deg C

Ti = inlet, temperature of coolant to evaporator (chiller) in 0C

To = outlet temperature of coolant from evaporator (chiller) in 0C

Coefficient of Performance (COPCarnot)

•Standard measure of refrigeration efficiency

•Depends on evaporator temperature Te and condensing

temperature Tc:

•COP in industry calculated for type of compressor:

COPCarnot = Te / (Tc - Te)

Cooling effect (kW)COP =

Power input to compressor (kW)

Assessment of Air Conditioning

3024

h h ρ Q TR outin

Measure

• Airflow Q (m3/s) at Fan Coil Units (FCU) or Air

Handling Units (AHU): anemometer

• Air density (kg/m3)

• Dry bulb and wet bulb temperature:

psychrometer

• Enthalpy (kCal/kg) of inlet air (hin) and outlet air

(Hout): psychometric charts

Calculate TR:



1.Optimize process heat exchange

• 1oC raise in Te = 3% power savings

2. Multi-staging systems

• 0.55◦C reduction in returning water from

cooling tower = 3.0 % reduced power

ConditionTe

(0C)

Tc

(0C)

Refrigeration

Capacity* (TR)

Specific

Power

Consumption

(kW/TR)

Increase

kW/TR (%)

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

3. Matching capacity to system load

4. Capacity control of compressors

• continuous modulation through vane control

5. Multi-level refrigeration for plant needs

• Monitor cooling and chiller load: 1 chiller full

load more efficient than 2 chillers at part-load

6. Chilled water storage

Economical because

• Chillers operate during low peak demand

hours: reduced peak demand charges

• Chillers operate at nighttime: reduced

tariffs and improved COP

7. System design features• FRP impellers, film fills, PVC drift eliminators

• Softened water for condensers

• Economic insulation thickness


Thank You


energy efficiency of industrial utilities

Engineering

analysis of energy

energy use

energy wastecosts

energy efficiencyaudit

energy conservation

energy consumption

energy input

detailed energy auditit