Lecture-4-Singapore.pdf

8/10/2019 Lecture-4-Singapore.pdf

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INTRODUCTION TO ENERGY MANAGEMENT

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Introduction: Why Energy Management?

Energy is essential

Fossil fuel is a finite resource

No alternative energy source is readily available

Environmental impact of energy use

Economic considerations

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Principles of Energy Management

The following general considerations are required in the

energy management process:

More efficient equipment and processes

Energy recovery

Economy in material selection and use

Smoothing energy use patterns

Using alternative energy sources and

Economic evaluation

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Environmental Impact of Energy Use

The world has focussed attention on the need for energy

management and the sustainable use of energy as a result

of :

Continuing evidence to the increased

concentration of Carbon Dioxide in the

atmosphere and its subsequent serious environmental effects

due to global warming.

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The major source of emission is the burning of

fossil fuels, particularly coal and oil. Figure 1 shows the expected build up of

greenhouse gases in the atmosphere under a

number of scenarios .

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WEC: World Energy Counci l

IPPC: Integrated Pollution

Prevention Control

Figure 1: Scenarios of carbon dioxide emissions in the next

century from energy generation for IPPC scenarios IS92a

and WEC scenarios A, B and C.

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WEC scenario A assumes high economic growth especially in

.

WEC-B assumes moderate economic growth.Al l scenarios assume that there wi ll be signi ficant env ironmental and

economic pressures to achieve major improvements in energy

efficiency compared to historic performance;

WEC-C assumes the application of very strong pressure to reduce

emissions in order to combat global warming.7/17

A cut in global emissions by 5.2% below 1990 levels

-

This has lead to the Kyoto protocol in 1997.

The key outcomes of the Kyoto Protocol are summarised

below:

.

Reduct ions of 7% for US, 8% for EU and 6% for

Japan.

The global target is equal to 30% reduction onbusiness-as-usual growth in emissions.

No obligations, either voluntary or legally binding,

on eve op ng coun r es o cu em ss ons.

Protocol to cover all 6 gases, CO2, CH4, N2O, HFCs

(Hydroflurocarbons), PFCs (Perflurocarbons) and

SF6 (Sulfur Hexafluoride).

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Sustainable Energy Technology:

This is defined as the products, processes, practices,

designs and services which:

,

facilitate the utilisation of renewable energy and

implement the production, transmission and use of energy

in ways which minimise the levels of greenhouse gases

and other emissions harmful to the environment.

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Renewable Energy :

One way of reducing greenhouse gas emissions is the

use of renewable energy sources.

not result in damage to the environment.

Sources of renewable energy are:Solar

Wind

Biomass

Hydro

Waves, currents, t idal etc.....

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Non-Renewable Energy :

Non-renewable sources of energy include:

Coal

Oil } Fossil fuels

Gas }

Nuclear

Geothermal

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CO2 Emission :

As an approx imate guide to the level of emissions f rom

conventional fuels, use the following figures:

. 2

1 kWh of electrici ty produces 1 kg CO2

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Energy Conversion:

Energy cannot be created or destroyed.

However, it can be converted from one form to another.

Irreversible processes, which constitute most real

processes, involve some losses of energy in the

conversion process.

This can be summarised in the figure below:

USEFUL

ENERGY OUT

ENERGY IN CONVERSION

PROCESSES

LOSSES

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In order to evaluate how well we are using available

energy in a conversion process, we must consider the

process efficiency:

inEner

outenergyUseful=Efficiency

In order to reduce energy use requirement, we need to

consider one or more of the following:

Improve conversion efficiency

Recover some of the losses by reusing some of

them in the same system or another system.

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Conversion Efficiency of Thermal Systems :

The second law of thermodynamics implies that themaximum possible efficiency is that of a reversible

system (Carnot efficiency). It is given by:

T

1T-

CARNOT

where the temperatures are in degrees KelvinT1source

System

T2sink

This value represents the theoretical maximum limit for

the efficiency.

Real thermal systems have lower efficiency values. 15/17

Example:

Estimate the overall cumulative efficiency for incandescent

and fluorescent lighting, taking in to account energy losses

inStep Efficiency of step

ercentue pro uc on

Fuel transportation

Energy conversion to

electricityTransmission of electricity

Light bulb

Production of coal 96

Transportation of coal 97

Generation ofelectricity

33

Transmission of

electricity

85

Li htin incandescent 5 20,

(fluorescent)

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Reduction of Losses :

In thermal systems this involves:

Reducing lost fuel

Reducing heat losses from the system

The reduction of waste in fuel use during transportation

and filling as well as the reduction of hot or cold fluids

during various operations are subject to normal

considered sound energy management processes.

The reduction of heat losses and energy recovery are the

subject of the next module.

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