Integrated Pollution Prevention and Control Draft ... · Waste Incineration WI ......

Edificio EXPO, c/Inca Garcilaso s/n, E-41092 Sevilla - Spain Telephone: direct line (+34-95) 4488-284, switchboard 4488-318. Fax: 4488-426. Internet: http://eippcb.jrc.es; Email: [email protected]

EUROPEAN COMMISSION DIRECTORATE-GENERAL JRC JOINT RESEARCH CENTRE Institute for Prospective Technological Studies Sustainability in Industry, Energy and Transport European IPPC Bureau

Integrated Pollution Prevention and Control

Draft Reference Document on

Energy Efficiency Techniques Draft April 2006

Measure energy consumptionand production

Review performanceand action plan

Implement energysaving measure

Develop targets

Produce reports to monitor energy use

against output

mailto:[email protected]://eippcb.jrc.es/mailto:[email protected]://eippcb.jrc.es/

This document is one of a series of foreseen documents as below (at the time of writing, not all documents have been drafted):

Reference Documents on Best Available Techniques. Code Large Combustion Plants LCP Mineral Oil and Gas Refineries REF Production of Iron and Steel I&S Ferrous Metals Processing Industry FMP

Non Ferrous Metals Industries NFM Smitheries and Foundries Industry SF Surface Treatment of Metals and Plastics STM Cement and Lime Manufacturing Industries CL Glass Manufacturing Industry GLS Ceramic Manufacturing Industry CER

Large Volume Organic Chemical Industry LVOC Manufacture of Organic Fine Chemicals OFC Production of Polymers POL Chlor Alkali Manufacturing Industry CAK Large Volume Inorganic Chemicals - Ammonia, Acids and Fertilisers Industries LVIC-AAF Large Volume Inorganic Chemicals - Solid and Others industry LVIC-S

Production of Speciality Inorganic Chemicals SIC Common Waste Water and Waste Gas Treatment/Management Systems in the Chemical Sector CWW Waste Treatments Industries WT Waste Incineration WI Management of Tailings and Waste-Rock in Mining Activities MTWR Pulp and Paper Industry PP

Textiles Industry TXT Tanning of Hides and Skins TAN

Slaughterhouses and Animals By-products Industries SA

Food, Drink and Milk Industries FDM Intensive Rearing of Poultry and Pigs ILF Surface Treatment Using Organic Solvents STS

Industrial Cooling Systems CV Emissions from Storage ESB

Reference Documents.

General Principles of Monitoring MON Economics and Cross-Media Effects ECM

Energy Efficiency Techniques ENE

Executive Summary

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EXECUTIVE SUMMARY

To be written upon completion of the whole document.

Preface

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PREFACE

1. Status of this document Unless otherwise stated, references to the Directive in this document means the Council Directive 96/61/EC as amended by Directive 2003/87/EC on integrated pollution prevention and control. As the Directive applies without prejudice to Community provisions on health and safety at the workplace or any energy efficiency provisions, so does this document. This document is a working draft of the European IPPC Bureau. It is not an official publication of the European Communities and does not necessarily reflect the position of the European Commission.

2. The mandate of the work The mandate for this document is threefold: a) to implement a special request from the Commission Communication on the

implementation of the European Climate Change Programme (COM(2001)580 final) ECCP concerning energy efficiency in industrial installations. The ECCP asks that effective implementation of the energy efficiency provisions of the IPPC Directive are promoted and that a special horizontal BREF addressing generic energy efficiency techniques is prepared,

b) gives general guidance to operators and regulators on how to approach and implement

energy efficiency requirements set out in the IPPC Directive, and c) be one of several measures foreseen in the European Climate Change Programme aimed at

reducing the emissions of greenhouse gases. This document on energy efficiency has links to other Commission instruments, e.g. the following actions have an interface with this document: Green Paper on Energy Efficiency COM(2005)265 final of 22 June 2005 Directive on greenhouse gas emission trading (2003/87/EC) Directive on the promotion of cogeneration (2004/8/EC) Directive on the energy performance of buildings (2002/91/EC) proposal on energy end-use energy efficiency and energy services COM(2003)739 the framework Directive for the setting of eco-design requirements for energy using

products, EuP (2005/32/EC) an Energy Efficiency Toolkit for SMEs developed in the framework of the EMAS

Regulation several studies and projects under the umbrella Intelligent Energy Europe and SAVE,

which deal with energy efficiency in buildings and industry.

3. Relevant legal obligations of the IPPC Directive and the definition of BAT In order to help the reader understand the legal context in which this document has been drafted, some of the most relevant provisions of the IPPC Directive, including the definition of the term best available techniques, are described in this preface. This description is inevitably incomplete and is given for information only. It has no legal value and does not in any way alter or prejudice the actual provisions of the Directive.

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The purpose of the Directive is to achieve integrated prevention and control of pollution arising from the activities listed in its Annex I, leading to a high level of protection of the environment as a whole including energy efficiency. The legal basis of the Directive relates to environmental protection. Its implementation should also take account of other Community objectives such as the competitiveness of the Communitys industry thereby contributing to sustainable development. More specifically, it provides for a permitting system for certain categories of industrial installations requiring both operators and regulators to take an integrated, overall look at the polluting and consuming potential of the installation. The overall aim of such an integrated approach must be to improve the management and control of industrial processes so as to ensure a high level of protection for the environment as a whole. Central to this approach is the general principle given in Article 3 that operators should take all appropriate preventative measures against pollution, in particular through the application of best available techniques enabling them to improve their environmental performance including energy efficiency. Competent authorities responsible for issuing permits are required to take account of the general principles set out in Article 3 when determining the conditions of the permit. These conditions must include emission limit values, supplemented or replaced where appropriate by equivalent parameters or technical measures. According to Article 9(4) of the Directive, these emission limit values, equivalent parameters and technical measures must, without prejudice to compliance with environmental quality standards, be based on the best available techniques, without prescribing the use of any technique or specific technology, but taking into account the technical characteristics of the installation concerned, its geographical location and the local environmental conditions. In all circumstances, the conditions of the permit must include provisions on the minimisation of long-distance or transboundary pollution and must ensure a high level of protection for the environment as a whole. Member States have the obligation, according to Article 11 of the Directive, to ensure that competent authorities follow or are informed of developments in best available techniques.

4. The IPPC Directive and energy efficiency Energy efficiency is not restricted to any one industry sector mentioned in Annex 1 to the Directive as such, but is a horizontal issue which is required to be taken into account in all cases. In the Directive there are indirect and direct references in energy efficiency in the following articles, which will then be explained: 2.11 definition of BAT, indirect reference Annex IV, considerations included in BAT, direct reference. This Directive requires that permits must contain conditions based on Best Available Techniques (BAT) as defined in Article 2.11 of the Directive, to achieve a high level of protection of the environment as a whole. A high level of protection means that in issuing the installations permits the regulators have to consider all environmental effects caused by the installation including the effects of energy use. Article 2.11 of the Directive specifies BAT in the following way: Best shall mean most effective in achieving a high general level of protection of the environment as a whole; Available techniques shall mean those developed on a scale which allows implementation in the relevant industrial sector, under economically and technically viable conditions, taking into consideration the costs and advantages, whether or not the techniques are used or produced inside the Member State in question, as long as they are reasonably accessible to the operator;

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Techniques shall include both the technology used and the way in which the installation is designed, built, maintained, operated and decommissioned Furthermore, Annex IV specifies what considerations must be taken into account generally or in specific cases when determining best available techniques, as defined in Article 2 (11), bearing in mind the likely costs and benefits of a measure and the principles of precaution and prevention. The references to energy efficiency in the IPPC Directive are: a) Annex IV. One of the issues to be taken into account is the consumption and nature of raw

materials (including water) used in the process and their energy efficiency (item 9).b) Article 3 (d), direct reference. The Directive requires that Member States shall take the

necessary measures to provide that the competent authorities ensure that installations are operated in such a way that, among other things, energy is used efficiently (Article 3 (d)).

c) Article 6.1, direct reference. In Article 6 it is said that Member States shall take the necessary measures to ensure that an application to the competent authority for a permit includes a description of the raw and auxiliary materials, other substances and the energy used in, or generated by, the installation.

d) Article 9.1, indirect reference. In Article 9.1 concerning conditions of the permit, it is stipulated that Member States shall ensure that the permit includes all measures necessary for compliance with the requirements of Articles 3 and 10.

e) Article 9.3, direct reference (amendment). In Article 9.3 (amendments by Directive 2003/87/EC) concerning limit values, it is stipulated that IPPC-permit shall not include an emission value for direct emissions of that gas, meaning greenhouse gases specified in Annex 1 to Directive 87/2003.

Furthermore, it is stipulated that for activities listed in Annex 1 to Directive 2003/87/EC, Member States may choose not to impose requirements relating to energy efficiency in respect of combustion units or other units emitting carbon dioxide on the site. Directive 2003/87/EC covers some but not all, activities covered by the IPPC Directive. This document gives general advice how to implement those requirements.

5. Objective of this document Article 16(2) of the Directive requires the Commission to organise an exchange of information between Member States and the industries concerned on best available techniques, associated monitoring and developments in them, and to publish the results of the exchange.

The purpose of the information exchange is given in recital 25 of the Directive, which states that the development and exchange of information at Community level about best available techniques will help to redress the technological imbalances in the Community, will promote the worldwide dissemination of limit values and techniques used in the Community and will help the Member States in the efficient implementation of this Directive. The Commission (Environment DG) established an information exchange forum (IEF) to assist the work under Article 16(2) and a number of technical working groups have been established under the umbrella of the IEF. Both IEF and the technical working groups include representation from Member States and industry as required in Article 16(2).

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The aim of this series of documents is to reflect accurately the exchange of information which has taken place as required by Article 16(2) and to provide reference information for the permitting authority to take into account when determining permit conditions. By providing relevant information concerning best available techniques, these documents should act as valuable tools to drive environmental performance including energy efficiency. The special target of this document is to provide a comprehensive energy management structure which makes it possible for companies to demonstrate their energy efficiency and competent authorities to verify it. This general structure will later be tailored for different sectors in sectoral BREFs. The background and mandate of this work concerning generic energy efficiency techniques for industry differs from other BREFs in the sense that this document is prepared in the IPPC context but it can be used in a broader scope.

6. Information Sources This document represents a summary of information collected from a number of sources, including in particular the expertise of the groups established to assist the Commission in its work, and verified by the Commission services. All contributions are gratefully acknowledged.

7. How to understand and use this document The information provided in this document is intended to be used as an input to the recommendations for good/best practices to contribute energy efficiency in IPPC installations. When determining BAT and setting BAT-based permit conditions, account should always be taken of the overall goal to achieve a high level of protection for the environment as a whole including energy efficiency. The rest of this section describes the type of information that is provided in each section of this document. Chapter 1 provides general information on the basics of energy and thermodynamics. It explains main features of energy and principles of thermodynamics as an introduction for understanding energy applications in industry and their restrictions. Chapter 2 provides information on the definitions of energy efficiency relevant for industry and how to develop indicators to monitor energy efficiency. Furthermore, it deals with different aspects which influence energy efficiency, some of them which company has control and some of them not. It also gives examples how different system boundaries influence the energy efficiency. Chapter 3 provides information on good energy management in industrial installations in broad terms. It explains why good structured management is important and which issues will be considered and taken into account in a good system. It covers the elements which are crucial to manage energy issues efficiently both from an environmental and economical point of view. It gives examples of good management structures, approaches, audits, methodologies and other tools which could be implemented to improve energy efficiency. Systematic and transparent way to deal with energy issues is essential to reach best economical and environmental results. Chapter 4 provides information on generic energy producing and using systems and unit operations which can be found in several industries. It describes energy saving techniques related to these systems (e.g. steam system) and unit operations (e.g. motors). The approach is to describe different strategies to improve energy efficiency in these systems and also describe commonly used energy saving techniques (e.g. heat recovery) separately.

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Chapter 5 recommends the best practices to be used in companies to manage energy issues. Since the best available techniques change over time, this document will be reviewed and updated as appropriate. All comments and suggestions should be made to the European IPPC Bureau at the Institute for Prospective Technological Studies at the following address:

Edificio Expo, c/Inca Garcilaso, s/n, E-41092 Sevilla, Spain Telephone: +34 95 4488 284 Fax: +34 95 4488 426 e-mail: [email protected] Internet: http://eippcb.jrc.es

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Best Available Techniques Reference Document on ENERGY EFFICIENCY TECHNIQUES

EXECUTIVE SUMMARY.........................................................................................................................I PREFACE................................................................................................................................................ III SCOPE ................................................................................................................................................. XVII 1 GENERAL FEATURES ON ENERGY .......................................................................................... 1

1.1 Introduction................................................................................................................... 1 1.1.1 Forms of energy ..................................................................................................................... 1 1.1.2 Energy transfer and storage .................................................................................................... 2 1.1.3 Energy losses.......................................................................................................................... 3 1.1.4 Exergy .................................................................................................................................... 3

1.2 Principles of thermodynamics....................................................................................... 4 1.2.1 Characterisation of systems and processes............................................................................. 4 1.2.2 Forms of energy storage and transfer ..................................................................................... 4 1.2.3 Properties: enthalpy and specific heat .................................................................................... 5 1.2.4 Properties: entropy and exergy............................................................................................... 6

1.3 First and second laws of thermodynamics .................................................................... 7 1.3.1 First law of thermodynamics energy balance ...................................................................... 7

1.3.1.1 Energy balance for closed systems ...............................................................................................7 1.3.1.2 Energy balance for open systems..................................................................................................7 1.3.1.3 Calculation of internal energy and enthalpy changes....................................................................8 1.3.1.4 First law efficiencies: thermal efficiency and coefficient of performance ....................................8

1.3.2 Second law of thermodynamics - entropy balance ................................................................. 9 1.3.3 Combination of the first and second laws - exergy balance ................................................. 10

1.3.3.1 Exergy balance for a closed system ............................................................................................10 1.3.3.2 Exergy balance for an open system.............................................................................................10 1.3.3.3 Calculation of flow exergy changes............................................................................................11 1.3.3.4 Second law efficiency: exergetic efficiency................................................................................11

1.4 Property diagrams, tables, databanks and computer programs ................................... 12 1.4.1 Pressure-temperature diagram .............................................................................................. 12 1.4.2 Pressure-specific volume and temperature-specific volume diagrams ................................. 13 1.4.3 Temperature-entropy diagram .............................................................................................. 14 1.4.4 Enthalpy-entropy diagram.................................................................................................... 15 1.4.5 Property tables, databanks and simulation programs............................................................ 15

1.5 Identification of inefficiencies .................................................................................... 16 1.5.1 Case 1. Throttling devices .................................................................................................... 17 1.5.2 Case 2. Heat exchangers....................................................................................................... 19 1.5.3 Case 3. Mixing processes ..................................................................................................... 21

2 ENERGY EFFICIENCY ................................................................................................................ 27 2.1 Definitions of energy efficiency ................................................................................. 27 2.2 Energy efficiency indicators in industry ..................................................................... 28

2.2.1 Production processes ............................................................................................................ 29 2.2.2 Energy intensity factor and energy efficiency index ............................................................ 29 2.2.3 Energy efficiency in production units .................................................................................. 30 2.2.4 Energy efficiency of a site .................................................................................................... 34

2.3 Issues to be considered when defining energy efficiency indicators .......................... 35 2.3.1 System boundaries................................................................................................................ 35

2.3.1.1 Definition of the system boundary..............................................................................................35 2.3.1.2 Examples of system boundaries..................................................................................................36 2.3.1.3 Some remarks on system boundaries ..........................................................................................40

2.3.2 Other items to be decided by the company........................................................................... 41 2.3.3 Structural issues.................................................................................................................... 45

2.4 Examples of application of energy efficiency............................................................. 48 2.4.1 Mineral oil refineries ............................................................................................................ 48 2.4.2 Ethylene cracker ................................................................................................................... 49 2.4.3 VAM production .................................................................................................................. 50 2.4.4 A rolling mill in a steel works .............................................................................................. 51 2.4.5 Heating of premises.............................................................................................................. 53

3 ENERGY MANAGEMENT IN INDUSTRIAL INSTALLATIONS.......................................... 55 3.1 The structure and the content of energy management ................................................ 55

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3.1.1 General features and factors ................................................................................................. 55 3.1.2 Commitment of the top management ................................................................................... 58 3.1.3 Planning................................................................................................................................ 59

3.1.3.1 Initial energy audit ......................................................................................................................59 3.1.3.2 Energy performance targets ........................................................................................................60 3.1.3.3 Action plan .................................................................................................................................61

3.1.4 Doing.................................................................................................................................... 61 3.1.4.1 Structures and responsibilities ....................................................................................................62 3.1.4.2 Awareness raising and capacity building....................................................................................62 3.1.4.3 Communication and motivation..................................................................................................63

3.1.5 Checking............................................................................................................................... 63 3.1.5.1 Monitoring and measurement .....................................................................................................63 3.1.5.2 Records .......................................................................................................................................64 3.1.5.3 Periodic energy audits.................................................................................................................64

3.1.6 Acting................................................................................................................................... 64 3.1.7 Examples of energy management systems and its implementation...................................... 65

3.2 Methodologies and tools for energy use optimisation and energy efficiency............. 65 3.2.1 Energy audits........................................................................................................................ 65

3.2.1.1 Audit models...............................................................................................................................66 3.2.1.1.1 The scanning models..............................................................................................................67 3.2.1.1.2 The analysing models.............................................................................................................68 3.2.1.1.3 The technical coverage of energy audit models .....................................................................69

3.2.1.2 Audit tools ..................................................................................................................................71 3.2.2 Energy monitoring................................................................................................................ 72 3.2.3 Energy models...................................................................................................................... 73

3.2.3.1 Example 1. Electric energy models.............................................................................................74 3.2.3.2 Example 2. Thermal energy models............................................................................................77 3.2.3.3 Energy diagnosis using the energy models .................................................................................79

3.2.4 Pinch methodology............................................................................................................... 81 3.2.5 Benchmarking ...................................................................................................................... 84 3.2.6 Assessment methods............................................................................................................. 88

3.2.6.1 Time series comparison ..............................................................................................................88 3.2.6.2 Comparison with theoretical approaches ....................................................................................89 3.2.6.3 Benchmarks approaches..............................................................................................................90

3.2.7 Qualification of components in representative conditions ................................................... 91 3.2.8 Cost calculations .................................................................................................................. 93 3.2.9 Checklists ............................................................................................................................. 93 3.2.10 Good housekeeping.......................................................................................................... 93 3.2.11 E-learning......................................................................................................................... 93

3.3 Energy services company (ESCO) concept ................................................................ 93 3.4 Public schemes and tools to motivate energy saving in industry................................ 94

3.4.1 Tax deductions for energy saving investments..................................................................... 94 3.4.2 Ecology premium ................................................................................................................. 95 3.4.3 Support for demonstration projects in energy technology.................................................... 96 3.4.4 Cogeneration certificates (blue certificates) ......................................................................... 96 3.4.5 Energy planning regulation .................................................................................................. 97 3.4.6 Benchmarking covenant ....................................................................................................... 98 3.4.7 Audit covenant ..................................................................................................................... 99 3.4.8 Energy saving certificates (white certificates).................................................................... 100 3.4.9 EMAT - energy managers tool.......................................................................................... 102 3.4.10 Energy saving agreements ............................................................................................. 103

4 APPLIED ENERGY SAVING TECHNIQUES.......................................................................... 105 4.1 Introduction............................................................................................................... 105 4.2 Combustion ............................................................................................................... 106

4.2.1 Choice of combustion techniques....................................................................................... 106 4.2.2 Strategies to decrease losses in general .............................................................................. 107 4.2.3 High temperature air combustion technology (HiTAC) ..................................................... 111

4.3 Steam systems........................................................................................................... 114 4.3.1 General features of steam ................................................................................................... 115 4.3.2 Measures to improve steam system performance ............................................................... 117 4.3.3 Use of economisers to preheat feed-water.......................................................................... 119 4.3.4 Prevention removal of scale deposits on heat transfer surfaces.......................................... 120 4.3.5 Minimising blowdown ....................................................................................................... 122 4.3.6 Recovering heat from the boiler blowdown ....................................................................... 124

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4.3.7 Implementing a control and repairing programme for steam traps..................................... 126 4.3.8 Collecting and returning condensate to the boiler for re-use.............................................. 128 4.3.9 Re-use of flash steam ......................................................................................................... 130 4.3.10 Insulation on steam pipes and condensate return pipes.................................................. 131 4.3.11 Installation of removable insulating pads on valves and fittings ................................... 132 4.3.12 Use of flash steam on the premises through recovery of condensate at low pressure.... 133 4.3.13 Installing an air preheater............................................................................................... 134 4.3.14 Minimising boiler short cycling losses .......................................................................... 136

4.4 Power production ...................................................................................................... 137 4.5 Cogeneration ............................................................................................................. 138

4.5.1 Different types of cogeneration .......................................................................................... 138 4.5.2 CHP in soda ash plants ....................................................................................................... 144 4.5.3 Stationary reciprocating engine solutions........................................................................... 145 4.5.4 Trigeneration ...................................................................................................................... 148 4.5.5 District cooling................................................................................................................... 151

4.6 Waste heat recovery.................................................................................................. 154 4.6.1 Direct heat recovery ........................................................................................................... 155 4.6.2 Heat pumps......................................................................................................................... 157 4.6.3 Surplus heat recovery at a board mill ................................................................................. 161 4.6.4 Mechanical vapour recompression (MVR) ........................................................................ 163 4.6.5 Acid cleaning of heat exchangers....................................................................................... 166 4.6.6 Heat exchangers with flashed steam - design ..................................................................... 168

4.7 Electric motor driven systems................................................................................... 171 4.8 Compressed air systems ............................................................................................ 177

4.8.1 General description............................................................................................................. 177 4.8.2 Improvement of full load/no load regulation system.......................................................... 181 4.8.3 Variable speed drive technology (VSD)............................................................................. 182 4.8.4 Optimising the pressure level ............................................................................................. 184 4.8.5 Reducing leakages.............................................................................................................. 186

4.9 Pumping systems ...................................................................................................... 187 4.9.1 General description............................................................................................................. 187 4.9.2 Choice between steam turbine driven pumps and electrical pumps ................................... 188 4.9.3 Vacuum pumps replacing steam ejectors ........................................................................... 192

4.10 Drying systems.......................................................................................................... 193 4.10.1 General description ........................................................................................................ 193 4.10.2 Techniques to reduce energy consumption .................................................................... 195

4.10.2.1 Mechanical processes ...............................................................................................................195 4.10.2.2 Computer-aided process control/process automation................................................................195 4.10.2.3 Selecting the optimum drying technology ................................................................................196

4.11 Process control systems ............................................................................................ 196 4.11.1 General features ............................................................................................................. 196 4.11.2 Energy management and optimisation software tools.................................................... 200 4.11.3 Energy management for paper mills .............................................................................. 201 4.11.4 Fluidised bed boiler combustion optimisation ............................................................... 204 4.11.5 Steam production and utilisation optimisation using a model predictive controller ...... 205

4.12 Transport systems ..................................................................................................... 207 4.13 Energy storage .......................................................................................................... 211

5 BEST PRACTICES....................................................................................................................... 213 5.1 Generic best practices ............................................................................................... 214 5.2 Energy efficiency indicators ..................................................................................... 214 5.3 Energy management structure and tools ................................................................... 215 5.4 Techniques to improve energy efficiency................................................................. 216

5.4.1 Combustion ........................................................................................................................ 216 5.4.2 Steam systems .................................................................................................................... 217 5.4.3 Cogeneration ...................................................................................................................... 217 5.4.4 Heat recovery ..................................................................................................................... 218 5.4.5 Electric motor drive systems .............................................................................................. 218 5.4.6 Compressed air systems ..................................................................................................... 219 5.4.7 Pumping systems................................................................................................................ 219 5.4.8 Drying systems................................................................................................................... 219 5.4.9 Transport systems............................................................................................................... 219

6 CONCLUDING REMARKS........................................................................................................ 221

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7 REFERENCES .............................................................................................................................. 223 8 GLOSSARY ................................................................................................................................... 227 9 ANNEXES...................................................................................................................................... 233

9.1 Annex 1..................................................................................................................... 233

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List of figures Figure 1.1: Pressure-temperature diagram ................................................................................................. 12 Figure 1.2: P-v diagram.............................................................................................................................. 13 Figure 1.3: T-v diagram.............................................................................................................................. 14 Figure 1.4: Temperature-entropy diagram ................................................................................................. 14 Figure 1.5: Enthalpy-entropy diagram ....................................................................................................... 15 Figure 1.6: Steam throttling process........................................................................................................... 18 Figure 1.7: T-s and h-s diagrams for the steam throttling process of the example..................................... 18 Figure 1.8: Counterflow heat exchanger .................................................................................................... 20 Figure 1.9: Reheating process of a steam flow........................................................................................... 20 Figure 1.10: T-s and h-s diagram for the steam reheating process of the example .................................... 21 Figure 1.11: Ii/RT0 versus molar fraction of one component in the mixture .............................................. 22 Figure 1.12: Mixing chamber of two flows................................................................................................ 23 Figure 1.13: T-s diagram for the mixing process of the example............................................................... 24 Figure 2.1: Energy vectors in a simple production unit. ............................................................................ 30 Figure 2.2: Energy vectors in a production unit. ........................................................................................ 32 Figure 2.3: Inputs and outputs in a site ...................................................................................................... 34 Figure 2.4: System boundary old electric motor ..................................................................................... 36 Figure 2.5: System boundary new electric motor.................................................................................... 37 Figure 2.6: System boundary electric motor + old pump. ....................................................................... 37 Figure 2.7: System boundary electric motor + new pump ...................................................................... 38 Figure 2.8: Electric motor + new pump with constant output .................................................................... 38 Figure 2.9: New electric motor, new pump and old heat exchanger .......................................................... 39 Figure 2.10: New electric motor, new pump and two heat exchangers...................................................... 40 Figure 2.11: Inputs and outputs for a vinyl acetate monomer (VAM) plant .............................................. 50 Figure 2.12: Flow chart of a rolling mill .................................................................................................... 51 Figure 2.13: Specific energy consumption in a rolling mill ....................................................................... 52 Figure 2.14: Specific energy consumption in a rolling mill ....................................................................... 53 Figure 2.15: Energy consumption depending on outdoor temperature ...................................................... 53 Figure 2.16: Energy consumption depending on outdoor temperature ...................................................... 54 Figure 3.1: The plan-do-check-act-cycle (PDCA) ..................................................................................... 57 Figure 3.2: Continuous improvement of an energy management system................................................... 57 Figure 3.3: Basic energy auditing models .................................................................................................. 66 Figure 3.4: The properties of energy audit models..................................................................................... 66 Figure 3.5: Coverage of an industrial site energy audit.............................................................................. 69 Figure 3.6: Coverage of a district heating connected to a residential building energy audit...................... 70 Figure 3.7: Coverage of a CHP plant energy audit .................................................................................... 70 Figure 3.8: Structure of a monitoring system............................................................................................. 72 Figure 3.9: Monitoring process .................................................................................................................. 73 Figure 3.10: Power factor of a device depending on the load factor .......................................................... 75 Figure 3.11: Scheme of energy diagnosis................................................................................................... 80 Figure 3.12: Hot and cold streams in Pinch methodology ......................................................................... 81 Figure 3.13: Energy savings identified by pinch methodology.................................................................. 83 Figure 3.14: Mechanism when an ESCO is involved............................................................................... 100 Figure 4.1: Energy balance of a combustion installation ......................................................................... 107 Figure 4.2: Working principle for regenerative burners........................................................................... 111 Figure 4.3: Different regions of combustion ............................................................................................ 112 Figure 4.4: The net heat output of test furnaces resulted by both conventional and HiTAC burners....... 113 Figure 4.5: Distribution of the energy content of steam in the sensible and latent component depending on

absolute pressure................................................................................................................ 116 Figure 4.6: Back-pressure plant ............................................................................................................... 139 Figure 4.7: Extraction condensing plant................................................................................................... 139 Figure 4.8: Gas turbine heat recovery boiler ............................................................................................ 140 Figure 4.9: Combined cycle power plant ................................................................................................. 140 Figure 4.10: Reciprocating plant .............................................................................................................. 141 Figure 4.11: Comparison between efficiency of condensing power and combined heat and power plant142 Figure 4.12: Trigeneration compared to separate energy production....................................................... 148 Figure 4.13: Trigeneration enables optimised plant operation around the year ....................................... 149 Figure 4.14: District cooling in the winter by free cooling technology.................................................... 152 Figure 4.15: District cooling by absoption technology in the summer..................................................... 152 Figure 4.16: Diagram of a compression heat pump.................................................................................. 158 Figure 4.17: Diagram of an absorption heat pump................................................................................... 159

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Figure 4.18: Heat recovery system connected to the district heating system ........................................... 162 Figure 4.19: Simple MVR installation ..................................................................................................... 163 Figure 4.20: COP versus temperature lift for a typical MVR system ...................................................... 164 Figure 4.21: Process scheme of Eurallumina alumina refinery................................................................ 166 Figure 4.22: Operative cycle of heaters.................................................................................................... 167 Figure 4.23: A section of the heater ......................................................................................................... 169 Figure 4.24: Scales in the tube bundle ..................................................................................................... 170 Figure 4.25: A compressor motor with a rated output of 24 MW ............................................................ 173 Figure 4.26: Some methods of capacity control of a centrifugal pump.................................................... 175 Figure 4.27: Performance of compressors with different controls ........................................................... 175 Figure 4.28: Pump power consumption ................................................................................................... 176 Figure 4.29: Fans with different controls ................................................................................................. 176 Figure 4.30: Compressed air system ........................................................................................................ 178 Figure 4.31: Energy flow diagram for an inefficient compressed air station ............................................ 179 Figure 4.32: Compressor lifecycle costs .................................................................................................. 183 Figure 4.33: Different kinds of compressor control ................................................................................. 184 Figure 4.34: Steam distribution scheme of the alumina refinery.............................................................. 189 Figure 4.35: Bandwidths for the specific secondary energy consumption of different types of dryer when

vaporising water ................................................................................................................ 194 Figure 4.36: Structure of an energy management tool ............................................................................. 200 Figure 4.37: Paper mill energy management (system layout) .................................................................. 202 Figure 4.38: Tracking deviations from optimum consumption ................................................................ 202 Figure 4.39: Steam flow depending on fuel and time............................................................................... 204 Figure 4.40: Variable definition matrix.................................................................................................... 206

Scope

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List of tables Table 1.1: Some values of the derivatives.................................................................................................. 22 Table 1.2: Maximum values for mistures................................................................................................... 23 Table 3.1: Energy management matrix ...................................................................................................... 56 Table 3.2: A simple electric model ............................................................................................................ 75 Table 3.3. Data ina thermal energy model (generators side) ...................................................................... 77 Table 3.4. Data in a thermal energy model (users side) ............................................................................. 78 Table 3.5: Steps in Pinch methodology...................................................................................................... 82 Table 3.6: Information template for energy efficiency motivation tools.................................................... 94 Table 3.7: Areas covered in the application ............................................................................................. 102 Table 4.1: The template for information on energy efficiency techniques............................................... 105 Table 4.2. Higher and lower calorific values of certain fuels................................................................... 107 Table 4.3: Differences in heat transfer ..................................................................................................... 121 Table 4.4: Energy content of blowdown .................................................................................................. 123 Table 4.5: Recovered energy from blowdown losses............................................................................... 125 Table 4.6: Various operating phases of steam traps ................................................................................. 126 Table 4.7: Operating factors for steam losses in steam traps ................................................................... 127 Table 4.8: Load factor for steam losses.................................................................................................... 127 Table 4.9: Percentage of total energy present in the condensate at atmospheric pressure and flash steam

........................................................................................................................................... 129 Table 4.10: Percentage of total energy present in the condensate at atmospheric pressure and flash steam

........................................................................................................................................... 130 Table 4.11: Heat losses per metre of pipes in function of the operating temperature and insulation

thickness ............................................................................................................................ 132 Table 4.12: Calculation of the Siegert Co-efficient for different types of fuel......................................... 135 Table 4.13: Technical data for the Barajas Airport trigeneration plant .................................................... 151 Table 4.14: Components of an electric motor drive system ..................................................................... 171 Table 4.15: Possible energy saving measures in compressed air systems................................................ 180 Table 4.16 Leakage costs ......................................................................................................................... 186 Table 9.1: Saturated water properties....................................................................................................... 234 Table 9.2: Superheated water properties I................................................................................................ 235 Table 9.3: Superheated water properties II............................................................................................... 236

Scope

SS/EIPPCB/ENE_Draft_1 Version April 2006 xvii

SCOPE This document together with other BREFs in the series (see list on the reverse of the title page), are intended to cover the energy efficiency issues under IPPC Directive. This document also responds to the special request from the Commission Communication on the implementation of the European Climate Change Programme (COM(2001)580 final) ECCP concerning energy efficiency in industrial installations. The ECCP asks that effective implementation of the energy efficiency provisions of the IPPC Directive are promoted and that a special horizontal BREF addressing generic energy efficiency techniques is prepared. The target of this document is to provide information on how to improve energy efficiency in industrial installations by giving generic guidance on how to approach, assess, implement and deal with energy efficiency related issues along with corresponding permit and supervising procedures. Many of the proposed measures, tools and methodologies dealt with may also be implemented in non-IPPC installations. This document deals with generic energy efficiency techniques and best practices which can be applied in several industrial sectors without duplicating the work done in sectoral BREFs. However, it can feed other work that is in progress with information and ideas. The coverage of this document is as follows: industrial sectors which use or produce energy and apply generic techniques which are

possible to transfer to other sectors are covered it does not develop or conclude on sector specific techniques but will use examples from

various industry sectors to derive generic conclusions equipment (e.g. pumps, fans) as parts of systems and installations are dealt with without

drawing conclusions which could conflict with EuP implementing measures it does not respond to fuel specific (e.g. bio, fossil, waste) issues the system boundary is set in most cases round the site, but in some cases, also smaller or

larger boundaries are considered. The main question to be answered in this document is the following: How to demonstrate if energy is used and produced efficiently?

For finding answers to this question, this document deals with the following issues: what are appropriate definitions for energy efficiency? what are, and how to use, energy efficiency indicators? what methodologies, techniques, etc. contribute to good energy management? what are the possible measures, both techniques and practices, to improve energy

efficiency? what are possible motivation tools? To answer all the above-mentioned questions, this document deals with the following issues: energy management including different types of auditing, methodologies, monitoring, indicators and measurements, applied techniques and good practices.

xviii Version April 2006 SS/EIPPCB/ENE_Draft_1

In order to further clarify the scope, the following can be said: because energy efficiency means different things for different stakeholders, clarification on

what energy efficiency means in this document is required. First, a distinction needs to be made between energy efficiency at the macro level (e.g. national) and at the micro level (e.g. company level). In this document, only the latter is discussed.

energy efficiency is dealt with from an industrial perspective within the installation boundaries without considering a products life cycle. This is in line with the IPPC Directive which deals with production and not with products. The fuel by which energy is produced is also not considered in this document.

this document deals with production activities in industrial installations but energy demand of products is outside the scope. Furthermore fuel specific issues are neither dealt with in this document.

those techniques and measures to improve energy efficiency, which are sector specific are not dealt within here but in sectoral BREFs. For example, it exists a BREF on large combustions plants where energy efficiency is also covered.

Chapter 1

SS/EIPPCB/ENE_Draft_1 Version April 2006 1

1 GENERAL FEATURES ON ENERGY [2, Valero-Capilla, 2005], [3, FEAD and Industry, 2005], [97, Kreith, 1997] This chapter deals with the basics of energy and thermodynamics. It explains the main features of energy and the principles of thermodynamics as an introduction for understanding energy applications and their restrictions in industry. There is a lot of generic information on thermodinamics available in the general literature.

1.1 Introduction Energy is needed to fulfil the necessary or imagined needs of people. To do this energy is needed directly (e.g. heating, lighting) or indirectly (e.g. energy in products). Industry needs energy as one production factor to manufacture goods and provide services to the society. Decoupling energy demand and supply is a challenging task.

1.1.1 Forms of energy Energy can take a wide variety of forms. There are five main forms of energy generally required in industry: chemical energy, the energy that bonds atoms or ions together (e.g. fuels) mechanical energy, associated with motion thermal energy (or heat), the internal motion of particles of matter electrical (or electromagnetic) energy, associated with the electrical charges and the

movement of them nuclear energy, energy in the nuclei of atoms, which can be released by fission, or fusion of

the nuclei. Chemical energy is stored in fuels and can be converted directly to mechanical energy (combustion engines) or to thermal energy (direct process heating). However, most often the chemical energy is converted to a more usable form, generally either to electrical energy or mechanical energy to drive machines, or thermal energy as the source of a process.

Mechanical energy can exist into two states, kinetic or potential. Kinetic energy is the energy that moving objects have due to their motion. For example, it can be an alternative motion (e.g. a piston), a rotary motion (e.g. transmission shaft), or a waterfall. Potential energy is the energy stored in an object due to its position, for instance water stored by a dam. Thermal energy/heat is quantified by temperature. It can be created by chemical reactions such as burning, nuclear reactions, electromagnetic dissipation (as in electric stoves), or mechanical dissipation (such as friction).

Electrical energy or electromagnetic energy is a form of energy present in any electric field or magnetic field, or in any volume containing electromagnetic radiation. Nuclear energy will not be dealt within this document. Energy can also be expressed as primary and secondary energies, usually for statistical purposes. Primary energy is energy contained in raw fuels and any other forms of energy received by a system as input to the system. Primary energies are transformed to secondary energies in energy conversion processes to more convenient forms of energy, such as electrical energy.

Chapter 1

2 Version April 2006 SS/EIPPCB/ENE_Draft_1

1.1.2 Energy transfer and storage Transfer Energy cannot be created or destroyed. Energy can only be converted from one form to another (first law of thermodynamics, see Section 1.3.1). Energy is converted to make it more useful for different purposes in industry and all society. Energy found in fossil fuels, solar radiation, or nuclear fuels needs to be converted into other energy forms, such as electrical, propulsive, or cooling, to be useful. Energy conversion is any process of converting energy from one form to another. The efficiency of a converting machine characterises how well it can convert the energy. Energy conversion can be done by, e.g. the following means: electricity can be turned into mechanical energy by an electrical motor inversely, mechanical energy can be converted into electricity by an alternator thermal energy can be transformed into mechanical energy by a turbine electricity can be converted into heat by a resistance chemical energy can be turned into heat during a chemical reaction and also into (kinetic)

mechanical energy and heat, for instance in an explosion an internal combustion engine converts chemical energy in the gasoline to the propulsive

energy that moves a car a solar cell converts solar radiation into electrical energy that can then be used to light a

bulb or power a computer. Storage The storage of different forms of energy (see Section 1.1.1) are quite different. Some are difficult or even impossible to store as such. Electricity can hardly be stored as such. Batteries store potential electrical energy but in fact chemically. Mechanical and thermal energies can be stored in the medium term as potential energy: water dams/hot water tanks, but in general, they are not so easy to store. One of the most convenient ways for storing energy is undoubtedly as chemical energy in a material. It can be stored for a long, and even sometimes very long, time. It can be transported and it is often easy and quick to implement. The most important chemical sources of energy are the fuels.

Chapter 1


1.1.3 Energy losses Energy losses are very different according to the transformation it undergoes. Furthermore, the transformation is neither total nor unique, e.g. an electrical motor also generates heat. Losses are unavoidable to some extent (second law of thermodynamics, see Section 1.3.2). The following examples illustrate the losses from a combustion plant and from electricity/heat conversion: Combustion plant the first energy losses are due to incomplete combustion of the fuel. Part of the fuel is not

burnt at all or only partially and in this case produces other reactants (such as CO2) than the ones resulting from complete combustion. This is an incomplete conversion of chemical energy into thermal energy

some other losses are due to an incomplete transfer of the heat of the combustion gases to the water/steam of the boiler: losses through the lagging of the combustion chamber and of the boiler, losses to the air by the flue-gas, losses to the air via the ashes

the heat of the combustion gases is mostly transferred to the steam cycle but part of it is transferred to the air instead of the fluid which is required (water/steam)

similarly, if heat is exported via a heat exchanger, there will be some losses by transfer of part of it to the air instead of to the secondary fluid

when steam is sent to a turbo generator set, part of its energy is transferred to the air by direct heat losses and mechanical frictions in the turbo generator set. However, most of the losses here are due to the latent heat which is released by steam when condensed at the cold source. The latent heat is the energy released or absorbed during a change of state (released when passing from the gaseous state of steam to the liquid state of water). Of course the losses are significantly reduced if this energy can be used as happens in the case of cogeneration.

Electricity/heat conversion when turning electricity into heat, nearly 100 % of the electricity input will be turned into

heat. However, converting the heat released by the combustion of a fuel into electricity can typically result a conversion efficiency of about 35 % of the fuel energy input. Using electricity just for making heat is not considered to be an efficient use of energy since the electricity which is used was most probably made from heat in a thermal cycle. So, it is much more beneficial when possible to use a heat source directly than to convert heat into electricity then electricity into heat, even if the second transformation is made with high efficiency.

1.1.4 Exergy The term exergy is used to describe differences in energy quality, in other words exergy shows the maximum useful work obtainable in the system. The exergy content of a system indicates its distance from the thermodynamic equilibrium. See Section 1.2.4 and 1.3.3. For instance, 1 GJ of steam at 400 C/40 bar contains the same energy as 1 GJ of water at 40 C but different exergy. The usefulness of these energies are really different: on the one hand, there is 300 kg of steam, on the other, 6 tonnes of water; and steam at 40 bar can be used for generating electricity, moving mechanical equipment, heating, etc. but there is little use for water at 40 C. The exergy of low temperature energies can be raised by, e.g. heat pumps.

Chapter 1


1.2 Principles of thermodynamics Thermodynamics is the physics that deals with the relationships and conversions between heat and other forms of energy. 1.2.1 Characterisation of systems and processes A system (as a thermodynamic concept) is the quantity of matter within the prescribed boundary under consideration; everything external to the system is called the surroundings. Systems may be considered as closed or open. A system can be considered closed if there is no interchange of matter between the system and the surroundings. If there is an interchange, the system is considered to be open. A very important class of systems that is frequently encountered by engineers is steady-flow systems. A steady-flow system can be defined as any fixed region-of-space system through which a fluid flows and the properties of this fluid, either internal to the system or at its boundaries, do not change as time passes. Typical examples include air compressors, gas turbines, steam turbines, boilers, pumps, heat exchangers, etc. All these devices have in common that each has one or more fluid streams entering and leaving. Devices with these characteristics are also known as steady-state, steady-flow systems, steady-flow control volumes and flow systems. Any characteristic of a system is called property. Temperature, volume, pressure or mass are some of the most familiar examples.

1.2.2 Forms of energy storage and transfer The energy of a system consists of the kinetic, potential and internal energies expressed as:

mgzmCUPTKNUU PK ++=++= 2

2

, (J) Equation 1.1

Where:

U is the internal energy which is associated with the microscopic forms of energy, i.e. to the motion, position, and internal state of the atoms or molecules of the substance

KN is the kinetic energy which is associated to the motion of the system as a whole relative to some reference frame C is the velocity of the system relative to some fixed reference frame m is the mass of the body in motion

PT is the change in gravitational potential energy which is associated with the position of the system as a whole (elevation) in the earths gravitational field g is the gravitational acceleration

z is the elevation of the centre of gravity of a system relative to some arbitrarily selected reference frame. Thermal energy is a huge drain of energy when compared with kinetic or potential energies. Therefore, in many energy analyses these two last energies may be disregarded. Energy storage Energy can be stored in numerous forms (some more information in Section 1.1.2). The most important encountered forms in thermodynamic applications are: internal, kinetic and potential energy. Other forms of energy such as magnetic, electric, and surface tension effects are significant only in some specialised cases and will not be considered here.

Chapter 1


Energy transfer The forms of energy discussed above which constitute the total energy of a system are static forms of energy and can be stored in a system. However, energy can also be transformed from one form to another and transferred between systems. For closed systems, energy can be transferred through work and heat transfer. Heat and work are not properties because they depend on the details of a process and not just the end states: heat (Q) can be defined as energy in transit from one mass to another because of a

temperature difference between the two. It accounts for the amount of energy transferred to a closed system during a process by means other than work. The transfer of energy occurs only in the direction of decreasing temperature. Heat can be transferred in three different ways: conduction, convection and radiation. Conduction is the transfer of energy from the more energetic particles of a substance to the adjacent particles that are less energetic due to interactions between the particles. Conduction can take place in solids, liquids and gases. Convection is the energy transfer between a solid surface at a certain temperature and an adjacent moving gas or liquid at another temperature. Finally, thermal radiation is emitted by matter as a result of changes in the electronic configurations of the atoms or molecules within it. The energy is transported by electromagnetic waves and it requires no intervening medium to propagate and can even take place in vacuum

work (W) has the following thermodynamic definition: work is done by a system on its surroundings if the sole effect on everything external to the system could have been the raising of a weight. Like heat, work is also energy in transit.

1.2.3 Properties: enthalpy and specific heat Enthalpy A property related to internal energy U, pressure p, and volume V is enthalpy H, defined by:

H = U + pV (J) Equation 1.2 Or per unit of mass, using specific internal energy u and specific volume v (internal energy and volume per unit of mass) as follows: h = u + pv (J) Equation 1.3 Specific heat capacity The property specific heat capacity C (commonly named specific heat) relates energy and temperature. The specific heat is defined as the energy required to raise the temperature of a unit mass of a substance by one degree. Two different specific heats are usually considered in thermodynamics: specific heat at constant volume CV and specific heat at constant pressure CP.Specific heat at constant volume CV expresses the energy required to raise the temperature of the unit mass of a substance by one degree as the volume is maintained as constant. The energy required to do the same to the pressure being maintained as constant is the specific heat at constant pressure CP. CV and CP are expressed as follows:

vv T

uC

= (J/K) Equation 1.4

pp T

hC

= (J/K) Equation 1.5

Chapter 1


The values of internal energy, enthalpy and heat capacities can be calculated as shown in Section 1.3.1.3 and they are extensively available through property tables, databases and programs for a great variety of substances as explained in Section 1.4.5.

1.2.4 Properties: entropy and exergy Entropy The concept of entropy is very important to state the second law of thermodynamics in (see Section 1.3.2) a general and usable form. When two stable states of a system are connected by different internally reversible processes, the integral of the heat interchanged over its temperature is found not to be dependent on process path. This proves the existence of the function called entropy, which only depends on the state of the properties of the system. The change of entropy is defined as follows:

(J/K) Equation 1.6

Entropy is an abstract property and can be viewed as a measure of disorder. Unlike energy, entropy is a non-conserved property. However, entropy is easily calculated following procedures like those explained in Section 1.4.3. Thermodynamic databanks as explained in Section 1.4.4, include values of entropy for many substances, mixtures and pressure and temperature ranges. Exergy Exergy of a thermodynamic system is the maximum theoretical useful work (shaft work or electrical work) obtainable as the system is brought into complete thermodynamic equilibrium with the thermodynamic environment while the system interacts with this environment only (some more information can be found in Section 1.1.4). A system is said to be in the dead state when it is in thermodynamic equilibrium with its surroundings. In the dead state, a system is at the temperature and pressure of its surroundings; it has no kinetic or potential energy and it does not interact with the surroundings. Exergy can be defined as well as a measure of the departure of the state of a system from the environment. Once the environment is specified, a value can be assigned to exergy in terms of property values for the system only and exergy can be regarded as a property of the system. The value of exergy, as defined in Equation 1.7, cannot be negative and is not conserved but destroyed by irreversibilities. The specific exergy on a unit mass basis is: e = (u-u0) + p0 (v-v0) T0(s-s0) + C2/2 + gz (J) Equation 1.7 Where: 0 denotes the dead state. When a mass flows across the boundaries of a control volume, there is an exergy transfer accompanying the mass and work flows. This is named specific flow exergy or physical exergy of a material stream, and is given by: e = (h-h0) - T0 (s-s0) + C2/2 + gz (J) Equation 1.8 Flow exergy is commonly used in the analysis of open systems, and calculating it is as simple as any other thermodynamic property as explained in Section 1.4.

Chapter 1


1.3 First and second laws of thermodynamics The two fundamental and general laws of thermodynamics are: (1) energy is conserved and (2) it is impossible to bring about any change or series of changes. The sole net result of which is the transfer of energy as heat from a low to a high temperature. In other words, heat will not flow from low to high temperatures by itself. A thermodynamic process will not occur unless it satisfies both the first and the second laws of thermodynamics.

1.3.1 First law of thermodynamics energy balance The first law of thermodynamics is the general principle of physics and it states that energy is conserved. Although the law has been stated in a variety of ways, all have essentially the same meaning. The following are examples of typical statements: whenever energy is transformed from one form to another, energy is always conserved energy can neither be created nor destroyed the total sum of all energies remains constant for a given system the net energy in the form of heat added or removed from a system that operates in a cyclic

manner equals the net energy in the form of work produced or consumed by the system the value of the net work done by, or on, a closed system undergoing an adiabatic process

between two given states depends solely on the end states and not on the details of the adiabatic process.

1.3.1.1 Energy balance for closed systems For a closed system, the first law implies that the change in system energy equals the net energy transfer to the system by means of heat and work. That is: U2 U1 = Q - W (J) Equation 1.9 In systems undergoing cycles, the net work output equals the net heat transfer to the cycle. Wcycle = Qin - Qout (J) Equation 1.10

1.3.1.2 Energy balance for open systems Most applications of engineering thermodynamics are conducted on a controlled volume basis. In such cases, the conservation of the mass principle must be applied: The time rate of accumulation of mass within the control volume equals the difference between the total rates of mass flow in and out across the boundary as shown below:

=2

.

21

.

1 mmdtdm

(kg/s) Equation 1.11

The energy rate balance for such a system is:

++

+++= 2

22

22

.

1

21

11

...

22gzChmgzChmWQ

dtdU

(W) Equation 1.12

Chapter 1


For steady-flow systems, the mass flowrates and the rates of energy transfer by heat and work are constant with time.

=2

.

21

.

1 mm (kg/s) Equation 1.13

Hence, at steady state, the first law of thermodynamics can be expressed as:

++

++= 2

22

22

.

1

21

11

...

22gzChmgzChmWQ (W) Equation 1.14

1.3.1.3 Calculation of internal energy and enthalpy changes The change in internal energy and enthalpy for an ideal gas during a process from state 1 to state 2 is determined as follows:

==2

112)( dTTCuuu v (J) Equation 1.15

==2

112)( dTTChhh p (J) Equation 1.16

The values of CV and CP can be obtained through tables, databases and programs for many substances as explained in Section 1.2.3. For incompressible substances (those whose specific volume or density is constant), CV = CPand following equations can be applied:

(J) Equation 1.17

Where: Cav is a C value at the average temperature for small temperature intervals. h = u + vP (J) Equation 1.18

1.3.1.4 First law efficiencies: thermal efficiency and coefficient of performance

The thermal efficiency measures the performance of a heat engine and can be defined as the fraction of the heat input that is converted to net work output:

in

outnet

QW ,= (-) Equation 1.19

Chapter 1


It can also be expressed as:

in

out

QQ

= 1 (-) Equation 1.20

For a power cycle operating between thermal reservoirs at temperatures TH and TC(T: temperature, H: hot and C: cold), the thermal efficiency is:

H

C

QQ

= 1 (-) Equation 1.21

The maximum efficiency that can be achieved is given by the Carnot efficiency which is shown in Equation 1.22 below:

H

C

TT

= 1 (-) Equation 1.22

The equations above are also applicable to refrigeration and heat pump cycles operating between two thermal reservoirs, but for these QC represents the heat added to the cycle from the cold reservoir at temperature TC and QH is the heat discharged to the hot reservoir at temperature TH. More informative coefficients are perhaps the Coefficients of Performance COP of any refrigeration cycle, COPR, and heat pump cycles, COPHP, given by:

CH

CR QQ

QCOP

= (-) Equation 1.23

CH

HHP QQ

QCOP

= (-) Equation 1.24

Unlike the thermal efficiency, the value of COP can be greater than unity. This means that the amount of heat removed from the refrigerated space can be greater than the amount of work input.

1.3.2 Second law of thermodynamics - entropy balance The second law of thermodynamics shows which types of transformations are possible or not and in which direction they occur. Like the first law, the second can be assumed in many different ways and some of them are listed below: it is not possible to construct a heat engine which produces no other effect than the

exchange of heat from a single source initially in an equilibrium state and the production of work. Heat engines must always reject heat to a thermal-energy reservoir

no cyclical device can cause heat to transfer from thermal-energy reservoirs at low temperatures to reservoirs at high temperatures with no other effects

the total entropy of an engine and all of the surrounding components that interact with the engine must increase when the heat engine is not completely reversible

the only processes that can occur are those for which the entropy of the isolated system increases. This statement is known as the increase of entropy principle.

Chapter 1


1.3.3 Combination of the first and second laws - exergy balance The first and second laws can be combined into a form that is useful for conducting analyses of exergy, work potential and the second law efficiencies among others. This form also provides additional insight into systems, their operation and optimisation.

1.3.3.1 Exergy balance for a closed system The exergy balance for a closed system is obtained with the combination of the energy and entropy balances. The exergy change in a closed system is equal to the sum of the exergy transfer accompanying heat, the exergy transfer accompanying work minus the destruction of exergy. The final equation is:

[ ]{

ndestructioExergy

workngaccompanyi

transferExergy

heatngaccompanyi

transferExergy

jchangeExergy

TVVpWQTT

EEE 01202

1

012 )(1

== 44 344 21

443442143421

(J) Equation 1.25

T0 denotes the temperature at ambient conditions p0 denotes pressure at ambient conditions Tj is the surface temperature where the heat transfer takes place The term T0 accounts for the destruction of exergy or thermodynamic irreversibility and is often denoted as I. The value of exergy destruction is always positive and ideally zero when no irreversibilities are present within the system. As explained in this section, if the principal task of any energy analyst is to pinpoint irreversibilities, it is quite logical to make use of exergy balances instead of the entropy ones. This is because exergy has the familiar units of energy rather than units of energy over temperature, and exergy can be easily interpreted as the thermodynamic quality part of an energy stream. As explained in this section exergy can easily be calculated as any other thermodynamic property once the properties of the surrounding environment are defined. Note that exergy is a definition of thermodynamic availability and equivalence, and is not a definition of technical usefulness. As an example, if natural gas is needed for a given process, the same amount of exergy with say, steam or coal, does not satisfy the needs and could not be used alternatively. Lack of interpretation is in many cases the real cause of the not so widely used exergy analyses. Energy analysts should be quite knowledgeable about thermodynamics.

1.3.3.2 Exergy balance for an open system The exergy rate balance for a control volume is equal to:

{{

ndestructioExergyofRate

transferexergyofRate

eee

iiicvj

j j

changeexergyofRate

cv Iememdt

dVcvpWQTT

dtdE ...

0

..01 +

=

4444444444 34444444444 21

(W) Equation 1.26

Chapter 1


For steady-flow systems, the balance obtained is:

.....010 IememWQ

TT

ee

eiii

cvjj j

+

= (W) Equation 1.27

1.3.3.3 Calculation of flow exergy changes The specific exergy change can be evaluated using following equation:

)(2

)()( 212

22

12102121 zzg

CCssThhee ++= (J/kg) Equation 1.28

The values of enthalpy and entropy can be obtained either through property tables or with equations in Sections 1.2.3, 1.2.4, and 1.3.1.

1.3.3.4 Second law efficiency: exergetic efficiency The thermal efficiency and coefficient of performance defined in Section 1.3.1.4 are based only on the first law of t

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