Development of an energy management solution for mine compressor systems

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Development of an energy management

solution for mine compressor systems

Johan Nicolaas du Plessis

Dissertation submitted in partial fulfilment of the requirements for the degree

Master of Engineering in Computer and Electronic Engineering

at the Potchefstroom campus of the North-West University

Supervisor: Dr R. Pelzer (CRCED Pretoria) November 2010

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ABSTRACT

Title: Development of an energy management solution for mine compressor systems

Author: J. N. du Plessis

Supervisor: Dr R. Pelzer

Degree: Master of Engineering (Computer/Electronic)

Keywords: Compressor control, compressor system, DSM, energy management, mine compressor Eskom is under increasing pressure to provide reliable and sustainable electricity. Demand Side Management (DSM), offers a short- to medium-term solution to this problem. During 2009, the mining sector consumed approximately 16% of the domestic electricity supplied by Eskom. This made the mining sector one of the major targets for Eskom-initiated DSM programmes.

The mining industry uses compressed air for a wide variety of applications and production purposes. This creates many opportunities to reduce electricity consumption and operating costs. Reducing the air-system demand may however not result in significant electrical energy savings, unless the compressed-air supply is accurately managed to meet the reduced demand.

Until recently, compressor control in the mining sector generally consisted of operating the compressors continuously, regardless of the actual demand for compressed air. Excessive compressed air is blown off into the atmosphere resulting in energy loss. This usually occurs when the compressors are operated manually.

A computer-controlled compressor management solution, which optimises the efficiency potential of the compressed-air supply, is required to obtain significant electrical energy savings. The need for such a solution was addressed by the development of an energy management solution for mine compressor systems. This solution is referred to as Energy Management System (EMS) and is capable of starting, stopping, loading and unloading compressors. In addition to this, compressor output can be controlled to maintain a desired pressure set-point.

In this study, the development and implementation of EMS on ten different mine compressor systems is presented. Automatic compressor capacity control was implemented, while an operator manually initiated compressor starting; stopping; loading and unloading, according to EMS control schedules.

Centralised compressor control is one of the main advantages offered by EMS, especially for compressed-air systems with multiple compressor systems at different geographic locations. EMS facilitated effective and sustainable electrical energy reductions for all these compressed-air systems.

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SAMEVATTING

Titel: Ontwikkeling van ŉ energie bestuursoplossing vir myn kompressorstelsels

Outeur: J. N. du Plessis

Studieleier: Dr R. Pelzer

Graad: Meestersgraad in Ingenieurswese (Rekenaar/Elektronies)

Sleutelwoorde: DSM, enegriebestuur, kompressorbeheer, kompressorstelsels, mynbou kompressor

Eskom verkeer onder toenemende druk om ŉ betroubare en volhoubare bron van elektrisiteit te verskaf. “Demand side management” (DSM) bied ŉ korttermyn oplossing hiervoor. Gedurende 2009 het die mynbousektor bygedra tot 16% van die totale elektrisiteitsverbruik in Suid-Afrika. Mynbou is dus een van die hoof teikens van die Eskom DSM-program.

Die mynbousektor gebruik pneumatiese stelsels vir ŉ wye verskeidenheid van toepassings en produksieprosesse. Daar is baie geleenthede om die elektrisiteitsverbruik van hierdie pneumatiese stelsels te verminder. Noemenswaardige besparings in elektrisiteitskoste is nie moontlik deur die druk aanvraag van pneumatiese stelsel te verlaag, sonder om die bron dienooreenkomstig aan te pas nie.

Tot onlangs het kompressorbeheer bestaan uit kontinue gebruik van die kompressors, ongeag van die aanvraag van die pneumatiese stelsel. Energie word deurgaans vermors deur oortollige saamgeperste lug wat in die atmosfeer in afgeblaas word. Dit is tipies van ŉ kompressorstelsel wat volledig handmatig beheer word.

ŉ Rekenaarbeheerde energiebestuursoplossing word benodig om noemenswaardige besparings in

elektrisiteitskoste op myn kompressorstelsels te bewerkstellig. Hierdie behoefte is aangespreek deur die ontwikkeling van ŉ energiebestuur-sisteem. Hierdie sisteem staan bekend as energiebestuur-sisteem (EMS) en is in staat om kompressors aan te skakel; af te skakel; te laai en te ontlaai. Hiermee saam word die kompressor-uitset beheer om ŉ gewensde druk stelpunt te handhaaf.

In hierdie studie word die ontwikkeling en implementering van EMS op tien verskillende kompressorstelsels bespreek. Outomatiese kompressor kapasiteitbeheer was geïmplementeer terwyl ŉ operateur kompressors handmatig aanskakel, afskakel, laai of ontlaai volgens die EMS beheer-skedule.

Gesentraliseerde kompressor-beheer is een van die hoof voordele wat deur EMS gebied word, spesifiek vir pneumatiese stelsels wat bestaan uit verskeie kompressorstelsels met verskillende geografiese liggings. EMS het effektiewe en volhoubare verlagings in elektrisiteitsverbruik behaal op al tien die pneumatiese stelsels.

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ACKNOWLEDGEMENTS

I would firstly like to thank God almighty for blessing me with the talents to pursue my passion in life.

To Prof. E. H. Mathews and Prof. M. Kleingeld, thank you for affording me the opportunity to further my education.

To Dr. Ruaan Pelzer, Mr. Doug Velleman and Dr. Johann van Rensburg, thank you for the time you sacrificed in support of my study. The lessons I learned from your combined wisdom are invaluable.

To my family, Nadine du Plessis, Pieter du Plessis, Ronel Marais and Willie Marias, I thank you for your love and support throughout my years of study. Home will always be where my heart is.

To Cindy Loots, the love of my life, thank you for your undying encouragement and faith in me. I truly adore you.

Finally I would like to thank Kobus van Tonder and André Botha for the years of study we shared. I value your friendship.

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LIST OF FIGURES

Figure 1-1: Electricity consumed per category of Eskom customers for 2009 (constructed from [2]) ... 1

Figure 1-2: The effect of load shifting... 3

Figure 1-3: The effect of peak clipping ... 3

Figure 1-4: The effect of energy efficiency ... 3

Figure 1-5: Eskom’s TOU structure [12] ... 4

Figure 1-6: Cost components in a typical compressed-air system (adapted from [19]) ... 5

Figure 2-1: Breakdown of compressor classification (adapted from [17], [25]) ... 9

Figure 2-2: Application ranges of different compressor types (adapted from [25]) ... 10

Figure 2-3: Simplified lubrication and seal oil schematic (adapted from [26]) ... 11

Figure 2-4: Main components of a centrifugal compressor [25], [26] ... 12

Figure 2-5: Single-stage centrifugal compressor (adapted from [26]) ... 13

Figure 2-6: Multistage centrifugal compressor (adapted from [26]) ... 13

Figure 2-7: Flow path of a multistage centrifugal compressor ... 14

Figure 2-8: Centrifugal impeller [26] ... 14

Figure 2-9: Velocity and pressure development through an impeller and diffuser (adapted from [27]) ... 15

Figure 2-10: Simplified compressor setup ... 15

Figure 2-11: Fictional compressor curve ... 16

Figure 2-12: Pressure and flow variation during a typical surge cycle (adapted from [26]) ... 17

Figure 2-13: Propagation of stall ... 18

Figure 2-14: Compressor map with efficiency contours ... 19

Figure 2-15: Compressor performance with different throttle positions (adapted from [32]) ... 22

Figure 2-16: Compressor performance map with surge control line (adapted from [26]) ... 23

Figure 2-17: Typical surge avoidance system (adapted from [27])... 23

Figure 2-18: Surge avoidance; surge detection and avoidance; and surge suppression (adapted from [30]) ... 24

Figure 3-1: Compressor control strategy ... 35

Figure 3-2: Typical compressor measurement instrumentation ... 37

Figure 3-3: Instrumentation diagram for a typical compressor ... 38

Figure 3-4: Functional flow diagram ... 41

Figure 3-5: Pressure set-point calculation ... 42

Figure 3-6: Compressor control schedule calculation ... 43

Figure 3-7: Compressor schedule implementation ... 44

Figure 3-8: Software architecture ... 45

Figure 3-9: Basic software platform GUI ... 47

Figure 3-10: Compressor Options window ... 48

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Figure 3-12: PressureControlNode Options window ... 49

Figure 3-13: CompressorController Options window ... 50

Figure 3-14: CompressorController View window ... 50

Figure 4-1: Mine A surface compressed-air system layout ... 54

Figure 4-2: Typical pre-implementation compressor operation at Mine A ... 55

Figure 4-3: Mine A communication infrastructure ... 56

Figure 4-4: Modelled surface compressed-air system of Mine A ... 56

Figure 4-5: Compressor control at Mine A ... 57

Figure 4-6: Typical post-implementation compressor operation at Mine A ... 57

Figure 4-7: Impact on system pressure at Mine A for the average (a) weekday, (b) Saturday and (c) Sunday ... 58

Figure 4-8: Impact on power consumption at Mine A for the average (a) weekday, (b) Saturday and (c) Sunday ... 59

Figure 4-9: Comparison of impact on typical weekday, Saturday and Sunday at Mine A ... 61

Figure 4-10: Mine B surface compressed-air system layout ... 62

Figure 4-11: Modelled surface compressed-air system of Mine B ... 64

Figure 4-12: Compressor control at Mine B ... 64

Figure 4-13: Typical post-implementation compressor operation at Mine B ... 65

Figure 4-14: Impact on system pressure at Mine B for the average (a) weekday, (b) Saturday and (c) Sunday ... 66

Figure 4-15: Impact on power consumption at Mine B for the average (a) weekday, (b) Saturday and (c) Sunday ... 67

Figure 4-16: Comparison of impact on typical weekday, Saturday and Sunday at Mine B ... 69

Figure 4-17: Baseline electricity consumption vs. achieved impact ... 70 Figure B-1: UML diagram of EMS ... B-1

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LIST OF TABLES

Table 1-1: Electricity consumption per customer for the major sectors for 2009 ... 1

Table 2-1: Consumers of compressed air on mines (constructed from [17], [23], [24]) ... 8

Table 2-2: Centrifugal compressor characteristics [19] ,[25], [26] ... 10

Table 2-3: Surge prevention patents [30] ... 24

Table 2-4: Procedures for starting-and-stopping a compressor ... 25

Table 2-5: Procedures for loading and unloading compressor ... 25

Table 2-6: Comparison of compressor control systems ... 27

Table 3-1: Compressed-air system parameters ... 31

Table 3-2: Real-time inputs ... 32

Table 3-3: Real-time user input ... 32

Table 3-4: Control constraints ... 33

Table 3-5: Compressor motor instrumentation ... 37

Table 3-6: Compressor instrumentation ... 37

Table 3-7: Control instrumentation ... 38

Table 3-8: Functionality available to the respective privilege levels ... 46

Table 3-9: Compressor data logging ... 47

Table 3-10: EMS modes of operation... 48

Table 4-1: Average weekday power and electricity cost reduction at Mine A ... 60

Table 4-2: Summary of impact at Mine A ... 61

Table 4-3 : Compressor specifications for Mine B... 62

Table 4-4: Average weekday power and electricity cost reduction at Mine B ... 68

Table 4-5: Summary of impact at Mine B ... 68

Table 4-6: Summary of average monthly results achieved on all implementations ... 69

Table 5-1: DSM potential on other mines ... 73 Table A-1:Example of procedures to manually start-and-stop a compressor ... A-1 Table C-1: Average weekday, Saturday and Sunday impact profiles for Mine A ... C-2 Table C-2: Summary of results for Mine A ... C-2 Table C-3: Average weekday, Saturday and Sunday impact profiles for Mine B ... C-3 Table C-4: Summary of results for Mine B ... C-3 Table C-5: Average weekday, Saturday and Sunday impact profiles for Mine C ... C-4 Table C-6: Summary of results for Mine C ... C-4 Table C-7: Average weekday, Saturday and Sunday impact profiles for Mine D ... C-5 Table C-8: Summary of results for Mine D ... C-5 Table C-9: Average weekday, Saturday and Sunday impact profiles for Mine E ... C-6 Table C-10: Summary of results for Mine E ... C-6

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Table C-11: Average weekday, Saturday and Sunday impact profiles for Mine F ... C-7 Table C-12: Summary of results for Mine F ... C-7 Table C-13: Average weekday, Saturday and Sunday impact profiles for Mine G ... C-8 Table C-14: Summary of results for Mine G ... C-8 Table C-15: Average weekday, Saturday and Sunday impact profiles for Mine H ... C-9 Table C-16: Summary of results for Mine H ... C-9 Table C-17: Average weekday, Saturday and Sunday impact profiles for Mine I ... C-10 Table C-18: Summary of results for Mine I ... C-10 Table C-19: Average weekday, Saturday and Sunday impact profiles for Mine J ... C-11 Table C-20: Summary of results for Mine J ... C-11

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NOMENCLATURE

ºC Degree Celsius A Ampère

CRCED Centre for Research and Continued Engineering Development CSV Comma Separated Values

DLL Dynamic-Link Library DSM Demand Side Management E-mail Electronic mail

EMS Energy Management System ESCos Energy Service Companies FT Flow Transmitter

GUI Graphical User Interface GW Gigawatt

GWh Gigawatt-hour

HMI Human Machine Interface

Angle of attack

IDE Integrated Development Environment I/O Input and output

IGV Inlet Guide-Vane kg/s Kilogram per second kPa Kilopascal

kW Kilowatt kWh Kilowatt-hour LED Light Emitting Diode LQG Linear Quadratic Gaussian m³/h Cubic meter per hour mm Millimetre

mm/s Millimetre per second MW Megawatt

MWh Megawatt-hour

NERSA National Energy Regulator of South Africa Nm Newton meter

OLE Object Linking and Embedding OOD Object-Oriented Design

OPC Object Linking and Embedding for Process Control

Total input pressure Total output pressure

PCP Power Conservation Programme PI Proportional-Integral

PID Proportional-Integral-Derivative PLC Programmable Logic Controller PT Pressure Transmitter

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R Rand

R2 Coefficient of determination REDS Regional Electricity Distributors rpm Revolutions per minute

RS-422 Recommended Standard 422

SCADA Supervisory Control and Data Acquisition SCL Surge Control Line

SLL Surge Limit Line SMS Short Message Service SP Set-point

TOU Time of Use

UML Unified Modelling Language V Volt

VGD Variable Geometry Diffuser VSD Variable Speed Drive

Development of an energy management solution for mine compressor systems