The rotary kiln is of central importance to any cement plant process whose overall reliability

135 Pages·2009·1.34 MB·English

Ministry of higher Education and Scientific Research
University M’hamed BOUGARA Boumerdes
Faculty of Engineering
Department of Electrical Engineering and Electronics

DOCTORATE THESIS
In Electrical Systems Engineering

Reliability Assessment and Improvement of the Electrical,
Control and Instrumentation Systems of a Cement Plant
Baking Process Using FMECA.

By CHAFAI Mahfoud Said

Defended in front of the following Examining board

Pr. DJ. BENAZZOUZ Prof. at Univ. of Boumerdes President
Pr. L. REFOUFI Prof. at Univ. of Boumerdes Supervisor
Pr. N. BENAMROUCHE Prof. at UMM T-O Examiner
Dr. H.ZERROUG Maître de Conférences , USTHB Examiner
Dr. M. BOUDOUR Maître de Conferences, USTHB Examiner
Dr. H. BENTARZI Maître de Conférences , U.Boumerdes Examiner
Year: 2008 - 2009

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Acknowledgement

I would like express my sincere gratitude and appreciation to my supervisor
Professor Larbi Refoufi for his guidance, contribution and support during the
completion of this work. It has been a definite challenge we had to face when
deciding to address these types of industrial problems that acutely felt in Algerian
industry.

I extend my thanks to Dr. Bentarzi, Mr. Ouadi and Mr. Zitouni with whom we
have had passionate but certainly scientific and fruitful debates.

My Thanks are extended to Pr. Dj. Benazzouz , Pr. N. Benamrouche , Dr. H.
Zerroug and Dr. M. Boudour who have accepted to be members of my jury .

Finally, I would like to thank the technical staff of Chlef , Ain Kebira and Beni-saf
cement plants for their collaboration.

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Table of contents

ABTRACT

INTRODUCTION

CHAPTER 1: SYSTEM DESCRIPTION OF CEMENT BAKING PROCESS

1.1- Cement industry process…………………………………………………………… 5
1.2- The Baking process………………………………………………………………... 6

1.3- The Existing environment………………………………………………………… 10

CHAPTER 2: FAILURE ANALYSIS AND RELIABILITY MODELING IN CEMENT
BAKING PROCESS

2.1- Failure analysis……………………………………………………………………. 13
2.2- Reliability modeling ……………………………………………………………… 24

CHAPTER 3: FAILURE MODE EFFECTS AND CRITICALITY ANALYSIS
(FMECA)

3.1- FMECA of the Baking Process Subsystems……………………………………….. 28
3.2- Criticality analysis 29
3.3- Hierarchical breaking down of the baking system structure : 33
……………………………………….. 35
3.4- Applications : FMECA Work sheets
…………………………………………... 45
3.5- Pareto criticality hierarchisation
.

CHAPTER 4: RELIABILITY ASSESSMENT OF ELECTRICAL, PROCESS
CONTROL AND INSTRUMENTATION SUSBSYSTEMS

4. 1 - Sensors-instrumentation …………………………………………………………. 49
4. 2 - Electrical motor drives …………………………………………………………... 54
4.3- Relay Output Units …………….………………………………………………… 69
…………………………………………………………. 73
4. 4- PLC Controller
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………………………………………………………. 74
4.5- LV Power supply

CHAPTER 5: APPLICATION OF RCM TO BAKING ZONE

5.1- Introduction to RCM approach…………………………………………………….. 76
5.2 .Systematic preventive maintenance program application 77
5.3- Condition Based Maintenance (CBM) …………………………………………… 80

CHAPTER 6: RELIABILITY ENHANCEMENT OF THE ELECTRICAL PROCESS
CONTROL AND INSRUMENTATION SYSTEM

6.1- Pressure and temperature sensor-transmitters ………………………………… 82
6.2- Relay output unit……………………………………………………………….. 86
6.3- PLC reliability improvement …………………………………………………… 90
6.4- Power supply reliability improvement……………………………………………. 92

CHAPTER 7: RELIABILITY ENHANCEMENT OF THE ELECTRICAL MOTOR
DRIVES
7.1- DC kiln drive…………………………………………………………………… 94
7.2- Induction motor ID fan………………………………………………………… 98

CHAPTER 8: CONCLUSION…………………………………………………. 109

- REFERENCES

- Published papers

- Appendices

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ABSTRACT

The present work is a contribution towards a solution of some important reliability problems as
found in some existing Algerian cement plants focusing on the baking system, the heart of the
process, with special emphasis on electrical and electronic systems. Any failure that leads to shut
down of the baking system will inevitably force the process to stop with heavy economical losses;
these problems are further compounded by serious maintainability and safety problems which must
be faced during the effort of putting the system back into operation .
Reliability assessment is developed focusing principally on the electrical and electronic apparatus
and devices of the cement baking process. For this, Failure Mode Effects and Criticality Analysis
(FMECA) in conjunction with Fault Tree Analysis (FTA) , Event Tree Analysis (ETA) and
Reliability Bloc Diagram (RBD), are developed in order to determine all possible types of failures
and the types of failures that will most negatively affect the operational capability of the system
considered. . This is done by gauging the level of failure criticality by working out a Risk Priority
Number (RPN). Critical subsystems, circuits and components are identified and classified for its use
in a subsequent decision making process in order to take actions in the frame work of a Reliability
Centred Maintenance (RCM) with the objective of achieving the required reliability level in a cost
effective manner. Are the object of particular attention, the ways and means of reliability
enhancement of the Process Control and Instrumentation (PCI) subsystems; the most adequate
choice of solutions among several are proposed to improve the reliability of sensor-transmitters,
electric drives , controllers and power supply.
In the course of this research effort, investigations have been carried out to set up field data base
with particular reference to Algerian cement plants with the use of other main sources such as The
American Military Handbook Standards series , the MIL- HDBK 217 F, AVCO corporation and
Faradip data bases.

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LIST OF ABBREVIATIONS AND SYMBOLS:

-FMECA: Failure Mode Effect and Criticality Analysis:
-FTA : Fault Tree Analysis
-ETA: Event tree analysis
-RBD : Reliability Block Diagram
-RCM: Reliability Centred Maintenance
-EOS: Electrical Overstress
-IFM: Insulation Failure Mechanism
-MTBF: Mean time between failure
-MTTR: Mean time to repair
-CB: Condition based maintenance
-SPM: Risk priority number
-P: probability of failure occurrence
-N: Probability of non detection
-S: severity
-PLC: programme logic controller
-PCI: process control and instrumentation
-ID fan: Induced Draft fan
-MIL-HDBK : military handbook
ג:failure rate:
Β: shape factor of weibull distribution
IFM: insulation failure mechanism

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- INTRODUCTION-

Cement industry is a key economic industry in the nation economic system. Needs for transport,
schooling, health and building infrastructures are huge and the cement industry must take up the
challenge of meeting those ever pressing basic needs in a reasonable span of time lest the battle for
economic development may be lost.
Success will depend chiefly on its ability to substantially improve the operational reliability and
availability of cement manufacturing process.
Cement industry has obvious reasons for recognizing the importance of reliability, the linchpin of
availability and dependability. There are economic as well as safety and environmental reasons:
avoidance of damages due to failures, of losses due to enforced down time, of repair costs and loss
of business; also avoidance of hazards to health and life and to the environment because of
technology failures or malfunctions.
Reliability, customarily thought as being the province of the equipment designer only, must also be
of direct importance to the equipment user. This is particularly true in our national context where
operational (field) reliability clearly falls short of attaining the predicted (theoretical) reliability
level given by the technology manufacturer or the operational reliability of the same technology in
some other place. The problems are compounded by lack of proper cooperation between the
original equipment manufacturer or the consultant on the one hand and the user on the other for an
effective technology transfer that should boost customer capabilities and make of him a full partner
in implementing a reliability growth scheme beneficial to both equipment manufacturer and user.
The current situation of Algerian cement industry generally points to a lower performance level in
comparison to cement plants outside the country in terms of lower equipment availability, higher

specific energy consumption and higher than tolerated gases and ashes emissions ; this is due to a
lack of maintenance management, equipment aging , acquisition and choice of the inadequate
technology and human factors .
The problems of the reliability of Algerian cement plant processes are yet to be tackled in a
systematic way from a system point of view.
The present work is a contribution toward a solution of some important reliability problems as
found in some existing Algerian cement plants with emphasis on the baking zone, the heart of the
process.

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It is of vital importance to any cement plant process whose overall reliability depends crucially on
this system. Any failure leading to the shut down of the baking system will inevitably force the
process to stop. Financial consequences are dire: loss of revenues of the order of 10 thousands
millions DA per day of lack of production. Furthermore, the serious maintainability and safety
problems involved during the efforts of putting process back into operation following shut down
failure are other compelling reasons for ensuring maximum availability of the system hence the
continuity of plant production. Actions to be taken for reliability and availability improvement of
the baking zone must be preceded by identifying potential failures occurring on three different main
items: the rotary kiln system , the pre heater and the cooling system. For this purpose, assessment
techniques such as Failure Modes Effects and Criticality Analysis (FMECA) in coordination with
other predictive methods Fault Tree (FTA) and event tree Analyses, can be developed and applied
to determine failures which may affect the operational capability of the considered system.
This inductive technique can help identify potentially occurring maloperations in the process. It can
constitute a diagnosis support system and offers a high degree of integration and a
comprehensiveness as data base stemming from it can readily be used more targeting or tuned
techniques developed to address a dominant potential problems such as safety and quality system.
The FMECA , in association with predictive methods such as the Fault Tree , Event Tree ,
Reliability Bloc Diagram (RBD) and hazard and operability can provide an integrated analysis.
Through FMECA, The critical systems and/or functions are then classified in view of deciding what
priority actions to take in the framework of a Reliability Centred Maintenance. This will be an
attempt to maintain the designed (inherent) reliability of the equipments of the baking system
through proactive maintenance which is based on preventive systematic maintenance
complemented by CBM from which the actual condition knowledge, obtained via condition
monitoring, is additionally used to determine the physical state of critical items
Following RCM, reliability improvement is attempted focusing principally on the electrical parts
that is control and instrumentation systems of a cement plant baking process. The basic information,
upon which the reliability assessments are based is the failure rates of the used components. In
consequence major task in any reliability assessment is the acquisition of appropriate failure rates
data. Being a case of study, investigations have been carried out to gather operational field data
particularly the failure rates from cement industry and /or from several sources such as MIL-
HDBK ,FARADIP, AVCO corporation to complete the study.
For reliability estimation using these data bases, two methods are commonly used: the part count
method and the part stress analysis method. Best estimates from generic data sources need to be
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adjusted for the specific conditions under which the item is expected to operate. It impacts
prediction of the frequency and types of system failure during operation for an existing system .
The Reliability enhancement can be obtained using several measures. The best solution is chosen but
always associated with ways to effectively protect the system against the harsh environment of the
cement industry.

The general philosophy of the present work can be read through the diagram depicted in fig 1 that
shows the steps involved in the present endeavour of reliability assessment and enhancement of the
baking process of cement industry.

In Chapter 1 are presented the structural as well as the functional description of the baking process
the object of the present study. Thorough knowledge of the process from the structural and
functional point of view is required for developing FMECA and RAMS analyses.

Chapter 2 deals with the analysis of failure modes and mechanisms followed by reliability
modeling of the processes under investigation. Failure mechanisms and reliability models are given
for the different electrical, mechanical and software engineering domains such as found in cement
manufacturing processes.

Chapter 3 describes the Failure Modes Effects and Criticality Analysis fundamentals and procedure
that will be applied to determine potential dominant failures affecting the operational reliability of a
cement plant baking system.
Once the critical points are identified on this strategic system, corrective actions are recommended
and applied allowing an improvement in reliability of the baking system and therefore the
availability of the overall process.
A well conducted FMECA will rely on a good evaluation of the criticality parameters on the base of
Risk Priority Number (RPN). The FMECA has been carried out on the baking system at the
following different levels: rotary kiln, pre-heater, cooling system, ID fan and finally the electrical
process controller.

In Chapter 4 reliability modeling and assessment are developed for the critical electrical parts of
the baking system. According to criticality hierarchisation established, the failure mechanisms, the
FMECAs and reliability assessment are carried out on the sensor-transmitters, the actuators and
finally the controls with the objective of improving their reliability.
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Chapter 5 describes the application of Reliability Centred Maintenance (RCM) whose approach
must be global and comprehensive; is used a preventive maintenance program and control plan for
the electrical , structural and mechanical subsystems of the baking system again with the objective
of continuous improvement and maintaining the inherent reliability at its required level .

Chapter 6 addresses the ways and means of reliability enhancement of the Process Control and
Instrumentation (PCI) subsystems. The most adequate choice of solutions among several are
proposed to improve the reliability of sensor-transmitters, controllers and power supply.

Chapter 7 deals with the two strategic high power drives; the kiln drive DC motor and the 5.5 KV
ID fan Induction motor from which any operational failure will cause plant shut down and hence
considerable economic losses. The enhancement sought after relied on using better performance
technology and improved protection system reliability.

The thesis finishes with a general conclusion together with suggestions for further work.

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