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TitleElectrical Operation Of Electrostatic Precipitators
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Table of Contents
                            Contents
Preface
Acknowledgements
1 The range and application of electrostatic precipitators
	1.1 Introduction
	1.2 Arrangement and basic operation of a precipitator
	1.3 Versatility
	1.4 Characteristics of the gases as they affect precipitator design
		1.4.1 Composition
		1.4.2 Temperature
		1.4.3 Pressure
		1.4.4 Gas flow rate
		1.4.5 Viscosity and density
	1.5 Characteristics of the suspended material and their possible impact on precipitator performance
		1.5.1 Concentration
		1.5.2 Composition and electrical resistivity
		1.5.3 Particle sizing
		1.5.4 Particle shape
		1.5.5 Particulate surface properties
	1.6 Sizing of electrostatic precipitators
	1.7 References
2 Fundamental operation of an electrostatic precipitator
	2.1 Introduction
	2.2 Ion production
	2.3 Particle charging
	2.4 Particle migration
	2.5 Particle deposition and removal from the collector electrodes
	2.6 Precipitator efficiency
	2.7 Practical approach to industrial precipitator sizing
	2.8 References
3 Factors impinging on design and performance
	3.1 Effect of gas composition
	3.2 Impact of gas temperature
	3.3 Influence of gas pressure
	3.4 Gas viscosity and density
	3.5 Impact of gas flow rate and gas velocity
	3.6 Gas turbulence
	3.7 The importance of gas distribution
		3.7.1 Correction by model testing
		3.7.2 Computational fluid dynamic approach
	3.8 Effect of particle agglomeration
	3.9 Particulate cohesivity effects
	3.10 References
4 Mechanical features impacting on electrical operation
	4.1 Production of ions
		4.1.1 Quasi-empirical relationships
	4.2 Discharge electrode forms
	4.3 Spacing of discharge electrodes
	4.4 Collector electrodes
	4.5 Specific power usage
	4.6 Precipitator sectionalisation
	4.7 High tension insulators
	4.8 Electrical clearances
	4.9 Deposit removal from the collector and discharge systems
		4.9.1 Impact of collector deposits on electrical operation
		4.9.2 Measurement of rapping intensity on dry precipitatorcollectors
	4.10 Hopper dust removal
	4.11 Re-entrainment from hoppers
	4.12 References
5 Development of electrical energisation equipment
	5.1 Early d.c. energisation techniques
	5.2 Development of a.c. mains frequency rectification equipment
		5.2.1 Valve rectifiers
		5.2.2 Mechanical switch rectifier
		5.2.3 Metal oxide rectifiers
		5.2.4 Silicon rectifiers
	5.3 HT transformers
		5.3.1 Transformer losses
	5.4 Cooling of transformer and rectifier equipment
	5.5 Primary input control systems
		5.5.1 Manual methods
		5.5.2 Motorised methods
		5.5.3 Saturable reactors
		5.5.4 Silicon controlled rectifiers (SCRs)
	5.6 Automatic control systems
		5.6.1 Early current control
		5.6.2 Voltage control method
		5.6.3 Computer control methods
	5.7 Summary of developments
	5.8 References
6 Modern mains frequency energisation and control
	6.1 Basic operation of mains frequency equipment
	6.2 High voltage equipment supply ratings
		6.2.1 Mean precipitator current
		6.2.2 Primary r.m.s. current
		6.2.3 Precipitator peak voltage under no-load conditions
		6.2.4 Apparent input power
		6.2.5 Practical example
	6.3 Influence of the linear inductor
		6.3.1 The main function of the inductor
		6.3.2 Physical implementation of the linear inductor
	6.4 Automatic voltage control and instrumentation
		6.4.1 Secondary metering approach
		6.4.2 Primary metering system
		6.4.3 Opacity signal and full energy management
	6.5 Basic AVC control principles
	6.6 Back-corona detection and corona power control
	6.7 Specific power control
		6.7.1 Control by the use of intermittent energisation
		6.7.2 Supervisory computer control using a gateway approach
	6.8 Advanced computer control functions
	6.9 References
7 Alternative mains frequency energisation systems
	7.1 Two-stage precipitation
		7.1.1 Air cleaning applications using positive energisation
		7.1.2 Two-stage precipitation as applied to power plantprecipitators
	7.2 Intermittent energisation
		7.2.1 Basic principles of intermittent energisation
		7.2.2 Comparison of IE with traditional d.c. energisation
		7.2.3 Collection efficiency evaluation
	7.3 Pulse energisation
		7.3.1 Introduction
		7.3.2 Electrical configurations
		7.3.3 Electrical operation with pulse chargers
	7.4 Major operational aspects of pulse energisation
		7.4.1 Current control capabilities
		7.4.2 Current distribution on collectors
		7.4.3 Electrical field strength in the inter-electrode area
		7.4.4 Particle charging
		7.4.5 Power consumption
		7.4.6 Worked example of energy recovery
	7.5 Collection efficiency
	7.6 Typical applications using pulse energisation
	7.7 References
8 High frequency energisation systems
	8.1 Introduction
	8.2 Development of switch mode power supply systems
		8.2.1 Expected operational improvements
		8.2.2 System requirements
		8.2.3 Design considerations
		8.2.4 SMPS circuit configurations
	8.3 Input rectification stage
		8.3.1 Three phase six switch mode UPF converter
		8.3.2 Three phase boost type UPF rectifier
		8.3.3 Three phase full wave rectifier with a.c. side filtering
		8.3.4 Comments on the various input stage topologies
	8.4 High frequency inverter stage
		8.4.1 PWM controlled ‘H’ bridge inverter
		8.4.2 Resonant converter
		8.4.3 Matrix converter
		8.4.4 Comments on the various inverter topologies
	8.5 High voltage, high frequency transformer
		8.5.1 Parasitic capacitance
		8.5.2 Magnetic leakage flux
		8.5.3 Insulation and electric stress management within thetransformer
		8.5.4 Corona effects
	8.6 Transformer output rectification
	8.7 Short duration pulse operation
	8.8 Advantages of the SMPS approach to precipitator energisation
	8.9 Review of the various topologies leading to a prototype SMPS development under a UK EPSRC grant
	8.10 Operational field experience with SMPS precipitator energisation
		8.10.1 SMPS system of Supplier No. 1
		8.10.2 SMPS system of Supplier No. 2
		8.10.3 SMPS system of Supplier No. 3
		8.10.4 SMPS system of Supplier No. 4
		8.10.5 Advantages/conclusions reached from these field trials
	8.11 References
9 The impact of electrical resistivity on precipitator performance and operating condition
	9.1 Particle composition
	9.2 Particle resistivity
	9.3 Measurement of particulate resistivity
	9.4 Resistivity effects on low temperature power station precipitators
	9.5 Correlation between precipitator performance and particulate resistivity
	9.6 Low resistivity ash and its effect on performance
	9.7 Equipment for flue gas conditioning
		9.7.1 Sulphur trioxide conditioning
		9.7.2 Ammonia conditioning
	9.8 Humidity conditioning
	9.9 Reducing inlet gas temperature
	9.10 Summary of resistivity effects on precipitator performance
	9.11 References
10 ‘On-line’ monitoring, fault finding and identification
	10.1 Corrosion condition monitoring
	10.2 Electrical operating conditions
		10.2.1 TR control cubicle information
		10.2.2 TR set panel meter readings
		10.2.3 TR equipment lamp test
	10.3 Deposit removal from the internals
	10.4 DE and collector system voltage/current relationships
		10.4.1 Clean air load characteristic
		10.4.2 Operational curves with gas passing through the system
		10.4.3 Dirty air load test, without gas passing through system
	10.5 Collector/discharge electrode alignment
	10.6 High tension insulators
	10.7 Hoppers
	10.8 Gas distribution and air inleakage
	10.9 Changing inlet gas conditions
		10.9.1 Particle resistivity
		10.9.2 Particle sizing and opacity monitoring
	10.10 Systematic fault finding procedure
	10.11 References
Index
                        
Document Text Contents
Page 1

IET Power and Energy Series 41

Electrical Operation
of Electrostatic

Precipitators

Ken Parker

Page 142

The values obtained when the short circuit reactance of the transformer z is
9 per cent are shown in Table 6.3 in comparison to the same rated mean current
and voltage as obtained with a linear inductor. (The figures in parentheses corres-
pond to the values obtained with a normal short circuit reactance of 35 per cent.)

Comparing the results without added impedance to those obtained with a
normal short circuit reactance (� 40 per cent), Figure 6.2, for the same precipita-
tor mean current and precipitator load, the following disadvantages become
apparent.

(a) The peak value of the precipitator current is larger and its duration is
shorter, resulting in a 36 per cent higher form factor.

Figure 6.5 Precipitator waveforms without added impedance

Modern mains frequency energisation and control 127

Page 143

(b) The higher form factor results in a higher primary current and apparent
input power for the same precipitator mean current.

(c) The time incidence of the precipitator voltage peak is closer to that of the
line voltage peak value.

(d) Since sparking occurs around the peak of the precipitator voltage, the
current surges have a higher amplitude and longer duration.

These characteristics are detrimental for stable operation of the precipitator,
especially in relation to voltage recovery after spark.

In addition to the above the precipitator current, obtained with a delayed
firing angle, produces a larger phase angle difference between the line voltage
and the fundamental component of the primary current giving in a lower power
factor, which is not desirable by the power supply companies.

However, the advantages of operation without adequate impedance can be
theoretically claimed, as follows.

The precipitator voltage waveform is more pulsating because the peak value
is higher, which could have a positive effect in the case of high resistivity
particles. (Currently one system of resolving this problem is to use
intermittent energisation or pulse charging techniques – see Chapter 7.)

In the case of precipitator loads requiring a higher voltage, the power
supply is better suited to deliver its rated values because of the lower voltage
drop across the short circuit reactance.

6.3.2 Physical implementation of the linear inductor

The linear inductor usually comprises an iron core inductor with a suitable air
gap providing a linear impedance characteristic. This is normally placed inside
the high voltage tank and its inductance cannot be changed. This is a good
economic solution, provided a good match exists between the size of the power
supply and the bus section.

Some manufacturers, however, locate the inductor inside the control cabinet,
which can then be provided with changeover tappings. These allow one to
change the inductance value to overcome any mismatch between the power

Table 6.3 Current and voltages with insufficient short circuit impedance compared
with values obtained with normal design impedance level (courtesy FLS Miljö a/s)

Firing angle t0 (ms) 5 (3)
Primary current Ip r.m.s. (A) 302 (223)
Precipitator current I0 r.m.s. (mA) 1900 (1400)

I0 peak (mA) 4400 (2350)
I0 mean (mA) 1000 (1030)

Precipitator voltage V0 peak (kV) 90 (78)
V0 mean (kV) 61 (61)
V0 min (kV) 38 (46)

128 Electrical operation of electrostatic precipitators

Page 284

Hard switching HFDC supplies 205
Heavy metals 55
High resistivity particles, see Particle

resistivity
High temperature/high pressure precipitation

13, 43, 44
High voltage measurement

mean kV resistance 114
peak kV capacitance 114

High voltage supplies, see Electrical
energisation

History of precipitation
early designs and applications 89

Hoppers
air inleakage 86
overfilling effects of 85–6

Hot side ESPs 225
Hydrofiners 12

Instrumentation for AVC
secondary 130
primary 131
opacity/energy saving 132, 134
energy management 133, 135

Insulators
HT. lead through 76, 77
heating & purging 259
rapping drives 77

Intermittent energisation see Electrical
energisation

Ionisation 4, 22, 25–6
Ionisation coefficient 24, 25
Ion production 63

Laplace equation 19, 22
Linear inductors 109, 115, 120, 126, 128, 128
Line control resistors 108, 109
Low resistance particles 236

Materials of construction 12
for high temperature applications 41
for wet precipitators 41

Maxwell equation 64–5, 121
Mechanical design features

DE formats 18, 65, 69–70, 70, 215
DE separation 71, 72
DE radius of curvature 68, 68
Electrical clearances 79, 80
Electrode support insulators 70, 77, 78
Gas distribution 48–54
Hoppers, overfilling/inleakage 85–6
Rapping 4, 32, 48, 80
Re-entrainment 32, 44, 48, 84, 86, 262
TR sectionalisation 5, 75, 75, 76

Mist precipitators
applications and design 8, 9

Modelling of precipitators
Modified Deutsch Formulae

Matts Ohnfeldt 34–5, 44, 45
Petersen(FLS) 34

Navier Stokes equations 50

Particle charging mechanisms 4
Cochet’s model 27–8
Impact/collision charging 4, 27–8
ion diffusion 27–8
saturation charge 27–8, 28
particle concentration 14

Particle migration 29
exponential law 33
practical consideration 33
theoretical 30

Particle re-entrainment 48
Particle resistivity 1, 216

critical value 15, 224
effect on performance 41, 220
effect of temperature 41, 42, 218, 218, 219,

234
effect of sodium in ash 221, 222
effect of sulphur + sodium on resistivity 222
effect of sulphur + sodium on perform. 222
measurement laboratory/site 217, 218, 219
Bickelhaupt prediction of resistivity 222
resistivity change conditioning 41, 224–5,

234
low resistivity dust 16, 226
surface properties of particulates 18, 216
matrix resistivity 18, 216
difficult dusts 19

Particle size
distributions 16, 215
grade efficiency relations 16, 31
shape 17, 216

Particle transport 30
see Effective migration velocity

Pilot precipitators
Plasma region 27
Poisson’s equation 19, 22, 123
Positive/negative energisation 23, 26–7
Precipitator Applications 10–11, 170–1
Pulse charging see Electrical energisation

Rapping 4
collectors 32, 80
discharge elements 32

Rapping optimization 4, 32, 80, 82
Rapping intensity and frequency 84
Re-entrainment effects 32, 44, 48, 84, 86, 236,

262
Rectifiers

Mechanical switch 92, 95, 96
Valve cold/hot cathode 91, 92, 93
Metal oxide copper oxide 97, 97
Metal oxide selenium 97, 98
Silicon 2, 98–101, 98

Rectifier control methods
early transformer tap changing 107
autotransformer motorised 108, 109
transductor/magnetic saturable reactors

109, 110

Subject index 269

Page 285

thyristors 2, 110, 111, 121
see also Automatic voltage control

Residence time 44
Resistivity see Particle resistivity
Reverse ionisation 15, see Particle resistivity
Reynolds number 29, 51
Ruhmkorff coil 89, 90, 91
Ruhmkorff output waveforms 90

Saturation charge on particle 27
Scouring of dust from internals 48
Sectionalization 5, 75, 75, 76
Selective dust separation
Single stage precipitation 2–3
Sneakage and sweepage 49
Sodium depletion 225
Space charge effects 7
Space charge region 26
Sparking 138, 138, 139
Spray irrigation 6, 32
Specific collecting area (SCA) 35, 44, 45
Specific power input 73, 74, 76, 142
Stokes-Cunningham correction 29, 55
Switch mode power supplies 175–212
(see also HFHV operation)
Sulphur reducing bacteria 41
Supervisory AVCs 143–4

Temperature effect on performance 40–1
Temperature effect on design 12
Theory of precipitation 1
Theoretical migration velocity 30, 31, 34
Treatment time 19, 44
Trichel pulses 27
Transformer – HV mains design

Winding arrangements 101
Losses 102
Cooling of units 105

Equivalent circuit 105
Oil testing 106, 107
Current form factor 121
TR ratings 123
Secondary current 123–4
Primary current 125
Secondary voltage
Apparent power 125

Transformer – HFHV design
Parasitic capacitance 188
Magnetic leakage flux 188
Insulation and stress management 188
Corona effects 190

Tube type precipitators 8, 60
Turbulence in ESPs 46, 47
Two stage precipitation 2, 3, 21, 147, 148, 149

Ultra-violet region 27
Upgrading of precipitator performance 35,

36

van der Waal forces 4, 32, 58
Velocity of gas 44, 45, 47
Viscosity and density of gas 44
Volatile materials 56
Voltage and current waveforms 102, 120, 122,

127
Voltage doubler circuit 95

Wet precipitators 6, 7
applications 57–8
collector film flow 32
spray irrigation 6, 32
washdown system 6, 32
water treatment 57

Wimshurst & Voss generators 21

Zero crossing (thyristor switching) 119

270 Subject index

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