Electrostatic precipitator modeling and simulation

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• Electrostatic precipitator modeling and simulation

Kejie Fang Longhua Ma Institute of Industrial
Control Zhejiang University
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OUTLINE OF PRESENTATION

• Introduction

• Research and design in ESP

• Simulation results and analysis

• Conclusion

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• INTRODUCTION

1. Background
Nowadays, the environment protection has
become a crucial problem and the authorities are
requested to set increasingly more stringent
limits , one of which is the emissions from the
industrial plants of solid particulate and other
gaseous pollutants.
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• Introduction

2. ABOUT ELECTROSTATIC PRECIPITATOR

2.1 What is ESP
Electrostatic precipitator (ESP) is a widely used
device in so many different domains to remove the
pollutant particulates, especially in industrial
plants.
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• Introduction

2.2 HOW ESP WORKS
2.2.1 Main process of ESP
Generally, the processes of electrostatic
precipitator are known as three main stages
particle charging, transport and collection.
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• Introduction

These are stages interacted that originated from
the complexity of the processes of precipitator.
To characterize all these stages determines to
take a great number of basic phenomena into
account from a physical point of view when they
occurred.
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Schematic of wire-plate ESP

• Introduction

Fig.1 Schematic of wire-plate electrostatic
precipitator
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Mechanism of ESP

• Introduction

Fig. 2 Mechanism of electrostatic precipitator
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• Introduction

2.2.2 PROCESS OF Particle charging
Particle charging is the first and foremost
beginning in processes.
As the voltage applied on precipitator reach
threshold value, the space inside divided into
ionization region and drift region.
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• Introduction

The electric field magnitude around the negative
electrode is so strong that the electrons escape
from molecule.
Under the influence of electric field, the
positive ions move towards the corona, while the
negative ions and electrons towards the
collecting plates.
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• Introduction

2.2.3 Particle transport
In the moving way, under the influence of
electric field, negative ions cohere and charge
the particles, make the particles be forced
towards collecting-plate as well as Fig.2 shows.
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• Introduction

2.2.4 Particle collection
As soon as the particles reach the plate,
they will be neutralized and packed by the
succeeded ones subsequently. The continuous
process happens, as a result, particles are
collected on the collecting plate.
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• Research and design in ESP modeling

The numerical model describes in time and
space the relevant processes that are involved in
transport, charging, migration and collection of
fly ash. To represent the complete processes, the
model is therefore structured into several
modules.
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The model here is organized into the following
three sections

• electric field and discharge processes

• particle charging

• particle collection

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3.1 electric field and discharge processes
The particle collection in electrostatic
precipitators is largely dominated by the
distribution of the electric field in the
interelectrodic space.
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In the absence of particles, neglecting the
transport gas velocity and by assuming that the
magnetic field due to the corona current is
negligibly small.
Electronical conditions are described by next
three equations
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(1)
(2)
(3)
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Here, we adopt equations (4) (5) (6) to describe
the electric field distribution with the initial
and boundary conditions.
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V( x, y) means the electric potential of the
position (x, y), V0 is the initial potential on
the wire, Sx is distance between collecting plate
and wire, Sy is half length of the two nearest
wires ,a is the radius of particle, when x, y
means the coordinates direction, shown as Fig.3.
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Fig. 3 Sketch of precipitator geometry and
computed grid
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(5)
(6)
and V0 mean the charge density and electric
potential at the position as Fig.3 shown.
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3.2 particle charging
The field charging refers to the local distorsion
caused near the particle surface by the
difference in dielectric constants.
This process continues until the particle goes up
to the saturation charge, which produces an
electric field on particle surface equal and
opposite to the external field.
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Equation (7) is chosen to describe the model of
particle charging
(7)
Where is the relative dielectric constant
and E0 is the external field, qs and R are the
particle charge and radius.
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3.3 particle collection
This module simulates in detail the boundary
layer near the collecting plates and the
interchange that take place.
Here, we choose equation (8) to describe particle
collection .
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(8)
C is the particle density, C0 is the entry
density of particle, a is the unit collecting
area in the flow way, f is area of ESP cross
section, when w means particle velocity towards
plate and v is the velocity moving to outlet.
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4 Simulation results and analysis
According the above analysis of the
mechanism and modeling of ESP, we design a simple
ESP simulation platform which is based on Scilab
.
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Fig.4 Simulation Platform
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Fig.5 Input Interface
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Simulation of electric field
Fig.6 Distribution of electric field Ex
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we can find that around the wires, Ex get a
largest value, when at the connecting way of two
wires, Ex is no more than zero. The cause of this
distribution is the potential, at the connecting
way of wires, nearly zero. Ex is decreased
regularly from the wire at the coordinate line x,
but larger when close to the collecting plate.
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Simulation of electric field
Fig.7 Distribution of electric field Ey
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Simulation of particles density distribution
Fig.8 Particle density distribution in ESP
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From Fig.8, we see the particles density
distribution obviously. The density reaches the
largest value at the entry of the ESP under the
influence of electric wind. The value of density
gets smallest near the wire at the direction to
collecting plate.
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Simulation of deposit density
Fig.9 Distribution of deposit density
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Fig.9 shows us the deposit density, along the
collecting plate deposit density is decreased
definitely, since as time go on, the particle is
collected by the plate continuously. So at the
later part, the deposit density is lower, and
reasonable.
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• CONCLUSION

we construct a numerical model of
electrostatic precipitator and design base on
Scilab. The simulation results of these processes
are according with laboratory experimental tests
to obtain physical information and useful
validations.
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The
End
Thanks