LITERATURE REVIEW

Development of aParticle Flow Monitor

Using ElectrostaticSensors

Awais Zafar (az65) Supervisor: Prof. Yong Yan Date: 17/10/2014

Table of Contents1: Introduction......................................1

2: Literature Review.................................1

2.1: Types of Sensing Techniques....................1

2.1.1: Optical System..............................1

2.1.2: Digital Imaging.............................2

2.1.3: Electrostatic Sensing.......................3

3: Proposed Technical Approach.......................3

3.1)...........................Ring Shaped Electrodes

4

3.2)..........................Probe Shaped Electrodes

4

4: Technical Challenges..............................5

4.1) Noise Reduction................................5

4.2) Software Design................................5

4.3) Electrodes.....................................5

5) BIBLIOGRAPHY...................................6

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1: Introduction:

Industrial plant operators in UK and other developed industrialized

countries are really interested in continuously monitoring of

particulate emissions from industrial stacks. One of the reason is that

these techniques provides a purpose of proving to environmental

legislation that their industrial plant’s emission are not exceeding the

agreed emission limit. Also, it provides a feedback to the plant’s

operators on the performance of the arrestment plant, so if any faulty

condition occurs it can be detected as soon as possible. Continuous

particulate emission monitoring is a very challenging technical field

not only because of the demand of the accurate system by the industrial

plant operators but also because of the very harsh environment in which

the system must work properly, the environment includes dust particles

which will test the robustness of any instrument.

This project aims to develop a particle flow measurement monitor which

can continuously monitor the flowing particles in pneumatic conveying

pipelines using suitable electrostatic sensors which will derive the

signals produced by the particles passing through them. The signals will

then go through a process of conditioning and amplification to get the

acceptable values for the software. The objectives of this project

includes:

To design and implement a new particle flow monitor using

electrostatic sensors and digital signal processing techniques.

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To design upper and lower stream electrostatic sensors in a way

that it can be insulated in the pipes.

To design an electronic circuit which will derive the signals from

the electrode for digital processing.

The monitor should be capable of indicating the basic status of the

flow conditions such as pipe blockage, pipe empty or normal.

2: Literature Review: 2.1: Types of Sensing Techniques:

Following are the existing sensing techniques which are being used for

the continuous monitoring of particles in the pipelines:

2.1.1: Optical System:

This method requires a suitable light emitting source at one side of the

pipe and light detecting sensors on the other side of the pipe [2]. This

method works on the principle that the particles in a gas stream will be

interrupting the light from the light source and will be causing a

variation in the intensity of the light received at the light detecting

sensor [3]. So, the greater the particle concentration in the gas stream

the greater the variation in the amplitude of the light signal received

[3]. The velocity of the particles in the pipeline can be measured using

spatial filter and the mass concentration of the particles can be

determined by the using suitable algorithms which can measure the light

intensity on the light sensor [2].

Figure 1 The optical system to monitor the flow of particles [4]

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The advantage of using this technique is that it is not needed to

insert any sort of device in the pipeline thus the particle flow is not

disturbed and also as it is contactless technique the instruments does

not wear out [2]. However, maintenance of this device can be a problem

as light passing through a transparent material to the detector. So, the

transparent material needs to be always clean of any dust particles etc.

2.1.2: Digital Imaging:

Another technique which can also be used for these type of application

is the digital imaging sensing technique which require a laser source

and a charge-coupled device (CCD) camera [5]. Particles in a pipeline

can be illuminated using a laser source which is positioned in such a

way that it highlights the slice through the flow of the particles [5].

Images of the slice can be obtained by using CCD camera [5]. The next

step is the digital image processing which can be applied to extract the

required results or information. The arrangement for this type of

technique is shown in figure 2.

The advantage for this technique is that this contactless sensing

technique as well but it requires more power usage and it is limited to

one type of application only.

Figure 2:Digital imaging sensor arrangement [5]

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2.1.3: Electrostatic Sensing:

The continuous online monitoring of particulate in industrial stacks

using electrostatic sensors with cross correlation has been used before

and the paper written about it entitled “Continuous Measurement of

Particulate Emissions” [6]. In this paper the two electrostatic sensors

are used for the upper and

lower stream signals as

shown in figure 3.

The working principle is based on the theory that the average speed of a

car can be estimated from the known distance between two locations over

the transit time measured by a stopwatch [6]. So, the same principle is

applied on the moving charged particles using cross-correlation

technique to find the velocity of the particles [6]. And then using the

velocity values, the mass emission from the stacks can be mathematically

calculated using the following equation [6]:

qm=3.6Avβm (eq 1)

Where,

qm = mass emission (g/hour)

A = cross-sectional area of the duct (m2 )

V = velocity of the particles (m/s)

βm = mass concentration of the particles (mg /m3 )

Figure 3 Working of a probe type electrostatic sensors [6]

Figure 4 Ring type electrode [8](diameter > 500mm)

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The technique of using electrostatic sensor to monitor the particulate

emission have many advantages over other existing techniques. Some of

them are 1) Robustness, 2) High sensitivity of the sensors, 3) The probe

shaped electrodes are much suitable for monitoring the particle flow for

large stack sizes and 4) Easy to install on a process.

3: Proposed Technical Approach:The working principal of the technique which is to be used for this

project is based on the theory that particles in pipeline carry

electrostatic charges [7]. The amount of charge on the particles can be

detected using electrostatic sensors which will be insulated in the

pipes [7]. When the particles pass through them they produce

fluctuations in the electric field which produces signals which can be

analysed using signal processing techniques [7]. There are two types of

electrostatic sensor which is used for these type of applications:

3.1) Ring Shaped Electrodes: Ring type electrode are very useful in smaller diameter stack

(diameter < 300mm) [7]. Also, they don’t obstruct the particles in

the duct. However, it can create issues in case of duct with larger

diameter (>500mm) as the size of the electrodes depend on the size

of the ducts for proper electrostatic sensing. The larger ring type

electrode will be harder to install and to maintain as it will be

heavy and also it will be more expensive.

Figure 5 Probe Shaped Electrodes [6]

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3.2) Probe Shaped Electrodes:Probe shaped electrode can be mounted through drilled hole on the

duct and they are more suitable in these applications [6]. Also, if

the electrodes are directly exposed to the charged particles, the

charge transfers because of the contact between the electrodes and

the particles [6]. However, if electrodes are coated with non-

conductive material to avoid direct contact with the charged

particles in stacks and so the system can sense the fluctuations

through electrostatic induction [6].

After getting the required charges of the particles, it will go through

a signal conditioning circuit which will be designed for each electrode

and it will be consisting of three circuits and they are 1) Pre-

Amplification, 2) Post-Amplification and 3) Low-pass filter [1]. And

when the signals conditioning process is complete for both electrodes

the signals will be pass to analogue to digital signals converter then

to the software for analysing. Following is the block

diagram of the complete system.

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4: Technical Challenges:

The technique which will be used to develop the monitor is the most

inexpensive and easy to install on a process because of its robustness

and compact in size makes it the most suitable technique in these

applications. However, there are some technical challenges which needs

to be taken in consideration while following this technique.

4.1) Noise Reduction: Electrostatic sensors are very sensitive to noise which can

affect the signals and don’t produce the required result but if they are

housed in a proper shielded box which will minimize the noise from the

environment then this problem can be overcome but some tests needs to be

done before making the final product for noise effects [1].

4.2) Software Design: The software could be the most challenging and time consuming

part of this project because the cross correlation is a very complex

technique, how the signals can manipulated and how the software handles

them is going to be the challenging task. Also, the software need to

have the intelligent aspect to it to indicate when there is a pipe

blockage, pipe empty or normal. And user friendly graphical interface

must be developed.

4.3) Electrodes:Another challenging task on which the accuracy of the whole project is

depending is the designing of the electrostatic sensors. As previously

mentioned probe shaped electrodes are suitable for this project but the

Figure 6 Block diagram showing important

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distance between the sensors should not be much greater nor too less. In

first case it will affect the accuracy of the software and in the second

case the charges on one electrode can affect the charges on the other

electrode. So the perfect distance between the sensors needs to be

determined by some tests.

5) BIBLIOGRAPHY

[1]: Y. Yan, S. J. Rodrigues and Z. Xie “Non-contact strip speed measurement using

electrostatic and correlation signal-processing techniques” Measurement Science and

Technology, vol. 22(7), 075103, doi:10.1088/0957-0233/22/7/075103.

[2]: Ichikura, Y. 1995. Measurement of particle flow by optical system. [ONLINE] Available at:http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=483963&tag=1. [Accessed 14 October 14].

[3]: Bivins, D. 2000. CURRENT KNOWLEDGE OF PARTICULATE MATTER (PM) CONTINUOUS EMISSION MONITORING. [ONLINE] Available at:http://www.epa.gov/ttnemc01/cem/pmcemsknowfinalrep.pdf. [Accessed 14 October 14].

[4]: Topas. 2005. Particle Measurement - Aerosol Spectrometer / Particle Counter / Photometer. [ONLINE] Available at: http://www.topas-gmbh.de/_510_en.htm. [Accessed 10 October 14].

[5]: Carter, R.M. and Yong, Y. 2005. An Instrumentation System Using Combined Sensing Strategies for Online Mass Flow Rate Measurement and Particle Sizing. [ONLINE] Available at:http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1468550. [Accessed 05 October 14].

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[6]: Yong, Y. 2005. continuous measurement of particulate emissions. [ONLINE] Available at:http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1518620. [Accessed 08 October 14].

[7]: H. Seraj. 2012. Measurement of velocity of solid/air two phase fluid using electrostatic sensors and cross correlation technique . [ONLINE] Available at:http://www.sciencedirect.com/science/article/pii/S1026309812003021. [Accessed 10 October 14].

[8]: Yan, Yong, 2013. Case Studies Lecture. (EL565), 21 November. 5.