School of Engineering Engineering and Digital Arts

Flame characterisation in a multi-burner heat recovery boiler through Digital Imaging andrecovery boiler through Digital Imaging and Spectrometry

James Cugley, Gang Lu and Yong Yan, University of KentGavin Marshall, British Sugar

11th European Conference on Coal Research and its Applications, Sheffield, 5th-6th Sept 2016

Outline

• Introduction

• Technical Strategiesg

• System Development

• System configuration

• Flame analysis

• Initial Lab Test

• Conclusions and Future work• Conclusions and Future work

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Introduction

• Fossil fuel fired utility boilers are firing a range of fuels under variable operation conditions.

• This variability in fuel diet and load conditions can lead to various combustion problems in boiler such as furnace safety, combustion efficiency and pollutant emissions such as NOx and CO.

• For instance, British Sugar operates a heat recovery water tube boiler which recovers the energy in the exhaust gas from two LM6000 gas turbinesturbines.

• It has been reported that if the flame properties (such as size, shape, location, colour, and temperature distribution) particularly at the start/stop stage of burners change, the emissions would change.

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Introduction

• AimTo develop an instrumentation system for monitoring burner flames and predicting emissions on a multi-burner heat recovery boiler using digital imaging and spectrometric techniques.

• Objectives• to develop a prototype instrumentation system (hardware platform and

computer algorithms) for flame monitoring and predicting emissions (NOx and CO);

• to evaluate the system initially on a laboratory combustion test rig and then on full-scale heat recovery boilers under a range of combustion conditions;

• to study the spectroscopic characteristics of the flame including main free radicals (CH*, CN*, C2*) and their relationships to emissions;

• to make recommendations for improvements of existing furnaces through the use of the new technology developed.

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Introduction

• Technical challenges

• Multiple parameter measurement– the measurement of the flame p pcharacteristic parameters must be simultaneous to reflect the fast-changing nature of a flame.

• Quantitative assessment of flame– Effective algorithms should be• Quantitative assessment of flame– Effective algorithms should be developed to quantify the flame sensorial data and thus flame stability.

• Hostile environment– Given the high temperature and dust inside th b il d ibl ib ti ll ti l d l t ithe boiler and possible vibrations, all optical and electronic components must be appropriately protected.

• Variable operation conditions– The system should be able to give p y gvalid measurements over a wide range of operation conditions.

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Technical Strategies

• Digital imaging and spectrometric techniques are employed to acquire

g

• Digital imaging and spectrometric techniques are employed to acquire flame images and spectrometric characteristics.

• The flame characteristics are analysed so as to produce the quantified information to assess the performance of the boiler.

Optical probe & fib& fibre

Geometry, luminosity,

Temperature

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Schematic of the technical strategies

System Developmenty p

• System configuration• The system consists of an optical probe with a 70 tilted objective

lens and a 90 angle of view, a CCD camera, a UV-VIS fibre optic cable, a spectrometer, a water-air cooled jacket, an embedded computer and system application software.

• The water-air cooled jacket with an isolation mechanism is to ensure the probe working under a high temperature and positive pressure of the boilerthe boiler.

• Flame data collected by the camera and the spectrometer are processed concurrently by the embedded computer.

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System Developmenty p

Furnace wall

• Schematic of the system design

Embedded computerWater

inAir in

Furnace wallSupporting flange Probe

assembly Spectrometer

Boiler

58.50

90°

View port Water out

Ball valve CameraWater jacket

FlameComp ter

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Computer(control room)

System Developmenty p

• Overview of the system

Supporting flange

Ball valve

Water jacketCamera

Optical probe assembly

Objective lens

Water-air jacket and probe assembly Optical probe and objective lens

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System Development

S f

y p

• Software• Application software including GUI is developed to process and

display the measurement resultsdisplay the measurement results.

GUI for spectroscopic analysis GUI for Image processing

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Flame Analysisy

• Flame parameters to be measured

• Geometric parameters• Iignition point (Lip)• Length (L)

Luminous region

• Luminous region (Rf )

o

Burner

• Luminous parameters• Brightness o

Lip

L

• Brightness• Non-uniformity

• Temperature distributionL

• Spectra-parameters• Flame Emission spectroscopy (FES)• Intensity Indexes

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• Intensity Indexes

Flame Analysis

T t

y

The flame temperature is determined from the relationship between the two primary colours of the images captured by the RGB colour camera

• Temperature

primary colours of the images captured by the RGB colour camera.

• Three separate channels corresponding to primary colours Red (R), Green (G) and Blue (B) are captured from the camera.

• A combination of the colour-banded images can thus be used for the determination of the flame temperature distribution based on the two-colour principle.

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Flame Analysis

S t i t

y

There are two elements to the radiation spectrum produced by th b ti Th i i d b ti li

• Spectroscopic parameters

the combustion process. The emission and absorption lines as well as the blackbody curve.

• The blackbody curve is resulted from the heat emitted from the solid/soot particles produced during combustion.

• The radiative information of free radicals (e.g., OH*, CH*, CN*( g , , ,and C2

*) is of interest.

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Flame Analysisy

• The measurements of OH*, CH*, CN* and C2* emission show in

• Spectroscopic parameters

The measurements of OH , CH , CN and C2 emission show in the past to give a strong correspondence to the quality combustion. The information obtained can be used,

• to monitor combustion state.

• to compute the flame intensity index to ensure the burner balance and to provide better feedbacks to boiler controland to provide better feedbacks to boiler control.

• to study the condition of the combustion for an optimal performance, particularly the production of emissions (e.g., NOx).

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Initial Lab Tests

• Experiments were conducted in the university laboratory to evaluate the system before industrial trials.

• Initial tests were carried out on a lab scale gas fired combustion rig• Initial tests were carried out on a lab-scale gas fired combustion rig with different equivalence ratios.

Test rig Test conditions

Condition Air flow(l/m)

Propane (l/m)

Equivalence Ratio (ϕ)

1 7.49 0.6 0.625Optical probe

Camera2 7.45 0.65 0.556

3 7.32 0.8 0.455

probe

Experimental setup

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Experimental setup

Initial Lab Tests

• Below shows the flame images taken under the different equivalence ratios, with the raw spectrum data for each alongside it. It is clear that as the flame spectrum varies with the equivalence ratiothat as the flame spectrum varies with the equivalence ratio.

0.6250.5560.455

Flame images for different

0.625 0.556 0.455

Flame spectrum for different

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Flame images for different equivalence ratios (ϕ)

Flame spectrum for different equivalence ratios (ϕ)

Initial Lab Tests

• It is also observed that there are clear peaks of radicals OH* and CN*/CH* in the flame spectrum.

• Studying those information will allow us to find a connection to the• Studying those information will allow us to find a connection to the production of emission such as NOx.

OH* spikes CN*/CH* spikes

0.6250.5560.455

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UV spectrum of fame for different equivalence ratios (ϕ)

Conclusions and Future Work

• The existing technique for flame imaging and spectrometry analysis has been reviewed.

• A system featuring a camera and spectrometer is under• A system featuring a camera and spectrometer is under development to access industrial boilers.

• The system constructed and the flame parameters to be measured has been identified.

• Initial lab tests have been carried out to evaluate the new system.

• Future work is to install and test the system on an industrial boiler at British Sugar under a range of combustion conditions (March 2017) and to study the spectroscopic characteristics of the flame2017), and to study the spectroscopic characteristics of the flame and their relationships to emissions.

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Acknowledgement

Authors would like to thank the Biomass and FossilAuthors would like to thank the Biomass and Fossil Fuels Research Alliance (BF2RA ) to provide a financial support for this research programme.pp p g

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Thank you!Thank you!

Any Questions?Any Questions?

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