IMPROVING FINE PARTICLE REMOVAL FROM FLUE GASES IN COAL-FIRED PROCESSES. FINAL REPORT

Directorate-General For Energy

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• Publié par: DIRECTORATE-GENERAL-FOR-ENERGY
• Nombre de lectures: 38
• Langue: English
• Poids de l'ouvrage: 3 Mo

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Commission of the European Communities
technical coal research
IMPROVING FINE PARTICLE REMOVAL
FROM FLUE GASES
IN COAL-FIRED PROCESSES
Blow-up from microfiche original Commission of the European Communities
technical coal research
IMPROVING FINE PARTICLE REMOVAL
FROM FLUE GASES
IN COAL-FIRED PROCESSES
Coal Research Establishment
British Coal Corporation
Stoke Orchard
UK-Cheltenham/Glos. GL52 4 RZ
Contract No. 7220-ED/809
FINAL REPORT
Directorate-General Energy
1990 EUR 12649 EN Published by the
COMMISSION OF THE EUROPEAN COMMUNITIES
Directorate-General
Telecommunications, Information Industries and Innovation
L-2920 LUXEMBOURG
LEGAL NOTICE
Neither the Commission of the European Communities nor any person acting on behalf
of then is responsible for the use which might be made of the following
information
Catalogue number: CD-NA-12649-EN-C
© ECSC — EEC — EAEC, Brussels - Luxembourg, 1990 ABSTRACT
Studies have been conducted on specially constructed fabric filter,
multicyclone and electrostatic precipitator test rigs, and other
established test facilities, to improve the design and operation of these
particulate control technologies. The completion of the work coincides
with the introduction of new particulate emission limits for coal fired
combustion plant in the European Community. This report should make a
useful contribution to increased understanding and knowledge of particulate
control technologies and assist in improving control equipment to meet
emission limits at minimum cost.
The work has allowed two important general conclusions to be made:
1. There is considerable scope for improving the performance and reducing
the costs of fabric filtration. Three of the more important options
identified in this work are: (a) introducing the dirty flue gas into
the top of the filter housing rather than the bottom, (b) using a new
heavyweight glass fibre fabric for increased durability at acceptable
cost, and (c) the use of a new proprietary polymeric fabric finish to
increase overall filter performance.
2. Improvements in the design of cyclone systems should increase the
prospects of compliance with the new EC grit emission limit of 100
mg/m3, when the improved cyclones are fitted to chain and travelling
grate stokers. Improvements identified in the report include: (a)
the use of two cell modifier devices to increase grit collection
efficiency and reduce pressure drop, (b) the development of an
intercell baffle arrangement to increase collection efficiency and (c)
the need to design carefully the geometry of the entry and exit
ductwork either side of the multicyclone for maximum equipment
performance.
Further work is required before a mathematical model can be developed
to predict optimum design and performance of electrostatic precipitators.
Studies on the test rig at CRE have confirmed the importance of coal
sulphur content on particle collection by the precipitator. High sulphur
coal promotes particulaten by absorption of SO on the dust
particles which, in turn, reduces the electrical resistivity of the fly
ash. In addition, it has been shown that high combustion efficiency, which
produces low carbon fly ash, is necessary for more effective precipitator
performance.
Ill CONTENTS
Page No.
ABSTRACT III
1. INTRODUCTION 1
2. PARTICULATE EMISSIONS 2
3. FABRIC FILTRATION 3
3.1 Experimental Equipment
3.1.1 Hot gas filter test rig at CRE
3.1.2 Fabricr at Marden test centre 3
3.1.3c filter at Sutton Bonington 4
3.2 Experimental Programmes and Results Obtained 5
3.2.1 Laboratory tests on filter fabrics
3.2.2 Effect of dirty gas entry location on
filter performance 9
3.2.3 Testing of a fabric polymer coating 12
3.2.4 Fabric durability trials at the Marden
test centre 17
3.2.5 Cagey trials at Marden and
Sutton Bonington 23
3.2.6 Costs of fabrics and cages 2
3.3 Discussion of Results (Fabric Filtration)
3.4 Conclusions (Fabric Filtration) 31
4. MULTICYCLONES 3
4.1 Experimental Equipment3
4.1.1 Laboratory test rig at Imperial College 3
4.1.2 Ambient temperature test rig at CRE
4.2 Experimental Programmes and Results Obtained 34
4.2.1 Studies on laboratory-scale test rig5
4.2.2s on CRE test rig 42 4.3 Discussion of Results (Multicyclones) 50
4.4 Conclusions (Multicyclones)3
5. ELECTROSTATIC PRECIPITATION 55
5.1 Electrostatic Precipitator Test Rig at CRE 5
5.2 Experimental Programmes and Results Obtained6
5.2.1 Commissioning tests on ESP test rig
5.2.2 Fly ash electrical resistivity measurements 58
5.2.3 Effect of coal sulphur content on ESP
performance9
5.3 Discussion of Results (Electrostatic Precipitation) 61
5.4 Conclusions (Electrostatic Precipitation) 63
6. GENERAL CONCLUSIONS 64
7. REFERENCES 66
TABLES 1 - XV9
FIGURES 1-49 85
APPENDICES 137
APPENDIX 1 - Particulate Control Technologies 13
Al.l Fabric Filters 13
Al.2 Mechanical Collectors 141
Al.3 Electrostatic Precipitators3
APPENDIX 2 - Particulate Sampling And Measurement Procedures 146
A2.1 BCURA Isokinetic Sampling Method 146
A2.2 Size Distribution by the Coulter Method 147
VI IMPROVING FINE PARTICLE REMOVAL FROM FLUE GASES IN COAL-FIRED PROCESSES
1 INTRODUCTION
There is worldwide concern at the levels of pollutant emissions arising
from the combustion of fossil fuels. A major emphasis of this concern has
been directed towards emissions of sulphur and nitrogen oxides, as
precursors of acid rain and, more recently, towards the "greenhouse " gas,
carbon dioxide. These gases, once emitted, recognise no national
boundaries and it is accepted that international cooperation will be
required to control such emissions to more acceptable levels.
Although the emissions of particulates into the atmosphere do not
normally result in trans-boundary migration phenomena similar to those
experienced by gaseous pollutants, nevertheless, international pollution
control initiatives usually include consideration of particulates as well
as NOx, SO etc. One reason for this attention is the potential health
hazards associated with fine particles below 10 micron diameter. Fine
particles are more likely to penetrate the respiratory system and may have
enhanced levels of toxic trace elements adsorbed onto the particle
surface
In 1988 new environmental standards were specified by the European
Community. This is the Directive which limits emissions of pollutants into
the air from large combustion plants, known as the Large Combustion Plants
3
Directive (Commission of the European Communities, 1988) . The Directive
sets particulate emission standards for each Member State for new plants
over 50 MWt. The particulate emission standards for solid fuel are 100
mg/Nm3 for 50-500 MWt input plant and 50 mg/Nm3 for plant greater than 500
MWt.
The three most important technologies used for cleaning flue gases
derived from coal combustion are fabric filtration (FF), electrostatic
precipitation (ESP) and mechanical collection, including cyclones. Wet
scrubbing is also used. The EC Directive will ensure that the more
efficient gas cleaning systems (le filtration and ESP's) will have to be
specified for many new coal-fired plants. However, cyclones will continue
to have a role in the United Kingdom for email (i.e. less than 20 MWt)
stoker-fired boilers and possibly, also, for large (up to 80 MWt)
travelling grate stokers, where uncontrolled particulate emissions
delivered to the cleaning equipment are often very low. This report describes work conducted over a four year period by the
Coal Research Establishment (CRE) into FF, ESP and cyclone technologies for
coal fired combustion processes. A substantial proportion of the work was
carried out on three pilot-scale test rigs installed at CRE, with ECSC
support, specifically to study the three main methods of particle control:
photographs of the rigs are shown in Figures 8, 38 and 48.
Summary descriptions of fabric filtration, cyclone collection and
electrostatic precipitation technologies are given in Appendix 1.
Descriptions of the isokinetic BCURA particulate sampling method and
the Coulter Counter particulate sizing technique, both of which were widely
used in the test programmes, are provided in Appendix 2.
2 PARTICULATE EMISSIONS
The quantity and size distribution of uncontrolled particulate emissions
arising from the combustion of coal depend upon:
(i) the type of combustion appliance
(ii) operating conditions of the equipment
(iii) coal quality (especially mineral matter content)
Figure 1 shows typical uncontrolled particulate emissions from
different coal combustion appliances firing British coals of typical ash
content. The data in Figure 1 clearly show with some designs of stoker
equipment, where the coal is not fed above the grate through the furnace
region (underfeed, chaingrate, travelling grate etc), that cyclone
equipment may still be able to meet a particulate emission limit of 100
mg/Nm3. Figure 2 shows typical particle size distributions of fly ash
(measured at CRE by the Coulter method) arising from the