Case Studies on Biomass and Co-FiringPresented to FFF OIB Workshop
Peter McIntyre19th September 2013
ALSTOM JOHN THOMPSON
MAY 2007Introduction
• This presentation describes a number of case studies of units put into service by JT and sister companies over a 30 year period.
• As a preface, some fundamental physical and chemical parameters are given which played a role in the selection of the units or influenced their performance in operation
ALSTOM JOHN THOMPSON
MAY 2007Fuel Considerations
An accurate, detailed knowledge of the fuel is fundamental for proper boiler selection and design
ALSTOM JOHN THOMPSON
MAY 2007Fuel Considerations
Chemical properties
Proximate analysis– Indicates combustion properties
• Volatiles• Ash• Moisture• Fixed carbon • Gross calorific value
ALSTOM JOHN THOMPSON
MAY 2007Fuel Considerations
Chemical properties (cont).
Ultimate analysis– Gives basic chemical constituents
• Carbon• Hydrogen• Oxygen• Nitrogen• Sulphur• Chlorine
ALSTOM JOHN THOMPSON
MAY 2007Fuel Considerations
Chemical properties
Ash chemistry
Knowledge of ash constituents gives an idea of the fuel’s propensity for:
• Slag formation• Clinker formation• Fouling of heat transfer surfaces• Fuming problems
ALSTOM JOHN THOMPSON
MAY 2007
Chemical and Physical Characteristics of typical fibrous fuels
Sunflower
Seed Husks
CottonStalks
Bagasse Furfuralresidue
Pine Bark
Rice Hulls
Jack Pine
Waste
Cotton Seed
Husks
Proximate
Ash 3.0 3.8 1.7 2.9 1.5 21.5 1.3 2.3
Volatile 66.1 57.3 37.9 37.3 36.5 35.7 44.6 68.7
Carbon 19.6 22.1 5.4 8.0 12.1 34.8 14.2 19.3
Moisture 10.5 16.8 55.0 51.9 50.0 8.0 40.0 9.7
Ultimate(DAF)
C 55.1 53.6 47.7 56.2 55.0 49.4 53.4 49.9
H 603 5.2 5.9 5.8 5.8 6.2 5.9 6.3
O 41.5 38.9 44.6 37.4 39.0 43.8 38.6 42.7
N 0.9 1.3 1.8 0.5 0.1 0.3 0.1 1.0
S 0.2 1.0 - 0.1 0.1 0.4 - 0.1
GCV(daf) 20870 18110 18950 18000 21630 17370 20755 19380
ALSTOM JOHN THOMPSON
MAY 2007
Chemical and Physical Characteristics of typical fibrous fuels
Sunflower Seed Husks
CottonStalks
Bagasse
Pine Bark
Rice Hulls
Jack Pine Waste
Cotton Seed Husks
Ash Composition
Na2O 0.4 2.0 2.8 1.3 0.1 - 1.4
K2O 39.3 30.0 2.9 6.0 1.2 4.1 42.0
CaO 9.2 16.4 4.5 25.5 0.2 51.6 7.8
MgO 7.2 5.2 - 6.5 0.2 5.5 12.1
Al2O3 0.1 0.8 3.3 14.0 2.0 6.3 0.6
Fe2O3 0.6 0.5 2.4 3.0 0.1 5.0 0.9
SiO2 1.7 8.4 62.6 39.0 95.6 16.0 0.4
Ash Fusion Temp deg C
IDT 940 - - 1193 +1400 1343 1390
HT 980 - 1350 1227 +1400 +1400 +1400
FT 1020 1200 - 1266 +1400 +1400 +1400
ALSTOM JOHN THOMPSON
MAY 2007
Ash Chemistry, Fouling and Slagging
ALSTOM JOHN THOMPSON
MAY 2007Ash Chemistry
These Include:-• SiO2, Al2O3, Fe2O3, P2O5, TiO2, CaO, MgO, • K2O, Na2O, SO3, Cl
The chemical composition of the ash as well as the ratio in which the elements occur gives a indication of the tendency of the ash to form slagging and clinkering as well as fuming and other problems
ALSTOM JOHN THOMPSON
MAY 2007Ash Chemistry
Alkali IndexRa = Ash x (Na2O + K2O)
Ra < 0.17 Fouling unlikely
Ra >0.17 Fouling probable
Ra > 0.34 Fouling virtually certain
GCV
ALSTOM JOHN THOMPSON
MAY 2007Ash Chemistry
Base to Acid Ratio:
Fe2O3 + CaO + MgO + Na2O + K2OSiO2 + Al2O3, +TiO2
B/A =
From this ratio a Slagging index can be derived:
ALSTOM JOHN THOMPSON
MAY 2007
Rs < 0,6 Low slagging
Rs 0,6 – 2,0 Medium slagging
Rs 2,0 – 2,6 High slagging
Rs > 2,6 Very intensive slagging
Slagging Index:Rs = B/A * S (dry)
Ash Chemistry
ALSTOM JOHN THOMPSON
MAY 2007Ash Chemistry
Fouling Index:Fa = Rs x Na2O + K2O
Fa < 0,6 No fouling
Fa 0,6 – 40 Fouling possible
Fa > 40 Fouling likely
S (dry)
ALSTOM JOHN THOMPSON
MAY 2007Ash Chemistry
Fouling Index:Rf2 = Na2O + K2O
Rf2 < 0.10 No fouling
Rf2 0,10 – 1.0 Fouling possible
Rf2 > 1.0 Fouling likely
SiO2
ALSTOM JOHN THOMPSON
MAY 2007
Effect of Ash Alkali Metal Oxide to Silica ratio
Ratio Na2O + K2ORatio Na2O + K2O
SiO2SiO2
ALSTOM JOHN THOMPSON
MAY 2007
Influence of Moisture and Ash on Boiler Capacity
55
60
65
70
75
80
85
90
95
100
105
49 50 51 52 53 54 55 56 57BAGASSE MOISTURE CONTENT %
% M
CR C
APAC
ITY 1% Ash
3% Ash
1.5%
6% Ash
9% Ash
10% Ash
Reference point 50 % Moisture Bagasse1.5% Ash in Bagasse
= 100% MCR
ALSTOM JOHN THOMPSON
MAY 2007Case Studies
Case studies are presented in the following pages for boilers burning:
• Sunflower seed husks/lignite• Furfural residue/bagasse/coal• Cotton stalks• Woodwaste• Bark• Bagasse/coal/cane tops and trash
ALSTOM JOHN THOMPSON
MAY 2007Sunflower Seed Husk/Lignite fired Boiler
Problem Solution
Sunflower seed husks contain high potassium content. Lignite contains sodium. Both promote fouling.
• Tall fully watercooled combustion chamber designed for low exit gas temperatrure
• Wide tube pitching selected to minimise build-up
• Heat recovery equipment includes large economiser only since hot air exacerbates fouling
Even with large furnace, some fouling can be expected
• Extensive set of sootblowers in furnace (wall type), screen, superheater, mainbank, economiser.
• Hopper to collect ash belowsuperheater
ALSTOM JOHN THOMPSON
MAY 2007Sunflower Seed Husk/Lignite fired Boiler
ALSTOM JOHN THOMPSON
MAY 2007Sunflower Seed Husk/Lignite fired Boiler
• Fouling occurs on the heat transfer surfaces of the boiler, mostly in the superheater
• Fouling can be removed by soot blowing on a regular basis
• Note wall de-slaggers on upper sidewalls
ALSTOM JOHN THOMPSON
MAY 2007
• Close-up of accumulations on lower side wall
Sunflower seed husk/lignite fired boiler
ALSTOM JOHN THOMPSON
MAY 2007Boiler firing Furfural Residue
• Boiler 4 at Sezela was designed as a coal/bagasse/furfural residue fired unit.
• Special precautions had to be taken in the design to overcome problems resulting from three very different fuels.
ALSTOM JOHN THOMPSON
MAY 2007Bagasse/coal/furfural residue fired boiler
ALSTOM JOHN THOMPSON
MAY 2007Bagasse/coal/furfural residue fired Boiler
Problem Solution
There were few references worldwide on combustion of furfural residue at the time of the installations
• A TGA was carried out to confirm the combustion properties
The three fuels were substantially different. Problems included:
• These problems necessitated features to ensure stable, safe and continuous combustion in operation.
Ø Bulk density of residue was three times that of bagasse
• Since the common bagasse/residue feeders are of thevolumetric design, a density compensation feature was included in the control scheme to avoid over-feeding.
ALSTOM JOHN THOMPSON
MAY 2007Bagasse/coal/furfural residue fired Boiler
Problem Solution
Ø The size grading of residue was much finer that of bagasse
• The feeder design was designed to incorporate a “herring bone” arrangement on the carding drum in order to ensure continuous regular feed with no lumps.
Ø The moisture content of residue was higher than that of bagasse
• A refractory backed watercooledsandwich wall was introduced in the furnace to ensure stable combustion of wet fuel whilst observing the requirements of the coal-burning scenario.
ALSTOM JOHN THOMPSON
MAY 2007Bagasse/coal/furfural residue fired Boiler
Problem Solution
Ø Whilst no explosions occurred on the boiler specifically designed for residue/bagasse and coal, a number did occur in the adjacent boiler#1 which did not have a coal burning facility
Ø These explosions were all attributed to build-up of wet fuel on the grate.
• It became apparent that a regular small coal feed was essential in order to stabilise combustion of wet/fine residue.
• Coal feeders were subsequentlyfitted to boiler #1 to minimise the risk
• As a further precaution, flame failure devices were eventually installed on all 4 boilers at the mill.
ALSTOM JOHN THOMPSON
MAY 2007Thermogravimetric Analysis (TGA)
Moisture Volatile
Char
Der
ivat
ive
(%/m
in
Temperature (OC)
Residue Bagasse
Vol from thermal decomposition
% 26,9 31,0
Weighted mean ionactivation energy
kJ/mol 80,7 66,2
ALSTOM JOHN THOMPSON
MAY 2007Combustion Profiles
Der
ivat
ive
(%/m
in)
Temperature (OC)
Initial Moisture Release
Combustion Residue BagasseT at onset of comb Deg C 249 228
Activation energy kJ/mol 109 101
T at max mass loss Deg C 369 366
Heating rate start to peak
Deg C/min
53,2 59,5
ALSTOM JOHN THOMPSON
MAY 2007Cotton stalk fired Boiler
ALSTOM JOHN THOMPSON
MAY 2007Cotton stalk fired Boiler
Problem Solution
The rate of fouling in the boiler was higher than anticipated even with an extensive set of sootblowers.
This was attributed to higher than expected alkali metal oxides and ash content.
• An extra economiser bank was installed to afford some protection to the bag filter.
• Additionally the boiler was periodically brought off-line for cleaning.
Extreme fuming was experienced when poor quality fuels containing high alkali metal oxide to silica ratio was burnt.
• In such cases the bag filter was utilised to capture the fine fume particles. Otherwise the venturi-type scrubber was used.
ALSTOM JOHN THOMPSON
MAY 2007Woodwaste fired boiler in board factory
Fuel moisture 42% 55%
MCR T/h 23 21
Pressure KPa 2 400 2 400
Temperature oC dry sat dry sat
NCV Efficiency % 79,1 74,4
Fuel moisture
42%
MCR T/h 23
Ash % % 1,0
Carbon % 28,4
Hydrogen % 3,6
Oxygen % 25,0
GCV kJ/kg 11 200
NCV kJ/kg 7 400
ALSTOM JOHN THOMPSON
MAY 2007Bark/coal fired boiler in paper mill
Coal Bark
MCR T/h 85 85
Steam pressure KPa
83 000 83 000
Steamtemperature oC
480 480
Efficiency on NCV %
85,3 83,9
ALSTOM JOHN THOMPSON
MAY 2007Bark/coal fired boiler in paper mill
ALSTOM JOHN THOMPSON
MAY 2007Combustion of cane tops/trash in sugar mill
ALSTOM JOHN THOMPSON
MAY 2007
Current energy distribution in typical sugar mill
ALSTOM JOHN THOMPSON
MAY 2007
Cogeneration boiler burning bagasse,coal & cane tops and trash
ALSTOM JOHN THOMPSON
MAY 2007
Cogeneration boiler burning bagasse,coal & cane tops and trash
Fuel (as fired) Bagasse Coal
Fixed carbon % 5,9 58,3
Moisture % 49,6 4,9
Ash % 4,7 11,8
Volatiles % 39,8 25,0
Brix % 2,1 N/A
GCV Kj/kg 8 894 27 466
NCV Kj/kg 7 025 26 538
Design Data t/h Bagasse Coal
Evaporation t/h 105 85
Steam pressure initial kPa 3 100 3 100
Steam pressure final kPa 4 500 4 500
Steam temp initial oC 385 385
Steam temp final oC 450 450
Feed temperature oC 112 112
Final gas temperature oC 162 183
GCV Efficiency % 69,8 84,1
NCV Efficiency % 87,5 87,1
ALSTOM JOHN THOMPSON
MAY 2007Modern energy distribution in sugar mill
ALSTOM JOHN THOMPSON
MAY 2007Factory Layout
Thank you