Case Studies on Biomass and Co-Firing Presented …...Case Studies on Biomass and Co-Firing...

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


MAY 2007Fuel Considerations

An accurate, detailed knowledge of the fuel is fundamental for proper boiler selection and design



Chemical properties

Proximate analysis– Indicates combustion properties

• Volatiles• Ash• Moisture• Fixed carbon • Gross calorific value



Chemical properties (cont).

Ultimate analysis– Gives basic chemical constituents

• Carbon• Hydrogen• Oxygen• Nitrogen• Sulphur• Chlorine



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


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


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


MAY 2007

Ash Chemistry, Fouling and Slagging


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



Alkali IndexRa = Ash x (Na2O + K2O)

Ra < 0.17 Fouling unlikely

Ra >0.17 Fouling probable

Ra > 0.34 Fouling virtually certain

GCV



Base to Acid Ratio:

Fe2O3 + CaO + MgO + Na2O + K2OSiO2 + Al2O3, +TiO2

B/A =

From this ratio a Slagging index can be derived:


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



Fouling Index:Fa = Rs x Na2O + K2O

Fa < 0,6 No fouling

Fa 0,6 – 40 Fouling possible

Fa > 40 Fouling likely

S (dry)



Fouling Index:Rf2 = Na2O + K2O

Rf2 < 0.10 No fouling

Rf2 0,10 – 1.0 Fouling possible

Rf2 > 1.0 Fouling likely

SiO2


MAY 2007

Effect of Ash Alkali Metal Oxide to Silica ratio

Ratio Na2O + K2ORatio Na2O + K2O

SiO2SiO2


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


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


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



• 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


MAY 2007

• Close-up of accumulations on lower side wall

Sunflower seed husk/lignite fired boiler


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.


MAY 2007Bagasse/coal/furfural residue fired boiler


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.



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.



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.


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


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


MAY 2007Cotton stalk fired Boiler


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.


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


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


MAY 2007Bark/coal fired boiler in paper mill


MAY 2007Combustion of cane tops/trash in sugar mill


MAY 2007

Current energy distribution in typical sugar mill


MAY 2007

Cogeneration boiler burning bagasse,coal & cane tops and trash


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


MAY 2007Modern energy distribution in sugar mill


MAY 2007Factory Layout

Thank you


MAY 2007

www.johnthompson.co.za

http://www.johnthompson.co.za

Case Studies on Biomass and Co-Firing Presented …...Case Studies on Biomass and Co-Firing...

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