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Selection of combustion equipment for Industrial Power generation and cogeneration
to Suit the fuel propertiesPeter McIntyre21st August 2014
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 2007Boiler requirements and fuel properties
Items to be considered:• What fuel or fuels to be burned• Boiler load for each fuel• Necessity to co-fire• Boiler load in co-firing mode• Fuel properties• Emission requirements
ALSTOM JOHN THOMPSON
MAY 2007Fuel properties
• Size grading• Proximate analysis• Ultimate analysis• Ash analysis
ALSTOM JOHN THOMPSON
MAY 2007Fuel properties
Proximate analysis:
• Volatiles• Ash• Moisture• Fixed carbon • Gross calorific value
ALSTOM JOHN THOMPSON
MAY 2007Fuel properties
Ultimate analysis:
• Carbon• Hydrogen• Oxygen• Nitrogen• Sulphur
ALSTOM JOHN THOMPSON
MAY 2007Fuel properties
Ash chemistry:
Knowledge of ash constituents gives an idea of the fuel’s propensity for:• Slag formation• Clinker formation• Bed agglomeration• Fouling of heat transfer surfaces• Fuming problems
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
Base to Acid Ratio:
Fe2O3 + CaO + MgO + Na2O + K2O
SiO2 + Al2O3, +TiO2
B/A = Fe2O3 + CaO + MgO + Na2O + K2OB/A =
ALSTOM JOHN THOMPSON
MAY 2007Ash Chemistry - Indicators
Property IndexSlagging Index
Alkali Index
Fouling Index
Fouling Index
Agglomeration Indices
ALSTOM JOHN THOMPSON
MAY 2007Combustion system options
OptionsDump gratePinhole grateVibrating grateContinuous ash discharge (CAD)Bubbling fluidised bedCirculating fluidised bed
Typical dump grate stoker
ALSTOM JOHN THOMPSON
MAY 2007Conversion from pile burning to Dump grate
Steam Cleaned Pin-Hole Grate
Continuous Ash Discharge (CAD) Stoker
ALSTOM JOHN THOMPSON
MAY 2007Importance of minimising carbon in ash
Coarse Ash from CAD Stoker
CEL CTBV CTDS CSAV200 248 302 330
Grate Ratings on Mauritius projects
ALSTOM JOHN THOMPSON
MAY 2007
Combustion of cane tops and trashin sugar mill
ALSTOM JOHN THOMPSON
MAY 2007
Energy distribution in Sugar mill
ALSTOM JOHN THOMPSON
MAY 2007
Cogeneration boiler burning bagasse,coal & cane tops and trash
• BFB Boiler
Open bottom BFB
Features
• Easy rock removal• Bed temperature controlled by staging
air flow and FGR• Sub-stoichiometric bed conditions• Low elutriation from bed
• low carbon loss• No need for cinder refiring• No need for MDC• Bag filter acceptable for stack
emission control• Large fuel inventory – tolerant of fuel
quality excursions• Bed agglomeration monitored via
pressure drop• Agglomerations reduced via increased
bed drain
ALSTOM JOHN THOMPSON
MAY 2007Declining quality of South African coal
ALSTOM JOHN THOMPSON
MAY 2007
ALSTOM JOHN THOMPSON
MAY 2007
ALSTOM JOHN THOMPSON
MAY 2007
The solution - CFB Boiler
• Longer residence time• Constant lower temperature
in furnace• Large fuel inventory• Tolerant of fuel quality
variations• High combustion efficiency• Low NOx• Addition of limestone
reduces SO2
Alternative CFB designs
Case study – 60 MWe CFB
• Fuel Mine waste coal• GCV 16.7 mJ/kg• Ash 45%• Sulphur 2.0%• Steam flow 250 T/h• Pressure 107 Bar• Temperature 513 deg C
Mine Dump before and after
1989 2010
ALSTOM JOHN THOMPSON
MAY 2007Factory Layout
Thank you
