Download - Fuel Additive Training
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Fuel Additive Training
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Cost Factor in Oil Fired Plant
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Fireside Concerns of Solid and Liquid Firing
Preburner corrosion/fouling Burner corrosion/fouling Furnace slagging High temperature corrosion Cold end corrosion Gaseous emissions Poor combustion
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nozzle pluggage tank corrosion sludge in oil (asphaltenes) water in oil MB growth
Minimizing Preburner and Burner Fouling:
Adding dispersants to fuel to minimize fouling Dispersants promote a homogeneous fuel mixture Improves suspension of Asphaltenes and solids
Preburner and Burner Fouling- MFO Case:
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FUEL INJECTION SPRAY PATTERNS
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Furnace Slagging Concerns of solid & Liquid Firing
Poor heat transfer
Gas path pluggage
Fireside damage
Inhibit ash removal
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Typical Location of Fouling and Slagging in Coal Fired Boiler
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Major Slagging Elements
Vanadium Sodium Nickel Potassium Calcium Lead Zinc Iron
Oxidized Element Melting Temperature
K2O 662 F
K2O2 914 F
KO2 716 F
Na2O2 860 F
V2O5 1247 F
PbO 1626 F
PbO2 554 F
P2O3 74.8 F
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CHEMICAL NATURE OF PROBLEM (cont)
Alkali oxides of Na & K adhere to metal surfaces through reaction with SO3
S (usually present as iron pyrites) converted to SO2 SO2 + ½ O2 -> SO3 Na2O + SO3 -> Na2SO4 3 SO3 + 3 Na2SO4 + Fe2O3 -> 2 Na3Fe(SO4)3
Ash constituents adhere to molten film building in thickness
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Minimizing Slagging in Furnace Mechanically
- retrofit boiler to burn different fuel
- tune burner guns
- tune grate speed
- check for proper soot blower alignment Operationally
- change fuel
- change load/firing rate
- increase excess air
- increase soot blow frequency
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Minimizing Slagging in Furnace Chemically
Elevate melting point of impurities in fuel Increase friability of slag Promote passivation of boiler surfaces
Additive Melting Temperature Magnesium oxide 3180 oF Calcined Alumina 3875 oF Calcium Silicate 3255 oF Aluminum oxide 5166 oF Titanium oxide 3659 oF
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How Fuel Additive Works: Fuel additives function by elevating the
melting point of the compounds formed by the impurities in the fuel
The goal is to minimize the amount of sticky, slag forming material in the flue gas
If the compounds formed remain dry, they are more likely to fall out the bottom as ash or be collected in the precipitators.
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Melting Temperature of Compounds after Treatment
COMPOUND MELTING TEMPERATURES
3MgO * V2O5 2175 F
NaO * AlO3 2875 F
NiO * Al2O3 3362 F
Al2O3 * Na2O * 6SiO2 2010 F
K2 * Al2O3 * SiO3 1800 F
K2O * Al2O3 2SiO2 * Al2O3 3056 F
K2O * Al2O3 4SiO2 * Al2O3 2890 F
K2O * Fe2O3 * 4SiO2 2875 F
2K * AlSi2O6 * Mg2SO 2825 F
K2SO4 * MgO 1953 F
K2O * MgO * SiO2 1750 F
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Typical MFO Analysis
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Typical Coal Analysis
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COMBUSTION
Combustion is the breakdown of the organics to a gas during the slow chemical reaction of oxidation Coal combustion &/or fouling problems determined by :
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Combustion Reactions
Generic Reaction
HC Fuel + O2 CO2 + H2O + SOx + NO x + Heat
Specific Reaction: HC (BTU/lb) C + O2 CO2 14,100 CO + ½O2 CO2 3,960 H2 + O2 H2O + ½O2 61,100 S + O2 SO2 3,980
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Poor Combustion Concerns
Smoking stack
High carbon in ash (LOI)
Increased fuel usage
Particulate emissions
Poor boiler efficiency
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Combustion Catalyst
improves boiler efficiency
reduces volume of ash produced
reduces carbon content in ash
reduces particulate in flue gas
lowers excess air requirements (lowering NOx and
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COMBUSTION IMPROVEMENT
Continuous application of combustion catalyst Reduced activation energy to accelerate
combustion Reduced carbon content in fly ash Reduced % excess air requirement
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FUEL + AIR
FREE RADICALS
EACT1
Progress of Reaction
EACT2
Pot
enti
al E
nerg
y
HEAT OF COMBUSTION FLUE GAS
POTENTIAL ENERGY DIAGRAM FOR COMBUSTION REACTIONS
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HOT END PROBLEMS
Hot Section defined as operating temperature > 1000 F (535 C) Furnace, convective zone, superheaters
Low viscosity ash formation Slag deposits Metal surface corrosion
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FURNACE SLAG DEPOSITS
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Untreated vs Treated Slagging1000x SEM
Highlighted area #2 -Treated:
• Larger pores
• Weaker and lighter deposits
• Easier to remove
Highlighted area #1- Untreated:
• Small pores and packed
• Hard and tenacious deposits
• Create problems
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COLD END PROBLEMS
Cold section defined as operating temperature < 1000 F (535 C) Air preheaters, ID fans, economisers, boiler
stack
Caused by sulphuric acid attack formed when flue gas cooled below the acid dew point
Metal sulphates formed result in fouling
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Minimizing Cold End Corrosion Can be minimized by adding magnesium and/or
magnesium oxide to the fuel at the time of combustion.
The magnesium reacts with the sulfur to reduce the concentration of SO3 compounds in the flue gas.
Reducing the amount of sulfur available to form sulfur dioxide compounds which result in the formation of H2SO4
By minimizing the amount of sulfuric acid present in the flue gas, the magnesium oxide effectively elevates the acid dew point of the sulfuric acid that does form.
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Neutralization Reaction
Mg + 2O2 + S MgSO4
MgO + 3/2O2 + S MgSO4
Mg + 1/2O2 MgO
Mg + Cl MgCl
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Treatment Strategies
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TREATMENT STRATEGIES
Neutralisation Alkaline additive to neutralise sulphuric acid
as formed
Catalyst Deactivation Coating &/or reaction with catalysts (Cu, Fe)
Continuous application to coal prior to pulverisers
Often combined treatment with combustion catalyst
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FIRESIDE ADDITIVES
Raises fusion temperature of adherent deposits Produces dry, friable, high mp compound Weakens bonding of slag to metal surface
Reacts with complex sulphates & other slag components Changes slag from a hard, dense material to
soft, expanded, porous powder
Forms metallic film on metal surface Protects surfaces from corrosive action Minimises catalytic action of SO2 to SO3
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Diffusion of Additive Throughout Slag Materials
Particle size of additive (MgO) in fireside gas is 0.3 – 0.03
The combustion gas diffuses throughout slag due to permeability of slag materials
This mechanism keeps the slag formed is lighter, softer, and easier to remove via shootblowing
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Treatment Results
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Treatment Results
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Fly Ash pH
• The easiest means to measure the efficacy of chemical treatment
• Sample taken from Air Heater outlet
• pH checking thru 1% slurry of fly ash (fly ash + demin water)
• Target fly ash pH: 6.5 - 8.5
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IMPROVING COMBUSTION EFFICIENCY
AMERGY 5800 Plus ® Combustion Catalyst Data
0
2
4
6
8
10
12
14
16
April 14, 2002 April 24, 2002 May 4, 2002 May 14, 2002 May 24, 2002 J une 3, 2002
% O
xyge
n Rea
ding
(Blu
e)%
CO2 R
eadi
ng (R
ed)
Amergy 5800Plus ® Feed Initiated
% CO2 Curve
% Oxygen Curve
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ACID DEWPOINT & TEMPERATURE RELATIONSHIPS
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Fuel Additive Products
Powder Products FST 5370
• Slag inhibitor with corrosion inhibitor Drew 11-GFM
• Slag inhibitor & combustion catalyst Drew 11-GFS
• Slag inhibitor ~ dosage 0.1 kg/Ton fuel
Liquid Product: Amergy 222N for MFO preburner ~ dosage 0.15 – 0.25 kg/Ton fuel
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Questions?