It s the coal Rod Hatt 859-873-0188 rod_hatt@coalcombustion.com
Gas Coal Molecular Structure
CAPP is easiest coal to use: Easy to Low NOx Little to no Slag Little to no Corrosion Easy on Operators
NAPP is easier coal to use: High Btu High HGI Grind Low ash =Less Slag Can be Easy Operators
PRB Coal: Handling Issues Low Sulfur Good Low NOX Slagging & Fouling Low Btu/Low Price
Illinois Basin: Plant Operators have to stay on top of their game Not low NOX friendly Slagging & Fouling Best Value
Measuring Coal Quality Power plant operators rarely get CQ info Coal Sales Data Actual ASTM Analyses On-Line information Lots of Confusion Major impacts Design and Operation of plant
Measuring Coal Quality ASTM only produces average data Power plants respond to swings in quality
60 Pure Coal Analyses 50 40 30 20 10 0 1 2 3 4 5 Ash What is Easy to sell What causes plant problems
Lowest cost coal is always raw.
Small and Large Variability 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 ASTM reports same ash level
5.7 6.1 Plant Limit Average Does this coal met spec?
5.4 6.2 Slag potential of fuel
Washed Coal is: More Consistent Little to no OSD (rocks) Typically Lower Fusion
Self Heating Temp Bituminous A, B = Low Bituminous C Sub Bituminous = Medium = High Gillette PRB = Very High
Pulverizers Dry and Grind More Moisture - Lower Outlet Temp Lower Kg/Kcal - Higher Tonnage Rate - Higher PA Flow www.asiansbcusers.com 22
Moisture sensitive only three values High, Medium, Low
Mill Capacity And HGI
Sizing Set for Coal type Set for Slag control May be opposite directions www.asiansbcusers.com 25
Ash Wears Them Out Impacts load High Maintenance Performance Testing Most miners I know will sell you rocks at the price of coal. rmh
Raask Quartz %Quartz ~ SiO 2 1.5x Al 2 O 3 % Quartz X Kg ash/mkcal = Kg Quartz per Million Kcals
Mill Outlet Temperature Usually lower with ILB coals verses CAPP and NAPP Typically 150-165 o F.
Bituminous Coal Combustion 1.Maintain 70% passing 200 mesh screen 2.High Calorific Value and low moisture allow for low mill loading 3.Lower Primary Air due to lower coal flow can allow for rejects 29
Bit Coal Combustion 30
Coal Combustion Sub - Bituminous 1.Maintain 60-70% passing 200 mesh screen to increase though put. 2.Low Calorific Value and high moisture make for high mill loading 3.High Primary Air for drying and high coal flow sends reject material into the furnace 31
Sub-Bit Coal Combustion 32
Coal Combustion Sub - Bituminous 1.Hence sub-bit coal. 2.Low Calorific Value and high moisture make for high mill loading 3.High Primary Air for drying and high coal flow sends reject material into the furnace 33
Coal Combustion 34
Coal Combustion 35
Coal Combustion 36
Causes Fuel Related Pyrite Clays Alluminosilicates Organic Alkalis
Causes Equipment Soot Blowers Pulverizers Air to Fuel Ratio Burners Changes
Causes Design Furnace Size Tube Material/Spacing Soot Blower Coverage Observe/Measure Slag
The Many Faces of Slag Kansas Style Washington State Style Ohio Style Texas Style
Common Denominator? Not the Coal Not Sulfur or Minerals Not the Boiler Not the Company Low NOx Burners Over Fire Air
Most Slag Starts on walls
Waterwall deposits force heat to convection pass.
FeS2
Coal Combustion Chemistry Sulfur 101 or why rocket scientists have it easy Member: American Society of Mechanical Engineers American Chemical Society Society for Mining, Metallurgy, and Exploration North Carolina Coal Institute Contacts: sponsor 859-873-0188 rod_hatt@coalcombustion.com
Sulfur in Coal Bad to the bone Slag Fouling deposits Pluggage Corrosion Pollution Money $
All coal has sulfur It comes from sea water vs. fresh water environment
Sulfur in Coal Coal typically is 0.3 to 4.0% Sulfur
Sulfur can be in two main forms: Organic Pyritic
Organic H-C-C-S-C-C-H sulfur is attached to coal carbon
Pyritic FeS 2 sulfur is attached to iron in fool s gold
FeS2
Large sulfur balls can be washed out or rejected by pulverizers Small framboids (raspberries) of pyrite are mixed in with the coal 50 microns
Cleat pyrite has to be ground up
Chemistry Issues FeS 2 High Sulfur Coal Low NOx Poor Fineness H 2 S + FeO Corrosion and Slag
Fusion Spread Ox-Red Iron Level delta Temp. 5 20 10 70 20 200 25 300
Role of Iron Acid Base Fe2O3 Oxidized FeO Fe3O4 Reduced Good Poor
Slag is a build up of rate process so, the amount of ash should matter.
Lbs. of ash/mbtu = %ash / (Btu/10,000)
Lbs. of element/mbtu = %ash / (Btu/10,000) X (%Element/100)
Many slagging concerns have been addressed using Ash Loading and Elemental loading levels; especially Fe 2 O 3, CaO, Na 2 O
Common Denominator? Not the Coal Not Sulfur or Minerals Not the Boiler Not the Company Low NOx Burners Over Fire Air
With low NOx Waterwall Corrosion Tube Leaks
Slag Related to: Coal Quality Getting Worse? Plant Equipment Boiler/Mills Fixed Combustion Process - NOx and Air distribution Superior Mill Performance Maintain Mills to Preserve BOILER
FeS2
Chlorine waterwall corrosion issues are minimal in oxidizing atmosphere (not lowest NOX) First 200 years of use Oxidizing atmosphere also Minimizes pyrite related corrosion Minimizes slag (raises ash fusion temperatures 100-300 degrees)
Coal Combustion 74
Pulverizers 70 % passing a 200 mesh screen Minimum or Maximum? Old School! Need 75% for high pyrite low NOx
POST MORTUM Microscopic Investigation of Deposits
CaO + SO3 = CaSO4 Think Fluid Bed Boiler & Fouling Deposits
What does the SO3 represent? SO3 CaO
Organically Bound Alkalis COAL -O- -O- -O-
Sodium Condenses on Surface
Causing a Molten Layer on Surface
Fouling Index = B/A x Na2O works on ILB
Iron, Fe2O3 Calcium, CaO Sodium, Na2O are the glues
Chemistry Issues Sulfur & FeS 2 SO 2 + SO 3 SO 3 + NH3 Air Heater Pluggage
Choke Point
SO2 to SO3 Conversion is excess oxygen sensitive
Sulfur burns to SO 2 Then some SO 2 burns Fe 2 O 3 pyrite, boiler, slag SO 2 + ½ O 2 SO 3 V 2 O 5 Oil, Petcoke, SCR
More Reactants? Sulfur in Coal --- SO2 Excess Oxygen (helps slag) More catalyst? Pyrite FeS 2 Slag Fe 3 O 4, Fe 2 O 3 SCR Vanadium V 2 O 5 in fuel
SO 3 Zone
SO 3 Zone H 2 SO 4 Zone
Fouling Deposits Think Fluid Bed Boiler CaO + SO 3 = CaSO 4 PRB convection pass fouling and it can be harder to measure SO3 with high alkalis (Na, K) and alkaline earths (Mg, Ca) in coal
After the economizer SO 3 combines with H 2 O SO3 + H 2 O H 2 SO 4 to form sulfuric acid
thanks Cal
H 2 SO 4 combines with all sorts of stuff to plug, foul, corrode and then it can leave the stack and form a visible plume of smoke sulfuric acid mist SAM
Industry Examples Walhco SO 3 Orimulsion Cold End Corrosion
Chemistry Issues Cl HCl + H2O Cl - = Soluble Chlorides Scrubber Blowdown Ponds Release off to the sea
Thank you!