1 Recovery Boiler Deposit Formation Recovery Boiler Deposit Formation and and Plugging Prevention Plugging Prevention Honghi Tran Pulp & Paper Centre University of Toronto Toronto, Canada Tappi Kraft Recovery Course St. Petersburg, Florida, January 7-10, 2008 Problems with Deposits Problems with Deposits Reduce boiler thermal efficiency Create a corrosive environment at tube surfaces Lead to unscheduled boiler shutdowns for deposit removal or tube repair
21
Embed
4-7 Recovery Boiler Deposits and Plugging Prevention · Recovery Boiler Deposit Formation and Plugging Prevention ... 350 psig steam 60 to 100 sootblowers ... 4-7 Recovery Boiler
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Honghi TranPulp & Paper Centre University of Toronto
Toronto, Canada
Tappi Kraft Recovery CourseSt. Petersburg, Florida, January 7-10, 2008
Problems with DepositsProblems with DepositsReduce boiler thermal efficiencyCreate a corrosive environment at tube surfacesLead to unscheduled boiler shutdowns for deposit removal or tube repair
2
Presentation OutlinePresentation OutlineEntrained ParticlesDeposit PropertiesPlugging in Different RegionsDeposit CleaningPlugging Prevention
Appearance of a Deposit ConeAppearance of a Deposit Cone
1200
1400
1600
800
1000Tem
pera
ture
(oF)
600 700 800 900500
Firstmelting
Flowing
Completemelting
Temperature (oC)
Sticky0%
70%15%
~1%
100%
LiquidPhase
First melting temperature is important for corrosionSticky and flowing (slagging) temperatures are important for fouling/pluggingThese temperatures are related to liquid content, which is a function of:
deposit composition (mainly chloride)temperature
Melting TemperaturesMelting Temperatures
7
Deposit Sticky TemperatureDeposit Sticky Temperature
0 mole% K/(Na+K)
mole% Cl/(Na+K)0 102 124 146 168 18 20
850
700750800
500550600650
Tem
pera
ture
(oC
)
0 mole% Cl/(Na+K)
1
5
10
20
ChlorideChloride
8
Deposit Sticky TemperatureDeposit Sticky Temperature
mole% K/(Na+K)
mole% Cl/(Na+K)0 102 124 146 168 18 20
0
10 20
5
850
700750800
500550600650
Tem
pera
ture
(oC
)
SurfaceDiffusion
BulkDiffusion
Materialtransfer
Particle SinteringParticle Sintering
Temperature
9
Dust Sintering Dust Sintering Test (1 hour)Test (1 hour)
Plugging in the SuperheaterPlugging in the SuperheaterCaused by carryover deposition
High gas temperatureLarge amount of sticky carryover
Not by fume depositionSmall amount of fume
Deposits
12
Plugging at the GB InletPlugging at the GB Inlet
Plugging at the GB inletPlugging at the GB inletNarrow tube spacing (2”)Carryover deposition upstream (superheater)
High gas temperatureSticky carryover
Fume deposition and sintering
High gas temperatureLarge amount of fume
Deposits
13
Cause of Plugging at the GB InletCause of Plugging at the GB Inlet
TimeMassive depositbuildup zone
Clean PluggedFouled
Plugging in the Generating BankPlugging in the Generating Bank
Fume deposition and sintering
High gas temperatureLarge amount of fume
Inadequate sootblowing
DepositsDeposits
Deposits
14
Flue Gas
Steam6200 KPa(900 psi)
Deposit
Tube
550oC
450oC (Hard)
270300oC (Soft)
Temperature across a GB Tube and Temperature across a GB Tube and Deposit LayerDeposit Layer
Deposits sinter rapidly if they are:Deposits sinter rapidly if they are:jammed between tubeson stabilizing bars and baffleson sealed tubes (no steam inside)on mud drum (for bi-drum boilers)
15
Plugging in the Generating BankPlugging in the Generating Bank
Plugging in the Generating Bank of a Plugging in the Generating Bank of a Single Drum BoilerSingle Drum Boiler
Flue Gas
16
Plugging in the EconomizerPlugging in the Economizer
Fume deposition and sinteringSticky fume (acidic sulphate formation)
Low bed temperatureHigh sulphidity
Inadequate sootblowing
Na2SO4 + SO2 +½ O2 +H2O = 2 NaHSO4
Deposits
Baffle
Deposits
Baffle
Presentation OutlinePresentation OutlineEntrained ParticlesDeposit PropertiesPlugging in Different RegionsDeposit CleaningPlugging Prevention
17
Nozzle Throat JetPIP
Lance Tube
Sootblower LanceSootblower Lance
350 psig steam60 to 100 sootblowers per boilerConsume 3 to 12% total boiler stream production
Plugging due to Fume SinteringPlugging due to Fume Sintering
Main CausesExcessive fume High flue gas temperatureIneffective sootblowing
Preventive MeasuresMinimizing fume quantity (low bed temperature, coarse spray)Lowering flue gas temperaturesIncreasing sootblowing efficiency
Plugging due to Sticky FumePlugging due to Sticky FumeMain Causes
Low carbonate content in the fumeHigh SO2/SO3 conc. in the flue gasIneffective sootblowing
Preventive MeasuresIncreasing bed temperatureLowering liquor sulphidityIncreasing sootblowing efficiency
21
SummarySummaryDeposit formation and characteristics vary greatly with location within a boiler, and differ from boiler to boiler.It is important to identify the exact cause in order to devise appropriate solutions