tecniche primarie per la riduzione delle ... - prime glass
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Tecniche primarie per la riduzione delle emissioni: Ottimizzazionecombustione forni fusori, diagnostica e bilancio termico
Walter Battaglia - Alessandro Migatta - Roberto Dall’Igna(Stazione Sperimentale del Vetro ScpA)
SummaryThe presentation will take into consideration the following topics:
1. Primary techniques to reduce NOx emissionsa. Mecanism of NOx production
2. Description of a dynamic approacha. Combustion Optimizationb. Energy balancec. Periodic Audit - Diagnostic measurements: endoscopy, check markers of
combustion optimization and energy saving
2. Description of a dynamic approacha. Combustion Optimizationb. Energy balancec. Periodic Audit - Diagnostic measurements: endoscopy, check markers of
combustion optimization and energy saving
3. Prime Glass Project - EU LIFE program (LIFE12 ENV/IT/001020)a. General description of two primary techniques :
I. Strategic waste gases recirculationII. Enhanced hot air staging
“….The major environmental challenges for theglass industry are emissions to air andenergy consumption. The glass production isenergy-intensive and high activity inhigh temperature which results in the emissionof products of combustion:Dust, CO2, CO, NOx, SOx, HF, HCl, Heavy Metal”
BAT CONCLUSION:
“….The major environmental challenges for theglass industry are emissions to air andenergy consumption. The glass production isenergy-intensive and high activity inhigh temperature which results in the emissionof products of combustion:Dust, CO2, CO, NOx, SOx, HF, HCl, Heavy Metal”
BAT – ENERGY EFFICIENCY
• Process optimization, by control of operating parameters• Regular maintenance of the melting furnace• Optimization of the furnace design and the selection of the
melting technique• Application of control techniques in combustion processes• Using higher levels of cullet, where available and where
feasible from an economic and technical point of viewUse of a boiler with heat recovery for energy recovery, iffeasible from an economic and technical point of view
• Preheating of batch mixing and cullet, if feasible from aneconomic and technical point of view
The BAT correspond in the reduction of the specific energyconsumption through the use of one of the following techniquesor a combination of them:• Process optimization, by control of operating parameters• Regular maintenance of the melting furnace• Optimization of the furnace design and the selection of the
melting technique• Application of control techniques in combustion processes• Using higher levels of cullet, where available and where
feasible from an economic and technical point of viewUse of a boiler with heat recovery for energy recovery, iffeasible from an economic and technical point of view
• Preheating of batch mixing and cullet, if feasible from aneconomic and technical point of view
TECHNIQUES TO REDUCE NOX EMISSIONS
The most appropriateNOx emissions control
techniques are generally
The most appropriateNOx emissions control
techniques are generally
PrimaryPrimary Oxy fuel meltingOxy fuel melting Selective Reductionwith reagents
Selective Reductionwith reagents
Selective Catalytic(selective catalytic
reduction - SCR)
Selective Catalytic(selective catalytic
reduction - SCR)
selective non-catalyticreduction
(Selective non-catalyticreduction - SNCR)
selective non-catalyticreduction
(Selective non-catalyticreduction - SNCR)
PRIMARY TECHNIQUES: Mechanism of NOx formation
There are four mechanisms for the production of NOx in the glass furnaces: three arelinked to the combustion and the fourth to the use of nitrates in the batch; thecontribution which comes from Nitrate is obviously overlooked.
The main mechanism of NOx formation is the one defined as “thermal NOx”, theundesired compounds are generated from the breaking of air molecular nitrogen (N2represents about 80% of ambient air) at high temperature, in presence of oxygen. Themain sources of the nitrogen are combustion air, atomizing air (in oil-fired furnaces) andair leakage into the furnace.
Mechanism of NOx formationBy an approximate calculation conducted on a waste gas generated by a natural gascombustion with 10% excess air, the NOx formation is a function of the temperature asshowed in the following diagram.
Equilibriumconcentration 0% O2
wet fumes
The Nox formation rate (growing exponentially over 1550 ° C.) it is such important as thevalue of the equilibrium concentration,
NOxformation
rate
Mechanism of NOx formationThis means that the time to reach the equilibrium concentration is shorter increasingthe temperature, therefore the flame temperature at the root (Tf) must be lower takinginto consideration both N2 and O2 flame distribution and the dwell time at Tf.
1.Controlled distribution of fueland combustion air in the flame
2.Increase of flame irradiation(e.g. mixed fuel combustion, fuelcracking)
Q Fuel flowtf Dwell timeLHV Lower Heating Valuevg Gas velocityd0 Nozzle diameter
Process operating variablesThe equations above explain the effects of the following process operating variables:
1. Excess combustion air (“Smoking point”):a. Increase of the combustion velocity (NOx increase)b. Increase of O2 and N2 concentration
2. Preheating temperature of combustion air:a. Decrease flame temperature (NOx decrease)
3. Air fuel atomization:a. Decrease of the combustion velocity and combustion density (NOx decrease)b. Decrease preheating combustion air (NOx decrease)
3. Air fuel atomization:a. Decrease of the combustion velocity and combustion density (NOx decrease)b. Decrease preheating combustion air (NOx decrease)
4. Furnace size implies a flame longest and an increase of fuel flow:a. Increase the flame radiation capability (NOx decrease)b. Decrease the dwell time (increase the reaction time) (NOx increase)
5. Main other operatig variable related with NOx content:a. Boosting (NOx decrease)b. Increase cullet amount and preheated cullet (NOx decrease)c. Fuel injection techniques
Process operating variables
c. Fuel injection techniques
angle and velocity of the air flow
position injection under the air stream (UP), above (OP), lateral (SP) etc ormixed;
Injector shape: a single hole, multi-hole, ring etc.
asymmetric combustion, internal recirculation, combustion selective zoning
Adjust the combustion velocity to:
1. Reduce flame temperature peaks
2. Lead to the combustion in oxygen deficiency zones
SummarizingSummarizing NOxNOx reduction techniquesreduction techniques
Reduce air/ fuel ratio and fuel choise
Reduce combustion temperature
Stage combustion and flue gas recirculation:1. Reducing the proportion of either the air or the fuel injected at the burner (air/fuel staging)2. The remaining fuel, air is added later in the combustion zone.
Stage combustion and flue gas recirculation:1. Reducing the proportion of either the air or the fuel injected at the burner (air/fuel staging)2. The remaining fuel, air is added later in the combustion zone.
Low NOx burners:• Slower mixing of fuel and air to reduce peak flame temperatures (flame shaping).• Minimum injection velocities that still allow complete combustion (delayed but complete combustion).• Increased (radiation) emissivity of the flame, with optimisation of the heat transfer to the glass melt.• Different nozzles and nozzle designs.
Metodology: Dinamic approachMetodology: Dinamic approach
Combustionoptimization Energy
EmissionsDetailedenergybalance
Carachterization of Initial
setup
1. Long term processcontinuously monitoringwith accurate data
2. Simultaneous continuousmonitoring in several
points
EmissionsDetailedenergybalance
ProcessOptimization
Process control
1. Long term processcontinuously monitoringwith accurate data
2. Simultaneous continuousmonitoring in several
points
The CEMS used to carry out combustion optimization/ energy balance is composed of:
Gas: O2, CO, NOxCooled probe for the extraction of the gaseousflow and cooler system equipped of filter. Thegas sampled is delivered to analyzers
Temperatures
Cooled suctionprobes
Pressures
Micromanometers
Continuous Monitoring System – Dynamic approach
Lab 1
Data
acquisition unit
Trend emissions values
Combustion optimization Thermal Balance
During the optimization combustion campaign/ Energy Balance emissionsgenerated by the furnaces are characterized. Below are reported theparameters monitored.
Trend emissions values – Analytical Method
n° Measurements Data Method of analysis Principle of method
1 Stack temperature, velocity andvolume flow rate of the exhausts gases EN ISO 16911-1:2013 Discontinuous
2 Volume concentration of dry Oxygen EN 14789:2005 Continuous(Paramagnetic)2 Volume concentration of dry Oxygen EN 14789:2005 Continuous(Paramagnetic)
3 Carbon dioxides conc. (CO2) EPA 3A:2006 Continuous (NDIR)
4 Carbon oxides conc. (CO) EN 15058:2006 Continuous (NDIR)
5 Oxides of Nitrogen conc.(NOx) EN 14792:2005,UNI 10878:2000
Continuous(Chemiluminescence, NDIR)
6 Temperatures and PressuresSuction Probe + K, B or STC’s andMicromanometers
7 Thermography Endoscope + Thermo-camera VIS, NIR
Cooled ProbeMicromanometer(Pressure Meter)
STEP 1: Initial emissions and combustion characterization
Radiation shields
Thermocouplehead
Suction Pyrometer
Gas conditioningsystem
Analyzers
EnergyBalance
Sampling points
Gas conditioningsystem
Analyzers NOx, CO, O2
Pressure
Control room
STEP 1: Initial emissions and combustion characterization
Sampling points
Furnace Recuper. FuelFuel
consuptionKg/h
Airconsuption
Nm3/h
BoostingkWh/h Product Pull t/d Cullet %
Unit Melter Double pass Oil ---- ----- ---- Flint 340 ----
Metodology: Dinamic approachMetodology: Dinamic approach
Combustionoptimization Energy
EmissionsDetailedenergybalance
Carachterization of
Initial setup
EmissionsDetailedenergybalance
ProcessOptimization
Process control
Dynamic approach - Optimization Combustion Procedure
The combustion optimization procedure could be summarized as follow:
Initial emissions characterization
Preliminary data acquiring
2
STEP ACTIVITY
1 Currentcombustion
processmanagement
characterization
Final optimization which (long term)emissions characterization
Optimization strategy specific for:Regenerative furnacesRecuperative furnaces
Initial emissions characterization2
3
4
Currentcombustion
processmanagement
characterization
Combustion/emissions
optimization
Characterizationof Combustion/
emissionsoptimized process
STEP 1: Preliminary data acquiring
Fuelconsumption
(kg/h);
Airconsumption
(Nm3/h);
Set-pointfuel/air ratio;
Currentcombustion
process previousmanagement
characterization
Pull rate(t/d);
Cullet (%);
Batchcompositionand humidy
Currentcombustion
process previousmanagement
characterization
1. Definizione della strategia diottimizzazione da adottare
2. Verifica consumi teorici
1. Definizione della strategia diottimizzazione da adottare
2. Verifica consumi teorici
1a Determination in different points of gas composition (O2, NOx, CO) andPressure furnace/ regenerator chambers in the starting combustion setting(initial set-up)
1b Determination of “smoking point” by air/fuel ratio or pressure exchangeDetermination of “burners map”
STEP 2: Initial emissions characterization
1b Determination of “smoking point” by air/fuel ratio or pressure exchangeDetermination of “burners map”
1c Furnace pressure checkThe pressure adjustment of the furnace must be at a slight overpressure to avoidfalse air combustion contribute which can make the fuel combustion ratioreading of the reports difficult and unstable
58,2 57,3 48,5 77,6 93,9 144,4 72,7 121,1 87,0 91,4 127,5
mg/Nm3@8%
80,1 93,0 51,3 111,1 122,0 137,3 157,0 108,7 93,4 103,8 107,8
Oil flow (kg/h)
Oil flow (kg/h)
UNIT 5
B01 B02 B03 B04 B05 B06 B07 B08 B09 B10 B11
B01 B02 B03 B04 B05 B06 B07 B08 B09 B10 B11
STEP 2: Initial emissions and combustion characterization
1. Smoking Point
2. Burners Map
UNIT-MELTER FURNACE
58,2 57,3 48,5 77,6 93,9 144,4 72,7 121,1 87,0 91,4 127,5
mg/Nm3@8%
80,1 93,0 51,3 111,1 122,0 137,3 157,0 108,7 93,4 103,8 107,8
Oil flow (kg/h)
Oil flow (kg/h)
UNIT 5
B01 B02 B03 B04 B05 B06 B07 B08 B09 B10 B11
B01 B02 B03 B04 B05 B06 B07 B08 B09 B10 B11Burners Map
Burner n° Oil flow [kg/h] Air flow [m3/h] Air index
Burner 01 59,8 781 13,07
Burner 02 59,8 781 13,07
Burner 03 59,8 781 13,07
Burner 04 119,6 1563 13,07
Burner 05 119,6 1563 13,07
Burner 06 119,6 1563 13,07
Burner 07 119,6 1563 13,07
Burner 08 179,3 2344 13,07
Burner 09 179,3 2344 13,07
Burner 10 179,3 2344 13,07
Burner 11 179,3 2344 13,07
Burners Map
Left Burner Right Burner
Burner Ext Int Ext Int
Oil Flow (kg/h) n/a n/a n/a n/a
Inclination (°) 3 3.8 2.8 2
NozzleDiameter
(mm)4 4 4 4
Section (mm2) 12.57 12.57 12.57 12.57
STEP 2: Initial emissions and combustion characterization
Flue gas
Port Right Left Units
O2 % dry
CO2 % dry
SO2 mg/Nm3 8% O2Flue gas
REGENERATOR FURNACE
Oil velocity(m/s) 12.94 12.94 12.94 12.94
Impulse (N) 1.96 1.96 1.96 1.96
NOx mg/Nm3 8% O2
CO mg/Nm3 8% O2
Regenerator Right Left Units
O2 % dry
CO2 % dry
SO2 mg/Nm3 8% O2
NOx mg/Nm3 8% O2
CO mg/Nm3 8% O2
Flue gas
Channel RightLeft Units
O2 % dry
CO2 % dry
SO2 mg/Nm3 8% O2
NOx mg/Nm3 8% O2
CO mg/Nm3 8% O2 Regenerative: End Port
To optimize the NOx, the air flow in the burners must be slightlyreduced when the flow rate of fuel is high and increased when theflow rate of fuel is low.This position can not be chosen right awaybecause you absolutely must be avoid.
STEP 3: Optimization strategy for recuperative furnace
Combustionoptimization
Recuperativefurnaces
Burnersset up
Set upcombustion
density
Smoking points comparison (NOx mg/Nm3 8% O2)
STEP 4: Optimization strategy for recuperative furnace
SO2
In the following diagram we reported the emissions trend during many hoursof monitoring at hole at the recuperators bottom of an optimize furnace.
STEP 4: Optimization strategy for recuperative furnace
Combustionoptimization
Recuperativefurnaces
NOx
O2
Burnersset up (air/fuel
ratio)
Combustiondensity
Long term monitoringLong term monitoring
STEP 4: Final optimization which emissions characterization
To achieve the combustion optimization it’s necessary to carryon with the set up of each/ group of burners, by determiningthe optimal condition of both emissions (NOx, O2, CO) and thefurnace pressure and temperature
Determination of smoking pointby air/fuel ratio exchange
Determination of NOx, O2 and CO concentrations in the flue gasesemitted into the atmosphere from ducts and stacks.
STEP 3: Optimization strategy for regenerative furnace
Combustionoptimization
Renerativefurnaces
Burnersset up (air/fuel
ratio)
Relation between NOx and process management parameters:velocity of air/ fuel and slope, % Gas ∝Oil Vs heat flow (kW/m2), etc..
Burnersset up (air/fuel
ratio)
Combustiondensity
Fuel andatomizingPressure
Slope andAzimut
Metodology: Dinamic approachMetodology: Dinamic approach
Combustionoptimization Energy
EmissionsDetailedenergybalance
Carachterization of
Initial setup
EmissionsDetailedenergybalance
ProcessOptimization
Process control
BatchHeat loss through therefractories
Cooling electrodes, loaders,throat, barrage, etc
System under consideration and energy and material flowsFor the elaboration of the furnace energy balance it is necessary to measure the flows ofenergy and matter in the diagram below:
Energy Balance
Air
Fumes
Air Combustion
Boosting
Glass
Fumes
infiltrationcold air
Heat loss through therefractories
forced coolingflux-line
Borderof thesystem
Energy Balance: Measurements
Flue gasRegenerator Right Left Units
O2 1.86 2.20 % dryCO2 11.6 11.5 % drySO2 768 685 mg/Nm3 8% O2NOx 805 817 mg/Nm3 8% O2CO 30 9 mg/Nm3 8% O2 -2.5 hPa
4.2 hPa 5.7 hPa 5.9 hPa
Pressure checkFlue gas composition: (O2, CO2, CO, NOx)
Determination of amount and location (air) leakagesDetermination of wall losses (glass bath, combustion space, regenerators)Other balance measurement details (batch umidity, dog houses losses, etc..)
9.3 hPa6.4 hPa6.6 hPa
30 hPa
Energy Balance: Measurements
Trend emissions, temperatures and pressure values, Endoscopic inspection
Fumi immessi in Atmosfera
DispersioniRigeneratore
Aria Preriscaldata
Fumi torrino
Aria fredda
2,5%
26,9%0,4%
52,4% 1,7%
80,3%
Energy Balance: Sankey Diagram
GasVetro
Boosting ElettricoPerdite energetiche (dispersioni,
raffreddamenti, infiltrazioni)
Gas di calcinazione
Fumi torrino
49,7%95,6%
4,1% 19,2%
2,5%80,3%
Metodology: Dinamic approachMetodology: Dinamic approach
Carachterization of
Initial setup
Combustionoptimization Energy
EmissionsDetailedenergybalance
Carachterization of
Initial setup
Process control
EmissionsDetailedenergybalance
ProcessOptimization
METODOLOGY: DYNAMIC APPROACH – FLOW CHARTInitial
characterization/Energy Balance
Regenerative/Recuperative
Furnaces
Emissions andPressureFurnace/
Regeneratorchambers
Combustionoptimization
Regenerativefurnaces
Burnersset up
Recuperativefurnaces
Burnerset up
Finalcharacterization/Energy Balance
Regenerative/Recuperative
Furnaces
Emissions andPressureFurnace/
Regeneratorchambers
Diagnostic AuditPeriodic check
Regenerative/Recuperative
Furnaces
EndoscopyEmissions and
PressureFurnace/
Regeneratorchambers
Burners Map
Smoking point
Temperatures,Leakeage,
infiltration andother Balance
details
Set upcombustion
density
Reducecombustiontemperature
Slope and Azimutset up
Fuel andatomizingPressure
Set upcombustion
density
Emissions andPressureFurnace/
Regeneratorchambers
Burners Map
Smoking point
Temperatures,Leakeage,
infiltration andother Balance
details
Energy Balance
Optimizationcombustion
check
EmissionsAnalysis and
periodicmonitoring
EnergyThermal balance
Glass defectsbubbles,fractures,inclusions
RefractoryCO trend,carry-over
determination
Periodic Audit
EnergyThermal balance
CombustionoptimizationBurners Map
Smoking pointEndoscopicmonitoring
VIS, NIR
Batchcomposition
check
Glass defectsbubbles,fractures,inclusions
Periodic Audit
airp
hase
Thermography (NIR) and Endoscopic(VIS) to check periodically: Refractory structure of crown,regenerators, melting bath, walls,doghouse, Burners and Flame plumes
was
tefu
mes
phas
e
The PRIME Glass Project is aimed at developing, implementing and testing twoinnovative Primary Measures for the abatement of NOx emissions produced byglass melting furnaces. These techniques have already been researched and testedat pilot scale in the past, and are now being experimented at full industrial scalein several Italian furnaces in the Prime Glass project (LIFE-ENV-IT-001020), to beachieved with the contribution of LIFE, the financial instrument of EuropeanCommunity.
Innovative Primary TECNIQUES - Overview of the project
Both the PRIME Glass innovative techniques are “external” to the combustionchamber: one is installed at the bottom of the regenerator and the other at theport neck level; moreover, both the techniques are meant to be applied inaddition to the aforementioned “internal” measures, in order to providefurther benefits.
Both the PRIME Glass innovative techniques are “external” to the combustionchamber: one is installed at the bottom of the regenerator and the other at theport neck level; moreover, both the techniques are meant to be applied inaddition to the aforementioned “internal” measures, in order to providefurther benefits.
1. Strategic waste gases recirculation: with thistechnique a fraction of flue gases is drawn from thebottom of the regenerator chamber and injected intocold combustion air (at the bottom of the otherchamber) by means of a high T resistant fan and of apurposely designed ducting system. Bearing less O2and more radiating species (H2O, CO2), injected fluegases reduce NOx generation and enhance heatexchange in the regenerator, increasing energyefficiency.
Furnace
Waste GasChamber
AirChamber
PRIME Glass Project: Innovative Primary TECNIQUES
1. Strategic waste gases recirculation: with thistechnique a fraction of flue gases is drawn from thebottom of the regenerator chamber and injected intocold combustion air (at the bottom of the otherchamber) by means of a high T resistant fan and of apurposely designed ducting system. Bearing less O2and more radiating species (H2O, CO2), injected fluegases reduce NOx generation and enhance heatexchange in the regenerator, increasing energyefficiency.
2. Enhanced hot air staging: also called hybrid air staging,this technique reduces the amount of thermal NOxreleased by the furnace by lowering excess air andcompleting combustion at lower T inside the wastegases port neck, by means of high speed injection ofpreheated air, which is spilled from the other port andpropelled by jets of compressed cold air (thus “hybrid”).This leads to less NOx formation while minimizing theenergy losses with respect to a pure cold air staging.
1. Strategic waste gases recirculation: Furnace
Waste GasChamber
AirChamber
PRIME Glass Project: Innovative Primary TECNIQUES
Snorkelintakes
2. Enhanced hot air staging:
The waste gases produced by Trezzano (MI) furnace No. 3 with the recirculation systemturned off were characterized to determine the reference state of combustion.At the top of the regenerator chambers the flue gases stream was mapped just abovethe checkerworks in 9 different positions, following a 3 x 3 grid; in the port neck theprobe was placed only in the central position. The results, averaged over severalcomplete inversions, are reported below.
Waste gases recirculation OFF – Flue gases Chamber
PRIME Glass Project: Baseline characterization - off gas analysis
Waste gases recirculation OFF – Flue gases Chamber
Port neckNOx
Top chamber NOx
NO
xm
g/N
m3
8%O
2
The average NOx emissionsmeasured at the top of theregenerator chamber areconsistently higher than in theport neck; this is probably due tospontaneous post-combustion ofresidual CO, that passes from3000 mg/Nm3 in the port toaround 60 ÷70 mg/Nm3 in the topof the regenerator.
Metodology: Dinamic approach - off gas analysis
Port neck NOx
Top chamber NOx
O2%
The average NOx emissionsmeasured at the top of theregenerator chamber areconsistently higher than in theport neck; this is probably due tospontaneous post-combustion ofresidual CO, that passes from3000 mg/Nm3 in the port toaround 60 ÷70 mg/Nm3 in the topof the regenerator.
This is confirmed by the NOx vs.O2 data measured in the 2points: their linear regressionsare parallel, as expected fromflue gases produced by the samefurnace, but offset one withrespect to the other by the NOxcontribution connected with COout-of-furnace “burnout”.
NO
xm
g/N
m3
8%O
2
During the tests both pictures andvideos of right and left flames weretaken with the PRIME Glassrecirculation system turned off andturned on.With the system in operation it’snoticed a slight increase of thelength flame.
Left flame
PRIME Glass Project: Flame study
During the tests both pictures andvideos of right and left flames weretaken with the PRIME Glassrecirculation system turned off andturned on.With the system in operation it’snoticed a slight increase of thelength flame.
An image processing algorithm isbeing developed at the moment fora quantitative interpretation of therecorded footage.The aim is to objectivelycharacterize the flame shape andemissivity, in order to be able tocompare on a scientific basis thedifferent flames.
Rightflame
Periodic Audit
Thank you for your kind attention!