Tecniche primarie per la riduzione delle ... - Prime Glass

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


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


Sampling points

Furnace Recuper. FuelFuel

consuptionKg/h

Airconsuption

Nm3/h

BoostingkWh/h Product Pull t/d Cullet %

Unit Melter Double pass Oil ---- ----- ---- Flint 340 ----




Carachterization of

Initial setup


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


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


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)


SO2

In the following diagram we reported the emissions trend during many hoursof monitoring at hole at the recuperators bottom of an optimize furnace.




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


Renerativefurnaces


ratio)

Relation between NOx and process management parameters:velocity of air/ fuel and slope, % Gas ∝Oil Vs heat flow (kW/m2), etc..


ratio)

Combustiondensity

Fuel andatomizingPressure

Slope andAzimut




Carachterization of

Initial setup


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%


Carachterization of

Initial setup



Carachterization of

Initial setup

Process control


ProcessOptimization

METODOLOGY: DYNAMIC APPROACH – FLOW CHARTInitial

characterization/Energy Balance

Regenerative/Recuperative

Furnaces

Emissions andPressureFurnace/

Regeneratorchambers


Regenerativefurnaces

Burnersset up


Burnerset up

Finalcharacterization/Energy Balance


Furnaces


Regeneratorchambers

Diagnostic AuditPeriodic check


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


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!

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