Tecniche primarie per la riduzione delle emissioni: Ottimizzazione combustione forni fusori, diagnostica e bilancio termico

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1 Tecniche primarie per la riduzione delle emissioni: Ottimizzazione combustione forni fusori, diagnostica e bilancio termico Walter Battaglia - Alessandro Migatta - Roberto Dall Igna (Stazione Sperimentale del Vetro ScpA)

2 Summary The presentation will take into consideration the following topics: 1. Primary techniques to reduce NOx emissions a. Mecanism of NOx production 2. Description of a dynamic approach a. Combustion Optimization b. Energy balance c. 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 recirculation II. Enhanced hot air staging

3 BAT CONCLUSION:.The major environmental challenges for the glass industry are emissions to air and energy consumption. The glass production is energy-intensive and high activity in high temperature which results in the emission of products of combustion: Dust, CO2, CO, NOx, SOx, HF, HCl, Heavy Metal

4 BAT ENERGY EFFICIENCY The BAT correspond in the reduction of the specific energy consumption through the use of one of the following techniques or 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 view Use of a boiler with heat recovery for energy recovery, if feasible from an economic and technical point of view Preheating of batch mixing and cullet, if feasible from an economic and technical point of view

5 TECHNIQUES TO REDUCE NOX EMISSIONS The most appropriate NOx emissions control techniques are generally Primary Oxy fuel melting Selective Reduction with reagents Selective Catalytic (selective catalytic reduction - SCR) selective non-catalytic reduction (Selective non-catalytic reduction - SNCR)

6 PRIMARY TECHNIQUES: Mechanism of NOx formation There are four mechanisms for the production of NOx in the glass furnaces: three are linked to the combustion and the fourth to the use of nitrates in the batch; the contribution which comes from Nitrate is obviously overlooked. The main mechanism of NOx formation is the one defined as thermal NOx, the undesired compounds are generated from the breaking of air molecular nitrogen (N2 represents about 80% of ambient air) at high temperature, in presence of oxygen. The main sources of the nitrogen are combustion air, atomizing air (in oil-fired furnaces) and air leakage into the furnace.

7 Mechanism of NOx formation By an approximate calculation conducted on a waste gas generated by a natural gas combustion with 10% excess air, the NOx formation is a function of the temperature as showed in the following diagram. Equilibrium concentration 0% O2 wet fumes NOx formation rate The Nox formation rate (growing exponentially over 1550 C.) it is such important as the value of the equilibrium concentration,

8 Mechanism of NOx formation This means that the time to reach the equilibrium concentration is shorter increasing the temperature, therefore the flame temperature at the root (Tf) must be lower taking into consideration both N2 and O2 flame distribution and the dwell time at Tf. 1.Controlled distribution of fuel and combustion air in the flame 2.Increase of flame irradiation (e.g. mixed fuel combustion, fuel cracking) Q tf LHV vg d0 Fuel flow Dwell time Lower Heating Value Gas velocity Nozzle diameter

9 Process operating variables The 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) 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

10 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 or mixed; 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

11 Summarizing NOx reduction 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. 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.

12 Metodology: Dinamic approach Combustion optimization Carachterizati on of Initial setup Energy 1. Long term process continuously monitoring with accurate data Emissions 2. Simultaneous continuous monitoring in several points Process Optimization Process control Detailed energy balance

13 Continuous Monitoring System Dynamic approach The CEMS used to carry out combustion optimization/ energy balance is composed of: Gas: O2, CO, NOx Cooled probe for the extraction of the gaseous flow and cooler system equipped of filter. The gas sampled is delivered to analyzers Temperatures Pressures Cooled probes Micromanometers Data Lab 1 acquisition unit Trend emissions values Combustion optimization Thermal Balance suction

14 Trend emissions values Analytical Method During the optimization combustion campaign/ Energy Balance emissions generated by the furnaces are characterized. Below are reported the parameters monitored. n Measurements Data Method of analysis Principle of method 1 Stack temperature, velocity and EN ISO :2013 volume flow rate of the exhausts gases Discontinuous 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) Temperatures and Pressures Suction Probe + K, B or S TC s and Micromanometers 6 7 Thermography Endoscope + Thermocamera VIS, NIR

15 STEP 1: Initial emissions and combustion characterization Cooled Probe Micromanometer (Pressure Meter) Gas conditioning system Analyzers Radiation shields Thermocouple head Suction Pyrometer Energy Balance

16 STEP 1: Initial emissions and combustion characterization Control room Pressure Analyzers NOx, CO, O2 Gas conditioning system Sampling points Furnace Recuper. Unit Melter Double pass Fuel Oil Fuel Air Boosting consuption consuption Product Pull t/d Cullet % kwh/h Kg/h Nm3/h Flint

17 Metodology: Dinamic approach Carachteriza tion of Initial setup Combustion optimization Energy Emissions Detailed energy balance Process Optimization Process control

18 Dynamic approach - Optimization Combustion Procedure The combustion optimization procedure could be summarized as follow: STEP ACTIVITY 1 Preliminary data acquiring 2 Initial emissions characterization 3 4 Optimization strategy specific for: Regenerative furnaces Recuperative furnaces Final optimization which (long term) emissions characterization Current combustion process management characterization Combustion/ emissions optimization Characterization of Combustion/ emissions optimized process

19 STEP 1: Preliminary data acquiring Fuel consumption (kg/h); Set-point fuel/air ratio; Current combustion process previous management characterization Batch composition and humidy Air consumption (Nm3/h); Pull rate (t/d); Cullet (%); 1. Definizione della strategia di ottimizzazione da adottare 2. Verifica consumi teorici

20 STEP 2: Initial emissions characterization 1a Determination in different points of gas composition (O2, NOx, CO) and Pressure furnace/ regenerator chambers in the starting combustion setting (initial set-up) 1b Determination of smoking point by air/fuel ratio or pressure exchange Determination of burners map 1c Furnace pressure check The pressure adjustment of the furnace must be at a slight overpressure to avoid false air combustion contribute which can make the fuel combustion ratio reading of the reports difficult and unstable

21 STEP 2: Initial emissions and combustion characterization UNIT-MELTER FURNACE 1. Smoking Point 2. Burners Map 58,2 57,3 48,5 B01 B02 B03 77,6 B04 Oil flow (kg/h) 93,9 144,4 72,7 B05 B06 B07 121,1 87,0 B08 B09 91,4 127,5 B10 B11 UNIT 5 B01 B02 B03 B04 B05 B06 B07 B08 B09 B10 B11 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) Burners Map Burner n Oil flow [kg/h] Air flow [m3/h] Air index Burner 01 59, ,07 Burner 02 59, ,07 Burner 03 59, ,07 Burner , ,07 Burner , ,07 Burner , ,07 Burner , ,07 Burner , ,07 Burner , ,07 Burner , ,07 Burner , ,07

22 STEP 2: Initial emissions and combustion characterization REGENERATOR FURNACE Burners Map Left Burner Right Burner Burner Ext Int Ext Int Oil Flow (kg/h) n/a n/a n/a n/a Inclination ( ) Nozzle Diameter (mm) Section (mm2) Flue gas Regenerator Right Oil velocity O2 (m/s) CO2 Units % dry Impulse (N) SO2 Left % dry Flue gas Port Right Left Units O2 % dry CO2 % dry SO2 mg/nm3 8% O2 NOx mg/nm3 8% O2 CO mg/nm3 8% O mg/nm % O 2 NOx mg/nm3 8% O2 CO mg/nm3 8% O2 Flue gas Channel Right Left Units O2 % dry CO2 % dry SO2 mg/nm3 8% O2 NOx mg/nm3 8% O2 CO mg/nm3 8% O2 Regenerative: End Port

23 STEP 3: Optimization strategy for recuperative furnace To optimize the NOx, the air flow in the burners must be slightly reduced when the flow rate of fuel is high and increased when the flow rate of fuel is low.this position can not be chosen right away because you absolutely must be avoid. Combustion optimization Recuperative furnaces Burners set up Set up combustion density

24 STEP 4: Optimization strategy for recuperative furnace Smoking points comparison (NOx mg/nm3 8% O2)

25 STEP 4: Optimization strategy for recuperative furnace In the following diagram we reported the emissions trend during many hours of monitoring at hole at the recuperators bottom of an optimize furnace. Combustion optimization SO2 Recuperative furnaces Burners set up (air/fuel ratio) Combustion density NOx O2 Long term monitoring

26 STEP 4: Final optimization which emissions characterization To achieve the combustion optimization it s necessary to carry on with the set up of each/ group of burners, by determining the optimal condition of both emissions (NOx, O2, CO) and the furnace pressure and temperature Determination of smoking point by air/fuel ratio exchange Determination of NOx, O2 and CO concentrations in the flue gases emitted into the atmosphere from ducts and stacks.

27 STEP 3: Optimization strategy for regenerative furnace Combustion optimization Renerative furnaces Burners set up (air/fuel ratio) Combustion density Slope and Azimut Fuel and atomizing Pressure Relation between NOx and process management parameters: velocity of air/ fuel and slope, % Gas Oil Vs heat flow (kw/m2), etc..

28 Metodology: Dinamic approach Carachteriza tion of Initial setup Combustion optimization Energy Emissions Detailed energy balance Process Optimization Process control

29 Energy Balance System under consideration and energy and material flows For the elaboration of the furnace energy balance it is necessary to measure the flows of energy and matter in the diagram below: Heat loss through the refractories Air Air Batch Cooling electrodes, loaders, throat, barrage, etc Combustion Glass Fumes Fumes Boosting Border of the system infiltration cold air forced cooling flux-line

30 Energy Balance: Measurements Flue gas composition: (O2, CO2, CO, NOx) Regenerator O2 CO2 SO2 NOx CO Flue gas Right Left Units % dry % dry mg/nm3 8% O mg/nm3 8% O mg/nm3 8% O2 Pressure check 4.2 hpa 5.7 hpa 5.9 hpa -2.5 hpa 6.6 hpa 30 hpa Determination of amount and location (air) leakages Determination of wall losses (glass bath, combustion space, regenerators) Other balance measurement details (batch umidity, dog houses losses, etc..) 6.4 hpa 9.3 hpa

31 Energy Balance: Measurements Trend emissions, temperatures and pressure values, Endoscopic inspection

32 Energy Balance: Sankey Diagram 0,4% Aria fredda Fumi immessi in Atmosfera 26,9% 52,4% Aria Preriscaldata Dispersioni Rigeneratore Fumi torrino 80,3% Gas di calcinazione 95,6% Gas 4,1% Boosting Elettrico 1,7% 2,5% Vetro 49,7% Perdite energetiche (dispersioni, raffreddamenti, infiltrazioni) 19,2%

33 Metodology: Dinamic approach Carachteriza Carachteriza tion of tion of Initial setup Initial setup Combustion optimization Energy Emissions Detailed energy balance Process Optimization Process control

34 METODOLOGY: DYNAMIC APPROACH FLOW CHART Initial characterization/ Energy Balance Regenerative/ Recuperative Furnaces Emissions and Pressure Furnace/ Regenerator chambers Burners Map Regenerative furnaces Recuperative furnaces Burners set up Burner set up Set up combustion density Set up combustion density Reduce combustion temperature Smoking point Temperatures, Leakeage, infiltration and other Balance details Final characterization/ Energy Balance Combustion optimization Slope and Azimut set up Fuel and atomizing Pressure Regenerative/ Recuperative Furnaces Emissions and Pressure Furnace/ Regenerator chambers Burners Map Smoking point Temperatures, Leakeage, infiltration and other Balance details Diagnostic Audit Periodic check Regenerative/ Recuperative Furnaces Endoscopy Energy Balance Optimization combustion check

35 Periodic Audit Refractory CO trend, carry-over determination Emissions Analysis and periodic monitoring Glass defects Energy bubbles, fractures, inclusions Thermal balance Combustion optimization Batch composition check Endoscopic monitoring VIS, NIR Burners Map Smoking point

36 waste fumes phase Thermography (NIR) and Endoscopic (VIS) to check periodically: Refractory structure of crown, regenerators, melting bath, walls, doghouse, Burners and Flame plumes air phase Periodic Audit

37 Innovative Primary TECNIQUES - Overview of the project The PRIME Glass Project is aimed at developing, implementing and testing two innovative Primary Measures for the abatement of NOx emissions produced by glass melting furnaces. These techniques have already been researched and tested at pilot scale in the past, and are now being experimented at full industrial scale in several Italian furnaces in the Prime Glass project (LIFE-ENV-IT ), to be achieved with the contribution of LIFE, the financial instrument of European Community. Both the PRIME Glass innovative techniques are external to the combustion chamber: one is installed at the bottom of the regenerator and the other at the port neck level; moreover, both the techniques are meant to be applied in addition to the aforementioned internal measures, in order to provide further benefits.

38 PRIME Glass Project: Innovative Primary TECNIQUES 1. Strategic waste gases recirculation: with this technique a fraction of flue gases is drawn from the bottom of the regenerator chamber and injected into cold combustion air (at the bottom of the other chamber) by means of a high T resistant fan and of a purposely designed ducting system. Bearing less O2 and more radiating species (H2O, CO2), injected flue gases reduce NOx generation and enhance heat exchange in the regenerator, increasing energy efficiency. 2. Enhanced hot air staging: also called hybrid air staging, this technique reduces the amount of thermal NOx released by the furnace by lowering excess air and completing combustion at lower T inside the waste gases port neck, by means of high speed injection of preheated air, which is spilled from the other port and propelled by jets of compressed cold air (thus hybrid ). This leads to less NOx formation while minimizing the energy losses with respect to a pure cold air staging. Furnace Air Chamber Waste Gas Chamber

39 PRIME Glass Project: Innovative Primary TECNIQUES 1. Strategic waste gases recirculation: Snorkel intakes 2. Enhanced hot air staging: Furnace Air Chamber Waste Gas Chamber

40 PRIME Glass Project: Baseline characterization - off gas analysis The waste gases produced by Trezzano (MI) furnace No. 3 with the recirculation system turned off were characterized to determine the reference state of combustion. At the top of the regenerator chambers the flue gases stream was mapped just above the checkerworks in 9 different positions, following a 3 x 3 grid; in the port neck the probe was placed only in the central position. The results, averaged over several complete inversions, are reported below. Waste gases recirculation OFF Flue gases Chamber

41 Port neck NOx This is confirmed by the NOx vs. O2 data measured in the 2 points: their linear regressions are parallel, as expected from flue gases produced by the same furnace, but offset one with respect to the other by the NOx contribution connected with CO out-of-furnace burnout. The average NOx emissions Top chamber NOx measured at the top of the regenerator chamber are consistently higher than in the port neck; this is probably due to spontaneous post-combustion of residual CO, that passes from 3000 mg/nm3 in the port to around mg/nm3 in the top of the regenerator. NOx mg/nm3 8% O2 NOx mg/nm3 8% O2 Metodology: Dinamic approach - off gas analysis Top chamber NOx Port neck NOx O2%

42 PRIME Glass Project: Flame study During the tests both pictures and videos of right and left flames were taken with the PRIME Glass recirculation system turned off and turned on. With the system in operation it s noticed a slight increase of the length flame. Right flame Left flame An image processing algorithm is being developed at the moment for a quantitative interpretation of the recorded footage. The aim is to objectively characterize the flame shape and emissivity, in order to be able to compare on a scientific basis the different flames.

43 Periodic Audit

44 Thank you for your kind attention!