A Numerical Investigation of the Effect of Electric Boosting in an Oxy Fuel Fired Glass Fiber Furnace

Transcription

1 A Numerical Investigation of the Effect of Electric Boosting in an Oxy Fuel Fired Glass Fiber Furnace Burçin Gül, Merve Durubal Şişecam, Science and Technology Center, Kocaeli, Turkey

2 OUTLINE ŞİŞECAM FURNACE MODEL AN OXY-FUEL FIRED FURNACE DESIGNED WITH AN ELECTRIC BOOSTING SYSTEM CONCLUSION INTRODUCTION 1

3 1. INTRODUCTION Polymer reinforcing agent Bulk properties Transparency Hardness Chemical / Mechanical Durability Electrical Resistance Figure 1: Utilization area of glass fiber products Fiber properties Strength Flexibility 2

4 1. INTRODUCTION Challenges in production of glass fiber: Strongly corrosive interaction of molten glass with refractories Excessive foam layer formed on glass surface Increase in undesired foam layer in oxy-fuel glass furnaces Figure 2: Glass fiber furnace 3

5 2. ŞİŞECAM FURNACE MODEL The equations describing the mass, momentum and heat transfer in combustion space; x u y v z w S x x y y z z variables diffusion coeff. S source term Transformed into linear equations for certain volumes by the Finite Volume Method. Solved with SIMPLER Algorithm (Patankar) for variables. Heat transfer with radiation into glass bath: Rosseland Approach rad n T 3 (W/(m.K)) T = Average Temperature, K, = Stefan Boltzmann coeff. n = Average Refractive Index a = Average absorption coeff. of molten glass Figure 3: Radiation heat transfer 4

6 3. OVERVIEW OF THE OXY-FUEL-FIRED UNIT-MELTER FURNACE DESIGNED WITH AN ELECTRIC BOOSTING SYSTEM Aim: To investigate supplementary electrical heating to the glass melting process of an oxy fired glass fiber furnace to increase pull rate. To examine effect of zones in a multi zone boosting system in defining temperature profile of glass bath. Figure 4.a: Combustion space of oxy fuel fired glass fiber furnace To analyze effect of electric boosting and bubbler system on glass current pattern and temperature profile in glass bath. 5 Figure 4.b: Glass bath of oxy-fuel fired glass fiber furnace

7 3. OVERVIEW OF THE OXY-FUEL-FIRED UNIT-MELTER FURNACE DESIGNED WITH AN ELECTRIC BOOSTING SYSTEM Increase in pull rate up to %28, kw of electrical power Substitution of natural gas by electrical energy: %15 decrease in specific fuel consumption Amount of supplementary electrical energy Economical optimization of electricity + oxygen cost 6 Figure 5: Ratio of electricity in total energy given to the furnace

8 3.1 EFFECT OF ELECTRICAL BOOSTING SYSTEM Electrical energy required to gradually increase specific pull rate from 1.60 ton/m2.day to 2.0 ton/m2.day OBJECTIVE: Cost Optimization Energy Efficiency Figure 6: Electrode zone array in each case 7

9 CASE1 3.1 EFFECT OF ELECTRICAL BOOSTING SYSTEM Z1 Z2 Z3 Z4 Bubbler B 800kw CASE2 CASE3 400kw ( C) CASE4 300kw CASE5 200kw 200kw 300kw 400kw 800kw *Z: Zone Figure 7: Temperature distributions obtained with different amount of electrical energy *B: Bubbler 8

10 3.1 EFFECT OF ELECTRICAL BOOSTING SYSTEM Z4 800kW Z3 400kW Zone 4 (+ 800 kw) T refining increased Z1 200kW Z2 300kW Zone 3 (+ 800 kw) Impact on defining T riser Zone 1 and 2: less effective in increasing T in refining zone Main ΔT along the furnace length: Zone 3 + Zone 4 Figure 8: Glass bottom temperatures with/without electric boosting 9

11 3.1 EFFECT OF ELECTRICAL BOOSTING SYSTEM ΔT Permit for an increase in specific pull rate Zone 4 (+ 800 kw) NO contribution on T glass surface on batch side. Zone 3 (+ 400 kw) enforcement of upper convection currents (under the batch blanket). Noticeable temperature escalation! Zone 3 + Zone 1,2 Convection currents flows through the back wall of the furnace by moving hotter glass downwards Result: increase in T glass bottom. Figure 9: Glass bottom temperatures along glass depth with/without electric boosting at batch side 10 *ΔT= T1700KW-T0KW

12 3.1 EFFECT OF ELECTRICAL BOOSTING SYSTEM Foam Reduce energy efficiency! Lead to poor glass quality! Z1 Z2 Z3 Z4 T profile to control refining behaviour Electrical boosting system Refining time Higher T refining Better refining efficiency 11 Figure 10: Glass bottom temperatures along glass depth with/without electric boosting

13 3.2 EFFECT OF BUBBLER Bubbler location: 70% of the furnace length as double rows Distance between Zone 4 and bubbler row is crucial Zone 4 is placed close to bubbler row: Decrease in furnace efficiency! Thermal barrier Regulate glass flow pattern! Coupling electric boosting system (1700 Kw) a bubbler system T avg furnace increases ~35 C Figure 11: Temperature and flow distribution in the longitudinal cross section of the glass bath with and without bubbling 12

14 3.2 EFFECT OF BUBBLER Bubbling through the glass significantly improves the heat exchange Between glass melt and the flame Inside the glass melt itself. Expected to see higher T bottom when the bubbler system is introduced. Homogenizing action of bubblers can significantly speed up color or composition changes. Figure 12: Glass bottom temperatures profile with/without bubbling 13

15 Elect. boosting system vs. Bubbler system 3.2 EFFECT OF BUBBLER Effect of an electrode row in keeping batch piles back was found to be not as effective as a bubbler row would be. Barrier effect Comparision of T profiles across the glass depth. Bubbling is much more effective on T distribution in glass bath. 14 Figure 13: Glass temperatures along glass depth for melting and refining sections

16 4. CONCLUSION Study: A series of cases are investigated with different amount of electrical boosting for a specific oxy-fuel fiber glass furnace. Electrical boosting system: Enforces convection currents in the melt T avg furnace Enables increased pull rates Better fining and glass quality improvement Locations of the electrode zone have large impacts on the temperature distributions in the glass bath. Bubbler system: Reinforce convection flows more Improve T bottom and glass quality Electrical boosting system Temperature profile Bubbler system: Regulate glass flow Temperature profile 15

17 THANK YOU FOR YOUR ATTENTION! 16

18 REFERENCES 1. Önsel, L. and Eltutar, Z., Modelling of a Container Furnace for Electric Boosting Evaluations, 4. International Seminar on Mathematical Simulation in Glass Melting, Vsetin, Czech Republic, Spremulli, F., Electrical Modelling and Scale-up Rules for Glass Melters. Glastech. Ber. Glass Sci. Technol. 69 (1996). No Pchelyakov, K.,A., Tank Models and the Use of Bubbling and Electric Heating in Tank-Melting Furnaces Glass Ceram., (Engl. Transl.), 28[7-8], (1971). 4. Hoke, B., C., Application of Glass Melt Modeling for Examining Forced Bubbling Design, Ceramics Silikaty 44(1) (2000). 5. Stanek, J., Improved Modelling Technique of Electric Glass Melting, Journal of Non-Crystalline Solids 73 (19S5)