Modeling Furnaces in the Chemical Process Industry Committed Individuals Solving Challenging Problems 746 E. Winchester St., Suite 120 Murray, Utah 84107 www.reaction-eng.com
REI Profile Slide 2 Energy And Environmental Consulting Firm Specializing In:» Combustion System Design and Performance Analysis» Complex CFD Simulations Performance Emissions Operational Impacts» Customized Software» Specialized Equipment» Proof-of-Concept Testing Strong Network of Experts Objective: Solve Challenging Combustion Problems Using Specialist Talent & Technology
REI Modeling Strengths Slide 3 Modeling and Analysis Expertise» Combustion, Fuel Conversion & Pollutant Emissions» Unique, Proprietary Modeling Capabilities & Tools Ability to develop and apply advanced chemistry to CFD and process modeling tools» Qualified Combustion Modelers Understand physics, chemistry, mathematics, software Industrial perspective» Experience Over 200 Combustion Systems Modeled Network of Consultants Objective Analyses
Slide 4 Selected Industrial Applications & Clients Applications Melting Furnaces Reheat Furnaces Blast Furnace Injection Flash Smelters Cement Kilns Phosphate Kilns CO Boilers Sulfur Recovery Units Process Heaters Cracking Furnaces Incinerators Thermal Oxidizers Burners Enclosed Flares Selected Clients Bayer BHP BP Cadence Callidus Chemtrade Chevron China Steel Cominco ConocoPhillips CPC CPChem Dow Hexcel Holnam Huntsman Chemicals INCO Inland Steel John Zink LaFarge Lone Star Monsanto NOVA Chemicals PCA Persee Chemical Philip Morris Praxair Searles Valley Minerals Technip Solena Solutia SunCoke Thai Olefins
Chemical Process Applications Slide 5 Systems Process Heaters Cracking Furnaces Thermal Oxidizers Incinerators Burners Flares Applications Pollutant Emissions (NOx, CO) Waste Stream Disposal Tube Overheating Heat Flux & COT Uniformity Process Yield & Conversion Radiant Efficiency
Why Use CFD Modeling? Slide 6 Modeling is a cost effective approach for evaluating system performance, pollutant emissions, and operational impacts Improve understanding Estimate performance Provide conceptual designs Identify operational problems Cheaper than testing More information than testing Does NOT make decisions for engineers, but does help them be more informed
REI s Proprietary CFD Software Slide 7 BANFF & GLACIER» 20+ years development and application» Targeted to gas, oil and coal-fired utility boilers ADAPT» ~10 years development and application» Improved geometry resolution (adaptive mesh refinement)» Advanced chemistry» Improved turbulencechemistry interaction» Targeted to gas-fired ultra low-nox systems and premixed combustion Combustion Chemistry Pollutant/ Emissions Chemistry Turbulence Combustion Surface Properties Radiation & Convection Heat Transfer Particle Reactions
Chemical Furnace Modeling Challenges Slide 8 Scales! millimeter meter tens of meters» Geometric resolution» Jet velocities» Chemistry vs turbulent mixing Input accuracy» Garbage-in garbage out Chemical Time Scale Slow time scale 10 0 s Physical Time Scale Trade-off between accuracy and turn-around time Intermediate time scale 10-2 s 10-4 s Time scales of flow, transport, turbulence» What are most critical factors for problem of interest Fast time scales, equilibrium chemistry 10-6 s 10-8 s
Furnace Model Requirements Slide 9 Accurately represent furnace geometry and operation Sub-models for:» Turbulent fluid mechanics» Combustion chemistry» Turbulence-chemistry interactions» Finite-rate kinetics for ppm-level NOx, CO» Surface properties» Gas-wall-tube heat transfer (conduction, convection, radiation)» Process chemistry Computationally efficiency (parallel execution)
Modeling Approach Slide 10 REI currently uses advanced ADAPT CFD software for process heaters/cracking furnaces Accurate modeling provides accurate flame shape, flow patterns, temperature profiles, major species profiles, heat transfer/heat flux profiles, tube temperatures, process fluid heat absorption Provides capability to analyze:» New generation ultra-low NOx burners for new furnaces and revamps» Burner spacing, distribution and burner-burner interactions» Lower emissions (CO and NOx)» Impacts of fuel changes» Non-uniform heat flux profiles and surface temperatures» Sources and fixes for process or convective tube overheating» Test furnace to full-scale furnace scale-up
Sample Uses of Modeling Slide 11 Improved Performance» Enhance furnace efficiency» Lower emissions» Study particulate behavior during de-coking process Reduce risk of new technology» Evaluate burner designs and spacing for new furnaces» Compare different burner designs for furnace revamps» Assess impacts of fuel changes» Evaluate coating impacts» Scale burner performance from test furnace to full-scale furnaces Troubleshooting» Identify causes and fixes for process or convective tube overheating» Identify source of heat flux non-uniformities
Pyrolysis Furnaces Slide 12
Example - Retrofit Burner Evaluation Full-Scale Pyrolysis Furnace Slide 13 Objectives» Improve flame quality» Maintain low NO x emissions Compare retrofit burners» Flame quality (no rollover)» Low NO x and CO emissions» Heat flux profile Use ¼-furnace model» Capture burner-burner interaction» Capture tube heat flux profiles» Maximize burner resolution
Retrofit Burner Evaluation Isosurfaces of 5000 ppm CO Slide 14 Original burner Option 1 Option 2 Option 3 Excess fuel between burners Propensity for flame rollover Limited heat flux distribution Good combination of flame quality and heat distribution
Retrofit Burner Evaluation NO x Profiles Slide 15 Original burner Option 1 Option 2 Option 3 Option 3 improved flame quality and slightly lowered NO x emissions
Example New Furnace Slide 16 Identified improved burners for new ethylene cracking furnace, helped adjust heat flux design basis Incident Flux
Example New Burner Slide 17 Evaluated new ultra low-nox burner performance, helped guide burner spacing and port placement 2500 F 5 mol% O 2 0.5 mol% CO 45 40 Height From Furnace Floor (ft) 35 30 25 20 15 10 5 Average Coils 1-5 Coils 6-10 Coils 11-15 Coils 16-20 0 50000 60000 70000 80000 90000 Incident Heat Flux (Btu/hr-ft 2 ) 2748 Btu/hr-ft 2
Example Burner Retrofit Slide 18 Evaluated different burner designs to determine best flux profile and NO emissions for furnace retrofit 12 10 Height From Floor (m) 8 6 4 2 4 Burner Coil Aver 1 4 Burner Coil Aver 2 4 Burner Coil Aver 3 4 Burner Coil Aver 4 0 50000 60000 70000 80000 90000 100000 110000 Surface Temperature NO Concentration Average Net Heat Flux to All Coils (W/m 2 )
Example Fuel Change Slide 19 Evaluated performance of back-up fuel with new burners Fuel Fraction CO Concentration Back-up Fuel Baseline Fuel Back-up Fuel Baseline Fuel
Industrial Furnaces Slide 20
CO Boiler Slide 21 Simulation of a CO boiler with process tubes for heating crude oil. CO plenum was simulated to predict the mixing of injection air into the CO plenum to account for impacts of non-uniform air and CO mixing
CO Boiler Slide 22 Simulation of CO oxidation and NOx formation in a CO boiler to assess flue gas properties in the boiler that would impact SNCR design.
CO Boiler Slide 23 Simulation of flue gas flow, gas temperature, CO, and NOx distributions in approximately 10 different waste-heat recovery CO boilers augmented by natural gas combustion for assessment of SNCR for NOx control.
Refinery Process Heater Slide 24 Simulation of a refinery process furnace for evaluation of impacts of modifications of process tube arrangement to mitigate tube overheating.
Spent Acid Furnace Slide 25 Simulation of a spent acid furnace fired by fuel oil. Modeling used to verify adequate fuel burnout and aqueous spent acid vaporization achieved with limited droplet impaction on walls
Thermal Oxidizer Slide 26 Simulation of an absorber off-gas oxidizer. Simulations were conducted in order to optimize burnout of the waste gas while minimizing NOx formation.
Detailed Example Xylene Reboiler Slide 27 Xylene Splitter Reboiler (XSR) 52.5 MMBtu/hr Firing Rate Xylene (l) Bridgewall Convective Section Circumferential Tubes 95/5% Oil/Gas 20% Excess Air 4 Process Tubes Radiant Section Xylene (l,v) Six Natural Draft Oil/Gas Burners Radiant Tubes Hottest At 1/3 Height (why?) Bridgewall Temperatures Too Hot (measurement system reliable?) Convective Tube Localized Overheating (how to fix?)
Flow and Temperature Patterns Slide 28 Recirculating Flow Field Long Flames Mix Slowly CO & O 2 Have Similar Profiles Flames Highly Emissive Flow Velocity Temperature Temperature
Temperature Profiles Slide 29 Gas Temperature (F) Radial Gas Temperature Profiles 2200 10 ft 2000 20 ft 1800 30 ft Convection Inlet 1600 1400 Profile Impacts: Flame Emission Tube Heat Flux & Temperatures Bridgewall Temperatures Convective Tube Temperatures 1200 1000 0 1 2 3 4 5 6 7 8 9 Radial Distance (ft)
Flame Emission Slide 30 Process Tube Emission Dependent on Temperature & Emissivity Peak Flame Emission ~1/3 Up Furnace Flame Peak Incident & Net Flux at Same Height (~1/3 up) Peak Temp at Same Height; Location Agrees With Hot Tube Observation
Slide 31 Radiant Section Tube Heat Flux Profiles Flux peak 2/3 down tube Incident Flux (BTU/hr/ft 2 ) 16000 14000 12000 10000 8000 6000 4000 2000 16000 Flux peak 1/3 up tube 14000 0 0 0 50 100 150 200 250 300 350 400 450 Distance Along Tube (ft) 12000 10000 8000 Top crossover 6000 Bottom crossover 4000 Qinc D Qnet D 2000 Net Flux (BTU/hr/ft 2 ) High Flux Locations Correlate with Hot Tube Temperatures
Bridgewall Temperatures Slide 32 Temperature Contours Probe Measures Max Temperature Entering Convective Section 1400 F 1420 F Hot Gas Hot Tubes 1400 F 1480 F 1460 F 1440 F 1420 F 1400 F Probe Location Gradient Impacts Measurement & Control of Temperature
Convective Section Slide 33 Gas Flow Finned Tubes Bare Tubes Tube D 2 1 3 4 6 5 7 8 10 9 11 12 14 13 15 16 18 17 Tube Has 2 Passes in Each of 9 Rows Upper 6 Rows Have Fins, Lowest 3 Rows Are Bare Radiant Load Highest at Lowest Tubes Tube 12 Overheating hotter high velocity flue gas due to more open flow area
Convective Section Tube Heat Flux Profiles Slide 34 16000 16000 14000 Qinc D Qnet D 14000 Incident Flux (BTU/hr/ft 2 ) 12000 10000 8000 6000 4000 1 2 3 4 5 6 7 8 9 10 11 12 15 16 13 14 1718 12000 10000 8000 6000 4000 Net Flux (BTU/hr/ft 2 ) 2000 2000 0 0 0 50 100 150 200 250 Distance Along Tube (ft) Observation - Net Flux Changes w/ Finned Tubes
Slide 35 Convective Section Tube Temperature Profile 800 Tube Section 12 16000 Tube Skin Temperature (F) 700 600 500 400 300 200 100 Temp D Qnet D 0 0 0 50 100 150 200 250 Distance Along Tube (ft) 14000 12000 10000 8000 6000 4000 2000 High Tube Temperatures Correlate w/ High Net Fluxes Net Flux (BTU/hr/ft 2 )
Recommended Modification Slide 36 800 750 700 Reduce Row 4 Fins Tube Skin Temperature (F) 650 600 550 500 Row 9 Row 8 Row 7 Row 6 Row 5 Row 4 Row 3 Row 2 Row 1 Add Row 3 Fins Evens Out Net Flux & Tube Skin Temperatures 450 Baseline 400 Rows 3,4 mod. 0 50 100 150 200 250 Distance Along Tube (ft)
XSR Modeling Conclusions Slide 37 Modeling Useful For Furnace Evaluation» Recirculating Flow with Long, Highly Emissive Flames» Radiant Furnace Tube Temperatures Reflect Flame Emission & Match Observation» Long Flames Create Gradients at Bridgewall Modeling Useful For Furnace Troubleshooting» Temperature Gradient at Bridgewall Impacts Measurements & Control» Convective Tube Temperatures Reflect Net Flux Change with Finned Tubes» Design Modification Identified to Minimize Convective Tube Hot Spots
For More Information Slide 38