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New Approach to Optimizing Fired Heaters

New Approach to Optimizing Fired Heaters

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New Approach to Optimizing Fired Heaters

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  1. New Approach to Optimizing Fired Heaters • Ashutosh Garg, Furnace Improvements Sugar Land Texas, USA

  2. Energy Consumption • Petroleum Refining • 7.5% of the total energy consumption in USA • 0.40 MMBtu/ BBL of oil • Total Energy consumed in refining- 7.1 Quadrillion BTU/yr • Energy cost -$6/MMBtu • Total Energy Cost- 42 Billion /yr • Fired heaters -40-70% of the energy

  3. Energy Consumption • A Typical refinery process 100,000 BPD • Consumption of 0.40 MMBTU/BBL • $6 per MMBTU • Energy bill of $ 87.6 million per year. Potential Saving • $876,000/Year • 1% Efficiency improve

  4. Fired Heaters • Essential component in Petrochemical and Chemical Plants • Each refinery has ≈ 20-50 fired heaters • Design efficiency - 70-90% • Operating efficiency is even less than design.

  5. Maintain the design conditions (very difficult) In the field, heater loads change constantly due to variations in: Feed flow rate Feed temperature Fuel composition Ambient temperature The heater will be operating a non-optimal conditions Requires optimization 24/7 Maintaining Design Operation

  6. When the heater conditions change, adjustments in the heater are required. Manual adjustments are provided- not adequate Optimizing the fired heater will: Reduce Energy Consumption Increase run length Minimize maintenance FIS has proposed two prong approach Software based- Heater Performance Index Hardware based- Draft & Excess O2 Control How to Maintain the Design Efficiency?

  7. www.heatflux.com Fired Heater • Heat liberated by the combustion of fuels is transferred to fluids contained in coils • Fired Heater: • Radiant Section • Convection Section • Stack

  8. Natural Draft- 70-84% Balance Draft-90-92% Natural Draft heaters in Industry- 86% Balanced Draft heaters in Industy-12% Typical stack temperature – 500-800 F Typical stack Oxygen- 2-10% Target Oxygen-2-3% Plenty of room for optimization Typical heater efficiency

  9. Combustion • Combustion Requires • Air ( 0.21O2 + 0.79 N2) • Fuel • Ignition source • Complete Combustion • Excess air • Incomplete Combustion • Energy Loss • CO and H2 are released

  10. Draft • Pressure inside the heater • Combustion air is drawn inside the heater through the burner’s air register • Hot Flue gas flows out of the heater through the stack • Types of Draft • Natural Draft (ND) > 80% • Forced Draft (FD) < 1% • Induced Draft (ID) ≈ 10% • Balanced Draft ≈ 10%

  11. Draft • Stack Dampers helps control the draft • Arch is the highest pressure point in the heater • Excess or shortage of draft is not acceptable

  12. Burner Operation • Correct combustion in firebox include: • The firebox is clear • No smoky appearance • Burners flames are steady and well-formed • Check burners regularly • Adjusting burner registers to control air intake

  13. Air Leakages • Air entering in to furnace from a number of places: • Peepholes • Header box doors • Tube guide opening • Feed tubes entering and exits • Not pressure tight structure

  14. Heater Optimization • Target set 2-3% O2 in the flue gas. • Operating conditions fluctuates : • Manual control /adjustments • Operators • Number going down • Experience going down • Need training

  15. Optimisation Case Study -1 • FIS performed a tuning job for a refinery. • Heater: • Depentanizer reboiler heater • Horizontal tube box • Absorbed heat duty - 87 MMBtu/hr • 15 up fired burners • The stacks is connected to a large common stack • Two off take ducts provided with manual dampers

  16. Check draft Adjust using off-take dampers Check excess O2 Adjust burner register Check burners Light up all burners Check Flames/Firebox Optimisation Approach

  17. Crude Heater TuningCase Study -2 • Natural Draft Crude Heater • Horizontal tube • Up-fired burners • 11 burners

  18. Fuel gas Flow and Pressure Before & After Tuning Fuel gas flow, MSCFD Fuel gas pressure, psig

  19. Tube Skin Temp Before & After Tuning

  20. Observations in Refineries Recommendations • Furnace working off design conditions • Poor quality of dampers • Lower number of operators • Operator without sufficient training • Software • Heater Performance Index (HPI) • Hardware • Draft control system • Excess O2 control system

  21. Heater Performance Index • Analyzes the performance of Fired Heater 24/7 • Built into DCS • Generates guidelines • Built in intelligence • Customized modeling • Thermal Efficiency • Fuel gas rate, • Draft, • Excess O2, • Tube skin temperatures, • Feed flow rate, • Pressure drop, • Coking rate, • Air preheater performance

  22. Crude Flow Rates

  23. Coil Inlet Pressure

  24. Fluids Cross-over Temperatures.

  25. Coil Outlet Temperatures

  26. Heater Performance Index. Remarks

  27. Heater Performance Index. Remarks

  28. Heater Performance Index

  29. Oxygen & Draft Control System (Natural Draft Heater)

  30. Draft Control System

  31. Stack dampers Reliable Correctly sized Pneumatically operated Opposed blades

  32. Reliable DampersOpposed blades vs. Parallel Blades

  33. Excess O2 Control Control air supply to burners Pneumatically operated dampers or registers Provide proper control scheme Damper opening is provided based on Draft Excess O2 Firing rate Other parameters Savings realized through out the day

  34. Summary Manual controls are not adequate Energy prices are high Advanced Controls possible Use DCS based or PLC based Provide adequate safe guards Intelligent analysis of heater parameters Substantial savings can be realized Payout will be less than a year in most cases

  35. Thank you very much • Questions and comments are welcome