New Firing Patterns in Heaters Provide Uniform Heat Transfer

Paper from the AFRC 2015 conference titled New Firing Patterns in Heaters Provide Uniform Heat Transfer

Fired heaters are used for heating hydrocarbons fluids in the refineries and petrochemical plants. They are used for high temperature heat transfer. In most fired heaters, we are burning fuel gas as source of heat . Heaters that are processing hydrocarbons services are prone to coking and cracking depending upon the nature of the hydrocarbons being processed. Typically heaters may run length of anywhere from 3 months for coking service to 6 years for different services. Heater designers and operators are always faced with the challenge of providing uniform heat transfer to all the tubes. Engineers use equations that assume uniform heat transfer to heater tubes when designing fired heaters. However, in reality, most fired heaters do not experience uniform heat transfer, and as a result, hot spots develop on the tubes. These hot spots cause coking inside the tubes which requires the heater be shutdown periodically to remove the coke and clean the tubes. Any shutdown to clean the tubes in a fired heater causes a substantial production loss. Furnace Improvements has developed a new patented firing technology that provides uniform heat transfer to heater tubes. This technology can be applied to most fired heaters. Our patented technology reorients the burners at a slight angle away from the tubes. We are able to direct the hottest part of the flames and flue gases away from the tubes without affecting the heat transfer in any way. FIS has installed this in 6 heaters ranging from 14 MMBtu/hr. to 280 MMBtu/hr. The clients are experiencing significant reduction in tube metal temperatures. This is translating into lower coking rates and higher tube life. We have been able to increase the capacity of the heaters in most of the cases. In this paper, we will present two case studies utilizing new firing patterns. in the first, the Inclined Firing System was installed in a very large vertical cylindrical crude heater. The client experienced 250 F to 350F lower tube metal temperatures after the heater was fitted with inclined firing system. In the second study, IFS was incorporated in a small vertical cylindrical heater Diesel Hydrotreater heater. In this case, the heater duty was increased from 14 MMBtu/hr. to 21 MMBtu/hr.

New Firing Patterns in Heaters provide Uniform Heat Transfer AFRC 2015 Industrial Combustion Symposium Ashutosh Garg Furnace Improvements Uniform Heat Transfer vObjective is to achieve uniform heat transfer in the heaters vNo hot spots vNo high tube metal temperatures vNo coking vExtended Run Length Low NOx and Ultra Low NOx Burners v Low NOx and Ultra Low NOx Burners being used in heaters v Larger foot print due to fuel gas recirculation and fuel gas staging v Flame length and diameter are larger v Burners require minimum spacing for flue gas recirculation CL.BURNERS B.C.D. ! B.C.D. 5° (TYP .) CL.BURNERS Existing Arrangement C L.BURNERS vBurners should be as far away from the tubes as possible v In conventional heaters it will result in a very large tube circle diameter vLarger diameter results in expensive heater design C L.BURNERS Uniform heating ! Inclined Firing B.C.D. 5° (TYP .) CL.BURNERS CL.BURNERS vOptimum solution for Low NOx Burners and VC heater design Inclined Firing Arrangement Patented Technology-7484478B2 Benefits of Inclined Firing System vSignificant reduction in tube metal temperatures vLow coking rates vHigher tube life and run lengths vIncreased capacity possible in most heaters vUniform firing achieved across the tubes Inclined Firing System v8 burner system vTCD of 20'-8" BCD Φ20'-8" TCD Height in Elevation Φ21''-9 1/2" I/S INS. 0'-0" 8'-0" 5'-0" 7'-1.5" 10'-0" 6'-3" 15'-0" 5'-4.5" 20'-0" 4'-6" 25'-0" 3'-7.5" 3'-7 1/2" 4'-6" 7'-1 1/2" B.C.D. Φ8'-0" B.C.D. 2'-7" 10'-0" 25'-0" 20'-0" 6'-3" 15'-0" 5'-4 1/2" 5'-0" 45'-8 5/8" 57'-10" WELD TO WELD LENGTH 61'-4 1/2" 10'-5" I/S INS. 5' 5' 4'-6" 5' 5' 6' 5' 5' 4'-6" 35'-6" 35'-6" 5-10deg. INTERHEATER -2 INTERHEATER -1 CHARGE HEATER Inclined firing in a down fired steam reformer Base Case High flue gas temperature going towards the tubes. Proposed Case High flue gas temperature going away from the tubes. [°F] In the proposed case, temperature contours clearly show the reduction in the flue gas temperature around the radiant tubes. Inclined Firing in a Double Fired Coker heater Inclined Firing Vertical Up Firing www.heatflux.com 10 Inclined Firing in Horizontal Tube Cabin Heater with End Wall Firing Existing Case 7 deg. inclined firing Case High temperature region is in the centre of the heater, flue gas temperature near the radiant tubes is reduced. Crude Heater v Client facing flame impingement and high tube metal temperatures in radiant section v FIS recommended inclined burner firing system to eliminate flame impingement v Carried out CFD modeling of the burners and radiant section to demonstrate the benefit of the inclined burner firing system Design Parameters Process Conditions: PARAMETER Total Heater Absorbed Duty Feed Flow Rate Feed Inlet/ Outlet Temperature Feed Inlet/Outlet Pressure FGT leaving Stack Thermal efficiency Firing Rate UNIT VALUE MMBTU/hr 261.4 Lb/hr 1,545,460 oF 475 / 650 Psia oF % MMBTU/hr 134.7/ 34.7 280 90.5 288.85 Radiant Section v120 tubes § 6"NPS, Sch. 40 vTube Material § A-335 Gr. P9 vNo. of Passes § 12 vMaximum/Average Heat Flux § 18,000/10,000 Btu/hr.ft2 v24 Low NOx Forced Draft Burners vFuel Gas Fired vOperates at 10% Excess Air vHeat release per burner § 15 MMBtu/hr (maximum) § 12 MMBtu/hr (normal) Existing Burners Arrangement Inclined Firing System Burner Arrangement Crude Heater: Twin Cell Vertical Octagonal Type Velocity Vectors Base Case vs Inclined Firing System 50 ft 36 ft 19 ft [ft/sec] Existing Case with Vertically Fired Burners 0 ft Height in Feet Proposed Case with Inclined Firing System Temperature Contours Base vs. Inclined Firing System [°F] Base Case Inclined Firing System Temperature Contours at 10ft Base Case vs Inclined Firing System [° F] At 10 ft Base Case At 10 ft Inclined Firing System Temperature Contours at 15 ft Base Case vs Inclined Firing System 1 [°F] At 15 ft Base Case At 15 ft Inclined Firing System CO Mass Fraction Contours at 10 ft Base Case vs Inclined Firing System [ppm] At 10 ft Base Case At 10 ft Inclined Firing System CO Mass Fraction Contours at 15 ft Base Case vs Inclined Firing System [ppm] At 15 Ft Base Case At 15 Ft. Inclined Firing System Iso Surface of CO MF 2000 PPM Colored by Temperatures Base Case vs Inclined Firing System [°F] Base Case [°F] Top View Inclined Firing System Iso Surface of CO Mass Fraction 2000 ppm Colored by Flame Height [ft] Base Case Inclined Firing System Radiant Wall Temperatures Base Design [°F] Proposed Design For h =100 Btu/ft2∙h and T= 800 °F Summary v Client reported almost 250 °F reduction in tube metal temperatures after the revamp. v Inclined Firing is proven in solving high tube metal temperatures problems v CFD modeling demonstrated the ability of FIS to improve performance v FIS is ready to evaluate your heater to determine whether it is a suitable candidate for Inclined Firing at no cost. Case Study 2 Diesel Hydrotreater Heater Client looking to Increase the Capacity from 14 MMBtu/hr. to 21 MMBtu/hr. (by 50%) Existing DHT Heater www.heatflux.com 29 Proposed Design Parameters Process Conditions: PARAMETER Total Heater Absorbed Duty Feed Flow Rate Feed Inlet/ Outlet Temperature Feed Inlet/Outlet Pressure FGT leaving Convection Section Thermal efficiency Firing Rate UNIT VALUE MM BTU/hr 22.5 Lb/hr 188,705 oF 600 / 715 psia 1150.6 / 1104.7 oF 773 % MMBTU/hr 79.5 28.29 HYDROCARBON COIL 7 FINNED ROWS HYDROCARBON COIL 3 BARE ROWS 4'-8" I/S INS. EXISTING 8FT ADDITIONAL NEW MODULE 9'-9" T.C.D. 4'-0" B.C.D. ER 6° CL.BURN C L.HEATER 6° C L.BURNER v 23 tubes § 8"NPS, Sch. 80 v Tube Material § A-312 TP 347 v No. of Passes § 1 v Maximum/Average Heat Flux § 17,087/9,580 Btu/hr.ft2 NEW DHT Reactor Charge Heater Hydrotreater Heater vInstallation of 4 burners in inclined firing pattern Burners 6o 6o CL BURNER C L BU R N ER v 4 Ultra Low NOx Callidus LE-CCQ-8W Burners v Fuel Gas Fired v Operates at 15% Excess Air v Heat release per burner § 7.78 MMBtu/hr (maximum) § 7.08 MMBtu/hr (normal) 4'-0" B.C.D. Contours of Velocity (ft/s) Contours of Velocity Vectors (ft/s) Flow coming from back of radiant tubes and going at bottom of heater Recirculation loops are formed Contours of Temperature (oF) Contours of Temperature (oF) and CO (ppmv) Contours of Temperature (oF) Tube Walls View -1 View -2 Heater Operation vThe heater has been successfully commissioned. vThe client is very happy running the heater. www.heatflux.com 39 Thank you very much vQuestions and Comments are welcome www.heatflux.com 40