Hydrodynamic Thermal Flow Maps

This video is one of a 10 part series. Visit our channel's playlist to watch the full set. If you would like more information about Opgrade or Nate Barber visit www.opgrade.com. Narrator: Nate Barber Video slides: How to Predict Circumferential Anisothermalities in Horizontal Fired Heater Tubes -INTRODUCTION *Semi-empirical relationships use modified Froude numbers to define anisothermality boundaries on hydrodynamic maps for diabatic flows in tubes -Simple English *We can use superficial vapor and liquid velocities to predict if horizontal fired heater tubes will have uniform temperatures around their circumferences -WHY IS IT IMPORTANT? *If tubes aren’t the same temperature around the circumference, it’s because the interior tube walls aren’t continuously wetted and vapor is concentrating on the upper side of the tube, leading to a temperature gradient -WHAT IS A HYDRODYNAMIC-THERMAL MAP? *Hydrodynamic charts define the two-phase flow-regime in a pipe (dispersed bubble, intermittent wavy, annular and slug flows) based on superficial gas and liquid velocities *Hydrodynamic-Thermal Maps overlay boundary lines that don’t directly define the flow regime, but indicate whether the tube walls are empirically shown to be isothermal based on the superficial gas and liquid velocities *The boundary lines are based on Froude numbers that are fluid and tube geometry specific, so they’re different for every application *Anisothermal tube (bad) regions roughly translate to intermittent and slug flow regimes and isothermal tube (good) regions roughly translates to the dispersed bubble and annular regimes Anisothermal Tube Studies -A multi-discipline approach *Anisothermal tube studies often require both Mechanical Engineering and Process Engineering -Mechanical Engineering *Fired Heater tools (such as FRNC) are required because the geometry and firing conditions drive the heat transfer *Process simulators don’t handle this well (or at all) -Process Engineering *Process Simulators (such as HYSYS) are often required because the process fluid composition in the tubes may be changing (reacting, cracking, etc.) *Fired Heater tools don’t handle this well (or at all) CASE STUDY -A client had tubes ruptures and wanted to fix it * Rupture occurred in the first radiant section tube *Tube monitored 400 oF hotter on top than bottom *Vapor-phase contains caustic H2S in small amounts -Hydrodynamic-Thermal Maps yield insight *For this particular configuration all of the tubes in the convection section and the first few rows of the radiant section are expected to have anisothermal tube walls (temperature gradients) *Both approximates location of tube rupture and confirms anisothermality is feasible at that location OPTION 1 -Reduce tube diameter *Makes the liquid and gas move faster and transitions the flow up and out of the bad anisothermal tube wall region *In this example, the tube diameter went from 8 inches to 6 inches *Same results may also be achieved by increasing flowrates by 89% (if possible) -Appears to be an effective solution assuming the pressure loss is acceptable OPTION 2 -Velocity Steam *Inject velocity steam as in vacuum tower heaters *Gas moves faster and forces annular flow sooner *Pushes out of the anisothermal region to the right *Velocity steam may also have the benefit of diluting any caustic H2S in the vapor-phase -Appears to be an effective solution assuming that adding steam and the resulting pressure loss are both acceptable