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Show Refinery Heater Simulation by Hottel Zoning Hethod 3 The flow field is generated by a modified Thring-Newby3 for confined jets based on the current firing rate. The zonal gas volume and refractory surface temperatures are computed by solving the energy balances. The flux profile to the process coil is calculated as well as the heat absorbed. The pressure drop through the burner and the draft available at the burner are computed. The convection bank algorithm computes the energy pickup and pressure drop on a row by row basis for bare, solid circumferential and segmental fins. User may elect Gardner's4 theoretical solution for solid fins or the Weierman 5 empirical method for solid or segmental fins. The program compares the calculated energy absorbed with the user specified duty. If a match is not made the firing rate is updated and the program returns to the flow field generation etc. II. Fired Refinery Heaters All fired refinery heaters heat fluids inside tubular coils (Figure 1). All have a radiant section where the open flame sees the tubes and nearly all have a convection section to improve thermal efficiency. There are two general shapes for the radiant section: cylindrical or rectilinear box. The cylindrical heater (Figure 2) is simpler to describe. The majority are floor fired with usually 3 or more burners equally spaced and with the process fluid in vertical tubes located adjacent to the wall. The convection section is usually mounted above the cylinder. The process fluid flows in one or more parallel passes from the top of the process convection section to the bottom then crosses over to the radiant coil(s). The fluid leaves the top or bottom of the heater depending on whether there are an odd or even number of tubes per process pass. There may also be another convection section above the process section where the flue gases are further cooled to improve the overall effici~ncy of the heater. In the simplest case a stack is mounted above the convection section and the natural draft 6urners are used. In the box heater (Figure 3) the process flow is similar but 3. Thring, H.W. and H.P. Newby: 3rd Sym. on Combustion, Combustion Institute (1953) pp 789-96. 4. Gardner, K. A.: Trans ASHE, 67:Nov. 1945, pp 621-31. 5 . Weierman, C.: Oil and Gas J 73:44, Nov 3, 1975 and 74:36, Sept 6, 1976 |