Process Furnace Program FRNC5
FRNC5 is a mainframe computer program for rating the performance of a fired heater. The program can handle most types of heaters found in refineries and chemical plants. It is mainly of interest to process engineers in operating companies and Engineering Technology Department (ETD). Uses include:
• Modeling existing heaters to analyze performance
• Predicting the effects of proposed modifications
• Preparing process designs for new heaters
• Evaluating alternatives in design of retrofits or new heaters
The heat transfer and fluid flow correlations used in the program are similar to those presented elsewhere in this manual. In particular, the firebox is “well mixed” as discussed in Section 231. The power of the computer is used to handle complex coil geometry and to obtain converged solutions to the large number of simultaneous equations which describe the heater. Where necessary, each tube of a pass may be broken up into several sections in order to closely model the phase behavior of the process streams.
Program input includes a complete description of the heater and the process and utility streams. The user may specify either duty or firing rate; however, a duty specification results in a longer, trial and error calculation. The program does not have a “design mode”; it will not change any part of the physical description of the heater.
Physical and thermodynamic properties of each process stream are stored in internal arrays as functions of temperature and pressure. A subprogram called PGRID will use standard correlations to create these arrays.
Standard output includes process temperatures and pressures, fluxes, duties, heat transfer coefficients, flue gas temperatures, tube wall and fin tip temperatures, draft at various points, firing rate and thermal efficiency. Optional output includes coordinates for the Talmor Flow Maps (see Figures 200-2 and 200-3) and “hot spot” calculations .
At present (1988), FRNC5 can be accessed through the Unit Operations Menu System on any of the Concord computers, COVMA through COVMD. Instructions for use are in “FRNC5 User’s Guide” , available from the Technical Standards Division, ETD. For assistance, contact the process engineering program specialist in the Process Planning and Simulation Division of ETD. Cost per run varies from $20 for simple cases to $200 for complex heaters with duty specified.