Simulator subroutine form

The FCC simulator program was converted to subroutine form a few years ago and incorporated into a nonlinear programming model representing a complex of process units in the Toledo refinery. It is this subroutine version which has been linked with the LP preprocessor. 

The hydrocracker simulator was also converted to subroutine form for inclusion in the nonlinear programming model of the Toledo process complex. The subroutine was considerably simplified, however, to save computer time and memory. The major differences are (1) the fractionation section is represented by correlations instead of by a multi-stage separation model, (2) high pressure flash calculations use fixed equilibrium K-values instead of re-evaluating them as a function of composition, and (3) the beds in each reactor are treated as one isothermal bed, eliminating the need for heat balance equations. 

The reformer simulator was converted to subroutine form for inclusion in nonlinear programming models of two refinery complexes. To save computer time and memory, the subroutine uses a linearized version of the original kinetic model, with 28 components and 33 reactions. Instead of numerical integration, the linearized model is solved analytically at constant temperature, pressure, and total mols using special subroutines to find the eigenvalues and eigenvectors of the reaction rate constant matrix. 

With this change to the Jacobian generator and a user supplied routine to evaluate the extents of reaction and at the user s option the partial derivatives 3r/3x, 3r/3l, and 3R/3T along with the ECES generated subroutines, this form of process can be successfully modeled. This type of model has been successfully used to simulate proprietary processes developed by our clients. 

The simulation program contains a built-in subprogram corresponding to each block type. To simulate a process, you would use the simulation program to build a flowchart and then enter known block and stream variable values in forms provided by the program. When you subsequently run the simulation, a series of calls to the block subroutines would lead to the solution of the process material and energy balance equations. 

In a real flowchart simulator, the code would be written so that the module could be inserted as a block in the flowchart (see, for example, the flowchart block diagram on p. xxx), and the tear stream variables XC (I) would then be recalculated from assumed values of XA(I) by proceeding around the cycle. To simplify the coding in this problem, however, have the subprogram call a function-generating subroutine of the form... 

The steady state simulations (QUIKBAL and ASPEN) comprise a number of flashes exchangers, splits, compressors, towers and tailor-made fortran subroutines which are structured in sequential modular form. 

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