Flowsheeting systems

The User Interface. A wide variety of stand alone steady state simulation programs and flowsheet systems are available to the process engineer. These have been reported in a series of articles by Peterson, Chen and Evans in 1978 (j>) and by Chen and Evans in 1979 (6). Some practical advice on the use of the computer Tn design is reported by Weismantel (7 ). A course in the use of several commercially available systems is given in the AIChE Today Series ( ). A report on the use of networks to share chemical engineering programs among educators was recently issued (9 ). ... 

General Direction of the Field. The characteristics of early flowsheeting systems and their limitations were defined by Evans and Seider in 1976 (11 ). They also attempted to define the criteria for an advanced computing system. 

Use of flowsheeting systems has become widespread. Many have been developed to meet the particular needs of their environments (12, 13, 14) and often serve as a repository of the company s or developer s expertise. 

Physical Properties. A symposium held at Asilo-mar and subsequently published as an ACS Symposium Series volume Phase Equilibria and Fluid Properties in the Chemical Industry (33) addressed the state-of-the-art in this field. Motard and Winter (34)discussed the history and implementation of physical property subsystems in flowsheeting systems and indicated the future needs of such systems. 

A major limitation in many flowsheeting systems is the inability to handle electrolytes. New work in this area is now being reported ( 1, 42) and two commercial systems are available (43, 44TT The ASPEN system ( ) has incorporated a solids handling capability to overcome another common deficiency. 

Attention has also focused on the reliable solution to the three phase (liquid-liquid-vapor) flash problem. That the solution is difficult is attested by the fact that few flowsheeting systems have this capability. Three papers (48, 49, 50) recently appeared which proposed solution algorithms. Generally infinite dilution activity coefficients are used to generate starting compositions. 

Many of the recently suggested architectures for flowsheeting systems have been reviewed by Motard ( 58). Table 1 is a list of selected system architectures and some representative systems. 

Sequential Modular. By far the most experience with flowsheeting systems has been with the sequential modular architecture (59- 3). It is this architecture that is most easily understood by the process engineer. Each module calculates all output streams from input streams subject to module parameters. Generally, the stream variables consist of component flows, temperature (or enthalpy) and pressure as the independent variables. Other dependent variables such as total flow, fraction vapor and total enthalpy (or temperature) are often carried in the stream. 

Equation (8) is of the form of the Newton-Raphson method. The A(X) matrix, however, is not necessarily the Jacobian, J(X). Just how the A(X) is set up depends on the application. Bending and Hutchison (88) developed the method for pipe flow networks. Hutchison and Shewchuk (89) applied the method to multiple distillation towers. Gorczynski and Hutchison (90) detail the method for flowsheeting systems. Quasilin (91) is a flowsheeting system based on this approach. MULTICOL (92) appears to solve interconnected columns by means of this approach as well. 

RIGOROUS MODULES LINEARIZED FLOWSHEET SYSTEM WITH LINEARIZED MODULES ... 

Perris, F. A. Sheppard, A. J., "FLOWPACK II - A Third Generation Flowsheeting System", Paper B-6 to EFCE Conference "Design Congress 176", Aston, England, September 1976. 

The Newton/sparse matrix methods now used by electrical engineers have become the solution method of choice. Hutchison and his students at Cambridge were among the first chemical engineers to publish this approach, in the early 1970s. They used a quasi-linear model rather than a Newton one, but the ideas were really very similar. (It appears that the COPE flowsheeting system of Exxon was Newton based it existed in the mid-1960s but slowly evolved into a sequential modular system. One must assume the Newton method failed to compete.)... 

Presently, several equation-based flowsheeting systems exist perhaps the best known of these is SPEED-UP, which continues to be developed at Imperial College by Sargent and Perkins and their students. Now commercially available, its strongest attraction in industry seems to be as a dynamic simulator. TISFLO at Dutch State Mines is also often mentioned in the literature. As a complete flowsheeting system, no equation-based approach is yet very popular. One might wonder why. 

Kuru, S., Dynamic Simulation with an Equation Based Flowsheeting System. Ph.D. thesis, Carnegie Mellon University, Pittsburgh, 1981. 

We can predict azeotropic behavior as follows from infinite-dilution /T-values. Using a flowsheeting system, we perform a bubble-point calculation for each species in the mixture. Assuming a mixture contains the species A, B, C, and D, we wish to compute the infinite-dilution L-values for three of the species in the remaining one. For example, we perform a flash calculation where A is dominant and B, C, and D are in trace amounts, using something like a feed composition of 0.99999, 0.000003333, 0.000003333, 0.000003334. It does not... 

Stadtherr, M. a., H. S. Chen, and C. M. Hilton, Development of a New Equation-Based Process Flowsheeting System Numerical Studies, Selected Topics on Computer-Aided Process Design and Analysis, R. S. H. Mah and G. V. Reklaitis, eds., AIChE Symposium Series, v. 78, no. 214, p. 12 (1982). 

Integration of complementary products around a central flowsheeting system. 

The integrated system includes both all-purpose flowsheeting system, and specialised packages. Different packages communicate via specific files, but share the same physical property methods and data. Here we mention only the major components. More complete and updated list can be found by consulting the website. 

The special feature of the flowsheeting system proposed by Hyprotech is that steady state and dynamic simulation are available in the graphical environment. Other products have been developed as stand-alone applications for engineering or operation purposes. The system is designed for complete customisation. The main components are ... 

We present hereafter a description of generic capabilities in commercial flowsheeting systems. More information may be found by consulting the user manual of different simulators. User programming is a powerful method to handle the limitations concerning the simulation of some industrial equipment items. 

The algorithmic treatment depends on the architecture of the flowsheeting system. In Equation-Oriented mode, the approach consists of solving all the equations describing the problem simultaneously. In Sequential-Modular approach the mathematical solution must take into account the convergence of units and tear streams, as well as of all design specifications. Supplementary equations must be added, so that the general formulation of the optimisation problem (3.10) becomes ... 

A vertical assembly of elements, in conjunction with a high rate of liquid circulation, can represent plug flow with dispersion of the upward flowing gas and the high level of liquid backraixing typical of a bubble column. Plate columns and stirred vessels can be likewise represented by suitable assemblies as shown in Fig. 6. If a generalised sub-routine for the gas-liquid element were available, assemblies like those in Fig. 6 can be readily solved with a standard flowsheeting system. 

This paper investigates an approach to process optimisation that allows construction of flowsheets in modular systems that can then be optimised using interval global optimisation methods based on branch and bound methods. The modular flowsheets are constructed with generic unit modules that can provide the interval bounds, linear bounds and derivative bounds using extended arithmetic types. Modular flowsheets are convenient and modular flowsheeting systems very popular. 

Flowsheet optimisation can provide significantly better designs at modest cost during the early stages of design. Modular flowsheeting systems dominate the market and are used by much of the design community. 

Table 13.3 provides the control performance qualitatively for these five systems. As expected, the MeAc system (type I flowsheet) exhibits relatively poor control performance as can be seen early from qualitative argument or quantitative nonlinearity measures. The closed-loop behaviors of the EtAc and IPAc (type II flowsheet) systems are not quite as nonlinear as the steady-state measures predict. Relatively fast and symmetrical dynamics... 

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