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Don't lose your balance.

The time slots available for industrial plant modifications can be both very short and very infrequent with schedules prepared months and sometimes years in advance. This necessitates the ability to predict how an operation will behave prior to making any new installation or process adjustment. One of the needs is a mass balance. This review looks at two recently issued process simulation programs that perform mass balances: MASSBAL C for chemical and mineral processes and STEAMBAL C for steam-water processes. Both are Written in C and can operate with as little as 64k of RAM (512k recommended). As they are similar in nature with many functions overlapping, I have chosen to describe MASSBAL C in more detail.

MASSBAL C comes with a file containing the user's manual, and example problem input and output files identified by .IN and .OUT extensions. The user provides input in response to screen prompts. Upon program execution, a menu appears that allows you to select the calculation mode. In the interactive mode, you provide all input interactively at the keyboard. In the batch mode, you create an ASCII input file which is read in by MASSBAL C. The output is an .OUT file in ASCII text format, suitable for use with a wordprocessor. The interactive menu mode is normally used to create new process simulation models. Process functions defining the stream connectivity for the process are selected from a sub-menu, Table 1.

[TABULAR DATA OMITTED]

To create an input file interactively, you must first enter the number of components in your problem. This is followed by entering the component names. At this point you are ready to select any one of the process functions, e.g., FEED, REACT. Each function requires input parameters strictly adhering to a particular format. The required input parameters are different for each process function and are explained in detail in the user's manual. The last function of every input file must be an END statement.

A sample input file was created for a batch problem involving a chemical reactor where hydrogen and nitrogen form ammonia according to the reaction:

[3H.sub.2] + [N.sub.2] - [2NH.sub.3]

Hydrogen was chosen as the limiting reactant and the conversion at 75%. The logic of the sample input file can be seen from the format of the input parameters, Table 2.
Table 2. Input parameters format.

3 number of components

H2,N2,NH3 names of components

FEED FEED

INPUT stream name

4,80,0 component flow rates

REACT REACT

INPUT, PRODUCT input stream, output stream

2,1 number of products, number of products

H2,2,3 reactant name, molecular wt., coefficient

N2,28,1 "

NH3,17,2 product name, molecular wt., coefficient

H2,0.75 Limiting reagent, fractional conversion

END END


As a test run using BATCH MODE, I named the above file AMMONIA.IN and created a file called AMMONIA.OUT to receive output data. The calculation took approximately one second with an IBM PS/2 Model 50z (10 MHz - 80286 system). The MASSBAL output file can be divided into three basic sections:

* A formatted presentation of user input: The names of the Input and output Files are given along with the Number of Components and a tabulated Summary of the component Names. This is followed by a Summary of the Process Function input, Number of Unique Streams Identified, and the Number of Unique Streams Counted.

* Error checking and program execution monitoring messages: if all errors are zero, program execution will continue.

* Stream output: This starts with a Stream Summary presenting all streams in "Stream Number - Stream Name" format in tabulated form. The calculation mode is stated and the Number of Process Functions and Independent Equations are given with the Maximum Coefficient Index. At this point, calculation of the Stream output begins. in tabulated form, the flow rate for each component and the total flow rate are presented. The format win be determined by the OUTPUT function.

STEAMBAL C follows a similar format to that of MASSBAL C. It also requires an input file that may be either run in batch mode or created and run in the interactive mode. it is a process simulator that will calculate stream heat and material balances for steam:water configurations. STEAMBAL C is designed for steady state process operation and assumes all simulations to be adiabatic.

Twenty-six unique process functions are available allowing the simulation of heaters, evaporators, condensers, heat exchangers, separators, distillation towers and more. STEAMBAL C also contains sample problems using each incorporated process function at least once in the set. Typical problems included are:

* Simulation of single, double and triple effect, reverse flow and forward flow evaporator processes;

* Turbine cycle for a nuclear reactor that includes flashing of hot water and expansion of dome steam;

* A direct steam sour water stripper process. MASSBAL C/STEAMBAL C are both simple to use and intended for individuals with engineering or chemistry backgrounds. With the low price, they are also within reach of students. Knowledge of programming is not a requirement. However, it was my experience that one must be familiar with the contents of the manual before beginning to model. It is best to begin with small simplified process or steam models to gain some familiarity before launching into large complicated models. it may be useful to start with a block diagram of the process you plan to simulate. This will act as a check list as you program, and assist in trouble shooting programming errors.

MASSBAL C, Version 2.0: A process simulator to calculate stream material balances for chemical, mineral, and metallurgical process of unlimited size. Menu-driven process function selection. Window-based data input. Process simulation functions include stream adding, stream splitting, component splitting, chemical reactor and staged separation. Price (includes hard copy manual): US$80.

STEAMBAL C: Model steam power plant cycles and evaporator processes. This simulator for steam-water systems is based on Keenan and Keyes Steam Tables. Menu-driven process function selection. Simulator functions include steam adding and splitting, isenthalpic and isentropic pressure change, and heat exchange. Price: US$59.95.

Both operate on IBM compatible system and are available from: PPS Systems, 1012 Marshall, Richland, WA 99352, USA (509) 943-6025.
COPYRIGHT 1992 Chemical Institute of Canada
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Copyright 1992 Gale, Cengage Learning. All rights reserved.

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Title Annotation:computer simulation programs for mass balances
Author:Serwotka, Peter C.
Publication:Canadian Chemical News
Article Type:Evaluation
Date:Apr 1, 1992
Words:1030
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