Lecture purpose: studying of modern software products for calculation of CTS

Plan of a lecture:

1. A task of calculation of CTS by means of modern software products.

2. Program covers: off-line and on-line

3. Firms – software developers.

 

It is well known that recently special attention in the industry began to be paid on the engineering analysis and optimization of production processes. However, because of high integration of chemical engineering procedures their analysis and optimization are very difficult and steadily require application of computer facilities. Lack of the corresponding software, along with restriction of cost of works and time, necessary for performance of works, can lead to the analysis and optimization only parts of the existing technology or to consideration of smaller quantity of options of technical solutions. Besides, for more complete study of operating modes of technology and management in scales of the plant in certain cases there is a need of modeling of chemical and technological systems for dynamic conditions.

Earlier, process of modeling of engineering procedures and systems required application of programming languages and therefore it was used only by the specialists who are freely understanding chemical technology, modeling and programming. Rapid development of powerful personal computers and intuitive graphical interfaces of the user allowed to create the specialized program covers which are automating difficult calculations and visually displaying results of calculation. Now in the world there is a small choice of the competitive program covers allowing to calculate material and thermal balances of the technological systems taking into account physical and chemical regularities and intended for modeling of stationary, dynamic and periodic chemical and technological systems. When using these program covers the user doesn't have any more need to well know programming languages as process of creation of model of production consists in use of the screen interface by means of which on the computer screen in a convenient type the technological scheme is constituted. Further the software itself determines the optimum sequence of calculation of CTS, interacts with databases on processes and substances, starts process of the solution of a task and removes results in a user-friendly type.

Until the end of the 90th years such software in Russia wasn't applied that was possibly connected with the fact that along with rather high price of acquisition of the license on its use and rather high costs for training of skilled users it belonged to the category of "high technologies" on which there was a restriction for sale to Russia for political reasons until recently. Now these restrictions don't exist, however unlike countries of Western Europe and America, in Russia of wide use of the similar software didn't occur. Possibly, it is connected with level of training of an engineering personnel as successful application of similar program covers requires availability at the entity of the highly skilled specialists technologists having the corresponding theoretical preparation and a work experience with similar software products.

There are two families of program covers: off-line and on-line. The on-line family of covers is connected with PILES devices in real time. In case of its functioning information from systems, sensors and controllers in real time gathers, further this information is archived and provided to operators, technologists and managers in a form, convenient for them. These data are also transferred to the operational database from where get the software for handling. In the presence of feedback (system of "intellectual" regulation of work as production), on the basis of the acquired information the corresponding modules calculate optimum values of managing parameters, transfer them to external devices and monitor process reaction, consistently optimizing a production operating mode. However for work of on-line of products it is necessary to have the working system of the distributed management (industrial control system: sensors, controllers, computer-controlled equipment) and adequate models of basic processes and system (shop or plant) in general. In a general view, the scheme of work on-line of the software (without feedback) is provided in Fig. 5.1.

Fig. 5.1. Scheme of work on-line of the software.

 

The optimizer of a ratio of H2/N2 in ammonia production delivered on some new productions of ammonia, allowing to support the set H2/N2 ratio in the nitrogen hydrogenic mix given to a synthesis cycle can be an example of on-line of the software.

The off-line family of the covers (which aren't interacting directly with engineering procedure) is used in technical departments of the companies. They allow to design new production, help to eliminate bottlenecks in a technological chain, model separate installations or all plant, allow to model reconstruction of the operating installations for assessment of opportunities of transition from the existing technology to perspective. For the purpose of optimization of production or the analysis of the existing problems and emergencies, these systems help to estimate economic aspects of production, to plan resources, products and the working schedule, etc. The scheme of work off-line of the software is provided in Fig. 5.2.

Fig. 5.2. Scheme of work off-line of the software: (a) – on production; (b) – when designing.

It should be noted that these covers are universal, i.e. can be applied to various productions at the same time. Besides, depending on requirements to calculations, there are program covers as for modeling of CTS in the stationary (set) operating modes (steady state), and in the dynamic (dynamic) modes. The broadest application was found by the software products for modeling of CTS in stationary operating modes realizing an iterative method of calculation. The program covers intended for modeling of dynamic operating modes of production are applied rather seldom and generally to development of systems of management (development of the system of management of transition processes).

Now in the world there is rather small choice of competitive program covers for the specified modeling of CTS in stationary and dynamic operating modes. The basic principles of functioning of covers are single and rather well described in domestic and foreign literature, and also in this abstract of lectures.

Rapid development of computer modeling of CTS began in 1958, and was connected with transfer of calculation of material and thermal balances of CTS to the computer. Calculations were carried out by means of the modeling Flexible Flowsheet program. Further, within the 60-70th years, there was a rapid development of both the concept of computer modeling of CTS, and the software products realizing this concept. Except Flexible Flowsheet programs were abroad created: Cheops, Macsim, Chess, Flowtran, Process, etc. Software products gained the most rapid development with the advent of personal computers. A number of programs for modeling of CTS was created also in the USSR: RSS and ROSS (NIFHI), ASTERS and BASTR (GIAP), NEFTEKHIM (VNIPINEFT), CAMXTC (NIUIF), SYNSYS-78 (MHTI), etc. However, from the beginning of a transition period, the majority of domestic software products stopped the existence therefore now domestic software products are practically not used. Prime vendors of the software for modeling of CTS are the American companies now: AspenTech Inc. (http://www.aspentech.com), Honeywell (http://www.honeywell.com) and Simulation Science Inc. (http://www.simsci.com). Some time ago suppliers of the software was more, however in the world continuously there are processes of enlargement of one companies due to purchase of others that leads to reduction of their quantity.

As it was told above, all software products for calculation of CTS are based on unified theoretical bases of synthesis, the analysis, calculation and optimization. Possibly, these can explain the single functional structure of the specified covers provided on Rice 5.3.

Fig. 5.3. The functional structure of software products for simulation of CTS

 

According to the functional structure of software products, a basis of shell program the functional kernel of system which directly makes the analysis of structure of CTS and calculations of the material and heat balances is, exchanges data with databases, makes an input/output, etc.

Necessary part of the software are the databases on pure substances (viscosity, density, a heat capacity, heat conduction, etc.) and thermodynamic rules of their mixing, and also the database on elementary processes (the specified models of reactors, adders, dividers, columns of rectification, heat exchangers, etc.) completed with firm manufacturer. As all substances and all processes existing in the nature can't be put in databases, software products usually have an opportunity to expand databases on substances and on processes, creating temporal databases of the user. Thus, in case of unified bases and one functional structure shell programs differ from each other only in different set of databases on substances and on processes, quality of the interface and opportunities of a kernel of system. In turn these differences affect the price of a software product and conditions of its acquisition.

As well as the majority of software products for simulation of CTS, Design-II for Windows it is intended for the specified simulation of stationary chemical and petrochemical processes, including rectification, cooling, movement of liquid and gas on pipelines and other processes of oil processing, gas processing, productions of ammonia, methanol and hydrogen. The database on substances contains data on 886 substances and 50 thermodynamic methods of their mixing, tables of properties of saturated and superheated steam, parameters of models of vapor-liquid equilibrium for compounds etc. The database on processes contains 63 models of processes, including their varieties and modifications. Along with opportunities to make simulation and optimization of difficult chemical and technological systems this shell program allows to make at the same time project calculation of parameters of some technology equipment and has the opportunities which are absent at other shell programs:

• the specified modeling of system of pipelines (horizontal, vertical, inclined) for two-phase systems taking into account a heat transfer;

• calculation of parameters of various mixes of the amines allowing to model columned devices (with mixes of amines) taking into account mass transfer kinetics;

• the specified calculation of rectifying columns with determination of their diameter;

• calculation of design data of heat exchangers and separators;

• detailed setup of the modes of calculation of each module by means of keywords and by means of implementation of programs of the user in algorithmic language of FORTRAN;

• handlings of experimental data and calculation of missing properties of substances for the existing properties and structure of substances with simultaneous creation of the file of the database of the user;

• possible extension of databases on substances and processes;

• creations of CTS of the unrestricted sizes by means of "a stitching of sheets";

• access for users to the database on properties of net substances including: the molecular weight, structure, critical properties, pressure of saturated steam, warmth of steam formation, a thermal capacity of ideal gas, viscosity of gas and liquid, heat conductivity of gas and liquid, specific amount, a superficial tension, etc. as to the reference book;

• export of results of calculation to MS Excel.

The screen type in case of the solution of a task on modeling of a cycle of synthesis of ammonia is provided in Fig. 5.4.

The graphical interface of a program cover isn't really convenient, however also the price of its license which for the beginning of 2003 constitutes US$3895 a year in case of the annual conclusion of the agreement, or US$6995 upon purchase of the termless license (a comment is rather low: other suppliers don't sell the termless license). Except one-time payment it is necessary to pay US$1295 a year for support of the software product. Thus, without being "favourite" in the software market for technological calculations, but, having effectively working kernel and expanded opportunities, Design-II for Windows allows to achieve result for smaller money and is purchased by small engineering firms.

Fig. 5.4. The copy of the screen in case of the solution of a task in Design-II for Windows

 

If to exclude influence on the price of the license of a variable marketing component, then the cost of the license is usually determined by convenience of use of a program cover (the graphical interface), amount of databases on substances and processes, and also performance of a kernel. Besides, undoubted impact on the price is exerted by trademark of firm. However, it should be noted that the cost of the license of the most expensive software products different from the cost of the license Design-II for Windows for orders isn't comparable with the cost of the capital expenditure for reconstruction of chemical plant estimated by millions of dollars. For example, the cost of one cubic meter of the catalyst loaded into the reactor by tens of cubic meters usually constitutes US$5000030000-US$. Thus, even in case of standard standard rates, the profit got as a result of reconstruction will be many times more, than the cost of the most expensive tool for calculations. However in case of the solution of the small engineering tasks having rather low profitability, the price of the software will be determining since payback of less expensive, and even less productive software, can be reached quicker, than more productive and more expensive.

It should be noted that when carrying out any calculations correct basic data since the software for modeling of CTS accepts the basic data entered by the user as the truth are necessary. Therefore, when using wrong basic data results of calculations can be far from reality. By use reason in calculations of wrong basic data it can be connected with the fact that production work parameters (temperature, pressure, an expense and structure) are measured by the instrumentations (I) with some error. Depending on flow parameter, the size of an error can reach 5-10%. Besides, KIP can fail, showing plausible, but incorrect values.

From the specified parameters of the flows necessary for calculation of material and thermal balances, temperature and pressure can be measured rather precisely and cheap, and the structure of a flow can be checked in laboratory of the entity on the model laboratory equipment. Thus, the main problems on production arise with measurement of expenses of flows since the most widely used method of measurement of an expense by means of pressure difference on a diaphragm has rather big errors. Therefore, sizes of expenses of the flows received from PILES can't be used for job evaluation of production without additional handling. Use of the devices based on other physical principles and allowing to measure an expense with high precision will lead to rather high costs for their acquisition and servicing, and doesn't exclude mistakes.

For preprocessing of these expenses of the flows received from flowmeters there is a software allowing to make preprocessing of the measured expenses with subsequent their coordination. Along with coordination of expenses of material flows the software determines the sensors measuring an expense with a margin error, exceeding set. Because the technological scheme may contain as continuous processes (the reactor, columns, mixers etc.) and periodic processes (reservoirs, reservoirs, etc.) coordination of data on amount of substance is made per day taking into account structure of movement of material flows and errors of sensors. DATACON can be examples of this software (SimSci Inc.), SIGMAFINE (OSI Software Inc.) and some other. The principle of work of the software is provided in Fig. 5.5.

 

Fig. 5.5. The diagram of functioning of the software in coordination of primary information

 

According to the diagram, data on process are transferred to the operational database "uncoordinated data" through industrial control system and/or entered by a technological staff (in the absence of industrial control system or if industrial control system doesn't envelop all installation), and further are transferred to the software in coordination of data. Matched data register in the operational database "matched data" and can be used as for input in the program of the specified calculation of CTS, and for the analysis of a correctness of indications of PILES or for other purposes.

Example of submission of the technological installation diagram AT-6 in a software product of SIGMAFINE and results of coordination are provided in Fig. 5.6.

 

Fig. 5.6. Results of coordination of data for AT-6 by means of SigmaFine

 

Information on operability of sensors of an expense of flows and levels in reservoirs can be received, comparing the approved and uncoordinated data (in Fig. 5.6. near the sensor – a circle with figure – the approved value of a mass daily issue of a flow is under uncoordinated). Apparently from Fig. 5.6, the approved data differ from uncoordinated in spite of the fact that the KIP is issued by the indications which aren't exceeding them an error. Thus, the real data obtained from installation PILES originally shall be approved, and only after that can be used in the specified calculations.

Any mathematical model of an object or CTS is only its analog within the accepted assumptions and restrictions. When carrying out technological calculations with use of the specialized software for calculation of CTS issued by well-known companies, or carrying out calculations by means of the calculator or own programs, it is necessary to pay special attention on adequacy to the used model. If adequacy of model or its proximity to a real object isn't proved, then results of calculation can't be used to do any technological conclusions and recommendations on their basis. There are several methods of assessment of adequacy of model, however their essence comes down to comparison of settlement and experimental data by means of statistical criteria based on which draw a conclusion about adequacy or inadequacy of model.

As an example we will consider system of parametrical monitoring of the copper producing dry saturated steam which technological scheme is provided in Fig. 5.7.

 

Fig. 5.7. The traffic pattern of material flows of the copper producing dry saturated steam.

 

The essence of work of parametrical system of monitoring is that emission of pollutants in the atmosphere continuously is calculated based on a consumption of combustion gases, certain of material and thermal balances, and concentration of the pollutants calculated on adequate model of a copper. The example of handling of experimental data in case of creation of model is provided in Fig. 5.8.

 

Fig. 5.8. An example of handling of experimental data in case of creation of mathematical model of emissions of nitrogen oxide (NO).

 

Apparently from the drawing, both mathematical models (lines) rather well describe the corresponding sets of experimental values (point). The average error of models constitutes 2,52% and 2,76%. Adequacy of models was checked by criterion of Fischer, which in both cases exceeds tabular value, therefore, both models are adequate, and can be used for calculation of mass emission of nitrogen oxide in the environment.

If adequacy of mathematical model isn't proved, i.e. the mathematical model doesn't correspond to engineering procedure, to use this model inadmissibly. Thus, check of adequacy of model for all planned intervals of change of parameters is the necessary procedure before use of any mathematical model for the purposes of optimization.

 

Test questions

1. What problems of calculation of CTS by means of modern software products are solved.

2. Features of program covers of off-line and on-line.

3. Firms – software developers.