ChENGINEER SPACE

This post starts to our sec­tion of HOW-TO texts. My obje­tive with this spe­cific post is to intro­duce using some free tools to dif­fer­ent applications.

A clas­sic prob­lem in process engi­neer­ing is the case of a dynamic tank where the out­put flow is pro­por­tional to its level (Fig. 1). This exam­ple is part of EMSO tuto­r­ial so that more details would be to con­sult in the EMSO man­ual.

Fig. 1. Dynamic tank.

In this approach­ing, the prob­lem of dynamic tank involves 3 vari­ables and 2 para­me­ters such below:

Vari­ables:

• Fⁱⁿ: Input flow (m³/h)
• F^out: Out­put flow (m³/h)
• h: Tank level (m)

Para­me­ters:

• A: Tank area (m²)
• k: Valve con­stant (m^2.5/h)

This sys­tem is mod­eled as sim­ple mate­r­ial bal­ance given to:

where the pro­pri­eties are con­sid­ered con­stants so that, the vol­ume that goes into tank minus the vol­ume that goes out tank are equal to accu­mu­lated volume.

The out­put flow is given to valve equation:

where F^out is pro­por­tional to square root of the tank level h and a valve con­stant k.

EMSO mod­el­ing lan­guage is based on con­cepts of object-oriented pro­gram­ing. These kinds of appli­ca­tions get us pos­si­ble to rep­re­sent the prob­lem through a code. As a result, when we are read­ing the code we are also read­ing a descrip­tion of the prob­lem. EMSO mod­el­ing lan­guage presents 3 basic enti­ties: Model, DEVICES, and Flow­Sheet. An flow­sheet of process is rep­re­sented by the entity Flow­Sheet which is con­sti­tuted by a set of com­po­nents calls DEVICES. The DEVICES are equiv­a­lent to the true units of a process. In its turn, the math­e­mat­i­cal descrip­tion of each DEVICES is rep­re­sented by the entity Model.

The Model of a sin­gle tank is given below:

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using "types";
 
Model tank
    PARAMETERS
    k as Real (Brief="Valve constant", Default=4, Unit='m^2.5/h');
    A as area (Brief="Tank area", Default=2);
 
    VARIABLES
in  Fin  as flow_vol(Brief="Input flow");
out Fout as flow_vol(Brief="Output flow");
    h    as length(Brief="Tank level");
 
    EQUATIONS
    "Material balance"
    diff(A*h) = Fin - Fout;
 
    "Valve equation"
    Fout = k*sqrt(h);
end

The line 1 indi­cates that Model used a exter­nal file (“types”) where con­tains all use­ful def­i­n­i­tion of unit of mea­sure­ments such as area (line 6), flow_vol (lines 9–10), length (line 11), etc. In the line 4, the para­me­ters are declared. In the line 8, the vari­ables are declared. The in and out indi­cate that are input and out­put vari­ables respectively.

Since there is a struc­ture that rep­re­sents a sin­gle tank, we can eas­ily model a set of tanks in series (Fig. 2).

Fig. 2. Dynamic tanks in series.

That set of tanks in series can be rep­re­sented by Flow­Sheet below. This struc­ture requires 1 input spec­i­fi­ca­tion (line 32) and 2 ini­tial con­di­tions (line 35). The time of inte­gra­tion, step, and other spec­i­fi­ca­tions to solver are made in the sec­tion OPTIONS (line 39).

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FlowSheet tanks
    VARIABLES
    Fin        as flow_vol;
 
    DEVICES
    tank1      as tank;
    tank2      as tank;
 
    CONNECTIONS
    Fin        to tank1.Fin;
    tank2.Fout to tank2.Fin;
 
    SPECIFY
    Fin = 10*'m^3/h';
 
    INITIAL
    tank1.h = 1*'m';
    tank2.h = 1*'m';
 
    OPTIONS
    TimeStep = 0.1;
    TimeEnd = 2;
    TimeUnit = 'h';
end

The solu­tion of prob­lem can be viewed in the own simulator’s GUI. Plots of vari­ables to an ana­lyze of the sys­tem dynam­ics are showed at Fig. 3–4.

Fig. 3. Tank input and out­put flows.

Fig. 4. Tank levels.

The Reac­tor Lab is a didac­tic soft­ware pro­gram that pro­vides sim­u­la­tions of a vari­ety of chem­i­cal reac­tors. Stu­dents can actively learn about chem­i­cal reac­tions and reac­tors by per­form­ing exper­i­ments and ana­lyz­ing data — quickly, safely, and inex­pen­sively. The pro­gram can be down­loaded free of charge and is avail­able for most com­put­ers and in Eng­lish, Span­ish, and Por­tuguese. The Lab is not a gen­eral pur­pose simulator.

Those who have used the Lab range from high school chem­istry stu­dents to chem­i­cal engi­neer­ing uni­ver­sity and grad­u­ate stu­dents, to pro­fes­sion­als in indus­try. Lit­tle or no train­ing is required for oper­a­tion of the lab because of its con­sis­tent design. In addi­tion, infor­ma­tion about each object is dis­played at the bot­tom of the win­dow as the cur­sor passes over that object.

Project web­site:

• http://reactorlab.net

Screen­shot:

Simulator42 is an open source process sim­u­la­tor project with the goal of pro­vid­ing an afford­able and acces­si­ble chem­i­cal process sim­u­la­tor to the chem­i­cal engi­neer­ing community.

Some inter­est­ing fea­tures of the project:

• It is being writ­ten in the Python language.
• The sim­u­la­tor core has been designed to be inde­pen­dent of both user inter­faces and thermo providers.
• The flow sheet solver can prop­a­gate par­tial infor­ma­tion both back­ward and for­ward through the flow sheet. This fea­ture allows many com­plex prob­lems to be solved with­out iter­a­tive cal­cu­la­tion of recy­cle loops. Con­sis­tency checks are used to avoid unin­tended over spec­i­fi­ca­tion of problems.
• A dis­til­la­tion col­umn employ­ing a Rus­sell inside/out algo­rithm and capa­ble of solv­ing com­plex pump around and side strip­per prob­lems has been implemented.
• Sev­eral user inter­faces are already avail­able or being devel­oped for Sim42, includ­ing a basic com­mand line inter­face, a graph­i­cal inter­face based on wxWin­dows, a web browser based interface/server and a pro­fes­sional com­mer­cial interface.

Simulator42 does not have an owner thermo pack­age how­ever it makes avail­able using the com­mer­cial thermo pack­age of VMG (Vir­tual Mate­ri­als Group, Inc). VMG pack­age is free to use through Redlich-Kwong model.? In 2007 OllinTS project started the devel­op­ing of an open source ther­mo­dy­namic server that could be used by Sim42.

Unfor­tu­nately Sim42 project was aban­doned in 2005/2006. So there is not a sup­port web­site or offi­cial repos­i­tory from Sim42’s code/package (see the old orig­i­nal web­site in Inter­net Archive Way­back Machine). Nev­er­the­less, the last ver­sion (2.0.0.0) for Win­dows can be down­loaded from alter­na­tive mirrors.

Mir­rors:

• http://sourceforge.net/project/showfiles.php?group_id=206963
• http://engenhariaquimica.googlegroups.com/web/sim42full_2v0.zip

Sim42 requires the instal­la­tion of Python 2.2.2+, Numer­i­cal Python 22+ pack­age and a ther­mo­dy­namic server (VMG or OllinTS).