CN101986320B - Modeling method for heterogeneous azeotropic rectification solvent dehydrating tower of industrial purified terephthalic acid (PTA) device - Google Patents

Abstract

The invention relates to a modeling method for a heterogeneous azeotropic rectification solvent dehydrating tower of an industrial purified terephthalic acid (PTA) device. In the method, the vapor-liquid balance experimental data of an acetic acid, n-propyl acetate, water, p-xylene and methyl acetate quinary mixture system are associated and fitted with the binary interaction parameters of the quinary mixture system according to a thermodynamic property model; and according to the process data of the solvent dehydrating tower under the actual device design condition, a heterogeneous azeotropic rectification solvent dehydrating tower model of the industrial PTA device under the design condition is established, the accuracies of the thermodynamic model and parameters thereof of the quinary mixture system in a laboratory and a rectification tower mathematical steady model are verified, key parameters representing the separating property of the solvent dehydrating tower under the actual condition are acquired, the model is corrected and a process mechanism steady model capable of accurately describing the operating characteristics of the solvent dehydrating tower under the actual condition is established.

Description

A kind of modeling method of industrial pure terephthalic acid's device heterogeneous azeotropic rectification solvent dehydration tower

Technical field

The present invention relates to a kind of modeling method of heterogeneous azeotropic rectification solvent dehydration tower, is the modeling method of the heterogeneous azeotropic rectification solvent dehydration tower of entrainer with the n-propyl acetate in especially industrial pure terephthalic acid's device.

Background technology

Pure terephthalic acid's (Purified Terephthalic Acid is called for short PTA) is a kind of important chemical material, is widely used in polyester and other Chemical Manufacture.The production of PTA generally is be raw material with P-xylene (PX) earlier, and acetic acid (HAC) be that solvent catalytic oxidation under certain temperature and pressure generates crude terephthalic acid (TA), and then to make with extra care be highly purified pure terephthalic acid.When terephthalic acid (TPA) is produced in the PX oxidation, make solvent with acetic acid, water (H is arranged in the course of reaction ₂O) generate, therefore can the acetous WS.Simultaneously, because oxidation reaction is incomplete and the generation of subsidiary reaction, also can contain the by-product methyl acetate (MA) of unreacted precursor PX and reaction in the acetate solvate.PX and acetic acid can form homogeneous azeotrope, form two liquid phase azeotropic mixtures with water.Little P X is constantly accumulation in tower, when its concentration is increased to a certain degree, will certainly weaken the performance of tower, influences the effect of azeotropic separation.MA can form the azeotropic mixture be positioned at the monophase field with water, makes that water cut reduces in the overhead water azeotropic mixture, thereby reduces the liquid water content that the condensation of azeotropy rectification column overhead generates, and has increased the diameter of energy consumption and tower.

In order to reduce consumption, the general solvent dehydration tower that adopts separates and the useful component acetic acid, PX and the MA that recycle in this low-concentration acetic acid solution and the vapor stream in the PTA device.At present; Widespread use be azeotropic distillation solvent dehydration tower; Introduce entrainer and help improving the VLE relation of treating between separation component, entrainer can form new minimum azeotropic mixture with one or two component in the material liquid, is steamed by cat head; Make rectifying separation become the separation of " azeotropic mixture one pure component " system, solution separating is become realize easily because of it has bigger relative volatility.Compare with the conventional distillation method, azeotropic distillation has more efficiently separating effect and more effective energy utilization efficiency and operation cost still less.The azeotropic distillation solvent dehydration tower process of domestic certain PTA device (is seen accompanying drawing 1) as follows: the automatic oxidation reaction device extracts the washings WDO of water and high pressure attraction tower out, from the cat head gas phase of PX recovery tower, from the gas phase of stripping tower, from the flash distillation gas phase of second crystallizer and enter into the solvent dehydration tower from the condensation product of the first crystallizer vapor-liquid separation tank and separate with entrainer NPA; LP steam provides thermal source; Make cat head almost not detect acetic acid (ppm level), the massfraction of acetic acid is designed to about 95% at the bottom of the tower.Between first and second sections fillers of dehydration tower, extract one liquid out; Send into the PX recovery tower and remove the PX that accumulates in the azeotropic dehydration tower; The steam that comes out in top condensation in the dehydration tower evaporator overhead condenser, temperature be by by-pass governing, and lime set is gentle/and vapour gets into dehydration tower condenser decanter; Water separates with organic phase (entrainer NPA); Entrainer NPA gets into the entrainer basin and sends the solvent dehydration tower back to by reflux pump and reflux, and gas phase and uncondensated steam are sent into entrainer recovery tower upper rectifying section, the water stripping section bottom the entrainer recovery tower of making a gift to someone.

The simulation of solvent dehydration tower heterogeneous azeotropic rectification process, particularly the simulation to actual production process is the basis of all optimal control processes.For the heterogeneous azeotropic rectification solvent dehydration process that with the n-propyl acetate is entrainer; Because acetic acid-water in this solvent dehydration tower-n-propyl acetate-P-xylene-complicated physical property characteristic of five yuan of mixture series of methyl acetate; The multicomponent system that contains 9 boiling point components in this mixture series; Wherein have four groups of azeotropic mixtures; Two groups is heterogeneous azeotrope, and the association of acetic acid molecule that more main is makes the VLE of whole system present serious imperfection, and the mass transport process between the essence of the distillation process weight component that to be vapour-liquid two alternate realizes through VLE; Therefore will accurately simulate this azeotropic distillation process, the solvent dehydration tower process mechanism model that actual condition can be accurately described in foundation is very difficult.

Summary of the invention

The objective of the invention is: the modeling method that a kind of industrial pure terephthalic acid's device heterogeneous azeotropic rectification solvent dehydration tower is provided; The method adopts activity coefficient method UNIQUAC model correction liquid phase imperfection, contains the theoretical state Equation Method HOC model correction vapour phase imperfection of chemical association.Utilize experimental data and data in literature; Obtain the binary interaction parameter of UNIQUAC model through the maximum-likelihood method regression fit; Accurately analyze the VLE characteristic of describing mixture series in the solvent dehydration tower; Homeostasis level model M ESH equation based on rectification column; According to design conditions and actual production data, the solvent dehydration tower process mechanism model of actual condition can be accurately described in foundation, for the further optimization and the control of industrial pure terephthalic acid's device heterogeneous azeotropic rectification solvent dehydration tower provides solid foundation and foundation.

The present invention program is following:

A kind of modeling method of industrial pure terephthalic acid's device heterogeneous azeotropic rectification solvent dehydration tower may further comprise the steps:

1. according to the thermodynamic characteristics of n-propyl acetate, confirm correctly to describe the thermodynamical model of this mixture series VLE phase behavior as contained mixture series in the solvent dehydration tower of entrainer.Thermodynamics method is selected for use the UNIQUAC model of forming based on the part in the activity coefficient method to revise the liquid phase imperfection and by the deviation that the acetic acid associating effect causes, is selected for use the second virial coefficient HOC model that contains chemical theory in the state Equation Method that the associating effect and the imperfection behavior of vapour phase are revised;

2. through experiment and the consulting of authoritative document, obtain binary vapour-liquid or the liquid-liquid equilibrium data and the part ternary phase equilibrium criterion of this solvent dehydration tower mixture series;

3. the binary experimental data of utilizing step to be obtained in 2. adopts maximum-likelihood method that the binary interaction parameter in the UNIQUAC model is carried out regression fit; The binary interaction parameter that utilization obtains goes to predict the multicomponent system behavior that balances each other, set up can these five yuan of mixture series rerum natura characteristics of accurate description thermodynamical model and parameter;

4. according to the equilibrium stage steady-state model MESH equation of rectification column; 1. the thermodynamic argument model that is obtained in conjunction with abovementioned steps, step be the binary interaction parameter of match gained 3.; Dehydration tower condenser and decanter are selected the flash evaporator model for use, set up the mathematics steady-state model of heterogeneous azeotropic rectification solvent dehydration tower;

5. adopt industrial pure terephthalic acid's device heterogeneous azeotropic rectification solvent dehydration design conditions data, confirm this steady-state model each item input parameter, design code and variable: said input parameter comprises temperature, pressure, flow, the composition of each incoming flow thigh, the number of plates; On-stream pressure, tower pressure drop, charging and discharging position; The phase-splitting key component; Plate efficiency, flow is extracted at the middle part out, and according to the simulation requirement; Form, the setting of design code such as flow, satisfy its design code requirement through the correlated variables adjustment;

6. according to the actual industrial device data and each the component analysis data that obtain; Abovementioned steps is revised by each item input parameter, design code and the variable of the solvent dehydration tower design conditions steady-state model of proving correctness in 5.; Model is carried out correction adjustment, obtain correctly to describe the process mechanism steady-state model of industrial pure terephthalic acid's device heterogeneous azeotropic rectification solvent dehydration actual condition; Said data comprise that extracting the washings WDO of water and high pressure attraction tower, the cat head gas phase from the PX recovery tower, the gas phase from stripping tower, the flash distillation gas phase from second crystallizer, the condensation product from the first crystallizer vapor-liquid separation tank, the discharging of pushing up backflow and middle part backflow, cat head and tower still and middle part out from oxidation reactor extracts material temperature, pressure, flow out; Component is got the mean value under the steady working condition in the image data to the analysis and the pre-service of data.

Said step 1. in, except the acetic acid in the system, water, n-propyl acetate, also have the by-product methyl acetate of unreacted precursor P-xylene in the acetate solvate and reaction in the said mixture series;

The said step 2. system of middle required balance data comprises: n-propyl acetate+acetic acid, acetic acid+P-xylene, n-propyl acetate+methyl acetate; Methyl acetate+P-xylene, n-propyl acetate+P-xylene, methyl acetate+acetic acid; Acetic acid+water; Methyl acetate+water, water+n-propyl acetate, water+P-xylene.

Said step selects for use in 2. round-robin method in the Ai Lisi equilibrium still, to carry out the isobaric VLE experiment of binary, has measured acetic acid/P-xylene that data in literature lacks, n-propyl acetate/methyl acetate, methyl acetate/P-xylene, the n-propyl acetate/P-xylene vapor-liquid equilibrium data under normal pressure of totally four groups of binary systems respectively.

τ in the 3. middle UNIQUAC model of said step _IjAdopt τ _Ij=exp (A _Ij+ B _Ij/ T) expression-form carries out regression fit to the binary interaction parameter.

The complicated heterogeneous five yuan mixture series of said step in 3. contain the multicomponent system of 9 boiling point components, four groups of azeotropic mixtures, and wherein two groups is heterogeneous.

The actual condition image data of said step in 6. comprises each charging and goes out temperature, pressure, the flow of materials flow thigh that the component application of sample is analyzed data and comprised each charging and go out materials flow thigh composition.

The invention has the beneficial effects as follows: the influence of the by-product methyl acetate of unreacted precursor P-xylene and reaction in the consideration acetate solvate, set up the thermodynamical model that can correctly describe contained acetic acid-water-n-propyl acetate-P-xylene in the solvent dehydration tower-five yuan of mixture series VLEs of methyl acetate characteristic, and utilized experiment and data in literature; Obtain the binary interaction parameter of UNIQUAC model through the maximum-likelihood method regression fit; Polynary stream-liquid phase balance is predicted, based on the homeostasis level model M ESH equation of rectification column, according to design conditions and actual production data; Set up the solvent dehydration tower process mechanism model that accurately to describe actual condition; Be familiar with its rule and mechanism, thereby regulate, with foundation as actual transformation through model parameter; Provide each parameter that reaches production capacity and optimization aim preliminary scope; Avoided reducing to optimize cost, improved production efficiency through actual blindness operation for system.

Description of drawings

Fig. 1 is industrial pure terephthalic acid's device heterogeneous azeotropic rectification solvent dehydration tower process process flow diagram;

Fig. 2 is the rectification column structure diagram;

Fig. 3 is a rectification column tower plate structure synoptic diagram;

Embodiment

Below in conjunction with accompanying drawing and embodiment the present invention is further specified.

Accompanying drawing 1 is domestic certain industrial pure terephthalic acid's device heterogeneous azeotropic rectification solvent dehydration tower process process flow diagram.This azeotropic distillation solvent dehydration tower is the syllogic packed tower; Adopt n-propyl acetate (NPA) as entrainer; Wherein charging comprises from the WDO that gets between first and second section filler (extracting the washings of water and high pressure attraction tower from oxidation reactor out) with from the cat head gas phase of PX recovery tower, from the gas phase from stripping tower that gets between second and third section filler, from the flash distillation gas phase of second crystallizer and from the condensation product of the first crystallizer vapor-liquid separation tank.Between first and second sections fillers of dehydration tower, extract one liquid out; Send into the PX recovery tower and remove the PX that accumulates in the azeotropic dehydration tower; The steam that comes out in top condensation in the dehydration tower evaporator overhead condenser, temperature be by by-pass governing, and lime set is gentle/and vapour gets into dehydration tower condenser decanter; Water separates with organic phase (entrainer NPA); Entrainer NPA get into the entrainer basin by reflux pump send back to the solvent dehydration tower do to reflux (top that gets between the one or two section filler reflux and the two or three section filler between the middle part that gets into reflux), gas phase and uncondensated steam are sent into entrainer recovery tower upper rectifying section, the water stripping section bottom the entrainer recovery tower of making a gift to someone.This solvent dehydration tower provides thermal source by LP steam, makes the cat head acetic acid content less than 0.1%, and the massfraction of acetic acid is designed to about 95% at the bottom of the tower.

Stream-liquid phase balance behavior and the introduction of thermodynamics method model involved among the present invention are following:

When balancing each other; The middle mutually corresponding fugacity of forming of vapour-liquid two equates that promptly

specifically can be expressed as:

$y_i{{\mathrm{\φ}}_i}^{V}p=x_i{\mathrm{\γ}}_i{\mathrm{\φ}}_i^s{p}_i^s\exp {\∫}_{p_i^s}^p\frac{{V_i}^L}{\mathrm{RT}}\mathrm{dp}---\left(1\right)$

In the formula: x _iAnd y _iBe respectively component i mole fraction in the liquid and vapor capacity;

For component i in the vapour mixture at the fugacity coefficient of system temperature T and pressure p; p _i ^sBe the saturated vapor pressure of pure component i when the system temperature T; P is the stagnation pressure (1.013bar) of system;

Be the Poynting factor, the correction of liquid phase fugacity when it provides steam to be pressed onto system pressure; Under mesolow power, the Poynting factor generally is taken as 1;

Be pure component i its saturated vapor pressure under system temperature and this temperature

Under fugacity coefficient; γ _iActivity coefficient for component i.(table 1 parameter sees for details five kinds of material correlation parameters that relate among the present invention, J.M.Prausnitz, T.F.Anderson at table 1; C.A.Grens; C.A.Eckert, R.Hsieh, and J.P.O ' Connell; Computer Calculation for Multicomponent Vapor-Liquid and Liquid-Liquid Equilibria.New Jersey:Prentice-Hall, 1980; And John M.Prausnitz, John P.O ' Connell, The Properties of Gases and Liquids; Fifth Edition; The Mcgraw-Hill Companies, Inc, 2001) in list; Also comprise other physicochemical property of five kinds of pure materials in the table 1, like normal pressure boiling point, emergent pressure, critical temperature etc.

The basic physical properties and the correlation parameter of five kinds of pure materials of table 1

A. expression component 1 in (1)-(2) interacts with component 2, and other by that analogy.

The saturated vapor pressure of pure component

is by the Antoine Equation for Calculating:

$\ln p_{\mathrm{vp}}\left(\mathrm{bar}\right)=A-\frac{B}{T\left(K\right)+C}---\left(2\right)$

In the present invention; We adopt activity coefficient method UNIQUAC model (to see for details: Abrams D S; Prausnitz J M.Statistical thermodynamics of liquid mixtures:A new expression for the excess gibbs energy of partly or completely miscible systems [J] .AIChE J.1975; 21:116.) revise the liquid phase imperfection; Select for use the state Equation Method HOC model that contains the chemical association theory (to see for details: Hayden J G; O ' Connell J P.A generalized method for predicting second virial coefficients [J] .Ind Eng Chem, Process Des Dev.1974,14 (3): 209-216.) the imperfection behavior of vapour phase is revised.

Liquid phase imperfection (activity coefficient γ _i) correction---activity coefficient method UNIQUAC model can be expressed as:

$\frac{g^E}{\mathrm{RT}}=\underset{i}{\overset{N}{\mathrm{\Σ}}}{x}_i\ln \frac{{\mathrm{\Φ}}_i}{x_i}+\frac{z}{2}\underset{i}{\overset{N}{\mathrm{\Σ}}}{q}_i{x}_i\ln \frac{{\mathrm{\θ}}_i}{{\mathrm{\Φ}}_i}-\underset{i}{\overset{N}{\mathrm{\Σ}}}{q}_i{x}_i\ln \left(\underset{j}{\overset{N}{\mathrm{\Σ}}}{\mathrm{\θ}}_j{\mathrm{\τ}}_{\mathrm{ji}}\right)---\left(3\right)$

$\ln {\mathrm{\γ}}_i=\ln \frac{{\mathrm{\Φ}}_i}{x_i}+\frac{z}{2}{q}_i\ln \frac{{\mathrm{\θ}}_i}{{\mathrm{\Φ}}_{\mathrm{ii}}}-{q_i}^{\′}\ln t_i^{\′}-{q_i}^{\′}\underset{j}{\overset{N}{\mathrm{\Σ}}}\frac{{\mathrm{\θ}}_j^{\′}{\mathrm{\τ}}_{\mathrm{ji}}}{t_j^{\′}}+l_i+{q_i}^{\′}-\frac{{\mathrm{\Φ}}_i}{x_i}\underset{j}{\overset{N}{\mathrm{\Σ}}}{x}_j{l}_j---\left(4\right)$

Various calculating below each parameter adopts in the formula:

${\mathrm{\θ}}_i=\frac{q_i{x}_i}{\underset{k}{\overset{N}{\mathrm{\Σ}}}{q}_k{x}_k}---\left(5\right)$

${\mathrm{\θ}}_i^{\′}=\frac{q_i^{\′}{x}_i}{\underset{k}{\overset{N}{\mathrm{\Σ}}}{q_k}^{\′}{x}_k}---\left(6\right)$

${\mathrm{\Φ}}_i=\frac{r_i{x}_i}{\underset{k}{\overset{N}{\mathrm{\Σ}}}{r}_k{x}_k}---\left(7\right)$

$l_i=\frac{z}{2}(r_i-q_i)+1-r_i---\left(8\right)$

In the above formula, x _iBe the mole fraction of component i, Φ _iBe volume fraction, θ _iBe area fraction, r _iAnd q _iRepresent i molecule volume and area parameters respectively, z is a coordination number.

$t_i^{\′}=\underset{k}{\mathrm{\Σ}}{\mathrm{\θ}}_k^{\′}{\mathrm{\τ}}_{\mathrm{ki}}---\left(9\right)$

In the present invention, τ _Ij=exp (A _Ij+ B _Ij/ T+C _IjLnT+D _IjT), for for simplicity, under the situation that does not influence correlation accuracy, except that specifying, adopt following expression-form among the present invention

τ _ij＝exp(A _ij+B _ij/T) (10)

All the other parameters all are made as zero.

Two adjustable binary parameter τ in the following formula _IjAnd τ _IjAdopt maximum-likelihood method (Maximum likelihood method) to decide objective function, draw according to ten groups of liquid Equilibrium for Binary data regression fits of five yuan of mixture series from experiment and document.

Coordination number z does in the calculating

z＝10 (11)

Correction---the viral type state Equation Method HOC equation of vapour phase imperfection (fugacity coefficient

):

Fluid compressibility factor in the HOC equation is expressed as

$z\≡\frac{\mathrm{pV}}{\mathrm{RT}}=1+\frac{\mathrm{Bp}}{\mathrm{RT}}---\left(12\right)$

B is a second virial coefficient, is expressed as

$B=\underset{i}{\overset{N}{\mathrm{\Σ}}}\underset{j}{\overset{N}{\mathrm{\Σ}}}{y}_i{y}_j{B}_{\mathrm{ij}}\left(T\right)---\left(13\right)$

Thereby fugacity coefficient can be provided by following formula

$\ln {\mathrm{\φ}}_i=(2\underset{j}{\overset{N}{\mathrm{\Σ}}}{y}_i{B}_{\mathrm{ij}}-B)\frac{P}{\mathrm{RT}}---\left(14\right)$

Following formula only is applicable to the potpourri that does not contain carboxylic acid, and wherein second virial coefficient adopts the HOC method to obtain.

According to the generalized method of HOC, the pure component and the second virial coefficient B that intersects _IjBy two effects and constitute:

B _ij＝B _ij ^F+B _ij ^D (15)

Wherein:

B _ijF＝(B _nonpolar ^F) _ij+(B _polar ^F) _ij (16)

B _ij ^D＝(B _metastable) _ij+(B _bound) _ij+(B _chemical) _ij (17)

Subscript F representes " freedom " molecule (weak physical force) contribution in the formula, and D representes to receive the molecule contribution of " constraint " or " two form " effect.

Various influences to second virial coefficient; Can be respectively calculated by pure material correction coefficient relevant with temperature and temperature independent parameter, the five kinds of pure material correlation parameters and the required two non-interaction action parameters of HOC equation that relate among the present invention are listed in table 1.

Because five yuan of mixture series thermodynamic behaviours among the present invention are complicated; The phase behavior research of these five yuan of mixture series does not also appear in the document; We determine to go out through the liquid Equilibrium for Binary data association binary interaction parameter of thermodynamical model, utilize this binary interaction parameter to predict the behavior that balances each other of multicomponent mixture system again.Consider that five yuan of mixture series equilibrium measuring workloads in this research are huge, we only data in literature are lacked and partial data system of the remote past has been carried out measuring, and all the other systems all adopt data in literature.The actual condition that is because of the industrial acetic acid dehydration tower approaches normal pressure, so the data that we select for use all are the isobaric equilibrium under normal pressure or the nearly normal pressure.The reference literature data, we select for use round-robin method to measure acetic acid/P-xylene, n-propyl acetate/methyl acetate, methyl acetate/P-xylene, the n-propyl acetate/P-xylene vapor-liquid equilibrium data under normal pressure of totally four groups of binary systems respectively.

Round-robin method is selected in this research for use, utilizes the Ellis equilibrium still to carry out the experiment of normal pressure VLE.Temperature is by measuring through the accurate mercury thermometer of demarcating of 1/100K, and to its reveal neck proofread and correct the true equilibrium temperature, pressure is read by mercury manometr, and it is passed through instrument error correction, temperature correction and gravity correction successively.

The experiment material has: the w that Chemical Reagent Co., Ltd., Sinopharm Group provides >=99.5% (massfraction; Down together) acetic acid and w >=98.0% methyl acetate; The Shanghai phenanthrene reaches the n-propyl acetate of w >=98.0% that industry and trade company limited provides and the P-xylene of w >=99.7%, and all materials are AR, and purity is confirmed through the gas chromatograph analysis; Inclusion-free peak, water are secondary water.

The experimental implementation step is following:

The Ellis equilibrium still is simple in structure, and is easy to operate, only needs the sample solution of a series of variable concentrations of configuration in advance, adds in the still respectively to get final product.When heating,, need be incubated processing to the distiller outside owing to there is the vapour phase condensed fluid to produce.The concrete operations step is following:

A) binary or the about 270mL of three-part system mixed solution of configuration definite composition slowly add in the Ellis equilibrium still, make liquid level a little less than the coiled pipe spout, and the coiled pipe major part is immersed in the solution.

B) open condensate water, open primary heater, regulate suitable voltage solution is heated, and improve the voltage of primary heater gradually along with the rising of solution temperature.

C) when liquid comes to life in the still,, need regulate the heating power of liquid phase and vapour phase insulation jacket in order to prevent the too early condensation of steam.

D) control heating boil-off rate, the speed that condensed fluid is produced is about 60～100 of per minutes.The liquid that gets off when condensation overflows and refluxes when getting into the liquid phase still from cold liquid pool, and beginning is intermittently observed and the temperature of record boiling point and steam.When the temperature of boiling point and steam reaches when stablizing, can think that vapour, liquid two have reached balance mutually, note the reading of boiling temperature, auxiliary temperature evaluation, vapor (steam) temperature, mercury manometr and the reading of appended thermometer respectively.

E) in condensate tank(trap) and liquid phase still, respectively liquid and vapor capacity is taken a sample rapidly behind the record data, analyze with gas chromatography behind the mark solvent in adding.So repeat, can obtain the complete Vapor--Liquid Equilibrium Data of a cover.

Obtain four groups of binary vapour-liquid balance test data, just can carry out regression fit model binary interaction parameter in conjunction with other six groups of binary systems data in literature that balances each other.

Table 2 is the binary interaction parameter result according to experiment and the UNIQUAC equation that comes out of data in literature match.

Table 2UNIQUAC equation binary system interaction parameter fitting result

Table 3 is the boiling point component table of heterogeneous five yuan of mixture series complicated in this solvent dehydration tower of trying to achieve according to gained binary interaction parameter, contains the multicomponent system of 9 boiling point components, four groups of azeotropic mixtures, and wherein two groups is heterogeneous.

The boiling point component of five yuan of mixture series of table 3

Thermodynamical equilibrium equation is the basis of distillation process, and the mathematical model of rectification column distillation process can be correctly described in cooperation just can calculate simulation to distillation process.

Adopt the equilibrium stage steady-state model of rectification column among the present invention.Each phase logistics that the equilibrium stage model hypothesis leaves column plate is in equilibrium state, for any one multistage equilibrium separation, always can describe with following each fundamental equation: (1) mass balance equation (M); (2) equation (E) that balances each other; (3) concentration adds and equation (S); (4) (H) thermal balance equation.Therefore, the equilibrium stage model is commonly called the MESH equation.The MESH equation of each column plate and condenser, reboiler equation and corresponding rerum natura equation etc. are united find the solution vapour phase mole fraction, liquid phase mole fraction, column plate temperature and the vapour-liquid that can obtain on every block of column plate separating of variable such as flow rate mutually.

For convenience's sake, shown in accompanying drawing 2, also regard condenser and reboiler as the one-level column plate respectively here.Still establish total n the equilibrium stage of full tower, the level preface from top to bottom, overhead condenser is the first order, arbitrary equilibrium stage level preface of centre is j, tower bottom reboiler is the n level.Adopt the general tower plate structure of accompanying drawing 3, material and heat balance figure in the representation model tower on the j piece column plate.

Suppose:

1) vapour-liquid two of leaving each grade has all reached the state of balancing each other mutually;

2) liquid on each column plate and the gas between plate all mix fully, can handle by lumped parameter model;

3) each plate efficiency can be represented with Murphree liquid phase efficient;

4) ignore the thermal loss of tower (comprising reboiler and condenser) and the thermal capacitance of column plate itself;

5) there is not chemical reaction in the tower;

Then can be listed as and write out the equilibrium stage steady-state model:

1. mass balance equation

To the 1st grade, j level (2≤j≤n-1) and n level do respectively component i (mass balance of 1≤i≤C) can obtain:

V ₂y _i，2-(L ₁+SL ₁)x _i，1-SV ₁y _i，j＝0 (18)

L _j-1x _i，j-1+V _j+1y _i，j+1-(L _j+SL _j)x _i，j-(V _j+SV _j)y _i，j+F _jz _i，j＝0，j＝2，…，n-1 (19)

L _n-1x _i，n-1-SL _nx _i，n-V _ny _i，n＝0 (20)

The individual independently mass balance equation of total n * C.

2. heat balance equation

(2≤j≤n-1) make heat balance respectively with the n level can obtain to the 1st grade, j level

V ₂H ₂-(L ₁+SL ₁)h ₁-SV ₁H ₁+Q ₁＝0 (21)

L _j-1h _j-1+V _j+1H _j+1-(L _j+SL _j)h _j-(V _j+SV _j)H _j+F _jh _F，j+Q _j＝0，j＝2，…，n-1 (22)

L _n-1h _n-1-SL _nh _n-V _nH _n+Q _n＝0 (23)

The individual independently heat balance equation of total n

3. equation and plate efficiency formula balance each other

The vapour, the liquid two that leave arbitrary equilibrium stage are balance mutually, and it forms the satisfied equation that balances each other.((equation that balances each other on 1≤j≤n) does component i in the j level for 1≤i≤C)

$y_{i,j}=K_{i,j}{x}_{i,j}^{*}=K_{i,j}\frac{x_{i,j}-(1-E_{\mathrm{Mi},j})x_{i,j-1}}{{\mathrm{EM}}_{i,j}}---\left(24\right)$

E wherein _MBe plate efficiency, adopt Murphree liquid phase efficient:

$E_{\mathrm{Mi},j}=\frac{x_{i,j}-x_{i,j-1}}{x_{i,j}^{*}-x_{i,j-1}}---\left(25\right)$

Because each equilibrium stage has C the equation that balances each other, full tower has n equilibrium stage, so total n * C the equation that balances each other.

4. concentration adds and equation

For arbitrary equilibrium stage, vapour, liquid phase are formed should satisfy the normalization equation, promptly

$\underset{i=1}{\overset{C}{\mathrm{\Σ}}}{x}_{i,j}=1,\underset{i=1}{\overset{C}{\mathrm{\Σ}}}{y}_{i,j}=1,j=\mathrm{1,2},...,n---\left(26\right)$

Full tower has n equilibrium stage, so total 2n concentration adds and equation.

Tower plate structure is as shown in Figure 3, wherein, and F _jRepresent the charging on the j piece column plate, L _jRepresent the liquid phase flow rate on the j piece column plate, V _jRepresent the vapour phase flow rate on the j piece column plate, SL _jRepresent the liquid phase discharging on the j piece column plate, SV _jRepresent the vapour phase discharging on the j piece column plate, y _IjThe gas phase mole fraction of representing component i on the j piece column plate, x _IjThe liquid phase mole fraction of representing component i on the j piece column plate, z _IjThe gas phase mole fraction of representing component i in the charging on the j piece column plate, Q _jRepresent the heat output on the j piece column plate, h _jThe evaporation enthalpy of representing j piece plate liquid phase, H _jThe vapour phase enthalpy of representing j piece plate vapour phase, K _IjThe VLE constant of representing component i on the j piece column plate, E _MijThe plate efficiency of representing component i on the j piece column plate.

Above-mentioned mass balance equation, heat balance equation, balance each other equation and concentration add the steady-state model that the system of equations of forming with equation has just constituted rectifier unit, and this system of equations has the individual independent equation of n (2C+3).Cooperate to go up the relevant thermodynamics correlation that balances each other again, just can find the solution this model.

Among the present invention, for industrial pure terephthalic acid's device heterogeneous azeotropic rectification solvent dehydration tower, the plate column of helping the conversion of the packed tower in the commercial plant the total individual equilibrium stage of N (N >=minimum number of theoretical plate) of tower calculates; 5 components; Substitution n (2C+3) obtains 793 independent equations altogether, combines foregoing UNIQUAC-HOC equation again, confirms the input parameter of model; Select Newton method for use, just can find the solution model.

Shown in accompanying drawing 1 industrial solvent dehydration tower process chart.The solvent dehydration tower has 5 strands of incoming flow thighs: what get into from the tower middle and upper part extracts that water and high pressure attract the washings WDO of tower out and from the cat head gas phase of PX recovery tower from oxidation reactor, from the gas phase from stripping tower of tower middle and lower part entering, from the flash distillation gas phase of second crystallizer and from the condensation product of the first crystallizer vapor-liquid separation tank.According to the design conditions material balance data, import the input of the temperature, pressure, flow, composition of these 5 strands of incoming flow thighs as model.Because entrainer recycle in tower during normal running; There is not charging; And model does not calculate the component that does not have charging, breaks off top and the two strands of reflow stream thighs in middle part when therefore calculating, for its flow, composition and state are established initial value; Try difference and calculate, the oil phase composition in the cat head layering and state and backflow difference partly less than a certain numerical value till.The rerum natura method adopts the UNIQUAC-HOC model, and its interaction parameter is seen table 1 and table 2; The normal low pressure of on-stream pressure; The middle part is extracted out and is located at the somewhere of temperature between PX/H2O azeotropic point and PX/HAC azeotropic point; The phase-splitting key component is H2O; According to PX content in the charging and material balance table extraction flow in middle part is set; Tower still flow is set satisfies operating provision, promptly the content according to HAC in the material balance calculating charging is provided with its value; It is design code that tower still liquid water content is set, and by separation requirement its value is set, and variable is made as the overhead reflux amount, promptly makes tower still liquid water content reach requirement through regulating the overhead reflux amount; Condenser temperature is made as the H2O/NPA azeotropic point, and pressure is normal low pressure; Decanter is selected three-phase flash evaporator model, and water is key component, and it is identical that temperature, pressure and condenser temperature are made as, and finely tunes up and down according to separation requirement.

Select the Newton method that is applicable to azeotropic mixture and the large-scale Nonlinear System of Equations of strong imperfect liquid-phase system for use; Converge to principle with model; Under the prerequisite that satisfies the main technique index; Disperse each item error calculated through regulating each parameter and design code, make each Key Performance Indicator of model in the error range that allows, overall analog result average error is minimum.

The relative design load of design conditions result of calculation of gained, under the situation that top acid content and still liquid water content meet design requirement fully, the relative error that temperature is extracted at tower top temperature, tower still temperature and middle part out is respectively-0.349%, 0.756% ,-1.042%; The relative error of cat head produced quantity, tower still produced quantity and middle part extraction amount is respectively 3.429% ,-1.537%, 0.015%; Capacity of returns is also in the designing requirement scope.So it is identical basically to draw this analog computation result and design conditions; The temperature and the flow error of crucial stream strand be no more than ± and 5%; Explain that the binary interaction parameter of regression fit gained is fit to the analog computation of this azeotropic distillation system; The rerum natura method that this model is selected for use, regulation is set all is that wider epitaxy is arranged, and institute's established model can more correctly be described the solvent dehydration process mechanism under the design conditions, can be further used for the simulation of actual condition azeotropic distillation solvent dehydration tower system.Research solvent dehydration tower is processes such as the simulation of azeotropic distillation DYNAMIC PROCESS, sensitivity analysis, control and optimization.

The calculating of practical operation operating mode model is for the practical operation situation of equality circuit timing signal, when analog computation; Parameters such as the flow of charging, temperature adopt the mean value of actual condition service data; When a stream burst component is basic analog computation with the assay result data, be modified to corresponding actual condition parameter value to parameter values all in the design conditions model, converge to prerequisite with model equally; Under the prerequisite that satisfies actual condition main technique index; Disperse each item error calculated through regulating each parameter and design code, make each Key Performance Indicator of model in the error range that allows, overall analog result average error is minimum.

The actual condition analog computation of gained and the operation of actual industrial device match; The data of relative actual condition; Satisfy under the situation of on-the-spot technological requirement in top acid content and still liquid water content, the relative error that temperature is extracted at tower top temperature, tower still temperature and middle part out is respectively-0.467%, 3.251% ,-0.526%; The relative error of cat head produced quantity, tower still produced quantity and middle part extraction amount is respectively 4.355% ,-3.572%, 0.024%; Capacity of returns is also in actual condition is regulated fluctuation range.From Simulation result, the analog computation result meets better with present plant operator condition, though the design conditions error calculated increases to some extent relatively, its relative error is generally also all less than ± 5%, within the scope that error allows.Can find out that the model that the present invention adopted is correct, the thermodynamics method of employing and thermodynamic parameter are reliably, are the optimization of production operating conditions, and the transformation of production technology is energy-saving and cost-reducing etc., provides the foundation and foundation.

For example, research and analyse according to device operation experience and mechanism model, the still liquid water content is to be related to the energy-saving and cost-reducing key parameter of solvent dehydration tower.We are benchmark with aforementioned actual condition model, and when the still liquid water content increased by 0.5%, the heating steam of boiling again descended 1.5 tons/hour, promptly improves the still liquid water content, reduce solvent dehydration tower separation accuracy, will significantly reduce the steam consumption that boils again.

According to the model analysis result; Industry pure terephthalic acid device is on the basis of solvent stability dehydration tower system operation; Improved 1% the controlling index of solvent dehydration tower still liquid water content is corresponding; Transfer the steam consumption that boils again after excellent to descend 2.5 tons/hour, descended 3.5 tons/hour in the time of at most, reached good energy-saving effect.

Being merely the preferred embodiment of invention in sum, is not to be used for limiting practical range of the present invention.Be that all equivalences of doing according to the content of claim of the present invention change and modification, all should be technological category of the present invention.

Claims (7)

1. the modeling method of industrial pure terephthalic acid's device heterogeneous azeotropic rectification solvent dehydration tower is characterized in that said method comprising the steps of:

1. according to the thermodynamic characteristics of n-propyl acetate, confirm correctly to describe the thermodynamical model of this mixture series VLE phase behavior as contained mixture series in the solvent dehydration tower of entrainer; Thermodynamics method is selected for use the UNIQUAC model of forming based on the part in the activity coefficient method to revise the liquid phase imperfection and by the deviation that the acetic acid associating effect causes, is selected for use the second virial coefficient HOC model that contains chemical theory in the state Equation Method that the associating effect and the imperfection behavior of vapour phase are revised;

2. data in literature shortage and partial data system of the remote past have been carried out measuring, all the other systems all adopt data in literature, obtain binary vapour-liquid or the liquid-liquid equilibrium data and the part ternary phase equilibrium criterion of this solvent dehydration tower mixture series through experiment;

3. the binary experimental data of utilizing step to be obtained in 2. adopts maximum-likelihood method that the binary interaction parameter in the UNIQUAC model is carried out regression fit; The binary interaction parameter that utilization obtains goes to predict the multicomponent system behavior that balances each other, set up can these mixture series rerum natura characteristics of accurate description thermodynamical model and parameter;

4. according to the equilibrium stage steady-state model MESH equation of rectification column; 1. the thermodynamic argument model that is obtained in conjunction with abovementioned steps, step be the binary interaction parameter of match gained 3.; Dehydration tower condenser and decanter are selected the flash evaporator model for use, set up the mathematics steady-state model of heterogeneous azeotropic rectification solvent dehydration tower;

5. adopt industrial pure terephthalic acid's device heterogeneous azeotropic rectification solvent dehydration design conditions data, confirm this steady-state model each item input parameter, design code and variable: said input parameter comprises temperature, pressure, flow, the composition of each incoming flow thigh, the number of plates; On-stream pressure, tower pressure drop, charging and discharging position; The phase-splitting key component; Plate efficiency, flow is extracted at the middle part out, and according to the simulation requirement; The setting of form, flow design being stipulated is satisfied its design code requirement through the correlated variables adjustment;

6. according to the actual industrial device data and each the component analysis data that obtain; Abovementioned steps is revised by each item input parameter, design code and the variable of the solvent dehydration tower design conditions steady-state model of proving correctness in 5.; Model is carried out correction adjustment, obtain correctly to describe the process mechanism steady-state model of industrial pure terephthalic acid's device heterogeneous azeotropic rectification solvent dehydration actual condition; Said actual industrial device data and each component analysis data comprise that extracting the washings WDO of water and high pressure attraction tower, the cat head gas phase from the PX recovery tower, the gas phase from stripping tower, the flash distillation gas phase from second crystallizer, the condensation product from the first crystallizer vapor-liquid separation tank, the discharging of pushing up backflow and middle part backflow, cat head and tower still and middle part out from oxidation reactor extracts material temperature, pressure, flow out; Component is got the mean value under the steady working condition in the image data to the analysis and the pre-service of data.

2. the modeling method of a kind of industrial pure terephthalic acid's device heterogeneous azeotropic rectification solvent dehydration tower according to claim 1; It is characterized in that: said step 1. in; Except the acetic acid in the system, water, n-propyl acetate, also has the by-product methyl acetate of unreacted precursor P-xylene in the acetate solvate and reaction in the said mixture series.

3. the modeling method of a kind of industrial pure terephthalic acid's device heterogeneous azeotropic rectification solvent dehydration tower according to claim 1 is characterized in that: the said step 2. system of middle required balance data comprises: n-propyl acetate+acetic acid, acetic acid+P-xylene; N-propyl acetate+methyl acetate, methyl acetate+P-xylene, n-propyl acetate+P-xylene; Methyl acetate+acetic acid, acetic acid+water, methyl acetate+water; Water+n-propyl acetate, water+P-xylene.

4. the modeling method of a kind of industrial pure terephthalic acid's device heterogeneous azeotropic rectification solvent dehydration tower according to claim 1; It is characterized in that: said step selects for use in 2. round-robin method in the Ai Lisi equilibrium still, to carry out the isobaric VLE experiment of binary, has measured acetic acid/P-xylene, n-propyl acetate/methyl acetate, methyl acetate/P-xylene, the n-propyl acetate/P-xylene vapor-liquid equilibrium data under normal pressure of totally four groups of binary systems respectively.

5. the modeling method of a kind of industrial pure terephthalic acid's device heterogeneous azeotropic rectification solvent dehydration tower according to claim 1 is characterized in that: the τ in the 3. middle UNIQUAC model of said step _IjAdopt τ _Ij=exp (A _Ij+ B _Ij/ T) expression-form carries out regression fit to the binary interaction parameter.

6. the modeling method of a kind of industrial pure terephthalic acid's device heterogeneous azeotropic rectification solvent dehydration tower according to claim 1; It is characterized in that: the complicated heterogeneous five yuan mixture series of said step in 3. contain the multicomponent system of 9 boiling point components; Four groups of azeotropic mixtures, wherein two groups is heterogeneous.

7. the modeling method of a kind of industrial pure terephthalic acid's device heterogeneous azeotropic rectification solvent dehydration tower according to claim 1; It is characterized in that: the actual condition image data of said step in 6. comprises each charging and goes out temperature, pressure, the flow of materials flow thigh that the component application of sample is analyzed data and comprised each charging and go out materials flow thigh composition.

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