Jeremy Choon Liang Tan | CHE3161 | May 7, 2016

Flash VaporiserLAB REPORT

Table of ContentsTable of ContentsSummary:....................................................................................2Aim:.............................................................................................2Background and Introduction:...................................................2Background Information:.................................................................................2Relevant Theory:..............................................................................................3Motivation for Study:.......................................................................................3Intended Scope:...............................................................................................3

Key Equations:............................................................................4Experimental Work:....................................................................5Apparatus:.......................................................................................................5Method:...........................................................................................................5

Results:.......................................................................................7Discussion:................................................................................12Mass Balance:................................................................................................12literature values:...........................................................................................12Raoult’s law:..................................................................................................12NRTL Equation:.............................................................................................13Wilsons equation:..........................................................................................13Overall:..........................................................................................................13Errors, assumptions and limitations:.............................................................14

Conclusion:...............................................................................14References:...............................................................................16Appendix:..................................................................................17Calculation for Deviation:..............................................................................20Table used to gather constants for wilsons equation:...................................21HYSYS simulation, Activity Coefficients and Molar Volume:........................22Schematic setup of appartus:........................................................................23

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Summary:This experiment was carried out to study the concepts involved when operating a steady state flash

vaporization system. Additionally, the experiment was also to conclude if the experimental data matched

with theoretical data which include mass balances, NRTL, Raoult’s Law and Wilsons Equation. This was

conducted using a flash vaporiser whereby initially the feed stream was 6L of ethanol and water mixture.

As the system was allowed to reach steady state we had adjusted the flow rate to 0.5g/s. Once the system

had reached steady state we had collected samples from the liquid and vapor streams and measured how

much of each we had obtained in 60 seconds or 90 seconds. We then used a densitometer to measure the

mass fraction of the liquid. This was then repeated by changing the feed flow to 1.0g/s. From results

obtained after calculation we have discovered that the increase in temperature had led to an increase in the

bottom and top stream’s mass fractions increase and the ethanol mass fraction was higher at the top rather

than at the bottom. T-X-Y diagrams have been generated to show the correlation between the theoretical

model and the experimental data. Overall the experiment was a success and that the objectives of the

experiment were met. To conclude, Wilsons Equation gives us the least deviation from the literature values

and thus is the theoretical model to use.

Aim: To study the flash vaporization of an ethanol/water binary system and to compare these results with theoretical models.

Background and Introduction: BACKGROUND INFORMATION:

There are several types of separation process that’s used in the chemical engineering industry, absorption, distillation and liquid-liquid extraction. Flash vaporization is a single-stage separation technique and is often found in the distillation process.

Distillation is the process of separating the component substance from the liquid mixture by selective evaporation and distillation. Distillation can lead to complete separation where pure components are separated and partial separation where the concentration of certain components in the mixture are increased. As distillation is based on the relative volatility of components in the liquid mixture that’s being boiled in order to separate the liquid into its respective components.

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Thus the vapor generally contains more of the volatile components whereas the liquid stream contains less volatile components.

RELEVANT THEORY:Distillation process such as absorption, extraction and distillation utilize the

different phases of composition. The mass transfers between phases will alter the compositions, thus to analyse a system the equilibrium pressure, temperature and phase composition have to be known. Universally the most common phases that coexist in a system are liquid and vapor. This experiment conducted specifically used a feed of ethanol and water in a binary system with a fixed flow rate. After a certain amount of time the system was assumed to have reached equilibrium and is then separated into liquid and vapor phases at their respective flow rates.

This experiment utilized Rault’s Law, NRTL and Wilson’s Equation to find out the different compositions and other specific values needed to generate the T-X-Y Diagrams and to calculate the vapor pressure of a specific species. Rault’s Law was used to solve for the composition of a component and the vapor pressure of the species at the temperature of the system. The vapor pressure of a system can be found using the Antoine Equation which uses specific constants at certain temperature ranges to give an accurate approximation of the vapor pressure.

MOTIVATION FOR STUDY:The flash vaporizer is used commonly in industry for separating components,

thus it is important for engineers to understand the way the equipment works and to understand its mechanism. Flash vaporization is the process of a saturated liquid continuously passing through heated coils to obtain fractional vapor. The liquid commonly passes through a throttling valve after having gone through a pump, once is goes through the throttling valve the pressure is decreased and as it enters the heating coils/heater it separates and vapor is collected via a condenser as a liquid and the liquid bottom is collected as well. This gives us the distillate (top) and the liquid (bottom) for analysis. Additionally, this experiment utilizes hand calculation, MATLAB and HYSYS for comparison of results.

INTENDED SCOPE:The experiment was intended to allow us to learn more of the phenomena of

flash vaporization using the given equipment. To allow the experimenter to be familiar with the equipment and the process of flash vaporization, the experimenter

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has to measure the mass fraction of the overhead and the bottom samples at different flow rates and temperatures and being compared to the literature values given.

MATLAB and HYSYS was used to present the effect of the feed flow rate and temperature has on the composition of the product in a graphical manner. The program HYSYS was used to solve for constants needed for the MATLAB file as they were not given and through multiple simulations we have discovered that these variables were the constants for the Antione Equation component in the given MATLAB file. The use of these programming tools will improve the experimenter’s understanding of flash vaporization.

Key Equations:Several significant equations were used in the calculation of the data

obtained in the experiment. The equations are listed as shown, when no reaction is taking place.

Overall Mass Balance:

F=L+V (1.1 )

Overall Ethanol Mass Balance:

F x i=L xi+V x i (1.2 )

Antoine’s Equation:

ln Pisat

kPa=A− B

TK

+C(1.3 )

Raoult’s Law:

y iP=x iPisat (1.4 )

Wilson’s Equation:

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Ge

RT=x1ln (x1+x2 A12 )−x2 ln (x2+x1 A21) (1.5 )

ln ( y1 )=−ln (x1+ x2 A12 )−x2( A12

x1+x2 A12−

A21

x2+x1 A21)(1.6 )

ln ( y2 )=−ln (x2+ x1 A21 )−x1( A12

x1+x2 A12−

A21

x2+x1 A21)(1.7 )NRTL Equation:

Ge

x1 x2RT=

G21 τ21

x1+x2G 21+G12τ12

x2+x1G12(1.8 )

ln ( y1 )=x22[ τ12( G21

x1+x2G12)2

+G21 τ12

(x2+ x1G12)2 ]ln ( y2 )=x1

2[τ12( G12

x2+ x1G12)2

+G21 τ21

(x1+ x2G21)2 ]

Experimental Work:

APPARATUS:The apparatus used is shown in the diagram below.

Feed Tank: Where the 17% ethanol/water mixture is held before it is sent through the flash vaporization system. Pump: Where the pressure is increased. Throttling Valve: where the saturated liquid experiences a pressure drop before it enters the heater.Heater: Where the liquid is heated into a vapor/liquid mixture. Flash Vaporizer: Where the liquid and vapor are separated into their respective phases.Condenser: Where the vapor is condensed into a liquid so that it can be collected as the overhead.Cooler: Where the liquid is cooled so it can be collected as the bottom.Gas Chromatograph: A device used to analyze the separated compounds which are

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vaporized without decomposition. Densitometer: A device used to measure the density of the liquid collected. This is used to measure the mass fraction.

METHOD:The method for this experiment is as follows,

6L of the 17% ethanol/water solution is stored in the feed tank and the stirring motor and heater were switched on. The temperature in the feed tank and vaporizer were set to a desired temperature. After the temperatures have reached this desired set point, the condenser and cooling water were then turned on.

Next, we set the pump to the correct opening percentage such that the feed flow is approximately 2.19g/s. The overhead and bottom stream products were then collected for 60 seconds and when we change the feed flow rate to 1.07g/s and then the overhead and bottom products were collected for 90 seconds. This was repeated 3 times each for each flow rate. After having obtained all 6 samples and recorded down the mass of the solution obtained the experiment was then shut down.

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Results:Table 1.1 Experimental Data

Bottle Number

Weight Of Empty Bottle

Weight of Whole Bottle

Weight of Solution Time Flow

Rate

F1 124.7 190.4 65.7 30 2.19B1 131.6 215.1 83.5 60 1.39T1 132.9 139.9 7 60 0.12B2 132.3 209.8 77.5 60 1.29T2 131.8 145.1 13.3 60 0.22B3 131.5 221.4 89.9 60 1.5T3 131.4 150.1 18.7 60 0.31F2 124.7 156.8 32.1 30 1.07B4 131.3 255.5 124.2 90 1.38T4 132.8 137.7 4.9 90 0.05B5 132.1 240.2 108.1 90 1.2T5 131.7 146.5 14.8 90 0.16B6 131.2 222.9 91.7 90 1.01T6 131.6 158.4 26.8 90 0.3

Table 1.2Experimental Data

Run Number

Feed Rate

Feed Mass

Fraction

Power Setting

Liquid Temperature

Bottom Flow Rate

Bottom Mass

Fraction

Overhead Flow Rate

Overhead Mass

Fraction1 2.19 0.17 95 86.3 1.39 16.5 0.12 60.82 105 87.9 1.29 13.5 0.22 55.73 115 88.5 1.5 12.1 0.31 55.74 1.07 0.17 80 86.2 1.38 16.2 0.05 60.55 95 87.9 1.2 13.3 0.16 57.86 110 89.9 1.01 9.7 0.3 51.6

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Graph 1.1T-X-Y Diagram of the experimental data calculated

0 10 20 30 40 50 60 7085

85.5

86

86.5

87

87.5

88

88.5

89

Bottom and Overhead Flow Rate Vs Temperature @ 2.19g/s

Bottom

Top

Mass Fraction

Tem

pera

ture

Graph 1.2T-X-Y Diagram of the experimental data calculated

0 10 20 30 40 50 60 7084

85

86

87

88

89

90

91

Bottom and Overhead Flow Rate Vs Temperature @ 1.07g/s

BottomTop

Mass Fraction

Tem

pera

ture

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Table 1.3Literature values of the Liquid and Vapor Weight Percentage of Ethanol

Temperature Liquid Weight Percentage of Ethanol Vapor Weight Percentage of Ethanol100 0 098.9 1 696.75 3 20.594.95 5 3891.45 10 5288.95 15 59.587.15 20 64.885.75 25 68.684.65 30 71.4

Graph 1.3T-X-Y Diagram of the Literature values

0 10 20 30 40 50 60 70 807580859095

100105

Literature Values

LiquidVapor

Weight Percentage

Tem

pera

ture

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Graph 1.4T-X-Y Diagram NRTL

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.4580859095

100105

T-X-Y Diagram NRTL Temperature Vs Mass Fraction

LiquidVapor

Mass Fraction

Tem

pera

ture

Graph 1.5 T-X-Y Diagram Raoult’s Law

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1340345350355360365370375

T-X-Y Diragram Raoult's Law Temperature Vs Mass Fraction

LiquidVapor

Mass Fraction

Tem

pera

ture

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Graph 1.6T-X-Y Diagram Wilsons EquationRed Line – VaporBlue Line – Liquid

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Discussion:

MASS BALANCE:The mass balance first done on the system was to find the theoretical mass

flow rate of ethanol in the bottom. A boundary was set around the flash vaporiser, on the experimental data (Table 1.2) we have recorded the mass flow rate of the ethanol coming out at the bottom. From the data we can observe that at times when temperature is increased the overhead flow rate increases as well, however there are instances where this does not hold true. We can account this for errors experienced in the practical. Theory suggests that overhead flow rates do increase when the temperature increases and this is due to vaporisation of the saturated liquid which at higher temperatures yield higher distillate flow rates thus decreasing the bottom flow rate which was seen in most cases.

In the experimental data (Table 1.2) the mass fraction of the overhead was significantly greater than that of the bottom which abides with theory as the boiling point of ethanol is lower than that of water and thus the distillate collected will be much greater than the bottom product. As the flow rate increases in the last 3 runs (runs 4-6) we can see that the mass fraction has decreased which once again abides with the theory of the experiment as the higher flow rates means that less contact time is made with the liquid and the heating coils which means less of the saturated liquid is vaporised.

LITERATURE VALUES:Graph 1.3 shows us the T-X-Y diagram of the binary ethanol/water system

given in the lab manual. This is the successful data collected when the experiment is carried out properly where error margins are relatively small compared to the experimental data collected. The system was assumed to be at constant pressure and temperature but in practice this was not the case as the temperature fluctuated 1C.

RAOULT’S LAW:Raoult’s Law was used to simulate and model the experiment and

comparisons between the mass fraction that was calculated and the mass fraction that was collected for both the bottom and overhead streams were made. Graph 1.5

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shows the mass fraction of the overhead and the bottom streams at varying temperatures. When comparing Raoult’s Law to the experimental data we can see that for the different flow rates that the bottoms don’t really match Raoult’s Law but the overhead stream is similar to Raoult’s law this can be credited to the fact that the assumptions the Raoult’s law makes is that the system is at low pressure and that the fluid is an ideal gas and the liquid phase contains an ideal solution.

The deviation in the Raoult’s Law compared to the experimental data is quite large but that’s due to the system being at a different pressure and temperatures to the pressure and temperature that the Raoult’s Law uses. Using the modified Raoults Law will yield better and more accurate results.

NRTL EQUATION:The NRTL equation utilizes the program HYSYS, which is a simulation

program that models the way the actual experiment would have been carried out. Once a binary system was generated the HYSYS program had calculated the different compositions for ethanol and water at varying temperatures.

Graph 1.4 shows a strong correlation with the experimental data (Graph 1.1 and 1.2). The binary coefficients for the NRTL graph found was off the HYSYS program and will later be shown in the appendix.

WILSONS EQUATION:The Wilson’s equation uses feed flow rate and temperature to calculate the

bottom and overhead mass fractions. This was modeled through the use of MATLAB as shown in MATLAB Code 1.1 and Graph 1.6. The mass fractions calculated from the MATLAB and was compared to the experimental data. We can see from Graph 1.6 that with the increase of temperature the mass fractions increase as seen from the experimental data Table 1.2.

The iterations on the MATLAB code was needed to calculate the compositions with the effect temperature has on the products. The coefficients found for the Wilson’s equation was gotten off HYSYS once the binary system was generated. As ethanol and water are two polar molecules they are miscible thus making the Wilson’s Equation applicable to the system.

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OVERALL:Overall the experiment was a success as experimenters are supposed to use

the experimental data to figure out the trends from the different models (Raoult’s, NRTL, Wilsons) and compare these to the literature values. Additionally, the model that is most applicable to the experiment would be the Wilsons Equation as it gives us the least deviation from the literature values and this can be seen on Graph 1.6. The Raoult’s law isn’t as applicable as certain assumptions were made for this particular model that did not hold true in the experiment as discussed above. The NRTL equation had correlations that matched with experimental data however it did not match the literature values as well as the Wilson’s Equation. Thus we can conclude that the Wilsons Equation is the most applicable to the experiment as it holds strong correlations to the literature values.

ERRORS, ASSUMPTIONS AND LIMITATIONS:

The errors in the experiment were mostly human errors. These errors consisted of the collection of liquid for 60 and 90 seconds as a little bit of extra liquid may have gone into the bottle. The bottles were not 100% dry when weighing the bottles and may have affected the measurement of the weight of the bottles. When taking the initial sample (marked F1 and F2 on Table 1.1) there may have been slight inaccuracies as it was done through the accuracy of the naked eye. So slight errors may have been incurred here.

Additionally, the HYSYS simulation used the assumption that the change in pressure in certain components of the system were zero and that the delta H was also zero in the cooler, condenser and pump. The 17% ethanol/water mixture was pre-made, this would mean that the mixture may not have been exactly 17% ethanol. Furthermore, the apparatus set up had also malfunctioned in during the practical, and once it was fixed it may not have been calibrated to the exact same settings as before.

The limitations of this experiment tended to be equipment focused. An example of a limitation of the experiment was the non-uniform heating in the heating coils and poor insulation as heat was lost to the atmosphere. To overcome this limitation, we would have to ensure that the heater component of the system is properly insulated to ensure minimal heat loss.

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Conclusion:

In conclusion, the experiment was a success. The investigation and analysis of a flash vaporization binary system of a 17% ethanol/water mixture. Calculations carried out were done on Excel and the necessary graphs were generated using a combination of MATLAB and HYSYS programs and Excel.

All trends were discussed and shared similar traits whereby when temperature increases the mass fraction of the ethanol in both streams decrease. The overhead stream also had higher mass fractions of ethanol. After careful analysis of the different models the Wilsons Equation had the best correlation to the literature values.

The deviations experienced between the experimental values and calculated data can be accounted for by the assumptions, errors incurred during the practical and limitations of the apparatus. Assumptions included that the system was at VLE, steady state and no loss or accumulation of mass was present.

Conclusively all the objectives of the experiment were met.

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References:

J. M. Smith, 2005. Introduction to Chemical Engineering Thermodynamics, 7th Edition. 7th Edition. McGraw Hill Higher Education.

Lecture Slides from CHE3161

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Appendix:MATLAB Code 1.1:% ======================================================================

% PROGRAM DESCRIPTION: Generate a T-x-y diagram for Ethanol(1)/Water(2).

% ======================================================================

% Group 8

% Student Name: Jeremy Choon Liang Tan

%

% ==================

% Setup environment.

% ==================

clear all;

close all;

clc;

% ==================================================================

% Define system pressure and pure component saturation temperatures.

% ==================================================================

P=101.33;

T1sat = 351.35;

T2sat = 373.15;

% ==================================================================

% Define parameters neccesary for Wilson activity coefficient model.

% ==================================================================

a12 = 276.756;

a21 = 975.486;

v1 = 58.492;

v2 = 17.883;

% =====================

% Antoine coefficients.

% =====================

A1 = 16.8958;

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B1= 3795.17;

C1 = -42.232;

A2 = 16.262;

B2 = 3799.89;

C2 = -46.80;

% =============

% Setup arrays.

% =============

x1 = [0:0.01:1];

y1= zeros(1,length(x1));

Temp = zeros(1,length(x1));

% =================================================================

% Setup first and last values in compostion and temperature arrays.

% =================================================================

y1(1) = 0;

y1(length(x1)) = 1;

Temp(1) = T2sat;

Temp(length(x1)) = T1sat;

% ==============================================

% Begin main loop (over composition of Ethanol).

% ==============================================

for i = 2:(length(x1)-1);

T = x1(i)*T1sat + (1-x1(i))*T2sat;

% ==============================================

% Begin secondary loop (to find temperature).

% ==============================================

for j=1:100 % to ensure convergence, technically should use a while loop. So 100 iterations chosen to ensure high probability of convergence.

D12 = v2/v1*exp(-a12/(8.314*T));

D21 = v1/v2*exp(-a21/(8.314*T));

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gam1 = exp(-log(x1(i)+(1-x1(i))*D12)+(1-x1(i))*((D12/(x1(i)+(1-x1(i))*D12))-(D21/((1-x1(i))+x1(i)*D21))));

gam2 = exp(-log((1-x1(i))+x1(i)*D21)-x1(i)*((D12/(x1(i)+(1-x1(i))*D12))-(D21/((1-x1(i))+x1(i)*D21))));

P1sat = exp(A1-B1/(T+C1));

P2sat = exp(A2-B2/(T+C2));

alpha = P1sat/P2sat;

P1satnew = P/(x1(i)*gam1+(1-x1(i))*gam2/alpha);

Tnew = B1/(A1-log(P1satnew))-C1;

T=Tnew;

end % this ends the loop to find temperature for a single liquid composition

% calculate y1 corresopnding to x1 using temperature found above.

Temp(i)=Tnew;

y1(i) =x1(i)*gam1*P1sat/P;

end % this ends the loop over the composition x1

% ===========================================================

% Convert temperatures from Kelvin to Celcius for T-x-y plot.

% ===========================================================

TempCelcius = Temp - 273.15;

% =======================

% Plot the T-x-y diagram.

% =======================

plot (x1,TempCelcius,'b-');

hold on;

plot (y1,TempCelcius,'r-');

grid on;

hold on

% =======================

% Plot experimental data

% =======================

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z=xlsread('filename',1);

Texp=z(:,1);

xexp=z(:,2);

yexp=z(:,3);

plot(xexp,Texp,'g-');

plot(yexp,Texp,'r-o');

% use appropriate title

title('T-x-y diagram for Ethanol(1)/Water(2) at P=101.3 kPa');

xlabel('x1,y1');

ylabel('T');

CALCULATION FOR DEVIATION:The data used for this equation is the mass fraction of the calculated data

from the models (Raoult’s, NRTL, Wilsons) and the experimental data is the mass fraction calculated from the experimental data gathered.

calculated data−experimental datacalculated data

∗100=percetnage deviation

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TABLE USED TO GATHER CONSTANTS FOR WILSONS EQUATION:

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HYSYS SIMULATION, ACTIVITY COEFFICIENTS AND MOLAR VOLUME:

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SCHEMATIC SETUP OF APPARTUS:

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