FINAL Evaporator Final Report

Roger Adams Chemical 600 S. Mathews Ave. Urbana, IL 61801

DATE: September 30, 2009 TO: Victor Shum, Plant Supervisor FROM: Ben Mack, Melissa Medrano, Jason Pulley, Process Engineers SUBJECT: Double-Effect Evaporator Replacement Investigation Final Report REFERENCE: Memo Dated August 23, 2009, Double-effect Evaporator Evaporator Replacement – Rotation 1 and 2; Double-Effect Evaporator Replacement Investigation Workplan 1. Abstract

In order to fully understand the operation and effectiveness of the replacement double-effect evaporator, an investigation was carried out to determine the effects of steam and vacuum pressure on the heat transfer coefficients of each exchanger, the condensate flow rate at the end of the process, and the overall steam efficiency efficiency in the system. system. The steam pressure and 2nd effect vacu vacuum um pres pressu sure re were were foun found d to have have a posi positi tive ve corr correl elat atio ion n with with the the 2nd effect effect overhead overhead condensate flow rate. Steam efficiency is to to a large degree affected by changes in the steam steam and vacuum pressure, as an increase in steam pressure and vacuum pressure causes an increase in the steam efficiency. The two parameters have the same significance in regards regards to steam efficiency. efficiency. The heat transfer transfer coefficient coefficient for each evaporator heat was determined determined for different different vacuum and steam pressures pressures.. The patterns patterns indicate an increase in heat transfer coefficient coefficient for both effects effects with increasing steam pressure. pressure. Conversely, increasing the vacuum pressure pressure causes a decrease in the heat transfer coefficient and a decrease in the vacuum pressure causes an increase in the heat transf transfer er coeffic coefficien ientt for both effect effects. s. The heat transf transfer er coeffic coefficien ientt for the heat exchanger exchanger increases with increasing steam and vacuum pressure. However, the heat transfer coefficient for the heat exchanger exchanger decreases with decreasing steam and vacuum pressures. pressures. Literature Literature has been found suggesting possible reasons for discrepancies in the heat transfer coefficients, including scali scaling, ng, frothing frothing,, and bubbling bubbling of the liquid. liquid. The evaporat evaporator or was predic predicted ted to run more effect effectivel ively y and effici efficient ently ly under under doubledouble-eff effect ect feed feed forwar forward d mode mode to ensure ensure that that the 90% minimum concentration would be met in the system. It was recommended for the Senior Senior Chief Technician to use Careclean F Descalex P produced by Marine Care, as the cleaning product for the U.S. Coast Guard Ship scaled up evaporator due to its cleaning efficiency on heavy scale and safe use in evaporators. 2. Introduction

The suitability of replacing the current double-effect evaporator used for concentrating high fructose corn syrup by an old evaporator found in storage was investigated due to a scheduled shutdown shutdown for routine maintenance maintenance of the current double-effect double-effect evaporator. evaporator. The shutdown will 1

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occur in approximately 8 weeks.1 Therefore, an immediate study of the old evaporator was necess necessary ary.. The replacem replacement ent of the evaporat evaporator or was propose proposed d due to curren currentt cost cost saving savingss meas measur ures es,, spec specif ific ical ally ly so that that prod product uctio ion n is not not temp tempor orar aril ily y halte halted d durin during g the the rout routin inee maintenance maintenance period of the current double-eff double-effect ect evaporator. evaporator. To simplify simplify the process and to understand the effects of the different variables, this study was performed using industrial tap water instead of high fructose corn syrup as the non-concentrated solution and concentrated product. product. This study included included an analysis analysis of the steam efficiency efficiency of the replacement replacement evaporator evaporator and the development of a model for predicting the replacement evaporator’s operation. The physical physical and economic economic feasibilit feasibility y of producing high fructose fructose corn syrup syrup using the replacement replacement double-effect evaporator will also be determined in the second 4-week rotation, which is not included in this report. This report will focus on the first 4 week term, Rotation 1 objectives, which included the calibration of the height of the sight glass level against volume for both effects, characterization of the double-effect evaporator for wide ranges of steam and vacuum pressures, the effects of steam and 2nd effect pressure on 2nd effect effect vapor vapor condens condensate ate flow rate, rate, and the effect effectss of operat operating ing condition conditionss on steam steam effici efficienc ency. y. In additio addition, n, the heat transf transfer er coeffic coefficien ients ts in the evaporator effects were calculated from experimental data, and their changes as a function of all relevant parameters were established. established. Finally, single-effect single-effect and parallel-effect as well as doubleeffect feed backward modes were studied to determine the optimum effectiveness and efficiency in the double-effect evaporator. A recommendation for a product to clean a scaled up evaporator for a U.S. Coast Guard Ship is also provided. The experimen experimental tal procedure procedure described described in this this report report was based based on the vacuum and steam steam pressures’ effects on the operation of the evaporation system. These measurements provided data on how each of these two variables alters the 2nd effect condensed vapor flow rate as well as the heat transfer coefficients. In addition, the most influential variables were examined and their effects determined. 3. Theory

The general purpose of evaporation is to boil off a volatile solvent (in this case water) from a nonvolatile solute to produce a more concentrated product solution.2 This concentrated product (often (often referred referred to as the liquor) liquor) is the stream of value in this process. process. In this case, the current current double-effect evaporator is being used to concentrate a high fructose corn syrup from 10% to 90%. However, for experimental purposes, industrial industrial water will be used in this rotation rotation in place of the high fructose corn syrup. A multiple-effect evaporator uses a series of evaporators (called effects) effects) to accomplish accomplish the previously previously stated stated goal. This system system utilizes utilizes the latent heat from the water vapor from the previous effect to boil off excess water in the solution.3 Steam efficiency is greatly greatly increased in a multiple-ef multiple-effect fect evaporation evaporation setup compared to a single-eff single-effect ect evaporator, as less direct direct steam is required required to produce the same product concentrat concentration. ion. This is due to the reuse of the water vapor boiled off the solution. Raw steam is used as the heating source for the 1st effect, and then the boiled off vapor from the 1st effect is used as the heating source for the 2nd















stream is fed using a single pump, starting with the effect that the steam is directly fed to, and ending at the effect where concentrated product is collected. Figure 1 shows the general setup for a forward-feed double-effect evaporator similar to the one investigated on this rotation.

Figure 1: General Double-effect Evaporator Schematic3

The functionalit functionality y of this equipment equipment is based on heat-based separation separation principles principles.. Solutions Solutions containing components with different boiling points can be separated through the application of heat, where the heat transfer from the steam line to the solution in the tank raises the temperature of the solution to its boiling point and (when enough heat is provided) vaporizes the more volatile volatile component off of the solution. This heat transfer transfer lowers the temperature temperature of the steam, condensing it into a liquid. The heat transfer for evaporators can be quantified using the following general equations (Refer to Appendix A for more rigorous calculation methods):2 q=UA∆ T lm lm

(1)

q= Sλ

(2)

U is the heat transfer coefficient, A Where q is the heat transfer rate, U is coefficient, A is the heat transfer transfer area of the effect, ∆ T is the temperature difference between the steam into the evaporator and the boiling point of the solvent, S is S is the mass flow rate of the steam entering the evaporator, and λ is the latent heat of the steam. steam. By setting setting these two equations equations equal to one another, it becomes possible to calculate the overall heat transfer coefficients (U (U ) at different steam pressures to















The efficiency of the steam is defined as the amount of product produced divided by the amount of steam fed to the system. system. Multiple-e Multiple-effect ffect systems systems increase increase the efficiency efficiency because the waste streams are used as heat sources rather than just direct fed steam. Normally, evaporators are constructed from a form of steel, usually stainless steel to prevent damage from any ferrous metals or other corrosive materials that may be run through the system. One common problem problem in evaporation evaporation is scaling. Scaling Scaling occurs when buildup is deposited deposited on the heating surfaces by the solution being boiled. This buildup has been reported to diminish diminish the overall heat transfer coefficient. coefficient. Normal solutions to this this problem call for the shutdown of the evaporator to clean the heating surfaces. The current system system also makes use of the functionality functionality of heat exchangers. Heat exchangers are designed designed with the purpose of transferrin transferring g heat between streams streams of different energy. energy. In some cases, heat exchangers utilize a heated vapor to raise the temperature of another stream or to vaporize the stream. In this case, heat exchangers are utilized utilized as condensers after each effect to condense the waste steam into liquid water by passing a sufficient amount of cold water through the heat exchanger. Condensing the overhead vapor from the 2nd effect steam allows the vapor to be collected, collected, quantified, quantified, and then discharged discharged at atmospheric atmospheric pressure. pressure. The main equations equations 2 governing the heat exchangers are (also found in the calculations in Appendix A): q=UA∆ T lm lm

(3)

q=mC p∆ T+∆ H v (4) U is the overall heat transfer coefficient, A is the heat transfer Where q is the heat transferred, U is area of the device, m is the mass flow rate, ∆ T is T is the temperature change of the stream, C p is the heat capacity of the stream, and ∆ T lm mean temper temperatu ature re differ differenc encee of the heat lm is the log mean exchanger. 4. Experimental Apparatus and Procedure

The double-effect evaporator setup consists of two identical insulated effects, a heat exchanger used to condense the 2nd effect overhead, and two collection tanks used to collect the condensed overhead.6 Each of the effects was custom fabricated with an inner diameter of 11.75 inches and a height of 4 feet. The exchanger used to condense the 2nd effect vapor is an American Standard heat exchanger with a temperature rating of 450°F, tube pressure rating of 150psi, and a shell pressure pressure rating rating of 225psi. The two effects effects also have small Blackmore Blackmore and Giant brand heat exchangers that serve as condensers on the steam outlet lines. All of the exchangers used are of the shell and tube variety. variety. More information about the effects effects and 2nd effect overhead condenser can be found in Table 1 below.















Condenser Manufacturer

Custom fabricated

Custom fabricated

American Standard

Feed (Hot Stream)

RAL steam supply

1st effect overhead

2nd effect overhead

Feed (Cold Stream)

RAL water supply

RAL water supply

RAL water supply

Water Flow Meter Brand

Neptune

Hersey

Hersey

Heat Transfer Area (ft 2)

1 .8

3 .3

16

Low-pressure steam (approximately 35psi) enters the 1st effect from the RAL steam supply line and is fed through through a tube bundle side mounted mounted near the bottom of the 1st effect. effect. The overhead overhead nd stream of this effect is then used to boil water in the 2 effect. Steam feed pressure is is monitored using two analog pressure gauges: one before the steam flow throttling valve to measure supply pressure and one after the valve to measure the actual pressure of the steam added to the evapor evaporati ation on syste system. m. Each Each effect effect has a mounte mounted d analog analog pressu pressure re gauge to monito monitorr vessel vessel nd pressure. The vacuum pressure pressure on the 2 effect can be monitored and controlled off of the main vacuum line that is located on the south wall of RAL 8 with the process water lines. The process water is metered from the building supply line and is fed to both of the effects. Unlike the 1st effect flow meter, the 2nd effect and vapor overhead condenser flow meters record the volume of water that enters the vessels vessels instead of the flow rate. Analog temperature gauges are used to monitor the feed temperature of the water to the 1 st effect, the cooling water inlet and outlet temperatures to the 2nd effect vapor condenser, and also on the hot stream outlet from the condenser. Digital gauges monitor monitor the temperatures of the water near the bottom of the effects where the the steam coils coils enter. enter. Figure Figure 2 below diagram diagramss the setup setup of the evaporato evaporatorr unit. Each measurement point for temperature, pressure, and flow rate is indicated with squares, circles, and triangles, respectively.















Figure 2. Double-effect evaporator design setup7

In order to investigate the effects of steam and vacuum pressure, several measurements were recorded recorded per trial to perform the necessary necessary calculations calculations.. Starting Starting from a completely completely drained st nd st system, the 1 and 2 effects were filled with water; the 1 effect feed is metered by a level controller, and the 2nd effect flow meter reads the actual volume of water being added to the effect. effect. Calibrati Calibration on curves were created created for both of these effects by adding adding known amounts of water and measuring the resulting resulting height from grade in each sight glass. The calibration curve in nd the 2 effect was the most crucial since it was used to quantify exactly how much water boiled out in the overhead. Initial Initial and final heights in the sight glass glass were recorded and plugged into the calibration curve to measure this this amount of water. The actual calibration curves used in the the experiment can be found in Section 5.1. Once the steam supply line was opened to the system, it typically took a couple of minutes for the line to stabilize. stabilize. Stabilizat Stabilization ion was determined determined as the point in which the pressure pressure gauge readings stopped increasing and leveled out. This pressure reading was indicated in Figure 2 as P1. Additionally, the steam supply temperature was measured and represented represented as T2. After the st steam had passed through the 1 effect, it passed through a condenser before passing to the drain. By collecting the condensed steam out of this condenser, the steam flow rate to the 1st effect, F2, was measured measured by collecting collecting the water over a specified specified period of time. time. In the same fashion, fashion, the

















were used to evaluate the amount of water boiled in each effect. To monitor the progression progression of the boiling, boiling, the thermocouples thermocouples represent represented ed by T3 and T6 were utilized. utilized. The thermocouple thermocoupless provided temperature readings of the water in each effect and indicated when boiling had occurred. Once these temperatures reached the boiling boiling point of water at the the operating pressure of each effect (measured as P2 and P3 by pressure gauges on top of the effects), it was assumed that full boiling was rampant and that vapor was being transferred transferred to the next unit in the system. system. The nd operating pressure of the 2 effect, effect, P3, was dictated dictated by P4, the vacuum pressure of the system. system. nd The selected vacuum pressure for the system was the operating pressure of the 2 effect. After the 1st effect water began to boil, monitoring the temperature gauge indicated that vapor was in fact being transferred to the 2nd effect, and T4 confirmed this thought. Without any vapor present, this thermometer would read room temperature. The same reasoning follows with T7, the temperature of the 2nd effect vapor overhead. As the 2nd effect water boiled, the overhead was condensed using the heat exchanger in the system. Another indication of boiling boiling in the 2nd effect was the outlet temperature of the cooling water, T9, which began to increase from its inlet temperatur temperature, e, T8. The flow rate of this cooling cooling water, F5, dictated dictated how much the temperature temperature increased: a higher flow rate resulted in less of a temperature increase. This is based on equation 5 in the Appendix which shows that with the same heat transfer, q, increasing m will result in a decrease of ∆T. Once the overhead overhead condensed, condensed, it was collected collected in the two collection collection tanks. On its way to the tanks tanks,, the the over overhe head ad vapor vapor pass passed ed a temp temper erat ature ure gauge gauge,, T10, T10, whic which h meas measur ured ed the the fina finall temperature of the condensed vapor. The condensed vapor flow rate was determined determined in the same st nd fashion that steam flow rates were measured in the 1 and 2 effect. One of the collection collection tanks was selected selected for collection collection prior to testing. testing. During a timed interval, interval, the collection collection tanks were switched so that only the vapor produced during that time period was collected in the 2nd tank. At the end of the collection period, the valves were switched so that the 1st tank was once again collecting the condensed overhead. After the 2nd tank was isolated, the vacuum was lifted from it and the vapor was collected through one of the drains. In the ideal situation, the sight glasses of the collection tanks could have been calibrated to the volume in the tanks; however, during normal operation, the fluctuations in the sight glass level were significant, and it was deemed more reliable to manually collect samples and measure the exact amount collected rather than using a calibration.















Figure 3. Experimental 2 level partial factorial design for 3 factors. X’s represent data points not collected.

The decision was made to run a replicate of the high steam and high vacuum pressure data point in favor of running another another unique sample point such as the medium/medium medium/medium sample. sample. Both of these points are valuable, but, with only a couple samples, replicates were deemed to be a higher priority instead of a unique unique middle data point. Data analysis based on only a couple of samples is difficult as small errors in a sample point can cause severe inaccuracies in the data trends. Having a replicate of a data point provides some validation to the data whereas a middle point may just make the data more unclear; for example, if the middle point does not fit the trend of the other couple data points, it is unclear which point is inaccurate and what the actual trend should look like. A summary of the design matrix detailing detailing the order that the the experiments were run can be found in Table 2 below. Table 2. Experimental design matrix9 X1 (ste (steam am P, psig psig)) X2 (vac (vacuu uum m P, P, in in Hg) Hg)















Accurate volume measurements were obtained ob tained by first calibrating the sight glasses for the effects to known volumes volumes and creating calibrati calibration on curves from this this data. For each effect, effect, an initial height on the sight glass was marked, and a specific amount of water, measured with the supply line flow meters, meters, was added to the effect. effect. The new height was marked marked and measured, measured, and the process process was repeated for several data points. points. Using these points, points, the calibration calibration curves seen in Figures 4 and 5 below were determined.

Figure 4. 1st effect sight glass calibration curve















on the collection tanks were not successfully calibrated due to oscillations in the sight glass height. 5.2. Data Analysis

For the low level steam steam pressure pressure samples samples,, a pressure pressure of 10 psig psig was chosen. chosen. As the steam pressure is directly correlated to the flow rate, decreasing the steam pressure below 10 psig would not boil water in the 1st effect in a timely timely manner. During experimentation, 10 psig psig steam st was capable of boiling water in the 1 effect within 1.5 hours. The rate that steam was produced produced nd in this effect, however, was insufficient to boil water in the 2 effect. During this sample, water in the 2nd effect only reached a temperature of 82.3°F, which was far from the boiling point (212°F (212°F at atmospheric atmospheric pressure). pressure). Therefore, Therefore, data could not be collected for the heat exchanger since since no vapor vapor was produce produced d to be condens condensed. ed. This This point was thus excluded excluded from from further further st analysis since an overall steam efficiency efficiency could not be calculated. calculated. Similar to the 1 sample, the nd 2 sample at 10 psig steam and 10 in Hg also could not be used in data analysis since the low pressure steam inlet only raised the 2nd effect temperature temperature to 138°F. Qualitative comparison comparison of nd these 2 samples indicates the benefits of operating the 2 effect under a vacuum; the vacuum helped the 2nd effect reach a higher temperature while the steam to the 1st effect remained the same. A summary of the data collected for these these 2 samples can be found in Table 4 below. Full data can be found in Appendix B. Table 4. Data summary for the 1st and 2nd trials Trial # 1 2 Vacuum P (in Hg) 0 10 Steam P (psig) 10 10 254 254 Steam T (°F) Effect 1 Initial T (°F) 79.4 73.6 200 201 Effect 1 Vapor T (°F) Effect 2 Initial T (°F) 74.3 75.6 82.3 138 Effect 2 Vapor Temp (°F)

Based on the findings discussed above, it was deemed impractical to operate the steam pressure















Vacuum Pressure (in Hg) Steam Pressure (psig) U1 (Btu/min °F ft 2) U2 (Btu/min °F ft 2) Uhe (Btu/min °F ft 2) Condensate Flow Rate (ml/min) Efficiency (%)

17 30 10.77 2 .7 6 1 .2 7 265 74.39

17 30 10.11 2.63 1.29 274 84.31

8 30 14.66 2.96 0.49 200 58.26

17 25 8.41 2.50 1.16 160 57.76

Table Table 5 shows shows the key calcul calculated ated variab variables les:: heat heat transf transfer er coeffic coefficient ientss (U1, U2, and Uhe), condensate flow rates, and efficiencies efficiencies for each trial. trial. Trending the vacuum and steam pressures pressures individually against each key variable resulted in data that produced no distinct correlation. Figures of these trends can be found in Appendix C. Since only 4 data points were collected, collected, it was was diff diffic icul ultt to know know wheth whether er a corr correl elat atio ion n exis existe ted d or if an outs outsid idee sour source ce was was caus causin ing g inconsistencies with the data. One potential source for this variation was in the data collection. collection. Samples Samples taken at the highest possible vacuum pressure experienced experienced fluctuations fluctuations in the vacuum pressure; pressure; the pressure pressure would cycle cycle from 17 in Hg down to 8 in Hg and vice versa. To account for these vacuum pressure changes, sample points were taken over complete cycles by starting at 8 in Hg and measuring the time until it returns back to 8 in Hg. A potential explanation for this cyclic cyclic action action is discusse discussed d in detail detail in Section Section 5.3. 5.3. Sampli Sampling ng while while the vacuum vacuum pressure pressure is varying is not ideal since some of the samples may have the vacuum pressure stay at the maximum for longer than than others. This would result in more water boiling in the 2nd effect and, theref therefore ore,, a higher higher q value value for the heat exchange exchanger. r. Since Since the heat heat transf transfer er coeffici coefficient ent is calculated from this q value, the coefficient may be artificially high as is the case in Trial #5. Heat transfer coefficients should remain constant regardless of steam and vacuum pressures under normal operation.10 If scaling is present within the effects, the heat transfer area will decrease. decrease. By not taking this scaling scaling into account and using the unscaled exchanger exchanger area in the calculations, the heat transfer coefficient will be calculated artificially low. Since both steam and vacuum pressures affect the system simultaneously, a true correlation bet betwee ween n the the heat heat tran transf sfer er coef coeffi fici cien ents ts and and the the pres pressu sure ress take takess them them both both into into acco account unt simultaneously. To accomplish this, correlations correlations were determined using using the ANOVA regression regression tool of Microsoft Microsoft Excel to trend trend how the pressures influenc influencee these values together. together. Linear

















Steam Pressure Coefficient Vacuum Pressure Coefficient Intercept R 2 Standard Error

0.31 -0.49 9.27 0.97 0.84

0.03 -0.03 2.39 0.87 0.12

0 .0 2 0 .0 9 -0.81 1 .0 0 0 .0 1

18.16 6.96 -400.61 0.98 0.07

0.04 0.02 -0.75 0.99 0.03

Efficiency in the system is affected in the same fashion as the heat transfer coefficient: both pressures affect it at the same time, and their their joint effect must be considered. The relationship between the pressures and efficiency can be seen in the regression line described in Table 6 above. Higher Higher steam pressures pressures increase increase the amount of steam produced in the 1st and 2nd effects and, hence, will lead to a higher efficiency efficiency.. Additional Additionally, ly, the higher the vacuum pressure, pressure, the nd easier it is for the steam produced in the 2 effect to be transferred to the heat exchanger and collection collection tanks. tanks. Lower vacuum vacuum pressures pressures may result in some of the steam condensing condensing in the effect effect before it can leave. This will decrease decrease the efficiency efficiency as more energy energy is required required to boil this water again. Condensate flow rates are also affected affected by both pressures. The regression for this correlation correlation can also be found in Table Table 6 above. The condensate condensate collection collection flow rates rates have both system system and experimental error associated with them. The system error is is due to the head built up in one of the collection collection tank drainage lines. This head would not drain from the line unless unless significant significant water water built up to force it out. This This head head of water led to some some possib possible le inaccura inaccuracie ciess in the measurement of the condensate flow rate. Experimentally, the setup of the collection tanks left certain certain areas of The vacuum presented presented difficulties difficulties in pulling pulling the water into the proper















pressure pressure swings swings would lead to inaccuracies inaccuracies.. Further Further investigatio investigation n needs to be performed performed to identify the maximum allowable steady state working pressure. 8 in Hg was the chosen sample as typical typical vacuum vacuum pressu pressure re swings swings with with the valve valve fully fully open settled settled at this this pressu pressure. re. As nd mentioned before, the vacuum pressure has significant effect on the operation of the 2 effect, so it is recommended that the vacuum pressure be optimized to its highest possible level. Another issue encountered with the vacuum system lies in the manual valve that controls the vacuum to the 2nd effect. In initial trials, trials, this valve was opened completely and the main vacuum line valves valves were throttled. throttled. Operating Operating in this mode led to some of the vapor from from the 2nd effect flowing flowing back through the vacuum vacuum line. Evidence Evidence for this backflow backflow was that the vacuum vacuum line became became very hot during operation. operation. Loss of steam through through the vacuum resulted resulted in lost heat and affected heat transfer calculations since not all of the steam created will pass through the heat exchanger. exchanger. Opening Opening this valve only a fraction fraction of the way in later later trials limited limited the amount of vapor flowing through the vacuum system resulting in less steam loss and more accurate results. Levels in the sight glasses on the 2nd effect and collection tanks were affected by the vacuum pressure pressure and boiling process process making accurate readings readings difficult difficult to obtain. During During boiling and collection, the levels in the sight glasses did not demonstrate accurate levels as air bubbles would form in them them and levels levels would move up and down in in the sight glass. glass. In the 2nd effect, initial readings were thus taken and compared to the final level once the effect stopped boiling and the water water settle settled. d. This This allowed allowed overall overall volume volume changes changes to be calcul calculate ated d but not timed timed sample sample volume changes. Anothe Anotherr issue issue with the system system that that had an influe influence nce on result resultss was that the thermo thermomet meter er















product. In order for the the study to be performed, the the height of the sight glass glass level against volume was calibrated as shown in Figures 4 and 5. The operation of the double-effect evaporator was characterized for a wide range of steam and vacuum pressures, and the values can be found in Table 5. It was found that the the steam pressure pressure and 2nd effect pressure have a positive correlation with the 2nd effect condensed vapor flow rate, with the steam pressure being the most influential parameter. parameter. In addition, addition, steam efficiency efficiency is greatly greatly affected by changes in steam and vacuum pressures. Namely, an increase in steam pressure and vacuum pressure increases the steam efficiency efficiency.. Moreover, Moreover, the two parameters parameters have the same significance significance in steam efficiency. efficiency. The heat heat trans transfer fer coeffi coefficie cients nts in the evapor evaporato atorr heat heat exchang exchangers ers were were determ determine ined d for differ different ent vacuum and steam steam pressures pressures as tabulated tabulated in Table 5. The patterns patterns indicate indicate an increase in heat transfer coefficient with increasing steam pressure for both effects. On the other hand, increasing the vacuum pressure causes a decrease in the heat transfer coefficient and a decrease in the vacuum pressure pressure causes an increase in heat transfer transfer coefficient coefficient for both effects. effects. Furthermor Furthermore, e, based based on data data collect collected ed the heat transfer transfer coeffic coefficien ientt for the heat heat exchang exchanger er increa increases ses with with increasing steam and vacuum pressures. 6.1. Recommendations

The results outlined in this report were derived from a few data points due to time constraints; theref therefore ore,, it is recomm recommende ended d that that more more experi experimen ments ts be perfor performed med with with repeti repetiti tions ons so that that conclusions could be drawn more reliably reliably and accurately. accurately. For this same reason, a medium level experiment should be performed to accurately characterize the operation of the double-effect evaporator. It is also recommended recommended that the double-effect evaporator be operated at a maximum steam pressure (30-35 in Hg) as it provides the greatest heat and reduces the time frame required















more significant scaling issues due to the increased viscosity of the product, producing a poor quality heat transfer coefficient. The backward-feed backward-feed arrangement arrangement has a lower operating operating cost, but a higher equipment equipment cost due to the multipl multiplee pumps pumps required required to work work against against the pressure pressure drop of the system system.. This This feed feed arrangement is also useful for viscous solutions, but does not produce the product concentration that is achievable in a forward-feed system.5 Parallel-feed splits the feed stream into each effect, and removes concentrated product from each effect. The economy of this method of operation operation is between that of forward- and backward-feed effects, but the concentrated product is not up to standards of the forward-feed, as it produces more of slurry.5 Finally, a single-effect evaporator uses more steam upfront to produce a concentrated product similar similar to that of a multiple-effe multiple-effect ct system. system. Generally, Generally, this steam cost is not an efficient efficient use of 2 money and multiple-effects are used for large-scale production. Based on the relative advantages and disadvantages of each, a multiple-effect system is the most economical for large-scale large-scale production. The feed system system depends on the required concentration of the product. In this case, the goal is to concentrate a 10% solution to a minimum of 90%. It was thus concluded that this degree of concentration is significant enough to warrant the system producing producing the most concentrated concentrated liquor. This system system has the potential potential for scaling issues, issues, but these risks are deemed to be allowable to meet the concentration requirements. requirements. Because this unit will be run on a temporary basis, it is not economically responsible to invest the higher startup















A more practical solution to this scenario was found in Careclean F Descalex P, a product made by Marine Care out of Holland.13 This product is a heavy duty acid descaler that contains sulphamic sulphamic acid. The descaler descaler comes as either a light-brown light-brown colored liquid liquid or as a completely completely water-miscible powder with the powder method being the preferred variety for this situation; the liquid version would require an extra circulation pump for the product while the powder can just be added in the water feed stream to the evaporator. The acid powder is highly effective effective even at room temperature. However it provides quickest scale removal results results when added as close to its o maximum temperature of 60 C as possible. This cleaner can be used with most common metals (except for zinc, aluminum, and galvanized materials) and is designed to not harm clean, nonscaled surfaces of the metal.13 Treatment length depends on the thickness and type of scaling but usually take less than 24 hours. An additional treatment treatment with Careclean Alkaline Alkaline Extra product may also be used to remove any calcium sulfate that may remain in the ev aporator.14 Other solutions were found for preventing scaling from occurring, but these are not ideally used for for remo removi ving ng buil builtt up scal scale. e. Once Once the the ship ship is succes successf sful ul in remo removi ving ng the the scal scalee in thei their r evaporator, further investigation should be taken to find the most cost effective solution for mainta maintaini ining ng the evaporato evaporatorr to prevent prevent scale scale buildu buildup. p. Exampl Examples es of such scale scale preven preventio tion n compounds compounds include include polyphosphat polyphosphate-lig e-lignosulf nosulfonate onate mixtures, mixtures, sodium polymethacr polymethacrylate ylate,, and surfactant compounds such as N-lauryliminodiacetic acid and any of its ammonium or alkali metal metal salts. salts.12 Each Each of thes thesee has has its its own advant advantage agess for for diff differ eren entt situ situat atio ions ns.. Sodi Sodium um polymethacrylate would be a sufficient solution for routine scale prevention in this particular case since it is works best in temperatures up to 240oF and against calcium carbonate.12,15 Another ideal solution would be to use a treatment program such as one designed by Nalco. Nalco Nalco’s ’s Nalfle Nalfleet et Maxi-v Maxi-v Plu treat treat t vic cifica cifically lly design designed ed for wat

















7. Nomenclature Symbol A1 A2 Aex C p F Hv hl L mcw q1 q2

Definition 1st Effect Heat Transfer Area (ft²) 2nd Effect Heat Transfer Area (ft2) Condenser Heat Transfer Area (ft2) Specific Heat Capacity Feed Mass Vapor Specific Heat Liquid Specific Heat Liquid Mass flow rate Mass flow rate of cold water Heat transfer rate of effect 1 Heat transfer rate of effect 2















1. Miletic, Marina. "Double Effect Evaporator Replacement - Rotation 1 and 2." Letter to Chris Brockman, Sudipto Guha, Cody Jensen, Victor Shum, Shannyn Stuart, Plant Supervisors. 23 Aug. 2009. MS. Roger Rog er Adams Chemical, INC., Urbana, Illinois. 2. Geankoplis, Christie J. Transport processes and separation process principles (includes unit operations). operations). Upper Saddle River, NJ: Prentice Hall Professional Technical Reference, 2003. Print. 3. Earl, R.L. "Multiple Effect Evaporation." Unit Operations in Food Processing . New Zealand Institute of Food Science and Technology. Web. 1 Sept. 2009. . 4. McCabe, Warren L. Unit operations of chemical engineering. Boston: McGraw-Hill, 2005. Print.















14. "Careclean Alkaline Extra." Marine Care B.V . Marine Care Baltic. Web. 28 Sept. 2009. . 15. Evaporator Saline Feed Water Treatment for Scale Control. W.R. Grace & Co, assignee. Patent 3,444,054. 13 May 1969. Print. 16. "Marine transportation chemicals: water treatment for evaporators/boilers/diesel engine cooling systems." Nalco systems." Nalco Company - Water Treatment and Process Chemical Technologies. Technologies. Nalco Company. Web. 28 Sept. 2009. . 17. "Physical characteristics of water." Thermexcel . June 2003. Web. 28 Sept. 2009. .















9. Appendix Appendix A – Calculation Method 21 Appendix B – Experimental Raw Data 22 Table B.1. Experimental data recorded for each trial 22 Table B.2. Calculated data for each piece of equipment 23 Appendix C – Regression Charts 24 Figure C.1. Vacuum Pressure vs. U1































Appendix A – Calculation Method

The following equations are used to calculate the flow rates, heat transfer, and heat transfer coefficients for the two effects and the heat exchanger in the system:















Appendix B – Experimental Raw Data Table B.1. Experimental data measured for each trial 1 2 3 4

Run #

V

P

(i H )

0

10

17

17

5

6

17

8















Table B.2. Calculated data for each piece of equipment17,18 Run # Effect 1

∆T (°F) Area (ft^2)

1 54 1 .8

2 53 1 .8

3 38 1 .8

4 37 1 .8

5 38 1 .8

6 27 1 .8















Vacuum Pressure Line Fit Plot 16.0 15.0















Vacuum Pressure Line Fit Plot 3.0





































































































FINAL Evaporator Final Report

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