CLIMBING-FILM EVAPORATOR

A Final Report for CM 4402

submitted to the Faculty of the

Chemical Engineering Department Worcester Polytechnic Institute

Worcester, MA 01609

October 24, 2017

______________________ Michael Bodanza

______________________Hayley Boigenzahn

______________________Martin Burkardt

______________________ Marcus Lundgren

CLIMBING-FILM EVAPORATOR Abstract This report delineates the planned procedure for determining the feasibility of employing an evaporator for concentrating a 10 wt% glycerol stream in preparation for the new Secret SolventTM process at the Beaumont facility. Testing took place at the Worcester R&D pilot plant with similar process conditions to the actual operating facility. Within this study we were particularly interested in assessing the feasibility, and if so, optimizing the process, given the constraints of the steam pressure and feed flow rate. In the end optimal conditions reflect on the maximum glycerol concentration as well as the cost of this endeavor. The optimal conditions found to maximize glycerol product concentration were at a pressure of 15 psig, and at a feed flow rate of 250 mL/min. This also affected total utility cost for steam, and cooling water.

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Table of Contents Abstract 1

Table of Contents 2

Introduction 4

Experimental Methods 5 Mass Balance 5 Component Balance 5 Energy Balance 5 Heat transfer rates, coefficient, losses 6 Determination of Flow Rate 6 Glycerol Concentration 7 Boiling-point Elevation 7 Cost Analysis 7 Response surface analysis 8 Evaporator Operating Procedure 8

Procedure 9 Safety Precautions 9

Results and Discussion 11

Energy Balance 14

Boiling Point Elevation 16

Cost Analysis 17

Error Analysis 18

Recommendations 19

References 20

Appendix 21 Sample Calculations 21

Cost 21 Mass Balance 21 Boiling Point Elevation 21

Raw Data 21

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Introduction Similar to other separation techniques, evaporation relies on the relative volatility of a mixture. Evaporation, however, is optimally employed for separations that require a product of concentrated thick liquor and an undesirable vapor that can be discarded. The basic design of climbing/falling-film evaporators consists of two phases: In the “climbing-phase,” the feed liquid is introduced at the bottom of the evaporation column and is heated by high-pressure steam, allowing partial vaporization to occur. This evaporation causes the vapor produced from the liquid feed to expand, shifting the feed’s physical properties toward that of the vapor phase. This allows a thin film of liquid to rise along the side of the evaporator-tube, and the shear force of the vapor rising will continue to push the thin film to “climb” the wall of the evaporation column. The vapor, lacking the desirable component of the feed, is then allowed to vent at the top of the column, and the unevaporated liquid, or the concentrated thin-film of liquor, is allowed to pass across to the “falling phase.” In the “falling phase,” the thin-film of liquid then flows downward due to gravitational forces. The main advantage of climbing/falling-film evaporation is the relatively short residence time, and the main drawback is the process’ energy consumption. Evaporation processes are temperature sensitive, and applicable to many industries including wastewater treatment and pharmaceuticals. This report is made to assess the feasibility of employing an evaporator for concentrating a 10 wt% glycerol stream in preparation for the new Secret SolventTM process at the Beaumont operating facility. Testing took place at the Worcester R&D pilot plant with similar process conditions to the facility. Within this study we are particularly interested in optimizing the process, given the constraints of the steam pressure and feed flow rate. In the end optimal conditions reflect on the maximum glycerol concentration as well as the cost of this endeavor. The climbing-film unit at this pilot plant consists of a long-tube vertical evaporator with an upward flow, and is comprised of two main parts: a shell-and-tube heat exchanger with concentrated liquid flowing on the tube-side, steam flowing on the shell-side, and a separator that removes entrained liquid from the vapor. In this evaporation process water is used as the solvent, and glycerol is the desired solute that must be concentrated to at least a 16 wt% solution for the development of the new aforementioned process. Objectives:

1) Measure specific gravity of product to find density/concentration of product. 2) Alter flow-rate/high-pressure steam conditions to measure, and optimize effect on

product concentration. 3) Complete heat and material balance to evaluate total heat loss.

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Experimental Methods Mass Balance Assuming no accumulation of mass or chemical reactions occur within the evaporator, the mass balance can be simplified to equation (1). Therefore, a generic mass balance can be done between the feed entering the system over operational time, equalling the mass over operational time of the output streams. This can be formulated as, F (feed) = W (distillate) + G (liquor) (1)

Where F is the feed stream flow rate, W is distillate stream flow rate, and G is liquor stream flow rate (all in units of mass/time). Feed flow rate was calibrated, and put to a setpoint, while outlet stream weights were measured. Component Balance Similar to overall flow rates, the mass of each individual component entering and leaving the system should remain constant, under the same assumptions of the overall mass balance. For example, the mass flow of glycerol entering the system must be conserved throughout the process, and equal the sum of glycerol in all product streams. This relationship can be described as follows, FxF = WxW + GxG (2)

Equation (2) represents a mass-balance on glycerol based on compositions in the feed, xF, the distillate stream, xW, and the liquor stream, xG. Feed composition of glycerol remains constant throughout this experiment at a value of 0.1 (or 10 wt%), and outlet stream weight percents were determined from specific gravity measurements. Energy Balance Under the assumption there is no accumulation of energy within the evaporator, and no chemical reactions are occurring, energy entering and leaving the system should remain constant as well. All heat provided from the pressurized stream utility is either transferred to the process stream, or lost to the environment due to material, and insulating inefficiencies. The energy balance can be described as the following,

(3) ΔH ΔH ṁ vap = F latent + Qloss

Where describes the mass flow rate of condensing steam in the system, is the enthalpy ṁ HΔ vap of vaporization of water, is the specific heat capacity of the product stream, is the Cp,F TΔ

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temperature change experienced by the process stream throughout the heat exchanger, and Qlossis the rate of heat lost to the environment. Mass flow rate and temperature will be measured systematically, and the enthalpy of vaporization of water will remain constant at 2.257 kJ/g. The specific heat capacity is assumed to be constant and can be found by interpolating between tabulated values of heat capacity for glycerol and water depending on stream composition in the feed. (4)(1 ) (x ) 4.184 ) 0.9) 221.9 ) 0.1) 5.96Cp,F = Cp,W − xF + Cp,G F = ( J

mol K* * ( + ( Jmol K* * ( = 2 J

mol K*

Heat transfer rates, coefficient, losses Heat transfer in a climbing-film evaporator is comparable to that of a shell-and-tube heat exchanger. The overall heat transfer rate is necessary for determining the evaporator capacity. The general formula for heat transfer in the evaporator is shown below, where U is the overall heat transfer coefficient. (5) UAΔTQvap = lm

The overall heat transfer coefficient is dependent on the individual heat transfer coefficients of the system. This includes the inside and outside fouling factors (hod, hid) as well as the inner and outer fluid film coefficients (ho, hi). The overall heat transfer coefficient is also related to the pipe geometry, specifically the diameters and the pipe conductivity. The below equation describes the relationship between the overall heat transfer coefficient and the aforementioned constants.

(6)

Determination of Flow Rate The mass flow rate of the steam condensation ( ), liquor (G), and distillate (W) streams were ṁ calculated using a timed collection. Empty collection buckets were pre-weighed, and then using the time and weight of fluid collected mass flow rate can be found in the following manner: (7)W = t

M −Msample bucket

Where Msample represents the mass of the sample for each of the three flow rates, Mbucket represents the weight of the empty collection bucket, and t represents the time over which the sample was collected.

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Glycerol Concentration The glycerol concentration in the distillate (xF) and liquor (xG) streams can be calculated using the known densities of each component (water and glycerol) at standard temperature, and then interpolating based on the composition of the streams to find the density of the mixture. This relationship can be described in the following manner: (8)(1 ) (1 ) (1 ) (x )ρw = ρw − xw + ρw = ρg − xG = ρw − xG + ρG G

Where and represent the calculated densities of the distillate and liquor streams ρw ρG respectively. At standard temperature, the densities of water and glycerol are 0.997 g/mL and 1.258 g/mL, respectively. Boiling-point Elevation Boiling point elevation is a colligative property that occurs for all solute-solvent systems. Boiling point elevation, as the name implies, describes the increase in the solvent’s boiling point once a solute is added. It occurs because the solute decreases the concentration of the solvent, which in turn increases its vapor pressure. Boiling point elevation is best measured experimentally for high solute concentrations, because the nonideality of the system makes it difficult to characterize. Generally, the equation used to describe boiling point elevation is (9)TΔ b = Kb * bsolute * i

where bsolute is the molality of the solution, i is the van’t Hoff factor (the ratio between the actual concentration of particles from a dissolved substance and the concentration of the substance as calculated by mass), and Kb is the ebullioscopic constant, which is dependant on the solvent. The van’t Hoff factor can often assume to be approximately 1 for nonelectrolytes in water. The ebullioscopic constant depends on the boiling point and molar mass of the solvent, as well as the heat of vaporization per mole of the solvent. For water as a solvent, Kb = 0.512 [°C*kg/mole]. Cost Analysis Since we must use a pre-existing column, we can assume that the capital cost will remain null. We can also assume that the feed cost, labor cost, and waste disposal costs stay approximately constant. Therefore, the variable cost of the column is mostly from utilities, which we can use as an optimization parameter. The steam available during the experiment remains at low pressure and can be assumed to cost approximately $29.29/1000 kg ($14.05/GJ)[2]. The process also uses cooling water, which is estimated to cost approximately $14.8/m3 ($0.354/GJ)[2].

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Response surface analysis Once our experimental data is obtained, we must evaluate the optimal operating conditions for the evaporator. We will plot the dependent variables - flow rate and steam pressure - against possible response variables, such as utilities cost and glycerol concentration. Based on these plots, we can draw conclusions about the optimal operating parameters for the evaporator.

Figure 1. Process-flow schematic of the Filmed-Evaporation Unit located in the Worcester R&D pilot plant facility. Evaporator Operating Procedure To determine the range of glycerol product concentrations in the product stream, experiments were performed in triplicate under three various operating steam pressures, and three various feed flow rates. Under each run condition, the product’s density and temperature were found using temperature measurements of the solution, and a specific gravity calculation detailed below. The general relationship, and optimal conditions required to produce the maximum glycerol concentration was found. Experimental procedure was conducted as follows:

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Procedure

1. First, drain the steam line to allow any trapped water to exit the line prior to experimentation.

2. Using the throttling calorimeter, located in the basement of GH116, measure the ambient pressure, temperature, and steam temperature.

3. Next, take a hydrometer reading to verify feed solution concentration (nominal 10% glycerol in water).

4. Then, the steam condensate, liquor collection, and vapor condensation buckets’ weights will be measured and recorded to later calculate the weight of bucket contents.

5. To start the first run, calibrate the rotameter by comparison to timed measurements of glycerol product flow rates.

6. Turn on the house cooling water for the condenser. 7. Set feed pump to a target flow rate to introduce glycerol feed to the system. 8. Turn on steam and set at a constant steam pressure. (Use extreme caution, supervision). 9. Allow the system to reach steady state. 10. Drain liquor and vapor condensate from streams, then close the liquid and vapor drains. 11. Put the steam bucket in place to capture condensate. Start the stopwatch, and record all

process information. 12. After a specified time is reached, shut down glycerol feed, and remove the heavy liquor

and vapor condensate buckets for measurement. 13. Weigh all samples. 14. Use an ice water bath to cool product solution and measure the specific gravity using the

density meter in the laboratory. Safety Precautions Maximizing safety and minimizing potential hazards should always be our highest priority. Thus, throughout this experiment, it is required that the appropriate personal protective equipment (PPE) be worn at all times. This equipment includes a hard hat, safety glasses, closed-toed shoes, and gloves (while handling chemicals, and hot materials). Material safety data sheets, or MSDSs, must be reviewed by each team member prior to operation. Contact a lab supervisor before turning on the steam and adjusting the steam pressure for the first time in order to ensure that we understand the system and can use it safely. Specific caution should be held when heat exchanger operation, due to burning risks from hot equipment and high-temperature steam that is purged from the system. A supervisor should be present during the first start-up of steam utilities. Pressure limits should also be kept in mind, and not exceed safe operational conditions. Caution should also be taken when handling any chemicals, to

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prevent spills, or any unwanted direct contact with skin or eyes. If an incident occurs, the affected area should be flushed at an eyewash station and a supervisor or an instructor should be notified immediately. Lastly, if any unanticipated conditions are observed, such as changes in material properties (melting, vibrating), or indications of a possible explosion, an instructor or supervisor should also be notified immediately, and emergency exit procedures should be followed.

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Results and Discussion One challenge encountered during experimentation was wash-over from the liquid in the evaporator column, or the “climbing” column, into the “falling” column designed to collect the concentrated glycerol product. The wash-over effect was created by a buildup of vapor pressure in the feed at the bottom of the evaporator column. Ideally, the steam will evaporate the top of the liquid in the column; however, if the conditions are not set correctly (feed flow, steam pressure) evaporation can occur further down in the column. From our trials, none of the flow rate/steam pressure combinations were able to prevent wash-over from happening. However, at the lower flows and steam pressures, the frequency of vapor buildup decreased. As flow and steam pressure increase, the frequency of wash-over also increases. Due to the wash-over effect, the concentrated product was repeatedly diluted with non-processed, and thus less concentrated, liquid. Another challenge encountered was the concept of accumulation within the evaporator column. The entire system was not purged between every each run, and thus mass balance data may not be resolved perfectly.

Mass Flow Rates, Week 1 - No Insulation Mass Flow Rates, Week 2 - Insulation

Run Feed kg/hr

Product kg/hr

Vapor kg/hr

dM kg/hr

Run Feed kg/hr

Product kg/hr

Vapor kg/hr

dM kg/hr

1 6.13 5.50 0.24 0.39 1 6.14 5.46 0.12 0.56

2 7.35 8.02 0.22 -0.88 2 7.37 8.40 0.12 -1.15

3 7.35 6.90 1.02 -0.57 3 9.21 8.40 0.18 0.63

4 7.35 9.07 0.18 -1.90 4 10.4 9.34 0.12 1.0

5 9.19 8.69 1.02 -0.51 5 12.3 10.3 2.0 0.0

6 10.4 10.2 0.18 0.04 6 13.5 11.9 2.0 -0.4

7 10.4 10.1 1.00 -0.72 7 15.3 14.1 1.9 -0.7

8 12.3 11.6 1.90 -1.27 8 15.3 12.8 3.2 -0.7

Table 1 & 2. Mass flow rates. In the above tables, the accumulation term, dM, is negative for taken as the outlet subtracted from the inlet. Therefore, negative values reflect circumstances where the wash-overs and residuals contributed to the output. In contrast, positive values indicate where product was lost in tubes due to the residual being trapped in piping. The errors resulting from these wash-overs and residual products in the equipment is evidenced by the system not being in steady state. This can be observed in the fact that the assumption made in Equation (1) does not hold (Table 1, 2).

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To see if there was a difference between the collected liquor samples (with wash-over) and straight distillate (without wash-over), samples had to be collected between wash-over episodes. A distillate sample was collected between wash-overs by purging the system immediately after a wash-over is observed and ceasing collection before another wash-over occurred. Overall, the collected liquor sample concentration data was similar (Table 3) to that of the distillate sample captured between wash-overs.

% Glycerol

Run Liquor Sample Distillate Sample Difference 3 9.51 10.27 +0.76 4 10.85 11.00 +0.15 5 12.26 11.85 -0.41 6 10.98 11.24 +0.26 7 12.12 12.24 +0.12 8 13.06 12.33 -0.73

Table 3. Glycerol percentage comparison between samples. This shows the percent glycerol differences between the collected liquor and distillate samples. Distillate samples started to be collected at the third run. In week 1, experiments were run for on average 10 minutes, with feed flow rates varying from 100-200 mL/min, and operating pressures from 1-15 psig. In week 2, a heating-jacket for the column was equipped to the evaporation column to reduce heat lost to the environment. Experiments were again for on average 10 minutes, with feed flow rates from 100-250 mL/min, and steam pressures 1-15 psig. The initial feed solution was continuously replenished with the products formed (concentrated liquor and condensate), and is assumed to remain at a constant feed composition because all components (glycerol, water) are recycled. The dependent variables altered throughout our experiment were feed flow and steam supply pressure, and their respective responses in terms of glycerol product concentration, and utility cost were analyzed. Based on these plots, we can draw conclusions about the optimal operating parameters for the evaporator. For one aspect of the experimental design, flow rates were varied while maintaining constant steam pressure to observe the effect of feed flow on the product glycerol concentration. This was done in both weeks (with and without the steam jacket). For the first week, flows between

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100-170 mL/min were investigated at 1 psig of pressure (Fig. 2a). From this, it is apparent glycerol product concentration decreases when increasing flow rate without adjusting the steam pressure. This makes sense as a greater flow would increase the height of the liquid column in the evaporator. This resulted in a large amount of wash-over when there was a vapor buildup, and ultimately the dilution of the liquor. Another trial was run with flows between 200-250 mL/min under 10 psig pressure conditions (Fig. 2b) Here too, a negative effect on glycerol concentration is observed. Both of these trials are illustrated in Figure 2 below. (a) (b)

Figure 2. Flow rate vs Glycerol Concentration, no steam jacket equipped. The effect on glycerol product concentration caused by varying flow rate was observed under 1 psig (left) and 10 psig (right) pressure conditions. These runs were both completed without the steam jacket equipped. In order to compare glycerol concentration with respect to varying steam pressure, we completed a trial of the runs at different operating pressures and constant flow rate. This was done for 100-170 mL/min flows at both 1 psig and 6 psig pressure conditions. As aforementioned, product concentration generally decreases with higher flow rates. The negative trend observed further reinforces the necessity of re-adjusting operating conditions when a parameter is adjusted. The evaporator performance to concentrate is heavily dependent on both the feed flow rate and steam pressure. The same study was run on week two, investigating the effect of feed flow on the liquor glycerol concentration. As mentioned before (Fig. 2), it was found increasing the feed flow while maintaining a constant steam pressure negatively impacted the glycerol product concentration. However, when this study was repeated (same steam and feed flow conditions) with an insulated jacket around the evaporator column, a positive trend was observed (Fig. 3). This is most likely due to a more efficient and directed heat transfer between the steam and the liquid column. Without the jacket, heat is lost to the environment (Qloss), but when insulated the same heat energy is better contained and directed towards evaporating the liquid column (ΔHvap). It is also

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observed that, for the data points that do overlap, the system run at 6 psig results a higher concentration in the glycerol product. (a) (b)

Figure 3. Flow rate vs Glycerol Concentration, steam jacket equipped. The effect on glycerol product concentration caused by varying flow rate was observed under 1 psig (left) and 6 psig (right) pressure conditions. These runs were both completed without the steam jacket equipped. Energy Balance For an ideal system, the energy balance in the evaporator is fairly straightforward. The energy of the feed and the energy of the steam enter the system, and energy of the product, the condensate (from the product condenser) and the steam condensate leave the system. However, our system is nonideal, especially the data gathered on the first day before the insulating jacket was added to the column because a large amount of heat was lost from the system to the surroundings via routes that are not easily measured, such as through the walls of the column or the pipes carrying the condensate. The energy balance is easier to solve if the steam enters as saturated steam and exits as saturated liquid, because then its temperature and specific enthalpy can be found knowing only the pressure. According to the thermometer in the basement of the lab, the temperature of the inlet steam was approximately constant at around 100℃. We attempted to measure the temperature of the steam condensate by measuring its temperature as it exited the system at the drain, shown in Tables 5 and 6. At higher pressures, the steam condensate was a higher temperature, and at the lowest pressure used the temperature of the steam condensate was about 35℃ below the steam inlet temperature. From this, we can conclude that the steam condensate was not a saturated liquid. We also observed that the amount of steam condensate is greater at higher pressures, which makes physical sense because we would expect the steam to be moving through the system faster at higher pressures.

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Pressure (psig) 1 10 15

Saturated Steam Temperature (oC)

101.83 115.2 120.96

Latent heat (kJ/kg) 2251.33 2215.48 2199.47

Table 4. Latent heat and temperature of saturated steam at various pressures. Assuming that the latent heat of the steam is approximately equal to what it would be if we were dealing with saturated steam and that the Cp of water is roughly constant and equal to 4.219 kJ/kg*K at 100℃, we can calculate some information about the energy change of the steam and the condensate collected from the system. The constant Cp assumption is reasonable considering how many other larger sources of error there are in the data.

Trial Outlet Steam

Temp (℃)

Feed Temp (℃)

ΔT (℃) Steam Enthalpy change (kJ)

Latent Heat Steam (kJ)

Steam Energy

Change (kJ)

1 65.4 20.55556 34.6 72.99 1125.665 1198.654

2 67.6 20.55556 32.4 75.18 1238.232 1313.414

3 67.6 - - 82.02 1350.798 1432.815

4 68.6 23.33333 31.4 78.16 1328.285 1406.446

5 82.8 - - 42.81 2348.409 2391.223

6 83.1 25.83333 16.9 75.57 2304.099 2379.678

7 82.3 26.66667 17.7 77.66 2370.564 2448.227

8 96.3 28.33333 3.7 16.70 2353.433 2370.136

Table 5. Steam Condensate Energy Change for Week 2 Trials. Although it is possible to calculate some of the energy changes in the steam and the condensate, it is virtually impossible to create a true energy balance because there is so much heat loss from the steam that is unaccounted for. Since we had no way to measure the outlet temperature of the steam while it was still in the vapor phase, we are accounting for several steps of energy change that are occurring as the steam leaves the main system and travels down the pipe to the drain, which is one source of error.

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Trial Condensate Temperature (℃)

Condensate Latent Heat (kJ)

Condensate Enthalpy (kJ)

Condensate Energy Change (kJ)

1 83.61 45.0266 2.919548 47.946148

2 71.94 45.0266 2.733912 47.760512

3 76.11 67.5399 4.100868 71.640768

4 87.22 45.0266 2.649532 47.676132

5 100 44.3096 23.94704 68.256644

6 101.11 731.1084 24.24237 755.350774

7 101.1 753.2632 24.64318 777.906379

8 101.67 725.8251 8.273459 734.098559

Table 6: Condensate Energy Change for Week 2 Trials. We can observe several trends in the energy estimates, such as that the higher the steam pressure and flow rate, the higher the estimated energy change from the steam. Since we also noticed a general trend of greater steam pressure and flow rate resulting in higher separation, we can tentatively conclude that higher heat duties result in higher separation, however, this is also dependent on the amount of wash-over, which strongly affected our results. Boiling Point Elevation Since we know the mass of product and the amount of glycerol in it, we can easily calculate the boiling point elevation of the products if we assume that the van’t Hoff factor is approximately 1, which is a standard assumption for nonelectrolytes in water. (See Boiling Point Elevation in Experimental Methods for a more detailed explanation of the van’t Hoff factor.) Thus, the equation for boiling point elevation reduces to:

TΔ b = Kb * bsolute

where Kb is a solvent dependent constant called ebullioscopic constant and bsolute is the molality of the product. For water as a solvent, Kb = 0.512 °C*kg/mole, and the molality is calculated from experimental data. Using 290℃ as the standard boiling point for glycerol, Table 7 below shows the boiling point elevation for the various trials: The boiling point elevation in the glycerol-water solution produced by our experiments is relatively small, never exceeding 1℃. The maximum boiling point elevation occurred in the

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solution with the highest concentration of glycerol, as expected, which was also the experiment performed at the highest steam pressure. This implies that at higher steam pressures, although the separation might be greater, more heat is required to reach the boiling point.

Trial Product Glycerol Water Glycerol Glycerol Molality ΔTb BP

Units kg % kg kg moles kg watermol glycerol °C °C

1 0.91 11.065 0.809 0.101 1.093 1.351 0.692 290.69

2 1.4 11.006 1.246 0.154 1.673 1.343 0.688 290.69

3 1.4 10.578 1.252 0.148 1.608 1.284 0.658 290.66

4 1.59 10.848 1.418 0.172 1.873 1.321 0.676 290.68

5 1.72 12.259 1.509 0.211 2.290 1.517 0.777 290.78

6 1.98 10.978 1.763 0.217 2.360 1.339 0.686 290.69

7 2.4 12.120 2.109 0.291 3.159 1.498 0.767 290.77

8 2.13 13.056 1.852 0.278 3.020 1.631 0.835 290.83

Table 7. Boiling Point Elevation. For various trials. Cost Analysis A cost analysis was performed using the cost of low pressure steam ($29.29/1000 kg[2]), and the calculated flow rate of steam using a mass balance. Steam cost was estimated for three steam pressures, 1 psig, 6 psig, 10 psig, at various flow rates, because those operating conditions had the most data points for comparison. Steam cost was based off of a timescale of one 10-minute run. From this it is clear to see that an increase in pressure results in both the cost (for a 10 min. operation) and the glycerol concentration in the product to increase proportionally. There is also a clear point of intersection between both trends, which shows one possible optimization point (near 10 psig). At this operating steam pressure, the highest glycerol percentage can theoretically be reached at the lowest steam cost. It is recommended however more operating pressures are tested as well for longer durations to verify a scale-up would carry the same trend.

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Figure 8. % Glycerol vs. Steam Utility Cost. This graph compares the average steam utility cost for a 10 minute run to the percentage of glycerol in the product concentrate for various steam pressures. Error Analysis Error bars were not included on data presented because with as few data points as collected, and as many sources of error which exist, it is too difficult to estimate, or propagate, error through all calculations. Instead, qualitative sources of error were outlined in this text, and main sources of error are summarized below. Main sources of error include:

● Wash-over of the feed stream into the concentrated glycerol product stream. ● Heat loss to the environment (more prevalent in data without heat jacket equipped). ● Unbalanced material balance due to the accumulation of liquid in the column.

With the buildup of vapor beneath the liquid column, many instances of wash-over occurred throughout operation. As a result, the liquor was diluted with a lower concentrated glycerol solution, heavily impacting the final product concentration. Heat loss was also an observed operational complication. With an un-jacketed evaporator column, a large portion of heat energy was lost to the ambient air environment. Heat loss to the environment was one of the contributing factors to wash-over, because the steam could not evaporate the rising liquid column fast enough.

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Recommendations Based upon the preliminary dataset collected through testing at the Worcester R&D pilot plant facility, it is suggested that the operating conditions, or equipment are deemed unfeasible in producing a concentrated 16 wt% glycerol stream from a 10 wt% glycerol feed stream. The highest concentration achieved during our experimentation was 13 wt% glycerol, using a flow rate of 250 mL/min, and under 15 psig pressure conditions. We found that, using a jacketed-evaporation column, an increase in operating flow and operating pressure both correlate to increases in glycerol product concentration. This means that although minimum design requirements were not satisfied in this pilot study, it is recommended that the process be optimized keeping in mind the general cost of utilities, and this trend in product concentration. In terms of the general cost of utilities, as feed flow rate and operating pressure increase, so do heating and cooling requirements. Our data is recognized as potentially diluted, however, comparison of normal distillate samples to distillate samples collected in between occurrences of wash-over resulted in similar values for glycerol product concentration. Cost and error analysis, and optimization were difficult to perform due to various sources of error, and since experimental data suggested that design requirements were unfeasible given current operational conditions and equipment available.

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References McCabe, W.L., Smith, J.C., and Harriott, P. Unit Operations of Chemical Engineering, 7th Ed.

McGraw-Hill, New York (2005). Perry, R. H., Green, D. W. Perry’s Chemical Engineers’ Handbook, 8th Ed. McGraw-Hill, New

York (2008). Saturated Steam Table by Pressure. (n.d.). Retrieved November 08, 2017. Turton, R., Bailie, R.C., Whiting, W.B., Shaeiwitz, J.A., and Bhattacharyya, D. Analysis,

Synthesis, and Design of Chemical Processes, 4th Ed. Pearson, New York (2012). Welty, J. R., Wicks, C. E., Wilson, R. E., and Rorrer, G. Fundamentals of Momentum, Heat, and

Mass Transfer, 4th Ed. Wiley, New York (2001).

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Appendix Sample Calculations Cost Cost of steam for a 10 minute operation ($29.29/1000 kg steam) = ($0.03/kg steam)*(4.14 kg/hr steam at 1 psig)*(60 min/hr) * (10 min operation duration) = $0.02 cost of steam for 10 min run Mass Balance Product Flow rates (1.84 kg total weight - 0.91 kg bucket)/(609 seconds)*(3600 s/hr) = 5.50 kg/hr of glycerol product (0.95 kg total weight - 0.91 kg bucket)/(609 seconds)*(3600 s/hr) = 0.24 kg/hr of vapor Feed flow rate (100 mL/min) * (1.0214 g/mL) * (1/1000 kg/g)*(60/1 min/hr) = 6.13 kg/hr Balance (6.13 kg/hr of feed) - (5.50 kg/hr of glycerol) - (0.24 kg/hr of vapor) = 0.39 kg/hr of negative accumulation Boiling Point Elevation 0.91 kg total) 0.11065 f raction glycerol) 0.101 kg glycerol( * ( = 0.101 kg glycerol) 1000 g/kg) 92.09382 g/mol) 1.093 mol glycerol( * ( * ( = .093 mol glycerol/(0.91 .101 kg water) .351 molal1 − 0 = 1 T 0.512 ℃ g/mol) .351 molal 0.692 ℃Δ b = ( * k * 1 = oiling P oint 290℃ 0.692℃ 2.692℃B = + =

Raw Data In our document, we recorded trial number. For each run we recorded steam pressure, feed flow rate, and operating time. Additionally, we measured total product, condensate, and steam condensate weight to perform a mass balance on the system. We also collected the temperature of the feed, condensate of the column, and steam outlet temperature. Lastly, the specific gravity of our product sample was measured and used to calculate product concentration.

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Table 8: Raw data for week 1 without insulation.

Table 9: Raw data for week 2 with insulation.

Table 10: Raw temperature data with insulation.

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Table 11: Concentration of Product without Insulation.

Table 12: Concentration of Product with Insulation.

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