Tritium Removal by Membrane Separation

University of Tennessee, Knoxville TRACE: Tennessee Research and Creative Exchange Chancellor’s Honors Program Projects Supervised Undergraduate Student Research and Creative Work Spring 4-2001 Tritium Removal by Membrane Separation Courtney Georgette Woods University of Tennessee-Knoxville Follow this and additional works at: https://trace.tennessee.edu/utk_chanhonoproj Recommended Citation Woods, Courtney Georgette, "Tritium Removal by Membrane Separation" (2001). Chancellor’s Honors Program Projects. https://trace.tennessee.edu/utk_chanhonoproj/506 This is brought to you for free and open access by the Supervised Undergraduate Student Research and Creative Work at TRACE: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Chancellor’s Honors Program Projects by an authorized administrator of TRACE: Tennessee Research and Creative Exchange. For more information, please contact trace@utk.edu. University Honors 458 Senior Honors Project Tritium Removal by Membrane Separation Final Report Courtney G. Woods University Honors Program University of Tennessee Knoxville, Tennessee 37996-2200 Submitted: 4124/01 UNIVERSITY HONORS PROGRAM SENIOR PROJECT - APPROVAL Name: em uttne(j Lctt:ds 1 EiYjirffr({ r;:j Department: CremiCD I Faculty Mentor: l)rz 83u I 6tm IurnQJu' College: I PROjECT TITLE: (Z-tMO ut3i JlLlf,lAAtvl l£~fr I have revi~ is a project Signed: Date: om ~ KuJ rYl&~ this completed senior h\>n01;s thesis with this student and certify that it ensu.fywit hZ'lvel undergraduate research in this field. 17 /, Lf/3 U;'0/ Comments (Optional): "v tv 'f<v6 Faculty Mentor Abstract A 13-stage recycling cascade polyphosphazene membrane process was designed to separate tritium from water. The waste water stream is fed to the separation process at a flowrate of I gallon per minute and has an activity of 240,000 pCi/L (9.35e-11 g/min). This is twelve times the permissible activity level, as specified by the Environmental Protection Agency (EPA). The membrane separation process is designed to remove 95.00% of the tritium into the permeate, with 99.90% of the flow as EPA approved clean water (483,626 gal/yr). The process is contained in a 17 m 3 glove box (operated at negative pressure) to prevent tritium contamination to the environment. The feed is filtered to remove calcium carbonate, and the solid waste is mixed with the tritium from the permeate into cement that is placed in 55 gal stainless steel barrels. Should any tritium leak into the glove box, a cryogenic cooler will condense the water from the air and return it to the cement mixer. The barrels will be shipped to a landfill (35 barrels/yr). The net present value of for this preliminary design is -$10,113,610 (most of which is the cost oflabor). 1 Economic Basis Start-up Year Project Life MARR Equipment Costs: Fixed Costs: Feed Pump (2.5 hp) Vacuum Pump (1 hp) Stage Pump (2.5 hp) Cryogenic Unit Solid Filter Concrete Mixer Glove Box 2002 20 12% years $352 $1,500 $352 $50,000 $4,950 $19,000 $12,950 Variable Costs: Membrane Module Concrete 55-Gallon SS Drums Waste Disposal (includes shipping) Gloves for Glove Box Liquid N2 Electricity $97 $0.38 $250 $33.42 $120 $0.80 $0.04 m2 gallon each gallon pair gallon kWhr 8 @ $40,000 1 @ $60,000 100% of Salary 30% of Salary 10% of Salary 15% of Labor Cost year year Labor: Technicians Engineers Labor Overhead Benefits Social Security/Worker's Compo Supervisors Net Present Value of Project -$10,113,610 ii Process Design Basis (Preliminary Design) Plant Capacity (Clean Water) Operating Factor 483,626 93% (8150hrs/yr) gallon/year Designed for: 95.00% HTO Removal 99.90% Retentate Flow Feed: Flow Rate Density Feed Composition: H 20 HTO CaC03 gallon/min glcm 3 Solid Filter: Removal of Solids Life Retentate: HTO must be less than EPA max. of 20,000 pCi/L Flow Rate Retentate Composition: H 20 HTO CaC03 99.82 2.24e-12 0.18 mol% mol% mol% 100% 20 years 0.989 gallon/min 99.99+ 1.12e-13 mol% mol% mol% o Permeate: HTO must be less than 0.5% per Liter for safe handling Flow Rate 9.90e-4 Permeate Composition: H 20 99.99+ HTO 2.13e-9 o Membrane Module: Life Temperature Dimensions: Length Diameter Packing Density Separation Factor Pressures: i1P from Feed to Retentate Feed Retentate Permeate Thickness Area per Stage Units per Stage # of Stages Recovery basis for water permeablility Permeance gallon/min mol% mol% mol% 2 years 4 °C 1.0160 0.2002 690 2.33 0.681 3.26 2.58 1.00 1 248 12 13 15% 7.68 iii atm atm atm atm /lm m2 mol/(min m 2 atm) Process Design Basis (cont.) Cryogenic Condenser: Liquid N z Consumption Air Flow Rate Air Humidity Life 1 0.17 20% 20 gal/day m 3/day 5 90% 1 years 5 90% 2.5 years Glove Box: Size Box Life Glove Life # of glove ports 17 20 1 10 m3 years year Concrete Mixer: Capacity Life 0.59 20 m 3/min years years Pumps: Vacuum: Life Efficiency Capacity Centrifugal: Life Efficiency Capacity iv hp hp Process Flow Sheet (Overall System) Air evacuated into the Atmoshpere Leakage Stream from Glove Box T rrtiated Water Source Feed Stream T-1 Vacuum pump feed G Glove Box Clean Water leaving system Cement Supply Stream Processed Waste Stream (0 Air Flow from negative pressure Stainless Steel Barrel Outside glove box Flow Diagram of Titriated Water System v Process Flow Sheet (Inside Glove Box) Glove Box 81 Vacuum pump I eed Solid Wasste Filter 8 F e d Stream [:>! I ( ~ I I ) leed pump Solid Waste tream Cryo enic Liquid V aste Stream G 0 8 (0 Cement mixer y 8 Cement mixer waste feed Cement Proce sed Waste 8 Clean water I aving the system 8 0 Cement Stream Membrane Separaton System Membrane Feed G _iL-l- A irflow from negative Pressure -L-I- Stainless Steel Barrel vi Tritiated'" aste Water • Material Balance Stream Component HTO H2 O CaC03 Air 1 2 3 4 Feed Stream Retentate Permeate Solid Filter Air in Mass (9) 9.35E-11 3747.15 37.85 Mass (9) 4.68E-12 3743.4 Mass (9) 8.80E-11 3.75 Mass (9) Mass (9) 5 6 Vacuum Feed 7 Cryo. Return 5.53E-4 Mass (9) Mass (9) 1.05E-18 1.05E-18 5.53E-4 5.53E-4 1.42E-01 1.42E-01 8 Membrane Feed 9 Mixed Waste 10 Cement Supply 12 11 Cement processed Clean Air Mass (9) 9.35E-11 3747.15 Mass (9) 8.80E-11 3.75 37.85 Mass (9) Mass (9) 8.80E-11 3.75 37.85 37.85 1.42E-01 Cement Totals 3785.00 Mass In (9) 3941.14 3743.40 3.75 37.85 1.42E-01 1.42E-01 5.53E-04 Mass Out (9) 3941.14 vii Mass (9) 3747.15 41.60 156 156 156.00 197.60 0.14 List of Assumptions Feed • • • • • • • Flow of 1 gal/min Tritiated Water enters from reservoir at 4°C HTO is 12 times EPA minimum of20,000 pCiIL Solids (CaC0 30nly) make up 1% by weight of feed stream and are 50-200llm in diameter and density of 2gIL Feed density is that of H20 Cesium is removed upstream of tritium removal process Solids filter removes 100% of solid particles Effluent • HTO leaves retentate at EPA max of 20,000 pCilL • HTO leaves permeate at max of 0.5% per Liter Membrane • Membrane life of2 years 2 • Packing density is 690 m /m 3 from Seader • Model membrane from Hwang and Kennemeyer using constant cut and constant overflow • Separation factor is 2.33 (best case from paper 43% reject) • Operating pressures from paper - Pp = latm, PF = 3.26atm, PR = 2.58atm • f.P = 0.681 atm = PF-PR from vendor, over operating range of 4.76 to 27.22 atm and PP is 1 atm • 15% recovery through membrane yields permeance of7.68 (mollm2 min atm) from Osmonics (using MgS04 also used for water) • Membrane Thickness is 1 micron • Each stage consists of 12 units Misc • • • • • • • Process life of 20 years 1% of glove box volume leaks into system (requires vacuum pump) 1% of HTO leaks into glove box during maintenance periods, there are 11 maintenance periods in 20 years, thus 11 % leakage over 20 years, therefore 0.55%/year All equipment except membranes and pumps last entire project life Assume plant up time of 8150 hours per year (~93%) All pumps operate at 90% efficiency Unit to be installed in pre-existing facility Economics • Net Present Value • Private consultant with 12% interest rate • Disposal cost is $1 00-$500/ft3 , assume $250 (includes shipping) • No depreciation Labor • • • • • • 8 operators on 4 rotating shifts (2 per shift) 1 engineer and 1 supervisor Employee benefits = 30% of salary Employee overhead = Employee salary Worker's Comp & S.S. = 10% of salary Supervisor Salary = 15% (Technician + Engineer Salary) viii Table of Contents Abstract .......................................................................................................................................................................... i Economic Basis ............................................................................................................................................................ ii Process Design Basis (Preliminary Design) ................................................................................................................. iii Process Flow Sheet (Overall System) ........................................................................................................................... v vi Process Flow Sheet (Inside Glove Box) .............................................................. Material Balance ......................................................................................................................................................... vii List of Assumptions ................................................................................................................................................... viii Table of Contents ......................................................................................................................................................... ix List of Figures ............................................................................................................................................................... x List of Tables ............................................................................................................................................................... xi List of Tables ............................................................................................................................................................... xi Introduction and Background ....................................................................................................................................... 1 Problem Statement ............................................................................................................................................ 1 Background ....................................................................................................................................................... 1 Mathematical Model ......................................................................................................................................... 2 Process Equipment and Operating Conditions .............................................................................................................. 6 Membrane ......................................................................................................................................................... 6 Filter .................................................................................................................................................................. 6 Cryogenic Condenser ........................................................................................................................................ 7 Auxiliary Equipment. ........................................................................................................................................ 7 Results and Discussion ................................................................................................................................................. 8 Membrane Process ............................................................................................................................................ 8 Economic Analysis ........................................................................................................................................... 9 Conclusions ................................................................................................................................................................ 11 Nomenclature .............................................................................................................................................................. 12 Literature Cited ........................................................................................................................................................... 13 APPENDIX A. Membrane Specification Sheet from Osmonics ................................................................................ 14 APPENDIX B. EPA Regulations for Drinking Water.. .............................................................................................. 17 APPENDIX C. Membrane Curves ............................................................................................................................ 18 APPENDIX D. Cost Tables ........................................................................................................................................ 20 0 ••••••••••••••••••••••••••••••••••••••••••••••••••••••• ix List of Figures Figure 1. Schematic of a membrane separator .............................................................................................................. 2 Figure 2. Schematic of a countercurrent cascade membrane separation process .......................................................... 3 Figure 3. Cash Flow Diagram ....................................................................................................................................... 9 Figure 4. Tritium Equilibrium Curve .......................................................................................................................... 18 Figure 5 . McCabe-Thiele Method to Determine Number of Stages ........................................................................... 19 x List of Tables Table 1. Summary of Membrane Conditions (per min basis) ....................................................................................... 8 Table 2. Initial Equipment Cost .................................................................................................................................. 20 20 Table 3. Labor Costs ............................. Table 4. Annual Variable Costs .................................................................................................................................. 20 Table 5. Annual Electricity Costs ............................................................................................................................... 20 Table 6. Membrane Cost (2 year life) ......................................................................................................................... 21 Table 7. Pump Cost (5 year life) ................................................................................................................................. 21 Table 8. Net Present Value Analysis .......................................................................................................................... 21 oo • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • xi Tritium Removal By Membrane Separation Introduction and Background Problem Statement A wastewater stream from a nuclear plant has been identified as containing tritium along with some solid waste particles. Tritium is a radioactive isotope of water, 3H, which causes little hazard or risk at low concentrations and in gaseous form. At higher concentrations, tritium poses a more serious threat, especially when suspended in water, because it can be ingested or absorbed into the body easier. The Environmental Protection Agency (EPA) requires that all waste streams released to the environment must meet drinking water standards (see Appendix B). The maximum contaminant level as specified by EPA is 20,000 picocuries per liter. This limit corresponds to the maximum permissible body burden and maximum permissible concentration of radionuclides in water for occupational exposure. Therefore, the waste stream from the nuclear plant must be purified to comply with these standards. Currently the tritium concentration in the stream is 240,000 picocuries per liter, which is twelve times that of the (EPA). A separation process is to be designed that will effectively remove tritium from the water. The entire operation will be housed in a large glove box that will allow the operators protected access to the process. The glove box will be operated at negative pressure so that tritium does not leak into air outside the glove box. A technique for recovery of the tritiated air must be identified. The vacuum causes a small air leak into the box, through apertures around the gloves. This too must also be accounted for in the process design. The size, cost and optimum operating conditions of this process are to be evaluated for a project life of20 years. Background Because tritiated water (HTO) differs from normal water only in ways affected by mass, there are a limited number of separation techniques available that yield high separation factors. Some that have been identified are electrolysis-catalytic exchange and water distillation, but require very high concentrations of tritium, and high capital and operating costs. Some work using polyphosphazene membranes for tritium separation has already been done, and much of the results of our research is based on these studies. Nanoporous membranes were employed, which suggests that polyphosphazene membranes are perm-selective to tritium. This suggests that most of the tritiated water passes through the membrane as the permeate, while most of the normal water passes over the membrane as the retentate (or reject). Figure 1 shows a schematic of a membrane separation system. To determine the separation that can be achieved, the system must be mathematically modeled. Through mathematical modeling, one can determine the size of membrane process required to achieve the desired separation. Retentate Feed Membrane Separator Permeate np, YPA, Pp Figure 1. Schematic of a membrane separator. Mathematical Model The previous research cited in The Journal of Membrane Science, provided a basis for the initial calculations. Also, membrane specifications were derived from data obtained from Osmonics TM. Given the permeate flow rate and membrane size, the flux, N, of tritium can be calculated by (1) where Vp is the molar flow rate and A is the area of the membrane. Because the membrane thickness is known, as well as the range of pressures at which the system can be operated, the permeability is determined using the following equation (Seader and Henley) PMA where ~P _ Nl m - M (2) is the change in pressure and 1m is the membrane thickness. Permeability is used to calculate the area of the membrane used in each stage. 2 Cascading operations are often used when a high degree of separation (that cannot be achieved in a single stage process) is desired. Figure 2 is a schematic of a countercurrent recycle cascade of membrane and illustrates the flow from each stage. Penneate /\ ..... Ftl';~i2\j!/ S / It I...... • j' Feed Stage t-- ± /T. . . - - Feed N-l !W!!JX ;.!li\/J~ 1'~ ,...... N " ':'<7T ... .1 t-- ,- \V Retentate Figure 2. Schematic of a countercurrent cascade membrane separation process The retentate and permeate of each stage are recycled in countercurrent flow. The feed stage is usually positioned in the middle of the operation. An enriching section concentrates the highly permeable component, while the stripping section concentrates the component with the low permeability. The permeate of the first stage and retentate of the last are withdrawn. There are three methods of operating cascade membrane processes: 3 1. Constant cut, 8, constant overflow 2. Constant cut, varying overflow 3. Varying cut, varying overflow. The cut, 8, is the ratio of permeate flow rate to feed flow rate: n cut , 8=~ (3) nF By keeping the cut and the overflow constant, all calculations are greatly simplified. In addition, fewer stages are required for a given separation. For this reason, the first case was selected over cases two and three. A disadvantage to using case one is that a larger amount of membrane is required because each stream remains constant. Also, the permissible range of cut values is Y2 ::;; 8 ::;;. 0 (Hwang and Kammermeyer). The number of stages required to achieve the desired separation, can be determined graphically using the McCabe-Thiele method. This method involves stepping off between the equilibrium line and the operating line. The equilibrium line is obtained using the following equation (Porter): Xn y=----n a + (1- a)xn (4) The operating line for the enriching section is (Hwang and Kammermeyer): Enriching: where Y n+l r= = rxn (1- r)x D (5) 1-8 8 (6) To obtain the operating line for the stripping section, a value for the mole fractions of the bottoms is plotted. Another point is plotted where the enriching section line intersects with the mole fraction in the retentate of the feed stage. A line drawn between these two points represents the stripping section. A 45° line is plotted and equilibrium stages are stepped off a staircase from the top (XD' yD) to the bottom (XB' YB). One stage is represented by a step on the staircase, which goes from the operating line to the equilibrium line, then back down to the operating line. 4 The membrane area is related to the mole fractions, pressures and permeability by the following equation: A= YPAnp PMA(XRAPR - YPAPp) (7) This area is calculated for the feed stage only. To obtain the membrane area for the entire process, simply mUltiply by the number of stages. This will be used to size the process and generate some capital and operating cost estimates for the process. 5 Process Equipment and Operating Conditions Thorough assessment of the type of equipment necessary and operating conditions has been conducted. Along with the necessary components for the separation process, auxiliary equipment has also been identified. Appendix provides schematics, product specifications and detailed descriptions. Membrane A polyphosphazene membrane is examined for use in separating tritium from water. Several membranes, configured into hollow cylinders, are placed into modules. This configuration offers a large surface area for separation in a small volume. The modules are representative of one stage. Therefore, the total number of modules, and thus the size of the process, is largely dependent on the number of stages. The modules will operate much like heat exchangers, in that the streams are fed to each module shell side. The retentate also leaves shell side, while the permeate leaves tube side. Based on the research conducted by Nelson, the membrane thickness is about 1 micron. The feed, retentate, and permeate are operated at pressures of 3.26, 2.58 and 1.00 atm respectively. The optimum operating temperature is about 4°C but should not exceed lOOC (Nelson). Product specifications for nanoporous membranes were obtained from Osmonics ™ and used for the process design. Their membranes offer 15% recovery (in the permeate) of the Mg S04 feed solution, which is used to determine the permeability for water. The membranes are 8 inches in diameter with a length of 40 inches. Filter Removal of any solid particles from the stream will be necessary to uphold the life of the membrane. A filter will be necessary to remove solid CaC03 particles from the waste stream. These particles constitute 1% (by weight) of the stream content. The filter will be located just upstream of the membrane system. Orival, Inc., a manufacturer of automatic water filters has been identified. These filters have the capability to remove particles as small as 10 microns. 6 Upon removal of solids, the filtered water will be sent to the membrane. The CaC03 particles will be mixed with the cement for disposal. Cryogenic Condenser A cryogenic condenser will be used to condense the tritiated water vapor from the air. This technique is often used for recovery of VOCs that are emitted during manufacturing process. Liquid nitrogen is the most commonly used as a low-temperature refrigerant for the system. Because the water vapor will account for such a small volume, it will not be purified, and rather routed for disposal. Auxiliary Equipment A glove box with air lock chambers and 10 sets of glove ports will encase the entire process. The volume of the box is most dependent on the number of stages for the separation operation. In addition enough space must be incorporated to allow removal of membrane units and other equipment. Several centrifugal pumps will be needed for transporting streams from each stage of the separation system. A vacuum pump will also be required to maintain a negative pressure in the encasement. A cement mixer and 55 gallon steel drums will be used for disposal. The concentrated tritiated water will be used to make the cement. Drums will be filled and disposed of in a landfill. 7 Results and Discussion Membrane Process Using the Nelson paper as a guide, the maximum reject conditions were used to establish the separation factor of 2.33 (this corresponds to 43% reject). With this separation factor, an equilibrium curve was constructed using equation 4 as shown in Figure 4 (located in Appendix). We decided to remove 95.00% of the tritium from the feed and have 99.9% of the flow leave the bottom (retentate). With these conditions, the retentate is just below the EPA regulations. The first approach attempted to complete this separation using one stage, with the given tritium feed fraction, the desired retentate fraction is impossible to obtain using just one stage. This was determined by using equation 8 (Hwang and Kammermeyer): xoM = x1[1 + (a -1)Pr(l- x I)] ( ) a\l-xl + xI (8) The minimum reject fraction in one stage was determined to be 1.46e-14, which is too large. Thus, multiple stages would be required to obtain the desired separation. As discussed earlier, a Case 1 recycle cascade was used to perform the separation. Since the feed contains an extremely small amount oftritium (xF2.25e-14), a different approach would be needed to use the McCabeThiele method on this equilibrium, thus the equilibrium curve was plotted using log-log axis. This allows several orders of magnitude to be displayed over a small area. Table 1 shows the results of for the design conditions. Table 1. Summary of Membrane Conditions (per min basis) yf 2.25E-14 xb 1.12E-15 yd 2.13E-11 y 0.999 F (mol/min) 208.18 D (mol/min) 0.208 B (mol/min) 207.97 xf 2.03E-14 Moles HTO Moles HTO Bottom Feed 2.34E-13 4.68E-12 Mass HTO Bottom 4.68E-12 Moles H2O Bottom 207.97 Mass H2O Bottom 3743.40 vol (Llmin) Bottom 3.74 Ci Bottom 4.54E-08 Ci/l Bottom 1.21 E-08 Moles HTO Top 4.44E-12 Mass HTO Top 8.88E-11 Moles H2O Top 0.208 Mass H2 O Top 3.75 vol (Llmin) Top 3.75E-3 Ci Top 8.63E-07 Ci/l Top 2.30E-4 a 2.33 e 0.50025 Area 248.60 HTO Balance %HTO Removed %Flow Bottom 0 95.00% 99.90% 8 The results of the McCabe-Thiele method for determining the number of stages required are shown in Figure 5 (located in Appendix). Economic Analysis The net present worth of the project was determined in order to estimate its economic scope. Figure 3 is a cash flow diagram for the project. It is important to note that there is no income associated with the project; therefore all cash flows are negative. These costs were divided into several different categories in order to calculate the net present worth (Tables 2 through 8 located in the Appendix summarize each cost). These categories include initial equipment costs, labor costs, membrane costs, pump costs, variable costs, and electricity cost. Evaluating separate categories is useful because different pieces of the process equipment have different lives and must be replaced at different times. For example, the glove box is assumed to last the entire project life of 20 years, while the pumps are expected to last for only 5 years. There is no discount factor applied to the 2 3 5 4 7 6 Time (Years) 10 11 12 9 8 13 14 15 16 17 18 19 20 $0 ·$200,000 ·$400,000 ·$600,000 ·$800,000 "'coco" N N co ~ N N "'t N N ~ co C") (() (() C") C") ai co ai co 0. 0. ~. ° (() (() ~ .0 C") 'I: ~ ° N ~ .r v ~ ~ C") (() v .g 0. C") (() (() v ai co ai co 0. 0. ~ "'t en (() C") ~ "'t ~ C") 10 v ai co "'". C") . ~ ~ "'t (() (() C") ai co C") (() v ai co (() (() C") ai co 0. 0. 0. 0. ~ ~ ~ ~ "'t "'t "'t "'t LO LO (() (() C") C") cD en ai co ~ 0. C") (() v ai co 0. 0. ~ "'t ~ (() (() C") ai co 0. ~ "'t :::E ·$1 ,000,000 ~ iii o ·$1,200,000 () "'t -$1 ,400,000 'I: ~ -$1,600,000 "'". -$1,800,000 -$2,000,000 Figure 3. Cash Flow Diagram 9 tit costs that are incurred in year 1 because they are at their present value. Two different discount factors were applied to determine the present worth for costs not applied in year 1. For costs that are applied every year (labor, electricity, and variable costs) the present value of an annual cost discount factor was used. Equation 9 shows how these annual costs were calculated: P= A( (i + 1) N -1 i(i+1)N J (9) where P is the present worth, A is the annual payment, N is the number of years, and i is the interest rate. For costs with unequal lives, a table was generated which gave the present worth of the future cost. Equation 10 shows how the present worth of a future cost is generated: (10) where P, N, and i are as above and F is the future cost. The Net Present Value is determined by the sum of each present value and is -$10,113,610. There really is no need to optimize the design because as bottoms (retentate) flow increases, the top (permeate) flow decreases, causing the disposal costs to decrease. Also, as the cut is lowered (closer to total reflux), the area decreases, as do the number of stages required, thereby reducing costs. The major cost associated with the design is the labor cost. 10 Conclusions For the design specifications of 95.00% removal of tritium with 99.90% flow of EPA approved water, the following conclusions can be made: • 13 stage recycling cascade membrane process • 483,626 gal/yr of clean water produced • 35 barrels/yr of waste produced • NPV of -$10,113,610 • Majority of cost due to labor • As cut decreases, area, stages, and cost decrease 11 Nomenclature np permeate flow rate, mollmin nF feed flow rate, mollmin XD, YD ml fraction of tritium at the top of the cascade XFA mol fraction oftrituim in feed XRA mol fraction of tritium in the retentate XoM minimum mol fraction in the retentate using one stage YPA mol fraction of tritium in the permeate Pp permeate pressure, atm PR retentate pressure, atm PMA Permeability ,mol-mlmin-m2-atm PMA Permeance, mollmin-m2 -atm ~P difference in retentate and permeate pressures, atm N flux through membrane, mollm2-s 1m membrane thickness, f.!m Vp molar permeate flow rate, mollmin A membrane area, m 2 Greek a separation factor e cut, ratio permeate flow to feed flow y ratio of retentate flow to permeate flow 12 Literature Cited Hwang, S.-T., Kammermeyer, K.L., Membranes in Separations. New York: Wiley Interscience, 1975, pp. 332-335. Nelson, D.A., Duncan, 1., Jenson, G., Burton, S. "Isopomeric Water Separation with Supported Polyphosphazene Membranes," Journal of Membrane Science, ed. 112, pp. 105-113. Porter, Mark. Handbook of Industrial Membrane Technology. New Jersey: Noyles Publications, 1990, pp.364-367. Seader, J.D., Henley, Ernest, 1. Separation Process Principles. 1st ed. New Yark: Wiley & Sons, Inc, 1998, pp. 713-775. http://www.access.gpo.gov/naralcfr/cfrhtml_0040/40cfr141_00.html, "Code of Federal Regulations" http://www.orival.com/water.shtml. Automatic Water Filters http://www.osmonics.com 13 APPENDIX A. Membrane Specification Sheet from Osmonics ~ N anofiltration Membrane Elements - DS-5, Standard Flux OSMONICS Product Information These elements are used for dye removal/concentration, and sodium chloride diafiltration. They feature a fiberglass outerwrap and standard feed spacers. Other materials of construction and special feed spacers are available. The proprietary DS-5 thin-film nanofiltration membrane is characterized by an approximate molecular weight cut-off of 150-300 daltons for uncharged organic molecules. Divalent and multivalent anions are preferentially rejected by the membrane while monovalent ion rejection is dependent upon feed concentration and composition. Since monovalent ions pass through the membrane, they do not contribute to the osmotic pressure thus enabling DS-5 nanofiltration systems to operate at feed pressures below those of RO systems. Membrane Specification - DS-5 Membrane: Proprietary nanofiltration thin-film membrane (TFM®). Applications: Dye removal/concentration, heavy metals removal, acid purification, and sodium chloride diafiltration. Rejection characteristics: Divalent and multivalent anions are preferentially rejected by the membrane while monovalent ion rejection is dependent upon feed concentration and composition. The membrane is characterized by a molecular weight cutoff of 150-300 daltons for uncharged organic molecules. Recommended pH: 2.0-11.0 operating range and 1.0-11.5 cleaning range for standard construction elements. Chlorine tolerance: 1,000 ppm-hours, dechlorination recommended. Maximum temperature: 122°F (50°C) with standard element construction and up to 158°F (70°C) with special element construction. 14 Element Series Designation: DK, DL Element Specifications R~jection ActiveArea ftl (ml) 2,000 (7.56) 98% 90 (8.36) DK8040F 8,000 (30.24) 98% 350 (32.52) rMOdel DK4040F L~pn(3/d)J M~04 Specifications are based on a 2,000 mgIL MgS04 solution at 100 psig (690 kPa) net pressure, 77°F (25°C), 10% recovery, after 24 hours. Individual element flux may vary ± 15%. Operating and Design Parameters Membrane: Thin film membrane (TFM) Typical operating pressure: 70-400 psig (483-2,758 kPa). Maximum pressure: 500 psig (3,448 kPa). Maximum temperature: 122°F (50°C). Recommended pH: Operating range 2-11 (pH<1 with special element construction), cleaning range 1-11.5. Chlorine tolerance: 1,000 ppm-hours, dechlorination recommended. Recommended per vessel in a system delta P - psig (kPa) % Recovery Elements per pressure vessel 1 2 3 4 5 6 10 (69) 20 (138) 30 (207) 38 (262) 45 (310) 50 (345) 15 25 35 45 53 53 15 Element Dimensions and Weight ~-A1 iModel I ! Dry boxed weight Ibs. (kg) Dimensions, inches (cm) A B C IDK4040F 40.00 (101.6) 0.625 (1.59) IDK8040F 40.00 (101.6) 1.187 (3.01) 7.88 (20.02) Length includes ATD's. All elements are shipped dry. 16 I 3.88 (9.86) [ 12 (5.45) 32 (14.53) APPENDIX B. EPA Regulations for Drinking Water [Code of Federal Regulations] [Title 40, Volume 15, Parts 136 to 149] [Revised as of July 1, 2000] From the U.S. Government Printing Office via GPO Access [CITE: 40CFR141.16] [Page 344] TITLE 40--PROTECTION OF ENVIRONMENT CHAPTER I--ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) PART 141--NATIONAL PRIMARY DRINKING WATER REGULATIONS--Table of Contents Subpart B--Maximum Contaminant Levels Sec. 141.16 Maximum contaminant levels for beta particle and photon radioactivity from man-made radionuclides in community water systems. (a) The average annual concentration of beta particle and photon radioactivity from man-made radionuclides in drinking water shall not produce an annual dose equivalent to the total body or any internal organ greater than 4 millirem/year. (b) Except for the radionuclides listed in Table A, the concentration of man-made radionuclides causing 4 mrem total body or organ dose equivalents shall be calculated on the basis of a 2 liter per day drinking water intake using the 168 hour data listed in "Maximum Permissible Body Burdens and Maximum Permissible Concentration of Radionuclides in Air or Water for Occupational Exposure, I I NBS Handbook 69 as amended August 1963, U.S. Department of Commerce. If two or more radionuclides are present, the sum of their annual dose equivalent to the total body or to any organ shall not exceed 4 millirem/year. Table A--Average Annual Concentrations Assumed to Produce a Total Body or Organ Dose of 4 mrem/yr Radionuclide Critical organ Tritium.............................. Strontium-90 . . . . . . . . . . . . . . . . . . . . . . . . . Total body . . . . . . . . . . . . . . Bone marrow . . . . . . . . . . . . . [41 FR 28404, July 9, 1976] 17 pCi per liter 20,000 8 APPENDIX C. Membrane Curves Figure 4. Tritium Equilibrium Curve 1.0 0.9 0.8-.--S 0.7 111 CD __ .________ ._____ .__ E 0.6 L~ CD ----------- ---------.-7"'~ ._-------- CL .5 lS --------- .-----. ____ 0.5~! - - - - /.. -.~ e. ._----- ~ +I U 0.4 CD '0 E 0.3 0.2 ~_ - _ . / _ _ _ _e • • _ _ _ . _ _ _ _ _ . • _ __ I 0.1 .,----0.0.· 0.0 -.~ 0.1 _. - _ . _ - - . _ - _ . , - - - - 0.2 0.3 0.4 0.5 0.6 x mole fraction in retentate 18 0.7 0.8 0.9 1.0 Figure 5. McCabe-Thiele Method to Determine Number of Stages 1.0E-10 co ~ 1.0E-11 1.0E-12 >- enriching section operating line fE equilibrium line :. 1.0E-13 c E :s :;::; .;: I- Feed Stage 9 1.0E-14 TOTAL STAGES: 13 stripping section operating line 1.0E-15 1.0E-6~ / 1.0E-16 --1---T 1.0E-15 1.0E-14 1.0E-13 Tritium in Retentate, x 19 l-,r~ 1.0E-12 1.. 0E-11 1.0E-10 APPENDIX D. Cost Tables Table 2. Initial Equipment Cost CAPACITY UNITS QUANTITY TOTAL SIZE COST TOTAL COST Water Feed Pump Stage Pump Cryogenic Unit Solid Filter 2.5 2.5 50 125 hp hp fe/min 3 in 1 20 1 1 1 20 50 125 $352 $352 $50,000 $4,950 $352 $7,040 $50,000 $4,950 Membrane Module Concrete Mixer Vacuum Pump 1 21 1 m fe/min hp 2 3224 1 1 3224 $97 $19,000 $1,500 $312,341 $19,000 $1,500 Glove Box 0.89 m 3 15 17 $12,950 EQUIPMENT COST $220,150 $615,333 Equipment Table 3. Labor Costs Labor Salary Technicians $40,000 Engineer $60,000 Benefits S.S./Worker's Comp. Overhead Cost per worker $12,000 $18,000 $4,000 $6,000 $40,000 $60,000 $96,000 $144,000 S #of Workers Labor Cost ($/year) 8 1 1 Total $768,000 $144,000 $1 800 $1,048,800 Table 4. Annual Variable Costs Variables Cost Unit Yearly Usage Unit Total Cost Concrete 55-Gallon Drums Disposal Cost Gloves $0.38 $4.55 $33.42 $120.00 gal gal gal pair 1444 35 1925 10 gal/yr barrels/yr gallons/yr pair/yr $551.25 $159.09 $64,333.50 $1,200.00 Liquid N2 $0.80 gal 365 gal/yr Total $292.00 $65,335.84 212711 6077 Total Cost $8,508.44 $243.10 $8,751.54 Table 5. Annual Electricity Costs Electricity $0.04 kW hr Feed Pump Vacuum Pump hp 2.5 1 kW/hr 15194 6077 # 14 1 20 r Table 6. Membrane Cost (2 year life) Membrane Cost Year DCFR Cost 2 4 6 8 10 12 14 16 18 20 0.797 0.636 0.507 0.404 0.322 0.257 0.205 0.163 0.130 0.104 $248,996 $198,498 $158,242 $126,149 $100,565 $80,170 $63,911 $50,950 $40,617 $32,379 $312,341 2 year life $1,100,478 Table 7. Pump Cost (S year life) Pump Cost Cost Year DCFR 5 10 15 20 $8,892 0.567 0.322 0.183 0.104 5 year life $ $ $ $ 5,045.56 2,862.99 1,624.54 921.80 $10,455 Table 8. Net Present Value, Analysis n P/A(i, n) 20 7.4694 Initial Equipment Cost Labor Cost Variable Cost Energy Cost Membrane Cost Pump Cost $615,333 $1,048,800 $65,336 $8,752 $312,341 $8,892 12% PW st 1 year yearly yearly yearly every 2 years every 5 years Net Present Worth 21 $615,333 $7,833,952 $488,022 $65,369 $1,100,478 $10,455 -$10,113,610