OF THE NITRATE TO AMMONIA AND CERAMIC (NAC) PROCESS

Transcription

1 RHEOLOGCAL PROPERTES OF THE PRODUCT SLURRY OF THE NTRATE TO AMMONA AND CERAMC (NAC) PROCESS. Muguerca, G. Yang, and M. A. Ebadan' Department of Mechancal Engneerng Florda nternatonal Unversty Mam, FL D. D. Lee, A. J. Mattus, and R. D. Hunt Chemcal Technology Dvson Oak Rdge Natonal Laboratory Oak Rdge, TN f DSCLAMER Ths report was prepared as an account of work sponsored by an agency of the Unted States Government. Nether the Unted States Government nor any agency thereof, nor any of ther employees, makes any warranty, express or mpled, or assumes any legal lablty or responsblty for the accuracy, completeness, or usefulness of any nformaton, apparatus, product, or process dsclosed, or represents that ts use would not nfrnge prvately owned rghts. Reference heren to any specfc commercal product, process, or servce by trade name, trademark, manufacturer, or otherwse does not necessarly consttute or mply ts endorsement, recornmendaton, or favorng by the Unted States Government or any agency thereof. The vews and opnons of authors expressed heren do not necessarly state or reflect those of the Unted States Government or any agency thereof. ~ - DlSTRlBUTQN OF THS D0.C -. 'ASME Fellow, The author to whom all correspondence should be addressed. *. J -*..\

2 DSCLAMER Portons of ths document may be llegble n electronc mage products. mages are produced from the best avalable orgnal document.

3 ABSTRACT The Ntrate to Ammona and Ceramc (NAC) process s an nnovatve technology for mmoblzng the lqud from Low Level radoactve Waste (L,LW). An expermental study was conducted to measure the rheologcal propertes of the ppe flow of the NAC product slurry. Test results ndcate that the NAC product slurry has a profound rheologcal behavor. At low solds concentraton, the slurry exhbts a typcal dlatant flud (or shear thckenng) behavor. At hgh solds concentraton, the slurry changes to a pseudo-plastc (or shear thnnng) flud. The transton from dlatant flud to pseudo-plastc flud wll occur at between 25% to 30% solds concentraton n temperature ranges of C. Correlaton equatons are developed based on the test data.

4 NOMENCLATURE d ppe dameter, m f frcton coeffcent K flud consstency, N*sec3-W2 L ppelength, m Re, general Reynolds number urn slurry mean velocty, m sec-' V volume flow rate, m3 sec-' Greek Symbols AP pressure drop along the test secton Y shear rate, sec-' Po effectve vscosty, N sec 2-n P slurry densty, kg m-3 z shear stress, N m-2 Superscrpts ' n flow ndex

5 1. NTRODUCTON Over the past 50 years, mllons of tons of low-level radoactve waste (LLW) have been generated at varous U.S. weapons facltes. Ths LLW s stored manly at fve U.S. Department of Energy stes, Fernald, Hanford, Oak Rdge, Rchland and Savannah Rver. More than three hundred underground storage tanks have been used to process and store LLW. Radoactve waste n the lqud state poses a great threat due to the potental for seepage nto groundwater supples. Therefore, t must be mmoblzed before fnal dsposal. Prelmnary studes have ndcated that more than 80% of the chemcal concentraton n ths LLW s composed of sodum ntrate wth a radaton level of 0.1 to 1.2 Wh. The characterstcs of ths sodum ntrate-based waste, n addton to the levels of radoactvty, are as follows: ph, ether < 1or > 12, wth a total salt content of >5M, and a sodum content of > 1.5M. Currently, the most common mmoblzaton method for the LLW s the use of cement-based grout. However, ths method wu ncrease the volume of the waste, does not effectvely retan certan contamnants, and has questonable long term stablty. Other alternatve long term dsposal methods, such as polyethylene and bdentrfcaton, are stll n ther early development stage. Recently, a new mmoblzaton technque for LLW, the Ntrate to Ammona and Ceramc (NAC) process, has been developed (Mattus et al. 1993and Mattus and Lee 1993). nstead of mxng the lqud waste drectly wth the cement to make concrete blocks, the NAC process elmnates the ntrate from the LLW by convertng t to ammona gas. Alumnum partcles are used as a reductant to complete ths converson. The fnal product of the NAC process s gbbste, whch can be further sntered to a ceramc waste form. Radoactve speces, such as plutonum and strontum, wll enter the sold ceramc phase durng the reducton process. The alumna-based ceramc wll be further calcned pressed, and sntered to generate the sold waste form. Prelmnary tests have ndcated that the NAC process not only produces envronmentally acceptable waste, but can also reduce the volume of the fnal waste by up to 70%, as compared wth the cement-based grout method. Ths volume reducton represents a sgnfcant reducton n cost for fnal land dsposal. The NAC process s an exothermc process, whch generates large amounts of heat durng the

6 chemcal reacton. n order to mantan a desred operatng temperature of between 50" to 85 C nsde the NAC reactor, a coolng system s requred. To desgn a coolng system and the NAC reactor, one needs to know the rheologcal behavors of the product slurry. Past experence has shown that the product slurry of the NAC process behaves as a non-newtonan flud, and that the use of correlaton equatons from Newtonan fluds for desgn applcaton could result n consderable error. Unfortunately, ths nformaton s not avalable n the open lterature. Therefore, the objectve of ths study s to expermentally determne the rheologcal behavor of the fnal product slurry. n ths paper, a descrpton of the test faclty s gven frst, and an error analyss of the test s then dscussed. Fnally, the expermental results of the rheologcal behavor of the product slurry are presented.. THE TEST APPARATUS A test apparatus has been desgned and constructed to measure the rheologcal propertes and the frcton coeffcent of the ppe flow. Fgure 1 llustrates the test faclty, whch conssts of the NAC process reactor, the test loop, and the assocated nstrumentaton. The NAC reactor s a 6 lter chemcal reactor (model BoFlo C manufactured by New Brunswck Scentfc), whch automatcally controls the slurry temperature. Non-radoactve gbbste slurry, chemcally and rheologcally smlar to the fnal product of the NAC process, was used to smulate the actual product slurry. The chemcal compostons and the partcle sze dstrbutons of the dred powder from the slurry are lsted n Tables and, respectvely. The gbbste slurry s pumped from the reactor to a test loop and then dscharged back to the reactor. The test loop s constructed of an 0.86" D stanless steel ppe. The test loop has two sectons: the test secton and the temperature control secton. The 8-ft-long test secton s used to measure the pressure drop of the slurry ppe flow. The test secton s nsulated wth fberglass packng to mantan a constant temperature durng the test. The 8-ft-long temperature

7 control secton s a double-ppe heat exchanger, that s used to provde addtonal temperature control for the slurry nsde the reactor. Table Composton of the Dred Powder of the Slurry - Larger than 15 pm 10 % Between 7 and 15 pm 40% Between3and7pm 40 % Smaller than 3 pm 10%

8 Two pressure transducers were connected to the nlet and outlet of ths secton. The uncertanty of the pressure measurement was k0.5 %. An FE-125 magnetc flowmeter was used to measure the slurry flow rate through the ppe. The uncertanty of the flow measurement s +2 %. Two thermocouples were used to measure the slurry temperatures at both the nlet and outlet of ths secton. All thermocouples were connected to a Hewlett-Packard data acquston system, and the temperatures were automatcally recorded by a computer. The dfference n the readng of all thermocouples was less than k0.2 "C. The overall uncertanty of the temperature measurement was +0.3 "C Data Reducton Methodology Durng the test, the slurry flow rate, the temperature, and the pressure dfference were contnuously recorded. For the ppelne vscometer, the shear rate, shear stress, and the effectve vscosty can be calculated based on ths measured nformaton (nhe and Karn, 1987, and Wasp et. al. 1977). The shear rate s determned by: y = 32 V/d3, (1) where V and d are the slurry volume flowrate and the ppe dameter, respectvely. The shear stress can be found by: z =d Ap/(4L), (2) where L s the dstance between the two pressure transducers, and Ap s the correspondng pressure drop. The effectve vscosty can then be calculated by: pc = y-' = K yn-', (3)

9 where the n and K are the flow ndex and flud consstency, respectvely. The Reynolds number s defmed by: Re, = (p u,2" d")/k, (4) where p and u,are the densty and the mean flow velocty of the slurry, respectvely. Through the uncertanty analyss (Fglola and Beasley, 1991), the uncertantes of major parameters are lsted n Table. Table 111 The Uncertantes of the Major Results PARAMETERS % Shear rate 2.6 Shear stress 1.5 Effectve vscosty 3.0 Reynolds number 3.5 V Rheologcal Propertes of the Product Slurry Sx sold concentraton slurres, 17%, 20%,23 %, 30%, 33 %, and 40% wt. of gbbste by weght, have been tested. To ensure the repeatablty of the test results durng the test, the slurry was dsposed of after fnshng the test for certan solds concentratons. The repeated test for ths solds concentraton slurry was conducted usng the separately mxed slurry. Durng the test, the slurry was kept at three constant temperatures, 50 C, 65"C,and 8OoC,through a heater nsde the reactor. n each case,the slurry flow rate was vared between 5 Zlmn to 37 Zlmn. The test condtons are lsted n Table V. Table V Test Condtons of the Pressure Measurement

10 The frst step of the test was to determne whether the flud s rheologcal property was tmendependent flud. For ths test, the slurry flow was to be ncreased from the mnmum value to the maxmum value, and then reduced to the mnmum value. The shear-stress/sh-rate relaton ndcated that the rheologcal property of the slurry was tme-ndependent.

11 Fgure 2 shows the effectve vscosty changes wth the slurry solds concentraton at dfferent shear rates. The fgure ndcates that at a hgh solds concentraton (40% solds concentraton, at 65 C and SOOC), the slurry exhbts a pseudo-plastc behavor-that s, the effectve vscosty decreased as the shear rate ncreased. At low concentraton (20% solds concentraton, at 50 C and SOOC), the slurry exhbted a dlatant behavor, or the effectve vscosty ncreased as the shear rate ncreased. n both cases, the rheologcal behavor of the slurry was not very senstve to the temperature change. The rheologcal behavor of the 30% concentraton slurry les somewhere n between. The transton from dlatant flow to pseudo-plastc flow wll be occur between the 25 % to 30 % concentraton. The change n the rheologcal behavor of the slurry s due to the change n the water-bondng structures at dfferent solds concentraton. The physcal appearance of the 20% slurry was a mlk-lke soluton, whle the 40% slurry was smlar n appearance to yogurt or whte pant. n the lqudkold suspenson flud (slurry), the contnuous lqud s called the dspersng phase, and the dscontnuous partcles are known as the dspersed phase. The rheologcal behavor of the sluny wll depend on the rheologcal behavor of the dspersng phase and the sze, shape, stffness, concentraton and degree of dsperson of the sold partcles. When the partcles tend to agglomerate together at rest, the slurry may exhbt as pseudo-plastc flud. f the agglomeraton of partcles ncreases wth shear rate, the slurry may exhbt dlatant behavor. Fgure 3 shows the shear stress and shear rate relaton for the slurry wth 17%, 20 %,and 23 % concentratons. The results ndcate that the slurry exhbts a dlatant flud behavor (or shear thckenng)-that s, the shear stress ncreases rapdly as the shear rate ncreases. The shear- stresskhear-rate relaton s ndependent of the slurry temperature and the solds concentraton, and can be well correlated by the power law: z =1.267x 104 y 1.74, (5) Fgure 4 shows the slurry effectve vscosty as a functon of shear rate for the same case. The fgure ndcates that the slurry's effectve vscosty ncreases from 6 cp (N*s/m2 ) at y=200

12 to 15 cp at y=560, and agan, the change of the slurry temperature and solds concentraton n ths test regon wll not affect the slurry vscosty. For the power law flud, the effectve vscosty can be wrtten as:. p, = z y-' = y0.74 (6) Fgure 5 shows the frcton coeffcent changes wth the general Reynolds number of the slurry. For the case n Fg. 3, the test range of the general Reynolds number n ths study s approxmately 12,000 to 15,000. Prevous research has ndcated that the transton occurs when Re, exceeds approxmately 2100 for a power law flud n a crcular tube, and the flow can be consdered as turbulent when Reg> Therefore, the test conducted for slurry below a 23% solds concentraton was n the turbulent regon. The correlaton equaton s adequate for the expermental data: f = Reta2. (7) When the gbbste concentraton was hgher than 40%, the rheologcal property of the slurry changed from a dlatant flud (shear thckenng) to a pseudo-plastc flud (or shear thnnng). Fgure 6 shows the shear stresdshear rate relaton for the 33 % and 40 % solds concentraton slurry-that s, the shear stress ncreased as the shear rate ncreased. t can also be seen that the shear stress ncreased slghtly as the slurry temperature ncreased. The test data can be correlated by: z =1.75yoen. (8) Fgure 7 shows the correspondng effectve vscosty as a functon of the shear rate change. The effectve vscosty has a hgh value at a low shear rate, and gradually decreases to 20 cp when the shear stress ncreases to 500 6'. t can be seen that the effectve vscosty of the hgh concentraton slurry was much hgher than that of the low solds concentraton slurry. Although the

13 effectve vscosty s slghtly affected by the slurry temperature, the test data can be well correlated by a regresson equaton wth & 15%devatons:. pc = z y-l = 1750y4*73 (9) Fgure 8 shows the fcton coeffcent changes wth the general Reynolds number flow. Due to the hgh effectve vscosty, the fgure shows that the slurry flow was n the range where the general Reynolds number less than 6W-that s, n the lamnar flow regon. The tested data can be correlated by: f = 15.U Ream. (10) V. SUMMARY Expermental study has been conducted to measure the rheologcal propertes of the ppe flow for the NAC product slurry. The test results ndcate that the NAC product slurry has a tme ndependent non-newtonan rheologcal behavor. At a low solds concentraton, the slurry exhbts a dlatant flud (or shear thckenng) behavor, and at a hgh solds concentraton, the slurry changes to pseudo-plastc (or shear thnnng) flud. Transton from the dlatant flud to pseudo-plastc flud wll be occur between 25% to 30%solds concentraton n the temperature ranges of 50-80"C. The correlaton equatons have been developed from the test data. Durng operaton of the NAC reactor, the solds concentraton wll be vared from 20 % to 40%. Unfortunately, ths study ndcates that the slurry's rheologcal propertes has a transton n ths concentraton range. To ensure safe operaton and to obtan a desred fnal product, the desgn should consder the worst case. Therefore, the rheologcal values of 40% sold concentraton slurry, whch has the hghest vscosty, s recommended for engneerng desgn.

14 ACKNOWLEDGMENT The results presented n ths paper were obtaned n the course of research sponsored by the Department of Energy's Offce of Technology Development under Grant No. 19X-SN855C.

15 REFERENCES Fglola R. S. and D. E. Reasley, neory and Desgnfor Mechancal Measurements, Chapter 5, John Wley & Son, New York, T. F. rvne and J. Karn, "Non-Newtonan Fud Flow and Heat Transfer," Chapter 20 of the Handbook of Sngle Phase Convectve Heat Transfer, ed. by S. Kakac, R. K. Shah, and W. Aung, Wley nterscence, New York, Lma, G. G. C., R. F. Navarro, 0. L. S. de Alsna, "nfluence of the Concentraton on the Power Law ndex of Alumna Suspensons n Hgh Vscosty Newtonan Fluds," Proceedng of 7th nternatonal Symposum on Transport Phenomena n Manufacturng Processes, Acapulco, Mexco, August, A. J. Mattus, D. D. Lee, T. A. Dllon, E. L. Youngblood, T. Tegs, and L. L. Farr, "A Low Temperature Process for the Dentraton of the Hanford Sngle Shell Tank, Ntrate-Based Waste Utlzng the Ntrate to Ammona and Ceramc WAC) Process, Phase Report, a report to the U. S. Department of Energy, DE-AC05-840R21400, Oak Rdge Natonal Laboratory, ' A. J. Mattus and D. D. Lee, '#TheNtrate to Ammona and Ceramc (NAC) Process-A Newly Developed Low Temperature Technology," Second nternatonal Mxed Waste Symposum, Aug. 1720, 1993, Baltmore, Maryland, E. J. Wasp, J. P. Kenny, and R. L. Gandh, Sold-Lqud Flow Slurry Ppelne Transportaton, Trans Tech Publcatons, Clausthal, Germany, 1977.

16 Magnetc a1 Flow Meter Crculatng m Chller k 9).c,! 0 0 n U. s v) Fg. 1 Schematc of the test loop. 15

17 40 35 P * A A Shear rate [l/sec] Fg. 2 Effectve vscosty changes wth the shear rate. 16! c;oncentratlon/ ernperature ~ ! 600! : 700

18 &"p Concentratonnemperature a 17/50,! Shear rate [l/s] Fg. 3 Shear stress as a fmcton of the shear rate for low solds concentraton slurry. 600

19 * Tp ! : c n X 0 om0 -- Y : 0 Concentratonnemperature x o A o 23150,, ; l Shear rate [l/s] Fg. 4 Effectve vscosty as a hncton of the shear rate for low solds concentraton slurry. 600

20 Concentratonflemperature A o T, 0sJ Fg. 5 Frcton coeffcent changes wth the general Reynolds number

21 r -E Shear rate [l/s] Fg. 6 Shear stress as a hncton of the shear rate for hsh solds concentraton slurry. 700

22 80 - a A 8 A \\. a ConcentratonTernperatature u core1 f f A A ;,750.p73 / ; A 0 : Shear rate [l/s] Fg. 7 Effectve vscosty as a hncton of the shear rate for h,oh solds concentraton slurry

23 Concentratonflemperature ' f T a 33/ A J 33165: o A ' Re, Fg. S The fcton coeffcent as a functon of the general Reynolds number for the hgh solds concentraton slurry. 22 U 700