High voltage generator. Fig. 1. Schematic diagram of the Los Alamos electron-beam test bed for hazardous waste treatment.

Transcription

1 APPLCATONS OF PULSED POWER N ADVANCED OXDATON AND REDUCTON PROCESSES FOR POLLUTON CONTROL L.A. Rosoha, J. J. Coogan, D. A. Seeker, and J.D. Smith Los Alamos National Laboratory P.O. Box 1663, MS J564 Los Alamos, NM Abstrat Pulsed power shows strong promise in developing innovative tehnologies aimed at pollution ontrol. At Los Alamos we are applying pulsed power tehnology to the environment through the use of relativisti eletron beams and nonequilibrium plasmas for the destrution of hazardous organi ompounds in aqueous-based and gaseous-based media, respetively. These two tehniques have also been applied to the treatment of flue gases suh as SOx and NOx by other researhers. n this paper, we will desribe our eletron-beam and plasma experiments arried out on hazardous waste destrution. Additionally, we will desribe the saling of eletron-beam and nonequilibrium plasma systems to industrial sizes, inluding disussions of eletron aelerator arhiteture, omparison of ontinuous-duty versus repetitively pulsed aelerators, plasma-disharge modulators, and needed pulsed power tehnology development. ntrodution A growing soial awareness of the adverse impat of pollutants on our environment and the promulgation of environmental laws and regulations has reently stimulated the development of tehnologies for pollution abatement and hazardous waste destrution. We are working on a promising lass ofnonthermal methods, advaned oxidation and redution proesses (AOPs and ARPs), in whih we employ eletrial energy, rather than thermal energy, to reate large quantities of highly reative (oxidative and/or redutive) free radials. These radials subsequently reat with hazardous organi hemials, onverting them to nonhazardous substanes (C0 2, H 2 0, and mineralized ompounds). Nonthermal proesses allow for the promotion of desired hemistry without the large enthalpy losses and potential augmentation of waste streams (e.g., with greenhouse gases) harateristi of thermal proesses. Our AOPs/ARPs apply relativisti eletron beams and nonequilibrium plasmas to the destrution of aqueous-based and gaseous-based hazardous organi ompounds, respetively. We are fousing on the optimization of eah tehnology for a partiular waste stream, but beause eah shares ommon hemistry and pulsed power, developing one method often aids development of another. We are exploring the onnetion between the optimal formation of free radials and the properties of the eletrial driver for eletron beams and nonequilibrium plasmas. Eletron-Beam Treatment of Aqueous-Based Hazardous Wastes the expeted removal effiieny and to ompare standard eletrostati aelerators to pulsed aelerators in terms of reative free radial prodution [4]. Typial me~sured single-pulse de~trutions for trihloroethylene (TCE) are m the range 90-95%, m good agreement with our model. t should be pointed out that this short, singlepulse destrution is muh l~ss effiient than othe~ dose p~ofiles (e.g., ontinuous-duty proftle) beause of the radtal-radtal.. reombination phenomenon disussed further below. n add1t10n, we have implemented a laser absorption system for measuring aqueous eletron onentrations produed by the eletron beam. High voltage generator Eletrial pulse forming line Reation hamber (ontainin!j water and organ1 hazardous waste sample) Probe laser.---- Wet hemistry / sampling port Data reorders/analyzers Fig. 1. Shemati diagram of the Los Alamos eletron-beam test bed for hazardous waste treatment. Saling Studies & Aelerator Arhitetures Conventional eletrostati eletron aelerator equipment has generally been employed for high average power irradiation appliations, while single-pulse aelerators have been utilized for high dose rate researh. Reent tehnology developments [5,6] have lead to a new generation of pulsed linear indution aelerators driven by solid-state eletrial power onditioning elements (see Fig. 2). These are onsidered to be less expensive per unit delivered e-beam dose, physially smaller, modular, and more reliable than onventional eletrostati aelerators. One demonstrated, these new aelerators will allow a onsiderable simplifiation in treatment plant arhiteture. Bakground and General Results High energy eletron beams have been shown to be effetive for the removal of hazardous organi ontaminants in aqueous media and show great potential as a generally appliable tehnology for disinfetion and sterilization [1,2]. The proess of eletron-beam irradiation is best understood in aqueous solutions in whih sizable quantities of free radials eaq-, H, and OH, as well as the more stable oxidant H are produed. These highly reative speies reat with organi ontaminants to produe substanes that are not hazardous (C0 2, H 2 0, and mineral salts or aids). E-beam tehnology also appears to be eonomially ompetitive with existing methods [3]. We have onfigured an eletron aelerator for tehnology evaluation studies and demonstrated the destrution of two harateristi hazardous organi ompounds. The test bed (see Fig. 1) operates in single-pulse mode (65-ns pulse width), typially produing beam voltages of MeV and doses in the range 4-7 Mrad (40 x x 103 Gy). To better understand the waste removal proess and explore e-beam treatment saling issues, we have employed a omputer-based hemial kinetis model to predit Command Resonant Charge Ciruit ntermediate Magneti Storage and Magneti Pulse-Compression Pulse-Compression piru~s Ciruits (e.g., 10 JS- 500 ns) {e.g., 500 ns- 100 ns) Tr;~~f~~~[Gr Magneti Pulse-Compresso PFL (100 ns- 50 ns) '!fo ~;o (Aele;a~~~ Cells or ndution Adder) Fig. 2. Shemati diagram of ompat high average power solid-state modulator for driving advaned pulsed linear indution aelerators. 448

2 Report Doumentation Page Form Approved OMB No Publi reporting burden for the olletion of information is estimated to average 1 hour per response, inluding the time for reviewing instrutions, searhing existing data soures, gathering and maintaining the data needed, and ompleting and reviewing the olletion of information. Send omments regarding this burden estimate or any other aspet of this olletion of information, inluding suggestions for reduing this burden, to Washington Headquarters Servies, Diretorate for nformation Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA Respondents should be aware that notwithstanding any other provision of law, no person shall be subjet to a penalty for failing to omply with a olletion of information if it does not display a urrently valid OMB ontrol number. 1. REPORT DATE JUN REPORT TYPE N/A 3. DATES COVERED - 4. TTLE AND SUBTTLE Appliations Of Pulsed Power n Advaned Oxidation And Redution Proesses For Pollution Control 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNT NUMBER 7. PERFORMNG ORGANZATON NAME(S) AND ADDRESS(ES) Los Alamos National Laboratory P.O. Box 1663, MS J564 Los Alamos, NM PERFORMNG ORGANZATON REPORT NUMBER 9. SPONSORNG/MONTORNG AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONTOR S ACRONYM(S) 12. DSTRBUTON/AVALABLTY STATEMENT Approved for publi release, distribution unlimited 11. SPONSOR/MONTOR S REPORT NUMBER(S) 13. SUPPLEMENTARY NOTES See also ADM EEE Pulsed Power Conferene, Digest of Tehnial Papers , and Abstrats of the 2013 EEE nternational Conferene on Plasma Siene. Held in San Franiso, CA on June U.S. Government or Federal Purpose Rights Liense. 14. ABSTRACT Pulsed power shows strong promise in developing innovative tehnologies aimed at pollution ontrol. At Los Alamos we are applying pulsed power tehnology to the environment through the use of relativisti eletron beams and nonequilibrium plasmas for the destrution of hazardous organi ompounds in aqueous-based and gaseous-based media, respetively. These two tehniques have also been applied to the treatment of flue gases suh as SOx and NOx by other researhers. n this paper, we will desribe our eletron-beam and plasma experiments arried out on hazardous waste destrution. Additionally, we will desribe the saling of eletron-beam and nonequilibrium plasma systems to industrial sizes, inluding disussions of eletron aelerator arhiteture, omparison of ontinuous- duty versus repetitively pulsed aelerators, plasma-disharge modulators, and needed pulsed power tehnology development 15. SUBJECT TERMS 16. SECURTY CLASSFCATON OF: 17. LMTATON OF ABSTRACT SAR a. REPORT b. ABSTRACT. THS PAGE 18. NUMBER OF PAGES 4 19a. NAME OF RESPONSBLE PERSON Standard Form 298 (Rev. 8-98) Presribed by ANS Std Z39-18

3 Resolving questions about how one hooses a partiular aelerator system arhiteture for overall maximum effetiveness requires an understanding of the basi removal proesses. To better understand the waste removal proess and e-beam mahine saling, we have also employed a omputer-based hemial kinetis model to relate destrution effetiveness to eletron-beam dose profiles and eletron-beam mahine parameters, and to make omparisons with experimental data. The first of these studies examined radial prodution with very short(< 100 ns), high dose-rate pulses in pure water. We examined the prodution and reombination of these transient speies as a funtion of dose parameters. Our goal was to maximize the average free radial onentrations over a given period of time, for a given dose, by varying dose rate, pulse duration, and pulse repetition rate, thus providing greatest destrution potential. Our preliminary simulation results show that low dose rates have advantages over higher dose rates for the effiient prodution of radials. This is apparently due to nonlinearities within the water model that favor radial reombination over radial prodution at higher dose rates. With TCE or other pollutants present, it has been postulated (although not demonstrated) that the formation of radial adduts and their subsequent reations will produe favorable nonlinear effets that possibly make the pulsed ase more advantageous in terms of hemial effiieny. Our saling studies have also explored the optimal dose profiles for free radial prodution and waste destrution using both onventional ontinuous-duty aelerators and repetitively pulsed aelerators. Although the omputer modeling shows that a ontinuously applied dosage is more effiient in destroying waste than the same amount of single-pulse dosage, the modeling does show that a repetitively pulsed mahine an produe similar radial onentrations to those of a DC mahine when pulsed at high pulsed repetition rates (e.g., 10kHz). This is shown in Fig. 3, whih gives running averages of radial onentrations for both DC and repetitively pulsed dose profiles. Tables 1 and 2 give TCE and CCl 4 destrution Vs dose for four different methods of dose appliation. The initial onentrations and applied doses are hosen in an attempt to reprodue results from another faility. Table 1. TCE Destrution Calulated for Different Doses and Methods of Appliation Dose Method Frational Destrution (%) 100-krad 150-krad 100-ns pulse kHz pulse train kHz pulse train DC Notes: initial TCE onentration is 100 ppm; residene time is 0.1 se. Table 2. CC 4 Destrution Calulated for Different Doses and Methods of Appliation Dose Method Frational Destrution (%) 50-krad 100-krad 100-ns pulse kHz pulse train kHz pulse train DC Notes: initial CC1 4 onentration is 10 ppm; residene time is 0.1 se. n terms of destrution effetiveness, both the 1-kHz and 10-kHz pulse trains approah the DC-ase frational removal. Nonequilibrium Plasma Treatment of Gaseous-Based Hazardous Wastes ;:--._ ""......_ [H],... /.. ' '""... ~, [eaql '. DC Dose Profile '' 1 oo Time, log(s) Bakground and Experimental Results Nonthermal plasma hemial reator work at Los Alamos has demonstrated the potential for removing hazardous organis to very low levels (approahing tens of ppb to several ppb) by freeradial "old ombustion" [7]. We employ nonthermal plasmas reated by silent eletrial disharges in the gas stream - arrested transient eletrial disharge streamers, generated with a dieletri barrier onfiguration (see Fig. 4). The plasma produes energeti eletrons (typial energies of 1-10 ev), whih in turn generate opious quantities of highly reative free radials. The eletrons are seletively heated, whih results in an effiient transfer of eletrial energy to desirable hemial reations at near-ambient temperatures and pressures. Although the volume of the mirodisharges is quite small, an extremely large number of them are statistially spread out -o~ <D:2: n~ ~ 0> (!).2 ~ 0> : :J a: ns, 10-kHz Pulse Train Dose Profile _,, '' 1 oo Time, log(s) Fig. 3. Plots of running averages of free radial onentrations for DC and repetitive short pulse dose profiles. Fig. 4. Dieletri Barrier Metal Eletrode Shemati drawing of representative dieletri barrier disharge onfiguration. Single or double barriers are typially employed in either planar (shown) or ylindrial geometry. 449

4 in spae and time, resulting in a large effetive proessing volume. The free radials, primarily atomi oxygen 0(3P) and hydroxyl OH, oxidize organi ompounds to nonhazardous, easily managed ompounds suh as H 2 0, C0 2, and HC. The potential of nonthermal plasma proessing (dieletri barrier, orona, pulsed orona, et.) is atively being pursued through a variety of international researh efforts direted at flue gases (SOx and NOx) and hazardous organis (volatile organi ompounds- VOCs). We have foused on the silent disharge, whih is sometimes alled silent disharge plasma (SDP) beause of the potential for high energy effiieny, large volume proessing, sientifi and tehnologial maturity, and salability (all typial of ommerial ozone generation). Silent disharges are a natural means of reating plasmas whih are potentially lose to the optimal redued eletri field E/N for the prodution of oxidizing speies. They also operate at high pressures (atmospheri and above), resulting in high rates of hemial reation and large reator throughput. We have employed both single-barrier and double-barrier SDP reators in our experiments. A typial planar ell has approximate dimensions of 71-m length, 18-m width, and 2.5-mm gap, giving a mean disharge area of 1238 m2 and an ative disharge volume of 310 m3. Our prinipal eletrial power supply is a series inverter, whih swithes harged apaitors through a high-quality pulse transformer by means of high-power thyristors (see Fig. 5). This unit presently supplies nearly 4 kw of power at voltage pulse repetition frequenies up to 4.5 khz. Using this power supply and the planar ell, representative operating onditions for benh-sale tests are a flow rate of 10 std lit/min and an average power of 200 W. This gives an average eletrial energy density in the disharge of 1.2 J/m3, while the average area power density is approximately 0.16 W/m2. Fig. 5. +DC 1 -DC Lt SOP Cell v2 2 C!JHvA Ciruit shemati for the high-voltage, variable{requeny series inverter driver used in most of our experiments. Typial ell peak voltages are in the range kv for J1S pulses. The frequeny an be varied over a range of approximately 10Hz -3500Hz. We have demonstrated prototype-sale SDP destrution of aliphati hydroarbons, CFCs (hloro-fluoroarbons), TCE (trihloroethylene), and CC1 4. Gas flows of std lit/min and TCE onentrations in the range 650-1,000 ppm have been typial influent parameters for our tests, although higher flow rates have now been ahieved. Summary data is given in Fig. 6, whih plots the destrution effiieny for TCE and CCl 4 versus energy density for both wet ( -1% water vapor) and dry mixtures. At the water vapor onentrations employed in the illustrated results, the dry mixture gives greater removal for both TCE and CCl 4, whih may be a onsequene of Cl hain reations in the dry ase. 'C DryTCE WetTCE 90 v Dry CC4 'f WetCC4 > 80 e 1ii 'C : 70 0 n f! u Energy density (Joules/liter) Fig. 6. Plots oftce and CCl 4 removal versus energy density showing summary data for both wet and dry gas mixtures. The arrier gas was 80% Ar, 20% 02, order ppm hloroarbon, and 1-2% water vapor (if wet). Silent Dishar~e Plasma Reator Salin~ To sale SDP reators, the frational removal is related to the plasma energy density (average power <P>, divided by gas flow rate. For our wet experiments, doubling the reator power or halving the flow rate will result in the same destrution. For dry mixtures, whih may be dominated by hain reations, this saling parameter does not neessarily apply. A figure of merit for removal an be defined as the energy delivered to the plasma per hazardous moleule removed from the gas stream. A onvenient unit for the figure of merit is the number of kilowatt-hours required to remove a kilogram of hazardous ompound (i.e., kw -hr/kg). From the data presented previously, the removal figures of merit are determined to be approximately 12 kw-hr/kg for 90% removal oftce, 84 kwhr/kg for» 99% removal oftce (650-1,000 ppm to -100 ppb) and 270 kw-hr/kg for 90% removal of CCl 4. Another way to express this is in terms of the amount of energy required to destroy the ontaminant level by a fator of 10. We have named this fator the 9-fator, sine if three 9's destrution (i.e., or 99.9% destroyed) is required, three times the 9-fator must be applied to the waste stream. This fator has the units of J/lit (or J/m3). Preliminary values of the 9-fatorfor TCE are: 25.3 J/lit dry, and 75 J/lit wet. One advantage of this parameter, unlike kw -hr/kg, is that it is valid regardless of the initial onentration of waste. Using the 9-fator, saling alulations are simplified. For example, the removal of TCE under wet onditions an be saled as shown in Fig. 7, a plot of degree of destrution versus gas flow rate for one, two, and four ells. "0 6 ~ iii "0 4 -~~~ : ~ E : z Flow rate (liter/min) Fig. 7. Saling plot for the destrution oftce under hamid onditions. The number of nines destroyed is plotted versus the flow rate for one, two and four plasma ells. 450

5 The salability of SDP reators and assoiated power supplies is influened by the desired gas flow rate and the onentration of hazardous ompounds to be treated. Consideration of mehanial onstraints, single-point failures, and suessful arhitetures used in the ommerial ozone generation industry has led us to hoose modularization as a preferred approah. Currently, we are onsidering salable modules onsisting of ombinations of several smaller modules (see Fig. 8). This design will quikly enable a sale up of gas flow rates by fators of 10 to 100. For more orrosive ompounds double barriers an be used so that there is no ontat between the orrosive gas mixture and any metal surfae. Dieletri r shtets l 1 Gas teed (in) Manifold )/ HV eletrode "" """('"'""""'""'"""'"'"""" '" """""'"/ """""" '''''''' ''''' ' ( Ground eletrode #, J :~ ) (out), "''""""'""'"''""'"",,,,,,,,,,,,,,,,,,,,,,.,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, ~.. Disharge/ spae ~, ~ - Manifold Fig. 8. Shemati diagram of staked module ontaining four planar SDP ells, operated in parallel. Future Diretions Additional fators an influene the prodution of free radials in nonequilibrium plasmas. nvestigations worldwide are in progress on the effets of eletrial driver pulse width and rise time, eletrial drive iruit oupling to plasma ells, and the role of UV light in the plasma hemistry and disharge proesses. We speulate that, if free radial utilization is dominated by radial-radial reombination (whih may happen in mirodisharges), a fast rise time, homogeneous disharge may be more effiient in destroying ontaminants. This is yet to be demonstrated, but we plan to study this effet for SDP proessing. Summary and Conlusions We have alulated free radial prodution in aqueous solutions irradiated with eletron beams by varying dose rate, pulse duration, and pulse repetition rate. When radial-radial reombination dominates, low dose rates are more advantageous than high dose rates. However, a suitable appliation of repetitive short-duration pulses (e.g., 100 ns) gives radial onentrations and frational removals similar to a DC applied dose. New high-average-power pulsed linear indution aelerators are judged to be advantageous to onventional eletrostati aelerators for waste treatment beause of relaxed requirements on high voltage isolation, ease of saling to high power, modularity, smaller physial size, and broad range of power ontrol. Referenes [1] W.J. Cooper, M.G. Nikelsen, T.D. Waite, and C.N. Kuruz, "High Energy Eletron Beam rradiation: An Advaned Oxidation Proess for the Treatment of Aqueous Based Organi Hazardous Wastes," in Proeedings of the Symp. on Advaned Oxidation Proesses for the Treatment of Contaminated Water and Air, Toronto, Canada (June 1990). [2] L.A. Rosoha, D.A. Seeker, and J.D. Smith, "Eletron-Beam Tehnology for Detoxifiation and Sterilization of Aqueous Based Hazardous and Biologial Wastes," EPR/NSF Symposium on Environmental Appliations of Advaned Oxidation Tehnologies, San Franiso, California, February [3] R.B. Kidman and K.S. Tsuji, "Preliminary Cost Comparison of Advaned Oxidation Proesses," Los Alamos National Laboratory report, LA MS (June 1992). [4] L.A. Rosoha, D.A. Seeker and J.D. Smith, "Kineti Modeling oftce and Carbon Tetrahloride Removal from Water by Eletron-Beam rradiation," Amerian Chemial Soiety & EC Speial Symposium on Emerging Tehnologies in Hazardous Waste Management, Atlanta, Georgia (September 1992). [5] J.H. Jaob, "Reliable Low Cost ndution Aelerator System for Treatment of ndustrial and Muniipal Wastewater," private ommuniation, Siene Researh Laboratory, Sommerville, Massahusetts (August 1991). [6] H.C. Harjes, K.J. Penn, K.W. Reed, C.R. MClenahan, G.B. Laderah, R.W. Wavrik, J. Adok, M. Butler, G.A. Mann, L. Martinez, F.A. Morgan, G.J. Weber, and E.L. Neau, "Status of the Repetitive High Energy Pulsed Power Projet," in Proeedings of the 8th EEE Pulsed Power Conferene (June 1991), [7] L.A. Rosoha, G.K. Anderson, L.A. Behtold, J.J. Coogan, H.G. Hek, M. Kang, W.H. MCulla, R.A. Tennant, and P.J. Wantuk, "Treatment of Hazardous Organi Wastes Using Silent Disharge Plasmas," in Proeedings of NATO Advaned Researh Workshop on Nonthermal Plasma Tehniques for Pollution Control, Cambridge, England, September , 1992 (to be published by Springer-Verlag). [8] L.A. Rosoha, "Nonthermal Disharge Session Summary,"and other papers, EPR/NSF Symposium on Environmental Appliations of Advaned Oxidation Tehnologies, San Franiso, California, February Nonthermal disharge plasmas also show promise for the removal of VOCs and other air toxis suh as SOx and NOx in flue gas. Removal figures of merit have been established and reators have been saled to energy density levels that will permit industrial servie. Basi understanding of the plasma hemistry has evolved to the point where trends and equipment saling an be predited with reasonable onfidene [8]. Beause the proess an simultaneously remove different types of pollutants, it is partiularly attrative for future environmental appliations. 451