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F E A T U H E t

Electron beam processing off lue gases: Clearing the airStricter environmental standards are demanding a system thaisimultaneously removes SO2 and A/Ox from th e burning of fuels

M l u c h h as happened over th e past 5 years toes tab l ish the economic and env i ronm enta lc reden t ia ls o f what could be a t imely rad ia t iontechno logy electron beam processing for theremoval o f po l lu tan ts f rom combust ion f luegases. Stud i e s ha v e i n d i c a t ed t ha t the a i rbornetransport of pollutants such as su l fur d iox ide(SO2) a n d n i t r o g e n o x i d e ( N O X ) a r e m o r ewidespread than p rev ious ly thought . N O X emiss ions areconsidered to be aneq ua lcause of acid rain when compared to SO2, a factw h i c h i s leading to the development of systemsthat s i m u l t a n e o us ly remo v e b o th g a se s . Many coun t r i es have passed more s t r ingen tai r qua l i ty regula t ions w hich w i l l requi re h i g h e rr e m ova l ef f i c i enc ies . The use of byproduc ts f rom removal sys temsw i l l be more impor tan t in the f u t u r e to e l i mi n a t eano ther waste p rob lem which occurs f rom thes ludges p roduced in ma ny sys tems. The electron beam process has had ex t en s i v etest ing over the past 3 years, an d many improve-ments have been made in its re l i ab i l i ty and ener -g y r eq u i r emen t s .

It is easy to see why many coun t r i es a rebe g inn ing to consider m ore s t r ingen t regu la t ionsto remove SCh and N O X at the source of emis-s ions they recogn ize th e t ransport and conver -sion t ha t can take place in the atmosphere. (Seefigure, next page.) E mi ss i o n s f r o m c o mb us t i o ngases from a bo i le r can be carr ied ma n y k i lo -meters . Along th e w a y , t hey un d e rg o n umero usconvers ions , as the SO: aerosols change intosu l fu r i c acid and the N O X aerosol in to ni tr ic acid.This then creates a wet disposal of su l fur ic andnitr ic acids in rain , sleet, and sno w. Cu rre ntl y ,

M r Frank is Pres ident of Ebara Envi ronmenta l Corpora t ion inG r e e n s b u rg , P e n n s y l v a n i a , U S A . a n d M r M a r k o v i c is a staffmember in t he IAEA D ivis ion of Phys i ca l and Chemica lSc iences .

dry deposi t ions of the original p o l l u t a n t s t ravelgreat distances from the source.More s t r ingen t env i ronmenta l regula t ionshave been put in to e f fec t throughout EuropeJapan , th e U n i t ed States, Asia , an d severa l La t inAmer ican coun t r i es . It is an t i c ipa ted tha t increas ing ly s t r i c te r regula t ions wi l l appear in th rfu ture , i n l ight o f con t inu ing concerns over bo ths u l f u r an d n i t r o g en p o l lu t a n t s .I t is fur ther an t i c ipa ted tha t m eet ing requi remen t s f o r "ozone n o n -a t t a i n men t " w i l l r eq u i r emore str ingent N O X standards. This is alreadybe ing seen in some of the coming regulat ions. Itis fo reseen tha t ex t reme ly e f f i c i en t s i m u l t a n e o u sSO2 an d N Ox r em o v a l sy s tems w i l l be needed .A t the p resen t t ime, the conven t iona l tech-no log ies to reduce SO 2 and N O X emissions arebas ica l ly used fo r low -sul fur coa ls tha t a reburned in Japan and Europe. T hese systems arereferred to as wet f lue gas d esu l fu r i za t i o n ( F G D )and se lec t ive ca ta ly t i c reduc t ion (SCR). SCR i sthe most popula r N O X r emo v a l sys tem, ev enthough it has not been proven for use w i th h i g h -

by Norman WFrank andVitomir Markovic

IAEA BULLETIN, 1/1994

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FEATURES

Atmospheric conversionSO - SulfatesNOX -NitratesSulfates Sulfuric acidNitrates -> Nitric acid Wet dispositionSulfuric and nitric acids

in rain, sleet, and snow

Transport and mixingLess than 200 kmdry depositionSOx, NO participates Dry depositionOriginal pollutantsSulfates, Nitrites

EmissionsUtility and industrial boilersSOx, NOX participates

Terrestrial transport and conversionAdditional chemical reactions and acidification

Atmospheric s u l f u r coal. FG D and SCR a re s ys tems w hichtransport require tw o different technologies integratedprocesses into a pollu tion control process for the boiler.Therefore, it is importan t that s ys tems u t i l i z -in g a s ingu lar technology be developed to meetth e f u t u r e r e q u i r e m e n t s for the simultaneousre m o v al of both SCh and N O X f rom both l o w -and h i g h - s u l f u r coal an d oil.T he electron beam process fi ts very wel l intothis category s ince it is a s ys tem which u t i l i z e sthe same basic technology to simultaneouslyremove both pollutants. (See diagram.) Japanese,Germ an, Un ited States, and Polish demonstrationplants have shown that th e s ys tem's to tal ef f icien-cy fo r SO 2 removal n ormal ly exceeds 95% andreaches 80% to 85% for N O X remov al. That levelof ef f iciency meets th e mos t s t r in gen t regu la toryre q u i re m e nts .N O x removal requires more energy than SChremoval , w hich i s why n u m e r o u s s t u d i e s h a v ebeen done on the technique known as zone ir-

radiation to low er th e en ergy requi remen ts forN O x removal. Tests have been and are c u r r e n t l ybeing conducted to m i n i m i z e th e en ergy i np u tfor N O X removal . B y u t i l i z i n g zon e i r rad iat ion ,th e res u l t s have s how n that en ergy s avin gs of20% to 30% can be realized, which w o u l d bringth e system into a very competitive range wi t hother combined technologies . Work w il l con-t i n ue on r e d u c i n g th e s ys tem's en ergy requi re -men ts .E xi s t i n g electron beam test facil i t ies an ddemonstration plants have been b u i l t in a n umberof countries, an d f o u r test facilities remain inoperation. They are being operated by theJapanese Atomic Energy Research Institute(JAERI ) in Takasaki , Japan; th e Ins t i tute ofCh e m is t ry and Nuclear Techn ology in Wars aw ;

K FK in Karls ruhe , German y; an d Ebara inFujisawa, Japan. These test facilities ar e con-d uc t i n g programmes to improve th e process andre du ce en ergy requi remen ts .M a n y n otew orthy accompl is hmen ts havebeen made in the past few years at the v a r i o u sresearch facil i t ies and pilot plants : The mass balances of both nitrogen and sul-fu r have been confirmed with th e finding thatab o u t 22% of the nitrogen is released as N 2 O . Du ct configur ations have been s tudied andtested so that dif ferent ones ar e available to s u i tth e conditions. Zone irradiation has been tested and con-f i rmed as a s ignificant reducer of en ergy requi re -men ts . Different methods for avoiding the b u i l d u pof b y p r o d u c t s and d uct c loggin g w ere an alyzedan d tested which will allow long-term operationof th e process. Low N O X concentrations in gases have beentested with good res u l t s . Tes t in g is c o n t i n u i n g on the r e m o v a l ofvolati le organic compounds. Testing is con t in uin g on incinerator gases;this is provid in g valu ab le in format ion con cern-ing the r e m o v a l of other po l lu tan ts , s uch ash y dro g e n chloride (HCL). A recent report by the Electric Power Re-search Institute (EPRI) in the United States hasshown that the electron beam process is beingconsidered as one of the f u t u r e s i m u l t a n e o u sremoval s ys tems for SCh and N O X . Existing electron beam accelerators haveprogressed to larger s izes (300-400 k i l o w a t t s )with good reliability for immediate use. The United States Defen s e N ucl ear A gen cyis d evelopin g an accelerator in the s ize ran ge of

8 IAEA BULLETIN, 1/1994

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