CA1272179A - Catalytic combustion type exhaust gas processing device and coating drying furnace utilizing the same - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A catalytic combustion type exhaust gas processing device wherein noxious/smelly components contained in exhaust gases are deodorized and purified through sequential oxidative decomposition by at least one catalyst layer composed of platinum and/or palladium catalysts and a copper-cerium catalyst compris-ing chemically active species of copper and cerium in a com-pounded form. The device can be applied effectively to a drying furnace, for example, used in the coating for automobile use.

Description

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Thls lnven-tlon concerns a cataiytic comi~ustlon-tYPe cxllnu~ JM3 procc3~In~ dovlco ror dcoclor 1~1 n~ ~n~l plJr I ry I n~ nox--lous/smelly components contalned In exhaus-t gases through oxida-tlve decompos~t~on ~n a ser~es of cata~yst layers, as well as a 5 coating drylng furnace that ut~llzes suci~ a catalytlc exhaust gas combust1on devlce.

In -those facllltles such as drylng ~urnaces for use In coatlng and prln~ln~, manu~acturlng apparatus for plastlcs or plywoods, food processlng facllltles, Industrlal wastes process-ing facllltles and facllltles for manufacturlng Fire extlngulsh-Ing agents or perfumes, whlch use palnts, ~nks, so~vents, adhe-slves, synthetlc reslns or chemlcal agents, noxlous/smeily compo-nents such as alcohols or esters and phenols or aldehydes whlch are noxlous and have pecullar odors are produced tendlng to dete-rlorate the alr qualIty of the workplace.

Therefore, l~ has been requlred to dlscharge such exhaust gases contalnlng noxlous/smelly components out of the 20 f acllltles, but It has been prohlblted to release them dlrectly to the atmosphere, In vlew of the deslre for preventlon of pol lu-tlon. Accordlngly, the exhaust gases have usually been deodor-lzed and puri f led by belng passed through a cataIytic combustlon-type exhaust gas processlng devlce and dlscharged after the nox-25 lous/smelly components are flnally decomposed oxldatlvely Intonon-toxic and odorless gaseous carbon dloxlde and water.

As the catalyst for constltutlng the catalyst layer In the exhaust gas processlng devlce, varlous catalysts such as platlnum, palladlum, cobalt oxlde and manganese oxide have been used. Among them, those catalysts comprising platlnum group met-als such as platlnum (Pt), palladlum (Pd) and a platinum-palla-dlum mlxture (herelnafter collectlvely referred to as a platlnum-type catalyst) have becn used generally slnce they have an 3~ extremely hlgh oxldlzlng actlvlty and are thermally stable.

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However, although a platlnum-type catalyst can promote the dehydrogenatlng reactlon of phenols or alcohols and effec-tlvely produce aldehydes, It has been conflrmed experlmentally that even such platlnum-type catalysts are poor In the perfor-mance of further convertlng ~he aldehydes Into carboxyllc acldsand flnally decomposlng them Into non-toxlc and odorless, gaseous carbon dloxlde and water. Accordlngly, exhaust gases deodorlzed In an exhaust gas processlng devlce havlng a catalyst layer com-posed only a plat I num-type catalyst cont~ln a gre~t amount of aldehydes as the Intermedlate products of the catalytlc oxlda-tlon, whlch causes atmospherlc pollutlon.

Further, In a drylng furnace for use In coatlng adapted, for examp I e, for baklng or drylng automoblle bodles, slnce the Inslde of the furnace Is usually heated to such a hlgh temperature (to about 170 to 180C) for reactlng to harden the palnt fllms, noxlous/smelly components such as organlc solvents, for example, thlnner and toluene, curlng agents or palnt reslns are evaporated from the palnt fllms. When the concentratlon of the noxlous/smelly components In the furnace Is Increased, It causes yellowlng and defectlve drylng of the palnt f I Im~, thereby lowerlng the qualIty of products and worsenlng the worklng clr-cumstances. Accordlngly, the exhaust gases In the furnace have also been deodorlzed and purlfled In a catalytlc combustlon-type

2~ exhaust gas processlng devlce and then dlscharged Into the atmo-sphere.

Slnce the gases deodorlzed and purlfled by passlng through a catalyst layer of an exhaust gas processlng devlce are heated to a hlgh temperature of about 300 to 500C, whlch Is the reactlon temperature of the catalyst, there has recently been proposed a technology for effectlvely utlllzlng the processed gases as a heat source for the Inslde o~ the furnace by recyclIng them Into the furnace agaln wlthout releaslng them dlrectly to

3~ the atmosphere, for example as descrlbed In Japanese Patent Pub-llcatlons Nos. 175785/1983 and 12946/1984.

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How~v~r, slnce a platlnum-type catal y5 t has been used for the catalyst layer In the exhaust gas processlng devlce of thls klnd, processed gases recycled through the furnace contain a great amount of aldehydes, and It has been exPerlmentallY found by the present Inventors that t~le concentratlon of oxo comPounds or the llke havlng aldehyde groups In the furnace Is Increased, to produce a great amount of tarry or reslnous substances that cause yellowlng or In~er-layer defollatlon of the palnt fllms.

The present Inventlon provldes a catalytlc combustlon-type exhaust gas processlng devlce havlng a serles of dlfferent catalyst layers together capable of promotlng the dehydrogenatlon of noxlous-smelly components contalned In exhaust gases and effectlvely decomposlng them oxldatlvely Into aldehydes, further, effectlvely convertlng the aldehydes through oxldatlon Into car-boxyllc aclds and, further, oxldatlvely decomposlng them flnally Into non-toxlc and odorless gaseous carbon dloxlde and water.

The present Inventlon also provldes a coatlng drylng furnace that utlllzes the novel exhaust gas processlng devlce, capable of suppresslng the formatlon of tarry or reslnous sub-stances In the exhaust gases whlch are dlscharged from the drylng furnace and then recycled agaln Into the furnace, In order to surely prevent the yellowlng or Inter-layer defollatlon of the 2~ palnt flIms.

Accordlng to the present Inventlon there Is provlded a catalyst combustlon-type processlng devlce for exhaust gas dls-charged from Industrlal facllltles and contalnlng volatlle nox-lous/smelly components, sald devlce comprlslng a catalytlc reac-tor houslng comprlslng wall means deflnlng a chamber havlng an Inlet and an outlet for a gas stream followlng In a dlrectlon along a path; a fIrst catalyst layer dlsposed In sald chamber for dehydrogena~lng noxlous/smelly components contalned In a gas 3~ stream, sald flrst catalyst layer comprlslng, In sequence along sald path, a flrst sub-layer and a second sub-layer, each sald ~' L~3 sub-layer comprlslng at ieast one platlnum group metal selected from the group conslstlng of pla~lnum, palladlum, and rnlxtures thereof, sald at leas-t one platlnum group metal belng carrled on a support; said support, In sald flrst sub-layer belng made of heat-reslstant ~lbers; and a second catalyst layer dlsposed In sald chamber downstream of sald second sub-layer oF sald fIrst catalyst layer, sald second ca-talyst layer comprlslng a copper-cerium compound carrled on a support, for oxldatlvely decomposlng components dehydrogentated by sald ~Irst and second sub-layers of said f I rst catalyst layer and thereby effectlvely decomposlng noxlous/smelly components. Sultably sald support ~or sald second catalyst layer Is made of porous ceramlc materlal. Deslrably sald support -For sald second catalyst layer Is made of heat-reslstant flbres. Sultably sald support for sald second sub-layer of sald f Irst layer belng one whlch Is made of pellets, andsald support for sald second layer belng made of porous ceramic materlal.

Thus, the catalytlc combustlon-type exhaust gas pro-cesslng devlce comprlses a serles of catalyst layers for deodor-lzlng and purlfylng noxlous/smelly components contalned In exhaust gases through oxldatlve decomposltlon, In whlch the cata-lyst layers are composed of a platlnum-type catalyst comprlslng at least one platlnum group metal ranked before a copper-cerlum 2~ catalyst comprlslng chemlcally actlve copper and cerlum In a com-pounded form.

The present Inventlon also provldes a furnace for heat-lng and drylng a coatlng on an obJect, comprlslng: an enclosure for recelvlng an obJect havlng a coatlng whlch Is to be heated and drled; a recycle loop communlcated both at a return duct end thereof and at a supply duct end thereof wlth sald enclosure and Incorporatlng a means for heatlng In sald recycle loop a gas stream belng recycled from and to sald enclosure, and a catalytlc 3~ combustlon-type processlng devlce for exhaust gas dlscharged from Industrlal facllltles and contalnlng volatlle noxlous or smelly ` ~

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components, sald devlce comprlslng: a catalytlc combustlon-tYPe exhaust gas-processlng devlce, comprlslng: a catalytlc reactor houslng comprlslng wall means deflnlng a chamber havlng an Inlet and an outlet for a gas stream flowlng In a dlrectlon along a path; a fIrst catalyst layer and a second catalyst iayer, dls-posed In sald chamber, for belng sequentlally contacted by sald gas stream when flowlng In sald dlrectlon along said path; sald flrst catalyst layer comprlslng at leas~ one quantum of at least one platlnum group metal, each such at least one quantum belng dlsposed on a respectlve fIrst support; and sald second catalyst layer comprlslng by a quantum of chemIcally actlve copper, and cerlum, In the form of a copper-cerlum compound, dlsposed on a second support; sald Inlet of sald chamber belng In communlcatlon vla duct means wlth sald enclosure and adapted to recelve through sald duct means a gas stream wlthdrawn from sald chamber for pas-sage along sald path, whereby thls gas stream Is processed In sald chamber and, after belng proce sed, passes therefrom through sald outlet of sald chamber. Sultably sald heatlng means com-prlses a heat exchanger, a heater posltloned and arranged to heat a gas stream In sald duct means, a duct to atmosphere connected to sald outlet of sald chamber, and sald recycle loop, Intermedl-ate saId ends thereof, and saId duct to atmosphere belng dlsposed In Indlrect heat exchange relatlon through sald heat exchanger.
Deslrnbly sald chamber of sald cat~lytlc reactor houslng Is 2~ Interposed In sald recycle I oop, I ntermedlate sald ends of sald recycle loop, wlth a correspondlng part of sald recycle loop pro-vldlng a portlon of sald duct means; and sald heatlng means com-prlses a heater Interposed In sald recycle loop, Intermedlate sald chamber of sald catalytlc reactor, and sald return duct end of sald recycle loop. Preferably sald heatlng means comprlses a heater for heatlng a gas stream In sald duct means, and a duct connectlng sald outlet of sald chamber wlth sald recycle I oop, Intermedlate sald ends thereof.

3~ Thus the coatlng drylng furnace comprlses a catalytlc combustlon-type exhaust gas processlng devlce havlng a serles of 1?-`

catalyst layers for deodorlzlng and purlfylng noxlous/smelly com-ponents formed In a drylng furnace, In whlch the catalyst layers are composed of a platlnum-type catalyst comprlslng at least one platlnum group me~al and a copper-cerlum catalyst comprlslng chemlc~lly nctlv~ copp~r and c~r I um In a compounded Form.

In the exhaust gas processlng devlce accordlng to thls Inventlon, slnce the noxlous/smelly components In the exhaust gases passed throush the catalyst layer are decomposed through dehydrogenatlon Into aldehydes by the ald of the platlnum-tyPe catalyst havlng a hlgh oxldlzlng actlvlty and the thus-decomposed aldehydes are effectlvely decomposed oxldatlvely by way of car-boxyllc aclds and fInally Into non-toxlc/smelly gaseous carbon dloxlde and water through the substantlally complete oxldatlon by the ald of the copper-cerlum catalyst, the concentratlon of the aldehydes In the gases processed by passlng through the catalyst layer Is remarkably reduced.

Further, In the drylng furnace for use In coatlng accordlng to thls Inventlon, If the noxlous/smelly components In the exhaust gases dlscharged from the furnace are effectlvely decomposed In the exhaust gas processlng devlce as descrlbed above and then recycled through the furnace as a clean hot flow at an extremely low aldehyde concentratlon, formatlon of the tarry or reslnous substances In the furnace can be suppressed.

Preferred embodlments of thls Inventlon are further Illustrated by way of the accompanylng drawlngs, whereln:-Flgure 1 Is a longltudlnal cross-sectlonal vlew for one embodIment of a catalytlc combustlon-type exhaust gas processlng devlce accordlng to thls Inventlon;

Flgure 2 Is a flow sheet of one embodlment of a coa-tlng drylng furnace uslng the exhaust gas processlng devlce of thls Inventlon;

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Flgures 3 and 4 are, respectlvely, flow sheets of, respectlvely, second and thlrd embo~lments o~ the coa-tlng drylng furnace accordlng to this Inventlon; and 5Flgure 5 Is a longltudlnal cross-sectlonal vlew, slml-lar to Flgure 1, of a varlatlon of the devlce.

Thls Inventlon wlil now be descrlbed more speclflcally In detall by way of preferred embodlment.~ shown I n the dr~w I ngs.

Exampls 1 Flgure 1 shows a longltudlnal cross-sectlon for one embodlment of a catalytlc combustlon-type exhaust gas processlng devlce accordlng to thls Inventlon.

The exhaust gas processlng devlce 1 comprlses a reactor 2 and a serles a catalyst layers 5 dlsposed thereln between an Inlet 3 and an exlt 4 thereof. The serles of catalyst layers 5 Is constltuted by ~In thls embodlment) a platlnum-palladlum cata-lyst 5a carrled on a support made of heat-reslstant flbers, another platlnum-palladlum catalyst 5b carrled on a support made of pellets and a copper-cerlum catalyst 5c carrled on a porous ceramlc support, ranked In the order Just descrlbed, from the Inlet 3 to the exlt 4.

In thls embodlment, the catalyst 5a carrled on the sup-port made of heat-reslstant flbers Is dlsposed nearest the Inlet 3 of the reactor 2, so that solId partlcles such as dust con-talned In exhaust gases or obstacles produced through Incompletecombustlon of noxlous/smelly components may not deposlt on the pellet-lIke catalyst 5b nor on the porous ceramlcs catalyst 5c and, by dolng so, Increase the pressure drop or degrade the cata-lysts ~b and ~c to Impalr the catalyst llfe.

Further, the platlnum-type catalysts, I.e., the cata--ty~

Iyst 5a and the catalyst ~b of the same platlnum-palladlum combl-natlon are cascaded In thls embodlmen-t, so that t~)e dehydroyena-tlon ror -the componcnt~ cont~lncd In thc cx11~u5t Drlscs may bc effectlvely promoted further. Furthermore, pellets of a hlgher heat conductivlty are used as the support for the catalyst 5b, so that the heat of reactlon can be removed wlth ease to prevent the degradation in the oxldlzlng actlvlty and the selectlvlty due to overheatlng of tl~e cataIyst ~b belng put between the cataIysts ~a and 5c, thereby promotlng the catalyst llfe.

Furthermore, the copper-cerlum catalyst 5c comprlslng chemlcally active specles of copper and cerlum In the compounded form Is carrled on a porous ceramlc support, because the porous ceramlc support can carry the copper-ceramTc type catalyst more easlly, as cornpared with a heat-reslstant fIber support for thls catalyst, and It results In a lower pressure drop as compared wlth other supports known at present. Although It Is posslble to carry the copper-cerlum ca-talyst on pellets, slnce the pellets cause a greater pressure drop, It Is not preferred to dlspose a Cu-Ce pelle-t-lIke catalyst In cascade succeedlng to the catalyst 5b.

The operatlon o~ the flrst embodIment of a coatlng dry-lng furnace uslng the exhaust gas processlng devlce accordlng to 2~ thls Inventlon wlll now be explalned referrlng to Flgure 2.

The coatlng drylng furnace of Flgure 2 Is deslgned such that automoblle bodles 8,8, etc. are contlnuously conveyed to the Inslde of a reactor maln body 7, and heated thereln to a hlgh 30 temperature of about 170 to 180C for baklng to dry palnt fllms thereon.

A hot gas flow recycllng path N Is dlsposed for recyclIng a hot gas flow through the furnace rnaln body 7 by way 3~ of a recyclIng blower 9 and It Is adapted so as to feed alr In the furnace sucked (I.e. drawn) from a return duct 10 Into a heat ~S~

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exchanger 11, and to Introduce hot alr heated throu~h heat exchange In the hea-t exchanyer 11 into ~he furnace maln bod~ 7 agaln by way of a supply duct 12.

Exhaust gases containing noxiousJsmelly components pro-duced ~n the furnace maln body 7 upon heatlng the palnt fllms on the nlltomobllo ho~ , etc. ~rc sucke~l nnd dlsch~r~ed at an exhaust duct 14 by way oF the suction blower 1~, supplled to the exhaust gas processlng device 1 accordlng to thls Inventlon, deodorlzed and cleaned by belng passed through the series of cat-alyst layers 5 dlsposed In the reactor 2, sent by way of the duct 15 Into fInned tubes of the hea-t exchanger 11 and then dIscharged to the atmosphere by way of the duct 16 after causlng heat to release from the flns or the tubes to thereby ~eat the alrs In the furnace flowlng through the hot gas flow recycllny path N.
The catalyst layer dlsposed In the reactor 2 of the exhaust gas processlng devlce 1 Is heated to about 300-500C, whlch Is a reactlon temperature oF the catalyst, by a heater 17 such as a burner. When the exhaust gases contalnlng the nox-lous/smelly components such as phenols or alcohols are supplled from the Inlet 3 of the reactor 2 and passed through the catalyst layer 5, the solId partlcles such as dust contalned In the exhaust gases dlscharged from the Inslde of the furnace maln body 7 are at flrst removed by the fllterlng effect of the catalyst 5a carrled on the respectIve heat-reslstant flber support and, slmultaneously, the catalyst 5a together wlth the catalyst 5b, whlch Is dlsposed Just downstream thereof and carrled on the respectlve pellet support, effectlvely promote dehydrogenatlon to oxldatlvely decompose the noxlous/smelly components, I.e., phe-nols or alcohols Into aldehydes.

Then, the copper-cerlum catalyst 5c, carrled on the respectlve porous ceramic support, effec-tlvely promotes the oxl-datlon of the thus-formed aldehydes and fInally decomposes them through carboxyllc acIds Into non-toxlc and odorless gaseous car-y~

bon d I ox I de ~nd water.

Slnce clean, deodorlzed gases at an extremely low alde-hyde concentra~lon are dlscharged from the exlt 4 of the reactor 2 and they have served for the effectlve utlllzatlon of the waste heat by way of ~he heat exchanger 11 and are then dlscharged through the duct 16 to the atmosphere, It Is posslble to surely prevent atmospherlc pollutlon by the exhaust yases.

Partlcularly, atmospherlc pollutlon can slgnlflcantly be reduced by the structure In thls embodIment whereln the plat-lnum-palladlum type catalysts 5a,5b havlng hlgh oxldlzlng actlv-lty and capable of effectlvely promotlng the dehydrogenatlon of the noxlous/smelly comPOnents Into aldehydes are dlsposed In cas-cade, I.e. sequentlally, and the copper-cerlum catalyst 5c cap-able of effectlvely promotlng the oxldatlon of the aldehydes Into non-toxlc and odorless gaseous carbon dloxlde and water Is pro-vlded as a subsequent layer In the sequence.

Furthermore, slnce the catalyst 5a carrled on a support made of heat-reslstant fIbers havlng a fllterlng effect Is dls-posed nearer the Inlet 3 of the reactor 2 to whlch the exhaust gases are fed, dust or the llke In the exhaust gases Is removed through the catalyst 5a to prevent clogglng In the catalyst 5b carrled on the pellet support and the copper-cerlum catalyst 5c carrled on the porous ceramlc support dlsposed downstream thereof. Therefore, the entlre pressure drop of the catalyst layer 5 and wearlng degradatlon In the catalysts 5b and 5c can surely be prevented, thus remarkably Increaslng the catalyst life.

Furthermore, slnce the catalyst 5b put between the cat-alyst 5a and the catalyst 5c Is carrled on a pellet-lIke support wlth a smaller surface area In thls embodlment, the heat of reac-tlon can easily be removed from the catalyst 5b to suppress thedegradatlon due to overheatlng In the oxldlzlng actlvlty and the _ 10 -selectlvl ty, by Whl ch the catal yst ~ I fe can be Improved also In thls regard. In addltlon, If a porous ceramlc member wlth a small pressure drop Is used as the support for the copper-cerlum catalyst 5c dlsposed as the final stage In thls embodlment~ the use of the Pellet-llke support wlth a relatlvely large pressure drop Is enabled for the catalyst sb whlch Is put between the cat-alyst 5c and the catalyst 5a and ll~ely to undergo overheatlng.

As descrlbed above, the exhaust gas processlng devlce 1 can effectlvely remove the aldehyde components In the exhaust gases dlscharged from the varlous facllltles such as a coating--drylng furnace thereby preventlng the atmospherlc pollutlon.

Although the catalyst 5b Is put between the catalysts 5a and 5c In the embodlment of the exhaus~ gas processlng devlce Illustrated In Flgure 1, the catalyst 5b may be omltted In thls Inventlon. In addltlon, the copper-cerlum catalyst 5c may be carrled on other support3 than a porous ceramlc support; for Instance, It may be carrled on a heat-reslstant flber support as Is Illustrated for the catalyst serles 5' at 5c' In Flgure 5.

Example 2 Flgure 3 shows a flow sheet Illustratlng a second embodIment of a coatlng drylng furnace accordlng to thls Inven-tlon.

In the drawlng, a hot gas flow recyclIng path N1 com-prlses a return duct 10 for sucklng to dlscharge exhaust gases contalnlng noxlous/smelly comPonents produced In a furnace maln body 7 and supplylng them to a catalytlc combustlon type exhaust gas processlng devlce 1 as shown In Flgure 1 and a supply duct 12 for dlrectly recyclIng processed gases at hlgh temperature cleaned by oxldatlon In the exhaust gas processlng devlce 1 dlrectly to the Inslde of the furnace maln body, In whlch a dust fllter 18 and a recyclIng blower 9 are provlded for the return ~7~

duct 10 and the supply duct 12, respectlvely.

The exhaust gas processlng devlce 1 disposed Intermedl-ate the ends of the hot flow recyc~lng path N1 Is adapted to heat tlle catalyst layer 5 In t~)e reactor 2 to abut 300-500C by uslng a burner 17 as a hea~er. Further, the serles of catalys-t layers ~ has a structure comprlslng a platlnum--type catalyst comprlslng platlnum and/or palladlum ranked before a copper-cerlum catalyst comprlslng chemlcally actlve copper and cerlum In a compounded form.
The opera-tlon oF the Flgure 8 embodlment oF the coatlng drylng furnace in accordance wl~h thls Inventlon wlll now be explalned.

At fIrst, the Inslde of the furnace maln body 7 Is pre-heated, alr and relatlvely clean fuel such as clty gas or llque-fled propane gas are supplled form a blower 19 to a burner 17 to produce gases, whlch are recycled through a recycllng blower 9 dlsposed at the mldway of the supply duct 12 to the Inslde of the furnace maln body 7 to heat the Inslde to a predetermlned temper-ature.

Then, when the Insl~e of the furnace maln body 7 2~ reaches a predetermlned temperatur~, for example, from 170 to 180C, automoblle bodles 8,8, etc., as coated obJects, are con-tlnuously conveyed to the Inslde of the furnace maln body 7 where palnt fllms are baked and drled.

In thls case, noxlous/smelly components such as phe-nols, thlnner and toluene are evaporated from the palnt fllms on the respectlve automoblle bodles 8 heated to a hlgh temperature In the furnace maln body 7 to contamlnate the hot gas In the fur-nace. The contamlnated hot gas In the furnace Is suclced to dls-3~ charge from the return duct 10 as exhaust gases whlch are removed wlth dust through the dust-fllter 18 and then supplled to the exhaust gas processlng devlce 1.

The exhaust gas processlng devlce 1 Includes a serles Q F catalyst l~yers 5 llavlng a platlnum-type ca~nlys~ cupable of effectlvely promotlng the dehydrogenatlon ~or converting the nox-lous/smelly components In the exhaust gases Into aldehydes ranked before a copper-cerium catalyst capable of effectlvely promotlng the oxldatlon of flnally decomposlng oxldatlvely the thus formed aldehydes by way of carboxyllc aclds Into non-toxlc and odorless gaseous carbon dloxlde and water, whereby the noxlous/smeliy com-ponents In the exhaust gases sucked to dlscharged ~rom the return duct 10 are oxldatlvely decomposed substantlally completely to reduce the amount of unreacted aldehydes that form tar-lIke or reslnous substances causlng the yellowlng and Inter-layer defoli-1~ atlon of the palnt fllms as compared wlth usual case.

Further, slnce the catalyst layer 5 Is heated to thecatalytlc reactlon temperature from 300 to 500C (usually about 400C), by the burner 17, the exhaust gases deodorl~ed and purl-fled In the catalyst layer and purlfled In the cataIyst layer 5are recycled agaln In the furnace maln body 7 through the supply duct 12 In the form of a clean processed gases heated to a suffl-clent temperature to heat the lnslde of the furnace maln body 7.

2~ As descrlbed above, In the coatlng drylng furnace In accordance wlth thls Inventlon, since the concentratlon of the aldehydes in the processed gases recycled through In the furnace maln body 7 Is extremely low, formatlon oF tar-llke substances causlng the yellowlng or Inter-layer defollatlon In the palnt fllms can be suppressed to slgnlfIcantly Improve the coatlng qualIty, whlch Is extremely useful for the automoblle coatlng for whlch an especlally hlgh quallty coatlng Is demanded.

Although the descrlptlons have been made In the above 3~ embodlment to a drylng furnace for use In coatlng In whlch the exhaust gas processlny devlce 1 Is dlsposed at the mldway of the ~' , . ~

h-~3 hot flow recycllng path N1, thls Inventlon Is no way llmlted to such a constructlon. For Instance, as shown In Flgure 4, the dryl n~ furnace may be desl~ned such that exhaust gases sucked by a recyclIng fan 21 provlded In an exhaust duct 20 are supplled to and odorlzed and purlfied In the exhaust gas processlng devlce 1, the processed gases are Introduced by way of a connectlon duct Z2 Into a hot blow recyclIng Path N2 and alrs In the furnace sucked by a recyclIng blower 9 dlsposec~ Intermedlate the ends oF the hot flow recyclIng path N2 are heated and recycled ~hrough the supply duct 12 to the Inslde of the furnace maln body 7. Further, If an auxlllary burner for temperature control ~not Illustrated) Is dlsposed Intermedlate the ends of the hot flow recycllng path N2 In Flgure 4, the alrs in the furnace sucked from the return duct 10 of the hot flow recyclIng path N2 can be heated to a predeter-mlned temperature wlthln a short tlme, and the temperature In theInslde can aIways be malntalned constant by varlably controlllng the heat of combustlon In the auxlllary burner even In a case where the temperature Inslde the furnace maln body 7 varles due to the Increase/decrease of the number or amount of the automo-blle bodles 8 conveyed Into the furnace maln body 7.

As descrlbed above, the exhaust gas processlng devlce accordlng to thls Inventlon has an advantageous effect of remark-ably reduclng atmospherlc pollutlon or the llke as compared wlth the conventlonal devlce, slnce exhaust gases contalnlng the nox-lous/smelly components are passed through a serles of cataIyst layers Includlng a platinum-type catalyst capable of effectlvely promotlng the dehydrogenatlon ran~ed In sequence before a copper-cerlum catalyst capable of effectlvely promotlng the oxldatlon for oxldatlvely decomposlng the aldehydes formed through the dehydrogenatlon through carboxyllc acIds flnally Into non-toxlc and odorless gaseous carbon dloxlde and water, and the concentra-tlon of the aldehydes as the Intermedlate products of the cat-alytlc oxldatlve reactlon In the processed gases Is extremely lowered~

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Furthermore, the coatlng drylng furnace accordlng to thls Inventlon has an excellent effect, In that the concentratlon or the aldehydes In ~le proce~ed ga3e3 3U~ Lo ~ rl~ I ~C O r the furnace Is slgnlflcantly reduced as compared wlth ~he conven-tlonal drylng furnace of thls type and the formatlon of the tar-llke or reslnous substances causlng yellowlng or Inter-layer defollatlon of ~he Palnt fllms Is suppressed to slynlfIcantly Improve the coatlng quallty, slnce the ex~laust gases contalnlng the noxlous/smelly components generated In the furnace are deodorlzed nnd purlfled In the exhaust ga~ proces31ng devlce as descrlbed above and then, In some embodIments, recycled to the drylng furnace.

~5 ~0 3~

Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A catalytic combustion-type processing device for exhaust gas discharged from industrial facilities and containing volatile noxious/smelly components, said device comprising a cat-alytic reactor housing comprising wall means defining a chamber having an inlet and an outlet for a gas stream following in a direction along a path; a first catalyst layer disposed in said chamber for dehydrogenating noxious/smelly components contained in a gas stream, said first catalyst layer comprising, in sequence along said path, a first sub-layer and a second sub-layer, each said sub-layer comprising at least one platinum group metal selected from the group consisting of platinum, palladium, and mixtures thereof, said at least one platinum group metal being carried on a support; said support, in said first sub-layer being made of heat-resistant fibers; and a second catalyst layer disposed in said chamber downstream of said second sub-layer of said first catalyst layer, said second catalyst layer comprising a copper-cerium compound carried on a support, for oxidatively decomposing components dehydrogentated by said first and second sub-layers of said first catalyst layer and thereby effectively decomposing noxious/smelly components.

2. The catalytic combustion-type exhaust gas-process-ing device of claim 1, wherein said support for said second cata-lyst layer is made of porous ceramic material.

3. The catalytic combustion-type exhaust gas-process-ing device of claim 1, wherein said support for said second cata-lyst layer is made of heat-resistant fibres.

4. The catalytic combustion-type exhaust gas-process-ing device of claim 1, wherein said support for said second sub-layer of said first layer being one which is made of pellets, and said support for said second layer being made of porous ceramic material.

5. A furnace for heating and drying a coating on an object, comprising: an enclosure for receiving an object having a coating which is to be heated and dried; a recycle loop communi-cated both at a return duct end thereof and at a supply duct end thereof with said enclosure and incorporating a means for heating in said recycle loop a gas stream being recycled from and to said enclosure, and a catalytic combustion-type processing device for exhaust gas discharged from industrial facilities and containing volatile noxious or smelly components, said device comprising: a catalytic combustion-type exhaust gas-processing device, compris-ing: a catalytic reactor housing comprising wall means defining a chamber having an inlet and an outlet for a gas stream flowing in a direction along a path; a first catalyst layer and a second catalyst layer, disposed in said chamber, for being sequentially contacted by said gas stream when flowing in said direction along said path; said first catalyst layer comprising at least one quantum of at least one platinum group metal, each such at least one quantum being disposed on a respective first support; and said second catalyst layer comprising by a quantum of chemically active copper, and cerium, in the form of a copper-cerium com-pound, disposed on a second support; said inlet of said chamber being in communication via duct means with said enclosure and adapted to receive through said duct means a gas stream withdrawn from said chamber for passage along said path, whereby this gas stream is processed in said chamber and, after being processed, passes therefrom through said outlet of said chamber.

6. The furnace of claim 5, wherein said heating means comprises a heat exchanger, a heater positioned and arranged to heat a gas stream in said duct means, a duct to atmosphere con-nected to said outlet of said chamber, and said recycle loop, intermediate said ends thereof, and said duct to atmosphere being disposed in indirect heat exchange relation through said heat exchanger.

7. The furnace of claim 5, wherein said chamber of said catalytic reactor housing is interposed in said recycle loop, intermediate said ends of said recycle loop, with a corre-sponding part of said recycle loop providing a portion of said duct means; and said healing means comprises a heater interposed in said recycle loop, intermediate said chamber of said catalytic reactor, and said return duct end of said recycle loop.

8. The furnace of claim 5, wherein said healing means comprises a heater for healing a gas stream in said duct means, and a duct connecting said outlet of said chamber with said recy-cle loop, intermediate said ends thereof.