AU660921B2 - Improvements in or relating to drying systems - Google Patents

Description

66 092 COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952-62 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: Application Number: Lodged: o mplete Specification Lodged: Accepted: Published Priority: *.Gemplete Specification Lodged: Accepted: Published: Priority: Related Art: Class int. Class a l .*Name of Applicant: Address of Applicant: Actual Inventor: Address for Service: Complete Specification TO BE COMPLETED BY APPLICANT PATRICK POTTER ASSOCIATES 74 Lake Road, Mico-Wakefield Building, Frankton, Hamilton, New Zealand PATRICK POTTER Care of R K MADDERN ASSOCIATES, 345 King William Street, Adelaide, South Australia, Australia for the invention entitled: "IMPROVEMENTS IN OR RELATING TO DRYING SYSTEMS" The following statement is a full description of this invention, including the best method of performing it known to-4e. us This invention relates to improvemenits in, or rel ating to, dry ing systems.

K(nown drying systems tYpically include a fnn to force ci rou].al~c hot air or gas through a drying Chahlber and an air or gas heating arrangemen~t, To mainrtain ain even temfperaf~ure distri butioni throughout the drying chamnber the fan circul ati~oo nust be periodiunlly reverned Of ten i relatively oxten Aive lag imes can be expeniricod as the J fan reverses direction. Accordingly, it wil~l be appreciated that precise oontrol of telmperixture variatoi within the drying chamber is difI'ictilt to achieve.

a part of the drying pr~ocess it ia comnmonly necessary to "condition" a product. Typicall~y ecniinn agent used is low pressure steam, In the drying procese the moisture content of the product is usual, y ]oweredl to a level, below that actually requiired. The ,low pressure steam is then i ntroduced into the drying chamber to 7: 20 coondition" the product.. and thereby bring the moisture content of the product back up to the level. desi red.* The low pressure sten isa usually produved by a separate boiler plant, which can be an expensive piece of capital equ ipment.

rlurther$ tho furnaces of many known direat fired drying systeme are l~imited in~ the types of fuel, that may be suiitably burnt in them to provide a suipply of cleanI hot gas for use in the dryi ng chamber, Thus, the ability to take advantage of a cheap fuel. source when it is available, such as waste hiomasa nuteri partiocilarly sawdust, does not exist i~n many systems.

It is an object of the present invenition to provide comnponent~s for a drying system which go at leant some way towardR obviating the problems outlined above.

In a. first broad aspect of this invention t:here i~s provided a gaa flow directing valve Pui tajbe for use i drying system, said valve contpri sing at least one- flow directing vane. and a housing having at. least. three passages therei~n, each passage havi.iig a Ni..t end lending into a central. ahaniber, and a secoml eind open to the exterior of the housing, each fl ow diracting vane being pivotally mounted i 1the contral chamber so its Lt in use, direct one or m~ope flows of gam passing through the passageso 0 as S 0.55

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0 5 a S 20 Desirably, all. of the pagsages lie in a coni~non p1 ane., Coliveniently, four passages myay pr-ovid,(ed in thp housing, with the flow of gag being directed by fi Aingl e f low di rectinrg vane. Expedi ent.y, the fl ow directing Vane may pivot about. i ts central ax is peiupend iculai7 to the plane of the passages, In a. second broad aspect of thism invention theyre J.s provided a duct system coniprising a. gas flow directing valve of the preceding aspect; having at least four 25 passages, and a plurality of ducts corresponding In number to the passages of the gas flow directing val]ve, a diuct connected to the aecond end of a sid pnssagc, thct ducts compri sing a primary supply duct, a primary exhiust duct, and at least two secondary duats w)hich may finnotion as Secondary supply or exhaust ductB deperiding on the posiiJon of t.he f Iow dbirecti ng vane, o vanes.

In a t~hird broad aspect of this :Inventlon there is provided a vapour genorating apparatus for use in a dryinrg Bystem, Eial vapour generating apparatus comprising a duct eg

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seO-.on having a. peripheral 1-70-. through which) One or More spray nozzles extenid, each sai d nozle being ivrranged to direct, in uzaep a fog like sprayr of a .1ii ud conditioning agent. into a fazil moving flow of hot. gas passing through the duct section.

Preferab].y the duct Section is (-ircular in croas- action, and each spray nozzi~e isa di rected radi a).Iy i uwards towards thle Central, ax is of thle duct Secti on, In a forth broad aspect of this Invention there i a provided a~ furnace for use in a drying ts'stcm, Said Ni-mce comprising a ho) low, kpright closed cyli ndor hav'ing Side wal.3st a buse, and a top, wherei n an opon 15 erid~d cylindrical tube is susperided inside said chamber by a wallJ di viding the hollow interior of t~he cyl inder into lower and upper chambercs, such that counication between the two chambers .is possible only by pasmae~f~ tLhiough the cy] insdrica-l tubes, the longitudinal atxis of which 20 cylindrical tube Is colinear with the longitudinal. axis of then cylinder, and the cylindrical tube extend" Port WAY .into the lower chamber of the cylinder, fortiti g ari annular gap between the periphery of the cyl indr:11cit. tube and the innor Surface of the sidewall of the oyl.inrdor, tile 2 5 cyl~inder further hayving a burner in) ot in the lowerob(Amber tbrokigh tho sidewall of the cylinder adjacent the arinkila~r air gap, through whicoh i niel, combustibl hIm aterial's voay be admitted substantially tangentially into thle onno.1fir air gap, secondary air inlets opening into the tipper chamber through the sidewall] of the cy) I mide adjacent the dividing wall, it hot gas outle-t froM te upper chamber in the sidewallI of tho nylI rder adjacemnt the top of the cyl indIer, and means for controlli.ing thle Pressure inside the furnace.

Preferably 1 the furnace further i ucludos a buy-ner (.,ioibinatlion comprininrg a primary burner and a sc'.ooridary, startup, bur'ner. Q onvei-iient y the primary burner i s adapted to burn a macro particul.ate fiiel such as powered Ii sawdust., and the secondary burner i.s adapted to bioni fuiel 01:I., TY) a fifth broad aspect of this invention there is provided a dir ~ect fi.red dryling oyaten incJud itig appara.ltu' 1 0 aICcor0ding to at l.east ono of the above d(,soribed Hecond, *.third, adfourth aspects of hiis 3Alveft3~of.

4004 0 1 order that the invention way be better u-dor.4tood, and so that further features thereof wi,.11 be appreciated, a .15 presently- pref erred embodiment ivil]. now he d~rbdb way of examplei only with reference to the accompany ig drawings, in which: 4:00 20 0 Figure I i 3..iustraxten soheuaicaly ta direct, fired high temperetture timber drying kIl.n in accordance with the ])res~ent ijnvent.ion; 1Nigvre 2 illu1tstrates a side el evation of a gas3 flow d Irecting valve in accordanico with the pr'esent. iavontion' N'guro 3 illustrates a front eleIvation of' a vap-.ou~r generating apparatus in accordance wlith tbe preowit Figure 4 1 ~ertsa plan view of at cycl one furruweo in. accordance with the present invention; Figure 5 1J ,ustratea a sido elev'et1 on of th1e0 cyClone furnace of Figure 4; Vigure 6 JIi]ustratc8s a Sectional view of the cyclone furnace of' Fisture 4 showing detail, of the burner i~nlet r:egioni; and, Yigure 7 illustrates a sectional el eveation of a burner nozzle skii.tab].e for use with the furnnce of Figure 4.

As shown in Pigule J1 tIbemre is provi.ded a. direct fired high temperature timber dryi ng kiln, as genorally indi cated at 1, comprising a cyclone furnace 2 connec~ted into a ducting arrangement 3 which in turn is ronectocu to a drying chumber 4.

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0@ h* 1 5 An outliet 5 of the furnace 2 is connected to a Side .1 iletf 6 of a venturi mlixing sectiori 7 which in turn ik connected to an inlet 8 of a circulating fAn 9. An outlet 10 of the fan 9 is connected to at Primary hiot gas sillpiy duct 31 whic terminates at an i nleti 312 of a fl~ow direct-ing vnl yo 13, In use, the flow (Ii,)'cting -ral*ve 33 li vorts the flow of hot gas from the primary supply duct I.1 into eithler of two ojondary ducts I d 15. The secondary duots 34adl connmect i nto and are open to the drying chamber 4. T n lie a flow of hot gas PaXsses down the prim&a, suip-ply duct 11 and into ei ther of the -two secondary ducts 14 ,15 Th e hot gas then flows througli the Secondary duct 34 (or 165) and ivi',o the drying chamber After c roul ating11 through the drying chamber 4 the hot gas oxhausts into the other.

secondary doot. 15 (or 14), back to the fi ow di reoting valve 1 3 wherein -the hot gas ise diverted -to a pri mary exhaust duct 16. The downstream end 17 of the pri nmary exhaust duct 16 i s connected to a Steam gemnerati ng apparatus TO8, whicoh in turn i s oonneotecd to a main Inlet 19 of the venturAl mixer Thun, the (Nocti ng airrangmnent 3 of the drying kiln I. pr'ovides for a fulliy looped gas flow.

The furniawe 2 may be fired by any No), for ex.ample, o:il, gafs, coal, or biomass material. Preferably however, wet sawdust reiidue resoltiAng from the mAilling of green 12 iber is utilised. Ti order to Utilise wet sawdust havilng an initiali moistu-.re content of 160% an a fuel, a two qtage sawdust drying system mustl first be empiloyed.

6 0 The first stage of the sawdust drying Rystem may tvpioully 3.0 comprise a drying apparatus 20, as described in New Zealand Patent Spec.ification No 224218. Tn the. socoiid stage 21 the sawdust is fed into a secondary stream of hot, gas akenfromthefurnace ottet 0 and is corivey,'ed in suspetnsion to a grinding mill 22 where drnylng is 1 5 comnpleted and the sawdust reduced in partiol e aize( to form wood flour capable of' being rapidly combusi-ed in) siuspe ns ion From thbe mll. 1 22 the grouind fuel is blown through a Pulverised fuel, burner 23 into tho oyclone furnaoo 2.

Referring now also to Figure 2p the fl ow dirocting val~ve 13 comprises a housing 24 ilthin which there is provideid a centra. chamber 25. Typioally four passagea, 12,26,27 arnd 28 are provided In the housing 24 allowing acce4ss to the central ohamber 25.* When in iise) the Passnges 121,26,127 and 28 may be oonnected to the primary nupIpiy duct. .1.1 the primary exhaust duct, 10, and the secondary ductsq 14 and 1 of the drying kiln .1 respectively, The passages 12,26,27, and 28 lie inr a oomnion plane, and are oriented Wl. 90* to each other, it will readily be appreciated, however, that any number of secondary duots may be used, that then relative passage ori.entation may be chanigod, and that the passages connected to the secondary ducts need not al] lie in the same plane an the passages connected to the primary ducts. However, it has been found thant when two passage8 are provided for ithe secondary dacts, and ho thjese PaRRAeges are oriented at 90* and coplanay' wvith the passages Connecting to the prj ,fay."y ductIs itJ J.S mjore converkient to later dd.vido the ScOCOnd( ducts I flI.C) 6 ducts to provide a zatisfactory d istribi. on of hot gfas in thie drying chiamber 4. A flow directIng v ane 29 isg pi~tI~lymounted about its central axi s predicl to tbhe plane of the passageB 1 2 26,27, and 28 so that,) in ms,io by pivo-ting between a fly-st, position and a tec(ond 1 0 positi on the fi ow directing v'ajn 29 cank camse thce flow froml t-be Primary dkiat 31, into, for example thie Beoondar~y duct 1 4 to ahift to the sec-ondury duct 15 ond Ooiversel y, to cause the tlow of exhaust gas 1to cbange fr'om the *seomidary~ duct J- f3 to the secondary dtic 1 J1 Vo ocase of consitruct-.on the flow directing vane 29 may be plai-mr. However, to miniinmize pressure I ossos ol, to accommodate a di fferent set of passage or i.entatiorms :11, may be advantageous to mtI.I so a mo-ved vai n form.

Incorporating a flow direoting valve 13 Into a drying system bas a primar~y benefit of allowng for~ cobtinu~ous- Ooc'ation of the circuJlal ug fari 9 in thme snme di recti orn Operation of the va].ve 13 may be carried out by' insn of a meclinnlcal actuated programmed to oporai,e atitom,3001a3y fat preset. timed interva).s.

ITlu st~eaml generating apparatus 8 as il m I uted in IVigin' 3 comprises a ci zcul ar duct sectionk 30 throughi -te wall, of which- extend five spray nozzlee 31 cflrc e~td radiailly inwards. Tbe nov-P es 31 nro displaced tiround tho duot section 30 in a semici rculaor confi guiratimJ ortt in torv alIs A suppl)?y p1 pe 32 )-ni-Orcroncts, 10.1 of theo nozzIeo 31 and mipp)i3s onch with) hig) pressure writer.

36 Fi gures 416 and 6 show detaiJ. of' the cyclone furitaco 2.

Tbe furnace 2 compri s an uipright cy].indrio-al. abel] 33 having sidewaIl 34, a bage 3,51 tnd a top 36. An open ended cyilindri.cal tube 37 ise nuspended inside the cyliridrica1 shell. 33 by a wal 38 such thMt the .1ongtudi.njal axi a of the cy] iniat]. Rhoel] 33 IS colinear with the cy] indrical. tube 37 and the wa].1 38 divides i~bn interior of t~he cyl indri cal. sbeJ]. 33 inuto an i7ppor chantibor 39 arid lowzr chamber 40. The cylindrional tube 37 extendsl 0**10 part way into the lower chbamber 40 so thai. n nnunr gap 41 is form~ed between the outer periphery of the cylindrica. t:ube 37 and the Inner imirface of the wtdewallm A burner i nIet 42 in provided through the a] dowa] 1 34 :of the cylinfdricfal shell 33 Into Ah lower ciabor 1 5 adjacent the annular gcapl 41 The hzr-nern 23 und A~ Btflrtlip buirner- 43 are positioned so as to emii. oonbiuei ble maiteria], subs tantia].y tangentiallIy inuto the annular gap) 41. 31 willi b e appy-ciated that, the sltartup burner 411 may *Co dianpensed,( Witbt #And ror exantp]t o oihb~ustJon may be ljitlatted by simply H gbinrg a fire in the lo0wer Chamber 41., wi th the smcl, e tc reoulti ng being vented to t~he atmosphere. An the t.otal air oupplied at the burner 23 iii leas than that requil:'ed to complete conibustion, sooondary Air i nlets 4.4 arranged to :1nltroduoo atir tAngenti(Ai.1 y into the ohamber, are provided In the upper chamber 39 through lte oideowall 34 of the cy] lidrie sb ~ell 33 adjacent, wel] The outlet 6 for hot gas prolucad inH the furnace 2 lin located in the sidewiall 34. of the oy] indri cal. shall. 331 adjaxcent the top 36. iF.na]]~y, an oxcenn pressure relief 36 valve 45 arid flarnce pressure control, dampor 46 are located i n the top of the oy i ndrion), Hholl 43 to maintai n the deuired pretire in the furnace 2.

Fl gir-c 7 i11tustraten a burrner bWi i tuMbo 47 wli table f'or use with the burnor 23. J3caiise the rao].,ivel y Inargo mansa 3 5 of aJ~r in which the wood fi our is eritranid would( ret,ardi ignition at the biurner 23, the blirr)eq. blast tube 47 isl divided into a central. core 48 surrounded by an ouite-r annUlus 49. Tbe air Auel. mixture fr-om the. grJ uding mij, 22 is conveyed through a firot por7tion 50 of 1_tk)e un er blast tube 47 incorporating a, spinnex' 51. arranged to0 centri fuge the wood flour to the outer wa,1 I of the porti on concentrating it into somne 25% of the t~otal. air flow, This concentrated air fuel. mixture panse through the outer nnulus 49) of the burner blast tuibe 4 7 nnd iF a slowed to the velooity of flame proptagation of the fuel, and at the same time is reduced in spin ve-Iooi.y. The i'emairling 76% ot the nir is relatively devoid of wood flour anid *passes through the Oentra. Core 48 of tho bhtri-er blast tube 47. While the outer air fuel envelope igni tes at, 15 slower velocity t;he ,inner oore air at hiigher vel ooity spins outwards into the NO. f treaem to suppl~y comhutition (tir as it scrubs the air fuol onvolope and in slowed to the velocity of the ai i, fuol mixtuiro in the outter envelope.

:In use, the drying chamber 4 of the diroct fireOd high to temperature timber drying 11) 1. wi lt wet 4 j timber stacked in a manner which pormuilts air to flow through the stack and contact all sitrfaaeR to be dri 0(3 A 2 5 baffle (Arrangement is. set iip inside tbo drying chnmbcar 4 to direat the air low its Ahown in, and descri bed with reqpeot to Pi gure 1.

The furnace 2 i~s then kr'ought up to temperature by ei ther l ighting the startup borner 43, or by %imply I ighting it wood fire in the base of' the lower cliamber 40 of the fzsrnace 2 At, thi~s stage all. gas produced by the furnaceo is vented to atmosphere, When the fXMWCe 2 is At 1-h10 cor-rect, iteiiparatkure the sawdust drying process is ml Listed arid su:itable wood flour fuel produced. Full soale combustion In the fu~rnace 2 is begun. 1n the lower chamber '10 of the furnace 2 any oversized parl.ioles that, havO 013caped t br'ough the Y0.11 22 are contri fuged to the waJ.i, of th'e Chamber 40 and drop out of the oonvoy ing gas stream to complete coinbunti on on the bnso 35 of the furnace 2 Thwi, the. furnnoe design enqiirne.5 that no particle that is incompl.etely ooiplusted is allowed t"o pass from the lower chamber 410 of the cyclone furace, 2. Thijs ensures t.ha~t a clecan atmosphere inside the drying cbiibeir s* 1 0 4 .is miaintained, As tho fuel. is burnit comipletely al. t-ho so ;'tatwih it is metered to the furnace 2 the swi thing 0ff of the. fue. wiLl imnodiately exItiiguish tho flame and there be rno combustible reide It will be appreciated that it j.R essential. that the cycl~one furnace 2 produce i Aean hot gas so that thli s gas does not; damago the timber to be dried, Not gas from tho tipper chamber, 39 of th<- furoace 2 enteors venturi. mixing section 7 to ml dc Intimatoly with gas returning from the drying chamber d to innintain the proSet, temperature the gas entering the furwnace 2 for optimuil drying codto~ Thke vent Ai wixinrmg soction 7 performs a num~be~r of Ir'rt)e~r functions, i ncludi~ng ithe miri irtenct-ce 0090 2t~ of a vacuum Inside tbe furnace Tho outlet of the venturi il xing section 7 slows the velocity.,N of gwaez and A.I.IOws static regain to Occur to provide IXn even flobw of gas to the i n.1et 8 of the ci x'clabing fan 9 without shoch _P-riod ice] the flow directing v'aJ v' 1 3 reverses th." air, flow fin the diryi ng chamber 4 in order to maintain as even a temper'etui'e as possibl e throughout the dryinig ohntunber 4.

When the average mnoisture content in Lhe dryin'g chiamncr charge haes been reduced to approxi mAte]y 6 n pi'ct1med conditioning period iB carried out bY subjeol.ing the dried charge to an atmosphere of low ressu~re stnaw at approximately 100'0. Pressuris~ed water, injected tjirough the flo2zl.ef3 31 of the steamn generating apparatus 18 into the returno air from Onhe drying chamber I1. WI. n u A.( partio es of w-ter from the nozzlw.'s 11. co] 11 de with the high vel1oci ty air, and are rapidl.y d:ispersed through tho hot gas exi sting the furvnace 2 by way of the oult 6.

Tho. teinperalturo of the aiv/gas mixture leaving the jo circiil ating fun 9 I s reduced frolm approximapteiy 120'C for 0the drying inode to 100'C, for, the conditioning mode. A nlght surplus of wat.er is, added through the ~v ,e 31,t ensure that 1 00% Paturation I s maintained during the S.9 ondition)ing oycle. 1coes water mav be removed by a 16 Sealed trap positioned at thei ouitlet of the vonturi mixi ng secti on 7, During the voniditicring cyc.l e extra, heat is provided by the burner 23 to comp.-enonto for, the latent heat demand of the evaporated waterf and vapour Js continuous].y emitted froin a. ventilating door provi ded! 1) 20 the drying chamber 4.

It is to be usiderstood that all ducting for the direct fixed high temperatvre timber drying WiIn I iv-- described above lis to be designed and constrlictod for, high Vel oci ty ciretilation Conveni~entliy, all bendsinooretung d vai us for, low system presesure l1osses, anid eqtulisern for eqtiial f low to and f rom the drying chamber 4 1Lb i s is nee-ssury with the air o1. raulation iside tbe chfumber 4 being at a very high rate, uip to 22 chtkngoes per minute deperidi ug on the nature of the ohage, Additional advantages of the present invenition will. become apparent to those skill1ed in the art after consi dering the prinoipl.oa in ptkrtliular form tin disciusd arid iJ..,11" ~tPat L Accor%'ljgl.y, it be appreci ated that c hfxnges wmy be made to the above described em\bodimenent of the i nveotion withoti. departing from the princilples tought beredrn, Final] y, it wil..l be understood tbat this inventi on is not l.inited to the particular embodiment described or lusstvated b ut is intended to cover a3 alterni. ons, addiitions or modifications wh~ich Are within the scope thereof.

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Claims (10)

1. A drying system including a drying chamber and a furnace to generate hot gas, the furnace including a hot gas outlet connected to discharge hot gas into the drying chamber, said furnace comprising a hollow, closed cylinder having a sidewall, a base, and a top, wherein an open ended cylindrical tube is suspended inside said cylinder by a wall dividing the hollow interior of the cylinder into lower and upper chambers, such that communication between the two chambers is possible by passage through the cylindrical tube, the cylindrical tube extending part way into the lower chamber and forming an annular gap between the periphery of the cylindrical tube and the inner surface of the sidewall of the cylinder, the cylinder further having a burner inlet in the lower chamber adjacent the annular gap, through which inlet combustible material can be admitted substantially tangentially into the annular gap, a secondary air inlet opening into the upper chamber, the hot gas outlet being from the upper chamber, and means for controlling the pressure inside the furnace.

2. A drying system according to claim 1, wherein the secondary air inlet is adjacent the dividing wall. S

3. A drying system according to claim 1 or 2, further including a burner combination S comprising a primary burner and a secondary startup burner.

4. A drying system according to claim 3, wherein the primary burner is adapted to burn a S micro particulate fuel carried in a suspension of air.

A drying system according to claim 4, wherein the micro particulate fuel is powdered sawdust.

6. A drying system according to any preceding claim, in which first and second spaced apart ducts open into the drying chamber, and a gas flow directing valve connected to the hot gas outlet and to the first and second ducts, the valve being operable between a first condition in which the hot gas outlet is connected to the first duct and the second duct is connected to an exhaust duct, and a second condition in which the hot gas outlet is connected to the second duct and the first duct is connected to the exhaust duct, whereby the direction of flow of the hot gas through the drying chamber may be reversed.

7. A drying system according to claim 6, in which the exhaust duct is connected to feed into the burner inlet.

8. A drying system according to any preceding claim, including vapour generating apparatus comprising a duct section having a peripheral wall through which one or more spray nozzles extend, each said nozzle being arranged to direct, in use, a fog like spray of a liquid conditioning agent into a fast moving flow of hot gas passing through the duct section, the duct section being connected to feed the vapour through the drying chamber.

9. A drying system according to claim 8 in which the duct section is connected to feed into the burner inlet.

10. A drying system substantially as herein described with reference to the accompanying drawings. By his Patent Attorneys R K MADDERN ASSOCIATES PIKPTTE Byhioatn Atrny Ro MDER &ASOIAE oo* *oo