THE FeB CONTINYOUS - Y~CUUM PJrn

Transcription

1 THE FeB CONTNYOUS - Y~CUUM PJrn r~mrrt'l ifij =-~.- ~~.,-.::~ (ASSBT28th Biennaia Meeting - New Orleans March -8-11,l995) ABSTRACT A. BELOTT 1, and F. ROUSSET 2, 1 FCB, Sugar Division, Boulevard de l'usine - BP LLLE, and 2 APPLEXON - 264, Avenue de la Mauldre EPONE The FeB Continuous Vacuum Pan FCB continuous vaccum pan presents special features such as the number of compartments, feeding of liquor, anti clogging devices, control principle, allowing its use on every kind of massecuite, from low purity to refined strikes. Particularities of calandria, combined with the continuous process make of this pan a major equipment for energy saving

2 C O N TENT' ********* 1. NTRODUCTON 2. DESCRPTON OF THE PAN AND RANGE 2.1. Vessel 2.2. End plates 2.3. Calandria 2.4. Range of pan capacities 3. SPECAL FEATURES OF THE FCB CONTNUOUS VACUUM PAN 3.1. Number of compartments 3.2. Liquor feeding 3.3. Anti-incrustation devices 3.4. Control 4. THERMAL ADVANTAGES 4.1. Steadiness of steam bleedings 4.2. Heating steam 4.3. Vapour space steam recovery 4.4. Non-condensable gas extraction 4.5 nfluence of grain size quality on massecuite curing 5. TYPCAL DATA FOR BEET APPLCATONS 6. CONCLUSONS '-- ' _._--

3 1. NTRODUCTON - FCB launched the continuous crystallization in sugar industry in 1968, with the manufacture of a prototype delivered to NASSANDRES refinery (FRANCE); this continuous vaccum pan produced refined sugar. - Since this date, the continuous crystallization technology widely spread au around the world. Nowadays, FCB has manufactured more than one hundred twenty continuous vacuum pans for all strikes in beet and cane sugar factories and refineries. - After having reminded the principles of FeB continuous vacuum pan which are today well known, we will develop the special features of this pan and its last developments, by bringing out its advantages for the production of marketable sugar and its technical advantages. 2. DESCRPTON OF THE PAN 2.1. Vessel (figure 1) - One hoop- reinforced horizontal cylindrical shell having a vertical plane of symmetry, with end faces fitted with welded supporting legs. - One longitudinal partition and 7 tranverse partitions which divide the unit into several compartments and allow a horizontal U- shape methodical circulation. - Side shields intented to improve the vertical circulation of the massecuite inside each compartment (figure 2). - One entrainment-separator with deflector plate and outlet branch to vacuum. - One massecuite oulet branch and 3 quick-drainage pipes. - Liquor feeders and stirring steam devices. - One manhole, one air valve, one vacuum breaker and miscellaneous accessories End plates - Two reinforced flat end faces supporting of the pan. - Two steam boxes integral with the end faces and closed by bolted doors, on either sides of the pan. - One steam inlet, condensed water oulets and one incondensable gas outlet. - One magma inlet at the top of the end face

4 2.3. Calandria x 1.5 tubes arranged longitudinally in vertical rows go through the end faces and the tranverse partitions, and open into the steam boxes. - Two tube plates acting as tube supports. - Rings fitted with sealing O-rings fasten each tube to the tube plates. 1bis FCB-patented device ensure tightness between the vapour space and the massecuite space Range of pan capacities FCB continuous vacuum pans are offered in 4 diameters and 7 lengths (Figure 3). 3. SPECAL FEATURES OF THE FCB CONTNUOUS VACUUM PAN 3.1. Number of compartments For the production of a good quality marketable sugar, a continuous vacuum pan requires a number of compartments as great as possible, so as to practically reach a piston- flow, resulting in a good crystals quality. Figure 4 shows the influence of the compartments number on the residence time dispersion. Of course, a compromise is essential to stay between reasonable limits. FCB continuous vacuum pans are provided with 13 compartments with progressive volume (Figure 5) ; this arrangement e els out the residence times in each compartment and lead to less crystal size dispersion. CV Values (coefficient of variation representing the grain size distribution) usually reached for marketable sugars are between 30 and 34 % ; under some particular running conditions (15 compartments and feeding liquor at the top and at the bottom together), we have reached CV values between 26 and 29 % Liquor feeding n a horizontal continuous vacuum pan with compartments, massecuite stirring results from evaporation. As water to be evaporated is in the liquor, it is better, to have a quick mixing with massecuite, that this liquor is directly injected in the massecuite

5 When the liquor is enough diluted, massecuite agitation is naturally high. When the brix of liquor is higher, we recommend an original device to compensate for the lack of natural agitation. Liquor is injected after mixing with a small quantity of stirring steam. This mixture is made in a special mixer-injector located just before entering the pan. This device allows a speeding-up of the liquor, and a quick mixing with the massecuite. The result is a big improvment in the massecuite agitation motion Anti-incrustation devices For high purity massecuite (Refined and 1st beet strikes), massecuite deposit on the internal partitions can occur quickly if nothing is done to prevent it. n FCB pan, we take advantage of undersaturation of the feeding liquor to wash internal partitions with rotating devices. However, liquor fed at the top by rotating devices doesn't mix so quickly with the massecuite ; that is the reason why liquor is also fed through the bottom of each compartment. When liquor is close to saturation, a special partitions cleaning device, fed with thin juice or water, fights efficiently against massecuite build-ups on internal partitions. This washing operation is realized by a sequencial spraying to minimize the water quantities used, which remain always negligible in comparison to the quantities of steam in pan calandria. All these devices allow long working periods between two cleaning operations : 7 days minimum for refined strike. 10 to 15 days for 92 to 95 massecuite purity (1st strike), between 3 and 4 weeks for 86 to 89 massecuite purity (2nd strike), 3 to 4 months for 74 to 78 massecuite purity (3rd strike) Control The previous control principles of FCB continuous vacuum pan based on the control of a measured massecuite parameter : temperature or conductivity, with feed back action on the liquor quantity introduced into the pan. This type of control has several drawbacks : the measured va lue~s can only give an "image" of the mother-liquor and this "image" changes with the non-sugars, purity, crystals yield, vacuum (or massecuite temperature), the sensors used got incrustated and had to be cleaned periodically. This type of control often leads to a more or less regular fluctuation of the running conditions. 179

6 To avoid these various drawbacks, FCB has launched a new concept of control based on a predictive calculation of the mass balance of the pan : the flow of liquor introduced into the pan is calculated by an algorithm in which the water contained in the liquor corresponds to the flow of steam or of condensate in the calandria of the pan, the flow of feeding liquor is then divided in several flows, each one controlled by a flowrate loop; usually, one loop for 2 compartments for high purity massecuite, Brix of liquor can be a constant, or a measured value, Flow of magma is proportional to the flow of dry substances entering the pan. This automatic control system works in open loop; however, the brix of massecuite produced by the pan is measured, and the operator can remedy to a difference between measure and set point by modifying a general balance coefficient. This type of control leads to an excellent working stability in spite of the rate of speed variations of the pan, or variations of liquor density. The results of this control are gains in crystals quality, exhaustion of mother- liquor, and energy saving. Figure 6 shows the stability of a continuous vacuum pan after an important variation of its rate of speed. 4. THERMAL ADVANTAGES FCB continuous vacuum pan is an equipment allowing substantial energy savings Steadiness of steam bleedings First, we must speak of steadiness of steam bleedings. Let us compare 2 boiling houses, one with classical batch pans, and the other one with 3 continuous vacuum pans and 1 footing pan. We 'can consider that the boiling house equipped with batch pans requires peaks of steam bleedings which can represent between 20 to 30 % of the total steam flow; while the boiling house equipped with continuous vacuum pans will only required peaks for the footing pan, representing 10 to 15 % of average steam flow. Of course, these variations of steam bleedings lead to variations of thick juice brix entering the boiling house, with negative consequences on the crystallization process. FCB delivered fully continuous boiling houses in beet factories, such as ZEMAMRA (4 000 TBD) MAROCCO, with : - 2 continuous vacuum pan for 1st strike 2 x 450 H 900 H - 1 continuous vacuum pan for 2nd strike 380 H - 1 continuous vacuum pan for 3rd strikes 540 H - 2 footing pan for 1st ans 3rd strikes 2 x 250 H 500 H TOTAL CAPACTY H 180

7 t is interesting to note that a boiling house for the same capacity, and equipped with batch pans would require : - 4 batch pans 350 H for 1st strike H - 2 batch pans 350 H for 2nd strike 700 H - 3 batch pans 350 H for 3rd strike H TOTAL CAPACTY H 4.2. Heating steam The continuous vacuum pan concept allows to work with a constant hydrostatic pressure of massecuite ; this pressure is lower than the one of a batch pan. Moreover, FCB continuous vacuum pan can be used with a ratio heating area/massecuite volume of 10 to 12 m2/m3 while this ratio is only 6 to 8 m2/m3 in a batch pan. n FCB continuous vacuum pan, the combination of these two parameters allows a low difference of saturated steam temperature between calandria and vapour space (35 to 40 C AT). So, the calandria steam can be 3rd or 4th bleeding of evaporation plant. The effect of moving back of a steam bleeding can reduce the steam flow from the boilers by about 15 %. One of the last continuous vacuum pan installed by FCB in MOERBEKE Plant (BELGUM) works with the following parameters : - strike: 2 - massecuite flow: 72 T/H - magma flow: 11 T/H - calandria saturated steam temperature: 95 C - vapour space temperature: 62 C - area/volume: m 2 /160 m Vapour space steam recovery Beet plants having to face with energy prices escalation have widely used possibilities of vapour space steam recovery for juice heating, or for returning to calandria after mechanical compression. Figure 7 shows 3 examples of steam mechanical compression on FCB continuous vacuum pans. 181

8 4.4. Non condensable gas extraction Calandria steam circulation organized in 3 passages (Figure 8) allows a steam speed which is sufficient to have a methodical sweeping of condensates and non-condensable gases. So, noncondensable gases are concentrated at the end of the 3rd passage where a single pipe allow their extraction with a small quantity of steam. Most of the time, these non-condensable gases can be used for injection in the pan, instead of steam. By comparison, a conventional tubular calandria requires several points for non-condensable gas extraction. For high purity massecuite, these non-condensable gases pass through a double envelope around the lower shell to prevent incrustations (Figure 9). 4.5 nfl uence of grain size quality on massecuite curing The good quality of sugars produced by FCB continuous vacuum pans allows savings on washing water quantity. The coefficients of variation (CV) obtained in high purity and refined strikes range from 30 to 34 %. For example: a reduction of CV from 38 to 30 % allows a saving on washing water quantity corresponding in tum to a reduction of the boiling house steam consumption of 4 to 5 %. 5. TYPCAL DATA FOR BEET APPLCATONS Figure CONCLUSONS The special features and advantages of the FeB continuous vacuum pan make it work on exhaustion strikes as well as on marketable sugar strikes. n this last application, the important number of compartments, good massecuite agitation, low calandria steam temperatures (allowing less massecuite coloration), predictive control, and reduction of incrustations are essential features. 18 2

9 LST OF LLUSTRATONS FGURE 1 - GENERAL LAYOUT OF A FCB CONTNUOUS VACUUM PAN FGURE 2 - MASSECUlTE CRCULATON FGURE 3 - TYPES AND SERES OF FCB CONTNUOUS PAN FGURE 4 - RESDENCE TME DSPERSON FGURE 5 - PAN PARTTONS AND MASSECUTE CRCULATON FGURE 6 - PAN STEADNESS N SPTE OF CHANGES N PAN RATE OF SPEED FGURE 7 - VAPOUR COMPRESSON FGURE 8 - STEAM CRCULATON N CALANDRA FGURE 9 - STEAM AND CONDENSATE CRCULATON FGURE 10 - TYPCAL DATA FOR BEET APPLCATONS 183

10 7 8 2' t:'~ -'l f-' 00 d~ *'" 10 r'-'-'-'-'~~'-'-'-'-' ~o '~ *~,.{+~L ""'/! *!::t ~ ' :::t 13' ' Shell 2. Longitudinal Partition 2'. Transversal Partition 3. Tube Nest Protection i ' -'~'-'-'l:'-'n-', "... '\.'\ i.. i '\..'-..,, v-/. ~ (1~ ~ (1 o Z~ ~ Z ~.n;: /.).. (10..-.Jl-./ ~~ stea m Box es & Covers 9. Steam nlet 4. Entrai nment Separator 10. Condensed Water Outlet 5. Ma sseculte Extraction Pipe 11, Non-Condensable Gas Outlet 6. Quic k- Drainage Pipes 12. Tube Nest 7. Reinforced Ends 13. Magma nlet d~ ~O "'O~ ~ ~

11 - fig. 2 : MASSECUlTE CRCULATON

12 - figure 3 TYPES OF PANS Double Steel Casing Molasse nlet Refinery & Beet High Purity (1st strike) YES rotary distributors Cane & Beet Mean and Low Purity (2nd & 3st strike) NO bottom inlet SERES OF PANS NOMNAL CAPACmES (h) Working Lenght (m) 3,500 4,000 4,600 5,300 5, , , , , , , _.._. --

13 ~ ~ a:: w U <t: 70 a:: f- LL 0 ~ 60 o RESDENCE TME DSPERSON COMPARSON Nber of Cpts & Magma Ratio' f" - -.,. l ;;, i =- ~ ~,./ ~ V~~ ~/ \ j/ /; f,, 711 ro 50 ~ f-' f --.J Z <t: :::l W > 30 ~ :::l 2 :::l U cpts 25 % magma -,/ /// f //~, ~~ / ~ 13 cpts --;l / / ~ "., 15% & 25 % magma 4 cpts - 25 % magma REDUCED TME (t/mean_t), i ~ (1Cl = ""1 ~

14 bn, )...,.. \0..,.,, '., M ~ ~~ D = > L rj:j u.. rj:j ~ (j~ > > : :! ~ 9~ < ~ i, S3 ~ f-' < :l T ~ OJ OJ - :l, ~ (j~ 0 o ~ ;: ~ ::a~ ~o , ~ UPPER PASSAGE M : MAGMA NLET _~r \- -!' [--v> LOWER PASSAGE D : QUCK-DRA NAGE PPE S o : MASSECU TE OUTLET

15 - fi g. 6 : PAN STEADNESS N SPTE OF - CHANGES N PAN RATE OF SPEED

16 CONTNUOUS VACCUM PAN VAPOUR COMPRESSON - - BUCY ERSTEN St GERM. Useful Volume h Heating Area m i-' \.D o unght m 10~3 6 13,3 Diameter m 4,6 3,1 4,0 Massecuite Output t/h 70 15,5 85 Magma Flowrate % MC % Me % MC 15 % MC Tube Bundle Pressure bar abs. 1,3 1,1 1,3 i Vapour Space Pressure bar bas. 0,30 0,25 0,29 Steam Flowrate t/h 10 4,3 18 nstalled Power kw Power Consumption kw

17 - fig. 8 : STEAM CRCULATON N CAANDRA - ncondensable Ga s Outlet side of compartments 1 t o 8 / / _~.;----,...J / / /... _.--- SDE OF STEAM NLET OPPOS TE SD E OF STEAM NLET ncondensa ble Ga s Ou t let s ide side side s ide 1to 8 9 to1 3 9 t o13 1to 8 D :--c t E A Condensates Outlets B Condensates Outlets 191

18 CONTNUOUS VACUUM PANS STEAM AND CONDENSATE CRCULATON - llsa TDK(E BEET SUGAR T.3l> 2:::'"";> STEAM CONDENSATES f-' <.0 N rr -1-,..; C1Cl 7~"- = ~ -~-=i1-, ,,--"~ f]1' l-~' _...J~,--.. r.....,.,.. '~,.-.,\.-,...- l... "-''', ~- '. '. '"... i '- " ~"--,- - ' 17 '-'~ ""tt ~r"'- f'" ~~'/ ~~..~. nr...'" T "....,\'/. f~~t~, --< ~ - U ;, ~J!/ '.j 1/,.' LJ ~-_L..-.--':L-.-. -', ;'~--.,-J" --J;..."..-._...,,:._... '~"' fl', \,<0.. '1 \' '~ '1. n n _ -{ _ 4>- -<}>. )! -(i)' -(;~.. -~~-l- "." - ~ \ \'..--.,~, ~-:-~~~:::=:7~~: ~~ C.. r~ g -~o c'-' " 0l-- ij <"--' ~" ld, ~l.-:'~. -{ "c.~-::t ::::: '::;,..1 c;;,q '".«..1.,~.,-:::t.;.. ~. t '. -~ ',....,1 "r""'«!11-(' l'~j"' j '...=...~-~.-----=.~-~-.;...,...,..... ~:,:"'..=~~:::...\ \ 1'1 r \' )( (f,t ::::-;, ~> r:;;::.-.> ~ r:::::::.> r:::. - r."::-') ~, r.::. > r::=.t> L"?:$ ~--.:;, \j t J V,\ [l /... ~;_ - ;.,.,. :-.-..-~ _: r.::~-:::==:~_---; _n~~;:~~ 1,.'. '.~.-..'-~.: - ~.!. \\~~~\J2>} J;V ~':>!~. :::::c.> ~ ~.. ~.i=:n. ~.::l <".r.:::: ~.:::'( ~-d.~ <i.. ~7. <...L..._! G....,.~...~.';:.,! '(')... ' " :i ;>. w _~ ~M ".~_... ~". \~ 1/ \\,,~~~ V \ U.c::r. --.cr :T; ~~;':;j".\t ~ ~" d~.:.:-.:..--=:':::::.::::= \\.. 1/ v~~nv- V ~ h ' UR~nv V,.;",,._. ",~ ~.(.,... _r \. / \j ""-'J. 1-" '" r.: '... ' " =-,.) \. V \ " 1 V.. :'1 \./ i.1,.j..,) ~

19 - fi gure 10 FCB CONTNUOUS VACUUM PAN TYPCAL DATA FOR BEET APPLCATONS Plant Country Genappe (Belgique) Colleville (France) Moerbeke (Belgique) Strike CVP MC - Number of unit Capacity Heating Area Purity Flowrate M.A. C.V. Magma Flowrate M.A. Mag. flow/mc flow Evaporated water fl ow_rate Steam Flowrate in Calandria Steams in Calandria in Vapour space (m3) (m2) (%) (tlh) (mm) (%) (t/h) (mm) (%) (t/h) (t/h) ec) (OC) a Stirring flowrate (t/h) Exhaustion (PtyMC - PtyML) (%) Workin g period (day)