IE832326L

IE832326L - Crystallizing a sugar syrup

Info

Publication number: IE832326L
Application number: IE832326A
Authority: IE
Original assignee: Beghin Say Sa
Priority date: 1982-10-18
Filing date: 1983-09-30
Publication date: 1985-04-18
Also published as: DK86984A; DK86984D0; WO1984001584A1; EP0121522B1; IT8368071A0; PT77514B; ES8405443A1; IT1160223B; EP0121522A1; IE56053B1; JPS60500041A; PT77514A; DE3365320D1; DE121522T1; ES525934A0; FR2534595B1; CA1205803A; FR2534595A1

Abstract

The cooked mass (7) is subjected to a continuous vacuum kneading in an apparatus (8) allowing to carry out such treatment in at least two successive steps. The crystals of the mother liquor are then separated from the crystallization jet and the poor sewer is then recycled during the vacuum malaxing steps. The enlargement of the crystals for a first refined jet exceeds 60 %. Application to the sugar industry. [FR2534595A1]

Description

0 53 2 The present invention relates to a process and & device for continuous nixinu of e fsiassecuite obtained par-ticulerly during the menufecturs of sugar, it beirio understood thot "sugar" is understood to mean "sucrose".

The processes for the extraction of sugar rely, in general, on tuo kinds of factories: factories for manufacture as such (sugar saills) and factories for after-treatment (refineries) in which the sugars are refined, filtered, crystallised and formed.

The sugar Bills have equipment which is adapted to the raw material employed which is sugar beet or cane. Thus, sugar sail Is have specific equipment whilst the refineries process raw sugars, whether they be from cane or froia sugar beet.

When the raw material is sugar beet, a diffusion process is employed to obtain a juice which will have collected the sugar contained in the sugar beet, which is first cut up into thin strips or cossettes.

In general terras, the diffusers are devices in which water is circulated countercurrentwise. The juices which are obtained contain approximately 11 to 12% of impurities, calculated on the dry materials.

A treatment with lis® followed by a carbonation and a separation by filtering or decanting permits a satisfactory purification from organic non-sugars.

Uhen the raw material is cane, the operation involves crushing and pressing in "mills" to eutract the 3 Jul 6®, rarely involving diffusion* Since it does not con® t-in in the game i mpuP 11 i ®s as the sugar best .juice, the cans Jwic® undergoes ® different purl f i c Kit i on and the carbonate on stf»@« is eliminated,, 0f> the other h&nd, insofar es the concentration end cfyst&llisistion stages ere concerned, the required operations sre eorop&rGble in both kinds of sugar mill,, Ttus present invention relates raore particularly to the stages permitting the sugar to be crystallised and 10 applies to all th« sugar juices, whatever the ray ssste-rial ssploysd.

Th« crystallisation at the ia111 (for cane or beet) and at th© refinery (for cane or best) is aimed at extracting in a crystallised fors, with as high a yield as pos" 15 sible, the sugar dissolved in this syrup and thus to sepa-rate it fro® the soluble impurities which accompany it. The rate of crystallisation depends principally on the following interr re lated parameters: supsrsaturation, viscosity, temperature, internal agitation, purity and pH, 20 French Patent Ho. 1,520,738, describes a process for the crystallisation of sugar mi 11 syrup according to which concentrated sugared juices mherein a fraction of the? sugar is crystallised are introduced into an evaporator. Th® raassscuite obtained is isixed for a tine at an elevated 2S temperature and then is screened in a centrifugal filter Mher® the crystals ar<s separated frota the syrup. The mother syrup is then lalxtd with crystals and then unde r-goes a second si nine in ordsr to induce the crystallisation of the sugar contained in the said syrup. 4 In this process, the fact that the operation takes place at an elevated temperature, which is essential on account of its characteristics, does not permit a sufficiently high degree of crystallisation to be reached. 5 Moreover, the consumption of energy is high.

French Patent No. 2,064,277 describes a process for producing crystals continuously according to which a sugar syrup, in the presence of previously added crystalline seeds, is concentrated under vacuum in a crystalliser having sever-10 al successive compartments. This process requires a relatively high temperature, which, on the one hand, increases the energy cost and, on the other hand, reduces the crystallisation yield.

French Patent 1,368,118 describes a crystallisation 15 process consisting in removing a part of the massecuite at the outlet of the cooling apparatus, subjecting said part to a centrifugal turbine action operation and reinjecting the mother liquor thereby obtained at the level of one of the crystallisation steps. This process necessitates, on 20 the one hand, a supplementary treatment of centrifugal turbine action and, on the other hand, results in a loss of energy to the detriment of the crystallisation. Furthermore, on setting aside a large part of the massecuite one reduces the surface of crystallisation of the remaining 25 massecuite which is directed towards the mixer. In this way, the reinjected mother liquor crystallises spontaneously on cooling, giving rise to small-sized extraneous particles which pass across the strainer of centrifuges, which further reduces the extraction of crystals at the jet 30 assembly.

The crystallisation process according to the invention makes it possible to obtain immediately after the end of the mixing of the massecuite a much more substantial quantity of crystallised sugar than when the processes which are known 35 at present are employed. In fact, the process aims at a maximum lowering of the temperature of the massecuite to increase the crystallisation. s According to the invention there is provided a process for the crystallisation of a sugar syrup comprising subjecting the syrup to a continuous or non-continuous boiling so as to obtain a massecuite, subjecting the massecuite to one or more 5 stages of continuous mixing under vacuum, and separating the crystals from the mother liquor of the crystallisation stage in question, at least a part of the mother liquor being recycled during the stage or stages of mixing tinder vacuum. 6 Another subject of the invention is a device for mixing a nossecuite, comprising one or more cylindrical mixers,means for entry and exit of the massecuite, at least one vacuum takeoff, means for entry of mother liquor connected to an exit for the centrifugal run-5 ning from a centrifuging device, the exit for the massecuite and the means for entry for mother liquor being connected, respectively, one to the entry for the massecuite and the other to an exit for the mother liquor from the same centrifuging device.

Preferably, only the part called "centrifugal runnings" is 10 recycled during the vscuuei fixing stages. The part called "wash syrup" is reinjected, for example, at the boiling stage. The terras "centrifugal runnings and wash syrup" are defined according to J= DUBOURG, Sucreries de betteraves (Sugar manufacture froei sugar beet) 1952, Also preferably, the recycled part of the mother liquor is reheated and de~erauIsified before the said recycling. Although the viscosity of the massecuite increases, the louering in temperature is made possible by the vacuum self-evaporation, in a continuous process, of the water 20 contained in the massecuite and by the recycling of all or a part of the mother Liquor, which thereby produces a violent and continual agitation.

This agitation is all the more efficient because it takes place in a regular manner in a thin and uniform layer of 25 the massecuite.

It is advantageous that the continuous vacuum mixing comprises several successive stages. In the case of two stages, the first is operated under a vacuum between 82.6 i'iPa and 88.0 HPa, the second under a vacuum between 30 88„0 HPfi and 96.0 fSPa. 7 The aiess'seuit® Must haiw® un initial teEiporsture of approui-Basely 80°C end, at the outlet frora the continuous waeuum mining its temperature should have decreased to » value-between a>0°C end 50°C. 3 The crystallised roassseulte is then filtered (spinning): the crystals 6r® separated from the aother liquor and the centrifugal runnings frois the crystallisation stags in question is recycl^d^ for the taost part, in the region of the continuous vacuus nixer or mixers. The recycled can-10 t r i fuge I runnings maintain a sufficient fluidity so that the sessecuite does not set and that the mobility of the crystals el Iobs t hera to taove.

Preferably, the aeans for entry of the centrifugal runnings consist of one or raore pipes situated in the lower part of 15 the cylinder. Preferably, these pipes arrive at the cylinder tangent1 a Ily. Preferably, their nuraber is between :uo and ten.

The process and the device according to the invention will be better understood by virtue of the descrip-20 tion of Figures 1, 2, 3, &, 5 and 6, and by virtue of an example of embodiment„ Figure 1 shows s flow-sheet of an erabodiraent of the process according to which, after continuous boiling, the continuous vacuum fsixing is carried out in a device 25 consisting of a single siiter.

Figure 2 shows u flow-sheet of s preferred embodiment of the process according to which, after continuous boiling,, the continuous vacuum mixing is carried out in a device consisting of tyo separate mixers. 3 Figure 3 shows the devie® for carrying out the process Illustrated In Figure 1 , Figure ® shows the device for carrying out the process Illustrated in H$ure 2.

Figure 5 is a transverse view in a cross-section which is broUen in e parallel plane of a vacuus Mixer illustrated in Figure 4.

Figure 6 is a view of the same mixer in profile a long A„A.

According to Figures 1, 2, 3 and 4, a fraction 1a, 21a of the sugar syrup 1, 21 is directed to a vertical device 2, 22 to forsa the seed. The device has a voljiae of 300 hectolitres and comprises a calandria, with tubes supported by two plates of a frustoconica I shape, sloping 15 towards the central well equipped with a propeller stirrer.

The feet 3, 23 of the vertical device 2, 22 supply the magma mixer &, 24.

The Eiagraa isiixer is a coiapletely closed cylindrical horizontal capacity/, fitted with an agitator consis-20 ting of a helix supported by a longitudinal shaft turning at 1 rpm and equipped with a double jacket for the circulation of hot water @t 80°C enabling the whole to be controlled at constant temperature; this magma mixer acts only as buffer storage..

The magma 5, 25 travelling from the mixer Up 2U and the fraction 1b, 21b of the sugar syrup supply the continuous boiling device 6, 2e„ The continuous boiling device 6, 26 consists of a cylindrical horizontal vessel, made of steel, inside which 8 hit'fttIfig 1s supplied by & bundle of longitudinal tub?s of stainless steelp arranged in layers. Th® lower part of ■stis vessel 1 s? provided «1t!i a double jacket In ahlch cic-. culnte the vapours which isps; not condensed In the bundle. S Steaw is Injected a? » eartain flow~r«it® into the lower pert of the device for boiling, to provide agitation of th® aass«cuits.

The device is divided Into cotsp&rttaents by transverse partitions and a longitudinel partition at th« bass? of 10 which an orific® pereits the forward raoveaent of the assse-cuite. The first coepartment is supplied with the aegma, the following ones with the massecuite originating from the preceding c oispartrsent.

Each cotapeftitient is also provided with a supply of syrup 15 1b, 21b which sprinkles through turning pipes the emerging wells of the rasssecui t e« Th® massecuite arriving at the last compartment is extracted st its base by a varieble-speed pump.

The circulation and the flow-r&te of the fluids in the 20 device srs controlled by control chains for vacuura, staata pressures, agitation, density and massecuite level. fts an axanplc, the raain characteristics of a device for continuous boiling (constructed by Fives-Ca1l- Babcock) are as followss Overall length 9.0 fii Xnternel length ?,» a Overs lltiidth 3.5 fa Overall height 4.1 m Xnternol dieraeter of the shell 3.1 ft Volume occupied by the raasseculte Toteil heating surface Stainless tubes,, length Total number of tubes Test piste of the bundle Empty unlfiht Operat1n0 weight Wuraber of compartments 32 fa3 324 IB2 y .5 si Z bars 32 tonnes 77 tonnes 10 The operating conditions of the device described 10 above are ss follows: Seed aagt-is 3, 23: Bri x Purity Rate Content of crystals Average Opening of the crystals Feed liquor lb, 21b! B r 1 x Purity 20 Rste Massecuite 7f 27: Bri a Purlty Rote Content of crystals average Opening of the crystals 0.5 to 0„6 mm (BrlK being defined ©s the value of the ratio of the us1ght of dry wetter/total weight of the syrup). 86 ~ 88° 99.0 - 99.5 6 to 7 tonnes/hour to 40% 0.20 to 0„25 rata 68 - 70° 99.0 - 99.5 26 to 30 tonnes/hour 90 - 91° 99.0 - 99.5 26 to 30 tonnes/hour 50 to SS% i 1 ?h® messecult® 27 Is .woo®(S towards & device for continuous ulitinsi under vacuum 28. ftceofdlngi so an ermbodiwent of tfie intension -Figures 1 and 3 - this device consists of o witter 3 co«-5 prising (sn fusfsietic„ t&er«©lly insul&tsd, horizontal shell fisted with is longitudinal shaft 10 supporting a heliu SI and divided into two-cospertwents 12, 13 by e leefetight well 14 which 1s equipped in its low part with an orifice 15 permitting the transfer of the masse" 10 cuite frora an entry comportment to the esit coBpartsent, each cofapsrtsaent being provided with a tubing 35 permitting a connection to e source of vacuum. The entry co«~ partraent and the suit coespartsent are respectively provi-dad with tubings for the entry 16a and exit 16b of the IS Bias s ecu i te, these tubings bsing of ssiell cross-section and situated In the lou pert of each comportment.

As an example, the first compartment is subjected to a vacuus) of 32.2 BPa, and the second to a vacuus of 89.4 HPa. The delivery and the discharge of the raasseeuite take 20 place through the low part of the mixer with the aid,, respectively, of a verieble-speed positive displacement vacuum puiap - which can be the extraction pu&p for the continuous boiling 6 - and a variable speed positive dis* p leceiaent vacuum extraction pusp. 2S As the growth of the crystals takes place, f luidi f 1 cat ion of the massecuite is produced with the centrifugal running 1® obtained when the crystallised massecuite is filtered (centrifugina stage 40 permitting the crystallised sugar 41 to b« Isolated),, This centrifugal running is delivered i 2 to t hs bottom part of each of the coapartraents 12, 13 by three tangential tubings 19, the flow-rotes therein being control led.

According to a preferred eobodiwent of the inven-5 tlon - Figures 2, 4,;. 5 snd 6 - the two successive sixlng stages are carried out in two continuous vacuum Mixers 28, 29, with a single compartments and mounted in series,. The crystallised eiassecuite 27 leaving the first continuous vacuum mixer 28 is sent to the second mixer 29„ 10 Each mixer 28, 29 consists of a horizontal cylin der 30 fitted with e low-posner internal movement scraping the uells and thus preventing the build-ups of sugar. It also comprises tubings for the entry 31a and exit 31b of the massecuite/ of o sisal I cross-section and situated in 15 its lower part. The massecuite level is maintained essentially in the plane of the diaiaeter, so as to offer the maximum surface area for the evaporation.

The fraction called "centrifugal runnings" 39, origina™ ting frois the massecuite after filtration 40, reheated &2 20 and de-eiau I s 1 f i ed «>3 beforehand, is injected 211a, 211b into the mixers 28, 29 in four places through hori zon-tal deliveries 32 distributed along the lower generatrix 33. The fraction called "wash syrup" 44 is recycled i-i 1th the fraction 21b. Each mixer 28, 29 forms a stage 23 which 1s placed under a specified vacuum which corresponds to the required massecuite teraperature. The stagewiso change in the vacuum allows the lower limit of tempera" ture to be reduced, whilst avoiding the spontaneous for» raation of "false grains". 13 Th# whole ay stem Is continuously fed by & va r 16b le-speed positive cH 3P Icici'wffint woe hub puiap 34, from the outlet of a continuous boiling or of a charge mixer of e> non-contin-uoug boiling.

Each otafle is connected 3S to 6 high-veeuun station 37, tha vacuus be1n@ regulated by raesns of an eutosatic velve 3©, After a residence tltse of 90 sinutes, the cooled laesse-cuite is continuously eatracted by o variable-speed pos i-10 tiv® displacement vecuun purap 38.

The speeds of the is&sseculte pumps are controlled by level' regu lators.

The vecue are regulated, at displayed set-points, by automatic valves.

The rate of delivery of running to each stage is regulated proportionally to the flaw-rate of massecuite and corrected in the last stag® depending on the e«is 0rixo Eaaraple 1; The characteristics of e device for continuous isiHing under vacuus^ formed by two Separate continuous vacuuia miners ere es follows: tier si ae f i rst Second Overall length 7.25 la S.04 m Internal length li„95 a 6.15 a Ovsrall height 3.0 ra 4.65 is Internal diameter of the shell 2.4 in 2.90 m Toto I vo luiiie 250 hi 373 hi Working voIuei© 160 hi 200 hi Sixer sisg V1 rat Second Height sspty 8,3 t 12.9 t Hovfewent motor power 2.2 kH 4 'tW Vacuuw station; Veeuu® pu»p giving 1,000 r»^/h et 96.0 BPa with 40 fcW installed power.

Operation conditions for a first stage of refining; Vacuum: first stage 85.3 RPa second stage 95„S HPa Wassecuite teaperstures; first stage entry 82°C first stage exit 60°C second stage exit 40°C Characteristics of the iaassecuite entering: Brix 90.72° Rate 16,23 tonnss/hour Crystals 48.68%/siassecui t e 53„66J!/ dry matter 20 Characteristics of the massecuite leaving: Brix 86.76° Rate 26.24 tonnes/hour Crystals 49.60%/iaasseeui te 57.17%/dry matter flow-rates of recycled runnings: 11.08 tonnes/hour Dimensions of the crystals: Entry average opening 0.50 mm vorietion coefficient 30 Exit average opening 0.60 mm 18 variation coefficient 27 Weight of crystalss Entry 7.90 tonnes/hour EJsit 13.01 tonnes/hour S ®royth 1.65 By comparison to a conventional process coapr1s1n@ boil** ings heated with steeei, the process according to the in~ vention peraits approiii met e ly 60S of the steam consumption to be saved.

In the example described, a significant growth of th® crystals is observed, in excess of 60" for a first stags of refining.

The essential difference between the continuous 15 vacuus iai aer and the other types of crystalliser is that the cooling does not take place by an exchange with a fluid but by self-evaporation. The continuity of the operation favours the uniformity of the final product, which is obtained by raaintaining the value of all the parameters of 20 the control systeras0 The "flash" which is produced at the delivery of th® aassecuite and the running which has previously been reheated and de-emulsifled creates a turbulent regime which facilitates the material transfers from the fluid 25 to the? crystal. The fact that the running is rsheated ■» which introduces heat into the system - results in an 16 additional crystallisation of this funning by scIf~evapors? 1 on„ Depending on the conditions of operation of th® continuous v©cuur« nixing pliant, the growth coefficient 5 of the crystals Is between 1.30 and 1.80* The crystallisation process according to the invention can be celled a "cold crystallisation process"; it eliminates all phenomena of recolorstion of the massecuite, thereby reducing the quantity of water required in the Mashing stage, an 10 operation which is always accompanied by a redissolution of th® sugar crystals.

Thus, the process and the device for crystallisation of a sugar syrup according to the invention perait the extraction to be raised to a level which has never 15 been attained, whatever the technique employed. Further-more, they confer on the mixing all the advantages of a continuous process, namely: steady running - hence a better quality of the product obtained -, a reduction in the s i <se of the plant, e s i rap Ii f i eat i on of the control 20 systems and of automation, and a very marked improvement in the operating cost of the plant. £7

Claims

CLAIMS:

1. A process for the crystallisation of a sugar syrup comprising subjecting the syrup to a continuous or non-continuous boiling so as to obtain a massecuite, subjecting 5 the massecuite to one or more stages of continuous mixing under vacuum, and separating the crystals from the mother liquor of the crystallisation stage in question, at least a part of the mother liquor being recycled during the stage or stages of mixing under vacuum. 10

2. A process for the crystallisation of a sugar syrup according to claim 1, wherein the crystals are separated from the mother liquor by spinning.

3. A process for the crystallisation of a sugar syrup according to claim 1, wherein the mother liquor is recycled 15 into the lower part of the mixer or mixers forming said stage or stages of mixing under vacuum.

4. A process for the crystallisation of a sugar syrup according to claim 1 or 2, wherein the recycled fraction of the mother liquor is the fraction called "centrifugal 20 running".

5. A process for the crystallisation of a sugar syrup according to any one of claims 1 to 4, wherein the recycled fraction of the mother liquor is reheated and de-emulsified before the said recycling. 25

6. A process according to claim 1, wherein the continuous mixing of the massecuite under vacuum comprises several successive stages.

7. A process according to claim 6, wherein the continuous mixing of the massecuite under vacuum comprises two success-30 ive stages.

8. A process according to claim 7, wherein the first stage of mixing is conducted under a vacuum of between 82.6 18 and 88.0 MPa.

9. A process according to claim 7 or 8, wherein the second stage of mixing is conducted under a vacuum of between 88.0 and 96.0 MPa. 5

10. A process according to any one of the preceding claims, wherein the temperature of the massecuite is in the region of 80°C.

11. A process according to claim 10, wherein the temperature of the crystallised syrup is between 40°C and 50°C 10 at the end of the (last) stage of mixing under vacuum.

12. A process according to any one of the preceding claims, wherein, between the end of the continuous or non-continuous boiling stage and the end of the continuous mixing under vacuum, the ratio weight of crystals 15 discharged/weight of crystals entered is between 1.30 and 1.80.

13. A process according to claim 7, wherein the two successive stages of continuous mixing under vacuum are carried out in a single mixer. 20

14. A process according to claim 6, wherein each stage of continuous mixing under vacuum is carried out in a separate mixer.

15. A process according to one of the preceding claims, wherein the level of massecuite is maintained essentially 25 in the plane of the diameter of each continuous vacuum mixer.

16. A device for mixing a massecuite, comprising one or more cylindrical mixers, means for entry and exit of the massecuite, at least one vacuum takeoff, means for entry 30 of mother liquor connected to an exit for the centrifugal 19 running from a centrifuging device, the exit for the massecuite and the means for entry for mother liquor being connected, respectively, one to the entry for the massecuite and the other to an exit for the mother liquor from the same 5 centrifuging device.

17. A device for mixing according to claim 16, wherein the means for entry consists of one or more tubings situated in the lower part of the cylinder.

18. A device for mixing according to claim 17, wherein 10 the tubings come to the cylinder tangentially.

19. A device for mixing according to one of the preceding claims 16 to 18, wherein each mixer comprises between two and ten tubings.

20. A device for mixing according to one of claims 16 to 15 19 consisting of a horizontal cylindrical mixer comprising a hermetic, thermally insulated shell, fitted with a longitudinal shaft supporting a helix and divided into two compartments by a leak-tight wall which is equipped in its low part with an orifice permitting the transfer of the 20 massecuite from a discharge compartment to a delivery compartment, each compartment being provided with a tubing permitting a connection to a source of vacuum, each compartment being provided with tubing forming said means for entry of a mother liquor. 25

21. A device for mixing according to claim 20, wherein each compartment is provided with three tangential tubings.

22. A device for mixing according to one of claims 16 to 19 consisting of two horizontal cylindrical mixers arranged in series fitted with a low-power internal movement, each 30 mixer being fitted with tubing forming said means for entry of a mother liquor.

23. A device according to claim 20, wherein the compartments for delivery and for discharge of the massecuite are 20 provided with tubings for entry and exit of massecuite with a small cross-section and situated in their low part.

24. A process for the crystallisation of a sugar syrup as claimed in claim 1, substantially as hereinbefore 5 described with reference to and as illustrated in the accompanying drawings.

25. Sugar syrup whenever crystallised by a process claimed in any one of claims 1 to 15 and 24.

26. A device for mixing a massecuite as claimed in 10 claim 16, substantially as hereinbefore described with particular reference to and as illustrated in Figs. 3-6 of the accompanying drawings. F. R. KELLY & CO., AGENTS FOR THE APPLICANTS.