AU663610B2 - Evaporator - Google Patents

Description

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T A 0% Patents Act COMPLETE SPECIFICATION

(ORIGINAL)

Application Number: Lodged: Class Int. Class Complete Specification Lodged: Accepted: Published: Priority Related Art: i 0 e 6 4 r~ rri r r ri

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Applicant(s): ANCON CHEMICALS PTY LTD 3 PYINGERRA CRESCENT CHELTANHAM VICTORIA 3192

AUSTRALIA

Address for Service is: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA Complete Specification for the invention entitled: EVAPORATOR Our Ref: IRN 338562 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): 3309S r i i i

EVAPORATOR

The present invention relates to an evaporator for use in preparing concentrated liquids or powders such as powdered ;:wd milk or the like, -te A a distributor plate for use in an evaporator and to a method of use of such an evaporator.

The invention is particularly suited to use with evaporators which are used in the manufacture of concentrated milk products such as powdered milk and will be described with reference to that exemplary application. The evaporator of the invention is not however limited to that application and may be used in evaporation and concentration of other liquids such as sugar solutions and concentrated beverage products.

In preparation of powdered milk procucts, liquid milk, or a S" product of liquid milk such as skim milk or whey is passed through an evaporator system. The evaporator system generally includes a series of units known as "effects". Each effect includes a multiplicity of elongated evaporator tubes, also o. known as callandria, through which milk is passed. Milk is passe tr ogitbs on passed through the evaporator tubes as a film on their interior surface. The exterior of the tubes is heated and the effects are subject to a vacuum to provide evaporation. The milk is fed through a series of at least three and typically four effects and a finishing effect.

During use of the evaporation system a crust known as "milk stone" tends to build up on the surfaces of the equipment, particularly in the evaporation tubes, which if not removed results in reduction in efficiency of evaporation, reduced product quality and to blockages of the callandria which require expensive maintenance procedures. The invention provides an evaporation system which facilitates improved system maintenance and reduces the down time associated with maintenance and cleaning of equipment.

We provide in accordance with one aspect of the invention an 3vaperater system for use in preparing pewdered milk or the -2- L evaporator system including a plurality of effects arranged in series for progressively concentrating a liquid, the effects including: a header chamber for receiving liquid to be concentrated; a multiplicity of tubes adapted to provide evaporation of liquid from the inner surfaces of the tubes and a perforated distributor plate located in the header chamber to distribute liquid to the openings of the tubes; and wherein the evaporator system is provided with wash liquid conduits for feeding wash liquid to the effects in parallel and the distributor plates include an essentially planar plate member having a multiplicity of distributor holes therein for o distributing liquid to be evaporatored to said multiplicity of tubes and a series of overflow conduits for providing a flow S oo of wash liquid through the plate, the inlets of the conduits being disposed above the surface of the plate to provide an overflow for wash liquid during washing. i fti 39 ft i 2 •Ph -2a- i like compricing a plurality of effects arranged in Gori-ac effect comprising a multiplicity of eva ubes for evaporation of liquid from .eernal surfaces thereof and wherein thee rovided wash liquid conduits adapted to feed c-aning liquid into each of the effectS in parallel.

Typically each effect comprises: a header chamber for receiving liquid to be concentrated; a multiplicity of tubes adapted to receive liquid from the header chamber the tubes (callandria) being adapted to provide evaporation of liquid from the inner sarfaces thereof; a perforated distributor plate located in the header chamber to distribute liquid to the openings of the tubes; and a lower chamber for receiving liquid which has passed through the tubes.

The effects generally each have a housing with a cylindrical side wall and closed end walls. The cylindrical wall may be for example in the range of from 0.5 meters to 2 meters in diameter. Preferably the evaporator system includes at least three falling film type evaporation effects.

Preferably the evaporationsyse includes-a leastthre S*in Preferably the evaporation system includes at least one wash liquid holding tank, a pump for transferring liquid from the tank and a branched wash liquid feed line to feed wash liquid to each of the evaporative effects in parallel.

The system is preferably adapted to feed wash liquid into the header chamber of each effect.

It is particularly preferred that the system include a branched wash liquid feed line to provide parallel feeding of wash liquid to the header chambers of the effects and each F effect comprises a wash liquid outlet line for transferring -3 lli s~IiiSili I_ _~lll. -~IYI- 1. I- i liquid from the lower chamber of the effects. The outlet lines may retain wash liquid to the wash solution holding bank or may transfer it to a separate tank.

In one embodiment the system is provided with two or more wash liquid holding tanks each tank being in communication with the branched wash liquid feed line and provided with one or more values to control flow from the tank into the effects. Two or more tanks enable a number of wash liquids to be used for more effective cleaning. For example two or more of a caustic, acid, and rinse liquid tanks may be provided.

It is particularly preferred that the effects comprise distributor plates which provide an overflow of wash liquid on 6° .reaching a certain level of liquid.

Distributor plates comprise a multiplicity of fine holes so that a head of the liquid to be evaporated is produced during operation resulting in even distribution of liquid from an inlet above the plate to the openings of the collandria which are spread over a wide area below the plate. The distributor plate may extend to the inner circumferential wall of the effects.

The preferred distributor plate for use in the invention provides overflow from above the level of the head of liquid maintained during operation to provide rapid flow of liquid to the callandria during washing. This arrangement has been found to significantly improve the efficiency of cleaning and reduce the length of time taken to clean the effects to a minimum.

SIn accordance with a further embodim.ent. the invention provides a distributor plate for- use in liquid .vap.ratr which comprises an essentially planar plate having a multiplicity of orifices therein and further comprising a series of overflow conduits adapted to provide an overflow of liquid through the plate the inlet of said conduits being disposed above the upper surface of the plate.

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Preferably the conduits will extend to a height abo-ve the upper surface of the plate which is greater than the level of liquid product which is achieved during evaporation. The level of liquid achieved during evaporation will depend on the rate of flow of the liquid onto the distributor plate, the size of the distributor plate, the diameter of the holes in the distributor plate and the number of those holes. In the case of milk evaporators the level of liquid on the plate varies between different types and sizes of evaporative effect. The choice of suitable inlet height will therefore depend on the operating conduits and the particular effect.

The height of the inlet of the overflow conduits is preferably o fro-m 1.5 to 6 times the average level of product liquid.

o5 Typically the inlet of the conduits are in the range of from o~o 12 to 250mm above the upper surface of the plate. Preferably :o the inlets are from 12 to 150mm above the surface of the plate.

so Preferably the overflow conduits are of greater diameter than 8 ~the distributor holes and more preferably at least twice the diameter of the distributor holes.

The distributor holes may for example be in the range of from 4 to 12mm diameter and the overflow conduit in the range of 7 to 25mm diameter.

i: e6 The distributor holes and overflow conduits are preferably evenly spaced, the spacing between the centre of each hole preferably being from 20 to 100mm (most preferably about 50mm). The separation between the centre of the orifices and the centre of adjacent conduits is preferably from 10 to most preferably 22.5mm. The separation of the distributor holes will be dictated by callandria pattern.

Under washing conditions the Idistributor plate of the invention allows a significant increase in the throughput of wash solution enabling efficient cleaning of the plate itself and the other components of the evaporator (particularly the 39 callandria) while at the same time providing efficient 5 distribution under evaporative conditions. The distributor plate of the invention is particularly useful in falling-film evaporators and particularly in multiple effect evaporators.

The method of cleaning heretofore used to clean multiple effect evaporation has been to pass cleaning liquid, in place of the liquid to be concentrated through the series of effects. This process is slow often taking up to 3 hours to clean the system.

The parallel wash liquid feed of the invention provides rapid cleaning and enables cleaning to be conducted at ambient pressure. Cleaning at ambient pressure allows wash liquids to 4tW be used at a higher temperature to achieve more effective 151 cleaning.

at o.# ooo: For example whereas cleaning is normally carried out using cleaning solutions such as aqueous caustic solution at about 0 C the present invention allows temperatures of 85 to 1120 to be used. It has been found that by increasing the t temperature by 400 and using aqueous caustic solution at about to 98 0 C a significant increase in cleaning efficiency is achieved. Furthermore higher temperatures have been found to allow a trebling in washing reagent strength.

.c 3 The present invention also enables cleaning liquids to be more effectively utilized. Preferably the method of the invention 'o comprises passing acid wash liquid and a caustic wash liquid through the effects. Preferably the effects are washed with acidic wash liquid before the caustic and preferably the effects are rinsed with water at the commencement and end of the washing sequence. The acid wash liquid is preferably a dilute solution containing nitric and/or phosphoric acid in an amount of from 1 to 5% by weight. A dilute mixture of nitric and phosphoric acids may be prepared from a concentrated mixture containing 10 to 30% phosphoric acid w/v and 20 to nitric acid w/v.

-6r i i The caustic wash liquid may be selected from hydroxides of alkali and alkaline earth metals with sodium hydroxide and potassium hydroxide being most preferred. Aqueous potassium hydroxide is the most preferred caustic wash liquid. The concentration of sodium and/or potassium hydroxide is preferably in the range of from 1 to 20% w/w with from 3 to w/w being preferred. The preferred reagent concentration will depend on the wash liquid temperature and flow velocity.

At higher flow velocities the concentration of the wash liquid becomes less critical. At wash liquid temperatures in the range of from 85 to 95 0 C caustic concentrations of from 2 to 4% w/w whereas at temperatures of 95 to 1120C in the range of S from 4 to 10% are more preferred. The acid wash liquid rtr preferably prepared from a concentration of 17% w/v phosphoric 15 acid and 45% nitric acid for use at 85 to 950C whereas seC, concentrates of 20% w/v phosphoric acid and 43% w/v nitric acid are most preferred at 95 to 112 0

C.

This enables a significant reduction in cleaning time thereby minimising the down-time of the evaporator, for example 5155 whereas cleaning of conventional evaporators generally takes at least 2.5 to 3 hours the present invention enables superior cleaning to be obtained in under one hour.

During evaporation product flow is either laminar or in the lower end of the turbulent range. The distributor plate of the invention allows small flows to be maintained during the evaporation process by using the appropriate size and distribution of distributor plate holes. Furthermore the distributor plate of the invention provides the significant advantage of allowing rapid flow of wash solution to the callandria to provide turbulent flow in the callandria during I cleaning.

In accordance with a further embodiment the invention provides a method of operating a multiple effect evaporator system including feeding a liquid to be evaporated through a series of effects operating under vacuum to provide progressive cT concentration of the liquid, returning the system to ambient -7- I pressure and cleaning the system by feeding a wash liquid into the effects in parallel.

The method preferably utilizes the hereinbefore described preferred distributor plate to provide rapid flow rates.

Accordingly the method preferably each effect includes: a header chamber for receiving liquid to be concentrated, a multiplicity of tubes (callandria) adapted to provide evaporation of liquid from a falling film on the inner surface thereof and a perforated distributor plate located in the header chamber to distribute liquid to the openings of the tubes the distributor plate including an essentially planar plate having ro~o a multiplicity of distributor holes therein said plate o restricting flow and providing distribution of liquid to be S. evaporated via said orifices to said multiplicity of tubes and further including a series of overflow conduits for providing a rapid flow of liquid through the plate during washing the inlet of the conduits being disposed above the surface of the plate and wherein during evaporation the level of liquid on the distributor plate is less than the height of the inlet of the overflow conduits and wherein during washing wash liquid fed into the header chamber to produce overflow to said tubes 4 via the overflow conduits.

The Reynolds number of the wash liquid in the tubes is preferably at least 2300. More preferably 5500 to 7500.

It has been found that an increase in temperature and flow rate to provide turbulence in many cases results in an improvement in cleaning efficiency of over 300%. The present invention therefore enables evaporators to be cleaned significantly more efficiently than has previously been possible enabling a higher quality prQduct to be maintained and reducing the time required for cleaning.

39 The evaporator of the invention has a significantly reduced 8 ii IS I Ii ii i i iil- 8 r 1 1. i CX incidence of blocked callandria. During operation of conventional evaporators build up of residues such as milk stone lead to blockage. The conventional cleaning method which involves passing cleaning liquid through the series of effects does not adequately remove such residues and indeed can result in the baking on of milk stone leading to blockages of callandria. Once callandria are blocked they can often only be cleaned by removing them from the effect and drilling out the blockage. As callandria are often 5 to 8 metres in length this process is extremely expensive both in labor and down time of the evaporator.

The distributor plate of the invention provides rapid flow during cleaning dramatically improving cleaning efficiency and .1 avoiding blockages of distributor holes and callandria.

rr 1 The running costs of the evaporator during cleaning are significantly reduced. The method of the invention in contrast to previous methods does not require that cleaning be carried under vacuum and does not require the use of steam to heat the callandria. A sav g of at least 70% in steam usage during cleaning can therefore be made using the evaporator of t the present invention.

The significant increase in cleaning efficiency provided by the present invention also allows washing waste to be minimized. Aqueous sodium hydroxide which is frequently used as a cleaning liquid poses a significant disposal problem as it is damaging to the environment. Potassium hydroxide provides much more efficient cleaning and is not as difficult to dispose of as sodium hydroxide. However it has generally not been utilized in'washing evaportors as it is more costly A than sodium hydroxide. The economies provided by the present invention enable small volumes of potassium hydroxide to be used in cleaning.

The invention will now be described with reference to the exemplary embodiments shown in the attached drawings, 39 9 rI i .16 r o i 4 4 4 In the drawings:- Figure 1 is a schematic plant of a multiple effect evaporator.

Figure 2 is a schematic plan of an enlarged view of an effect.

Figure 3 is a schematic plant of an evaporator system in accordance with the invention.

Figure 4 is a schematic plant showing an enlargement of the first portion of the evaporator system of Figure 3.

Figure 5 is a schematic plant showing an enlargement of the final portion of the evaporator system of Figure 3.

Figure 6 is a part cross-section view of a distributor plate of the invention.

Figure 7 is a longitudinal section of the left half of the upper part of an evaporative effect comprising a distributor plate of the invention under evaporative conditions.

Figure 8 is a longitudinal section of the right half of the upper part of an evaporative effect comprising a distributor plate of the invention under washing conditions.

Referring to Figures 1 and 2 there is shown an evaporator system comprising five evaporative effects in series.

As shown in Figure 2 the evaporative effects each comprise housing header chamber for receiving liquid to be concentrated, a multiplicity of tubes (callandria) to provide evaporation from a falling film on the inner surfaces 39 thereof, a perforated distributor plate located in the

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10 4 1 1- r header chamber to distribute liquid to the openings of the callandria and a lower chamber (10) for receiving liquid which has passed through the callandria As shown in Figure 1 a steam inlet (11) is provided in the first effect to heat the external surfaces of the callandria and vapour ducts (12) are provided between the lower chamber of the effects to allow steam to be transferred to heat the callandria of the next effect in the series.

A product storage tank (13) stores the liquid to be evaporated which is preheated by being passed to the inlet (14) of the first effect via heat transfer means (15) in the vapour ducts (12) of effects A temporary holding tank (16) may. be provided to hold the preheated liquid before S- evaporation. During the evaporation procedure the evaporator system is operated under vacuum and steam is fed into the first effect and is fed to subsequent effects via vapour ducts The product to be evaporated is fed to the first effect via inlet valve (17) and onto the distributor plate and through the cqlandria where evaporation occurs from a falling film of the product from the callandria concentrated product falls into the lower chamber (10) where concentrated product is transferred via pump (18) through product transfer conduit (19) to the inlet valve (17) of the U next effect From the lower chamber of the last effect in the series (often referred to as finisher effect) product is transferred via the respective product outlet pump (18) for further processing for example where powdered concentrate is to be produced the pump may transfer product to a predryer (20) from which it is dried to form a powder.

Referring to Figure 3 there is shown an evaporator system in accordance with the .invention comprising the evaporator as hereinabove described (the product preheater has been omitted for clarity). The evaporator includes a washing system including at least one wash liquid holding tank (21) and V-11 4/~ Fr preferably three such tanks as shown (21a), (21b) and (21c).

A wash liquid inlet manifold (22) for feeding wash liquid to the effects in parallel and a wash liquid inlet pump (23) for transferring wash liquid to the inlet manifold under pressure. The wash liquid inlet manifold may be brought into communication with the inlet (14) of each effect and via three way valves The three way valves (17) allow the effects to be in line with the product transfer conduits (19) during evaporation and to be in line with the wash inlet manifold (22) during the washing cycle. A wash liquid recycle manifold (24) is in communication with the lower chamber (10) of each effect via wash liquid recycle conduit (25) which is provided with wash liquid outlet pump The wash liquid i: recycle manifold (24) is adapted to transfer wash liquid to "1 the holding tanks (21) via return line (27).

Referring to figures 4 and 5 the wash liquid tanks are preferably provided with steam sparge lines (28) and water inlet lines The wash liquid tanks preferably include a 20 caustic holding tank (21a) provided with inlet (30) for *~concentrated caustic and an acid wash holding tank (21c) with an inlet (31) for concentrated acid. The outlet of each wash liquid holding tank (21) is preferably provided with automated valves (32) and manual valves (33) which allow transfer to a common inlet manifold feed line (34) provided with the outlet feed pump (23) and automated valve S *S As shown in Figure 5 the lower chamber of each effect is provided with automatic valve (36) to control passage of liquid into the wash liquid recycle conduit (25) and flow metre (37) to enable determination of when liquid flow through the effects is complete. The wash liquid recycle conduit is also provided with a waste line (38) having an automated waste line valve (39) to allow heavily contaminated washing liquid to be diposed of. A turbidity analyser j) is also provided to measure turbidity of the wash liquid -nstream of the waste line The turbidity analyser (40) enables measurement of the level of contaminants in the wash liquid 39 which has passed through respective effects and provides 12-

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c4 I a basis for determining whether water is to he recycled via wash liquid recycle manifold (24) or disposed of via waste line A manually operated valve (41) is preferably provided in wash liquid recycle conduit between waste line (38) and turbidity analyser The effect inlet valve (17) of the first effect is preferably adapted to allow wash liquid to be fed to the temporary product holding tank (16) which is preferably provided with a recycle line (25a) to the wash liquid recycle manifold (24) having automated valve (39a) waste line (38a) and turbidity analyser It is particularly preferred that the vapour duct3 (12) and lower chamber (10) are provided with wash liquid spray means An example of a spray means is known in the industry as a "sprayball". Wash liquid is preferably fed to the spray means via spray means fed line (43) from effect inlet valve The spray means fed line (43) may include automatic valve (44) to control wash liquid flow to the spray means (42).

Wash liquid fed to the recycle manifold (24) is returned to the respective wash liquid holding tank (21) via return valve (32b).

To enable recycling wash liquid held in the outlet manifold and inlot manifold feed line (34) after washing it is preferred to use an inlet manifold recycle line (50) to S provide a flow of wash liquid from the inlet manifold feed line to the return line (27).

Inlet manifold recycle line (50) is preferably provided with two valves (51) and a flow metre (52) and pump (53) each disposed between the valves (51).

To facilitate rapid flow of wash liquid through the effects the invention provides an improved distributor plate.

Referring to Figure 6 the distributor plate (19) comprises an essentially planar plate (45) comprising a multiplicity of product transfer holes (46) which are preferably in the M- 13 Lj

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range of from 2-15 millimeters diameter (most preferably 7 millimeters). The plate may be constructed of any suitable material however where the liquid to be evaporated is milk stainless steel is particularly preferred, the suitable thickness of the plate will depend on the rigidity of the material however from 1 to 20mm is preferred.

The distributor plate further comprises a multiplicity of overflow conduits the inlet (47a) of the conduits being above the surface of the plate. The inlet (47a) of the conduits is preferably disposed at least 10 millimeters more preferably in the range of from 20-100 millimeters above the surface of the plate. The height of the inlet (47a) of the overflow conduits above the upper surface of the plate is preferably in the range of from 1-20 times the diameter of the orifices The diameter of the overflow conduit (47) is S preferably greater than the diameter of the orifices (46) and r. most preferably from 1.5 to 3 times the diameter of the orifices.

The operation of the distributor plate will now be disclosed with reference to Figures 7 and 8.

The header chamber of each effect is preferably provided with an inlet flow deflector (48) to deflect flow of liquid to the periphery of the effect (that is, adjacent the wall of the o effect). The deflector is preferably in the form of a plate disposed in the header chamber at right angles to the axis of the effect between the inlet (14) and distributor plate A. Liquid flowing from the inlet of the effect is deflected by the deflector (48) toward the wall of the effect and flows onto the distributor plate at its periphery.

The edges of the distributor plate preferably abut the inner side of the housing of the evaporator. During evaporation the distributor plate operates as shown in Figure 7. The liquid to be evaporated flows over the surface gr~~of the deflecter plate and is preferably introduced at a rate -14r 7 I~ suitable to maintain a head of product liquid (49) in the range of from 10-50 millimeters above the surface of the distributor plate (most preferably 20 millimeters). The height of the overflow conduits the diameter of the orifices the surface area of the plate (45) and the rate of product flow are selected such that the level of product on the distributor plate is below the inlet of the upriser conduits. The overflow conduits (47) are preferably located between adjacent distributor holes (43) so that the overflow is evenly distributed beneath the plate during washing.

The evaporator is preferably washed out periodically by introducing a wash solution at a rate such that overflow of S° the wash solution into the upriser conduits occurs. The flow of wash solution is preferably is selected to give a falling o, film velocity of at least lm per second.

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Operation of the distributor plate during washing is shown in Figure 8. Rapid flow of wash liquid from the effect inlet causes a head of liquid (49) to be maintained on :he distributor plate which is at least as high and preferably higher than the inlet (47a) of the overflow conduits (47) Sthereby providing flow of wash liquid to the callandria (8) via overflow conduits (47) and distributor holes (46).

i o IO During evaporation the effect inlet valves (17) provide o* communication between temporary product holding tank (16) and first effect and all subsequent effects in series via product transfer conduits Effect inlet valves (17) are closed to wash liquid inlet manifold (27) and the wash liquid automated outlet values (26) are closed and spray means feed line valve (44) is closed. The system is maintained under a vacuum and steam is fed into steam inlet After being heated by heat transfer means (15) product is delivered to temporary product holding tank (16) from which it is fed to the first effect and then is pumped through product transfer conduit (19) via pump (18) through the next effect This procedure is repeated until product has passed 39 through the last effect in the series. The product may then 15 r c i PT i L.

be predryed in the predryer (20) and subsequently processed into powder.

During evaporation, particularly in the case of milk, residue builds up in the callandria lower chamber (10) and vapour ducts distributor plate and header chamber To commence cleaning the product line is closed, the system is returned to ambient pressure and steam inlet (11) is shut off. The wash liquid outlet valve (36) in the lower chamber of each effect is opened and the waste line valves (39) are opened. The wash liquid outlet pumps are operated until flow meters (37) show zero flow indicating that o remaining product has been pumped from the system.

The wash liquids are placed in respective tanks (21) and are *q heated to a temperature in the range of 85 to 100 0 C by steam from sparge lines The most preferred caustic wash liquids are aqueous sodium hydroxide and aqueous potassium .20. hydroxide. Concentrations of 3 to 4% by weight of sodium hydroxide or potassium hydroxide are particularly effective.

The preferred acid wash liquid is aqueous nitric acid most preferably of concentration of about 1% by weight. The wash liquid tanks (21) ar preferably jacketed to reduce heat loss.

To commence cleaining the appropriate tank outlet valve (32a) and the appropriate tank return valve (32b) is opened. Effect Sinlet valves (17) and inlet manifold feed line valves (35) are opened. Wash liquid inlet pump (23) is activated and spray means feed line valve (44) are also opened to provide efficient cleaning of lower chamber (10) and vapour ducts Effect product outlet pump (18) is activated to ensure thorough cleaning of all lines.

To empty the inlet manifold (22) and inlet manifold feed line (34) the inlet manifold feed line (34) is brought into communication with return line (27) by opening valves (51) of the manifold recycle line The pump in the manifold recycle line (53) is activated to return liquid from the inlet manifold (22) and inlet manifold at feed line (34) to the -16 L t i: i: F 6i~3 I e -4 1f I Ii appropriate storage tank (21) via return tank (27).

The pump (53) is stopped when flow metre (52) indicates zero flow and valves (50) are closed. Drain line valves (39) are then opened to purge remaining wash liquid from the system.

When flow metres (37) indicate zero flow or wash liquid tank liquid level is too low pump (23) will stop and valves (23) will shut.

The cleaning reaction between caustic wash liquid and the residue on the inside of the effects can be monitored by measuring turbidity using turbidity analyser (40) which is preferably an infra-red turbidity analyser. Monitoring of S' turbidity allows the time of completion of the cleaning reaction between caustic and contaminant such as milk stone to be determined to optimize cleaning efficiency and minimize S down time.

rrr or The flow rate to achieve a Reynolds number of 2300 will depend °Zo on the temperature of the liquid and diameter of the callandria. Tables 1, 2 and 3 below show variation in the Reynolds number for tubes of 35, 40 and 50mm diameter respectively. Each table shows the effect of flow rate, film thickness and temperature on Reynolds Number.

It is particularly preferred the flow rate of wash liquid is I greater than 1 rrmetre per second and temperature is from 85 0

C

to 100 0

C.

Although a specific example of the invention has been described in detail in the foregoing for the purposes of illustration it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention.

39 17 I .4 T1011-, I VAIA'ION OF REYNOLDS NO. WITH1 TEM\PERtATURZE AND FLOW RATE Recynolds No, Ve ocity nd Filml Thricknecss lit 50 0 70 0 C 0 C 70iC Flow Re )Ills t 111111 Het rn/s 111m1 Re I n/s t rum 11mi 0.7 723 0.397 0.27 988 0.441 0.41458 0.502 0.21 1.4 1446. 0.631 0.34 1976 0.700 0.30 2916 0.797 0.27 2.1 2169 0.826' 0.39 2964 0917 '0,35 4374 1.044 0.30 2.8 2i892 1.001 0.42 .3952 1.111 0.38 5832- [.26.5 0.34 3615 1.162 0.46' 4940 1.289 .0.41 7290 L.468 0.36 4.2 4338 1.312 0.49 5928 1.456 0.44 8748 1.657 0.38 5681 1.570 0.53 7763 1.743 0.48 11456 1.984 0.42 6.2 64 0-4 1.701 0.55 8751 .1.887 0.50 12914 2.149 0.44 6.9 17127 1.826 0 57 9739 2.027 0.52 14312 2.308 0.45 "I S per sec. t111 iLIIKucmsss Transition lanunasi to tuwbutnt flow occuiEs at Rc-> 1200 Note: ncressing Lcrnpecaturc 500(2 to 950(C incascs luibufcncc 10-0 pe-rccni. Rr.±cio tacs also b1Jca.$cd Increasing temzper-turc 70'C to 95C( incxcnscL turbulacc 33 pciceni.

Inccsing flow 3 Linies icrean3 Luibulcace 300 permei.

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C C S 0 0 C Ceo C C S

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cJ4* Ln cq D TAbL: 2 VARIATION OF REYNOLDS NO. WVI Ill 1 IT I1PERATURI AND) FLOW IRATE (Tube Diaitnler 40 111111) Reynolds No elocity aild Film Thlicknes it 50rC,70-&-95sC- 70C Flow Re tilts nIm Re rls t mm Re mns mm 1/min 0.7 633 0.363 0.26 865 0.403 0.20 1276 0.459 0.20 1.4 1265 0.577 0.32 1729 0.640 0.29 2552 0.729 0.25 2.1 1898 0.756 0.37 2594 0.839 0.33 3827 0.955 0.29 2.8 2530 0.916 0,41 .3458 1.016 0.37 5103 1.157 0.32 3163 1.063 0:44 4324 1.179 0.39 6379 1.343 0.35 4.2 3796 1.200 0.46 5187 1.333 0.42 7655 1.516 0.37 4971 1.436 0.51 6793 1.594 0.46 10024 1.815 0.40 TABLE 3 VARIATION OF REYNOLDS NO. WITH TEMPERATURE AND FLOW RATE (Iube Diumeter 50 mm) 0.7 506 0313 0.24 692 0.348 0.21 1021 0.396 0.19 1.4 1012 0.497 0.30 1383 0.552 0.27 2041 0.628 0.24 2.1 1518 0.652 0.34 2075 0.723 0.31 3062 0.823 0.27 2.8 2024 0.789 0,38 2707 0.876 0.34 4082 0.997 0.30 2530 0.916 0.41 3458 1.016 0.37 5103 1.157 0.32 4.2 3037 1.034 0.43 4150 1.148 0.39 6124 1307 0.34 3976 1238 0.47 5434 1.374 0.42 8019 1.564 0.37 6.2 4483 1.341 0.49 6126 1488 0.44 9040 1.694 0.39 6.9 4989 1.444 051 6818 1598 0.46 1000 1.819 040 In H- In 0I 0 too r 0 L

Claims (18)

1. An evaporator system including a plurality of effects arranged in series for progressively concentrating a liquid, the effects including: a header chamber for receiving liquid to be concentrated; a multiplicity of tubes adapted to provide evaporation of liquid from the inner surfaces of the tubes and a perforated distributor plate located in the header chamber to distribute liquid to the openings of the tubes; and wherein the evaporator system is provided with wash liquid conduits for feeding wash liquid to the effects in parallel and the distributor plates include an essentially planar plate member ti having a multiplicity of distributor holes therein for distributing liquid to be evaporatored to said multiplicity of 15 tubes and a series of overflow conduits for providing a flow 9S99 of wash liquid through the plate, the inlets of the conduits being disposed above the surface of the plate to provide an overflow for wash liquid during washing.

2. An evaporator system according to claim 1 wherein the .99 effects include a lower chamber for receiving liquid which has passed through the tubes.

3. An evaporator system according to claim 1 or claim 2 2f9, including at least one wash liquid holding tank and a pump to feed wash liquid to said effects.

4. An evaporator system according to claim 2 or claim 3 which includes at least three effects wherein the distributor plate of each effect maintains a head of product liquid during evaporation and provides an overflow of wash liquid to said multiplicity of tubes to facilitate rapid liquid flow during washing.

5. An evaporator system according to any one of claims 1 to 4 wherein the inlet of the overflow conduits are at a height above the upper surface of the plate which is greater than the level of liquid product achieved during product evaporation. V

6. An evaporator system according to claim 5 wherein the inlet of the overflow conduits are in the range of from 12 millimetres to 250 millimeters above the upper surface of the plate.

7. An evaporator system according to claim 5 or claim 6 wherein the distributor holes are of diameter in the range of 2-15 millimetres and the overflow conduits have a diameter in the range of from 7 to 25 millimetres. ar t a Ca a 0 a tr a a *G

8. A method of operating a multiple effect evaporator system including feeding a liquid to be evaporated through a series of effects operating under vacuum to provide progressive concentration, returning the system to ambient pressure and cleaning the system by feeding a wash liquid into the effects in parallel wherein each effect includes: a header chamber for receiving liquid to be concentrated; a multiplicity of tubes adapted to provide evaporation of liquid from a falling film on the inner surface thereof; and a perforated distributor plate located in the header chamber to distribute liquid to the openings of the tubes via holes therein the distributor plate including an essentially planar plate perforated with said holes and further including a series of overflow conduits for providing a rapid flow of liquid through the plate during washing, the inlet of the conduits being disposed above the surface of the planar plate and wherein during evaporation the level of liquid on the distributor plate is less than the height of the inlet of the overflow conduits and wherein during washing wash liquid is fed into the header chamber to produce overflow to said tubes via the the overflow conduits. -21-

9. A method according to claim 8 wherein the temperature of the wash liquid is in the r:nge of from 85 to 112 0 C. A method according to any one of claim 8 or claim 9 wherein the wash liquid flow has a Reynolds Number of at least 2300 in said tubes.

11. A method according to claim 10 wherein the Reynolds number is from 5500 to 7500.

12. A method according to any one of claims 8 to 11 S wherein the method includes passing an aqueous caustic solution through the effects in parallel and subsequently rinsing the effects. aa

13. A method according to any one of claims 8 to 12 4*40 oao wherein potassium hydroxide of concentration of 3 to percent by weight is passed through the effects and the effects are rinsed with water. 4.#

14. A method according to any one of claims 8 to 13 wherein the effects are washed with an aqueous acid solution comprising phosphoric acid and nitric acid.

15. A process according to any one of claims 8 to 14 wherein the method includes purging the system of excess of i, the liquid to be evaporated, rinsing the system with water, passing an aqueous acid wash liquid through the system, passing an aqueous caustic solution comprising potassium and/or sodium hydroxide through the system, purging the wash liquids from the system and rinsing the system with water.

16. A method according to any one of claims 8 to wherein the turbidity of the wash liquid after passing through the effect is monitored to determine the rate of removal of deposits from the inner surfaces of the effects and thereby determine when cleaning is completed.

17. A method according to any one of claims 8 to 16 -22- ~i wherein the liquid to be evaporated is milk or a product of milk.

18. An evaporation system according to claim 1 substantially as herein described with reference to the drawings.

19. A method according to claim 9 substantially as herein described with reference to the drawings. DATED: 27 October 1994 PHILLIPS ORMONDE FITZPATRICK Attorneys for: ANCON CHEMICALS PTY LTD 6484S t -23- ABSTRACT The invention provides an evaporator system comprising a plurality of effects arranged in series for progressively concentrating a liquid product wherein there is provided wash liquid conduits for feeding wash liquid to the effects in parallel. In a further aspect the invention provides a distributor plate for use in the header chamber of an evaporative effect the Sdistributor plate including an essentially planar plate having rr a multiplicity of distributor holes therein for distributing o~:o liquid to be evaporated to said multiplicity of tubes below the plate and further comprising a series of overflow conduits s for providing a flow of liquid through the plate the inlets of said conduits being disposed above the surface of the plate to provide an overflow for wash liquid during wash ng. 1 r 0 t