CONTINUOUS-FLOW HEAT EXCHANGER, APPARATUS COMPRISING THE SAME, AND EVAPORATOR SYSTEM

Abstract: Energy-saving apparatus for exchanging heat, in a flow process, comprising a plurality of cooperating assemblies each comprising a central tube (202), containing one or more static mixing elements (203), which comprise blade-shaped components which slope in the flow direction and fit the inner wall of a central tube (202), an annular space (224) surrounding said tube and a shell tube (204) which delimits the annular surrounding space (224), the assemblies communicating with one another in such a way that both the annular spaces and the central tubes form continuous compartments. The invention further comprises a water-saving evaporator in which an underpressure is generated by a water-jet ejector, the warm water vapour being absorbed in the water jet and said warmed water being able to circulate and to be supplied to other processing systems. The evaporator according to the invention may likewise be combined with the above-described energy-saving apparatus.

Description: Continuous-flow heat exchanger, apparatus comprising the same, and evaporator system The present invention in the first instance relates to an apparatus for exchanging heat, in a flow process, between an at least in part liquid to be treated first medium and a liquid or gaseous second medium, comprising a plurality of cooperating assemblies each comprising a central tube, provided with one or more static mixing elements, an annular space surrounding said tube and a shell tube which delimits the annular surrounding space, at least the annular spaces communicating with one another in such a way that an essentially continuous annular compartment is formed and the central tubes likewise being connected to one another in such a way that an essentially continuous central compartment is formed, in which, during operation, the first medium is flowing, the second medium flowing through the annular compartment In many preparative operations in the field of, for example, the food industry such as the sugar-processing industry and the dairy industry, in the field of manufacturing pharmaceutical products, of the cosmetic industry and chemistry, heat exchangers are employed, which are optionally connected to an evaporator system and/or other processing systems. An apparatus of the abovementioned type is disclosed by DE-A-23 11 568. In this apparatus, at the start of each straight central tube, so-called reversing elements are positioned which are constructed as an oblique hollow cone tip, whose base is in each case fitted, by means of a flange, to the rim of the central tube. Media to be cooled or to be heated are, each time they flow through a straight central tube, "reversed" once, which means that the medium located near the wall of the tube is directed to the centre thereof, which is associated with a turbulent flow character, according to this publication, said flow character at the other end of the tube being laminar once more, as stated by said publication. Viscous media which are processed, for example, in the food industry, as already mentioned above, in such an apparatus will very soon after the reversing element have reverted to a laminar flow character. This laminar flow character is an undesirable feature, since the medium located near the wall is not or virtually not flowing and therefore is in contact with the wall for a long time. The heat exchange is therefore inhomogeneous, with respect to the medium, and the medium located at the wall may become undercooled or overheated, or even char, which is a problem, for example, in the manufacture of caramel. To avoid this problem, the thermal difference between the two media must not be too large, which again implies a relatively long cooling/heating section. This latter feature has the drawback that the apparatuses are rela¬ tively large, occupy a great deal of space, require a great deal of energy etc. An additional drawback with the said apparatuses is the fact that owing to, for example, static mixing elements employed there are often "dead" spaces in the central tubes. In the apparatus according to the DE-A-23 11 568 this is the case, for example, in the region around the shell of the cone base of the reversing element, between this element and the tube wall. In these dead spaces the medium does not or virtually does not flow. In such dead spaces it is possible, if the medium to be processed is, for example, a sugar solution, for bacterial growth and the like to occur, which is highly undesirable and may render the product unusable. The object of the present invention is to solve and overcome, respectively, the abovementioned problems and drawbacks by providing an apparatus of the type mentioned in the preamble, which is of compact design, that is to say that its tube length is limited, and the residence time of the medium to be treated at the wall of the central tubes is short, and which is essentially free from dead spaces, being characterized in that the one or more static mixing elements comprise at least partly blade-shaped components which fit the inner wall of a central tube and which slope in the flow direction of the first medium. As a result of the apparatus comprising such static mixers within the central tubes, the medium, during operation, will be moved away from the wall at each blade- shaped component, which causes the residence time at the wall, depending on the flow velocity of the medium, its viscosity and the number of blade-shaped components present, to be reduced by quite a considerable amount. As a result of the medium to be treated in this apparatus, during operation, flowing continuously through the central compartment which does not contain any dead spaces, growth of microorganisms will essentially not take place. Owing to the expedient static mixing elements positioned in the tubular cavity within a central tube, and owing to the simple construction of abovementioned assemblies joined to one another, the apparatus according to the present invention is readily maintained, cleaned and operated. Cleaning can take place, for example, in situ by means of a cleaning fluid being pumped through the apparatus; owing to the absence of dead spaces, the cleaning fluid will not remain behind in the apparatus and will be able to be removed by means of relatively little rinse water. Advantageously, the central tubes are essentially completely filled with the static mixing elements, so that the medium to be treated, wherever heat exchange is taking place, has a short residence time at the wall. In a preferred embodiment of the present invention, the static mixing elements are positioned in such a way in the central compartment that they are in contact with the walls of the central tubes. During operation, the mixers will then themselves also conduct heat which is supplied or removed via the central tube wall . The heat exchange area can thus be increased, as a result of which the heat exchange section of the apparatus may in principle be shortened, or it is possible to opt for a smaller thermal difference between the two media or for a combination thereof . Preferably, the static mixing elements in the apparatus according to the present invention are positioned so as to be detachable, in order to facilitate inspection and maintenance of the apparatus . The static mixers, which comprise criss-cross ridges which are at an angle with respect to the tube axis, the ridges of the mixing elements being disposed in at least two groups and the ridges within one group being essentially parallel, whereas the ridges of the one group cross the ridges of the other group, proved to be usable in the apparatus to great advantage. Using this type of static mixing elements makes it possible for the medium to be treated to be caused to flow as a laminar flow having a turbulent character, as a result of which optimum heat transfer will take place. Owing to such a flow the velocity of the first medium at the central tube wall will not be zero; the first medium will, as previously described above, as it were constantly be guided away from the wall, charring or burning of the first medium thus being prevented. The apparatus may be designed so as to be considerably shorter compared with prior art apparatuses, which entails considerable savings in cost and weight. For use in, for example, the sugar-processing, confectionery and dairy industry, mixing elements commercially available from Sulzer in Switzerland as type SMX and described in the Dutch Patent Application NL-A- 8004240 can expediently be employed as static mixing elements in the apparatus according to the present invention, even though said mixing elements have been developed for mixing two liquids having extreme viscosity ratios (of 1: 1000 or more) and are indeed only being used as such in the art . These mixing devices have the following charac¬ teristics : the ratio between the maximum ridge width and the tube diameter is 0.1-0.167, the ratio between the perpendicular ridge spacing in each group and the tube diameter is 0.2-0.4, and the ratio between the length of a mixing element and the tube diameter is 0.75-1.5. If these mixing elements are positioned under a certain pressure in the central tubes, the ridges thereof will make contact with the central tube wall, as a result of which, as previously indicated hereinabove, the surface across which the heat transfer takes place is virtually doubled, compared with a tube without mixing elements. A very attractive preferred embodiment of the apparatus according to the present application therefore contains static mixing elements of the abovementioned type SMX. It is also possible for static mixing elements of the type SMXL to be used in the present invention; these, however, are somewhat less effective because they fit the wall of the central tube to a much lesser extent and consequently fouling may take place on the wall and under¬ cooling/overheating (charring) may occur. The poor fit between the mixing elements and the wall also means that the above-described heat exchange via the mixing element cannot take place as effectively. The ridges of the mixing devices of the Sulzer SMXL type are also at a smaller angle with respect to the tube wall, as a result of which, as is obvious to those skilled in the art, a lower pressure head drop will admittedly occur, but less heat transfer can take place per unit of tube length, so that the length of the heat exchange section in the apparatus is larger than if the mixing elements of the SMX type are used, which is undesirable if as compact as possible an apparatus is being aimed for. Given the above, the static mixing elements of the SMXL type are therefore less suitable in the apparatus according to the present application. Other static mixing devices can likewise be used in the apparatus according to the present invention, as long as they satisfy the above-described requirements. For cleaning and inspection purposes mixing elements, if more than two mixing elements are used for each straight central tube, are preferably connected in series with one another by means of, for example, soldered or cemented joints, preferably having a length of about half a tube length. In each straight central tube, two such series can then be accommodated which can be pushed into/out of the central tubes in a simple manner. Preferably, at least one of the connection means which connect the central tubes to one another is provided with one or more sealable orifices for adding constituents to the first medium. These can be used, for example, in the sugar-processing industry for admixing the first medium with colourings and flavourings. To keep the heat loss as low as possible, and also for safety reasons, a preferred embodiment of the apparatus according to the present invention is accommodated, at least in part, within a thermally insulating housing. A suitable insulation material is, for example, perlite; other insulating materials such as thermally stable organic foams are likewise suitable. The present invention also relates to the above- described apparatus for exchanging heat, in which the central compartment for the first medium on the downstream side is connected to an evaporator system. For many industrial purposes, solutions are first heated and then subjected to evaporation, the sugar-containing solution being treated in such a manner in the sugar-processing industry, for example. Preferably, the evaporator system includes an underpressure chamber which makes it possible for evaporation of the solution to take place under controlled conditions, in contrast to an evaporator system in which the vapour outlet is in direct contact with the atmosphere, such systems being used, for example, in the sugar- processing industry. With such known evaporator systems the atmospheric conditions are an important factor which cannot be influenced, evaporation therefore not being able to take place under controlled conditions, while product-containing vapour reaches the atmosphere, which may involve pollution of the environment . Preferably, the evaporator system which forms part of the apparatus according to the invention contains, in the underpressure chamber, a plate across which the medium can flow, so that the solution is spread out in this chamber to increase the surface area of the solution to be evaporated and allowing evaporation to proceed more effectively. Preferably, this plate is positioned at an angle with respect to the horizontal flow component of the medium to be evaporated, so that the liquid is able to move across the plate under the influence of gravity. Preferably, the plate is of corrugated design, in order to accomplish a certain degree of movement within the medium to be evaporated, the efficiency of the evaporation process being increased further as a result . Preferably, the reduced pressure in the evaporator system is accomplished, at least primarily, by an ejector. The advantage of using an ejector compared with, for example, a water ring vacuum pump consists in the fact that warm vapour can be absorbed in the seal water of the water ring pump, the pump performance decreasing as a result. Dry vacuum pumps have the drawback that no moisture, in the form of water or of solution to be evaporated, must get into the pump, which requires expensive measures known in the art, such as fitting a condenser, a water separator and a filter. Moreover it is absolutely undesirable for the solution to be evaporated to come into contact in any way with lubricants which are used in such pumps. An ejector is devoid of said drawbacks. Moreover, an ejector does not contain moving parts, implicating limited wear and maintenace. Advantageously, the ejector of the evaporator system is a water-jet ejector, so that in the case of an aqueous first medium the abstracted vapour is absorbed into the water jet. In a preferred embodiment of the present invention, the ejector of the evaporator system is incorporated in a water circulation system, so that the ejector consumes virtually no water. In a following preferred embodiment, the evaporator system is connected in such a way to one or more processing systems that the water from the evaporator system can be delivered to said systems. Thus, during operation, the water flowing through the ejector will, by absorbing vapour from the aqueous solution to be evaporated, be heated; this heated water can be fed to another processing system, so that it is not necessary for water to be heated separately for the latter system. This permits considerable savings in energy. In yet another preferred embodiment it is possible, between the apparatus for exchanging heat and the evaporator system, for one or more systems to be connected for carrying out operations, such as a system for applying a supplementary heat treatment, mixing, dilution and the like to the first medium. In yet a further preferred embodiment, the evaporator system is followed by a supplementary apparatus for exchanging heat, which latter apparatus for exchanging heat is preferably of the type as described hereinabove according to the invention; the medium subjected to evaporation can, upon leaving the evaporator system, be heated further or be cooled in this manner. Advantageously, the apparatus incorporates, between the evaporator system and the supplementary apparatus for exchanging heat, one or more systems for carrying out operations on the first medium, such as a system for applying a supplementary heat treatment, mixing, dilution and the like. The invention also relates to an evaporator system for evaporating liquid media, preferably solutions, at least comprising an underpressure chamber and an underpressure-generating system. This is characterized in that for the purpose of evaporating aqueous media the underpressure-generating system is a water-jet ejector which is incorporated in a water circulation system, and the underpressure chamber includes flow-guiding means for the media to be evaporated. The underpressure is established by a water-jet ejector, so that the vapour is absorbed into the water jet, and as a result of which the previously explained drawbacks of a water ring vacuum pump and a dry vacuum pump will not occur. As a result of the ejector being incorporated in a water circulation system, it consumes virtually no water. The evaporator system includes an underpressure chamber which makes it possible for evaporation of the solution to take place under controlled conditions, in contrast to an evaporator system in which the vapour outlet is in direct contact with the atmosphere, such systems being used, for example, in the sugar-processing industry. With such known evaporator systems the atmospheric conditions are an important factor which cannot be influenced, evaporation therefore not being able to take place under controlled conditions. Preferably, the evaporator system contains, in the vacuum chamber, a plate across which the medium can flow, so that the solution is spread out in this chamber to increase the surface area of the solution to be evaporated and allowing evaporation to proceed more effectively. Preferably, this plate is positioned at an angle with respect to the horizontal flow component of the medium to be evaporated, so that the liquid is able to move across the plate under the influence of gravity. Preferably, the plate is of corrugated design, in order to accomplish a certain degree of movement within the medium to be evaporated, the efficiency of the evaporation process being increased further as a result. By virtue of incorporating, in a preferred embodiment of the present invention, an evaporator system according to the invention without moving parts, the system is virtually maintenance-free, which has a cost-saving effect. In a following preferred embodiment of the invention, the evaporator system is connected to one or more processing systems in such a way that the water from the evaporator system can be delivered to said systems. Thus, during operation, the water flowing through the ejector will, by absorbing vapour from the aqueous solution to be evaporated, be heated; this heated water can, for example, in part be fed to another processing system, so that it is not necessary for water to be heated separately for the latter system. This permits considerable savings in energy. A system for heating sugar solutions is also known from EP-A-0 611 588. This describes a heat exchanger for heating a sugar solution which flows through a surrounding annular space. The inside of the annular space is defined by a central tube through which the heat-delivering medium, steam, is flowing. The outside of the surrounding annular space is defined by a tube wall which may or may not be encompassed by a second annular space, through which likewise heat-delivering medium can flow. The annular space contains small baffles which are fixed to the outer wall of the central tube and serve as static mixers which cause turbulence within the sugar solution to be heated, as a result of which heat transfer is alleged to be promoted. As a result of the solution possibly being heated from two sides in said apparatus, the heating surface can be doubled; nevertheless this apparatus has drawbacks: 1) because the central heating tubes are run to the outside, whereas the surrounding space, by means of a U-bend, is connected through to a following surrounding space, dead spaces are formed in the compartment for the solution to be heated, which may lead, in the case of, for example, a sugar solution being heated, to growth of microorganisms; 2) the apparatus is complicated in design and consequently expensive; replacing a central tube and the tube which delimits the annular space outwardly is laborious, and because of the many seals the risk of leaks which may arise during maintenance and/or replacement is high; 3) it is difficult to position effective static mixing elements in the annular space; the small baffles which, according to EP-A-0 611 588, are fixed to the outside of the central tube are relatively primitive mixers and do not meet the requirements of good mixing and heat distribution. The apparatus and how it operates is explained in more detail with reference to the accompanying drawing. Figure 1 is a simplified schematic representation of a heat exchanger according to the invention, Figure 2 gives a more detailed schematic repres¬ entation of a preferred embodiment of a heat exchanger according to the present invention, Figure 3 is a schematic representation of a cross- section of a preferred embodiment of the evaporator system according to the present invention. In Figure 1, 5 assemblies 101-105 positioned in parallel are indicated by arrows. Central tubes 106 which are connected to one another by means of U-bends 107 form a continuous central compartment (thick black line) . Shell tubes are represented by 108 and are likewise connected to one another by means of connections 109, an annular compartment (hashed) being formed as a result. The central compartment has an in- and outlet 110, 111, and the in- and outlet of the annular compartment are represented by 112 and 113. The whole is accommodated in a housing 114. Figure 2 gives a more detailed explanation of the mode of operation of the abovementioned apparatus: the first medium, which is to be treated, is directed to the apparatus via a supply line 201. There it enters the first of five central tubes 202. In these central tubes, Sulzer SMX mixing elements 203 are fitted so as to be detachable. Around each central tube 202 a shell tube 204 is positioned. Within the annular space formed thereby the second medium (such as, for example, steam, thermal oil, water, glycol) can flow. The central and shell tubes, 202 and 204, respectively, are fixed to two end plates 205, 206. The central tubes 202 project through the end plates 205, 206 and are welded so as to be gas-tight. The shell tubes 204 are welded between the end plates 205, 206 so as to be gas-tight. The end plates contain ducts 207, in order to pass the second medium from the one to the other annular space 224. Attached to the outside of the end plates, by means of detachable fastening means, are U-bends 208, via which the medium to be processed is conveyed to the next central tube. After having passed the last central tube, the first medium is conveyed onwards via a discharge line 209. The second medium is supplied via a line 210, this being controlled by a control valve 211. This in turn is controlled by a temperature sensor 212 which is fitted in the discharge line 209 for the first medium. Having passed the control valve 211, the second medium flows, via line 213, to an inlet 214 which is situated in the end plate 206. Having passed all the annular spaces, the second medium leaves the apparatus via connection 215 which is situated in the end plate 205. Then the second medium, if the apparatus is being used as a boiler, using steam as the heat-delivering second medium, is dicharged through a conventional assembly of filter, steam trap and the like, represented by 216. If the apparatus is being used as a cooler, using water, for example, as the heat-absorbing medium, the discharge line, represented by 216, contains a pressurizing valve to ensure that the annular compartment is at all times filled with cooling medium. The pressure prevailing in the annular compartment is read at a manometer 218 which is connected to the apparatus via a U- tube 219. To prevent heat loss a cowling 220 is attached to and between the end plates 205, 206 so as to form a closed housing. The cavity 221 thus created is filled with an insulation material such as perlite. This ensures that, for example in the case of the apparatus being used as a boiler, steam being employed as the heat-delivering second medium, the temperature at the outside of the apparatus does not exceed 45°C. Emission of radiation which may occur at the end of the plates 205, 206 and cooling of the U- bends 208 are limited by covers 222. These covers are similarly constructed in such a way that in this case a cavity 225 is likewise formed which may be filled with perlite. The passages at the underside and top side of these covers are sealed by small cover plates 223. The mode of operation of the evaporator system is explained in more detail with reference to Figure 3. The first medium to be evaporated is supplied via a supply line 301 and in the process passes through an outer and inner wall 328 and 329, respectively, of the underpressure chamber and enters an intercep-tion/spreading tray 302. The spreading tray distributes the medium over the entire width of a plate 303. The prevailing underpressure causes vapour to be liberated in a vapour space 304. To prevent cooling of the medium, the plate 303 is heated on the underside by, for example, steam present in space 305. This steam is supplied via a connection 306, and the condensate is discharged via a connection 307. The evaporated medium is collected in a receiver 308 and thence, via an outlet 309, is passed on to an extraction pump 310. Upstream and downstream of the extraction pump 310 stop valves 311 are positioned for cleaning purposes. To keep the amount of medium discharged constant, the speed of the extraction pump 310 is controlled electronically. The required control signal for the latter is obtained on a level electrode 312. For maintenance/cleaning operations, the underpressure chamber is provided with a removable cover 313. The unit is of double-walled construction to prevent premature condensation of the vapour. Between the double wall 328, 329 an insulation material 314 such as, for example, perlite is in place. The cover 313, likewise of double- walled and insulated design, incorporates a steam outlet 315 which, for cleaning purposes, is provided with a stop valve 316. The steam outlet is connected to a water-jet ejector 317 which creates and maintains the underpressure in the underpressure chamber. To keep the level of the underpressure constant, a pressure sensor 326 is fitted which electronically controls a control valve 327. The vapour is condensed in the water jet, and the heat released in the process is absorbed into the water and is transported onwards to a buffer vessel 318. To dissipate the velocity of the water in this buffer vessel 318, the buffer vessel 318 contains a tube 319 and a dish 320. The level of the amount of water available for circulation is controlled by means of level electrode 321 which, if the water level is low, opens a stop valve 322. Any excess of water is discharged through an overflow 323. The circulation of the water is maintained by a circulation pump 324 which pumps the water via a line 325 to the ejector 317. Optionally, this line 325 incorporates a tap 330 which passes the warmed water to another processing system. With reference to the following examples, the advantages of the apparatuses and systems according to the present invention will be explained in more detail and compared with apparatuses and systems being used according to the prior art. These examples, however, are by no means intended to limit the scope of the invention. The tables below give a comparison of the use of an apparatus according to the present invention, comprising a heat exchanger for heating a medium with the aid of steam, an evaporator system, and a second heat exchanger for cooling the medium to be treated, with the aid of water. The first and second column list various process parameters and the associated units, respectively; the third column gives the corresponding data as applicable to the respective conventional apparatuses and systems from the prior art, whereas the fourth column reports the data for the apparatus according to the present invention (new app.) . The fifth column shows any differences which may occur between the values of the conventional apparatuses and the apparatus according to the present invention. A possible further column is reserved for necessary comments. As the tables show, it is possible, in all cases, in the sugar-processing industry (Tables 1 and 2) , as well as in the baking industry (Table 3) and the dairy industry (Table 4) , to achieve considerable savings in the areas of steam consumption, water consumption and energy. Owing to the simple, compact design involving a reduced length of central compartment compared with existing apparatuses, considerably less cleaning fluid is required; owing to a saving in weight linked to the compact design the apparatus according to the present invention is more easily handled and also provides considerable savings in space compared with known apparatuses. Owing to the residence time of the medium in an apparatus according to the present invention being considerably shorter than in apparatuses which are known from the prior art and are used in the industries in question, the media to be treated are to a far lesser extent subject to any detriment they may suffer during an operation, for example by charring, degeneration etc. If the apparatus according to the present invention is used for preparing hard caramel on the basis of sugar (Table 1) it affords, in comparison with a conventional apparatus, for example a saving in steam of 56%, whereas 90% less water is consumed m the boiling-down process The cooling water for the cooler can, m addition to the process water, be reused m its entirety, as decribed hereinabove. As a result of evaporation taking place as described hereinabove by absorption of the vapour into the water which runs through the elector and is suitable for reuse, there is no emission of this intensely odorous vapour into the atmosphere. In the apparatus according to the present invention it is also possible, n contrast to the situation in the conventional apparatuses, for the caramel solution to be cooled rapidly, so that the preparation of white caramel is possible (see note to Table 1) . TABLE 1 * Production of 700 kq/h of hard caramel (suqar- processinα industry) On the basis of sugar (sucrose) Conv New Diff Comments app app Initial capacity g/h 930 930 - Final capacity kg/h 700 700 - Water to be kg/h 230 230 - evaporated Heat required kW 200 200 - Steam consumption kg/h 410 176 -56 boiler Water consumption kg/h 2000 200 -90 for evaporation Reused process water kg/h 0 230 +100 Cooling water for kg/h n/a 500 See NOTE cooler Steam consumption kg/h 250 250 0 rotary boiler Cleaning fluid kg/h 2000 1000 -50 Emission of product- kg/h 230 0 -100 containing vapour Weight of installa¬ kg 4300 1800 -58 Residence time sec 490 48 -90 Important in connection with charring due to protein-contain¬ ing product Also inversion NOTE : The conventional installations cannot be used to make white caramel , because of charring In the case of white caramel rapid cooling is necessary to stop the Maillard reaction, for this purpose the third cooler is used If , m the abovementioned case , sugar is replaced by a sugar substitute such as , for example , xylitol (Table 2) , the apparatus affords savings m steam of 65%, and 85- less water is consumed in the boilmg-down process. TABLE 2 : Production of 500 kq/h of hard caramel (sugar- processmg industry) On the basis of sugar substitute xylitol Conv New Diff Comments app app Initial capacity kg/h 630 630 - Final capacity kg/h 500 500 - Water to be kg/h 130 130 - evaporated Heat required kW 113 113 - Steam consumption kg/h 275 95 -65 boiler Water consumption kg/h 1500 225 -85 for evaporation Reused process water kg/h 0 130 +100 Cleaning fluid kg/h 2000 1000 -50 Emission of product- kg/h 130 0 -100 containing vapour Weight of installa¬ kg 3500 1300 -63 tion Residence time sec 310 33 -89 Important in connection with degeneration and inversion of the product In the course of producing fondant (Table 3) the use of the apparatus according to the present invention likewise affords considerable savings in steam (± 63%) and cooling water (68%) , whereas the water used in the evaporation process can be reused in its entirety, just like the process water. Moreover, there is no emission of vapour. I S TABLE 3 : Production of 450 kq/h of fondant (baking industry) For the preparation of custard (Table 4) two heat exchangers according to the present invention are connected directly to one another, the first one supplying heat to the product (the first medium) and the second heat exchanger removing heat from the product. Exactly as in the case of producing hard caramel, the use of an apparatus according to the present invention for preparing custard affords considerable savings in terms of steam (71%) and cooling water (80%) . TABLE 4 : Production of 1000 kg/h of custard (dairy processing industry) Set-up: boiler followed by cooler. Conv. New Diff app. app. Initial capacity kg/h 1000 1000 - Final capacity kg/h 1000 1000 - Water to be evaporated kg/h 0 0 - Heat required kW 181 181 - Steam consump . boiler kg/h 558 163 -71 Cooling water consumption kg/h 2000 400 -80 cooler Cleaning fluid kg/h 3000 1500 -50 Weight of installation kg 3000 1000 -67 Residence time sec 279 32.4 -88 Table 5 shows what characteristics media should advantageously have to be processed effectively in a preferred embodiment of the present invention. This preferred embodiment serving as an example comprises: 3-9 straight central tubes having a total length of 1.35-6.25 m and an internal diameter of 32 mm, 2-8 U-bends having an internal diameter of 32 mm, mixing elements of the type SULZER SMX, each having a length of 32 mm and a diameter of 32 mm, positioned under tension in each central tube and filling it completely. It should be noted that the apparatus for exchanging heat can be adapted as required, depending on the field of application and desired capacity, and can be extended or shortened by adding or removing assemblies such as those described hereinabove. Thus the preferred internal diameter in the case of heating is in the range between 25 and 40 mm, and in the case of cooling is in the range between 25 and 50 mm. It goes without saying that the values mentioned in Table 5 can vary correspondingly. Table 5 Preferred characteristics of media (product) which can be heated or cooled, respectively, m a preferred embodiment of the apparatus according to the present invention having an internal central tube diameter of 32 mm. HEATING COOLING minimum maximum minimum maximum value value value value Tube length 3 3 6 25 1 35 2 45 m Production capa¬ 285 535 215 395 kg/h city Viscosity of 0 3 0 36 0 85 0 92 Pa s product Specific mass of 1418 1440 1440 1480 kg/m 3 product Specific heat of 1 75 1 8 1 7 1 75 kJ/kgK product Heat conduction 0 364 0 367 0 55 0 56 W/mK coefficient of product Flow velocity 0 09 0 17 0 055 0 1 m/s Reynolds number 11 7 22 2 Average tempera¬ 32 46 35 58 °c ture difference Steam temperature 134 160 °c Temperature of 40 52 °C incoming cooling water Line resistance 1 25 4 5 1 7 5 8 bar The scope of the present invention also includes an apparatus, described herein, for exchanging heat, in which the annular compartment is discontinuous as a result of connection 109 having been replaced by an additional inlet and outlet for, respectively, supplying a new second medium and discharging the second medium used upstream of this outlet; such a set-up makes it possible to use two different media, whose temperatures may differ, in separate surrounding compartments. Such a set-up can be regarded as two apparatuses according to the present invention connected in series.

Claims: C L I M S 1. Apparatus for exchanging heat, in a flow process, between an at least in part liquid to be treated first medium and a liquid or gaseous second medium, comprising a plurality of cooperating assemblies each comprising a central tube (202) , provided with one or more static mixing elements (203) , an annular space (224) surrounding said tube and a shell tube (204) which delimits the annular surrounding space (224) , at least the annular spaces (224) communicating with one another in such a way that an essentially continuous annular compartment is formed and the central tubes (202) likewise being connected to one another in such a way that an essentially continuous central compartment is formed, in which, during operation, the first medium is flowing, the second medium flowing through the annular compartment, characterized in that the one or more static mixing elements (203) comprise at least partly blade-shaped components which fit the inner wall of a central tube (202) and which slope in the flow direction of the first medium. 2. Apparatus according to claim 1, characterized in that the central tubes (202) are essentially completely filled with the static mixing elements (203) . 3. Apparatus according to claim 1 or 2, characterized in that the mixing elements (203) are positioned in such a way in the central compartment that they are in contact with the wall of the central tube (202) . 4. Apparatus according to claims 1-3, characterized in that the static mixing elements (203) are positioned so as to be detachable. 5. Apparatus according to claims 1-4, characterized in that the static mixing elements (203) comprise criss-cross ridges which are at an angle with respect to the tube axis, the ridges of the mixing elements being disposed in at least two groups and the ridges within one group being essentially parallel, whereas the ridges of the one group cross the ridges of the other group. 6. Apparatus according to any one of the preceding claims, characterized in that at least one of the connec¬ tion means which connect the central tubes to one another is provided with one or more sealable orifices for adding constituents to the first medium. 7. Apparatus according to claims 1-6, characterized in that the apparatus is accommodated, at least in part, within a heat-insulating housing (221) . 8. Apparatus according to claims 1-7, characterized in that the central compartment for the first medium on the downstream side (209) is connected to an evaporator system. 9. Apparatus according to claim 8, characterized in that the evaporator system includes an underpressure chamber (304) . 10. Apparatus according to claim 9, characterized in that the evaporator system includes, in the underpressure chamber, a plate (303) across which the medium can flow. 11. Apparatus according to claim 10, characterized in that the plate (303) of the evaporator system is positioned at an angle with respect to the horizontal flow component of the medium. 12. Apparatus according to claims 10-11, characterized in that the plate (303) is of corrugated design. 13. Apparatus according to claims 8-12, characterized in that the evaporator system includes an ejector (317) . 14. Apparatus according to claim 13, characterized in that the ejector (317) is a water-jet ejector for evaporating an aqueous first medium. 15. Apparatus according to claims 13-14, characterized in that the ejector (317) of the evaporator system is incorporated in a water circulation system. 16. Apparatus according to claim 15, characterized in that the evaporator system is connected in such a way to one or more processing systems that the water from the evaporator system can be delivered to said systems. 17. Apparatus according to claims 8-16, characterized in that between the apparatus for exchanging heat and the evaporator system one or more systems are connected for carrying out operations on the first medium, such as a system for applying a supplementary heat treatment, mixing, dilution and the like. 18. Apparatus according to claims 8-17, characterized in that the evaporator system is followed by a supple¬ mentary apparatus for exchanging heat . 19. Apparatus according to claim 18, characterized in that between the evaporator system and the supplementary apparatus for exchanging heat one or more systems are connected for carrying out operations on the first medium, such as a system for applying a supplementary heat treatment, mixing, dilution and the like. 20. Evaporator system for evaporating liquid media, preferably solutions, at least comprising an underpressure chamber (304) and an underpressure-generating system, characterized in that for the purpose of evaporating aqueous media the underpressure-generating system is a water-jet ejector (317) which is incorporated in a water circulation system, and the underpressure chamber includes flow-guiding means for the media to be evaporated. 21. Evaporator system according to claim 20, charac- terized in that the evaporator system includes a plate (303) across which the medium to be evaporated can flow. 22. Evaporator system according to claim 21, charac¬ terized in that the plate (303) of the evaporator system is positioned at an angle with respect to the horizontal flow component of the medium. 23. Evaporator system according to claims 21-22, characterized in that the plate (303) is of corrugated design. 24. Evaporator system according to claims 20-23, characterized in that the evaporator system does not contain any moving parts. 25. Evaporator system according to claims 20-24, characterized in that the evaporator system is connected to one or more processing systems in such a way that the water from the evaporator system can be delivered to said systems.

Inventors: OOMS ALBERT, TWILT ADRIANUS HENDRIKUS, OOMS, ALBERT, TWILT, ADRIANUS, HENDRIKUS
Applicants: INDUPAL B V, OOMS ALBERT, TWILT ADRIANUS HENDRIKUS, INDUPAL B.V., OOMS, ALBERT, TWILT, ADRIANUS, HENDRIKUS
Application year: 1996
Main classification: F28D7
IPC codes: A23G3, F28D7