RU2814720C1 - Vacuum evaporator for milk raw material condensation - Google Patents

Abstract

FIELD: food industry.

SUBSTANCE: vacuum evaporation plant contains in-series installed five milk raw material heaters, the latter is connected with plate heat recuperator connected with pasteuriser and made with possibility of milk raw materials heating from the last heater due to milk raw materials cooling from pasteuriser. Plate-type recuperator is connected to the first housing of four in-series housings of the evaporation plant. First housing is connected to second, second to fourth, and fourth to third housing, wherein second and fourth housings are provided with two successive sections of evaporator heating tubes, while third housings are provided with four consecutive sections of evaporator heating tubes. Each housing of the evaporation plant is equipped with a steam discharge union connected to the heating steam supply union to the evaporator of the next housing, and comprises evaporator with coaxially installed steam separator with formation of steam space between walls for removal of secondary steam. Steam discharge union from the second housing is made with the possibility of withdrawing a part of steam to the ejector, which is made with the possibility of obtaining heating steam for the first housing due to thermal compression with live steam. Finished product discharge union of the third housing is connected to a vacuum crystallizer-cooler or a finished product storage tank.

EFFECT: invention provides higher energy efficiency of the vacuum evaporator.

1 cl, 3 dwg, 1 tbl

Description

The invention relates to the food industry, namely to installations for the production of condensed dairy products from dairy raw materials, which means whole milk, cream, skim milk, whey, cheese and curd whey, including pre-concentrated ones.

To thicken milk raw materials in industry, evaporation units are usually used in which a vacuum is created, and boiling therefore occurs at low temperatures, usually not higher than 78 ° C, which is why the units are called vacuum evaporation units.

The most well-known companies supplying technologies and equipment for thickening are Wiegand, GEA, Thermohran, Anhydro, SSP, Alfa Laval.

There are vacuum evaporation units of circulation and film type.

The thickening time in circulation units is slightly longer than the thickening time in film units due to the nature of boiling, which occurs in circulating units in the volume of the product under the influence of hydrostatic depression and is about 40 minutes. In film vacuum evaporation units, boiling occurs in a thin film distributed over the surface of the heating tubes, and the total duration of thickening does not exceed 15 minutes, which ensures the greatest preservation of whey proteins and vitamins.

Circulation units are currently used mainly for the production of canned condensed milk with sugar, but before the widespread use of film vacuum evaporators in the dairy industry and in lines for the production of dry milk products, circulation units were used (Strakhov, Vasily Vasilyevich. Vacuum evaporation units dairy industry and their exploitation [Text] / Candidate of Technical Sciences V. V. Strakhov - Moscow: Food Industry, 1970. - 142 pp.: drawing; 21 cm.).

The general structure and principle of operation of vacuum evaporation units is as follows: a set of tubular heaters, a pasteurizer, evaporators, which are also tubular heat exchangers for boiling and thickening the product due to evaporation, steam separators necessary for separating entrained drops and foam of the product from the exhaust vapors. The evaporator and steam separator are connected to each other by a steam line and together form the body of the installation. This arrangement of the steam separator is called remote, while the steam line enters the steam separator tangentially to separate steam from the product flow under the influence of centrifugal force, and the volume of entrained product, and therefore losses, can be significant. This design of the steam separator and the housing is bulky, metal-intensive, and results in a large area occupied by multi-body installations.

Also required components of the installations are product and condensate centrifugal pumps, an ejector block or a vacuum pump to create a vacuum and a condenser to condense the evaporated steam and thereby maintain the necessary vacuum in the installation (Vagn Vestergaard / Technology for the production of milk powder. Evaporation and spray drying / Vagn Vestergaard/Niro A/S, Copenhagen, Denmark, October 2003).

Usually, after heating in heaters, the raw materials are sent for heat treatment (pasteurization), which is carried out at fairly high temperatures from 95 to 107 ° C, to minimize the number of microorganisms and destroy lipolytic enzymes that could accumulate as a result of long-term storage of raw materials before thickening during the development of psychrophilic microorganisms (developing at low temperatures). Also, at such high pasteurization temperatures, a large amount of whey proteins and other micronutrients in milk are destroyed.

After heat treatment, the raw material enters the thickening chamber, where, entering the vacuum zone, it instantly and intensively boils due to self-evaporation. In this case, there is an additional effect on the components of the milk, as well as the formation of foam. The foam may be partially carried away due to vacuum, which leads to losses, as well as disruption of the boiling process due to incomplete coverage of the heating tubes and overheating of the thin film of foam, resulting in the destruction of even more whey proteins and trace elements.

There is a known method of reducing the temperature of milk before entering the housing for condensation using a vacuum cooling chamber in SSP vacuum evaporation units. However, this method does not fundamentally solve the problem, since cooling also occurs due to self-evaporation, as a result of which sudden boiling and foaming occurs, and part of the foam also enters the housing along with the cooled raw materials and ends up on the heating tubes, where it overheats (Dytnersky Yu .I. Basic processes and apparatus of chemical technology: A manual for design / G. S. Borisov, V. P. Brykov, Yu. I. Dytnersky, etc. Edited by Yu. I. Dytnersky, 2nd ed., revised . and additional - M.: Chemistry, 1991. - 496 pp.).

In the dairy industry, mainly two-, three-, four- and five-body plants are used, in which the vacuum and boiling point decrease from the first to the last body. The condensed raw material passes sequentially through all the housings and at the outlet has a temperature of (45-55) ° C. A decrease in temperature with a simultaneous increase in the concentration of dry substances leads to thickening of the condensed mixture, so the usually recommended concentration of dry substances in the mixture is (43-48)%. This is not enough for the production of canned condensed milk with sugar (Lipatov N.N., Kharitonov V.D. Powdered milk: theory and practice of production. M.: Light and food industry, 1981. 264 p.).

As is known, the viscosity of the condensed raw material depends on the temperature and at low temperatures, which reaches (45-55) ° C at the outlet of the vacuum evaporation unit, it is very difficult to achieve intense boiling and effective evaporation, the thick mixture does not flow well as a film or circulate in circulation-type apparatus, this often leads to deposits in the apparatus, severe burning, loss of milk components, pumping thick mixtures or requires more powerful and expensive pumps, greater energy consumption, or in some cases is not possible at all. To reduce the viscosity of thick condensed milk raw materials, it is necessary to increase its temperature.

For film vacuum evaporation plants, an important issue is the distribution of the condensed product along the walls of the heating tubes, as well as ensuring that the tubes are covered with a product film of optimal thickness.

Distribution devices based on shower spray devices and single- and multi-level plates with holes are known, which have both positive aspects and disadvantages. Shower sprayers do not ensure that all the product is applied to the walls of the tubes and some of the product “flies” along the heating surface. The design of tray-based distribution devices is often complex and does not take into account the need for steam movement, so the crossing flows of product and steam do not allow the film to be distributed evenly over the heating surface.

As a result of boiling and evaporation of moisture, the volume of the condensed product constantly decreases, the viscosity and thickness of the film on the heating surface increases, therefore, in multi-case installations, the heating surface area, determined by the number of heating tubes, is reduced from case to case to ensure coverage of the surface of the tubes, however, the solution to this problem is only due to the reduction of tubes from body to body, it does not take into account the degree of thickening and viscosity of various raw materials, which leads either to ineffective boiling in a film that is too thick, or to insufficient coverage of the surface of the tubes with the formation of “islands” and burning of the product at the border of the “island”, which worsens its quality.

The closest analogue to the patented solution is an evaporation plant for food products, including film-type evaporators installed sequentially along the direction of steam movement, each of which is equipped with a heating chamber with heat exchange tubes with upper and lower tube sheets, as well as a device for introducing the evaporated product, fittings for draining and introducing condensate and non-condensable gases, a separator having a device for draining steam into the annulus of the heating chamber of the evaporator next in the direction of steam movement, and a pipe for draining the separated evaporated product from the separator, while the first evaporator in the direction of steam movement is made with drain fittings condensate and non-condensable gases from the chamber under the lower tube sheet, and each subsequent evaporator is equipped with fittings for supplying and discharging condensate and non-condensable gases from the chamber under the lower tube sheet, in which a through hole is made, and the condensate drain fitting is in communication with the fitting for introducing condensate into the chamber under the lower tube plate of the subsequent evaporator, and a fitting for removing non-condensable gases with a fitting for introducing non-condensable gases into the chamber under the lower tube plate of the subsequent evaporator along the steam path (RF patent No. 2039438, published 07/20/1995).

However, this solution has the following disadvantages:

- high costs are required for pumping a viscous condensed product, the concentration of which is limited by the yield strength of the mixture at a given temperature due to the fact that the movement of the product through the housings occurs sequentially through the first, second and third housings, and the condensed product of the highest concentration is pumped out from the third housing of the installation at the most low temperature, which means the highest viscosity;

- low energy efficiency of the installation due to the presence of only three buildings;

- difficulties with maintenance due to the fact that the heating tubes are U-shaped, which complicates the design and makes it difficult to inspect, clean and wash the tubes in case of heavy carbon deposits on the product;

- a high probability of disruption of the movement of the product and its critical thickening and, as a consequence, burning inside the installation due to the fact that pumping between the installation bodies is carried out due to vacuum.

The technical problem solved by the present invention is the elimination of these disadvantages.

The technical result of the claimed invention is to increase the energy efficiency of the vacuum evaporation unit, reduce its metal consumption and overall dimensions; improving product quality by ensuring optimal distribution of the product film over the surface of the heating tubes; ensuring high microbiological indicators due to the exclusion of the development of thermophilic microorganisms; as well as increasing the concentration of the finished product to 48-74%.

The specified technical result is achieved through the use of a vacuum evaporation unit, which contains:

five heaters of raw milk materials installed in series, the last of which is connected to a plate heat recuperator connected to the pasteurizer and configured to heat the milk raw materials from the last heater by cooling the milk raw materials from the pasteurizer,

the plate recuperator is connected to the first housing of four consecutive housings of the evaporator unit, the first housing of which is connected to the second, the second to the fourth, and the fourth to the third housing, while the second and fourth housings are made with two consecutive sections of the evaporator heating tubes, and the third housing made in four consecutive sections of evaporator heating tubes,

each housing of the evaporator installation is equipped with a steam outlet connector connected to a fitting for supplying heating steam to the evaporator of the subsequent housing, and contains an evaporator with a coaxially installed steam separator,

the steam outlet fitting from the second body is configured to drain part of the steam into an ejector, which is designed to produce heating steam for the first body due to thermal compression with live steam,

the finished product outlet fitting of the third housing is connected to a vacuum crystallizer-cooler or a finished product storage tank.

In addition, each housing of the evaporator installation contains a distribution device located between the upper cover of the housing and the evaporator, and is a plate with pressure tubes forming channels for the passage of secondary steam, and holes for the passage of the condensed product.

Each housing of the evaporator unit consists of an evaporator and a steam separator made coaxially in such a way that the space between the walls of the steam separator and the evaporator forms a steam space for the removal of “secondary” steam. The condensed raw material and “secondary” steam enter the lower part of the evaporator, the raw material, under the influence of gravity, enters the bottom of the evaporator and is discharged through a pipeline, and the “secondary” steam, under the influence of kinetic energy and vacuum, from the lower part of the evaporator through the steam window enters the steam space and moves around the outer walls of the lower part of the evaporator to the outlet steam line.

The method of condensing milk raw materials in a patented vacuum evaporation unit is carried out as follows.

Dairy raw materials are first sequentially heated in heaters to 46±2°C, 52±2°C; 57±2°С; 61±2°С; 65±2°C, respectively, after which it is sent to a plate heat recuperator, where it is heated to a temperature of 74-104°C and then to a pasteurizer, where the raw materials are cooked at a temperature of 76-107°C with a holding time of 5-7 seconds, the flow from the pasteurizer is recirculated into a plate recuperator, in which the milk raw materials are cooled to a temperature of 68±2°C and, accordingly, the raw materials coming from the last heater are heated;

Next, the milk raw materials are subjected to condensation in four successively located buildings of the evaporation plant, while the milk raw materials are first fed into the first housing of the evaporation plant, in which condensation is carried out to a concentration of 10-35% due to boiling and evaporation of moisture at a residual pressure of 0.0685 MPa and temperature 68±2°С,

then sent to the second housing, in which the milk raw materials are sequentially thickened in two sections of the evaporator heating tubes at a pressure of 0.026 MPa and a temperature of 64±2°C to a concentration of 18-50%,

after which the milk raw materials are sent to the fourth housing, in which thickening is sequentially carried out in two sections of the heating tubes of the evaporator at a pressure of 0.015 MPa and a temperature of 56±2°C to a concentration of 33-58%, then the raw materials are returned to the third housing of the evaporator unit, in which sequentially thickening is carried out in four sections of the heating tubes of the evaporator at a pressure of 0.020 MPa and a temperature of 60±2°C to a final concentration of 48-74%,

in this case, the secondary steam removed from each housing is heating steam for the evaporator of the subsequent housing,

part of the secondary steam of the second housing is sent for thermal compression with live steam in the ejector to produce heating steam for the first housing,

from the third body, the condensed product is sent to a vacuum crystallizer-cooler for the production of sweetened condensed milk, or to a tank for short-term storage before drying for whole, skim milk or whey.

In particular, the starting raw materials may include whole milk, whole milk with sugar, skim milk, and whey.

The heat treatment temperature in the pasteurizer is selected depending on the type of raw material and is - (95±2)°C for whole milk, (105±2)°C for whole milk with sugar, (84±2)°C for skim milk and (78 ±2)°С.

Also, the temperature to which the raw materials are heated in the plate recuperator depends on the type of raw material and is (92±2)°C for whole milk, (102±2)°C for whole milk with sugar, (82±2)°C for skim milk milk, (76±2) for whey.

The concentration to which the raw materials are condensed in each building is selected depending on the type of raw material and for raw materials condensed in the first building, it is: for whole milk (16±2)%, whole milk with sugar (33±2)%, skim milk - (12±2)%, whey (24±2)%; in the second building - for whole milk (26±2)%, whole milk with sugar (48±2)%, skim milk - (20±2)%, whey (36±2)%; in the fourth building - for whole milk (35±2)%, whole milk with sugar (56±2)%, skim milk - (38±2)%, whey (43±2)%, the final concentration in the third building - for whole milk (52±2)%, whole milk with sugar (72±2)%, skim milk (50±2)%, whey (55±2)%.

Before entering the pasteurizer, raw milk passes through a plate heat recuperator, where it is heated by raw materials that have already undergone heat treatment. Thus, heat recovery is carried out - heating of raw milk before heat treatment due to the heat of the raw material after heat treatment. Thanks to recovery, milk raw materials are supplied for condensation at a given temperature, as a result of which there is no sudden boiling due to self-evaporation and foam formation, since sudden boiling and the presence of foam worsen boiling conditions and lead to excessive denaturation of whey proteins and the loss of other micronutrients.

In the present invention, the temperature of the mixture before thickening is reduced through the use of heat recovery using a plate heat exchanger, when the mixture before heat treatment is heated by the mixture after heat treatment, which in turn is cooled almost exactly to the boiling point in the first housing. Heat recovery allows you to significantly save steam consumption for heating to the heat treatment temperature in the pasteurizer, increasing the overall energy efficiency of the installation.

Thus, the use of a plate recuperator in a vacuum evaporation installation allows not only to save energy for heat treatment, but also to provide optimal temperature and conditions for the start of boiling, thereby achieving maximum preservation of the components of milk raw materials, in particular whey proteins of milk.

Condensation of milk raw materials in a film vacuum evaporation unit, the time of thermal exposure of whey proteins in which is less than when condensing in a circulation unit, ensures the greatest preservation of whey proteins.

Calculations and reference data show that four-body film installations have optimal energy efficiency indicators. Thus, in two-body installations, steam consumption is about 0.43 kg per 1 kg of evaporated moisture, for a three-body unit it can vary from 0.25 to 0.31 depending on the manufacturer, for four-body units from 0.195 to 0.21, for five-body units from 0.19 to 0.20. Thus, five-effect installations no longer provide a significant increase in steam savings, while they are more expensive to manufacture and more complex in design and maintenance, occupy a large production area (Portnov V.V. Multi-stage evaporation plants: a textbook / V.V. Portnov. V .V. Mayorov. Voronezh: Voronezh State Technical University, 2008. 173 p.).

The peculiarity of the proposed solution is that the raw milk passes through the buildings not in order, but in the sequence 1, 2, 4 and 3 buildings. Thus, entering from the second housing into the fourth, the condensed product first cools to a temperature of (56±2) ° C, corresponding to the boiling point at a vacuum of 0.015 MPa, and entering after the fourth housing into the third, the product is first heated before boiling and condensation begins, and the temperature at the outlet of the vacuum evaporation unit after the end of thickening is (60±2)°C.

This temperature is higher than when implementing known methods for producing a condensed product in vacuum evaporation units, when the condensed product leaves the fourth housing at temperatures of the order of (45-55) ° C ° C and lower, which allows condensing milk raw materials to a higher concentration of dry substances , since a mixture with a higher temperature has a higher fluidity due to lower viscosity. Thus, it becomes possible to thicken milk raw materials to a higher concentration of solids without significant loss of fluidity and increasing the cost of pumping it: for whole milk up to (52±2)%, whole milk with sugar - (72±2)%, skim milk - (50±2)%, serum (55±2)%.

At the outlet of the installation, the condensed mixture has a higher boiling point in the third housing - up to 62°C. This makes it possible to obtain an output mixture with a lower viscosity, and therefore a higher concentration from 48 to 74%, depending on the raw materials and the product being produced.

In addition, all dairy raw materials are characterized by the content of non-heat-resistant components, these are primarily whey proteins, vitamins and microelements. Minor destruction of milk components begins at temperatures above 62°C, intensive coagulation of whey proteins and destruction of vitamins begin at temperatures above 70°C.

Temperatures up to 62°C are lower than the temperature at which the most heat-resistant fractions of milk whey proteins begin to denature, therefore such an increase in the temperature of the mixture at the outlet of vacuum evaporation units does not lead to unnecessary loss of whey proteins and most other milk components.

The increased temperature of the condensed mixture at the outlet of the vacuum evaporation unit of the proposed design helps prevent the development of microorganisms and prevent an increase in their number in the finished product.

Also, the viscosity of the condensed raw material depends on the temperature and at low temperatures, which reaches (45-55) ° C at the outlet of the vacuum evaporation unit, it is very difficult to achieve intense boiling and effective evaporation, the thick mixture does not flow well as a film or circulate in the circulation apparatus type, this often leads to deposits in the apparatus, severe burning, loss of milk components, pumping thick mixtures or requires more powerful and expensive pumps, greater energy consumption, or in some cases is not possible at all. To reduce the viscosity of thick condensed milk raw materials, it is necessary to increase its temperature.

Thus, at a temperature of 55°C, the viscosity of condensed whole milk of 50% concentration is 0.0231 Pa*s, and at a temperature of 62°C - 0.0183 Pa*s. Thus, increasing the temperature of condensed whole milk from 55 to 62°C ensures a reduction in its viscosity by more than 26%.

The solution is further explained by reference to the figures, which show the following:

figure 1 - general installation diagram;

figure 2 shows the switchgear of the evaporator housing with an enlarged view A of the movement of steam and raw materials;

Figure 3 shows a coaxial evaporator and steam separator.

The vacuum evaporation unit for thickening milk raw materials, shown in Figure 1, includes the following functional units:

receiving container 1 to ensure a stable supply of raw materials to the installation;

product pumps 2-12 to ensure the supply of raw materials, circulation and removal of the condensed mixture from the installation;

shell-and-tube type raw material heaters 13-17 for heating raw materials before heat treatment (pasteurization);

plate-type recuperator 18 for heating unpasteurized raw materials using the heat of raw materials that have already been subjected to heat treatment, due to which the latter is cooled before thickening;

shell-and-tube pasteurizer 19 for heat treatment of raw materials;

shell-and-tube evaporators 20-23 for boiling milk in the form of a thin film and evaporating moisture;

steam separators 24-27, made coaxially with the evaporators, to separate entrained drops and product foam from the “secondary” steam formed during boiling. The evaporator and steam separator together form single buildings (stages) of the installation - I, II, III and IV;

ejector 28 for increasing the pressure of “secondary” steam B of the second stage II due to mixing (compression) with “hot” steam and producing heating steam for the first stage A;

condenser 29 for condensation of residual secondary vapors of stage IV to maintain vacuum in the installation;

condensate pumps 30 and 31 for removing condensate vapor from the installation;

vacuum water ring pump 32 for creating and maintaining vacuum in the installation during operation.

Milk raw materials enter the receiving tank of installation 1, where due to automatic control of the supply its constant level is maintained. This is necessary for a continuous and uniform supply of raw materials to the installation. In addition to raw materials, drinking water can be supplied to the installation, which is always done before the thickening of raw materials begins in order for the installation to reach stable technological conditions “on water”; or washing solutions can be supplied to carry out automatic, non-dismountable circulation washing of the installation, which is carried out after the thickening process is completed.

Next, the raw material is fed into the installation by pump 2 and passes through five heaters, where it is sequentially heated to (46±2)°C in heater 13, to (52±2)°C in heater 14, to (57±2)°C in heater 15, up to (61±2)°C in the heater 16 and up to (65±2)°C in the heater 17, and then sent to the pasteurizer 19 for heat treatment. The pasteurizer provides heat treatment at a temperature of (95±2)°C for whole milk, (105±2)°C for whole milk with sugar, (84±2)°C for skim milk and (78±2)°C for whey with a shutter speed of 5-7 seconds. This treatment ensures the lowest degree of denaturation of whey proteins and high microbiological parameters.

Before entering the pasteurizer 19, the milk raw material passes through a plate heat recuperator 18, equipped with a pump 3 to increase the pressure, where it is heated to a temperature of (92±2)°C for whole milk, (102±2)°C for whole milk with sugar, ( 82±2)°С for skim milk, (76±2) for whey, which has already undergone heat treatment with raw materials. Heat exchange occurs through the surface of the heat exchange plates and, due to the design of the recuperator, mixing of the flows of raw materials that have undergone heat treatment and those that have not undergone heat treatment does not occur. Thus, heat recovery is carried out - heating of raw milk before heat treatment due to the heat of the raw material after heat treatment.

Dairy raw materials, which have undergone heat treatment in pasteurizer 19, are cooled in recuperator 18 to a temperature of (68±2)°C and sent to the first building I to begin thickening. Condensation is carried out due to boiling and evaporation of moisture under reduced pressure (rarefaction). The residual pressure in the first housing is 0.0685 MPa, which corresponds to the boiling point (68 ± 2) ° C, thus, thanks to recovery, the milk raw material is supplied to condensation at a given temperature, as a result of which sudden boiling does not occur due to self-evaporation and foam formation. Sudden boiling and the presence of foam worsens boiling conditions and leads to excessive denaturation of whey proteins and loss of vitamins and microelements.

Thus, the use of a plate recuperator in the vacuum evaporation installation for the proposed production method allows not only to save energy for heat treatment, but also to provide optimal temperature and conditions for the start of boiling, thereby achieving maximum preservation of the components of raw milk materials, in particular whey proteins milk and vitamins.

Boiling of the raw material is carried out due to the heat of heating steam A in the form of a thin film distributed over the surface of the heat exchange tubes using a special distribution device located between the flanges of the shell and the evaporator cover.

The distribution device 33, the principle of design and operation of which is presented in Figure 2, is located between the top cover 34 and the evaporator housing 35 and is a stainless metal plate with pressure tubes 36 for secondary steam and holes for the passage of the condensed raw material 37. The raw material is supplied through the pipe 38 and is distributed over the surface of the distribution device 33, and then through the passage holes of the raw material 37 it reaches the surface of the tube sheet 38, from where it flows down in the form of a film over the surface of the heating tubes 39. The thickened raw material is heated through the surface of the tubes by heating steam located in the steam space 40 and boils, evaporating moisture. The steam generated when the raw material boils is called “secondary”. “Secondary” steam, due to the boiling of the raw material entering the rarefaction zone, begins to form in the space of secondary steam 41, from where it rushes through the pressure tubes 36 along the axis of the heating tubes 39. Thus, the movement of secondary steam and raw materials does not intersect, but occurs in the same direction , while the moving secondary steam promotes uniform distribution of the film of the thickened raw material over the surface of the heating tubes 39.

The film flows over the surface of the heating tubes and, during the boiling process, loses moisture in the form of steam. The steam generated during the boiling of raw materials is called “secondary”. Partially condensed raw materials with a concentration for whole milk (16±2)%, whole milk with sugar (33±2)%, skim milk - (12±2)%, whey (24±2)% are collected in the lower part of the evaporator 20 of the first building I on the conical bottom and is discharged by pump 4 for thickening into the second stage of installation II, “secondary” steam in the lower part of the housing through the steam window enters the steam space of the steam separator 24, where product particles and foam are separated, which can be carried away by “secondary” steam. Next, the “secondary” steam is removed from the steam separator 24 of the first housing I to the second stage of the installation II, where it already acts as heating steam B for the evaporator of the second housing 21 and the heater 16.

The coaxial steam separator makes it possible to significantly reduce the size of the installation body, and therefore the production area it occupies. A diagram of the design and operation of a coaxial steam separator is presented in Figure 3. The steam separator 42, which is a cylindrical container, is designed in such a way that the lower part of the evaporator 43 is located inside it, and the space between the walls of the steam separator 42 and the evaporator 43 forms a steam space for removing secondary steam 44. The condensed raw material is supplied from below and sent to the upper part of the evaporator 43 through pipeline 45, and the condensed raw material and “secondary” steam enter the lower part through heating tubes 46. The condensed raw material, under the influence of gravity, enters the bottom of the evaporator 47 and is discharged through pipeline 48. “Secondary” steam, under the influence of kinetic energy and vacuum, from the lower part of the evaporator 49 through the steam window 50 enters the steam space 44 and moves around the outer walls of the lower part of the evaporator 49, to the outlet steam line 51. Despite the fact that the condensed raw material does not enter directly into the steam separator 42 and is discharged from the lower part of the evaporator 43, small particles of raw material and foam, which can form under certain conditions, are carried away by the flow of “secondary” steam into the steam separator. Under the influence of kinetic energy and centrifugal force that arises when the “secondary” steam passes through the steam space, particles of raw materials and foam hit the walls of the steam separator and flow to its bottom, from where they are discharged through pipeline 52.

Next, the dairy raw materials are subjected to condensation in the second building II (figure 1) of the installation at a residual pressure of 0.026 MPa and a temperature of (64±2)°C to a concentration of whole milk (26±2)%, whole milk with sugar (48±2)%, skim milk - (20±2)%, whey (36±2)%.

The evaporator of the second housing 21 consists of two sections of heating tubes; first, the condensed raw material enters the first section and passes along the surface of the first part of the tubes, and then, using pump 5, enters the second section and passes through the second part of the tubes. The evaporator tubes can be divided into two, three or four sections depending on the type of raw material, the degree of concentration and its volume entering the given installation body. The optimal number of sections is determined by a special calculation. Dividing the total number of evaporator tubes into sections is necessary to uniformly distribute the raw material over their surface and ensure complete coverage of the tubes, since the volume of condensed raw material decreases due to the evaporation of moisture from housing to housing. If the raw material passes through all the tubes at once, then the film thickness becomes small, which can lead to incomplete coverage of the surface of the tubes, the formation of so-called “islands” and burning of the raw material at their boundaries with a deterioration in the quality of the finished product. Thus, dividing the evaporators into sections with their sequential passage allows us to solve the issue of completely covering the surface of the heating tubes with a film of boiling raw materials of optimal thickness.

Pump 6 supplies thickened raw material from the second section of the second building II for thickening into the fourth building of the installation IV. “Secondary” steam B of the second body II is removed and used as heating steam for the evaporator 22 of the third body III and the heater 15, part of the “secondary” steam B of the second body II is mixed with “hot” steam in the ejector 28 to produce heating steam A for evaporator 20 of the first body I and heater 17.

The use of “secondary” steam to produce heating by mixing (compression) in an ejector with “hot” steam allows reducing the consumption of live steam by almost 40%, which significantly increases the energy efficiency of the installation. The use of “secondary” steam from the previous stage of the installation to heat the next one makes it possible to use the heat already expended in the previous stage to maintain boiling and evaporation at this stage. In this way, huge heat savings are achieved and the estimated consumption of “hot” steam by the installation per kilogram of evaporated moisture is 0.207 kg, which is in the range of values of the best known foreign samples.

Next, the dairy raw materials are subjected to condensation in the fourth building of the IV installation at a residual pressure of 0.015 MPa and a temperature of (56±2)°C to a concentration of whole milk (35±2)%, whole milk with sugar (56±2)%, skim milk - ( 38±2)%, serum (43±2)%. The evaporator 23 of the fourth building IV also consists of two sections, pump 7 supplies the condensed raw material to the second section, and pump 8 supplies the raw material to the third building of the installation III. The heating steam for evaporator 23 of the fourth housing IV is the “secondary” steam G of the third housing III. “Secondary” steam D from the steam separator 27 of the fourth building IV is sent to heat the raw materials in the heater 13, and its excess amount is sent for condensation to the condenser 29 to maintain a vacuum in the installation.

In the evaporator 22 of the third building of the III installation at a residual pressure of 0.020 MPa and a temperature of (60±2)°C, the raw materials are thickened to the final concentration for whole milk (52±2)%, whole milk with sugar (72±2)%, skim milk (50±2)%, serum (55±2)%. The volume of condensed raw materials by the final stage of condensation is significantly reduced, therefore the evaporator 22 of the third building III consists of four sections, pumps 9, 10, 11 ensure the sequential passage of raw materials through the sections, and pump 12 pumps out condensed milk raw materials of a given concentration from the installation for further intermediate storage and technological operations.

The condensate formed in all heaters, evaporators, pasteurizer and condenser is pumped out of the installation by condensate pumps. It is possible to separately pump out the “hot” condensate of the pasteurizer 19 and the evaporator 20 of the first stage I by pump 30 for its reuse in the boiler room to produce steam, which also increases the energy efficiency of the installation. “Cold” condensate from heaters 13 - 17, evaporators 20 - 23 and condenser 29 is pumped out of the installation by pump 31.

A design feature of the described installation is that the condensed milk raw material does not pass through buildings in order, but in the sequence of buildings I, II, IV and III. Thus, entering from the second body II into the fourth IV, the condensed mixture first cools to a temperature of (56 ± 2) ° C, corresponding to the boiling point at a vacuum of 0.015 MPa, and entering after the fourth body IV into the third III, the mixture is first heated before boiling and thickening begins and the temperature at the outlet of the vacuum evaporation unit after the end of thickening is (60±2)°C.

This temperature is higher than that of installations of known designs, when the condensed mixture leaves the last housing at temperatures of the order of (45-55) ° C, which allows condensing milk raw materials to a higher concentration of dry substances, since a mixture with a higher temperature has a higher fluidity ( low viscosity). Condensation of milk raw materials in the installation occurs for whole milk up to (52±2)%, whole milk with sugar up to (72±2)%, skim milk up to (50±2)%, whey up to (55±2)%. A higher content of dry substances in the condensed mixture allows you to use the installation for the production of condensed milk with sugar, and obtain larger particles of the dry product during the drying process, since the mass content of dry substances in a “drying” drop of equal volume is greater.

After condensation until the required concentration is achieved, the condensed milk raw material is sent to a vacuum crystallizer-cooler for the production of sweetened condensed milk, or to a tank for short-term storage before drying for whole, skim milk or whey.

The increased temperature of the condensed mixture prevents the development of thermophilic microflora during intermediate storage of the mixture before drying, which also ensures high microbiological characteristics of the finished product. At the same time, the temperature of the condensed mixture does not exceed the lower limit for the beginning of whey protein coagulation of 62°C, therefore, there is practically no decrease in the content of whey proteins and vitamins during storage.

The following are examples of the production of condensed milk raw materials.

Example 1.

Whole milk is supplied to the receiving tank of the installation from where it is sent by a product pump for sequential heating in five heaters and a plate recuperator to (46±2)°C; (52±2)°С; (57±2)°С; (61±2)°С; (65±2)°C and (92±2)°C in the recuperator, respectively, and enters the pasteurizer, where it undergoes heat treatment at a temperature of (95±2)°C with a holding time of 5-7 seconds, after which it is redirected to the recuperator, where cooled to a temperature of (68±2)°C.

Next, whole milk enters sequentially into the first, second, fourth and then third buildings for evaporation, where it boils at a vacuum and temperatures of I - 0.0685 MPa, (68 ± 2) ° C; II - 0.026 MPa, (64±2)°C; IV - 0.015 MPa, (56±2)°C and III - 0.020 MPa, (60±2)°C, respectively, after which it reaches the required concentration of milk solids (52±2)%, and with temperature (60±2) °C is sent for short-term storage before drying.

Example 2.

Whole milk with sugar is supplied to the receiving tank of the installation, from where it is sent by a product pump for sequential heating in five heaters and a plate recuperator to (46±2)°C; (52±2)°С; (57±2)°С; (61±2)°С; (65±2)°C and (102±2)°C in the recuperator, respectively, and enters the pasteurizer, where it undergoes heat treatment at a temperature of (105±2)°C with a holding time of 5-7 seconds, after which it is redirected to the recuperator, where cooled to a temperature of (68±2)°C.

Next, whole milk enters sequentially into the first, second, fourth and then third buildings for evaporation, where it boils at a vacuum and temperatures of I - 0.0685 MPa, (68 ± 2) ° C; II - 0.026 MPa, (64±2)°C; IV - 0.015 MPa, (56±2)°C and III - 0.020 MPa, (60±2)°C, respectively, after which it reaches the required concentration of milk and sugar solids (72±2)%, and with temperature (60± 2)°C is sent for cooling to a vacuum crystallizer.

Example 3.

Skim milk is supplied to the receiving tank of the installation, from where it is sent by a product pump for sequential heating in five heaters and a plate recuperator to (46±2)°C; (52±2)°С; (57±2)°С; (61±2)°С; (65±2)°C and (82±2)°C in the recuperator, respectively, and enters the pasteurizer, where it undergoes heat treatment at a temperature of (84±2)°C with a holding time of 5-7 seconds, after which it is redirected to the recuperator, where cooled to a temperature of (68±2)°C.

Next, the skim milk enters sequentially into the first, second, fourth and then third buildings for evaporation, where it boils at a vacuum and temperatures of I - 0.0685 MPa, (68 ± 2) ° C; II - 0.026 MPa, (64±2)°C; IV - 0.015 MPa, (56±2)°C and III - 0.020 MPa, (60±2)°C, respectively, after which it reaches the required concentration of milk solids (50±2)%, and with temperature (60±2) °C is sent for short-term storage before drying.

Example 4.

The whey is fed into the receiving tank of the installation, from where it is sent by a product pump for sequential heating in five heaters and a plate recuperator to (46±2)°C; (52±2)°С; (57±2)°С; (61±2)°С; (65±2)°C and (76±2)°C in the recuperator, respectively, and enters the pasteurizer, where it undergoes heat treatment at a temperature of (78±2)°C with a holding time of 5-7 seconds, after which it is redirected to the recuperator, where cooled to a temperature of (68±2)°C.

Next, the whey enters sequentially into the first, second, fourth and then third buildings for evaporation, where it boils at a vacuum and temperatures of I - 0.0685 MPa, (68 ± 2) ° C; II - 0.026 MPa, (64±2)°C; IV - 0.015 MPa, (56±2)°C and III - 0.020 MPa, (60±2)°C, respectively, after which it reaches the required concentration of milk solids (55±2)%, and with temperature (60±2) °C is sent for short-term storage before drying.

Table 1. Actual indicators of the thickening process in a vacuum evaporation plant of the proposed design Technical result indicators: Boiling point in body I, °C Temperature at the exit from housing III, °C Concentration of the condensed mixture at the outlet, %: Steam consumption, kg per 1 kg of evaporated moisture per hour Raw materials Repeatability of measurement Whole milk 1 68.2 61.1 53.4 0.196 2 68.3 61.3 51.2 0.193 3 67.9 61.1 52.9 0.195 Whole milk with sugar 1 68.7 61.5 72.2 0.191 2 68.5 61.2 71.4 0.197 3 69.1 61.3 73.1 0.191 Skim milk 1 67.3 60.9 51.7 0.207 2 68.1 61.3 51.2 0.198 3 67.9 61.1 51.4 0.203 Whey 1 68.6 61.1 56.5 0.195 2 67.7 61.5 55.9 0.201 3 69.1 61.4 56.2 0.197

Thus, the patented invention allowed:

ensure high energy efficiency of the installation with a consumption of “hot” steam per 1 kg of evaporated moisture per hour of no more than 0.21 kg;

ensure the boiling point of milk raw materials at temperatures not higher than the temperature of the beginning of mass coagulation of whey proteins and destruction of vitamins - 70°C;

ensure an increased temperature of the condensed raw material at the outlet of the installation in order to achieve the required concentration during condensation and to exclude the development of thermophilic microorganisms during storage, but not higher than the temperature at which the destruction of milk components may begin (62°C).

Claims (2)

1. Vacuum evaporation installation for thickening dairy products, characterized in that it contains five heaters of milk raw materials installed in series, the last of which is connected to a plate heat recuperator connected to a pasteurizer and configured to heat milk raw materials from the last heater by cooling the milk raw materials from the pasteurizer, the plate recuperator is connected to the first housing of four consecutive housings of the evaporation unit, the first housing of which is connected to the second, the second to the fourth, and the fourth to the third housing, while the second and fourth housings are made with two consecutive sections of evaporator heating tubes, and the third housing is made in four consecutive sections of heating tubes of the evaporator, each housing of the evaporator installation is equipped with a steam outlet fitting connected to a fitting for supplying heating steam to the evaporator of the subsequent housing, and contains an evaporator with a coaxially installed steam separator with the formation of a steam space between the walls for the removal of secondary steam, the steam outlet fitting from the second body is configured to discharge part of the steam into the ejector, which is configured to produce heating steam for the first body due to thermal compression with live steam; the finished product outlet fitting of the third body is connected to a vacuum crystallizer-cooler or a finished product storage tank. 2. Vacuum evaporation unit according to claim 1, characterized in that each housing of the evaporation unit contains a distribution device located between the upper cover of the housing and the evaporator, which is a plate with pressure tubes forming channels for the passage of secondary steam, and holes for the passage condensed product.