RU2500449C1 - Evaporation of fluids and device to this end - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to heat treatment and concentration of fluids with the help of various equipment. Evaporation of fluids comprises circulation of fluid in vessel and its heating. Fluid is circulated via evaporating circuit whereto fluid portion is forced and heated in evaporating circuit heater to ensure a required temperature increase so that heated product is injected back into vessel top part above product surface.

EFFECT: evaporation without foaming, higher quality of finished products, lower power consumption.

22 cl, 3 dwg, 3 ex

Description

The invention relates to methods for heat treatment (evaporation) and concentration of fluid products using various equipment.

According to the claimed method, any flowing products and mixtures can be subjected to heat treatment with evaporation.

Evaporation (concentration), as a technological operation, is the removal from the complex product of an excessive amount of the most volatile components, in particular water or other solvents, and is used to give the product the desired composition and the desired physicochemical properties, including the necessary rheological properties. As a rule, evaporation is accompanied by heating of the concentrated product.

Traditional and widely used methods for evaporating fluid products combine their heating through a heat exchange surface with the evaporation of a volatile component into the surrounding gas environment. The heat exchange surface during the process may be the wall of the container with the product or the surface of a heating element of any design immersed inside the tank.

The simplest and most widely used method of evaporation is carried out by boiling the product on a heated surface (Patent RU 2067016, IPC B01D 1/22, publ. 09/27/1996). In this case, the vapor spontaneously leaves the evaporator due to its excess pressure. Despite its simplicity and compactness of the equipment, this evaporation method has several disadvantages.

To ensure a high process speed with a small heat transfer surface, it is necessary to maintain a high temperature of the heater or vessel wall. But with a high viscosity of the processed product, convective heat and mass transfer is very difficult, and this leads to a significant local overheating of the product and the formation of soot, which negatively affects the quality of the finished product. In addition, there is a significant amount of liquid products prone to foaming. Evaporation of the volatile component inside such a product when it boils inevitably leads to abundant formation of foam, which also impairs heat and mass transfer with all the ensuing consequences, and is also able to fill the entire evaporation tank until pouring out of it.

A technically more advanced evaporation option is boiling under reduced pressure. A known method of evaporation (Patent RU 2432537, IPC F26B 9/06, F26B 5/04, publ. 10/27/2011), which can largely remove the problem of soot and overheating of the product, but requires much more complex and expensive equipment. Evaporation of foaming products in this way also causes additional technical difficulties. In addition, a significant decrease in boiling point requires a significant vacuum and the use of a coolant for condensation of vapors, and this, in turn, affects the increase in the cost of the finished product.

A number of methods are known in which the evaporation of a volatile component is carried out without boiling, due to the contact of the product with a "dry" gas medium. The effective operation of these methods requires a significant free surface of the product and a low relative vapor pressure of the removed component (for water vapor, relative humidity) above it. With this method of evaporation, the heating of the product is usually carried out either by an arbitrary solid-state heater, or by contacting the product with a heated gas medium. And in order to ensure a sufficient rate of the evaporation process, it is necessary to perform it in special evaporation devices, forcibly creating a significant contact area of the product with the gas medium.

According to the method of creating a free surface of the product, evaporation devices can be divided into the following classes:

- drip evaporators (or cooling towers);

- bubble or bubbling evaporators;

- film evaporators, in which the free surface of the product is formed during its film flow along the structural elements of the evaporation device (Patent RU 2223130, IPC B01D 1/22, publ. 02/10/2011, Patent RU 2425708, IPC B01D 1/22, publ 08/10/2011, Patent US 6146493, IPC B01D 1/22, publ. 11/14/2000).

The film apparatus according to the patent RU 2223130, as well as evaporating devices of all the above classes, allows for evaporation without the boiling process, which means at a lower temperature. In this case, to lower the evaporation temperature, it is necessary to forcefully remove vapors, ensuring the circulation of the gaseous medium above the surface of the product.

With a closed circulation of the gas medium through the evaporation device, the gas must be drained, and drainage, in turn, requires additional equipment and the use of a coolant to condense the vapor, which negatively affects the cost of the product.

If open circulation of the gaseous medium is allowed and the evaporation device is purged with atmospheric air, then in order to avoid product contamination, it is necessary to thoroughly clean the supply air, which also requires additional equipment and increases the cost of the product. And if the evaporated component is water, the variable humidity of the supply air will inevitably affect the evaporation mode and, again, additional air conditioning equipment will be required to stabilize it.

There are also “individual" disadvantages inherent in the listed classes of evaporation devices. The use of drip evaporators with a sufficiently high viscosity and complex rheological properties of the product is difficult. Bubble evaporators are not suitable for heavily foaming products. Film evaporators are more bulky and metal-intensive.

The closest technical solution is a method of heat treatment of fluid products and a device for its implementation (Patent RU 2267350, B01J 8/10, B01J 19/18, publ. 10.01.2006).

In this method and device, the treatment is carried out using heat generated by liquid friction, which is created by mechanical forced circulation of the product in a heat treatment device with at least one mechanical heater.

The disadvantage of this method and the device proposed for its implementation is that they do not provide technical means for the effective evaporation of the product, which greatly complicates the heat treatment of the product at a temperature close to the boiling point, and does not allow heating and evaporation of heavily foaming products.

The problem solved by the invention is the development of a heat treatment method with the evaporation of highly viscous and foaming products, allowing to obtain high quality products, and the development of a compact and high-performance device for implementing this method.

The problem is solved using the method of evaporation of fluid products, including the circulation of the product in the tank, and its heating.

The product is circulated through an evaporation circuit, which includes at least one pump for taking the product from the tank and circulating it in the evaporation circuit, at least one heater to ensure heating of the product in the evaporation circuit, and at least one injection device for reverse injection of the product part of the product is forcibly taken to the tank and connected in series by pipelines from the tank to the evaporator circuit, it is heated in the evaporator heater and the heated product is injected CT back to the top of the container above the surface of the product.

Preferably, the total power released by the heaters in the evaporation circuit at the stage of evaporation of the product satisfies the condition:

where W _Σ is the total power released by the heaters (W), W ∗ is the total heat loss power (W), Ť is the product heating rate (deg / s), C is the heat capacity of the product (J / (kg · deg)), m - the mass of the product subjected to heat treatment (kg), the i component of the product being evaporated is numbered, q _i is the specific heat of vaporization of the i-th component (J / kg), M _i is the required rate of evaporation at the process temperature (kg / s). At the stage of product evaporation, its heating rate Ť depends on the course of the evaporation process, i.e., on the last component of the inequality.

Preferably, to eliminate overheating of the product, the heater satisfies the requirement:

where Q is the instantaneous mass flow rate of the product through the heater (kg / s), W is the power released by the heater (W), C is the heat capacity of the product (J / (kg · deg)), τ = TT ₀ is the maximum allowable overheating of the product relative to temperature in the tank (deg), T ₀ is the temperature of the product in the tank, and T is the temperature at the outlet of the evaporation circuit.

Preferably, the heater satisfies the requirement:

where Q is the instantaneous mass flow rate of the product through the heater (kg / s), W is the power released by the heater (W), C is the heat capacity of the product (J / (kg · deg)), Δ = TT ₀ is the minimum allowable overheating of the product relative to temperature in the tank (deg), T ₀ is the temperature of the product in the tank, T is the temperature at the outlet of the evaporation circuit.

Preferably, a vacuum is maintained in the container during evaporation of the product.

Preferably, the container is vented with dry gas or air when evaporating the product.

The problem is also solved using a device for evaporation of current products, including a container with inlet and outlet openings, a heater.

The device includes at least one evaporative circuit, which includes at least one pump for collecting the product from the tank and ensuring its circulation in the circuit, at least one heater for heating the product in the evaporative circuit and at least one injection device for reverse injection product into the tank and connected in series by pipelines, the injection device is installed in the upper part of the tank above the level of filling with its product.

Preferably, the total power released by the heaters in the evaporation circuit at the stage of evaporation of the product satisfies the condition:

where W _Σ is the total power emitted by the heaters (W), W ∗ is the total heat loss power (W), Ť is the product heating rate (deg / s), C is the heat capacity of the product (J / (kg · deg)), m - the mass of the product subjected to heat treatment (kg), the index i numbers the evaporated components of the product, q _i is the specific heat of evaporation of the i-th component (J / kg), M _i is the required rate of evaporation at the temperature of the process (kg / s).

Preferably, to eliminate overheating of the product, the heater satisfies the requirement:

where Q is the instantaneous mass flow rate of the product through the heater (kg / s), W is the power released by the heater (W), C is the heat capacity of the product (J / (kg · deg)), τ = T-T ₀ is the maximum allowable overheating of the product relative to the temperature in the tank (deg), T ₀ is the temperature of the product in the tank, and T is the temperature at the outlet of the evaporation circuit.

Preferably, the heater satisfies the requirement:

where Q is the instantaneous mass flow rate of the product through the heater (kg / s), W is the power released by the heater (W), C is the heat capacity of the product (J / (kg · deg)), Δ = TT ₀ is the minimum allowable overheating of the product relative to temperature in the tank (deg), T ₀ is the temperature of the product in the tank, T is the temperature at the outlet of the evaporation circuit.

Preferably, an irrigation device or a valve with or without an irrigation nozzle, an adjustable flow nozzle, or an adjustable valve or throttle attached to the top wall of the vessel are used as an injection device to form a gap between the injection device and the surface of the product in the process vessel.

Preferably, the pump and the heater in the evaporator circuit are made as a single device.

Preferably, the injector device is also a hydraulic throttle to create excess pressure in the evaporator circuit and prevent product from boiling in it.

Preferably, the injector device is provided with a valve for adjusting the pressure in the evaporator circuit and increasing the temperature of the product therein.

Preferably, a filter separator for lump inclusions in the evaporated product is installed at the inlet to the evaporator circuit.

Preferably, a breather is installed in the lid of the process vessel.

Preferably, the process vessel is equipped with a stirrer.

Preferably, the process vessel in its upper part is connected to a vacuum steam exhaust line.

Preferably, the vacuum line includes a steam condenser.

Preferably, the upper part of the container above the product is connected to a closed or open ventilation circuit.

Preferably, the ventilation circuit includes a fan and at least one gas or air conditioning device.

Preferably, the conditioning device includes a purification filter and / or a desiccant.

In the proposed method for the evaporation (concentration) of fluid products using the circulation of the product through the evaporation circuit, in addition to the necessary pipelines, the following elements are used:

- at least one pump for taking the product from the tank and ensuring its circulation in the circuit;

- at least one injector device for reverse injection of the product into the container;

- at least one heater to provide additional heating of the product in the circuit and to intensify the evaporation process.

To enable evaporation of products with piecewise inclusions at the inlet to the evaporator circuit, a filter separator for piecewise inclusions can also be installed.

The evaporator injector device is installed in the upper part of the tank above the level of filling with its product. The type of injection device is selected depending on the properties of the product. It can be a sprinkler device, a nozzle, or simply an adjustable valve fixed on the upper wall of the tank. The minimum required clearance between the injection device and the surface of the product should ensure the normal course of the evaporation process. For each specific product, it is determined empirically.

As pumps and heaters can be used any device known from the prior art.

They are selected so as to ensure the normal execution of the functions assigned to them with the existing rheology of the product. In addition, instead of a heater or both of these devices, it is possible to use a device that performs both functions, namely, a mechanical heater according to patent RU 2267350, B01J 8/10, B01J 19/18, publ. January 10, 2006, and this embodiment of the evaporator circuit provides additional benefits.

Evaporative circuit elements, including pipelines, can be located both outside and inside the product container. The choice of the location of the evaporation circuit is carried out in the design of a particular evaporator.

To ensure product uniformity, the container may be equipped with a mixing device of any suitable type.

Depending on the capacity and dimensions of the evaporator of the proposed type, one or more evaporative circulation circuits of the described type can be installed in it. By a single evaporative circuit here is meant a simultaneously controlled and consistently functioning set of the necessary equipment listed above, regardless of the number of devices of each type installed in it.

The evaporation process takes place directly in the tank from the surface or above the surface of the product. Due to the need to remove vapors, the volume above the surface of the product communicates with the atmosphere, preferably through a valve or breather, or is evacuated, or ventilated with dried gas or air. The first two listed options imply boiling of the product, and in the scheme with tank ventilation, the boiling process may not be used.

Evaporation is carried out using the heat generated by the heater in the evaporation circuit. To eliminate overheating of the product, the heater satisfies the requirement:

$$Q\ge \frac{W}{C\cdot \tau },\left(\mathrm{one}\right)$$

where Q is the instantaneous mass flow of the product through the heater (kg / s), W is the power released by the heater (W), C is the specific heat of the product (J / (kg · deg)), and τ = TT ₀ is the maximum allowable overheating of the product relative to temperature in the tank (deg), i.e. T ₀ is the temperature of the product in the tank, and T is at the outlet of the circuit, i.e. in the injector device.

It is preferable to use a mechanical heater (Patent RU 2267350, B01J 8/10, B01J 19/18, publ. 10.01.2006), since there is no local overheating of the product.

Since heating is carried out for the purpose of evaporation of the product, the total power released by the heaters at the evaporation stage satisfies the condition:

where W _Σ is the total power released by the heaters (W), W ∗ is the total heat loss power (W), Ť is the product heating rate (deg / s), C is the heat capacity of the product (J / (kg · deg)), m - the mass of the product subjected to heat treatment (kg), the i component of the product being evaporated is numbered, q _i is the specific heat of vaporization of the i-th component (J / kg), M _i is the required rate of evaporation at the process temperature (kg / s).

The principle of operation and the advantages of the proposed method of evaporation of fluid products can be demonstrated by the example of several implementations of the method and their corresponding evaporation devices.

So, for example, products are known (in particular, milk and candy caramel), the moisture content of which at the end of evaporation must strictly correspond to a certain value. Accordingly, evaporation of the product should be completed when this value is reached. Under production conditions, it is difficult to carry out express control of the moisture concentration in a hot product using the analytical method or using weight control. At the same time, there is a dependence of the boiling point of the product on its humidity, which allows you to set the moment of the end of evaporation using a simple measurement of the boiling point at a given pressure. Using this fact, the technology of cooking products involves evaporating the product with boiling. The smaller the error in determining the actual boiling point of a product, the more stable will be its product characteristics, i.e. Ultimately higher quality.

The task of preparing products of this variety with consistently high quality is solved in the most technically simple implementation of the proposed method. In this variant of the method, the evaporation of the product is carried out with boiling and spontaneous displacement of steam into the atmosphere. To evaporate moisture, the product is forcibly taken from the tank, heated in the evaporation circuit and injected back into the tank through the injection device. Due to heating in the circuit, the product injected from above has a higher temperature than the one in the tank.

In order for the product to boil in the container, and not in the circuit, the injector device is designed to simultaneously serve as a hydraulic throttle, for example, it is equipped with a control valve that allows creating an excess pressure in the circuit that is sufficient to prevent boiling of the product.

If the temperature of the product injected into the tank exceeds the boiling point of the product at the pressure in the tank, leaving the injection device, the product boils. The boiling process stops quickly enough due to a decrease in the local temperature of the product during evaporation. Thus, only a product in a thin surface layer or in a droplet-suspended state can boil. Foam practically does not form with such boiling, which allows the process to be carried out without any difficulties even for heavily foaming products, unlike other methods.

According to the proposed method, by controlling the flow rate through the evaporator circuit at a given heating power in it, an increase in the temperature of the product in the evaporator circuit in a fraction of a degree was obtained. This means that the actual boiling point of the product lies within this temperature differential and is determined with very high accuracy. And the use in the circuit of a mechanical heater according to patent RU 2267350 allows us to guarantee the absence of areas of strong local overheating and high uniformity of the product. Thus, it becomes possible to precisely determine the moment of completion of the evaporation process and to obtain a guaranteed moisture product without using weight control or analytical methods.

An additional condition for reliable determination of the boiling point of the product during this evaporation is the lack of ventilation of the free space of the container. The access of dry air to the container should be difficult, while the steam should freely leave the container. Sealing the container is not required, just keep it closed and, if necessary, install a breather on it.

Residual slow boiling in the surface layer of a thick product can lead to its microporous structure and to undesirable deviations in its rheological and organoleptic properties. So, hot caramel acquires viscoelastic properties, which is undesirable in technology, and candy caramel loses transparency, acquires a milky color and becomes rough when resorbed, i.e. losing its consumer qualities.

To avoid such undesirable deviations, the operation mode of the evaporator circuit is selected so that it satisfies the condition:

$$Q\le \frac{W}{C\cdot \Delta },\left(3\right)$$

where Q is the instantaneous mass flow rate of the product through the heater (kg / s), W is the power released by the heater (W), C is the specific heat of the product (J / (kg · deg)), and Δ = TT ₀ is the minimum allowable overheating of the product relative to temperature in the tank (degrees), determined empirically. Subject to the specified conditions, the product that has left the injector device boils up intensively and manages to free itself from the internal vapor bubbles in the droplet-suspended state, which ensures the desired product properties.

According to the proposed method, it is also possible to carry out vacuum concentration of products. As in the previous example, the process is carried out with boiling of the product, and evacuation only reduces the boiling point. All conditions and patterns of operation of the evaporation circuit disclosed in the previous example remain valid, but the design of the entire evaporation device is complicated. The container for the product is sealed, and in the upper part a vacuum steam line is connected to it, in which a suitable vacuum pump and, if necessary, a steam condenser are installed. With sufficient performance of the vacuum pump (usually at low vacuum), a steam condenser may not be installed in front of it.

When concentrating the product according to the proposed method, there is an alternative to vacuum method of reducing the temperature of the process. This method is based on dry ventilation of the tank, i.e. depleted in vapor of the vaporized component, gas or air. If due to the ventilation of the tank the vapor pressure of the vaporized component above the product surface remains significantly lower than the saturated vapor pressure, this ensures an efficient course of the evaporation process.

When carrying out evaporation according to such an embodiment of the proposed method, the vapor pressure of the component removed from the product always remains below the pressure in the product and boiling does not occur.

When evaporating according to this variant of the method, the evaporation device is equipped with a tank ventilation circuit, which can be open to the atmosphere or closed. When using an open ventilation circuit, the air entering it must be cleaned to avoid product contamination. When using a closed loop, it is possible to ventilate the tank with any gas inert to the product and the gas must be drained, i.e. remove from it a pair of volatile product component. In both cases, a rather complicated additional equipment is required.

The lack of boiling also leads in many cases to the need for analytical or weight control of the current concentration of the volatile component in the product; especially if the product is multicomponent and there are no instrumental methods for measuring this concentration in it. In this regard, evaporation with venting is also less convenient than boiling.

But in comparison with the previously described implementations of the method, evaporation with ventilation of the tank allows the process to be carried out at a lower temperature, which for some products may simply be a necessary condition for their preparation. This already justifies a significant complication of the evaporation plant and makes such an embodiment of the evaporation method industrially applicable.

When choosing one of the listed embodiments of the invention to concentrate a particular product in the best way and the evaporation device will be the most suitable for this product. Regardless of the technology of preparation of the product, they cannot be named. At the same time, any evaporation device according to the proposed method contains an obligatory element - an evaporation circuit, the best implementation of which, according to the author, can be indicated. Below, in order of increasing complexity, three embodiments of the invention and their corresponding evaporation devices, which are best-in-class processes, are described. Simplified schematic diagrams of the construction of evaporation devices for each of the options are shown in the figures.

Embodiments of the invention.

1. The scheme of the evaporation device.

In the simplest embodiment of the invention (See FIG. 1), the evaporation (concentration) of the liquid product in the tank 1 according to the proposed method is carried out with the product circulating through the evaporation circuit 2, which, in addition to the necessary pipelines, includes:

- pump 3 for taking the product from the tank and ensuring its circulation in the circuit;

- injector device 4 for reverse injection of the product into the container;

- heater 5 to provide additional heating of the product in the circuit and the intensification of the evaporation process.

In the simplest implementation of the evaporation circuit, a mechanical heater is used, combined with the pump in one device.

To eliminate overheating of the product, the heater satisfies the requirement:

$$Q\ge \frac{W}{C\cdot \tau },\left(\mathrm{one}\right)$$

where Q is the instantaneous mass flow rate of the product through the heater (kg / s), W is the power released by the heater (W), C is the heat capacity of the product (J / (kg · deg)), and τ = T-T ₀ is the maximum allowable overheating product relative to the temperature in the tank (deg), i.e. T ₀ is the temperature of the product in the tank, and T is at the outlet of the evaporation circuit, i.e. in the injector device.

To ensure better evaporation conditions of the product, the operation mode of the evaporation circuit is selected so that it also satisfies the condition:

$$Q\le \frac{W}{C\cdot \Delta },\left(3\right)$$

where Q is the instantaneous mass flow rate of the product through the heater (kg / s), W is the power released by the heater (W), C is the heat capacity of the product (J / (kg · deg)), T ₀ is the temperature of the product in the tank, and T is at the outlet of the evaporation circuit, Δ = T-T ₀ - the minimum allowable overheating of the product relative to the temperature in the tank (deg), determined empirically.

The injector device 4 of the evaporator circuit is installed in the upper part of the tank 1 above the level of filling with its product. The type of injection device is selected depending on the rheological properties of the product and can be any. But in order to exclude boiling inside the evaporator circuit, as well as to be able to regulate the instantaneous flow rate of the product in it in order to ensure conditions (1) and (3), the injection device is endowed with the function of an adjustable hydraulic throttle. Thus, in the best implementation, the injection device is a variable flow nozzle, or simply an adjustable throttle or valve with or without a sprinkler nozzle.

The minimum required clearance between the injection device and the surface of the product should ensure the normal course of the evaporation process. For each specific product, it is determined empirically.

Since heating is carried out for the purpose of evaporation of the product, the total power released by the heaters at the evaporation stage satisfies the condition:

where W _Σ is the total power emitted by the heaters (W), W ∗ is the total heat loss power (W), Ť is the product heating rate (deg / s), C is the heat capacity of the product (J / (kg · deg)), m - the mass of the product subjected to heat treatment (kg), the index i numbers the evaporated components of the product, q _i is the specific heat of evaporation of the i-th component (J / kg), M _i is the required rate of evaporation at the temperature of the process (kg / s).

If necessary, the concentration of fluid products with lump inclusions at the entrance to the evaporator circuit is installed filter separator lump inclusions 6.

To ensure stable evaporation conditions, free access of atmospheric air to the product container is prevented. To do this, the container is closed, and in its upper part, if necessary, a breather 7 is installed.

To ensure product uniformity, the tank is equipped with a suitable type of mixing device. The mixing device can be any, both mechanical and inkjet.

The above-described embodiment of a method for evaporating (concentrating) fluid products is best for evaporating boiling products at atmospheric pressure.

2. The scheme of the evaporation device using evacuation.

If the boiling point at atmospheric pressure is too high and fatal for the product, it can be lowered by lowering the total hydraulic pressure, i.e. using evacuation. For this, the evaporation device shown in FIG. 2 is proposed.

The container 1 with the product is sealed and a vacuum line 8 is removed to its upper part, containing at least one vacuum pump 9 of the required capacity. With a significant vacuum, to reduce the performance requirements of the vacuum pump, a steam condenser 10 is also installed in front of it in the steam exhaust line. At the same time, the parameters of the vacuum pump and condenser are selected in concert to ensure the required steam performance.

3. The scheme of the evaporation device when using tank ventilation.

In some cases, the product needs to be concentrated at a very low temperature. Evaporation with boiling at this temperature may require a too significant reduction in hydraulic pressure, up to the technical impracticability of the process with boiling due to the impossibility of normal operation of the hydraulic devices of the evaporator circuit (pump, mechanical heater) and unreasonably high demands on the performance of vacuum equipment. Nevertheless, evaporation at such a low temperature is still possible by the proposed method, but without boiling the product, using forced ventilation of the container with the product.

When a container is evaporated with ventilation through it above the product surface, a gas medium is circulated with a reduced concentration of steam of the component removed from the product. When using such an evaporation scheme, as a rule, conditioning of the gas entering the tank is required. Air conditioning includes, at a minimum, gas purification if the ventilation circuit is open, and gas drainage (condensation of the vapor of the removed component) if the ventilation circuit is closed. Schematic diagram of the evaporation device shown in Fig.3.

A ventilation circuit 11 comprising a fan 12 and at least one conditioning device 13 is connected to the upper part of the tank 1. Depending on the organization of the process and the type of circuit, the conditioning device may include a cleaning filter 14 or a dehumidifier (condenser) 15, or both of these devices.

Evaporation with ventilation of the tank does not require the use of reduced or increased hydraulic pressure, which means that it does not cause any technical difficulties in the manufacture and use of devices of both the evaporator circuit and the ventilation circuit. At the same time, despite the low temperature of the product, the evaporation process can be quite effective due to the creation of a significant evaporation surface (in a droplet suspension, for example) and maintaining a low concentration of vapor of the removed component in the tank by draining the vented gas.

The application of the proposed method of heat treatment with evaporation of the product, subject to the requirements for the technical performance and operation mode of the evaporation device, allows the production of high-quality products using compact and high-performance technological devices.

The technical result of the proposed solution is the evaporation of highly viscous fluid products without foaming, obtaining end-products of high quality and reducing energy consumption.

For a better understanding of the invention, examples of its use for various products are given below.

Example 1

The present invention was used to create cooking-evaporation apparatus for cooking various types of caramel "Siberian Burenka" and candy caramel "Dropsi". According to the production conditions, the cooking of a portion of caramel weighing 50-70 kg should have been carried out in a period of not more than 40 minutes. Evaluation by formula (2), taking into account the initial recipe and the final moisture of the product, as well as trial cooking of caramel, indicated a minimum heating power of 15 kW. As a heater and a pump in the evaporation circuit, a mechanical heater according to the patent RU 2267350 was used, namely a submersible centrifugal pump, which was manufactured as part of each cooking-evaporation apparatus. The installed engine power of the mechanical heater was 17 kW for the Sibirskaya Burenka caramel and 15 kW for the Dropsi candies, with the possibility of obtaining power above the rated one due to the supply of the engine with alternating current with a frequency above 50 Hz.

Thanks to the use of a centrifugal pump, the conditions of formula (1) are automatically satisfied for the caramel, and the appearance of excessive (more than 1 ° C) heating in the evaporator circuit indicates a hydraulic jam in the pump or another part of the circuit and the need for emergency measures to restore the normal operation of the device.

For reasons of simplicity and low cost, the apparatus for cooking caramel was deprived of the means of mechanical mixing of the mass and equipped with only one evaporation circuit, but to improve the homogeneity of the mass, two injection devices were installed in one circuit, which were located diametrically on the container lid to each other. As an injection device, valves of adjustable output section were used, which, when using a centrifugal pump, made it possible to control the flow rate in the evaporator circuit and change the power and heating value in the desired direction, i.e. increment of product temperature in the circuit.

On the above-described cooking and evaporation apparatus for caramel, a breather was not installed, and its role was played by technological holes and gaps between the parts of the apparatus.

So that the product boils in a suspended state, and there is no residual boiling inside the product, the operation mode of the evaporator circuit is selected so that it satisfies the condition:

where Q is the instantaneous mass flow rate of the product through the heater (kg / s), W is the power released by the heater (W), C is the specific heat of the product (J / (kg · deg)), and Δ = TT ₀ is the minimum allowable overheating of the product relative to temperature in the tank (degrees), determined empirically. Subject to the specified conditions, the product that has left the injector device boils up intensively and manages to free itself from the internal vapor bubbles in the droplet-suspended state, which ensures the desired product properties.

Relation (3) shows the relationship between the process parameters and allows you to evaluate and correctly select the technical characteristics of the devices used in the evaporator to obtain the required heating of the product in the circuit. If we are talking about controlling the actual process of evaporation, then to obtain the desired temperature increment in the circuit, it is no longer necessary to do calculations, especially since the heat capacity of the product may not be known. It is enough to be able to regulate the instantaneous flow rate of the product included in relation (3) and directly measure the temperature increment of the product in the circuit.

The process of cooking caramel in the cooking-evaporation apparatus according to the claimed method is divided (in the order of execution) into three stages: the stage of heating and mixing, where the initial components are introduced and subjected to heating, melting and mixing, the stage of evaporation (boiling) and the stage of making flavorings and dyes, on which temperature-sensitive components are introduced and mixed without heating and boiling.

Actually evaporation (boiling) begins at a temperature of about 112 ° C. The boiling point may vary depending on the formulation of the product and deviations in the moisture content of the components to be laid. The evaporation process is performed until the product reaches a temperature of 117-118 ° C for Sibirskaya Burenka caramel and 135-137 ° C for Dropsi candy caramel. In the first case, the difference in the temperature at the end of evaporation is due to the recipe difference of different types of sweets, and in the second, due to deviations in the quality of the feedstock, in particular molasses, and the ability to “dry” the mass during subsequent vacuum unloading from the apparatus.

According to the experience of cooking caramel, the Δ value included in relation (3) is from 0.2 to 0.5 ° C, depending on the type of product and the quality of the raw materials used. Accordingly, at the boiling stage of the product, the temperature increment in the circuit is maintained by the operator not lower than the indicated values due to the flow control, while the rest of the time it can be about 0.1 ° C.

At the stage of heating and mixing, the flow rate control in the evaporator circuit is already carried out in order to maintain the optimum power of the mechanical heater - pump, since at this stage the density and viscosity of the mass being processed vary greatly. The power of the heater in the first and second stages of cooking is maintained at a level of 80-100% of the maximum, in order to simultaneously provide sufficient performance and the absence of motor overload.

The third stage is performed at a reduced power due to a decrease in power revolutions for several minutes with visual inspection of the product uniformity, then the product is drained.

Example 2. Drainage of glycerol.

An example of such an implementation of the method may be the concentration (drainage) of glycerol. This product is hygienically safe and is widely used in the chemical and light industry, as well as in the technique and manufacture of cosmetics. In a concentrated state, glycerin has a boiling point of 290 ° C, which allows it to be used as a harmless and chemically passive coolant for use in a wide temperature range. At the same time, glycerin is very hygroscopic and is produced in water with an admixture of water.

Glycerin used as a heat transfer medium should not boil inside the heat exchange circuit up to the maximum temperature reached in it. This, taking into account the pressure available in the circuit, imposes a restriction on the saturated vapor pressure of the polluting solvent, i.e. water, and ultimately the concentration of a polluting solvent. The higher the temperature of use of the coolant, the cleaner it should be.

To obtain a coolant with a wide temperature range from “wet” glycerin, it is necessary to evaporate it at atmospheric pressure to temperatures above 200 ° C, which have a detrimental effect on widely used hydraulic seals and require the use of special means (special pumps).

To avoid the use of expensive special tools, glycerol is drained by boiling in a vacuum tank. Unlike the previous example, the tank is sealed and equipped with a vacuum steam vent line with a built-in steam condenser and a serial vacuum pump. The steam condenser is cooled by an external refrigerant with a temperature of preferably about 0 ° C. The required final concentration of water in glycerin is recalculated to the boiling temperature of the mixture at a pressure in the tank, which is set by the used vacuum pump.

The power of the vacuum pump and heater are selected based on the required performance for the finished product, taking into account the ratio (2), the initial moisture content of glycerin and its possible deviations.

In the context of the task being performed, glycerin is not thermally sensitive, therefore, the temperature increment in the evaporation circuit is limited from above by the technical capabilities of the equipment. In practice, an increment of 1 ° C or lower is sufficient for the successful evaporation of technical grade liquids with volume boiling. In this case, the developer of the evaporator can set this parameter to a value of, for example, 1 ° C or more, in order to equip the device with devices that are coordinated among themselves according to technical characteristics.

In this example, as in the previous one, volume boiling of the product is used, therefore, the injection device must satisfy the same principles and, in the specific case, is in the form of an adjustable or unregulated nozzle.

Due to the presence of a significant vacuum in the tank for feeding the product into the evaporator circuit, a vane pump with a significant inlet section and a low rotor speed is used. The performance of the pump is consistent with the power of the heater using the relation (3), in which Δ is determined empirically, or is taken equal to, for example, 1 ° C or higher, as previously indicated. Due to the fact that a volume principle pump is used, regulation of the injection device can no longer affect the flow rate in the evaporator circuit and the increment of the product temperature, but can affect the pressure inside the evaporator circuit and the dispersion of product droplets returned to the tank.

The evaporation process is as follows.

A portion of the initial glycerin mixture is placed in the capacity of the evaporator. Turns on through the evaporator circuit. The vacuum pump is turned on, and the pressure inside the tank is reduced to the working one. If there is a danger of volume boiling of the mixture in the tank, do not reduce the pressure very quickly. After reaching the working pressure in the tank, heating in the circuit is switched on and evaporation with boiling is performed until the calculated temperature is reached (see above), after which the process stops and the glycerin coolant that is ready for use is discharged. For a consistently high quality coolant, it is necessary to stabilize the pressure in the tank at the final stage of the process in each unit evaporation cycle. If this is difficult to achieve, then the evaporation process is carried out to a boiling point above the calculated one.

Example 3. Evaporation of extracts containing biologically active components.

Active substances of biological origin often do not differ in high heat resistance and begin to collapse and lose properties even at temperatures above 30-40 ° C. And if the extract is aqueous, then it is also subject to the destructive effects of microflora, which develops quite actively at temperatures of 10-40 ° C. The use of the vacuum evaporation method at such temperatures requires a relatively high vacuum and the use of a sufficiently powerful vacuum pump, since as the pressure decreases, the mass capacity of the vacuum pump decreases. Under these conditions, more energy-efficient and technically simple may be just evaporation with ventilation tanks.

Evaporation of these extracts by the present method is carried out in an apparatus with a closed tank ventilation circuit, since it is necessary to ensure the proper purity of the product. Since air oxygen adversely affects the quality of the product, a gas inert to the product, such as nitrogen or carbon dioxide (carbon dioxide), is used to ventilate the tank. Carbon dioxide is also used as a preservative (E290).

Since such products are too sensitive to elevated temperatures, the intensification of the evaporation process due to accelerated heating and the use of boiling is practically impossible, and the process of evaporating a portion of the product can be very long. It is extremely difficult to sterilize such products, and in order to avoid the detrimental effect of microflora on aqueous extracts during the evaporation process, it is preferable to use carbon dioxide and the lowest possible temperature for the process to ventilate the tank, since at a lower temperature the development rate of microorganisms is lower and the concentration of preservative dissolved in water is higher - carbon dioxide.

In view of the foregoing, the evaporation of aqueous extracts according to the claimed method is carried out in a carbon dioxide atmosphere at atmospheric pressure and a temperature inside the tank of 10-20 ° C. In the tank ventilation circuit (closed), a steam condenser is used, cooled by a coolant with a temperature of preferably 0 ° C, and any hermetically built-in fan corresponding to a given steam output (taking into account its concentration in the gas). To avoid product losses in the condenser, a droplet eliminator of any suitable design can also be installed in the ventilation circuit at the outlet of the tank.

Since the product does not allow significant heating, the temperature at the outlet of the evaporation circuit is limited to 30 ° C, and to exclude the possibility of local overheating, a plate heat exchanger with a coolant temperature of 30 ° C or an electric heater controlled by a thermostat according to the heating surface temperature is used as a heater. Since evaporation is carried out without boiling the product, an overpressure in the evaporator circuit under the conditions of heating and evaporation is not required. Therefore, any circulation pump that is satisfactory in performance can be used as a pump, and the pressure drop across the injector device, unlike the previous examples, is no longer necessary. On the other hand, with such evaporation, it is preferable to have a developed free surface, and to feed the product in a droplet form. The injector device of the evaporator circuit in this case is preferably performed in the form of a sprinkler device or nozzle. In the case of using the nozzle, the minimum necessary pressure drop on it is required for the normal operation of the device.

The time-average power of the heater is selected on the basis of the required performance for the initial or finished product, taking into account ratio (2) and the degree of evaporation, defined as the mass ratio of the initial and finished concentrated extract.

Overheating of the product is excluded due to the use of heaters of the above types, therefore, relation (1) is not used, and the pump capacity is selected so as to provide the required average power of the heater. At a low flow rate, a fixed-temperature heater will not provide the required power, therefore, the parameters of the heater and pump are selected consistently and jointly.

The use of ratio (3) in this implementation of the method is also not necessary, since product boiling and foaming in this case are absent.

If the evaporated product allows for significant mechanical stresses, then, as in the previous examples, the pump and the evaporator circuit heater can be implemented as a mechanical heater according to RU 2267350. The task of preventing overheating of the product in this case is easily solved by the method described in the patent description.

Evaporation of aqueous or alcoholic extracts with biologically active components using tank ventilation in the described example is performed as follows.

A portion of the feedstock is placed in a container, after which the ventilation circuit and the space above the product in the container are filled with an inert gas (nitrogen or carbon dioxide). Then, all the devices included in the evaporation apparatus are turned on, and the process is performed until the required degree of evaporation is achieved, i.e. in fact, until the desired mass of the product remaining in the tank or obtained in the process of condensation is reached. During the evaporation, the inert gas pressure is maintained at atmospheric pressure or slightly higher to prevent air from entering the apparatus due to possible violation of the integrity of the seals. Upon reaching the required degree of evaporation, the evaporator devices are turned off and the finished product is drained.

Claims (22)

1. The method of evaporation of fluid products, including the circulation of the product in the tank, and its heating, characterized in that the circulation of the product is carried out through the evaporation circuit, which includes at least one pump for withdrawing the product from the tank and ensuring its circulation in the evaporation circuit, at least one heater to ensure heating of the product in the evaporator circuit and at least one injector device for reverse injection of the product into the tank and connected in series by pipelines from the tank A part of the product is forcibly taken to the evaporator circuit, it is heated in the evaporator heater and the heated product is injected back into the upper part of the container above the product surface. 2. The method according to claim 1, characterized in that the total power generated by the heaters in the evaporation circuit at the stage of evaporation of the product satisfies the condition:

where W _Σ is the total power emitted by the heaters (W), W ∗ is the total heat loss power (W), Ť is the product heating rate (deg / s), C is the heat capacity of the product (J / (kg · deg)), m - the mass of the product subjected to heat treatment (kg), the index i numbers the evaporated components of the product, q _i is the specific heat of evaporation of the i-th component (J / kg), M _i is the required rate of evaporation at the temperature of the process (kg / s). 3. The method according to claim 1, characterized in that to eliminate overheating of the product, the heater satisfies the requirement:

where Q is the instantaneous mass flow rate of the product through the heater (kg / s), W is the power released by the heater (W), C is the heat capacity of the product (J / (kg · deg)), and τ = TT ₀ is the maximum allowable overheating of the product relative to temperature in the tank (deg), T ₀ - temperature of the product in the tank, T - temperature of the product at the outlet of the evaporation circuit. 4. The method according to claim 1, characterized in that the heater meets the requirement:

where Q is the instantaneous mass flow rate of the product through the heater (kg / s), W is the power released by the heater (W), C is the heat capacity of the product (J / (kg · deg)), Δ = TT ₀ is the minimum allowable overheating of the product relative to temperature in the tank (deg), T ₀ is the temperature of the product in the tank, T is the temperature at the outlet of the evaporation circuit. 5. The method according to any one of claims 1 to 4, characterized in that a vacuum is maintained in the vessel during evaporation of the product. 6. The method according to any one of claims 1 to 4, characterized in that the container is vented with dry gas or air when evaporating the product. 7. A device for evaporating the current products, including a container with inlet and outlet openings, a heater, characterized in that the device includes at least one evaporative circuit, which includes at least one pump for collecting the product from the container and ensuring its circulation in the circuit, at least one heater to provide heating of the product in the evaporator circuit and at least one injector device for reverse injection of the product into the container and connected in series by pipelines, an injector th device is installed in the upper part of the tank above the level of its filling product. 8. The device according to claim 7, characterized in that the total power generated by the heaters in the evaporator circuit at the stage of product evaporation satisfies the condition:

where W _Σ is the total power released by the heaters (W), W ∗ is the total heat loss power (W), Ť is the product heating rate (deg / s), C is the heat capacity of the product (J / (kg · deg)), m - the mass of the product subjected to heat treatment (kg), the i component of the product being evaporated is numbered, q _i is the specific heat of vaporization of the i-th component (J / kg), M _i is the required rate of evaporation at the process temperature (kg / s). 9. The device according to claim 7, characterized in that to eliminate overheating of the product, the heater satisfies the requirement:

where Q is the instantaneous mass flow rate of the product through the heater (kg / s), W is the power released by the heater (W), C is the heat capacity of the product (J / (kg · deg)), τ = TT ₀ is the maximum allowable overheating of the product relative to temperature in the tank (deg), T ₀ is the temperature of the product in the tank, T is the temperature at the outlet of the evaporation circuit. 10. The device according to claim 7, characterized in that the heater meets the requirement of:

where Q is the instantaneous mass flow rate of the product through the heater (kg / s), W is the power released by the heater (W), C is the heat capacity of the product (J / (kg · deg)), Δ = TT ₀ is the minimum allowable overheating of the product relative to temperature in the tank (deg), T ₀ is the temperature of the product in the tank, T is the temperature at the outlet of the evaporation circuit. 11. The device according to claim 7, characterized in that the sprinkler device or a valve with or without sprinkler nozzle, an adjustable flow nozzle or an adjustable valve or throttle attached to the top wall of the tank are used as an injection device, with a gap between the injection device and the product surface in technological capacity. 12. The device according to claim 7, characterized in that the pump and the heater in the evaporator circuit are made in the form of a single device. 13. The device according to claim 7, characterized in that the injection device is simultaneously a hydraulic throttle to create excess pressure in the evaporator circuit and prevent product boiling inside the evaporator circuit. 14. The device according to claim 11, characterized in that the injection device is equipped with a valve for controlling the instantaneous flow rate and increment of the product temperature in the evaporation circuit. 15. The device according to claim 7, characterized in that at the entrance to the evaporator circuit a filter separator of lump inclusions in the evaporated product is installed. 16. The device according to claim 7, characterized in that the process vessel is equipped with a mixing device. 17. The device according to claim 7, characterized in that a breather is installed in the upper part of the process vessel. 18. The device according to any one of claims 7 to 16, characterized in that the process vessel is sealed and connected in the upper part to the vacuum line for steam removal. 19. The device according to p, characterized in that the vacuum line includes a steam condenser. 20. A device according to any one of claims 7-16, characterized in that the upper part of the container above the product is connected to a closed or open ventilation circuit. 21. The device according to claim 20, characterized in that the ventilation circuit includes a fan and at least one gas or air conditioning device. 22. The device according to item 21, wherein the conditioning device includes a cleaning filter and / or dehumidifier.

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