RU2480016C1 - Method for automatic control of continuous hfc defrostation of products in blocks - Google Patents

Abstract

FIELD: food industry.

SUBSTANCE: method involves variation of the power of radiation of the electrode pairs from the generators, of the conveyor movement rate, of the electrode pairs position and of the product block temperature within different unfreezing zones. Information is transmitted to a microprocessor that determines rated heating parameters. Obtained rated temperature values are compared to those measured within the corresponding treatment zones; in case of the latter's deviation from the rated ones the conveyor movement rate and the power of the corresponding electrode pair generators are corrected. The unfreezing process completion is identified by information on uniform distribution of temperature within the block as obtained from the thermal imagery device.

EFFECT: invention ensures unfreezing with uniform heat distribution which excludes the product local boiling.

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Description

The invention relates to dielectric processing of food products in blocks, in particular to the fishing industry, and can be used for dielectric defrosting of fish and seafood at coastal fish processing enterprises, as well as in enterprises for thawing meat, fruits, vegetables, and other products.

A device is known in which a method for controlling the dielectric processing of products in blocks is carried out [RF Patent No. 2280988, MKI A23B 4/07. The method of dielectric processing of products in blocks / S.T. Antipov, S.V. Shakhov, A.A. Chirkov, E.V. Ryazhskikh, V. B. Popov, S. P. Telegin. - Declared. January 31, 2005, No. 2005102255/13, publ. 08/10/2006 in BI No. 22], including the placement of a frozen block of products between rectangular plate electrodes or in the form of rings connected to power sources, and exposure to high frequency current blocks, while plate electrodes are a set of separate electrodes, as sources power supply, autonomously using separate generators, the power of which is regulated so that the radiation power of each electrode increases from the periphery to the center when they act on the product blocks, which Several are placed between the electrodes in a bath having a rectangular or circular shape according to the configuration of the electrodes and filled with water with a temperature of 17-20 ° C.

The disadvantage of this method of controlling the dielectric processing of products in blocks is the inability to control continuous defrosting by high-frequency currents.

A known method of controlling continuous defrosting by high-frequency currents of products in blocks, carried out in the device [RF Patent No. 2238125, MKI A23B 4/07. Installation of continuous high-frequency defrosting of products in blocks / S.T. Antipov, S.V. Shakhov, A.A. Chirkov, A.A. Stepygin, A.Yu. Baranov, E.V. Ryazhskikh. Claim 02/19/2007, No. 2007106337/13, publ. 07/10/2008 in BI No. 19], in which the power of each electrode, which is independently powered by separate generators, is set so that it decreases from the center to the periphery when they affect the blocks, while the maximum power electrode is located above the central part of the block, and subsequent pairs of electrodes are displaced along the conveyor by the length of the electrode, and along the width of the block by distances exceeding the zones of action of the edge effects of the electromagnetic field of high-frequency currents formed by the electrodes.

The disadvantage of this method of controlling continuous defrosting by high-frequency currents of products in blocks is the lack of control over the temperature of the blocks during defrosting in continuous mode and, accordingly, changes in the conditions for supplying heat to the blocks.

The closest in technical essence and the achieved effect to the proposed is a method for controlling the process of defrosting blocks of frozen food products [RF Patent No.2016518, А23В 4/07. Application: 5020424/13, 01/03/1992. Publ. 07/30/1994], the essence of which is that the temperature of the product at the inlet to the defroster is determined, the obtained value is compared with the reference value and the amount of steam necessary for the defrosting process is determined, then the surface temperature of the tray at the outlet of the defroster is determined and the steam flow rate is adjusted.

The disadvantages of the method of controlling the process of defrosting blocks of frozen food products are the low accuracy of controlling the process of defrosting the product, low quality of the product and high energy consumption, because there is a problem of regulating the temperature of the product in a continuous mode and ensuring a uniform temperature distribution over the area of the product block due to the dosed effect of radiation power on it, excluding local boiling.

An object of the invention is to improve the quality of the product by increasing the accuracy of controlling the process of defrosting the product, its quality, as well as reducing energy costs by regulating the temperature of the product in a continuous mode and the uniformity of temperature distribution over the area of the product block due to the dosed effect on it of radiation power, eliminating local boiling .

The technical problem of the invention is achieved in that in a method for automatically controlling continuous defrosting by currents of high frequency products in blocks, including measuring the temperature of the product at the inlet of the defroster, comparing the obtained value with the set value and determining the amount of energy necessary for the defrosting process, determining the temperature conditions at the outlet of the defroster and adjustment of energy supply, new is that energy supply is carried out dosed from a pair of electrodes acting on the central part of the block, and from pairs of electrodes displaced along the conveyor by the length of the electrode, and along the width of the block, by distances exceeding the zone of action of the edge effects of the electromagnetic field of the high-frequency currents formed by the electrodes, while during the defrosting process, the radiation power is measured pairs of electrodes from generators, conveyor speed, position of pairs of electrodes, as well as the temperature of the unit in various defrost zones, the information is transmitted to the microprocessor, which is previously there is a restriction on the temperature of the product and the thermophysical parameters of the block — density, heat capacity, thermal conductivity, geometric characteristics of the block — length and width, the calculated values of the heating rate, thermal diffusivity of the block, Peclet’s criterion, the residence time of the block in the processing zone, the characteristic Fourier number, and the parameter corresponding to for heat transfer by thermal conductivity, a parameter obtained by the ratio of the latter to the Peclet criterion, dimensionless characteristics of the generator of a pair of electrodes acting on the neutral part of the block, and, depending on this generator, the dimensionless characteristics of the generators of other electrode pairs are determined, which ensure uniform heating of the block and block heating temperature at the outlet of the corresponding treatment zone, the calculated temperature values are compared with the temperature values determined using non-contact non-contact methods of measuring temperature using pyrometers in the respective processing areas of the product block and when the latter deviates from the calculated ones, they are adjusted first the conveyor speed by transmitting the signal from the microprocessor through the digital-to-analog converter to the actuator, and then the power of the corresponding generators of the electrode pairs by transmitting the signal from the microprocessor through the digital-to-analog converters to the executive mechanisms, and the end of the defrosting process is carried out according to the information received from the thermal imager on the uniform temperature distribution block.

The technical result of the invention is to improve the quality of the product by increasing the accuracy of controlling the process of defrosting the product, its quality, as well as reducing energy consumption by regulating the temperature of the product in a continuous mode and the uniformity of temperature distribution over the area of the product block due to the dosed exposure to radiation power excluding it local boiling.

Figure 1 shows a diagram of the automatic control of continuous defrosting currents of high frequency products in blocks

The automatic control circuit for continuous defrosting by high-frequency currents of products in blocks (Fig. 1) includes a chain conveyor 1 with a working chamber 2. The floor of the chain conveyor 1 consists of plates made of dielectric material, on the surface of which product blocks 3 are located. In the working the chamber 2 under the plates of the floor of the conveyor 1 and above the product blocks located on the floor of the conveyor 1, respectively, the lower and upper electrodes are installed in the form of separate plates, forming a pair of electrodes 4-11. Each pair of electrodes 4-11 is connected to separate power sources - generators 12-19, with the ability to control the power supplied to the pairs of electrodes 4-11.

Under the plates of the flooring of the conveyor 1, a tray 20 is installed for collecting water formed during the melting of ice blocks.

The conveyor 1 is driven by a drive sprocket 21 mounted rotatably with an electric motor 22 connected by a coupling 23 to a gearbox 24 and a chain gear 25.

The pairs of electrodes 4-11 in the zone of their influence on the product blocks 3, located on the conveyor 1, are set so that the pair of electrodes 4 is at the beginning of the defroster in the zone of influence on the central part of the block 3 and provides maximum power for the product, and subsequent pairs electrodes 5-11 are displaced along the conveyor 1 by the length of the electrode, and along the width of the block 3 by distances exceeding the zone of action of the edge effects of the electromagnetic field of high-frequency currents formed by the electrodes, and installed with the possibility th reciprocating movement using autonomous drives 26-31.

The circuit contains temperature sensors of the surface of the blocks by remote non-contact methods of measuring temperature in the form of pyrometers 32-43 and in the form of thermal imagers 44 and 45, sensors 46-53 of the radiation power of the pairs of electrodes 4-11 from generators 12-19, an angular velocity sensor 54 of the drive sprocket 21 conveyor 1, sensors 55-60 position of the pairs of electrodes 5-10, secondary devices 61-89, microprocessor 90, digital-to-analog converters 91-105, actuators 106-120.

The method of automatic control of continuous defrosting currents of high frequency products in blocks is as follows.

Frozen blocks 3 are laid on the floor of a moving chain conveyor 1. Through the receiving window of the working chamber 2 of the installation, blocks 3 fall into the processing zone, where, passing between the pairs of electrodes 4-11, they warm up and thaw.

Uniform heating of blocks 3 occurs due to the location of the electrodes 4-11 and the ability to control the power of their radiation from power sources - generators 12-19.

The energy supply from the generators 12-19 in the required amount of radiation energy from the electrodes 4-11 to defrost, measured using sensors 46-53, is metered first from a pair of electrodes 4 acting on the central part of the block 3 with the maximum permissible maximum power, and then from pairs of electrodes 5-11 with lower power and placed with an offset along the conveyor 1 by the length of the electrode, and along the width of the block 3 by distances exceeding the zone of action of the edge effects of the electromagnetic field of high-frequency currents formed oh electrodes. In this case, the maximum permissible speed of the conveyor 1 is set using the actuator 120, which is measured using the sensor 54.

When the block 3 passes between the first pair of electrodes 4, its central part warms up. In this case, the maximum power is supplied to the electrodes 4 from the power source-generator 12 using the actuator 106. The central part of the block 3 under the influence of an electromagnetic field warms up from temperature t ₁ to t ₂ , and a temperature gradient arises in the direction of decreasing temperature, t .e. from the center of block 3 to its periphery.

After warming up the central part, a continuously moving block 3 passes between two subsequent pairs of electrodes 5, 6, where the heating of a part of the block 3 remote at a certain distance from the center takes place to temperature t ₂ , however, the energy costs will be lower and the power of the sources - generators 13, 14 - must be reduced. The size of the heated zone is increasing. Despite the fact that the second electrodes are arranged in one row, overheating of the product due to the occurrence of the edge effect does not occur due to the greater distance between adjacent electrodes.

Similarly, the rest of the block 3 is heated to the required temperature.

In this case, during the defrosting process, the radiation power of the pairs of electrodes from the generators is measured, the conveyor speed, the position of the pairs of electrodes, as well as the temperature of the unit in its various defrost zones, information about which is transmitted using sensors 32-60 and secondary devices 61-89 into the microprocessor 90, into which the restriction on the product temperature and the thermal parameters of the blocks are preliminarily introduced: density ρ [kg / m ³ ], specific heat c _p [J / (kg · K)], thermal conductivity λ [W / (m · K)] geometric x The block characteristics are length l [m] and width h [m].

Power control of power sources - generators 12-19 is carried out on the basis of information about the temperature of the product obtained using remote non-contact methods of measuring temperature at the beginning and at the end of the defroster using thermal imagers 44 and 45, and in different areas of the defrosting of the product block using pyrometers 32- 43.

The choice of thermal imagers 44 and 45 and pyrometers 32-43 as remote non-contact methods of measuring temperature is justified by the fact that during the processing of blocks with high-frequency currents, volumetric energy is supplied uniformly over the entire height of the block, and it is assumed that the temperature at the site of exposure of a pair of electrodes it is constant in height, therefore it is enough to obtain information about the temperature of the block in its various zones from its surface, which is effectively and reliably carried out using thermal imagers and pyrometers.

In order to regulate the power of power sources - generators, the calculated values are first determined in microprocessor 90:

heating rate:

q = Q / (c _p ρ),

where Q is the volumetric power of the electrode located above the Central part of the block, W / m ³ ; ρ is the density, kg / m ³ ; c _p - heat capacity, J / (kg · K); λ - thermal conductivity, W / (m · K),

thermal diffusivity of the block:

a = λ / (c _p ρ)

Peclet test values:

Pe = h ² ν / (4al)

where l, h is the length and width of the block, m, ν is the speed of movement of the block, m / s,

block residence time in the processing zone:

τ * = l / ν

characteristic Fourier number:

Fo = a τ * / (h / 10) ²

parameter K, responsible for heat transfer by thermal conductivity:

.

.

parameter

K / Re

dimensionless characteristics of the generator of a pair of electrodes acting on the central part of the block

W ₃ = qν / (t ₀ l)

where t ₀ is the initial temperature of the block.

And depending on this generator, the dimensionless characteristics of other generators of electrode pairs are determined, which ensure uniform heating of the block

;

;

Where

A ₁₁ = A ₂₂ = A, A ₁₂ = A ₂₁ = B

A ₁₁ = 2 [(α ₁₁ -α ₂₁ ) ² + (α ₁₁ -α ₃₁ ) ² + (α ₂₁ -α ₃₁ ) ² ];

A ₁₂ = 2 [(α ₁₂ -α ₂₂ ) (α ₁₁ -α ₂₁ ) + (α ₁₂ -α ₃₂ ) (α ₁₁ -α ₃₁ ) + (α ₂₂ -α ₃₂ ) (α ₂₁ -α ₃₁ )] ;

A ₁₃ = 2 [(α ₁₃ -α ₂₃ ) (α ₁₁ -α ₂₁ ) + (α ₁₃ -α ₃₃ ) (α ₁₁ -α ₃₁ ) + (α ₂₃ -α ₃₃ ) (α ₂₁ -α ₃₁ )] ;

A ₂₁ = 2 [(α ₁₁ -α ₂₁ ) (α ₁₂ -α ₂₂ ) + (α ₁₁ -α ₃₁ ) (α ₁₂ -α ₃₂ ) + (α ₂₁ -α ₃₁ ) (α ₂₂ -α ₃₂ )] ;

A ₂₂ = 2 [(α ₁₂ -α ₂₂ ) ² + (α ₁₂ -α ₃₂ ) ² + (α ₂₂ -α ₃₂ ) ² ];

A ₂₃ = 2 [(α ₁₃ -α ₂₃ ) (α ₁₂ -α ₂₂ ) + (α ₁₃ -α ₃₃ ) (α ₁₂ -α ₃₂ ) + (α ₂₃ -α ₃₃ ) (α ₂₂ -α ₃₂ )]

Where

;

;

;

;

;

;

;

;

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;

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;

;

;

.

.

and the temperature of the block warming up at the outlet of the corresponding treatment zone

,

,

,

,

.

.

And then, the calculated temperature values obtained are compared with the determined non-contact temperature measuring methods using pyrometers 32-43 as the temperature values in the respective processing zones of the product block 13 and, if the latter deviate from the calculated ones, they first correct the conveyor 1 speed by transmitting a signal from microprocessor 90 via a digital-to-analog converter 105 to the actuator 120, and then the power of the respective generators 12-19 pairs of electrodes 4-11 by transmitting a signal from m processor 90 through digital-to-analog converters 91, 92, 94, 95, 97, 98, 100, 101 to actuators 106, 107, 109, 110, 112, 113, 115, 116, and the end of the defrosting process is carried out according to information received from thermal imager 45, on the uniform distribution of the temperature of the block, for example (-3) - (- 2) ° C.

Despite the fact that the spaced apart arrangement of electrodes 5-11 avoids the application of electromagnetic fields from two adjacent sources when the electrodes are too close to each other and the product’s cooking zones are avoided, but when the temperature uniformity deviates from the block according to the information received from the thermal imager 45, the correction of the position of the pairs of electrodes 5-10 by transmitting a correction signal from the microprocessor 90 through digital-to-analog converters 93, 96, 99, 102, 103, 104 to the actuators 108, 111,114, 117, 118, 119 autonomous drives 26-31.

The thawed product is discharged through the unloading window of the working chamber 2. The water formed during defrosting is collected in a tray 20 installed under the conveyor flooring, from which it is then removed.

The method of automatic control of continuous defrosting by currents of high frequency products in blocks has the following advantages:

- the implementation of a metered supply of energy from a pair of electrodes acting on the central part of the block, and from pairs of electrodes displaced along the conveyor by the length of the electrode, and along the width of the block by distances exceeding the area of action of the edge effects of the electromagnetic field of high-frequency currents formed by the electrodes, allows to carry out uniform heating with continuous defrosting by high-frequency currents of the product by controlling the distribution of radiation power over the product area, which eliminates the local zones regreva;

- the use of a consistent algorithm for defrosting product blocks, which first sets the maximum permissible maximum power of the generator of a pair of electrodes acting on the central part of the block and the speed of the conveyor, their measurement, as well as the initial temperature of the block, and then the information is transmitted to the microprocessor, in which the calculated values of the heating rate, thermal diffusivity of the block, the values of the Peclet criterion Re, the residence time of the block in the treatment zone, x the characteristic Fourier number, the parameter K, which is responsible for heat transfer by heat conduction, the parameter K / Pe, the dimensionless characteristic of the generator of a pair of electrodes acting on the central part of the block, and the dimensionless characteristics of other generators of electrode pairs that ensure uniform heating of the block are determined depending on this generator, and block heating temperatures at the outlet of the corresponding treatment zone, which are compared with the values determined by remote non-contact methods of temperature measurement the temperatures in the respective processing zones, and when they deviate from the calculated ones, first correct the speed of the conveyor, and then the power of the corresponding generators of the pairs of electrodes, allows you to optimize the energy supply and minimize energy consumption;

- the use of non-contact temperature measurement of pyrometers and thermal imagers allows to increase the control accuracy by measuring the temperature parameters of the process on-line, which provides targeted energy supply that excludes local product boiling, as well as guaranteed end of the defrosting process when a uniform temperature distribution of the unit is achieved.

Claims (1)

A method for automatically controlling continuous defrosting by high-frequency currents of products in blocks, including measuring the temperature of the product at the defroster inlet, comparing the obtained value with the set value and determining the amount of energy needed for the defrosting process, determining the temperature conditions at the defroster exit and adjusting the energy supply, characterized in that energy is supplied in a dosage form from a pair of electrodes acting on the central part of the block, and from pairs of electrodes displaced along the fan over the length of the electrode, and over the width of the block, at distances exceeding the area of action of the edge effects of the electromagnetic field of the high-frequency currents formed by the electrodes, while during the defrosting process, the radiation power of the pairs of electrodes from the generators, the speed of the conveyor, the position of the pairs of electrodes are measured as well as the temperature of the unit in various defrost zones, information is transmitted to the microprocessor, into which a restriction on the temperature of the product and thermal The unit’s parameters - density, heat capacity, thermal conductivity, geometric characteristics of the unit — length and width, the calculated values of the heating rate, thermal diffusivity of the block, Peclet’s criterion, residence time of the block in the treatment zone, the characteristic Fourier number, the parameter responsible for heat transfer by thermal conductivity, are determined obtained by the ratio of the latter to the Peclet criterion, the dimensionless characteristic of the generator of a pair of electrodes acting on the central part of the block, and depending on this, the generator The dimensionless characteristics of generators of other pairs of electrodes are determined that ensure uniform heating of the block and block heating temperature at the outlet of the corresponding treatment zone, the calculated temperature values are compared with the temperature values determined using remote non-contact methods of pyrometer measurement in the corresponding processing zones of the product block and when the latter from the calculated first correct the conveyor speed by transmitting a signal with the microprocessor through the digital-analog converter to the actuator, and then the power of the corresponding generators of the electrode pairs by transmitting the signal from the microprocessor through the digital-analog converters to the actuators, and the end of the defrosting process is carried out according to the information received from the thermal imager about the uniform distribution of the block temperature.

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