RU2428038C1 - Unit for microwave drying and disinfection of meat-and-bone mince - Google Patents

Abstract

FIELD: food industry.

SUBSTANCE: invention is intended for usage in meat industry in the process of drying and disinfection of meat-and-bone mince. The unit contains a transporter, chains of microwave chambers positioned thereon and serially connected with wave-guiders, microwave generators, undesirable radiation energy absorbers, two detector heads. The number of chambers is chosen depending on initial moisture content of mince as well as on its flow width and thickness. The unit performance enhancement is provided by summation of N chains; each of them powered from a dedicated generator. The chains are serially positioned on the transporter along each of the n branches of one power level. Introduction of a continuous mince flow into the system of microwave chambers is performed through the minimum power level chambers which enables mince drying and disinfection in one passage through the unit.

EFFECT: unit performance enhancement, reduction of specific energy- and-labour costs.

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Description

The installation can be used for microwave processing of minced meat from any initial to a given final moisture during drying and disinfection of the product.

Considering that the structure of meat and bone mincemeat allows forming a stream of almost any width and thickness, cameras can be used for its microwave processing, creating conditions for achieving the highest process efficiency and power utilization factor. It is known / N.Ya. Feldman. Pass-through microwave cameras and their use in installations for the electromagnetic processing of materials. “Modern Electronics”, 2009, No. 8 /, which includes a camera based on a rectangular waveguide and allowing the processed material to pass through it through the axial plane of the waveguide wall “a”, that is, at the maximum of the electromagnetic field. Therefore, such a camera is taken as the basis of this installation.

Known / Microwave Energy, ed. E.Okressa. M., Mir, 1971, v.2, p. 183-202 /, that the serial connection of microwave cameras located on a single conveyor makes it possible to practically fully use the power of microwave generators, thereby increasing the efficiency of the installation as a whole.

The disadvantages of the device are:

- it uses waveguide chambers that introduce a material flow into the perpendicular axis of the waveguide, which sharply worsens the matching conditions in the chamber, that is, increases losses due to an increase in the reflected power and requires the introduction of a ferrite valve into the installation to match the microwave generator;

- it provides for the input of the material flow into the system of series-connected cameras through the first camera connected to the microwave generator, which leads to a decrease in the microwave power acting on the material during the process.

The objective of the invention is the creation of a microwave installation, making it possible to implement the law of changing the power acting on the material of microwave electromagnetic waves, optimal for solving both of its problems / drying and destruction of microorganisms / during one pass of the material flow through the installation. This provides increased productivity of the installation, reduction of specific energy and labor costs.

The optimality of the law of change in the power acting on the material is determined, first of all, by the power requirements put forward by the need to destroy microorganisms. It is known / Rogov I.A. Electrophysical methods of food processing. M., 1988, p.184-185, Table 5.4 /, which, although there is currently no consensus on the mechanism of this phenomenon, the results of experimental studies show that under all equal conditions / the same exposure duration, i.e. equal energy of microwave electromagnetic oscillations / bacterial survival / of both Escherichia coli and staphylococci / with microwave heating in a pulsed mode is lower than in continuous. Hence, the conclusion suggests itself that, in addition to the significance of microwave energy, the absolute value of the acting power / in the pulsed mode is of great importance in the pulse power is higher than the power in the continuous mode /. It should be borne in mind that electromagnetic energy in direct contact with a microorganism or with their combination is determined not only by microwave energy supplied to the processed material, but also by the degree of absorption of this energy by the material. It is known / Rogov I.A. Microwave heating of food products. M., 1986, Table 2.19 /, that the dielectric constant of bone tissue with a low water content in the microwave range is low / ε = 5.6 /, and in meat and bone mincemeat bone accounts for 70% of the total mass of minced meat, i.e. in dry minced meat or minced meat containing a small amount of water / W = 5-10% /, the absorption of electromagnetic energy by the processed material is negligible. Meanwhile, as with a large water content in it / W = 40% /, given that water has ε = 80, a significant part of the energy is absorbed by the material, and its residues interact with microorganisms. / In experimental drying of meat and bone meat in the laboratory of microwave power engineering in the Novosibirsk laboratory, in the same waveguide microwave chamber, with the following: the volume of the meat, its configuration and location in the chamber, the absorption of the power of microwave oscillations of the frequency 915 MHz with raw meat - / W _o = 35% / amounted to R _pogl = 0.87 P _pad , and when it reaches a moisture content of W = 5-10% P _pogl = 0.25 P _pad /.

The obvious conclusion follows from this: the microwave installation must first ensure the drying of the meat and bone meat, using for this purpose the remnants of the power of electromagnetic waves, which ensure the destruction of microorganisms and dry the forcemeat in the previous batch of its flow (Fig. 2) and only after reaching the required final humidity process the material the maximum microwave power level in this installation, but allowing to inactivate the microorganisms present in the minced meat.

The solution to this problem is achieved by the fact that the installation of microwave drying and disinfection of meat and bone meat, characterized in that it contains microwave generators, each of which is connected to a chain of waveguides connected in series to microwave cameras placed on a single conveyor, with each camera at the entrance and the minced meat stream is equipped with parasitic energy absorbers, and at the waveguide inlet of the first and last chambers, there are holes for removing steam and two detector heads removed apart from each other by an odd number of quarters of the wavelength in the waveguide. In this case, the input of the flow of wet mincemeat into the installation is carried out through the last in each chain microwave chamber, i.e. a chamber powered by the power of microwave oscillations of the lowest level in each chain, and the output of the finished product stream through cameras powered directly from microwave generators.

The system under consideration ensures the sequential implementation of two processes: the drying process of meat and bone meat, during which the meat is prepared for the process of destruction of microorganisms, and the second, final process - the destruction of microorganisms. The use of chambers in the microwave processing system, which include introducing material into them at an angle of 30 ° to the axis of the camera’s waveguide, ensures matching of microwave energy and processed material fluxes in a wide range of the dielectric and overall characteristics of the latter.

The authors are not aware of technical solutions or sources of information that describe the signs that:

- the input of the forcemeat stream into the camera system is carried out through the camera, powered by the power of microwave oscillations of the lowest level in the chain, that is, through the last chamber of the chain;

- the output stream of the finished product is carried out through the camera, fed directly from the microwave generator.

Therefore, the present invention meets the criterion of "inventive step".

The number of "n" / Fig.1/ series-connected microwave cameras in the installation is determined by the level of power utilization

where R _pogl - power absorbed by the processed material;

P _pad - power radiated by the microwave generator.

All material non-absorbed power

will go into a coordinated load, i.e. will be direct power losses, determining a decrease in β, and, consequently, a decrease in the efficiency of the installation. In this scheme, the value of P _CR is determined by the number n of chambers connected in series and can be achieved, as shown in figure 2, arbitrarily small. Indeed, from figure 2 it follows that with n = 3, with r = 3 cm and L = 15 cm in the cross section of the stream B, corresponding in this case to the energy output from the camera system, the unused in the last chamber of the chain P _pr is relative to P _pad microwave generator / chamber 1-1 / 3-1-β = 0.04, i.e. β = 0.96. Using the same method, it can be shown that for L = 10 cm and r = 3 cm, for n = 5 β = 0.94, and for n = 6 β = 0.99, etc.

In (1), the value of P _is determined:

- dielectric characteristics of the processed material and their change during the drying process, caused, first of all, by a change in the moisture content of the material;

- thickness and width of the material flow.

When choosing the thickness, r, and width, L, of the material flow, it is necessary, first of all, to take into account that their values are in no way related to the capacity of the installation, P. Productivity during drying of the material is determined only by the amount of water, Δm _in , which must be removed from the material acting on the material, P _pad , and absorbed by it, P _sweep , power and process efficiency, η _n .

where q is the specific heat of water vaporization, q = 2256 kJ / kg = 0.627 kWh / kg;

Δt _i is the transit time of the material stream of the i-th camera of the chain;

P _abs - _power absorbed by the material in the i-th chain.

The absolute value of P _sweep . depends on the stream width L _i , but in a chain of series-connected cameras, L _{i is} summed over n cameras. Therefore, when the minimization condition P _{ol is} fulfilled, n and L _{i are} simultaneously optimized.

A similar picture takes place in the dependence P _ogl = f (r). Indeed, in the waveguide chamber / Berger M.N., Kapilevich B.Yu. Rectangular waveguides with dielectric. M., Soviet radio 1977 / dielectric absorption coefficient, α, dependent on the dielectric thickness, r, which leads to a change in P _abs

P _chill = P _pad (1st ^-2αL )

But, as in the dependence P _ch = f (L _i ), the change in P _ch in each i-th camera of the chain can be compensated by the number, n, of the chains without changing the power utilization factor, β, cm (1).

The efficiency of the process (3) depends only on the following characteristics:

1. The distribution of the electromagnetic field in the cross section of the material.

In a microwave camera built on a rectangular waveguide, when the material to be processed is placed symmetrically relative to the axial plane of the waveguide and parallel to the waveguide wall “c”, the field maximum is always in the mid-section of the material, and therefore the process of heating the material and water evaporation begins in the middle material. Hence, all three gradients / vapor concentration, temperature and vapor pressure / are directed to one side / from the middle to the outer layers /, which accelerates the flow of steam from the material, i.e. maximizes process efficiency.

2. The adhesion of water molecules to the material.

3. The resistance of the material to the exit of water vapor.

The last two characteristics are individual for each material. It was experimentally established that when drying meat and bone meat, the efficiency of the process in the waveguide chamber is η _n = 0.7-0.8.

From these data, assuming that the chosen value of n, consecutive chambers in _straight chain F is negligible, i.e. ΣР _sweep ≅P _pad , the performance of the installation for drying the stuffing is determined only from the condition that for the time Δt = 1 hour, for example, when the microwave generator power is P _pad = 40 kW, the unit can evaporate, cm (3).

If the raw material has a moisture content W _o = 40%, then one of its kg contains m _in = 0.4 kg of water. If after drying it is necessary to achieve a moisture content W _k = 10%, then the residual water content of this portion of minced meat will be m _bk = 0.07 kg, i.e. 1 kg of raw sausage meat during drying must evaporate _during Δm = m _in -m _VC = 0,4-0,07 = 0.33 kg of water. Then, according to (4), the amount of kg of raw minced meat, which the unit is able to dry in 1 hour at P _pad = 40 kW, will be

Accordingly, the volume of the minced meat processed by the installation will be

/ specific gravity, p = 0.64 kg / dm ³ corresponds to the stuffing, on which experimental studies were conducted by the laboratory of microwave energy, i.e. which corresponds to the experimentally established value η _n = 0.7-0.8 /. Based on these data, the width of the stream, L, the thickness of the stream, r, the number of branches of the waveguide chambers, n, and the speed of the flow through the camera system can be selected. When choosing the values of r and L, it should be taken into account that the smaller the cross section of the stream S = r · L, the higher the speed of its movement on the conveyor to ensure that the processing of the volume U is performed and, accordingly, the shorter the time it passes through each branch of the chamber.

This will lead to a smaller change in the dielectric characteristics of the stuffing during the passage of each chamber / this is especially important for the cameras of the first chains /, which will reduce, on the one hand, losses on reflected power, and on the other hand, will increase the stability of the microwave generator. The increase in the number n of the cameras connected in series in the chain does not cause any technical problems.

So, for example, in order to pass the forcemeat volume U = 230 dm ³ (see (5)) at r = 0.3 dm and L = 1.5 dm through the microwave cameras for t = 1 hour, speed is required, V, minced meat flow movements through the chambers

Accordingly, the time, Δt, of the passage of each section of the forcemeat flow through the camera waveguide is determined as

But with a decrease in the flow width L to 1 dm, V increases to 1.28 m / min, and Δt decreases to 11.5 sec.

An increase in the productivity of the installation, relative to the value П = 145 kg / h, can be achieved by introducing additional microwave generators into it. At the same time, the productivity of the installation will increase in proportion to an increase in the total power of all the generators that feed it, due to an increase in the speed of the stuffing flow through the microwave cameras. An example of the installation scheme, providing its doubled productivity, P = 300 kg / h and, accordingly, fed from two microwave generators, is shown in Fig.3. The forcemeat flow rate in this setup / ΣР _pad = 80 kW /, at r = 0.3 dm, L = 1.5 dm will be (6), (7) V = 1.7 m / min, and the transit time of one cameras, Δt = 9 sec.

Alternating passage of the processed minced meat by microwave cameras powered from different generators and having an equal power level in the installation of FIG. 3 ensures that the general law of change in the power acting on the minced meat / relative to the circuit of FIG. 1 / is maintained. An additional advantage of this scheme is the opposite direction of wave propagation in each pair of adjacent equal-level chambers, which in total over these chambers increases the uniformity of the distribution of the microwave field along the width of the stream L of the stuffing. So the uniformity coefficient

δ = P _max / P _min

in the scheme of figure 3, relative to the scheme of figure 1 decreases with L = 15 cm in chambers 1 - 1.5 times; in chambers 2 - 2.2 times; in chambers 3 - 4.5 times.

The installation of microwave drying allows you to control and automatically control the drying process. The drying process is controlled by measuring the power at the waveguide input of the first and output of the last chambers, by comparing the readings of two detector heads installed at each of these points (pos. 8), separated from each other by an odd number of quarters of the wavelength in the waveguide. The powers of P _pad and P _pr can be measured using detector heads. It should be borne in mind that in the path of propagation of electromagnetic waves, due to the addition of the incident and reflected waves, a standing wave is created. The length of the standing wave is λ _st = λ _in / 2, where λ _in is the length of the traveling wave in the waveguide.

The location of the standing wave in the waveguide depends on many factors (the relative position of the cameras connected in series, the length, thickness and dielectric characteristics of the material, etc.). Therefore, it is impossible to determine the phase of the standing wave in the cross section of the location of the detector head, and the change in power within 180 degrees of the standing wave can be very significant. Acceptable accuracy of power measurement can be achieved using both detector input and output cameras with two detector heads mounted at a distance of λ _in / 4. If these heads are previously jointly calibrated for power, then averaging their readings always allows you to find the value of P _pad and P _CR with acceptable accuracy:

, где P₁ и P₂ - результаты измерения мощности каждой детекторной головкой. Управление же процессом осуществляется изменением мощности СВЧ-генератора и скорости движения транспортера.

where P ₁ and P ₂ are the power measurement results of each detector head. The process is controlled by changing the power of the microwave generator and the speed of the conveyor.

All of the characteristics of the drying process of meat and bone meat presented here are confirmed by the above results of experimental studies conducted with the thickness of the meat layer r = 30, 40, 50 mm, flow width L = 15 cm and power P _pad = 5, 10 and 20 kW.

According to microbiological indicators, the following results were achieved:

Sample MAFANM BGKP Salmonella Minced meat (control) 28.7-10 ⁶ CFU / g discovered not found Minced meat (20 kW, 30 sec) 43 CFU / g not found not found Minced meat and bone (20 kW, 40 sec) I. not found not found not found II. not found not found not found III. not found not found not found

Thus, as a result of microwave processing of minced meat and bone, the MAFAnM decreased by 6 orders of magnitude and the disinfection efficiency was 99.999%.

The temperature of the meat did not exceed 108 ° C.

The following illustrative materials are described.

Figure 1. Connection diagram of microwave waveguide chambers located on a common conveyor and constituting a single microwave oven. (All microwave cameras (pos. 1) included in the installation (Figs. 1, 3) are structurally identical. But the power of microwave oscillations, the direction of their propagation relative to the forcemeat flow change from camera to camera depending on the location, n, each chamber in the chain (n = 1 in the first chamber connected to the generator) .In addition, the characteristics of the process taking place in the microwave camera system depend on which of the K generators (G ₁ , G ₂ , G _to ) is connected each chain of cameras. Therefore, here on the microwave cameras the designation is entered: 1-K / n.)

Figure 2. Distribution of the acting power, P _pad , along the branches of the installation with a continuous flow of minced meat and L = 15 cm, r = 3 cm.

a - camera 1-1 / 1; in - camera 1-1 / 2; s - camera 1-1 / 3.

Figure 3. Connection diagram of microwave waveguide chambers located on a common conveyor when powering the system from 2 microwave generators.

The number of microwave generators, G _to , in the installation can be any - it is determined by its required performance / 1, 3 /. Each generator feeds one chain of n cameras. The minimum number of cameras in the chain is n _min = 3. The maximum number of cameras in a chain is not limited. It is due to the need to make full use of the power of each generator for a selected value of width, L, thickness, r, flow, which, in turn, depend on the initial humidity of the meat and bone meat. Unused power from each circuit along the waveguides, 3, is transferred to its agreed load, N, the number of which in the installation is equal to the number of generators. At the inlet and outlet of the forcemeat stream, in each chamber there are installed boxes, 4, absorbing parasitic microwave radiation. The length of the box along the flow axis is 0.5 m and it determines the minimum distance between any two adjacent cameras / 1 /. If the boxes are interconnected by flanges 6 / Fig. 3/, then the total length of two boxes interlocking with each other can be reduced to 0.5 m. The connection of microwave cameras located in one chain is carried out by waveguides, 3 connected to each other using flanges, 2.

Forcemeat flow, 5, is introduced into the installation from the side of the chambers powered by the lowest power level in each chain.

To remove steam from the microwave chambers, a waveguide with a transverse pipe (pos. 7) is installed at the input of each circuit fed by the generator, through which free air is introduced into the chain of chambers. At the output of each chain, an exhaust fan is connected to a similar waveguide.

Claims (1)

Microwave drying and disinfection of minced meat, containing microwave generators, each of which is connected to a chain of microwave chambers connected in series by waveguides placed on a single conveyor, with each chamber at the input and output of the processed meat flow equipped with parasitic radiation absorbers and at the waveguide inlet of the first and the last chambers of each chain, with holes for removing steam and two detector heads spaced apart from each other by an odd number of quarters of the wavelength in the waveguide, and the feed of wet minced meat into the system of chambers is carried out through chambers powered by the microwave power of the lowest level in the chain, and the output of the finished product stream through chambers fed directly from microwave generators.

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