SU1430019A1 - Method of automatic control of pasteurization of milk in the flow - Google Patents

Abstract

The invention relates to methods for automatically controlling the process of pasteurization of milk in a stream in installations with film electric heating elements. The purpose of the invention is to increase the accuracy of support for a given pasteurization effect — it is achieved by calculating the set temperature of pasteurization of milk and thermal resistance under the condition of a change in the rate of deposits on the heat-transfer surfaces, flow rate and product temperature at the entrance to the installation. At the same time, the correction of the setting of the pasteurization controller improves the accuracy of maintaining the pasteurization mode of the milk under conditions of varying productivity and accumulation of protein deposits on the heat-giving surfaces of the installation. 1 un (L

Description

four:

00

The invention relates to methods for automatically controlling technological parameters, for example, a pasteurization mode for milk, and can be used to create automatic control systems for continuous pasteurization installations with milk electric heating elements used on dairy products.

farms and complexes.

i The aim of the invention is to improve the accuracy of maintaining a given Pasteurization effect.

j The drawing shows a diagram of the device with which the proposed method is carried out.

I Device, contains a heat exchanger 1, 4, a section of pasteurization with film electric heating elements 2, a programmable computing control device 3, to the input of which Temperature sensor 4 is connected and Product flow sensor 5, received processing, product pressure sensor 6 at the entrance to the pasteurization section, sensors 7 and 8 of the power and temperature of the film electric heating elements and sensor 9 of the pasteurization temperature, and the output are connected With an actuator JO the change in power of the film is electro-heated "Elements.

I In a programmable computational control device 3 (microprocessor controller), a sensor interrogation unit and 1 | Primary processing of the results of measurements are implemented in software, a control unit for generating control ijero action directed to the "compensation of measured disturbances, pi-temperature regulator, pasteurization section, the unit for calculating the optimal settings of the controller and the set value of the asterisation temperature n,

The product is pumped (not shown) to the recovery section 1 and is fed to the final heating to the pasteurization section with film electric heating elements 2. At the same time, the product flow rate provided by the installation pump is changed according to the change in the milking supply line -.

Signals from sensors 4-9, proportional to the measured parameters, temperature and consumption of the product entering the treatment, product pressure at the entrance to the pasteurization section, power

the temperature and temperature of the film electric heating elements, the pasteurization temperature, is fed to the input of the programmable computing control device 3. The function according to the program based on the results of pressure measurement at the entrance to the pasteurization section and the product consumption is determined by the speed of the product in the pasteurization section atsii.

The speed of the product in the channels of the pasteurization section is determined as follows.

Pressure loss is found in the heat exchanger on the cooled side in accordance with the Darcy-Weisbach equation

R

ek

1p

pWp

(one)

3k6. rivers

1 - length of the heat exchanger channels;.

pek resistance coefficient, which can be determined according to the expression

About, Guards Ursk ArRf. ,

. (2)

where A is the coefficient determined by the type of heat exchanger heat exchanger plates (for example, for plates 11.2).

e reka treynolds test

R

WP d eq. fe

(3)

- equivalent diameter

heat exchanger channel; - coefficient of kinematic viscosity of the product;

- product speed in the channels of the heat exchanger; W p in turn ovidrazheni

W

R

I- hp- hp

(four)

D is the mass flow rate of the product;

f is the specific gravity of the product;

BP is the width of the recuperator channels;

hp - plate gap in the recuperator.

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Subtracting from the measured pressure at the inlet to the pasteurization section the calculated value of the pressure loss in the recuperator on the cooled side, we obtain the value of the pressure loss in the channels of the pasteurization section.

Thus, for the channels of the pasteurization section, the following system of equations can be written

ten

.

pWn ... 2

D W. f BP-LP,

(6)

where hf, is the interplate gap in the pasteurization section; BP is the width of the channels of the pasteurization section. It takes into account that dgNB.n 2hp.

Solving the system of equations (5) and (6), we can obtain an expression for determining the speed of the product in the channels of the pasteurization section,

W, 4D Pn. 1/3

P V 1 p in

Vo l gp

The coefficient of friction is found in accordance with expression (2). The value of the Reynolds criterion is determined by the ratio

R

2D

er

f-b.

which is obtained by jointly solving the system of equations

Ren

Wn- 2hn

Wh

D P Bp- Ь „

(9)

Using relations (7) and (8), 45 as well as the criterial equation

N, K-. -p ;;, (Pc / Pcct) (10)

determine the heat transfer coefficient

A - NM / 114

d .-, (II)

 eq

- equivalent channel diameter, - product thermal conductivity; - constant depending on

plate type recuperator.

9

For the elementary section of the channel of the pasteurization section, the ratio

PEN

 V + q (+ R ,,),

t g

(12)

)

ten

15

20

25

about 35

40

45

50

;

.

55

where is the temperature of the film electric heating element; V - product temperature in

considered section; q is the specific heat flux (for our case it is equal to the specific surface of the power of the film-electric heating elements);

R is the total thermal resistance of heat transfer from the film electric heating element to the product.

From relation (12), using the measured power values of the film electric heating elements (q), their temperature (V), product temperature (V), as well as the calculated value of the heat transfer coefficient (o ()), the total thermal resistance of heat transfer is determined RT.

Subtract from K 2; the known value of the thermal resistance of the heat exchanger plate, is the thermal resistance of the relations on the heat transfer surfaces of the pasteurization section ..

The measured values of the parameters affecting the pasteurization effect of the installation, namely the product temperature at the entrance to the recovery section (V), product flow rate (D), product speed (W), determine the set value of the pasteurization temperature Vf. pasteurization effect, installation (P; 1). The calculated pasteurization temperature value V is introduced into the setting unit in the pasteurization temperature controller. The regulator, ensuring the stabilization of the given value of V, ensures the stabilization of the necessary pasteurization effect of the apparatus, i.e. P d 1.

In the case of changes in any of the parameters V,., D and W, device 3, a new value of the pasteurization temperature is determined, which is

the changed conditions provides the specified value of the pasteurization E: the effect of the installation. It is introduced into the pasteurization temperature controller, as a new setpoint of the specified value Vf ,.

The temperature of pasteurization,

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This effect can be determined from the following system of equations:

+ P

"fast

(13)

The equations for determining the pasteurization effect of the pasteurization and recovery sections are finalized as follows;

"Pastes

1 | de In

 Vv

Vo

r1

a, b dpina pasteurization section recovery factor; product temperature at the inlet to the recovery section;

product temperature at the entrance to the pasteurization section;

product temperature in the first section of the pasteurization section;

constants determined by the quality of raw milk (the type of inhibited microorganisms).

Analysis of expressions (14) and (15) allows us to conclude that the pasteurization effect of the installations depends on the values of the constant a and b, the jTHBHbix structure of the parameters 1p, BP, hp, Ip and. Is determined by the mode parameters 1. Wn, Vx, Vfl, VP, V; and Wherein

V and E pair p x p f p should be noted that Vp, y

determined by measurable

meters: D, VjK and V „. . Finally, we find that the pasteurization effect, the settings estimated by the Pasteur criterion, are determined by the following parameters: V V, D and Wn, i.e.

P “f (V ,, V ,, D, Wp).

From equations (lA) and (15), under the condition of ensuring the application of a digital computer and conducting a numerical factorial experiment, a simplified relationship V p back V

n ass

f CD, V ,, w,)

This dependency is implemented by the superficial supervisory device.

V - V

 rt rt

-V

(15)

For example, for an on-line pasteurization unit with an EPU-1 film heater, a dependency from which it is possible to determine a given pasteurization temperature, which ensures a specified pasteurization, the effective effect of treating milk on cows of patients with tuberculosis S has the following vi, c;

 85.5

+ 18 // D 16, ID

one

2.45 10-H,

+1.12 Wn / D

E

0

five

0

The relative error of determining the Vn distance is relative, while not exceeding 2%.

Thus, under the conditions when, with varying parameters D, Vj, Wf,, the specified pasteurization temperature value always corresponds to the specified pasteurization effect, the accuracy of its stabilization is entirely determined by the dynamic toughness of the pasteurization temperature controller (control quality),

In order to improve the quality of regulation, taking into account that the dynamic characteristics of the pasteurization unit depend on the consumption of the product, its speed in the channels of the pasteurization section and the amount of deposits on the heat release surfaces (thermal resistance), it is proposed to adjust the settings of the controller, ensuring their optimal value depending on the specified values.

On the signal of the mismatch between with the obtained set point. The temperature VPI .j, pasteurization and its iz-. the measured current value of V "the PI controller produces a control effect on the change in film power

electric heating elements, which, summing up with the control action produced by the disturbance compensation unit, goes to the actuator 10.

Thus, the proposed automatic control method ensures high accuracy of maintaining the pasteurization mode under conditions of varying productivity and accumulation of deposits. On heat transfer surfaces, which improves the quality of processing, eliminating underheating, or overheating of the product, reduces the intensity of pre-formation, improves the taste of the product.

In addition, the operation of the plant, with varying flow rates in the mode of maintaining a given pasteurization effect, allows one to have minimal energy consumption for the process.

Claims (1)

Invention Formula I Method for automatic control of the pasteurization process of milk in the stream in installations with film electric heating elements, including measuring the flow rate and temperature of the incoming milk, pasteurization temperature and adjusting the set pasteurization temperature with compensation of disturbing influences from the specified parameters by changing the heat load of the pasteurization section and so that with the aim of maintaining the accuracy of pasteurization effect, measure the pressure of milk at the entrance to the pasteurization section, the power and temperature of the film electric heating elements, determine the speed of milk in the pasteurization section, based on the results of measuring pressure and milk consumption, the heat transfer coefficient is calculated taking into account the speed of milk, the thermal resistance of protein proteins is calculated. deposits on the heat transfer surfaces of the pasteurization section, depending on the milk speed, power and temperature of the film heating elements, determine this pasteurization temperature taking into account the speed of the milk, its consumption to the temperature of the incoming milk, and correct the specified pasteurization temperature at the provision of a given pasteurization effect. .- r / ff f} ffftffffffrffi ffffff: f7f,