RU2294833C1 - Method of automatic control of extruder - Google Patents

Abstract

FIELD: grain processing.

SUBSTANCE: method comprises supplying extrudate downstream of the matrix to the vacuum chamber, measuring temperature and pressure of the material upstream of the matrix, flow rate and humidity of the raw material, flow rate of the cooling agent, and power of the extruder to be controlled. The flow rate and humidity of the extrudate at the exit of the vacuum chamber, pressure of the fluid in the vacuum chamber, ratio of pressure in the zone upstream of the matrix of the extruder and in the vacuum chamber, temperature and flow rate of the fluid evaporated from the extruder, and temperature of dried air and cooling water are also measured. Upstream of the extruder the initial raw material is heated by means of the steam-air mixture in the heat and mass exchanger. The steam-air mixture is first heated in the condenser of the cooling machine, is supplied to the heat and mass exchanger, and then is returned to the condenser of the cooling machine to cause the mixture to circulate between the heat and mass exchanger, condenser of the cooling machine, and the heat and mass exchanger.

EFFECT: improved method.

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Description

The invention relates to the grain processing industry, namely, to the automation of processes for producing extruded animal feed, and can be used in devices for the production of food concentrates, as well as in other industries using extrusion.

A known method of automatic control of the extruder, comprising feeding the extrudate after the matrix into the vacuum chamber, as well as measuring the temperature and pressure of the material in the pre-primary zone, the flow rate and humidity of the raw material, the flow rate of the cooling agent, the power of the adjustable drive of the extruder, measuring the flow rate and humidity of the extrudate at the outlet of the vacuum -chambers, pressure of the medium in the vacuum chamber, pressure ratios in the prematrix zone of the extruder and the vacuum chamber, temperature and flow rate of moisture evaporated from the extrudate, drying temperature air and cooling water with an impact on the rotational speed of the screw of the extruder, the costs of the cooling agent and raw materials, the power of the vacuum pump drive and the switching of the evaporator sections of the chiller from the condensation mode to the regeneration mode based on the current value of the heat transfer coefficient from the evaporated moisture to the refrigerant [RF Patent No. 2168413, IPC ⁶ B 29 C 47/92, declared 06/22/2000, publ. 06/10/2001, bull. No. 16].

The disadvantage of this device is the inability to carry out the extrusion process at temperatures below the temperature of inactivation of thermolabile substances contained in the feedstock.

An object of the invention is to improve the quality of the finished product by improving the scheme of automatic control and regulation of the process of extrusion of feed.

The problem is achieved in that in the proposed method for the automatic control of the extruder, which provides for the extrudate to be fed into the vacuum chamber after the die, measuring the temperature and pressure of the material in the pre-matrix zone, flow rate and humidity of the raw material, flow rate of the cooling agent, power of the adjustable extruder drive, measuring flow and humidity extrudate at the outlet of the vacuum chamber, the pressure of the medium in the vacuum chamber, the ratio of the pressures in the prematrix zone of the extruder and the vacuum chamber, the temperature and flow rate evaporated from the moisture extrudate, the temperature of the dried air and cooling water with an impact on the rotational speed of the screw of the extruder, the costs of the cooling agent and raw materials, the power of the vacuum pump drive and the switching of the evaporator sections of the chiller from the condensation mode to the regeneration mode based on the current value of the heat transfer coefficient from the evaporated moisture to the refrigerant, new is that they use a heat and mass exchanger for preliminary heat treatment of raw materials with a steam-air mixture, which is first heated in a condenser e of the refrigeration machine, then fed to the heat and mass exchanger, and then returned to the condenser of the refrigeration machine with the formation of the recirculation circuit of the steam-air mixture "heat and mass exchanger - condenser of the refrigeration machine - heat and mass exchanger", the spent steam-air mixture is partially discharged and the steam-air mixture is fed with saturated steam, and temperature, humidity are additionally measured the flow rate of the vapor-air mixture; carry out stabilization of the temperature and humidity of the raw materials before extrusion by influencing the temperature and moisture content of the steam-air mixture supplied to heat treatment of the raw materials, and the temperature of the steam-air mixture is affected in the condenser of the refrigerating machine by means of recuperative heat and mass transfer due to the heat of the refrigerant condensate by changing the compressor drive power of the refrigerating machine, and the effect on the moisture content of the vapor-air mixture is carried out by changing the ratio Flow rate of spent steam mixture and the saturated vapor in the recirculation loop.

The technical result is to improve the quality of the finished product by improving the scheme of automatic control and regulation of the process of extrusion of feed.

The drawing shows a diagram of the implementation of the proposed method.

The circuit includes an extruder 1 with a forming head 2 and a jacket 3, an adjustable extruder drive 4, a vacuum chamber 5 with a lock gate 6 and a 2-section evaporator of the refrigeration machine 7, a vacuum pump 8, a compressor of the refrigeration machine 9, a cooling water pump 10, a heat and mass exchanger 11, fan 12, condenser 13, lines: 2.1 supply of feedstock, 2.2 discharge of extrudate, 2.3 discharge of vapors from the vacuum chamber, 4.6 supply of refrigerant to a sectional evaporator, 4.7 discharge of spent refrigerant; cooling water circulation circuit 1.2, feedstock and extrudate flow sensors 14, 15, respectively, feedstock moisture sensors 16, 17, 18 before processing in a steamer, after treatment in a steamer and extrudate, respectively, feedstock temperature sensors 19, 20 before treatment in a heat and mass exchanger and after it, the sensor 21 of the material temperature in the prematrix zone of the extruder, the sensor 22 of the vapor pressure in the vacuum chamber, the sensor 23 of the material pressure in the prematrix zone of the extruder, the sensor 24 of the temperature of the exhaust vapor from um chambers and the temperature sensor 25 of the dried air after the evaporator, the sensor 26 of the flow rate of exhaust vapors from the vacuum chamber, the temperature sensor 27 of the cooling water, the sensor 28 of the flow of cooling water, the sensor 29 of the refrigerant flow, the sensor 30 of the refrigerant temperature, the sensor 31 of the power consumption of the adjustable drive extruder, sensor 32 of the power consumption of the compressor of the refrigeration machine, sensor 33 of the power consumption of the vacuum pump, sensor 34 of the power consumption of the cooling water pump, sensor 35 of the power consumption of the fan, sensor 36 temperature of the steam-air mixture, sensor 37 for humidity of the steam-air mixture, sensor 38 for the flow of steam-air mixture, switching unit 39, microprocessor 40, actuators 41-53, feedstock dispenser 61, on / off switches 55-60 (a, b, c, d, d , f, f, s, and, k, l, m, n, o, p, p, s, t - input control channels, y, f, x, c, h, w - output control channels).

The method is as follows.

According to the information of the sensors 14, 19, 16 in line 2.1 about the current values of the flow rate, humidity, temperature, the microprocessor 40 determines the actual flow of moisture and heat supplied with the feedstock for extrusion, depending on which it sets the mode of preliminary heat treatment of the feedstock in the heat and mass transfer with a steam-air mixture which is first heated in the condenser of the chiller 13, then fed to the heat and mass exchanger 11, and then returned to the condenser of the chiller 13 with the formation of a vapor recirculation loop zdushnoy mixture "teplomassoobmennik - condenser chiller - teplomassoobmennik". In the process of heat treatment of the feedstock with a steam-air mixture, it is moistened, the moisture is evenly distributed throughout the volume, the starch grains swell and the product temperature increases. Information about the readiness of raw materials for extrusion by sensors 17, 20 is continuously supplied to the microprocessor 40, which generates signals of deviation of the current values of temperature and humidity from the set values. When the moisture content of the feedstock deviates from the pre-extrusion value from the set value upward, the microprocessor 40 reduces the steam flow rate in the steam-air mixture feed line by means of an actuator 41, and when the moisture content of the feedstock deviates downward, the flow rate of saturated steam is increased. The temperature stabilization of the initial product is ensured by influencing the temperature of the steam-air mixture at the inlet to the heat and mass exchanger 11, while the temperature of the steam-air mixture changes in the condenser of the refrigeration machine due to the recuperative heat and mass transfer between the steam-air mixture and the refrigerant through the heat exchange surface of the compressor. The heat transfer rate is achieved by adjusting the compressor drive power of the refrigeration machine 9, and therefore, the refrigerant flow rate in the condenser, which directly affects the process of refrigerant condensation in the condenser and the amount of heat transferred to the refrigerant condensation to heat the vapor-air mixture. The performance of the extruder 1 is set by affecting the power of the adjustable drive 4 by means of an actuator 43. In this case, the microprocessor sets and constantly maintains a predetermined thermal regime in the pre-extruder zone 1 by affecting the flow of cooling water through the actuator 44 of the adjustable drive of pump 10. The temperature of the extrudable product, measured by the sensor 21 is a limitation on the developed product pressure in the pre-mold zone of the extruder. According to the current values of flow rate, humidity of the feedstock and extrudate, measured by sensors 17, 20, 15, 18, respectively, the microprocessor 40 calculates the amount of moisture evaporated in the vacuum chamber from the extrudate as a result of its structure formation, depending on which it determines the flow rate of the refrigerant using the executive mechanism 49 of the adjustable drive of the compressor of the refrigeration machine. The evaporated moisture in the vacuum chamber condenses in a 2-section evaporator 7 of the refrigeration machine, and the evaporator sections alternately operate in condensation and regeneration modes.

The process of condensation of moisture contained in the vapors leaving the product is accompanied by the formation of a “snow coat” on the cooling element of the evaporator, which leads to a decrease in the heat transfer coefficient from the refrigerant to the vapor through the wall of the cooling element when the thickness of the “snow coat” increases along the extrusion process and, as consequence, reduces the rate of drainage of water vapor discharged from the vacuum chamber. According to the sensors 24, 25, 26, 30, the microprocessor continuously calculates the current value of the heat transfer coefficient by the formula:

where Q = Vc _ca ρ _ca (t ₁ -t ₂ ) is the amount of heat supplied by the vapor to the evaporator-condenser of the refrigeration machine, kJ / h; V is the volumetric flow rate of vapor, m ³ / h; c _ca , ρ _ca , - average values of heat capacity, kJ / kg · K, density, kg / m ³ , vapor; F is the surface area of the cooling element of the evaporator-condenser section, m ² ;

- logarithmic temperature head, ° С; t ₁ , t ₂ - temperature, respectively, at the inlet and outlet of the evaporator, ° C; t ₃ - temperature of the refrigerant at the inlet to the evaporator, ° C; and generates a signal for deviating the current value of the heat transfer coefficient from the specified range of values, by which it corrects the refrigerant flow by affecting the drive power of the compressor 9 using the actuator 49. If the increase in the flow of refrigerant does not allow the current value of the heat transfer coefficient to be brought out to the specified value range, then the microprocessor disables the working section of the evaporator-condenser for regeneration and connects to the work section, working in regeneration mode.

The spent cooling water is discharged from the extruder body and sent to the regeneration of the evaporator-condenser section, where during the thawing process of the "snow coat" the water is cooled to the required temperature and again fed to the cooling of the extruder body. Thus, the cooling water is circulated in a closed cycle "extruder body - refrigeration machine evaporator regeneration section". At the time of the start of operation of the extruder, water may have an elevated temperature to heat it up and enter the operating mode.

Let us consider a method for automatically controlling the extrusion process using an example of an extruder of the KMZ-2U brand equipped with an adjustable drive installed at Maksatikhinsky feed mill OJSC, used for the production of feed mill products. The process is carried out with the following technical characteristics:

- extrudate productivity, kg / h 270 ... 450 - humidity of the feedstock,% 15 ... 17 - screw rotation speed, rpm 340 ... 380 - operating mode of the extruder autogenous - residual pressure in the vacuum chamber, Pa 10 ... 25 - temperature of cooling water at the inlet to the cooling jacket of the extruder, ° C 8 ... 15 - flow rate of cooling water, m ³ / h 4 ... 14 - surface area of the section of the evaporator-condenser of the refrigeration machine, m ² 8 - refrigerant (freon 22) R 22 - refrigerant consumption, kg / s 0.35 ... 0.58

After the extruder reaches the operating mode, the feed rate is 300.8 kg / h and the humidity is 16%; these values set the screw rotation speed to 360 rpm. The final moisture content of the extrudate is 5 ... 6%. Also, the cooling water flow rate in the circulation circuit 1.2, for example, 5 m ³ / h, is set to maintain the temperature in the pre-extruder zone of the extruder not more than the temperature of inactivation of thermolabile nutrients contained in the raw material, for example 100 ° C.

A residual pressure of 15 Pa is set in the vacuum chamber. In the event of a change in the composition of the feedstock, as well as possible random disturbances, the amount of vaporized vapor in the vacuum chamber will change, in accordance with which the operation of the vacuum pump is adjusted.

Set the flow rate of the refrigerant to 0.45 kg / s and adjust it depending on the amount of evaporated moisture in the vacuum chamber within the specified limits. To obtain dried air with a given moisture content, for example, 0.003 ... 0.005 kg / kg, the microprocessor continuously calculates the heat transfer coefficient from the refrigerant to the vapor removed from the vacuum chamber through the wall of the evaporator cooling element and the layer of “snow coat” formed as a result of moisture loss from air, and compares it with a given range of values, for example 5.8 ... 8.0 W / (m ² K).

If the current value of the heat transfer coefficient corresponds to a predetermined range of values, then the microprocessor 30 does not affect the power of the controlled drive of the compressor 9. If the current value of the coefficient of heat transfer is less than the specified interval of values, the microprocessor adjusts the task to the actuator 41 to increase the refrigerant flow in line 4.6 by increasing the refrigerating capacity refrigeration machine. If the increase in refrigerating capacity does not allow to bring the current value of the heat transfer coefficient to the interval of the set values, then the microprocessor 30 using the switching unit 29 switches the working section of the evaporator to regeneration and connects the backup.

Thus, the proposed method for automatic control of the extruder in comparison with the base has the following advantages:

- allows you to get a finished product of high quality by optimizing the temperature due to stabilization of the temperature of the finished product in the pre-matrix area;

- to provide higher accuracy of maintaining technological parameters and greater reliability of the system for automatic control of the extrusion process;

- stabilize the temperature at the minimum acceptable level in the prematrix zone of the extruder;

- rational use of secondary energy resources and, as a result, improve the quality of the extrudate obtained with additives of thermolabile nutrients and reduce specific energy consumption.

Claims (1)

A method of automatic control of the extruder, comprising feeding the extrudate after the matrix into the vacuum chamber, as well as measuring the temperature and pressure of the material in the pre-matrix zone, the flow rate and humidity of the raw material, the flow rate of the cooling agent, the power of the adjustable extruder drive, the flow rate and humidity of the extrudate at the outlet of the vacuum chamber, the pressure of the medium in the vacuum chamber, the ratio of pressures in the prematrix zone of the extruder and the vacuum chamber, the temperature and flow of moisture evaporated from the extrudate, the temperature of the dried air and cooling water with an impact on the rotational speed of the screw of the extruder, the costs of the cooling agent and raw materials, the power of the vacuum pump and switching the sections of the evaporator of the chiller from the condensation mode to the regeneration mode according to the current value of the heat transfer coefficient from the evaporated moisture to the refrigerant, characterized in that before supplying the feedstock to the extruder, it is subjected to preliminary heat treatment with a steam-air mixture, for which a heat and mass exchanger is used, the steam-air mixture is first heated they are fed into the condenser of the refrigerating machine, then fed to the heat and mass exchanger, and then returned to the condenser of the refrigerating machine with the formation of the recirculation circuit of the steam-air mixture “heat and mass exchanger - condenser of the refrigerating machine - heat and mass exchanger”, the spent steam-air mixture is partially discharged and the steam-air mixture is fed with saturated steam, and the temperature is additionally measured , humidity, flow rate of steam-air mixture, stabilize the temperature and humidity of the raw materials before extruding the temperature and the moisture content of the steam-air mixture supplied to the heat treatment of the raw materials, and the temperature of the steam-air mixture is affected in the condenser of the refrigerating machine through recuperative heat and mass transfer due to the heat of the refrigerant condensate by changing the drive power of the compressor of the refrigerating machine, and the effect on the moisture content of the steam-air mixture is carried out by changing the ratio of the costs of the exhaust steam-air mixture and saturated steam in the recirculation circuit.