JP5416375B2 - Drying method and drying apparatus - Google Patents

Description

  The present invention relates to a drying method and a drying apparatus in which a heat pump device is applied to drying resin, wood, food, clothing, etc., and COP of the heat pump device is maximized to enable energy efficient operation.

A heat pump device using CO ₂ as a refrigerant is widely used as a water heater because it has the property of efficiently performing high-temperature heating by operating in a supercritical state where the discharge pressure of the compressor is higher than the critical pressure. doing. The CO ₂ water heater can produce high-temperature water at 90 to 95 ° C. using a gas cooler (heater) that exchanges heat with supercritical gas of high-temperature and high-pressure CO ₂ refrigerant. The gas cooler can be a finned tube heat exchanger, and the outside air can be heated to 100 ° C. or higher by exchanging heat with air. This high-temperature heated air is promising for drying resin, wood, food, clothing and the like.

Patent Document 1 (Japanese Patent Application Laid-Open No. 2007-192464) discloses a wood drying system in which a heat pump device using CO ₂ as a refrigerant is applied to drying of wood to reduce energy consumption and improve thermal efficiency. ing. This drying system cools and dehumidifies the air in the drying chamber with CO ₂ refrigerant in the evaporation process of the heat pump device, pressurizes the CO ₂ refrigerant to a supercritical pressure, and converts the retained heat of the CO ₂ refrigerant into the air in the drying chamber. As a heat source for the air heater to be heated, air that has been cooled and dehumidified by the air heater is heated, so that drying air can be efficiently manufactured.

Patent Document 2 (Japanese Patent Application Laid-Open No. 2007-303756) discloses a drying system in which a heat pump device using CO ₂ as a refrigerant is applied to drying clothes and the like. In this drying system, a part of the CO ₂ refrigerant flowing into a heater (gas cooler) for heating the drying air is branched at a flow rate corresponding to a necessary heat release amount upstream of the heater, and the branched CO ₂ refrigerant is discharged to the outside air. The temperature of the drying air supplied to the drying chamber can be accurately controlled by radiating heat to the drying chamber.

  In the heat pump type water heater, the temperature of the water supply to the heat pump device varies from 7 ° C. (winter) to 25 ° C. (summer) depending on the season. However, there is little fluctuation in the time of day. The temperature of the hot water from the heat pump device is 65 to 90 ° C., and the hot water is temporarily stored in a hot water storage tank before use. The hot water temperature is controlled mainly by adjusting the feed pump with an inverter. The heat source of the heat pump device is outside air, and there is little fluctuation in the time zone of the day.

  On the other hand, when the heat pump device is applied to a drying device, the supply air to the heat pump device is outside air or exhaust from a drying chamber, or a mixture of outside air and exhaust, and the supply air temperature is about 0 ° C. (outside air) to It covers a range of about 70 ° C. (a mixture of exhaust air from the drying chamber and outside air). The temperature of the supply air to the dryer is in a wide temperature range according to the specifications of the dryer, and the preheating period in the drying process and the drying rate during which the drying rate decreases with the moisture content decrease the supply temperature to the dryer. It is necessary to change the air temperature. That is, as the moisture evaporates from the object in the reduced rate drying, the water vapor partial pressure decreases. Therefore, in order to promote evaporation, it is necessary to raise the drying temperature. Therefore, the temperature of the hot air supplied from the heat pump device to the drying chamber has a wide temperature range of 40 to 120 ° C. depending on the object to be dried and the drying process, and it is required to control the hot air temperature in real time.

The temperature control of the hot air supplied to the drying chamber is performed by controlling the number of refrigerant circulations by controlling the number of revolutions of the compressor of the heat pump device under the condition of a constant amount of hot air. The heat source of the heat pump device is the outside air or the exhaust of the drying chamber, and these temperatures vary widely over a wide range of 0 to 100 ° C. or more.
As described above, the operating conditions required for the drying apparatus are wider than those of the hot water heater and are often operated under large fluctuation conditions. Therefore, it is necessary to operate the heat pump device efficiently under a wide range of operating conditions.

On the other hand, as a heat pump device for obtaining heated air of 100 ° C. or higher, a heat pump device that uses CO ₂ as a refrigerant and operates in a supercritical state where the compressor discharge pressure is higher than the critical pressure is suitable. It is used.

JP 2007-192464 A JP 2007-303756 A

In order to operate the heat pump device efficiently, it is necessary to control the discharge pressure of the compressor according to the operation state. FIG. 7 shows a Mollier diagram of a heat pump apparatus using CO ₂ as a refrigerant. In FIG. 7, α and β indicate examples of heat pump cycles in which the gas cooler (heater) outlet temperature is the same 50 ° C. and the discharge pressure of the compressor is different. The lengths α ₁ and β ₁ of the horizontal line of the discharge pressure of the compressor indicate the specific enthalpy difference (kJ / kg) of heating by the gas cooler, and when this is multiplied by the refrigerant circulation rate (kg / s), the heating amount (kW )

Moreover, the diagonally upward line on the right side represents the compression work by the compressor. When the specific enthalpy differences α ₂ and β ₂ are multiplied by the refrigerant circulation amount, the power (kW) of the compressor is obtained. As can be seen from FIG. 7, by changing the discharge pressure of the compressor to the high pressure side (from the cycle α to the cycle β side), the heating amount of the heat pump device increases and the power of the compressor also increases. The ratio between the amount of heating and the power of the compressor is the COP in heating. In the COP, in the region where the pressure is higher than the critical point k, the isothermal line l is irregularly inclined, so that there exists an optimum value of the compressor discharge pressure at which the COP becomes maximum according to the outlet temperature of the gas cooler.

  The optimum value of the discharge pressure varies depending on the suction pressure of the compressor and the degree of superheat of the suction gas. In the case of a heat pump water heater, the factors that affect this optimum value are the feed water temperature to the gas cooler, the tapping temperature from the gas cooler, the feed water flow rate, and the outside air temperature. As a function of

On the other hand, in the case of a heat pump dryer, the supply temperature to the gas cooler, the air temperature at the outlet of the gas cooler, the air volume, the exhaust temperature of the drying chamber (drying load), the outside air temperature, and the amount of refrigerant circulation. It is necessary to determine the optimum discharge pressure value as a function.
Further, it is necessary to change the number of rows / stages and dimensions of the tubes of the heat exchanger used as the gas cooler in accordance with the processing air volume and the heating temperature by the gas cooler, and it is necessary to change the function when the shape of the heat exchanger changes.

  Thus, in the case of a heat pump dryer, there are many variables and the structure and shape of the heat exchanger used as a gas cooler to derive the optimum compressor discharge pressure that maximizes COP as a function of the parameters. It is necessary to derive a function that depends on. Therefore, it is difficult to derive an optimum discharge pressure value as a function of the parameter.

  In view of the problems of the prior art, the present invention can obtain the compressor discharge pressure that maximizes the COP in the heat pump type drying apparatus while operating, and is always highly efficient corresponding to the operating state of the drying apparatus. The purpose is to enable safe operation.

In order to achieve the above object, the drying method of the present invention comprises:
Using a heat pump device that operates using CO ₂ as a refrigerant and a compressor discharge pressure in a supercritical state equal to or higher than the critical pressure, heat the outside air or reheat the exhaust in the drying chamber to produce heated air. In a drying method for supplying to a drying chamber and drying an object to be dried in the drying chamber,
A first step of setting an initial set value of the compressor discharge pressure based on a set temperature of the heated air supplied to the drying chamber within a range of an allowable upper limit value of the compressor discharge pressure;
The heat pump device is operated so as to be the initial set value, and the suction pressure and suction temperature of the compressor, the discharge pressure and discharge temperature of the compressor, and the refrigerant temperature at the outlet of the gas cooler are measured. A second step of calculating a COP at an initial set value;
A third step of setting at least one compressor discharge pressure different from the initial set value in the manner of the first step, and calculating a COP at the one point from the measured value in the manner of the second step;
A fourth step of obtaining a discharge pressure at which COP is maximized from the initial set value and the COP calculation value at the one point, and setting the discharge pressure as a new set value;
Set at least two compressor discharge pressures different from the initial set value in the third step, calculate the COP at the two points from the measured value in the manner of the second step,
Seeking a quadratic curve passing through the initial setting value and the 2-point, the differential value of the quadratic curve is to the second step with a new discharge pressure setpoint points becomes zero as a point where COP becomes maximal first By repeating the four steps, the heat pump device can be operated at a discharge pressure at which the COP is always maximized in response to changes in the operating state.

In the method of the present invention, first, in the first step, an initial set value of the compressor discharge pressure is set based on the set temperature of the heated air supplied to the drying chamber. In this case, the initial set value does not exceed the allowable upper limit value. The allowable upper limit value is calculated so that the discharge pressure and discharge temperature of the compressor do not exceed the design allowable values.
Next, in the second step, the heat pump apparatus is operated by adjusting the discharge pressure to the initial setting value, and the COP at the initial setting value is calculated from the measured values.

Next, in the third step, at least one discharge pressure in the vicinity of the initial set value is selected as in the first step, and the one point COP is calculated in the second step. In the fourth step, the discharge pressure at which the COP is maximized is obtained from these two COPs including the initial set value, and the discharge pressure is set as a new set value.
This calculation method sets at least two compressor discharge pressures different from the initial set values in the third step, calculates the COP at the two points from the measured values in the manner of the second step, and A quadratic curve passing through the initial set value and the two points is obtained, and a point at which the differential value of the quadratic curve becomes zero is set as a new discharge pressure set value as a point at which the COP becomes maximum.
As a result, the discharge pressure that maximizes the COP can be obtained quickly and efficiently.

  By repeating the second to fourth steps while operating the heat pump device, it is possible to obtain the discharge pressure at which the COP is maximized in real time in response to changes in the operating state of the heat pump device. As a result, even if the structure and shape of the heat exchanger used as the heater or the operating conditions of the heat pump device change, the heat pump device can always be operated with the highest COP.

In the method of the present invention, CO ₂ is used as the refrigerant of the heat pump device, and the heat pump device can be heated to 100 ° C. or higher by operating the heat pump device in a supercritical state where the compressor discharge pressure is higher than the critical pressure. .

  In the method of the present invention, the compressor discharge pressure may be controlled by controlling the rotation speed of the compressor or the refrigerant circulation amount in the refrigerant circuit. As a result, the discharge pressure can be easily and accurately controlled. Conventionally known means may be used as means for controlling the refrigerant circulation amount. For example, by interposing a receiver in the refrigerant circulation path and adjusting the refrigerant circulation amount in the receiver, the refrigerant circulation amount in the refrigerant circulation path is controlled. Alternatively, there is a means for providing a supercritical refrigerant tank in which the temperature of the refrigerant is maintained at a critical temperature or higher by a heater in the refrigerant circulation path, and taking the refrigerant into and out of the refrigerant circulation path from the supercritical refrigerant tank.

Next, the drying apparatus of the present invention that can be used directly for carrying out the method of the present invention is:
Using a heat pump device that operates using CO ₂ as a refrigerant and a compressor discharge pressure in a supercritical state equal to or higher than the critical pressure, heat the outside air or reheat the exhaust in the drying chamber to produce heated air. In a drying apparatus that is supplied to a drying chamber and dries a material to be dried in the drying chamber,
A compressor that is provided in the refrigerant circulation path and compresses the refrigerant, a gas cooler that heats the outside air with the retained heat of the refrigerant or reheats the exhaust of the drying chamber to generate heated air, an expansion valve that decompresses the refrigerant, and a refrigerant An evaporator to evaporate,
A drying chamber for introducing heated air to dry the object to be dried, and a heating air supply path for supplying heated air heated by a gas cooler to the drying chamber;
A plurality of sensors for measuring the suction pressure and suction temperature of the compressor, the discharge pressure and discharge temperature of the compressor, and the refrigerant temperature at the condenser outlet;
An initial set value of the compressor discharge pressure is set based on the set temperature of the heated air supplied to the drying chamber, the operation of the heat pump device is controlled to be the initial set value, and the measured values of the plurality of sensors are set. Input, calculate the initial set value and COP at at least one discharge pressure different from the initial set value, obtain a discharge pressure at which the calculated COP value is maximum from these COPs, and set the discharge pressure to be the same A controller for operating the heat pump device and setting the discharge pressure to a new set value,
The controller sets at least two compressor discharge pressures different from the initial set values, calculates the COP at the two points from the measured values from the plurality of sensors,
A controller that obtains a quadratic curve that passes through the initial set value and the two points, and sets a point at which the differential value of the quadratic curve becomes zero as a new discharge pressure set value as a point at which the COP becomes maximum;
By repeating the process by the controller, the heat pump device can be operated at a discharge pressure at which the COP is always maximized in response to a change in the operating state.

In the device of the present invention, the controller sets the initial setting value of the discharge pressure, sets at least one discharge pressure in the vicinity of the initial setting value, calculates the COP at these two points, and sets the COP to the maximum. Using the value as a new set value, the discharge pressure is controlled to this new set value. By repeating this operation while operating the heat pump device, the heat pump device can always be operated with the highest COP in response to real time even if the operating conditions of the heat pump device change.
As a result, even if the structure and shape of the heat exchanger used as the heater or the operating conditions of the heat pump device change, the heat pump device can always be operated with the highest COP regardless of this.

According to the method of the present invention, at least two compressor discharge pressures different from the initial set values are set in the third step, and the COP at the two points is calculated from the measured values in the same manner as the second step. With
Seeking a quadratic curve passing through the initial setting value and the 2-point, the differential value of the quadratic curve is to the second step with a new discharge pressure setpoint points becomes zero as a point where COP becomes maximal first By repeating the four steps, the heat pump device can be operated at a discharge pressure at which the COP is always maximized in response to changes in the operating state.

  And by operating a heat pump apparatus with this discharge pressure, a heat pump apparatus can always be efficiently operated with the highest COP. Therefore, it is possible to always operate the heat pump apparatus with the highest COP without having to consider factors that affect the COP.

According to the apparatus of the present invention, by using the controller , the heat pump device can be operated at a discharge pressure at which the COP is always maximized in response to a change in the operation state. The compressor discharge pressure that maximizes the pressure can be obtained while operating, and the same effect as the method of the present invention can be obtained.

  Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in this embodiment are not intended to limit the scope of the present invention to that unless otherwise specified.

An embodiment in which the present invention is applied to a drying apparatus using a heat pump apparatus using CO ₂ as a refrigerant will be described with reference to FIGS. FIG. 1 is an overall configuration diagram of a drying apparatus 1 according to the present embodiment.
In FIG. 1, a drying device 1 includes a drying chamber 10 having a sealed space for drying an object to be dried d (for example, resin, wood, food, clothing, etc.), and a heat pump device that supplies heated air to the drying chamber 10. 20.

The heat pump device 20, the circulation path 21 CO ₂ refrigerant circulates (made from the high pressure portion 21a and the low-pressure section 21b), is rotated by a driving motor 22a, the CO ₂ refrigerant to a supercritical pressure above the critical point k A compressor 22 that compresses, a gas cooler 23 that heats the CO ₂ refrigerant that has been compressed into a high-pressure and high-temperature state with the outside air, heats the outside air, an expansion valve 24 that decompresses the high-pressure CO ₂ refrigerant, and an expansion valve 24 From the evaporator 25 that evaporates the CO ₂ refrigerant depressurized in step ₂ and removes the latent heat of evaporation from the exhaust discharged from the drying chamber 10 and cools it, and the CO ₂ refrigerant that goes out of the evaporator 25 toward the compressor 22 and the gas cooler 23. A heat exchanger 26 is provided for exchanging heat with the high-temperature CO ₂ refrigerant that has come out and preheating the CO ₂ refrigerant sucked into the compressor 22.

The drying chamber 10 is connected to a circulation path 11 for heating air to be used for drying the material to be dried d, and a fan 12 is interposed in the circulation path 11 so that the heated air passing through the drying chamber 10 and the circulation path 11 is supplied. A circulation flow is formed, and the material to be dried d is dried by this circulation flow. The outside air introduction path 13 is connected to the gas cooler 23, and the outside air a is introduced into the outside air introduction path 13 by the fan 14 interposed in the outside air introduction path 13 and supplied to the gas cooler 23. The outside air a is heated by exchanging heat with the CO ₂ refrigerant in the gas cooler 23 to become heated air, and then supplied to the circulation path 11 through the heated air supply path 15.

The exhaust e after having been used to dry the material to be dried d in the drying chamber 10 is introduced into the evaporator 25 through the exhaust path 16, and is cooled by heat exchange with the CO ₂ refrigerant in the evaporator 25. Thereafter, the exhaust e is exhausted through the exhaust path 17. A branch path 18 connected to the outside air introduction path 13 is connected to the exhaust path 17, and a damper 19 is provided on the branch path 18. In some cases, by opening the damper 19, a part of the exhaust e is supplied to the outside air introduction path 13 via the branch path 18.
Thus, by mixing the exhaust e with the outside air a, the temperature of the outside air a supplied to the gas cooler 23 can be adjusted over a wide range.

The heat pump device 20 is provided with a controller 30 that controls the operation of the heat pump device 20. Further, to measure the sensor 31 which measures the compressor suction pressure _{P 1} of the CO ₂ refrigerant, a sensor 32 for measuring the compressor suction temperature _{T 1} of the CO ₂ refrigerant, the compressor discharge pressure _{P 2} of the CO ₂ refrigerant sensor 33, a sensor 34 for measuring the compressor discharge temperature _{T 2} of the CO ₂ refrigerant, a sensor 35 for measuring the CO ₂ refrigerant temperature _{T 3} of the gas cooler outlet, a sensor 36 for measuring the heating air temperature _{T 4} of the gas cooler outlet Is provided.
The controller 30 controls the operation of the heat pump device 20 based on the measurement signals of these sensors.

Next, the configuration of the controller 30 will be described with reference to FIG. 2, the controller 30, the air temperature set point _{T S} of the gas cooler outlet, the compressor suction pressure measured value _{P 1} of the CO ₂ refrigerant by sensor 31, and the compressor suction of the CO ₂ refrigerant by the sensor 32 temperature measurement value _{T 1} based on a discharge pressure limit value calculation means 37 for calculating an upper limit value P _L of the compressor discharge pressure, discharge pressure of the initial set value P _S1 and initial setting value different from the two points of the compressor discharge pressure set value P A discharge pressure setting means 38 for setting _S2 and _PS3 ; a means 39 for calculating a COP value at the discharge pressure at these three points; a means 40 for determining a discharge pressure at which the COP is maximized from the three COPs; The memory 41 stores each measurement value and COP calculation value.

In this embodiment having such a configuration, the operation procedure of the drying apparatus 1 will be described based on the flowchart of FIG. 3, first the discharge pressure limit value calculation means 37 inputs the temperature set point T _S of the heated air supplied to the drying chamber 10 is heated by the gas cooler 23 (step 1). Next, each measured value of the sensors 31 to 36 is taken into the controller 30 (step 2).
Next, the discharge pressure upper limit value calculation means 37 calculates the compressor discharge pressure upper limit value P _L1 from the compressor discharge pressure measurement value P ₁ of the sensor 31 and the compressor discharge temperature measurement value T _{1 of the} sensor 32 ( Step 3). The upper limit value P _L1 is set so that the compressor discharge pressure / temperature of the CO ₂ refrigerant does not exceed the design allowable pressure / temperature.

Next, the automatic operation of the heat pump device 20 is confirmed (step 4). Next, the discharge pressure setting means 38 sets an initial set value P _S1 of the discharge pressure within the range of the discharge pressure upper limit value P _L1 with respect to the temperature set value T _S of the heated air (step 5). Then, the operation of the drying device 1 is started (step 6). Thereafter, the operation is continued while taking each measured value from each sensor 31 to 36 into the controller 30 as needed. This measurement value capture is performed at a constant time interval Δt.

After starting of the compressor 22, after a predetermined time (Delta] t ₁₎ has elapsed, the air temperature T ₄ of the gas cooler outlet does not reach the set value T _S, and if the compressor rotational speed is equal to or higher than the upper limit set value, the discharge The pressure initial set value _PS1 is changed (step 7). That is, the initial set value P _S1 is increased to, for example, (P _S1 + ΔP ₃ ). The compressor discharge pressure is changed by controlling the rotation speed of the drive motor 22a of the compressor 22 by the controller 30.
As another means, as described above, a receiver may be provided in the refrigerant circulation path, or a supercritical refrigerant tank may be provided in the refrigerant circulation path to change the refrigerant circulation amount.

Gas cooler or air temperature T ₄ at the outlet reaches the set value T _S, or when the compressor speed reaches the upper limit set value, the COP calculating section 39, the COP in the discharge pressure initially set value P _S1 Calculate (step 8).
That is, in FIG. 8, the suction pressure _{P 1} and the suction temperature _{T 1,} to calculate the intake enthalpy _{h s,} to calculate the discharge enthalpy _{h d} from the discharge pressure _{P 2} and the discharge temperature _{T 2,} the discharge pressure _{P 2} and the gas cooler outlet from the refrigerant temperature _{T 3,} to calculate the gas cooler outlet enthalpy _{h g.} From these values, the COP (COP ₁ ) at the discharge pressure initial set value P _S1 is calculated using a calculation formula (COP = (h _d −h _g ) / (h _d −h _s )). Then, it stores the discharge pressure setpoint _{P S1} and COP ₁ in the memory 41.

Considering the fluctuation of the discharge pressure (tolerance ± ΔP ₂ ), this procedure is repeated (about 10 times) to obtain data about 10 times of COP ₁ (step 9). Next, the average value of the data of COP ₁ is calculated (step 10). The number of data does not have to be 10, and the number of times that can ensure the accuracy is appropriately selected.
Next, each measurement value is taken into the controller 30 from the sensors 31 to 36, and real-time operation data of the heat pump device 20 is obtained (step 11). In the discharge pressure limit value calculation means 37, these operational data, in the same manner as in step 3, and calculates the compressor discharge pressure limit P _L2 (step 12).

Next, the discharge pressure calculation means 37 selects a discharge pressure set value P _S2 (for example, P _S2 = P _S1 + ΔP ₁ ) different from the initial set value P _S1 from the vicinity of the discharge pressure initial set value P _S1 (step _S1 ). 13). The set value P _S2 is within a range that does not exceed the upper limit value P _L2 .
Next, COP (COP ₂ ) at the set value P _S2 is calculated from the measured values of the sensors 31 to 35 in the same manner as in step 8, and the average value of the discharge pressure set value P _S2 and COP ₂ is stored in the memory 41. (Step 14). In the same procedure, the COP at the set value _PS2 is calculated about 10 times (step 15), and the average value is calculated. (Step 16).

Next, each measured value from the sensors 31 to 36 is taken into the controller 30 (step 17). Then, based on the respective measured values, it calculates the upper limit value PL ₃ of the compressor discharge pressure (step 18). Then, a discharge pressure set value P _S3 (for example, P _S3 = P _S1 −ΔP ₁ ) different from the initial set value P _{S1 is selected in} the vicinity of the initial set value P _S1 within a range not exceeding the upper limit value PL ₃ (step _S3 ). 19). Then, calculated COP value at the set value _{P S3} the (COP _3), and stores the discharge pressure setpoint _{P S3} and COP ₃ in the memory 41 (step 20). Then, the same COP calculated conducted 10 times at the set value _{P S3} in procedure (step 21), calculates the average value (step 22).

From the average values of COP ₁ , COP _2, and COP ₃ , the maximum COP determination unit 40 selects a discharge pressure that maximizes the COP. And the drive motor 22a of the compressor 22 is controlled by the controller 30 so that it may become this discharge pressure. At the same time, the discharge pressure is set as a new discharge pressure set value, the new set value is set as an initial set value, and the process returns to step 5 to calculate the COP value by the same procedure (step 23).
Hereinafter, a method for calculating the discharge pressure at which the COP is maximized will be described with reference to FIG. FIG. 4 is a graph with the COP value on the vertical axis and the compressor discharge pressure setting value on the horizontal axis. In FIG. 4, first, the three points b ₁ (average value of P _S1 and COP ₁ ), b ₂ (average value of P _S2 and COP ₂ ) and b ₃ (average of P _S3 and COP ₃ ) calculated in the above-described processing steps are used. Value) is plotted in the graph of FIG.

Next, a quadratic curve b passing through the three points is obtained, and a local maximum point c at which the differential value of the quadratic curve b is zero is obtained. Since the COP value becomes maximum at the maximum point c, the controller 30 controls the operation of the heat pump device 20 so that the compressor discharge pressure becomes the maximum point c.
Furthermore, by repeating this process step with this maximum point c as a new discharge pressure initial setting value, the operating state of the heat pump device 20 is always grasped in real time, and the COP value is maximized corresponding to the operating state. The heat pump device 20 can always be operated at the discharge pressure.

Instead of obtaining a quadratic curve passing through the three points, two straight lines passing through two arbitrary points out of the three points are drawn, and the COP of the three points is maximized from the inclination of these straight lines. You may make it obtain | require the point which becomes. Then, the compressor discharge pressure is operated so as to be the maximum point, and the same processing step is repeated with the maximum point as a new initial set value. An example is shown in FIG.
5, draw a straight line _{f 1} passing through the points _{b 1} and _{b 2,} the straight line _{f 2} passing through the points _{b 1} and _{b 3.} By obtaining the slopes of the straight lines f ₁ and f ₂ , it can be seen that the COP value becomes the maximum at b ₃ out of the three points. Then, while operating the heat pump device 20 so that the discharge pressure to b _3, the b ₃ as a new initial set value, and repeats the same processing steps. By repeating this processing step, the discharge pressure at which the COP is truly maximized can be approached as much as possible.

  Alternatively, as another calculation method, in addition to the initial setting value of the discharge pressure, one discharge pressure setting value different from the initial setting value is set, and a straight line connecting these two points is drawn. Determine the point with the larger. The larger point may be set as a new initial setting value, and the same processing may be repeated. Accordingly, similar to the calculation method of FIG. 5, the discharge pressure at which the COP is truly maximum can be approached as much as possible.

  Among the calculation methods shown in FIG. 4 or FIG. 5, the calculation method shown in FIG. 5 can find the local maximum point c of the quadratic curve b where the COP becomes the maximum value by one operation, so that the processing speed is increased. There are advantages that can be made.

6, in the heat pump apparatus using CO ₂ refrigerant compressor suction pressure (absolute value) of the CO ₂ refrigerant, suction superheat degree, and the temperature difference between the CO ₂ refrigerant in the gas cooler outlet and the heating air with a constant The relationship between the discharge pressure and the COP when the compressor discharge pressure is changed is shown. From FIG. 6, it can be seen that there is an optimum value of the discharge pressure at which the COP is maximum. Therefore, if the initial setting value of the discharge pressure is in the vicinity of the optimum value, the discharge pressure value at which the COP is maximized can be obtained quickly and efficiently by the calculation method shown in FIG.

  Note that the temperature difference between the refrigerant and the heated air at the gas cooler outlet varies depending on the shape of the heat exchanger used as the gas cooler, the air volume, the gas cooler inlet temperature and outlet temperature of the heated air, the compressor discharge pressure, or the refrigerant circulation amount. It is difficult to determine COP as a function of these variables.

According to the present embodiment, during operation of the heat pump device 20, the discharge pressure at which COP is maximized can be obtained while inputting the measured values of the sensors 31 to 36 to the controller 30. Even if the state fluctuates, the optimum COP value can be obtained in real time following the fluctuation of the driving state. Therefore, the heat pump device 20 can always be operated with the optimum COP.
Therefore, it is possible to operate with the optimum COP without taking into account complicated fluctuation factors that influence the COP of the heat pump device 20.

Further, the CO ₂ used as the refrigerant of the heat pump device 20, by the heat pump device 20 compressor discharge pressure is operated in a supercritical state above the critical pressure, it is possible to heat the heating air above 100 ° C.. Therefore, the temperature range of the heated air used for drying the material to be dried d can be set wide.

In addition, the discharge pressure initial setting value P _S1 and two setting values P _S2 and P _S3 different from the initial setting value P _S1 are measured a plurality of times to calculate a plurality of COP values, and the plurality of COP values are calculated. Since the average value of the calculated values is obtained, the COP value calculation accuracy can be improved.

  According to the present invention, it is applied to drying of resin, wood, food, clothing, etc., and in a drying device incorporating a heat pump device, the COP of the heat pump device is maximized to enable a heat efficient operation.

1 is an overall configuration diagram of a drying apparatus according to an embodiment of the present invention. It is a block diagram of the control system of the drying apparatus which concerns on the said embodiment. It is a flowchart which shows the operation procedure of the drying apparatus which concerns on the said embodiment. It is a diagram explaining the method of calculating | requiring the maximum value of COP with the drying apparatus which concerns on the said embodiment. It is a diagram explaining another method which calculates | requires the maximum value of COP with the drying apparatus which concerns on the said embodiment. It is a diagram which shows the relationship between compressor discharge pressure and COP with a heat pump apparatus. It is a Mollier diagram of a heat pump device using CO2 refrigerant.

Explanation of symbols

1 Drying apparatus 10 drying chamber 15 the heated air supply passage 20 heat pump unit 21 CO ₂ refrigerant circulation channel 22 compressor 23 gas cooler (condenser)
24 expansion valve 25 evaporator 30 controller 31 to 36 sensor a outside air d object to be dried

Claims (3)

Using a heat pump device that operates using CO ₂ as a refrigerant and a compressor discharge pressure in a supercritical state equal to or higher than the critical pressure, heat the outside air or reheat the exhaust in the drying chamber to produce heated air. In a drying method for supplying to a drying chamber and drying an object to be dried in the drying chamber,
A first step of setting an initial set value of the compressor discharge pressure based on a set temperature of the heated air supplied to the drying chamber within a range of an allowable upper limit value of the compressor discharge pressure;
The heat pump device is operated so as to be the initial set value, and the suction pressure and suction temperature of the compressor, the discharge pressure and discharge temperature of the compressor, and the refrigerant temperature at the outlet of the gas cooler are measured. A second step of calculating a COP at an initial set value;
A third step of setting at least one compressor discharge pressure different from the initial set value in the manner of the first step, and calculating a COP at the one point from the measured value in the manner of the second step;
A fourth step of obtaining a discharge pressure at which COP is maximized from the initial set value and the COP calculation value at the one point, and setting the discharge pressure as a new set value;
Set at least two compressor discharge pressures different from the initial set value in the third step, calculate the COP at the two points from the measured value in the manner of the second step,
Seeking a quadratic curve passing through the initial setting value and the 2-point, the differential value of the quadratic curve is to the second step with a new discharge pressure setpoint points becomes zero as a point where COP becomes maximal first A drying method characterized in that the heat pump device can be operated at a discharge pressure at which the COP is always maximized in response to a change in the operation state by repeating the four steps.   2. The drying method according to claim 1, wherein the compressor discharge pressure is controlled by controlling the rotation speed of the compressor or the refrigerant circulation amount in the refrigerant circulation path. Using a heat pump device that operates using CO ₂ as a refrigerant and a compressor discharge pressure in a supercritical state equal to or higher than the critical pressure, heat the outside air or reheat the exhaust in the drying chamber to produce heated air. In a drying apparatus that is supplied to a drying chamber and dries a material to be dried in the drying chamber,
A compressor that is provided in the refrigerant circulation path and compresses the refrigerant, a gas cooler that heats the outside air with the retained heat of the refrigerant or reheats the exhaust of the drying chamber to generate heated air, an expansion valve that decompresses the refrigerant, and a refrigerant An evaporator to evaporate,
A drying chamber for introducing heated air to dry the object to be dried, and a heating air supply path for supplying heated air heated by a gas cooler to the drying chamber;
A plurality of sensors for measuring the suction pressure and suction temperature of the compressor, the discharge pressure and discharge temperature of the compressor, and the refrigerant temperature at the condenser outlet;
An initial set value of the compressor discharge pressure is set based on the set temperature of the heated air supplied to the drying chamber, the operation of the heat pump device is controlled to be the initial set value, and the measured values of the plurality of sensors are set. Input, calculate the initial set value and COP at at least one discharge pressure different from the initial set value, obtain a discharge pressure at which the calculated COP value is maximum from these COPs, and set the discharge pressure to be the same A controller for operating the heat pump device and setting the discharge pressure to a new set value,
The controller sets at least two compressor discharge pressures different from the initial set values, calculates the COP at the two points from the measured values from the plurality of sensors,
A controller that obtains a quadratic curve that passes through the initial set value and the two points, and sets a point at which the differential value of the quadratic curve becomes zero as a new discharge pressure set value as a point at which the COP becomes maximum;
A drying apparatus characterized in that the heat pump device can be operated at a discharge pressure at which the COP is always maximized in response to a change in the operation state by repeating the processing by the controller.

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