Method for compressing gases

(42) Date of commencement of the patent: 15.10.1995 (45) Date of issue: 25. 6.1996 (56) Documentation:

(51) Int. Cl.⁶ : F04B 37/20

F048 39/16, F25B 47/02, F25D 21/12, F25J 5/00, B01D 53/26 (73)

DE 2950131A US 3258932A

US 4156350A US 4420943A US 3148040A EP 0142643A2 EP 0063158A2

GOSSLER EWALD ING.

A-4810 GMUNDEN, UPPER AUSTRIA (AT).

CQ (54) METHOD FOR COMPACTING GASES (57) The invention describes a method for compressing gases (4). In particular of air for a compressed air line system. In this case, the intake air of the compressor (2) with a refrigerant dryer (5) is cooled in a cooling section below 0 'C. The resulting in the form of ice condensate is excreted. During the defrosting of the refrigerant in the cooling section of the compressor (2) sucked air dryer (5), the circulation of the refrigerant in the refrigerant circuit (7) is interrupted. In this case, the pressure in the intake and optionally pressure line (11) of the refrigerant compressor (8) is monitored. After exceeding a temperature of the refrigerant dryer (5) of about 0 'C corresponding pressure of the refrigerant, the defrosting is terminated.

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The invention relates to a method for compressing gases, in particular air in a compressed air line system, in which the intake air of the compressor is cooled with a refrigerant dryer in a cooling section below 0'C and the precipitated in the form of ice condensate is eliminated.

US-A-3 148 040 discloses a method of defrosting ice sheets on heat exchangers by means of which the air is cooled below 0 ° C. In this case, the defrosting process is carried out in that the coolant normally used for cooling the heat exchanger is heated so as to remove the ice covering from the heat exchanger surface. For initiating and terminating the defrosting process, a pressure switch is arranged in the outlet region of the heat exchanger. If there is a pressure drop in the exiting from the heat exchanger air due to excessive ice in the heat exchanger, the defrosting process is initiated and continued until the pressure drop in the heat exchanger has reached the prescribed value again. The disadvantage here is that the refrigerant is passed through the refrigerant dryer, where it is heated before entering the refrigerant dryer, resulting in a high energy consumption.

Furthermore, from US Pat. No. 3,258,932 A, a method for initiating the defrosting process is known in which a negative pressure which is produced in the intake region of the air compressor is used. If this suppression on the icing of the heat exchanger is too high, then a hot liquid is sucked in the region of the heat exchanger by the action of this negative pressure and passed over the heat exchanger, whereby the ice is to be defrosted. The disadvantage here is that the hot liquid for defrosting the ice is passed over the refrigeration dryer away, and thus a high liquid consumption takes place.

US Pat. No. 4,156,350 A discloses a method for initiating the defrosting of a heat exchanger, wherein the heat exchanger is heated from the outside by means of an additional heating coil. The control for defrosting the heat exchanger takes place via a thermostat and a presettable timer, in which the defrost time can be set. The disadvantage here is that a high energy consumption must take place by the additional heating coil to completely defrost the heat exchanger.

Likewise, US Pat. No. 4,420,943 A describes a method for defrosting ice sheets on heat exchangers, by means of which the air is cooled below 0 *. In this case, the defrosting process is carried out in that the coolant normally used for cooling the heat exchanger is heated so as to remove the Eisbelag from the heat exchanger surface.

From EP-0 142 643 A2 a method and a device for defrosting of heat pumps is known. In order to monitor the defrosting process, a temperature difference is formed, for which purpose the temperature of the evaporator and that of the ambient air are determined and compared.

On the other hand, it is known from EP-0 063 158 A2 that for defrosting heat pumps at outside temperatures below 0C, the instantaneous value of a state variable, inter alia, for example, the pressure of the refrigerant in the evaporator can be used to initiate this defrosting process.

A known method for operating a Verdrängerverdichters of the same applicant - according to DE-29 50 131 A - prescribes for the production of compressed air in a compressed air line system to cool the intake air of the compressor in a refrigeration plant below 0 ° C. The resulting in the form of ice condensate is excreted. The temperature difference between the temperature of the intake air at the inlet of the refrigeration plant and the temperature of the intake air at the inlet of the compressor should be between 35'C and 45'C. The pressure dew point in the compressed air line immediately following the compression should be below the intake temperature of the intake air of the refrigeration drying system. The output of the compressor is connected directly to the compressed air line. This makes it possible, while saving the aftercooler due to the higher compressed air temperature at the consumer to provide a higher volume of dry compressed air available. In addition, condensate precipitation in longer compressed air lines or comprehensive compressed air systems avoided. The method has proven itself very well in practice. However, the defrosting of the refrigeration dryer could not be solved satisfactorily in all cases.

The present invention is based on the object to simplify the process of defrosting the heat exchanger in a method for compressing gases.

This object of the invention is achieved in that during the defrosting of the cooled in the cooling section of the compressor air sucked refrigerant dryer, the circulation of the refrigerant in the refrigerant circuit interrupted and monitors the pressure in the suction and optionally pressure line of the refrigerant compressor and after exceeding a temperature of the refrigerant dryer of about 0'C corresponding pressure of the refrigerant, the defrosting is terminated. By determining the pressure conditions in the suction and possibly pressure line of the defunct during the defrosting refrigerant circuit can be determined very precisely that time in which the temperature is in the range of the heat exchanger above 0'C and thus the defrosting is terminated. This temperature determination is independent of occurring in the refrigerant dryer flows or

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Gas or air movements, so that incorrect measurements are sufficiently avoided.

According to a further embodiment of this method according to the invention it is provided that the temperature of the compressed air sucked to the compressor detected after the exit from the refrigerant dryer and at a positive temperature value and optionally simultaneously a temperature of the refrigerant dryer of about O'C corresponding pressure of the refrigerant in the suction line to the refrigerant compressor, the defrosting is terminated. By the simultaneous determination of the gas or Air temperature in the output range of the refrigeration dryer is a vote of the two measured values ​​and a mutual check possible, so that the defrosting can be made economically and efficiently.

It is also advantageous when during the defrosting of the refrigerant dryer hot Käftemitteldampf the refrigerant dryer flows through and at the end of the defrosting process, the refrigerant is fed via an expansion valve to the refrigerant dryer, because that time span, in which the compressor draws in a single arrangement of a refrigeration dryer moist and possibly not purified air, can be reduced since, due to the flow of hot refrigerant vapor through the refrigerant dryer, the defrosting operation in addition to the defrosting effect, by the sucked gas or the air is caused is amplified.

After a further process step is provided that interrupted during the defrosting of the refrigerant dryer, the refrigerant circuit in the refrigerant dryer and the air required for compression for the compressor via the refrigerant dryer is sucked in and that at a pressure in the disused part of the refrigerant circuit of the refrigerant dryer, which corresponds to a positive temperature of the surface of the refrigeration dryer, and at a suction temperature of the compressed air at the outlet of the refrigerant dryer of at least + 1 'C, the refrigerant circuit is reactivated, whereby a favorable energy balance is achieved, since no additional energy is needed to defrost the condensate frozen on the refrigeration dryer.

For a better understanding of the invention, this will be explained in more detail below with reference to the embodiments shown in the drawings.

Show it:

Fig. 1 is a block diagram of an apparatus for compressing gases according to the invention in a highly simplified schematic representation;

Fig. 2 is a diagram showing the relationship between the refrigerant pressure and the temperature of the refrigerant and thus the surfaces of the heat exchanger.

1 shows a device 1 for compressing gases according to the method according to the invention. This comprises a compressor 2 and this in the suction direction - arrow 3 - of the gas to be compressed 4 - shown schematically by selected arrows - upstream refrigerant dryer. 5 In the refrigerant dryer 5, a heat exchanger 6 is arranged, which is arranged in a refrigerant circuit 7, which comprises a refrigerant compressor 8, a condenser 9 and a liquid separator 10. In a suction line 11 from the outlet 12 of the heat exchanger 6 to Ansaugstut2en 13 of the refrigerant compressor 8, a pressure measuring device 14 is arranged.

Furthermore, a temperature sensor 16 is arranged in the region of the suction pipe 15 downstream of the heat exchanger 6 to the compressor 2. Both the output of the pressure measuring device 14 and the temperature sensor 16 are connected to a control device 17, via which the drive of the refrigerant compressor 8 is controlled. The control device 17 comprises control elements 18 and 19, at whose inputs in each case the signal lines of the pressure measuring device 14 and of the temperature sensor 16 are applied. Furthermore, these control elements 18 and 19 are each an adjusting member 20 and 21, for example when using an analog controller 17, associated with a control potentiometer and the respective difference value is forwarded via connecting lines to an AND gate 22. If the two preselected with the adjusting members 20 and 21 measured values, the drive of the refrigerant compressor 8 is stopped and the activity of the refrigerant circuit 7 is interrupted.

As a result of the warm gas sucked in with the compressor, the condensate frozen on the heat exchanger due to the low temperature of the same is thawed and can flow away. If a pressure in the suction line 11 of the refrigerant circuit 7 detected by the pressure measuring device 14, which corresponds to a temperature of the refrigerant of about 0 * 0 in the region of the heat exchanger 6, a signal from the control element 18 to the AND gate 22 is passed. If then there is also a signal input from the control element 19, since the desired temperature of the gas is reached in the region of the temperature sensor 16, then the refrigerant compressor 8 is switched on again and the refrigerant circuit 7 is activated. This is immediately a subcooling of the heat exchanger 6 and a cooling of the intake air until the ice shell on the heat exchanger 6 is so thick that its insulating effect no longer allows a corresponding cooling of the sucked gas. This condition is determined on the one hand by the temperature sensor 16 and on the other hand by the Oruckverlauf in the suction pipe 11 of the refrigerant, since the heat extraction from the refrigerant at too high insulation of the

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Ice Mantle is no longer given.

Of course, the control device described can also be designed such that a complete control loop is present, so that the power of the refrigerant compressor 8 each continuously adapts to the required cooling energy in the region of the heat exchanger 6. Also, the adjusting members 20 and 21 may be provided with a plurality of adjusting members to respectively set the two target states in which to reduce the activity of the refrigerant compressor 8 or and to strengthen its activities or to begin with.

2, the temperature and pressure characteristics of some common refrigerants are shown in order to better represent the relationships between the pressure of the refrigerant and the respective temperature of the refrigerant. Thus, a characteristic curve 23 shows the relationships between temperature and pressure at a Frigen 12, while a characteristic 24 shows the same ratio for Frigen 22 and a characteristic curve 25 for Frigen 502.

From these curves it can be seen that at Frigen 12 a pressure of approximately 1.5 bar corresponds to a temperature of -20 ° C. and a pressure of approximately 3 bar corresponds to a temperature of O'C. It follows that due to the significant differences in pressure an accurate inference to the respective temperatures can be drawn.

It should be noted, however, that especially during the defrosting process, the refrigerant may have a pressure corresponding to a certain temperature, for example, is already in the range of a temperature of about O'C, although on parts of the line still ice residues are present or the air in the refrigeration dryer is still below O'C. Therefore, it is particularly advantageous to monitor the pressure of the refrigerant also to monitor the temperature in that area of ​​the refrigerant dryer, which is closest to the intake manifold of the compressor.