EP0172430A1 - Cooling method for a screw compressor, and a screw compressor for carrying out this method - Google Patents

Abstract

1. Method for cooling a screw compressor having a helical rib rotor and a helical groove rotor in mating engagement therewith, condensate being introduced into a compression chamber formed by the rotors and the wall of the working chamber surrounding the rotors, which condensate is recovered in a separator connected to the outlet side, characterized in that the condensate is introduced into the compression chamber after closure of the compression chamber against the inlet of the compressor and fresh water is introduced into the compression chamber downstream of the inlet position considered in the feed direction of the compressor, and in that the introduction of condensate and fresh water are controlled mutually independently in dependence upon the temperature of the feed medium in the outlet conduit.

Description

The present invention relates to a method for cooling a screw compressor and a screw compressor having meshing engagement with the screw groove rotor, wherein condensate is fed into a compression chamber formed by the rotors and the wall of the surrounding working space, which is obtained in a separator connected on the outlet side. The invention further relates to a screw compressor for performing the method.

In known screw compressors (cf. US Pat. Nos. 35 35 057 and 31 29 877), the condensate is usually fed into the compression space from a common collecting chamber via a large number of bores arranged in the wall of the compression space. These bores open into the compression chamber both in an area in which it is not yet sealed off from the inlet and in an area in which the so-called internal compression is already taking place. However, since the fed-in condensate only evaporates in the course of the compression process when the required temperature is reached, some of the condensate remains in the area of the inlet and at the beginning of the compression process inevitably still in a liquid state, especially since such compressors are usually run with excess water to achieve an effective washing effect.

This remaining condensate can collect in depressions and, depending on the suction-side pressure, can come into contact with the sealing arrangement for the rotor shafts. It is therefore necessary to manufacture these parts from stainless steel and to use special materials in this area. Condensate remains in the liquid state even in those operating phases in which the housing is not yet at operating temperature. This means that condensate can also accumulate on the pressure side, so that these areas must also be made of stainless steel and special materials. However, the use of stainless steel and special materials inevitably leads to very high manufacturing costs.

In order to prevent condensate from bleeding through on the oil side of the compressor, the sealing arrangements for the shaft bearings must also be designed in a relatively complex manner in the case of compressor designs of the type mentioned. So vacuum or overpressure air barriers must be provided, which requires a not inconsiderable additional effort and the use of external energy.

A further disadvantage is that the condensate injected in the area of the inlet can influence the volumetric efficiency in accordance with the evaporating amount, which is also undesirable.

The object of the present invention is to provide a procedure for cooling a screw compressor and a screw compressor for carrying out the method create, in which or in the use of stainless steel and special materials in the manufacture in favor of cheaper materials can be dispensed with and complex sealing arrangements for the rotor shafts and the shaft bearings are not required.

This object is achieved according to the invention by a procedure in which the condensate is fed into the compression chamber after the compression chamber has been closed, opposite the inlet of the compressor, and fresh water is fed into the compression chamber downstream of the feed point, the condensate and fresh water feeds in Depending on the temperature of the medium in the outlet line can be controlled independently.

The features according to the invention create a procedure in which the cooling water injection process is graded for the first time in all operating phases and is carried out precisely in a controlled manner depending on the temperature of the conveyed medium, so that only superheated steam is obtained in the compressor. As a result, condensate can neither accumulate on the suction side nor on the pressure side, so that. The use of stainless steel or special materials in these areas is not necessary and cheaper. Materials can be provided.

Elaborately designed sealing arrangements can also be dispensed with, since, due to the lack of condensate, strikethrough cannot occur. Furthermore, due to the lack of condensate in the inlet, there is no influence on the volumetric efficiency.

Due to the procedure according to the invention, the field of application of 1-stage "dry" screw connection you ren _t be expanded into areas where previously only oil-injected or two-stage dry compressor could be used. Compared to compressors with oil injection, the operating oil is thus saved according to the invention. The not inconsiderable effort for oil filter arrangements is also not necessary, since the compressed working medium no longer contains any oil components. If oil is not used, the environmental conditions are better and there is no risk of fire or explosion.

Basically, the control of the condensate and the fresh water feed depending on the temperature of the medium in the outlet line can be controlled in the most favorable manner for the respective operating conditions. A particularly simple and reliable control is achieved, however, when the condensate is fed in when a low temperature is reached and the fresh water is fed in when a second higher temperature is reached, and the feed is interrupted again when the temperature falls below the temperature. With such a preferred procedure, the condensate _K on- only in the compression chamber is injected when the compressed medium has at the end of the compression process reaches a certain temperature. If the temperature falls below the predetermined temperature value due to the condensate injection, the condensate injection is interrupted again so that the temperature can rise again. If, on the other hand, the temperature of the pumped medium continues to rise despite the condensate injection, fresh water is injected into the compression chamber when the second higher temperature value is reached, thus causing additional cooling of the pumped medium. If, due to the fresh water injection, the temperature drops again below the second higher temperature value, the fresh water supply falls below again broken. If the temperature rises again above the second higher temperature value, fresh water is then fed into the compression chamber again.

In a screw compressor according to the invention for carrying out the method, the condensate is fed into the compression space via a first feed line and the fresh water via a second feed line. This feed line is each equipped with a valve according to the invention, the valves being controlled by a temperature switch arranged in the outlet line of the compressor. Such an arrangement is simple in construction, requires little maintenance and is reliable.

In a preferred embodiment of a screw compressor according to the invention, the valves are controlled by a temperature switch which responds to two adjustable temperature values. This temperature switch opens the valve for the condensate supply line when the first lower temperature value is reached and the valve for the fresh water supply line when the second higher temperature value is reached. Furthermore, this temperature switch closes the respective valves as soon as the temperature drops below the respective temperature value.

Basically, the valves can be designed in any manner. However, it is advantageous if the valves are designed as solenoid valves or as water flow regulators.

In a preferred exemplary embodiment, a cooler is provided in the outlet line, as seen in the flow direction, upstream of the condensate separator.

Conveniently in such an arrangement, the _T emperaturschalter seen in the outlet in the flow direction upstream of the radiator.

Due to the feed of fresh water and the immediate evaporation during the feed process, a lime precipitate takes place in the compression chamber of the compressor. The resulting lime particles are deposited on the rotors and the wall of the work area. Since this process only takes place during operation, the limestone layer can only build up until the so-called zero backlash and thus the maximum possible sealing effect and efficiency is achieved. A further build-up of the lime layer is prevented by the rotors sliding past each other.

During the process described above, there is no increase in the drive power for the compressor, since the lime layer is very soft. The lime layer cures only after the compressor has been switched off and has cooled down. The rotors can be firmly connected to each other in such a way that the compressor cannot be restarted.

The procedure according to the invention now makes it possible to utilize this fundamentally positive effect of the zero play without having to accept the disadvantage of curing with the resulting consequences. Because of the method according to the invention, untreated fresh water can only be fed in until the lime layers do not touch each other over a large area and a new start is possible after switching off and cooling. From this point on, it will only be on prepared fresh water is fed in, so that the limestone layer is not further built up. The duration of the fresh water supply with lime precipitation can be determined by tests.

The coating of rotors of screw compressors is basically already known. Rotors of screw compressors are coated with plastic, for example, and such a coating also achieves an optimal sealing effect and efficiency. Plastic coatings, however, have the disadvantage that the compressors have to be dismantled and disassembled in the event of signs of separation. Lime-coated rotors, on the other hand, can be reworked in the installed state without dismantling. To do this, it is only necessary to selectively supply untreated fresh water in order to touch up the detached areas.

In the following, an exemplary embodiment of a screw compressor operating according to the method according to the invention is described in more detail with reference to the accompanying drawing for further explanation and better understanding.

The drawing shows a screw compressor 1 equipped with a screw rib rotor and a screw groove rotor, which has an inlet 2 and an outlet 3. The outlet 3 opens into an outlet line 4 in which a conventional cooler 5 is arranged. A condensate separator 6, which is also of a known type, connects to the cooler 5.

The condensate separator 6 is equipped with a first feed line 7, via which the condensate obtained in the condensate separator is returned to the compressor. The first feed line 7 is equipped with a valve 8 with which the feed of the condensate into the compression space of the compressor can be controlled. The condensate is fed into the compression space at a point where the compression space is already closed off from the inlet of the compressor.

via a second supply line 9, which is equipped with a valve 1 _0, fresh water can be fed into the compression chamber of the compressor. The feed point for the fresh water in the compression chamber is arranged such that it is downstream of the feed point for the condensate in the direction of conveyance of the compressor.

A temperature switch 11 is arranged in the outlet line 4 between the outlet 3 and the cooler 5. This temperature switch 11 has in the present embodiment example two adjustable temperature values T ₁ and T ₂ . Via the temperature switch 11, the valves 8 and ₁₀ , which are designed as solenoid valves in the present exemplary embodiment, are controlled.

The control is designed as follows

At a temperature of the medium in the outlet 3, which is below the temperature values T ₁ and T ₂ , both the valve 8 and the valve 10 are closed. If the temperature now rises to the temperature value T ₁ , the valve 8 for the condensate is opened via the temperature switch 11. If the temperature reaches the temperature value T ₂₁ , the valve 1o is also opened for the fresh water. If the temperature drops below the temperature value T ₂ , the temperature switch 11 closes the valve 10 again. If the temperature then drops below the temperature value T ₁ , the valve 8 is also closed via the temperature switch 11.

• Wird der Schraubenverdichter 1 angefahren, so hat die komprimierte Luft im Auslaß 3 zu Beginn eine Temperatur, die unter 200°C liegt. Das Ventil 8 für das Kondensat und das Ventil 1o für das Frischwasser sind deshalb in dieser Phase geschlossen. Ist der Anfahrvorgang abgeschlossen und wird der Betrieb mit dem Verdichter aufgenommen, so erhöht sich die Temperatur der kompromierten Luft im Auslaß 3 langsam. Sobald die Temperatur der Luft im Auslaß 3 2₀₀°C erreicht hat, öffnet der Temperaturschalter 11 das Ventil 8. Da zu diesem Zeitpunkt noch kein Kondensat vorliegt, wird die Temperatur der Luft im Auslaß 3 weiter ansteigen. Sobald sie den Temperaturwert 220° erreicht hat, öffnet das Ventil 8, so daß Frischwasser in den Verdichtungsraum eingespeist werden kann. Dadurch sinkt die Temperatur der Luft im Auslaß 3 wieder ab. Hat die Temperatur 22o°C unterschritten, schließt das Ventil 1o wieder, so daß die Frischwasserzufuhr unterbrochen wird. Dieser Vorgang erhöht sich so oft, bis im Kondensatabscheider 6 ausreichend Kondensat angefallen ist, das über die erste Zuführleitung 7 und das Ventil 8 in den Verdichtungsraum eingespeist werden kann. Sinkt nun die Temperatur im Auslaß 3 aufgrund der Kondensateinspeisung unter 22₀°C ab, so wird zuerst das Ventil 2 geschlossen und damit die Frischwassereinspeisung in dem Verdichtungsraum unterbrochen. Sinkt die Temperatur weiter unter 200°C ab, so wird auch das Ventil 8 geschlossen, so daß weder Kondensat noch Frischwasser in den Verdichtungsraum eingespeist wird.

If the temperature value T _{1 is set,} for example, to 2oo C and the temperature value T _2, for example, to 220 ° C, the following procedure results when compressing air:

• When the screw compressor 1 is started up, the compressed air in the outlet 3 initially has a temperature which is below 200.degree. The valve 8 for the condensate and the valve 10 for the fresh water are therefore closed in this phase. When the start-up process is complete and operation with the compressor is started, the temperature of the compressed air in outlet 3 slowly increases. As soon as the temperature of the air in the outlet has reached 3 2 ₀₀ ° C, the tempera opens door switch 11 the valve 8. Since there is no condensate at this time, the temperature of the air in the outlet 3 will continue to rise. As soon as it has reached the temperature value of 220 °, the valve 8 opens so that fresh water can be fed into the compression chamber. As a result, the temperature of the air in outlet 3 drops again. If the temperature has fallen below 22o ° C, the valve 1o closes again, so that the fresh water supply is interrupted. This process increases until there is sufficient condensate in the condensate separator 6, which can be fed into the compression space via the first feed line 7 and the valve 8. If the temperature decreases due to the condensate feed at 22 ₀ ° C in the outlet 3, the valve 2 is first closed and thus interrupting the fresh-water supply in the compression space. If the temperature drops further below 200 ° C, the valve 8 is also closed, so that neither condensate nor fresh water is fed into the compression chamber.

Due to the procedure described above, only superheated steam is produced in the compressor, so that liquid cannot accumulate on either the inlet or outlet side. The use of stainless steel or special materials in these areas is therefore not necessary, so that cheaper materials can be used which significantly reduce the manufacturing costs. Elaborately designed sealing arrangements can also be dispensed with, since, due to the lack of condensate, strikethrough cannot occur. In the absence of condensate in the inlet, there is no influence on the volumetric efficiency.

Claims (8)

1. A method for cooling a screw compressor having a screw-fin rotor and a screw-type rotor rotor meshing therewith, condensate being fed into a compression chamber formed by the rotors and the wall of the surrounding working space, which is obtained in a separator connected on the outlet side, characterized in that that the condensate is fed into the compression chamber after the compression chamber has been sealed off from the inlet of the compressor and that fresh water is fed into the compression chamber downstream of the feed point in the direction of delivery of the compressor, and that the condensate and fresh water feeds are independent of the temperature of the pumped medium in the outlet line can be controlled from each other. 2. The method according to claim 1, characterized in that the condensate feed occurs when a first lower temperature value is reached and the fresh water feed takes place when a second higher temperature value is reached and is interrupted again when these temperature values are undershot. 3. Screw compressor for performing the method according to claim 1, characterized in that the condensate via a first feed line (7) and the fresh water via a second feed line (9) are fed into the compression chamber and each feed line (7 and 9) with each a valve (8 and 1 ₀₎ equipped, the valves being controlled by a cylinder disposed in the outlet duct (4) temperature switch (11) (8 and _{1: 0).} 4. Screw compressor according to claim 3, for performing the method according to claim 2, characterized in that the valves (8 and 1o) are controlled by a temperature switch (11) responsive to two adjustable temperature values (T ₁ 'and T ₂ ) when the first lower temperature value (T ₁ ) is reached the valve (8) for the first feed line (7) for the condensate and when the second higher temperature value (T ₂ ) is reached the valve (10) for the second feed line (9) for the Fresh water opens and the respective valves (8 or 1 ₀ ) closes when the temperature drops (T ₁ or T ₂ ). 5. Screw compressor according to claim 3 or 4, characterized in that the valves (8 or 1 ₀ ) are solenoid valves. 6. Screw compressor according to claim 3 or 4, characterized in that the valves (8 or 1 ₀ ) are water volume controllers. 7. Screw compressor according to claim 3 or 4, characterized in that a cooler (5) is provided in the outlet line (4) seen in the flow direction upstream of the condensate separator (6). 8. Screw compressor according to claim 3 or 4 and 7, characterized in that the temperature switch (11) in the outlet line (4) seen in the flow direction is arranged upstream of the cooler (5).

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