EP0758054B1 - Oil circulation system for screw compressors - Google Patents

Description

The invention is about a Screw compressor device for refrigerants with refrigerant-soluble oils, preferably for ammonia polyalkylene glycol soluble therein, with a flow after a screw compressor in a under Oil separator at outlet pressure in a gas stream and is divided into an oil flow and the oil flow via a throttle and an oil inlet in the Screw compressor arrives.

Screw compressors roll two helical rotors, main and secondary rotor, in a housing (e.g. EP-A-0 030 619). Enlarged during the suction process the tooth gap between the rotors Gas is sucked in. As the rotors continue to turn closes this gap when crossing the Inlet control edge. The counter wheel engages when turning further into the gap and continuously reduces the enclosed gas space, the gas is compressed until finally reaches the exit control edge and that compressed gas is pushed out.

In the gas flow to be pumped is in the compression room a relatively large amount of oil is injected to a better seal and thereby an improvement of the To achieve delivery levels and part of the Dissipate heat of compression with the oil. This oil must on the pressure side of the compressor by a Oil separator separated from the gas stream again be, because otherwise the refrigeration cycle in undesirable Way would strain.

1 shows such a known device:

Screw compressor 1 becomes one with oil particles penetrated gas stream 30 via a pressure line 2 promoted an oil separator 3. From there the deoiled gas stream 31 in the sense of refrigeration Cycle to a condenser. That in Oil separator 3 separated oil passes through a Line 4 to a water or air-cooled oil cooler 5, in which the heat of compression is dissipated. The oil is from there via a line 6, an oil filter 7 Check valve 8, a solenoid valve 9 and one Oil inlet 10 fed back to the compressor 1, wherein usually the pressure difference between pressure and Suction side on the compressor used for oil delivery becomes. Part of this returned oil is used for the Lubrication of the bearings and in so-called "open" Compressors with the drive shaft facing outwards is performed for the lubrication and cooling of the Shaft seal used. The rotating one Shaft seal is used to drive the compressor drive shaft to seal against the atmosphere.

For example, NH3 refrigeration systems used to be almost exclusively with so-called flooded evaporators and operated with NH3-insoluble mineral oils. This Mineral oils could not because of the insolubility enrich with NH3, so that largely pure oil again for the lubrication of the bearings and the shaft seal for Was available. For NH3 screw compressors this is Supply of the shaft seal and that on the suction side lying drive side bearing with lubricating oil have become problematic since such times Screw compressor refrigeration systems increasingly with NH3-soluble Oil, a polyalkylene glycol, or PAG oil for short called, operated. These are NH3-soluble oils Prerequisite for a so-called Dry expansion evaporation, with which the NH3 filling quantity in the refrigeration cycle compared to flooded operation can be significantly reduced. Due to the applicable Accident prevention regulations are used in modern Refrigeration made great efforts, NH3 refrigeration systems with the smallest possible fill quantities to manufacture.

The NH3-soluble oils accumulate due to the Solution behavior according to the given in the oil separator Pressure and temperature conditions with a certain Amount of NH3 at a normal operating point e.g. With approx. 6% NH3 in oil. When supplying the oil The shaft seal and the drive-side bearing will Oil relaxed at suction pressure. The NH3 absorption capacity of oil decreases at a normal operating point e.g. to approx. 3% NH3 in the oil, so that the difference of approx. 3% NH3 inevitably evaporates from the oil. Because of the very large steam volume of NH3 is created by this Evaporation process a large volume of oil foam (at a normal operating point approx. 11 times the volume compared to pure oil), its lubricating effect compared to pure oil is much less. The often leads to very rapid wear the shaft seal and partly also the drive side Bearing due to insufficient lubrication. They are facilities known to remedy this circumstance to a limited extent.

Figure 2 shows a known device for Refrigerant-soluble oils on screw compressors that do oil intended for lubrication and sealing via a Throttle point 25 relaxed and over one Evaporation container 21 leads, the vapor space via a Line 12 with the suction side 29 of the screw compressor 1 communicates. This "degasses" the oil and can with better lubrication of the shaft seal and be supplied to the drive side bearing, the necessary pressure difference generated by an oil pump 13 becomes. This arrangement has the disadvantage that the Screw compressor during its operation from the Functionality of an oil pump depends. Another Disadvantage is that with the start of such Screw compressor device the oil behind the Throttle point 25 foams and partly as foam the lubrication points.

The object of the invention is to address these circumstances improve.

This problem is solved by in front of the throttle A partial oil flow for lubrication via a branch is branched off from bearings and / or shaft seals, which is passed through an evaporation tank, the gas side via a line with a Intermediate pressure connection on the compression path of the Screw compressor is connected to the partial oil flow with a pressure corresponding to the intermediate pressure Feed the lubrication connection to the screw compressor.

This arrangement has the advantage that with one Power failure the lubrication pressure does not collapse during the run-out of the screw compressor, because the pressure difference between final pressure and intermediate pressure if at all slowly after the standstill of the Dismantles screw compressor. In the further there is none Oil pump necessary. In addition, the lubricating oil discharged steam is fed in at intermediate pressure, so that its compression from suction pressure to intermediate pressure and thus the cooling capacity of the cycle is improved.

Further advantageous developments of the invention are shown in dependent claims 2 to 8. So it did proved to be beneficial in addition to Intermediate pressure the partial oil flow with a throttle or To align the regulatory body. It also makes sense to do that Oil in the evaporation tank to heat at a higher Temperature with lower gas solubility more gas to drive out. The reduction in the gas content compensated the reduced viscosity more than enough to make one useful lubrication to come. You could also the partial oil flow between the evaporation tank and Lubrication points still cool to a higher one Maintain viscosity and because of the higher solubility hardly any gas even when the pressure at the lubrication points drops to drive out. Furthermore, it is for a start and that Further operation makes sense, the evaporation tank above to arrange the screw compressor and with check valves emptying the evaporation tank and the supply line in the To prevent standstill, at least the geodesic To have gradients available. If the pressure difference between final pressure and intermediate pressure in the start phase is small, you can also use an oil pump after Provide evaporation containers which, after starting, i.e. at sufficient pressure difference is switched off.

Many of the screw compressor designs feature that Possibility of getting into the already partially compressed gas to additionally draw in a secondary gas flow. An opening in the housing is arranged so that in the tooth gap at this point a medium pressure from the suction and final pressure is reached. With a two-stage relaxation that will be Gas of the first relaxation stage through this opening in sucked the compression space. With this "economizer circuit" improves the efficiency of the Refrigeration system. One advantage of the above setup is in that the screw compressors that such Economizer connection, constructively not must be changed to use the facility close.

Fig.3

schematisch eine erfindungsgemässe Einrichtung, bei der ein Teilölstrom nach dem Durchlaufen eines Oelkühlers entnommen wird;

Fig.4

schematisch eine erfindungsgemässe Einrichtung, bei der ein Teilölstrom ungekühlt vor dem Oelkühler entnommen wird; und

Fig.5

schematisch eine Einrichtung analog zu Figur 3, bei der eine Hilfspumpe die Schmierung beim Start des Schraubenverdichters unterstützt.

The invention is described below using exemplary embodiments. Show it:

Fig. 3

schematically a device according to the invention, in which a partial oil flow is removed after passing through an oil cooler;

Fig. 4

schematically a device according to the invention, in which a partial oil stream is taken uncooled before the oil cooler; and

Fig. 5

schematically a device analogous to Figure 3, in which an auxiliary pump supports the lubrication when starting the screw compressor.

The figures are used to improve the lubrication of Bearings and shaft seals on screw compressors for Refrigerant shown with refrigerant-soluble oils. A typical application results for example for Ammonia with soluble polyalkylene glycol. Thereby, that the oil flow returned to the screw compressor before the pressure is reduced to approximately the compressor suction pressure a partial oil flow is withdrawn at an intermediate pressure and is passed over an evaporation tank significant proportions of dissolved refrigerant in one Intermediate pressure connection on the compression path of the Screw compressor can be fed. Corresponding the lubricating properties are more favorable than the rest Partial oil flow at the lubrication connection and the disadvantages of Pressure collapse or foam delivery at one Oil pumps are not required since there is no oil pump with a suitable one Intermediate pressure is necessary.

In Figure 3, a screw compressor 1 promotes ammonia Gaseous form from a suction line 29 and compresses it, being Polyalkylene glycol injected at an oil inlet 10 the sealing effect between the To improve compression chambers. For the resistance of the Nozzles or orifices during injection is symbolic a throttle point 25 is shown. The one against Final pressure emerging from the screw compressor 1 Flow 30 is a via a pressure line Oil separator 3 supplied, which has a gas space 3a, from which a gas stream 31 is not shown Condenser is supplied while at the bottom of the Oil separator 3 is an oil supply 3b, from which an oil flow 32 via a line 4 through an oil cooler 5 is performed. The cooled oil flow 32 enters one Line 6 via an oil filter 7, a check valve 8 and a solenoid valve 9 to the throttle point 25 and Oil entry 10. Before the throttle point 25 is in a Branch 11 is a partial oil flow 35 for the lubrication of Bearings and shaft seals branched and into one Evaporation tank led under the pressure of a Intermediate pressure port 14 on the compression path of the Screw compressor 1 stands. The pressure at entering the branch 11 must therefore be somewhat higher than the pressure in the Intermediate pressure port 14 to be with an aperture 26th to restrict the partial oil flow 35. In the evaporation tank 24 takes place through the dwell time in the container and through Vacuum zones on the edges of the aperture 26 a Outgassing of ammonia takes place via a line 23 is fed in at the intermediate pressure connection 14. The Outgassing can be by a heater 19, as in 4 and 5 is supported. The degassed partial oil flow enters via a line 15 and Solenoid valve 17 to a lubrication connection 16 and after Running through bearings and shaft seals in one Suction chamber 29 at the compressor inlet back into the gas flow. A so-called Economizer connection on screw compressor 1 used. This "economizer" connector is on every modern one Screw compressor available and ends in Screw compressor at one point on the Compression path, in which the suction space through the Screw profiles is already closed. The one on this The amount of gas supplied instead of this no longer burdens that sucked gas volume and is therefore largely neutral. There is also an economizer connection 14 an approximately 1.5 to 2 bar higher pressure than at the shaft seal of the Compressor, so this pressure difference for the Oil production can be exploited and an oil pump so in most cases it’s not necessary.

The evaporation tank 24 is above the Screw compressor 1 arranged and the solenoid valve 17th is closed at a standstill in order to take one under To have gravity supply of oil.

In FIG. 5, only the circle from partial oil flow 35 is shown Compared to Figure 3 expanded by further components been. In the branch 11 there is a solenoid valve 18 provided that a flow of Prevents oil from the higher areas, and the Partial oil flow 35 is limited by a control valve 20, which, for example, the oil level in the evaporation tank 24 holds constant. A heater 19 favors this Degassing refrigerant. Line 15 bifurcates the solenoid valve 17 in a line 15a, in which a Oil pump 22 with check valve 27 as a starting aid is installed, and in a strand 15b with a Check valve 28 to the shutdown oil pump 22nd to convey past into the lubrication port 16. Such Booster pump 22 could always run when the intermediate pressure for the lubrication is insufficient. The Control valve 20 would correspond to the partial oil flow 35 Track the pumping capacity of the pump 22.

Figure 4 shows one compared to Figures 3 and 5 Arrangement in which the branch 11 for the partial oil flow 35 goes in front of the oil cooler 5. The partial oil flow arrives already much hotter via a solenoid valve 18 and a Control valve 20 in the evaporation tank 24. One on Evaporation tank 24 attached heater 19 is therefore only be necessary in exceptional cases. The oil also arrives via a line 15 and Solenoid valve 17 in the lubrication port 16, which Solenoid valve 17 when the oil supply is at a standstill located evaporation container 21.

Claims (11)

1. Screw compressor apparatus for refrigerants with oils soluble in refrigerants, preferably for ammonia with polyalkylene glycol soluble therein, wherein a delivery flow (30) is divided after a screw compressor (1) in an oil separator (3) under exit pressure into a gas flow (31) and an oil flow (32), and the oil flow (32) enters into the screw compressor (1) via a restrictor (25) and an oil inlet (10),
   characterised in that a partial oil flow (35) is branched off before the restrictor (25) via a branch (11) for the lubrication of bearings and/or shaft seals, which partial oil flow (35) is led through a vapour separation container (24), which is connected on the gas side via a line (23) to an intermediate pressure connection (14) on the compression path of the screw compressor (1) in order to feed the partial oil flow (35) to a lubricating connection (16) at the screw compressor (1) with a pressure corresponding to the intermediate pressure.
2. Screw compressor apparatus in accordance with claim 1 characterised in that the vapour separation container (24) is geodetically arranged above the lubrication points at the screw compressor (1) in order to exploit a head for the lubrication pressure.
3. Screw compressor apparatus in accordance with claim 2 characterised in that a blocking valve (17) is arranged between the vapour separation container (24) and the lubricating connection (16) in order to prevent oil from running out of the vapour separation container the stationary state.
4. Screw compressor apparatus in accordance with one of the claims 1 to 3 characterised in that a blocking valve (18) is arranged in the branch (11) in order to prevent oil from flowing backward in the stationary state.
5. Screw compressor apparatus in accordance with one of the claims 1 to 4 characterised in that a heater device (19) is mounted at the vapour separation container (24) to assist the vapour separation performance and prevents an enrichment of the oil with refrigerant in the stationary state.
6. Screw compressor apparatus in accordance with one of the claims 1 to 5 characterised in that a restrictor member (26) is provided in the branch (11) in order to limit the partial oil flow (35).
7. Screw compressor apparatus in accordance with claim 6 characterised in that a control valve (20) is provided in the branch (11) as a restrictor member in order to regulate the partial oil flow (35) in the branch (11) accordance with a prespecified desired value.
8. Screw compressor apparatus in accordance with claims 1 to 7 characterised in that two parallel connection lines (15a, 15b) are provided between the vapour separation container (24) and the lubricating connection (16), of which one (15a) has a delivery pump (22) with a non-return valve (27) and the other (15b) has a non-return valve (28) in order to assist the transport of oil into the lubricating connection during start-up of the screw compressor (1).
9. Screw compressor apparatus in accordance with one of the claims 1 to 8 characterised in that the screw compressor has an economizer connection as intermediate connection (14) such as is provided for an intermediate infeed of a partial gas flow for multiple relaxation of the gas flow (31).
10. Screw compressor apparatus in accordance with one of the claims 1 to 8 characterised in that the intermediate pressure connection (14) has no connection to the suction space over the entire power range, in particular even at extreme partial loading, in order to maintain the intermediate pressure necessary for the lubrication.
11. Screw compressor apparatus in accordance with one of the claims 1 to 8, wherein the screw compressor in particular has a shaft seal and possesses a drive bearing on the suction side.

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