Method of controlling the temperature and mass flow of a liquid injected into the bearings and compressor space of a compressor using two separated liquid supplies

Abstract

A method for controlling the liquid injection of a compressor device, where the compressor device includes at least one compressor element, the compressor element includes a housing that includes a compression space in which at least one rotor is rotatably affixed by bearings, and liquid is injected into the compressor element. The method includes providing two independent separated liquid supplies to the compressor element, where one liquid supply is injected into the compression space and the other liquid supply is injected at the location of the bearings.

Claims

1. A method for controlling injection of a liquid into a compressor device, said compressor device comprising at least one compressor element, said compressor element comprising a housing that comprises a compression space in which at least one rotor is rotatably situated, the housing further including at least one cavity separated from the compression space that serves as a liquid reservoir for liquid supplied to the compression space, wherein the method comprises the step of: providing at least two independent separated liquid supplies to the compressor element, wherein at least a first liquid supply is injected into the cavity that serves as a liquid supply for liquid supplied to the compression space and at least a second liquid supply injected into bearings that rotatably support the rotor, wherein the two independent separated liquid supplies are supplied separately and independently from a liquid separator to the at least one cavity and from the liquid separator into the bearings, and controlling both a temperature and a mass flow of the at least first liquid supply using a first cooler and a first controllable valve and a temperature and a mass flow of the at least second liquid supply using a second cooler and at least a second controllable valve.

2. The method according to claim 1, wherein to control the temperature and the mass flow of the liquid supply, the method consists of first controlling the mass flow and then controlling the temperature.

3. The method according to claim 1, wherein the method further comprises steps of: determining an efficiency of the compressor element by comparing a specific energy requirement of the compressor element to standard operating conditions of the compressor element, and controlling the temperature and the mass flow of the at least two independent separated liquid supplies such that the specific energy requirement is a minimum, whereby the specific energy requirement is the ratio of electrical power of the compressor device to the flow supplied by the compressor device compared to the standard operating conditions of the compressor element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) With the intention of better showing the characteristics of the invention, a few preferred variants of a method for controlling the liquid injection of a compressor device and a liquid-injected compressor device thereby applied, are described hereinafter by way of an example, without any limiting nature, with reference to the accompanying drawings, wherein:

(2) FIG. 1 schematically shows a liquid-injected compressor device according to the invention;

(3) FIG. 2 schematically shows a liquid-injected compressor element according to the invention;

(4) FIGS. 3 to 5 schematically show an alternative embodiment of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

(5) The liquid-injected compressor device 1 shown in FIG. 1 comprises a liquid-injected compressor element 2.

(6) The compressor element 2 comprises a housing 3 that defines a compression space 4 with a gas inlet 5 and an outlet 6 for compressed gas.

(7) One or more rotors 7 are rotatably affixed in the housing 3 by means of bearings 8 that are affixed on the shafts 9 of the rotors 7. The rotors 7 are driven, for example, by engine/motor/gearbox 28, which is connected to controller 29.

(8) Furthermore, the housing 3 is provided with a number of injection points 10a, 10b for the injection of a liquid.

(9) This liquid can for example be synthetic oil or water or otherwise, but the invention is not limited to this as such.

(10) The injection points 10a, 10b are placed at the location of the compression space 4 and at the location of the aforementioned bearings 8.

(11) The compressor element 2 is shown in more detail in FIG. 2, with the realisation of the injection points 10a, 10b thereon.

(12) According to the invention the housing 3 is provided with separated integrated channels 11 that start from the aforementioned injection points 10a, 10b in the housing 3 and open into the compression space 4 and the aforementioned bearings 8 respectively.

(13) In the example shown in FIG. 1 it is the case that the injection points 10a, 10b are placed at the location of the aforementioned compression space 4 and at the location of the aforementioned bearings 8 respectively.

(14) However, this is not necessarily the case as due to the provision of the separated integrated channels 11, there is more freedom to place the injection points 10a, 10b at a different location.

(15) Furthermore, it is possible to provide a separate injection point 10a, 10b for each channel 11.

(16) However, it is also possible that more than one channel 11 starts from an injection point 10a, 10b.

(17) As can be seen in FIG. 2, in this case a separate separated integrated channel 11 is provided for each bearing 8.

(18) Moreover, in this case more than one channel 11 is also provided for the compression space 4. In this case there are two channels 11 that run from the injection points 10a to the compression space 4.

(19) Additionally one or more cavities 12 can be provided in the housing 3.

(20) In the example shown there are three cavities 12.

(21) One cavity 12 acts as a liquid reservoir for liquid for the compression space 4, the other two cavities 12 act as a liquid reservoir for liquid for the bearings 8.

(22) For the bearings 8 one cavity 12 is provided on the inlet side 5 and one cavity 12 on the outlet side 6.

(23) The cavities 12 ensure a connection between the injection points 10a, 10b and one or more of the separated integrated channels 11 connected thereto.

(24) It is clear that the injection point 10a at the location of the compression space 4 connects to the cavity 12 for liquid for the compression space 4.

(25) The channels 11 that open into the compression space 4 also connect to this cavity 12.

(26) Analogously, the injection points 10b at the location of the bearings 8 and the channels 11 that open into the bearings 8 connect to the cavities 12 for liquid for the bearings 8.

(27) It is clear that it is also possible that if the design of the compressor element 2 and the housing 3 so allows, only one injection point 10b is provided and one cavity 12 for liquid for the bearings 8. In this case the liquid will be brought to all bearings 8 using the channels 11.

(28) Furthermore, the liquid-injected compressor device 1 comprises a liquid separator 13, whereby the outlet 6 for compressed gas is connected to the inlet 14 of the liquid separator 13.

(29) The liquid separator 13 comprises an outlet 15 for compressed gas, from where the compressed gas can be guided to a consumer network for example, not shown in the drawings.

(30) The liquid separator 13 further comprises an outlet 16 for the separated liquid.

(31) The liquid separator 13 is connected to the aforementioned outlet 16 by means of an injection circuit 17 connected to the compressor element 2.

(32) This injection circuit 17 comprises two separate separated injection pipes 17a, 17b, which both start from the liquid separator 13.

(33) The injection pipes 17a, 17b will ensure two separate separated liquid supplies to the compressor element 2.

(34) The injection points 10a, 10b in the housing 3 ensure the connection of the compressor element 2 to the injection circuit 17.

(35) A first injection pipe 17a leads to the aforementioned injection point 10a at the location of the compression space 4.

(36) The second injection pipe 17b leads to the injection points 10 that are placed at the location of the bearings 8.

(37) As already mentioned above in this case, but not necessarily, there are two injection points 10b for the bearings 8, i.e. one for each end of the shaft 9 of the rotor 7.

(38) To this end the second injection pipe 17b will be split into two sub-pipes 18a, 18b, whereby one sub-pipe 18a, 18b will come out at each end of the shaft 9.

(39) If there is only one injection point 10b for the bearings, the channels 11 will take over the function of the sub-pipes 18a, 18b, or in other words: then these sub-pipes 18a, 18b are integrated in the housing 3 in the form of two separated integrated channels 11 that run from the injection point 10b to the bearings 8.

(40) It is clear that for the aforementioned channels 11, as shown in FIG. 2, it can be said that they form part of the injection circuit 17 and as it were form an extension of the sub-pipes 17a and 17b. In other words, a part of the injection circuit 17 is integrated in the housing 3.

(41) A cooler 19 is provided in the first injection pipe 17a. This cooler 19 can for example, but not necessarily for the invention, be provided with a fan for cooling the liquid that flows through this first injection pipe 17a. Of course the invention is not limited as such and another type of cooler 19 can also be used, for example with a cooling liquid such as water or similar.

(42) A controllable valve 20 is also provided, in this case, but not necessarily, a throttle valve.

(43) By means of this throttle valve the quantity of liquid that is injected in the compression space 4 can be adjusted.

(44) A cooler 21 is also provided in the second injection pipe 17b, whereby in this case use can be made of a cooling fluid, such as water for example, to cool the liquid or it can be cooled by a fan.

(45) Furthermore, in this case two controllable valves 22 are provided in the second injection pipe 17b, one in each sub-pipe 18a, 18b.

(46) It is also possible that one single controllable valve 22 is provided, for example in the form of a three-way valve at the location of the connecting point P between the two sub-pipes 18a, 18b.

(47) It is also possible to replace the two valves 22 by one valve 22 that is not a three-way valve, but for example is an ordinary (two-way) control valve, that is provided upstream from the division of the injection pipe 17b into the sub-pipes 18a, 18b.

(48) The operation of the compressor device 1 is very simple and as follows.

(49) During the operation of the compressor device 1 a gas, for example air, will be drawn in via the gas inlet 5 that will be compressed by the action of the rotors 7 and leave the compressor element 2 via the outlet.

(50) As liquid is injected into the compression space 4 during the operation, this compressed air will contain a certain quantity of the liquid.

(51) The compressed air is guided to the liquid separator 13.

(52) There the liquid will be separated and collected underneath in the liquid separator 13.

(53) The compressed air, now free of liquid, will leave the liquid separator 13 via the outlet 15 for compressed gas and can be guided to a compressed gas consumer network, for example, not shown in the drawings.

(54) The separated liquid will be carried back to the compressor element 2 by means of the injection circuit 17.

(55) A proportion of the liquid will be transported to the compression space 4 via the first injection pipe 17a and the channels 11 connected thereto, another proportion to the bearings 8 via the second injection pipe 17b, the two sub-pipes 18a, 18b and the channels 11 connected thereto.

(56) Hereby the coolers 19, 21 and the controllable valves 20, 22 will be controlled according to a method that consists of first controlling the mass flow of the liquid supplies, i.e. the controllable valves 20, 22, and then controlling the temperature of the liquid supplies, i.e. the coolers 19, 21.

(57) The aforementioned control is thus a type of master-slave control, whereby the master control, in this case the control of the controllable valves 20, 22, is always done first.

(58) It is important to note here that the coolers 19, 21 and controllable valves 20, 22 are controlled independently of one another, this means that the control of the one cooler 19 is not affected in any way by the control of the other cooler 21 or that the control of the one controllable valve 20 has no effect on the control of the other controllable valves 22.

(59) The control will be such that the properties of the liquid are attuned to the requirements for the compression space 4 and for the bearings 8 respectively.

(60) As mentioned above, by applying both controls a synergistic effect will occur as a result of a functional interaction between the two controls.

(61) Preferably the method consists of controlling the temperature and mass flow of the liquid supplies such that the specific energy requirement of the liquid-injected compressor device 1 is a minimum.

(62) The specific energy requirement (SER) is the ratio of the power (P), e.g., electrical power consumption by the motor 28, of the compressor device 1, which can be determined by the controller 29, to the flow rate (FAD) supplied by the compressor device 1 compared to the standard operating conditions of the compressor element 2. By comparing the SER to the specification of the compressor element 2, the efficiency of the compressor element can be determined.

(63) Although in the examples shown the injection circuit 17 is formed by two separated independent injection pipes 17a, 17b, it is not excluded that a third independent injection pipe is provided, which leads to the drive of the compressor device 1.

(64) A cooler 19, 21 and a controllable valve 20, 22 can also be incorporated in this third injection pipe.

(65) This third injection pipe will ensure the lubrication and cooling of the drive, whereby this drive can take on the form of a motor with the necessary transmissions and gear wheels.

(66) The control of the cooler 19, 21 and the controllable valve 20, 22 in this third injection pipe can be controlled in the same way as for the other two injection pipes 17a, 17b, whereby in this case it will be ensured that the quantity and temperature of the injected liquid are optimised for the requirements of the drive.

(67) Although in the example shown the injection circuit 17 comprises two separate separated injection pipes 17a, 17b both of which start from the liquid separator 13, it is not excluded that only one injection pipe 17a, 17b starts from the liquid separator 13, whereby this injection pipe 17a, 17b is split at a location downstream from the liquid separator 13 and upstream from the controllable valve 20. This location can be between the cooler 19 and the controllable valve 20, for example.

(68) An advantage of this is that only one connection between the injection circuit 17 and the liquid separator 13 has to be provided and that the cooler 21 may be omitted.

(69) FIG. 3 shows an alternative embodiment of a compressor device 1 according to the invention, which differs from the previous embodiment of FIG. 1 because in this case a bypass pipe 23 is provided across the cooler 19 and the controllable valve 20.

(70) In this case a three-way valve 24 is provided at the tap-off of the bypass pipe 23 upstream from the cooler 19 to control the quantity of liquid that can flow via the bypass pipe 23 and via the cooler 19.

(71) The operation of the compressor device 1 is largely analogous to the operation of the embodiment of FIG. 1.

(72) Only the control of the controllable valve 20 and the cooler 19 for the temperature and the flow rate of the liquid supply to the compression space 4 will be done differently in this embodiment.

(73) When the temperature T at the outlet 6 is still lower than the set value T.sub.set, the three-way valve 24 will send a proportion of the liquid supply through the bypass pipe 23 instead of through the cooler 19. The liquid that flows through the bypass pipe 23 will not be cooled so that the cooling capacity of the injected liquid in the compression space 4 will decrease.

(74) If necessary, an ever greater proportion of the liquid supply will be sent through the bypass pipe 23 to decrease the cooling capacity and let the temperature T rise above the set value T.sub.set.

(75) When all the liquid is sent through the bypass pipe 24 and the temperature T is still too low, the quantity of liquid that is injected will be reduced by closing the three-way valve 24 so that less liquid is allowed through.

(76) The quantity of liquid will be decreased until the temperature T is at least equal to the set value T.sub.set.

(77) Using the cooler 19 and the three-way valve 24 whereby the oil 15 can be sent partly through the bypass pipe 23 and partly through the cooler 19, the cooling capacity can be controlled continuously without the quantity of injected liquid, i.e. the flow rate of the liquid supply, having to be changed for this purpose.

(78) Moreover, only in the last instance is the quantity of injected liquid reduced so that the lubrication and the seal between the rotors 7 and/or the rotors 7 and the housing 3 by the liquid is not reduced.

(79) An analogous control can also be used to ensure that the temperature T at the outlet 6 is not higher than a set value T.sub.max.

(80) This set value Tmax is limited by an ISO standard and its maximum value is for example equal to the degradation temperature T.sub.d of the liquid. If need be, the set value T.sub.max can be a few degrees less than this degradation temperature T.sub.d in order to build in a certain safety, for example 1° C., 5° C. or 10° C., depending on the level of extra safety that is desired or necessary.

(81) If the temperature T at the outlet 6 is higher than the set value T.sub.max, the three-way valve 24 will increase the flow of the liquid supply that is injected via the bypass pipe 23 into the compression chamber 4 until the temperature T at the outlet 6 falls to the set value T.sub.max.

(82) If the maximum quantity of liquid is already being injected or if the temperature T at the outlet 6 is still too high when the maximum quantity of liquid is being injected, the three-way valve 24 will send at least a proportion of the liquid supply through the cooler 19.

(83) If this was already the case or if it is insufficient, a larger proportion of the liquid supply will gradually be sent through the cooler 19 until the temperature T falls sufficiently.

(84) When it turns out to be necessary to send the entire liquid supply through the cooler 19 and the cooling capacity is still insufficient to bring the temperature T down to the set value T.sub.max, then the cooler 19 will switch on, whereby the cooling capacity is increased.

(85) As a result the liquid in the cooler 19 will be cooled more.

(86) The cooling capacity of the cooler 19 is increased until the temperature T at the outlet 6 is, at a maximum, equal to the set value T.sub.max.

(87) Through a combination of both methods for controlling the temperature, it can be ensured that the temperature T is kept within certain limits in order to increase the lifetime of the liquid and the compressor installation 1.

(88) Moreover, such a method will ensure that the cooler 19 is always switched off first or switched on last when the cooling capacity of the injection circuit 17 has to be decreased or increased respectively, which will provide an energy saving.

(89) FIG. 4 shows a second alternative embodiment of a compressor device 1 according to the invention.

(90) In this case the aforementioned bypass pipe 23 only extends across the controllable valve 20, which is constructed as a throttle valve for example.

(91) The bypass pipe 23 acts as a safety device if the controllable valve 20 fails so that it can always be ensured that a liquid supply to the compression space 4 is possible.

(92) FIG. 5 shows a third alternative embodiment of a compressor device 1 according to the invention.

(93) In this case a third independent injection pipe 17c is provided that starts from the liquid separator 13 and leads to the inlet 5.

(94) A cooler 25 is also incorporated in this third injection pipe 17c. In this case a controllable valve 26 is also provided to control the liquid flow rate.

(95) Atomisation 27 is also provided in the third injection pipe 17c at the location of the inlet 5.

(96) This atomisation 27 will atomise, i.e. spray or nebulise, the liquid supply so that the liquid will go into the inlet 5 as small droplets.

(97) Due to this atomisation the heat transfer between the gas and the liquid will be optimum because a greater contact area between the two is created.

(98) The magnitude of the heat transfer will be determined, among others, by the size of the liquid droplets and their distribution in the gas flow.

(99) The atomisation 27 can comprise a number of high frequency vibrating rods and injection nozzles. An alternative can be an atomisation 27 based on the jet expansion of gas/liquid mixtures.

(100) Preferably the atomisation 27 can be controlled in order to control the size of the droplets and to be able to adapt the distribution of the droplets.

(101) For the third injection pipe 17c the temperature of the liquid supply can be controlled by means of the cooler 25, and the flow rate by means of the controllable valve 26, and the spray by means of the atomisation 27.

(102) This will enable the liquid to be injected and atomised in the inlet 5 with an optimum distribution of small liquid droplets and with the desired temperature and flow rate whereby it can respond to the changing (environmental) parameters and requirements regarding lubrication, sealing and cooling.

(103) According to the invention the aforementioned liquid can be oil or water.

(104) The present invention is by no means limited to the embodiments described as an example and shown in the drawings, but such a method for controlling the liquid injection of a compressor device and a liquid-injected compressor device can be realised according to different variants without departing from the scope of the invention.