Patent Application
20210324858
The present invention relates to an oil-injected multistage compressor device.
It is well known that with oil-free compression of gas using a compressor device, the technical limitations, especially as regards the maximum permitted outlet temperature of the compressed gas leaving the compressor element of said compressor device, dictate that the compression of the gas traditionally occurs in two or more steps or ‘stages’, whereby two or more compressor elements are placed in a series one after the other.
These technical limitations can be resolved by injecting a coolant such as water or oil into the compressor element, which makes single-stage compression possible.
Since having multiple stages involves substantial complexity and additional costs, the current preference is for an oil or water-injected single-stage compressor device.
Also, the fact that the maintenance of multistage compressor devices is more extensive and that they are more complex means that single-stage compressor devices are still often preferred.
The advantage of improved efficiency for the second and subsequent stages in a multistage compressor device would outweigh the aforementioned drawbacks. This improved efficiency would be possible by cooling the gas and thereby reducing the consumption of the second and subsequent stages. However, this is not as simple as it may seem.
There are already two-stage compressor devices in which oil is injected between the two stages in order to cool the compressed gas downstream from the first compression stage and upstream of the second compression stage, e.g. by using an oil curtain, whereby the cooler oil lowers the temperature of the gas.
However, such a solution only allows a limited cooling of the gas and provides only a limited improvement in efficiency over oil-free multistage compressor devices.
In addition, extra oil is added to the gas, which is not always desirable.
An oil-injected multistage compressor device can be used as an alternative, in which, for example, an intercooler is provided between the first and second compressor elements, whereby the intercooler will actively extract heat from the compressed gas after the first compression stage.
However, this is not done for the following reasons:
Due to the disadvantages that would be associated with using an intercooler in an oil-injected multistage compressor device, it should be possible, in principle, to achieve a significant gain in efficiency by cooling to ensure that the net result is favorable, whereby this gain can be limited by the presence of condensate.
Even if the problem of the condensate were not to come into play, it can be assumed that the cooling would still be insufficient because the temperature rise of the oil and gas mixture after the first compression stage would not be sufficient.
The present invention aims at providing a solution to at least one of the aforementioned and/or other disadvantages.
The object of the present invention is an oil-injected multistage compressor device that comprises at least one low-pressure stage compressor element with a gas inlet for gas to be compressed and a gas outlet for low-pressure compressed gas, and a high-pressure stage compressor element with a gas inlet for low-pressure compressed gas and a gas outlet for high-pressure compressed gas, whereby the outlet of the low-pressure stage compressor element is connected to the gas inlet of the high-pressure stage compressor element by a conduit, with the characteristics that a regulatable intercooler provided between the low-pressure stage compressor element and the high-pressure stage compressor element in the aforementioned conduit, which is configured in such a way that the temperature at the gas inlet of the high-pressure stage compressor element can be regulated so that it is above the dew point, that the intercooler comprises a regulatable air cooler and/or a regulatable water cooler, and that the intercooler is configured in such a way that the temperature of the air or the water can be changed by using a bypass conduit and/or by screening off part of the intercooler.
It has been found that cooling downstream from the low-pressure stage can cause a much bigger temperature drop in the gas than described in the literature.
When the temperature at the outlet of the low-pressure compressor element is measured, the temperature of the oil and gas mixture is measured. Due to the wet bulb effect, the temperature measured will be lower than the actual temperature of the gas.
In other words, the potential temperature drop of the gas that can be achieved is actually much greater than described in the literature.
This also means that the potential gain in efficiency by cooling is greater than previously assumed, so that the aforementioned disadvantages do not outweigh the improved efficiency.
One advantage is that, with the help of such an oil-injected multistage compressor device, greater performance can be achieved than with the known compressor devices without cooling or with an oil-injection in the form of an oil curtain.
According to the invention, the intercooler is also regulatable; the intercooler can be configured so that the temperature at the gas inlet of the high-pressure stage compressor element can be kept above the dew point.
Keeping the temperature at the inlet of the high-pressure stage compressor element above the dew point prevents condensate from forming at this location.
Making the intercooler regulatable means that maximum cooling is possible at any moment without forming condensate. It is therefore no longer necessary to assume a worst-case scenario when determining the cooling capacity of the intercooler. This is because, at the moment that the dew point would rise and the intercooler would cool the gas too much such that condensate would occur, the intercooler can be regulated to cool the gas less so that condensate does not form.
The intercooler can be made regulatable in various ways. A requirement of the regulatable intercooler is that the degree of cooling of the gas, or the temperature drop of the gas, can be changed. This can be done, for example, by changing the cooling capacity of the intercooler and/or by guiding part of the gas via a bypass conduit instead of via the intercooler.
As is already known, the dew point is not a fixed value but depends on various parameters such as temperature, humidity, and the pressure of the gas. There are various ways to determine this dew point.
The possible presence of condensate can be detected based on the dew point.
According to a preferred embodiment of the invention, the intercooler is provided with a heat pump.
This has the advantage that it is possible to cool to a much lower temperature, so that the maximum cooling capacity can be achieved when there is no risk of condensate forming downstream of the intercooler, so that the high-pressure stage compressor element will be much more efficient.
The total gain in efficiency or performance will therefore be a lot greater.
The invention also relates to a method for controlling an oil-injected multistage compressor device with a regulatable intercooler, characterized in that the method comprises the following steps:
The advantages of such a method are similar to the aforementioned advantages of the oil-injected multistage compressor device.
To better demonstrate the features of the invention, the following describes, as a non-exhaustive example, some preferred embodiments of an oil-injected multistage compressor device and method according to the invention, with reference to the accompanying drawings, in which:
The schematically shown oil-injected multistage compressor device 1 in
Both compressor elements 2 and 3 in this example are screw compressor elements, but this is not necessary for the invention since other types of compressors can also be used.
Both compressor elements 2 and 3 are also provided with an oil circuit for the injection of oil in the respective compression chambers of the compressor elements 2 and 3. For clarity, these oil circuits are not shown in the Figure.
The low-pressure stage compressor element 2 has a gas inlet 4a for gas to be compressed and an outlet 5a for low-pressure compressed gas.
Gas outlet 5a is connected to gas inlet 4b of the high-pressure stage compressor element 3 via conduit 6.
The high-pressure stage compressor element 3 is also equipped with a gas outlet 5b for high-pressure compressed gas, whereby the outlet 5b is connected to a liquid separator 7.
It is possible for the outlet 8 of this liquid separator 7 to be connected to an aftercooler.
An intercooler 9 is included in the aforementioned conduit 6 between the low-pressure stage compressor element 2 and the high-pressure stage compressor element 3 which, according to the invention, can be regulated.
This intercooler 9 can be designed in various ways.
Intercooler 9 can, for example, include air cooling that can be controlled by a fan, for instance, whereby the air flow can be regulated by adjusting the speed of the fan.
Alternatively, intercooler 9 can include, for example, a water cooler that can be regulated by a valve, for instance, which may control the flow of the water.
It is also possible, for example, to regulate intercooler 9 by changing the temperature of the air or water.
In this case, intercooler 9 is equipped with a heat pump 10, although this is not necessary for the invention.
This heat pump 10 may also be regulatable, but this is not necessarily the case.
With the help of heat pump 10, it will be possible to extract even more heat from the gas.
Compressor device 1 is also equipped with a control unit or regulator 11 for controlling or regulating intercooler 9. If heat pump 10 is regulatable, this control unit or regulator 11 can also control heat pump 10.
In the example in
This regards, for example, a sensor 12a that can measure one or more environmental parameters at the gas inlet 4a of the low-pressure stage compressor element 2.
This sensor 12a can measure the pressure, temperature, and/or humidity.
It is not excluded that, instead of this sensor 12a or in addition to it, second measuring means 13 are provided, which measure the humidity at gas inlet 4b of high-pressure stage compressor element 3.
These second measuring means 13 could be a sensor 13a, provided at gas inlet 4b of high-pressure stage compressor element 3. The schematic for this is shown with a dotted line in the Figure.
Furthermore, device 1 as shown in the example is equipped with third measuring means 14 in the form of a sensor 14a at gas inlet 4b of high-pressure stage compressor element 3 in order to measure the temperature at this location.
Finally, it is not excluded for device 1 to be equipped with an oil-injection 15 so that oil can be injected into conduit 6 downstream from intercooler 9. The schematic for this is shown with a dotted line.
The operation of the oil-injected multistage compressor device 1 is very simple and as follows.
During operation, the gas to be compressed, e.g. air, will be sucked in via gas inlet 4a of low-pressure stage compressor element 2 and will undergo an first compression stage.
The partially compressed gas will flow via conduit 6 to intercooler 9, where it will be cooled and then to gas inlet 4b of high-pressure stage compressor element 3 for subsequent compression.
Oil will be injected into both low-pressure stage compressor element 2 and in high-pressure stage compressor element 3, which ensures the lubrication and cooling of compressor elements 2, 3.
The compressed gas will leave high-pressure stage compressor element 3 via gas outlet 5b and then be guided to oil separator 7.
The injected oil will be separated and the compressed gas can then possibly be guided to an aftercooler before being sent to consumers.
In order to ensure that condensate is not formed when the gas is cooled by intercooler 9, this intercooler 9 must be properly regulated to accommodate changes in the environmental parameters and/or drive parameters of compressor elements 2, 3.
For this, the control unit or regulator 11 will regulate intercooler 9 so that the temperature of inlet 4b of high-pressure stage compressor element 3 is above the dew point. As previously mentioned, this results in no condensate forming after intercooler 9 at gas inlet 4b of high-pressure stage compressor element 3.
In a first step, the dew point, or accordingly the presence of condensate, at gas inlet 4b of high-pressure stage compressor element 3 is determined or calculated. The dew point depends on various parameters and is therefore a variable and not a fixed value.
There are different options or ways to determine the dew point.
In the case of the embodiment shown in
For this, the measured values of sensor 12a are transmitted to the control unit or regulator 11, which calculates the dew point on this basis.
If the oil-injected multistage compressor device 1 is equipped with a humidity sensor 13b at gas inlet 4b of high-pressure stage compressor element 3, it is also possible to directly determine the dew point, or accordingly the presence of condensate, based on measuring the humidity at gas inlet 4b. Humidity sensor 13b will also transmit the measured value to control unit 11 at this point.
Another alternative is to determine the dew point by following the course of the temperature at gas inlet 4b of high-pressure stage compressor element 3, e.g. by using temperature sensor 14b at inlet 4b of high-pressure stage compressor element 3 or another sensor specially provided for this purpose.
In this case, temperature sensor 14b will transmit the measured values of the temperature at gas inlet 4b to the control unit or regulator 11, which monitors and evaluates the course of the measured temperatures to use as a basis for determining the dew point.
Once the dew point has been determined, the control unit or regulator 11 will regulate intercooler 9 as necessary so that the temperature at gas inlet 4b of high-pressure stage compressor element 3 is above the dew point.
For this purpose, the control unit or regulator 11 will request the temperature at gas inlet 4b using temperature sensor 14b and compare it with the determined dew point.
Control unit 11 will allow intercooler 9 to cool more when this temperature at inlet 4b is higher than the dew point, since the temperature of the gas can fall even more without the formation of condensate.
If the temperature is still higher than the dew point when intercooler 9 is already cooling at maximum output, control unit 11 will start heat pump 10.
Of course, it is also possible that heat pump 10 is continuously in operation and that the regulation is carried out only using intercooler 9.
It is also possible for heat pump 10 to be regulated, so that when the dew point falls and there is then an increase in the required cooling capacity, control unit 11 allows an increase in cooling capacity first in intercooler 9 and then heat pump 10 or vice versa or both simultaneously or alternately.
If the temperature at gas inlet 4b of high-pressure stage compressor element 3 is lower or equal to the dew point, control unit 11 will have intercooler 9 cool less, so that the temperature of the gas will rise to prevent the formation of condensate.
If heat pump 10 is also regulatable, control unit 11 can first lower the cooling capacity of heat pump 10 or alternatively lower the cooling capacity of intercooler 9 and of heat pump 10.
If the dew point drops, the control unit or regulator 11 can have intercooler 9 once again cool more, so that the temperature of the gas will fall again.
In this way, maximum cooling is always possible without the formation of condensate.
Always being able to cool optimally means that the performance of high-pressure stage compressor element 3 can be maximized.
If device 1 is equipped with oil-injection 15, this can be used to achieve additional cooling of the gas. In addition, the injected oil will provide additional lubrication for high-pressure stage compressor element 3.
An alternative embodiment is shown in
The present invention is by no means limited to the embodiments described as examples and shown in the figures, but an oil-injected multistage compressor device according to the invention and a method for controlling a compressor device can be achieved following different variants without going beyond the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018/5657 | Sep 2018 | BE | national |
| 2018/5658 | Sep 2018 | BE | national |
| 2019/5205 | Apr 2019 | BE | national |
This application is a National Stage of International Application No. PCT/IB2019/058064 filed Sep. 24, 2019, claiming priority based on Belgian Patent Application No. 2018/5657 filed Sep. 25, 2018, Belgian Patent Application No. 2018/5658 filed Sep. 25, 2018 and Belgian Patent Application No. 2019/5205 filed Apr. 1, 2019.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2019/058064 | 9/24/2019 | WO | 00 |
