AIR-COOLED DEVICE AND METHOD FOR CONTROLLING AN AIR-COOLED DEVICE

A method for controlling an air-cooled device (1) for compressing a gas, which device includes at least one element (2) for compressing the gas, at least one air-cooled cooler (9, 12) for cooling a fluid in the device (1) and two or more fans (10, 13), at least one of the fans (10, 13) being an adjustable-speed fan (13) for generating a flow of cooling air for cooling the air-cooled cooler (9, 12). When the air-cooled cooler (9, 12) does not need to cool, the method includes controlling the speed of the adjustable-speed fan (13) to a minimum required speed in order to avoid at least a backflow of cooling air traveling in a direction opposite to the flow.

The present invention relates to a method for controlling an air-cooled device for compressing a gas.

In this context, “device for compressing a gas” can mean a compressor device, a blower device and a vacuum pump device.

In particular, the invention is intended to control an adjustable-speed fan, with which the device is equipped.

In this case, “air-cooled device” means that the device comprises at least one air-cooled cooler for cooling a liquid, for example oil, injected into an element of the device and/or for cooling the gas compressed by the device.

It cannot be ruled out that the air-cooled device according to the invention further comprises another type of cooler.

The air-cooled cooler is provided with a fan that generates a flow of cooling air for cooling the air-cooled cooler.

The device is typically provided with a plurality of such fans that generate a flow of cooling air to cool one or more air-cooled coolers.

Said air-cooled coolers cool the injected liquid and/or the compressed gas.

In some cases, it is temporarily unnecessary to cool the injected liquid and/or the compressed gas.

The air coolers concerned should then not cool the injected liquid and/or the gas.

It is known that in the known devices for compressing gas, the fans concerned can then be switched off to ensure that less power is consumed by the fans.

Stopping the fans can cause a backflow of heated cooling air across the air-cooled coolers in case a plurality of coolers are connected to a common outlet for cooling air. This backflow of heated cooling air can then be mixed with fresh cooling air, as a result of which a mean cooling air temperature increases on a cold side of the air-cooled coolers where cooling is still required, which then results in an undesired decrease in cooling capacity.

For this reason, slats or louvers are often used to stop this undesired backflow.

This has the disadvantage of being associated with an additional cost and making the device bulkier.

In addition, this is paired with a pressure drop in the cooling air across the slats, as a result of which more power is needed in order to achieve the same volume flow of cooling air, even when the slats are fully opened.

The present invention has the objective of providing a solution for at least one of the aforementioned and/or other disadvantages.

The present invention relates to a method for controlling a device for compressing a gas, which device comprises at least one element for compressing the gas, at least one air-cooled cooler for cooling a fluid in the device and two or more fans, at least one of the fans being an adjustable-speed fan for generating a flow of cooling air for cooling the air-cooled cooler, characterized in that, when the air-cooled cooler does not need to cool, the method consists of controlling the speed of the adjustable-speed fan to a minimum required speed in order to avoid at least a backflow of cooling air traveling in a direction opposite to the flow.

One advantage is that the method according to the invention allows an energy consumption of the device to be optimized by optimizing an energy consumption of the adjustable-speed fan or fans.

By running the adjustable-speed fan at the minimum required speed at the times when this is possible, energy consumption can be minimized.

A further advantage is that a backflow of heated cooling air is avoided without an additional pressure drop occurring in the cooling air flow when the adjustable-speed fan does provide cooling air for cooling.

This is because the minimum required speed of the fan ensures that the adjustable-speed fan generates a minimum cooling air flow that ensures that backflow is not possible.

The times when the air-cooled cooler does not need to cool not only depend on which function said cooler has, i.e., whether said cooler cools the compressed gas or a liquid injected into the element, but also on an operating mode of the device.

Said cooler can be a cooler for the injected liquid, an intercooler for the compressed gas or an aftercooler for the compressed gas.

The speed of the adjustable-speed fan is preferably reduced to the minimum required speed if:it is not necessary to cool the compressed gas in case the air-cooled cooler is used to cool the gas compressed by the device; and/ora heat recovery system provides a necessary cooling of the fluid instead of the air-cooled cooler; and/orthe element is stopped or running without a load.

In some cases, the compressed gas does not need to be cooled if a consumer of said compressed gas requires warm or hot gas for its application.

It is also possible for the device to be provided with a heat recovery system. If said system recovers enough heat, no additional cooling by the aforementioned air-cooled cooler is necessary. The heat recovery system can be used for a liquid circuit of the device and for the compressed gas.

In the case of devices having a plurality of elements connected in parallel, it is possible for one or more of the elements to be switched off or run without a load at certain times, for example when there is less demand for compressed gas, as a result of which no cooling is necessary for this element of the injected liquid and/or the compressed gas.

According to a preferred feature of the invention, the adjustable-speed fan is driven by a fan motor that is cooled by said fan, and the method consists of controlling the speed of the adjustable-speed fan to the minimum required speed if the air-cooled cooler does not need to cool in order to avoid the backflow of cooling air and in order to cool the aforementioned fan motor just enough to prevent the fan motor from overheating.

One advantage is that, in this manner, overheating of the fan motor is avoided and not only the backflow of heated cooling air.

The invention also relates to a device for compressing gas, which device comprises at least one element for compressing gas, at least one air-cooled cooler for cooling a fluid in the device and two or more fans for cooling the air-cooled cooler, at least one of the fans being an adjustable-speed fan for generating a flow of cooling air for cooling the air-cooled cooler, characterized in that the adjustable-speed fan is provided with a controller that is configured to carry out a method according to the invention.

The advantages of such a device are similar to those of the method.

With a view to better demonstrate the features of the invention, a number of preferred embodiments of an air-cooled device according to the invention and a method according to the invention for controlling an air-cooled device are described below, without any restrictive character, with reference to the accompanying drawings, in which:

The device1according to the invention shown inFIG.1comprises two elements2for compressing gas connected in parallel.

Each element2has an inlet3and an outlet4with an outlet line5connected thereto, the two outlet lines5converging to form an outlet line6of the device1.

The elements2can be screw compressor elements, but this is not necessary for the invention.

The elements2are in this case liquid-injected elements2, but this is not necessary for the invention.

Furthermore, a liquid separator7is provided in the respective outlet line5downstream of each element2for separating the liquid injected into the element2.

The separated oil is returned to and injected into the element2via a return line8.

In both return lines8, an air-cooled cooler9is provided with a fan13.

In this case, said fans13have a variable speed. Within the scope of the invention, it can of course not be ruled out that the fans have no variable speed provided that another fan in the device has a variable speed.

In this case, a heat recovery system11is provided in each return line8downstream of the liquid separator7and upstream of the air-cooled coolers9, which heat recovery system can recover heat generated by the element2from the liquid. Said heat is reused, for example, for heating applications or for heating domestic water.

Said heat recovery systems11are optional for the invention.

Downstream of both liquid separators7, the outlet lines5of the elements2converge into the outlet line6of the device1.

An air-cooled cooler12is arranged in said outlet line6of the device1with a fan10that is a fixed-speed fan10.

Said cooler12is also referred to as an aftercooler.

All coolers9,12are connected to a discharge (not shown in the figures) for cooling air that discharges the heated cooling air after it has passed through the coolers9,12.

The aforementioned adjustable-speed fans13are in this case each provided with a variable-speed fan motor14that is controlled by one controller15.

The aforementioned controller15is configured to control the adjustable-speed fans13according to a method according to the invention.

Furthermore, the controller15is connected to temperature sensors16that, in this case, each measure a temperature of the liquid in the return line8upstream of the cooler9. It cannot be ruled out that the temperature sensors16measure the temperature of the liquid downstream of the coolers9.

The controller15is also connected to an inlet sensor17that measures environmental parameters of the gas to be compressed and to pressure sensors18that each measure a pressure of the cooling air flow generated by the adjustable-speed fan13.

The aforementioned environmental parameters include, for example, but are not limited to an atmospheric pressure, ambient temperature and/or humidity of the gas in an environment of the device1.

The operation of the device1is very simple and as follows.

The elements2compress gas in the known manner, liquid being injected into the element2in order to lubricate and cool the element2.

The liquid is separated via the liquid separator7and passed through the heat recovery systems11via the return lines8. The liquid is then cooled in the air-cooled coolers9before it is injected back into the elements2.

The compressed gas then passes through the cooler12in the outlet line6of the device1, where it undergoes cooling.

The controller15controls the fan motors14according to a method according to the invention.

When the heat recovery systems11are in operation, the coolers9do not need to cool because the liquid is already cooled when it passes through said coolers9.

In such cases, the controller15controls the adjustable-speed fans13such that the speed of the adjustable-speed fans13is reduced to the minimum required speed to prevent a backflow of cooling air, i.e., to prevent heated cooling air in the discharge for cooling air coming from the other coolers9and/or the cooler12in the outlet line6of the device1flowing back to the coolers9.

The aforementioned minimum required speed is in this case determined on the basis of the environmental parameters and the pressure of the cooling air flow generated by the fan13.

If the fans10,13have a common outlet for cooling air, the minimum required speed can also be determined on the basis of a pressure of the cooling air in said common outlet for cooling air.

The controller15determines said minimum required speed on the basis of the signals of the inlet sensor17and the pressure sensor18.

It is also possible that only the environmental parameters or only the pressure of the air flow generated by the fan13or only the pressure of the cooling air in the common outlet for cooling air is taken into account.

If the controller15determines that the liquid is sufficiently cooled on the basis of the measurements from the temperature sensors16, the controller15controls the fan motors14in such a way that the speed of the fans13drops to the aforementioned determined minimum required speed.

In all these cases, the fan motors14consume less energy.

The aforementioned minimum required speed as described above is preferably determined at regular intervals, the minimum required speed being adapted if the parameters on the basis of which the minimum required speed is determined change.

However, it is also possible for the minimum required speed to be a predetermined fixed value that is determined on the basis of a worst-case scenario of the operating mode of another fan10and/or the cooler12in the outlet line6of the device1.

This means that the controller15controls the adjustable-speed fans13in the aforementioned cases in which no cooling is necessary in such a way that the speed of the adjustable-speed fan13is equal to said fixed minimum required value.

In this case, the adjustable-speed fan motors14also consume less energy.

It is important to note that the adjustable-speed fans13are brought back to their minimum possible speed in these cases, such that a reduction in energy consumption is also maximized.

It should be clear that the device1ofFIG.1is only one possible embodiment.

FIG.2shows by way of illustration a first variant ofFIG.1, three elements2for compressing gas being connected in parallel in this case.

In this case, air-cooled coolers9are provided in the return lines8, each having their own adjustable-speed fan13.

Each of said fans13is driven by a variable-speed fan motor14and all are controlled by one controller15.

This is not necessary because it is also possible for each fan13to have its own sub-controller.

It is also possible that some fans13are provided with one common controller15and that the other fans13are each provided with their own, separate sub-controller.

In this case, each of said adjustable-speed fans13also cools its associated fan motor14.

Furthermore, each fan motor14is provided with a temperature sensor19that can measure a temperature of the fan motor14, for example a temperature of a winding and/or bearing in the fan motor14.

Said temperature sensors19are connected to the controller15.

The controller15is also connected to pressure sensors18that measure a pressure of the cooling air flow generated by the fans13.

An aftercooler in the form of an air-cooled cooler12is also provided in the outlet line6of the device1, which aftercooler is provided with a fan10that has no adjustable speed.

In this case, a heat recovery system11is not provided, nor is a temperature sensor16provided downstream of the cooler9.

In this case, the controller15controls the fans13of the air-cooled coolers9in the return lines8in such a way that, if one or more of said coolers9does not need to cool, the speed of the respective fans13is brought back to the minimum required speed in order to prevent a backflow of cooling air and cool the aforementioned fan motor14.

One or more of said coolers9does not need to cool if the respective element2is stopped or running without a load.

If heat recovery systems11are provided, one or more of the coolers9also do not need to cool in the event that it is no longer necessary to cool the returned liquid if the heat recovery systems11can sufficiently cool the liquid.

In these cases, the speed of the respective fans13can be brought back to the aforementioned minimum required speed.

The minimum required speed is now determined on the basis of the environmental parameters, a pressure of the air flow generated by the fan13and a temperature of a fan motor14of the adjustable fan13.

On the basis of signals from the sensors17,18,19, the controller15determines said minimum required speed.

If the fans13or the fans10and13have a common outlet for cooling air, the minimum required speed can also be determined on the basis of a pressure of the cooling air in said common outlet for cooling air.

If the controller15receives the signal that cooling the returned liquid is not necessary and/or that one of the elements2is stopped or running without a load, the controller15controls the relevant fan motor14in such a way that the speed of the fan13drops to the aforementioned determined minimum required speed, which ensures that the fan13still cools the fan motor14sufficiently to avoid overheating and that the fan13avoids a backflow of heated cooling air.

In all these cases, the fan motor14consumes less energy.

FIG.3shows a second variant ofFIG.1.

In this case, it is an oil-free two-stage device having two two-stage installations installed in parallel.

Each two-stage installation comprises a low-pressure element2afor compressing the gas and a high-pressure element2bfor further compressing the gas compressed by the low-pressure element2a, which low pressure element and high-pressure element are installed in series.

The device1is provided with intercoolers9between the low-pressure element2aand the high-pressure element2b.

Each of said fans13is driven by a variable-speed fan motor14and all are controlled by one controller15.

In this case, each of said adjustable-speed fans13also cools its associated fan motor14.

Furthermore, each fan motor14is provided with a temperature sensor19that can measure a temperature of the fan motor14, for example a temperature of a winding and/or bearing in the fan motor14.

Said temperature sensors19are connected to the controller15.

The controller15is also connected to pressure sensors18that measure a pressure of the cooling air flow generated by the fans13.

Downstream of the high-pressure elements2b, a heat recovery system11is accommodated in each outlet line5.

In addition, a heat recovery system11is accommodated in each outlet line5of the two-stage installations upstream of the high-pressure elements2band the intercoolers9, in addition to the intercoolers9.

It is also possible that only the heat recovery systems11are present upstream of the high-pressure elements2b.

An aftercooler in the form of an air-cooled cooler12is also provided in the outlet line6of the device1, which aftercooler is provided with a fan10that has no adjustable speed.

The operation is otherwise analogous to the embodiments described above.

In this case, the respective fans13can be adjusted to the minimum required speed if the heat recovery between the low-pressure element2aand the high-pressure element2bis active and/or one of the two two-stage installations installed in parallel is switched off or stationary.

Although, in the examples described above, each air-cooled cooler9,12is cooled by one fan10,13, it cannot be ruled out that an air-cooled cooler9,12is cooled by more than one fan10,13and/or that one fan10,13cools a plurality of air-cooled coolers9,12.

Although, in all of the examples described above, the air-cooled cooler12in the outlet line6of the device1is provided with a fixed-speed fan10, it cannot be ruled out that said air-cooled cooler12is provided with an adjustable-speed fan13.

FIG.3shows this with a dotted line.

The adjustable-speed fan13is provided with a fan motor14that is driven by the controller15to which said fan motor is connected.

The speed of said fan13of the air-cooled cooler12can be controlled to the aforementioned minimum required speed if the compressed gas supplied by the device does not need to be cooled because the consumers do not need cooled compressed gas.

It cannot be ruled out that, in this case, the heat recovery systems11are not present in the outlet lines5downstream of the high-pressure elements2b.

The present invention is by no means limited to the embodiments described as examples and shown in the figures, but an air-cooled device according to the invention and a method according to the invention for controlling an air-cooled device can be realized according to various alternatives without going beyond the scope of the invention.