Not applicable.
Not applicable.
Not applicable.
The present invention relates to a method and an arrangement for controlling the flow of a coolant fluid in a compressor, in particular in a rotary compressor.
The compressors of interest here, in particular rotary compressors, are specifically screw-type compressors with fluid injection. Because such machines are frequently employed at a number of different sites, they are ordinarily movable or at least transportable. From these machines the compressed process fluid is sent through conduits to attached process-fluid consuming apparatus, for example compressed-air tools such as pneumatic hammers, pneumatic impact screwdrivers, pneumatic grinders etc.
Such compressors, for instance oil-injection screw compressors, have been known for many years. During the compression process a coolant fluid, in particular oil, is injected into the compression space to become mixed with the process fluid in these compressors. The coolant fluid serves to cool the process fluid by conducting the heat of compression away into a separate cooling circuit, and in addition acts to lubricate particular components of the compressor as well as to seal off the compression space. If the process fluid is air, it is usually sucked in from the surroundings and therefore usually contains an amount of water vapor that depends on its temperature.
A first problem, which in this case becomes apparent during the injection or recycling of the coolant fluid, lies in the risk that the temperature will fall below the condensation point for the water vapor present in the air used as process fluid. Water that has condensed out can to a certain extent become emulsified with the coolant fluid, in particular the oil, or can even be injected or recycled as an extra phase. This presents the following disadvantages, among others: reduction of the lubricant properties of the coolant fluid, increased corrosion of the components, and greater wear and tear of the bearings in the compressor.
A second problem, which should be distinguished from the first, arises when the process fluid, in particular the compressed air in the conduit leading to the pneumatic apparatus, cools off so that water contained in the process fluid condenses out. As a result, corrosion can occur in the pneumatic apparatus, with permanent damage as a potential consequence. The problem is exacerbated when within the conduits to the pneumatic apparatus, or in the apparatus itself, ice formation occurs because of the low ambient temperature and the conduits to or within the pneumatic apparatus are thereby partially or completely blocked. These effects can be made still worse by expansion of the compressed air in the apparatus, which can lead to functional inadequacies or even total failure of the associated pneumatic apparatus to operate.
A third, additional problem is created when the temperature regulation conventionally provided for the coolant fluid is designed to prevent only the first two problems, so that a process fluid at high temperatures is delivered to the pneumatic consuming apparatus. When the ambient temperature is high, only a slight degree of cooling occurs on the way to the pneumatic consuming apparatus, which can cause thermally induced injury to the operator of the apparatus.
Many preliminary considerations are known regarding ways to control the coolant fluid in compressors against the background of the problems cited above. A technical regulation principle in current use for controlling the temperature of a coolant fluid in compressors is disclosed, for example, in patent EP 0 067 949 B1. Here a thermostatic slide valve determines whether coolant fluid is sent through a fluid cooler to be used for cooling, or is shunted past the cooler in order to raise the temperature. With this form of regulation the temperature of the coolant fluid is kept relatively constant, and is set at a level such that on one hand it does not cause the temperature of the process fluid to fall below the condensation point, while on the other hand a temperature so high as potentially to damage the coolant fluid is avoided.
In U.S. Pat. No. 4,289,461 a further developed valve unit with an inlet and an outlet for coolant fluid is described. Here again, the volume flow of the coolant fluid in a bypass conduit that bridges the fluid cooler is regulated, such that a portion of the flow of coolant fluid is always passed through the fluid cooler. The regulation is achieved by means of a valve comprising two control units that act in opposite directions, one control unit operating dependent on the inlet temperature and the second one, dependent on the system temperature. One of the disadvantages of this design is that the control valve is complicated in structure and subject to malfunction, and furthermore a certain minimal volume flow of coolant fluid passes through the fluid cooler. Hence this proportion of the coolant fluid is constantly cooled, which thus also lowers the temperature of the process fluid.
U.S. Pat. No. 4,431,390 discloses a form of regulation in which a second bypass conduit is also provided as a shunt around the fluid cooler. In this second bypass conduit there is an additional valve which, when activated by a processor, allows a specific amount of coolant fluid to bypass the cooler in the form of a pulse. The release of these pulses by the processor depends on various parameters. Hence this solution is extremely elaborate to implement, both because multiple parameters must be monitored and evaluated and because an additional bypass conduit must be provided.
The solutions discussed above are predominantly concerned with the problem of keeping the coolant fluid in the compressor itself at a temperature such that water does not condense out and hence impairment of the coolant fluid and of the compressor is prevented. At the same time, the forms of regulation here disclosed are designed so as also to avoid raising the coolant fluid to a temperature high enough to be potentially damaging. However, the problems associated with the condensation of water while it is in the pneumatic consumer devices or in the conduits leading thereto are not addressed.
A variant of a solution relevant to this point is known from the patent DE 36 01 816 A1. There the compressed process fluid, which has been heated to about 60xc2x0 C. above the intake temperature of the compressor, is passed through an overdimensioned after cooler to bring it down to a temperature about 10xc2x0 C. above the intake temperature. A considerable proportion of the water vapor present in the process fluid is thereby caused to condense out and is eliminated by a condensate trap. The compressed process fluid is subsequently sent to a heat exchanger where it is rewarmed so that ultimatelyxe2x80x94influenced to some degree by the current ambient parameters, which in this design are assumed to be unchangingxe2x80x94a process fluid is produced that is quite dry and about 60xc2x0 C. above the intake temperature, i.e. very hot.
It is an object of the present invention to provide an arrangement for controlling the coolant fluid in a conventional compressor which has a simple, economical and reliable construction and wherein it is possible to reduce or, where possible, avoid the condensation of water out of both a coolant fluid and a process fluid output by the compressor to another apparatus, in particular with respect to condensation and freezing events in the receiving apparatus itself, while a high degree of operating facility is maintained.
According to a first aspect of the present invention there is provided an arrangement for controlling the flow of a coolant fluid through a compressor comprising: a coolant-fluid inlet for coolant fluid discharged from the compressor and a coolant-fluid outlet for returning the coolant fluid to the compressor; a fluid cooler through which at least a proportion of the coolant fluid can be passed for cooling, when necessary; a system-control actuator which controls the magnitude of the proportion of the coolant fluid that passes through the fluid cooler on the basis of system parameters including the temperature of the coolant fluid by fluid-control means; a fluid-control device; and a summer-/winter-operation actuator, which in a summer position takes priority over the system-control actuator so as to limit the action of the system-control actuator in one direction, such that when the summer-/winter-operation actuator is activated, the proportion of the coolant fluid that is passed through the fluid cooler is increased or diminished by the fluid-control device.
The present invention therefore provides a summer-/winter-operation actuator which, taking priority over the system-control actuator, in a summer position completely or partially overrides the action of the system-control actuator in a direction such that when the summer-/winter-operation actuator is activated, the proportion of the coolant fluid flow that is sent through the fluid cooler is appropriately increased or reduced by a fluid-control means.
The invention achieves its object by making use of the fact that the temperature of the process fluid at the point where it emerges from the installation is determined by the temperature of the coolant fluid, and in particular corresponds approximately to the maximal temperature of the coolant fluid. Control of the temperature of the process fluid at the installation output can therefore be accomplished by influencing both the injection temperature and the injection amount of the coolant fluid.
To avoid undesired condensation of moisture in the compressor, but especially in the conduits leading to apparatus receiving the compressed process fluid from the compressor and/or within the apparatus themselves, the arrangement can initially be adjusted so that the process fluid is less strongly cooled and is sent to the consuming apparatus or into the conduits leading thereto at a comparatively high temperature. The cooling that occurs within the conduits, or by the time the fluid reaches the consuming apparatus, then usually suffices to ensure the comfort of the personnel responsible for operating the consuming apparatus. Only when the ambient temperature is high, so that the cooling effect on the process fluid as it is conducted to the consuming apparatus is in some circumstances no longer as great, does the invention provide for further cooling of the process fluid under the influence of a summer-/winter-operation actuator.
The summer-/winter-operation actuator or, more generally speaking, an ambient-temperature-compensation actuator, is provided in order to compensate as far as possible a reduction or enhancement of cooling brought about by a higher or lower ambient temperature. The terms xe2x80x9csummerxe2x80x9d and xe2x80x9cwinterxe2x80x9d in the context of summer-/winter-operation actuator or summer/winter position are used herein and in the claims in order to facilitate understanding, and in general designate two different kinds of ambient conditions, namely warmer surroundings on one hand and colder surroundings on the other hand.
Hence the winter operation is intended to prevent the temperature from falling below the condensation point of the process fluid on its way to the consuming apparatus, whereas the summer operation is intended to avoid exceeding a maximal temperature at the apparatus.
With the arrangement described here it is possible by simple means to solve, in a reliable and economical manner, problems of all three kinds present in the state of the art, namely condensation in the compressor, condensation in the conduits leading to the consuming apparatus or in the apparatus themselves, and excessive heating of the consuming apparatus devices just when the ambient temperature is high.
In an alternative embodiment the summer-/winter-operation actuator, which in more general terms can be called an ambient-temperature-compensation actuator for compensating effects on the cooling of fluid associated with a higher or lower temperature of the ambient air, comprises a manual control apparatus by means of which the summer-/winter-operation actuator can be adjusted, in particular can be switched between two positions, namely a summer position and a winter position. Obviously the manual control apparatus can be constructed in various ways; for example, it can comprise a hand-operated lever, a setting wheel, where appropriate with a stepping-down action, and/or another suitable control device.
In one specific embodiment the summer-/winter-operation actuator comprises an actuating shaft with a cam structure such that the cam structure acts on the fluid-control device by way of a control element. In this case the actuating shaft can, for instance, cooperate with the manual control device or also be driven by an electric motor or by pneumatic or hydraulic means.
In another alternative embodiment the summer-/winter-operation actuator is functionally connected to a thermocouple in contact with the outside air, so that the outside-air thermocouple activates the summer-/winter-operation actuator in dependence on the external or ambient temperature.
In yet another alternative embodiment the summer-/winter-operation actuator is functionally connected to a thermosensor that activates the summer-/winter-operation actuator in dependence on the outside temperature. In both of the preceding embodiments the advantage over a manual control apparatus is that there is automatic compensation of an elevated or reduced cooling effect when the ambient air is colder or warmer, whereas with a manual control apparatus the activation of the summer-/winter-operation actuator has to be performed by the operating personnel.
In an especially preferred embodiment the system-control actuator and the summer-/winter-operation actuator are functionally connected to a common fluid-control device that adjusts the proportion of the coolant-fluid flow that is directed through the fluid cooler, such that the functional connection between the system-control actuator and the fluid-control device is completely or partially interrupted in one direction of action when the summer-/winter-operation actuator is adjusted in the direction towards a summer position. In this way, when both the system-control actuator and the summer-/winter-operation actuator influence the flow of the coolant fluid by way of only one common fluid-control device, control of the cooling of the process fluid can be especially simply and effectively accomplished. At the same time the actuator prioritization, which is regarded as a useful feature, is implemented in a particularly simple manner, inasmuch as when it is needed, the summer-/winter-operation actuator can be put into a position in which it completely or partly eliminates the action of the fluid-control device in one direction. This makes it possible to set the installation initially to a relatively high temperature of the process fluid, as described at the outset, and then, when the ambient temperature is high, to make corrections by means of the summer-/winter-operation actuator.
In one embodiment of the invention the system-control actuator and summer-/winter-operation actuator are disposed coaxially, which enables a relatively simple construction.
In another preferred embodiment a displaceably mounted control element is made integral with the fluid-control device, as a control cylinder. Here the displaceably mounted control element is a force- or action-transmitting means, which need not necessarily be immersed in the fluid flow. Preferably also, the one-piece cylinder extends into the fluid flow and simultaneously comprises sealing surfaces, to seal off the fluid channel.
In a structurally preferred embodiment the system-control actuator is attached to and preferably within the control element and is braced against a contact surface that is fixed in a given position regardless of the position of the summer-/winter-operation actuator. Thus depending on the position of the summer-/winter-operation actuator, the system-control actuator is only partially effective or in some circumstances entirely ineffective in one direction of action with respect to adjustment of the fluid-control device.
In one concrete, advantageous embodiment the summer-/winter-operation actuator acts on the control element by way of a displacement piston, directly or indirectly, to adjust the fluid-control device.
The summer-/winter-operation actuator can be switched between at least two positions. Preferably it can also occupy one or more intermediate positions or, as is especially preferred with respect to control technology, can be shifted continuously between a first (winter) position and a second (summer) position.
Furthermore, it is also possible to apply a logical reversal of the idea underlying the present invention, namely to use the arrangement for controlling the flow of coolant fluid so as to keep the process fluid in a compressor initially at a relatively low temperature, at which it is subject to condensation, and at critical, in this case cool ambient temperatures to give the summer-/winter-operation actuator or compensation actuator priority for influencing the flow of coolant fluid so as to raise the temperature of the process fluid. Moreover, with the concept of prioritization according to the present invention, the temperature of the process fluid can be influenced not only by controlling the temperature of the coolant fluid injected into the compressor but also, additionally or alternatively, by altering the volume flow of the coolant fluid.
Preferably also, the fluid-control device is positioned at a junction between a bypass conduit that bridges the fluid cooler and a cooling conduit associated with the fluid cooler, in such a way that when the flow of coolant fluid through the fluid cooler is increased, the amount of coolant fluid flowing through the bypass conduit is simultaneously reduced. In this case the junction at which the fluid-control device is positioned can be situated either ahead of the fluid cooler in the direction of flow or after the fluid cooler. Positioning of the fluid-control device at a junction is regarded as particularly advantageous because as the one flow component is increased, a simultaneous reduction of the other component is brought about, so that the influence of this action is extremely effective.
According to a third aspect of the present invention there is provided a method of controlling the flow of a coolant fluid through a compressor, in particular through a rotary compressor, in order to adjust the temperature of a process fluid wherein the coolant fluid discharged from the compressor can be directed through a fluid cooler when necessary for cooling, the proportion of coolant fluid injected into the compressor or the proportion of the coolant fluid that is directed through the fluid cooler being controlled on the basis of system parameters including the temperature of the coolant fluid, and wherein, in order to prevent condensation or ice formation in apparatus receiving the output from the compressor or in conduits connecting the compressor to such apparatus when the temperature of the outside air is low, in particular when the temperature of the outside air falls below a certain threshold TG, the proportion of coolant fluid injected into the compressor is decreased or the magnitude of the proportion of the coolant fluid directed through the fluid cooler is reduced or is interrupted.
In a preferred embodiment of this method, the coolant flow directed through the fluid cooler is initially reduced irrespective of the outside-air temperature and is only increased when the outside air becomes warm, in particular when its temperature rises above the threshold TG.
The present invention will now be described by way of example with reference to the attached drawings.