Rotary expansible chamber devices – Heat exchange or non-working fluid lubricating or sealing – With condition responsive control of non-working fluid
Reexamination Certificate
2002-10-29
2004-04-13
Vrablik, John J. (Department: 3748)
Rotary expansible chamber devices
Heat exchange or non-working fluid lubricating or sealing
With condition responsive control of non-working fluid
C418S001000, C418S085000, C418S087000, C418S097000
Reexamination Certificate
active
06719546
ABSTRACT:
RELATED U.S. APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
REFERENCE TO MICROFICHE APPENDIX
Not applicable.
FIELD OF THE INVENTION
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.
BACKGROUND OF THE INVENTION
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 60° C. above the intake temperature of the compressor, is passed through an overdimensioned after cooler to bring it down to a temperature about 10° 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 ultimately—influenced to some degree by the current ambient parameters, which in this design are assumed to be unchanging—a process fluid is produced that is quite dry and about 60° C. above the intake temperature, i.e. very hot.
BRIEF SUMMARY OF THE INVENTION
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
Kaeser Kompressoren GmbH
Sidley Austin Brown & Wood LLP
Vrablik John J.
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