Patent Application
20210017971
The present invention belongs to the sector of multi-cylinder reciprocating compressors, wherein a fluid is compressed thanks to the action exerted by a plurality of pistons which slide inside a respective cylinder, being driven by one motor which, by way of a crankshaft, transmits motion to the connecting rods used to drive the pistons.
In particular, this invention belongs to the sector of reciprocating compressors used in frigorific circuits to compress a thermal carrier fluid, by increasing the pressure of the latter in such a way that it can subsequently expand in a heat exchanger, thereby subtracting heat from another fluid.
The device according to the present invention is preferably, but not exclusively, used in carbon dioxide compressors.
The multi-cylinder reciprocating compressors of the prior art comprise a casing which develops according to a horizontal longitudinal axis and receives an electric motor internally thereto which drives a crankshaft into rotation, by means of which pistons slidingly coupled inside their respective cylinders are driven, these cylinders being defined internally to the casing. The casing is roughly shaped like a cylindrical surface developing along a horizontal axis. The crankshaft drives the pistons by way of connecting rods.
A head is associated with the upper portion of the cylinders and receives valves internally thereto and hermetically interfaces to a corresponding opening defined on the top of the casing; the oil used for lubricating the kinematic mechanisms is collected in the lower section of the casing.
The head is hollow and is generally subdivided in two portions by a longitudinal partition diaphragm, which lays in a vertical plane and defines a low-pressure suction chamber and a high-pressure delivery chamber internally to the head.
Generally, but not necessarily, one head is used for every cylinder bank, typically two or more cylinders for every head.
High pressures are reached internally to the compressors, which is one of the reasons why much attention is paid to seal upon manufacturing them; generally, one or more end covers are associated with the casing and co-operate with the head to hermetically close it.
Many compressors used in the frigorific industry are of a so-called “hermetic” type, which means compressors for which no disassembling capabilities exist; other compressors are of a “semi-hermetic” type, i.e. they have the capability of being partially disassembled, an operation which aims at taking the electric motor only out after removing an end cover.
The sucked fluid is input via an external low-pressure cock located on the outer wall of the casing; a sucking duct is defined downstream of this cock, internally to the casing, and is used to transfer the fluid up to the suction chamber of the head.
The flow of the fluid being sucked, which is in low pressure and low temperature conditions, cools the complete compressor and in particular the electric motor.
The compressed fluid, which is at a maximum temperature and tends to heat the complete compressor, is delivered to the external world via an external high-pressure cock which opens into a collective pressure chamber; the latter receives the compressed fluid coming from the delivery chambers of the individual heads, and the delivery chambers are in turn fed by the individual cylinders of the compressor.
Another function performed by the collective pressure chamber consists of homogenizing the pressure of the delivery fluid produced by the individual cylinders, so as to reduce the sudden changes in pressure that are typical of reciprocating compressors.
The collective pressure chamber comprises a safety overpressure valve, calibrated to open whenever the pressure inside the collective pressure chamber reaches excessive values; safety valves are usually calibrated to pressures ranging from 130 to 140 bars.
The collective pressure chamber is always at a maximum temperature and is never cooled by the fresh low-pressure fluid; in particular, should the frigorific fluid be carbon dioxide, the temperatures reached exceed 150° C. during the compression step and are much higher than the temperatures reached by the frigorific fluids belonging to the family of hydrofluorocarbon (HFC) fluids.
In traditional compressors, the collective pressure chamber is located inside the casing, however, in order to prevent these so high temperatures from jeopardizing the operation of the compressor, configurations have been developed aiming at reducing transmission of the heat generated by the compressed thermal carrier fluid towards the individual component parts of the compressor and up to the lubricating oil that is stored inside the casing; as a matter of fact, oil becomes less viscous and loses its lubricating power if its temperature increases too much, thus jeopardizing the internal members of the compressor.
In addition, if the compressor becomes too hot, the gas being sucked is also unavoidably heated before the compression step starts.
Patent IT1399335 discloses a compressor wherein the head, in which the thermal carrier fluid suction and delivery chambers are defined, defines an undercut with the casing, in order to foster heat dissipation in the head and to reduce the amount of heat that is transmitted from the head to the casing and to the oil contained therein, thus limiting compressor heating. The same patent document discloses an embodiment comprising two casing portions, angularly staggered from each other, on each of which a cylinder is defined for a respective piston of the compressor. Both casing portions are closed by one dual head, which defines two corresponding and opposed head portions which comprise suction chambers and sections of a common delivery chamber, whose central portions forms the collective pressure chamber, respectively; the latter is bridged between the two head portions, thus defining, together with the casing, a channel open to the environmental air, which fosters heat dissipation.
However, the configuration disclosed above is delicate and expensive to implement, because it obliges to manufacture a head with two different interfacing surfaces to their corresponding surfaces present on the casing for each cylinder bank; since the interfacing surfaces on the casing are not coplanar, the interfacing surfaces of the head are not coplanar either and, as known, it is not easy to manufacture accurately mechanical components that are hollow, are suitable for withstanding high pressures, and simultaneously offer hermetic surfaces laying in different planes, especially if these are not parallel.
This difficult, which is already considerable in the case of heads for two-head compressors, exponentially increases as the number of heads increases.
In the industry of frigorific plants, in particular in those which use carbon dioxide, a need is thus felt for compressors having a collective pressure chamber at least partially separated from the casing, so that it can transfer at least a part of the heat which develops during the operation to the environmental air; a need is also felt for devices that are easy and cost-effective to manufacture.
An object of the present invention is to provide a multi-cylinder reciprocating compressor that is capable of disposing of the heat generated by the operation, in particular if thermal carrier fluids are used that reach high temperatures, such as, for example, carbon dioxide.
A further object of the present invention is to implement a compressor that includes a collective pressure chamber at least partially separate from the casing and is licked by the environmental air to which it transfers a part of the compression heat.
A not less important object of the present invention is to provide a compressor that does not include component parts expensive to manufacture.
These objects and others, which will be apparent to those skilled in the art upon reading the following text, are achieved by a compressor wherein the delivery chambers of the heads of at least two cylinders are connected to each other by at least one external manifold, which makes up a collective pressure chamber which the compressed fluid goes out from via a high-pressure cock.
In the case of compressors with more than two cylinders, there might be a plurality of external manifolds, each of which having its own high-pressure cock and its own safety overpressure valve.
The following detailed description of an embodiment of the invention is given for explanatory non-limitative purposes only and makes reference to the attached drawings, and highlights further characteristics and advantages deriving therefrom and being an integral part of the subject invention.
The multi-cylinder reciprocating compressor according to the present patent application is enclosed within a casing (1), featuring a roughly cylindrical shape, which develops along a longitudinal axis and whose ends are hermetically closed by two covers; an electric motor is also accommodated inside the casing (1) and drives a crankshaft, by way of which motion is transmitted to pistons sliding inside cylinders. A lower lubricating oil collection area is defined inside the casing (1).
An opening hermetically closed by a hollow head (2) is defined at the upper end of each cylinder, on the top portion of the casing (1); the hollow head (2) is internally partitioned by a vertical longitudinal diaphragm which defines a suction chamber (21) and a delivery chamber (22) therein.
One and the same head (2) typically, but not mandatorily, serves one cylinder bank, which comprises a plurality of the latter.
On one of the outer walls of the delivery chambers (22) of at least two of said heads (2) there are defined respective exhaust openings, through which said delivery chambers (22) are hermetically connected to each other via a manifold (3), which is external and is at least partially not in contact with said casing (1) together with which it defines a channel which environmental air flows through and consequently removes heat; the manifold (3) also comprises a high-pressure cock (4) and a safety overpressure valve (31).
The input fluid, which is in low pressure conditions, enters the compressor through a low-pressure cock (5) placed on the outer lateral surface of the casing (1) and, from the low-pressure cock (5), it reaches the suction chamber (21) in every head (2) by crossing a suction duct defined internally to the casing (1) itself.
A particularly complete embodiment of the compressor according to the present invention comprises the presence of at least one transparent porthole for monitoring the level of the lubricating oil.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102019000012123 | Jul 2019 | IT | national |
