CA2202818C - Thermostatically controlled intercooler system for a multiple stage compressor and method - Google Patents
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Abstract
A thermostatically controlled intercooler system for use with a multiple stage compressor to prevent the condensation of water from the compressed gas, such as air, within the system, whereby the temperature of a compressed gas entering a second compressor stage following the first compressor stage is controlled to a target temperature, ideally up to about 250°F., as will not allow the partial pressure of the water vapor therein to exceed the saturation vapor pressure associated with and defined by the temperature achieved by cooling the air prior to the air entering the subsequent compression stage.
Description
THERMOSTATICALLY CONTROLLED INTERCOOLER SYSTEM
FOR A MULTIPLE STAGE COMPRESSOR AND METHOD
FIELD OF THE INVENTION
The present invention relates, in general, to multiple stage compressors and., more particularly, this invention relates to a thermostatically controlled intercooler system for use with multiple stage compresssors that functions to control the inlet temperature of the cc>mpressed gas at a second and/or subsequent compression stage to effectively prevent the condensation of water within the compressor. By permitting controlled, preselected amounts of uncooled compressed gas from one compressor stage to by-pass the in-line intercooler, the combined temperature of the compressed air emerging jointly from the intercooler and by--pass can be controlled to a predetermined value, selected to assure that the partial pressure of the water vapor therein does n.ot exceed the saturation vapor pressure associated with and defined by that temperature and compression ratio of the previous compression stage.
BACKGROUND OF THE INVENTION
Mechanical, single stage, air compressors are well known in the art which compri:~e one of several different types, such as piston and cyl.inder_ type, centrifugal type, axial-flow type, turbine type and even other types. The simplest and most common type in use is the piston and cylinder type. In this type compressor, air, or <~ny gas, is admitted via a valve into the cylinder where a reciprocating piston therein compresses the air or gas within the cy7_inder and displaces the compressed air to a conduit or reservoir from which it can be taken for use as may be required.
Multiple stage air compressors are also well known in the prior art. Such multiple stage compressors are utilized to compress air and/or other gas to pressures which are higher than can normally be achieved with a single stage compressor. These multiple stage compressors normally comprise a plurality of mechanical single stage compressors of any one type or the other, interconnected in series, wherein the compressed gas is passed from one stage to the next with the pressure thereof being increased at e<~ch succeeding stage. In the typical multiple stage compressor of the piston and cylinder type, air or gas, at ambient pressure and temperature, is admitted into the cylinder of the first compressor stage where a first reciprocating piston serves to compress t:he air therein and displace it to the second stage and so on through all the stages in the system, with each stage further compres:~ing the previously compressed gas until the final desired pressure is achieved.
It is also wel=L known that most multistage compressors normally includ~= a c:o~~ling step of the compressed air between at least some of the various compressor stages so that the overall compression may be more isothermal than adiabatic. That is to say, because of the ideal gas law, (PV = nRT), each compression stage of the air will, of course, cause an increase in pressure, P, as intended, and will also cause a directly proportional increase in the air temperature, T.
FOR A MULTIPLE STAGE COMPRESSOR AND METHOD
FIELD OF THE INVENTION
The present invention relates, in general, to multiple stage compressors and., more particularly, this invention relates to a thermostatically controlled intercooler system for use with multiple stage compresssors that functions to control the inlet temperature of the cc>mpressed gas at a second and/or subsequent compression stage to effectively prevent the condensation of water within the compressor. By permitting controlled, preselected amounts of uncooled compressed gas from one compressor stage to by-pass the in-line intercooler, the combined temperature of the compressed air emerging jointly from the intercooler and by--pass can be controlled to a predetermined value, selected to assure that the partial pressure of the water vapor therein does n.ot exceed the saturation vapor pressure associated with and defined by that temperature and compression ratio of the previous compression stage.
BACKGROUND OF THE INVENTION
Mechanical, single stage, air compressors are well known in the art which compri:~e one of several different types, such as piston and cyl.inder_ type, centrifugal type, axial-flow type, turbine type and even other types. The simplest and most common type in use is the piston and cylinder type. In this type compressor, air, or <~ny gas, is admitted via a valve into the cylinder where a reciprocating piston therein compresses the air or gas within the cy7_inder and displaces the compressed air to a conduit or reservoir from which it can be taken for use as may be required.
Multiple stage air compressors are also well known in the prior art. Such multiple stage compressors are utilized to compress air and/or other gas to pressures which are higher than can normally be achieved with a single stage compressor. These multiple stage compressors normally comprise a plurality of mechanical single stage compressors of any one type or the other, interconnected in series, wherein the compressed gas is passed from one stage to the next with the pressure thereof being increased at e<~ch succeeding stage. In the typical multiple stage compressor of the piston and cylinder type, air or gas, at ambient pressure and temperature, is admitted into the cylinder of the first compressor stage where a first reciprocating piston serves to compress t:he air therein and displace it to the second stage and so on through all the stages in the system, with each stage further compres:~ing the previously compressed gas until the final desired pressure is achieved.
It is also wel=L known that most multistage compressors normally includ~= a c:o~~ling step of the compressed air between at least some of the various compressor stages so that the overall compression may be more isothermal than adiabatic. That is to say, because of the ideal gas law, (PV = nRT), each compression stage of the air will, of course, cause an increase in pressure, P, as intended, and will also cause a directly proportional increase in the air temperature, T.
While thi:~ is not normally a problem in a typical single stage compressor, where a defined volume of air is compressed but once, the relatively high air pressures obtained in most multistage comb>ressors can result in the compressed air having excessive and problematical temperatures, but for the intermediate cooling of the compressed air between the various compression stages.
For example, compressed air temperatures in excess of 500°F.
are not only a. hazard to persons therearound, but can cause operating difficulties of various different forms, such as, malfunctioning valve; and other compressor components. As a result, practically all commercially available multiple stage compressors include ~~n intercooler system of some sort between at least some of the compression stages for the purpose of preventing excessive heating of the compressed gases compressed to such high pressure levels.
It is al~;o well known that water exists as vapor in practically any ambient air to be compressed in a conventional compressor, which is quantified as the relative humidity of the air. The relative humidity of the air, expressed as a percent value, is the ratio of (a) the water vapor actually present in the air, in comparison to (b) the saturation vapor pressure at the temperature in question. The saturation vapor pressure is a function of t:he air temperature, so that as the temperature increases for any given sample of air, the saturation vapor pressure incre<~ses, and accordingly, the relative humidity decreases.
For example, compressed air temperatures in excess of 500°F.
are not only a. hazard to persons therearound, but can cause operating difficulties of various different forms, such as, malfunctioning valve; and other compressor components. As a result, practically all commercially available multiple stage compressors include ~~n intercooler system of some sort between at least some of the compression stages for the purpose of preventing excessive heating of the compressed gases compressed to such high pressure levels.
It is al~;o well known that water exists as vapor in practically any ambient air to be compressed in a conventional compressor, which is quantified as the relative humidity of the air. The relative humidity of the air, expressed as a percent value, is the ratio of (a) the water vapor actually present in the air, in comparison to (b) the saturation vapor pressure at the temperature in question. The saturation vapor pressure is a function of t:he air temperature, so that as the temperature increases for any given sample of air, the saturation vapor pressure incre<~ses, and accordingly, the relative humidity decreases.
In a compressor, the above natural conditions can create a problem. Obviously, when the air is compressed, with little or no externally caused change in temperature, the temperature of the compressed air is increased in proportion to the increase in pressure, as noted above. Because the saturation vapor pressure of water is dependent: on the temperature of the air, it follows that when the temperature is increased the saturation vapor pressure is also increased.
Thereafter, if t:he compressed air is cooled by any means, such as an intercoole:r, for example, it is not uncommon for the water vapor pre:~sure in the compressed air to actually exceed the saturation vapor pressure for the compressed air. This is, particularly, t;he case if the compressed air is allowed to further cool th~sreafter. Therefore, it is not uncommon for this phenomenon to cause significant amounts of water to be condensed as liquid within the system.
Free water within the compressor, however, is known to cause a variety of problems, such as oxidation (rusting) of compressor components, and more importantly, cause condensed water to be admixed into the lubricating oil within the compressor sump.
Such dilution oi= the lubricating oil in the compressor with water can seriously impair the normal operation of the compressor as well as reduce _Lts overall useful life. Therefore, it is highly desirable to eliminate, or to at least substantially minimize, the condensation of such water within any compressor, particularly any such water that may find its way into the lubricating oil.
Thereafter, if t:he compressed air is cooled by any means, such as an intercoole:r, for example, it is not uncommon for the water vapor pre:~sure in the compressed air to actually exceed the saturation vapor pressure for the compressed air. This is, particularly, t;he case if the compressed air is allowed to further cool th~sreafter. Therefore, it is not uncommon for this phenomenon to cause significant amounts of water to be condensed as liquid within the system.
Free water within the compressor, however, is known to cause a variety of problems, such as oxidation (rusting) of compressor components, and more importantly, cause condensed water to be admixed into the lubricating oil within the compressor sump.
Such dilution oi= the lubricating oil in the compressor with water can seriously impair the normal operation of the compressor as well as reduce _Lts overall useful life. Therefore, it is highly desirable to eliminate, or to at least substantially minimize, the condensation of such water within any compressor, particularly any such water that may find its way into the lubricating oil.
SUMMARY OF THE INVENTION
This invention is predicated on our joint conception and development of a thermostatically controlled intercooler system for use with a multiple stage compressor, which can virtually prevent, or at :least significantly minimize, the condensation of water from the compressed air within the system. In the thermostatically controlled intercooler system of this invention, the inlet temperatures of the compressed air, at least at some of the compression stages following the first stage, are controlled to a value: that will prevent the partial pressure of the water vapor in the compressed air from exceeding the saturation vapor pressure at the pressure and temperature achieved by the previous compression stage, to virtually prevent, or at least greatly minimize, condensation of water within the compressor. Such a temperature control is effected by permitting controlled, preselected amounts of uncooled compressed air from the previous compre:>sor stages to by-pass the next in-line intercooler anc~ be. blended with the cooled compressed air emerging from -she intercooler. Such blending of cooled and uncooled compressed air will permit control of the temperature of the compres~~ed ai:r entering the next following compression stage, and with attention to such temperature control it is possible to select and control the temperature of that compressed air to a value that will not be increased upon further compression to a leve7_ that will exceed the normal safe operating temperature for an air compressor.
OBJECTS OF THE INVENTION
Accordingly, it is one of the primary objects of this invention to provide a new and improved multiple stage gas compressor having a significantly reduced tendency for water condensation therein.
Another object of the present invention is to provide a new and improved thermostatically controlled intercooler system for use with a multiple stage compressor that significantly reduces the tendency for water condensation within the multiple stage compressor.
A further object: of the present invention is to provide a new and improved thermostatically controlled intercooler system for use with a r~ulti.p:Le stage compressor that controls the inlet temperature of the compressed air at a second and/or subsequent compression stage t:o thereby substantially eliminate the condensation of water within the compressor.
Still anotJzer object of the present invention is to provide a new and improved thermostatically controlled intercooler system for use with a multip=Le stage compressor that controls the inlet temperature of the compressed air at a second and/or subsequent compression stage by permitting controlled amounts of uncooled compressed air to by-pass the intercooler, thereby raising the temperature of the inlet compressed gas entering the next compressor stage so that its temperature can be controlled to a level that will. prevent the saturation vapor pressure of the compressed gas from being reduced to a level below the partial pressure of wager vapor therein, to thereby prevent or minimize water condensation within the compressor.
These and other objects and advantages of the present invention will become more readily apparent to those persons skilled in the compressor art after a full reading of the following detailed description, particularly, when such description is taken in conjunction with the attached drawings as described below.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 i;s a simplified, schematic view of a two-stage gas compressor in.corpox~ating a thermostatically controlled intercooler system according to a presently preferred embodiment of this invention; and Figure 2 is a simplified, schematic view of a three-stage gas compressor incorporating a thermostatically controlled intercooler sy~~tem according to another presently preferred embodiment of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION
Prior to proceeding with a detailed description of the subject invention, it: is noted that for the sake of clarity, identical components which have identical functions have been identified with identical reference numerals throughout the several views of the attached drawings.
Reference i:o Figures 1 and 2 will illustrate in schematic form two presently preferred embodiments of this invention, namely, Figure 1 being a multiple stage compressor having two compressor stages with a single intercooler therebetween and Figure 2 being a multiple stage compressor showing the first three compressor stages in a system having a plurality of compressor stages, with an intercooler between at least the second and third compressor stages and between the third and any subsequent compressor stages.
In each of the Figures, the multiple stage compressors, generally designated 10, include a first compressor stage 10a, which is schematically illustrated as a piston and cylinder type of compressor having a piston 12 mounted for reciprocal movement within a cylinder 14.
While such piston and cylinder type of compressors are perhaps the most common, it should be appreciated that this invention can be incorporated into multiple stage compressors based on other forms of mechanical compressors, such as, a centrifugal type, an axial-flow type, a turbine type and other types, particularly any such multiple stage compressor wherein an intercooler is pro~aided between any two compressor stages for the purpose of preventing the compressed gas from becoming excessively heaved.
As is well known, piston and cylinder type mechanical compressors are provided with a suitable valve arrangement (not shown) which is closed during a compression stroke to permit the gas therein to be suitably compressed, with an outlet valve (not shown) opening thereafter, permitting the compressed gas to be directed out of the cylinder 14 and into a discharge line 18.
Thereafter, the outlet valve is closed as an inlet valve (not shown) is opened so that the reciprocating piston 12 will draw in fresh gas at ambient pressure to repeat the compression process. Such valuing arrangement is well known to those familiar with t:he art and need not be further described here.
As in sore.e two-stage compressors, an intercooler 16 is provided which is adapted to cool the gas compressed after a compressor stage, such as a first compressor stage 10a, before it is further compressed and heated in the next following compressor stage, i.e., compressor stage lOb. Accordingly, such discharge line 18 is :provided which is adapted to convey the gas compressed in c:ompre:~sor stage l0a into the intercooler 16 so that the gas heated in compression stage l0a by virtue of its compression can be cooled, at least to some degree, before it is further compressed :in compressor stage lOb.
As with other e7_ements of the compressor described above, the intercooler 16 is also well known to those familiar with the compressor art. Such intercooler 16, normally, comprises a radiator-type o.' cooler wherein the heated gas is passed through a plurality of thin radiator tubes spaced by cooling fins (not shown). Therefore, such intercoolers 16 need not be further described here :in detail.
As shown in Figure 2, the multiple stage compressor 10 may comprise more than two compression stages, such as three compression stages 10a, lOb and lOc, or even more, with an intercooler 16 operably disposed between any pair of adjacent compression stages. However, since excessive heating of the compressed gas is not normally a problem until a third or later compression stage i~~ involved, some commercially available multiple stage ~~ompressors may only utilize an intercooler before the third and a.ny subsequent compression stages.
In a like manner, as shown in the Figure 1 embodiment, an intercooler 16 is provided, in the embodiment of Figure 2, which is adapted to cool the gas compressed in compressor stage l0a before it is further compressed and heated in the second compressor stage lOb. Again, a discharge line 18 is provided which is adapted to convey the gas compressed in the first compressor stage l0a into the intercooler 16, so that the gas heated in compression stage l0a by virtue of its compression can be cooled, at least to some degree, before it is further compressed in compressor stage lOb.
In a similar manner to that described above, another intercooler 16b is provided which is adapted to cool the gas compressed in the second compressor stage lOb before it is further compressed arid heated in compressor stage lOc. Again, a discharge line 18b is provided which is adapted to convey the gas compressed in compressor stage lOb into the intercooler 16b so that the gas heated in compression stage lOb by virtue of its compression can be cooled, at least to some degree, before it is further compressed in compressor stage lOc.
In a like manner, additional intercoolers 16 are commonly operably dispow>ed between any pair of subsequent compressor stages for the purpose of cooling the previously compressed gas before it is further compressed and, accordingly, further heated in such following compression stage. The operation of the systems described above are conventional in the prior art and need not be further described here.
The crux of this invention resides in a selective by-pass system, incorporated with the intercoolers 16, which permits control of the compressed gas temperature admitted into any selected comprE:ssor stage after the first compressor stage so that such inlet: tempi=rature can be deliberately controlled and maintained at a predetermined level which will assure that prior to inlet into i_he next compression stage, the gas temperature will not reduct=_ to ~~ level whereby the associated saturation vapor pressure has been reduced to a value below the partial pressure of water va~~or at the intercooler pressure.
Accordingly, with reference to Figure 1, the inventive elements include a three-way valve 30 adapted to receive compressed gas cooled by the associated intercooler 16 and direct the compressed gas to the subsequent compressor stage lOb for further compression. In addition, a by-pass line 34 is also provided which interconnects the associated compressor stage l0a directly with t:he three-way valve 30. Accordingly, the by-pass line 34 is adapted t=o pass compressed gas directly from the associated compressor stage l0a to the three-way valve 30 without such compressed gas passing through the intercooler 16.
Therefore, the three-way valve 30 is adapted to selectively convey either cooled or uncooled compressed gas, or a controlled mixture thereof,, onto the next succeeding compressor stage lOb.
In additi0I1 to t:he three-way valve 30 and by-pass line 34, the inventive elements of this invention further includes a control means 36 for controlling the operation of such three-way valve 30. Obviously, control means 36 should be a control adapted to selectively pass either cooled or uncooled compressed gas, or mixtures thereof, as necessary to maintain a preselected target temperature of the compressed gas entering into the compression stage lOb.
The preselected target temperature will, of course, vary from one system to tree next but, as noted above, it should be a temperature which is determined to be one that will prevent the gas from cooling to a point where the associated saturation vapor pressure of the gas does not fall to a value below the partial pressure of the water vapor in the gas mixture at the point prior to the inlet for the next compression stage.
While the above description is addressed primarily to the thermostatically controlled intercooler system between the first and second compression stages of the multiple stage compressor shown in Figure 1, it should be readily apparent that any thermostatically controlled intercooler system should be substantially the same regardless of its location with respect to various compressor stages. The only differences, in essence, will be the tar<~et temperatures sought.
While a number of differing control means could be provided, and are within the scope of the present invention, we have preferred to use an "~~ff-the-shelf" three-way type valve having a built-in temperature controlled valve operation. Specifically, we have successfully used both a 1.5-inch and a 2-inch three-way valve manufactured by FLUID POWER ENERGY having the built-in, out-put temperature controller, whereby the desired out-put temperature can be selected and set on the valve, with the valve then automatically out-putting a mixture of the two in-put gasses as necessary to provide an out-put blend thereof matching the preselected ternperature. Since such valves are commercially available, it is believed that any further description and discussion thereof i~; not necessary here.
It may be apparent to those skilled in the art that exacting controls are not. in fact necessary. For a conventional two-stage compressor utilizing two compression cylinders in the first stage and one compression cylinder for the second stage, with an intercooler between the first stage and the second, we have determined that normal reliability levels and service life of the compressor can be expected if the ultimate temperature of the compressed gas, after compression in the second stage, remains below about 500°F. 7:n the above noted system, we have learned that such a goal can be achieved by controlling the compressed gas temperature enter_Lng the second stage at a level of generally no more than about 250°F.
Furthermore=_, in order to prevent the condensation of water due to excessivf=_ cooling of the air at the intercooler pressure for a compression ratio of about 4:1 per compression stage and design inlet con.ditiorLS for the preliminary compression stage set at about 150°F. and 100% relative humidity, a controlled output temperature at or abo~re about 213.4°F. is necessary. Thus, both objectives can be accomplished by controlling the output air between about 213.4°F. and about 250°F.
Therefore, if the temperature of the compressed air exiting the first stagE=_ is at or below about 250°F. , then all of that compressed air ~~an be passed directly to the second stage without any of it having to :be diverted through the intercooler. Only when the temperature of the compressed air emerging from any compressor stage is in excess of about 250°F., will it be necessary to divert a portion thereof through the following intercooler. By utilizing the temperature controlled three-way valve described above, the valve will itself adjust the temperature of the ou.t-put.
Further testing of the above described apparatus having a thermostatically controlled intercooler, as described herein, in contrast to a prior art compressor being identical in all other respects except for 'the absence of the inventive control, has shown that the prior art compressor has routinely caused water build-up in the lubricating oil in amounts exceeding 1.0 percent, and even 2.0 percent water after operating for a defined test period of time.
An identical compressor having the thermostatic control of this invention, has ~~anaged to keep such water build-up in the lubricating oil at amounts consistently below about 0.1 percent, when operating the controls as necessary only to keep the temperature of t:he cornpressed gas entering the second compressor stage, preferab:Ly, at or below about 200°F.
Having described in detail a presently preferred embodiment of this invent__on, it should be apparent that various other embodiments could be utilized and modifications incorporated therein by tho~~e persons who are skilled in the compressor art without departing from either the spirit of the invention or the scope of the appended claims.
This invention is predicated on our joint conception and development of a thermostatically controlled intercooler system for use with a multiple stage compressor, which can virtually prevent, or at :least significantly minimize, the condensation of water from the compressed air within the system. In the thermostatically controlled intercooler system of this invention, the inlet temperatures of the compressed air, at least at some of the compression stages following the first stage, are controlled to a value: that will prevent the partial pressure of the water vapor in the compressed air from exceeding the saturation vapor pressure at the pressure and temperature achieved by the previous compression stage, to virtually prevent, or at least greatly minimize, condensation of water within the compressor. Such a temperature control is effected by permitting controlled, preselected amounts of uncooled compressed air from the previous compre:>sor stages to by-pass the next in-line intercooler anc~ be. blended with the cooled compressed air emerging from -she intercooler. Such blending of cooled and uncooled compressed air will permit control of the temperature of the compres~~ed ai:r entering the next following compression stage, and with attention to such temperature control it is possible to select and control the temperature of that compressed air to a value that will not be increased upon further compression to a leve7_ that will exceed the normal safe operating temperature for an air compressor.
OBJECTS OF THE INVENTION
Accordingly, it is one of the primary objects of this invention to provide a new and improved multiple stage gas compressor having a significantly reduced tendency for water condensation therein.
Another object of the present invention is to provide a new and improved thermostatically controlled intercooler system for use with a multiple stage compressor that significantly reduces the tendency for water condensation within the multiple stage compressor.
A further object: of the present invention is to provide a new and improved thermostatically controlled intercooler system for use with a r~ulti.p:Le stage compressor that controls the inlet temperature of the compressed air at a second and/or subsequent compression stage t:o thereby substantially eliminate the condensation of water within the compressor.
Still anotJzer object of the present invention is to provide a new and improved thermostatically controlled intercooler system for use with a multip=Le stage compressor that controls the inlet temperature of the compressed air at a second and/or subsequent compression stage by permitting controlled amounts of uncooled compressed air to by-pass the intercooler, thereby raising the temperature of the inlet compressed gas entering the next compressor stage so that its temperature can be controlled to a level that will. prevent the saturation vapor pressure of the compressed gas from being reduced to a level below the partial pressure of wager vapor therein, to thereby prevent or minimize water condensation within the compressor.
These and other objects and advantages of the present invention will become more readily apparent to those persons skilled in the compressor art after a full reading of the following detailed description, particularly, when such description is taken in conjunction with the attached drawings as described below.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 i;s a simplified, schematic view of a two-stage gas compressor in.corpox~ating a thermostatically controlled intercooler system according to a presently preferred embodiment of this invention; and Figure 2 is a simplified, schematic view of a three-stage gas compressor incorporating a thermostatically controlled intercooler sy~~tem according to another presently preferred embodiment of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION
Prior to proceeding with a detailed description of the subject invention, it: is noted that for the sake of clarity, identical components which have identical functions have been identified with identical reference numerals throughout the several views of the attached drawings.
Reference i:o Figures 1 and 2 will illustrate in schematic form two presently preferred embodiments of this invention, namely, Figure 1 being a multiple stage compressor having two compressor stages with a single intercooler therebetween and Figure 2 being a multiple stage compressor showing the first three compressor stages in a system having a plurality of compressor stages, with an intercooler between at least the second and third compressor stages and between the third and any subsequent compressor stages.
In each of the Figures, the multiple stage compressors, generally designated 10, include a first compressor stage 10a, which is schematically illustrated as a piston and cylinder type of compressor having a piston 12 mounted for reciprocal movement within a cylinder 14.
While such piston and cylinder type of compressors are perhaps the most common, it should be appreciated that this invention can be incorporated into multiple stage compressors based on other forms of mechanical compressors, such as, a centrifugal type, an axial-flow type, a turbine type and other types, particularly any such multiple stage compressor wherein an intercooler is pro~aided between any two compressor stages for the purpose of preventing the compressed gas from becoming excessively heaved.
As is well known, piston and cylinder type mechanical compressors are provided with a suitable valve arrangement (not shown) which is closed during a compression stroke to permit the gas therein to be suitably compressed, with an outlet valve (not shown) opening thereafter, permitting the compressed gas to be directed out of the cylinder 14 and into a discharge line 18.
Thereafter, the outlet valve is closed as an inlet valve (not shown) is opened so that the reciprocating piston 12 will draw in fresh gas at ambient pressure to repeat the compression process. Such valuing arrangement is well known to those familiar with t:he art and need not be further described here.
As in sore.e two-stage compressors, an intercooler 16 is provided which is adapted to cool the gas compressed after a compressor stage, such as a first compressor stage 10a, before it is further compressed and heated in the next following compressor stage, i.e., compressor stage lOb. Accordingly, such discharge line 18 is :provided which is adapted to convey the gas compressed in c:ompre:~sor stage l0a into the intercooler 16 so that the gas heated in compression stage l0a by virtue of its compression can be cooled, at least to some degree, before it is further compressed :in compressor stage lOb.
As with other e7_ements of the compressor described above, the intercooler 16 is also well known to those familiar with the compressor art. Such intercooler 16, normally, comprises a radiator-type o.' cooler wherein the heated gas is passed through a plurality of thin radiator tubes spaced by cooling fins (not shown). Therefore, such intercoolers 16 need not be further described here :in detail.
As shown in Figure 2, the multiple stage compressor 10 may comprise more than two compression stages, such as three compression stages 10a, lOb and lOc, or even more, with an intercooler 16 operably disposed between any pair of adjacent compression stages. However, since excessive heating of the compressed gas is not normally a problem until a third or later compression stage i~~ involved, some commercially available multiple stage ~~ompressors may only utilize an intercooler before the third and a.ny subsequent compression stages.
In a like manner, as shown in the Figure 1 embodiment, an intercooler 16 is provided, in the embodiment of Figure 2, which is adapted to cool the gas compressed in compressor stage l0a before it is further compressed and heated in the second compressor stage lOb. Again, a discharge line 18 is provided which is adapted to convey the gas compressed in the first compressor stage l0a into the intercooler 16, so that the gas heated in compression stage l0a by virtue of its compression can be cooled, at least to some degree, before it is further compressed in compressor stage lOb.
In a similar manner to that described above, another intercooler 16b is provided which is adapted to cool the gas compressed in the second compressor stage lOb before it is further compressed arid heated in compressor stage lOc. Again, a discharge line 18b is provided which is adapted to convey the gas compressed in compressor stage lOb into the intercooler 16b so that the gas heated in compression stage lOb by virtue of its compression can be cooled, at least to some degree, before it is further compressed in compressor stage lOc.
In a like manner, additional intercoolers 16 are commonly operably dispow>ed between any pair of subsequent compressor stages for the purpose of cooling the previously compressed gas before it is further compressed and, accordingly, further heated in such following compression stage. The operation of the systems described above are conventional in the prior art and need not be further described here.
The crux of this invention resides in a selective by-pass system, incorporated with the intercoolers 16, which permits control of the compressed gas temperature admitted into any selected comprE:ssor stage after the first compressor stage so that such inlet: tempi=rature can be deliberately controlled and maintained at a predetermined level which will assure that prior to inlet into i_he next compression stage, the gas temperature will not reduct=_ to ~~ level whereby the associated saturation vapor pressure has been reduced to a value below the partial pressure of water va~~or at the intercooler pressure.
Accordingly, with reference to Figure 1, the inventive elements include a three-way valve 30 adapted to receive compressed gas cooled by the associated intercooler 16 and direct the compressed gas to the subsequent compressor stage lOb for further compression. In addition, a by-pass line 34 is also provided which interconnects the associated compressor stage l0a directly with t:he three-way valve 30. Accordingly, the by-pass line 34 is adapted t=o pass compressed gas directly from the associated compressor stage l0a to the three-way valve 30 without such compressed gas passing through the intercooler 16.
Therefore, the three-way valve 30 is adapted to selectively convey either cooled or uncooled compressed gas, or a controlled mixture thereof,, onto the next succeeding compressor stage lOb.
In additi0I1 to t:he three-way valve 30 and by-pass line 34, the inventive elements of this invention further includes a control means 36 for controlling the operation of such three-way valve 30. Obviously, control means 36 should be a control adapted to selectively pass either cooled or uncooled compressed gas, or mixtures thereof, as necessary to maintain a preselected target temperature of the compressed gas entering into the compression stage lOb.
The preselected target temperature will, of course, vary from one system to tree next but, as noted above, it should be a temperature which is determined to be one that will prevent the gas from cooling to a point where the associated saturation vapor pressure of the gas does not fall to a value below the partial pressure of the water vapor in the gas mixture at the point prior to the inlet for the next compression stage.
While the above description is addressed primarily to the thermostatically controlled intercooler system between the first and second compression stages of the multiple stage compressor shown in Figure 1, it should be readily apparent that any thermostatically controlled intercooler system should be substantially the same regardless of its location with respect to various compressor stages. The only differences, in essence, will be the tar<~et temperatures sought.
While a number of differing control means could be provided, and are within the scope of the present invention, we have preferred to use an "~~ff-the-shelf" three-way type valve having a built-in temperature controlled valve operation. Specifically, we have successfully used both a 1.5-inch and a 2-inch three-way valve manufactured by FLUID POWER ENERGY having the built-in, out-put temperature controller, whereby the desired out-put temperature can be selected and set on the valve, with the valve then automatically out-putting a mixture of the two in-put gasses as necessary to provide an out-put blend thereof matching the preselected ternperature. Since such valves are commercially available, it is believed that any further description and discussion thereof i~; not necessary here.
It may be apparent to those skilled in the art that exacting controls are not. in fact necessary. For a conventional two-stage compressor utilizing two compression cylinders in the first stage and one compression cylinder for the second stage, with an intercooler between the first stage and the second, we have determined that normal reliability levels and service life of the compressor can be expected if the ultimate temperature of the compressed gas, after compression in the second stage, remains below about 500°F. 7:n the above noted system, we have learned that such a goal can be achieved by controlling the compressed gas temperature enter_Lng the second stage at a level of generally no more than about 250°F.
Furthermore=_, in order to prevent the condensation of water due to excessivf=_ cooling of the air at the intercooler pressure for a compression ratio of about 4:1 per compression stage and design inlet con.ditiorLS for the preliminary compression stage set at about 150°F. and 100% relative humidity, a controlled output temperature at or abo~re about 213.4°F. is necessary. Thus, both objectives can be accomplished by controlling the output air between about 213.4°F. and about 250°F.
Therefore, if the temperature of the compressed air exiting the first stagE=_ is at or below about 250°F. , then all of that compressed air ~~an be passed directly to the second stage without any of it having to :be diverted through the intercooler. Only when the temperature of the compressed air emerging from any compressor stage is in excess of about 250°F., will it be necessary to divert a portion thereof through the following intercooler. By utilizing the temperature controlled three-way valve described above, the valve will itself adjust the temperature of the ou.t-put.
Further testing of the above described apparatus having a thermostatically controlled intercooler, as described herein, in contrast to a prior art compressor being identical in all other respects except for 'the absence of the inventive control, has shown that the prior art compressor has routinely caused water build-up in the lubricating oil in amounts exceeding 1.0 percent, and even 2.0 percent water after operating for a defined test period of time.
An identical compressor having the thermostatic control of this invention, has ~~anaged to keep such water build-up in the lubricating oil at amounts consistently below about 0.1 percent, when operating the controls as necessary only to keep the temperature of t:he cornpressed gas entering the second compressor stage, preferab:Ly, at or below about 200°F.
Having described in detail a presently preferred embodiment of this invent__on, it should be apparent that various other embodiments could be utilized and modifications incorporated therein by tho~~e persons who are skilled in the compressor art without departing from either the spirit of the invention or the scope of the appended claims.
Claims (3)
1. A method of operating a multiple stage compressor to minimize condensation of water therein, said method comprising the steps of:
(a) interconnecting at least two compressor stages in series for compressing a gas;
(b) cooling a gas compressed in a first compressor stage in an intercooler prior to further compression of said gas in a second compressor stage;
(c) interconnecting said first compressor stage with said first intercooler via a discharge line;
(d) passing said compressed gas compressed in said first compressor stage through said discharge line into said intercooler;
(e) passing said compressed gas from said intercooler to a three-way valve;
(f) directing said compressed gas from said three-way valve to said second compression stage;
(g) interconnecting said first compressor stage directly with said three-way valve via a by-pass line adapted to pass said compressed gas directly from said first compressor stage to said three-way valve without said compressed gas passing through said intercooler;
(h) controlling said three-way valve such that said compressed gas emerging therefrom and directed to said second compressor stage comprises one of cooled compressed gas from said intercooler, uncooled compressed gas from said by-pass line and a mixture of said cooled and uncooled compressed gases, as necessary to effect a preselected target temperature of such compressed gases directed by said three-way valve to said second compressor stage.
(a) interconnecting at least two compressor stages in series for compressing a gas;
(b) cooling a gas compressed in a first compressor stage in an intercooler prior to further compression of said gas in a second compressor stage;
(c) interconnecting said first compressor stage with said first intercooler via a discharge line;
(d) passing said compressed gas compressed in said first compressor stage through said discharge line into said intercooler;
(e) passing said compressed gas from said intercooler to a three-way valve;
(f) directing said compressed gas from said three-way valve to said second compression stage;
(g) interconnecting said first compressor stage directly with said three-way valve via a by-pass line adapted to pass said compressed gas directly from said first compressor stage to said three-way valve without said compressed gas passing through said intercooler;
(h) controlling said three-way valve such that said compressed gas emerging therefrom and directed to said second compressor stage comprises one of cooled compressed gas from said intercooler, uncooled compressed gas from said by-pass line and a mixture of said cooled and uncooled compressed gases, as necessary to effect a preselected target temperature of such compressed gases directed by said three-way valve to said second compressor stage.
2. A method of operating a multiple stage compressor, according to claim 1, wherein said target temperature is generally between about 150°F. and about 250°F.
3. A method of operating a multiple stage compressor, according to claim 2, wherein said target temperature is generally about 200°F.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/686,433 | 1996-07-26 | ||
| US08/686,433 US5885060A (en) | 1996-06-03 | 1996-07-26 | Thermostatically controlled intercooler system for a multiple stage compressor and method |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2202818A1 CA2202818A1 (en) | 1998-01-26 |
| CA2202818C true CA2202818C (en) | 2001-12-04 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2202818 Expired - Lifetime CA2202818C (en) | 1996-07-26 | 1997-04-16 | Thermostatically controlled intercooler system for a multiple stage compressor and method |
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| CA (1) | CA2202818C (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN110219793B (en) * | 2019-07-15 | 2024-01-26 | 耐力股份有限公司 | Oil-free piston compressor with two-stage compression |
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- 1997-04-16 CA CA 2202818 patent/CA2202818C/en not_active Expired - Lifetime
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| CA2202818A1 (en) | 1998-01-26 |
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