Patent Description:
Reciprocating piston compressors for compressing a process gas are well known and are used in many applications and for different process gases. A reciprocating piston compressor comprises at least one cylinder with at least one suction valve and at least one discharge valve for the process gas exchange. In the cylinder a piston reciprocates back and forth driven by a piston rod. A pressure packing surrounds the piston rod to seal the gas in the cylinder. A pressure packing comprises a packing case made up of several adjacent (in the axial direction of the packing case / piston rod) packing cups with sealing rings and/or wiper rings being arranged in the cups. A reciprocating piston compressor with a pressure packing is known from <CIT> or <CIT>, for example. The piston rod is connected to a crosshead which in turn is connected to a crank of a crankshaft. The crosshead translates the rotating movement of the crank into the reciprocating movement of the piston rod. The crank shaft is located in a crankcase. Between the crankcase and the cylinder (or the pressure packing) there is often arranged a distance piece in which the piston rod and sometimes also the crosshead or at least a part of the crosshead reciprocates. Between the distance piece and the crank case there can also be arranged an additional partition packing around the piston rod. In operation of the reciprocating piston compressor there is always a process gas leakage through the pressure packing or around the pressure packing as the pressure packing is never absolutely gastight. Such a process gas leakage is undesirable, not only because of the resulting process gas loss.

Depending on the process gas, process gas leakage can be problematic, especially when toxic, hazardous, combustible or explosive process gas is used.

Any process gas emission into the surroundings of the compressor is undesirable. There are even statutory limitations for such gas emissions that require avoidance of gas emissions into the surroundings. This is especially true if toxic or hazardous process gas is used. In case of combustible or explosive process gas there is additional risk of gas accumulating in the compressor, e.g. in the distance piece or crankcase, that need to be avoided. Gas leakage into the crankcase can also contaminate the crankcase lube oil detrimentally affecting the operation of the compressor. When using a distance the process gas leakage from the cylinder through or around the pressure packing would not directly enter the crankcase but would enter the distance piece first. Leakage of process gas into the crankcase can be reduced in that way but not completely avoided.

It is therefore a general desire in a reciprocating piston compressor to confine and collect process gas leakage from the piston rod pressure packing and to carry the leakage to a safe location away from the compressor.

To achieve this, it is already known to provide a vent line in the pressure packing which provides for connection from a location inside the pressure packing to a location on the exterior of the pressure packing. Connection of additional conduits to the external vent line exit from the pressure packing allows for directing the process gas leakage to a controlled point external to the compressor itself. The vent line is connected to a vent volume, e.g. arranged in a vent cup or between two adjacent sealing rings, in the pressure packing. Process gas leaking into the pressure packing is directed from the vent volume into the vent line.

A vent line in the pressure packing does however not totally prevent process gas leakage, as gas leakage can also occur between adjacent cups or even around the pressure packing.

To further reduce process gas leakage, it also known to use pressurised buffer gas, such as Nitrogen or any other inert or unproblematic gas, in the pressure packing and/or in the distance piece. The pressure of the buffer gas is set to be higher than the pressure of the process gas at the respective location, for example at the low-pressure side of the pressure packing. The buffer gas is fed between two adjacent sealing rings of the pressure packing and forms a gas barrier for the process gas in the pressure packing. In this case, only buffer gas exits the pressure packing. If a vent line is used in the pressure packing, the internal starting point of the vent line in the pressure packing is located between the sealing rings at the high-pressure side of the packing and the gas barrier. In this case, buffer gas would also be removed via the vent line. In the vent line there would be a mixture of buffer gas and process gas. Also, in the partition packing buffer gas could be used to form a gas barrier to reduce the risk of process gas leakage from the distance piece into the crankcase. A gas barrier in the pressure packing or partition packing does however not prevent process gas leakage between cups or around the packing itself. Therefore, it is sometimes also provided to purge the distance piece with purge gas. As purge gas, the same gas is usually used that is used as buffer gas. This means the purge gas is fed into the distance piece and a mixture of purge gas with any process gas leakage is drained from the distance piece. Use of purge gas fed directly into the distance piece works on the principle of diluting and sweeping away process gas leakage rather than to block flow of process gas leakage on the basis of pressure gradient (as in the buffer gas barrier). However, adequate pressure of the purge gas supply must be maintained to assure positive flow into the distance piece.

It is therefore also known to use so called purge panels that provide the required buffer gas for the reciprocating piston compressor. The purge panel comprises the necessary instrumentation, like valves, flow regulators, measurement instruments, etc., needed for providing the buffer gas. It is especially important to be able to control the pressure of the buffer gas, which has to be higher than the gas pressure of the gas to be sealed or has to be high enough to allow purging of the distance piece. Usually, it is requested that the buffer gas pressure is at least <NUM> bar higher than the gas at the respective location of usage of the buffer gas. For certain locations, for example in the distance piece or the partition packing, the buffer gas pressure could be set statically to a certain pressure. Usage of a buffer gas in a pressure packing with a vent line requires however a dynamically changing buffer gas pressure as the pressure in the packing, and especially in the vent line, usually varies dynamically (depending on the backpressure existing in the vent line, for example if connected to a flare system for flaring leaking process gas). Therefore, the pressure in the vent line is often used as pilot pressure to control a pressure regulator in the purge panel to set the buffer gas pressure.

In many instances, the vent line connected to the vent volume of the pressure packing would be routed through the panel itself in order to be able to use the vent line pressure as pilot pressure for the differential pressure regulator. It is also known to branch off a pilot line from the vent line and to lead the pilot line into the purge panel. This creates however several issues. On lubricated compressors, there is the necessity to install a liquid/gaseous separator for the vent line or pilot line between the compressor and the purge panel, causing extra cost. Another issue is the pressure drop in the vent line caused by flow of gas in the line. In operation of the compressor, the gas leakage from the pressure packing increases over time due to wear of the sealing rings in the packing. This causes the gas flow in the vent line to increase over time which corresponds to an increased pressure drop in the vent line over time. This variable (increasing) pressure drop means that the purge panel reads the wrong pilot pressure from the vent line for controlling the pressure regulator, and therefore the performance of the purge panel degrades over time. This can cause increased emissions of process gas from the compressor, which has to be avoided.

It is therefore an object of the present invention to provide a pressure packing with a vent volume and a buffer gas barrier for a reciprocating piston compressor that avoids the above-mentioned problems.

This object is achieved by providing a pressure packing as claimed in claim <NUM>, with a sensing line that is connected at a first end to the vent volume in the pressure packing with an opposite second end of the sensing line being closed, so that there is no gas flow in the sensing line, and by connecting a pressure regulator to the buffer gas feeding line for setting the buffer gas pressure in the buffer gas feeding line, whereas, during operation of the pressure packing, the pressure in the sensing line is used as pilot pressure for the pressure regulator for setting the buffer gas pressure. The sensing line is completely separated from the vent line by which process gas leakage is carried away from the pressure packing. As the sensing line is closed on the end opposite the vent volume and separated from the vent line, there cannot be a gas flow in the sensing line and consequently no pressure drop in the sensing line due to gas flow. This ensures correct readings of the vent pressure that is used as pilot pressure for controlling the pressure regulator for setting the buffer gas pressure for the pressure packing. The buffer gas pressure is preferably set a given differential pressure higher than the pilot pressure (vent pressure).

A corresponding method for operating a pressure packing is defined by claim <NUM>.

In an advantageous embodiment, a differential pressure control valve with a pilot input is used as pressure regulator, whereas the sensing sense line is connected to the pilot pressure input of the differential pressure control valve.

The sensing line is advantageously arranged in an upper part of the pressure packing. This, together with the fact that the sensing line is a static line without gas flow, reduces or even eliminates the amount of lubricant oil that can possibly be carried with the sensing line. Therefore, no liquid gas separator is required in the sensing line upstream of the pressure regulator, which reduces the overall costs and equipment complexity.

Using a purge panel with the pressure regulator being arranged in a gas line of the purge panel that connects a buffer gas inlet and a buffer gas outlet of the purge panel, whereas the buffer gas outlet is connected to the buffer gas feeding line and the buffer gas inlet is provided for connecting a buffer gas supply to the purge panel and whereas a sensing sense line inlet is arranged on the purge panel that is connected to the sensing sense line, allows for a neat arrangement of all required instrumentation for providing the buffer gas.

If a purge panel with an enclosure is used, it is especially advantageous to provide a pneumatic booster relay outside of the enclosure with the sensing line being connected to a pilot port of the pneumatic booster relay. In that way it can be ensured that the process gas in the sensing line cannot leak into the enclosure in case of malfunction, which would be hazard.

The present invention is described in greater detail in the following with reference to <FIG>, which show exemplary, schematic and non-limiting advantageous embodiments of the invention. In the drawings:.

<FIG> shows a typical configuration of a reciprocating piston compressor <NUM> having one cylinder <NUM> arranged in a cylinder head <NUM>. In the cylinder <NUM> a piston <NUM> is reciprocally moved back and forth. In the example of <FIG>, the compressor <NUM> is a double-acting piston compressor with two compression volumes in the cylinder <NUM>, one on each side of the piston <NUM>. The compressor <NUM> could however also be a single-acting piston compressor. The reciprocating piston compressor <NUM> of <FIG> has only one cylinder <NUM>, but could of course have any number of cylinders required. The reciprocating piston compressor <NUM> could also be implemented as single-stage compressor or as multi-stage compressor. In a multi-stage compressor, the compressed gas of a cylinder is fed into another cylinder for further compression, as is well-known. The cylinder <NUM> has at least one suction valve <NUM> and one discharge valve <NUM> (only schematically indicated in <FIG>) for every compression volume for process gas exchange. Any known configuration of a suction / discharge valve <NUM>, <NUM> can be used. The inlet line, connected to the suction valve <NUM>, for feeding process gas to the compressor <NUM> and the discharge line, connected to the discharge valve <NUM>, for compressed process gas are not shown in <FIG> for the sake of simplicity.

In a crankcase <NUM> a crank shaft <NUM> having a crank <NUM> is arranged. The crank shaft <NUM> is driven by a drive (not shown in <FIG>), e.g. an electromotor or an engine, and rotates around a rotation axis. A connecting rod <NUM> is connected to the crank <NUM> and to a crosshead <NUM> that is slidingly arranged in the compressor <NUM>, e.g. in the crank case <NUM> as in <FIG> or in any other part of the compressor <NUM>. The crosshead <NUM> is also connected to a first axial end of a piston rod <NUM>, that is connected on its opposite second axial end to the piston <NUM>. In well-known manner, due to this arrangement, the rotating movement of the crank shaft <NUM> is translated in a reciprocating movement of the piston rod <NUM> and consequently also of the piston <NUM> in the cylinder <NUM>.

A pressure packing <NUM> is provided around the reciprocating piston rod <NUM> for sealing the process gas PG in cylinder <NUM> against other components of the piston compressor <NUM>. The pressure packing <NUM> can be arranged in the cylinder head <NUM> or in any other component of the piston compressor <NUM>.

A pressure packing <NUM> of a reciprocating piston compressor <NUM> is well-known and comprises several packing cups <NUM> - in <FIG> the cups <NUM> and sealing rings <NUM> are denoted with lower case letters as 15a, 15b, 15c and 16a, 16b, 16c only to allow differentiation of the different cups <NUM> and sealing rings <NUM> if need be. In recesses <NUM> of the cups <NUM> sealing rings <NUM> and/or wiper rings are arranged that are in contact with the piston rod <NUM>. Any suitable sealing ring <NUM> or sealing ring combination, e.g. radially or tangentially cut sealing rings, non-cut sealing rings, etc., can be used as sealing ring <NUM>. Such sealing rings <NUM> are well-known in different configurations and do not need to be explained in more detail. Any known wiper ring can be used. Also, a combination of sealing ring(s) with wiper ring(s) in a cup <NUM> is possible. The sealing rings <NUM> are the primary process gas seals.

At the low-pressure side LP of the pressure packing <NUM>, i.e. at the side of the packing <NUM> facing away from the cylinder <NUM> when in use, a buffer gas barrier <NUM> is provided by providing a buffer gas volume <NUM> in the pressure packing <NUM> into which a buffer gas BG can be fed via a buffer gas feeding line <NUM>. At least a part of the buffer gas feeding line <NUM> can be arranged in the pressure packing <NUM>. The buffer gas volume <NUM> is sealed-off against other parts of the pressure packing <NUM>, e.g. by additional sealing rings 21a, 21b, so that the buffer gas volume <NUM> can be pressurised by means of pressurised buffer gas BG. The exemplary buffer gas volume <NUM> in <FIG> is implemented between two adjacent buffer cups 18a, 18b of the pressure packing <NUM>, whereas in each of the buffer cups 18a, 18b a sealing ring 21a, 21b, or a combination of sealing rings, is arranged in respective recesses <NUM> of the buffer cups 18a, 18b. When the buffer gas volume <NUM> is pressurised with the buffer gas BG, the sealing rings 21a, 21b are pressed against opposite axial walls in the pressure packing <NUM>, e.g. a wall of a respective recess <NUM> or a wall of an adjacent packing part, and against the piston rod <NUM> to form the buffer gas volume <NUM> therebetween. The buffer gas volume <NUM> in the pressure packing <NUM> could however be implemented in any other suitable manner, such as with a sealing ring 21a, 21b combination in a single cavity buffer volume <NUM> wherein the sealing rings 21a, 21b prevent gas flow in either direction out of the cavity.

As buffer gas BG an inert gas, like nitrogen, could be used.

The buffer gas volume <NUM>, or the buffer gas BG in the buffer gas volume <NUM>, prevents (or at least reduces) leakage of process gas PG from the high-pressure side HP, e.g. the cylinder <NUM> side, through the pressure packing <NUM> to the low-pressure side LP. To this end, the buffer gas pressure pB in the buffer gas volume <NUM> is set to be higher than the acting pressure in the pressure packing <NUM> at the location before (in direction of the high-pressure side HP) the buffer gas volume <NUM>.

Between the buffer gas volume <NUM> and the primary sealing rings 16a, 16b, 16c a vent volume <NUM> is formed that is connected to a vent line <NUM> of the pressure packing <NUM>. The buffer gas volume <NUM> is sealed against the vent volume <NUM>, e.g. by sealing ring 21a of the buffer gas barrier <NUM> as in <FIG>. At least a part of the vent line <NUM> can be arranged in the pressure packing <NUM>. There could also be additional sealing rings and or wiper rings be arranged between the sealing rings 21a of the buffer gas barrier <NUM> and the vent volume <NUM>. The vent volume <NUM> is preferably formed between the last sealing ring 16c before (in direction of the high-pressure side HP) the buffer gas barrier <NUM> and a sealing ring 21a of the buffer gas barrier <NUM> facing the high-pressure side HP of the pressure packing <NUM>, as in <FIG>. The vent volume <NUM> in <FIG> is formed in radial direction by the annular clearance between the piston rod <NUM> and the inner circumferential surface of the buffer cup 18a and in axial direction between the buffer ring 21a in the buffer cup 18a and the sealing ring 16c in the packing cup 15c adjacent the buffer gas volume <NUM>. The vent volume <NUM> could however also be implemented differently.

The vent volume <NUM> and the vent line <NUM> serve to drain any process gas PG leakage through the pressure packing <NUM>, i.e. through the sealing rings 16a, 16b, 16c.

In some cases, the vent line <NUM> also drains cylinder <NUM> and/or piston rod <NUM> lubricant oil that is for example transported with the process gas PG. The vent line <NUM> is therefore often arranged on a lower (in the direction of gravity) part of the pressure packing <NUM>, as shown in <FIG>, which allows collecting lubricant oil by gravity. As a consequence of a combined vent and drain line that carries away process gas PG leakage and lubricant oil, a liquid gas separator is usually required in the vent line <NUM> downstream of the compressor <NUM> for removing liquids (lubricant oil) in the leaked process gas before the leaked process gas may be processed further.

An additional wiper ring <NUM> could be arranged in the pressure packing <NUM> at the low-pressure side LP of the pressure packing <NUM> as indicated in <FIG> in dashed lines. The wiper ring <NUM> would serve to wipe off remaining crankcase lubricant oil from the piston rod <NUM>. The wiped off crankcase lubricant could be drained away from the pressure packing <NUM> in suitable and known manner.

In use of the pressure packing <NUM> in the compressor <NUM>, the low-pressure side LP of the pressure packing <NUM> is at the side of the crankcase <NUM> and the high-pressure side HP is facing the cylinder <NUM>.

The working principle of the pressure packing <NUM> with buffer gas barrier <NUM> and vent line <NUM> is well-known and is explained in <FIG> by the resulting pressures in the packing <NUM> at different locations. The dynamically changing cylinder pressure pcyl acts at the cylinder side (the high-pressure side HP is) of the pressure packing <NUM>. This cylinder pressure pcyl is reduced in the pressure packing <NUM> across the primary sealing rings 16a, 16b, 16c to the vent pressure pV in the vent line <NUM>. As it is not important for the invention how this pressure is reduced, the pressure reduction is only indicated in <FIG> as dashed line. The vent pressure pV depends on the acting backpressure in the vent line <NUM>, i.e. to which components the vent line <NUM> is connected to. At the crankcase side of the pressure packing <NUM> (the low-pressure side LP) the buffer gas pressure pB acts in the buffer gas volume <NUM> of the buffer gas barrier <NUM>. The buffer gas pressure pB is higher than the vent pressure pV, preferably at least <NUM> bar higher which prevents process gas PG leakage through the buffer gas barrier <NUM>. Via the vent line <NUM>, a mixture of buffer gas BG (leaking from the buffer gas barrier <NUM> towards the vent volume <NUM>) and process gas PG leaking through the pressure packing <NUM> from the high-pressure side HP towards the vent volume <NUM> is carried away from the compressor <NUM> to a safe location. A certain amount of buffer gas BG would also leak from the buffer gas barrier <NUM> into the adjacent part of the reciprocating piston compressor <NUM>, i.e. into the crank case <NUM> or a distance piece <NUM>, where usually the atmospheric pressure patm acts.

In the embodiment of <FIG>, there is also provided a distance piece <NUM> between the crank case <NUM> and the cylinder <NUM> (cylinder head <NUM>) - in the embodiment shown there are two distance pieces <NUM>, 13a, also called outbound distance piece <NUM> adjacent to the cylinder <NUM> and inbound distance piece 13a adjacent to the crankcase <NUM>. It should be mentioned that in a reciprocating piston compressor <NUM> according to the invention there could be any number of distance pieces <NUM> provided between the crankcase <NUM> and the cylinder <NUM> (cylinder head <NUM>), especially also no distance piece, one distance piece or more than one distance pieces.

Between the distance piece <NUM> (13a) and the crankcase <NUM> there can be a partition packing <NUM> in the partition wall between the distance piece <NUM> (13a) and the crank case <NUM>. Also between two adjacent distance pieces <NUM>, 13a an intermediate packing <NUM> could be arranged. The partition packing <NUM> and/or the intermediate packing <NUM> can be designed similar to the pressure packing <NUM>, i.e. with at least one cup with at least one sealing ring and/or wiper ring being arranged therein.

In an intermediate packing <NUM>, and/or a partition packing <NUM>, an additional buffer gas barrier <NUM> could be provided that could be implemented as described above for the buffer gas barrier <NUM> of the pressure packing <NUM>. In an intermediate packing <NUM>, and/or a partition packing <NUM>, there would however usually no vent line <NUM>. The pressurised buffer gas BG fed into the buffer gas barrier <NUM> of the intermediate packing <NUM> via intermediate packing buffer gas line 32b (indicated in <FIG> in dashed line) would therefore leak into both adjacent distance pieces <NUM>, 13a and would prevent passage of process gas PG from the cylinder side distance piece <NUM> into the crank case side distance piece 13a. The pressurised buffer gas BG fed into the buffer gas barrier <NUM> of the partition packing <NUM> via partition packing buffer gas line (not shown in <FIG>) would therefore leak into the crankcase <NUM> and the crankcase side distance piece 13a.

The buffer gas pressure of the buffer gas for the intermediate packing <NUM> or the partition packing <NUM> is set to be higher, preferably at least <NUM> bar higher, than the pressure in the adjacent distance piece <NUM>, 13a or crankcase <NUM>, usually atmospheric pressure patm. As the pressure in the distance piece <NUM>, 13a or crankcase <NUM> does usually not change, the buffer gas pressure could be set statically to a required value.

A distance piece <NUM> (13a) could optionally also be purged with buffer gas BG, as shown in <FIG>. In this embodiment, pressurised buffer gas BG is fed into the distance piece <NUM>, 13a via a distance piece buffer gas line <NUM>, 32a. A mixture of process gas PG and buffer gas BG that accumulates in the distance piece <NUM>, 13a could be drained from the distance piece <NUM>, 13a via a distance piece drain line <NUM>, 33a and carried away to a safe location. The buffer gas pressure of the buffer gas BG for purging the distance piece <NUM>, 13a is set appropriately. As the pressure in the distance piece <NUM>, 13a does usually not change, the buffer gas pressure for purging the distance piece <NUM>, 13a could be set statically to a required value.

From the above explanations it is obvious that buffer gas BG of different pressures could be required for operating a reciprocating piston compressor <NUM>. According to the invention, the reciprocating piston compressor <NUM> has at least a pressure packing <NUM> with a buffer gas barrier <NUM>. Hence, at least buffer gas BG with a buffer gas pressure pB that is always higher than the expected or existing vent pressure pv is required. In a possible embodiment, the vent pressure pV is dynamically changing over time. In such an embodiment, the buffer gas pressure pB is preferably also dynamically changing over time.

As explained above, the buffer gas pressure pB for the pressure packing <NUM> has to be higher than the vent pressure pV in the pressure packing <NUM>. The vent pressure pV is usually measured in the vent line <NUM> and is used as pilot pressure for setting a pressure regulator for the buffer gas BG. In case of a dynamically changing buffer gas pressure pB, "setting" means control of the buffer gas pressure pB in response to the vent pressure pV.

The pressure in the vent line <NUM> is however affected by the flow of gas through the vent line <NUM> that causes a pressure drop along the vent line <NUM>. Therefore, a misreading occurs, if the pressure in the vent line <NUM> is sensed and used for setting (controlling) the buffer gas pressure PB.

As is well-known, the main determinant of the pressure drop is the gas velocity through the vent line <NUM>, whereas the pressure drop increases with increasing gas velocity. As the leakage flow through the vent line <NUM> increases over time due to wear in the pressure packing <NUM>, the pressure drop increases uncontrollably over time. Consequently, when the buffer gas pressure pB is controlled with the sensed pressure in the vent line <NUM>, the buffer gas pressure pB, that is set in response to the pressure in the vent line <NUM>, decreases over time. This can cause the pressure difference (pB - pV) to decrease which will reduce the ability of the buffer gas barrier <NUM> in the pressure packing <NUM> to stop and contain the leaked process gas PG. The buffer gas pressure pB might even fall below the vent pressure pv, which would result in backflow of process gas PG into the buffer gas feeding line <NUM> and also increased leakage of process gas PG through the pressure packing <NUM> into the distance piece <NUM> or crankcase <NUM>.

Therefore, according to the invention, the pressure in the vent line <NUM> is not used as pilot pressure for setting (controlling) the buffer gas pressure pB, e.g. by means of a pressure regulator <NUM> for the buffer gas BG. Instead, an additional sensing line <NUM> is provided in the pressure packing <NUM>, as is shown in <FIG>. One end of the sensing line <NUM> is connected to the vent volume <NUM>, that is also connected to the vent line <NUM>. The other end of the sensing line <NUM> is closed, which means that there is no gas flow in the sensing line <NUM>. As there is no gas flow in the sensing line <NUM>, there cannot be a gas flow related pressure drop in the sensing line <NUM> and a static pressure would result in the sensing line <NUM> that corresponds to the vent pressure pv in the vent volume <NUM>. The sensing line <NUM> is not branched-off the vent line <NUM>, so that the pressure in the sensing line <NUM> is not affected by the gas flow related pressure drop in the vent line <NUM>.

By sensing the pressure in the sensing line <NUM>, for example using a pressure sensor <NUM>, it is possible to detect the vent pressure pV. If the pressure in the sensing line <NUM> (that corresponds to the vent pressure pV) is used as pilot pressure for a pressure regulator <NUM> for setting (controlling) the buffer gas pressure pB it is ensured that the buffer gas pressure pB is always kept sufficiently above the vent pressure pV, even in case of a deteriorating pressure packing <NUM>.

In the embodiment of <FIG>, a buffer gas reservoir <NUM> provides the buffer gas BG, e.g. nitrogen, to a pressure regulator <NUM> that is controlled by a pilot pressure, which is the pressure in the sensing line <NUM> detected by the pressure sensor <NUM>. The flow (volume flow or mass flow) of buffer gas BG depends on the leakage in the pressure packing <NUM> and does not affect the buffer gas pressure pB.

A differential pressure control valve could be used as pressure regulator <NUM>. A differential pressure control valve ensures a constant differential pressure in a line with variable flow. The differential pressure control valve has a pilot pressure input and allows to set a desired differential pressure with respect to the pilot pressure. In this case, the sensing line <NUM> could be connected to the pilot pressure input of the differential pressure control valve and the vent pressure pV in the sensing line <NUM> would be the pilot pressure for the differential pressure control valve. The sensing line <NUM> would terminate in the differential pressure control valve, ensuring again a static pressure in the sensing line <NUM>. The differential pressure control valve would be arranged in the buffer gas feeding line <NUM> to control the buffer gas pressure pB with a set pressure offset (differential pressure) to the pilot pressure (vent pressure pV).

The buffer gas BG for the pressure packing <NUM> is preferably provided by a purge panel <NUM>, as indicated in <FIG> in dashed lines.

The sensing line <NUM> is preferably arranged in an upper (in direction of gravity) part of the pressure packing <NUM>. This, together with the fact that the sensing line <NUM> is a static line without gas flow, reduces or even eliminates the amount of lubricant oil that can be carried with sensing line <NUM>. Therefore, no liquid gas separator is usually required in the sensing line <NUM> upstream of the purge panel <NUM>, which reduces the costs of the system.

<FIG> shows a schematic of a purge panel <NUM> for providing the buffer gas BG for the pressure packing <NUM>. The purge panel <NUM> can be arranged in a purge panel enclosure <NUM> (as indicated in <FIG>), could however also be proved without enclosure. In case of a purge panel enclosure <NUM> there would preferably be provided a door that allows access to the instrumentation arranged in the purge panel enclosure <NUM>. The purge panel <NUM> has a buffer gas inlet <NUM> for connecting a buffer gas BG supply line <NUM>, that is for example connected to a buffer gas supply <NUM>. If the purge panel <NUM> has a purge panel enclosure <NUM> and the buffer gas supply is provided in the purge panel enclosure <NUM>, the buffer gas inlet <NUM> could also be avoided.

The purge panel <NUM> has a sensing line inlet <NUM> for connecting the sensing line <NUM> to the purge panel <NUM>. The sensing line <NUM> extends from the sensing line inlet <NUM> into the purge panel <NUM>. The end of the sensing line <NUM> in the purge panel <NUM> is closed, so that there is no gas flow in the sensing line <NUM> when connected to the purge panel <NUM>. The purge panel <NUM> has a buffer gas outlet <NUM>, to which the buffer gas feeding line <NUM> is connected in use of the purge panel <NUM>. The buffer gas inlet <NUM> and the buffer gas outlet <NUM> are connected in the purge panel <NUM> by a gas line <NUM>. In the gas line <NUM> a pressure regulator <NUM> is provided, in the example of <FIG> a differential pressure control valve, for setting the puffer gas pressure pB at the buffer gas output connector <NUM>, and by that also in the buffer gas feeding line <NUM> connected thereto.

In this embodiment, the sensing line <NUM> is connected to a pilot input <NUM> of the differential pressure control valve at which the sensing line <NUM> terminates. The differential pressure, which is preferably preset, between the pressure at the pilot input <NUM> and the output pressure of the differential pressure control valve (the buffer gas pressure pB) is set by the differential pressure control valve. Hence, the buffer gas pressure pB is offset from the pilot pressure (vent pressure pV) by the preset differential pressure and follows the vent pressure pV in the sense line <NUM>.

When the purge panel <NUM> supplies more than one pressure packing <NUM> with buffer gas BG, in each case under control of a vent pressure pV in a sensing line <NUM> of the respective pressure packing, then the purge panel <NUM> could also be equipped with more than one pressure regulator <NUM>. In this case, there would be a sensing line inlet <NUM> for each pressure regulator for connecting the respective sensing line <NUM> to the purge panel <NUM>. There would also be a buffer gas output connector <NUM> for each pressure regulator <NUM> for connecting the respective buffer gas feeding line <NUM> to the purge panel <NUM>.

The purge panel <NUM> could also be equipped with additional instrumentation, as will be described with reference to <FIG>.

The buffer gas BG is fed into the purge panel <NUM> via buffer gas inlet <NUM>, to which a buffer gas supply line <NUM>, connected on the other end to a buffer gas supply <NUM>, is connected when the purge panel <NUM> is in use. In the purge panel <NUM>, the buffer gas inlet <NUM> is connected to a gas line <NUM>.

In the gas line <NUM> an isolation valve <NUM> is arranged downstream of the buffer gas inlet <NUM>. If an operator wants to perform a routine maintenance operation of the purge panel <NUM> and isolates the purge panel <NUM> from the buffer gas supply via the isolation valve <NUM>, the purge panel <NUM> will remain pressurized and pose a hazard when the operator tries to open a component which is under pressure. Therefore, preferably an isolation valve <NUM> with downstream vent is used, which automatically depressurizes the panel as soon as the isolation valve <NUM> is switched into closed position. Such an isolation valve <NUM> shuts off the gas line <NUM> upstream of the isolation valve <NUM> when in closed position. But, when in closed position, the isolation valve <NUM> opens a vent port on the isolation valve <NUM> that is connected to the gas line <NUM> downstream of the isolation valve <NUM>. Hence, the gas line <NUM> downstream of the isolation valve <NUM> is depressurized via the vent port when the isolation valve <NUM> is closed. In the embodiment of <FIG>, there cannot be any backflow of buffer gas BG from the outlets of the purge panel <NUM>, because there are check valves <NUM> upstream the outlets of the purge panel <NUM>. Such an isolation valve <NUM> with downstream vent together with check valves <NUM> at the outlets guarantees operator safety in all situations.

In the gas line <NUM>, preferably downstream of the isolation valve <NUM> and upstream of further instrumentation, there can also be provided a filter <NUM>, for filtering the buffer gas BG fed into the purge panel <NUM>.

In the inlet section of the gas line <NUM>, there can also be provided a first pressure control valve <NUM>. The gas pressure of the buffer gas BG fed into the purge panel <NUM> could be varying for different reasons. It is therefore advantageous to set a specified gas pressure in the gas line <NUM> in the purge panel <NUM> via the first pressure control valve <NUM>.

Downstream of the first pressure control valve <NUM> the gas line <NUM> is fed to the pressure regulator <NUM> for setting the desired buffer gas pressure as explained above.

In the embodiment of <FIG>, a second gas line 46a branches off from the gas line <NUM> downstream of the first pressure control valve <NUM> and upstream of the pressure regulator <NUM>. In this second gas line 46a a second pressure control valve 53a could be provided for setting the desired gas pressure in the second gas line 46a. Downstream of the second pressure control valve 53a, the second gas line 46a is connected to a number of buffer gas outlets 47a, 47b of the purge panel <NUM>, in the embodiment of <FIG> two buffer gas outlets 47a, 47b. At these buffer gas outlets 47a, 47b, a constant buffer gas BG pressure could be set via the first pressure control valve <NUM> and/or second pressure control valve 53a (if present). These buffer gas outlets 47a, 47b could for example be connected to the distance piece buffer gas lines <NUM>, 32a or intermediate packing buffer gas line 32b (see <FIG>) or to a partition packing buffer gas line for providing a buffer gas BG with constant gas pressure for purging the distance piece <NUM>, 13a or for supplying the buffer gas barrier <NUM> to the intermediate packing <NUM> or partition packing <NUM>.

There can however also be more second gas lines 46a be provided in a purge panel <NUM>, with each second gas line 46a being equipped with its own second pressure control valve 53a. Each second gas line 46a can be connected to a number of buffer gas outlets 47a, 47b.

In the embodiment of <FIG>, there are two buffer gas outlets <NUM>, 44a provided, for example, for supplying buffer gas BG to two pressure packings <NUM> of a reciprocating piston compressor <NUM>. The buffer gas outlets <NUM>, 44a are connected to the pressure regulator <NUM> as explained in <FIG>. There can be any number of pressure regulators <NUM> connected in each case to any number of buffer gas outlets <NUM>, 44a provided in the purge panel <NUM>.

The purge panel <NUM> can also be equipped with a pressure relief valve <NUM> that is connected to the gas line <NUM> downstream of the pressure regulator <NUM>, as in <FIG>. The pressure relief valve <NUM> would be set to a certain allowed buffer gas pressure pBmax. If the buffer gas pressure pB in the gas line <NUM> exceeds this allowed buffer gas pressure pBmax, the pressure relief valve <NUM> would open to prevent damage at the reciprocating piston compressor <NUM> connected to the purge panel <NUM>, e.g. damage of the pressure packing <NUM>. If a second gas line 46a is provided in the purge panel <NUM> there could of course also be a second pressure relief valve <NUM> provided for the second gas line 46a. The release pressure of the second pressure relief valve <NUM> could of course also be set differently as compared to other pressure relief valves <NUM> in the purge panel <NUM>.

A pressure relief valve <NUM> could also open into an overpressure line <NUM> in the purge panel <NUM> which in turn could be connected to an overpressure outlet <NUM>, that could open into atmosphere. This is especially preferred when the purge panel <NUM> is provided with a purge panel enclosure <NUM>.

Furthermore, some monitoring instrumentation can be provided in the purge panel <NUM> at certain locations. For example, a pressure indicator <NUM> could be used to display the acting pressure at certain locations in the gas line <NUM> and/or a second gas line 46a. A flow indicator <NUM> could be used to display the actual buffer gas flow through certain parts of the gas line <NUM> and/or a second gas line 46a.

In case of a purge panel enclosure <NUM> it is advantageous when the purge panel enclosure <NUM> is open or transparent in the region of a monitoring instrument so that the monitoring instrument is visible from outside. To this end a door of the purge panel enclosure <NUM> could partly be transparent.

The purge panel <NUM> can be designed to provide any required number of buffer gas outlets <NUM>, 44a. Each buffer gas outlets <NUM>, 44a could be connected to a separate pressure regulator <NUM>, for allowing to set the buffer gas pressure pB at each buffer gas outlets <NUM>, 44a separately. Some of the buffer gas outlets <NUM>, 44a could however also be connected to a common pressure regulator <NUM> (as in <FIG>). In addition, there can also be provided a number of second gas lines 46a connected to a number of additional buffer gas outlets 47a, 47b, at which a constant buffer gas pressure pB could be set via a first pressure control valve <NUM> and/or second pressure control valve 53a (if present). This allows to adapt the purge panel <NUM> flexibly to the requirements of a specific reciprocating piston compressor <NUM>.

A valve could also be provided upstream of a certain buffer gas outlet <NUM>, 44a, 47a, 47b to shut off this buffer gas outlet <NUM>, 44a, 47a, 47b in case it is not needed.

If the purge panel <NUM> is arranged in an enclosure <NUM>, it is advantageous for safety reasons to avoid hazardous process gas PG to accumulate in the enclosure <NUM> in case of malfunction. In operation, the sensing line <NUM> is filled with process gas PG mixed with some buffer gas BG. Theoretically, the sensing line <NUM> is gas-tight, but in reality, there is always the possibility of an accidental leakage in the enclosure <NUM> of the purge panel <NUM> and the possibility of fugitive leaks and accumulation of process gas PG in the enclosure cannot be excluded, which is a potential hazard. To avoid accumulation of process gas PG in the enclosure <NUM>, a pneumatic booster relay <NUM> could be used. Such a configuration is shown in <FIG>. A pneumatic booster relay <NUM> can however also be provided in other embodiments of the purge panel <NUM>, e.g. as in <FIG> or <FIG>.

A pneumatic booster relay is a known pneumatic device that regulates the pressure of a stream of gas based on a pilot pressure. According to a known embodiment, a pneumatic booster relay <NUM> has four ports, a supply port 54a, an outlet port 54b, a pilot port 54c and an exhaust port 54d. When a pilot pressure is applied to the pilot port 54c, the main valve assembly of the pneumatic booster relay <NUM> opens to allow flow from the supply port 54a to the outlet port 54b. When the sensing assembly of the pneumatic booster relay <NUM> detects that the outlet pressure at the outlet port 54b is equal to the pilot pressure, the main valve moves to a rest position in which the outlet port 54b and the exhaust port 54d are blocked (not connected to the any other port) and will remain in this position until there is a change in the pilot pressure or outlet pressure. If the sensing assembly detects that the outlet pressure is higher than the pilot pressure, the exhaust port 54d opens to vent the excess pressure, for example into an exhaust line or into the surroundings. If the sensing assembly detects that the outlet pressure is lower than the pilot pressure, the main valve opens to connect the supply port 54a to the outlet port 54b for recharging the system to the pilot pressure. In that way, the output pressure at the output port 54b corresponds to the pilot pressure at the pilot port 54a.

When the pneumatic booster relay <NUM> is arranged outside of the enclosure <NUM> of the purge panel <NUM> and the sensing line <NUM> is connected to the pilot port 54c of the pneumatic booster relay <NUM>, it can be ensured that no process gas PG enters the enclosure <NUM>, as the pilot port 54c of the pneumatic booster relay <NUM> cannot be connected to the output port 54b of the pneumatic booster relay <NUM>. The supply port 54a of the pneumatic booster relay <NUM> is connected to the gas line <NUM> of the purge panel <NUM> so that buffer gas is supplied to the pneumatic booster relay <NUM>. The sensing line <NUM> would in this embodiment not be connected directly to the pilot input <NUM> of the differential regulator <NUM> but to the pilot port 54c of the pneumatic booster relay <NUM> and would terminate there. Hence, the pilot pressure of the pneumatic booster relay <NUM> corresponds again to the vent pressure pV in the sensing line <NUM>. This means that the output pressure of the buffer gas at the output port 54b of the pneumatic booster relay <NUM> corresponds also to the vent pressure pV. The output port 54b of the pneumatic booster relay <NUM> is therefore connected to the sensing line inlet <NUM> and further to the pilot input <NUM> of the differential regulator <NUM> to set the pilot pressure for the pressure regulator <NUM>. As a result, the process gas PG contained in sensing line <NUM> is entirely kept outside of the enclosure <NUM> thereby preventing any leakage of process gas PG into the enclosure <NUM> even in case of malfunction of any component in the enclosure <NUM>.

<FIG> shows an embodiment of the purge panel with a pressure regulator <NUM> for every buffer gas outlet <NUM>, 44a. The buffer gas pressures pB at every buffer gas outlet <NUM>, 44a can be set independently from each other by means of the respective pressure regulator <NUM>.

In the embodiment of <FIG> valves <NUM> are shown that allow to shut-off certain outlets of the purge panel <NUM> as need be.

In a further advantageous embodiment of a purge panel <NUM> provisions can be made on the purge panel <NUM> to allow integration of digital measurement instruments <NUM>, like digital pressure or flow transducer. To this end certain connectors <NUM> could be provided at the purge panel <NUM> at certain locations which allow connection of such digital measurement instruments <NUM>. Usage of digital measurement instruments allow integration of a purge panel <NUM> in a digital control of the purge panel <NUM> or the reciprocating piston compressor <NUM>.

In <FIG> as example of digital measurement instruments <NUM> a pressure transducer PT is shown that is connected to a connected <NUM> at the purge panel <NUM>. The measurement signal of the pressure transducer PT could be send to a control unit for further processing and could be used for monitoring and/or controlling the function of the purge panel <NUM>.

It would be especially advantageous to arrange all analogue instrumentation and piping on a front side of a purge panel <NUM> and to provide the connectors for the digital measurement instruments at the back side of the purge panel <NUM>. This would allow easy and safe separation of the analogue and digital instrumentation. Furthermore, the user of a purge panel <NUM> could decide if and which (type, manufacturer) digital measurement instruments he wants to use.

Claim 1:
Pressure packing for a reciprocating piston compressor (<NUM>), the pressure packing comprising
a buffer gas barrier (<NUM>) at a low-pressure side of the pressure packing (<NUM>), the buffer gas barrier (<NUM>) including a buffer gas volume (<NUM>);
a number of sealing rings (<NUM>) at an opposite high-pressure side of the pressure packing (<NUM>);
a vent volume (<NUM>) between the buffer gas barrier (<NUM>) and a last sealing ring of the number of sealing rings (<NUM>) before the buffer gas barrier (<NUM>);
a vent line (<NUM>) connected to the vent volume (<NUM>);
a buffer gas feeding line (<NUM>) connected to the buffer gas volume (<NUM>) of the buffer gas barrier (<NUM>);
wherein buffer gas (BG) with buffer gas pressure (pB) is supplied into the buffer gas volume (<NUM>) via the buffer gas feeding line (<NUM>) during operation of the pressure packing (<NUM>), wherein the buffer gas pressure (pB) is higher than a vent pressure (pV) in the vent volume (<NUM>),
characterized in that the pressure packing further comprising
a sensing line (<NUM>) connected at a first end to the vent volume (<NUM>) with an opposite second end of the sensing line (<NUM>) being closed, so that there is no gas flows in the sensing line (<NUM>); and
a pressure regulator (<NUM>) connected to the buffer gas feeding line (<NUM>) for setting the buffer gas pressure (pB) in the buffer gas feeding line (<NUM>);
wherein, during operation of the pressure packing (<NUM>), the pressure regulator (<NUM>) uses the pressure in the sensing line (<NUM>) as pilot pressure for setting the buffer gas pressure (pB).