Patent Description:
When fossil fuels, such as oil and natural gas, are refined, it is necessary to remove impurities, such as carbon dioxide (CO<NUM>) and sulfur (S). Sulfur is often recovered as hydrogen sulfide (H<NUM>S) in a refining process. A fluid, handled by a pump used in the refining process, may contain a lot of hydrogen sulfide. Hydrogen sulfide is extremely toxic. If the hydrogen sulfide leaks into the atmosphere, it will cause serious damage to a human body. Therefore, it is necessary to pay full attention to design a pump that handles hydrogen sulfide so that the hydrogen sulfide never leaks to the outside of the pump.

A sealing system shown in <FIG> includes a double mechanical seal having a pump-side sealing mechanism (a slip ring <NUM> and a counter ring <NUM>) and an atmospheric-side sealing mechanism (a slip ring <NUM> and a counter ring <NUM>) which are disposed in a seal housing <NUM> for a rotational shaft <NUM> of a centrifugal pump. A pump mechanism <NUM>, driven by the rotational shaft <NUM>, is provided between the pump-side sealing mechanism and the atmospheric-side sealing mechanism. A first chamber 122a and a second chamber 122b are formed at both sides of the pump mechanism <NUM>. The first chamber 122a and the second chamber 122b are formed in the seal housing <NUM>. The atmospheric-side sealing mechanism is located in the first chamber 122a, and the atmospheric-side sealing mechanism is located in the second chamber 122b.

The pump mechanism <NUM> pressurizes a fluid barrier-and-cooling medium such that the medium has a pressure Pb higher than a discharge pressure Ph of the pump impeller, while the fluid barrier-and-cooling medium is delivered from the first chamber 122a to the second chamber 122b by the pump mechanism <NUM>. The pressurized fluid barrier-and-cooling medium in the second chamber 122b can prevent a medium, pressurized by the pump impeller <NUM>, from leaking into the second chamber 122b through the slip ring <NUM> and the counter ring <NUM> of the pump-side sealing mechanism.

The sealing system shown in <FIG> includes a recirculating system r located outside the seal housing <NUM>. The recirculating system r is coupled to the first chamber 122a and the second chamber 122b, and is configured to circulate the fluid barrier-and-cooling medium. The recirculating system r includes a heat exchanger <NUM>. The recirculating system r has a circulation path such that the fluid barrier-and-cooling medium, pressurized by the pump mechanism <NUM>, reaches the heat exchanger <NUM> via the second chamber 122b, the fluid barrier-and-cooling medium is cooled by the heat exchanger <NUM>, and the fluid barrier-and-cooling medium is then returned to the first chamber 122a and reaches the pump mechanism <NUM>.

The fluid barrier-and-cooling medium is a fluid itself handled by the centrifugal pump, and is pressurized in advance by the pump impeller <NUM> and injected into the sealing system. When the fluid barrier-and-cooling medium in the sealing system decreases due to leakage, the fluid, handled by the centrifugal pump, is pressurized by the pump impeller <NUM> to refill the sealing system. Therefore, when the fluid, handled by the pump, contains a toxic or flammable fluid, such high-pressure dangerous fluid exists in the immediate vicinity of the atmospheric air, and may leakage to the outside.

The pressure of the fluid barrier-and-cooling medium applied to the atmospheric-side sealing mechanism is equivalent to the discharge pressure of the centrifugal pump when the centrifugal pump is not in operation. Thus, when the fluid, handled by the pump, contains a toxic or flammable fluid, such a high-pressure dangerous fluid may leak to the outside. When the centrifugal pump is not in operation and the fluid barrier-and-cooling medium in the sealing system is reduced due to leakage, a fluid barrier-and-cooling medium, stored beforehand in an accumulator <NUM>, is supplied into the sealing system.

By the way, in <FIG>, the pump mechanism <NUM> serves to pressurize the fluid barrier-and-cooling medium and send it from the first chamber 122a to the second chamber 122b. As a result, a large quantity of heat is generated around the pump mechanism <NUM>. If the heat is left as it is, it may cause interference between components or deformation of components due to thermal expansion, or may cause plastic deformation of sealing materials, such as O-rings <NUM>, <NUM>, thereby possibly impairing the sealing function. In order to prevent this, the heat exchanger <NUM> is provided in the sealing system to positively cool the fluid barrier-and-cooling medium.

However, a driving force for circulating the fluid barrier-and-cooling medium through the sealing system is generated by the pump mechanism <NUM>. Therefore, if the centrifugal pump is stopped due to a power failure or other cause, the pump mechanism <NUM> is also stopped simultaneously. As a result, the heat generated in the operation immediately before the stop is not dissipated, and temperatures of components around the pump mechanism <NUM> may rise to an unacceptable level.

Carrier sleeves <NUM>, <NUM>' shown in <FIG> are pressed away from each other by a spring <NUM> provided between them. Ends of the carrier sleeves <NUM>, <NUM>' press the slip rings <NUM>, <NUM> against the counter rings <NUM>, <NUM>, respectively. During operation of the centrifugal pump, the carrier sleeve <NUM> is pressed toward the atmospheric side by the pressure Pb in the second chamber 122b. On the other hand, the pressure Pa in the first chamber 122a is applied to the carrier sleeve <NUM>'. Therefore, a differential pressure Pb-Pa is applied to the combination of the carrier sleeves <NUM>, <NUM>' as a whole in a direction from the pump side to the atmospheric side. For this reason, the pressure on the sealing surfaces of the slip ring <NUM> and the counter ring <NUM> at the atmospheric side is higher than that when the operation is not in operation, and therefore the sealing effect increases. However, the pressure on the sealing surfaces of the slip ring <NUM> and the counter ring <NUM> at the pump side is lower than that when the operation is not in operation, and as a result, the sealing effect decreases.

On the contrary, when the pressure in the first chamber 122a becomes higher than the pressure in the second chamber 122b, a differential pressure Pa-Pb is applied to the combination of the carrier sleeves <NUM>, <NUM>' as a whole in a direction from the atmospheric side to the pump side. For this reason, the pressure on the sealing surfaces of the slip ring <NUM> and the counter ring <NUM> at the atmospheric side becomes lower than that when the operation is not in operation. As a result, the sealing effect is reduced, and the fluid barrier-and-cooling medium is likely to leak.

Further, reference is made to <CIT>, which relates to a dual seal barrier fluid leakage control method in a dual seal assembly having a process fluid chamber containing pressurized process fluid, a barrier fluid chamber containing pressurized barrier fluid, a primary seal disposed between the process fluid chamber and the barrier fluid chamber, and a secondary seal disposed between the barrier fluid chamber and external atmosphere. The assembly has a recirculating line arranged to extract barrier fluid from the barrier fluid chamber and return the barrier fluid to the same barrier fluid chamber. Via the recirculating line cooling of the barrier fluid as well as replenishment may be provided.

As described above, in the technique shown in <FIG>, the pump impeller <NUM> pressurizes the fluid, to be handled by the centrifugal pump, to supply it to the sealing system, so that the pressurized fluid is used as the leak prevention fluid (or the fluid barrier-and-cooling medium) of the sealing system. The pressure of the fluid barrier-and-cooling medium applied to the atmospheric-side sealing mechanism is equivalent to the discharge pressure of the centrifugal pump when the operation of the centrifugal pump is not in operation. Accordingly, when the fluid, to be handled by the pump, contains toxic or flammable fluid, such high-pressure dangerous fluid exists in the immediate vicinity of the atmospheric air, and may leakage to the outside.

Furthermore, when the operation of the pump mechanism <NUM> is stopped due to a power failure or other cause, it is necessary to avoid an increase in temperature of components. However, the sealing system of <FIG> is insufficient to avoid the temperature increase.

As the fluid barrier-and-cooling medium, a harmless liquid, such as oil, may be used which is different from the fluid handled by the pump. However, in this case, it is necessary to provide an oil replenishment mechanism that replenishes the sealing system with oil during operation when the oil pressure decreases due to leakage or other cause. It is necessary for such an oil replenishment mechanism that the replenishment of oil does not prevent the flow of oil pressurized by the pump mechanism <NUM>. If the flow of oil pressurized by the pump mechanism <NUM> is disrupted, the heat generated near the pump mechanism <NUM> is not dissipated, and the temperature of peripheral devices of the pump mechanism <NUM> may rise to an unacceptable temperature.

Further, when the pressure in the first chamber 122a at the atmospheric side becomes higher than the pressure in the second chamber 122b at the pump side as a result of the replenishment of oil, a differential pressure Pa-Pb is applied to the combination of the carrier sleeves <NUM> and <NUM>' as a whole in a direction from the atmospheric side to the pump side, thus causing a decrease in the pressure on the sealing surfaces of the slip ring <NUM> and the counter ring <NUM> at the atmospheric side. As a result, the sealing effect is reduced, and the risk of leakage increases.

When the pump impeller of the centrifugal pump rotates in the reverse direction, the pump mechanism <NUM> also rotates in the reverse direction. In this case, the pressure Pa in the first chamber 122a is higher than the pressure Pb in the second chamber 122b. A differential pressure Pa-Pb is applied to the combination of the carrier sleeves <NUM> and <NUM>' as a whole in a direction from the atmospheric side to the pump side, thus causing a decrease in the pressure on the sealing surfaces of the slip ring <NUM> and the counter ring <NUM> at the atmospheric side. As a result, the sealing effect is reduced, and the risk of leakage of the fluid barrier-and-cooling medium increases.

As described above, in consideration of the case where the fluid to be handled by the pump contains a toxic or flammable fluid, the technique shown in <FIG> cannot be used as it is. It is necessary to design the pump so as not to allow such a harmful fluid to flow outside through the sliding surfaces of the mechanical seal.

It is a first object of the present invention to provide a sealing system that can appropriately cool a double mechanical seal and a pump mechanism, and does not allow a fluid, handled by a pump, to leak into an atmospheric side during normal operation and power failure, even in a case where the fluid, handled by the pump, contains a toxic or flammable fluid.

It is a second object of the present invention to provide a sealing system that can be safely and appropriately replenished with a fluid barrier-and-cooling medium during normal operation when pressure in the sealing system is lowered due to leakage of the fluid barrier-and-cooling medium, in a case where the fluid, handled by the pump, contains a toxic or flammable fluid.

It is a third object of the present invention to provide a sealing system that does not allow a fluid, handled by a pump, to leak into an atmospheric side even when a centrifugal pump and a pump mechanism rotate in a reverse direction, in a case where the fluid, handled by the pump, contains a toxic or flammable fluid.

In one aspect, there is provided a sealing system for sealing a rotational shaft of a centrifugal pump, comprising: a double mechanical seal having a pump-side sealing mechanism and an atmospheric-side sealing mechanism; a pump mechanism driven by the rotational shaft, the pump mechanism being located between the pump-side sealing mechanism and the atmospheric-side sealing mechanism; a first chamber defined by at least the atmospheric-side sealing mechanism and the pump mechanism; a second chamber defined by at least the pump-side sealing mechanism and the pump mechanism; a first medium circulation line for circulating a fluid barrier-and-cooling medium between the first chamber and the second chamber, the first medium circulation line being coupled to the first chamber and the second chamber, the fluid barrier-and-cooling medium being different from a fluid handled by the centrifugal pump; a heat exchanger and a shut-off valve attached to the first medium circulation line; a second medium circulation line having both ends coupled to the first medium circulation line, the second medium circulation line bypassing the shut-off valve; and a medium pressurizing pump and an on-off valve attached to the second medium circulation line.

In one aspect, the sealing system further includes a seal housing that accommodates the double mechanical seal therein, the first medium circulation line and the second medium circulation line being located outside the seal housing.

In one aspect, the sealing system further comprises: a power failure detector configured to detect a power failure of the centrifugal pump; and a system controller configured to, upon receiving a power failure detection signal transmitted from the power failure detector, close the shut-off valve, open the on-off valve, and start the medium pressurizing pump.

In one aspect, a first connection point at which one end of the second medium circulation line is coupled to the first medium circulation line is located between the shut-off valve and the heat exchanger; and a second connection point at which the other end of the second medium circulation line is coupled to the first medium circulation line is located between the shut-off valve and the second chamber.

In one aspect, the sealing system further includes a power source for supplying power to the medium pressurizing pump, the medium pressurizing pump having an electric motor as a prime mover.

In one aspect, the fluid barrier-and-cooling medium is oil, and the pressurizing medium pump is an oil pump.

The present invention can provide the sealing system that can appropriately cool the double mechanical seal and the pump mechanism, and can prevent leakage of a fluid, handled by the pump, into the atmospheric side during both normal operation and stoppage of the centrifugal pump and the pump mechanism, in a case where the fluid, handled by the pump, contains a toxic or flammable fluid.

In one aspect, there is provided a sealing system for sealing a rotational shaft of a centrifugal pump, comprising: a double mechanical seal having a pump-side sealing mechanism and an atmospheric-side sealing mechanism; a pump mechanism driven by the rotational shaft, the pump mechanism being located between the pump-side sealing mechanism and the atmospheric-side sealing mechanism; a first chamber defined by at least the atmospheric-side sealing mechanism and the pump mechanism; a second chamber defined by at least the pump-side sealing mechanism and the pump mechanism; a medium circulation line for circulating a fluid barrier-and-cooling medium between the first chamber and the second chamber, the medium circulation line being coupled to the first chamber and the second chamber, the fluid barrier-and-cooling medium being different from a fluid handled by the centrifugal pump; a heat exchanger attached to the medium circulation line; a branch line coupled to the medium circulation line; an accumulator coupled to the branch line, the accumulator being configured to pressurize and store a fluid barrier-and-cooling medium; an on-off valve attached to the branch line; a pressure detector arranged to measure pressure in the first chamber; a pressure detector arranged to measure pressure in the second chamber; and a system controller configured to open the on-off valve when the pressure in the second chamber is lower than a threshold value. The threshold value is higher than discharge pressure of the centrifugal pump.

In one aspect, the branch line and the accumulator are located between the heat exchanger and the first chamber.

In one aspect, the sealing system further includes a pressure detector arranged to measure discharge pressure of the centrifugal pump, and the threshold value varies according to the discharge pressure.

In one aspect, the system controller is configured to close the on-off valve when the pressure in the first chamber is higher than the pressure in the second chamber.

In one aspect, the sealing system further comprise: a medium reservoir configured to store a fluid barrier-and-cooling medium therein; a pump line coupled to the medium reservoir and the medium circulation line; and a medium pressurizing pump for pressurizing the fluid barrier-and-cooling medium supplied from the medium reservoir, the medium pressurizing pump being attached to the pump line, wherein a connection point of the pump line and the medium circulation line is located between the accumulator and the first chamber.

In one aspect, the system controller is configured to start the medium pressurizing pump when the on-off valve is open and the pressure in the second chamber is lower than the threshold value.

In one aspect, the system controller is configured to close the on-off valve or stop the operation of the medium pressurizing pump when the medium pressurizing pump is operated and the pressure in the first chamber is higher than the pressure in the second chamber.

The present invention can provide the sealing system that can be appropriately cooled and replenished with the fluid barrier-and-cooling medium without lowering the sealing performance of the double mechanical seal even if the fluid barrier-and-cooling medium in the sealing system leaks with age, in a case where the fluid, handled by the pump, contains a toxic or flammable fluid.

In one aspect, there is provided a sealing system for sealing a rotational shaft of a centrifugal pump, comprising: a double mechanical seal having a pump-side sealing mechanism and an atmospheric-side sealing mechanism; a pump mechanism driven by the rotational shaft, the pump mechanism being located between the pump-side sealing mechanism and the atmospheric-side sealing mechanism; a first chamber defined by at least the atmospheric-side sealing mechanism and the pump mechanism; a second chamber defined by at least the pump-side sealing mechanism and the pump mechanism; a medium circulation line for circulating a fluid barrier-and-cooling medium between the first chamber and the second chamber, the medium circulation line being coupled to the first chamber and the second chamber, the fluid barrier-and-cooling medium being different from a fluid handled by the centrifugal pump; a heat exchanger attached to the medium circulation line; a bypass line coupled to the medium circulation line; a check valve attached to the bypass line; a branch line coupled to the medium circulation line; an accumulator configured supply a pressurized fluid barrier-and-cooling medium to the second chamber, the accumulator being coupled to the branch line; and an isolation valve attached to the branch line, wherein the check valve is configured to allow the fluid barrier-and-cooling medium to flow only in a direction from the first chamber to the second chamber.

In one aspect, a first connection point at which one end of the bypass line is coupled to the medium circulation line is located between the first chamber and the heat exchanger, and a second connection point at which other end of the bypass line is coupled to the medium circulation line is located between the heat exchanger and the second chamber.

In one aspect, a first connection point at which one end of the bypass line is coupled to the medium circulation line, and a second connection point at which other end of the bypass line is coupled to the medium circulation line are located between the heat exchanger and the second chamber.

In one aspect, there is provided a sealing system for sealing a rotational shaft of a centrifugal pump, comprising: a double mechanical seal having a pump-side sealing mechanism and an atmospheric-side sealing mechanism; a pump mechanism driven by the rotational shaft, the pump mechanism being located between the pump-side sealing mechanism and the atmospheric-side sealing mechanism; a first chamber defined by at least the atmospheric-side sealing mechanism and the pump mechanism; a second chamber defined by at least the pump-side sealing mechanism and the pump mechanism; a medium circulation line for circulating a fluid barrier-and-cooling medium between the first chamber and the second chamber, the medium circulation line being coupled to the first chamber and the second chamber, the fluid barrier-and-cooling medium being different from a fluid handled by the centrifugal pump; a heat exchanger attached to the medium circulation line; a bypass line coupled to the medium circulation line; an on-off valve attached to the bypass line; a system controller configured to open the on-off valve when pressure in the first chamber is higher than pressure in the second chamber; a branch line coupled to the medium circulation line; an accumulator configured supply a pressurized fluid barrier-and-cooling medium to the second chamber, the accumulator being coupled to the branch line; and an isolation valve attached to the branch line.

According to the present invention, when the pump mechanism reversely rotates and the pressure of the fluid barrier-and-cooling medium in the first chamber becomes higher than the pressure of the fluid barrier-and-cooling medium in the second chamber, the fluid barrier-and-cooling medium flows from the first chamber through the bypass line to the second chamber, so that the pressure in the second chamber is maintained. As a result, the fluid barrier-and-cooling medium is prevented from leaking to the atmospheric side.

<FIG> is a view showing an embodiment of a sealing system including a double mechanical seal. The double mechanical seal has a function of sealing a gap between a rotational shaft <NUM> and a partition wall <NUM> that separates a high-pressure side h and a low-pressure side n.

In <FIG>, at the high-pressure side h, a pump impeller <NUM> of a centrifugal pump is fixed to the rotational shaft <NUM>, and a shaft sleeve <NUM> extends over an axial length of the double mechanical seal. The shaft sleeve <NUM> is fixed to an outer peripheral surface of the rotational shaft <NUM>. An O-ring <NUM> is provided between the shaft sleeve <NUM> and the rotational shaft <NUM>, and seals so as to prevent leakage of a fluid, handled by the centrifugal pump, through a gap between the shaft sleeve <NUM> and the rotational shaft <NUM>. The fluid, handled by the centrifugal pump, contains a toxic fluid or a flammable fluid.

The pump impeller <NUM> and a seal housing <NUM> are separated by the partition wall <NUM>. The rotational shaft <NUM> and a part of the pump impeller <NUM> extend through a through-hole 2a formed in the partition wall <NUM>. The partition wall <NUM> has a radial hole 2b communicating with the through-hole 2a. During operation of the centrifugal pump, the radial hole 2b is filled with the fluid pressurized by the pump impeller <NUM>. A pressure detector <NUM> is coupled to the radial hole 2b, so that a discharge pressure Ph of the pump impeller <NUM> is measured by the pressure detector <NUM>.

A cylindrical ring <NUM> has an inner peripheral surface in contact with the outer peripheral surface of the shaft sleeve <NUM>. The cylindrical ring <NUM> is located at substantially the center of the shaft sleeve <NUM>. A hollow cylindrical body <NUM> is fixed to the ring <NUM>. An axial length of the ring <NUM> is shorter than axial lengths of the shaft sleeve <NUM> and the hollow cylindrical body <NUM>. The hollow cylindrical body <NUM> has axially extending portions on both sides of an outer peripheral portion thereof. An axial length of an inner peripheral portion of the hollow cylindrical body <NUM> is the same as the axial length of the ring <NUM>. The inner peripheral portion of the hollow cylindrical body <NUM> faces the outer periphery of the ring <NUM>. The shaft sleeve <NUM>, the ring <NUM>, and the hollow cylindrical body <NUM> are arranged coaxially. A thread groove <NUM> is formed in the outer peripheral surface of the hollow cylindrical body <NUM>.

The ring <NUM> and the hollow cylindrical body <NUM> have a threaded hole extending therethrough in the radial direction. The ring <NUM> and the hollow cylindrical body <NUM> are fixed by a screw <NUM> inserted into the threaded hole. The tip end of the screw <NUM> engages with a recess <NUM> of the shaft sleeve <NUM>. The hollow cylindrical body <NUM> is fixed by the screw <NUM> such that the hollow cylindrical body <NUM> does not rotate and does not move axially relative to the ring <NUM>.

Two carrier sleeves <NUM>, <NUM>' are fitted in an annular recess defined by the shaft sleeve <NUM>, the ring <NUM>, and the hollow cylindrical body <NUM>. These carrier sleeves <NUM>, <NUM>' are arranged at both sides of the ring <NUM>. O-rings <NUM> are arranged between outer surfaces of the carrier sleeves <NUM>, <NUM>' and the inner surface of the hollow cylindrical body <NUM>. O-rings <NUM> are arranged between inner surfaces of the carrier sleeves <NUM>, <NUM>' and the outer surface of the shaft sleeve <NUM>. The carrier sleeves <NUM>, <NUM>' can be displaced in the axial direction of the rotational shaft <NUM>, but cannot rotate because the carrier sleeves <NUM>, <NUM>' are fixed by an axial protrusion <NUM> that contacts the screw <NUM>.

A spring <NUM> is arranged between the carrier sleeves <NUM>, <NUM>'. The spring <NUM> serves to push the carrier sleeves <NUM>, <NUM>' apart from each other. Slip rings <NUM>, <NUM> are attached to surfaces, apart from the ring <NUM>, of the carrier sleeves <NUM>, <NUM>', respectively. The slip rings <NUM>, <NUM> are pressed by the spring <NUM> against counter rings <NUM>, <NUM>, respectively. The counter rings <NUM>, <NUM> are fixed to a pump-side cover 14a and an atmospheric-side cover 14b of the seal housing <NUM>, respectively. The reference numeral <NUM> denotes the entirety of the seal housing. The combination of the slip ring <NUM> and the counter ring <NUM> constitutes a pump-side sealing mechanism of the double mechanical seal, and the combination of the slip ring <NUM> and the counter ring <NUM> constitutes an atmospheric-side sealing mechanism of the double mechanical seal.

The slip rings <NUM>, <NUM> and the counter rings <NUM>, <NUM>, constituting the double mechanical seal, are accommodated in the seal housing <NUM>. More specifically, the seal housing <NUM> has a hollow cylindrical portion <NUM> surrounding the double mechanical seal in the center of the hollow cylindrical portion <NUM>. A thread groove <NUM> is formed in an inner surface of the hollow cylindrical portion <NUM>. The thread groove <NUM> faces the thread groove <NUM> with a small radial gap therebetween. The thread groove <NUM> and the thread groove <NUM> have lead directions opposite to each other. The thread groove <NUM> is a male screw that rotates together with the rotational shaft <NUM>, and the thread groove <NUM> is a female screw which is stationary. The thread groove <NUM> surrounds the thread groove <NUM>. The thread groove <NUM> and the thread groove <NUM> constitute a pump mechanism <NUM> driven by the rotational shaft <NUM>. The pump mechanism <NUM> is located between the pump-side sealing mechanism (the slip ring <NUM> and counter ring <NUM>) and the atmospheric-side sealing mechanism (the slip ring <NUM> and the counter ring <NUM>) of the double mechanical seal.

An annular first chamber 22a and an annular second chamber 22b exist on both sides of the pump mechanism <NUM>. The first chamber 22a is a room at the low-pressure side n, and is a room defined by the pump mechanism <NUM>, the carrier sleeve <NUM>', the slip ring <NUM>, the counter ring <NUM>, the atmospheric-side cover 14b, and the hollow cylindrical portion <NUM>. The hollow cylindrical portion <NUM> has an inlet <NUM> coupled to a first medium circulation line <NUM> which will be described later, and the first chamber <NUM> a is coupled to the inlet <NUM>.

The second chamber 22b is a room at the high-pressure side h, and is a room defined by the pump mechanism <NUM>, the carrier sleeve <NUM>, the slip ring <NUM>, the counter ring <NUM>, the pump-side cover 14a, and the hollow cylindrical portion <NUM>. The hollow cylindrical portion <NUM> has an outlet <NUM> coupled to the first medium circulation line <NUM>, and the second chamber 22b is coupled to the outlet <NUM>. The outlet <NUM> communicates with the inlet <NUM> through the first medium circulation line <NUM>.

The sealing system includes the medium circulation line <NUM> coupled to the first chamber 22a and the second chamber 22b, a second medium circulation line <NUM> coupled to the first medium circulation line <NUM>, a throttle and check valve <NUM> constituted by a combination of a throttle valve and a check valve, a shut-off valve <NUM> which is closed when the second medium circulation line <NUM> is used, a heat exchanger <NUM> configured to cool the fluid barrier-and-cooling medium, and an accumulator <NUM> which stores a pressurized fluid barrier-and-cooling medium therein in a normal operation and pressurizes the fluid barrier-and-cooling medium in the first medium circulation line <NUM> in an emergency by opening an on-off valve <NUM>. Both ends of the second medium circulation line <NUM> are coupled to the first medium circulation line <NUM>. The second medium circulation line <NUM> extends so as to bypass the shut-off valve <NUM>.

A diaphragm (not shown) is arranged inside the accumulator <NUM>, and a gas, such as nitrogen gas, is enclosed in the accumulator <NUM>. The fluid barrier-and-cooling medium stored in the accumulator <NUM> is pressurized by the pressure of the gas. Therefore, the accumulator <NUM> has a function of storing the fluid barrier-and-cooling medium under pressure.

One end of the first medium circulation line <NUM> is coupled to the inlet <NUM>, and the other end of the first medium circulation line <NUM> is coupled to the outlet <NUM>. The throttle and check valve <NUM>, the heat exchanger <NUM>, and the shut-off valve <NUM> are attached to the first medium circulation line <NUM>. The heat exchanger <NUM> is located between the shut-off valve <NUM> and the first chamber 22a, and the throttle and check valve <NUM> is located between the shut-off valve <NUM> and the second chamber 22b. The accumulator <NUM> is coupled to a branch line <NUM> extending from the first medium circulation line <NUM>, and the on-off valve <NUM> is attached to the branch line <NUM>. The accumulator <NUM> is coupled to the first medium circulation line <NUM> via the branch line <NUM>. The branch line <NUM> and the accumulator <NUM> are located between the heat exchanger <NUM> and the first chamber 22a.

One end of the second medium circulation line <NUM> is coupled to the first medium circulation line <NUM> at a first connection point 20a, and the other end of the second medium circulation line <NUM> is coupled to the first medium circulation line <NUM> at a second connection point 20b. The first connection point 20a is located between the heat exchanger <NUM> and the shut-off valve <NUM>, and the second connection point 20b is located between the second chamber 22b and the shut-off valve <NUM>. In the present embodiment, the second connection point 20b is located between the outlet <NUM> and the throttle and check valve <NUM>.

The sealing system further includes a medium reservoir <NUM> for storing the fluid barrier-and-cooling medium therein, a medium pressurizing pump <NUM> for pressurizing the fluid barrier-and-cooling medium supplied from the medium reservoir <NUM>, an on-off valve <NUM> located between the first connection point 20a and the medium pressurizing pump <NUM>, a check valve <NUM> located between the medium pressurizing pump <NUM> and the second connection point 20b, and a pressure regulating valve <NUM> and a pressure detector <NUM> located between the medium pressurizing pump <NUM> and the check valve <NUM>. The pressure detector <NUM> is located downstream of the pressure regulating valve <NUM>. The medium reservoir <NUM>, the medium pressurizing pump <NUM>, the on-off valve <NUM>, the pressure regulating valve <NUM>, the pressure detector <NUM>, and the check valve <NUM> are attached to the second medium circulation line <NUM>. The first medium circulation line <NUM> and the second medium circulation line <NUM> are arranged outside the seal housing <NUM>. The first medium circulation line <NUM> and the second medium circulation line <NUM> are filled with the fluid barrier-and-cooling medium.

The sealing system further includes a power failure detector <NUM> for detecting a power failure, and a system controller <NUM> for controlling operations of the shut-off valve <NUM>, the on-off valve <NUM>, the on-off valve <NUM>, and the medium pressurizing pump <NUM> described above. When the power failure detector <NUM> detects a power failure, the power failure detector <NUM> emits a power failure detection signal, and sends the power failure detection signal to the system controller <NUM>. The system controller <NUM> is configured to, upon receiving the power failure detection signal, close the shut-off valve <NUM>, open the on-off valve <NUM>, and start the medium pressurizing pump <NUM>. Each of the shut-off valve <NUM>, the on-off valve <NUM>, and the on-off valve <NUM> may be an electromagnetic valve, a motor-operated valve, a pneumatically driven valve, a hydraulically driven valve, or the like.

The sealing system includes a pressure detector <NUM> for measuring the discharge pressure Ph of the pump impeller <NUM>, and a pressure detector <NUM> for measuring the pressure Pb in the second chamber 22b. The pressure detectors <NUM>, <NUM> are coupled to the system controller <NUM>.

The sealing system including the double mechanical seal provided within the seal housing <NUM> uses the fluid barrier-and-cooling medium. The fluid barrier-and-cooling medium is a medium having properties unrelated to the fluid handled by the centrifugal pump, and is a medium having no toxicity or danger. In one embodiment, the fluid barrier-and-cooling medium is oil, and the medium pressurizing pump <NUM> is an oil pump. In the present embodiment, the medium pressurizing pump <NUM> includes an electric motor as a prime mover.

Operations of the sealing system having the above configuration will be described below. The inside of the first medium circulation line <NUM> is filled with the fluid barrier-and-cooling medium having pressure equal to or higher than the discharge pressure Ph of the pump impeller <NUM> of the centrifugal pump. During normal operation, the on-off valve <NUM> is closed and the shut-off valve <NUM> is open. When the rotational shaft <NUM> rotates during the normal operation, the pump mechanism <NUM> sucks the fluid barrier-and-cooling medium in the first chamber 22a and pressurizes it, and discharges the fluid barrier-and-cooling medium to the second chamber 22b. The fluid barrier-and-cooling medium pressurized by the operation of the pump mechanism <NUM> returns to the first chamber 22a through the first medium circulation line <NUM>.

The pressure Pb in the second chamber 22b becomes higher than the discharge pressure Ph of the pump impeller <NUM> by the throttle and check valve <NUM> attached to the first medium circulation line <NUM>. While the fluid barrier-and-cooling medium flows through the first medium circulation line <NUM> from the throttle and check valve <NUM> to the inlet <NUM>, the pressure of the fluid barrier-and-cooling medium decreases due to pressure loss. As a result, the pressure Pa of the fluid barrier-and-cooling medium in the first chamber 22a is lower than Pb. Since the pressure Pb in the second chamber 22b is higher than the discharge pressure Ph of the pump impeller <NUM>, the fluid, handled by the centrifugal pump, does not enter the second chamber 22b via the sealing surfaces of the slip ring <NUM> and the counter ring <NUM> that constitute the pump-side sealing mechanism.

The carrier sleeve <NUM> is pushed by the pressure Pb in the second chamber 22b in a direction from the pump side to the atmospheric side. Since the pressure Pa in the first chamber 22a is applied to the carrier sleeve <NUM>', a differential pressure Pb-Pa is applied to the combination of the carrier sleeves <NUM>, <NUM>' as a whole from the pump side to the atmospheric side. As a result, the pressure applied to the sealing surfaces of the slip ring <NUM> and the counter ring <NUM>, constituting the atmospheric-side sealing mechanism, is higher than that when the pump mechanism <NUM> is not in operation, thereby increasing the sealing effect and reliably preventing the leakage of the fluid, handled by the pump, to the atmospheric side.

When the fluid barrier-and-cooling medium flows through the first medium circulation line <NUM>, the fluid barrier-and-cooling medium is cooled by the heat exchanger <NUM> provided on the first medium circulation line <NUM>. The cooled fluid barrier-and-cooling medium is returned to the first chamber 22a through the first medium circulation line <NUM> and the inlet <NUM>. In this way, during operation of the centrifugal pump, the fluid barrier-and-cooling medium circulates between the first chamber 22a and the second chamber 22b through the first medium circulation line <NUM> while being cooled by the heat exchanger <NUM>. The cooled fluid barrier-and-cooling medium cools the pump mechanism <NUM>, so that the temperatures of the pump mechanism <NUM> and peripheral devices (for example, the O-rings <NUM>, <NUM>) do not become high.

By the way, when a power failure occurs, the pump impeller <NUM> of the centrifugal pump stops and the pump mechanism <NUM> also stops. Thus, when the power failure detector <NUM> detects the power failure, the power failure detector <NUM> sends the power failure detection signal to the system controller <NUM>. The system controller <NUM> closes the shut-off valve <NUM> attached to the first medium circulation line <NUM>, opens the on-off valve <NUM>, and starts the medium pressurizing pump <NUM>. Since the medium pressurizing pump <NUM> is required to operate during the power failure, the medium pressurizing pump <NUM> is coupled to a power source <NUM> which is different from the power source for operating the centrifugal pump. The power source <NUM> supplies electric power to the medium pressurizing pump <NUM> to cause the medium pressurizing pump <NUM> to operate. The power source <NUM> may be composed of a battery, a diesel engine driven generator, or the like.

The medium pressurizing pump <NUM> pressurizes the fluid barrier-and-cooling medium supplied from the medium reservoir <NUM>. The pressurized fluid barrier-and-cooling medium passes through the pressure regulating valve <NUM> and the check valve <NUM>, and flows into the first medium circulation line <NUM> at the second connection point 20b. The fluid barrier-and-cooling medium further flows through the outlet <NUM> into the second chamber 22b. The medium pressurizing pump <NUM> is configured to be able to pressurize the fluid barrier-and-cooling medium to a pressure higher than the discharge pressure Ph of the pump impeller <NUM>. Since the shut-off valve <NUM> is already closed, no fluid barrier-and-cooling medium flows toward the throttle and check valve <NUM>.

The fluid barrier-and-cooling medium in the second chamber 22b that has been delivered from the medium pressurizing pump <NUM> flows through the gap between the thread groove <NUM> and the thread groove <NUM> of the pump mechanism <NUM> to reach the first chamber 22a. The difference between the pressure Pb in the second chamber 22b and the pressure Pa in the first chamber 22a is determined by a discharge flow rate of the medium pressurizing pump <NUM> and a resistance applied to the fluid passing through the pump mechanism <NUM> that is not in operation. The discharge pressure of the medium pressurizing pump <NUM> is adjusted by the pressure regulating valve <NUM> such that the outlet pressure of the check valve <NUM> measured by the pressure detector <NUM> is higher than the pressure Ph measured by the pressure detector <NUM>. The discharge pressure of the medium pressurizing pump <NUM> is measured by the pressure detector <NUM>, and the pressure regulating valve <NUM> operates based on the pressure measurement value sent from the pressure detector <NUM>.

The fluid barrier-and-cooling medium further flows from the first chamber 22a through the inlet <NUM> into the first medium circulation line <NUM>. The fluid barrier-and-cooling medium flows through the first medium circulation line <NUM>, is cooled by the heat exchanger <NUM>, enters the second medium circulation line <NUM> at the first connection point 20a, and returns to the medium reservoir <NUM> via the on-off valve <NUM>. The cooled fluid barrier-and-cooling medium in the medium reservoir <NUM> is delivered again to the second chamber 22b by the medium pressurizing pump <NUM>.

The cooled fluid barrier-and-cooling medium in the second chamber 22b flows to the first chamber 22a via the pump mechanism <NUM>, and is cooled again by the heat exchanger <NUM>. Since the fluid barrier-and-cooling medium also contacts the double mechanical seal (the slip rings <NUM>, <NUM> and the counter rings <NUM>, <NUM>) provided in the seal housing <NUM>, the fluid barrier-and-cooling medium can remove the heat of the entire double mechanical seal. In addition, the fluid barrier-and-cooling medium can quickly cool the double mechanical seal and its surroundings, thereby preventing interference between components due to thermal expansion, and preventing plastic deformation of elastic seals, such as the O-rings <NUM>, <NUM>. Therefore, their sealing functions can be maintained. As a result, the safety of the centrifugal pump increases.

The medium pressurizing pump <NUM> delivers the fluid barrier-and-cooling medium, cooled by the heat exchanger <NUM>, to the second chamber 22b at a pressure higher than the discharge pressure Ph of the pump impeller <NUM>, so that the fluid, handled by the centrifugal pump, is prevented from entering the second chamber 22b. Further, since the fluid barrier-and-cooling medium pressurized by the medium pressurizing pump <NUM> flows from the second chamber 22b to the first chamber 22a through the pump mechanism <NUM>, the pressure in the first chamber 22a is reduced to a pressure lower than the pressure in the second chamber 22b. As a result, a differential pressure Pb-Pa is applied to the combination of the carrier sleeves <NUM>, <NUM>' as a whole in the direction from the pump side to the atmospheric side. Therefore, the sealing surfaces of the slip ring <NUM> and the counter ring <NUM> at the atmospheric side can maintain their sealing effect not only when the centrifugal pump is in operation, but also when the centrifugal pump is not in operation. The difference between the pressure Pb in the second chamber 22b and the pressure Pa in the first chamber 22a is determined by the discharge flow rate of the medium pressurizing pump <NUM> and the resistance applied to the fluid passing through the pump mechanism <NUM> that is not in operation. The flow rate of the medium pressurizing pump <NUM> is selected so that an appropriate pressure difference Pb-Pa is achieved.

As discussed above, the present invention can provide the sealing system that can appropriately cool the double mechanical seal and the pump mechanism <NUM>, and can prevent leakage of the fluid, handled by the pump, into the atmospheric side during both normal operation and a halt of the centrifugal pump and the pump mechanism <NUM>, in a case where the fluid, handled by the pump, contains a toxic or flammable fluid.

Next, another embodiment of the present invention will be described with reference to <FIG>. Configurations of this embodiment, which will not be particularly described, are the same as those of the embodiment shown in <FIG>, and their repetitive descriptions are omitted. In the following descriptions, the first medium circulation line <NUM> will be simply referred to as medium circulation line <NUM>.

The sealing system includes the medium circulation line <NUM> coupled to the first chamber 22a and the second chamber 22b, throttle and check valve <NUM> constituted by a combination of a throttle valve and a check valve, heat exchanger <NUM> configured to cool the fluid barrier-and-cooling medium, and accumulator <NUM> which stores a pressurized fluid barrier-and-cooling medium therein in a normal operation and pressurizes the fluid barrier-and-cooling medium in the medium circulation line <NUM> in an emergency by opening on-off valve <NUM>. The medium circulation line <NUM> is arranged outside the seal housing <NUM>. The medium circulation line <NUM> is filled with the fluid barrier-and-cooling medium. The on-off valve <NUM> may be an electromagnetic valve, a motor-operated valve, a pneumatically driven valve, a hydraulically driven valve, or the like.

A diaphragm (not shown) is arranged inside the accumulator <NUM>, and a gas, such as nitrogen gas, is enclosed in the accumulator <NUM>. The fluid barrier-and-cooling medium stored in the accumulator <NUM> is pressurized by the pressure of the gas. Therefore, the accumulator <NUM> has a function of storing the fluid barrier-and-cooling medium under pressure. The pressure of the fluid barrier-and-cooling medium stored in the accumulator <NUM> is equal to or higher than the discharge pressure Ph of the pump impeller <NUM> of the centrifugal pump.

One end of the medium circulation line <NUM> is coupled to the inlet <NUM>, and the other end of the medium circulation line <NUM> is coupled to the outlet <NUM>. The throttle and check valve <NUM> and the heat exchanger <NUM> are attached to the medium circulation line <NUM>. The accumulator <NUM> is coupled to the branch line <NUM> extending from the medium circulation line <NUM>. The on-off valve <NUM> is attached to the branch line <NUM>. The accumulator <NUM> is coupled to the medium circulation line <NUM> via the branch line <NUM>. The branch line <NUM> and the accumulator <NUM> are located between the heat exchanger <NUM> and the first chamber 22a.

One end of a pump line <NUM> is coupled to the medium circulation line <NUM>. The other end of the pump line <NUM> is coupled to a medium reservoir <NUM> that stores a fluid barrier-and-cooling medium. A medium pressurizing pump <NUM> and a check valve <NUM> are attached to the pump line <NUM>. The medium pressurizing pump <NUM> is coupled to the medium circulation line <NUM> via the pump line <NUM> and the branch line <NUM>. The check valve <NUM> is configured to allow the fluid barrier-and-cooling medium, pressurized by the medium pressurizing pump <NUM>, to flow toward the medium circulation line <NUM> and not to allow the fluid barrier-and-cooling medium to flow backward The medium pressurizing pump <NUM> is configured to be capable of pressurizing the fluid barrier-and-cooling medium, supplied from the medium reservoir <NUM>, to pressure equal to or higher than the discharge pressure Ph of the pump impeller <NUM> of the centrifugal pump. The fluid barrier-and-cooling medium, pressurized by the medium pressurizing pump <NUM>, flows through the check valve <NUM> and is supplied to the medium circulation line <NUM>.

The pump line <NUM> may be directly coupled to the medium circulation line <NUM>, or may be coupled to the branch line <NUM> extending between the on-off valve <NUM> and the accumulator <NUM> as shown in <FIG>. Alternatively, the on-off valve <NUM> may be a three-way valve. One of three connection ports of the three-way valve may be coupled to the medium circulation line <NUM>, the other one may be coupled to the accumulator <NUM>, and the remaining one may be coupled to the pump line <NUM>. A connection point of the pump line <NUM> and the medium circulation line <NUM> is located between the accumulator <NUM> and the first chamber 22a.

The sealing system further includes system controller <NUM> configured to control operations of the on-off valve <NUM> and the medium pressurizing pump <NUM> described above. Further, the sealing system includes pressure detector <NUM> for measuring the discharge pressure Ph of the pump impeller <NUM>, pressure detector <NUM> for measuring the pressure Pb in the second chamber 22b, and pressure detector <NUM> for measuring the pressure Pa in the first chamber 22a. The pressure detectors <NUM>, <NUM>, <NUM> are coupled to the system controller <NUM>. The system controller <NUM> is configured to manipulate the on-off valve <NUM> and/or the medium pressurizing pump <NUM> based on measured values of the pressure transmitted from the pressure detectors <NUM>, <NUM>, <NUM>.

The sealing system with the double mechanical seal provided within the seal housing <NUM> uses the fluid barrier-and-cooling medium. The fluid barrier-and-cooling medium is a medium having properties unrelated to the fluid handled by the centrifugal pump, and is a medium having no toxicity or danger. In one embodiment, the fluid barrier-and-cooling medium is oil, and the medium pressurizing pump <NUM> is an oil pump. In the present embodiment, the medium pressurizing pump <NUM> includes an electric motor as a prime mover.

Operations of the sealing system having the above configuration will be described below. The inside of the medium circulation line <NUM> is filled with the fluid barrier-and-cooling medium having pressure equal to or higher than the discharge pressure Ph of the pump impeller <NUM> of the centrifugal pump. When the rotational shaft <NUM> rotates during the normal operation, the pump mechanism <NUM> sucks the fluid barrier-and-cooling medium in the first chamber 22a and pressurizes it, and discharges the fluid barrier-and-cooling medium to the second chamber 22b. The fluid barrier-and-cooling medium pressurized by the operation of the pump mechanism <NUM> returns to the first chamber 22a through the medium circulation line <NUM>.

The pressure Pb in the second chamber 22b becomes higher than the discharge pressure Ph of the pump impeller <NUM> by the throttle and check valve <NUM> attached to the medium circulation line <NUM>. While the fluid barrier-and-cooling medium flows through the medium circulation line <NUM> from the throttle and check valve <NUM> to the inlet <NUM>, the pressure of the fluid barrier-and-cooling medium decreases due to pressure loss. As a result, the pressure Pa of the fluid barrier-and-cooling medium in the first chamber 22a is lower than Pb. Since the pressure Pb in the second chamber 22b is higher than the discharge pressure Ph of the pump impeller <NUM>, the fluid, handled by the centrifugal pump, does not enter the second chamber 22b via the sealing surfaces of the slip ring <NUM> and the counter ring <NUM> that constitute the pump-side sealing mechanism.

When the fluid barrier-and-cooling medium flows through the medium circulation line <NUM>, the fluid barrier-and-cooling medium is cooled by the heat exchanger <NUM> provided on the medium circulation line <NUM>. The cooled fluid barrier-and-cooling medium is returned to the first chamber 22a through the medium circulation line <NUM> and the inlet <NUM>. In this way, during operation of the centrifugal pump, the fluid barrier-and-cooling medium circulates between the first chamber 22a and the second chamber 22b through the medium circulation line <NUM> while being cooled by the heat exchanger <NUM>. The cooled fluid barrier-and-cooling medium cools the pump mechanism <NUM>, so that the temperatures of the pump mechanism <NUM> and peripheral devices (for example, the O-rings <NUM>, <NUM>) do not become high.

By the way, the pressure of the fluid barrier-and-cooling medium in the sealing system decreases over time due to some causes including a small amount of leakage through the sealing mechanisms for the fluid barrier-and-cooling medium. Thus, the pressure Pb in the second chamber 22b is measured by the pressure detector <NUM>. When the pressure Pb is lower than a threshold value, the system controller <NUM> opens the on-off valve <NUM> to supply the fluid barrier-and-cooling medium in the accumulator <NUM> to the medium circulation line <NUM>. In order to prevent a large amount of fluid barrier-and-cooling medium from flowing into the first chamber 22a at the suction side of the pump mechanism <NUM> and to prevent rapid increase in pressure in the first chamber 22a when the on-off valve <NUM> is opened, a throttle mechanism may preferably be provided upstream or downstream of the on-off valve <NUM>.

The threshold value is higher than the discharge pressure Ph of the centrifugal pump. The threshold value may vary according to the discharge pressure Ph. In one embodiment, the threshold value may be a value determined by multiplying the discharge pressure Ph by a predetermined coefficient. For example, the discharge pressure Ph of the pump impeller <NUM> is measured by the pressure detector <NUM>, and the system controller <NUM> multiplies the discharge pressure Ph by <NUM> (this value can be set arbitrarily) to determine the threshold value. Then, the pressure Pb in the second chamber 22b is measured by the pressure detector <NUM>, and the system controller <NUM> compares the pressure Pb with the threshold value. The system controller <NUM> opens the on-off valve <NUM> when the pressure Pb is lower than the threshold value.

The pressure Pa in the first chamber 22a at the atmospheric side is measured by the pressure detector <NUM>. When the pressure Pa is higher than the pressure Pb in the second chamber 22b, the system controller <NUM> closes the on-off valve <NUM>.

Even when the on-off valve <NUM> is open, if the pressure Pb is lower than the threshold value, the system controller <NUM> starts the medium pressurizing pump <NUM>. The pressure of the fluid barrier-and-cooling medium is increased by the medium pressurizing pump <NUM>, and is supplied to the medium circulation line <NUM>. Specifically, the fluid barrier-and-cooling medium is supplied into the first chamber 22a at the suction side of the pump mechanism <NUM>. When the pressure Pa in the first chamber 22a is higher than the pressure Pb in the second chamber 22b, the system controller <NUM> closes the on-off valve <NUM> or stops the operation of the medium pressurizing pump <NUM>.

According to the above configurations, the fluid barrier-and-cooling medium supplied does not hinder the flow of the fluid barrier-and-cooling medium pressurized by the pump mechanism <NUM>. This is because, according to the present embodiment, the fluid barrier-and-cooling medium is injected not into the discharge side of the pump mechanism <NUM> but into the suction side of the pump mechanism <NUM>. Therefore, the heat generated in the vicinity of the pump mechanism <NUM> is delivered smoothly, along with the fluid barrier-and-cooling medium, to the heat exchanger <NUM>, and is dissipated in the heat exchanger <NUM>. Therefore, temperatures of devices arranged around the pump mechanism <NUM> do not increase.

When the pressure Pa in the first chamber 22a is higher than the pressure Pb in the second chamber 22b, the system controller <NUM> closes the on-off valve <NUM> or stops the operation of the medium pressurizing pump <NUM>. As a result, a differential pressure of Pb-Pa is applied to the combination of the sleeves <NUM>, <NUM>' as a whole in a direction from the pump side to the atmospheric side. Therefore, the pressure applied to the sealing surfaces of the slip ring <NUM> and the counter ring <NUM>, constituting the atmospheric-side sealing mechanism, does not decrease, and therefore the sealing effect can be maintained. Further, not only the backup of the pressure retained by the accumulator <NUM>, but also the supply of the fluid barrier-and-cooling medium by the medium pressurizing pump <NUM> as a mechanism for multiply pressurizing can be achieved. Therefore, the safety can be improved.

Next, another embodiment of the present invention will be described with reference to <FIG>. Configurations of this embodiment, which will not be particularly described, are the same as those of the embodiment shown in <FIG>, and therefore their repetitive descriptions are omitted. In the following descriptions, the first medium circulation line <NUM> will be simply referred to as medium circulation line <NUM>.

The sealing system includes the medium circulation line <NUM> coupled to the first chamber 22a and the second chamber 22b, a bypass line <NUM> having both ends coupled to the medium circulation line <NUM>, a check valve <NUM> attached to the bypass line <NUM>, throttle and check valve <NUM> constituted by a combination of a throttle valve and a check valve, heat exchanger <NUM> configured to cool the fluid barrier-and-cooling medium, and accumulator <NUM> which stores a pressurized fluid barrier-and-cooling medium therein in a normal operation and pressurizes the fluid barrier-and-cooling medium in the medium circulation line <NUM> in an emergency by opening on-off valve <NUM>. The medium circulation line <NUM> is arranged outside the seal housing <NUM>. The medium circulation line <NUM> and the bypass line <NUM> are filled with the fluid barrier-and-cooling medium.

One end of the medium circulation line <NUM> is coupled to the inlet <NUM>, and the other end of the medium circulation line <NUM> is coupled to the outlet <NUM>. The throttle and check valve <NUM> and the heat exchanger <NUM> are attached to the medium circulation line <NUM>. The accumulator <NUM> is coupled to branch line <NUM> extending from the medium circulation line <NUM>. The on-off valve <NUM> is attached to the branch line <NUM>. The accumulator <NUM> is coupled to the medium circulation line <NUM> via the branch line <NUM>. The branch line <NUM> and the accumulator <NUM> are located between the heat exchanger <NUM> and the first chamber 22a.

The sealing system includes pressure detector <NUM> for measuring the discharge pressure Ph of the pump impeller <NUM>, and pressure detector <NUM> for measuring the pressure Pb in the second chamber 22b. The pressure detectors <NUM>, <NUM> are coupled to the system controller <NUM>.

The sealing system with the double mechanical seal provided within the seal housing <NUM> uses the fluid barrier-and-cooling medium. The fluid barrier-and-cooling medium is a medium having properties unrelated to the fluid handled by the centrifugal pump, and is a medium having no toxicity or danger. In one embodiment, the fluid barrier-and-cooling medium is oil.

By the way, the pump impeller <NUM> of the centrifugal pump may rotate reversely during an initial operation, immediately after installation of the centrifugal pump. In addition to the initial operation, there is a case where two centrifugal pumps are arranged in parallel and one is operating and the other is stopped as a back-up machine. If a malfunction occurs in a discharge-side check valve (not shown) arranged at a discharge outlet of the centrifugal pump serving as the back-up machine, a fluid discharged from the operating centrifugal pump may flow backward through the other centrifugal pump that is not in operation. As a result, a pump impeller of the stopped centrifugal pump may rotate in the reverse direction.

If the pump impeller <NUM> rotates in the reverse direction as described above, the pump mechanism <NUM>, which operates together with the rotation of the pump impeller <NUM>, also rotates in the reverse direction. When the pump impeller <NUM> rotates in the reverse direction, a centrifugal force is generated in the fluid, handled by the pump, to a certain degree, and the fluid is pressurized. As a result, the pressure of the fluid is applied to the sliding surfaces of the slip ring <NUM> and the counter ring <NUM>. On the other hand, when the pump mechanism <NUM> rotates in the reverse direction, the fluid barrier-and-cooling medium in the second chamber 22b is pressurized and delivered to the first chamber 22a. Since the throttle and check valve <NUM> does not allow the fluid barrier-and-cooling medium to flow into the second chamber 22b, the pressure in the second chamber 22b decreases, and the fluid, handled by the centrifugal pump, may eventually enter the second chamber 22b through the sealing surfaces of the slip ring <NUM> and the counter ring <NUM>.

Moreover, the pressure Pa in the first chamber becomes higher than the pressure Pb in the second chamber, and a differential pressure of Pa-Pb is applied to the combination of the carrier sleeves <NUM>, <NUM>' as a whole in a direction from the atmospheric side to the pump side. As a result, the pressure on the sealing surfaces of the slip ring <NUM> and the counter ring <NUM> at the atmospheric side is lowered, and the sealing effect is reduced, thus possibly causing the leakage of the fluid barrier-and-cooling medium.

Therefore, the sealing system of the present embodiment includes a bypass line <NUM> coupled to the medium circulation line <NUM>. A first connection point 49a at which one end of the bypass line <NUM> is coupled to the medium circulation line <NUM> is near the inlet <NUM> and the first chamber 22a, and a second connection point 49b at which the other end of the bypass line <NUM> is coupled to the medium circulation line <NUM> is near the outlet <NUM> and the second chamber 22b. More specifically, the first connection point 49a is located between the first chamber 22a and the heat exchanger <NUM>, and the second connection point 49b is located between the heat exchanger <NUM> and the second chamber 22b. In this embodiment, the first connection point 49a is located between the first chamber 22a and the branch line <NUM>, and the second connection point 49b is located between the throttle and check valve <NUM> and the second chamber 22b. A check valve <NUM>, attached to the bypass line <NUM>, allows the fluid barrier-and-cooling medium to flow only in a direction from the first connection point 49a to the second connection point 49b (i.e., in a direction from the first chamber 22a to the second chamber 22b), and does not allow the fluid barrier-and-cooling medium to flow in the reverse direction.

Further, one end of a branch line <NUM> is coupled to the medium circulation line <NUM>, and the other end of the branch line <NUM> is coupled to an accumulator <NUM>. An isolation valve <NUM> is attached to the branch line <NUM>. The isolation valve <NUM> may be composed of an electromagnetic valve, a motor-operated valve, a pneumatically driven valve, a hydraulically driven valve, or the like. The opening and closing operation of the isolation valve <NUM> is controlled by system controller <NUM>. A connection point of the branch line <NUM> and the medium circulation line <NUM> is located between the second chamber 22b and the heat exchanger <NUM>. More specifically, the connection point of the branch line <NUM> and the medium circulation line <NUM> is located between the second chamber 22b and the throttle and check valve <NUM>.

According to such configurations, even if the pump mechanism <NUM> rotates in the reverse direction, the fluid barrier-and-cooling medium immediately flows from the first connection point 49a, which is close to the first chamber 22a, to the second chamber 22b through the bypass line <NUM>, so that the pressure in the second chamber 22b can be maintained. As a result, the fluid barrier-and-cooling medium in the second chamber 22b can prevent the fluid, handled by the centrifugal pump, from entering the sealing surfaces of the slip ring <NUM> and the counter ring <NUM> at the pump side. Moreover, the fluid barrier-and-cooling medium in the second chamber 22b prevents a decrease in pressure on the sealing surfaces of the slip ring <NUM> and the counter ring <NUM> at the atmospheric side, and can therefore prevent the fluid barrier-and-cooling medium from leaking to the atmospheric side.

When the system controller <NUM> detects that the difference between the pressure Pb in the second chamber 22b measured by the pressure detector <NUM> and the discharge pressure Ph of the pump impeller <NUM> measured by the pressure detector <NUM> is less than a threshold value, the system controller <NUM> opens the isolation valve <NUM> to allow the fluid barrier-and-cooling medium under pressure in the accumulator <NUM> to flow into the medium circulation line <NUM>. The fluid barrier-and-cooling medium is supplied to the second chamber 22b through the medium circulation line <NUM>, whereby the pressure in the second chamber 22b can be maintained. As a result, the fluid barrier-and-cooling medium in the second chamber 22b can prevent the fluid, handled by the centrifugal pump, from entering through the sealing surfaces of the slip ring <NUM> and the counter ring <NUM> at the pump side. Further, the fluid barrier-and-cooling medium in the second chamber 22b prevents a decrease in pressure on the sealing surfaces of the slip ring <NUM> and the counter ring <NUM> at the atmospheric side, and can prevent the fluid barrier-and-cooling medium from leaking to the atmospheric side.

As described above, according to the present embodiment, even if the pump impeller <NUM> and the pump mechanism <NUM> rotate in the reverse direction, there is no danger of leakage. Therefore, even if the fluid, handled by the pump, contains a toxic or flammable fluid, the sealing system does not allow any leakage of such fluid to the atmospheric side.

<FIG> is a diagram showing another embodiment of the sealing system. Configurations of this embodiment, which will not be particularly described, are the same as those of the embodiment shown in <FIG>, and therefore their repetitive descriptions are omitted. When the pump impeller <NUM> and the pump mechanism <NUM> rotate in the reverse direction for a long time, temperatures of the pump mechanism <NUM> and its peripheral devices may increase. Thus, the embodiment shown in <FIG> has a function of cooling the pump mechanism <NUM> and its peripheral devices.

Both a first connection point 49a at which one end of a bypass line <NUM> is coupled to the medium circulation line <NUM> and a second connection point 49b at which the other end of the bypass line <NUM> is coupled to the medium circulation line <NUM> are located between the heat exchanger <NUM> and the second chamber 22b. More specifically, the first connection point 49a is located between the heat exchanger <NUM> and the throttle and check valve <NUM>, and the second connection point 49b is located between the throttle and check valve <NUM> and the second chamber 22b.

The fluid barrier-and-cooling medium, delivered to the first chamber 22a by the reverse rotation of the pump mechanism <NUM>, flows through the medium circulation line <NUM> and is cooled by the heat exchanger <NUM>. The cooled fluid barrier-and-cooling medium flows into the bypass line <NUM> at the first connection point 49a, flows through the bypass line <NUM> into the second chamber 22b.

A check valve <NUM>, attached to the bypass line <NUM>, allows the fluid barrier-and-cooling medium to flow only in a direction from the first connection point 49a to the second connection point 49b (i.e., in a direction from the first chamber 22a to the second chamber 22b), and does not allow the fluid barrier-and-cooling medium to flow in the reverse direction.

The branch line <NUM> extending from the accumulator <NUM> is coupled to the medium circulation line <NUM>. The connection point of the branch line <NUM> and the medium circulation line <NUM> is located between the second chamber 22b and the heat exchanger <NUM>. More specifically, the connection point of the branch line <NUM> and the medium circulation line <NUM> is located between the second chamber 22b and the throttle and check valve <NUM>. In one embodiment, the branch line <NUM> extending from the accumulator <NUM> may be coupled to the bypass line <NUM> at a position between the second chamber 22b and the check valve <NUM>.

According to the present embodiment, even if the pump impeller <NUM> and the pump mechanism <NUM> rotate in the reverse direction for a long period of time, there is no danger of leakage. Therefore, even if the fluid, handled by the pump, contains a toxic or flammable fluid, the sealing system does not allow any leakage of such fluid to the atmospheric side.

<FIG> is a view showing still another embodiment of the sealing system. Configurations of this embodiment, which will not be particularly described, are the same as those of the embodiment shown in <FIG>, and therefore their repetitive descriptions are omitted. As shown in <FIG>, in the present embodiment, instead of the check valve <NUM>, an on-off valve <NUM> is attached to the bypass line <NUM>. This on-off valve <NUM> is closed during normal operation, and is opened during a reverse rotation. The on-off valve <NUM> may preferably have a valve element comprising a ball valve or a butterfly valve, because the smaller the pressure loss, the smaller the pressure difference between the first chamber 22a and the second chamber 22b. The on-off valve <NUM> may comprise an electromagnetic valve, a motor-operated valve, a pneumatically driven valve, a hydraulically driven valve, or the like.

The sealing system includes the system controller <NUM> configured to control the operation of the on-off valve <NUM>. Further, the sealing system includes the pressure detector <NUM> for measuring the pressure Pb in the second chamber 22b, and the pressure detector <NUM> for measuring the pressure Pa in the first chamber 22a. The pressure detectors <NUM>, <NUM> are coupled to the system controller <NUM>, which operates the on-off valve <NUM> based on the measured values of the pressure transmitted from the pressure detectors <NUM>, <NUM>. More specifically, when the pressure Pa of the fluid barrier-and-cooling medium in the first chamber 22a is higher than the pressure Pb of the fluid barrier-and-cooling medium in the second chamber 22b, the system controller <NUM> opens the on-off valve <NUM>. When the on-off valve <NUM> is opened, the fluid barrier-and-cooling medium flows from the first chamber 22a into the bypass line <NUM> via the heat exchanger <NUM>, and further flows through the bypass line <NUM> into the second chamber 22b.

The branch line <NUM> extending from the accumulator <NUM> is coupled to the medium circulation line <NUM>. The connection point of the branch line <NUM> and the medium circulation line <NUM> is located between the second chamber 22b and the heat exchanger <NUM>. More specifically, the connection point of the branch line <NUM> and the medium circulation line <NUM> is located between the second chamber 22b and the throttle and check valve <NUM>. In one embodiment, the branch line <NUM> extending from the accumulator <NUM> may be coupled to the bypass line <NUM> at a position between the second chamber 22b and the on-off valve <NUM>.

It should be noted that the present invention is not limited to the above-described embodiments, and may include other embodiments in various forms within the scope of the technical concept of the present invention.

Claim 1:
A sealing system for sealing a rotational shaft (<NUM>) of a centrifugal pump, comprising:
a double mechanical seal having a pump-side sealing mechanism (<NUM>, <NUM>) and an atmospheric-side sealing mechanism (<NUM>, <NUM>);
a pump mechanism (<NUM>) driven by the rotational shaft (<NUM>), the pump mechanism (<NUM>) being located between the pump-side sealing mechanism (<NUM>, <NUM>) and the atmospheric-side sealing mechanism (<NUM>, <NUM>);
a first chamber (22a) defined by at least the atmospheric-side sealing mechanism (<NUM>, <NUM>) and the pump mechanism (<NUM>);
a second chamber (22b) defined by at least the pump-side sealing mechanism (<NUM>, <NUM>) and the pump mechanism (<NUM>);
a medium circulation line (<NUM>) for circulating a fluid barrier-and-cooling medium between the first chamber (22a) and the second chamber (22b), the medium circulation line (<NUM>) being coupled to the first chamber (22a) and the second chamber (22b), the fluid barrier-and-cooling medium being different from a fluid handled by the centrifugal pump;
a heat exchanger (<NUM>) attached to the medium circulation line (<NUM>);
a branch line (<NUM>) coupled to the medium circulation line (<NUM>);
an accumulator (<NUM>) coupled to the branch line (<NUM>), the accumulator (<NUM>) being configured to pressurize and store a fluid barrier-and-cooling medium;
the sealing system being characterised in that it further comprises:
J an on-off valve (<NUM>) attached to the branch line (<NUM>);
an optional pressure detector (<NUM>) arranged to measure pressure in the first chamber (22a)
a pressure detector (<NUM>) arranged to measure pressure in the second chamber (22b); and
a system controller (<NUM>) configured to open the on-off valve (<NUM>) when the pressure in the second chamber (22b) is lower than a threshold value, the threshold value being higher than discharge pressure of the centrifugal pump.