ITUB20152842A1 - Pumping system equipped with a barrier fluid supply circuit for dry seals. - Google Patents

Description

PUMPING SYSTEM WITH BARRIER FLUID DELIVERY CIRCUIT FOR DRY GAS SEALS. "

DESCRIPTION

This document refers to a fluid pumping system, particularly, but not exclusively, for pumping carbon dioxide (CO2), comprising a plurality of pumps and a dry gas seal protection apparatus, for protect the integrity of the dry gas seals of said pumps, preferably centrifugal pumps, during stand-by conditions.

More specifically, this document refers to a pumping system that allows to protect the integrity of the dry gas seals of a centrifugal pump during stand-by conditions of said pump for CO2 applications, for example re-injection. , transport and sequestration of pure CC> 2 and CO2 hydrocarbons in oil and gas recovery plants.

The application of dry gas seals to centrifugal pumps for shaft sealing, instead of wet seals, offers several advantages, such as reduction of power consumption, reduction of the footprint of the sealing system , the increase in reliability and the elimination of maintenance costs related to filling with barrier fluid.

The many advantages of dry gas seals under centrifugal pump operating conditions conceal problems associated with using dry gas seals on centrifugal pumps in other operating conditions, such as stand-by conditions, as will be explained more clearly. right away.

The loss of gas, and in particular of CO2, through the primary seal is normal since even in the stand-by condition the pump is pressurized and is ready to start.

Therefore, the gas pressure inside the pump is greater than the external atmospheric pressure. Downstream of the primary seal, there is a pressure established by a buffer fluid, typically nitrogen or air available at a pressure between four and six bars. In addition, the higher pressure, untreated process gas permeates the primary dry gas seal, carrying liquid and particulate contaminants.

This problem is emphasized with carbon dioxide (CO2) as a process flow, and 0 with any other fluid capable of changing phase (ice or liquid) due to the expansion of fluid through the seal. The expansion of carbon dioxide (CO2) through the close tolerances of the dry gas sealing rings can form ice on the sealing rings. Subsequently, when the pump returns to normal operating conditions, the contamination between the dry gas seals causes premature wear and a failure of the dry gas seal.

With reference to Figures 1 to 3, a known configuration is illustrated comprising a single centrifugal pump using a dry gas seal.

Figure 1 describes a detailed schematic of a related art setup of a dry gas sealing system (DGS) 100 for a carbon dioxide (CO2) pump. It should be noted, in this configuration, that any fluid in a supercritical state can be employed as a barrier fluid in place of the exemplary carbon dioxide (CO2).

The configuration of Figure 1 reflects the behavior of the dry gas seal during operating conditions and includes a CO2 pump 102 with its associated area to be sealed, a primary (internal) seal 104 of a dry gas seal, a secondary (external) seal 106 of the dry gas seal, a process fluid filter 108, a process fluid heater 110, a valve and control element 120 for controlling flow to an anti-combustion safety area ( "flare-safe area"), an intermediate buffer gas filter 114, intermediate buffer gas 116, barrier fluid 118, pressure reducing valve 120, a primary dry gas-tight chamber 122 and a gas-tight chamber a secondary dry 124.

In the related art configuration of FIG. 1 there is illustrated a process fluid, e.g. carbon dioxide, from the pump exhaust which is used as a barrier fluid. The pressure of the barrier fluid is reduced by a valve 120 and is heated by a heater 110. The barrier fluid is then filtered by filters 108 and injected into the primary dry gas seal chamber 122.

The pressure of the barrier fluid is greater than the suction pressure of the pump and therefore prevents the entry of any untreated process gas into the primary seal 104.

The barrier fluid (carbon dioxide) partially flows into the pump through the internal labyrinth and partially into the primary vent through the primary dry gas seal. Later in the relevant technique setup, the carbon dioxide (CO2) flowing into the pump reaches a suction pressure that is greater than the critical pressure for carbon dioxide (CO2) and consequently no icing problems occur. Furthermore, in the considered configuration, the carbon dioxide (CO2) flowing through the primary seal towards the primary vent expands from P1 to a value set by the buffer gas (typically N2 / air at 4-6 bar). It should be noted that in the known configuration the temperature of the carbon dioxide (CO2) barrier fluid must be kept, by a heater, at a sufficiently high value to avoid, during expansion, the risk of ice formation.

An intermediate buffer gas 116, for example nitrogen or dry air is filtered by filters 114 and injected into the secondary dry gas sealing chamber 124. It should be noted in the known configuration that other gases besides nitrogen or air may also be employed. as a buffer gas. The pressure of the intermediate buffer gas 116 is greater than the pressure of the barrier gas passing through the primary seal 104 and prevents the barrier gas from reaching the secondary seal 106.

In the known configuration, the mixture of barrier gas 118 and intermediate buffer gas 116 in the secondary dry gas seal chamber 124 passes through a valve 112 and flows to an anti-combustion safety area.

Figure 2 shows the same diagram as Figure 1 when the pump is in a stand-by condition. In this condition, the discharge pressure from the pump is equal to the pressure in the area to be sealed 102. When the pump is in a stand-by condition, the pressure in the pump reaches a uniform value very close to the suction pressure.

It should be noted that in the configuration of the related art the result of the stand-by condition is that the process fluid from the pump discharge can no longer act as a barrier fluid to prevent the flow of untreated process fluid, from the area to be closed to seal 102 in primary seal 104. In addition, the untreated process fluid is neither heated nor filtered and therefore contaminants can enter primary seal 104 and ice formation can occur in primary seal 104.

Due to the fact that the pump is pressurized even in the stand-by condition, there is a natural loss of carbon dioxide (CO2) through the primary seal when the pump is in the standby condition.

According to the state of the art, refer to figure 3, to avoid the risk of damage and ice formation when the pump is in stand-by condition, additional auxiliary devices, not shown in the drawing, are provided so that the barrier fluid 118 maintains the gas barrier under the conditions foreseen during the operating condition of the pump. This solution requires similar treatment of the process fluid compared to filtering and heating to prevent contamination of the dry gas seal.

SUMMARY

Plants for carbon dioxide (CO2) applications are considered here, such as re-injection, transportation and sequestration of pure carbon dioxide and carbon dioxide hydrocarbons in oil and gas recovery plants.

In said systems, at least one centrifugal pump is provided, preferably at least two centrifugal pumps are provided which operate alternately, so that when a first pump is in an operating / operating condition, the second pump is in a stand-by condition.

The alternation of the pumps allows the reduction of maintenance costs due to the replacement of the barrier fluid and the increase of MTBF (average time between malfunctions).

Having more centrifugal pumps, each pump can operate for a shorter time, extending the expected time between one malfunction and the next (MTBF).

In addition, the use of multiple centrifugal pumps avoids the shutdown of the system, being able to activate a second pump when it is necessary to perform maintenance on a first pump.

The purpose of this document is to propose a pumping system suitable for obtaining, among others, the advantages listed above. Further details and specific embodiments will refer to the attached drawings, in which:

Figure 1 is a schematic view of a dry gas seal and associated gas support system when the pump is in an operating / operational condition;

Figure 2 is a schematic view of a dry gas seal and associated gas support system when the pump is in a dangerous stand-by condition (risk of damage and ice formation);

Figure 3 is a schematic view of a dry gas seal and associated gas support system when the pump is in a safe stand-by condition (no risk of damage or ice formation);

Figure 4 is a schematic view of the pumping system according to the present document;

• figure 5 represents a flow diagram of the steps of the method according to this document.

DETAILED DESCRIPTION

The following description of exemplary embodiments refers to the accompanying drawings. The following detailed description does not limit the document. In fact, the scope of the invention is defined by the attached claims.

This document refers to oil and gas recovery facilities, i.e. offshore oil and gas facilities. In detail, this document concerns industrial plants for carbon dioxide (CO2) applications.

Some of the most widespread applications of carbon dioxide are the reinjection, transport and sequestration of pure carbon dioxide and carbon dioxide hydrocarbons in oil and gas recovery plants.

In said systems, at least one centrifugal pump is provided, preferably at least two centrifugal pumps are provided which work alternately, so that when a first pump is in an operating / operating condition, the second pump is in a stand-by condition. by.

The alternation of the pumps allows the reduction of maintenance costs due to the replacement of the barrier fluid and the increase of MTBF (average time between malfunctions).

Having more centrifugal pumps, each pump can operate for a shorter time, extending the expected time between one malfunction and the next (MTBF).

In addition, the use of multiple centrifugal pumps avoids the shutdown of the system, being able to activate a second pump when it is necessary to perform maintenance on a first pump.

The purpose of this document is to propose a pumping system suitable for obtaining, among others, the advantages listed above. The pumping system 200 according to the present document comprises at least a first pump 300 and a second pump 400, preferably the first and second pumps are centrifugal pumps, at least one dry gas seal being associated with each of said first and said second pump.

The pumping system 200 according to the present invention comprises a shared process fluid delivery circuit 150, in turn comprising a first barrier fluid delivery circuit 301 which connects at the fluid level the pump discharge 330 of the first pump 300 to at least a dry gas seal of the second pump 400 for delivering a barrier fluid to said at least one dry gas seal of the second pump 400.

The shared process fluid delivery circuit 150 according to the present invention comprises a second barrier fluid delivery circuit 401 which fluidly connects the pump discharge 430 of the second pump 400 to at least one dry gas seal of the first pump 300 to deliver a barrier fluid to said at least one dry gas seal of said first pump.

According to a preferred embodiment of the present document illustrated in Figure 4, the first circuit 301 and the second circuit 401 for supplying barrier fluid of said shared supplying circuit 150 merge into a shared branch line 500 on which a valve is provided reducer 512 adapted to reduce the pressure of the barrier fluid coming from the pump exhausts 330, 430, a filter 514 and a heater 513.

A shared manifold 515 is also provided on said shared branch 500 downstream of said heater 513 with respect to the flow direction. From said shared manifold 515, the shared branch 500 divides into two return branch lines: a first return branch line 517 which connects at the fluid level said shared manifold 515 to the dry gas seals of the first pump 300, said first return line 517 in turn comprising a first section 517a and a second barrier fluid dispensing section 517b, each of said sections of said first return line 517 being fluidly connected to one of said dry gas seals of the first pump 300, and a second return branch line 518 which connects at the fluid level said shared manifold 515 to the dry gas seals of the second pump 400, said second return branch line 518 in turn comprising a first section 518a and a second barrier fluid dispensing section 518b, each of said first 518a and said second 518b section of said second return line 518 being do connected at the fluid level to one of the dry gas seals of the second pump 400.

Referring to Figure 4, the process fluid, for example carbon dioxide (CO2), coming from the shared manifold 515 from the first pump discharge 330 of the first pump 300 is used as a barrier fluid for the dry gas seals of the second pump. 400 when, in an operating condition, said first pump 300 is in an operating condition and said second pump 400 is in a stand-by condition.

Similarly, the process fluid coming from the shared manifold 515 from the second pump discharge 430 of the second pump 400 is used as a barrier fluid for the dry gas seals of the first pump 300 when, in an operating condition, said second pump 400 it is in an operating condition and said first pump 300 is in a stand-by condition.

The pressure of the barrier fluid is reduced by the reducing valve 512 and is filtered by the filter 514 and then heated by the heater 513. The barrier fluid is then injected into the dry gas-tight chamber of the pump in the stand-by condition.

To give an example, when the first pump 300 is in an operating condition, the process fluid is purged from the discharge 330 of the first pump 300 through the first barrier fluid delivery circuit 301 and enters the shared branch line 500. The process fluid pressure is then reduced in the shared branch 500 by the reducing valve 512, and then the fluid is filtered by the filter 514 and heated by the shared heater 513.

The process fluid, ready to be used as a barrier fluid for gas seals, then flows into the shared manifold 515 where all the fluctuations, due to discontinuous operations, are uniform and the fluid properties are stabilized. In this way, the more fragile components of the dry gas seals, which are the seal faces, are protected from sudden pressure changes.

Downstream of the shared manifold 515, the process fluid flows through the second return branch line 518 to the dry gas seals of the second pump 400, which is in a stand-by condition. A first check valve 302 is advantageously provided on said first barrier fluid delivery duct 301, and a second check valve 402 is provided on said second barrier fluid delivery duct 401.

The pumping system 200 according to the present document as described above is therefore adapted to supply a flow of fluid, for example carbon dioxide (CO2) from the pump discharge of a first pump in operation 300 and to purge the seal or the gas seals of the second pump 400 when said second pump is in a stand-by condition.

Likewise, when the first pump 300 is made to pass to a stand-by condition, and the second pump 400 to an operating condition, the pumping system 200 according to the present document is adapted to supply a flow of process fluid from the pump discharge of the second pump 400 and to purge the dry gas seal (s) of the first pump 300.

Thanks to the pumping system according to this document, it is not necessary to provide highly reliable and therefore also very expensive auxiliary compressors to supply the barrier fluid to the dry gas seals of the pump which is in a stand-by condition for the entire duration in which the pump is in a stand-by condition. Finally, if the pumping system includes only two pumps and both are in a stand-by condition at the same time, it may be sufficient to equip the system with simpler and more economical auxiliary devices. In fact, with the pumping system according to the present document, said auxiliary compressors will be activated only in rare cases and for a short period of time in which all the pumps of the pumping system are simultaneously in a stand-by condition.

Therefore, the pumping system according to this document allows to install cheaper auxiliary compressors and, since said auxiliary compressors are rarely activated, the system is very reliable and efficient from an energy point of view.

The pumping system 200 according to the present invention allows the pump function to pass from an operating condition to a stand-by condition.

When the first pump 300 is in an operating condition, the pump exhaust 330 supplies the barrier fluid through the first barrier fluid delivery circuit 301 to the shared manifold 515 and, finally, to the dry gas seals of the second pump 400 which is in a stand-by condition.

When circumstances require it, for example when maintenance operations are required on the first pump, or when it is advantageous to activate the two pumps alternately for shorter periods, for example to increase the MTBF of the pumps, the first pump 300 is made pass to a stand-by condition while the second pump 400 is made to pass to an operating condition. The pumping system according to this document is very versatile with regards to the possibility of switching the operating conditions of the two pumps so that the end user has a large number of possibilities to activate the pumps in the best way considering the circumstances and the results that yes they want to obtain. Thanks to the second barrier fluid delivery circuit 401, the second pump 400 which is now the pump in operation supplies the barrier fluid through the second barrier fluid delivery circuit 401 to the first pump, which is in a stand-by condition.

It will be obvious to those skilled in the art that the pumping system can advantageously comprise more than two pumps, for example three or four pumps. In these possible configurations, the pumping system will comprise a corresponding number of barrier fluid delivery circuits.

The pumping system 200 according to the present invention can advantageously comprise a control unit configured to switch the operating conditions of the pumps and control the operating conditions of the devices provided on the barrier fluid supply circuits.

Among other things, the pumping system according to this document achieves results consisting in reducing maintenance costs, increasing the MTBF and reducing the costs of auxiliary compressors, which are no longer needed.

This document also relates to a method of providing a barrier fluid to a dry seal of a pump.

The method according to the present document allows to provide a barrier fluid to a dry seal of a pump when said pump is in a stand-by condition and without the need to provide additional auxiliary devices. To achieve this result, a first running pump is connected at fluid level through a shared process fluid circuit, to said standby pump.

The method comprises at least the following steps, described in the flow chart of Figure 5.

A first phase 1 consisting in the reception of a barrier fluid from a discharge opening of a first pump in a shared process fluid recovery circuit coupled to the discharge opening.

A second step 2 consisting in reducing the pressure of the barrier fluid;

a third step 3 consisting in directing the barrier fluid at reduced pressure towards a dry seal of a second pump coupled to the shared process fluid recovery circuit.

The method described above advantageously further comprises a further step 2a consisting in filtering and heating the barrier fluid in said shared process fluid recovery circuit after having reduced its pressure and before directing the reduced pressure barrier fluid towards the seal. dry of the second pump.

According to the method described here, when the first pump is in an operating condition and the second pump is in a stand-by condition, the barrier fluid coming from the pump in the operating condition is supplied to the dry seal of the stand-by pump. by. At any time, the operating conditions of the two pumps can be switched so that the first pump is switched to a stand-by condition and the second pump is switched to an operating condition. Thanks to the shared process fluid recovery circuit, the barrier fluid coming from the second pump, now in an operating condition, is supplied to the dry seal of the first pump, now in a stand-by condition. The reference throughout the description to "an embodiment" or "the embodiment" indicates that a particular feature, structure or peculiarity described in relation to an embodiment is included in at least one embodiment of the described object. Thus, the expressions "in an embodiment" or "in the embodiment" at various points in the description do not necessarily refer to the same embodiment. Furthermore, the particular features, structures or features can be combined in any suitable way in one or more embodiments.

Claims (12)

CLAIMS 1. Pumping system (200), comprising at least a first pump (300) and a second pump (400), each of said pumps (300, 400) being equipped with one or more dry gas seals and being able to be switched between a stand-by condition and an operating condition, each of said pumps (300, 400) comprising at least one pump inlet and one pump discharge (330, 430), the pumping system (200) further comprising at least one shared process fluid delivery circuit (150) which connects at fluid level the pump discharge (330, 430) of each of said pumps (300, 400) to the dry gas seal of each of said pumps (300, 400). Pumping system (200) according to claim 1, wherein said shared process fluid delivery circuit (150) comprises a first barrier fluid delivery circuit (301) which fluidly connects the pump discharge ( 330) of said first pump (300) to a shared line (500) and a second barrier fluid delivery circuit (401) which connects the pump discharge (430) of the second pump (400) at the fluid level to said line shared line (500), said shared line (500) being in turn connected at the fluid level to the dry gas seals of said pumps. Pumping system (200) according to the previous claim, wherein said shared line (500) is equipped with at least one reduction valve (512) adapted to reduce the pressure of the barrier fluid coming from the pump discharges (330, 430) , at least one filter (514), at least one heater (513) and at least one shared manifold (515). Pumping system (200) according to the preceding claim, wherein downstream of said shared manifold (515) said shared branch (500) of said shared process fluid delivery circuit (100) is divided into a first line of return branch (517) which connects at the fluid level said shared manifold (515) to said one or more dry gas seals of the first pump (300), and in a second return branch line (518) which connects to fluid level said shared manifold (515) to the dry gas seals of the second pump (400). Pumping system (200) according to the preceding claim, wherein a first check valve (302) is provided on said first barrier fluid delivery duct (301), and a second check valve (402) is provided on said second barrier fluid delivery duct (401). Pumping system (200) according to any one of the preceding claims, wherein said pumps are centrifugal pumps. Pumping system (200) according to any one of the preceding claims, wherein said fluid discharged from the pump discharge (330, 430) of said first (300) and said second pump (400) is carbon dioxide (C02) . Pumping system (200) according to any one of the preceding claims, further comprising a control unit configured to switch the operating conditions of said pumps (300, 400) and control the operating conditions of said process fluid delivery circuit shared (150). 9. Method comprising the following steps: receive a barrier fluid from a discharge opening of a first pump in a shared process fluid recovery circuit coupled to the discharge opening; reduce the pressure of the barrier fluid; And directing the reduced pressure barrier fluid to a dry seal of a second pump coupled to the shared process fluid recovery circuit. Method according to claim 9, wherein the same further comprises the steps of: filtering and heating the barrier fluid in said shared process fluid recovery circuit after reducing its pressure and before directing the reduced pressure barrier fluid towards the dry seal of the second pump. The method according to claim 9 wherein when the first pump is in an operating condition and the second pump is in a stand-by condition, the barrier fluid from the operating condition is supplied to the dry seal of the stand-by pump. -by. The method according to claim 9 further comprising the step consisting in switching the operating conditions of the two pumps so that the first pump reaches a standby condition and the second pump reaches an operating condition, the barrier fluid coming from the pump in a Operating condition is provided to the dry seal of the pump in stand-by.