Subsea cooling apparatus, and a separately retrievable submersible pump module for a submerged heat exchanger

Abstract

The present invention concerns a cooling apparatus for subsea applications with a shell and tube heat exchanger. The heat exchanger includes a longitudinal shell. The shell forms a cavity with a fluid inlet port and fluid outlet port. A bundle of tubes extends from an inlet plenum chamber with an inlet port and into the shell on the same side of the shell as a bundle of tubes extending from an outlet plenum chamber with an outlet port. At least one tube sheet seals against the shell cavity and the inlet and outlet plenum chambers. The bundle of tubes extending from the inlet plenum chamber is in fluid connection with the bundle of tubes extending from the outlet plenum chamber. A retrievable pump module with a sealed pump module housing is placed adjacent the heat exchanger and includes a motor driving an ambient sea water pump.

Claims

1. A cooling apparatus for subsea applications, including: a support frame; a shell and tube heat exchanger, wherein the shell and tube heat exchanger comprises: a longitudinal shell with a first side and a second side opposite said first side, said longitudinal shell forming a shell cavity with a shell side fluid inlet port and a shell side fluid outlet port, and at least one end part; a bundle of tubes extending from an inlet plenum chamber with an inlet port, and into said longitudinal shell on said first side of said longitudinal shell; a bundle of tubes extending from an outlet plenum chamber with an outlet port, and into said longitudinal shell on said first side of said longitudinal shell; and at least one tube sheet sealing against the shell cavity, said inlet plenum chamber and said outlet plenum chamber, wherein said bundle of tubes extending from the inlet plenum chamber are in fluid connection with said bundle of tubes extending from the outlet plenum chamber for allowing fluid to flow from said inlet plenum chamber to said outlet plenum chamber; a retrievable pump module coupled to said shell and tube heat exchanger, wherein the retrievable pump module comprises: a sealed pump module housing; a liquid-filled subsea electrical induction motor; and an ambient sea water pump driven by said liquid-filled subsea electrical induction motor through a magnetic coupling allowing the liquid-filled subsea electrical induction motor to be in a hermetically sealed environment, without any leak paths to seawater, for providing circulation of ambient sea water through the shell and tube heat exchanger; a pump module receptacle housing configured to (i) releasably and retrievably connect the retrievable pump module to the shell and tube heat exchanger and an inlet for ambient sea water, and (ii) receive the retrievable pump module therein; a controller for controlling the retrievable pump module, the controller including a variable speed drive; and temperature sensors, wherein the controller and the temperature sensors are integrated in the retrievable pump module, and the support frame encloses the shell and tube heat exchanger, the retrievable pump module, and the pump module receptacle housing.

2. The cooling apparatus of claim 1, wherein the pump module receptacle housing communicates with the outlet port for providing cooling liquid, and a seawater inlet strainer is provided for limiting particle size sucked into the inlet port, such that seawater is used as the cooling liquid.

3. The cooling apparatus of claim 2, wherein the seawater inlet strainer is arranged below the shell and tube heat exchanger to minimize an amount of debris entering the seawater inlet strainer.

4. The cooling apparatus of claim 2, wherein the controller is contained in a canister, and the canister is cooled by the cooling liquid.

5. The cooling apparatus of claim 4, wherein the shell and tube heat exchanger further comprises at least one guidepost, the retrievable pump module further comprises at least one support leg, and the at least one support leg mates with the at least one guidepost to couple the shell and tube heat exchanger with the retrievable pump module.

6. The cooling apparatus of claim 1, wherein the retrievable pump module is adapted to be separately, diverlessly retrievably installed into the pump module receptacle housing.

7. The cooling apparatus of claim 1, wherein the retrievable pump module is connected to the pump module receptacle housing with an ROV operated locking mechanism.

8. The cooling apparatus of claim 1, wherein the pump module receptacle housing is integrated in the shell and tube heat exchanger.

9. The cooling apparatus of claim 1, further including diverless, vertical well fluid connectors to ease retrieval.

10. The cooling apparatus of claim 1, further including an ROV hot stab type port for injection of cleaning chemicals into a cavity between the longitudinal shell, the bundle of tubes extending from the inlet plenum chamber, and the bundle of tubes extending from the outlet plenum chamber.

11. The cooling apparatus of claim 1, wherein the shell and tube heat exchanger is thermally insulated to improve flow assurance.

12. The cooling apparatus of claim 1, wherein the support frame includes at least a top portion and two side portions, and supports the shell and tube heat exchanger and the pump module receptacle housing.

13. The cooling apparatus of claim 1, wherein the at least one tube sheet comprises a first tube sheet and a second tube sheet, the first tube sheet sealing against the shell cavity, said inlet plenum chamber and said outlet plenum chamber, said fluid connection between said bundle of tubes extending from the inlet plenum chamber and said bundle of tubes extending from the outlet plenum chamber is provided by a third plenum chamber limited by the second tube sheet sealing against the shell cavity and said third plenum chamber at the second side of the longitudinal shell.

14. The cooling apparatus of claim 1, wherein said fluid connection between said bundle of tubes extending from the inlet plenum chamber and said bundle of tubes extending from the outlet plenum chamber is provided by U-shaped tubes comprising each said bundle of tubes extending from the inlet plenum chamber and said bundle of tubes extending from the outlet plenum chamber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Short description of the enclosed figures:

(2) FIG. 1a is a side elevation of a cooling apparatus according to the invention;

(3) FIG. 1b is a top view of the of a cooling apparatus shown in FIG. 1a;

(4) FIG. 1c is a cross section B-B of a pump module and pump module receptacle as shown in FIG. 1b;

(5) FIG. 2 is a cross section of a shell and tube heat exchanger used in connection with the invention;

(6) FIG. 3a is a side elevation of a pump module according to the invention;

(7) FIG. 3b is a cross section A-A of the pump module shown in FIG. 3a;

(8) FIG. 3c is a cross section B-B of the pump module shown in FIG. 3b;

(9) FIG. 4a is a cross section of a motor module receptacle housing and a pump module installed in the motor module receptacle housing;

(10) FIG. 4b is a side elevation of the motor module receptacle housing shown in FIG. 4a;

(11) FIG. 5 is a schematic representation of a U-shaped tube of tubes used in connection with the invention;

(12) FIG. 6 is a schematic representation of a heat exchanger that can be used in connection with the invention; and

(13) FIG. 7 shows a cross section of a bonnet or integral cover forming plenum chambers; and

(14) FIGS. 8a, 8b show a centrifugal pump and motor assembly that may be used in connection with the invention.

(15) FIG. 9 is a side elevation of a retrievable pump module for a submerged shell and tube heat exchanger according to the invention;

(16) FIG. 10 is a perspective view of the retrievable pump module shown in FIG. 9; and

(17) FIG. 11 corresponds to the FIGS. 9, and 10, and shows the module connected to a portion attached to a heat exchanger.

DETAILED DESCRIPTION OF THE INVENTION

(18) FIGS. 1a-1c show a general arrangement of an embodiment of a subsea cooler according to the invention. A vertical shell and tube heat exchanger 10 is attached to two diverless process pipe connectors 11. A support frame 13 houses the heat exchanger 10 and a pump module 15. The frame 13 is provided for protection, ease of transportation, installation and recovery/retrieval. A pump module 15 is installed in a housing 14. Furthermore, the pump module 15 may include a ROV operated locking mechanism. External power and signals may be linked to the pump module using diverless connector(s). The pump module may be secured to the cooling apparatus with a ROV operated locking mechanism only. The pump is shown connected to the outlet, at the opposite side of the inlet but it could have been placed at inlet side of the heat exchanger. The inlet may include an inlet strainer, the inlet strainer should be connected to inlet to reduce pump wear, abrasion, contamination etc.

(19) An arrangement and running tool for pump module replacement that may be required is not shown. No external piping and connectors for coolant/cooling liquid (sea water) may be necessary as the ambient water is used for cooling.

(20) The cooler is based on forced convection as they use a pump to circulate the seawater.

(21) FIG. 2 shows a shell and tube heat exchanger which consists of a shell 26 (a large tube-shaped pressure vessel), with a bundle of tubes 24 inside it (not shown). The tubes run from an inlet chamber 21 to an outlet chamber 22. These chambers are formed by the shell 26 and at least one internal tube sheet 23. Both hot produced fluid to be cooled and the cold seawater, flow through the heat exchanger. The hot produced fluid flows through the tubes (the inside) and the seawater flows on the outside of the tubes but inside the shell (the shell side). The direction of the heat transfer may however be turned and the seawater may then flow through the tubes (the inside) and the hot produced fluid may flow on the outside of the tubes but inside the shell (the shell side). Heat is transferred from the produced fluid to the seawater through the tube walls. A large heat transfer area is preferred to transfer heat efficiently, normally leading to a high number of tubes. Diverless process piping connection hubs (not shown) for the produced fluid may be connected to the inlet chamber 21 and the outlet chamber 22. An inlet strainer may be, arranged below the shell to minimise the effect of e.g. silt that is settling down. The strainer may be coarse, to avoid clogging. An outlet 28 may be provided with a flange for connecting the pump module housing 14 in FIG. 1. The heat exchanger may include internal baffles 25 to direct the seawater across the tubes thus increasing the heat transfer.

(22) FIG. 3, shows a pump module with a housing 31, typically made in a metallic material or glass fibre material. The purpose of the housing 31 is to offer mechanical protection and to conduct discharged water from the pump 35 past electronic containers 32 thus providing cooling. Electrical connector(s) and interface to a recovery and installation arrangement are not shown. A subsea electrical induction motor 33 is housed in a hermetically sealed housing 38. Torque from the motor 33 to the pump 35 is transmitted via a magnetic coupling 34. Two electronic containers 32 are included, one redundant to the other. The containers 32 houses variable speed drives (frequency converters) and control electronics in e.g. nitrogen and at one atmosphere. A third container 37 includes a liquid compensator for the electric motor. Not shown are the diverless electrical connectors, its cabling to the electronic containers 32 and distribution between the connector(s), containers and motor. A lower flange 36 on the pump module, lands on a corresponding flat face 42 of a receptacle housing 41 shown in FIG. 4b.

(23) FIG. 4 shows the pump module receptacle housing 41, which is connected to the shell and tube heat exchanger by piping. The piping 18 is shown in FIG. 1. The housing 41 integrates a typical ROV operated locking mechanism that is shown in greater detail in FIG. 5. A soft gasket, not shown, between these surfaces 36, 42 can be used to provide additional sealing, if required.

(24) FIG. 5 is a schematic representation of a U-shaped bundle of tubes 52 used in connection with the invention. One side of the tubes in the bundle 52 is intended to extend from the an inlet plenum chamber (reference 21 in FIG. 2) with an inlet port and into said shell on said first side of the shell, and the other side of the tubes in the bundle 52 extends from an outlet plenum chamber (reference 22 in FIG. 2).

(25) FIG. 6 is a schematic representation of an alternative heat exchanger 10 where discrete bundles of tubes extend from the inlet plenum chamber 21 and the outlet plenum chamber 22 respectively. A third plenum chamber 50 connects the discrete tube bundles for allowing fluid to flow from the inlet plenum chamber 21 to the outlet plenum chamber 22. The third plenum chamber is sealed from the shell 26 with a second tube sheet 23. The third plenum chamber 50 may be confined by a bonnet. The shell 26 includes a shell inlet 28 and a shell outlet 51 at opposite ends of the shell 26.

(26) FIG. 7 shows a cross section of a bonnet 54 or integral cover forming an inlet plenum chamber 21 and an outlet plenum chamber 22. An internal sealing plate 53 divides the bonnet into the inlet and outlet plenum chambers.

(27) The FIGS. 8a, 8b show two views of a centrifugal pump and motor assembly 55 that may be used in connection with the invention.

(28) The FIGS. 9, 10 and 11 show a retrievable pump module for a submerged shell and tube heat exchanger according to the invention. Similar reference numerals refer to similar components, and the following description is relevant to all the FIGS. 9-11 unless something else is stated.

(29) FIG. 9 is a side elevation of the retrievable pump module according to the invention. An electric, oil filled motor 61 is connected to a pump 70 through a magnetic coupling 62. Oil filled motors are well known in the industry and special cooling loops are typically used to ensure sufficient cooling. The present invention proposes using a seawater channel in heat transferring connection with the motor and allowing seawater from the exit of the heat exchanger to flow through these channels to cool the motor 61. The seawater conduit 69 in FIG. 10 is an example of such a seawater channel. The conduit encloses all the critical components of the pump module and ensures that required operating temperatures for the components inside the conduit are maintained within a suitable operating temperature range. In other words, the seawater conduit 69 is arranged to direct seawater from a pump outlet to motor and electronic canisters in order to enhance cooling.

(30) The magnetic coupling 62 between motor 61 and pump 70 allows the motor to be hermetically sealed with no leak paths. The motor oil system may include an expansion tank for accommodating variations in volume. Typically, the volume varies due to thermal expansion of the material of the motor and of the oil. When a system of the above mentioned type is used, it is not necessary to use complex seal arrangements or overpressure systems.

(31) An interfacing structural element 63 provides a transition between the motor 61 and provides a connection to two power and signal electronic canisters 64. The two power and signal electronic canisters 64 provide a, fully redundant, power and control system in case of failure of one of the signal electronic canisters 64, thus providing enhanced reliability. Typically frequency converters are used for speed control. This control system also integrates temperature sensors for heat exchanger control as well as sensors verifying proper operation of the pump module. As for the motor cooling, the canisters 64 are cooled by directing the exiting seawater over them.

(32) An electrical junction box 65 is oil filled and at ambient pressure. The electrical junction box 65 is in fluid connection with the motor 61 and shears thus the expansion tank with motor 61. The electrical junction box 65 accommodates all electric interconnecting cabling with their splitter boxes. The electrical junction box 65 is arranged as a junction bridge above the motor 61 and the canisters 64.

(33) The pump module is typically connected with a ROV wet mate electrical connector (not shown), but with the connection at the junction box end.

(34) Support legs 66 fits into corresponding mini-guide posts 68 arranged on the heat exchanger/cooler.

(35) A lifting point 67 is attached at the top of the module to allow the module to be lowered or retrieved to the surface, using a suitable winch on a vessel.

(36) The mini guidepost 68 arranged on the cooler/heat exchanger and mates with the support legs 66 on the pump module.

(37) FIG. 10 also shows a seawater conduit 69 as a part of the pump module for protecting the pump module from mechanical impacts from falling objects etc. The seawater module 69 can also contribute in ensuring a controlled environment for the components inside the pump module, by allowing seawater from the exit from the heat exchanger to flow past the components of the pump module inside the seawater conduit 69.

(38) The description above proposes locating the pump module at an outlet side of the heat exchanger. The pump module may however be located on the heat exchanger inlet side (instead of outlet side as shown). The FIGS. 9-11 show a centrifugal pump. An axial pump may however be used instead. Furthermore, the number of control canisters with the pump control components may be higher than two. Only one control canister may also be used, but it is an advantage with a redundancy in the system as explained above.

(39) A ROV operated clamp may be used to lock a pump suction flange to a seawater outlet flange on the heat exchanger (not shown).