GB2534861A

GB2534861A - Submersible turbine system

Info

Publication number: GB2534861A
Application number: GB1501586.0A
Authority: GB
Inventors: Ibach Frank; Reed Matthew
Original assignee: Marine Current Turbines Ltd
Current assignee: Marine Current Turbines Ltd
Priority date: 2015-01-30
Filing date: 2015-01-30
Publication date: 2016-08-10
Also published as: GB201501586D0

Abstract

A submersible turbine system comprises a turbine housing 2 for turbine equipment 10 and a heat exchanger coupled between the turbine equipment and a body of water 15 outside the turbine housing. The heat exchanger comprises a heat pipe. The heat pipe may project into an extension 19 of the housing, so that it is exposed to the cooling action of the water flow, without any additional sealing requirement.

Description

SUBMERSIBLE TURBINE SYSTEM

This invention relates to a submersible turbine system and a method of thermal energy management of the system.

Tidal turbines include equipment which generates heat, for example, in order to make electricity produced by the drive train of the turbine grid compliant, frequency converters are used. These frequency converters may be part of the power train nacelle or in a separate module. Whichever construction is used, the frequency conversion process creates heat and so a heat sink to remove that heat is required.

Typically frequency converters are provided with a cooling circuit to remove the heat that they have produced. Typically, this cooling circuit pumps water from the vicinity of the frequency converter as the heat source to a heat exchanger that serves as a heat sink. This heat sink is typically cooled by seawater on the outside. Pumps tend to have a relatively high failure rate leading to costly subsea retrieval and maintenance requirements. One solution to this is to have redundant pumps installed which take over in the event of failure of the primary pumps, but although this would reduce the failure rate, it would result in increased cost and complexity.

In accordance with a first aspect of the present invention, a submersible turbine system comprises a submersible turbine housing including turbine equipment and a heat exchanger coupled between the turbine equipment and a body of water outside the turbine housing, wherein the heat exchanger comprises one or more heat pipes.

The present invention provides a high reliability solution for subsea cooling applications.

Preferably, the or each heat pipe projects into the water within an extension of the turbine housing.

Preferably, the heat exchanger further comprises a heat sink on an outer surface of the extension of the turbine housing.

Preferably, the heat sink comprises at least one of fins, plates or parallel ribs, Preferably, the turbine equipment comprises equipment in a turbine hub, or in a turbine housing, a turbine motor, a turbine generator, or a pitch control mechanism.

In accordance with a second aspect of the present invention, a method of thermal energy management of a submersible turbine system for generating energy in a body of water, the system comprising a turbine housing and turbine equipment; the method comprising mounting a heat exchanger comprising one or more heat pipes within the turbine housing such that a first end of the heat exchanger is in the vicinity of or coupled to the turbine equipment and a second end of the heat exchanger extends within the turbine housing into the body of water; whereby fluid in the heat exchanger at the first end is heated by heat from the turbine equipment, circulated to the second end and cooled by the body of water.

An example of a submersible turbine system and a method of thermal energy management of the system according to the present invention will now be described with reference to the accompanying drawings in which: Figures la to lc illustrate examples of subsea turbine installations suitable for a subsea turbine system according to the invention; and, Figure 2 illustrates the subsea turbine system of the present invention in more detail.

Subsea turbines may be mounted on a number of different types of support structure. Fig.l a illustrates a typical cylinder or pile 1, for example made from rolled steel, or concrete, with a turbine system on top of the pile 1, the system comprising a turbine drive train 2, which may be housed in a nacelle, or in direct contact with the water and turbine blades 3 mounted to a turbine hub. Figure lb illustrates powertrain mounted to a crossbeam 5, which can be moved up and down the pile 1 on a lift mechanism 4 to give access to the turbines for maintenance. Another alternative, an example of which is shown in Fig.lc is to mount the subsea turbine on a floating structure 6 floating on the sea surface 7 and connected to the turbine via a connection 8, typically a rigid support. As long as the turbine is sufficiently far down in the water to get clear flow past the blades 3, the turbine may be mounted on, beneath, or at one end of the floating structure and the floating structure may include further submerged support elements.

The housing 2 of the turbine system, contains turbine equipment, such as the turbine motor, or generator, or the frequency converter. In addition, there may be a pitch control mechanism, either in the housing or in the hub. All of these may be sources of heat that needs to be dissipated during operation without having a negative impact on the reliability of the turbine. In a tower mounted turbine system such as shown in Fig. lb, the issues of access and retrieval for maintenance are less severe, but the improvement in reliability provided by the invention is still beneficial.

Figure 2 illustrates a system according to the present invention in which the turbine equipment to be cooled is within the housing 2, but the same system may be applied to the turbine equipment in the hub. Equipment 10 is mounted within the housing, for example a frequency converter cabinet, but in operation the equipment generates waste heat. In order to remove this heat, the equipment 10 is connected to a heat exchanger formed of one or more heat pipes. These work on the basis of a fluid that vaporizes at a required cooling temperature in a low pressure environment in a sealed pipe. The heat pipes comprise a sealed hollow body, lined with a wicking material and provided with a fluid.

Heat generated in the turbine hub, or housing, heats up a first end 18 of the heat pipe or pipes within the powertrain or hub which causes fluid contained within the heat pipes to evaporate. The first end 18 of the heat exchanger receives heat from the vicinity of the heat generating equipment, the heat being transferred through the wall of the heat pipe to heat up the fluid. The gas vapour diffuses along the centre of the pipe and condenses again when it reaches a second end 19 of the heat exchanger which is in a cooler region, close to the temperature of the sea, losing heat in the process. The condensed liquid then wicks back to the hotter end 18, so that the process can be repeated. The condensed fluid within the heat pipes is wicked back towards the hot end of the pipes by a wicking material lining the heat pipes. The process repeats as long as there is a sufficient temperature differential caused by a relatively hot region at one end and a relatively cool region at the other end.

A level of fluid 12 inside the heat pipe system is circulated by evaporation transferring vapour and heat away from an end close to the heat generating equipment as indicated by arrow 13 and by condensation of the vapour when it contacts a surface 14 over which the fast flowing seawater 15 passes. In the cold region of the heat pipe, which extends into the surrounding cold sea water, the vapour condenses, releasing the thermal energy extracted from the hub into the sea, then the condensed liquid is wicked back to the heated end in the direction of arrow 16.

By using heat pipe technology to cool the equipment, the active, pumped, cooling circuit is replaced by a passive cooling system, which is more reliable. The effectiveness of the heat pipes may be increased by adding a heat sink 17, for example in the form of ribs, fins, or one or more plates, or a combination of these, to the outer surface of the heat exchanger, preferably in direct contact with the water. Fast flowing, cool sea water, as found in a tidal race, has excellent cooling properties, so the heat exchanger surface required for each heat pipe and the total number of heat pipes required to enable sufficient cooling may be quite small depending on what is being cooled, for example between three and fifty heat pipes according to the equipment being cooled.

A further feature of the present invention is that the heat exchanger does not need a seal through the watertight housing 2 into the seawater to transfer the heat effectively, but can simply be fitted within the powertrain housing or hub, with a slight change to the housing shape to allow the cooling end 19 to have sufficient surface area in the fast flowing water. This makes the system more reliable. The system works best in temperate zones where the annual sea temperature varies between 0°C and 20°C, giving the best differential between the temperature at the hot and cold ends of the heat pipes.

For cooling of high energy equipment such as drive motors, or high energy hubs carrying out frequent changes of pitch, the heat exchanger may be embedded in a heat sink in the motor, or hub, rather than simply extracting heat from air in the vicinity of that has been heated by the equipment.

The present invention has a number of advantages. It avoids the use of active cooling circuits in subsea equipment in tidal races to cool power electronics, so reducing the failure rate and therefore maintenance cost of operating the subsea turbines. Heat pipe based passive cooling circuits work very well in the fast tidal flows and provide excellent heat transfer rates in a heat exchanger that is smaller than conventionally required in subsea applications. This performance means that the overall cost of the system and its complexity are reduced.

Claims

CLAIMS1. A submersible turbine system comprising a submersible turbine housing including turbine equipment and a heat exchanger coupled between the turbine equipment and a body of water outside the turbine housing, wherein the heat exchanger comprises one or more heat pipes.
2. A system according to claim 1, wherein the or each heat pipe projects into the water within an extension of the turbine housing.
3. A system according to claim 2, wherein the heat exchanger further comprises a heat sink on an outer surface of the extension of the turbine housing.
4. A system according to claim 3, wherein the heat sink comprises at least one of fins, plates or parallel ribs,
5. A system according to any preceding claim, wherein the turbine equipment comprises equipment in a turbine hub, or in a turbine housing, a turbine motor, a turbine generator, or a pitch control mechanism.
6. A method of thermal energy management of a submersible turbine system for generating energy in a body of water, the system comprising a turbine housing and turbine equipment; the method comprising mounting a heat exchanger comprising one or more heat pipes within the turbine housing such that a first end of the heat exchanger is in the vicinity of or coupled to the turbine equipment and a second end of the heat exchanger extends within the turbine housing into the body of water; whereby fluid in the heat exchanger at the first end is heated by heat from the turbine equipment, circulated to the second end and cooled by the body of water.