GB2140206A

GB2140206A - Thermoelectric power generator associated with oil pipelines

Info

Publication number: GB2140206A
Application number: GB08412090A
Authority: GB
Inventors: David Chinery
Original assignee: BP PLC
Current assignee: BP PLC
Priority date: 1983-05-20
Filing date: 1984-05-11
Publication date: 1984-11-21
Also published as: GB8412090D0

Abstract

An electrical power generator for use at remote petroleum wells has thermo-electric cells 10 each having a hot junction in thermal contact with naturally occurring crude oil in a pipeline 2. The hot junction takes the form of a collar 6 in contact with the pipeline and the cold junction may be a finned member 7. In other arrangements the cold junction is provided by a heat pipe buried in the sub-soil. The generator may be used to power telemetry equipment, pumps and a valve submerged in the sea. In the latter case the generator unit is attached to the valve housing and is used to charge a battery supplying power to the valve. <IMAGE>

Description

SPECIFICATION Electrical Power Generator The present invention relates to power generation and more particularly relates to electrical power generation from a thermoelectric cell.

The physical phenomena forming the basis of thermo electric power generation are well known.

In particular the Seebeck effect occurs if a closed circuit is made of two conductors of dissimilar material and one junction is maintained at a different temperature than the other, an electric current will flow in the circuit.

Modern oil production management increasingly uses telemetry to monitor and control complex and extensive fields. The use of telemetry reduces or avoids the need for expensive land line cabling for information flow.

The lack of cabling however means that remote outstations e.g. well heads require an electrical power source. The present invention provides an electrical power generator suitable for use with a well head control and telemetry system in which the heat from naturally occurring crude oil is used to drive a thermo-electric cell.

Thus according to the present invention there is provided an electrical power generator comprising a thermo-electric cell having a hot and a cold junction, the hot junction being capable of thermal contact with a pipeline carrying naturally occurring crude petroleum at a temperature above that of the surroundings, and the cold junction being capable of thermal contact with a cold source whereby during use of the generator, the temperature difference of the hot and cold junctions produces electrical power by means of the Seebeck effect characterised in that the hot junction forms part of a collar capable of locating with the pipeline and allowing thermal communication between the hot junction and crude petroleum in the pipeline.

The generator is suitable for use with a well head control and telemetry system.

In a further embodiment of the invention, there is provided a valve suitable for underwater use in a pipeline, the valve having an associated electrical cell capable of powering the opening and closing of the valve and an electric generator (as hereinbefore described) capable of maintaining the charge of the electrical cell, the thermo electric generator adapted to have its hot junction in thermal contact with naturally occurring crude oil flowing through the pipeline.

Preferably the control of the valve is by remote means such as from an acoustic transmitter.

The invention will now be described by way of example only and with reference to Figures 1 to 4 of the accompanying drawings.

Fig. 1 is a schematic diagram of a well head having a thermo-electrically generated power supply. Figure 2 is a vertical section of the pipeline of Figure 1 showing the thermo-electric cell arrangement. Figures 3(a) to 3(e) show various examples of heat conductors for use with the cold junction of the thermo-electric cell.

Figure 4 shows an exploded diagram of a subsea valve for a pipeline between an oil drilling platform and an underwater satellite well. In Figure 1, a well head 1 comprises a horizontal crude oil output line 2 linked to a manifold 3. The well head 1 has associated equipment 4 for telemetric transmission of data related to the crude oil output e.g. oil flow, temperature, pressure. The manifold 3 has valves for controlling the flow of crude oil to pipe line which communicates with a gathering centre some distance away.

The area surrounding the well head is designated a safety zone 14 within which all electrical equipment must be either intrinsically safe or explosion proof.

External to the explosion proof area, a thermo electric generator 5 is attached to the pipe line.

The temperature of the crude oil issuing from the well head can be of the order of 1000C and the external surface of the pipe line can be made the hot sink of the generator by means of an appropriately shaped casting 6. A cold sink in the form of an extrusion 7 having heat dissipating fins 8 is bolted to the hot sink casting 6 through a gasket heat barrier 9, the space between the two castings housing the thermo-electric cell 10 (Figure 2).

In hot climates the high ambient temperature may elevate the achievable cold sink temperature, restricting the output from the cell. For these conditions, the cold junction may be connected to a heat pipe or conductor leading to a cold sink buried in the subsoil. To accommodate pipeline movement due to thermal expansion, etc, the heat pipe or conductor may be made flexible.

The thermo electric cell 10 is connected by cable 1 1 via a junction box 15 to the instrument and telemetry module 12 and supplies power to the electrically driven systems such as data transmission, pumps and valves. Connections to the well head are protected by zener barrier 13 which is outside the safety zone 14.

The module for attachment to the pipeline comprises three main components, the hot sink 6, the cold sink 7, and the thermocell assembly 10.

The hot sink 6 is clamped to the pipe and has a, flat face to conduct heat to the thermocells. The cold sink 7 is a standard black anodised aluminium extrusion with one polished flat face for heat input. The extrusion is drilled to accept a cable gland and penetration for the generator output cable. Three Marlow Industries Ml 1069 thermocells are wired together in series and connected to the output cable which passes through the cold sink and cable gland. The hot and cold sinks are clamped together by a number of screws, sandwiching the thermocell array 10 between the flat faces. Thermal conductivity is enhanced by use of conductive heat sink grease at the contact areas.

During use, crude oil at a temperature of say 1 000C flows from the well head 1 and along pipe line 2 to the gathering centre. The heat from the oil passes into the hot sink 6 and maintains a significant temperature difference between the hot and cold junctions of the thermo electric cell 10. The electrical current flow in the cell caused by the Seebeck effect is led out by cable 11 to the instrument and telemetry module 1 where it is used as a power supply. The supply can be used to maintain the charge of a battery. A typical daily mean output from the thermo electric module array is 250 mA at 12 volts.

In hot areas such as the Middle East where day time temperature may rise to 500 C, the large diurnal variation of the cold sink temperature can cause the day time output of the thermo electric cell to be limited.

An alternative embodiment designed to reduce or alleviate the above problem is to use a subsoil cold junction. It has been found that in desert regions that below a depth of about 1 metre the sub-soil temperature stays roughly constant at about 200C.

It is desirable that the dissipated energy from the thermo electric cell is transferred to the subsoil level as efficiently and economically as possible in order to maintain a substantially constant and predictable thermo electric cell output. The energy transfer may be achieved by the use of a heat pipe but a preferred embodiment is to use a conductive metal, such as copper or aluminium, which although less efficient than a heat pipe is cheapest and more rugged.

Embodiments of heat conductors are shown in Figures 3(a) to 3(e). Figure 3(a) shows a schematic diagram of a rigid sub-soil heat conductor and pipeline. Figure 3(b), 3(c) and 3(d) show embodiments of heat conductors formed from flexible laminations, laminated links and cable respectively. Figure 3(e) shows a schematic diagram of a pipeline with thermo electric generator, the generator being linked by flexible heat cable to the cold junction or sink.

In figure 4, a standard subsea ball valve and actuator 30 is operated by a self contained redundant path power pack 31 having a control module 32. The control module 32 is powered by a battery pack comprising typically a nickel/cadmium cell 33. The battery pack 33 has a 0.5 kWh rating giving a reserve of over 20 valve cycles. The control module 32 for the valve 30 is operable by an acoustic transponder 34 or transmitter capable of receiving and acknowledging control signals from a drilling platform up to 10 miles distant.

A thermo electric generator 35 converts heat from the crude oil to give the order of 100 watts of power to maintain the charge of the battery pack 33. The temperature difference between the hot and cold junctions of the thermo generator 35 is maintained by the hot junction being in heat exchange contact with the hot crude oil passing through the pipe line and the cold junction is in heat exchange contact with the surrounding sea water.

During use, in say a North Sea application, temperature difference between the hot and cold junctions of the thermo cell of about 1 000C yields an electrical output of the order 10 watts from a single layer of cells 18 cm square, the cross section of the heat path being 324 cm2. This is used to maintain the charge of the battery pack.

In order to use the valve to isolate a section of the pipe line in case of emergency, the acoustic transmitter is used to signal the control module to actuate closure of the valve. A number of valves can be used along the pipe line so as to isolate specific sections if required.

Claims

1. An electrical power generator comprising a thermo-electric cell having a hot and cold junction, the hot junction being capable of thermal contact with a pipeline carrying naturally occurring crude petroleum at a temperature above that of the surroundings, and the cold junction capable of thermal contact with a cold source whereby during use of the generator, the temperature difference of the hot and cold junctions produces electrical power by means of the Seebeck effect characterised in that the hot junction forms part of a collar capable of locating with the pipeline and allowing thermal communication between the hot junction and crude petroleum in the pipeline.

2. An electrical power generator according to claim 1 in which the collar is clamped to the pipeline.

3. An electrical power generator according to claim 1 or claim 2 in which the cold junction comprises means for removal of heat.

4. An electrical power generator according to claim 3 in which the heat removal means is a radiator or conductor.

5. An electrical power generator according to claim 4 in which the heat removal means has heat dissipating fins.

6. An electrical power generator according to claim 4 in which the heat removal means comprises a flexible heat conductor.

7. An electrical power generator as hereinbefore described and with reference to the accompanying drawings.

8. A valve suitable for underwater use in a pipeline, the valve having an associated electrical cell capable of powering the opening and closing of the valve and an electrical power generator as claimed in any one of claims 1 to 7 capable of maintaining the charge of electrical cell, the electrical power generator being adapted to have its hot junction in thermal contact with naturally occurring crude oil flowing through the pipeline.

9. A valve according to claim 8 in which the valve is controlled by a remote operator.

10. A valve as hereinbefore described and with reference to the accompanying drawings.

11. A petroleum well head telemetry system for use at a remote well head comprising a pipeline carying naturally occurring crude oil at a temperature above that of the surroundings, an electrical power generator according to any one of claims 1 to 7, and telemetry means capable of being powered by the electrical power generator.

12. A petroleum well head telemetry system as hereinbefore described and with reference to the accompanying drawings.