WO2017200388A1

WO2017200388A1 - Natural gas power plant arrangement

Info

Publication number: WO2017200388A1
Application number: PCT/NO2017/050121
Authority: WO
Inventors: Robert LØSETH
Original assignee: Blystad Energy Management As
Priority date: 2016-05-18
Filing date: 2017-05-18
Publication date: 2017-11-23
Also published as: NO20160837A1; NO341820B1

Abstract

A natural gas power plant arrangement, comprising a floating LNG storage (1) and a floating gas-to-electricity conversion power plant (4) configured to be moored in proximity to land. The floating gas-to-electricity conversion power plant (4) comprises at least one piston engine (5). The piston engine (5) is coupled to and drives an electric generator (7). The electric generator is coupled to a land-based electric grid (16). The floating gas-to-electricity conversion power plant (4) has a further LNG storage(6), which is fluidly coupled to said floating LNG storage (1). The arrangement also comprises an LNG export line(10) that is fluidly coupled to the further LNG storage (6). The export line (19) has a terminal end (27) on land.

Description

NATURAL GAS POWER PLANT ARRANGEMENT

The present invention relates to a natural gas power plant arrangement according to the preamble of claim 1 .

There are many examples of floating power plants that may be used over shorter or longer periods of time to cover up for the need of electric power in a geographical region, for example during peak consumption or while a land based power plant is being built. Natural gas is an environmentally friendly energy source. It is also relatively flexible. With a floating power plant, a substantial increase in electric power capacity can be made in a very short time compared to building a land-based power plant. There are also many examples of floating natural gas supply arrangements that supply natural gas to a land based power plant or to a natural gas distribution system.

Such examples include:

US 2006180231 , which describes an arrangement for supply of natural gas. It includes a floating hub that is arranged stationary off coast and receives liquid natural gas (LNG) from an LNG tanker. The hub has a large enough capacity to receive the whole load of the tanker. Smaller shuttle boats visit the hub to receive smaller volumes of LNG and bring this LNG to various local land based receiving stations. The shuttle boats has equipment on board that converts the LNG to natural gas by regasification before conveying the gas on shore. No floating power plant is described.

This arrangement has several drawbacks. One is that the regasified LNG has a very high pressure, hence, the gas lines that convey the gas from the shuttle boats has to withstand this high pressure. Another drawback is that an electric power plant has to be built on land to produce electric power from the gas. The known arrangement does not have the ability to receive the full cargo load from a large LNG tanker.

US 2005095068, which describes an LNG offloading arrangement. The offloading unit is arranged on the seabed in shallow water. A barge is moored to the offloading unit. The barge has an evaporator on-board. An LNG tanker visits the barge to offload LNG to the barge.

This arrangement has the same drawback as the previous one, that the natural gas has a very high pressure so that the gas lines that convey the gas from the barge has to withstand this high pressure. This system also lacks a floating power plant.

WO 2013109149 describes an arrangement where an LNG tanker has been sectioned to form a smaller LNG storage. It may comprise a evaporator and a power plant.

This arrangement has again the same disadvantage as above that the gas lines that convey the gas from the LNG storage facility has to withstand very high pressure.

WO 2005/032942 describes in a first embodiment a barge that is anchored close to land. A tanker is coupled to the barge, and LNG is transferred from the tanker to the barge via a line. On the barge is a re-gasification unit. Gas is injected into an underground reservoir. A pipeline extends to a gas distribution central on land. No electricity generation is described in connection with this embodiment.

In a second embodiment, WO 2005/032942 describes a similar embodiment to the first. Here the LNG is injected directly into the underground reservoir, where it is transformed into gas.

In a third embodiment, WO 2005/032942 only describes that all the gas is transferred to land and thereafter into the underground reservoir. In a fourth embodiment, WO 2005/032942 describes that LNG is transferred to land via a pipeline and thereafter into the underground reservoir as LNG or gas.

In a fifth embodiment, WO 2005/032942 describes a tanker and a barge. The barge having a re-gasification system. The gas is injected into an underground reservoir. From the reservoir, gas is transferred to land. It is briefly stated that an electric power station can be arranged on the barge or the tanker. The power is used for re-gasification and surplus power is transferred to land. In a sixth embodiment, WO 2005/032942 describes a floating structure that is moored to the seabed. Gas is transferred to an underground reservoir and to a pipeline to land. An electric generator is arranged on the floating structure.

Other prior art examples are WO 2013012985, EP 1918630, WO 2012072292, US 200921 1263, NO 331941 , NO 323093, NO 332708, WO 2009068731 , WO 2007039480 and WO 201 1059344.

None of the prior art examples solve the problem of avoiding high pressure gas lines from the floating facility to shore and at the same time being able to deliver electric power produced from natural gas to a land based grid. Many of the prior art arrangements do not have the possibility to receive the full cargo load of a large LNG tanker.

In many cases, there is a need for both electric power supply and supply of natural gas to an area. The present invention has as its main objective to facilitate both these needs in one compact arrangement.

The present invention has as an important objective to avoid having to have high-pressure gas lines on-board and from a floating facility to a land-based terminal.

According to the invention, the transfer lines, between the floating units and to land, are LNG lines and possible low-pressure boil off gas lines. Hence, they only need to withstand a pressure in the magnitude of up to approximately 10 bar, but preferably below 0,7 bar. This also means that flexible lines may be used, whereas high-pressure lines are normally rigid lines. With rigid lines, the floating units must be tightly moored or set on the seabed, so that they have no or very limited movement with respect to land. Flexible lines allows substantially more flexibility with regard to movement.

Another object of the invention is to be able to deliver LNG to a land-based terminal.

Land-based in this context is any surface that is stationary and includes piers and other man-made land extensions.

Yet another objective is to be able to receive the full cargo load of a large LNG tanker. Another objective is to be able to deliver electric power from a floating facility.

These and other objectives are achieved by the features defined in the characterizing clause of the subsequent claim 1 and its depending claims. The invention will now be described, referring to the enclosed drawings, in which:

Figure 1 shows a first embodiment of the invention, Figure 2 shows a third embodiment of the invention, and Figure 3 shows a third embodiment of the invention.

Figure 1 shows a large size LNG tanker 1 . This may be a tanker that has been designed for sea transport of LNG, which will be suitable also for use as a stationary LNG storage. The large size LNG tanker has preferable not been modified, and has in its original configuration a multiple of LNG tanks 2, having a total capacity of typically at least 125 000 m³ A quantity of 125 000 m³ is a typical trading quantity for LNG cargo loads. The LNG tanker 1 has also a set of pumps 3. The pumps 3 have a large capacity in the magnitude of 500 to 2000 m³ per hour.

The tanker 1 is moored next to one or more floating vessels, ships or barges, hereinafter called a barge 4. The barge 4 contains an electric power plant 5. The power plant comprises a multiple of piston engines (not shown) that are prepared for running on LNG. The engines are connected to generators 7.

The barge also contains an LNG storage tank 6 with a volume in the magnitude of 1000 to 30 000 m³, and at least one pump 8. The pump 8 has a significantly lower capacity than the pumps 3 on the tanker 1 , i.e. in the magnitude of 10 - 250 m³ per hour.

An LNG transfer line 9 is connected between the tanker 1 and the barge 4, so that the pumps 3 can pump LNG from the storage tanks 2 on the tanker 1 to the storage tank 6 on the barge 4.

The pump 8 on the barge 4 has an LNG line 10 that extends to a terminal end on land. The terminal end is in this embodiment of the invention connected to a small LNG storage tank 1 1 in a land based regasification facility 12. The regasification facility has an evaporator 13, which in turn is connected to an export line 14 for natural gas in gaseous form. A pump 17 pumps the LNG to the evaporator 13. The electric generators 7 are coupled to a power cable 15 that is connected to a landline 16 extending to a power grid (not shown).

The tanker 1 is a large reservoir of LNG, which is intermittently pumped into the smaller LNG storage 6 on the barge by using the large capacity pumps 3. The large capacity pumps 3 are designed to empty an LNG tanker in an as short as possible time. Hence, the pumps 3 purposely designed to run at a large rate. The storage tank 6 acts as a buffer for the much smaller tank 1 1 on the regasification facility 12. The smaller pump 8 has a capacity that is around 1 - 20% of the large capacity pump, and can therefore supply the evaporator 12 so to say continuously or according to the required demand capacity. The use of piston engines that are running on natural gas is well known from the boat or shipping area, where LNG is converted to gas by using a heat exchanger and a heat transfer fluid, such as a water/glycol mixture. Conversion of engines into dual fuel or pure gas drive is considered conventional technology.

The great advantage of using piston engines over gas turbines, which are the dominant solution in a gas power plant, is that piston engines need only a relatively low gas pressure of between 0,3 bar and 10 bar, typically in the lower part of this range. Gas turbines; on the other hand, requires a gas pressure in the magnitude of 40 - 50 bar. Such a high gas pressure means that the system on board the barge will have to be built to handle this high pressure. This means that higher safety standards have to be in place.

In the present invention, the piston engines are also supplied with LNG from the storage tank 6. Preferably, the natural evaporation of LNG from the tanks, due to heat gradually penetrating into the tanks, is used to supply the engines. This natural evaporated gas will have a relatively low pressure, typically in the range of 0,3 bar to 5 bar, after a moderate compression. Depending on the gas consumption of the piston engines, this natural evaporation may provide a significant volume of gas to be consumed by the piston engines. In addition, a pressurized evaporation of LNG to a maximum of 10 bar may also be used to ensure a sufficient gas supply. Separate pumps (not shown) may be used to pump LNG to the evaporator unit (not shown). The heat required for this evaporation may be taken from the cooling system of the engines.

The above use of the naturally evaporated gas effectively removes or at least reduces the necessity for other systems for handling evaporated gas.

When the LNG content in the tanker 1 is below a certain limit, a supply tanker (not shown) having approximately the same capacity as the large size tanker 1 will dock alongside the tanker 1 and transfer its cargo load of LNG to the tanker 1 , as illustrated by one or more transfer lines 19. The transfer lines 9 and 10 are both LNG lines. The may be accompanied by vapour exchange lines.

The land based natural gas line 14, which contains gas in gaseous form, has to withstand a pressure of approximately 100 bar.

Thereby is ensured that all the transfer lines between the floating units and from the floating units to land, are low-pressure lines.

The logistics, i.e. the supply of LNG to the large size tanker 1 is done by similar size LNG carriers as the large size tanker 1 . Thereby is avoided the expensive use of less available small scale LNG carriers, which often will require reloading of the LNG from a large size tanker to the smaller carrier, usually via a land- based storage. Figure 2 shows a second embodiment of the invention. This embodiment is similar to the first embodiment but has some additions.

The regasification of the LNG in the evaporator requires energy. It is common to draw this energy from a nearby water source, such as the sea. Seawater that has been used to heat the LNG, is dumped to the sea. This water is

substantially colder than the seawater entering the vaporizer and can create local environmental challenges.

In the arrangement of the present invention, heat energy is available from the cooling system of the piston engines in the power plant 5. Hence, a cooling fluid line 18 extends from the barge 4 to the regasification facility 12. The cooling fluid heats up the LNG in the evaporator 13 so that the LNG evaporates. The cooling fluid that has been cooled by this evaporation exits the evaporator 3 and is routed back to the barge 4 via a return line 20. The cooling fluid again flows through the cooling system of the piston engines, which are connected via at least one cooling fluid line 21 to form a ring main. Appropriate valves 22, 23, and 24 are arranged in the ring main to regulate the flow of cooling fluid. Preferably, the cooling fluid is seawater. This makes it simple to connect a pump 25 the ring main to add seawater to regulate the temperature. At the opposite end of the barge is a dump line 26 to dump a similar volume of seawater that has been added by the pump 25. Alternatively, the cooling fluid may be a freshwater/alcohol mixture, such as freshwater/glycol. In that case, the cooling system may be equipped with an additional heat exchanger (not shown) that exchanges heat with the seawater.

If the temperature and amount of excess heat or cold is beyond the limits allowed to be transferred to the sea, the arrangement can be equipped with a liquid to air heat exchanges, so that at least some of the excess heat can be transferred to the air or air can be used to regulate the temperature of the cooling fluid. This embodiment of the invention also solves an additional problem, namely to dispose of the excess heat from the cooling of the piston engines or excess cold water from the LNG vaporization.

Temperature emissions to the sea is often regulated, and has to be within certain limits. By the arrangement described above, it will be possible to a much greater extend to keep within those limits without having to use other means for regulating the temperature emission.

Figure 3 shows a third and basic embodiment of the present invention. It is simplified compared to the embodiment of figure 1 , by the absent of the regasification unit 12. Instead, the terminal end of the LNG line is terminated in a station 27 that can be connected to an LNG transport vehicle, such as a lorry, a train or a boat, or to a land based LNG storage tank. As for the previous embodiments, the barge 4 comprises an electric power plant that uses piston engines for driving electric generators.

Common to all the embodiments described is that the total capacity of the large size LNG tanker 1 , the storage 6 on the barge 4, and possibly the smaller tank 1 1 in the regasification facility, is at least the same as, but preferably bigger than, the capacity of the supply tanker that supplies the arrangement with LNG.

The barge 4 may conveniently be positioned within the dotted line area 28 that is delimited by the mooring arrangement (not shown) of the large size tanker 1.

The LNG tanks on the barge 4 may conveniently be positioned in the centre of the barge as to avoid ballasting operation during varying degrees of filling of the LNG tanks that occur during loading or during consumption or transfer of LNG.

Claims

1 .

A natural gas power plant arrangement, comprising floating structures, including a floating Liquid Natural Gas (LNG) storage (1 , 2) and a floating gas-to- electricity conversion power plant (4), configured to be moored in proximity to land; said floating gas-to-electricity conversion power plant (4) comprising at least one piston engine (5), said piston engine (5) being coupled to and driving an electric generator (7), said electric generator (7) being coupled to a land- based electric grid (16), characterised in that said floating gas-to-electricity conversion power plant (4) has a further LNG storage (6), which is fluidly coupled to said floating LNG storage (1 , 2); further comprising an LNG export line (10) fluidly coupled to said further LNG storage (6), and said export line (10) having a terminal end (12; 27) on land; thus avoiding high pressure lines extending between said floating structures, as well as between said floating structures and land.

2.

The arrangement of claim 1 , characterised in that the combined volume of said floating LNG storage (1 , 2) and said further LNG storage (6) is at least 125 000 m³

3.

The arrangement of claim 1 or 2, characterised in that said floating LNG storage (1 , 2) is coupled to at least one high capacity pump (3) adapted to pump LNG to the further LNG storage (6) and that said further LNG storage (6) has at least one lower capacity pump (8) adapted to pump LNG to the export line (10).

4.

The arrangement of any of the preceding claims, characterised in that said further LNG storage (6) is fluidly coupled to a land based regasification facility

(12) via said LNG export line (10).

5.

The arrangement of claim 4, characterised in that a cooling fluid arrangement for the at least one piston engine (6) is fluidly connected to an LNG evaporator

(13) of said regasification facility (12), so that heat from said cooling fluid arrangement is transferred to LNG in said evaporator (13).

6.

The arrangement of claim 5, characterised in that said cooling fluid

arrangement is coupled to seawater in order to heat exchange with the sea.

7.

The arrangement of claim 6, characterised in that said cooling fluid

arrangement has a heat exchanger exchanging heat with ambient air.

8.

The arrangement of claim any of the preceding claims, characterised in that said at least one piston engine (5) is driven by natural gas evaporating from said further LNG storage (6), said evaporated natural gas having a pressure of maximum 10 bar.

9.

The arrangement of claim any of the preceding claims, characterised in that said LNG lines (9) between said floating LNG storage (1 , 2) and said further LNG storage (6) and between said further LNG storage (6) and said terminal end (12, 27) on land, are flexible lines that allow movement of said floating storage (1 ) and said floating power plant (4).

10.

5 The arrangement of claim any of the preceding claims, characterised in that said gas-to-electricity conversion power plant (4) and said further LNG storage (6) are arranged on a barge, said barge being moored on the inside of said floating LNG storage and within an area (28) that is delimited by the moorings of said large LNG storage (1 ).

o

1 1 .

The arrangement of claim and any preceding claims, characterised in that the further LNG storage tank (6) is placed in the centre of the barge.