WO2009153143A1

WO2009153143A1 - Method of operating a compressor using concentrated solar power and an apparatus therefor

Info

Publication number: WO2009153143A1
Application number: PCT/EP2009/056410
Authority: WO
Inventors: Wiveka Jacoba Elion; Casper Krijno Groothuis; Irina Tanaeva
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 2008-05-29
Filing date: 2009-05-27
Publication date: 2009-12-23
Anticipated expiration: 2010-11-29

Abstract

The present invention provides a method and apparatus for operating a compressor using concentrated solar power (CSP), the method comprising at least the steps of: (a) providing a concentrated solar power system (10); (b) collecting solar energy from the sun in the concentrated solar power system (10) to provide captured solar thermal energy; (c) generating one or more heated expansion fluid streams (42) from one of more expansion fluid streams (12) using at least part of the captured solar thermal energy; (d) passing at least one of the heated expansion fluid streams (42) to the inlet (101) of a first turbine (100) to power the first turbine (100); and (e) mechanically driving a first compressor (200) with the first turbine (100).

Description

METHOD OF OPERATING A COMPRESSOR USING CONCENTRATED SOLAR POWER AND AN APPARATUS THEREFOR

The present invention provides a method of, and apparatus for, operating a compressor using Concentrated Solar Power (CSP) . The compressor operated using CSP may provide any number of functions, such as a compression in a liquefaction unit, for example for the production of Liquefied Natural Gas (LNG) , or compression in a gas turbine, which could be used to drive a refrigerant compressor or electric generator.

Natural gas is a useful fuel source, as well as being a source of various hydrocarbon compounds. It is often desirable to liquefy natural gas in a liquefied natural gas (LNG) plant at or near the source of a natural gas stream for a number of reasons. As an example, natural gas can be stored and transported over long distances more readily as a liquid than in gaseous form because it occupies a small volume and does not need to be stored at high pressure.

Usually, natural gas, comprising predominantly methane, enters an LNG plant at elevated pressures and is pre-treated to produce a purified feed stream suitable for liquefaction at cryogenic temperatures. The purified gas is processed through a plurality of cooling stages using heat exchangers to progressively reduce its temperature until liquefaction is achieved. The liquid natural gas is then further cooled and expanded to final atmospheric pressure suitable for storage and transportation.

In addition to methane, natural gas usually includes some heavier hydrocarbons and impurities, including but not limited to carbon dioxide, sulphur, hydrogen sulphide and other sulphur compounds, nitrogen, helium, water and other non-hydrocarbon acid gases, ethane, propane, butanes, C₅+ hydrocarbons and aromatic hydrocarbons. These and any other common or known heavier hydrocarbons and impurities either prevent or hinder the usual known methods of liquefying the methane, especially the most efficient methods of liquefying methane. Most if not all known or proposed methods of liquefying hydrocarbons, especially liquefying natural gas, are based on reducing as far as possible the levels of at least most of the heavier hydrocarbons and impurities prior to the liquefying process.

Hydrocarbons heavier than methane and usually ethane are typically condensed and recovered as natural gas liquids (NGLs) from a natural gas stream. The NGLs are usually fractionated to yield valuable hydrocarbon products, either as products streams per se or for use in liquefaction, for example as a component of a refrigerant.

Meanwhile, methane recovered from the NGL recovery is usually recompressed for use or reuse either in the liquefaction, such as a fuel gas, or being recombined with the main methane stream being liquefied, or it can be provided as a separate stream.

In a paper titled ^λMLNG DUA Debottlenecking Project' presented at the 15^th International Conference & Exhibition on Liquefied Natural Gas, 24-27 April 2007, by Ibrahim and Shukri, a plant comprising three identical LNG process modules is disclosed. As shown in Figure 2, the modules use a C3 (propane) refrigerant system compressor driven by a Frame 6 gas turbine with a steam turbine starter/helper drive, and mixed component refrigerant compressors driven by a Frame 7 gas turbine with a steam turbine starter/helper drive. The steam turbines are supplied by high pressure steam from boilers . The steam turbine starter/helper drives are useful to bring gas turbines driving the refrigerant compressors up to speed when functioning as a starter drive, but can additionally enhance the power of the gas turbine when functioning as a helper drive. The operation of the steam turbine starter/helper drives requires the presence of boilers to generate the steam to power them. The boilers operate by combusting a hydrocarbon fuel and generating steam from the heat of the reaction. The hydrocarbon fuel required by the boilers can be bled from the feed stream of the LNG process modules or by drawing a liquefied natural gas product stream from the module and vaporising this to provide a gaseous natural gas stream appropriate to fuel the boiler.

The use of boilers to generate the steam to power the steam turbine starter/helper drives consumes valuable hydrocarbon fuel and generates carbon dioxide as a combustion product. Carbon dioxide is a greenhouse gas and environmental concerns associated with the emissions of such greenhouse gases have resulted in a move towards reducing the carbon dioxide emissions associated with the operation of a manufacturing plant, such as a LNG module.

In a first aspect, the present invention provides a method of operating a compressor comprising at least the steps of: (a) providing a concentrated solar power system; (b) collecting solar energy from the sun in the concentrated solar power system to provide captured solar thermal energy; - A -

(c) generating one or more heated expansion fluid streams from one of more expansion fluid streams using at least part of the captured solar thermal energy;

(d) passing at least one of the heated expansion fluid streams to the inlet of a first turbine to power the first turbine; and

(e) mechanically driving a first compressor with the first turbine.

In a further aspect, the present invention provides an apparatus for operating a compressor comprising at least : a concentrated solar power system comprising: one or more concentrators to reflect and concentrate sunlight onto one or more receivers and one or more receivers to capture solar thermal energy; a first turbine having an inlet for a heated expansion fluid stream and a shaft, the heated expansion fluid stream generated using at least a part of the captured solar thermal energy; and a first compressor connected to the shaft of the first turbine.

The first compressor may, for instance, be any compressor in a hydrocarbon liquefaction plant such as an LNG plant, where it may be used in a process of producing a liquefied hydrocarbon product from a gaseous hydrocarbon feed gas stream, such as LNG from natural gas .

Embodiments and examples of the present invention will now be described by way of example only with reference to the accompanying drawings.

Figure 1 is a diagrammatic scheme for a first apparatus and method of operating a compressor using Concentrated Solar Power. Figure 2 is a diagrammatic scheme for a second apparatus and method of operating a compressor using CSP.

Figure 3 is a diagrammatic scheme for a third apparatus and method of operating the compressor of a turbine using CSP.

For the purpose of this description, a single reference number will be assigned to a line as well as a stream carried in that line.

The present invention proposes to use CSP to assist in the generation of a heated expansion fluid to drive a turbine, which turbine is arranged to mechanically drive a compressor.

Embodiments of the present invention also provide a process of liquefying a gaseous hydrocarbon feed stream to produce a liquefied hydrocarbon product, wherein at least one compressor, preferably a refrigerant compressor, is operated as described herein.

By using CSP to assist in the generation of the heated expansion fluid which powers the first turbine, the quantities of hydrocarbon fuel which must be burned in a boiler to generate the heated expansion fluid to drive such turbines can be reduced, and in some cases the boilers can be dispensed with entirely. By supplementing the heat of combustion in a boiler with captured solar thermal energy, the consumption of hydrocarbon fuel can be reduced, thus lowering the carbon dioxide emissions associated with the manufacturing plant.

A first turbine powered in this way can be used as a starter motor to provide the starting torque to initiate the start-up of the compressor of an industrial heavy duty gas turbine.

Furthermore, a CSP powered first turbine can be used to complement a gas turbine by co-driving the compressor of the gas turbine. This can result in a reduction in the consumption of the gaseous hydrocarbon fuel required by the gas turbine, producing a corresponding reduction in carbon dioxide emissions. In addition, it is known that the power output of gas turbines may be degraded at high ambient temperatures, such as during the daylight hours in hot environments, particularly in equatorial regions. The use of the first turbine powered by CSP heated expansion fluid as a helper motor for a gas turbine can alleviate such ambient temperature related power losses.

Figure 1 is a diagrammatic scheme for an apparatus and method of operating a compressor according to a first embodiment. A CSP system 10 is shown which comprises an expansion fluid circuit 40 which captures solar thermal energy to heat one or more expansion fluid streams to provide one or more heated expansion fluid streams 42. For simplicity, only a single expansion fluid stream 12 and heated expansion fluid stream 42 is shown in Figure 1 and these streams will be referred to in the singular for the discussion of Figure 1. However, the method and apparatus disclosed herein encompasses the use of a plurality of expansion fluid streams and heated expansion fluid streams. The CSP system 10 concentrates and collects direct solar radiation to provide medium to high temperature heat. A CSP system may contain three main elements: one or more concentrators, one or more receivers and one or more expansion fluid circuits 40. The one or more concentrators reflect and concentrate solar energy, comprising light from the sun, onto the one or more receivers. The one or more receivers receive the reflected and concentrated sunlight and heat the one or more expansion fluid streams 12 in the expansion fluid circuit 40 to provide the one or more heated expansion fluid streams 42. In Figure 1, the one or more concentrators and one or more receivers are represented by the unit CSP.

Parabolic trough CSP systems use trough-shaped mirrors as the concentrators to reflect and concentrate sunlight onto one or more receivers in the form of tubes. An expansion fluid can be heated in the receiver tubes to about 500 ⁰C. The heated expansion fluid can be used to power the first turbine directly. For example, direct solar steam can be generated at a pressure of 100 bar and a temperature of about 375 ⁰C.

Alternatively, the CSP system can be used to heat a thermal transfer fluid to provide a heated thermal transfer fluid. The heated thermal transfer fluid is then heat exchanged with an expansion fluid to provide a thermal transfer fluid and a heated expansion fluid, the latter being used to power the first turbine. As an alternative to parabolic trough concentrators, a linear Fresnel reflector array of concentrators can be used. This is a line focus system similar to parabolic trough systems in which solar radiation is concentrated on an elevated inverted linear receiver using an array of nearly flat reflectors. The use of linear concentrators provides a lower-cost alternative to parabolic trough concentrators and provides a number of advantages over parabolic systems such as lower structural support and concentrator costs, fixed fluid joints, a receiver separated from the concentrators and long focal lengths allowing the use of conventional glass.

Central receiver (solar tower) CSP systems use a circular array of large individually tracking plain mirrors (heliostats) as the one or more concentrators to concentrate sunlight onto a central receiver mounted on top of a tower. Such systems can provide high conversion efficiencies. If pressurised gas or air is used as the thermal transfer or expansion fluid, temperatures of about 1000 °C or more may be achieved. In a similar manner to the parabolic trough CSP systems, the solar thermal energy can be captured directly in the expansion fluid or used to heat a thermal transfer fluid, which can be subsequently heat exchanged against the expansion fluid to generate the heated expansion fluid to power the first turbine.

Parabolic dish CSP systems are smaller units which use dish shaped concentrators to reflect and concentrate sunlight onto a receiver situated at the focal point of the dish. The concentrated radiation is absorbed by the receiver and can heat a thermal transfer or expansion fluid to temperatures of about 750 ⁰C.

Returning to Figure 1, the CSP system 10 collects light from the sun and captures this solar thermal energy by heating the expansion fluid stream 12 to provide a heated expansion fluid stream 42. The expansion fluid preferably comprises H₂O, and the heated expansion fluid preferably comprises steam. The heated expansion fluid, such as steam, may preferably have a pressure of 100 bar and a temperature of about 375 ⁰C.

The heated expansion fluid stream 42 is passed to the inlet 101 of a first turbine 100 to power the turbine and exits first turbine 100 via outlet 102 as expansion fluid stream 12. The first turbine 100 is a rotary engine which extracts energy from the heated expansion fluid stream 42. Common turbines comprise a rotor assembly, which can be a shaft with blades attached and a casing around the blades. The heated expansion fluid stream 42 acts on the blades, or the blades react to the flow, so that they rotate and impart energy to the rotor. The casing contains and controls the heated expansion fluid stream 42.

There are two main types of turbine, reaction turbines and impulse turbines. Reaction turbines develop torque by reacting to the pressure of the heated expansion fluid. The pressure of the heated expansion fluid changes as it passes through the turbine rotor blades. A pressure casing is required to contain and direct the heated expansion fluid stream 42. Most steam turbines are of this type.

Impulse turbines utilise nozzles to accelerate the heated expansion fluid stream 42 and direct it at the turbine blades, thereby changing the pressure head of a fluid to a velocity head. The resulting impulse rotates the shaft with the blades and leaves the flow with decreased kinetic energy. In contrast to reaction turbines, there is no change in pressure of the heated expansion fluid stream 42 after contacting the turbine blades .

The first turbine 100 powered by the heated expansion fluid stream 42 is used to mechanically drive a first compressor 200. Figure 1 shows a first shaft 105 directly connecting the first turbine 100 to the first compressor 200. First compressor 200 has an incoming first compressor stream 202 and an outgoing first compressor stream 204. The first compressor may be a compressor in an LNG plant, such as a feed gas compressor, a refrigerant compressor, or an end-flash gas compressor.

In a preferred embodiment, the first compressor is part of a first gas turbine 250. First gas turbine 250 comprises the first compressor 200, a first combustion chamber C and a second turbine 210. The first compressor 200 is mechanically coupled to the second turbine 210. The first gas turbine 250 is operated by providing a first oxidant stream to the first compressor 200 as incoming first compressor stream 202. The first oxidant stream 202 comprises oxygen, and may be an air stream or be an oxygen-enriched stream (relative to air) . First compressor 200 compresses the first oxidant stream 202 to provide a compressed oxidant stream as outgoing first compressor stream 204. The compressed oxidant stream 204 is passed to a first combustion chamber C, where it is mixed with a first fuel stream 206 and the mixture is ignited. Energy is released when the compressed oxidant stream 204 and the first fuel stream 206 are ignited to produce a first combusted stream 208. The first combusted stream 208 is passed to a second turbine 210 where it is directed over the turbine blades, rotating the turbine and mechanically powering the first compressor 200. The first combusted stream 208 leaves the second turbine 210 as first exhaust gas stream 212. The second turbine 210 is mechanically connected to a second shaft 205, which can be used to operate further devices, such as the feed gas, refrigerant or end flash gas compressors of a LNG plant. The first turbine 100 may drive two or more compressors on one shaft, for instance a compressor that is part of the gas turbine 250 and a compressor external to the gas turbine 250 which may for instance be a feed gas compressor, a refrigerant compressor or an end flash gas compressor.

Alternatively or additionally, the first gas turbine 100 can be used to operate a fourth compressor, a generator, such as an electric generator or a pump, such - li as a water pump in a reverse osmosis desalination plant. The water pump can alternatively be driven electrically using the electricity generated from an electric generator mechanically driven by the method disclosed herein.

The first combusted stream 208 can be passed through a nozzle in the second turbine 210, generating additional thrust by accelerating the hot first combusted stream 208 by expansion back to atmospheric pressure. This expanded first combusted stream exits the second turbine 210 as first exhaust gas stream 212.

Thus, captured solar thermal energy can be used to generate a heated expansion fluid stream 42, which powers the first turbine 100. The first turbine 100 is mechanically connected to a first compressor 200, such that the first compressor 200 can be driven by the first turbine. In the embodiment in which the first compressor 200 is part of a first gas turbine 250, a method of starting-up the first gas turbine 250 is also provided in which the first turbine operates as a starter motor to provide the starting torque for the first compressor 200 of the first gas turbine 250.

In addition, the first turbine 100 can be used to complement the first gas turbine 250 by co-driving the first compressor 200 of the first gas turbine 250. By using the first turbine 100 to provide a portion of the driver power for the first gas turbine, the consumption of the gaseous hydrocarbon fuel provided in the first fuel stream 206 can be reduced, producing a corresponding reduction in carbon dioxide emissions. Thus, the thermal energy captured by the CSP system 10 during daylight hours can be used to replace the heat generated by hydrocarbon fuelled boilers. This allows "peak shaving", when the power requirements of the first compressor 200, and therefore the demand for heated expansion fluid, is highest. This is a further advantage of the method and apparatus disclosed herein. Furthermore, by co-driving the first gas turbine 250 with the first turbine 100, it is possible to maintain the power output of the first gas turbine 250 during circumstances in which the available power from the first gas turbine 250 is diminished. For instance, high environmental temperatures, such as those experienced in equatorial regions in the middle of the daylight hours, or at other latitudes at the height of the Summer, can lead to a reduction in the efficiency of the first gas turbine 250. The first turbine 100 can be used to co- drive the first gas turbine 250, supplementing its power. Because the first turbine 100 is powered by captured solar thermal energy, the availability of such energy during daylight hours, and particularly during the period when the sun is strongest, coincides with those periods in which the efficiency of the first gas turbine would be adversely effected by high temperatures.

Figure 2 is a diagrammatic scheme for an apparatus and method of operating a compressor according to a second embodiment. In this embodiment, the expansion fluid circuit 40, which provides heated expansion fluid 42 to the first turbine 100 is a different circuit from the circuit which captures the solar thermal energy from the sun.

In particular, a first thermal transfer circuit 140 is provided in the CSP system 10. The first thermal transfer circuit 140 comprises one or more first thermal transfer fluid streams 112 which are provided with captured solar thermal energy by the unit CSP to generate one or more heated first thermal transfer fluid streams 142. The first thermal transfer fluid stream 112 may be selected from the group comprising: H2O, liquid sodium, molten salt, natural or synthetic oil and air. The expansion fluid stream 12 may comprise H2O.

As discussed in relation to Figure 1, the CSP system 10 can additionally comprise one or more concentrators and one or more receivers, and may be of the parabolic trough, linear Fresnel reflector array, central receiver or parabolic dish types. The collecting of the solar energy may thus comprise reflecting and concentrating the solar energy with the one or more concentrators to heat one or more first thermal transfer fluid streams 112 in the one or more receivers to provide the one or more heated first thermal transfer fluid streams 42, and heat exchanging, in a first heat exchanger 50, the one or more heated first thermal transfer fluid streams 42 the against one or more expansion fluid streams 12 to provide the one or more first thermal transfer fluid streams 112 in the first thermal transfer fluid circuit 140 and the one or more heated expansion fluid streams 42 in the expansion fluid circuit 40.

The first heat exchanger can be any heat exchanger known in the art, such as a plate and fin heat exchanger or a shell and tube heat exchanger. Shell and tube heat exchangers, and more particularly kettle heat exchangers are preferred. Although only a single first heat exchanger 50 is shown in Figure 2, the method and apparatus disclosed herein encompasses the possibility of a plurality of heat exchangers, in series and/or in parallel .

In a further embodiment not shown in Figure 2, the captured solar thermal energy may be transferred between one of more further intermediate thermal transfer circuits, prior to the generation of the heated expansion fluid stream 42 in the first heat exchanger 50. Each intermediate thermal transfer circuit may comprise intermediate heat exchangers, intermediate thermal transfer fluid streams and heated intermediate thermal transfer fluid streams.

For instance, where a single intermediate thermal transfer circuit is present, the heated first thermal transfer fluid stream 142 would be heat exchanged against a second (intermediate) thermal transfer fluid in the first heat exchanger to provide the first thermal transfer fluid stream 112 in the first thermal transfer fluid circuit 140 and a heated second thermal transfer fluid in a second thermal transfer fluid circuit. The heated second thermal transfer fluid stream would then be heat exchanged with the expansion fluid stream 12 in a second heat exchanger to provide a heated expansion fluid stream 42 in expansion fluid circuit 40 and the second thermal transfer fluid stream in the second thermal transfer fluid circuit. The second thermal transfer fluid may be selected from the same thermal transfer fluids as the first thermal transfer fluid. The second thermal transfer fluid may be the same as or different from the first thermal fluid transfer fluid.

The heated expansion fluid stream 42, which may be a steam stream, is passed to the first inlet 101 of a first turbine 100 , which can be a steam turbine, to power the turbine as discussed for Figure 1. First shaft 105 mechanically connects the first turbine 100 to first compressor 200, thereby driving the first compressor 200.

First compressor 200 has an incoming first compressor stream 202a and an outgoing first compressor stream 204a. The first compressor 200 may be part of a first gas turbine as described for Figure 1, or may be another piece of equipment. For instance, first compressor 200 may be a refrigerant compressor used in the manufacture of LNG. In this case, incoming first compressor stream 202a would be a refrigerant stream, and outgoing first compressor stream 204a would be a compressed refrigerant stream. Preferably, the incoming first compressor stream 202a and the outgoing first compressor stream 204a are in a closed refrigerant circuit wherein a refrigerant is circulated physically separately from the hydrocarbon stream that is being liquefied. The hydrocarbon stream that is being liquefied may be indirectly heat exchanged against the refrigerant in the outgoing first compressor stream 204a after the refrigerant in the outgoing compressor stream 204a has been cooled and expanded. After the indirect heat exchange, the refrigerant may be provided to the first compressor in the form of incoming first compressor stream 202a. Alternatively, incoming first compressor stream 202a may be a hydrocarbon feed stream for a LNG plant, for instance a natural gas stream. In this case, the outgoing first compressor stream 204a would be a compressed natural gas stream, which could be sent for liquefaction to one or more heat exchangers as is known in the art. First compressor 200 could also be an end flash gas compressor, such that the incoming first compressor stream 202a is an end flash gas stream and the outgoing first compressor stream 204a is a fuel gas stream. Figure 3 is a diagrammatic scheme for an apparatus and method of operating a compressor according to a third embodiment. A CSP system 10 comprising concentrators 20, receivers 30 and first thermal transfer circuit 140 is disclosed. First thermal transfer circuit 140 comprises a first thermal transfer fluid stream 112, which is split into three parallel first thermal transfer fluid part streams 112a, 112b, 112c. Each first thermal transfer fluid part stream 112a, 112b, 112c is passed through three pairs of receivers 30 and associated concentrators 20 which capture solar thermal energy to provide three heated first thermal transfer fluid part streams 142a, 142b, 142c respectively. The three heated first thermal transfer fluid part streams 142a, 142b, 142c are then combined to provide heated first thermal transfer fluid stream 142.

The CSP system 10 shown in Figure 3 is a parabolic trough system comprising nine parabolic trough concentrators 20 each having an associated tubular receiver 30. Each parabolic trough concentrator 20 reflects and concentrates light from the sun onto a corresponding receiver 30. A first thermal transfer fluid part stream 112a, 112b, 112c is carried within each receiver and is heated by the solar thermal energy captured in each receiver 30.

The present invention is not limited to such a CSP system comprising an array of parabolic trough concentrators 20 and tubular receivers 30. Alternative arrays comprising a plurality e.g. two, four, five or more parallel first thermal transfer fluid part streams are encompassed together with associated concentrators and receptors, which are not limited to trough and tube systems and may be linear Fresnel reflector arrays, solar tower, or parabolic reflector systems as discussed above. Such systems may comprise a plurality of concentrators and/or receivers in each first thermal transfer fluid part stream. In a similar manner to the embodiment of Figure 2, the heated first thermal transfer fluid stream 142 is heat exchanged against an expansion fluid stream 40 to provide the first thermal transfer fluid stream 112 in the first thermal transfer fluid circuit 140 and a heated expansion fluid stream 42 in the expansion fluid circuit 40. The heated expansion fluid stream 42 is then passed to the inlet 101 of a first turbine 100 to power the turbine, and leaves the first turbine via outlet 102 as expansion fluid stream 12. The first turbine 100 is mechanically connected to a first compressor 200 by first shaft 105. The first compressor 200 may be part of a first gas turbine 250 as discussed for Figure 1.

CSP system 10 further comprises a heat storage unit 160. During the daytime when the CSP system can capture solar thermal energy to produce heated first thermal transfer fluid stream 142, a portion of the heated first thermal expansion fluid stream 142 may be passed to heat storage unit 160 via first junction 146, which can be a first shunt valve, along heated first thermal transfer fluid storage stream 144. Heat storage unit 160 functions as a heat exchanger to remove and store heat from the heated first thermal expansion fluid storage stream 144 to provide a first thermal transfer fluid storage stream 162, which is returned to first thermal transfer fluid stream 112 via second junction 164, which can be a second shunt valve.

When the stored heat in the heat storage unit 160 is required by the CSP system 10, for instance at night when the CSP system 10 cannot capture solar thermal energy to produce a flow of heated first thermal transfer fluid stream 142, second junction 164 can direct a part of first thermal transfer fluid stream 112 to the heat storage unit 160 along first thermal transfer fluid storage stream 162. First thermal transfer fluid storage stream 162 is heated in the heat storage unit 160 to provide heated first thermal transfer fluid storage stream 144, which can be returned to heated first thermal transfer fluid stream 142 via first junction 146. The heated first thermal transfer fluid stream 142 can then be heat exchanged with the expansion fluid stream 12 in the first heat exchanger 50. In this way, the heat storage unit 160 can release captured solar thermal energy to generate a heated expansion fluid stream 42 even when there is insufficient sunlight available to CSP system 10.

The heat storage unit 160 may be a molten-salt storage system. Inside the heat storage unit 160 the thermal energy from the heated first thermal transfer fluid storage stream 144 can be passed to a cold salt stream from a cold salt storage tank to generate a hot salt stream. The hot salt stream is passed to a hot salt storage tank where it can be stored until the thermal energy of the hot salt is required. For example, a sixteen hour molten-salt storage system can allow CSP systems to be run on a 24 hour basis in Summertime when there is sufficient daytime sunlight. In an alternative embodiment, the captured solar thermal energy can be stored in a subsurface geologic reservoir, as described in U.S. Patent Application Publication No. 2006/0048770. In this case, a supercritical fluid, such as brine, is generated from the captured solar thermal energy by heat exchange with heated first thermal transfer fluid storage stream 144 in heat storage unit 160. The supercritical fluid can be injected into a subsurface geologic reservoir through at least one injection well. Once charged with supercritical fluid, the subsurface geological formation forms a synthetic geothermal reservoir. The supercritical fluid can subsequently be extracted from the subsurface geologic reservoir through at least one extraction well bore, and the captured solar thermal energy released by heat exchange with first thermal transfer fluid storage stream 162 in heat storage unit 160 to provide heated first thermal transfer fluid storage stream 144 which can then be returned to heated first thermal transfer fluid stream 142.

Thus, the method disclosed herein may comprise the further steps of: (i) storing at least a portion of the captured solar thermal energy in a thermal storage system 160; and

(j) optionally releasing at least a part of the stored captured thermal energy and using this released captured thermal energy to generate one or more heated expansion fluid streams 42 from one of more expansion fluid streams 12.

Figure 3 exemplifies a further embodiment in which a second gas turbine 350 is present to provide a second exhaust gas stream 302, which is passed to the first heat exchanger 50 in a combined cycle. Second gas turbine 350 comprises a second compressor 310, a second combustion chamber Cl and a third turbine 300. The second compressor 310 is mechanically coupled to the third turbine 300. The second gas turbine 350 is operated by providing a second oxidant stream 312 to the second compressor 310. The second oxidant stream 312 comprises oxygen, and may be an air stream or be an oxygen-enriched stream (relative to air) . Second compressor 310 compresses the second oxidant stream 312 to provide second compressed oxidant stream 314. The second compressed oxidant stream 314 is passed to second combustion chamber Cl, where it is mixed with a second fuel stream 318, such as a hydrocarbon gas stream, and the mixture is ignited. Energy is released when the second compressed oxidant stream 312 and the second fuel stream 318 are ignited to produce a second combusted stream 316. The second combusted stream 316 is passed to a third turbine 300 where it is directed over the turbine blades, rotating the turbine. The second combusted stream 316 leaves the third turbine 300 as second exhaust gas stream 302. The third turbine 300 mechanically powers the first compressor 310. The third turbine 300 is mechanically connected to a third shaft 305, which can be used to operate further devices, such as electric generator 400.

The second exhaust gas stream 302 is passed to the first heat exchanger 50, where it transfers at least a portion of its heat to the expansion fluid stream 12, to generate heated expansion fluid stream 42. In this way, the exhaust gas stream of one or more gas turbines can be utilised to supplement the thermal energy captured from the sun and heat the expansion fluid stream. Such a combined cycle further boosts the fuel efficiency of the method and apparatus disclosed herein. The expansion fluid circuit 40 is not necessarily a dedicated closed circuit as depicted in the accompanying drawings. For instance, the heated expansion fluid stream 42 may be added to a high-pressure steam system that is usually provided in an LNG plant to supplement or the steam that is present in the high-pressure steam system and alleviate the need to generate steam in fired sources such as boilers. Also, there may still be heating duty available in the expansion fluid stream 12 downstream of the first turbine 100, for instance in the form of low-pressure steam. This duty may be used for providing heat to one or more another process steps. Typical duty for such low- pressure steam includes heating of reboilers; regeneration of sorbents; heating of a thermal desalination process; and more. Such processes are known the the person skilled in the art and will not be further discussed here. A convenient way of utilizing the low pressure steam may be by supplementing the low-pressure steam present in a conventional low-pressure steam system that may be provided in the LNG plant. After duty has been removed from the low-pressure steam, part of all of it may be fed to the heat exchanger 50 as described hereinabove .

Sorbents may be solid sorbents such as zeolites, metal oxide frameworks, activated carbon; or liquid sorbents such as those used in the solvent extraction of acid gases including, but not limited to carbon dioxide, oxides of sulphur and hydrogen sulphide. Examples include: primary, secondary and/or tertiary amines derived from alkanolamines, especially amines are derived from ethanolamine, especially monoethanol amine, diethanolamine, triethanolamine, diisopropanolamine and methyldiethanolamine or mixtures thereof; diglycolamines and sterically hindered amines.

A person skilled in the art will readily understand that the present invention may be modified in many ways without departing from the scope of the appended claims. For instance, the first exhaust gas stream 212 from the first gas turbine 250 can be passed to the first heat exchanger 50 to provide heat to the expansion fluid stream 12 in a similar manner to the second exhaust gas stream 302, thus further enhancing the fuel efficiency of the combined cycle.

Claims

C L A I M S

1. A method of operating a compressor comprising at least the steps of:

(a) providing a concentrated solar power system;

(b) collecting solar energy from the sun in the concentrated solar power system to provide captured solar thermal energy;

(c) generating one or more heated expansion fluid streams from one of more expansion fluid streams using at least part of the captured solar thermal energy; (d) passing at least one of the heated expansion fluid streams to the inlet of a first turbine to power the first turbine; and

(e) mechanically driving a first compressor with the first turbine.

2. A method according to claim 1, wherein the heated expansion fluid stream comprises H2O.

3. A method according to claim 1 or claim 2, further comprising using the first compressor for producing a liquefied hydrocarbon product from a gaseous hydrocarbon feed gas stream.

4. A method according to any one of the preceding claims wherein the first compressor is selected from the group consisting of: a feed gas compressor, a refrigerant compressor, and an end-flash gas compressor.

5. A method according to any one of claims 1 to 3, wherein the first compressor is the compressor of a first gas turbine.

6. A method according to claim 5, wherein the first turbine is a helper driver for the first gas turbine.

7. A method according to claim 5 or claim 6, wherein the first gas turbine mechanically drives a pump, a fourth compressor or a generator.

8. A method according to claim 5 or claim 6, wherein the first gas turbine mechanically drives the fourth compressor, the fourth compressor being selected from the group consisting of: a feed gas compressor, a refrigerant compressor, and an end-flash gas compressor.

9. A method according to any one of claims 5 to 8, wherein the gas turbine produces a first combusted stream that leaves the second turbine as first exhaust gas stream, and wherein the first exhaust gas stream is passed to the first heat exchanger to provide heat to the expansion fluid stream.

10. A method according to any one of the preceding claims, comprising the further steps of:

(f) providing a second gas turbine having a second exhaust gas stream;

(g) passing the second exhaust gas stream to the first heat exchanger; and

(h) heat exchanging the second exhaust gas stream with the expansion fluid stream to provide the heated expansion fluid stream.

11. A method of any of the preceding claims, wherein the first turbine is a steam turbine.

12. A method according to any of the preceding claims, further comprising the step of:

(i) storing at least a portion of the captured solar thermal energy in a thermal storage system.

13. An apparatus for operating a compressor, the apparatus comprising at least: a concentrated solar power system to capture solar thermal energy and to generate a heated expansion fluid stream using at least a part of the captured solar thermal energy; a first turbine having an inlet for the heated expansion fluid stream, and a shaft; and a first compressor connected to the shaft of the first turbine .