GB2571355A

GB2571355A - Method

Info

Publication number: GB2571355A
Application number: GB1803183.1A
Authority: GB
Inventors: Mainza De Koeijer Gelein; Johan Rørtveit Geir
Original assignee: Equinor Energy AS
Current assignee: Equinor Energy AS
Priority date: 2018-02-27
Filing date: 2018-02-27
Publication date: 2019-08-28
Also published as: GB201803183D0

Abstract

A method of generating electricity and/or shaft power and capturing CO2, comprises: (i) passing air through a turbocharger compressor to produce compressed air; (ii) combusting fuel using the compressed air in a reciprocating engine to generate electricity and/or shaft power and a pressurised exhaust gas comprising CO2; (iii) capturing CO2 contained in the pressurised exhaust gas comprising CO2 in a CO2 capture unit to produce a pressurised CO2-lean exhaust gas; and (iv) feeding the pressurised CO2-lean exhaust gas through a turbocharger expander to drive said turbocharger compressor. Between steps (ii) and (iii) some of the exhaust gas may be recycled into the reciprocating engine. Oxygen may be removed from the captured CO2 and the captured CO2 may be stored.

Description

FIELD OF THE INVENTION

The present invention relates to a method of generating electricity and/or shaft power and capturing CO₂. Optionally the method additionally comprises the generation of energy (e.g. heat). The invention further relates to systems for carrying out the method of the invention.

BACKGROUND

Greenhouse gases, such as CO₂, in the earth’s atmosphere help to regulate global temperatures through the greenhouse effect. Greenhouse gases are therefore essential to maintaining the temperature of the earth so that it is habitable to humans, animals and plants alike. However, excess greenhouse gases in the atmosphere contribute to global warming by raising the temperature of the earth to harmful levels. The effects of global warming have already begun to be observed, e.g. in rising sea levels and in the melting of polar ice caps. According to simulation models, an increased CO₂ concentration in the atmosphere is suspected to cause further and potentially more dramatic changes in the climate in the future. As a result, scientists, environmentalists and politicians throughout the world are driving initiatives to reduce the amount of CO₂ discharged into the atmosphere by combustion of fossil fuel.

A primary cause of increased CO₂ levels in the atmosphere is the burning of fossil fuels such as coal, oil, or natural gas. One approach being adopted to minimise the environmental impact of facilities that burn large amounts of fossil fuels is to capture CO₂ (i.e. prevent the release of CO₂) from the exhaust gases, e.g. from thermal power plants, before they are released to the atmosphere. The captured CO₂ may be injected into subterranean formations such as aquifers, oil wells for enhanced oil recovery or in depleted oil and gas wells for storage since tests indicate that CO₂remains in the subterranean formation for thousands of years and is not released back into the atmosphere.

With offshore operations, such as offshore facilities for generating electricity and/or shaft power (via mechanically coupled drives), there is a desire to employ compact low weight equipment in order to save space, while still ensuring a good efficiency. In light of this, various technologies exist for compact power and heat production, e.g. single cycle gas turbines, combined cycle gas turbines, etc.

In a typical single cycle gas turbine power plant, a fossil fuel is burnt in the presence of compressed air. The resultant high temperature and high pressure gas is used to drive a turbine, which in turn drives a generator to generate electricity or delivers shaft power to a shaft. A combined cycle gas turbine power plant operates in a similar fashion to a single cycle gas turbine power plant, except that the operation makes use of the remaining thermal energy of the exhaust gas exiting the gas turbine to produce extra electricity (e.g. by using it to generate steam which can drive a steam turbine).

Whilst it is known to combine single cycle gas turbines or combined cycle gas turbine with a CO₂ capture unit, these combinations are heavy and demand large amounts of space. The combinations are also not particularly energy efficient because numerous utilities and pre-treatment steps must be carried out as part of the CO₂capture process.

Sargas AS’s technology involves compressed air being diverted from a high pressure compressor of a gas turbine unit to an external fluidised-bed combustor unit. The airflow is first used to fluidise the solid fuel particles in the combustor unit. The air then mixes and reacts with the solid fuel particles in the combustor unit and the resultant combustion reactions release the heat required by the process. The external fluidised-bed combustor unit generates superheated steam for a steam cycle, and also diverts a hot pressurised CO₂-rich gas stream to a CO₂ capture unit where CO₂ is removed in a chemical adsorption process involving hot potassium carbonate. Finally, the CO₂-lean pressurised gas exiting the capture unit is directed to a power turbine. However, methods such as this involving a pressurized boiler can become inefficient and the large high temperature gas/gas heat exchangers that are often employed are known to have a short lifespan.

Statoil ASA’s CombiCap technology involves a power plant comprising gas turbines having compressor units and turbine units, and a combustor. The pressurised CO₂-rich flue gas from the combustor is ultimately passed through a CO₂ capture unit to remove CO₂ therefrom. However, this technology involves a complex turbine arrangement due to the need to avoid back pressure on the turbines and, again, the large high temperature gas/gas heat exchangers often employed are known to have a short lifespan.

SUMMARY OF INVENTION

Thus viewed from a first aspect the present invention provides a method of generating electricity and/or shaft power and capturing CO₂, comprising:

(i) passing air through a turbocharger compressor to produce compressed air;

(ii) combusting fuel using said compressed air in a reciprocating engine to generate electricity and/or shaft power and a pressurised exhaust gas comprising CO₂;

(Hi) capturing CO₂ contained in the pressurised exhaust gas comprising CO₂ in a CO₂ capture unit to produce a pressurised CO₂-lean exhaust gas; and (iv) feeding the pressurised CO₂-lean exhaust gas through a turbocharger expander to drive said turbocharger compressor.

Viewed from a further aspect the present invention provides a system for generating electricity and/or shaft power and capturing CO₂comprising:

(a) a turbocharger compressor having an inlet for air and an outlet for compressed air;

(b) a reciprocating engine for generating electricity and/or shaft power fluidly connected to said outlet for compressed air of said turbocharger compressor and having an inlet for fuel, an inlet for compressed air and an outlet for a pressurised exhaust gas comprising CO₂;

(c) a CO₂ capture unit fluidly connected to said outlet for a pressurised exhaust gas comprising C0₂of said reciprocating engine and having an inlet for pressurised exhaust gas comprising CO₂, an outlet for pressurised CO₂-lean exhaust gas and an outlet for CO₂; and (d) a turbocharger expander fluidly connected to said outlet for pressurised CO₂lean exhaust gas of said CO₂ capture unit having an inlet for pressurised CO₂lean exhaust gas, wherein said turbocharger compressor is driven by pressurised CO₂-lean exhaust gas being fed through said turbocharger expander.

DEFINITIONS

As used herein, the term “compact CO₂ capture unit” refers to a CO₂ capture unit having a 2 to 50 MW electricity or equivalent shaft power output, more preferably a to 20 MW electricity, or equivalent shaft power, output, when coupled to a reciprocating engine. The compact capture unit has a volume and/or weight which is less than a conventional CO₂ capture unit, e.g. a combined cycle gas turbine of ~25 MW electricity with monoethanolamine (MEA) based post-combustion with an equipment weight of roughly 1000 tonnes

As used herein, the term “means” includes a pipe.

DETAILED DESCRIPTION

The present invention provides a method of generating electricity and/or shaft power and capturing the CO₂ generated in the process, which is both more compact and efficient than the known technology. This is achieved in the method of the invention by employing a turbocharger compressor to generate compressed air, combusting fuel using the compressed air in a reciprocating engine and capturing CO₂from a pressurised exhaust gas comprising CO₂.

The method of the invention employs a reciprocating engine to generate electricity and/or shaft power. In contrast, most new technologies emerging today employ single cycle gas turbines (SCGTs) or combined cycle gas turbines (CCGTs) because these are more energy efficient. A reciprocating engine produces exhaust gas with a higher CO₂ partial pressure than either a SCGT or CCGT engine. Thus, it has been found that when CO₂ capture is carried out, the total efficiency, both in terms of energy, space and weight, of the method of the invention is improved over SCGT or CCGT technologies, particularly at sizes below 50 MW electricity per unit.

By operating with a pressurised exhaust gas comprising CO₂, with an increased partial pressure of CO₂, the active surface area for mass transfer of the CO₂ capture unit can be significantly reduced compared to processes capturing CO₂ from atmospheric pressure exhaust gas from, for example, SCGT and CCGT engines. This means that the overall size of the CO₂ capture unit, as well as the overall power generation unit, can be reduced and also that it requires less energy and resources to operate. In turn, this means that the total energy efficiency of the process is increased when the energy required to carry out CO₂ capture is taken into account.

A reciprocating internal combustion engine (or reciprocating engine or piston engine) converts chemical potential energy in fuel to shaft power using one or more reciprocating pistons. The reciprocating engines employed in the methods of the present invention can be two-stoke cycle engines, four-stroke cycle engines, or diesel engines. The reciprocating engines are able to tolerate back pressure. Preferred reciprocating engines for use in the methods and systems of the present invention include the currently manufactured engines by GE Jenbacher, GE Waukesha, MAN Turbo and Wartsila. Representative examples of suitable engines include e.g. Wartsila 31DF or GE Jenbacher 920 Flextra.

The reciprocating engine employed in the methods of the present invention is operated with a turbocharger. A turbocharger has three main components: an expander (also known as an expansion turbine) for converting energy of the exhaust gas flow to a rotational movement of the expander, a compressor rotationally connected to the expander for compressing intake air, and a housing enclosing the expander and the compressor as well as a rotating shaft, bearings, etc. Turbochargers are commonly provided for increasing load flexibility, efficiency and power of the reciprocating engine. In a turbocharged reciprocating engine, such as those employed in the methods of the present invention, the engine aspirates the same volume of air as a naturally aspirated engine but due to the higher air pressure, more air mass is supplied into the combustion chamber(s). This means that more fuel can be combusted, resulting in an increased power output.

In step (i), air is passed through the turbocharger compressor to produce compressed air which is ultimately fed into the reciprocating engine. The air that is fed into the turbocharger compressor preferably has a pressure of 0.9 to 1.1 bar (e.g. 1 bar) and/or a temperature of -30 to 60 Ό (e.g. 15 °C). Preferably, the air that is fed into the turbocharger compressor has a pressure of 0.9 to 1.1 bar (e.g. 1 bar) and a temperature of -30 to 60 °C (e.g. 15 °C).

The compressed air produced in step (i) preferably has a pressure of 2 to 10 bar, more preferably 4 to 8 bar (e.g. 6 bar), and/or a temperature of 80 to 350 °C, more preferably a temperature of 130 to 300 °C (e.g. 240 °C). Preferably, the compressed air produced in step (i) has a pressure of 2 to 10 bar, more preferably 4 to 8 bar (e.g. 6 bar), and a temperature of 80 to 350 °C, more preferably a temperature of 130 to 300 °C (e.g. 240 °C).

In preferred methods of the invention, the turbocharger is a two or more stage turbocharger, more preferably a two-stage turbocharger. A two-stage turbocharger comprises a smaller turbocharger operating at low speeds and a larger turbocharger operating at higher speeds. The two differently sized turbochargers are then connected in series so that boost pressure from one turbocharger is multiplied by the other. The preferred reciprocating engine for use in the methods of the present invention, has a 2stage turbocharger design.

The reciprocating engine employed in the methods of the present invention may drive a generator, which feeds the electricity generated into the consumer grid. The engine is started and accelerated to rated speed and synchronized with the grid. Alternatively, the reciprocating engine may drive a shaft for another reciprocating engine, e.g. for a compressor. Alternatively, the reciprocating engine may drive a generator and a shaft for another reciprocating engine, e.g. for a compressor.

In step (ii), the compressed air exiting the turbocharger compressor enters the combustion chamber(s) of the reciprocating engine. Combustion of a first fuel in the combustion chamber(s) in the presence of the compressed air causes the reciprocating pistons to move and thereby drive a shaft for another reciprocating engine or a generator to generate electricity.

A fuel is supplied to the combustion chamber(s) of the reciprocating engine in such a way that optimum efficiency or maximum possible output is achieved. Preferred fuels for use in the reciprocating engine include diesel, kerosene, gasoline, jet fuel, natural gas, oil, condensates, propane vapour, and biogas. A particularly preferred fuel is natural gas. The fuel is preferably supplied to the combustion chamber(s) at room temperature, i.e. 15 to 50 °C, more preferably 20 to 25 °C (e.g. 25 °C).

In preferred methods of the invention, the compressed air entering the reciprocating engine has a pressure of 2 to 10 bar, more preferably 4 to 8 bar (e.g. 6 bar), and/or a temperature of 80 to 350 °C, more preferably a temperature of 130 to 300 °C (e.g. 240 °C). Preferably, the compressed air entering the reciprocating engine has a pressure of 2 to 10 bar, more preferably 4 to 8 bar (e.g. 6 bar), and a temperature of 80 to 350 °C, more preferably a temperature of 130 to 300 °C (e.g. 240 Ό).

In further preferred methods of the invention, the compressed air is cooled prior to entering the reciprocating engine. The cooled compressed air preferably has a temperature of 10 to 350 °C, more preferably a temperature of 10 to 200 °C (e.g. 50 °C), and/or a pressure of 2 to 10 bar, more preferably 4 to 8 bar (e.g. 6 bar). Preferably, the cooled compressed air has a temperature of 10 to 350 °C, more preferably a temperature of 10 to 200 °C (e.g. 50 °C), and a pressure of 2 to 10 bar, more preferably 4 to 8 bar (e.g. 6 bar). In preferred methods of the invention, the compressed air is cooled using a heat recovery unit or a heat exchanger.

A pressurised exhaust gas comprising CO₂ is produced during combustion in step (ii). The pressurised exhaust gas comprising CO₂ exiting the reciprocating engine preferably has a temperature of 300 to 600 °C, more preferably 350 to 500 °C (e.g. 450 °C), and/or a pressure of 1.5 to 10 bar, more preferably 3.5 to 8 bar (e.g. 5 bar). Preferably, the pressurised exhaust gas comprising CO₂ exiting the reciprocating engine has a temperature of 300 to 600 °C, more preferably 350 to 500 °C (e.g. 450 °C), and a pressure of 1.5 to 10 bar, more preferably 3.5 to 8 bar (e.g. 5 bar). The amount of CO₂ in the pressurised exhaust gas comprising CO₂ is preferably 3.5 to 10 mol%, more preferably 4 to 8 mol% (e.g. 4.9 mol%). The pressurised exhaust gas comprising CO₂ may also contain an amount of oxygen, preferably 0 to 13 mol%, more preferably 3 to 12 mol% (e.g. 10.1 mol%).

In preferred methods of the invention, the partial pressure of CO₂ in the pressurised exhaust gas comprising CO₂ is higher than in the air supplied to the turbocharger compressor. In preferred methods of the invention, the partial pressure of CO₂ in the pressurised exhaust gas comprising CO₂ is higher than in the compressed air. In preferred methods of the invention, the partial pressure of CO₂ in the pressurised exhaust gas comprising CO₂ is higher than in the cooled compressed air.

In further preferred methods of the invention, the partial pressure of the CO₂ in the pressurised exhaust gas comprising CO₂ is 0.035 to 1 bar, more preferably 0.15 to 0.7 bar.

In preferred methods of the present invention, after step (ii) and before step (iii) the pressurised exhaust gas comprising CO₂ is divided into at least a first portion and a second portion, the first portion of the pressurised exhaust gas comprising CO₂ is recycled into the reciprocating engine, and the second portion of the pressurised exhaust gas comprising CO₂ is sent to the CO₂ capture unit. Preferably 5 to 80%, more preferably 20 to 60%, of the pressurised exhaust gas comprising CO₂ is recycled back into the reciprocating engine. The effect of recycling at least part of the pressurised exhaust gas comprising CO₂ back into the reciprocating engine is to increase the amount of CO₂ in the pressurised exhaust gas comprising CO₂ which thereby increases the partial pressure of the CO₂ entering the CO₂ capture unit. Recycling at least part of the pressurised exhaust gas comprising CO₂ back into the reciprocating engine also helps to reduce the amount of noxious NO_X gases in the pressurised exhaust gas comprising CO₂.

In preferred methods of the invention, the pressurised exhaust gas comprising CO₂ is cooled prior to entering the CO₂ capture unit. The cooled pressurised exhaust gas comprising CO₂ preferably has a temperature of 10 to 200 °C (e.g. 50 °C), more preferably to a temperature of 30 to 80 °C, and/or a pressure of 1.5 to 10 bar, more preferably a pressure of 3 to 8 bar (e.g. 5 bar). Preferably, the cooled pressurised exhaust gas comprising CO₂ has a temperature of 20 to 200 °C (e.g. 150 °C), more preferably a temperature of 30 to 80 °C, and a pressure of 1.5 to 10 bar, more preferably a pressure of 3 to 8 bar (e.g. 5 bar). The amount of CO₂ in the cooled pressurised exhaust gas comprising CO₂ is preferably 3.5 to 10 mol%, more preferably 4 to 8 mol% (e.g. 4.9 mol%). The cooled pressurised exhaust gas comprising CO₂may also contain an amount of oxygen, preferably 0 to 13 mol%, more preferably 3 to 12 mol% (e.g. 10.1 mol%).

In preferred methods of the invention, heat is recovered from the pressurised exhaust gas comprising CO₂, preferably using a heat recovery unit or a heat exchanger. The recovered heat can be used in numerous applications, e.g. reheat of the returning CO₂-lean exhaust gas from the capture, energy source for other onsite processes, hot water production, heating of buildings, etc. Furthermore, any waste water or steam from a cooling or heat recovery process can be recycled back to the reciprocating engine.

In step (iii), CO₂ contained in the pressurised exhaust gas comprising CO₂ is captured in a CO₂ capture unit. In preferred methods of the invention, the CO₂ capture unit is a compact CO₂ capture unit, preferably having a height of 10 to 40 m. In contrast, conventional absorber towers are typically 40 to 60 m tall. The volume and weight of the compact CO₂ capture unit employed in the methods of the present invention are also significantly decreased compared to conventional CO₂ capture units. In preferred methods of the invention, the volume and/or weight of the compact CO₂capture unit is at least 30% less, more preferably at least 40% less, even more preferably at least 50% less, than conventional CO₂ capture units, e.g. CO₂ capture units which use a 30 wt% monoethanolamine (MEA) absorption/desorption tower to treat a natural gas-based flue gas (i.e. an atmospheric flue gas containing about 4 mol% CO₂). In preferred methods of the invention, the weight of the compact CO₂capture unit is at least 30% less, more preferably at least 40% less, even more preferably at least 50% less, than conventional CO₂ capture units, e.g. CO₂ capture units which use a 30 wt% monoethanolamine (MEA) absorption/desorption tower to treat a natural gas-based flue gas (i.e. an atmospheric flue gas containing about 4 mol% CO₂). As discussed above, the reduced dimensions of the CO₂ capture unit are a direct result of the increased partial pressure of the CO₂ in the gas stream.

In preferred methods of the invention, the pressurised CO₂-lean exhaust gas exiting the CO₂ capture unit preferably has a pressure of 1.5 to 8.5 bar, more preferably 2.5 to 4.5 bar (e.g. 4.5 bar), and/or a temperature of 40 to 80 °C, more preferably 50 to 60 °C (e.g. 55 °C). Preferably, the pressurised CO₂-lean exhaust gas exiting the CO₂ capture unit has a pressure of 1.5 to 8.5 bar, more preferably 2.5 to 4.5 bar (e.g. 4.5 bar), and a temperature of 40 to 80 °C, more preferably 50 to 60 °C (e.g. 55 °C). The amount of CO₂ in the pressurised CO₂4ean exhaust gas exiting the CO₂capture unit is preferably 0 to 3 mol%, more preferably 0 to 2 mol% (e.g. 1 mol%). The pressurised CO₂4ean exhaust gas exiting the CO₂ capture unit may also contain an amount of oxygen, preferably 0 to 13 mol%, more preferably 3 to 13 mol% (e.g. 11.6 mol%).

In preferred methods of the invention, the CO₂ capture unit does not require steam, thereby reducing the number of utilities required. More preferably, the CO₂capture unit comprises a membrane and/or an absorber.

The CO₂ capture unit may be, for example, a CO₂ capture apparatus comprising an absorption tower and a regeneration tower. Such towers are conventional in the art. Preferably the pressurised exhaust gas comprising CO₂ is contacted, typically in counter flow, with an aqueous absorbent in an absorber column. The still pressurized gas leaving the absorber column is preferably CO₂ depleted and is returned to the heat exchanger for reheating with the exhaust gas from the reciprocating engine. The CO₂ preferably leaves the absorber column reacted to the absorbent. Typically the absorbent is subsequently regenerated in a regenerator column and returned to the absorber column. The CO₂ separated from the absorbent is preferably sent for storage, e.g. in a subterranean formation.

A particularly preferred absorber is a rotary system absorber such as that outlined in WO 2015/060723. For example, WO 2015/060723 describes a rotary system absorber comprising an absorber for absorbing CO₂ from a gas stream by use of an absorption liquid (e.g. amines, carbonates, amino acid salts) and a desorber for desorbing CO₂ from CO₂-rich absorption liquid. The absorber comprises a rotatable main cylinder having an absorption section provided with rotatable means for disintegration of droplets of absorption liquid and means for rotating the absorber, such that absorption liquid droplets are moved by aid of centrifugal force in a cross flowdirection in relation to the gas stream whereby CO₂ is absorbed from the gas stream by the absorption liquid droplets. The desorber is connected to the absorber to receive CO₂ rich absorption liquid, and the desorber is rotatable and comprises a desorption chamber provided with a rotatable heat exchanger and means for rotating the desorber, such that the absorption liquid droplets are moved by aid of centrifugal force through the heat exchanger whereby the absorption liquid droplets are heated and CO₂ is desorbed and separated from the absorption liquid droplets, and lean absorption liquid is circulated to the absorber. A similar rotary system absorber is described in WO

01/45825.

Preferred absorbents for use in absorption apparatus are, for example, aliphatic or cycloaliphatic amines having from 4 to 12 carbons, alkanolamines having from 4 to 12 carbons, cyclic amines where 1 or 2 nitrogens together with 1 or 2 alkylene groups form 5-, 6- or 7-membered rings, mixtures of the above and aqueous solutions of the above amines and mixtures. Representative examples of amines that may be used include monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), diethylethanolamine (DEEA), diisopropylamine (DIPA), aminoethoxyethanol (AEE), methyldiethanolamine (MDEA), piperazine (PZ), 2-amino-2-methyl-1-propanol (AMP) and mixtures of the above and aqueous solutions of the above.

In some preferred methods of the invention, the CO₂ capture unit comprises membranes. Gas separation membranes work on the principle that one component (in this case CO₂) in a gas stream is allowed to pass through the membrane faster than the other components, thereby allowing separation to be achieved. Preferred membranes for use in the methods of the invention include polymeric membranes (e.g. polyethylene, polyamides, polyimides, cellulose acetate, polysulphone, polydimethylsiloxane), porous inorganic membranes, carbon membranes, silica membranes, metal-organic framework membranes, zeolite membranes and perovskite membranes.

In preferred methods of the invention, up to 90 %vol of the CO₂ contained in the pressurised exhaust gas comprising CO₂is removed therefrom during step (iii) (e.g. 50 to 90 %vol). In more preferred methods, up to 98 %vol of the CO₂ contained in the pressurised exhaust gas comprising CO₂is removed therefrom during step (iii) (e.g. 50 to 98 %vol). In particularly preferred methods, up to 99 %vol of the CO₂ contained in the pressurised exhaust gas comprising CO₂is removed therefrom during step (iii) (e.g. 50 to 99 %vol). The gas stream exiting the CO₂ capture unit preferably has a pressure of 0.1 to 7 bar, more preferably a pressure of 0.3 to 5 bar (e.g. 0.5 bar), and/or a temperature of 20 to 200 °C, more preferably a temperature of 30 to 80 °C (e.g. 50 °C). Preferably, the gas stream exiting the CO₂ capture unit has a pressure of 0.1 to 7 bar, more preferably a pressure of 0.3 to 5 bar (e.g. 0.5 bar for membrane based capture and 1.8 bar for absorption/desorption based capture), and a temperature of 20 to 200 °C, more preferably a temperature of 30 to 80 °C (e.g. 50 °C). The amount of CO₂ in the gas stream exiting the CO₂ capture unit is preferably 70 to 100 mol%, more preferably 90 to 100 mol% (e.g. 82 mol%). The amount of oxygen in the gas stream exiting the CO₂ capture unit is preferably 0 to 10 mol%, more preferably 0 to 5 mol% (e.g. 2.5 mol%).

In preferred methods of the invention, water obtained by cooling in the CO₂capture unit is recycled to the reciprocating engine. Preferably 2 to 40%, more preferably 5 to 20%, of the liquid water produced in the CO₂ capture unit is recycled to the reciprocating engine. Water recycle to the engine helps to increase the mass flow through the engine and therefore also its power output, which in turn results in an increased CO₂ concentration in the exhaust gas. Some reciprocating engines and humidified air turbines (HATs) operate on a similar basis.

In preferred methods of the invention, the pressurised CO₂-lean exhaust gas is heated after exiting the CO₂ capture unit. The heated pressurised CO₂-lean exhaust gas preferably has a temperature of 250 to 570 °C, more preferably 320 to 480 °C (e.g. 416 °C), and/or a pressure of 1.5 to 10 bar, more preferably a pressure of 2.5 to 8 bar (e.g. 4.8 bar). Preferably, the heated pressurised CO₂-lean exhaust gas has a temperature of 250 to 570 °C, more preferably 320 to 480 °C (e.g. 416 °C), and a pressure of 1.5 to 10 bar, more preferably a pressure of 2.5 to 8 bar (e.g. 4.8 bar). The amount of CO₂ in the heated pressurised CO₂-lean exhaust gas is preferably 0 to 3 mol%, more preferably 0 to 2 mol% (e.g. 1 mol%). The amount of oxygen in the heated pressurised CO₂-lean exhaust gas is preferably 0 to 13 mol%, more preferably 3 to 13 mol% (e.g. 11.6 mol%).

In preferred methods of the invention, fuel is combusted in a combustion chamber in the presence of the pressurised CO₂-lean exhaust gas prior to step (iv). Preferably, the fuel is selected from gasoline, natural gas, propane vapour, and biogas. The fuel is preferably supplied to the combustion chamber at room temperature, i.e. 15 to 30 °C, more preferably 20 to 25 °C (e.g. 25 °C). Preferably, the fuel is supplied to the combustion chamber at room temperature, i.e. 15 to 30 °C, more preferably 20 to 25 °C (e.g. 25 °C), and at a pressure of 10 to 20 bar, more preferably 15 to 20 bar (e.g. 17 bar). The fuel is preferably the same as the one used in the reciprocating engine. Preferably, the fuel is a hydrocarbon stream from the upstream processing system that cannot be sold or disposed.

The combustion chamber may further employ a catalyst. Preferred catalysts for use in the combustion chamber comprise platinum, palladium, rhodium, or mixtures thereof. More preferably, the catalyst comprises platinum. The catalyst may be unsupported or supported, but is preferably supported. Examples of suitable supported platinum catalysts include Pt/AI₂O₃, Pt/ZrO₂, Pt/TiO₂, Pt/SiO₂ and Pt/H-ZSM-5 (where

ZSM-5 is Zeolite Socony Mobil-5).

The pressurised CO₂-lean exhaust gas exiting the combustion chamber preferably has a temperature of 250 to 650 °C, more preferably 340 to 550 °C (e.g. 465 °C) and/or a pressure of 1.5 to 10 bar, more preferably 2 to 8 bar (e.g. 4.8 bar). Preferably, the pressurised CO₂-lean exhaust gas exiting the combustion chamber has a temperature of 250 to 650 °C, more preferably 340 to 550 °C (e.g. 465 °C), and a pressure of 1.5 to 10 bar, more preferably 2 to 8 bar (e.g. 4.8 bar). The amount of CO₂in the pressurised CO₂-lean exhaust gas exiting the combustion chamber is preferably 0 to 4 mol%, more preferably 0 to 2 mol% (e.g. 1.5 mol%). The amount of oxygen in the pressurised CO₂-lean exhaust gas exiting the combustion chamber is preferably 0 to 12 mol%, more preferably 3 to 12 mol% (e.g. 11.2 mol%).

In step (iv), the pressurised CO₂-lean exhaust gas is fed through a turbocharger expander to drive the turbocharger compressor. The CO₂-lean exhaust gas exiting the turbocharger expander preferably has a temperature of 150 to 550 °C, more preferably 200 to 300 °C (e.g. 250 °C), and/or a pressure of 0.9 to 1.1 bar (e.g. 1 bar). Preferably, the CO₂-lean exhaust gas exiting the turbocharger expander has a temperature of 150 to 550 °C, more preferably 200 to 300 °C (e.g. 250 °C), and a pressure of 0.9 to 1.1 bar (e.g. 1 bar). The amount of CO₂ in the CO₂-lean exhaust gas exiting the turbocharger expander is preferably 0 to 4 mol%, more preferably 0 to 2 mol% (e.g. 1.5 mol%). The amount of oxygen in the CO₂-lean exhaust gas exiting the turbocharger expander is preferably 0 to 12 mol%, more preferably 3 to 12 mol% (e.g. 11.2 mol%).

When the pressurised CO₂-lean exhaust gas has been heated after exiting the CO₂ capture unit and/or fuel is combusted in a combustion chamber in the presence of the pressurised CO₂-lean exhaust gas prior to step (iv), the CO₂-lean exhaust gas exiting the turbocharger expander preferably has a temperature of 150 to 550 °C, more preferably 200 to 300 °C (e.g. 250 °C), and/or a pressure of 0.9 to 1.1 bar (e.g. 1 bar). Preferably, when the pressurised CO₂-lean exhaust gas has been heated after exiting the CO₂ capture unit and/or fuel is combusted in a combustion chamber in the presence of the pressurised CO₂-lean exhaust gas prior to step (iv), the CO₂-lean exhaust gas exiting the turbocharger expander has a temperature of 150 to 550 °C, more preferably 200 to 300 °C (e.g. 250 °C), and a pressure of 0.9 to 1.1 bar (e.g. 1 bar). The amount of CO₂ in the CO₂-lean exhaust gas exiting the turbocharger expander is preferably 0 to 4 mol%, more preferably 0 to 2 mol% (e.g. 1.5 mol%). The amount of oxygen in the pressurised CO₂-lean exhaust gas exiting the turbocharger expander is preferably 0 to 12 mol%, more preferably 3 to 12 mol% (e.g. 11.2 mol%).

When the pressurised CO₂-lean exhaust gas has been heated after exiting the CO₂ capture unit and/or fuel is combusted in a combustion chamber in the presence of the pressurised CO₂-lean exhaust gas prior to step (iv), heat is preferably recovered from the CO₂-lean exhaust gas exiting the turbocharger expander (e.g. at least part of the CO₂-lean exhaust gas exiting the turbocharger expander is passed through a heat exchanger). The cooled CO₂-lean exhaust gas exiting the turbocharger expander preferably has a temperature of 90 to 550 °C, more preferably 90 to 300 °C (e.g. 150 °C), and/or a pressure of 0.9 to 1.1 bar (e.g. 1 bar). Preferably, the cooled CO₂-lean exhaust gas exiting the turbocharger expander has a temperature of 90 to 550 °C, more preferably 90 to 300 °C (e.g. 150 °C), and a pressure of 0.9 to 1.1 bar (e.g. 1 bar). The amount of CO₂ in the cooled CO₂-lean exhaust gas is preferably 0 to 4 mol%, more preferably 0 to 2 mol% (e.g. 1.5 mol%). The amount of oxygen in the cooled CO₂lean exhaust gas is preferably 0 to 12 mol%, more preferably 3 to 12 mol% (e.g. 11.2 mol%).

The methods of the present invention may comprise the further step of:

(v) removing oxygen from the captured CO₂.

Oxygen can be removed from the captured CO₂ by way of either a catalytic combustion process or distillation. Preferably, step (v) involves a catalytic combustion process as this provides the most compact solution.

The methods of the present invention may comprise the further step of:

(vi) storing the captured CO₂.

The captured CO₂ is stored in pure form or, alternatively, is mixed with water or natural gas before being stored.

The captured CO₂ may be injected into subterranean formations such as aquifers, oil wells for enhanced oil recovery or in depleted oil and gas wells for deposition.

The present invention also relates to a system for carrying out the method of the invention hereinbefore described. Preferred features of the method hereinbefore described are also preferred features of the system. The systems of the present invention can be used either onshore or offshore, but are preferably used offshore.

The systems of the present invention comprise a turbocharger compressor having an inlet for air and an outlet for compressed air. The system further comprises a reciprocating engine for generating electricity and/or shaft power fluidly connected to said outlet for compressed air of said turbocharger compressor and having an inlet for fuel, an inlet for compressed air and an outlet for a pressurised exhaust gas comprising CO₂. The system further comprises a CO₂ capture unit fluidly connected to said outlet for a pressurised exhaust gas comprising CO₂ of said reciprocating engine and having an inlet for pressurised exhaust gas comprising CO₂, an outlet for pressurised CO₂lean exhaust gas and an outlet for CO₂. The system also comprises a turbocharger expander fluidly connected to said outlet for pressurised CO₂-lean exhaust gas of said CO₂ capture unit having an inlet for pressurised CO₂-lean exhaust gas. In the systems of the present invention, the turbocharger compressor is driven by pressurised CO₂lean exhaust gas being passed through said turbocharger expander.

As used herein the term “fluidly connected” refers to means to transport a fluid from a first unit to a second unit, optionally via one or more intervening units. The fluid connection may therefore be direct or indirect.

In preferred systems of the invention, the reciprocating engine tolerates back pressure and so the systems do not include a fan for blowing pressurised exhaust gas comprising CO₂ through the CO₂ capture unit.

Preferred systems of the invention further comprise a heat exchanger for cooling the compressed gas, the heat exchanger being in between the turbocharger compressor and the reciprocating engine and the heat exchanger having an inlet fluidly connected to the turbocharger compressor and an outlet fluidly connected to the reciprocating engine.

Preferred systems of the invention further comprise a heat exchanger for cooling the pressurised exhaust gas comprising CO₂, the heat exchanger being in between the reciprocating engine and the CO₂ capture unit and the heat exchanger having an inlet fluidly connected to the reciprocating engine and an outlet fluidly connected to the CO₂ capture unit.

Preferred systems of the invention further comprise a heat exchanger for heating the pressurised CO₂-lean exhaust gas, the heat exchanger being in between the CO₂ capture unit and the turbocharger expander and the heat exchanger having an inlet fluidly connected to the CO₂ capture unit and an outlet fluidly connected to the turbocharger expander.

Preferred systems of the invention further comprise a gas/gas heat exchanger between the inlet for pressurised exhaust gas comprising CO₂ and the outlet for pressurised CO₂-lean exhaust gas of the CO₂ capture unit.

Preferred systems of the invention further comprise a means for recycling pressurised exhaust gas comprising CO₂back into the reciprocating engine.

In preferred systems of the invention, the CO₂ capture unit further comprises an outlet for water, the reciprocating engine further comprises an inlet for water and the reciprocating engine is fluidly connected to the outlet for water of the CO₂ capture unit.

Preferred systems of the invention further comprise a combustion chamber for combusting fuel in the presence of the pressurised CO₂-lean exhaust gas, the combustion chamber being in between the CO₂ capture unit and the turbocharger expander and having an inlet fluidly connected to the CO₂ capture unit and an inlet for fuel and an outlet fluidly connected to the turbocharger expander.

In preferred systems of the invention, said CO₂ capture unit is a compact CO₂capture unit, preferably having a height of 10 to 40 m. In contrast, conventional absorber towers are typically 40 to 60 m tall.

In preferred systems of the invention, the CO₂ capture unit does not require steam, thereby reducing the number of utilities required. More preferably, the CO₂capture unit comprises a membrane and/or an absorber. Still more preferably, the CO₂capture unit comprises a rotary system absorber as hereinbefore described.

Preferred systems of the invention further comprise means for removing oxygen from captured CO₂ wherein the means are fluidly connected to the compact CO₂capture unit.

Preferred systems of the invention further comprise means for storing captured CO₂ wherein the means are fluidly connected to the CO₂ capture unit. In a preferred embodiment, the means has an inlet for water. In a preferred embodiment, the means has an inlet for natural gas.

Preferred systems of the invention further comprise means for recovering heat from the CO₂4ean exhaust gas exiting the turbocharger expander.

DESCRIPTION OF THE FIGURES

Figure 1 shows a system according to the present invention.

Figure 2 shows a preferred system according to the present invention.

Figure 3 shows a preferred system according to the present invention.

DETAILED DESCRIPTION OF THE FIGURES

Referring to Figure 1, air 1 is passed through a turbocharger compressor to produce compressed air 2. The compressed air 2 exiting a turbocharger compressor and fuel 4 are fed into a reciprocating engine to produce electricity. The compressed air preferably has a temperature of 80 to 350 °C and/or a pressure of 2 to 10 bar. The pressurised exhaust 5 from the reciprocating engine, which preferably has a temperature of 300 to 600 °C and/or a pressure of 1.5 to 10 bar, is fed into a compact CO₂ capture unit. Once CO₂ has been removed from the pressurised exhaust 5 via line 7, the resultant pressurised CO₂-lean gas stream 9 is passed through a turbocharger expander to drive the turbocharger compressor. The pressurised CO₂-lean gas stream 9 preferably has a temperature of 40 to 80 °C and/or a pressure of 1.5 to 8.5 bar. The CO₂-lean gas stream 13 exiting the turbocharger expander preferably has a temperature of 150 to 550 °C and/or a pressure of 0.9 to 1.1 bar. The CO₂ product is compressed in a compressor and sent for storage via line 8.

Referring to Figure 2, compressed air 2 exiting a turbocharger compressor is passed through a heat exchanger to effect cooling of or heat recovery from the compressed air 2 prior to it entering a reciprocating engine. The cooled compressed air preferably has a temperature of 10 to 350 °C and/or a pressure of 2 to 10 bar. Fuel 4 is also fed into the reciprocating engine to produce electricity. The pressurised exhaust 5 from the reciprocating engine is fed into a compact CO₂ capture unit and CO₂ is removed therefrom via line 7. The CO₂ is compressed in a compressor and sent for storage via line 8. A gas/gas heat exchanger is present between the inlet and outlet of the CO₂ capture unit to cause cooling of the flow into (line 6) and heating of the flow out (line 9) of the CO₂ capture unit. The pressurised exhaust 5 preferably has a temperature of 300 to 600 °C and/or a pressure of 1.5 to 10 bar. The reheated flow 10 out of the CO₂ capture unit preferably has a temperature of 250 to 570 °C and/or a pressure of 1.5 to 10 bar. The reheated flow 10 out of the CO₂ capture unit passes to a combustion chamber containing additional fuel 11 before being passed through a turbocharger expander to drive the turbocharger compressor. The purpose of the combustion chamber is to increase the output and efficiency of the turbocharger expander. The exhaust 12 exiting the combustion chamber preferably has a temperature of 250 to 650 °C and/or a pressure of 1.5 to 10 bar. The exhaust 12 exiting the combustion chamber is then passed through turbocharger expander to drive the turbocharger compressor. The CO₂-lean gas stream 13 exiting the turbocharger expander preferably has a temperature of 150 to 550 °C and/or a pressure of 0.9 to 1.1 bar. Heat recovery from the expanded air 13 occurs in a heat exchanger. The cooled expanded air 14 exiting the heat exchanger preferably has a temperature of 90 to 550 °C and/or a pressure of 0.9 to 1.1 bar.

The embodiment shown in Figure 3 is similar to that shown in Figure 2. The main difference is that approximately 20 to 95% of the pressurised exhaust 5 from the 5 reciprocating engine is fed into the compact CO₂ capture unit whilst approximately 5 to 80% of the pressurised exhaust 5 is recycled back to the reciprocating engine via line 17 in order to help increase CO₂ concentration and reduce levels of NO_X.

The embodiment shown in Figure 3 also incorporates water recycle from the CO₂ capture unit to the reciprocating engine via line 16 (approximately 2 to 40 %wt of 10 the water present in the CO₂ capture unit is recycled back to engine). This feature helps to increase the CO₂ concentration in the pressurised exhaust 5, and may also help to increase power output. Also in the embodiment shown in Figure 3, a fuel 18 is combusted in a combustion unit in the presence of the compressed CO₂ product 8 to give a purified CO₂ product 19. This additional combustion serves to remove oxygen 15 from the captured CO₂.

CLAIMS:

Claims

CLAIMS:

1. A method of generating electricity and/or shaft power and capturing CO2, comprising:

(i) passing air through a turbocharger compressor to produce compressed air;

(ii) combusting fuel using said compressed air in a reciprocating engine to generate electricity and/or shaft power and a pressurised exhaust gas comprising CO2;

(iii) capturing CO2 contained in the pressurised exhaust gas comprising CO2 in a CO2 capture unit to produce a pressurised CO2-lean exhaust gas; and (iv) feeding the pressurised CO2-lean exhaust gas through a turbocharger expander to drive said turbocharger compressor.

2. A method as claimed in claim 1, wherein compressed air produced in step (i) has a pressure of 2 to 10 bar and/or a temperature of 80 to 350 °C.

3. A method as claimed in claim 1 or 2, wherein the compressed air entering said reciprocating engine has a pressure of 2 to 10 bar and/or a temperature of 80 to 350 °C.

4. A method as claimed in any one of claims 1 to 3, wherein the compressed air is cooled prior to entering the reciprocating engine.

5. A method as claimed in claim 4, wherein the cooled compressed air has a temperature of 10 to 350 °C and/or a pressure of 2 to 10 bar.

6. A method as claimed in any one of claims 1 to 5, wherein the pressurised exhaust gas comprising CO2 has a pressure of 1.5 to 10 bar and/or a temperature of 300 to 600 °C.

7. A method as claimed in any one of claim 1 to 6, wherein the amount of CO2 in the pressurised exhaust gas comprising CO2 is 3.5 to 10 mol%.

8. A method as claimed in any one of claims 1 to 7, wherein the partial pressure of CO2 in the pressurised exhaust gas comprising CO2 is higher than in the compressed air.

9. A method as claimed in any one of claims 1 to 8, wherein the partial pressure of the CO2 in the pressurised exhaust gas comprising CO2 is 0.035 to 1 bar.

10. A method as claimed in any one of claims 1 to 9, wherein the fuel is selected from diesel, kerosene, gasoline, jet fuel, natural gas, oil, condensates, propane vapour, and biogas.

11. A method as claimed in any one of claims 1 to 10, wherein after step (ii) and before step (iii) said pressurised exhaust gas comprising CO2 is divided into at least a first portion and a second portion, said first portion of said pressurised exhaust gas comprising CO2 is recycled into said reciprocating engine, and said second portion of said pressurised exhaust gas comprising CO2is sent to said CO2 capture unit.

12. A method as claimed in claim 11, wherein 5 to 80% of the pressurised exhaust gas comprising CO2 is recycled back into the reciprocating engine.

13. A method as claimed in any one of claims 1 to 12, wherein the pressurised exhaust gas comprising CO2is cooled prior to entering the CO2 capture unit.

14. A method as claimed in claim 13, wherein the cooled pressurised exhaust gas comprising CO2 has a pressure of 1.5 to 10 bar and/or a temperature of 20 to 200 °C.

15. A method as claimed in any one of claims 1 to 14, wherein the pressurised CO2lean exhaust gas is heated after exiting the CO2 capture unit.

16. A method as claimed in claim 15, wherein the heated pressurised CO2-lean exhaust gas has a temperature of 250 to 570 °C and/or a pressure of 1.5 to 10 bar.

17. A method as claimed in any one of claims 1 to 16, wherein the CO2 capture unit is a compact CO2 capture unit.

18. A method as claimed in claim 17, wherein the compact CO2 capture unit has a height of 10 to 40 m.

19. A method as claimed in any one of claims to 18, wherein the CO2 capture unit does not require steam.

20. A method as claimed in any one of claims comprises a membrane.

21. A method as claimed in any one of claims comprises an absorber.

22. A method as claimed in any one of claims to 19, wherein the CO2 capture unit to 19, wherein the CO2 capture unit to 21, wherein the pressurised CO2lean exhaust gas exiting the CO2 capture unit has a pressure of 1.5 to 8.5 bar and/or a temperature of 40 to 80 °C.

23. A method as claimed in any one of claims 1 to 22 wherein during step (iii) up to 90 %vol of the CO2 contained in the pressurised exhaust gas comprising CO2 is removed therefrom.

24. A method as claimed in any one of claims 1 to 23 wherein water obtained by cooling in the CO2capture unit is recycled to the reciprocating engine.

25. A method as claimed in any one of claims 1 to 24, wherein the CO2-lean exhaust gas exiting the turbocharger expander has a temperature of 150 to 550 °C and/or a pressure of 0.9 to 1.1 bar.

26. A method as claimed in any one of claims 1 to 24, wherein fuel is combusted in a combustion chamber in the presence of the pressurised CO2-lean exhaust gas prior to step (iv).

27. A method as claimed in claim 26, wherein the pressurised CO2-lean exhaust gas exiting the combustion chamber has a temperature of 250 to 650 °C and/or a pressure of 1.5 to 10 bar.

28. A method as claimed in claim 26 or 27, wherein the CO2-lean exhaust gas exiting the turbocharger expander has a temperature of 150 to 550 °C and/or a pressure of 0.9 to 1.1 bar.

29. A method as claimed in any one of claims 26 to 28, wherein the CO2-lean exhaust gas exiting the turbocharger expander is cooled.

30. A method as claimed in claim 29, wherein the cooled CO2-lean exhaust gas exiting the turbocharger expander has a temperature of 90 to 550 °C and/or a pressure of 0.9 to 1.1.

31. A method as claimed in any one of claims 1 to 30, wherein at least part of the CO2lean exhaust gas exiting the turbocharger expander is passed through a heat exchanger.

32. A method as claimed in any one of claims 1 to 31, comprising the further step of:

(v) removing oxygen from the captured CO2.

33. A method as claimed in claim 32, comprising the further step of:

(vi) storing the captured CO2.

34. A system for generating electricity and/or shaft power and capturing CO2 comprising:

(b) a reciprocating engine for generating electricity and/or shaft power fluidly connected to said outlet for compressed air of said turbocharger compressor and having an inlet for fuel, an inlet for compressed air and an outlet for a pressurised exhaust gas comprising CO2;

(c) a CO2 capture unit fluidly connected to said outlet for a pressurised exhaust gas comprising C02of said reciprocating engine and having an inlet for pressurised exhaust gas comprising CO2, an outlet for pressurised CO21ean exhaust gas and an outlet for CO2; and (d) a turbocharger expander fluidly connected to said outlet for pressurised CO2lean exhaust gas of said CO2 capture unit having an inlet for pressurised CO2lean exhaust gas, wherein said turbocharger compressor is driven by pressurised CO21ean exhaust gas being fed through said turbocharger expander.

35. A system as claimed in claim 34 which does not include a fan for blowing pressurised exhaust gas comprising CO2 through the CO2 capture unit.

36. A system as claimed in claim 34 or claim 35, further comprising a heat exchanger for cooling said compressed gas, said heat exchanger being in between said turbocharger compressor and said reciprocating engine and said heat exchanger having an inlet fluidly connected to said turbocharger compressor and an outlet fluidly connected to said reciprocating engine.

37. A system as claimed in any one of claims 34 to 36, further comprising a heat exchanger for cooling said pressurised exhaust gas comprising CO2, said heat exchanger being in between said reciprocating engine and said CO2 capture unit and said heat exchanger having an inlet fluidly connected to said reciprocating engine and an outlet fluidly connected to said CO2 capture unit.

38. A system as claimed in any one of claims 34 to 37, further comprising a heat exchanger for heating said pressurised CO2-lean exhaust gas, said heat exchanger being in between said CO2 capture unit and said turbocharger expander and said heat exchanger having an inlet fluidly connected to said CO2 capture unit and an outlet fluidly connected to said turbocharger expander.

39. A system as claimed in any one of claims 34 to 36, further comprising a gas/gas heat exchanger between the inlet for pressurised exhaust gas comprising CO2 and the outlet for pressurised CO2-lean exhaust gas of the CO2 capture unit.

40. A system as claimed in any one of claims 34 to 39, further comprising means for recycling pressurised exhaust gas comprising CO2back into said reciprocating engine.

41. A system as claimed in any one of claims 34 to 40, wherein the CO2 capture unit further comprises an outlet for water, the reciprocating engine further comprises an inlet for water and the reciprocating engine is fluidly connected to the outlet for water of the CO2 capture unit.

42. A system as claimed in any one of claims 34 to 41, further comprising a combustion chamber for combusting fuel in the presence of said pressurised CO2-lean exhaust gas, said combustion chamber being in between said CO2 capture unit and said turbocharger expander and having an inlet fluidly connected to said CO2 capture unit and an inlet for fuel and an outlet fluidly connected to said turbocharger expander.

43. A system as claimed in any one of claims 34 to 42, wherein said CO2 capture unit is a compact CO2 capture unit.

44. A system as claimed in claim 43, wherein said CO2 capture unit is as described in claim 18 or 19.

45. A system as claimed in any one of claims 34 to 44, further comprising means for removing oxygen from captured CO2 wherein said means are fluidly connected to said compact CO2 capture unit.

46. A system as claimed in claim 45, further comprising means for storing captured CO2 wherein said means are fluidly connected to said CO2 capture unit.

47. A system according to claim 46, wherein said means has an inlet for water.

48. A system according to claim 46, wherein said means has an inlet for natural gas.

49. A system as claimed in any one of claims 34 to 48, further comprising means for recovering heat from said CO2-lean exhaust gas exiting said turbocharger expander.

50. A system as claimed in any one of claims 34 to 49 for use onshore.

51. A system as claimed in any one of claims 34 to 49 for use offshore.

Intellectual

Property

Office

Application No: GB 1803183.1

Claims searched: 1 to 51