GB2463477A

GB2463477A - Method of producing carbon dioxide from sea water and solidifying it for transport

Info

Publication number: GB2463477A
Application number: GB0816663A
Authority: GB
Inventors: David Leslie Mcneight
Original assignee: STRATOS FUELS Ltd
Current assignee: STRATOS FUELS Ltd
Priority date: 2008-09-12
Filing date: 2008-09-12
Publication date: 2010-03-17
Also published as: GB0816663D0

Abstract

A method of producing carbon dioxide from sea water and cooling the carbon dioxide to solidify it for storage and/or transportation. The carbon dioxide may be extracted by reducing the pressure over the sea water or heating the sea water. Preferably, the method is conducted on a marine platform or any ocean going vessel (ship) 31 and the solid carbon dioxide is loaded into containers 32. Hydroelectric, wind or solar power may be generated and used for the process. Preferably, on a ship, sea water may flow in through an intake 33 into a treatment chamber 34 where carbon dioxide is extracted 35 and the water exhausts through an outlet 36, providing propulsive power for the ship. A method of producing synthetic hydrocarbon fuel is disclosed by reacting carbon dioxide and hydrogen wherein the carbon dioxide is recovered from sea water and solidified preferably for transport to the hydrocarbon production plant. Preferably, the frozen carbon dioxide is used to provide a cold source for the cold part of a solar powered Stirling engine cycle and the hydrocarbons are produced in a Fischer Tropsch reactor.

Description

Manufacture of Fuels This invention relates to the manufacture of fuels.

Fossil fuels, namely coal, oil, natural gas, and their derivatives are held responsible for global warming by releasing carbon dioxide into the atmosphere. Carbon dioxide levels have risen since the Industrial Revolution from around 180 parts per million (ppm) to more than 380 ppm, and it is predicted that at current rates of usage, a dangerous level of 450 ppm will be reached around the year 2050. Before that, global warming due to the greenhouse effect of atmospheric carbon dioxide may effect irreversible changes, perhaps through the melting of polar ice caps reducing the albedo of the globe and accelerating warming beyond reasonable prospect of recovery, even were we to stop using fossil fuels altogether.

At the same time, fossil fuels are being depleted, and oil in particular is increasing in price alarmingly. The shortage is being politically exploited by states lucky enough to be oil producers, and the way of life of millions if not billions of people is under threat. The fact that fossil fuels are becoming scarce may reduce their use sufficiently that global disaster through greenhouse carbon dioxide emissions is substantially delayed, but neither prospect is anything other than daunting.

A solution to both problems is to be found in recovering carbon dioxide from the atmosphere and combining it with hydrogen, which may be got from seawater for example by electrolysis, in a reaction known as the Fischer-Tropfsch reaction, to make hydrocarbons such as heptanes, octane, decane and others, which are the paraffin fuels made cunently from fossil sources such as oil and natural gas. If these synthetic fuels were to replace fossils sourced fuel, no further release of carbon dioxide into the atmosphere would take place. Of course, the synthesis requires power, particularly to separate hydrogen from water, but also to power the synthesis reaction and extract the carbon dioxide from the atmosphere, bit power can be derived from non-damaging sources, the most appropriate being sunlight. Tropical desert-based solar power houses covering some three of four percent of the available desert area would be required, and the project would be expensive in terms of capital cost, but, of course, the raw materials are free, and it is calculated on a reasonably conservative basis that the fuels we use today such as petrol or gasoline, diesel and kerosene could all be produced at more or less the same cost as they are conventionally produced using fossil sources.

All aspects of this solution are proven technology. The Fischer-Tropfsch reaction was devised in the 1920s and has been used to make fuels since then, particularly when oil was unavailable, for example in WWII and in South Africa (the carbon source being coal) during sanctions. It is used on a daily basis by oil companies turning natural gas into liquid fuel for ease of storage and transportation. The electrolysis of water to make hydrogen is well known. Extraction of atmospheric carbon dioxide has been pioneered by Klaus Lackner in the USA.

Fischer-Tropfsch fuels are not by any means inferior substitutes for fossil hydrocarbons. On the contrary, they are better than ordinaiy fossil hydrocarbons, containing no sulphur at all, and they command a premium price. They can be used directly, without any engine modification whatsoever, in petrol and diesel powered vehicles and in gas turbine aero and other engines.

It has been proposed to set up square kilometre solar collectors in tropical deserts, each with atmospheric carbon dioxide extraction plant, electrolysis plant and a Fischer-Tropfsch reactor. Such large solar collectors are anyway planned by Desertec and the club of Rome to supply electric power to Europe, but a problem with that, of course, is that the sun does not shine 24 hours a day, and electricity cannot, using conventional technology, be stored in the quantities required to maintain round-the-clock power. Power generated during the day can, however, be conveniently stored' by converting it to hydrocarbon fuels.

Burning the synthetic hydrocarbon fuels will, of course, return the carbon dioxide to the atmosphere, but only that which was originally extracted from the atmosphere to synthesis the fuel in the first place, so the entire cycle is carbon neutral.

The current level of atmospheric carbon dioxide, at some 380 ppm requires very large volumes of air to be processed. A square kilometre solar collector will need nearly 600 tonnes of carbon dioxide every day (to produce about 160 tonnes of fuel) and this means that some two million tonnes of air have to be processed every day or about two billion cubic metres.

An alternative source of carbon dioxide is seawater. The oceans act as a carbon dioxide sink, dissolving atmospheric carbon dioxide. They are close to saturation, and are, in some areas, already saturated. This adds to the problem of atmospheric carbon dioxide by removing a natural sink, but it is also problematic in its own right, inasmuch as water with dissolved carbon dioxide is carbonic acid, and at current levels is seriously deleterious to marine life, dissolving mollusc shells and killing coral, among other things.

The present invention provides a means for extracting carbon dioxide from seawater on a sufficient scale to provide a source for large scale hydrocarbon fuels synthesis.

The invention comprises producing carbon dioxide from seawater and cooling the carbon dioxide to solidify it for storage and/or transportation.

The carbon dioxide may be extracted by reducing pressure over the seawater so that the carbon dioxide bubbles out of solution, or by heating the seawater, the gas being less soluble at higher temperatures.

Equipment for making solid carbon dioxide, or dry ice, is commercially available, it being necessary only to reduce its temperature to about -80°C.

The process can be carried out at sea, either on platforms situated in an ocean current, so that a plentiful supply of carbon dioxide-containing water flows past, or on marine vessels that can move around the sea returning to port or an ocean terminal to unload their cargo of solid carbon dioxide. Land-based operations are also, of course, possible, given pipeline access to flowing ocean, but it will probably be better to keep recovered carbon dioxide in its gaseous state, and use the same water to produce the hydrogen necessary for the Fischer-Tropfsch reaction and use them both as produced without the need to store, except, perhaps, for an overnight store to keep the Fischer-Tropfsch reactor operating on a 24 hour basis.

Extraction and freezing of carbon dioxide or course will require power. Using fossil fuel power is, at least to some extent, self defeating, and it will be preferred to use renewable energy, of which the most convenient is, perhaps, solar power. A deck or platform mounted solar collector can, especially in tropical regions, provide adequate power. The greater the collector area, the more power can be produced, and the faster can the carbon dioxide be extracted and frozen. A canopy of solar collector can be provided over the entire deck area, and, as a seagoing vessel is not required to move very far or fast, at least while engaged in carbon dioxide extraction, additional solar collector can be provided in deployable lateral extensions, perhaps supported on outrigger pontoons.

The solar collector may comprise photovoltaic panels or solar concentrators, such as mirrors, focussing on a steam raising boiler for generating electricity, or running a Stirling engine.

Locating a platform in an ocean current also facilitates generation of hydroelectricity, which can replace or augment power available from solar collectors. The open sea, with certain notable exceptions, is not often becalmed, and wind power is also a possibility.

With a marine vessel, seawater will have to be pumped through a treatment plant for extracting the carbon dioxide, and the exhaust water can provide or augment propulsive power for the vessel.

The solid carbon dioxide will be delivered to a Fischer-Tropfsch reactor that will conveniently be land-based, also solar powered, associated, perhaps, with a hydrogen source, which can be an electrolyser for seawater. If the solar power runs a Stirling engine, the solid carbon dioxide can be used in the low temperature part of its cycle.

Extracting carbon dioxide from the oceans indirectly reduces atmospheric carbon levels as more atmospheric carbon dioxide can be absorbed by the seawater.

The concentration of carbon dioxide in seawater is considerably greater than its concentration in air, and the capital cost of plant for extraction from water could be veiy much less than the cost for extraction from air, leading to lower fuel production costs.

The invention also comprises equipment for producing carbon dioxide comprising extraction means for releasing carbon dioxide dissolved in seawater and cooling means for cooling the carbon dioxide to solidify it for storage and/or transportation.

The extraction means may comprise vacuum means adapted to reduce pressure over the seawater, and/or heating means to heat the seawater.

The cooling means may comprise conventional solid carbon dioxide or dry ice making equipment.

The equipment may be comprised in a storage or transportation facility, and may, for example, be comprised in a marine platform, a marine vessel, or a shore-based establishment with access to seawater.

A marine platform may be located in an ocean current, which may provide hydroelectric power for the extraction and cooling. Wind turbine and/or solar power may also be used.

A marine vessel may comprise propulsion means enabling it to sail to and from a port or marine terminal comprising handling means for off-loading and storing solid carbon dioxide.

The equipment may comprise a power source, which may be a renewable energy source. The renewable energy source may comprise a solar collector, which may comprise photovoltaic panels, or a mirror system focussing on a boiler, or a Stirling engine, which may generate electricity.

A marine vessel may have an intake for seawater and an outlet for treated seawater and means to draw seawater through a treatment section in which carbon dioxide is extracted.

Exhaust seawater from the outlet may provide or augment propulsion for the vessel. A marine vessel may comprise a canopy of solar panel, and may have laterally deployable solar panel extensions, which may be supported on outrigger pontoons.

A fuels manufacturing plant may comprise a Fischer-Tropfsch reactor supplied with solid carbon dioxide and hydrogen. The manufacturing plant may include a hydrogen producing component, which may be a water electrolysis plant. The manufacturing plant may be powered by a renewable energy source, which may be solar power. When the solar power is used to drive a Stirling engine, cooling means may be provided using solid carbon dioxide for the cold part of the Stirling cycle.

Methods and equipment for producing carbon dioxide comprising extraction means for releasing carbon dioxide dissolved in seawater and cooling means for cooling the carbon dioxide to solidify it for storage and/or transportation will now be described with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic side elevation of a marine platform equipped for producing and storing solid carbon dioxide; Figure 2 is a diagrammatic side elevation of a marine vessel equipped for producing, storing and transporting solid carbon dioxide; Figure 3 is a diagrammatic plan view of the vessel of Figure 2; Figure 4 is a diagrammatic illustration of a shore-based establishment for producing and storing solid carbon dioxide; and Figure 5 is a diagrammatic illustration of a fuel synthesising plant using solid carbon dioxide produced by one or more of the equipments illustrated in Figures 1 to 4.

The drawings illustrate methods and equipment for producing carbon dioxide comprising extraction means 11 for releasing carbon dioxide dissolved in seawater 12 and cooling means 13 for cooling the carbon dioxide to solidify it for transportation and/or storage.

Figure 1 illustrates a marine platform 14 standing on legs 15 on the sea bed in a region of the sea in which a marine current flows. The platform 14 comprises a seawater intake 16 and an outlet 17 between which the seawater passes through an extraction chamber 18 in which the extraction takes place. Seawater enters the intake 16 by virtue of the orientation of the intake 16 with regard to the direction of the cunent, and drives a turbine 19 which generates electricity to power the various items of equipment on the platform.

A vacuum pump 21 applies less than atmospheric pressure over the seawater 12 in the chamber 18, and carbon dioxide bubbles out of solution, much as aerated water when the stopper is removed from its bottle.

Carbon dioxide released from the seawater is sent to a cryogenic facility 23 in which it is cooled down to below its freezing point (about -78°C) and the dry ice falls into a container 24 where it is compacted under its own weight into a solid block. As the carbon dioxide will have to be removed from the platform 14, containers will be appropriately sized, and may, for example, be standard shipping containers or half containers. The containers are also insulated and may have active refrigeration to prevent sublimation.

A container store 25 is provided, housing empty containers 24a and filled containers 24b.

Platform tender vessels will be scheduled to arrive with new, empty containers 24a and take off full containers 24b.

A wind turbine 25 atop the platform 14 provides further power.

Figures 2 and 3 illustrate a marine vessel 31 equipped for producing, storing and transporting solid carbon dioxide.

The vessel 31 is essentially a container ship holding containers 32 that initially are empty. As the vessel 31 leaves port, or an ocean terminal, seawater is drawn through an intake 33 into a treatment chamber 34 where carbon dioxide is released from solution in either of the ways described with reference to Figure 1. Cooling equipment 35 cools the carbon dioxide to below its freezing point and deposits it into the containers 32. It may be desirable to fill the containers in such order as will maintain the trim of the vessel 31, rather than starting at one end and proceeding to the other.

It is not necessary to extract all of the dissolved carbon dioxide from the seawater, and the seawater need not remain static in the treatment chamber 34, but may be pumped through an outlet 36, the exhaust water providing propulsive power for the vessel 31. The vessel 31 does not need to move very far or very fast, and will be desirably located in an area not subject to adverse sea conditions. Power for the operation is derived from a canopy 37 of solar panels, and deployable lateral extensions 38 supported, when deployed, on outrigger pontoons 39, as seen in Figure 3.

Figure 4 illustrates a fuel synthesising plant 41 using solid carbon dioxide produced by one or more of the equipments illustrated in Figures 1 to 4.

The plant 41 comprises a Fischer-Tropfsch reactor 42 supplied with solid carbon dioxide and hydrogen. Strictly speaking the Fischer-Tropfsch reaction proceeds from carbon monoxide and hydrogen, and a preliminary reaction between carbon dioxide and hydrogen is required to reduce the dioxide to monoxide, and it may be that the two reactions can proceed together given the right temperature, pressure and catalytic conditions.

The manufacturing plant includes a hydrogen-producing component 43, which is a water electrolysis plant. The manufacturing plant 41 is powered by a renewable energy source, which comprises a solar collector 44.

As illustrated, this is a large array of photovoltaic panels in a tropical desert location, but it could equally well comprise a solar concentrator arrangement heating a steam-generating boiler driving a turbine generator.

The solar power could, however, be used to drive a Stirling engine, for which cooling means may be provided using solid carbon dioxide for the cold part of the Stirling cycle.

The plant 41 is desirably close to a supply of seawater for hydrogen production (oxygen being a by product, of course, which can be sold) and a port or ocean terminal at which the carbon dioxide can be offloaded from delivery vessels. A conveyor or rail track may serve to ferry the containers to the plant 41, carbon dioxide deliveries to the port or terminal being scheduled to ensure a constant supply of carbon dioxide to keep the plant running at reasonable, if not maximum efficiency.

Claims

Claims: 1 Producing carbon dioxide from seawater and cooling the carbon dioxide to solidify it for storage and/or transportation.
2 Production according to claim 1, in which the carbon dioxide is extracted by reducing pressure over the seawater so that the carbon dioxide bubbles out of solution.
3 Production according to claim 1, in which the carbon dioxide is extracted by heating the seawater.
4 Production according to any one of claims 1 to 3, canied out on a marine platform.
5 Production according to claim 4, in which the solid carbon dioxide is loaded into shipping containers.
6 Production according to claim 5, in which the marine platform has a container store and filled containers are offloaded on to a container ship which replaces them with empty containers.
7 Production according to claim 5 or claim 6, in which hydroelectric power is generated from ocean current flow past the container and used for the extraction and/or cooling.
8 Production according to any one of claims 5 to 7, in which power from a wind turbine is used for the extraction and/or cooling.
9 Production according to any one of claims 1 to 3, canied out on an ocean-going vessel.
Production according to claim 9, in which seawater flows from an intake through a treatment chamber where carbon dioxide is extracted and exhausts through an outlet, providing propulsive power for the vessel.
11 Production according to claim 9 or claim 10, in which solid carbon dioxide is loaded into shipping containers that are removed from the vessel in port or at an ocean terminal, where the containers are replaced by empty containers.
12 Production according to any one of claims 9 to 11, powered by solar energy.
13 Production according to claim 12, in which the solar energy is provided by a canopy of solar collector.
14 Production according to claim 12 or claim 13, in which deployable lateral solar extensions augment the available power.
Equipment for producing carbon dioxide comprising extraction means for releasing carbon dioxide dissolved in seawater and cooling means for cooling the carbon dioxide to solidify it for storage and/or transportation.
16 Equipment according to claim 15, in which the extraction means comprise pressure reducing means reducing pressure over the seawater so that the carbon dioxide bubbles out of solution.
17 Equipment according to claim 15, in which the extraction means comprise heating means heating the seawater in which the solubility of carbon dioxide reduces with increasing temperature.
18 Equipment according to any one of claims 15 to 17, on a marine platform.
19 Equipment according to claim 18, in which solid carbon dioxide is loaded into shipping containers.
20 Equipment according to claim 19, in which the marine platform has a container store and empty containers are filled before being offloaded on to a container ship for onward delivery.
21 Equipment according to any one of claims 18 to 20, comprising hydroelectric generator means generating electricity from an ocean current in which the equipment is located.
22 Equipment according to any one of claims 18 to 21, comprising wind and/or solar power generating means.
23 Equipment according to any one of claims 15 to 17, on an ocean going vessel.
24 Equipment according to claim 23, the vessel comprising a store for containers for solid carbon dioxide.
Equipment according to claim 24, in which the extraction and cooling means traverse the container store to fill individual containers.
26 Equipment according to any one of claims 23 to 25, comprising a seawater intake connected to a treatment chamber where carbon dioxide is extracted and an outlet through which treated seawater exhausts, providing propulsive power for the vessel.
27 Equipment according to any one of claims 23 to 26, comprising a solar energy power source.
28 Equipment according to claim 27, in which the solar energy power source comprises a canopy of solar panels.
29 Equipment according to claim 27 or claim 28, comprising laterally deployable solar panels supported on outrigger pontoons.
A method for making synthetic hydrocarbon fuel by reacting carbon dioxide and hydrogen, characterised in that the carbon dioxide is recovered from seawater and frozen for transportation and storage.
31 A method according to claim 30, in which the frozen carbon dioxide is used to provide a cold source for the cold part of a solar powered Stirling engine cycle used to generate electricity for use in the method.
32 Equipment for making synthetic hydrocarbon fuel by reacting carbon dioxide and hydrogen, comprising a store for solid carbon dioxide connected to supply gaseous carbon dioxide to a Fischer-Tropfsch reactor.
33 Synthetic hydrocarbon fuel made using carbon dioxide produced according to any one of claims ito 14.
34 Synthetic hydrocarbon fuel made using carbon dioxide produced using equjipment according to any one of claims 15 to 29.
Synthetic hydrocarbon fuel produced according to a method as claimed in claim 30 or claim 31.
36 Synthetic hydrocarbon fuel produced by equipment according to claim 32.