WO2010131943A1

WO2010131943A1 - A method of operating an engine

Info

Publication number: WO2010131943A1
Application number: PCT/MY2010/000076
Authority: WO
Inventors: Azmi B. Osman
Original assignee: Petroliam Nasional Bhd Petronas
Current assignee: Petroliam Nasional Bhd Petronas
Priority date: 2009-05-14
Filing date: 2010-05-13
Publication date: 2010-11-18
Anticipated expiration: 2011-11-14

Abstract

A method of operating an engine comprising the steps of: a) producing work from the engine by burning a fuel in a gas in the engine, b) using said work to produce electricity, c) using said electricity to electrolyse water into hydrogen and oxygen, d) using said oxygen in said gas.

Description

A Method of Operating an Engine

The present invention relates to a method of operating an engine.

Coal fired power stations are known whereby coal is burnt to create steam which in turn drives a turbine. The turbine drives a generator which produces electricity for distribution to end users.

However, coal fired power stations generate significant amounts of pollutants including greenhouse gases such as carbon dioxide. If these exhaust gases are sent into the atmosphere there will be a consequential damage to the environment. Alternatively the exhaust gases may be treated to remove pollutants but such treatment is expensive.

There is therefore a requirement for a better form of producing power.

Thus according to the present invention there is provided a method of operating an engine comprising the steps of: a) producing work from the engine by burning a fuel in a gas in the engine, b) using said work to produce electricity, c) using said electricity to electrolyse water into hydrogen and oxygen, d) using said oxygen in said gas.

According to another aspect of the present invention there is provided a method of operating an engine comprising the steps of producing work from an engine by burning a fuel in an oxygen rich environment in the engine, producing an exhaust gas including carbon dioxide, sequestrating said carbon dioxide.

hi a further aspect of the invention, there is provided a method of operating an engine comprising the steps of producing work from an engine by burning a fuel in an oxygen poor environment in the engine, producing an exhaust gas including carbon monoxide and hydrogen; and harvesting the exhaust gas. The invention will now be described, by way of example only, with reference to the accompanying figure.

The figure shows the interaction between various features of the present invention.

In summary a heat engine 10 burns fuel 12/13 in oxygen 14 to produce work 16. The work drives a generator 18 which produces electricity, some of which (20) can be used to supply electricity grid for end users, and some of which (22) can be used in an electrolysis plant 24 to generate hydrogen 26 and the above mentioned oxygen 14. As will be appreciated, there is a synergistic effect of using heat energy to generate electricity which in turn is used to electrolyse water into hydrogen and oxygen, the oxygen being used in the heat engine.

An additional synergistic effect is that the exhaust gas from the heat engine is relatively pure carbon dioxide 28. As mentioned above, the electrolysis 24 also generates hydrogen 26 and the hydrogen 26 can therefore be combined with the carbon dioxide 28 in a reactor 30 to produce methanol 32. Thus synergistically, the carbon dioxide by-product from the heat engine is combined with the hydrogen byproduct from the electrolysis plant to produce a useful fuel, methanol.

In more detail, palm oil trees 40 use sunlight 42 from the sun 44 to photosynthesise carbon dioxide 46 from the ambient air 48 into oxygen 50. The palm oil fruit 52 can be harvested and processed in a palm oil mill 54 to produce triglyceride fuel 12. The biomass 56 from the palm oil trees together with the biomass 58 from the palm oil mill can together be processed in a pyrolysis oil plant 60 to produce either an oil or a gas pyrolysis fuel 13.

As mentioned above, the fuel 12 and/or fuel 13 are burnt in the heat engine 10 in an oxygen rich atmosphere. The oxygen rich atmosphere will primarily comprise oxygen 14 from the electrolysis plant 24, though under certain circumstances additional oxygen 62 may be required from a secondary oxygen generator 64. Additional oxygen 62 may be needed from oxygen generator 64 during start up and at a time when either thermal energy from sun is not available (e.g. at night) or is not enough (e.g. on a cloudy day) to sufficiently heat the water in the heat collector 74 (see below). During start up, when there may not be enough electricity available to generate oxygen through electrolysis, additional oxygen 62 can be made available from oxygen generator 64.

The usage ratio between fuel 12 and fuel 13 changes from time to time according to season and weather resulting in changes in the carbon dioxide and water combustion by-product ratio. Considering that the 2:1 production ratio between hydrogen (2H) and oxygen (O) from the electrolysis of water (H₂O) is fixed, there is a need for additional oxygen from the oxygen generator to optimally balance all the chemical reactions involved.

Additionally water 82 is injected into the heat engine.

The heat engine 10 produces work 16 which drives a kinetic to electric converter, in this case a generator 18. Some of the electricity 20 supplied by the generator 18 is provided to a grid for use by an end user. Other of the electricity 22 is fed to the electrolysis plant 24 which generates oxygen 14 which is used to create the above mentioned oxygen rich atmosphere for burning the fuel 12 and 13 in the heat engine 10.

For the purposes of explanation, it is assumed that the oxygen rich atmosphere used to burn fuel 12 and 13 is relatively pure oxygen, in this example 99% by volume of oxygen. Under these circumstances the exhaust gas will include carbon dioxide 28 and water 66 typically in the form of steam. The provision of an exhaust gas containing only carbon dioxide 28 and water 66, without nitrogen oxides, removes the need for a catalytic converter to be present. In the systems of the invention it is preferred that no catalytic converter be fitted.

Both the carbon dioxide 28 and the water 66 will be at an elevated temperature and therefore the exhaust gas includes heat 68. The heat 68 which is carried by both carbon dioxide 28 and water 66 assists reaction occurring at the reactor 30. The reactor 30 is any form of reactor to produce methanol from carbon dioxide and hydrogen 26 including any known type of reactor, such as catalytic hydrogenation of carbon dioxide with hydrogen. It is assumed that if gas compression is needed to increase the pressure in the reactor for the process to happen, the gas compressor is assumed to be part of the reactor. It is preferable that the reactor 30 is placed as close as possible to the heat engine 10 in order to retain the heat. For an internal combustion engine, the reactor 30 can be integrated to the exhaust port itself. For instance, the reactor 30 could be placed at the point in the exhaust system where a catalytic converter would be found in conventional engines. For an external combustion engine, the reactor 30 can be placed at the entrance of the exhaust system. This is to ensure that heat losses are minimized.

Reaction of carbon dioxide 28 and hydrogen 26 in the presence of a catalyst and heat 68 in the reactor 30 produces methanol 32 and water 70. These two products can be separated and water 70 will be directed (whilst still hot) to water reservoir 72 thereby retaining the heat energy.

Water within the reservoir can be fed to a heat collector (or heat exchanger) 74 to heat the water from external heat sources such as heat 76 from the sun or heat 78 from the heat engine. The heated water 80 can be fed to the electrolysis plant. This is advantageous since electrolysis becomes more efficient using heated water. Some of the heated water will be electrolysed into oxygen 14 and hydrogen 28, whereas the remainder of the heated water can be passed as heated water 82 to be injected into the heat engine as described above.

In this case the fuel 12 and 13 are derived from palm oil trees. In further embodiments the fuel could be any type of fuel including mineral derived fuels or other types of plant derived fuels. However, advantageously plant derived fuels such as fuel derived from palm oil trees can be used since this is a sustainable fuel. The fuel could be a fluid fuel e.g. a gas or a liquid. The fuel may have long chain carbon molecules, for example molecules having eight or more carbon atoms. The carbon atoms within the molecules may be in a straight chain, or alternatively the carbon atoms may be branched.

As mentioned above, the heat engine bums the fuel in an oxygen rich atmosphere. Air contains approximately 21% by volume of oxygen and the term oxygen rich atmosphere means that the atmosphere includes more than 21% by volume of oxygen. One method of producing oxygen is to remove the nitrogen from air. Such a process will produce a gas with 95% by volume of oxygen. Thus, the oxygen rich atmosphere used to burn the fuel in the heat engine may comprise 95% or more by volume of oxygen, alternatively it may comprise 90% or more by volume of oxygen, alternatively it may comprise 80% or more by volume of oxygen.

Advantageously the oxygen rich environment is substantially nitrogen free. Under these circumstances the exhaust gases will not include any NO_x gases. By burning the fuel in an oxygen rich environment the exhaust gases from a heat engine will comprise substantially only carbon dioxide and water, for example there will be substantially no NO_x gases. Whereas gas with a relatively low percentage of carbon dioxide is considered a waste product which requires expensive carbon dioxide scrubbers to remove the carbon dioxide therefrom, a gas comprising substantially only carbon dioxide and water is commercially valuable because it is relatively cheap to remove the water and hence produce a gas which substantially only contains carbon dioxide. Carbon dioxide in a pure form is commercially useful for producing methanol.

Thus the exhaust gas exiting the engine may comprise at least 80% by volume of carbon dioxide and water, preferably it may comprise at least 90% by volume of carbon dioxide and water, more preferably it may comprise at least 95% by volume of carbon dioxide and water, more preferably it may comprise at least 99% by volume of carbon dioxide and water. Once the water has been removed by condensing it out, the gas may comprise at least 90% by volume of carbon dioxide, more preferably it may comprise at least 95% by volume of carbon dioxide, more preferably it may comprise at least 99% by volume of carbon dioxide. As mentioned above, water is injected into the heat engine and turns to steam because of the combustion temperature of the fuel. The water can typically be injected at a relatively high pressure, for example 150 to 200 bar. The boiling point of the water at this pressure is significantly above boiling point of water at atmospheric pressure (approximately 100 ⁰C) and therefore the water can be heated to above 100 °C without vaporising. Injecting pressurised water which has been heated to just below its boiling point at that pressure means that less of the combustion energy is required to convert the water to steam. As will be appreciated from the figure, synergistically, excess heat 78 from the heat engine can be fed to the heat collector 74 to heat the heated water 80 which improves the efficiency of the electrolysis plant, and excess heated water 82 can be fed to the heat engine itself which in turn improves the efficiency of the heat engine.

As mentioned above, an external heat source such as the sun can be used to provide heat 76. In further embodiments, any form of external heat source could be used, for example geothermal energy could be used.

As mentioned above, the heat engine 10 produces an exhaust gas which comprises substantially only carbon dioxide and water. Because it is easy to condense the water out of the exhaust gas to leave a relatively pure carbon dioxide gas, this carbon dioxide gas can be sequestrated, i.e. it does not have to be returned to the atmosphere. Sequestration can be by any known type, for example it can be used for enhanced oil recovery (EOR) by injecting the gas into an oil bearing stratum under high pressure and that pressure will push the oil or gas or both (oil and gas) into the oil pipe and up to the surface. Alternatively the carbon dioxide could be sequestrated by using it as part of an enhanced coal bed methane recovery system.

The high purity carbon dioxide gas can also be directed to an enclosed volume with plants. The carbon dioxide is then photosynthesized into oxygen. An enclosed volume having plants that can easily be used for biofuel production is preferred.

In an alternative embodiment, the heat engine 10 can be operated in an oxygen poor atmosphere, so that the burning of the fuel 12 and 13 will result in an exhaust gas containing carbon monoxide and hydrogen (syngas - not illustrated). Where syngas is produced from an internal or external combustion engine, the generation of work 167 from the heat engine 10 may be regarded as a by-product of the syngas production process. The many uses for this work 167 would be well known to the person skilled in the art and include the generation of electricity 20, or direct conversion to kinetic energy 18 for the movement of mechanical devices.

In this embodiment, the oxygen 14 will be supplied primarily from the electrolysis plant 24, the secondary oxygen generator 64 will generally either be absent or inactive, although as described above, during start up or at times when the thermal energy from the sun 44 is either not available or insufficient, the secondary oxygen generator 64 may be used.

As with embodiments where the heat engine 10 is operated in an oxygen rich atmosphere, heat 68 will be produced. The heat 68 can be of use where the syngas is processed further, for instance to form methanol 32 or other fuels, by providing the energy necessary for further reaction to occur. Where the syngas is reacted further, reactors 30 such as that described above will typically be used.

Alternatively, the harvested syngas, a fuel, may be stored or further oxidized. Further, the carbon monoxide and hydrogen forming the syngas may be separated using known techniques for future use in different applications.

As mentioned above, in this embodiment the heat engine 10 burns the fuel 12, 13 in an oxygen poor environment. The term oxygen poor means that only 50-70% of the oxygen 14, 62 required to completely oxidize the fuel 12, 13 is supplied to the combustion chamber, the precise amounts of oxygen 14, 62 will depend upon the fuel 12, 13 ratio selected, hi other words, the heat engine 10 is run at about 40% richer (in the range 30 - 60% richer, often 40 - 50% richer) than stoichiometric in order to produce the carbon monoxide and hydrogen.

In piston engines it is typical for oxygen injection to be initiated slightly ahead of the fuel injection to ensure that the oxygen 14, 62 to occupies the piston bowl in the piston engine. By ensuring that the combustion chamber temperature is above the fuel auto-ignition temperature, fuel can be injected to initiate the fuel auto-ignition. Once fuel auto-ignition occurs, heat will be released and the fuel oxidation process will continue until all the injected oxygen 14, 62 is folly consumed.

By way of explanation, it is believed that the heat released from the initial fuel oxidation breaks down the hydrocarbon chain from the injected foel into mostly carbon monoxide and hydrogen with low levels of carbon dioxide and hydrocarbons. The production of carbon dioxide can be expected in the early stages of the foel oxidation process, a small amount of soot can be expected as a result of the partial oxidation of long chain hydrocarbons within the foel after oxygen 14, 62 depletion.

By controlling the levels of oxygen 14, 62 present it is possible to provide for the foil oxidation of the foel 12, 13 in the early stages of the foel oxidation process, specifically it will generally be the case that the first 40 - 60% of the foel 12, 13 may combust to form carbon dioxide 28 and water 66. The remaining foel 12, 13 may then be broken down into low molecular weight hydrocarbons once the oxygen 14, 62 has been consumed, and these may in turn dissociate into hydrogen, carbon monoxide and in some cases carbon dioxide 28. This is facilitated by the provision of a concentrated heat release in the piston bowl (for piston engines) or stratification chamber (for gas turbines), which ensures that sufficient thermal energy is present to accelerate the break down of the hydrocarbon foel into the syngas.

Thus the exhaust gas exiting the engine may comprise at least 80% by volume of carbon monoxide and hydrogen, preferably it may comprise at least 90% by volume of carbon monoxide and hydrogen, more preferably it may comprise at least 95% by volume of carbon monoxide and hydrogen, more preferably it may comprise at least 99% by volume of carbon monoxide and hydrogen.

As noted above, the use of high purity oxygen 14, 62 provides an exhaust gas which is substantially free of nitrogen and nitrogen oxides, for this reason the syngas produced is of a purity and yield comparable to that of conventional industrial syngas production processes. Known methods of operating engines which have been converted to produce syngas result in syngas contaminated with nitrogen oxides.

Typically, purification to remove water 66 will be required, and this can be achieved using simple condensation techniques. Other known purification methods may also be used. In addition, if desired, carbon dioxide 28 may be removed using the methods described above, for instance sequestration; or by reaction with amine solvents or hydroxides (such as sodium hydroxide). However, if the syngas is to be converted to methanol 32, carbon dioxide 28 will generally not be removed.

Depending upon the intended use of the syngas, the oxygen-to-fuel ratio can be tuned to alter the final mixture of products in the exhaust gas, in particular, to control the levels of carbon dioxide, water, low molecular weight hydrocarbons and soot which are present. For instance, where conversion of the syngas to methanol is desired, the presence of low levels of carbon dioxide are acceptable, and may even be preferred to increase the yield of the methanol production process.

The heat engine may be an internal combustion engine. The internal combustion engine may be a reciprocating four stroke engine. The internal combustion engine may be a reciprocating two stroke engine. The engine may be a spark ignition engine. The engine may be a compression ignition engine. The engine may be a gas turbine engine, hi embodiments where syngas is produced, the engine will typically be a compression ignition engine.

Claims

1. A method of operating an engine comprising the steps of: a) producing work from the engine by burning a fuel in a gas in the engine, b) using said work to produce electricity, c) using said electricity to electrolyse water into hydrogen and oxygen, d) using said oxygen in said gas.

2. A method as defined in claim 1 including the step of injecting water into the engine when burning the fuel in the gas.

3. A method as defined in claim 2 including the step of heating the water prior to injection.

4. A method as defined in claim 3 including using waste heat from the engine to heat the water, and/or using heat from an external heat source such as sunlight or geothermal energy to heat the water.

5. A method as defined in claim 4 including cooling the engine with said water prior to injection.

6. A method as defined in claim 5 including electrolysing at least some of said water prior to injection.

7. A method as defined in any preceding claim including providing a secondary oxygen generator, operating the secondary oxygen generator to provide secondary oxygen, using the said secondary oxygen in said gas.

8. A method as defined in any preceding claim wherein an exhaust gas from the engine comprises at least 80% by volume of carbon dioxide and water, preferably at least 90% by volume of carbon dioxide and water, more preferably at least 95% by volume of carbon dioxide and water, more preferably at least 99% by volume of carbon dioxide and water.

9. A method as defined in any preceding claim including producing an exhaust gas including carbon dioxide, combining said carbon dioxide with said hydrogen in a reactor to produce a further fuel.

10. A method as defined in claim 9 wherein said further fuel is methanol.

11. A method as defined in any preceding claim in which said fuel is a plant derived fuel.

12. A method as defined in any one of claims 9 to 11 including providing condensed water by condensing water from exhaust gas of the reactor, injecting said condensed water into the engine.

13. A method as defined in any preceding claim wherein said fuel is a fluid fuel.

14. A method as defined in claim 13 wherein said fuel is a gas.

15. A method as defined in claim 13 wherein said fuel is a liquid.

16. A method of operating an engine comprising the steps of producing work from an engine by burning a fuel in an oxygen rich environment in the engine, producing an exhaust gas including carbon dioxide, sequestrating said carbon dioxide.

17. A method as defined in claim 16 including injecting water into said engine when burning the fuel in the engine.

18. A method as defined in claim 16 or 17 in which the exhaust gas comprises at least 80% by volume of carbon dioxide and water, more preferably at least 90% by volume of carbon dioxide and water, more preferably at least 95% by volume of carbon dioxide and water, more preferably at least 99% by volume of carbon dioxide and water.

19. A method as defined in any one of claims 16 to 18 including condensing water from the exhaust gas to produce a processed exhaust gas.

20. A method as defined in claim 19 including the step of sequestrating the processed exhaust gas.

21. A method as defined in claim 19 including directing the said process exhaust gas to an enclosed volume containing plants.

22. A method of operating an engine comprising the steps of producing work from an engine by burning a fuel in an oxygen poor environment in the engine, producing an exhaust gas including carbon monoxide and hydrogen; and harvesting the exhaust gas.

23. A method as defined in claim 22, comprising the further step of separating the carbon monoxide and hydrogen from other exhaust gases.

23. A method as defined in claim 22 or claim 23 comprising the further step of reacting the carbon monoxide and hydrogen to produce a fuel.

24. A method as defined in claim 23, wherein the fuel is methanol.