DEVICE AND METHOD FOR USING CARBON DIOXIDE ORIGINATING FROM A COMBUSTION PROCESS

Abstract

A device for using carbon dioxide originating from the combustion of a byproduct has a preparing unit which is connected to a delivery station for fossil fuels, which has a burner for combusting a byproduct that is released when the fuel is delivered, and an exhaust gas line that is connected to the burner. A depositing device is fluidically connected to the preparing unit via the exhaust gas line, for carbon dioxide. The depositing device is fluidically connected to the delivery station to redeliver fuel via a supply line for carbon dioxide. Such a device allows the production and the subsequent controlled use of carbon dioxide from previously unused byproducts in the production of crude oil. A corresponding method by which carbon dioxide originating from the combustion of a byproduct is used in a controlled manner, in particular as part of a fossil fuel extraction process.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International Application No. PCT/EP2015/054249 filed Mar. 2, 2015, and claims the benefit thereof. The International Application claims the benefit of German Application No. DE 102014204646.7 filed Mar. 13, 2014. All of the applications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a device for using carbon dioxide that is formed in the combustion of particularly a gaseous by-product, in particular in the context of producing a fossil fuel. In addition, the invention relates to a method for using carbon dioxide formed in the combustion of particularly a gaseous by-product.

BACKGROUND OF INVENTION

The deposits of fossil fuels stored in the ground such as, for example, natural gas, or in particular oil, which are obtainable economically with current technology serve as energy reserves in order to cover the constantly increasing energy consumption of current times. Oil in this case is used as one of the most important raw materials for generating electricity, as a power fuel for vehicles and means of transport, and also as a starting material for numerous products of the chemical industry.

For oil extraction, it is recovered from subterranean reservoirs. In this case, in principle three recovery phases are distinguished. Primary recovery denotes the recovery phase in which the fuel is recovered by the naturally occurring overpressure of the oil, termed the reservoir pressure.

If, in the course of the primary oil recovery, the reservoir pressure falls, in the framework of the second recovery phase, secondary recovery, water or inert gas can be injected using injection probes installed by wells, and the reservoir pressure thus increased again in this manner, up to 40% of the oil present in total can be recovered.

The residual increasingly viscous and dense bituminous oil, however, makes this further recovery difficult. In this case, use is made of tertiary oil recovery (Enhanced Oil Recovery (EOR)). For the tertiary oil recovery, large amounts of carbon dioxide (CO₂) are required which are forced at high pressure into the oil reservoirs. The injected carbon dioxide dissolves in the oil, swells it and thus lowers its viscosity, in such a manner that the oil can more readily flow in the direction of the recovery site or the recovery well, finally be conveyed with the aid of pumps.

Possible sources for the carbon dioxide required for the recovery are, for example, natural reservoirs, exhaust gases of industrial processes or power plant exhaust gases. Since the carbon dioxide that is utilizable from these sources, however, is customarily not present in the concentration required for oil recovery, a corresponding concentration is necessary. For this purpose, known methods are available, such as physical or chemical absorption, adsorption or separation by means of selective membranes, which, however, are associated with high operational costs.

In addition, it is possible to recover carbon dioxide from fossil fuels by means of the oxyfuel method. In this case, a fuel is burnt with pure oxygen, wherein an exhaust gas is formed, the main constituents of which are substantially carbon dioxide and steam. The carbon dioxide can then be concentrated by condensing the steam. For use in tertiary oil recovery, the oxyfuel method, however, is possibly not usable economically.

In addition, it is necessary to consider that even with a sufficiently high concentration and the required purity of the carbon dioxide, the sites where CO₂-rich exhaust gases or other CO₂ sources are accessible are customarily spatially far removed from the recovery sites for oil production.

The supply of carbon dioxide to the corresponding recovery sites is therefore associated with corresponding additional complexity and high costs.

SUMMARY OF INVENTION

A first object of the invention is to specify a device that, with the lowest possible operating and capital costs, permits the production of economically usable carbon dioxide.

A second object of the invention is to specify a method which uses the advantages of the device and thus permits corresponding provision of the required carbon dioxide.

The first object of the invention is achieved according to the invention by a device for using carbon dioxide formed in the combustion of particularly a gaseous by-product, comprising a treatment unit which is connectable to a recovery site and having a burner for combustion of the by-product that is released in the fuel recovery and having an exhaust gas line that is connected to the burner, and also comprising a carbon dioxide separation device that is flow-connected via the exhaust gas line to the treatment unit. The separation device is in this case flow-connectable to the recovery site for renewed fuel recovery via a feed line for carbon dioxide.

In a first step, the invention proceeds from the fact that, in the context of oil recovery, together with the recovered oil, by-products, in particular gaseous fuel gases, always exit from a recovery well. Since, however, the costs of transporting these, in particular gaseous, by-products and/or treatment thereof usually exceed the expected sales proceeds, the use of the by-products, in particular the fuel gases, or treatment thereof is usually dispensed with solely for economic reasons. Instead, the by-products produced in oil recovery, in the absence of policy requirements, are usually flared off unused and the resultant pollutant emissions, such as, in particular carbon dioxide emissions, into the atmosphere are accepted.

In a second step, the invention takes into account the fact that the processes underlying pollutant minimization, in particular carbon dioxide separation, are already part of intensive research in other fields. For instance, in particular in the case of fossil-fuelled power plants for generating electrical energy, more and more frequently separation devices are being used that permit a targeted separation of pollutants and carbon dioxide present in exhaust gases, and thus markedly decrease the atmospheric pollution (Post-Combustion Capture Process).

In a third step, the invention recognizes that such a separation device already tested in power plants is also suitable for use in oil recovery. Owing to the combination with a suitable treatment unit, by-products that are produced during oil recovery, and have to date been unused, can be used in a targeted manner. In other words, the device permits, in particular, an on-site production and use of carbon dioxide at the recovery site of the oil.

The treatment unit that can be associated with the recovery site, serves in this case first generating a carbon dioxide-containing exhaust gas by combustion of the by-products. In the separation device that is flow-connected to the treatment unit via an exhaust gas line, the carbon dioxide can be separated off from the exhaust gas and fed to the recovery site for subsequent oil recovery. The feed in this case proceeds via a feed line that represents the flow connection between the separation device and the recovery site.

Overall, the use of such a device can markedly improve the economic efficiency of the oil recovery process. Since the carbon dioxide separated off from the combustion exhaust gas, in the ideal case, is produced directly at the site of use and used for oil recovery, the costs of providing and transporting carbon dioxide are absent. In addition, by the targeted treatment of the exhaust gas from the combustion of the by-products produced in the oil recovery, which exhaust gas is not technically utilizable to date, unwanted emissions of carbon dioxide into the atmosphere may be prevented or at least markedly decreased. The recovery site in this case, depending on the recovery operation, can have one or more recovery wells and corresponding injection wells.

Advantageously, a fuel feed line for feeding the by-products is connected to the burner of the treatment unit. Thus, a fuel gas exiting from the recovery site, or from a corresponding recovery well of the recovery site, can be fed to the burner and there burnt with formation of a carbon dioxide-containing exhaust gas.

The combustion proceeds in this case in particular atmospherically, with supply of air, for which purpose an air feed line for supplying combustion air is connected to the burner of the treatment unit. In particular, a gas mixer can further be connected into the air feed line, which gas mixer serves for setting the concentration of the carbon dioxide in the combustion exhaust gas.

In principle, for separating off the carbon dioxide from the exhaust gas, all methods are usable that have sufficiently high selectivity and a low energy requirement. Thus, in principle, absorption and adsorption processes, or else the use of membranes, would be conceivable.

Particularly, the carbon dioxide is separated off wet-chemically. For this purpose, the separation device comprises an absorber for separating off the carbon dioxide from the exhaust gas by means of a scrubbing medium, and also a desorber that is flow-connected to the absorber for releasing the carbon dioxide from the scrubbing medium. In the absorber, the carbon dioxide is removed from the exhaust gas by absorption in the scrubbing medium. In order to remove the absorbed carbon dioxide from the scrubbing medium and thus produce carbon dioxide, the loaded scrubbing medium is fed to the desorber. For this purpose the absorber is expediently flow-connected via a withdrawal line to a feed line of the desorber. In the desorber, the absorbed carbon dioxide is released from the scrubbing medium by thermal desorption and the regenerated scrubbing medium is fed back to the absorber for repeated absorption of carbon dioxide. For this purpose, the desorber is advantageously flow-connected via a withdrawal line to a feed line of the absorber.

The desorbed carbon dioxide, after it is separated off, can be used for oil recovery. For this purpose, the desorber of the separation device is particularly advantageously flow-connected to the recovery site via the feed line for carbon dioxide. Thus, the carbon dioxide that is released can be used on site for oil recovery. Expediently, the feed line for the carbon dioxide is connected to the top of the desorber.

In a particularly advantageous embodiment, the exhaust gas line is heat-connected to a steam generator. The steam generator is expediently connected into a steam circuit. The steam circuit, also termed water-steam circuit, serves for removing heat formed during the combustion. The hot combustion exhaust gas in this case is conducted past the steam generator and heats in this case water circulating in the steam circuit with formation of steam. The exhaust gas itself cools and can then be fed to the separation device to separate off the carbon dioxide that is present in the exhaust gas.

To use the resultant steam, it is, in particular, advantageous when the steam generator is flow-connected to a steam turbine. In other words, the steam turbine is integrated into the steam circuit. Since, in the combustion of the exhaust gas, more heat is produced than is originally necessary for the production of steam, in particular for the production of heating steam for a reboiler, the steam generator can advantageously be designed in such a manner that it is suitable for generating a higher-grade steam of high pressure which can then be expanded in the steam turbine and used for generating electrical power.

To generate the electrical power, expediently, a generator is connected to the steam turbine. The electrical power can then be used to cover the electrical requirement of the separation device itself. Alternatively, it can be used for compression of the carbon dioxide produced or fed into the general electric consumer grid.

It is particularly advantageous when the steam turbine in the steam circuit is heat-connected to the separation device. The steam that is expanded in the steam turbine to a predetermined pressure and temperature level can thus be used to support the desorption process. For this purpose, the steam turbine is expediently constructed as a counterpressure turbine. Alternative embodiments of the steam turbine include, for example, familiar condensation turbines in combination with a corresponding heating steam take-off at the steam turbine or at the steam generator.

In an embodiment of the heat connection of the steam turbine to the separation device in the steam circuit, the steam expanded in the steam turbine is fed via a steam line of the steam circuit to a reboiler. The reboiler, which is expediently connected to the desorber of the separation device functions in this case as a condenser for the steam circuit. Within the reboiler, the steam is conducted through a heat exchanger having scrubbing medium taken off from the desorber and condensed. The condensed steam can then be fed back to the steam generator via a condensate line of the steam circuit that is flow-connected to the steam line, and there, again used for heat removal from the combustion exhaust gas and at the same time for operating the steam turbine.

Expediently, the exhaust gas line is flow-connected to a feed line of the absorber of the separation device via a withdrawal line. Thus, the carbon dioxide present in the combustion exhaust gas, after it is cooled by the steam generator, can be removed from the exhaust gas by an absorption-desorption process within the separation device, and then fed to the oil recovery. Expediently, in this case, a first substream of 50% to less than 100% of the total combustion exhaust gas is fed to the absorber.

Particularly, the exhaust gas line is flow-connected to the burner via a return line. Via the flow connection, a substream of the exhaust gas, after it passes through the steam generator, is fed back to the burner. The recirculation in this case proceeds advantageously via a gas mixer connected into the air feed line and permits a recirculation of the combustion exhaust gas around the steam generator. Such a recirculation permits the targeted setting of the concentration of the carbon dioxide which otherwise could only be set via the air excess in the combustion, that is to say via the ratio of the actual amount of air to the amount of air required for stochiometric combustion. The desired high carbon dioxide concentration would be ensured in this case only by a slight air excess. However, with a slight air excess, to ensure a stochiometric combustion, high combustion temperatures are necessary. For corresponding combustion temperatures, at all events, the required hot gas parts are only available at very high costs and would require complex cooling. In addition, at high combustion temperatures, the concentration of nitrogen oxides in the exhaust gas increases.

Thanks to the recirculation, simple components can be made use of and owing to the lower combustion temperature, unwanted increase in harmful emissions of nitrogen oxides and carbon monoxide in the combustion can also be prevented. In other words, owing to the exhaust gas recirculation, the exhaust gas temperature can be held at a technically manageable level, with simultaneously an effective increase in the carbon dioxide concentration in the combustion exhaust gas.

The fraction of the substream which is reused via the return line for combustion of the influent gaseous by-product, that is to say the fuel gas, is in this case advantageously in a range from more than 0% to 50% of the total combustion exhaust gas.

It is additionally advantageous when a heat exchanger for preheating the combustion air is connected into the air feed line. For this purpose, the first substream of the heated exhaust gas, after passage through the steam generator, is passed via the heat exchanger. The substream and the combustion air are conducted in heat exchange here, wherein the combustion air takes up the waste heat of the exhaust gas and is preheated. The first exhaust gas substream fed to the separation device is in this case advantageously precooled to the absorption temperature necessary in the absorber.

Advantageously, the scrubbing medium used for separating off the carbon dioxide from the exhaust gas is an amino acid salt solution. An aqueous amino acid salt solution, and in particular a potassium-containing aqueous amino acid salt solution is expedient in this case. The use of in particular an aqueous amino acid salt solution is suitable in this case, in particular, since an amino acid salt has a negligibly low vapor pressure and does not vaporize even at high temperatures. As a result, in particular unwanted emissions into the atmosphere are avoided, and in addition, a decrease in the concentration of the active component of the scrubbing medium is prevented.

The second object of the invention is achieved according to the invention by a method for using carbon dioxide formed in the combustion of particularly a gaseous by-product, wherein a by-product released from a recovery site in a fuel recovery is fed to a treatment unit, wherein the by-product is burnt with feed of air in the treatment unit, wherein the carbon dioxide-containing exhaust gas formed in the combustion is fed to a carbon dioxide separation device, and wherein the carbon dioxide that is separated off from the exhaust gas in the separation device is fed to the recovery site for renewed fuel recovery.

The carbon dioxide which is produced by means of such a method can be used in a simple and inexpensive manner for oil recovery. By the targeted utilization of the by-products that are unused to date and arise during oil recovery, in addition, a contribution to climate protection can be achieved by preventing the carbon dioxide being emitted into the atmosphere.

Further advantageous embodiments result from the subclaims directed to the method. Said advantages of the device and advantageous developments thereof can be applied as appropriate to the method and developments thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereinafter, an exemplary embodiment of the invention will be described in more detail with reference to a drawing.

FIG. 1 shows a device for using carbon dioxide according to an embodiment of the invention.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 shows a device 1 for using carbon dioxide formed in the combustion of in particular a gaseous by-product of oil recovery. The device 1 comprises a treatment unit 3 having a burner 5 and a steam generator 7. In addition, the device 1 comprises a carbon dioxide separation device 9 that is flow-connected to the treatment unit 3. In the separation device 9, carbon dioxide that is formed in the context of the combustion is separated off from the exhaust gas by means of a scrubbing medium. For this purpose, the separation device 9 comprises an absorber 11 and a desorber 13 that is flow-connected thereto.

The device 1 permits an on-site production and subsequent utilization of carbon dioxide in tertiary oil recovery. In tertiary oil recovery, the oil that is to be recovered is produced by injecting carbon dioxide into corresponding wells of a recovery site 15. In addition to the oil, in this case, fuel gases that are no longer technically utilizable, that is to say gaseous by-products, are released. Instead of flaring off these fuel gases as is usual to date, the fuel gas stream is fed via a fuel feed line 17 to the burner 5 of the treatment unit 3. In the burner 5, the fuel gas is burnt atmospherically with feed of air. The air is fed to the burner 5 via an air feed line 19.

The burner 5 is heat-coupled to the steam generator 7 via an exhaust gas line 21 connected to the burner. The exhaust gas formed in the combustion is conducted via a heat exchanger 23 of the steam generator 7, via which the waste heat formed in the combustion can be taken off. The steam generator 7 is connected into a steam circuit 25, or water-steam circuit, in which water and/or steam circulate. The circulating water is heated in the steam generator 7 with formation of steam. In order to utilize the steam, the steam generator 7 is flow-connected to a steam turbine 27. The steam turbine 27 is operated by means of the steam generated in the steam generator 7. The steam is expanded within the steam turbine 27 and operates a generator 29 that provides electric power which is used for covering the electrical requirement of the separation device 9 itself.

The steam turbine 27 used for expanding the steam is in the present case constructed as a counterpressure turbine. The counterpressure turbine 27 expands the steam to a pressure and temperature level required for separating off the carbon dioxide in the separation device 9. The steam turbine 27 is heat-connected to a reboiler 31 in the steam circuit 25, which reboiler is arranged as bottoms evaporator at the bottom 33 of the desorber 13. The expanded steam flows from the steam turbine 27 via a steam line 35 of the steam circuit 25 to the reboiler 31. The reboiler 31 acts in this case as a condenser for the steam circuit 25. The steam exiting from the steam turbine 27 gives off its heat to the scrubbing medium circulating in the reboiler 31 and is itself condensed in this case. The condensed steam is fed back to the steam generator 7 via a condensate line 37 that is flow-connected to the steam line 35 and at the steam generator takes up—with cooling of the combustion exhaust gas and formation of new steam—the heat provided in the steam generator 7. The heat withdrawn in the reboiler 31 is used for desorption of the carbon dioxide from the scrubbing medium in the desorber 13.

In order to separate the carbon dioxide from the exhaust gas, the treatment unit 3 is flow-coupled to the separation device 9 via the exhaust gas line 21. A first substream 39 of the exhaust gas is in this case fed to the absorber 11 via the connection of a withdrawal line 41 to a feed line 43 of said absorber 11. In this case, the exhaust gas substream 39 passes through a heat exchanger 45 which further precools the exhaust gas substream 39 before the entry into the absorber 11. At the same time, the combustion air in the air feed line 19 is in this way preheated before the entry into the burner 5.

Within the absorber 11, the first substream 39 of the exhaust gas, in the present case 50% of the total exhaust gas stream, is contacted with the scrubbing medium and the carbon dioxide present in the exhaust gas is absorbed in the scrubbing medium.

The scrubbing medium used is in the present case an aqueous potassium-containing amino acid salt solution. The loaded scrubbing medium, for release of the carbon dioxide, flows into the desorber 13, where the carbon dioxide is thermally desorbed. The carbon dioxide is taken off at the top 47 of the desorber, optionally compressed and finally fed via a feed line 49 to the recovery site 15 for renewed fuel recovery.

A second substream 51 of the exhaust gas, in the present case 50% of the entire exhaust gas stream, after it passes through the steam generator 7 and after corresponding precooling in the context of an exhaust gas recirculation 53, is fed back via a return line 55 into the burner 7. In the exhaust gas recirculation 53, the second substream 51, before the entry into the burner, is further fed to a gas mixer 57, into which the combustion air also flows via the feed line.

Such an exhaust gas recirculation 53 ensures a sufficiently high carbon dioxide concentration in the exhaust gas, which through sole combustion of the exhaust gas with air could only be set via the ratio of the actual amount of air to the amount of air required for stochiometric combustion. In addition, thanks to the exhaust gas recirculation 53, the exhaust gas temperature may be kept at a technically manageable level.

Claims

1. A device for using carbon dioxide formed in the combustion of a gaseous by-product, comprising

a treatment unit which is connectable to a recovery site for fossil fuel and having a burner for combustion of a by-product that is released in the fuel recovery and having an exhaust gas line that is connected to the burner, and

a carbon dioxide separation device that is flow-connected via the exhaust gas line to the treatment unit,

wherein the separation device is flow-connectable to the recovery site for renewed fuel recovery via a feed line for carbon dioxide.

2. The device as claimed in claim 1, further comprising

a fuel feed line for feeding the by-product which is connected to the burner of the treatment unit.

3. The device as claimed in claim 1, further comprising

an air feed line for supplying combustion air which is connected to the burner of the treatment unit.

4. The device as claimed in claim 1,

wherein the separation device comprises an absorber for separating off the carbon dioxide from the exhaust gas by means of a scrubbing medium, and also a desorber that is flow-connected to the absorber for releasing the carbon dioxide from the scrubbing medium.

5. The device as claimed in claim 4,

wherein the desorber of the separation device is flow-connected to the recovery site via the feed line for carbon dioxide.

6. The device as claimed in claim 1,

wherein the exhaust gas line is heat-connected to a steam generator.

7. The device as claimed in claim 6,

wherein the steam generator is flow-connected to a steam turbine.

8. The device as claimed in claim 7, further comprising

a generator which is connected to the steam turbine.

9. The device as claimed in claim 7, further comprising

a steam circuit of the steam turbine which is heat-connected to the separation device.

10. The device as claimed in claim 7,

wherein the steam turbine is constructed as a counterpressure turbine.

11. The device as claimed in claim 4,

wherein the exhaust gas line is flow-connected to a feed line of the absorber of the separation device via a withdrawal line.

12. The device as claimed in claim 1,

wherein the exhaust gas line is flow-connected to the burner of the treatment unit via a return line.

13. The device as claimed in claim 3, further comprising

a heat exchanger for preheating the combustion air which is connected into the air feed line.

14. The device as claimed in claim 4,

wherein the scrubbing medium used for separating off the carbon dioxide from the exhaust gas is an amino acid salt solution.

15. A method for using carbon dioxide formed in the combustion of a gaseous by-product, the method comprising:

wherein feeding a by-product released from a recovery site in a fuel recovery to a treatment unit,

burning the by-product with feed of air in the treatment unit,

feeding the carbon dioxide-containing exhaust gas formed in the combustion to a carbon dioxide separation device, and

feeding the carbon dioxide that is separated off from the exhaust gas in the separation device to the recovery site for renewed fuel recovery.

16. The method as claimed in claim 15,

wherein the carbon dioxide present in the exhaust gas is separated off from the exhaust gas by means of a scrubbing medium in an absorber of the separation device, and wherein the carbon dioxide is released from the scrubbing medium in a desorber of the separation device that is flow-connected to the absorber.

17. The method as claimed in claim 15,

wherein the carbon dioxide that is separated off from the exhaust gas in the separation device is fed to the recovery site proceeding from the desorber.

18. The method as claimed in claim 15,

wherein the heat that is formed in the combustion is removed via a steam generator that is connected downstream of the combustion, and wherein steam is formed in the steam generator by the heat formed in the combustion.

19. The method as claimed in claim 18,

wherein the steam formed in the steam generator is expanded in a steam turbine.

20. The method as claimed in claim 19,

wherein a generator is operated by means of the steam turbine.

21. The method as claimed in claim 19,

wherein the steam expanded in the steam turbine is used for separating off the carbon dioxide from the exhaust gas in the separation device.

22. The method as claimed in claim 19,

wherein a counterpressure turbine is used as steam turbine.

23. The method as claimed in claim 16,

wherein a first substream of the exhaust gas of the combustion is fed via a withdrawal line to the absorber of the separation device.

24. The method as claimed in claim 15,

wherein a second substream of the exhaust gas of the combustion is fed via a return line to the combustion of the by-product.

25. The method as claimed in claim 23,

wherein the first substream of the exhaust gas preheats the combustion air before entry into the absorber.

26. The method as claimed in claim 15,

wherein the scrubbing medium used for separating off the carbon dioxide from the exhaust gas is an amino acid salt solution.