Method and an apparatus for producing energy by recycling materials during a fuel combustion process

Abstract

The present invention relates to a method for producing energy by recycling materials during a fuel combustion process, wherein the fuel combustion process comprises combusting fuel introduced into the fuel combustion process. Further, the invention relates to an apparatus for producing energy by recycling materials during a fuel combustion process.

Claims

1. A method for producing energy by recycling materials during a fuel combustion process (1) taking place in a fuel combustion device, which is a boiler or a furnace, wherein the fuel combustion process comprises combusting fuel introduced into the fuel combustion process, wherein the method comprises: introducing a stream of flue gas (4) comprising carbon dioxide and produced in the fuel combustion process (1) into a biomass cultivating process (2), where the flue gas takes part in the production of biomass and oxygen; introducing at least part of the biomass produced in the biomass cultivating process (2) into a biogas production process (3), where the biomass takes part in the production of biogas; introducing at least part of the oxygen produced in the biomass cultivating process (2) into the fuel combustion process (1); introducing at least part of the biogas produced in the biogas production process (3) into the fuel combustion process (1), where the biogas is combusted as fuel; and introducing combustion air (9) comprising oxygen and nitrogen into the fuel combustion process; such that the need to introduce fuel (11) selected from a group of fossil fuel comprising coal, biofuel, industrial waste, municipal waste and any combination thereof, into the fuel combustion process (1) during the fuel combustion process in addition to the biogas produced in the biogas production process (3) and introduced into the fuel combustion process is reduced.

2. The method of claim 1, wherein 300-1500 kg, preferably 650-850 kg, and more preferably 740-800 kg of oxygen (6) produced in the biomass cultivating process (2) is introduced into the fuel combustion process (I) per 1000 kg of carbon dioxide produced in the fuel combustion process.

3. The method of claim 1, wherein 100-800 kg, preferably 300-400 kg, and more preferably 330-370 kg of biogas (7) produced in the biogas production process (3) is introduced into the fuel combustion process (1) per 1000 kg of carbon dioxide produced in the fuel combustion process.

4. The method of claim 1, wherein 200-900 kg, preferably 400-600 kg, and more preferably 450-550 kg of biomass is produced in the biomass cultivating process (2) per 1000 kg of carbon dioxide (4) introduced into the biomass cultivating process.

5. The method of claim 1, wherein 0-500 kg, preferably 0-100 kg, and more preferably 40-80 kg of fuel (11) is introduced into the fuel combustion process (1) in addition to the biogas produced in the biogas production process (3) and introduced into the fuel combustion process per 1000 kg of carbon dioxide produced in the fuel combustion process.

6. The method of claim 1, wherein the stream of flue gas (4) further comprises NO, NO.sub.2 and/or N.sub.2.

7. The method of claim 1, wherein the biogas (7) comprises methane, carbon dioxide or a combination comprising methane and carbon dioxide.

8. The method of claim 1, wherein the biomass (5) is selected from a group of algae, water grass and a combination thereof.

9. The method of claim 1, wherein the method comprises introducing at least part of fermentation sludge (13) formed in the biogas production process (3) into the biomass cultivating process (2).

10. The method of claim 1, wherein the method comprises introducing growing media (8) comprising waste water into the biomass cultivating process (2).

11. The method of claim 1, wherein the fuel introduced into the fuel combustion process comprises coal.

12. The method of claim 1, wherein the method comprises recovering water (10) from the fuel combustion process (1).

13. The method of claim 1, wherein the method comprises introducing carbon dioxide (14) into the biomass cultivating process (2) in addition to the carbon dioxide contained in the stream of flue gas (4).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings, which are included to provide a further understanding of the invention and constitute a part of this specification, illustrate embodiments of the invention and together with the description help to explain the principles of the invention. In the drawings;

(2) FIG. 1 is a flowchart illustrating one embodiment of a method according to the present invention; and

(3) FIG. 2 is a schematical illustration of one embodiment of the apparatus according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(4) Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

(5) The description below discloses some embodiments of the invention in such a detail that a person skilled in the art is able to utilize the invention based on the disclosure. Not all steps of the embodiments are discussed in detail, as many of the steps will be obvious for the person skilled in the art based on this specification.

(6) For reasons of simplicity, item numbers will be maintained in the following exemplary embodiments in the case of repeating components.

(7) In step S1 of an embodiment of the method according to FIG. 1, there is produced energy as presented in step f in a fuel combustion process, taking place in a fuel combustion device, which is a boiler or a furnace, of step S1 by burning fuel, e.g. fossil fuel such as coal. As a result of the combustion process flue gas comprising carbon dioxide is produced. The stream of flue gas is introduced in step a into a biomass cultivating process, where the flue gas takes part in the photosynthesis of biomass, e.g. algae.

(8) As a result of the biomass cultivating process in step S2 biomass is produced, at least part of which is introduced in step b in FIG. 1 into step S3 comprising a biogas production process. Further, as a result of the biomass cultivating process in step S2 oxygen is produced, at least part of which is introduced into the fuel combustion process as presented in step c in FIG. 1.

(9) The biomass introduced into the biogas production process is used for producing biogas in step S3. At least part of the biogas produced in step S3 is introduced into step S1 comprising the fuel combustion process as presented in step d in FIG. 1.

(10) As a result of the recycling of materials presented in FIG. 1, the amount of fossil fuel needed to be introduced in step e into the fuel combustion process for producing energy in an efficient manner is decreased. Also the amount of combustion air to be introduced in step g into the fuel combustion process is decreased.

(11) Obviously the method according to the present invention may comprise further steps, which will be obvious for the skilled person based on what is presented in this patent application.

(12) The method according to the present invention can be realized by means of an apparatus illustrated schematically by the block diagram in FIG. 2. The apparatus 15 of FIG. 2 comprises a fuel combustion device 1, e.g. a boiler, by which fuel, e.g. fossil fuel such as coal, is combusted for producing energy at a power plant. The apparatus 15 of FIG. 2 further comprises means 4 for introducing or directing a stream of flue gas produced by a fuel combustion process at the fuel combustion device 1 into a biomass cultivating device 2, where the production of biomass and oxygen takes place.

(13) At least part of the biomass produced at the biomass cultivating device is directed into a biogas reactor 3 by means 5 for introducing biomass into a biogas reactor 3. The biomass introduced into the biogas reactor 3 takes part in the production of biogas.

(14) At least part of the biogas produced in the biogas reactor is introduced into the fuel combustion device 1 by means 7 for introducing biogas into the fuel combustion device.

(15) The apparatus 15 presented in FIG. 2 further comprises means 13 for introducing at least part of the fermentation sludge produced in the biogas reactor 3 into the biomass cultivating device 2.

(16) The biomass cultivating device 2 is further connected to means 14 for introducing carbon dioxide in addition to the carbon dioxide directed from the fuel combustion device into the biomass cultivating device and means 8 for introducing e.g. waste water into the biomass cultivating device 2.

(17) In FIG. 2 is also illustrated means 6 for introducing at least part of the oxygen produced in the biomass cultivating device 2 into the fuel combustion device 1.

(18) The apparatus of FIG. 2 further comprises means 9 for introducing combustion air into the fuel combustion device, means 11 for introducing fuel into the fuel combustion device, means 10 for recovering water from the fuel combustion device and means 12 for recovering the energy produced in the fuel combustion device.

Example 1

(19) By applying the method in accordance with the present invention, there was manufactured, with an apparatus in accordance with the present invention, energy, i.e. primary energy, in a fuel combustion process by burning coal as fossil fuel in a boiler. The flue gases produced during the combustion process were recovered and introduced into a photobioreactor, where they took part in the growing of algae and the production of oxygen based on the photosynthesis of the algae. The photobioreactor used in this example was a glass tube reactor having a tube diameter of about 100 mm, a tube length of about 900 m and a reactor volume of about 30 m.sup.3.

(20) The algae used in this example were of Closterium species. Further, nutrients needed for the growth of algae was received e.g. from municipal waste water, which was used as growing media for the algae. As the algae grew it collected the nutrients from the waste water and thus simultaneously the waste water was cleaned. Further, the algae absorbed carbon dioxide and nitrogen while growing and simultaneously produced oxygen. Of each carbon dioxide molecule, one carbon was taken to the biomass, i.e. the algae growing, and two atoms of oxygen were released.

(21) The oxygen produced by the algae in the biomass cultivating process was introduced into the boiler while at least part of the algae produced was introduced into a biogas reactor. The algae produced in the photobioreactor were centrifuged prior to being introduced into the biogas reactor such that the solids content increased from about 0.2% to about 1.5-2%.

(22) The biogas reactor type used in this example was Upflow Anaerobic Sludge Blanker (UASB), which is a device designed to treat liquids having a very low content of solid matter. The retention time was 1-2 days, which allowed the treatment of large quantities of liquid or sludge with reasonably sized reactor. The reactor volume was in this example about 5 m.sup.3.

(23) Part of the fermentation sludge formed in the biogas reactor was returned by pumping it into the photobioreactor and the biogas, including methane and carbon dioxide, formed was introduced into the boiler. The biogas introduced into the boiler was used as fuel for the coal-fired boiler thus replacing at least 50% of the coal needed if the recycling of materials in accordance with the present invention would not have been performed.

(24) As the combustion products of methane were carbon dioxide and water and as the water produced required almost half of the oxygen produced in the photobioreactor and introduced therefrom to the boiler, additional amount of oxygen was needed to replace the oxygen lost in form of water. Therefore, an additional amount of oxygen was introduced into the boiler in order to ensure an efficient combustion process.

(25) Nitrogen accumulation was prevented during the process by using a suitable nitrogen removal device.

(26) In a traditional coal-fired power plant about 350 kg of coal is needed for producing about 2.8 MWh (1.1 Mwh.sub.e) of energy and simultaneously about 1000 kg of carbon dioxide. In this example in accordance with the present invention, where materials were recycled during the production of energy only about 60 kg of coal was needed to be introduced into the boiler in addition to the recycled materials for producing the same amount of energy. In the similar manner 1000 kg of carbon dioxide was produced. The introduction of 1000 kg of carbon dioxide and 1250 kg of N.sub.2 into the photobioreactor produced about 770 kg of O.sub.2, which was recycled into the boiler, and about 500 kg of algae, which were introduced into the biogas reactor. From the 500 kg of algae about 230 kg of methane and about 120 kg of carbon dioxide were formed in the biogas production process and introduced into the boiler. About 330 kg of additional oxygen and about 1250 kg of nitrogen gas, per 1000 kg of carbon dioxide produced in the fuel combustion device, were also introduced into the boiler. The fuel combustion process of example 1 resulted in recovering about 370 kg of water from the boiler per 1000 kg of carbon dioxide produced in the fuel combustion device.

Example 2

(27) By applying the method in accordance with the present invention, there was manufactured, with an apparatus in accordance with the present invention, energy, i.e. primary energy, in a fuel combustion process by burning fuel in a boiler. The flue gas comprising carbon dioxide and nitrogen produced during the combustion process were recovered and introduced into a photobioreactor, where they took part in the growing of algae and the production of oxygen based on the photosynthesis of the algae. The photobioreactor used in this example was a glass tube reactor having a tube diameter of about 100 mm, a tube length of about 900 m and a reactor volume of about 30 m.sup.3. Further, in addition to the carbon dioxide introduced into the photobioreactor with the stream of flue gas, additional carbon dioxide was introduced into the photobioreactor.

(28) The algae used in this example were of Spirulina species. Further, nutrients needed for the growth of algae were received e.g. from municipal waste water, which was used as growing media for the algae. Further, the algae absorbed carbon dioxide and nitrogen while growing and simultaneously produced oxygen.

(29) The oxygen produced by the algae in the photobioreactor was introduced into the boiler while at least part of the algae produced was introduced into a biogas reactor. However, the algae produced in the photobioreactor were centrifuged prior to being introduced into the biogas reactor such that the solids content increased from about 0.2% to about 1.5-2%.

(30) The biogas reactor type used in this example was Upflow Anaerobic Sludge Blanker (UASB). The retention time was 1-2 days and the reactor volume was in this example about 5 m.sup.3.

(31) Part of the fermentation sludge formed in the biogas reactor was returned by pumping it into the photobioreactor and the biogas, including methane and carbon dioxide, formed was introduced into the boiler. The biogas introduced into the boiler was used as a fuel for fuel combustion process.

(32) In a traditional coal-fired power plant about 350 kg of coal is needed for producing about 2.8 MWh (1.1 Mwh.sub.e) of energy. Simultaneously about 1000 kg of carbon dioxide is formed. In this example the introduction of 1000 kg of carbon dioxide and 1250 kg of N.sub.2 with the flue gas and of 430 kg of additional carbon dioxide into the photobioreactor produced about 1100 kg of O.sub.2, which was recycled into the boiler, and about 770 kg of algae, which were introduced into the biogas reactor. From the 770 kg of algae about 354 kg of methane and about 185 kg of carbon dioxide were formed in the biogas production process and introduced into the boiler, where the biogas was used as fuel for the combustion process.

(33) It is obvious to a person skilled in the art that with the advancement of technology, the basic idea of the invention may be implemented in various ways. The invention and its embodiments are thus not limited to the examples described above; instead they may vary within the scope of the claims.