Patent Application
20190388834
It has been considered for years that climate change is caused by the greenhouse gas carbon dioxide. At the initiative of the Intergovernmental Panel on Climate Change, considerable efforts are underway to reduce CO2 emissions in order to limit the rise of global temperatures to a maximum of two degrees celsius by the end of this century. They not only call for reducing emissions, but also to start actively removing CO2 from the atmosphere in about 2030. Experts consider it to be very critical here to place CO2 under pressure in underground chambers. Chemists even have a negative view of storing CO2 in ammonia to produce nitrogenous fertilizers.
Since solar cells only function in daylight and good weather, and wind turbines do not rotate without wind, coal or natural gas are still considered necessary to produce electricity. Meanwhile, to reduce CO2 emissions, it is intended to generate power by operating solar cells and wind turbines to an extent that would make it possible to shut down coal-fired power plants. Even natural gas-processing power plants, which, until now, have been considered to be non-polluting, would be taken off of the grid.
Carbon dioxide is produced in large quantities in fossil fuel-fired combustion plants, such as gas-fired, coal-fired and brown coal-fired power plants, cement plants, cruise ships, container ships and waste incineration plants. For the most part, the flue gases, which are produced when coal or natural gas is used to generate power, contain very hot nitrogen, large quantities of carbon dioxide, and nitrogen oxides that are present in small amounts, but are classified as respiratory toxins, as well as soot particles.
It is known to use CO2 for the combustion of monosilane: SiH4+CO2=2 H2O+SiC. The German Patent Application DE 44 37 524 A1 discusses reacting silicon-hydrogen compounds with nitrogen and/or nitrogen compounds at elevated temperatures in a combustion chamber. Furthermore, the German Patent Application DE 101 45 115 A1 describes combusting silicon-containing fuels, such as silane oils and powdered silicon in a combustion chamber to drive a combustion engine.
There is a need to change the manner in which power is generated with the aid of natural gas or coal, so that the combustion gases containing heated nitrogen oxide, in particular traces of nitrogen oxides, as well as hot carbon dioxide, are not discharged into a chimney. It is, therefore, an object of the present invention to provide a method for removing carbon dioxide from flue gases.
The objective is achieved by the features of the independent claims. Advantageous embodiments are described in the dependent claims.
The method according to the present invention for the post-combustion of flue gases provides that
The term “flue gas” may also be understood to be a gaseous combustion product that forms during the industrial combustion of fuels, which, in particular contains nitrogen, carbon dioxide and traces of nitrogen oxides, and may contain solid particles, such as fly ash and soot. In the present case, a “post-combustion” of flue gases is understood to be a further combustion of a flue gas derived from a primary combustion.
In such a post-combustion method, in which silane or silicon and hydrogen or a hydrogen-releasing compound are used, the energy of the hot gases is not conducted by a chimney into the atmosphere, rather may be harnessed by a further combustion. In particular, the method according to the present invention makes it possible for carbon dioxide to be combusted in exhaust gases with the aid of liquid silanes. It is thus possible to achieve that the flue gases CO2 and NOx of the exhaust stream, which are considered to be toxic, are combusted by fossil fuel-operated plants.
The silane may be a liquid or solid silane, in particular a liquid silane. A preferred specific embodiment of the present invention provides that the silane be selected from the group that includes pentasilane Si5H12, hexasilane Si6H14, heptasilane Si7H16, octasilane Si8H18, nonasilane Si9H20, decasilane Si10H22, undecasilane Si11H24, dodecasilane Si12H26, tridecasilane Si13H28, tetradecasilane Si14H30 and/or pentadecasilane Si15H32.
Instead of a higher silane, silicon and hydrogen or a hydrogen-releasing compound may be fed to the flue gas for post-combustion. Ammonia may be used, for example, as a hydrogen-releasing compound. Silicon may be present in powdered or amorphous form. Silicon powder and ammonia (NH3) may be used as a source of hydrogen, for example. In place of silicon powder, amorphous silicon, which is expediently alkali-etched, may be used.
A preferred specific embodiment provides that the silane or the silicon and hydrogen or the hydrogen-releasing compound be fed to a post-combustion device of a combustion system for fossil fuels, such as coal. Prior to the feeding, the flue gas may be scrubbed to remove solid particles, such as fly ash and soot, in particular contained therein.
It is assumed that the hydrogen of the silane chain attacks the oxygen atoms of the carbon dioxide and combusts them to produce water, that the nitrogen reacts with the silicon to form silicon nitride, and that the carbon bonds with the silicon to form silicon carbide. Thus, water, as well as silicon carbide and silicon nitride are formed as post-combustion products. The products, such as silicon carbide, silicon nitride and water, formed by post-combusting the nitrogen, nitrogen oxide and carbon dioxide contained in the flue gas, with the silane or silicon and hydrogen or the hydrogen-releasing compound may be advantageously reused.
The post-combustion may be coupled to a primary power-generation combustion process, in particular a fossil combustion process. In the first place, it is advantageously possible to reduce CO2 emissions in exhaust streams of power plants based on fossil fuel combustion.
A further aspect of the present invention provides that the steam produced by the combustion process be used, for example, to generate power via a turbine. Much greater amounts of heat are generated in the post-combustion, in a waste gas combustion chamber, for example, than in the primary combustion of the fossil fuels. Thus, the post-combustion may provide additional combustion heat. Implementing the post-combustion method may advantageously make it possible to harvest thermal energy. Therefore, at the same power output, it is possible to reduce the amount of fossil fuel to produce the steam pressure needed to operate a turbine provided in a combustion system. In particular, in a combustion system for fossil fuels, in which a turbine for generating power is already provided, the full power output thereof may be harvested, and a second turbine may also be operated for an increased power generation. Therefore, it stands to reason that the need for the primary combustion of fossil fuels may ultimately be completely eliminated, and, for example, that only liquid silane be combusted.
The silicon carbide and silicon nitride compounds formed as post-combustion products constitute a sought-after recyclable material or material and may be collected and reused. Both materials have the diamond hardness 9. Silicon carbide has a diamond structure, while silicon nitride is substantially resistant to heat or chemical influences.
Another aspect of the present invention provides for using the silicon carbide and/or silicon nitride produced using the method according to the present invention in the construction industry, in particular in concrete construction. Thus, a mixture of the silicon carbide and silicon nitride obtained may be used in the construction industry. Mentioned here exemplarily is the use in concrete construction. Concrete, whether in building or road construction, is subject to ever greater loads. The loading capacity of mix concrete may be increased here by admixing silicon carbide and silicon nitride thereto.
A further object of the present invention relates to a device for implementing the inventive method for the post-combustion of flue gases, the device featuring a post-combustion device or post-combustion chamber that is adapted for combusting flue gas. Combustion systems for fossil fuels may, in particular be fossil fuel-fired combustion plants, such as gas-fired, coal-fired and brown coal-fired power plants, waste-incineration plants, cement plants, cruise ships, and container ships. The device may be a combustion system for fossil fuels, such as coal. The device may, in particular be a power plant for generating power using coal or natural gas. A preferred specific embodiment provides that the silane or the silicon and hydrogen or the hydrogen-releasing compound be fed to the post-combustion device, for example of a combustion system for fossil fuels, such as coal. Prior to the feeding, the flue gas may be scrubbed to remove solid particles contained therein, in particular fly ash and soot.
Specific embodiments of the device provide that it have a chamber adapted for containing silanes, for example, a tank and/or one or a plurality of chambers for containing silicon and hydrogen or a hydrogen-releasing compound.
An exemplary embodiment of the present invention will be described in greater detail below with reference to the drawings. In the drawing,
To illustrate the post-combustion processes,
Such a specific embodiment of a combustion system, where combustion chamber 1 for fossil fuels and waste gas combustion chamber 8 are immediately proximate to one another, may be implemented in a new construction of combustion systems. The dense configuration of the combustion chambers facilitates the feeding of the flue gases. In particular, the utilization of the combustion heat from the silane combustion to produce steam is also simplified; respectively, a utilization of this energy in a tank 2, in which water is co-heated by the combustion of fossil fuels and silane, is made possible.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2017 103 701.2 | Feb 2017 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2018/054567 | 2/23/2018 | WO | 00 |
