FI126249B - Combustion procedure and incinerator - Google Patents

Description

COMBUSTION METHOD AND BURNER

Background of the Invention

Field of the Invention

The present invention relates to a method for enhancing the combustion process by enabling combustion that operates with less entropy generation than conventional combustion. The invention also relates to a burner formed of tubular films suitable for use in said method.

Description of the Prior Art

There has been relatively little research on exergy losses in combustion. Conventional thermal combustion processes are constant pressure combustion (as in gas turbine plants) and constant volume combustion. The latter has a better efficiency when constant pressure combustion has the disadvantage of high entropy generation and a corresponding exergy loss, which, depending on the fuel and air factor, is about half the fuel calorific value. The ideal incineration is the so-called. isentropic combustion process with no entropy generated at all. Thus, electrochemical combustion, or fuel cell for improved efficiency in constant volume combustion, is closest to the idea of the present invention.

Conventional oxygen combustion uses cryogenic oxygen from the air and the cooling is effected by recycling carbon dioxide through heat exchangers. The device of the invention enables combustion that operates with less entropy generation, i.e. closer to equilibrium than conventional combustion.

The use of so-called oxygen films in combustion has also been studied (e.g., US 2008/0141672) and it has been found that this film can reduce the amount of energy required for combustion. These oxygen films utilize the ability of semipermeable membranes to carry oxygen ions. The equilibrium state of the combustion reaction is achieved by the difference in oxygen pressure between the different sides of the film. The reaction is carried out under conditions designed to separate oxygen from other combustion air components.

EP 1172135 and 2026004 disclose the use of a corresponding oxygen film in combustion which avoids the passage of nitrogen through the membrane, since the presence of nitrogen would prevent the production of a product rich in carbon dioxide. The publications also consider that an efficient process cannot be achieved by transporting nitrogen because it consumes energy to heat the nitrogen.

Hash im S.M. et al. (Current Status of Ceramic-Based Membranes for Oxygen Separation from Air, Advances in Colloid and Interface Science 160 (2010) 88-100), in turn, addresses the materials and development of such oxygen films.

EP1040861A1 relates to a combustion process for transporting oxygen ions through a semipermeable burner film.

Thus, with the aid of a known oxygen film, pressurized oxygen combustion can be realized. The problem is the extremely high combustion temperatures, which makes the process as such difficult to apply to thermal power processes.

The solution to this problem is the membrane of the present invention, which, in addition to oxygen, is permeable to nitrogen gas, whereby the nitrogen acts as a condenser and at the same time pressurizes as it passes through the membrane itself.

Thus, in the present invention, both oxygen and nitrogen gas in the air are transported from the combustion air to the pressurized space, which is achieved without the work required by the compressor, thereby significantly improving the efficiency of the thermal power plant connected to the combustion process.

Brief Description of the Invention

It is an object of the present invention to provide a new combustion process which is more efficient than known solutions.

In particular, it is an object of the present invention to provide a novel combustion process in which entropy generation can be minimized with respect to the use of prior art oxygen films.

The present invention thus relates to a process by which oxygen and nitrogen of combustion air are transported through a membrane into a space pressurized with fuel gas by a combustion reaction without a compressor. The method can be implemented with a burner made of tubular films. The tubular membrane is a ceramic coating conducting oxygen and nitrogen ions, which is disposed on the inner surface of a porous ceramic capillary tube serving as a support structure.

Thus, the oxygen ions can be transported to the pressurized combustion chamber without the aid of a compressor.

Preferably, both the combustion air and the nitrogen gas needed for cooling can be introduced into the pressurized state without the use of a compressor.

More specifically, the method of the present invention is characterized by what is set forth in the characterizing part of claim 1.

The burner of the present invention is characterized in what is set forth in the characterizing part of claim 11.

The present invention achieves numerous advantages over prior art solutions. The energy content of the fuel produces more energy suitable for power generation (exergy) and, in the case of internal combustion engines, more mechanical energy than known combustion solutions. The difference with some of the oxygen burners in use is that here oxygen is drawn from the air through the membrane, while conventional oxygen burning uses oxygen separated from the air by house technology. In addition, nitrogen gas is now used to lower the high temperature of the combustion chamber.

Brief Description of the Drawings

Figure 1 is a schematic representation of the known, so-called. oxygen membrane (oxygen-carrying membrane), a method of determining the oxygen content of an oxygen membrane by measuring the voltage at which the partial pressure of oxygen over the membrane can be calculated using the Nernst formula.

Fig. 2 is a schematic representation of a so-called embodiment according to the invention. 2A illustrates the principle of providing an electric field within the membrane by oxidation of the fuel gas, and FIG. 2B illustrates the flow of oxygen and nitrogen ions in the membrane.

Figure 3a is a graphical representation of a conventional diesel engine turbocharged process and Figure 3b a corresponding process with an external self-pressurized diaphragm process according to the invention.

Figure 4A is a graphical representation of the ideal combustion in a gas turbine process in which the combustion of the carbon occurs isentropically and the heat released in the combustion reaction is converted into work in a gas turbine, i.e. a self-pressurized combustion process with 5 ^ - = 0 (Theoretical thermal combustion). Figure 4B shows a preferred embodiment of the process of Figure 4A which also shows ceramic hollow fiber films of the burner.

In the figures the following reference numbering is used: 1 burner 2 combustion chamber 3 semipermeable burner film 31 perovskite (oxygen selective catalyst) 4 tubular support structure (capillary tube) 5 turbine 51 gas turbine 6 generator

Detailed Description of Preferred Embodiments of the Invention

The present invention relates to a combustion process designed to produce an exhaust gas stream at the highest possible pressure. This combustion method employs a burner 1 comprising one or more parallel tubular, semipermeable burner films 3 which in turn form one or more tubular pressurized combustion chamber 2. The combustion chamber 2 is supplied with fuel, preferably at the pressure of the combustion chamber 2, and simultaneously form, pass through the burner diaphragm 3 to the combustion chamber 2 without the aid of a compressor. The driving force for the transport of oxygen and nitrogen ions is the internal electric field of the burner film 3 as a result of the combustion reaction.

An embodiment of the invention also relates to a method of transporting nitrogen ions through a burner membrane 3 which passes through the oxygen ions of burner 1, wherein oxygen ions are transported through burner film 3 by an oxygen pressure difference through combustion to provide an electric field to burner film 3 nitrogen ions through the same burner film 3. The difference in oxygen pressure also affects the transport of nitrogen ions.

The invention further relates to a burner 1 for use in a combustion reaction, which burner 1 comprises one or more parallel-placed tubular combustion spaces 2 each containing a semipermeable burner film 3 and a porous ceramic support structure 4 surrounding it. This burner 1 can be utilized in the above process.

The invention seeks to improve the energy efficiency of combustion processes by reducing entropy generation and exergy losses, respectively. "Exergy" refers to the portion of energy that is capable of working, while "entropy" is used to describe the distribution of energy and matter within a system, such as in combustion space 2 and its surroundings. Reducing entropy generation (here, reducing disorder and directing matter to the desired state), as is known, requires external work / force, and is not accomplished with perfect efficiency. However, the invention seeks to optimize this efficiency.

Combustion air contains oxygen and nitrogen, and optionally other components. Preferably, the combustion air contains substantially the same components and at substantially the same concentrations as the outdoor air, i.e., about 78% by volume of nitrogen and about 21% by volume of oxygen.

The tubular burner film 3 is a material permeable to oxygen and nitrogen ions, such as yttrium-stabilized zirconia (YSZ). Particularly preferably, the burner film 3 is doped with nitrogen. The perovskite phase 31, which is particularly preferably placed in the membrane material, allows the electrons to be transported within the material, whereby the voltage difference between the anode and the cathode can be transferred to the electrolyte (which here is a membrane material such as YSZ). This burner film 3 may be disposed on the inner surface of a porous tube 4, such as a ceramic capillary tube, which acts as a support structure. The capillary tube 4 serving as the support structure is preferably porous zirconia.

Thin hollow tubes 4 are formed from these materials. Preferably, a plurality of these tubes 4, for example 3 to 1000 pieces, in particular 5 to 100 pieces, are bundled together and formed into a package (hereinafter referred to as a membrane tube system).

The capillary tube 4 serving as a support structure preferably has a wall thickness of 0.1 to 0.5 mm and a diameter of 2 to 4 mm. The thickness of the burner film 3 is preferably from 1 µm to 100 µm.

However, the size of the film burner 1 may be varied to suit each application. The reaction area is relatively easy to pack, for example, by means of tubes 4 in diameter to a very small volume.

The function of the prior art oxygen film is illustrated in Figure 1. Here, a mixture of zirconia and yttrium oxide (ZrCl 2 YiCF 92: 8), i.e. yttrium stabilized zirconia (YSZ, 8%), is used as the oxygen film material. The operation of the semi-permeable membrane 3 according to the invention is illustrated in Figures 2A and 2B. Herein, yttrium-stabilized zirconia (YSZ), 8%, is used as the membrane material, which membrane 3 contains the perovskite phase 31 and is doped with nitrogen (e.g. 7.5%).

The membrane material used in the invention resembles the materials used in high temperature fuel cell (SOFC) electrolytes, which aim to achieve a high potential difference between the electrodes conducting the membrane (because the work is taken out here) and a small one over electrolyte (because it is all loss).

However, in the invention, the situation is the opposite of the conventional use of SOFC materials. The goal is to make the internal potential difference across the membrane material electrolyte (YSZ) large and use it to pump oxygen and nitrogen ions. Preferably, the electron-conducting perovskite 31 is disposed in the well structure, which by closing the anode and cathode transfers the potential difference to the electrolyte (YSZ) as shown in Figure 2A. Compression of the combustion air into the combustion chamber 2 takes place in the form of ions using an electric field, according to the following basic thermodynamic phenomena: 1 °. In one embodiment of the invention, oxygen gas is fed to a low pressure 2-pressure combustion chamber 2 in an O "form of oxygen ion that allows oxygen delivery without reflux (Fig. 2A). At sufficiently high temperature (e.g., 900 ° C), ceramic )) begins to conduct fairly well oxygen ions (as well as nitrogen ions) At the burn site, on the surface of the burner film 3, some of the oxygen reacts directly with the fuel and some of the oxygen gasses and then reacts with the fuel. according to a simplified view, can be estimated by electrochemical oxidation reactions (1) and (2) (Figure 2A):

(1)

The resulting electric field E = U / As, of the order of 104 to 106 V / m, causes a force on the oxygen ions to draw oxygen towards the reaction surface, even though it is in a pressurized state.

2 °. Electrons released from oxygen ions

(2) migrate to the oxygen uptake site, i.e., to the other surface of the burner film 3, along a separate phase (perovskite 31) which has sufficient electrical conductivity and prevents electron recombination. Thus, the electrons are positioned over the burner film 3 at approximately the same potential and the potential difference is created in the film material YSZ.

3 °. Nitrogen doped ceramic burner film 3 (e.g. 7.5% YSZ) also allows the _ nitrogen ions (N ″) to pass through the crystal structure of the film material. as its partial pressure in the combustion air. Nitrogen gasification can occur through the ionization of oxygen according to the following equation (Figure 2A):

(3)

The nitrogen gas obtained in the combustion chamber 2 cools the exhaust gases, whose temperature in the pure oxygen combustion remains very high.

In the method of the invention, temperature control is based on the correct mutual flow of the combustion process within the fibers and the combustion air. These provide a uniform temperature distribution of the burner film 3 so that the tube has an operating temperature throughout the tube that is high enough to achieve good combustion. Preferably, the temperature of the combustion chamber 2 is maintained in the range of 500-1000 ° C, preferably near 900 ° C. This will further minimize entropy generation.

In the burner according to the invention, the porous ceramic support structure surrounding the burner film 3 is preferably formed of nanoparticles. These nanoparticulate support structure tubes 4 achieve very high strength even though the structure 4 is porous. Thus, relatively high pressures can be allowed inside the support tube 4 for strength. The membrane tube system should withstand pressure differences as large as 15 bar, or higher, such as up to 20 bar.

The operation of the burner film 3 according to the invention is controlled by reacting oxygen ions on the combustion surface with the fuel (formula (2), thereby creating a potential difference between the combustion surface and the oxygen receiving surface. Thanks to the perovskite phase 31, the potential difference is transferred to the electrolyte or YSZ structure. 3 a force driving oxygen into the combustion surface, as a result of which oxygen flows into the combustion chamber 2.

Nitrogen gas also begins to flow into the combustion chamber 2, because the nitrogen gas is also ionized at the high temperature of the burner film 3 and the electric field in the electrolyte (YSZ) draws nitrogen ions towards the combustion surface.

Thus, according to a preferred embodiment of the invention, the burner 1 according to the invention operates by introducing the fuel into a tubular ceramic combustion chamber 2 at one end while the combustion air is introduced into a space surrounding the tubular ceramic material (or center of the diaphragm system or tube package) uniformly, whereby the oxygen and nitrogen of the combustion air pass through the material of the support structure 4 and the burner diaphragm 3 and thus come into contact with the fuel, whereby the reaction is effected. As the temperature rises, the pipe material begins to conduct better oxygen and nitrogen.

According to a preferred embodiment of the invention, the combustion air is introduced outside the tubular structure 4 under atmospheric pressure. The gaseous fuel (such as CH4 (g)), in turn, is introduced at elevated (gas grid or fuel carburettor) pressure inside the tubular film 3 at elevated temperature (higher than the gasification temperature of the fuel). Inside the membrane 3, on its surface, combustion also takes place, whereby the fuel reacts to carbon dioxide and water. At high temperatures, the oxygen and nitrogen molecules first pass through the porous support material and then, in ionized form, to the semipermeable burner membrane 3. The fuel, in turn, is not capable of significantly permeating the membrane 3.

The exhaust gases generated in the oxidation of the fuel, i.e. the combustion reaction, exit at one end (outlet) of the tubular film 3 at approximately the same pressure as where the fuel gas is introduced at the other end (inlet) of the tube. Because the amount of exhaust gas exiting is greater than the amount of fuel gas, the gas flow rate inside the membrane tube increases in the direction of the tube flow.

The burner 1 according to the invention can be utilized in a combustion system which, in addition to the burner 1, includes fuel as its feeder systems and an exhaust gas treatment system.

The following non-limiting examples illustrate the invention and its advantages.

eXAMPLES

Example 1 - Exergy Losses of Combustion in the Internal Combustion Engine Process In this example, we investigate a conventional internal combustion engine (a turbocharged diesel engine).

The following can be derived from the theoretical efficiency of the internal combustion engine:

where Gm corresponds to the generation of entropy throughout the internal combustion process and - [H (BS) - H (A)] is the calorific value corresponding to isentropic combustion.

In the internal combustion engine of Example 3a, the combustion process accounts for about 79% of the total exergy loss. The corresponding overall efficiency of the engine when driving is approximately 48%. Assuming that the exergy loss of combustion can be eliminated, the efficiency would be about 89% (Figure 3b).

The thermodynamic efficiency of this engine is subject to the same limitations as the fuel cell efficiency (see Figure 3).

Comparative Example 1 - Combustion Losses in a Conventional Gas Turbine Process

The combustion exergy losses are also crucial to the gas turbine process. A compressor is commonly used to bring combustion air into the combustion chamber. In the exemplary case, the compressor draws 54 MW of shaft power from the gas turbine. The exhaust gases entering the gas turbine are at a temperature of 1100 ° C and a pressure of 11 bar. The total power of the gas turbine is 94 MW, of which the power transmitted to the generator is 94 - 54 = 40 MW.

Example 2 - Exergy Losses of Combustion in an Ideal Gas Turbine Process

By sufficiently reducing the entropy loss of the combustion of Comparative Example 1, sufficient combustion pressure of 11 bar is achieved in the combustion chamber, eliminating the need for a compressor and transferring the entire 94 MW to the generator. Figure 4A is a plan view of an ideal gas turbine process with an isentropic combustion process corresponding to a very high theoretical self-pressure (746 bar), and Figure 4B shows a corresponding process according to a preferred embodiment.

Claims (11)

A combustion process in which oxygen is withdrawn from the air space of the burner (1) and wherein the oxygen ions are conveyed through a semipermeable burner membrane (3) conducting oxygen burners (1) to the combustion chamber (2), characterized in that ) an electric field for transporting oxygen and nitrogen ions through the burner diaphragm (3) and the combustion reaction to convey oxygen through the semipermeable membrane (3) to a pressurized combustion chamber (2) having a total combustion gas pressure higher than atmospheric pressure and wherein the combustion chamber (2) the pressure is achieved by the combustion reaction, wherein the partial pressure of the oxygen in the combustion chamber (2) on the surface of the burner diaphragm (3) is adjusted according to the equilibrium condition of the combustion reaction by the partial pressure of oxygen in the air A method according to claim 1, characterized in that a structure conducting electrons and oxygen ions, such as perovskite (31), is used as the burner film (3). Method according to one of Claims 1 or 2, characterized in that one or more parallel tubular semipermeable burner films (3) are used as the burner film (3) and thus form the combustion chamber (2). Method according to one of Claims 1 to 3, characterized in that the temperature of the film (3) is kept constant throughout the combustion chamber (2), preferably between 500 and 1000 ° C, preferably at about 900 ° C. Method according to one of Claims 1 to 4, characterized in that the pressure in the non-pressurized air space is maintained at about 1 bar, and the pressure in the pressurized combustion chamber (2) is maintained at a higher level. Method according to one of Claims 1 to 5, characterized in that the pressure in the combustion chamber (2) is adjusted to a level higher than 1 bar, preferably 15 to 200 bar, and the pressurized exhaust gases are preferably supplied to a piston engine where the exhaust gases perform extrusion. Method according to one of Claims 1 to 6, characterized in that the pressure in the combustion chamber (2) is adjusted to a level higher than 1 bar, preferably 15 to 200 bar, and the pressurized exhaust gases are preferably introduced into a gas turbine (51). Method according to one of Claims 1 to 7, characterized in that the tubular film used as the burner film (3) is made of a ceramic material, wherein the fuel is oxidized on the outer surface of the film with oxygen released from the combustion air through the tubular film (3). Method according to one of Claims 1 to 8, characterized in that the combustion air is introduced inside the tubular film used as the burner film (3) without being pressurized at atmospheric pressure. Method according to one of Claims 1 to 9, characterized in that the fuel is introduced outside the tubular film used as the gaseous and pressurized burner film (3). A burner (1) for use in the combustion reaction of a process according to any one of claims 1 to 10, characterized in that it comprises one or more tubular membranes (3) permeable to oxygen and nitrogen forming a combustion chamber (2) and a porous ceramic support layer (4) surrounding it.