EP1926935A2

EP1926935A2 - Steam generator, power plant comprising a steam generator and method for operating a steam generator

Info

Publication number: EP1926935A2
Application number: EP06792951A
Authority: EP
Inventors: Jürgen Karl
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2005-09-05
Filing date: 2006-08-22
Publication date: 2008-06-04
Also published as: WO2007028709A3; WO2007028709A2

Abstract

The invention relates to a steam generator (2), which is heated by the combustion of fuel containing carbon according to the Oxyfuel-method. The aim of the invention is to obtain a particularly high energetic degree of efficiency and to also maintain low residue emissions and at the same time keeping the construction and operation thereof simple and economical and by reverting to suitable fuelling concepts. The inventive steam generator (2) comprises a fluidised bed combustion chamber (8) which is cooled by means of a number of immersion heating surfaces (24) and which comprises a number of oxygen inlet openings (16) which are arranged in the region of the base of the combustion chamber, wherein pure oxygen (O2) is guided via the fluidised bed combustion chamber (8), and is effective as an oxidation agent and as a fluidisation agent and is produced by an associated air separation system, when in operation. The fluidised bed combustion chamber (8) is fitted such that it can work with a stationary fluidised bed.

Description

description

Steam generator, power plant with a steam generator and method for operating a steam generator

The invention relates to a steam generator which is heated by the combustion of a carbonaceous fuel according to the oxyfuel process. The invention further relates to a power plant with such a steam generator and to a method for operating a steam generator.

Efforts to limit CO ₂ -related climate change have led to a whole range of technical options for the implementation of low-emission, fossil-fired thermal power plants. Comparisons of power plant concepts of different types with a CO ₂ separation have shown that the so-called oxyfuel processes have particularly favorable properties from a technical point of view and the expected efficiency. In addition, market readiness, investment costs and operating costs are favorable.

In the oxyfuel process, instead of nitrogen-containing combustion air, an oxygen stream of high purity (up to 99, 9%) is used as an oxidant in the combustion chamber of a

Steam generator introduced, which was previously extracted with removal of the nitrogen content in an associated air separation ^¬ plant from sucked ambient air. Since ^¬ fall through as the combustion products from the combustion of the carbonaceous fossil fuel in the ideal case only

Carbon dioxide (CO ₂ ) and water vapor (H ₂ O) on; Stick oxides (NO _x ) and other pollutants are only produced in comparatively ^small amounts due to proportions or impurities contained in the fuel. Thus, the effluent from the combustion chamber of the steam generator exhaust gas after Kondensa ^¬ tion of water vapor content contains virtually only carbon dioxide (CO ₂ ), which, for example, as a displacement medium for För ^¬ dermengenerhöhung at almost exhausted oil and gas can be used commercially or placed underground in saline aquifers and thus klimaunwirksam.

The technical feasibility of such "zero-emission power plants" is currently demonstrated ^¬ plants in some pilot projects and research, in particular the entspre ^¬ sponding combustion concepts still the subject of intense For are ^¬ research. Generally has sen the furnace at Kraftwerksprozes ^¬ and processes This also applies to oxyfuel processes to an even greater extent, so that the expense of corresponding research projects and optimization measures is justified.

One is for the technical realization of the oxyfuel process to be overcome problem is that insurance types for many Feue ^¬ and fuel within the combustion chamber to the passing ^¬ combustion temperatures, the maximum allowable ma- terialtemperaturen exceed the adjacent combustion chamber walls. In the case of incomplete oxyfuel incineration, there are also ashes residues, for which reasonable handling certain upper limit temperatures should not be exceeded either. Particularly in the case of near-stoichiometric combustion with pure oxygen as the oxidizing agent, such problems become particularly blatant, since in principle temperatures of more than 3000 ^° C. can occur.

In order to damage the combustion chamber by unauthorized high

To avoid temperatures, therefore, various concepts have been developed to lower combustion temperatures. All oxyfuel processes proposed so far have in common the near-stoichiometric oxidation of the fuel in an inert gas mixture. According to a first proposed combustion concept, for example, an internal flue gas recirculation can be provided, as used in so-called FLOX burners. By the admixture of Flue gas, the combustion process is non-adiabatic. That is, the combustion zones is removed already during the combustion heat and transferred to the already cooled, re ^¬ circulated flue gas, so that the local peak temperatures within the combustion chamber are significantly reduced. A disadvantage of this concept, however, is that the combustion chamber and its exhaust-carrying components connected downstream must be designed for comparatively high volume or mass flows, which results in a correspondingly bulky design with large flow cross sections. This results in relatively high completion costs for such a power plant.

As an alternative to flue gas recirculation, flame cooling by injecting water or steam or by the use of moist fuels can also be provided according to a second combustion concept. Such as reducing Feuerungs ^¬ temperature of the flue gas mass flow in the flue gas recirculation, however, also bought with increased exhaust gas losses, as the Erhö- hung efficiency moderate energy conversion principle ^¬ lowers.

In addition, in the context of conventional combustion processes that take place with the supply of nitrogen-containing combustion air, the concept of (atmospheric) fluidized bed combustion is known in which the combustion of the usually solid fuel takes place in a fluidized bed. The reduced combustion temperatures are intended primarily to reduce the emission of nitrogen oxides (NO _x ) and sulfur oxides (SO _x ).

The present invention is therefore based on the object of specifying a steam generator of the type mentioned and an associated power plant, the combustion of a koh ^¬ lenstoffhaltigen fuel according to the oxyfuel process in a simple and cost-effective construction and operation by resorting to suitable Feuerungskonzepte with a particularly high energy efficiency and with especially low residual emissions. Furthermore, a particularly suitable operating method for a system based on such principles is to be specified.

With respect to the steam generator, the object is it dissolved ^¬ inventively by the steam generator comprises a cooled by a number of immersion heating surfaces fluidized bed combustor, which has a number of arranged in the region of the combustion chamber bottom oxygen inlet openings through which during operation of an associated air separation plant he ^¬ staunch is introduced as an oxidant and as a fluidizing effective pure oxygen into the fluidized bed combustor, wherein the fluidized bed combustor is designed for egg ^¬ NEN operation with a stationary fluidized bed.

The invention is based on the consideration that for a particularly compact and cost-saving construction of a steam generator operated according to the oxyfuel principle, the volume flows through the combustion chamber and the downstream flue gas should be kept as low as possible. Therefore, the usually provided for controlling the high combustion temperatures flue gas recirculation should be largely avoided, or the proportion of recirculated in the combustion chamber exhaust gases should be kept at least lower than previously designed systems. In this case, however, the released heat in the combustion chamber should be as they arise are still at the site removed, fertil to the structural integrity of the containment walls and in the Verwen- constant of less quality or temperaturbe ^¬ and not to endanger therefore more cost-effective materials. According to the concept now proposed, combustion of the carbonaceous fuel in a fluidized bed combustion chamber cooled by a number of immersion heating surfaces is provided for this purpose, the fluidized bed combustion chamber being designed for operation with a stationary (non-circulating) fluidized bed. In other words, the stream of pure oxygen which ^¬ voltages of the fluidized bed combustor via arranged in the region of the combustion chamber bottom Einlassöff, for example in the form of inlet nozzle or egg nes intake grille is supplied while an in Vertika ^¬ ler (upward produced in the air separation unit ) Has direction-pointing pulse component, serves on the one hand as an oxidizing agent for the combustion processes taking place in the combustion ^¬ chamber and on the other hand as a fluidizing medium for the fluid contained in the combustion chamber. Due to the upward flow of the oxygen, the fine-grained sand or dust-like fluidizable material is whirled up ^¬ and placed in a fluid-like state of flow. The turbulence of the particles leads on the one hand due to the particle-particle shocks to a particularly efficient combustion (catalytic effect of the fluidized bed) and on ^¬ because of the particle wall shocks to a particularly intense ^¬ sive heat transfer to the guided through the combustion chamber , Conveniently to so-called Tauchheizflächen bundled ^¬ th heating or evaporator tubes and the flow medium guided therein, preferably water or a water / steam mixture. By thus effected, particularly efficient heat dissipation comparatively low combustion temperatures of, for example, less than 1000 ⁰ C are therefore also in the oxyfuel combustion feasible, so that the relevant requirements for the combustion chamber walls and other installations in the combustion chamber are relatively low.

Since, according to the now proposed concept, the inflow velocity and the volume or mass flow of the introduced into the fluidized bed combustor oxygen are sized to be that a stationary fluidized bed, before ^¬ preferably a weakly fluidized or a so-called bubbling fluidized bed with a well defined obe ^¬ ren Boundary forms, a comparatively complex recycling of discharged from the combustion chamber fluidized particles, as would be necessary at higher inflow velocities of the fluidizing, not required. That is, the circulation of circulating fluidized beds in the context of conventional, in a nitrogenous combustion atmosphere running combustion processes known equipment and operating expenses - return line, blower ^¬ se, gas cyclone for solids separation and so - - falls.

In order to achieve a particularly high heat dissipation and cooling effect within the combustion zone in the fluidized bed be ^¬ the ratio of the total surface area is sitting all Tauchheizflä- chen to the average cross-sectional area of the fluidized bed combustor is preferably a value that is greater than thermal in a conventional steam generator, "air-blown" fluidized bed of comparable . performance It is the planar dimension of the surface of a Tauchheizfläche - without considering the geometry or curvature of the individual heating tubes - meant, each of said heating ^¬ surfaces usually two effective for the heat exchange surfaces, comprising namely front and back, which at ^¬ de must be considered in the calculation. the cross-sectional area of the combustion chamber is a vertical boiler ^¬ construction in a horizontal, transverse to the flow direction of the flue gas extending plane.

Since in the fluidized bed combustor despite caused by the immersion heating cooling temperatures may prevail more of about 1000 ⁰ C or is enriched for the metallic immersion heating surfaces and distributor nozzles just in accordance with the oxyfuel combustion with pure oxygen combustion atmosphere a non-negligible risk of should be iron fire or other high temperature Erosionsschä ^¬, which entgegenge preferably appropriate measures acts ^¬. Contrary to the usual tendency to provide a fluidized bed material with a certain minimum grain size to minimize the necessary bed area, now advantageously a particularly fine-grained Bettma ^¬ material is used. This allows significantly less oxygen to the surface of immersion heating and Other pe ^¬ gen metallic internals in the fluidized bed combustion chamber, whereby the risk of an iron fire is reduced to an uncritical level. The fine-grained fluidized material reduces the oxygen concentration in the immediate vicinity of the heating surfaces, improves the cooling effect and "delete" a If appropriate onset of oxidation. Also, by a smaller particle size and mass reduces the mechanical erosion (sand-blasting effect). The effect can vorteilhaf ^¬ ingly be reinforced by the fact that the swirl ^¬ layer in the field of Tauchheizflächen only weakly, ie just above the Fluidisierungsschwelle, fluidized.

In an advantageous alternative or additional embodiment, the metallic immersion heating surfaces are provided with a highly thermally conductive, oxidation-inhibiting or -verhindernden- coating, in particular with a ceramic coating, whereby an iron firing is excluded. Furthermore, it is advantageous if a number of ceramic or ceramic coating installations are arranged in the combustion chamber between the oxygen inlet openings and the immersion heating surfaces so that the immersion heating surfaces lie at least partially in the flow shadow of the installations that reduce erosion in this way, do not be "blown" directly from the oxygen flow.

For a particularly good cooling, the combustion chamber before ^¬ geous enough, a Eindüsevorrichtung for water. It is particularly advantageous in terms of energy, when the water injected into the combustion chamber is condensed out together with the water vapor resulting from the combustion processes in a flue gas condensation plant and the heat absorbed in the evaporation is recovered again as Nutz ^¬ heat.

The above-described concept is particularly advantageous in the case of a fluidized-bed combustion chamber with a pulverized coal firing.

Advantageously, the steam generator is part of a power plant, which also has a Luftzerlegungsanla ge, z. For example, a cryogenic air separation plant or a membrane air separation plant, for generating the required sour ^¬ material stream comprises.

With regard to the method is the initially asked

Solved object by pure oxygen generated by an associated air separation ^¬ plant is introduced into the fluidized bed combustion chamber of the steam generator, the Sauer ^¬ mass mass flow and the Sauerstoffeinströmgeschwindigkeit be set such that forms a stationary fluidized bed in the fluidized ^¬ combustion chamber whose boundary layer above the Tauchheizflächen lies. Vorteilhaf ^¬ be ingly by the combustion of the fuel ^¬ standing flue gases ent derived from a fluidized bed combustor downstream Konvektionsgaszug, without being recirculated into the fluidized bed combustor.

The advantages achieved with the invention consist particularly in the fact that by the skillful combination of Prinzipi- en "oxy-fuel combustion" and "fluidized bed combustion with a stationary fluidized bed," a firing concept for a steam generator is realized which ^¬ temperatures at moderate combustion and thus low demands on the thermal load capacity of the surrounding walls of the steam generator enables energy conversion with a particularly high degree of efficiency with pollutant loading of the exhaust gas flow kept at a ^{comparatively} low level. In addition, significantly reduced due to the opposite herkömm ^¬ technologies or even attributable need for recirculation the related system components can be designed for lower flow rates or completely eliminated. Even the steam generator itself can be made much smaller in diameter and thus much lighter than previously necessary.

An exemplary embodiment is explained in more detail he ^¬ reference to a drawing. The figure shows a steam generator with fluidized bed combustion in longitudinal section. The steam generator 2 shown schematically in the Figure in longitudinal section has an upright boiler 4, the containment walls 6 made of gas-tight ver together ^¬ welded respectively to the evaporator, superheater and economiser miserheizflachen combined steam generator tubes are formed in which one is to be evaporated flow medium , z. B. water or a water / steam mixture flows. For firing the steam generator 2, a carbonaceous fossil fuel usually in the soil denseitig arranged combustion chamber 8, in particular coal, ver ^¬ is burned. The combustion takes place according to the so-called oxyfuel principle with supply of pure oxygen (O ₂ ) which acts as an oxidant, which is obtained in an associated air separation plant (not shown) and introduced into the combustion chamber 8 via pipelines.

The flue gas R produced during combustion, consisting essentially of carbon dioxide (CO ₂ ) and water vapor (H ₂ O) leaves the combustion chamber 8 in the vertical flow direction 10 and then flows through the section of the vertical gas flue which adjoins the combustion chamber 8 at the top 12, while at the same time deliver a large part of the residual heat contained in it by convective heat exchange via the convection heating surfaces 14 suspended in the gas flue 12 to the flow medium guided therein, for. As for overheating of the steam generated in the evaporator tubes of the surrounding walls 6 or 8 of the combustion chamber. Finally, the water fraction contained in the flue gas R is separated off in a condenser (not shown) connected downstream of the steam generator 2 on the flue gas side, so that only pure carbon dioxide can be disposed of as an environmentally harmful combustion product or supplied to another utilization.

The combustion chamber 8 is designed for a particularly effective and complete combustion of the fuel and constant for a particular ^¬ DERS effective heat transfer to the flow medium to be evaporated as a fluidized bed combustion chamber. It contains a loose bed of fine-grained fluid, z. As quartz sand, which is swirled under the action of the inflowing through the inlet nozzles 16 of a nozzle bottom 18 oxygen and is placed in a flow state. The Ver ^¬ incineration of carbon-containing fuel takes place within half of the forming "oxygen Blow-molded" fluidized bed 20. The fuel introduced into the combustion chamber 8 oxygen accepts therefore both the function of the oxidizing agent for combustion as well as the fluidizing medium for the generation and maintenance of the fluidized bed. The input flow rate of the oxygen into the combustion chamber 8 is selected to be that a comparatively weak fluidically ized, stationary fluidized bed 20 having an upper limit ^¬ surface the slightly expanded screened 22 in the transition region between the combustion chamber 8 and with respect to the combustion chamber 8 in cross-section Convection gas train 12 forms.

For an effective removal of the heat released in the combustion zone, a number of immersion heating surfaces 24 "immersing" in the fluidized bed 20 are provided, of which only one is shown schematically in the figure Each of the immersion heating surfaces 24 is defined by a number of meandering, extensively bundled heating tubes formed in which is guided the (vapor-water or water) to be vaporized or already partially or completely evaporated flow medium. Due to the good heat transfer Zvi ^¬ rule the fluidized bed and the respective Tauchheizfläche 24 large heat flows can the combustion chamber 8 comparatively be withdrawn so that the combustion chamber 8 even without the otherwise conventional flue gas recirculation is cooled well, the temperatures in the combustion zone lie with at ^¬ match, 900 ⁰ C relatively low thereby, -.. supported by the homogenizing and catalytic action of the fluidised bed - the m öglichst complete conversion of the carbonaceous fuel H ₂ O and CO ₂ drying products conveyed in the desired combustion.

In the exemplary embodiment, about 70% of the total fire ^¬ heat output of the steam generator 2 via the Tauchheizflächen 24 dissipated. The remaining portion, about 30%, is - as already described above - transferred to the flue gas R, which flows with a temperature of about 1000 ⁰ C through the throttle cable 12 upwards and thereby at least a portion of it contained (Remainder -) emits heat over the Konvektionsheizflachen 14.

To counteract the risk of iron fire contrary to that, the combustion chamber 8 is charged with a particularly fine-grained fluidized material on ^¬ due to the high oxygen concentration in the combustion chamber 8 and the prevailing therein temperatures is given, in principle, which heating surfaces evenly to the dive ^¬ 24 and other vulnerable metallic components anneals or reflected and thereby any oxidation onsvorgänge "nipped in the bud." Alternatively or additionally, the immersion heating surfaces 24 and / or the inner walls of the combustion chamber 8, and optionally further metal compo ^¬ can components with an iron fire and other erosion processes preventing or Furthermore, it is possible to arrange ceramic internals or the like, not shown in the figure, in the flow path of the oxygen injected into the combustion chamber 8 in such a way that the immersion heating surfaces 24 are not directly "blown" which also reduces erosion.

Claims

claims

A steam generator (2) heated by the combustion of a carbonaceous fuel according to the oxyfuel process, comprising a fluidized bed combustion chamber (8) cooled by a plurality of immersion heating surfaces (24) and having a number of oxygen inlet openings arranged in the region of the combustion chamber floor (16), via which in the operating case of ei ^¬ ner associated air separation plant produced, acting as Oxidati- onsmittel and as Fluidisierungsmedium pure oxygen (O ₂ ) in the fluidized bed combustion chamber (8) is introduced, wherein the fluidized bed combustion chamber (8) for operation with a stationary fluidized bed (20) is designed.

2. Steam generator (2) according to claim 1, the immersion heating surfaces (24) are provided with a ceramic coating.

3. steam generator (2) according to claim 1 or 2 with a number of ceramic fittings and / or with a number of provided with a ceramic coating internals, in such a way between the oxygen inlet openings (16) and the Tauchheizflächen (24) in the fluidized bed (20). arranged that the Tauchheizflächen (24) are at least partially in the flow shadows caused by the internals.

4. Steam generator (2) according to any one of claims 1 to 3 with a injection device for injecting water into the fluidized bed combustion chamber (8).

5. steam generator (2) according to one of claims 1 to 4 with a pulverized coal.

6. power plant with a steam generator (2) according to one of claims 1 to 5 and with an oxygen side with the steam generator (2) connected air separation plant.

7. A method for operating a heated with a carbonaceous fuel steam generator (2) with a one Number of Tauchheizflächen (24) containing fluidized bed combustion chamber (8), in which by an associated air separation plant generated pure oxygen (O ₂ ) is introduced into the fluidized bed ^¬ combustion chamber (8), wherein the oxygen mass flow and the Sauerstoffeinströmgeschwindigkeit be set such that a stationary fluidized bed (20) formed in the fluidized bed ^¬ combustion chamber (8), the boundary layer (22) is located above the immersion heating surfaces (24).

8. The method of claim 7, wherein the resulting during the combustion of the fuel flue gases (R) from one of We ^¬ belschichtbrennkammer (8) downstream Konvektionsgaszug (12) are derived, without being recirculated into the fluidized bed combustion chamber (8) ,