EP2726439A2 - Pressure casting slip and refractory ceramic produced therefrom for gas turbine units - Google Patents

Abstract

The invention relates to a pressure casting slip for producing a refractory ceramic for use as heat shield in the hot gas path of gas turbine units, which comprises a particulate mixture of at least two materials having different coefficients of thermal expansion and also organic and/or inorganic binders and floating agents, where the particulate mixture has a multimodal particle size distribution, the multimodal particle size distribution is divided into 10-20 per cent by weight of coarse particles in the size range 1-5 mm in diameter, 10-20 per cent by weight of medium particles in the size range 0.5-1 mm in diameter and 60-80 per cent by weight of fine particles in the size range up to 0.5 mm in diameter and the proportions in the particle size distribution are selected so that together they make up 100 per cent by weight of the particulate mixture.

Description

description

Die cast crackers and refractory ceramics made therefrom for gas turbine plants

The invention relates to a Druckgußschiicker for producing a refractory ceramic for use as a heat shield in the hot gas path of gas turbine plants according to the preamble of claim 1, and a refractory ceramic for use as a heat shield in the hot gas path of gas turbine plants according to the preamble of claim. 7

Gas turbine plants consist essentially of a compressor, a burner and a gas turbine. In the compressor intake air is compressed before they are mixed in nachgeschalte ^¬ th and arranged in the compressor plenum burner in a combustion chamber with fuel and this mixture is burned ^¬ ver. The gas turbine downstream of the combustion chamber then removes thermal energy from the resulting combustion exhaust gases and converts them into mechanical energy. A generator connected to the gas turbine converts this mechanical energy for generating electricity into electrical energy. Today, gas turbine plants, like other power generating plants, must also have the lowest possible pollutant emissions with maximum efficiency in all load ranges. The height of the combustion temperature is limited by statutory prescribed NOx values. The temperature in the combustion chamber, which forms the hot gas path between burner and gas turbine, is typically in the order of about 1300 to 1500 degrees Celsius. To maintain these high tempera ^¬ tures stand, corresponding combustor liners must be provided against such hot gas attack to protect the hot gas path components enclosing and supporting structures so. Such heat shields can be carried out both metallic and ceramic. In gas turbine plants due to the aggressive hot gases ceramic materials are be ^¬ vorzugt. In comparison with metallic materials, such refractory ceramics have a higher temperature and corrosion resistance, as well as a lower thermal conductivity. ^¬ plant material base for such ceramic heat shields are hochko- around containing refractory ceramics which are produced after the casting process, for example, described in DE 10 2008 011 820 AI Druckgußschlicker-.

Gas turbine systems must now be able to be adapted to the respective load conditions in a very short time. Highest loads on the components and supporting structures of the gas turbine system, including the heat shields, are created during rapid shutdown of base load. Here, the hot gas ^¬ temperature in the shortest time in the order of up to 1000 Kelvin fall. The thus induced in the heat shields requires thermal shock for the refractory ceramic material properties, the high strength at gleichzeiti ^¬ ger high thermal conductivity and allow at temperatures of up to about 1500 degrees Celsius and more. In addition, the refractory ceramics must have a high resistance to cracking. Refractory ceramics are known from EP 1 327 108 A1 which fulfill the abovementioned properties, with the refractory ceramic on the particularly stressed hot gas side having on average a different particle size distribution than on the opposite colder combustion chamber wall side. However, such a particle size distribution has the disadvantage that additional internal stresses can be induced at the interfaces of the different pore size distributions, which can have a negative effect on the passive safety of the heat shields. Ceramics with optimized homogeneous particle size distribution have a positive effect on the passive safety of the overall system.

The object of the invention is to provide a Druckgußschiicker and a refractory ceramic made therefrom, which has a high thermal shock resistance and is therefore particularly well suited for use as a heat shield in the hot gas path of gas turbines. This object is achieved with the Druckgußschiicker with the Merkma ^¬ len of claim 1.

Characterized in that the Druckgußschiicker a granular mixture of at least two materials with different coefficients of thermal expansion, and organic and / or inorganic binding and adjusting agent comprises, wherein the multimodal Korn ^¬ size distribution of the mixture is divided to 10-20 Ge ^¬ weight percent coarse grain in the size range 1-5 mm in diameter, 10-20% by weight of medium grain in the size range of 0.5-1 mm diameter, and 60-80% by weight of fine grain in the size range up to 0.5 mm in diameter, the weight distribution must be proportionally chosen so that together 100 percent by weight of the granular mixture results in a particularly preferred for use in gas turbine plants total porosity of the resulting Feuerfestkera ^¬ mik with a particularly high thermal shock resistance. Sol ^¬ che produced according to the invention refractory ceramics thus have a material behavior that can safely withstand the rapid thermal cycles resulting from rapid shutdown or generally when starting and stopping the gas turbine plant.

Preferably, the middle grain fraction itself consists of at least 20 percent by weight of the material with the lower coefficient of thermal expansion. This causes internal stresses to arise in the structure during the firing of the die cast strip, which leads to an increase in the strength of the refractory ceramic produced therefrom and thus to an improvement in the thermal shock behavior of the heat shield.

Is preferred as binders and adjusting means xanthan, insbeson ^¬ particular xanthan in a concentration of more than 0.05 overall percent by weight of the die casting slip. The use of xanthan leads to a stabilization of the multimodal particle size distribution in Druckgußschiicker. This stability is necessary in order to achieve the desired uniform pore size distribution and a homogeneous porosity over the GESAM ^¬ te prepared therefrom refractory ceramic, in particular for complex heat shield geometries.

The figure shows schematically a Elektronenrastermikroskop- annähme an exemplary section through a fiction, ^¬ produced refractory ceramic, which is designed as Hitzeschildkera ^¬ mik for use in gas turbine plants. Schematically indicated in the sectional view is the uniform Ver ^¬ distribution of the coarse, medium and fine grains HO- like that runs through the entire refractory ceramic, thus causing a targeted virtually uniformly distributed porosity of about 18- 20% over the entire ceramic.

The setting of a uniform as possible porosity is not insignificantly influenced by the binder used. If the binder provided is a silicate binder or a combination of silicate binders, it is possible to achieve a die casting slurry which can be modulated particularly well. In contrast to the known from DE 10 2008 011 820 AI cement-containing, phosphate-containing, aluminum hydroxide-containing binders binds a silicate binder only during sintering of Druckgußschiickers. For this purpose, the flowable and pumpable Druckgußschiicker from the inventive particle mixture consisting of oxides on the basis of A1 ₂ 0 _3, MgO, MgAl ₂ 0 _4, CaO, Zr0 _2, Cr ₂ 0 _3, Ce0 _2, Y ₂ 0 _3, Ti0 ₂ , bauxite, andalusite, dolomite, pubic Motte, spinels, mullite and / or non-oxides based SiC, C and / or those containing raw materials ^¬ mixed with an aqueous dispersion medium and the binder system. Subsequently, kaolin or clay or bentonite or combinations of these three silicates is added as a silicate binder system before the pressure casting slip is then pressurized into a liquid or liquid permeable casting mold of a diecasting system. is introduced so that the molded part is formed from the granular mixture on an inside surface of a casting chamber of the casting mold by discharging liquid contained in the slurry through the casting mold.

Alternatively, when a binder system of two polysaccharides is provided as a binder, there is a higher viscosity, which is further increased by dewatering in the mold by means of pressure or negative pressure, so that a solidification of the Druckgußschiickers is generated in the mold. Advantageously, binder systems of xanthan gum and guar gum solution, or alternatively based on xanthan or locust bean gum or carrageenan or agar or tragacanth or karaya or gum arabic or tara gum or konj ak-mannan or cassia gum are used as the first polysaccharide with a second polysaccharide. It has surprisingly been shown that such binder systems ^¬ a stronger dependence of the viscosity of the dispersion medium Mi ^¬ mixing ratio / polysaccharides having a single mixed in equal amounts in water polysaccharide. Already a small reduction of Wasseran ^¬ part of the mixture of water / polysaccharides has a strong increase in the viscosity of the binder result. OF INVENTION ^¬-making according to the use of such a Bindemittelsys- tems caused by the dewatering in the mold by means of pressure or vacuum viscosity increase and crosslinking of the binder, so that a solidification of the molded part is generated in the mold.

Claims

claims 1. Druckgußschiicker for producing a refractory ceramic for use as a heat shield in Gastgasinanlagen hot gas path, comprising a granular mixture of at least two materials with different thermal expansion coefficients, and organic and / or inorganic binding and Stell ^¬ medium, wherein the granular mixture is a multimodal having Korngrö ^¬ size distribution, The multimodal particle size distribution is divided into two parts  10-20% by weight of coarse grain in the size range of 1-5 mm diameter,  10-20% by weight medium grain in the size range of 0.5-1 mm diameter, and  60-80 weight percent fine grain in the size range up to 0.5 mm diameter, and where  the weight distribution is proportionally chosen so that together they give 100 percent by weight of the granular mixture. 2. die casting foamer according to claim 1, characterized in that the ^¬ telkornanteil itself consists of at least 20 weight percent of the material with the smaller coefficient of thermal expansion. 3. die cast sheet according to claim 1 or 2, In this case, xanthan gum, in particular xanthan gum, is provided in a concentration of not more than 0.05 percent by weight of the pressure casting slip as the binding and setting agent. 4. Die casting cracker according to claim 1 or 2, characterized in that as Bin ^¬ demittel a binder system is provided from two polysaccharides. 5. die cast foamer according to claim 4, characterized in that the Bin ^¬ demittelsystem consists of xanthan gum and Guarkernmehllösung. 6. die casting foamer according to claim 1 or 2, characterized in that as Bin ^¬ demittel a silicate binder or a combination of silicate binder is provided. 7. refractory ceramic for use as a heat shield in the hot gas path of gas turbines, produced from the Druckgußschli- cker according to one claims 1 to 6 characterized by drying and burning, characterized in that the Feu ^¬ erfestkeramik has a total porosity of 18-20%. 8. refractory ceramic according to claim 7, Before drying and firing, the particle sizes in the die cast slab are distributed in such a way that a refractory ceramic with a virtually uniform pore size distribution is produced.