DD294698A5 - SILICON CARBIDE REFRACTORY MATERIAL FOR THE SUPPLY OF FIXED BED PRESSURE GASES - Google Patents

Abstract

The invention relates to silicon carbide bricks for the delivery of fixed bed pressure carburetors. According to the invention, a mass for the production of silicon carbide stones in a proportion of 65 to 90%, consisting of coarse * mm), medium * mm) and feinkoernigem (0.3 mm) silicon carbide, a proportion of 5 to 15% 5 to 20% finely ground alumina (a-Al 2 O 3 content 85 to 95%) and 2 to 5% pyrogenic silica in the form of the product of the dedusting system of ferrosilicon production and / or 2 to 6% silica sol with a plastic binder Content of amorphous SiO2 of about 30% added. On the one hand, the special clay is so stable that it does not shrink in the calcareous fire and thus does not adversely affect the stone, but on the other hand it is so reactive that it forms a solid fine-grained mullite matrix with the amorphous SiO2. Mullitbindung; Fixed bed pressure gasifier; alumina; a-Al2O3 content; amorphous SiO2; silica; Structure; mullite; SiC oxidation protection}

Description

Field of application of the invention

The invention relates to the refractory ceramic delivery of fixed bed pressure carburetors in which under a pressure <3.5 MPa and temperatures <130O ⁰ C, the solid fuel brown coal is converted into high-quality gases. In particular, the invention relates to the delivery of Festbettdruckvergaser with mullitgebundenen silicon carbide bricks.

Characteristic of the known state of the art

Due to the prevailing temperature and corrosion conditions, it is not possible to significantly increase the service life of the inner shell without ceramic delivery for the gasification of ostelbischer brown coal in the Festbettdrucl isern. Therefore, the lining of the fixed-bed pressure carburetor with refractory materials is considered to be the currently most optimal solution. The lining prevents the direct contact of the corrosion-active ashes with the metallic wall. Due to the nature of the resulting ash / slag medium to higher viscosity and the high temperatures in the fixed-bed pressure carburetor, only a few refractory materials are known, which can withstand these stresses for a long time hinwog. The chamotte and mullite corundum stones previously used in the fet, bed pressure gasification were due to the hotter driving the fixed-bed pressure carburetor, not suitable for these changed demands. Higher-grade materials, such as clay-bonded silicon carbide stones with a SiC content of 65%, which are currently used, although better than the aforementioned stone qualities, but also their durability is unsatisfactory. When using the o. G. Coals with an increased ash content may cause the lining material SiC to undergo reactions and slag wall formations, most of which are associated with slag infiltration of the lining material and corrosion behind the lining.

Due to the very good thermal conductivity of the SiC bricks In connection with the cooling of the inner shell of Festbettdruckvergaser soli on the one hand prevents the melting process of the ash and the reaction with the lining material and on the other hand, the thermal stress of the inner shell can be lowered. A decisive disadvantage is the oxidation behavior of the silicon carbide, which is not resistant to oxidation. The SiC is converted by oxygen, oxygenated compounds as well as water vapor and hydrogen, which are also present in the fixed bed pressure carburetor. With the transformation of the SiC a structural loosening and a reduced thermal conductivity is connected. The high clay content of the stones used and the free SiO ₂ formed by the SiC oxidation represent good reactants for the ashes, which form improved reaction conditions in connection with the increase of the inner wall temperature. This can lead to slag approaches on the inner wall of Festbettdruckvergasers and thus constrictions of the gasification space and finally to decommissioning of the fixed bed pressure carburetor. It is known that in various business patents solutions for increasing the efficiency of the fixed-bed pressure carburetor by improving the heat removal have been set out, which, however, did not lead to a satisfactory result. For example, DD WP 220026 proposed a lining of two layers of different types of material to prevent slag deposits on the inner wall of fixed-bed pressure gasifiers, with a firebrick being used on the fuel side to achieve an insulating effect. The ash produced in the fixed-bed pressure gasifier should flow off the chamotte layer through a very hot driving manner in the form of liquid slag. This principle could not be realized in practice, as it came to Schlackaansetzungen.

Object of the invention

It is the object of the invention to prevent caking of slag on the inner wall of the fixed bed pressure carburetor and thereby improve the economy by

- Increasing the availability of fixed-bed pressure carburetors

- Reduction of the need for process steam and

- To achieve a reduction of the maintenance effort.

-2- 294 6S8 Explanation of the nature of the invention

The invention has for its object to change the composition of the SiC bricks so that the strength and thermal conductivity of the ceramic refractory lining is increased in Festbettdruckvergaser. According to the SiC mass used for the production of SiC bricks for refractory lining, which are coarse (1-2.5 mm), medium (0.1 lead mm) and fine-grained (<0.3 mm) silicon carbide with a Proportion of 65 to 90% and a reduced proportion of plastic binder in the form of slaked kaolin and / or refractory binding clay (5-15%), in addition 5 to 20% of finely ground alumina with an a-Al ₂ O ₃ content between 85 and 95% and 2 to 6% of silica sol containing about 30% of amorphous SiO ₂ and / or fumed silica in the form of the precipitate of the ferrosilicon production dedusting plant. The mass is brought to the desired moisture content with water and sulphite waste liquor and / or a clay slip and molded onto hydraulic or spindle presses by the dry pressing method. The moldings are then sintered at temperatures between PK 146 and PK 156.

The finely ground alumina with an a-Al ₂ O ₃ content between 85 and 95% is on the one hand so stable that it does not shrink during the erosion of rocks and so does not adversely affect the stone structure, but on the other hand by the remaining proportion of Übergangststonerden and the high fineness still so reactive that the amorphous SiO _2, a solid, fine-grained mullite matrix is formed, which gives the stone high mechanical strength and low open porosity. The special clay is, due to the defined a-Al ₂ O ₃ content and a favorable crystal state, which is due to the need to obtain this a-Al ₂ O ₃ content Calcinationführung, with conventional in the ceramic industry aggregates such as drum or Tube mills very finely milled (half grain size 2,5μηη). The mullite matrix also protects the SiC from oxidation to SiO ₂ .

The composition of the composition is preferably chosen so that after the erosion of the stone an excess of alumina is retained, which reacts with possibly formed SiO: immediately to MuMt.

The use of the mullite-bonded silicon carbide bricks in the fixed-bed pressure gasifiers results in good thermal conductivity over a long period of time because of the excellent microstructure and oxidation protection of the silicon carbide. The reaction of the ash with the refractory material, due to the low clay content, the dense structure and the absence of free SiO formed from SiC; Anyway, this is further hampered. The service life of the ceramic lining is hereby extended. In addition, the reaction temperature of the process can be increased by lowering the steam / oxygen ratio with known advantages, without the formation of slag at the lining.

Embodiment 1

A solid bed pressure carburetor with silicon carbide bricks based on a mass of 45% silicon carbide, grain fraction 1-2.5 mm 25% silicon carbide, grain fraction 0.1-1 mm 12% silicon carbide, grain fraction <0.3 mm 10% refractory binding clay 6% finely ground Alumina (a-Al ₂ O ₃ content between

85 and 95% Halbwertskorngröße 2,5μηη) and 2% pyrogenic silica in the form of the seizure product

the dedusting plant of ferrosilicon production

delivered. The silicon carbide stones have a stable mullite binder matrix, the open porosity is 17%. Since the SiC is well protected against oxidation by the mullite matrix and the stones have good microstructures, the refractory lining has a good thermal conductivity over a long period of time. The reaction of the coal ash with the refractory material, which is low anyway due to the low content of binder clay and the dense structure, is further delayed by the lower internal wall temperature. As a result, longer life of the fixed bed pressure carburetor are given; the gasification process can take place without the formation of slag mixtures at a steam / oxygen ratio of <6.5 kg / m ³ i. N. be carried out.

Embodiment 2

A solid bed pressure carburetor with silicon carbide bricks based on a mass of 45% silicon carbide, grain fraction 1-2.5 mm 20% silicon carbide, grain fraction 0.1-1 mm 5% silicon carbide, grain fraction <0.1mm 5% refractory tether 20% finely ground Alumina (a-Al ₂ O ₃ content 85-95%,

Half grain size 2.5 μηη) and 5% fumed silica in the form of the seizure product

the dedusting plant of ferrosilicon production delivered.

The stones have an open porosity of 14% after the product firing of PK 146. The advantages described in Example 1 can be exceeded by this delivery. The gasification process can be carried out without the formation of slag mixtures at a steam / oxygen ratio of <6.5 kg / m ³ i. N. be carried out.

Claims (2)

Silicon carbide refractory for the delivery of fixed bed pressure carburettors based on a mass of 65 to 90% coarse (1-2.5mm), medium (0.1-1mm) and fine grained (<0.3mm) silicon carbide 5 to 15% refractory binding clay and / or kaolin and in which the product fire in a Cone drop point of preferably at PK 146 to PK 156, characterized in that additionally
5 to 20% alumina with an a-Al ₂ O ₃ content between 85 to 95%, which in the Ceramics industry conventional aggregates to high fineness (half grain size 2.5 pm) is ground,
2 to 5% of fumed silica in the form of the product of the dedusting plant Ferrosilicon production and / or 2 to 6% silica sol with an amorphous SiO ₂ content of approx. 30% are included.