DD294701A5 - SILICON CARBIDE MOORDS FOR THE REFRACTORY DELIVERY OF FIXED BED PRESERVERS - Google Patents

Abstract

The present invention relates to a silica sol-bound mortar for the delivery of fixed bed pressure carburetors with silicon carbide. According to the invention, 5 to 20% of finely ground alumina (half-value grain size 2.5 m) having an α-Al 2 O 3 content of 85 to 95% and 5 to 5% is added to the finely granulated (0.5 mm) silicon carbide core in a proportion of 70 to 90% Added 30% silica sol with a proportion of about 30% amorphous SiO2. The silica sol causes after drying in conjunction with the alumina high strength of the mortar and its good adhesion to the steel shell. On the one hand, the clay is so well calcined that it scarcely fades under temperature load, but on the other hand it is still so reactive that it is formed from 780C with the amorphous SiO2 mullite as SiC oxidation protection. Mortar; mullite; silica; Silicon carbide stones; alumina; a-Al2O3 content; amorphous SiO2}

Description

Field of application of the invention

The invention relates to the refractory ceramic inner lining of Festbettdruckvergasern in which under a pressure <3.5 MPa and temperatures <1300 ° C, the solid fuel brown coal is converted into high-quality gases. The invention relates in particular to the necessary for the preparation of the ceramic masonry SiC mortar.

Characteristic of the known state of the art

In fixed bed pressure gasification, domestic lignite is the most important gasification substance, which is converted in a moving fixed bed with an oxygen / water vapor mixture in countercurrent to city gas. The fixed bed pressure carburetors can not currently be operated under the prevailing temperature and corrosion conditions without ceramic lining. To protect the metallic inner shell of the fixed-bed pressure carburetor with refractory material is delivered. The refractory material is extremely stressed at a high efficiency of fixed bed pressure gasification. Silicon carbide bricks as refractory liners have heretofore been found to be the most suitable material. For masonry of SiC stars, a fine-grained mixture of clay and silicon carbide is currently used as mortar. This is located both in the joints between the stones as well as behind the masonry between clad inner jacket and the stones. Due to the wall temperatures in fixed bed pressure carburetor, the formation of a stable ceramic bond in the mortar is not given. In addition, the mortar does not adhere to the inner shell of Festbettdruckvergasers. When starting the Festbettdruckvergasers escapes due to the effects of temperature, the water contained in the mortar and leads to a porosity increase.

These processes reduce the diffusion resistance of the mortar. The facilitated diffusion causes pollutants also penetrate behind the lining materials and in conjunction with dew point violations on the water-cooled inner jacket lead to severe corrosion phenomena. The corrosion products have a strong thermal insulation and cause an increase in the temperature in the masonry despite cooling the inner shell with water. These temperature increases lead u. a. with the adhesive phenomena of SiC refractory including the mortar, and manifest in a SiC removal. The thermal conductivity of the masonry is known to depend on the Si-C content. It decreases with decreasing SiC content. Due to the delayed heat dissipation and the consequent increased masonry temperature ash melting phenomena occur, which eventually lead to Schlackewandbildungen and thus to decommissioning of Festbettdruckvergasers.

The SiC mortar has no firm bond both as a joint and as a backfilling mortar between inner shell and SiC masonry. In addition to the lack of strength, the clay-bonded SiC mortar used is less protected against oxidation than the SiC stone. The strength of the mortar is further reduced by the increase in volume during the oxidation of SiC to SiO ₂ in Festbettdruckvergaser and reduces the thermal conductivity. The ash of the coal also reacts with both the silicate components (clay) of the mortar and with the free SO ₂ formed from SiC. This reaction is favored by the reduced thermal conductivity.

In DD-WP 227975 it was proposed to use instead of / on mortar '.Värmeleitkitt as a binder for the delivery of fixed bed pressure carburetor. The insert showed that due to the high porosity of the Wärmeleitkitts severe damage to the metallic inner shell occurred. The result meant that is dispensed with a further use of Wärmeleitkitt.

Object of the invention

It is the object of the invention to prevent by a suitable mortar caking of slag on the inner wall of the fixed bed pressure carburetor and thereby improve the economics of fixed bed pressure gasification

- Increasing the availability of fixed-bed pressure carburetors

- Reduction of the need for process steam

- To achieve a reduction of the maintenance effort.

Explanation of the essence of the invention

The object of the invention is to improve the resistance to slag attack and the strength and thermal conductivity of the composite material between refractory lining and metallic inner shell of Festbettdruckvergazers.

According to the invention, a mortar composed of 70 to 90% silicon carbide, grain fraction <0.5 mm and a reduced fraction of refractory binding clay and / or -kaolin (5-15%) and 5-20% alumina is ground to connect refractory lining and Innenmantei the fixed-bed pressure <0.04mm, wherein the clay has a content of 0-Al ₂ O ₃ between 85 and 95%.

To this mortar mixture silica sol with about 30% amorphous SiO _{2 is} added before processing. The silica sol, upon drying in conjunction with the clay, forms a type of zeolitic bond, thereby providing a strong bond between the refractory material and also good adhesion to the inner shell of the fixed bed pressure carburetor. This alumina used according to the invention is so active by virtue of the proportion of transitional toners still present and the high fineness that mullite (3Al ₂ O ₃ 2SiO ₂ ) is formed from 78O ⁰ C with the amorphous SiO _{2 of} the silica sol. On the other hand, the a-Al ₂ O ₃ content is so high that the strength of the mortar is not lowered by shrinkage processes of the clay. The forming mullite matrix imparts high strength to the mortar and protects the silicon carbide most closely before conversion to silica. Since the alumina is in excess, the small amount of SiO ₂ still formed is immediately converted to mullite. The Spfcrialtonerde is due to the defined 0.-Al ₂ O ₃ content (85-95%) and a favorable crystal state, which is due to the calcination necessary to obtain this a-Al ₂ O ₃ content, with in the ceramic industry usual Aggregates such as drum or tube mills can be very finely ground (half-grain size around 2.5 pm). The strength of the mortar, the firm adhesion to the water-cooled Innenmantei the fixed-bed pressure carburetor and the oxidation protection of silicon carbide, a good dissipation of heat from the refractory material and thus a low temperature on the inside of the refractory material is ensured. Thereby, the reaction temperature of the process can be increased by lowering the steam / oxygen ratio with known advantages without forming slag at the lining. In addition, the mortar itself is hardly a reaction partner for the ashes, since it contains only little clay or kaolin and no free SiO ₂ formed from SiC. The access of corrosive gases to the inner shell of the fixed bed pressure carburetor is also prevented. This reduces the erosion of the inner jacket of the FDV behind the refractory lining and increases its stability.

Embodiment 1 A fixed bed pressure carburetor is delivered with clay or mullite bonded SiC bricks, with a fine-grained mortar Mixture off

85.0% silicon carbide, grain fraction <0.5 mm 10.0% refractory binding kaolin 5.0% finely ground alumina (a-Al ₂ O ₃ content 8595%), half-grain size around 2.5 pm

is used. The mortar is mixed before processing with 5% silica sol with 30% SiO ₂ content and set the desired mortar consistency with water. The laying of the SiC stones is then carried out in the usual way. The mortar has a high strength in the masonry and good adhesion to the inner shell. The SiO _{2 of} the mortar is protected from oxidation by the mullite binder matrix. This ensures good heat dissipation from the masonry. Due to the low clay content of the mortar, the prevention of the formation of free SiO ₂ from the SiC and the lower temperatures of the inner shell, the reaction of the ± molten ash with the refractory material is greatly hindered and the stability of the refractory lining is prolonged. The gasification process can be carried out without the formation of slag mixtures at a steam / oxygen ratio of 6.5 kg / m ³ iN.

Embodiment 2 A fixed bed pressure carburetor is supplied with clay or mullite bonded SiC bricks, the mortar being dry

has the following composition:

75% silicon carbide, grain fraction <0.5 mm 5% refractory binding clay 20% finely ground alumina, half-grain size 2,5μπι (a-Al ₂ O ₃ content 85-95%).

The mortar is mixed prior to processing with 30% silica sol, which has a SiO ₂ content of about 30%, whereby the necessary consistency of the mortar is achieved. The mortar of the stones is done in the usual way. The described in the embodiment 1 positive effects of this mode of delivery are still exceeded by the higher proportion of silica sol and clay and the elimination of the binding clay. The gasification process can be carried out without the formation of slag acids at a steam / oxygen ratio <6.5 kg / m ³ iN.

Claims (1)

Silicon carbide mortar for refractory lining on the basis of fine-grained silicon carbide with a content of 70-90%, 5-15% refractory binding clay and / or -kaolin, characterized in that additionally
5-20% of finely ground alumina with an a-Al ₂ O ₃ content of between 85 and 95%, which is ground to a high degree of fineness (half-value grain size by 2.5 μm) by means of aggregates customary in the ceramics industry and 5-30% silica sol containing about 30% amorphous SiO _{2 are} included.