The gasifier lining refractory material is a multilayer structure, from the inside to the outside, it can be divided into a fire-facing refractory bricklayer, a back support layer, a heat insulation layer, and a compressible layer. As the part directly in contact with coal ash and slag, the fire-facing surface has been under high temperature and high pressure working environment. It has been eroded by cinders and airflow for the longest time, and the erosion is the most serious. Therefore, the refractory bricks used in this part need to have the characteristics of high-temperature resistance, corrosion resistance, excellent creep strength, high thermal shock stability, and good chemical stability at high temperatures. Generally choose high-purity chromium oxide refractories, also known as chrome-alumina-zirconia bricks or high chrome bricks.
Damage Factors of High Chrome Bricks for Gasifier
In the process of use, due to the influence of the working conditions of the gasifier on the fire surface, the main damage factors of the high chrome bricks for the gasifier are as follows.
(1) Chemical Attack
High chrome bricks are mainly corroded by molten slag during use, followed by corrosion by strong reducing gas in the furnace. The erosion of high-chromium bricks by molten slag includes the dissolution of ZrO2 and Al2O3 in the high chrome bricks into the slag. In addition, the SiO2 and CaO in the slag penetrate strongly into the brick and react with the refractory components to form a thicker metamorphic layer. The corrosive effects of CO and H2 strongly reducing gases on high chrome bricks are mainly gases and impurities in the bricks. For example, SiO2, iron-containing oxides react to generate gas overflow or react with CO under the action of iron oxides to generate C and deposit in the bricks, causing swelling and cracking of high-chromium bricks.
(2) Mechanical Wear
Mechanical wear mainly comes from the erosion of high chrome bricks used in gasifiers by high-speed gas and carried slag. The consequence of this erosion is that, on the one hand, it accelerates the chemical reaction between the slag and the high-chrome brick, and on the other hand, it will take the low melting point reaction product away from the surface of the brick, and finally accelerate the spalling process of the metamorphic layer and cracked parts of the brick body.
(3) Operating Conditions
The operation process of the gasifier is also a key factor causing the damage of high chrome bricks.
- Operating temperature. The practice has proved that every time the operating temperature of the gasifier increases by 100°C, the corrosion rate of refractory bricks may increase by nearly 3-4 times.
- Coal type. The ash melting point of coal determines the operating temperature of the gasifier. If the raw material coal ash melting point is too low, the viscosity of the coal ash under production conditions will be very small, which will aggravate the erosion and penetration of the slag on the hot tile. For coal with too high ash melting point, a certain amount of additives, such as CaO, Fe2O3, etc., are often introduced in the preparation of coal water slurry to reduce its melt flow temperature to the optimal value. But with the increase of CaO and Fe2O3, the erosion of high chrome bricks is also intensified.
- Production load and the number of starts and stops. According to statistics, for every 30% increase in production load, the service life of the hot tile is reduced by about 33%. Usually, every time the furnace is turned on and off, the hot-faced bricks will be damaged by 5-20mm, especially when the content of CaO in the slag is high.
- Burner. Experimental research and actual field operation show that the normal burner nozzle spray angle should be around 35°. If the angle is too large, it will cause serious erosion and peeling on the upper part. If the injection angle is too small, it cannot be completely vaporized, resulting in a decrease in vaporization efficiency. If the installation of the burner is offset, the local corrosion of the furnace lining will increase.
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