GE water-coal slurry gasifiers, the shell (including combustion chamber and quenching chamber) and forgings are made of SA387Grade11ClasS2, which has good high-temperature strength, oxidation resistance and sulfide corrosion resistance below 500℃ after normalizing + tempering refining and vacuum degassing treatment. Among them, the core equipment - the gasifier combustion chamber is divided into three parts: the upper part is the arch, (from the inside to the outside) it is built with high chrome bricks, chrome corundum castables, and fiber coatings (compressible materials). The design service life of the arch high chrome bricks is generally 15,000 hours; the middle part is the cylinder, (from the inside to the outside) it is built with high chrome bricks, chrome corundum bricks, insulation bricks, and fiber coatings (compressible materials). The design service life of the cylinder high chrome bricks is generally 12,000 hours; the lower part is the cone bottom and slag mouth, (from the inside to the outside) it is built with high chrome bricks and chrome corundum castables. The design service life of the cone bottom high chrome bricks is generally 6,500 hours, and the design service life of the slag mouth high chrome bricks is generally 4,000 hours.
The combustion chamber of the gasifier is designed to be lined with four layers of refractory materials - high chrome bricks, chrome corundum bricks, insulation bricks, and fiber coating (compressible material). Their functions are as follows: high chrome bricks use Cr90 bricks (Cr2O3), which are high-density high-chrome bricks that can protect the insulation refractory materials from slag erosion, hydrogen erosion and flame damage; the gasifier support lining layer is a high-density low-chrome high-aluminum material (Cr2O3 and Al2O3), that is, chrome corundum bricks, which mainly support the vault bricks and can greatly reduce the weight of the gasifier; the insulation bricks (insulation layer) are hollow alumina ball bricks (low iron content), which can effectively reduce the temperature of the metal shell and improve the shell's ability to resist CO corrosion; the fiber coating (compressible material) is an insulation material made of crushed refractory fibers (some designs also use 25.4mm thick refractory felt), which can be compressed when the refractory bricks are heated and expanded, and play a role in thermal insulation protection for the shell.
Analysis of the causes of corrosion and wear of high-chrome bricks in gasifiers
1. High-temperature ablation
The high-temperature operation of the gasifier caused by the unstable quality of the raw coal has a great impact on the service life of the furnace bricks. Within 35 days when the gasifier temperature is 100℃ higher than the normal operating temperature, the ablation rate of the high-chrome bricks increases significantly, and the service life of the refractory material is reduced by 2000~5000h.
2. Chemical erosion under high pressure
The combustion chamber of the water-coal slurry gasifier undergoes cracking and oxidation reactions at an operating pressure of 6.15MPa, producing crude synthesis gas with H2 and CO as the main components. The refractory material in the combustion chamber, the high-chrome brick, will be enveloped by these two strong reducing gases, and any refractory body must have some fine gaps and pores, which will become the channel for the gas in the gasifier to enter the furnace bricks. The gas penetrates into the refractory material and reacts with oxides such as SiO2 and Fe2O3 in the high-chrome bricks, destroying the structure and strength of the furnace bricks and affecting their service life. Therefore, the requirements for the masonry quality of refractory bricks in water-coal slurry gasifiers are very strict. If the masonry quality of refractory bricks is unqualified, it is likely that the refractory bricks will be damaged in a short time, greatly affecting the service life of the refractory bricks and endangering the safe and stable operation of the gasifier.
3. Scouring of ash and airflow
During operation, high-temperature gas and molten ash will be continuously generated in the water-coal slurry gasifier. These two media fill the gasifier and flow downward at a certain flow rate, which will cause serious scouring and wear on the wall of the refractory material-high chrome bricks, that is, erosion damage.
4. Frequent start and stop of gasifier
The water-coal slurry gasifier of a coal chemical enterprise adopts a five-start and two-standby operation mode. The coal feeding capacity of a single gasifier is 1500t/d. Since it was put into operation in May 2010, the average service life of each set of process burners is less than 30d, and the process burners are replaced more than 60 times a year. Frequent start and stop have a serious impact on the service life of the gasifier refractory material - high chrome bricks. The service life of the high chrome bricks of the cylinder is only 10000h, the service life of the high chrome bricks of the cone bottom is only 4500h, and the service life of the high chrome bricks of the slag mouth is only 2500h. Their service life does not meet the design requirements. To this end, the coal chemical enterprise established a process burner research group in March 2012. After taking corresponding measures, the average service life of each set of process burners exceeded 65 days, and the annual replacement frequency of process burners dropped to about 26 times. The reduction in the number of starts and stops has significantly extended the service life of the gasifier refractory material - high chrome bricks. The service life of high chrome bricks has reached the design requirements and even exceeded the design service life. Among them, the service life of high chrome bricks in the 5# furnace has reached 15647h. It can be seen that the number of starts and stops of the gasifier has a great influence on the service life of the gasifier refractory material. According to statistics, for every doubling of the number of starts and feeds, the erosion rate of the gasifier refractory material will increase by 1 time.
5. High load of gasifier
When the gasifier is running at high load, the coal slurry flow and oxygen flow entering the gasifier are large, and the amount of slag is also bound to be large, which will inevitably accelerate the scouring and ablation of high chrome bricks, and have a great impact on the service life of high chrome bricks.
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