Research on Quality Control of Gasifier Construction and Service Life of Refractory Bricks

Research on Quality Control of Gasifier Construction and Service Life of Refractory Bricks

In modern coal chemical industry, gasification is a crucial link in the continuous and stable operation of the entire production system, and the quality of gasifier furnace construction directly affects the continuous operation time of gasification. Gasifier furnace construction refers to the initial construction of the refractory lining of the gasifier and the partial replacement during operation.

Analysis of the Main Structure of the Texaco Coal-Water Slurry Gasifier

The internal structure of the Texaco coal-water slurry gasifier is generally divided into a combustion chamber and a quench chamber. The combustion chamber is further divided into three parts: the conical bottom, the cylindrical body, and the arched top. The refractory lining is mainly distributed in the combustion chamber. The conical bottom is composed of refractory facing bricks and castable refractory; the cylindrical body is composed of refractory facing bricks, an insulation layer, and a heat preservation layer; and the arched top is composed of refractory facing bricks, backing castable refractory, and fiber compressed material. The main structural forms of the arched top are conical and spherical. The conical top has an angle of approximately 36° and connects to the cylindrical body in an arc shape; the spherical top is entirely arc-shaped and connects to the cylindrical body. The straight cylindrical part of the furnace cavity is the cylindrical body. The slag outlet at the bottom of the furnace cavity and the conical bottom constitute the conical bottom, with a slope angle mostly around 45°. In terms of detailed structure, expansion joints are retained at the top of the cylinder and the connection between the top of the arch; all the upper and lower surfaces of the refractory bricks at the top of the arch are equipped with rivets, mainly to allow them to interlock during construction; 2-3mm expansion joints are left between refractory linings of different materials, which are filled with combustible materials.

Quality Control Points for Furnace Construction During Inspection and Maintenance

Furnace construction during inspection and maintenance refers to the removal of old refractory bricks and the laying of new refractory bricks. The term “furnace construction” as used below refers to the construction during inspection and maintenance. Refractory brick removal is done manually using electric picks, and bricklaying is done manually using a plastering and pressing method. Domestic gasifier refractory bricks are mainly high-chromium bricks, laid using high-chromium fire mortar. Furnace construction generally involves replacing the cone bottom, cylinder, and arch separately, or simultaneously depending on actual usage and production schedule. Below is a brief analysis of general quality control points for furnace construction and quality control points for local replacement of various parts.

2.1 General Quality Control Points for Furnace Construction

1.After removing the old refractory bricks, ensure the interface is flat, free of unevenness and ash, with a flatness deviation of <1mm;

2.High-chromium fire mortar must be thoroughly stirred before use. First, mix the dry materials, then add 28-30% clean water. The total stirring time should be no less than 10 minutes. ① The mixed high-chromium fire mortar should be used as soon as possible; high-chromium fire mortar that has just begun to set must not be used.

3.The width of the mortar joints between refractory bricks should be 1.2mm, and the deviation should be in accordance with the design specifications. The mortar joints should be uniform and full, with a fullness of not less than 90%. The mortar joints between upper and lower layers, and between inner and outer layers, should be staggered. A straight line running horizontally from the refractory bricks to the gasifier wall is not allowed.

4.A certain gap, usually 2-3mm, should be left between different refractory lining structures to buffer the thermal expansion of the materials, thereby eliminating the thermal compressive stress generated between different refractory lining structures.

5.After the refractory bricks are laid, the overall dimensions should meet the following requirements: surface flatness deviation not greater than ±5mm; verticality deviation per meter not greater than ±3mm; total height deviation not greater than ±15mm.

6.After the furnace construction is completed, it should be left to stand for at least 24 hours before drying. Drying should be carried out according to the drying curve provided by the supplier/design unit.

2.2 Quality Control Points for Cone Bottom Construction

To improve the service life of refractory bricks, in addition to meeting the general quality control points, the construction of the cone bottom should also meet the following quality control requirements: ① The slag slope must meet the design requirements, generally 45°; ② The inner diameter of each layer of refractory bricks at the slag outlet should not deviate from the design requirements by more than ±5mm, and the horizontal deviation of the lowest layer of refractory bricks should not exceed ±1.5mm; ③ To maintain the overall reliability of the cone bottom refractory bricks, brick cutting is generally prohibited.

2.3 Quality Control Points for Shell Construction

To improve the service life of refractory bricks, in addition to meeting the general quality control points, the construction of the shell should also meet the following quality control requirements: ① Expansion joints should be reserved at the upper end of the shell strictly according to the design dimensions, and the expansion joints must be thoroughly cleaned; ② If brick cutting is used, the cut brick size should not be less than 1/2 of the original brick size; ③ The inner diameter of each layer of refractory bricks should not deviate from the design requirements by more than ±8mm.

2.4 Quality Control Points for Arch-Top Furnace Construction

To improve the service life of refractory bricks, in addition to meeting general quality control points, the following quality control requirements should also be met for arch-top furnace construction:

① The expansion joint between the castable and the furnace shell should be filled with fiber-reinforced material, and the size of the expansion joint should meet the design requirements;

② Waterproofing measures must be taken for the parts of the refractory bricks in contact with the castable to prevent the bricks from absorbing moisture;

③ The corundum bulk material is high in chromium. First, mix the dry materials, then add 23-26% clean water, and mix with a mortar mixer for a total time of not less than 10 minutes. Pouring should be done in sections and vibrated to ensure compaction. It is strictly forbidden to use the material after initial setting. Natural curing for 24 hours is required after pouring;

④ When setting up the formwork, the inner diameter of each layer of the mold should conform to the design requirements;

⑤ The overall dimensions of the refractory bricks at the process nozzles must be strictly controlled according to the design requirements to ensure that the centerline of the process nozzle coincides with the centerline of the furnace body, with a deviation of no more than ±2mm;

⑥ To maintain the overall reliability of the arch-top refractory bricks, brick cutting and laying are generally prohibited.

Research on Improving the Service Life of Refractory Bricks

The service life of refractory bricks is mainly affected by three factors: furnace construction quality, refractory materials, and process operating conditions. Improving furnace construction quality can be achieved by addressing the aforementioned aspects to ensure normal process operation is not affected. Refractory materials are mainly controlled through design selection, manufacturing process supervision, and finished product appearance acceptance, thereby extending their service life. Refractory material manufacturers provide detailed technical requirements, which will not be elaborated upon here.

In addition, process operating conditions are a major factor affecting the service life of refractory bricks. These include operating temperature, central oxygen ratio, oxygen-to-coal ratio, coal ash content, and melting point. Among these, operating temperature and central oxygen ratio are the main influencing factors. Especially when the operating temperature is above 1400℃, the temperature increase will significantly shorten the service life of the refractory bricks; the central oxygen ratio directly affects the reaction zone within the gasifier. High operating temperatures lead to the removal of slag buildup on refractory bricks, with slag directly eroding the surface, resulting in severe wear and erosion of the cylinder and cone bottom. Simultaneously, the high temperature and kinetic energy of the slag in the reflux zone, located near the arch top, cause significant erosion, hindering the lifespan of the refractory bricks. Conversely, low operating temperatures result in poor slag removal, impacting process operation. A higher central oxygen ratio leads to a larger atomization angle, a wider and shorter reaction zone, and severe erosion of the upper cylinder and arch top; a lower central oxygen ratio results in a smaller atomization angle, a narrower and longer reaction zone, and severe erosion of the lower cylinder and cone bottom. The oxygen-to-coal ratio is the primary method for controlling operating temperature. The ash content of the coal affects the amount of slag buildup in the gasifier, while the melting point of the coal restricts the operating temperature, both indirectly affecting the lifespan of the refractory bricks.

The core of the gasification process is producing a high proportion of effective gas, namely a high proportion of CO and H2; a higher proportion of effective gas leads to better overall economic benefits. Adjustments to process operating conditions will inevitably lead to changes in the effective gas ratio. Therefore, improving the service life of refractory bricks requires not only adjustments to furnace construction quality, refractory materials, and process operating conditions, but also consideration of process effects and implementation from the perspective of overall economic benefits.