Refractory liners

In a gasifier utilizing gas or liquid as a carbon source, refractory failure is primarily caused by thermal, chemical, and structural wear of the refractory liner. The hot face refractory lining in the gasifier is typically a dense high-alumina material (low in Si02 and FeO), followed by a porous layer composed of a material such as... 

Bennett, J.P. Refractory liner materials used in slagging gasifiers. Refractory Applications, 2004, 9, 20-25. 

Hot lines and equipment are usually thermally insulated to conserve energy and to ensure safe service at temperatures above the oxidation limits of the materials. Care must be taken to ensure that the process stream chemistry is either nonoxidizing or that the process-side surface is protected by an insulating or refractory liner. In such cases, the limiting factor will be the availability of a code maximum allowable stress. 

Figure 13.2 Porous media and refractory liner before build.

As an example, as far as the plant modifications are concerned, for pressurized plants the following provisions were considered necessary alternative means for cooling of components in extreme emergency situations, containment venting, a refractory liner on the cavity walls below the vessel, improvements in the control of leaks from the containment, if accidentally higher than the specified ones. 

Some of the high-temperature transfer lines are protected by castable or firebrick linings, with the outer retaining piping water-cooled. The inner refractory liners also are protected by shrouds of Type 304 or 321 stainless steel. 

In order to read fair off the chart in Fig. 6.1.3, we need, in addition to Rep from Eq. (6.1.6), the wall relative roughness kg/R. The relative roughness is simply an estimate of the absolute roughness of the inside surface of the cyclone walls kg, divided by the inside radius of the cyclone R, expressed in any consistent set of imits. Here, kg is normally taken to be about 0.046 mm or 0.0018 inches for commercial steel pipe. In some apphcations wherein brick or erosion protecting, refractory liners are installed, kg may as high as 3 mm or 0.125 inches. 

Refractory work should be inspected and tested while the work is being done. Refractory should be smooth, hard, evenly applied and should just cover the top surface of the metal anchoring grating as shown, for example, in the photograph of the refractory liner installed on the roof of the cyclone shown in Fig. 12.1.13. 

Ceramics tend to have a much smoother surface than refractory liners and this can result in improved cyclone efficiency. This statement is qualified somewhat, however, by the fact that some ceramic cyclone installations consist of fiat pieces of tile that produces a surface finish which only approximates a smooth, continuous surface. From a cyclone design point of view, a surface that only approximates a smooth cylindrical or conical inner surface is difficult to simulate in any computer model of separation performance. The difficulty lies in establishing a reasonable estimate of the effective wall roughness of the tiled surface. This effect, however, is less of a concern as the cyclone diameter increases. This is because cyclone performance is affected by the relative roughness (roughness divided by the radius or diameter of the cyclone) and not the absolute roughness, per se. The tile effect is also of less concern in units greater than about 2 meters in diameter. If the tile surface is curved... 

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