STUDY OF THE FLUID DYNAMICS OF STEAM IN CEMENT AUTOCLAVE ON DIFFERENT GREEN SHEET ARRANGEMENTS AND THERMAL ANALYSIS OF GREEN SHEET

Portland cement, silica, gypsum, water, and the wood pulp mixed as industrialscale fibre cement has the problem of green sheet stack damage from thermal cracking in an autoclave. This article proposes a green sheet arrangement in an autoclave to limit product damage due to non-uniform heat distribution. The fibre cement curing process was simulated by a CFD method which was divided into three parts. The first part was to understand the fluid dynamics of steam inside the autoclave and arrangement. The second part studied heat transfer inside the green sheet in two different palettes; spacer palette, and solid palette. In the third part, thermal stress from rapid cooling was studied. The results showed that an interval space of 5 cm and overlapped stacks would be sufficient because the steam temperature and pressure are maintained uniformly. The different surface temperatures in the cooling down step of no-interval stacks (scenario I) and 5 cm of interval stack (scenario II) were 24.57 and 6.22 K; respectively. The thermal cracking found in scenario I was due to the rapid cooling of the green sheet surface. The maximum deformation at the surface was about 2.3 mm. Thus, the upper layer could be damaged due to the expansion of a green sheet stack. In scenario II, the maximum stress did not develop over the ultimate stress because the space between green sheets can support the expansion.