Design and Implementation of Energy Recovery System from Autoclaves in Fiber Cement Industry

The fiber cement composite process has extremely high fuel consumption and a lot of waste energy released. This study focuses on the recovery methods from two waste heat streams; the condensate and the exhaust steam from the autoclaves. An analysis of the heat loss from the autoclave shell showed that the optimum insulation thickness is 0.085 mm. To recover heat from either condensate or exhaust steams, a pinch location can recover the waste heat for fresh boiler feed water at 100°C. Introduction of multiple heat exchanger optimization and control proposed two series of shell and tube exchangers for the condensate and the exhaust steams. The fuel consumption from the heat recovery can approximately be reduced to 8.37 MTHB/year with a payback period of one and a half year

Early Age Carbonation of Fiber-Cement Composites under Real Processing Conditions: A Parametric Investigation

This paper presents the outcome of a comprehensive experimental program undertaken to study the performance of cellulose pulp and synthetic PVA (polyvinyl alcohol) based fiber-cement composite under both carbonated and non-carbonated curing conditions at early age. The composites were produced at different rolling pressures (2.5 to 9.0 bar) and subjected to various curing conditions in which the effects of CO2 pressure (1 to 3 bar) and curing time (3 to 9 h) were studied. The mechanical properties (modulus of elasticity (MOE), modulus of rupture (MOR), and toughness), as well as the physical properties (porosity, bulk density, and water absorption), were measured for all samples. Scanning electron microscopy (SEM) was used to investigate the effect of carbonation on porosity change and adhesion of fiber-matrix. A parametric investigation of the effects of the carbonation curing period, CO2 pressure, and rolling pressure on the improvement of the physical and mechanical properties during carbonation curing was performed. Results showed that fiber-cement composites cured with an elevated CO2 pressure of 3 bar, rolling pressure of 3 bar, and 5 h of curing time provided optimal curing conditions resulting in the most desirable mechanical and physical properties. However, toughness was greatly reduced with the increase of the CO2 pressure, curing time, and rolling pressure. Additionally, the carbonation curing improved the bonding between the fiber and the cement matrix because of the precipitation of calcite particularly in the pores of the interfacial transition zone (ITZ) between the cement matrix and the fibers