Ash characteristics investigation from co-firing of Calliandra calothyrsus and Gliricidia sepium with a high-sulfur and -iron coal in drop tube furnace.

Calliandra calothyrsus and Gliricidia sepium ash characteristics as co-firing fuel to high-sulfur and -iron coal were investigated through theoretical prediction, FactSage modelling, and combustion experiment in drop tube furnace. The results show that the addition of Calliandra and Gliricidia were able to mitigate the slagging risk according to theoretical prediction and FactSage modelling. Slag formations were predicted to occur at higher combustion temperature compared to coal which was reflected in higher ash fusion temperature. The results of combustion experiment showed an agreement with less ash deposition and cleaner probe surface. The addition of Calliandra and Gliricidia increased the high-melting minerals and decreased Fe-based minerals. However, domination of Ca2SO4 in addition of 25 wt% Gliricidia can be detrimental with presence of strongly adhered ash and material degradation. This research provides an important insight of Calliandra and Gliricidia utilization as co-firing fuel that improve the ash characteristics of high-sulfur and -iron coal.

Failures analysis of tube coating in Circulating Fluidized Bed (CFB) boiler.

Circulating Fluidized Bed (CFB) boiler often experience leaks in the wall tube due to corrosion and abrasion of the bed material after use that varies between 3 and 8 months. To avoid erosion corrosion, a coating was done in the form of Chrome Clad Tube Armor (CTA). In this research, a Failure Analysis (FA) was performed on the characterization of the boiler tube using several types of samples, which are Wall Tube Without Coating (WT) and CTA (in new condition and after eight months of use). Macro visual, Field emission scanning electron microscopes (FE-SEM), Fourier-transform infrared spectroscopy (FTIR), corrosion, and Thermogravimetric analysis (TGA) tests showed that the CTA type has better corrosion and thermal resistance. The hardness values of the CTA and WT coating substrates after eight months of use were 197.75 and 195.2 HV. The failure mechanism on the tube was caused by high temperatures (long-term overheating) and friction between the tube and the fluid or metal. Wall tubes in furnaces fail due to erosion and corrosion due to fluid and solid particle mixtures and environmental contact.