Tjokorde Walmiki Samadhi

Thermomechanical Characterization of Blended Biomass-Coal Ash Waste Materials

The combustion of biomass for energy generation is practiced in an increasing scale in Indonesia as the country heads towards the long-term national energy mix targeted by 2025. However, biomass combustion is prone to operational problems caused by the generally low-melting nature of biomass ashes. This work discusses the effects of co-combusting coal with POEFB (palm oil empty fruit bunch) and bamboo with respect to the thermomechanical behavior of the produced ashes. Coal is observed to increase the ash fusion temperatures (AFT) of neat and combined POEFB and bamboo ashes by as much as 300 °C. Aluminosilicate minerals in the coal combine with potassium in the biomass during co-combustion, producing high-melting K-aluminosilicates. A linear correlation is identified between measured AFT and ash liquidus temperatures estimated by FactSage thermochemistry calculation software, enabling the prediction of AFT of coal-biomass co-combustion systems.

Development of Hydrocracking Catalyst Support from Kaolin of Indonesian Origin

The global shift of petroleum refinery towards heavier crude oils means an increasing demand of hydrocracking catalysts. This work studies the conversion of a kaolin originating from the Bangka island in Indonesia into a hydrocracking catalyst support consisting of zeolite-Y and amorphous alumina-silica phases. After a beneficiation process combining controlled settling and adsorption of the kaolin suspension in water with the addition of 125 ppm of 0.01% polyacrylamide solution as flocculant and 156 ppm of 0.1% calcium chloride solution as the adsorbent, the kaolinite phase content is increased from 63.6 to 74.3 %-mass. After spray drying, the kaolin is calcined at three temperatures for 2 hours each, producing calcined kaolin phases K700C at 700 °C, K1013 at 1013 °C, and K1050C at 1050 °C. Temperatures of calcination for obtaining calcined kaolin phases is determined based on result of DSC/TGA. Synthesis of zeolite-Y is done by mixing varying proportions of these three calcined kaolin products, and zeolite-Y crystal seeds. These mixtures are aged at room temperature for 11 hours prior to reaction in a hydrothermal condition at 93 °C for 15-21 hours. The best calcined kaolin composition is found to be K700C : K1013C : K1050C = 10:85:5 (%-mass), resulting in a zeolite NaY purity of 86-88 % as characterized by X-ray diffraction (XRD), average ratio of SiO2/ Al2O3 of 5.35, mean pore diameter of 23.1 Å, specific surface area of 186 m2/g, and a total pore volume of 0.107 mL/g as measured by N2 adsorption. In a parallel manner, a series of amorphous silica-alumina (ASA) synthesis experiments is done to identify the best metakaolin calcination temperature and metakaoline activation pH. These are found to be 527 °C and 8.0, respectively, producing an ASA product with a 65 %-mass amorphous phase content as estimated by XRD data processing. To prepare the hydrocracking catalyst support, the zeolite NaY is added into the ASA-forming metakaolin sol at a pH of 8.0, aged for 8 hours at 50 °C. An initial morphological characterization of the obtained zeolite-ASA composite catalyst support suggests a good dispersion of the smaller zeolite NaY particles in the ASA microspheres.

Development of Geopolymer Utilizing Inorganic Waste Materials

Geopolymers, which are produced by the reaction between aluminosilicate solid precursors and concentrated alkali solutions, is an environmentally attractive construction material due to its much smaller carbon footprint compared to ordinary Portland cement (OPC), and its ability to consume a wide range of solid inorganic waste materials. This work describes the synthesis of geopolymers utilizing local aluminosilicate materials and the evaluation of several key engineering properties of the geopolymer product as a construction cement. A simple 22 factorial experiment is undertaken to measure the effect of types aluminosilicate solids (metakaolin produced by calcining a Belitung kaolin at 750 °C, and coal fly ash from an East Java baseload powerplant) and alkali activators (NaOH and KOH solutions) on the initial and final setting time of the geopolymer cement mortar. All geopolymer mortar samples exhibit longer setting times compared to OPC mortars. Statistical analysis indicates that KOH produces faster initial setting than NaOH, while fly ash produces faster setting times compared to metakaolin. A 23 factorial experiment is conducted subsequently, adding curing temperature (60 and 80 °C) to the experimental factors. The key engineering property measured in the second experiment is the compressive strength of geopolymer mortars. ANOVA treatment of the measured data indicates that all three experimental factors significantly impacts the compressive strength. Consistent with the preceding experiment, the use of fly ash and KOH significantly increases the strength of the geopolymer mortar. Higher curing temperature is also found to increase the strength. The use of metakaolin as geopolymer precursor produces compressive strength approximately 50% than that of the OPC mortar, while fly ash produces a geopolymer mortar strength that is at least as good as OPC.

Thermochemical analysis of laterite ore alkali roasting: Comparison of sodium carbonate, sodium sulfate, and sodium hydroxide

The abundance of global nickel reserve is in fact dominated by low grade laterite ores containing only approximately 1.0-1.8 %-Ni. Indonesia is a major limonite and saprolite ores source, particularly in the Sulawesi, northern Maluku, and Papua islands. Production of nickel from laterites typically requires a pre-concentration step which breaks down the mineral crystalline structure, thereby facilitating the subsequent extraction of the valuable metals. This work discusses the thermochemical analysis of the alkali roasting of an Indonesian saprolite ore using Na2CO3, Na2SO4, and NaOH. These alkali compounds are selected due to their relatively low cost. The Factsage thermochemical computation package is used to predict thermodynamically stable gaseous, solution, pure liquid, and pure solid phases present in the roasting process at temperatures from 100 to 1200°C at ambient pressure, in inert atmosphere. The formation of a liquid solution (or slag) phase is interpreted as a major indicator of mineral struc...

Reuse of Coconut Shell, Rice Husk, and Coal Ash Blends in Geopolymer Synthesis

Mixtures of biomass and coal ashes are likely to be produced in increasing volume as biomass-based energy production is gaining importance in Indonesia. This work highlights the reuse of coconut shell ash (CSA), rice husk ash (RHA), and coal fly ash (FA) for geopolymer synthesis by an activator solution containing concentrated KOH and Na2SiO3. Ash blend compositions are varied according to a simplex-centroid mixture experimental design. Activator to ash mass ratios are varied from 0.8 to 2.0, the higher value being applied for ash compositions with higher Si/Al ratio. The impact of ash blend composition on early strength is adequately modeled by an incomplete quadratic mixture model. Overall, the ashes can produce geopolymer mortars with an early strength exceeding the Indonesian SNI 15-2049-2004 standard minimum value of 2.0 MPa. Good workability of the geopolymer is indicated by their initial setting times which are longer than the minimum value of 45 mins. Geopolymers composed predominantly of RHA composition exhibit poor strength and excessive setting time. FTIR spectroscopy confirms the geopolymerization of the ashes by the shift of the Si-O-Si/Al asymmetric stretching vibrational mode. Overall, these results point to the feasibility of geopolymerization as a reuse pathway for biomass combustion waste.

Formulation of portland composite cement using waste glass as a supplementary cementitious material

Utilization of waste glass in cement is an attractive options because of its pozzolanic behaviour and the market of glass-composite cement is potentially available. The objective of this research is to evaluate the formulation of waste glass as supplementary cementitious material (SCM) by an extreme vertices mixture experiment, in which clinker, waste glass and gypsum proportions are chosen as experimental variables. The composite cements were synthesized by mixing all of powder materials in jar mill. The compressive strength of the composite cement mortars after being cured for 28 days ranges between 229 to 268 kg/cm2. Composite cement mortars exhibit lower compressive strength than ordinary Portland cement (OPC) mortars but is still capable of meeting the SNI 15-7064-2004 standards. The highest compressive strength is obtained by shifting the cement blend composition to the direction of increasing clinker and gypsum proportions as well as reducing glass proportion. The lower compressive strength of comp...

Synthesis of geopolymer from biomass-coal ash blends

Geopolymer is an environmentally attractive Portland cement substitute, owing to its lower carbon footprint and its ability to consume various aluminosilicate waste materials as its precursors. This work describes the development of geopolymer formulation based on biomass-coal ash blends, which is predicted to be the prevalent type of waste when biomass-based thermal energy production becomes mainstream in Indonesia. The ash blends contain an ASTM Class F coal fly ash (FA), rice husk ash (RHA), and coconut shell ash (CSA). A mixture of Na2SiO3 and concentrated KOH is used as the activator solution. A preliminary experiment identified the appropriate activator/ash mass ratio to be 2.0, while the activator Na2SiO3/KOH ratio varies from 0.8 to 2.0 with increasing ash blend Si/Al ratio. Both non-blended FA and CSA are able to produce geopolymer mortars with 7-day compressive strength exceeding the Indonesian national SNI 15-2049-2004 standard minimum value of 2.0 MPa stipulated for Portland cement mortars. As...