Combustion of coal and co-combustion of their co-fuel contribute to gas emissions. Among the gas emissions are SO x , NO x , CO and CO 2 . Introduction of calcium based adsorbent is addressed to absorb SO 2 that release to the atmosphere during the combustion process. Objective of the research is at first to observe the physical characteristics of biobriquettes as a function of briquette compositions (coal to palm kernel shell ratios) and Ca/S ratios (Ca in adsorbent and S in briquette) using a natural adsorbent (shellfish waste). The second objective is to investigate desulfurization characteristics as a function of Ca/S ratios and desulfurization temperatures at coal to palm kernel shell ratio of 90:10 (wt %). Ratios of coal to palm kernel shell in this study are 90:10, 80:20, 70:30, 60:40 and 50:50; and Ca/S ratios are 1:1, 1.25:1, 1.5:1, 1.75:1 and 2:1. Binding agent used is the mixture of Jatropha curcas seeds and starch as much as 10% (wt). It was found that introducing the palm kernel shell and adsorbents in the coal briquette affect the water resistant and compressive strength. The highest water resistance and compressive strength were 5,165 second and 34 kg/cm 2 , respectively. The lowest SO 2 level found in this study was 1 ppm for all Ca/S ratios, except for 1:1.

Abundant potential of renewable energy (RE) in Indonesia is predicted to replace conventional energy which continues to experience depletion year by year. However, until now, the use of RE has only reached 2% of the existing potential of 441.7 GW. The main overview of this work is to investigate the availability of RE that can be utilized for electricity generation in Indonesia. National energy demand and targets in the long run during the 2017–2050 period are also discussed. Besides, government policies in supporting RE development are considered in this work. The results show that the potential of RE in Indonesia can be utilized and might replace conventional energy for decades. The use of RE for electricity generation can be achieved by employing a government policy that supports the investor as the executor of RE development. The selling price of electricity generated from RE is cheaper than electricity generated from fossils; this makes economy is more affordable for people. Finally, the target set by the government for utilizing RE as the main energy in Indonesia can be done by implementing several policies for the RE development. Thus, greenhouse gas emissions and the use of petroleum fuels can be reduced.

The ultrasound method is used to improve mass transfer between incompressible reactants which increases their chemical reaction and reduces reaction time as well as energy consumption. In this research, transesterification process variables of rice bran oil were optimized using response surface methodology (RSM). Three process parameters were investigated, namely methanol to oil molar ratio, catalyst concentration, and time. The optimum conditions of the transesterification process based on RSM were: (1) methanol to oil molar ratio: 1:6; (2) catalyst concentration: 0.5% wt.; and (3) time: 48 min, with methyl ester yield of 94.12 %. The optimum rice bran methyl ester yield predicted by RSM was validated by replicating three independent parameters with showed average rice bran methyl ester yield of 93.98%. The properties of the rice bran biodiesel properties were measured and the values met the requirements of the ASTM D6751 and EN 14214 standards.

Abstract. Presently, biomass is mostly utilized as co-fuel in coal combustion in view of energy diversification and emission reduction. However, since the coal content of bio-briquettes is high (up to 80% in this study), gas emissions such as those of SO x still occur. Therefore, the introduction of SO 2 adsorbent is common in coal briquette or bio-briquette combustion. A calcium-based material is usually used for this goal. The aim of this study was to observe the effects of desulfurization temperature and Ca/S ratio (Ca = calcium content in adsorbent; S = sulfur content in coal and biomass) on desulfurization efficiency and kinetics. The ratio of coal to biomass (palm kernel shell/PKS) was fixed at 90:10 (wt/wt) and the ratios of Ca to S were varied at 1:1, 1.25:1, 1.5:1, 1.75:1 and 2:1. The mixtures of coal, PKS and adsorbent were briquetted at a molding pressure of 6 ton/cm 2 with Jatropha curcas seeds and starch mixture as binding agents. Desulfurization was performed within a temperature range of 300 to 500°C for 720 seconds at an airflow rate of 1.2 L/min. The results showed that the highest desulfurization efficiency (90.6%) was associated with the Ca/S ratio of 2:1 and temperature of 400°C. Moreover, the highest reaction rate constant of desulfurization was 0.280 min -1 .

Implementation of learning in class 11th MAN 1 and MAN 2 Banda Aceh City Students only get information without going through discussion activities, students who are not brave enough to express ideas or ideas, so that students are not trained in using their critical thinking skills. This study aims to determine the improvement of students' critical thinking skills through the application of the STEM-based discovery learning model to the motion system concept. The research approach used is quantitative with the type of pre-experimental research. The research design used is the one-group pretest-postest design. The population was all of 11th grade students, amounting to 292 people. The sampling technique used was a total sampling. The sample in this study consisted of 292 students. The instruments in this research were pretest and posttest multiple choice questions with reasoned. Data analysis consisted of normality test, paired sample t-test at a significant level of 0.05 and n-gain. The results of the paired sample t-test obtained tcount 48 and value (ρ.001), so it was concluded that there were differences in critical thinking skills and learning outcomes of students before and after learning with the application of the STEM-based discovery learning model to the motion system concept. The results of the n-gain test using the Meltzer formula showed that the gain in critical thinking skills was 0.85, so there was an increase in critical thinking skills with a high category.