• Energy Research

This study addresses the change of char morphology and fuel conversion during pyrolysis in a laminar entrained flow reactor by experiments and particle simulation. Three experimental parameters were examined: reaction temperature (1073 and 1273 K); particle size (125–250, 250–500, and 500–1000 μm); and the length of reaction zone (650 and 1885 mm). The scanning electron microscopic (SEM) images showed that biomass swelled during heating and shrank during initial stage of pyrolysis. Then, char morphology transformed to cenospheres after the plastic stage. The yields of solid residue from the experiments were reasonably predicted by particle simulation. To give a guideline for the design of laminar entrained flow pyrolysis reactors, the required reactor length for complete conversion of biomass was also calculated for the pyrolysis. High reaction temperature, small particles, and slower gas flow were favorable for high fuel conversion.

The introduction of alkali catalyst during hydrothermal liquefaction (HTL) improves conversion and allows the aqueous liquid product to be used as gasification feedstock. This study investigates the effect of reaction temperature (240–300°C), sawdust mass fraction (9.1–25%) and reaction time (0–60 min) during K2CO3-catalytic HTL of pine sawdust. The highest biomass conversion (75.2% carbon conversion and 83.0% mass conversion) was achieved at a reaction temperature of 270°C, 9.1% sawdust mass fraction and 30 min reaction time; meanwhile, the maximum aqueous product (AP) yield (69.0% carbon yield and 73.5% mass yield) was found at a reaction temperature of 300°C, 9.1% sawdust mass fraction and 60 min reaction time. Based on the main experimental results, models for carbon and mass yields of the products were developed according to face-centered central composite design using response surface methodology. Biomass conversion and product yields had a positive correlation with reaction temperature and reaction time, while they had an inverse correlation with sawdust mass fraction. Further investigation of the effects of biomass/water and biomass/K2CO3 ratios revealed that both high water loading and high K2CO3 loading enhanced conversion and AP yield.

This paper presents results from a thermogravimetric analysis and modelling based study using a fresh water alga, Chlorococcum humicola, and a Victorian Brown Coal and their blends at different proportions. Pyrolysis was studied using the pure coal and pure algae as well as their blends to a final temperature of 1000 °C at different heating rates to understand the kinetics. The kinetic data of pure algae and pure coal were used to predict the pyrolysis characteristics of coal–algae blends at various heating rates using a modified distributed activation energy model which closely matched the experimental data. The experimental results also indicate that there is no chemical interaction between the algae and coal during pyrolysis.

Municipal solid waste (MSW) management is a major concern for Bangladesh, given its high population density and increasing waste production rate. Conventional waste management methods, such as landfilling, result in high carbon emissions for the environment. With over 70% of MSW being organic, hydrothermal carbonization (HTC) has emerged as a promising technology for recovering energy and nutrients from such heterogeneous waste streams. This study aimed to compare the environmental effects of HTC coupled with electricity generation (HTC-EG) from MSW with traditional landfilling using life cycle assessment in the context of Bangladesh. The HTC-EG scenario showed lower environmental impacts in three out of five impact categories, specifically reducing climate change, freshwater ecotoxicity, and photochemical ozone formation. For a functional unit of 6000-ton MSW, HTC-EG reduces the climate change impact by 7.7 × 106 kg CO2 eq. Additionally, HTC-EG has 46.77% less impact on freshwater ecotoxicity compared to landfilling and reduces the photochemical ozone formation impact by 1.86 × 104 NMVOC eq. However, the HTC-EG scenario leads to increased particulate matter formation and marine water eutrophication due to SO2, SO3, and PM2.5 emissions during hydrochar combustion and nitrate release from the liquid stream of the HTC reactor, respectively. Addressing these challenges through appropriate post-processing of flue gas from hydrochar combustion and HTC liquid streams could make HTC-EG a viable alternative to landfilling for MSW management in Bangladesh.

This paper presents an ASPEN PLUS TM simulation study for excess methanol recovery in continuous biodiesel production process using a distillation column. The feedstock used for biodiesel production was Triolein containing 15% free fatty acid (Oleic Acid). The special attention was devoted to the effect of different alcohol to oil ratio and important design and operating parameters of distillation column on excess methanol recovery from the product. The energy consumption is represented by reboiler heat duty of distillation column. Analysis of simulation results shows that for a certain distillation operating condition and reaction parameters it is possible to recover around 95-98% of excess methanol before phase separation of biodiesel and glycerol, although for high alcohol to oil ratio the energy requirement increases exponentially. DOI: 10.3329/cerb.v13i2.3538 Chemical Engineering Research Bulletin 13 (2009) 55-60

Abstract The catalytic activity of alkali compounds in black liquor (BL) enables gasification at low temperatures with high carbon conversion and low tar and soot formation. The efficiency and flexibility of the BL gasification process may be improved by mixing BL with fuels with higher energy content such as pyrolysis oil (PO). The fate of alkali elements in blends of BL and PO was investigated, paying special attention to the amount of alkali remaining in the particles after experiments at high temperatures. Experiments were conducted in a drop tube furnace under different environments (5% and 0% vol. CO 2 balanced with N 2 ), varying temperature (800–1400 °C), particle size (90–200 µm, 500–630 µm) and blending ratio (0%, 20% and 40% of pyrolysis oil in black liquor). Thermodynamic analysis of the experimental cases was also performed. The thermodynamic results qualitatively agreed with experimental measurements but in absolute values equilibrium under predicted alkali release. Alkali release to the gas phase was more severe under inert conditions than in the presence of CO 2 , but also in 5% CO 2 most of the alkali was found in the gas phase at T = 1200 °C and above. However, the concentration of alkali in the gasification residue remained above 30% wt. and was insensitive to temperature variations and the amount of PO in the blend. Thermodynamic analysis and experimental mass balances indicated that elemental alkali strongly interacted with the reactor’s walls (Al 2 O 3 ) by forming alkali aluminates. The experience indicated that adding PO into BL does not lead to alkali depletion during high temperature gasification.

Hydrothermal carbonization (HTC) is a prominent thermochemical technology that can convert high-moisture waste into a valuable product (called hydrochar) at a relatively mild treatment condition (180–260 °C and 2–10 MPa). With rapidly growing research on HTC and hydrochar in recent years, review articles addressing the current and future direction of this research are scarce. Hence, this article aims to review various emerging applications of hydrochars, e.g., from solid fuel to soil amendment, from electron storage to hydrogen storage, from dye adsorption, toxin adsorption, heavy metal adsorption to nutrient recovery, and from carbon capture to carbon sequestration, etc. This article further provides an insight in the hydrochar’s working mechanism for various applications and how the applications can be improved through chemical modification of the hydrochar. Finally, new perspectives with appropriate recommendations have been made to further unveil potential applications and its improvement through hydrochar and its modified version.

Abstract In this study, the pyrolysis behavior of two lipid-extracted microalgal biomasses, specifically freshwater microalgae Chlorella sp. and marine microalgae Tetraselmis suecica , was examined using a thermogravimetric analyzer. The study assessed the effects of different heating rates (5, 10, and 15 °C/min) on the devolatilization stage and determined the kinetics using the Flyn–Wall–Ozawa and Kissinger–Akahira–Sunose methods. The activation energy and pre-exponential factor values for T. suecica were slightly lower compared with Chlorella sp. and other types of microalgal and lignocellulose biomasses. The results obtained from this study provide useful information for designing a pyrolytic processing system using lipid-extracted microalgal biomass as a feedstock.