Khanh-Quang Tran

Towards Sustainable Production of Biofuels from Microalgae

Renewable and carbon neutral biofuels are necessary for environmental and economic sustainability. The viability of the first generation biofuels production is however questionable because of the conflict with food supply. Microalgal biofuels are a viable alternative. The oil productivity of many microalgae exceeds the best producing oil crops. This paper aims to analyze and promote integration approaches for sustainable microalgal biofuel production to meet the energy and environmental needs of the society. The emphasis is on hydrothermal liquefaction technology for direct conversion of algal biomass to liquid fuel.

Pyrolysis of microalgae residues--A kinetic study.

Pyrolysis of residues from the oil extraction process of two types of microalgae, Chlamydomonas (C. sp. JSC4) and Chlorella sorokiniana (C. Sorokiniana CY1) was studied by means of a thermogravimetric analyzer. Five pseudo-components (hemicellulose, cellulose, lignin, lipid and protein) model with n=1 or n#1 was assumed for a kinetic analysis of the collected pyrolysis data. The model with n#1 resulted in a slightly better fit quality and reasonable kinetic parameters. The calculated activation energy of hemicellulose, cellulose, lignin, lipid, protein was 115.12-117.12 kJ/mol, 181.67-198.30 kJ/mol, 61.74-62.75 kJ/mol, 104.93-114.14 kJ/mol and 90.75-99.31 kJ/mol, respectively, for C. sp. JSC4; and 113.12-117.12 kJ/mol, 218.73-28.79 kJ/mol, 64.77-66.39 kJ/mol, 131.97-143.63 kJ/mol and 108.03-118.13 kJ/mol, respectively, for C. Sorokiniana CY1.

Development of a biomass torrefaction process integrated with oxy-fuel combustion.

Torrefaction of forest residues was studied under conditions relevant to oxy-fuel combustion flue gases. The results showed that the torrefaction in CO2 had a lower solid mass yield (81.36%) than that (83.06%) in N2. Addition of steam into CO2 (CO2/H2O=1/0.7 mole/mole) resulted in a higher mass yield (83.30%) compared to 81.36% in CO2. The energy yield was consistently increased from 79.17% to 84.12% or 88.32% for the torrefaction in N2, CO2, or the CO2 and steam mixture, respectively. On the other hand, additions of O2 into the mixture of steam and CO2 led to reductions in both mass yield (from 83.30% to 82.57% or 76.44%) and energy yield (from 88.32% to 84.65% or 79.16%, for the torrefaction in steam and CO2 without O2, with 5% v/v, or 10% v/v of O2, respectively).

Fast hydrothermal liquefaction for production of chemicals and biofuels from wet biomass - The need to develop a plug-flow reactor.

Hydrothermal liquefaction (HTL) is a promising technology for converting wet plant biomass directly to liquid fuels and chemicals. However, some aspects of the technology are not fully understood and still disputed. The reactor material constraints and difficulties coupled with the formation of unwanted products are the main challenges limiting the applications of the technology. In addition, heat and mass transfer limitations in the reaction system result in a lower conversion efficiency and selectivity, of which the later would make it difficult and expensive for products separation, purification, and/or modification of the products. This paper discusses the challenges and current status of possible solutions to the challenges, focusing on the need of developing a special plug-flow reactor for scaling up of the HTL process.

Cost modeling approach and economic analysis of biomass gasification integrated solid oxide fuel cell systems

This paper presents a cost modeling approach and the economic feasibility for selected plant configurations operating under three modes: air gasification, mixed air-steam gasification, and steam gasification combined cycle solid oxide fuel cell (SOFC) systems. In this study, three cases of biomass gasification integrated SOFC without combined cycle (base case 1) are compared with biomass gasification integrated SOFC-gas turbine (GT) with heat recovery steam generator (HRSG) hybrid configuration (case 2) and biomass gasification integrated SOFC-steam turbine (ST) cycle (case 3) for biomass feed stock. The plant design cases of integrated biomass gasification processes, SOFC, and combined cycles are investigated primarily employing aspen plus™ flow sheeting models. Based on the mass and energy balance results of the system simulations, the economic model calculates the size and cost estimates for the plant configuration equipments. Detailed purchase cost estimations for each piece of equipments and the corr...

Hydrochar slurry fuels and high-grade activated carbon for electricity production and storage Conceptual process design and analysis

This paper describes and analyzes a conceptual design of a bioenergy system for sustainable electricity production from low-grade biomass resources such as forest and agricultural residues, which is suitable for rural areas in developing regions susceptible to intermittent electricity supply. In order to make it a closed-loop system, the paper also identifies a bio-refining strategy focusing on production of high-grade activated carbons for energy storage using supercapacitor.

CO2 Reactivity Assessment of Woody Biomass Biocarbons for Metallurgical Purposes

Replacing the use of fossil reductants with biocarbons in metallurgical industries has a great potential with respect to reducing CO2 emissions and the contribution from this industry to the increasing greenhouse gas effect. However, biocarbons are significantly different from fossil reductants and the biocarbon properties vary in a wide range depending on the raw biomass properties and the biocarbon production process conditions. A key property of the biocarbons is their reactivity in the specific metallurgical process. The reactivity should be appropriate for the specific metallurgical process, to ensure an optimum reduction process. Especially important is the biocarbon reactivity towards CO2, i.e. the CO2 gasification of biocarbon fixed carbon. A standard method has earlier been developed by the metallurgical industry to test the CO2 reactivity of coal and coke. This can be adopted also for biocarbons. However, a simpler and more cost-efficient reactivity test method is wished for. For the silicon industry, also SiO reactivity is important and a standard method has been developed. This is very expensive to carry out, and also here a simpler and more cost-efficient reactivity test method is wished for. If a qualitative correlation between SiO and CO2 reactivity could be established as well, this would be very beneficial for this metallurgical industry. In this study, the main objectives were to assess the CO2 reactivity of biocarbons produced from different woody biomass in two experimental setups, a standardized setup and a thermogravimetric analyser (TGA), and to compare with the reactivity of fossil reductants. Spruce and birch stem wood and in addition their forest residues were tested. The results show that even if quantitatively different results were found in the two experimental setups, the qualitative results were the same, and hence the TGA test provides the opportunity of a simplified and cost-efficient CO2 reactivity test method. The biocarbon from the forest residues showed a higher reactivity than stem wood biocarbon, probably due to the higher ash content in the forest residues and their biocarbons, giving a catalytic effect. Compared to coke the biocarbons were more reactive.

Process Intensification and Process Integration for Hydrothermal Processing of Forest Residues and Agricultural Wastes

Abstract Hydrothermal processing involves the use of hot-compressed water as reaction medium. Therefore, it is very suitable for treatment of low-grade (wet) biomass resources such as forest residues, agricultural wastes, and aquatic biomass. The technology offers a number of potential advantages, over other methods, including the ability to use mixed feedstock like wastes and lignocelluloses, the production of direct replacements for existing fuels, and no need to predry the feedstock. However, a number of engineering challenges remain hindering the technology from industrial application for large-scale production of biofuels and chemicals. In addition, hydrothermal media itself is energy-sensitive, which requires good solutions for heat recovery to make the process energetically sustainable. This chapter provides state-of-the-art information and presents knowledge of hydrothermal processing of wet forest residues, agricultural wastes, and aquatic biomass for the production of biofuels and chemicals. Details of the remaining engineering challenges will be discussed in combination with an introduction of two concepts, process intensification and process integration.