Thermochemical conversion of press seed cake produced from non–edible biomass

Dhanavath, K 2017, Thermochemical conversion of press seed cake produced from non–edible biomass, Doctor of Philosophy (PhD), Engineering, RMIT University.

Document type: Thesis
Collection: Theses

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Title Thermochemical conversion of press seed cake produced from non–edible biomass
Author(s) Dhanavath, K
Year 2017
Abstract Demand for energy and its resources are increasing every day due to the rapid growth of population and urbanization. As the major conventional energy resources like coal, petroleum and natural gas are on the verge of getting depleted in this century, biomass, which is an important renewable energy resource, can be used to produce renewable bioenergy (i.e., heat and electricity), biochemical and biofuels. However, the use of biomass for energy, fuels and chemicals production has generated significant concerns across the globe, especially in developing nations, due to the shortage of food and cultivable land and extremely high population density. This has led to the use of non–edible biomass resources such as Karanja, Jatropha, Neem, Mahua, and Sorghum. These biomass resources are widely used for extracting bio–oil in countries like India, Pakistan, Bangladesh, China, and Sri Lanka. However, after the extraction of bio–oil, a significant portion of biomass (i.e., ~60 wt.% of the total biomass) is left as a residual waste and generally referred as Press Seed Cake (PSC). These PSCs, despite having a very high organic content, are currently being landfilled. The current work focuses on the thermochemical conversion of PSCs with an aim to produce bioenergy, biochemical and biofuels. The present study has utilized PSC generated from Karanja, Mahua, and Sorghum. Thermochemical conversion processes that include torrefaction, pyrolysis, gasification, and liquefaction have been investigate in detail. The focus of the thesis is therefore to study the thermochemical conversion of PSC produced from lignocellulosic biomass regardless of the type of original plant source.

The first part of this study demonstrated the efficiency of torrefaction process in upgrading the transport, storage and grinding characteristics of Karanja PSC, which is a lignocellulosic biomass. Torrefaction was carried out at different temperatures using residence time ranging from 10 to 90 min. The torrefaction experiments were performed using temperature in the range of 20–300 °C in a bench–scale vertical fixed bed reactor. The results showed that a significant change in elemental composition occurs with the reduction in O/C and H/C thereby increasing the calorific value and hydrophobicity of the torrefied biomass. The weight loss and the total energy remained in the fuel after torrefaction was found to be 30–35% and 80–85%, respectively. The HHV of the torrefied biomass was determined to be in the range of 19.5–21.5 MJ/kg. The kinetic parameters for thermal degradation namely, activation energy and pre–exponential factor, were determined from the experimental data as10.55 kJ/mol 0.341 min-1, respectively using a simple kinetic model involving single–step reaction mechanism for bio–char.

The second and third parts of this study systematically investigated the pyrolysis of Mahua PSC and Sorghum, respectively in a bench–scale vertical fixed bed reactor. Both Mahua and PSC and Sorghum are also valuable lignocellulosic biomasses. Effect of pyrolysis temperature on the production of bio–char, bio–oil and bio–gas was studied in detail. The advanced characterisation of bio–char, bio–oil and bio–gas was performed using scanning electron microscope (SEM), x–ray diffraction (XRD), elemental analyser (CHNS), calorific value (CV), Fourier transform infrared (FTIR) spectroscopy and gas chromatography–mass spectrometry (GC–MS). The results obtained indicate that an increase in the pyrolysis temperature from 350 to 550 °C leads to a decrease in the bio–char yield from 42.55 to 30.38%. On the other hand, the maximum bio–oil yield of 15.94% was obtained at 450 °C. The GC–MS analyses of bio–oil samples revealed the presence of various important chemicals such as octadecenoic acid, p–cresol, 2,6–dimethoxy phenol, 4–ethyl 2–methoxy phenol, phenol, o–guaiacol, octadecanoic acid and free fatty acids.

In the fourth part of the study, experimental investigations on the liquefaction of Karanja PSC were carried out in the presence of pyrolytic bio–oil (PBO) produced from the slow pyrolysis of the same feedstock. The effects of PBO to PSC ratio and liquefaction temperature were investigated with an aim to achieve the highest liquefaction conversion. Also, a study was carried out to compare the influence of PBO on liquefaction with that of a mixture of a conventional solvent such as phenol and an acid catalyst such as sulphuric acid. A detailed chemical analysis of PBO and liquefied product (bio–crude) was carried out using FT–IR, and GC–MS techniques. The results showed that the Karanja PSC could be directly liquefied in the presence of PBO at moderate reaction conditions. A maximum liquefaction conversion of 99% was obtained at a reaction temperature of 240 °C, a residence time of 160 min and a Karanja PSC to PBO ratio of 1:6. In contrast, ~ 94% conversion was obtained for the same residence time but at a significantly lower temperature of 160 °C when Karanja PSC, phenol and sulphuric acid were used in the mass ratio of 1:2:0.6.

In the fifth part of the study, oxygen–steam based entrained flow gasification of torrefied Karanja PSC was carried out in a bench–scale entrained flow reactor with a capacity of 1 kg/hr. The temperature was varied from 600 to 1100 °C. The equivalence ratio (ER), and steam to biomass ratio (SBR) values was ranged from 0.1 to 1.0 while the particle size, Dp was ranged from 0.5 to 3.0 mm. The aim was to obtain the optimum operating conditions for the entrained flow gasification of the torrefied Karanja PSC. The results obtained show that the optimum operating parameters include the temperature of 1100 °C, ER of 0.3, SBR of 0.4 and the particle size of 0.5 mm. The highest values of LHV, CGE, and the carbon conversion were found to be ~12 MJ/Nm3, ~90% and of 98%, respectively for the torrefied Karanja PSC.

In the sixth part of the study, an ASPEN Plus process simulation was carried out. A thermochemical equilibrium model (RGIBBS) in ASPEN Plus was used to predict the gasification behaviour of Karanja PSC. The modelling results were validated with experimental results obtained in an updraft fixed bed gasifier. Further to this, the model simulation was extended for different biomass wastes such as sawdust, rice husk, and sunflower husk. The effects of operating parameters like temperature, ER, and SBR on syngas composition, LHV and CGE were investigated.

The results obtained from the current study have made a significant contribution in demonstrating the value addition to PSC from lignocellulosic biomass. The knowledge gained from the present study can be applied to develop large–scale thermochemical conversion processes for PSC from any lignocellulosic biomasses with suitable modifications.
Degree Doctor of Philosophy (PhD)
Institution RMIT University
School, Department or Centre Engineering
Subjects Non-automotive Combustion and Fuel Engineering (incl. Alternative/Renewable Fuels)
Environmental Engineering not elsewhere classified
Chemical Engineering not elsewhere classified
Keyword(s) Thermochemical conversion
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Created: Fri, 20 Jul 2018, 11:53:48 EST by Denise Paciocco
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