Understanding optimal
process conditions is an essential step in
providing high-quality fuel for energy production, efficient energy
generation, and plant development. Thus, the effect of process conditions
such as the temperature, time, nitrogen-to-solid ratio (NSR), and
liquid-to-solid ratio (LSR) on pretreated waste pine sawdust (PSD)
via torrefaction and solvolysis is presented. The desirability function
approach and genetic algorithm (GA) were used to optimize the processes.
The response surface methodology (RSM) based on Box–Behnken
design (BBD) was used to determine the effect of the process conditions
mentioned above on the higher heating value (HHV), mass yield (MY),
and energy enhancement factor (EEF) of biochar/hydrochar obtained
from waste PSD. Seventeen experiments were designed each for torrefaction
and solvolysis processes. The benchmarked process conditions were
as follows: temperature, 200–300 °C; time, 30–120
min; NSR/LSR, 4–5. In this study, the operating temperature
was the most influential variable that affected the pretreated fuel’s
properties, with the NSR and LSR having the least effect. The oxygen-to-carbon
content ratio and the HHV of the pretreated fuel sample were compared
between the two pretreatment methods investigated. Solvolysis pretreatment
showed a higher reduction in the oxygen-to-carbon content ratio of
47%, while 44% reduction was accounted for the torrefaction process.
A higher mass loss and energy content were also obtained from solvolysis
than the torrefaction process. From the optimization process results,
the accuracy of the optimal process conditions was higher for GA (299
°C, 30.07 min, and 4.12 NSR for torrefaction and 295.10 °C,
50.85 min, and 4.55 LSR for solvolysis) than that of the desirability
function based on RSM. The models developed were reliable for evaluating
the operating process conditions of the methods studied.
The reaction kinetics
of solid fuel is a critical aspect of energy
production because its energy component is determined during the process.
The overall fuel quality is also evaluated to account for a defined
energy need. In this study, a two-step first-order reaction mechanism
was used to model the rapid mass loss of pine sawdust (PSD) during
torrefaction using a thermogravimetric analyzer (Q600 SDT). The kinetic
analysis was carried in a MATLAB environment using MATLAB R2020b software.
Five temperature regimes including 220, 240, 260, 280, and 300 °C
and a retention time of 2 h were used to study the mechanism of the
solid fuel reaction. Similarly, a combined demarcation time (i.e.,
estimating the time that demarcates the first stage and the second
stage) and iteration technique was used to determine the actual kinetic
parameters describing the fuel’s mass loss during the torrefaction
process. The fuel’s kinetic parameters were estimated, while
the developed kinetic model for the process was validated using the
experimental data. The solid and gas distributions of the components
in the reaction mechanism were also reported. The first stage of the
degradation process was characterized by the rapid mass loss evident
at the start of the torrefaction process. In contrast, the second
stage was characterized by the slower mass loss phase, which follows
the first stage. The activation energies for the first and second
stages were 10.29 and 141.28 kJ/mol, respectively, to form the solids.
The developed model was reliable in predicting the mass loss of the
PSD. The biochar produced from the torrefaction process contained
high amounts of the intermediate product that may benefit energy production.
However, the final biochar formed at the end of the process increased
with the increase in torrefaction severity (i.e., increase in temperature
and time).
The data provided in this article supplements the data information provided in “Techno-economic analysis of electricity and heat production by co-gasification of coal, biomass and waste tyre in South Africa” [1]. The generation of the data considered co-generation of a coal sample (Matla coal) with pine sawdust, sugarcane bagasse, corn cob, and waste tyre at a blend ratio of 1:1, 3:2, and 4:1. The cost evaluation of the use of the feedstocks was considered with feedstock costing (WFC) and without feedstock costing (WOFC). Profitability assessment tools for the case study included NPV, IRR and PBP. The data as contained in this article could be useful for a quick decision making on a similar project by the government and stakeholders in the sector.
Kinetic studies of heterogeneous catalytic reactions form a crucial step necessary for the understanding of catalytic behaviour of a catalyst towards designing, controlling and optimizing a reactor. This study reports kinetics of waste animal fat oil (AFO) transesterification to biodiesel using waste-derived heterogeneous catalyst, hydroxy sodalite (HSOD) in a batch reactor. The catalyst was synthesized from coal fly ash and waste industrial brine via hydrothermal treatment. At a temperature range of 49 - 62 °C and a time range of 30 -120 minutes, the transesterification of animal fat oil to biodiesel was conducted at a fixed methanol/oil mass proportion 9:1, percent mass weight of catalyst 3 (based on the AFO) and stirring intensity of 300-500 rpm. Experimental findings reveal that reaction rate, which is first-order, was anticipated to increase with increasing temperature, resulted in an activation energy and a pre-exponential factor of 58554.65 J mol-1 and 2.83 min-1, respectively. The value of the activation energy suggests that the reaction is endothermic and a minimum energy of 58.55 kJ is required to achieve an effective collision at a frequency of 2.83 min-1. The highest biodiesel yield was 90 % at 62 °C and this corresponds to a highest AFO conversion of 93 % at a reaction time of 120 minutes.
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