Thermogravimetric and kinetic analyses of oil palm empty fruit bunch (OPEFB) pellets using the distributed activation energy model

The thermal degradation behaviour and decomposition kinetics of oil palm empty fruit bunch (OPEFB) pellets were investigated using a thermogravimetric analyser and the distributed activation energy model (DAEM). The OPEFB pellets were heated from 30°C to 1000°C at three different heating rates (5, 10, 20°C min-1) under a nitrogen atmosphere. The thermogravimetric-derivative thermogravimetric (TG-DTG) curves revealed that the non-isothermal decomposition of OPEFB pellets occurred in the following three stages: drying (35°C-175°C), active pyrolysis (200°C-370°C) and passive pyrolysis (370°C-1000°C), which resulted in the loss of moisture, volatile matter and char, respectively. The distributed activation energy model was subsequently used to determine the apparent activation energies (E) and pre-exponential factors (A), which ranged from 37.89 kJ mol-1 to 234.05 kJ mol-1 and from 2.05 × 102 min-1 to 3.54 × 1018 min-1, respectively, for conversions of α = 0.05-0.70 during the thermal degradation. The wide E and A distributions obtained from the kinetic analysis are attributed to the complex chemical reactions of pyrolysis. The kinetic analysis revealed the kinetic compensation effect (KCE), with the highest E and A values occurring in the range of α = 0.2-0.4. This result indicates that the active pyrolysis stage is the rate-determining step during the thermal decomposition of OPEFB pellets

Model free kinetics analysis of Imperata cylindrica (Lalang)

This study is the first attempt at investigating the solid state decomposition and the devolatilization kinetics of Imperata cylindrica (lalang) grass termed the “farmer’s nightmare weed” as a potential solid biofuel of the future. Biomass conversion technologies such as pyrolysis and gasification can be utilized for future green energy needs. However an important step in the efficient utilization and process optimizing of biomass conversion processes is understanding the thermal decomposition kinetics of the feedstock. Consequently, thermogravimetric analysis (TGA) of Imperata cylindrica was carried out in the temperature range of 30-1000 °C at four heating rates of 5, 10, 15, and 20 K min-1 using Nitrogen at a flow rate of 20 L min-1 as purge gas. Using the TGA results, the kinetic parameters activation energy (Ea) and pre-exponential frequency factor (ko) of the grass were estimated via the model free or isoconversional methods of Kissinger and Starink. The results obtained for Kissinger model were 151.36 kJ mol-1 and 5.83 × 109 min-1 for activation energy and pre-exponential frequency factor respectively. However, Starink model activation energy and pre-exponential frequency factor were a function of conversion (α) with average values of 159.93 kJ mol-1 and 6.33 × 1022 min-1 respectively

Combustion kinetics of Shankodi-Jangwa coal

The lack of comprehensive data on the fuel properties of newly discovered coal deposits in Nigeria has hampered the prospective utilisation for power generation. Consequently, this study is aimed at characterising the physicochemical and thermokinetic properties of Shankodi-Jangwa (SKJ) coal recently discovered in Nassarawa state, Nigeria. The results indicate that SKJ comprises 40.50% fixed carbon, 43.34% volatile matter, and 2.36% sulphur with a higher heating value (HHV) of 27.37 MJ kg-1. Based on this HHV, SKJ was classified as high-volatile B bituminous coal. Thermal analysis of SKJ under oxidative thermogravimetry (TG) at multiple heating rates revealed that SKJ is highly reactive and thermally degradable below 1000°C. Kinetic analysis using the Flynn-Wall-Ozawa model for conversions α = 0.05-0.90 revealed the activation energy to range from Ea = 113-259 kJ mol-1, with the frequency factor ranging from A = 2.9 × 1013-1.5 × 1023 min-1 and a range in R2 = 0.8536-0.9997; the average values of these ranges are Ea = 184 kJ mol-1, A = 9.2 × 1023 min-1 and R2 = 0.9420, respectively. The study highlighted fuel property data vital for modelling and designing future SKJ coal power generation

Dynamic control of sensor and actuator failures in multivariable distillation column

This paper examines the impact of sensor and actuator failures in the operation of a multivariable distillation column. Several failure scenarios are evaluated including failures of sensors and actuators in various scales of magnitudes and durations. The results obtained illustrate the ability of process controllers in suppressing the impact of these unwanted events. Closed-loop dynamic responses of the process revealed capabilities of these controllers in dealing with upsets that are small in magnitude and duration. In the case of larger and longer process upsets, process controllers are not adequate in providing the necessary corrective measures. This leaves the necessary interventions to be taken by the plant operators, following alarms that would have been triggered in typical plant operation scenario

Gasification of oil palm empty fruit bunches (OPEFB) briquettes for bio-syngas production

Gasification of Oil Palm Empty Fruit Bunches (OPEFB) briquettes was investigated in an air blown 4.5 kW allothermal fluidized bed gasifier to examine the effects of bed temperature (600-800 °C) and equivalence ratio (λ = 0.25) on bio-syngas yield and composition. In addition, physicochemical and thermochemical characterization of the fuel properties of the OPEFB briquettes were also examined. The results demonstrate that pelletization improved the solid biomass fuel (SBF) properties of OPEFB including moisture content and higher heating value (HHV). The gasification of OPEFB briquettes produced bio-syngas comprising H2, CO, CO2, CH4 as well as solid biochar with a HHV higher than the original OPEFB briquettes. The highest yield of H2 was obtained at 600 °C while HHV of the bio-syngas was within the range 4-8 MJ/Nm3 for air gasification in fluidized bed gasifiers. In addition, agglomeration of bed materials did not occur during OPEFB briquettes gasification despite its high bed agglomeration potential (BAP). In conclusion, the gasification of OPEFB briquettes into bio-syngas and biochar is a practical route for bioenergy production in Malaysia

Sensitivity analysis of biohydrogen production from Imperata cylindrica using stoichiometric equilibrium model

This paper investigated the production of biohydrogen from Imperata cylindrica, using stoichiometric equilibrium model. The stoichiometric equilibrium model uses biomass ultimate analysis, thermodynamic equilibrium and elemental balance on biomass gasification reaction. The sensitivity analysis was studied over a wide range of operating conditions involving temperature (250-1500 °C), ressure (1-5 atm) and Steam to fuel ratio (0-5). The result shows biohydrogen and other biogas product were sensitive to temperature and steam-feed ratio, whereas effect of pressure is negligible. The operating condition for optimal biohydrogen production in moles (23%) was atmospheric pressure, temperature, 1500 °C and steam-feed ratio, 5. Biogas product mixtures are H2, 23%, CO, 17%, CO2, 12% CH4, 0% and H2O, 60%. Increase in steam-feed ratio (0, 1, 2, 3, 4 and 5) significantly increase the biohydrogen by 1381%, 90%, 46%, 31% and 24%. The stoichiometry equilibrium model could effectively be used in determining biohydrogen production and its sensitivity to temperature and steam

Unknown input observer design for fault detection and diagnosis in a continuous stirred-tank reactor

Early and accurate fault detection and diagnosis (FDD) minimises downtime, increases the safety and reliability of plant operation, and reduces manufacturing costs. This paper presents a robust FDD strategy for a nonlinear system using a bank of unknown input observers (UIO). The approach is based on structure residual generation that provides not only decoupling of faults from model uncertainties and unknown input disturbance but also decoupling the effect of a fault from the effects of other faults. The generated residual was evaluated through the statistical threshold to avoid fault missing or false alarm. The performance of the robust FDD scheme was assessed by some sensor fault scenarios created in a continuous stirred-tank reactor (CSTR). The simulation result showed the effectiveness of the proposed approach