Bio-oil production from agro-residues by ablative pyrolysis and utilization in small engines

Abstract

Bio-oil from agro-residues by thermochemical conversion process is a value-added liquid biofuel that has potential to be upgraded to chemical products. This research studied the properties, production of bio-oil and utilization in a small engine. This work included three stages, (i) properties and thermal degradation kinetic analysis including FWO, KAS, Kissinger methods, and discrete DAEM method in different heating rates for predicting behavior of biomass decomposition. (ii) Experimental ablative pyrolysis simplified heat conduction model to represent the temperature and heating rate at various thickness of biomass during pyrolysis. (iii) The bio-oil production through the pyrolysis process in a fixed-bed reactor at 600C, the analysis of performance (including brake thermal efficiency (BTE), brake-specific fuel consumption (BSFC)) and emission characteristics (including carbon monoxide (CO), and unburnt hydrocarbon (HC)) in a small four-stroke compression ignited engine fueled with biomass pyrolysis oil/diesel blends. From the results the kinetic parameters by FWO, KAS, and Kissinger methods of hemp residue pyrolysis between the heating rates of 15 and 50 C/min included three various zones (i) water evaporation, (ii) passive, and (iii) active pyrolysis. The main conversion changed the mass of raw materials by 70% w/w in the range of temperature from 250-350C. The activation energy of the FWO and KAS method was reported to be 250 and 370 kJ/mol with the mean value of 265.5 and 291.5 kJ/mol, respectively. The Kissinger method gave a constant value to be 282.3 kJ/mol. It was found that the KAS and FWO method completely showed the complex devolatilization of the hemp residues pyrolysis. For the discrete DAEM method, heating rates from low (10, 25, and 50 ◦C/min) to intermediate (100, 125, and 150 ◦C/min) were considered. The discrete DAEM was found to be more accurate and very highly correlated. Totally, the kinetic and thermodynamic parameters indicated that the low heating rates were more relevant than intermediate heating rates due to its high reactivity. The low and intermediate heating rates were evident that the two different reaction mechanisms at 60 and 25 parallel first-order pyrolytic reactions, respectively. The activation energy and enthalpy change (ΔH) changed in range of 240–320 kJ/mol. The Gibbs free energy (ΔG), and the entropy change (ΔS) were 120–200 kJ/mol, and 120–300 J/mol∙K, respectively. The reactions under intermediate heating rates were near thermodynamic equilibrium and stability. Fluctuation of E and ΔH were between 80 and 250 kJ/mol. The ΔG, and ΔS were within 160–200 kJ/mol, and - 100 and 100 J/mol∙K, respectively. It was suggested that hemp hurds can be future converted to bioenergy and biochemical production by pyrolysis process. The heat evolution of the ablative process showed two main regions (transient and steady states). At high temperature, a small size sample allowed the shortest time to the steady state, and the major region were transient period, which released volatiles. The hot plate was given at the temperature of 550C, and the rate of heat transfer was also peaked to a maximum value of 11C/s or 660C/min which was the fast pyrolysis. This study was valuable to design a high performance ablative pyrolysis reactor for generating high yield of liquid biofuel. In the final part, production of pyrolysis oil and engine test were carried out. The liquid biofuel “Teak Sawdust Pyrolysis oil (TSPO)” was generated from teak sawdust at 600◦C through a fixed-bed reactor with water content < 1% after its properties was improved. The TSPO/diesel blend was prepared for 10,25,50% with diesel. For the engine performance of TSPO/diesel blends, the highest BTE was reported for the lowest BSFC of 25% TSPO blend, at 2000 rpm. Higher TSPO blends contained high oxygen level for combustion reducing HC and CO emissions. In addition, CO, and HC level showed lower emission at 50% TSPO blend, 2000 rpm. It is noted that the bio-oil from biomass pyrolysis could be mixed with diesel fuel and run in a small engine successfully.