Serdar Yaman

Pyrolysis of biomass to produce fuels and chemical feedstocks

This review presents the summary of new studies on pyrolysis of biomass to produce fuels and chemical feedstocks. A number of biomass species, varying from woody and herbaceous biomass to municipal solid waste, food processing residues and industrial wastes, were subjected to different pyrolysis conditions to obtain liquid, gas and solid products. The results of various biomass pyrolysis investigations connected with the chemical composition and some properties of the pyrolysis products as a result of the applied pyrolysis conditions were combined. The characteristics of the liquid products from pyrolysis were examined, and some methods, such as catalytic upgrading or steam reforming, were considered to improve the physical and chemical properties of the liquids to convert them to economic and environmentally acceptable liquid fuels or chemical feedstocks. Outcomes from the kinetic studies performed by applying thermogravimetric analysis were also presented.

Production of fuel briquettes from olive refuse and paper mill waste

Some processes have been widely applied to biomass in order to take advantage of its energy potential. In particular, these processes are based on pyrolysis or gasification. In this study, briquetting was applied to olive refuse and paper mill waste to form fuel briquettes. For this purpose, the particle sizes of both biomass samples were decreased to −250 μm and then they were briquetted in a steel die under pressure between 150 and 250 MPa at ambient temperature. Effects of the moisture content of the biomass samples and briquetting pressure on the shatter index, compressive strength, and water resistance of the briquettes obtained were investigated. This study showed that the mechanical strength of the briquettes produced only from the olive refuse was not high enough. On the other hand, strong briquettes were produced using paper mill waste. When olive refuse was blended with fibrous paper mill waste, briquettes with sufficiently high mechanical strength could be produced. Burning profiles of the samples were derived applying derivative thermogravimetry technique under dynamic dry air atmosphere up to 1273 K with a heating rate of 40 K·min−1 and then combustion characteristics of the briquettes were compared.

FUEL BRIQUETTES FROM BIOMASS-LIGNITE BLENDS

In this study, a western Turkish lignite (Kutahya-Seyitomer) was blended with some biomass samples such as molasses, pine cone, olive refuse, sawdust, paper mill waste, and cotton refuse, and these blends was used in the production of fuel briquettes. Blends were subjected to briquetting pressures between 50 and 250 MPa; the ratio of biomass to lignite was changed between 0 and 30 wt.%. The mechanical strength of obtained briquettes was investigated considering shatter index and compressive strength. Effects of the ratio of biomass to lignite and applied pressure on the strength of the briquettes were examined. This study indicated that the mechanical strength of the briquettes produced from Kutahya-Seyitomer lignite can be improved by adding some biomass samples. For example, the presence of paper mill waste increased the shatter index of the briquettes obtained. Similarly, sawdust and paper mill waste increased compressive strength of the briquettes. Water resistance of the briquettes can be augmented by adding olive refuse, cotton refuse, pine cone or paper mill waste.

Effect of lignite properties on reactivity of lignite

The purpose of this study is to relate the combustion reactivity of lignite to its physical and chemical properties. Non-isothermal thermogravimetry, where the sample whose temperature increased at a linear rate (40 K/min) was heated in air, has been used to investigate the combustion reactivities of 25 lignite samples originating from different areas of Turkey. Since combustion reactivity is affected by the chemical and physical properties of coal, the combustion reactivity of the lignites used in this study was related to their proximate and ultimate analysis results and physical properties such as pore structure and surface area. The calculated activation energy values for the combustion reactions of the lignites ranged between 64 and 139 kJ/mol. Definite correlations between the activation energy values and the above-mentioned properties were found.

Sulfur removal from lignite by oxydesulfurization using fly ash

The sulfur removal potential of the water-soluble fraction of fly ash in oxydesulfurization of coal was investigated using some high-sulfur Turkish lignites. The effects of the amount of fly ash used, temperature, partial pressure of oxygen and time were studied in the ranges 5–40 g, 403–498 K, 0.0–1.5 MPa and 15–90 min respectively. The extents of pyritic and organic sulfur removal and recoveries of coal and calorific value were investigated for each of these variables. Reactivity and some combustion characteristics (ignition temperature, end temperature of combustion and combustion rate) of original and desulfurized lignite samples were compared using combustion curves obtained from thermogravimetric analysis (t.g.a.) results. FT-i.r. spectroscopy was used to determine the effects of the desulfurization process on the coal structure.

Is torrefaction of polysaccharides-rich biomass equivalent to carbonization of lignin-rich biomass?

Waste biomass species such as lignin-rich hazelnut shell (HS) and polysaccharides-rich sunflower seed shell (SSS) were subjected to torrefaction at 300°C and carbonization at 600°C under nitrogen. The structural variations in torrefied and carbonized biomasses were compared. Also, the burning characteristics under dry air and pure oxygen (oxy-combustion) conditions were investigated. It was concluded that the effects of carbonization on HS are almost comparable with the effects of torrefaction on SSS in terms of devolatilization and deoxygenation potentials and the increases in carbon content and the heating value. Consequently, it can be proposed that torrefaction does not provide efficient devolatilization from the lignin-rich biomass while it is relatively more efficient for polysaccharides-rich biomass. Heat-induced variations in biomass led to significant changes in the burning characteristics under both burning conditions. That is, low temperature reactivity of biomass reduced considerably and the burning shifted to higher temperatures with very high burning rates.

Kinetic modelling of RDF pyrolysis: Model-fitting and model-free approaches

In this study, refuse derived fuel (RDF) was selected as solid fuel and it was pyrolyzed in a thermal analyzer from room temperature to 900°C at heating rates of 5, 10, 20, and 50°C/min in N2 atmosphere. The obtained thermal data was used to calculate the kinetic parameters using Coats-Redfern, Friedman, Flylnn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) methods. As a result of Coats-Redfern model, decomposition process was assumed to be four independent reactions with different reaction orders. On the other hand, model free methods demonstrated that activation energy trend had similarities for the reaction progresses of 0.1, 0.2-0.7 and 0.8-0.9. The average activation energies were found between 73-161kJ/mol and it is possible to say that FWO and KAS models produced closer results to the average activation energies compared to Friedman model. Experimental studies showed that RDF may be a sustainable and promising feedstock for alternative processes in terms of waste management strategies.

Effect of oxydesulphurization on the combustion characteristics of coal

Abstract Desulphurization of a Turkish lignite by oxydesulphurization using dilute alkaline solutions, obtained by the extraction of fly ash with water, was carried out under 0–1.5 MPa partial pressure of oxygen at temperatures between 403 and 498 K for 30–90 min time intervals. TGA was performed to compare the combustion characteristics of original and desulphurized lignite samples. DTG curves were derived and the effects of desulphurization conditions such as temperature, partial pressure of oxygen and time on coal reactivity were studied considering ignition temperature, maximum combustion rate, combustion period, and the end temperature of combustion. Relations between coal reactivity and removals of sulphur and ash contents were also studied.

THERMOGRAVIMETRIC INVESTIGATION ON THE THERMAL REACTIVITY OF BIOMASS DURING SLOW PYROLYSIS

Agricultural biomass samples such as sunflower shell, colza seed, cotton refuse, and olive refuse were submitted to nonisothermal thermogravimetric analysis to examine the effects of the sample properties on the thermal reactivity during slow pyrolysis with heating rate of 20 K/min from ambient to 1273 K. The activation energies were determined in the range of 37.4–46.6 kJ/mol. The proximate- and ultimate- analysis results and the major constituents in biomass such as hemicellulosics, cellulosics, and lignin were found to have significant influences on thermal behavior such as the maximum decomposition rates and their temperatures, and the char yields.

Investigation of the Combustion Characteristics of Zonguldak Bituminous Coal Using DTA and DTG

Combustion characteristics of coking, semicoking, and noncoking Turkish bituminous coal samples from Zonguldak basin were investigated applying differential thermal analysis (DTA) and differential thermogravimetry (DTG) techniques. Results were compared with that of the coke from Zonguldak bituminous coal, a Turkish lignite sample from Soma, and a Siberian bituminous coal sample. The thermal data from both techniques showed some differences depending on the proximate analyses of the samples. Noncombustible components of the volatile matter led to important changes in thermal behavior. The data from both methods were evaluated jointly, and some thermal properties were interpreted considering these methods in a complementary combination.