Colette Braekman-Danheux

Characterization of refuse-derived char from municipal solid waste: 1. Phase-mineral and chemical composition

Abstract The composition of refuse-derived char (RDC) generated by thermolysis of municipal solid waste (MSW) was studied to provide a detailed phase-mineral and chemical characterization of RDC and RDC ash. The examined RDC has main chemical characteristics similar to some subbituminous and bituminous coals, but seems to be enriched in ash and N, and depleted in VM, H and S. The high-temperature ash of RDC belongs to calsialic coal ashes abundant in P and Ti. This char is a complex mixture of intimately mixed original and newly formed organic and inorganic constituents with fluid inclusions. The organic matter consists of slightly changed and char (semicoke and coke) components generated from paper, wood, textile, plastic materials, food remains and other organic products in MSW. The major inorganic phases and minerals identified in the RDC are generally quartz, calcite, glass, kaolinite, talc, illite, muscovite, zeolite, K-feldspar, chlorite, magnetite, hematite, rutile, gypsum, halite and apatite. A number of minor (vermiculite, plagioclase, montmorillonite, sepiolite, corundum, anhydrite, barite, hydrophilite, aluminium and alloys) and accessory (cristobalite, biotite, wollastonite, goethite, spinel, portlandite, brucite, jarosite, hexahydrite, ettringite, thenardite, Na–K–Mg–Fe chlorides, dolomite and ankerite) mineral phases are also present in RDC. Modes of occurrence, abundance and some genetic features of the minerals and phases found are described and summarized. The behaviour of minerals, phases, major and minor elements during the thermolysis of MSW and combustion of RDC (500–1200°C) is also discussed.

Characterization of refuse-derived char from municipal solid waste: 2. Occurrence, abundance and source of trace elements

Abstract The trace elements in refuse-derived char (RDC) generated by thermolysis of municipal solid waste (MSW) were studied to elucidate their occurrence, abundance and source. The content, enrichment factor, concentration trend, distribution, nature and modes of occurrence of major, minor and trace elements in RDC and RDC ash were characterized. It was found that a number of trace elements (Ag, Cd, Cl, Cr, Cu, Ho, I, Pb, Pr, Re, Sb, Sm, Sn, and Zn) in RDC have concentrations significantly higher (enrichment factor ≥10) than the respective Clarke (worldwide averaged) values for coals. The distribution of trace elements such as Cr, Cu, Mn, Ni, Pb, Sb, and Zn, is controlled mostly by the organic matter, clay minerals and Fe oxyhydroxides, and in some cases by carbonates, sulphates, phosphates, chlorides and alloys. Organics, heavier, magnetic, fine and especially accessory minerals and phases in RDC are concentrating phases for these trace elements. Trace elements in RDC may be present, in decreasing order of significance, as: element-organic compounds; impurities in the mineral matter; major components in the mineral matter; major and impurity components in the inorganic amorphous matter; and elements in the fluid constituents. This characterization also reveals those elements that have the greatest potential for environmental impacts or for possible resource recovery. The results show that the effective economic and environmental management of MSW and RDC requires a long-term strategy based on a detailed understanding of the source, formation, behaviour and fate of the modes of trace element occurrences in MSW, RDC and combustion waste residues.

Behaviour, capture and inertization of some trace elements during combustion of refuse-derived char from municipal solid waste

Abstract An investigation of refuse-derived char (RDC) generated by thermolysis of municipal solid waste (MSW) was undertaken to elucidate the behaviour of some toxic and potentially toxic trace elements (Cr, Cu, Mn, Ni, Pb, Sb, and Zn) plus Fe during combustion of RDC. About 87% of Sb, 66% of Pb, 60% of Cu and significant parts of Fe>Zn>Ni>Mn>Cr from the RDC are volatile at 1200°C, and their behaviour in the temperature interval 500–1200°C is characterized. The use of sorbents (zeolite, kaolinite, montmorillonite, coals enriched in kaolinite and calcite, and lime plus portlandite) for capture, solidification and inertization of the most volatile elements during combustion of RDC is also described. Perspective sorbents and inertants for a retention of the most volatile Pb, Sb and Cu in RDC ash are kaolinite and montmorillonite or coals enriched in these minerals. In addition, when there is an effective RDC washing (dechlorination and desulphurization), the use of sorbents for capture of some metals could be reduced or even avoided. Recommendations are given for RDC utilization and improvisation of the collection, separation procedures and removal efficiency of some heavy-metal, chloride and sulphate compounds from MSW and RDC prior to their use. The results show that a long-term strategy based on detailed understanding of the source, formation, behaviour and fate of the elements and their modes of occurrence in MSW, RDC and combustion waste residues is required in order to validate a perspective waste pyrolytic processes development.

Low cost catalytic sorbents for NOx reduction - 1. Preparation and characterization of coal char impregnated with model vanadium components and petroleum coke ash

Abstract Spanish coal, char and activated char doped with model vanadium components (V 2 O 5 and NH 4 VO 3 ) and petroleum coke ash (enriched in V, Fe, and Ni) were prepared and characterized as potential catalytic sorbents for NO x reduction. The phase-mineral and chemical composition, content and behavior (capture, retention, distribution, and redistribution) of transition metals, as well as morphogenesis, surface area, acid–base properties, surface active sites and oxidation–reduction transformations of the catalytic sorbents were characterized. It was found that minerals and phases such as anhydrite, calcite, clay minerals, pyrite, pyrrhotite, magnetite and fusinoid-type ingredients have a leading role for the behavior of loaded transition metals. Some original (pyrite, jarosite, shcherbinaite, coulsonite, trevorite, Ni oxide) and newly formed (pyrrhotite, magnetite, wuestite, hematite, paramontroseite, karelianite) Fe, V and Ni minerals in the catalytic sorbents are perspective redox indicators for the physicochemical conditions in such complex system. The data indicate that the V–Fe–Ni containing minerals dispersed onto and into the carbon support may be the most active catalytic sites. The preparation procedure that could provide the most favorable conditions for the production of effective and low cost catalytic sorbents for NO x reduction is also described.

Coal hydromethanolysis with coke-oven gas: 2. Influence of the coke-oven gas components on pyrolysis yields

Abstract To improve the economics of the hydropyrolysis of coal by reducing the hydrogen cost, it has been suggested that coke-oven gas be used instead of pure hydrogen. The present paper describes the role of methane and some minor components in the coke-oven gas during pyrolysis and their influence on the oil and gas yields. Pyrolysis was conducted at 765°C under 3 MPa of various gas mixtures simulating coke-oven gas. The results clearly demonstrate the possibility of using coke-oven gas for coal pyrolysis and lead to the conclusion that synergy between metallurgical cokemaking and ‘creaming-off’ coal by hydropyrolysis will be profitable to both processes.

Coal hydromethanolysis with coke-oven gas: 1. Influence of temperature on the pyrolysis yields

Abstract In order to improve the economy of the hydropyrolysis process by reducing the hydrogen cost, pyrolysis of coal has been carried out with a simulated coke-oven gas (55% H2, 30% CH4, 15% N2) as the reactive gas at 3 MPa and between 700 °C and 900 °C. Comparisons have been made with hydropyrolysis, pyrolysis with helium and methanolysis under the same conditions. The results indicate that there are no major obstacles to the use of coke-oven gas as the reactive gas in coal pyrolysis. The experimental conditions have to be improved to optimize the yields of the valuable chemicals.

CATALYTIC HYDROPYROLYSIS BY IMPREGNATED SULPHIDED MO CATALYST

Catalytic hydropyrolysis (HyPy) using impregnated sulphided Mo catalyst is studied in a thermobalance and in a 100 g fixed-bed reactor. Mo loading (0.5%) in impregnated coal is effective. Higher yields of oil and phenols (PCX) and lower concentration of sulphur in oil are obtained in catalytic HyPy than in non-catalytic HyPy, showing that the quality and quantity of oil are markedly improved in catalytic HyPy. The presence of catalyst remarkably increases the rate of oil formation, indicating that the rate of saturation of free radicals is greatly enhanced by hydrogenation. Catalytic HyPy can be performed at a lower temperature compared with non-catalytic HyPy, thus increasing the efficiency of hydrogen utilization. An increase in coal particle size (< 90 μm, 90–250 μm and 250–500 μm) leads to an enhance in conversion and oil yield in both catalytic and non-catalytic HyPy, which indicates that hydrogen diffusion is extensively depressed when coal agglomeration is extended. The catalytic ability increases with enhancing hydrogen pressure. The promotion of hydrogenation by impregnated MoS2 catalyst is related to the ability of adsorption and dissociation of gaseous hydrogen.

Evolution of pore structure and active surface areas of coal and char during hydrogenation

Abstract A Belgian coal (Beringen) has been used in a fundamental study of the changes in pore structure and active surface area during hydrogenation. The coal was devolatilized under N2 and then hydrogenated at constant temperature up to various conversion yields. Reactivities of the chars were determined by isothermal thermogravimetric analysis. Changes in total surface area, calculated from CO2 adsorption isotherms at 298 K, and in macropore distribution, obtained by mercury penetration, were found to lead to the same conclusion. In the first reaction stage, the preponderant phenomenon was the opening of previously closed micropores, induced by the material consumed by the reaction. This stopped completely when conversion yield exceeded 55 wt% when the maximum surface area was observed. Then removal of material from pore walls became predominant, pores were enlarged and pore walls disappeared gradually with increasing hydrogenation yields. Oxygen chemisorption capacities were measured at 383 K and 0.1 MPa air to give a relative indication of the concentration of carbon active sites. Active surface area results were compared to total surface area values and correlated with reaction rates.

Upgrading of waste derived solid fuel by steam gasification

Compared to the incineration, thermolysis can be considered as an interesting alternative or complementary way to eliminate the municipal solid waste or other kinds of dispersed waste, especially in rural regions with a low population density. The economic feasibility of the thermolysis depends mainly on the energetic valorization of the solid fuel generated by the process: steam gasification, in selected conditions to avoid toxic metals emissions, is a possible way to valorize this fuel. The results presented here show that steam gasification of waste derived solid fuel produces a synthesis gas with good calorific value. The behaviour of Pb, Cd, Cu and Mn has been studied as a function of the gasification conditions. The main toxic species can be trapped in the ashes in a non-leachable form if kaolinite is added as sorbent during the gasification. The behaviour of the Pb derivative present in the waste derived solid fuel seems to be due to PbCl2 formation during the thermolysis. As an alternative to combustion, energetic valorization of waste derived solid fuel can be considered either by local small scale gasification as well as by co-gasification with coal, rich in kaolinite, in new IGCC processes.

Ultrasonic removal of heavy metals from waste oils

The elimination of lead from used motor oils is performed by ultrasonic lixiviation using nitric acid, the lead being recuperated as lead sulfate during the acid regeneration. Beside the treatment of waste oils by the traditional methods, this new processing way gives alternative routes, not used usually for waste oils, such as introduction through the blowpipes of a blast furnace, addition to the coal in coke oven plants, coprocessing with coal in liquefaction or gasification plants, or even in copyrolysis with coal.