Advanced CFD modelling of air and recycled flue gas staging in a waste wood-fired grate boiler for higher combustion efficiency and greater environmental benefits.

Grate-fired boilers are commonly used to burn biomass/wastes for heat and power production. In spite of the recent breakthrough in integration of advanced secondary air systems in grate boilers, grate-firing technology needs to be advanced for higher efficiency and lower emissions. In this paper, innovative staging of combustion air and recycled flue gas in a 13 MWth waste wood-fired grate boiler is comprehensively studied based on a numerical model that has been previously validated. In particular, the effects of the jet momentum, position and orientation of the combustion air and recycled flue gas streams on in-furnace mixing, combustion and pollutant emissions from the boiler are examined. It is found that the optimized air and recycled flue gas jets remarkably enhance mixing and heat transfer, result in a more uniform temperature and velocity distribution, extend the residence time of the combustibles in the hot zone and improve burnout in the boiler. Optimizing the air and recycled flue gas jet configuration can reduce carbon monoxide emission from the boiler by up to 86%, from the current 41.0 ppm to 5.7 ppm. The findings of this study can serve as useful guidelines for novel design and optimization of the combustion air supply and flue gas recycling for grate boilers of this type.

Effect of thermal processing on the characteristics of incineration fly ash.

UNLABELLED: This work investigated the possibilities of immobilizing incineration fly ash by applying different processing methods. Direct sintering of fly ash at 1050 degrees C produced material with increased resistance to leaching; however, the high content of halides prevented the achievement of appropriate strength. Fly ash melting and casting into metallic moulds resulted in the formation of glass with good chemical resistivity and mechanical properties, which were further improved by devitrification, and the formation of glass-ceramics. The most successful combination of strength and resistance to leaching was obtained by a process consisting of fly ash melting, by pouring the melt into water, then grinding, and sintering without additives at 850-950 degrees C. In this way, a material was produced that cannot only be landfilled as a stabilised and non-reactive waste in landfills for non-hazardous wastes, but can also be utilized as a valuable material for manufacturing useful products. This article provided valuable results for policy-makers in Slovenia, about the handling fly ash from incineration plants. IMPLICATIONS: Fly ash from an incineration plant was thermally treated using several processing routes. Ash-melting, by pouring the melt into water and sintering, produced glass-ceramics having an optimal combination of strength and resistance to leaching that can find applications as useful products. These results provide important data for policy makers in Slovenia regarding the building of incineration plants, and handling the solid-waste products, especially fly ash.

Detection of nanomolar concentrations of copper(II) with a Tb-quinoline-2-one probe using luminescence quenching or luminescence decay time.

We present a time-resolved (gated) luminescence-based method for determination of Cu2+ ions in microtiterplate format in the nanomolar concentration range using the novel long-lived terbium-[1-methyl-4-hydroxy-3-(N-2-ethyl-5-aminothiadiazolyl-)-carbamoyl-quinoline-2-one] (TbL) complex. The probe works best in Tb:L = 1:2 stoichiometry at neutral pH. The dynamic range is from 10 to 300 nmol L(-1) of Cu2+ and the limit of detection is 4.3 nmol L(-1). This is the lowest limit of detection achieved so far for luminescent lanthanide-based probes for copper. It is shown that gating can efficiently suppress intense, short decaying background fluorescence e.g. that of Rhodamine 6G. The assay can be performed by measurement of luminescence decay time, as well. Stern-Volmer studies indicate that static quenching dominates over dynamic quenching. TbL2 was tested for the effect of some relevant interferents and the assay was applied to the determination of copper in tap water samples. The results achieved were in good agreement with those of a reference method.

Utilization of bottom ash from the incineration of separated wastes as a cement substitute.

Waste incineration is still an essential technology in the concept of integrated waste management. Most of the combustion residues are incinerator bottom ash. It has been discovered that incinerator bottom ash from the incineration of separated waste in the primary chamber of the modular two-stage incinerator mainly consists of metal oxides, especially SiO2 and CaO, in proportions that are quite similar to those in cement and so the feasibility of its application as a substitute for cement in concrete was investigated. It was found that after 28 days, the flexural and compressive strengths of the binder using bottom ash were practically comparable with those of a pure cement mixture. The results show that it is reasonable to use a binder containing incinerator bottom ash for applications in which an early-stage lower strength of concrete element is acceptable.

Spent potlining utilisation possibilities.

As the world's capacity for aluminium production increases, the amount of waste connected with this industry is also increasing. Spent potlining (SPL) from aluminium reduction cell cathodes presents a major environmental concern in the primary aluminium industry. It is concluded, after laboratory tests, that leachable cyanide and fluoride compounds present the major problem in SPL disposal. The behaviour of cyanide and fluoride under high temperature treatment has been investigated. On the basis of this laboratory investigation, the possibilities for SPL utilisation in red brick manufacturing, cement industry and thermal power stations were evaluated. SPL refractory material is already re-used in red brick manufacturing. In the cement industry, a pilot test on the utilisation of 25 t SPL carbon waste mixed with green petrol coke gave positive results. Additionally a fluoride emission forecast for a thermal power station utilising carbon waste SPL mixed with coal was elaborated.