N. Paterson

Removal of toxic and alkali/alkaline earth metals during co-thermal treatment of two types of MSWI fly ashes in China.

This study aims to vaporize heavy metals and alkali/alkaline earth metals from two different types of fly ashes by thermal treatment method. Fly ash from a fluidized bed incinerator (HK fly ash) was mixed with one from a grate incinerator (HS fly ash) in various proportions and thermally treated under different temperatures. The melting of HS fly ash was avoided when treated with HK fly ash. Alkali/alkaline earth metals in HS fly ash served as Cl-donors to promote the vaporization of heavy metals during thermal treatment. With temperature increasing from 800 to 900°C, significant amounts of Cl, Na and K were vaporized. Up to 1000°C in air, less than 3% of Cl and Na and less than 5% of K were retained in ash. Under all conditions, Cd can be vaporized effectively. The vaporization of Pb was mildly improved when treated with HS fly ash, while the effect became less pronounced above 900°C. Alkali/alkaline earth metals can promote Cu vaporization by forming copper chlorides. Comparatively, Zn vaporization was low and only slightly improved by HS fly ash. The low vaporization of Zn could be caused by the formation of Zn2SiO4, ZnFe2O4 and ZnAl2O4. Under all conditions, less than 20% of Cr was vaporized. In a reductive atmosphere, the vaporization of Cd and Pb were as high as that in oxidative atmosphere. However, the vaporization of Zn was accelerated and that of Cu was hindered because the formation of Zn2SiO4, ZnFe2O4 and ZnAl2O4 and copper chloride was depressed in reductive atmosphere.

Fuel behaviour studies in the air-blown gasification cycle

Abstract The air-blown gasification cycle (ABGC) is being developed in the UK and this paper gives an overview of the different parts of the programme. Pilot-scale investigations of the fuel flexibility of the gasification process have been conducted. A selection of world coals have been gasified at elevated pressure. The performance and operability of the gasifier with these coals is discussed. The successful development of the components of the ABGC is nearing completion, although there are some outstanding areas that need further investigation.

The fate of injectant coal in blast furnaces: The origin of extractable materials of high molecular mass in blast furnace carryover dusts

Abstract The aim of the work was to investigate the fate of injectant coal in blast furnaces and the origin of extractable materials in blast furnace carryover dusts. two sets of samples including injectant coal and the corresponding carryover dusts from a full sized blast furnace and a pilot scale rig have been examined. The samples were extracted using 1-methyl-2-pyrrolidinone (NMP) solvent and the extracts studied by size exclusion chromatography (SEC). The blast furnace carryover dust extracts contained high molecular weight carbonaceous material, of apparent mass corresponding to 107-108 u, by polystyrene calibration. In contrast, the feed coke and char prepared in a wire mesh reactor under high temperature conditions did not give any extractable material. Meanwhile, controlled combustion experiments in a high-pressure wire mesh reactor suggest that the extent of combustion of injectant coal in the blast furnace tuyers and raceways is limited by time of exposure and very low oxygen concentration. It ...

Gasification Tests With Sewage Sludge and Coal/Sewage Sludge Mixtures in a Pilot Scale, Air Blown, Spouted Bed Gasifier

A series of tests have been done in a pilot scale air blown gasifier, to assess the performance of sewage sludge pellets and sewage sludge pellet/coal mixtures. The aim has been to compare the performances with that achieved with coal alone and to assess the suitability of the sewage containing fuel as a candidate fuel for the Air Blown Gasification Cycle (ABGC). The co-gasification of sewage sludge with coal raised both the CV of the fuel gas and the fuel conversion compared with values achieved with coal alone. The mixtures were operated under very similar conditions to those needed with coal and no adverse operational problems were encountered. A lower fluidising velocity was needed with the neat pellets to enable a stable bed height to be achieved. However, the conversion of the pellets to gas was very high and the fuel gas CV was higher than that achieved during the co-gasification tests. Overall, the results suggest that sewage based materials are suitable for use in the ABGC and that their use can improve the process performance.Copyright

The use of wire mesh reactors to characterise solid fuels and provide improved understanding of larger scale thermochemical processes

Most reaction products from the pyrolysis and the early stages of gasification of solid fuels are chemically reactive. Secondary reactions between primary products and with heated fuel particles tend to affect the final product distributions. The extents and pathways of these secondary reactions are determined mostly by the heating rate and the size and shape of the reaction zone and of the sample itself. The wire-mesh reactor configuration discussed in this paper allows products to be separated from reactants and enables the rapid quenching of products, allowing suppression of secondary reactions. The design allows decoupling the experimental results from the nature of the experimental technique, providing a more accurate assessment of solid fuel behaviour than other available experimental designs. In its various configurations, the wire-mesh reactor configuration has provided new information that helps to further the understanding and improvement of pilot and commercial scale plant and has served as a valuable first stage in the development of new concepts. This paper presents an overview of the development of wire-mesh reactors, describing several diverse applications and offers some perspectives for ensuring the reliability of the data.

Investigation of Ammonia Formation During Gasification in an Air Blown Spouted Bed

High NH3 concentrations were measured in the fuel gas produced by a pilot scale, air blown gasifier that was operated by British Coal. A laboratory scale gasifier has subsequently been developed to investigate the reactions that produce these potentially high concentrations. It has been found that in addition to the NH3 formed through pyrolytic processes, the introduction of steam (or H2 produced by its decomposition) increases the amount formed. The latter reaction produced the higher proportion of the total NH3 . The effect of the gasifier operating conditions on the amount of NH3 formed has been studied. The main control options to minimise the NH3 formed are using an alternative method of bed temperature control (i.e. avoid the use of steam), operating with higher bed temperatures and operation at lower pressures.Copyright