The release of toxic trace elements from the combustion of fuels in power plants is an environmental issue of increasing concern. Trace element release mechanisms are known to be complex and may depend on the levels of chlorine and sulfur in the fuel burned. This dependency has been investigated experimentally by injecting first hydrogen chlorine, and then sulfur dioxide, into a suspension-firing reactor burning wood-bark under simulated fluidized bed combustion conditions. Data interpretation has been aided by parallel theoretical studies, using a thermodynamic equilibrium model based on the principle of Gibbs free energy minimization. The influence of chlorine and sulfur was confirmed for some, but not all, of the 10 trace elements studied. Injection of HCl served to increase the emission of Cd, but to reduce emission of Cu, Mn, Zn, and possibly Cr and Ni. Injection of SO2 served to increase emissions of Cd, but reduced emissions of As and Hg. The thermodynamic model proved valuable for interpreting the experimental data. However, evidence suggests that predictions not validated by measurement should be treated with caution, given the complexity of the systems being studied.
Trace element emissions from the co-combustion of coal with biomass and waste secondary fuels have been measured, under conditions relevant to commercial fluidized bed combustors, using a novel, bench-scale, suspension-firing reactor. Experiments have been conducted using two coals (one Polish, one Colombian), four biomass fuels (wood-bark, straw, pulp sludge, and paper sludge), and three waste fuels (agricultural waste, sewage sludge and plastic waste). Concentrations of eighteen trace elements have been measured in these raw fuels and a variety of combustion and co-combustion ashes, using inductively coupled plasma-mass spectrometry (ICP-MS) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES), plus an atomic absorption based mercury determination devise. The influence of chlorine and sulfur on trace element release from combustion has been tested also, in the case of wood-bark, by injecting first HCl and then SO 2 into the reactor during combustion. Experimental data have been compared with the predictions of a thermodynamic equilibrium model throughout this study. The Metallurgical and Thermochemical Databank (MTDATA) Gibbs free energy minimization software has been used to predict the speciation of individual trace elements. The trace elements have been ranked according to their average retention in combustion ashes, the most volatile being Hg and Se, followed by Cd, Tl, Pb, and As. Potentially problematic trace element emissions have been noted in certain cases, e.g., Cu and Zn from wood-bark, As and Pb from Polish coal, and Cd and Hg from sewage sludge. The injection of HCl served to decrease the retention by ash of the elements Cd, Cu, Zn, Mn, and Ba, while injection of SO 2 increased the retention by ash of As and Hg, but decreased that of Cd.
BackgroundAspirin-exacerbated respiratory disease is under-diagnosed and therefore effective and inexpensive therapy with aspirin desensitization is rarely performed.MethodsWe present an audit of 150 patients with difficult to treat nasal polyposis, 132 of whom also had asthma, 131 of whom underwent challenge with the only soluble form of aspirin, lysine aspirin (LAS), to confirm or exclude the diagnosis of aspirin-exacerbated respiratory disease (AERD).ResultsOne hundred patients proved positive on nasal challenge, 31 who were negative went onto oral LAS challenge and a further 14 gave positive results, leaving 17 who were negative to a dose equivalent to over 375 mg of aspirin. Nineteen were not challenged because of contraindications.With the exception of one patient who developed facial angioedema and two patients with > 20% drop in FEV1 (following nasal plus oral challenge) no other severe adverse events occurred. No hospitalization was required for these three patients.Nasal inspiratory peak flow monitoring was less sensitive to obstruction caused by aspirin than was acoustic rhinometry – which should be employed when aspirin challenge is an outpatient procedure.ConclusionsProvided patients are carefully chosen and monitored LAS challenge is suitable for ENT day case practice where respiratory physician help with asthma is available and should reduce the under-diagnosis of this condition.
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