A comparative evaluation of recarbonated CaCO3 derived from limestone under oxy-fuel circulating fluidized bed conditions.

SO2 emissions from coal-fired boilers are air pollutants and a source of acid rain, causing extensive environmental pollution. Limestone (CaCO3) is a Ca-based sorbent which is injected into circulating fluidized bed (CFB) boilers, where it combines with SO2 to produce calcium sulfate (CaSO4). As a result, SO2 emissions from a power plant are reduced. In this study, CaCO3 addition was proposed and the desulfurization efficiency improved. The direct desulfurization reaction is dominant in a commercial CFB boiler due to the high CO2 partial pressure, but CaO is formed at a fast reaction rate by calcination in the high temperature or in the low CO2 partial pressure region. When CaO remains in the loop seal, it is exposed to a high CO2 partial pressure condition moving through the recirculation section for an extended period and re-injected into the furnace as recarbonated CaCO3. To analyze the direct desulfurization reaction kinetics, a shrink core model in which the reaction proceeds inside the particle was adopted. Surface observations through FE-SEM of CaSO4 produced by the 180 minute long desulfurization experiment using TGA suggest that the CaSO4 crystal growth rate increased after the pre-treatment (recarbonation) of limestone. Recarbonation lowered the limestone crystallinity, causing a faster reaction. The CaCO3 recarbonation increased the Ca utilization by more than 20% when the direct desulfurization reaction occurred. The TGA experiments show that recarbonation contributes to CaSO4 conversion. Increasing the desulfurization efficiency using recarbonation can reduce the fixed investment and operating costs of oxy-fuel CFB plants because only desulfurization in the furnace is able to meet SO2 emission regulations or lower the flue gas desulfurization (FGD) dependence. Accordingly, the desulfurization conversions of recarbonated CaCO3 and limestone were compared in this study. Morphological changes in the limestone were also evaluated using XRD, FE-SEM, and other analysis methods.

Anti-pneumococcal antibody response in normal subjects: a meta-analysis.

BACKGROUND: The diagnosis of anti-polysaccharide antibody deficiency is based on the presence of normal serum immunoglobulin levels and the lack of specific antibody response to polysaccharide antigens, such as the pneumococcal vaccine. However, a normal response to pneumococcal vaccine is not well defined. "Modified meta-analysis" was undertaken in an attempt to define the normal antibody response to pneumococcal vaccine. METHODS: Studies identified by a MEDLINE search were selected. Data of the normal control groups, rather than the patient groups, were collated for analysis. RESULTS: Twenty-three studies fulfilled the selection criteria. Prevaccination antibody titers, postvaccination titers, and post- to prevaccination titer ratios varied widely. On the basis of weighted mean ratios, serotype 8 appeared to be the most antigenic. It appeared that normal subjects do not mount a response of even a twofold increase in antibody titer to all the serotypes present in the vaccine. Moreover, no minimal absolute antibody level that could be of diagnostic value, either before or after vaccination, was evident. CONCLUSION: Response to pneumococcal vaccine among normal subjects varies widely. Better designed and prospective studies are needed to define the parameters of a normal antibody response to pneumococcal vaccine so that uniform guidelines of interpretation can be formulated.

Clinical and molecular epidemiology of acinetobacter infections sensitive only to polymyxin B and sulbactam.

A nosocomial outbreak of infections due to imipenem-resistant Acinetobacter baumannii occurred in a New York hospital after increased use of imipenem for cephalosporin-resistant klebsiella infections. We identified all A baumannii isolates over 12 months, reviewed corresponding patient records, and compared strains with different antibiotic susceptibility patterns by restriction endonuclease analysis. Environmental surveillance cultures were done before and after institution of control measures. 59 patients harboured imipenem-resistant A baumannii, and 18 were infected. Isolates from patients were resistant to all routinely tested antibiotics, including imipenem. Further studies showed susceptibility to polymyxin B and sulbactam. These isolates were identical by restriction endonuclease analysis to A baumannii isolates susceptible to imipenem alone, or to imipenem and amikacin, but differed from broadly susceptible isolates. Surveillance cultures showed hand and environmental colonisation by imipenem-resistant strains. Infection and colonisation were eliminated by intensive infection control measures, and irrigation of wounds with polymyxin B. Increased use of imipenem against cephalosporin-resistant klebsiella may lead to imipenem resistance among other species, particularly acinetobacter. Such resistance appears to derive from a prior multi-resistant clone, in contrast to one which retains susceptibility to several antibiotics.