The modelling of a hybrid combined cycle with pressurised fluidised bed combustion and CO2 capture

This study investigates the possibility of capturing CO₂ from flue gas under pressurised conditions, which could prove to be beneficial in comparison to working under atmospheric conditions. Simulations of two hybrid combined cycles with pressurised fluidised bed combustion and CO₂ capture are presented. CO₂ is captured from pressurised flue gas by means of chemical absorption after the boiler but before expansion. The results show a CO₂ capture penalty of approximately 8 percentage points (including 90% CO₂ capture rate and compression to 110 bar), which makes the efficiency for the best performing cycle 43.9%. It is 5.2 percentage points higher than the most probable alternative, i.e. using a natural gas fired combined cycle and a pulverised coal fired condensing plant separately with the same fuel split ratio. The largest part of the penalty is associated with the lower mass flow of flue gas after CO₂ capture, which leads to a decrease in work output in the expander and potential for feed water heating. The penalty caused by the regeneration of absorbent is quite low, since the high pressure permits the use of potassium carbonate, which requires less regeneration heat than for example the more commonly proposed monoethanolamine. Although the efficiencies of the cycles look promising it will be important to perform a cost estimate to be able to make a fair comparison with other systems. Such a cost estimate has not been done in this study. A significant drawback of these hybrid cycles in that respect is the complex nature of the systems that will have a negative effect on the economy.     

Plant and Soil System Responses to Ozone After 3 Years in a Lysimeter Study with Juvenile Beech (Fagus sylvatica L.)

A lysimeter study was performed to monitor effects of elevated ozone on juvenile trees of Fagus sylvatica L. as well as on the plant–soil system. During a fumigation period over almost three growing seasons, parameters related to plant growth, phenological development and physiology as well as soil functions were studied. The data analyses identified elevated ozone to delay leaf phenology at early and to accelerate it at late developmental stages, to reduce growth, some leaf nutrients (Ca, K) as well as some soluble phenolics (hydroxycinnamic acid derivatives, total flavonol glycosides). No or very weak ozone effects were found in mobile carbon pools of leaves (starch, sucrose), and other phenolic compounds (flavans). Altered gene expression related to stress and carbon cycling corresponded well with findings from leaf phenology and chemical composition analyses indicating earlier senescence and oxidative stress in leaves under elevated ozone. Conversely in the soil system, no effects of ozone were detected on soil enzyme activities, rates of litter degradation and lysimeter water balances. Despite the fact that the three reported years 2003–2005 were climatically very contrasting including a hot and dry as well as an extremely wet summer, and also mild as well as cold winters, the influence of ozone on a number of plant parameters is remarkably consistent, further underlining the phytotoxic potential of elevated tropospheric ozone levels.     

Bushcricket song structure and predation by the acoustically orienting parasitoid fly Therobia leonidei (Diptera: Tachinidae: Ormiini)

Males of most bushcricket species produce acoustic advertisement signals to attract females for mating. These signals can also increase conspicuousness to predators. In the genus Poecilimon (Orthoptera: Phaneropterinae) males are attacked by the parasitoid fly Therobia leonidei (Diptera: Tachinidae: Ormiini) which locates males by their calls. In Greece T.leonidei parasitizes several Poecilimon species with different song structures: we examined whether host choice is related to song structure by comparing parasitism rates in two closely related Poecilimon species. One of these species produces monosyllabic songs, the songs of the other species being polysyllabic. The tachinid fly parasitized the polysyllabic species to a greater extent. We demonstrate in a field-experiment that this preference for the polysyllabic species does not depend on local adaptations of the fly. The most probable explanation for the preference of the fly for the polysyllabic singing species seems to be better detection of longer songs. This result is discussed in the context of male song evolution. Received: 4 November 1997 / Accepted after revision: 22 March 1998     

Effect of fertilizer on the growth of radish plants exposed to simulated acidic rain containing different sulfate to nitrate ratios

Two successive experiments were performed in the greenhouse to test the hypothesis that plant response to the amounts and ratios of sulfuric and nitric acids in rain is affected by the amount of fertilizer added to the growing medium. Radish plants, grown with different levels of N?P?K fertilizer, were given ten 1-h exposures over a 3-week period to simulate acidic rain at pH values from 2.6 to 5.0 and sulfate to nitrate mass ratios from 0.3 to 7.5. Increased acidity of simulated rain reduced plant growth, with a greater depression of hypocotyl mass than shoot mass. The reverse growth response occurred with increased supply of fertilizer: plant biomass rose with a larger increase in shoot mass than hypocotyl mass. In one experiment, plants that received a greater supply of fertilizer exhibited more obvious reductions in growth of hoots at the higher levels of acidity of simulated rain. There were no significant effects of sulfate to nitrate ratios in simulated rain on plant growth, nor any effect of this ratio on the response of shoots and hypocotyls to acidity of simulated rain. Addition of fertilizer had no effect on plant response to sulfate to nitrate ratios. These results do not support the hypothesis that nutrient-deficient plants are either more or less responsive to sulfate and nitrate in rain than plants grown with optimal supplies of nutrients. They support previous results indicating no effects of sulfate to nitrate ratio in simulated acidic rain on plant growth. The results also suggest that the greatest risk of harmful effects on vegetation may come from the combination of high sulfate and high acidity in rainfall.