A methodological approch for estimating turbidity in a river

During the operations of purging and disposal of sediments of a reservoir it is necessary to know the values of turbidity in the river downstream in natural condition, in the absence of dams or river training works. The paper shows that under these conditions the ratio of the average values of sediment discharge to the annual maximum value of water discharge is a function of the average annual turbidity. Turbidity can be considered as representative synthetic index of the climatic conditions, the lithological features and the land cover of the basin, and the geometric characteristics of the river network. The proposed relationship of sediment discharge as a function of water discharge were validated on the basis of data collected from different Italiana regions that have very different morphological, geo-lithological and rainfall features and that are characterised by a basin area changing between a few dozen and thousands of square kilometres. The results can be considered satisfying

Preparation of activated carbons from heavy-oil fly ashes

The use of heavy oil fly ash with high ash content (45 wt.%) as a precursor for the preparation of activated carbons has been investigated. The raw fly ash and the fly ash with lower ash content, obtained by a HCl/HF washing treatment, have been pyrolyzed at 900 C and then activated with CO2 in the temperature range of 800–900 C for different times. The activated carbons have been characterised as regards the surface area and the pore volume. The evolution of the porosity has been related to the burn-off degree

Post-combustion carbon capturemediated by carbonic anhydrase

The emissions of carbon dioxide from fossil fuel-fired power plants emphasize the need for efficient carbon capture and storage. Post-combustion capture strategies are apparently more feasible in the short-term, as existing plants may be more easily retrofitted for implementation of CCS technologies with minimal capital costs. Among these processes, CO2 absorption into aqueous solutions along a biomimetic route is an attractive option in view of its eco-friendliness. The process, which has received consideration both at the scientific and technological levels since the early sixties, is based on CO2 absorption enhanced by the enzyme carbonic anhydrase (EC 4.2.1.1). The scientific literature regarding biomimetic carbon capture and patented technologies proposed over the last decade are hereby surveyed, with specific consideration of key issues related to design of process units for implementation of biomimetic CO2 capture. Both regenerative and non-regenerative options are considered. The contribution of carbonic anhydrase, in either the free or the immobilized form, and the effect of operating conditions on process performance are analyzed, with an eye on the open issues and the research priorities

Electricity and solid fuel production by small biomass plants vs CHP and district heating

In this paper, the possible use of heat surplus from a biomass-fired cogeneration unit, for treating a share of the biomass and produce a new and more compact fuel, like pellets, is discussed. Such a fuel could be easily stored and then distributed, for a more widespread and diffused utilization close to the consumers, for heating purposes. This shape of energy storage makes time and geographical shift of heat utilization possible. A technical-economical comparison is carried out and discussed, between the above mentioned system and a district heating, supplied by a traditional biomass boiler or a conventional chip-fired cogeneration plant without pellets production

Synthesis of Special Cements from Mixtures Containing Fluidized Bed Combustion Waste, Calcium Carbonate and Various Sources of Alumina

Special cements are obtained from non-portland clinkers. In particular applications, when rapid hardening and high chemical resistance are required, they behave better than ordinary cements [1-4]. The peculiar composition of special cements can also be exploited for giving a more pronounced environment-friendly character to their manufacturing process. In this regard important features are: a) low synthesis temperatures; b) reduced thermal input and CO2 generation; c) easy grindability; d) possibility of using hardly recoverable wastes and by-products. All the above mentioned features are present in calcium sulphoaluminate cements [5-14] based on 4CaOּ 3Al2O3ּ SO3 (C4A3S, according to the cement chemistry notation under which C=CaO; A=Al2O3; S =SO3; S=SiO2, H=H2O). Calcium sulphoaluminate is able to generate, upon hydration, ettringite (C6AS3H32 ), a compound which regulates all the technical properties of calcium sulphoaluminate cements. When C4A3S reacts with calcium sulphate and water, in the absence of lime, a non-expansive ettringite is rapidly formed together with aluminium hydroxide, thus giving a high mechanical strength at early ages [4, 15-17]. Among the other phases present in C4A3S-based cements, dicalcium silicate (C2S) can play an important role because it is able to add strength and durability at later ages. Secondary constituents, such as gehlenite (C2AS), calcium sulphosilicate (C S S 5 2 ) and various calcium aluminates, have generally a poor hydraulic behaviour and provide a small contribution to the technical properties.Fluidized bed combustion (FBC) waste, mainly composed by exhausted sulphur sorbent and coal ash, contains CaO, SiO2, Al2O3 and SO3 as major oxides, thus representing a potential raw material for the manufacture of calcium sulphoaluminate cements [18]. Both disposal in landfill and re-use of FBC waste is generally made difficult by its chemical and mineralogical composition. Upon hydration, exothermal and expansive phenomena occur due to the relatively high content of lime and calcium sulphate [13]. Moreover the utilization of FBC ash in the ordinary cement and concrete industry is hindered by its poor pozzolanic activity due to the reduced glass content related to combustion temperatures which are significantly lower than those of traditional pulverized coal combustors [14]. The identification of suitable application fields for such waste is therefore of critical importance. This paper is focused on the use of a CFBC (circulating fluidized bed combustion) fly ash as raw mix component for the synthesis of calcium sulphoaluminate cements. The raw mix composition was designed in order to combine all available sulphate and silica into calcium sulphoaluminate and dicalcium silicate, respectively. To this end additional sources of calcium and aluminium oxides were required: the former was given by pure calcium carbonate; the latter by pure alumina, red mud and/or bauxite