Vattenfall

About: Vattenfall is a company organization based out in Stockholm, Sweden. It is known for research contribution in the topics: Wind power & Combustion. The organization has 685 authors who have published 857 publications receiving 18912 citations. The organization is also known as: Vattenfall AB & Kungliga Vattenfallstyrelsen.

Nitrate Removal by Continuous Electropermutation Using Ion-Exchange Textile I. Modeling

Abstract: Increased levels of nitrate in ground water have made many wells unsuitable as sources for drinking water. In this thesis an ion-exchang eassisted electromembrane process, suitable for nitrate removal, is investigated both theoretically and experimentally. An ion-exchange textile material is introduced as a conducting spacer in the feed compartment of an electropermutation cell. The sheet shaped structure of the textile makes it easy to incorporate into the cell. High permeability and fast ion-exchange kinetics, compared to ion-exchange resins, are other attractive features of the ion-exchange textile. A steady-state model based on the conservation of the ionic species is developed. The governing equations on the microscopic level are volume averaged to give macro-homogeneous equations. The model equations are analyzed and relevant simplifications are motivated and introduced. Dimensionless parameters governing the continuous electropermutation process are identified and their influence on the process are discussed. The mathematical model can be used as a tool when optimising the process parameters and designing equipment. An experimental study that aimed to show the positive influence of using the ion-exchange textile in the feed compartment of an continuous electropermutation process is presented. The incorporation of the ion-exchange textile significantly improves the nitrate removal rate at the same time as the power consumption is decreased. A superficial solution of sodium nitrate with a initial nitrate concentration of 105 ppm was treated. A product stream with less than 20 ppm nitrate could be obtained, in a single pass mode of operation. Its concluded from these experiments that continuous electropermutation using ion-exchange textile provides an interesting alternative for nitrate removal, in drinking water production. The predictions of the mathematical model are compared with experimental results and a good agreement is obtained. Enhanced water dissociation is known to take place at the surface of ion-exchange membranes in electromembrane processes operated above the limiting current density. A model for this enhanced water dissociation in presented in the thesis. The model makes it possible to incorporate the effect of water dissociation as a heterogeneous surface reaction. Results from simulations of electropermutation with and without ion-exchange textile incorporated are presented. The influence of the water dissociation is investigated with the developed model.

Development of an alkali chloride vapour-generating apparatus for calibration of ultraviolet absorption measurements.

Abstract: A novel design of alkali chloride vapour-generating cell has been developed, which can serve as a calibration cell for quantitative ultraviolet absorption concentration measurements and meticulous spectral investigations of alkali compounds. The calibration cell was designed to provide alkali vapour of well-controlled concentrations and temperatures, and consisted of a sealed quartz cell measuring 0.4 m in length with a temperature-controlled reservoir containing solid alkali salt. The cell was placed in a furnace and the alkali vapours generated from the reservoir have direct access to the measuring chamber. Investigations of potassium chloride (KCl) were made on sublimated vapour at temperatures 650, 700, 750, 780, and 800 °C while the reservoir temperature was kept 50 °C lower to avoid condensation. The cell provides stable KCl vapour pressures, and the furnace provides a homogenous temperature profile along the cell. KCl vapour pressures are well characterised and conform the base for determination of the KCl concentration in the cell. The alkali chloride levels matched the concentration range of the absorption setup and indicated a previously employed calibration method to overestimate KCl concentrations. The KCl absorption cross sections for wavelengths λ=197.6 nm and λ=246.2 nm were calculated to be 3.4 × 10-17 and 2.9 × 10-17 cm2/molecule, respectively. The absorption cross section spectra did not show any structural differences with increasing temperature, which could indicate influence of dimers or significant changes of the population in the KCl vibrational states. The KCl absorption cross sections thus did not show any temperature dependence in the temperature region of 700-800 °C. Moreover, the applicability of the calibration cell for measurement of other alkali chlorides and hydroxides is discussed.

Forecasting intrahourly variability of wind generation

Abstract: Intrahourly fluctuations in wind power generation cause various technical and economic challenges for wind farm integration. With increasing levels of wind energy uptake, managing these fluctuations is likely to require further attention. Intrahourly fluctuations in wind power are caused by fluctuations in wind speed that can be linked with a range of atmospheric phenomena. Explicitly forecasting intrahourly wind variability requires both statistical and physical modelling. Predictors of wind and power variability include large-scale weather patterns, the wind speed timeseries itself, and information about approaching weather regimes. Numerical weather prediction models have been shown to be a useful tool for day-ahead forecasts of intrahourly variability. A promising application of intrahourly variability forecasts is the management of variable wind farm output using a flexible dispatch margin.

Towards population-based structural health monitoring, part VII: EOV fields – environmental mapping

Abstract: In a population-based structural health monitoring setting, data from one structure in a population, where the health state is known, may be used to make inferences about the health state in any nominally-identical structure. Any deviation from the learned ‘healthy response’ potentially indicates damage. However, as in standard applications of structural health monitoring, the healthy response from different structures also varies with the changes in environmental conditions across the population. This paper investigates the modelling of the change in environment across a population of structures located in one geographical region, such as a wind turbine farm. A data-driven mapping method (based on Gaussian process regression) will be introduced that aims to quantify and normalise variation stemming from the environment, such that the remaining response is only sensitive to damage or performance anomalies. The way in which environmental maps are constructed and implemented is demonstrated via a case study from an offshore wind farm. The ideas introduced here will constitute a field in the framework of population-based structural health monitoring presented elsewhere in the conference.