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.

The multi-commodity network flow problem with soft transit time constraints: Application to liner shipping

Abstract: The multi-commodity network flow problem (MCNF) consists in routing a set of commodities through a capacitated network at minimum cost and is relevant for routing containers in liner shipping networks. As commodity transit times are often a critical factor, the literature has introduced hard limits on commodity transit times. In practical contexts, however, these hard limits may fail to provide sufficient flexibility since routes with even tiny delays would be discarded. Motivated by a major liner shipping operator, we study an MCNF generalization where transit time restrictions are modeled as soft constraints, in which delays are discouraged using penalty functions of transit time. Similarly, early commodity arrivals can receive a discount in cost. We derive properties that distinguish this model from other MCNF variants and adapt a column generation procedure to efficiently solve it. Extensive numerical experiments conducted on realistic liner shipping instances reveal that the explicit consideration of penalty functions can lead to significant cost reductions compared to hard transit time deadlines. Moreover, the penalties can be used to steer the flow towards slower or faster configurations, resulting in a potential increase in operational costs, which generates a trade-off that we quantify under varying penalty functions.

Production Planning for Distributed District Heating Networks with JModelica.org

Abstract: The short term production planning optimization problem for a district heating system is solved in two steps by integrating physics-based models into the standard approach. In the first step the unit commitment problem (UCP) is solved using mixed integer linear models and standard mixed-integer solvers. In the second step the economic dispatch problem is solved, utilizing the unit statuses from the UCP. This step involves dynamic optimization of nonlinear physics-based models. Both optimizations aim at maximizing the production profit. The modeling has focused on distributed consumption and production. Optimization results show that modeling of the district heating net impacts the production planning in several ways, with results such as reduction of production peaks and delay of costly unit start-ups. The physics-based modeling and dynamic optimization techniques provide a flexible way to formulate the optimization problem and include constraints of physically important variables such as supply temperature, pressures and mass flows.

Frequency support by synthetic inertia from variable speed wind turbines

Abstract: This paper investigates the possibilities for frequency support by synthetic inertia from variable speed wind turbines. A model for representing synthetic inertia in PSS/E (Power System Simulator for Engineering) has been developed. It allows the user to relatively simple implement different control strategies to find the most suitable strategy for a particular power system. Furthermore, it can be used regardless of the existence of wind turbine models in the power system model and is connected separately to any arbitrary bus in the power system. The results from the simulations show that the frequency nadir is reduced when implementing frequency support by synthetic inertia from wind turbines. As the wind power integration increases the frequency nadir is further improved when wind turbines can provide synthetic inertia. Regarding recovery, the results indicates that in order to minimise the risk of an under-frequency event the energy should be taken during a frequency overshoot and/or distributed in time, i.e. not all wind power plants should recover at the same time. However, these studies of synthetic inertia provided by wind turbines are still in the early stage and further work will be performed.

Effects of load variation on a Kaplan turbine runner

Abstract: Introduction of intermittent electricity production systems like wind and solar power to electricity market together with the deregulation of electricity markets resulted in numerous start/stops, l ...

Modeling the geochemical impact of an injection of co2 and associated reactive impurities into a saline reservoir

Abstract: Numerical simulations performed with the TOUGHREACT code focus on the chemical reactivity of deep reservoir rock impacted by an injection of CO2 and associated reactive impurities (mainly SO2 and O2). A simplified two-dimensional radial geo-model representing the near wellbore domain of a saline reservoir enabled us to capture the global geochemical behaviour of this underground zone. Two ratios CO2/SO2 are investigated. The results of the numerical simulations highlight the high reactivity of the near-well zone in the case where ancillary gases (SO2 and O2) are injected with CO2 with dissolution of carbonates and precipitation of sulfate minerals. Major reactions occur in the reservoir formation, whereas clays of the caprock are only slightly affected by the injection of CO2 and associated reactive impurities.