• Energy Research
• Open Access close
• Closed Access close
• Restricted close
• Open Source close
• Embargo close
• FI close

This paper presents a stochastic factor based approach to mid-term modeling of spot prices in deregulated electricity markets. The fundamentals affecting the spot price are modeled independently and a market equilibrium model combines them to form spot price. Main advantage of the model is the transparency of the generated prices because each underlying factor and the dynamics between factors can be modeled and studied in detail. Paper shows realistic numerical examples on the forerunner Scandinavian electricity market. The model is used to price an exotic electricity derivative.

Abstract Algae have been considered as a promising biodiesel feedstock. One of the major factors affecting large-scale algae technology application is poor wintering cultivation performance. In this study, an integrated approach is investigated combining freshwater microalgae Chlorella zofingiensis wintering cultivation in pilot-scale photobioreactors with artificial wastewater treatment. Mixotrophic culture with the addition of acetic acid (pH-regulation group) and autotrophic culture (control group) were designed, and the characteristics of algal growth, lipid and biodiesel production, and nitrogen and phosphate removal were examined. The results showed that, by using acetic acid three times per day to regulate pH at between 6.8 and 7.2, the total nitrogen (TN) and total phosphate (TP) removal could be increased from 45.2% to 73.5% and from 92.2% to 100%, respectively. Higher biomass productivity of 66.94 mg L−1 day−1 with specific growth rate of 0.260 day−1 was achieved in the pH-regulation group. The lipid content was much higher when using acetic acid to regulate pH, and the relative lipid productivity reached 37.48 mg L−1 day−1. The biodiesel yield in the pH-regulated group was 19.44% of dry weight, with 16–18 carbons as the most abundant composition for fatty acid methyl esters. The findings of the study prove that pH adjustment using acetic acid is efficient in cultivating C. zofingiensis in wastewater in winter for biodiesel production and nutrient reduction.

Musta hiili on yksi ilmaston muutokseen eniten vaikuttavimmista partikkeleista. Tyypillisiä lähteitä sille ovat pienpoltto, liikenne ja metsäpalot. Mustan hiilen vaikutus ilmastoon korostuu arktisilla alueilla, joilla se laskeutuu lumipinnoille ja edistää niiden sulamista. Musta hiili syntyy hapettomissa olosuhteissa erilaisista hiilivedyistä. Kaasumaiset hiilivedyt, kuten C2H2, C2H4 ja C6H6, kiinnittyvät toisiinsa ja muodostavat monirenkaisen aromaattisen hiilivedyn. Kun useita monirenkaisia aromaattisia hiilivetyjä yhdistyy, syntyy kiinteä nokipartikkelin ydin. Ydin kasvaa suureksi, haarautuneeksi ja huokoiseksi nokipartikkeliksi toisten nokipartikkeleiden törmätessä siihen. Tässä diplomityössä tutkittiin mustan hiilen syntymistä biomassan pölypoltossa, jossa hienoksi jauhetut kiinteät partikkelit poltetaan siihen suunnitellulla polttimella. Tutkimuksessa käytettiin ANSYS Fluent virtauslaskentaohjelmaa. Tehtiin CFD-mallinnus yksinkertaisesta C2H4 polttimesta, 120 kWth biomassan pölypolttoliekistä sekä 100 MWth biomassan pölypolttolämpölaitoksesta. C2H4 liekkiä mallinnettiin ja tuloksia verrattiin kirjallisuudesta löydettyyn validointidataan, jotta saataisiin ymmärrystä nokimallin toiminnasta. Biomassan pölypolton nokimallinnuksessa on haastavaa sisällyttää noen prekursorit biomassan pyrolyysituotteisiin. Noen prekursori C2H2 päätettiin sisällyttää pyrolyysituotteisiin ja sen pitoisuutta arvioitiin kirjallisuuden ja testimallinnusten perusteella. 120 kWth pölypolttoliekkiä mallinnettiin useilla eri C2H2 pitoisuuksilla ja noen muodostumista seurattiin ja verrattiin kokeelliseen dataan. Noen muodostumista täyden mittakaavan 100 MWth lämpölaitoksessa mallinnettiin pienen mittakaavan malleista opitulla tiedolla. Lämpölaitoksessa tehtiin paljon kokeellisia mittauksia BC Footprint mittauskampanjan aikana ja mallinnuksen tuloksia verrattiin kokeelliseen dataan. Mallinnuksia ja mittauksia tehtiin eri kuormilla. Integroimalla C2H2 biomassan pyrolyysituotteisiin, noen muodostumista voidaan mallintaa suuntaa antavasti. Pyrolyysituotteiden riippuvuus kemiallisesta kinetiikasta täytyy huomioida, jotta noen muodostumista voidaan mallintaa eri kuormilla. Suhteet mustan hiilen päästöissä mittauspisteiden välillä ovat yhteisymmärryksessä mallinnuksen kanssa, mutta pitoisuus on kertaluokkaa suurempi CFD-mallissa. CFD-malli pystyi mallintamaan noen minimipitoisuuden 1.25 mg/Nm3 kattilan pohjalla ja sen lisääntymisen pitoisuuteen 2.25 mg/Nm3 tyhjässä vedossa täydellä 100 MWth kuormalla. Vastaavat pitoisuudet kokeellisissa mittauksissa mittauskampanjan ajalta ovat keskimäärin 90 and 219 µg/Nm3. Mallinnuksesta oli apua kokeellisten tulosten tulkitsemisessa. Jatkotutkimuksia varten pyrolyysikoostumus täytyy huomioida tarkemmin, jotta menetelmällä voitaisiin mallintaa eri biomassojen palamista ja palamista eri polttimissa. Black Carbon (BC) is one of the most influential particles affecting on the climate change. Typical sources for BC are residential combustion, traffic and forest fires. The impact of BC on the climate is emphasized at the arctic regions, where it descends on the snow surfaces and increases the melting. BC is formed from various hydrocarbons at fuel rich conditions. Gaseous hydrocarbons, such as C2H2, C2H4 and C6H6, connect and form Polycyclic Aromatic Hydrocarbons (PAH). When multiple PAHs are combined, a solid BC nucleus is formed. The nucleus grows into a large, branched, porous soot particle as other soot particles collide into it. This thesis studied the formation of BC in pulverized biomass combustion, where finely ground solid particles are combusted with a specifically designed burner. A commercial Computational Fluid Dynamics (CFD) software ANSYS Fluent was used. CFD modeling was performed on a simple C2H4 burner, a 120 kWth pulverized biomass combustion flame and a 100 MWth pulverized biomass combustion boiler. The C2H4 flame was modeled and the results compared with the validation data obtained from literature, to gain an understanding of the soot formation modeling. It is challenging to integrate soot precursors into biomass devolatilization products, when modeling BC formation in pulverized combustion. BC precursor C2H2 was included in the devolatilization products, but its concentration had to be estimated based on the literature and test simulations. The 120 kWth pulverized combustion flame was modeled with different concentrations of C2H2 in the devolatilization products and the formation of BC was observed and compared with experimental data. BC formation in the 100 MWth full scale boiler was modeled with the help of information learned from the small scale CFD models. A large amount of experimental measurements were made at the heating plant during a BC Footprint measurement campaign and the results of the CFD model were compared with the experimental data. Modeling and measurements were carried out under different loads. By integrating C2H2 into the biomass devolatilization products, BC formation can be approximately modeled. Devolatilization products’ dependency on chemical kinetics need to be noticed in order to simulate BC formation under different loads. Relations in BC emissions between measuring points are in agreement with the experimental measurements, but the concentration is an order of magnitude higher in the CFD model. The model was able to predict minimum soot concentration of 1.25 mg/Nm3 at the bottom of the boiler increasing up to 2.25 mg/Nm3 towards the empty pass at full 100 MWth load. Corresponding experimental concentrations are 90 and 219 µg/Nm3 on average, respectively. Results of the CFD model were helpful in explaining the experimental results. For further studies, the devolatilization composition needs to be modeled more accurately in order to model BC formation from different biomasses and in different burners.

This paper presents an optimal control strategy for a district heating power plant with thermal energy storage. The main goal of the control strategy is to reduce the operation costs of the power plant, by scheduling the boilers, the operation of the thermal energy storage and the curtailment on the loads. The problem is stated as a constrained optimization in the form of a Mixed Integer Linear Program (MILP), embedded on an Model Predictive Control (MPC) framework. Particular attention is paid to modeling of boilers operating constraints, including the outlet water flow temperature, to the energy exchanged with the thermal energy storage and to the operating modes of the power plant layout, including the constraints related to the supply water temperature needed from the network. The results are performed using the data and the layout of the power plant located in the city of Ylivieska, in Finland. The cost analysis performed shows the advantages of using the predictive control strategy.

Meteorological forcing at the air-water interface is the main determinant of the heat balance of most lakes (Edinger et al., 1968; Sweers, 1976). Year-to-year changes in the weather therefore have a major effect on the thermal characteristics of lakes. However, lakes that differ with respect to their morphometry respond differently to these changes (Gorham, 1964), with deeper lakes integrating the effects of meteorological forcing over longer periods of time. Other important factors that can influence the thermal characteristics of lakes include hydraulic residence time, optical properties and landscape setting (e.g. Salonen et al., 1984; Fee et al., 1996; Livingstone et al., 1999). These factors modify the thermal responses of the lake to meteorological forcing (cf. Magnuson et al., 2004; Blenckner, 2005) and regulate the patterns of spatial coherence (Chapter 17) observed in the different regions (Livingstone, 1993; George et al., 2000; Livingstone and Dokulil, 2001; Jarvinen et al., 2002; Blenckner et al., 2004)

Molecular dynamics (MD) computer simulations are used routinely to compute atomistic trajectories of complex systems. Systems are simulated in various ensembles, depending on the experimental conditions one aims to mimic. While constant energy, temperature, volume, and pressure are rather straightforward to model, pH, which is an equally important parameter in experiments, is more difficult to account for in simulations. Although a constant pH algorithm based on the $\lambda$-dynamics approach by Brooks and co-workers was implemented in a fork of the GROMACS molecular dynamics program, uptake has been rather limited, presumably due to the poor scaling of that code with respect to the number of titratable sites. To overcome this limitation, we implemented an alternative scheme for interpolating the Hamiltonians of the protonation states that makes the constant pH molecular dynamics simulations almost as fast as a normal MD simulation with GROMACS. In addition, we implemented a simpler scheme, called multisite representation, for modeling side chains with multiple titratable sites, such as imidazole rings. This scheme, which is based on constraining the sum of the $\lambda$-coordinates, not only reduces the complexity associated with parameterizing the intra-molecular interactions between the sites, but is also easily extendable to other molecules with multiple titratable sites. With the combination of a more efficient interpolation scheme and multisite representation of titratable groups, we anticipate a rapid uptake of constant pH molecular dynamics simulations within the GROMACS user community.

The growing concern on global warming has pushed to set ambitious targets of carbon neutrality or net zero at the water sector. Meanwhile, poor data availability has been reported to restrict the national assessment of climate impacts and mitigation strategies in water sector. In national greenhouse gas (GHG) inventories, water sector is embedded in other sectors' emissions making it difficult to monitor separately. This study presents a national scale evaluation of climate change impacts for water sector in Finland based on life cycle analysis (LCA). In addition, the effectiveness of currently available emission reduction measures is evaluated by scenario analysis until the year 2035. According to the results, the life cycle climate change impacts from the Finnish municipal water sector were 0,67 (0,46-0,88) million tonnes CO2-eq./year (142.8 (98.9-187.1) kg CO2-eq./person/year). Drinking water services accounted for 12.5-13.9 % and wastewater services 86.1-87.4 % of the total emissions. With currently feasible emission reduction measures, the climate change impacts could be reduced approximately 14-30 % in total by 2035. The aim of carbon neutrality in the water sector was found to be unrealistic to achieve with existing and currently feasible measures for Finland and thus significant new emission mitigation measures are needed. The vague definition of carbon neutrality and system boundary of water sector as well as the uncertainties related to the assessment of direct emissions, undermine the credibility of the ambitiously set target. Prioritizing emission offsets to reach the target may inadvertently lead to unintended negative consequences due to the limitations and incompleteness of offset methods.

Abstract The accelerating sea-ice, ice sheet and glacial melt associated with climate warming have resulted in important changes in the Arctic region over the past decades. In northern Baffin Bay, the formation of the North Open Water (NOW) polynya, which is intrinsically linked to regional sea-ice conditions and ocean circulation, has become more variable in recent years. To understand how climate-driven changes affect sea-surface conditions in the polynya, we analyzed dinoflagellate cyst assemblages from a sediment core record that covers the past ca. 3800 years, and developed an index based on the locations of modern analogues from a large regional reference dataset. Our results suggest a prolonged open-water season characterized by higher summer sea-surface salinity and temperature between ca. 3800 to 2500 years BP, followed by gradual cooling, freshening and increased sea-ice influence from 2500 to 1500 years BP, and continued sea-surface cooling with a shorter open-water season from 1500 to 156 years BP. The modern warming translates into a rapid turnover in the composition of dinoflagellate cyst assemblages during the last 50 years of our record, unprecedented for at least the past 3800 years studied here. For the uppermost part of our core (ca. 2009 to 2015 CE), the dinoflagellate cyst assemblages suggest increased stratification and sea-surface freshening resulting from increased glacial runoff and Arctic sea-ice export into the NOW region. Arctic climate projections indicate accelerated sea-ice thinning and ice sheet melt in the future, pointing to a shorter polynya season and increased polar inflows leading to fundamental changes within the NOW polynya into future years.