With the increasing stringency on sulfur content in petrodiesel, there is a growing tendency of broader usage of ultra low sulfur diesel (ULSD) with sulfur content of 15 ppm. Refineries around the world should develop cost-effective and sustainable strategies to meet these requirements. The primary objective of this work is to analyze alternatives for producing ULSD. In addition to the conventional approach of revamping existing hydrotreating facilities, the option of blending petrodiesel with biodiesel is investigated. Blending petrodiesel with biodiesel is a potentially attractive option because it is naturally low in sulfur, enhances the lubricity of petrodiesel, and is a sustainable energy resource. In order to investigate alternatives for producing ULSD, several research tasks were undertaken in this work. Firstly, base-case designs of petrodiesel and biodiesel production processes were developed using computer-aided tools ASPEN Plus. The simulations were adjusted until the technical criteria and specifications of petrodiesel and biodiesel production were met. Next, process integration techniques were employed to optimize the synthesized processes. Heat integration for petrodiesel and biodiesel was carried out using algebraic, graphical and optimization methods to maximize the integrated heat exchange and minimize the heating and cooling utilities. Additionally, mass integration was applied to conserve material resources. Cost estimation was carried out for both processes. The capital investments were obtained from ASPEN ICARUS Process Evaluator, while operating costs were calculated based on the updated chemical market prices. The total operating costs before and after process integration were calculated and compared. Next, blending optimization was performed for three blending options with the optimum blend for each option identified. Economic comparison (total annualized cost, breakeven analysis, return on investment, and payback period) of the three options indicated that the blending of ULSD with chemical additives was the most profitable. However, the subsequent life-cycle greenhouse gas (GHG) emission and safety comparisons demonstrated that the blending of ULSD with biodiesel was superior.

The paper at hand presents the environmental impact analysis of a photovoltaic (PV) power station sited in Stockholm, Sweden, using life cycle assessment (LCA). The LCA considers the primary energy return on investment and global warming potential of the PV-station, including; resource extraction, manufacturing, transportation, operation and maintenance, and decommissioning. Other environmental impact indicators are also presented, such as; the eutrophication, acidification, human toxicity, and ozone depletion potentials. The results show that the most critical phase of the lifecycle is the upgrade from metallurgical to solar grade silicon due to the high consumption of energy. The emissions results are compared to the emissions factors used for calculations in Sweden in accordance with the Swedish Energy agency and the European Commission’s directive for emissions calculations. The results for the other environmental indicators showed inconsistencies compared to existing studies, something that is according to the IEA’s guideline for PV-systems LCA caused by data scarcity and the indicators lacking consensus within the PV LCA-community. The studied PV-station is expected to reach energy neutrality after 2,4 years and offset annual GHG emissions of up to18 ton of CO 2 equivalents. / Studien tillhands presenterar miljöutvärderingen av en fotovoltaisk solcellsanläggning i Stockholm. Detta utfördes med hjälp av livscykelanalysverktyget. Analysen använder energiåterbetalningstiden och den globala uppvärmningspotentialen som indikatorer på anläggningens miljöinverkan. Både återbetalningstiden och den globala uppvärmningspotentialen beräknas för gruvarbetet, transporten, drift och underhåll samt avveckling och bortskaffning av anläggningen. Överföringsförluster beräknas också över anläggningens livscykel. Andra indikatorer som beräknas i denna studie är potentialen för försurning, övergödning, ozonnedbrytning och humantoxicitet. Dessa beräknas endast för modulens tillverkningskedja. Studiens resultat visar att den mest kritiska processen under solcellsanläggningens livscykel är kiselmetallens omvandling till solkisel, detta med avseende på energiförbrukningen och utsläpp av växthusgaser. Anläggningens globala uppvärmningspotential uttrycks i växthusgasutsläpp och jämförs med den nordiska elmixens utsläppsfaktor. Jämförelsen görs enligt dem gällande EU-direktiven. Resultaten för dem andraindikatorerna har visat på väsentliga avvikelser jämfört med tidigare studier. Detta beror enligt det internationella energirådet på databrist och på att dessa indikatorer saknar stöd inomLCA samfundet. Solcellsanläggningen beräknas bli energineutral efter 2,4 år samt eutralisera utsläpp på upp till 18 ton koldioxidekvivalenta per år.