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Several waste incinerators in Iceland were closed down in 2011/2012 due to environmental problems and health concerns. To date no cost effective and environmentally acceptable replacement has been found for disposing of the waste that was combusted at these facilities up to 2012. As a result, large amounts of waste have been transported by ferry and road to be landfilled or incinerated hundreds of kilometers away (for example routes include from Vestmannaeyjar to Reykjavik or even in some cases Blönduós, with similar long journeys in other remote locations, for example Vestfirðir). The aim of this PhD project was to take steps towards adapting a greener solution developed elsewhere for waste disposal to Iceland. The process is called gasification which is a waste-to-energy technology. The challenges for waste gasification are its adaption to the Icelandic scale, using waste as feedstock and determining operational parameters. Downscaling must be done while still eliminating the pollution problems of incinerators and the cost constraints of small-scale plants. To overcome these challenges, the experimental and pilot work at the University in Iceland was conducted by modeling and simulation. Described in this thesis is the following modelling and simulation work: An integrated small-scale gasification system with power production unit was simulated by using ASPEN Plus. This model helps to understand under what conditions and in which ways the system can operate. The system’s model was used to analyze and assess the potential of adapting gasification-based waste to power systems for conditions in Iceland. The analysis and assessment includes techno-economic and environmental perspectives. The project’s contribution to the field of gasification is the knowledge regarding simulation of small-scale gasifiers as well as the assessment of their performance and various operating parameters. This knowledge is valuable for developing gasification solutions for smaller communities that have similar waste streams and waste disposal challenges. The results indicate that electricity production from waste gasification could be technically feasible, environmentally, and economic acceptable option replacing incinerators and landfilling sites for waste disposal in Iceland. Among all the studied feedstock alternatives, timber and wood waste are the most beneficial when certain factors are considered. The production of 1 kWh electricity from timber gasification comes with the relatively low global warming potential of 0.07 kgCO2eq, acidification potential of 0.09 kgSO2eq, and eutrophication potential of 0.36 kgNO3eq. The results of techno-economic assessment show that the net present value is positive for a gasification system with the capability to generate greater than 45 kW. Discounted payback period (DPP) will be also lower than 2 years for a gasification with capacity higher than 75 kW. However, it could be lower than 6 months if gasification is applied in capacity greater than 200 kW. It is also worth to mention that, if cogeneration of heat and power (CHP) is used – instead of only power production – the DPP can be shortened even further (i.e., in cold locations where cheap geothermal hot water is not available) and that will make gasification even more feasible than shown in this thesis., Icelandic Research Fund, (in Icelandic: Rannsoknasjodur) with grant number of 196458-051, financially supported the work.

Wood and forestry residues are usually processed as wastes, but they can be recovered to produce electrical and thermal energy through processes of thermochemical conversion of gasification. This study proposes an equilibrium simulation model developed by ASPEN Plus to investigate the performance of 28 woody biomass and forestry residues’ (WB&FR) gasification in a downdraft gasifier linked with a power generation unit. The case study assesses power generation in Iceland from one ton of each feedstock. The results for the WB&FR alternatives show that the net power generated from one ton of input feedstock to the system is in intervals of 0 to 400 kW/ton, that more that 50% of the systems are located in the range of 100 to 200 kW/ton, and that, among them, the gasification system derived by tamarack bark significantly outranks all other systems by producing 363 kW/ton. Moreover, the environmental impact of these systems is assessed based on the impact categories of global warming (GWP), acidification (AP), and eutrophication (EP) potentials and normalizes the environmental impact. The results show that electricity generation from WB&FR gasification is environmentally friendly for 75% of the studied systems (confirmed by a normalized environmental impact [NEI] less than 10) and that the systems fed by tamarack bark and birch bark, with an NEI lower than 5, significantly outrank all other systems owing to the favorable results obtained in the environmental sector., This paper was a part of the project funded by Icelandic Research Fund (IRF), (in Icelandic: Rannsoknasjodur) and the grant number is 196458-051

Publisher's version (útgefin grein), Abiotic formation of n-alkane hydrocarbons has been postulated to occur within Earth's crust. Apparent evidence was primarily based on uncommon carbon and hydrogen isotope distribution patterns that set methane and its higher chain homologues apart from biotic isotopic compositions associated with microbial production and closed system thermal degradation of organic matter. Here, we present the first global investigation of the carbon and hydrogen isotopic compositions of n-alkanes in volcanic-hydrothermal fluids hosted by basaltic, andesitic, trachytic and rhyolitic rocks. We show that the bulk isotopic compositions of these gases follow trends that are characteristic of high temperature, open system degradation of organic matter. In sediment-free systems, organic matter is supplied by surface waters (seawater, meteoric water) circulating through the reservoir rocks. Our data set strongly implies that thermal degradation of organic matter is able to satisfy isotopic criteria previously classified as being indicative of abiogenesis. Further considering the ubiquitous presence of surface waters in Earth's crust, abiotic hydrocarbon occurrences might have been significantly overestimated., This work became possible through DFG grant FI 948/8-1.

In order to accurately anticipate the proficiency of downdraft biomass gasification linked with a water–gas shift unit to produce biohydrogen, a model based on an artificial neural network (ANN) approach is established to estimate the specific mass flow rate of the biohydrogen output of the plant based on different types of biomasses and diverse operating parameters. The factors considered as inputs to the models are elemental and proximate analysis compositions as well as the operating parameters. The model structure includes one layer for input, a hidden layer and output layer. One thousand eight hundred samples derived from the simulation of 50 various feedstocks in different operating situations were utilized to train the developed ANN model. The established ANN in the case of product biohydrogen presents satisfactory agreement with input data: absolute fraction of variance (R2) is more than 0.999 and root mean square error (RMSE) is lower than 0.25. In addition, the relative impact of biomass properties and operating parameters on output are studied. At the end, to have a comprehensive evaluation, variations of the inputs regarding hydrogencontent are compared and evaluated together. The results show that almost all of the inputs show a significant impact on the smhydrogen output. Significantly, gasifier temperature, SBR, moisture content and hydrogen have the highest impacts on the smhydrogen with contributions of 19.96, 17.18, 15.3 and 10.48%, respectively. In addition, other variables in feed properties, like C, O, S and N present a range of 1.28–8.6% and proximate components like VM, FC and A present a range of 3.14–7.67% of impact on smhydrogen., This paper was a part of the project funded by Icelandic Research Fund (IRF), (in Icelandic: Rannsoknasjodur) and the grant number is 196458-051.

Publisher's version (útgefin grein), A simulation model for integrated waste biomass gasification with cogeneration heat and power has been developed using Aspen Plus. The model can be used as a predictive tool for optimization of the gasifier performance. The system has been modeled in four stages. Firstly, moisture content of biomass is reduced. Secondly biomass is decomposed into its elements by specifying yield distribution. Then gasification reactions have been modeled using Gibbs free energy minimization approach. Finally, power is generated through the internal combustion engine as well as heat recovery system generator. In simulation study, the operating parameters like temperature, equivalence ratio (ER) and biomass moisture content are varied over wide range and their effect on syngas composition, low heating value (LHV) and electrical efficiency (EE) are investigated. Overally, increasing temperature and decreasing ER and MC lead to improvement of the gasification performance. However, for maximum electrical efficiency, it is important to find the optimal values of operating conditions. The optimum temperature, ER and MC of the down draft gasifier for timber and wood waste are 800˚C, 0.2-0.3 and 5%. At such optimum conditions, CO and H2 reach to the highest production and LHV and EE are around 7.064 MJ Nm-3 and 45%, respectively., This paper was a part of the project funded by Icelandic Research Fund (IRF), (in Icelandic: Rannsoknasjodur) and the grant number is 196458-051.