A novel integrated renewable-based energy system for production of synthetic diesel is proposed and simulated in this study. This system merges solid oxide electrolyser (SOE), entrained gasification (EG) and Fischer-Tropsch (FT) technologies. Two case scenarios are considered here. In the first case, the electrolyser unite produce syngas through co-electrolysis of steam and carbon dioxide, while in the second case only steam is electrolyzed. The effects of SOEC and EG operating pressure and temperatures on the system performance in each case are investigated and compared. It is shown that the operating condition of electrolyser subsystem has a more considerable effect on the performance of the integrated system as compared to the gasification subsystem. Also waste heat recovery results in about 43 and 2 percentage point increase in energy and exergy efficiency, respectively. It is also shown that internal recovering of oxygen has the best effect on the system performance.

In this study, a novel integrated system for production of advanced synthetic diesel is proposed and analyzed from thermodynamic, economic, and environmental perspectives. This system consists of a solid oxide electrolyzer, entrained gasification, a Fischer Tropsch reactor (FT), and upgrading processes. Eleven different combinations of precursor syngas production through steam and CO, co-electrolysis and biomass gasification are investigated. Results show that an increasing share of produced syngas in the electrolyzer unit results in higher system efficiencies, emission savings, and levelized cost of FT diesel. Moreover, different options of heat and mass :flow recovery are considered. It is concluded that recovery of produced medium pressure steam in the system is highly beneficial and recommended. Besides, it is shown that while oxygen recovery is the best choice of mass recovery, hydrogen recovery for internal use has adverse effect on the system performance.

Production of synthetic hydrocarbon fuels as a means for renewable energy storage has gained attention recently. Integration of solid oxide co-electrolysis of steam and carbon dioxide with the Fischer-Tropsch process to transform renewable electricity into Fischer-Tropsch diesel is one of the promising suggested pathways. However, considering the intermittency of produced renewable electricity such integration will have a low capacity factor. Besides, locating a reliable source of carbon dioxide near the installed integrated system may prove to be difficult. A novel integration for production of Fischer-Tropsch diesel from various renewable sources is suggested in this study. The proposed integrated system includes solid oxide electrolysis, entrained gasification, Fischer-Tropsch process and an upgrading system. Gasification is assumed to have a continuous operation which increases capacity factor of the integrated system. Carbon dioxide supplied via gasification of biomass provides a reliable source for on-site co-electrolysis. Technical capabilities of the proposed integrated system examined by investigating performance in relation with electricity, and diesel demand of four different European cities. Results show that the proposed system is capable of supplying Fischer-Tropsch diesel of between 0.9-32% of the annual diesel demand for road transportation respective to the location of installation, with a high emission savings (around 100%). Cost of produced diesel is not competitive with conventional diesel for all cases, even when all the other by-products were assumed to be sold to the market.

A pressurized solid oxide electrolyser (SOE) system for syngas production is analyzed. The system is modeled and analyzed considering energy and exergy aspects. The main consideration is to quantify the effect of operating pressure on the system performance when syngas is used for synthetic diesel production. At elevated pressures methanation reaction within the electrolyser causes internal production of methane from syngas. The results show that methane fraction increase from almost zero percent to 14% at 25 bar. Since methane is not a favorable outcome of this system, elevated pressure has adverse effect on the total system performance and consequently system efficiency drops by about 20% points by increasing the electrolyser operating pressure from atmospheric to 25 bar. This effect also results in higher levelized cost of syngas at elevated pressures. Effects of other operating parameters like temperature and utilization factor on the syngas production rate and system performance are also explored. In addition, relative irreversibility of each component is estimated. It is concluded that the solid oxide electrolyser has the highest relative irreversibility amongst other system components which can be minimized by changing operating temperature. At last but not least, levelized cost of produced syngas is estimated.

An entrained gasification system for syngas production is modeled and analyzed. The system is capable of producing enough syngas for further production of 15 m3/h Fischer-Tropsch diesel which is suitable for independent medium scale renewable energy systems. The system is modeled using ASPEN Plus and analyzed considering energy and exergy aspects. The model includes all the required units to achieve desired properties of syngas such as air separation unit to provide pure oxygen as oxidant feed, water-gas shift reactor to achieve desired hydrogen to carbon monoxide ratio, and selexol unit for selective and bulk removal of H2S and CO2. Results showed that including all of these units in the analysis will result in system energy and exergy efficiencies as low as 53.4% and 48.9%, respectively. Also, it is shown that although methane content increases at elevated operating pressures, due to high gasification temperature it is still negligible compare to other elements of syngas. It is also shown that system will have its higher valuse of efficiency when operated at 6 bar. On the other hand temperature has not any major effect on total system performance due to several contradictory effects that eventually counterbalance each other. 

Gasification may be an attractive alternative for converting heavy oil residue - petroleum coke into valuable synthetic gas. Due to the low reactivity of petroleum coke, it is maybe preferable to convert it in combination with other fuels such as biomass. Co-gasification of petroleum coke and biomass was studied in an atmospheric bubbling fluidised bed reactor and a thermogravimetric analyser (TGA) at KTH Royal University of Technology. Biomass ash in the blends was found to have a catalytic effect on the reactivity of petroleum coke during co-gasification. Furthermore, this synergetic effect between biomass and petcoke was observed in the kinetics data. The activation energy Ea determined from the Arrhenius law for pure petcoke steam gasification in the TGA was 121.5 kJ/mol, whereas for the 50/50 mixture it was 96.3, and for the 20/80 blend - 83.5 kJ/mol.

Previous studies in an atmospheric bubbling fluidised bed (BFB) gasification system indicated significant tar variability along the system. In this paper the experimental procedure has been improved for reliable results and understanding of tar variability in the producer gas. By introducing a new sample point for tar analysis to the system, experiments indicated tar reduction in the gasifier, probably due to continuous accumulation of char and ash in the bed, as well as in the ceramic filter because of thermo- and catalytic effects. Thermogravimetric analysis of the filter sample indicated 14 % of volatile inorganic compounds, and additional analysis of inorganic parts showed alkali and alkaline earth metal content, well known as tar breakdown catalysts.

A study has been performed using experimental iron based granules as a tar breakdown catalyst in a biomass gasification gas. Previous examinations established that metallic iron located in a separate catalytic bed reactor has a stronger influence on the tar content and composition in the product gas than their corresponding iron oxides. The results from the present study show that tar diminution in the product gas is dependent on temperature, catalyst material and oxygen potential. Typically, values of 50-75% tar reduction were achieved when varying the catalytic bed temperature between 750 and 850 degrees C. Also, the oxidation state of the catalyst material has an influence on the tar content and gas composition in the gas. When changing the gasification temperature from 800 degrees C to 850 degrees C the oxygen potential in the producer gas also changes, resulting in a transition from oxidative to reductive conditions in the gas. This implies that when the gasification temperature is 800 degrees C, the catalyst is transformed from its metallic state to the iron oxide, wustite. Consequently, the tar reduction capacity of the catalyst is reduced by approximately 20%. In view of the overall results it can be concluded that the catalysts in their metallic states in general exhibits a better tar cracking capacity than their corresponding oxides. The iron material used is sintered iron powders manufactured at Hoganas AB, Sweden. The iron materials were dispensed in the metallic state.

The present study investigates the effect of several experimental iron-based granules on biomass tar decomposition. The iron-based materials were provided by Höganäs AB and were all in their metallic state when they were applied in a secondary catalytic reactor. Bark-free birch was employed as fuel in an atmospheric fluidised bed reactor, and the tar concentration and gas composition in the producer gas were measured before and after the catalytic bed. The results demonstrate a clear tar reduction capacity for all the tested iron-based materials.