Friedemann Georg Albrecht

Alternative fuels from biomass and power (PBtL) - A case study on process options, technical potentials, fuel costs and ecological performance

Greenhouse gas emissions in the transport sector shall be reduced to reach globally agreed COP21 goals. One option is to replace fossil based fuels with bio-based alternatives. The technical potential of biofuels made from energy crops (1st generation), biomass and waste wood (2nd generation) typically suffer from the limited technical potential of biomass resources in central Europe. Biofuel output can significantly be increased in the Power&Biomass-to-Liquid (PBtL) concept utilizing renewable electricity in modified BtL plants. The case study presents detailed results on promising process configurations of Fischer-Tropsch PBtL concepts based on different gasifiers and electrolyzers in terms of fuel production potentials, fuel costs and CO2 footprint. Results from the study indicate that the biomass specific fuel output can be quadrupled when utilizing green electricity for hydrogen generation in the PBtL process. The increased fuel output results in lower fuel production costs due to the effects of the economy of scale. Fuel production costs below 1.3 €/l were estimated for a large PBtL plant (225 kt/year) assuming an electricity price of 31.4 €/MWh (average EEX-Phelix index of the year 2015). The exergy analysis reveals that the electrolysis and the gasification processes are characterized by the most significant thermodynamic optimization potentials. The PBtL concept is characterized by a lower CO2 footprint, as high carbon conversion rates close to 100 % can be achieved by using oxy-fuel technology and recycling the entire CO2 within the system. Hence, largest CO2 emissions arise from harvesting and transportation of the biomass feedstock.

Synthetic jet fuel from renewable energy sources for sustainable aviation

Advanced technologies, optimized operation and infrastructure are not sufficient to achieve the CO2 mitigation goals agreed on for the aviation sector. Carbon neutral alternative liquid fuels are required to fill the gap towards a carbon-neutral growth from 2020 on. The Power-to-Liquid process is one option to produce synthetic jet fuels from renewable energy. The technical and economic performance of production processes based on renewable electricity and CO2 was investigated and evaluated. Hydrogen can be generated by water electrolysis from fluctuating renewable power sources. Together with CO2 the reverse water-gas-shift reaction forms syngas. The Fischer-Tropsch synthesis produces long chained hydrocarbons from syngas. Downstream product separation and upgrading generates gasoline, jet fuel and diesel. Another process concept is based on high temperature co-electrolysis of steam and CO2 producing synthesis gas at high temperature and pressure. The process performance is evaluated via flowsheet simulation models and pinch point analyses comparing the Power-to-Fuel efficiency as well as carbon conversion into liquid fuels. A baseline Power-to-Fuel efficiency of 44 % for the concept based on water electrolysis can be increased to 60 % using the co-electrolysis concept. The baseline carbon conversion of 73 % grows to 98 %. The sensitivity of various operation conditions was analyzed. A cost analysis based on market data and equipment factors was performed for the investment year 2014. Employing stationary power input of 105 €/MWh, production costs of 3.38 €/kg were found for the water electrolysis concept. The production costs of the co-electrolysis concept compare to 2.83 €/kg. The sensitivity of the electrolyzer capital cost and electricity prices were analyzed and their effect on the production costs will be presented. Investment and operating costs to fill the gap towards carbon-neutral air transport growth from 2020 on can be predicted based on 2014 costs and technology status. A comparison to other renewable jet fuels regarding land use, feedstock potential and economic measures will be provided.

The potential of using power-to-liquid plants for power storage purposes

The Power-to-Liquid (PtL) concept offers the potential to interlink the power and fuel market by producing high quality fuels from electricity and CO2. In addition, gaseous by-products from fuel synthesis can be used to generate electricity in peak load hours. In this work, a PtL concept comprising of a reversible solid oxide cell (SOC) is presented and evaluated in terms of 2014 fuel net production costs (NPC) and power storage potential. Results were compared with a reference system operating steady-state in electrolysis mode. A 100 % SOC run factor was realized, whereby the SOC unit runs primarily in co-electrolysis mode. Fuel net production costs (NPC) were slightly higher for the reversible SOC system, since increased capital costs exceed the revenue from lower average electricity costs. Though, fuel costs below 1 €/l are possible if every kWh of effectively stored electricity is credited with 3-9 €ct/kWh, which is the typical storage costs of state-of-the-art pump storage plants.