• Energy Research

Abstract Feeding solid oxide fuel cells (SOFCs) with gas from biomass gasification is promising with regard to highly efficient power generation. But it is also intricate since biogenic contaminants are harmful to state-of-the-art anode materials. In this work the influence of phenol as a biogenic model contaminant on the performance of single solid oxide fuel cells was studied under realistic conditions. For this purpose Ni/YSZ anode supported cells were operated with simulated bio-syngas, applying an electrical load of 0.34 A/cm2. Over a duration of several hundreds of hours phenol was periodically added to the fuel gas. The tests showed that for the lowest concentration of phenol no accelerated degradation could be observed regarding cell potential and electrical impedance measurements, but disintegration of the Ni/YSZ support took place. Metal dusting of the anode support was found to be the most important mechanism of degradation.

The partial substitution of coal with biomass in the existing power plant fleet can reduce the carbon dioxide pollution in a cost effective way at high efficiencies. The goal of this study was to identify suitable co-firing ratios during co-combustion of straw and three different coal types (0, 10, 25, 40, 60, 100% straw on energy basis in fuel blend) minimizing the corrosion risk. An online corrosion monitoring systems based on the linear polarisation resistance method has been used for measurements in two pulverised fuel co-firing systems: An externally heated entrained flow reactor at the Technical University of Munich and a 300 kWth drop down fired reactor at University of Stuttgart. The experiments at the entrained flow reactor have been conducted for 8 h per blend at 1200 °C with an excess oxygen of 3-5 vol-%. Online corrosion measurements were performed at a flue gas temperature of about 700 °C – 900 °C representing the superheater region of a power plant. Material temperature was set to 530 °C utilizing 10CrMo9-10 as the examined alloy. The pilot scale tests were performed for 0, 25, 40, 60% e.b. straw content. Each blend was combusted for 24 hours. At lab scale tests a constant sensor signal was measured for 0, 10, 25, 40% e.b. straw content which increased steeply after changing the ratio to 60%, indicating a corrosive atmosphere. This phenomenon was found for all three different coals, however the overall corrosion signal was lower for coal from South Africa and El Cerrejon. Nevertheless, all series of measurements showed an increasing signal for a higher share of straw in the fired fuel blend. These tendencies were also confirmed at the pilot scale test with El Cerrejon coal. Deposition and fuel analysis show correlations between the Cl-content in fly ash, Al2O3 content in the fuel and the corrosion signal.

Operation of solid oxide fuel cells (SOFCs) with bio-syngas from the gasification of biomass is a promising approach to highly efficient and sustainable power generation. At the same time, the coupling is challenging as several biogenic impurities in the bio-syngas have a negative effect on the SOFC. For this paper the impacts of the impurities naphthalene and phenol on SOFC short-stacks were investigated experimentally for the first time. The cell in the stacks were anode-supported SOFCs with Ni/YSZ anode. The experiments were performed at 700 °C under load with simulated bio-syngas consisting of hydrogen, carbon monoxide, carbon dioxide, methane and water vapor. 2 g Nm−3 of naphthalene (350 ppm) caused a pronounced voltage drop and an increase in cell temperature. By analysing the anode off-gas and recording of I–V-curves, it could be shown that naphthalene blocked the electrochemical hydrogen oxidation as well as the reforming of methane and the shift reaction of carbon monoxide. Up to 8 g Nm−3 of phenol (1900 ppm), on the other hand, led to carbon deposition and irreversibly damaged the structure of the anode substrate by metal dusting. This form of degradation was not visible in the electrochemical data during operation.

Abstract A novel approach, combining electrolysis and oxygen-blown entrained flow gasification enables high carbon efficiency for producing sustainable Fischer–Tropsch fuels. This Power-and-Biomass-to-Liquid process combines the concepts of using biomass as the carbon and energy source (Biomass-to-Liquid) and hydrogen as an energy carrier supplied from carbon-neutral renewable energies (Power-to-Liquid). A highly integrated Biomass-to-Liquid process is modeled in detail using Aspen Plus®. To enhance process performance, integrating green hydrogen and oxygen from water electrolysis is modeled and the use of polymer electrolyte membrane and solid oxide electrolysis at elevated temperature is compared. The energy efficiency of a conventional Biomass-to-Liquid process with advanced heat and material integration is about 46%, while overall carbon efficiency is about 41%. By adding hydrogen from electrolysis, the product yield is increased by a factor of 1.7–2.4. The improvement in fuel production comes at the price of a hydrogen demand in the range of 0.19–0.24 tH2/tfuel. For 200 MWth biomass input, this results in electrolyzer sizes between 120–320 MWel, depending on the process configuration and the electrolysis technology used. The detailed process models show the high potential for increasing carbon efficiency to up to 67%–97% by integrating renewable power into a Biomass-to-Liquid process.

A review of power-to-liquid for methanol, DME and FT-fuels focusing on commercial synthesis technologies and current power-to-liquid concepts.

Anode-supported solid oxide fuel cells (SOFCs) with a state-of-the-art Ni/YSZ anode have been tested in simulated bio-syngas with controlled addition of phenol as a model molecule to study the influence of tars on the degradation of SOFCs operated with gasified biomass. The post-test analysis results of SOFCs are described after operation with different concentrations of phenol. The tests with pure syngas and up to 2 g/Nm3 of phenol show a relatively stable performance in a short-term period of 500 h, but the test with 8 g/ Nm3 phenol shows drastic degradation. The microstructural changes of anode and support layers, phase changes, and carbon deposition were analyzed and discussed based on performance degradation and post-test analysis. No structural changes were found after tests with pure syngas. On the other hand, the addition of phenol causes macro- and micro-scale structural changes in the support, spreading from the fuel inlet. The support shows an erosion pattern and both Ni and YSZ were found as dust after the test. In these eroded areas, carbon fibers were observed by SEM and it was more pronounced with higher phenol content. There was no material phase transformation related to syngas or phenol, but surface carbon deposition was confirmed by Raman spectroscopy in the support and anode layers.

The impact of residence time and temperature during hydrothermal carbonization (HTC) on hydrochar properties and CO2 gasification properties has been studied for brewers' spent grain (BSG), treated at temperatures from 180 °C to 280 °C and residence times from 0.5 to 12 hours. Lower heating values (LHV) of the hydrochars are found to increase to values of bituminous coal and anthracite as reaction severity increases. Temperature is found to have a greater influence on the LHV of the hydrochar than residence time. Mass and energy yields decrease with increasing reaction severity. With higher reaction severity decreased molar O/C and H/C ratios as well as decreased volatile contents and increased fixed carbon contents are observed. The influence of residence time is more pronounced for the formation of fixed carbon, main carbonization reactions occur for a reaction severity greater than 180 °C and 0.5 hours. Char reactivity is found to decrease with increasing carbonization reaction severity with a strong influence of both residence time and temperature due to the formation of fixed carbon in the hydrochar. Activation energies are decreased with increased carbonization temperature but only mildly affected by residence time. Hereby the catalytic influence of ash compounds has to be further determined.