Conversion of Syngas From Biomass in Solid Oxide Fuel Cells

Abstract

Conversion of biomass in syngas by means of indirect gasification offers the option to improve the economic situation of any fuel cell system due to lower costs for feedstock and higher power revenues in many European countries. The coupling of an indirect gasification of biomass and residues with highly efficient solid oxide fuel cell (SOFC) systems is therefore a promising technology for reaching economic feasibility of small decentralized combined heat and power production (CHP).The predicted efficiency of common high temperature fuel cell systems with integrated gasification of solid feedstock is usually significantly lower than the efficiency of fuel cells operated with hydrogen or methane. Additional system components like the gasifier as well as the gas cleaning reduce this efficiency. Hence common fuel cell systems with integrated gasification of biomass will hardly reach electrical efficiencies above 30%. An extraordinary efficient combination is achieved in case that the fuel cells waste heat is used in an indirect gasification system. A simple combination of a SOFC and an allothermal gasifier enables then electrical efficiencies above 50%. However, this system requires an innovative cooling concept for the fuel cell stack. Another significant question is the influence of impurities on the fuel cell degradation. The European Research Project “BioCellus” focuses on both questions—the influence of the biogenous syngas on the fuel cells and an innovative cooling concept based on liquid metal heat pipes. First experiments showed that, in particular, higher hydrocarbons—the so-called tars—do not have any significant influence on the performance of SOFC membranes. The innovative concept of the TopCycle comprises to heat an indirect gasifier with the exhaust heat of the fuel cell by means of liquid metal heat-pipes. Internal cooling of the stack and the recirculation of waste heat increases the system efficiency significantly. This concept promises electrical efficiencies of above 50% even for small-scale systems without any combined processes.

Efficient Conversion of Lignin to Electricity Using a Novel Direct Biomass Fuel Cell Mediated by Polyoxometalates at Low Temperatures

“…Ac learc haracteristic absorption peak at around 750 nm was observed for the reduced PMo 12 ,w hich is known as molybdenum blue. When the H n -POM red was discharged using O 2 as the oxidanti nt he fuel cell at room temperature, the maximum power densities for H 3 [16] Thus, the redox potential of the POM used should be in the range of 0.6-1.2 Vt oo xidizet he phenolic structure of lignin and serve as an electron carrieri n the fuel cell. Theoretically,t he standard cell potentiali sl ess than 0.63 Vb ased on the followingc ell reaction [Eq.…”

“…However, externalp rocessing is required to convert lignin to suitable fuels. For example, gasification of lignin to syngasi sn ecessary for SOFCs, [3,4] or carbonization to biochar or blending with active carbon prior to fueling DCFCs. [5][6][7] The requirement of external processing to convert lignin to gaseous fuels or biochar not only increases the complexity of the system but also greatlyr educes exergy efficiency.…”

Planar High Temperature Heat Pipes for SOFC/SOEC Stack Applications

“…to develop integrated heat pipe interconnector layers (Figure 1), preventing degradation promoting hotspots and performance impeding cold zones. The concept of combining SOC systems and heat pipes has already been successfully tested within the EU-research project BioCellus [13][14][15]. Experimental results showed that internal cooling of stacks could be realized and temperature distributions were equilibrated.…”

Thermal contact resistance in solid oxide fuel cell stacks

“…Further stack related problems, in particular fuel leakage and contact loss between electrodes may occur [3]. Thus, the theoretically fast electric load modulation of solid oxide cells is intensely restricted by inertial thermal adaption of cell and stack and the need to prevent fracture of cell components [4,5]. Thermal gradients within the stack structure are to be minimized, notably for cyclic load changing operation conditions.…”