Entrained flow gasification : experiments and balancing for design and scale-up

Reduction of CO2 emissions in the long-distance transport sector is still a mayor issue and will only be feasible by renewable liquid fuels in the medium term. At Karlsruhe Institute of Technology (KIT), the bioliq® process was developed which allows the production of synthetic fuels from biomass residues. It consists of several stages (fast pyrolysis, slurry production, high-pressure gasification, gas cleaning, gas conditioning and gas synthesis) and was realised between 2005 and 2013. The bioliq entrained flow gasifier (bioliq EFG) in the high-pressure gasification stage has got a fuel power of 5 MW and has been in operation since 2013. Model fuels and technical fuels with a high-ash content (e.g. pyrolysis oil slurries) can be supplied. Ash is deposited as slag on the refractory of a segmental cooling screen. The slag flows down the refractory and leaves the inner reactor through a water quench, which has also to be passed by the hot synthesis gas. The extensive measurement equipment at bioliq EFG enables a detailed modelling, balancing, characterisation and simulation of the entrained flow gasification process. The main objective is to develop robust tools based on ASPEN plus and CFD for the industrial design and scale-up. This paper reports the status quo of the ASPEN plus flowsheet model and on recent experimental and balancing results to provide validation data for numerical simulation of the bioliq EFG. The ASPEN plus flowsheet model provides the framework for an equilibrium model of the bioliq EFG pilot plant including tools for an elemental and energy balance of the gasifier. The balancing tool considers the CO2 solubility in the water quench and calculates the carbon conversion and the gas phase composition and temperature before the water quench which have not been measurable yet. In order to verify the gas phase temperature TWB, the gas phase equilibrium temperature Teq and the water-gas-shift temperature TWGS are calculated. The water-gas-shift temperature is based on the equilibrium constant of the water-gas-shift reaction computed using the gas phase composition. The results are focused on the bioliq campaign V82.1 carried out at 40 bar with a model fuel (96 % ethylene glycol + 4 % A glass). In addition to flow rates, the compositions of the feed streams and the gas phase composition after the water quench, the total heat flux removed from the gasifier via cooling screen have been determined as input data for balancing. The balancing results show similar gas phase compositions and gas phase temperatures as the equilibrium calculations due to high carbon conversion (99 %). Dry concentrations of H2, CO, CO2 and CH4 measured after gas conditioning via gas chromatography (GC) represent the gas phase composition in the gasifier accurately since the CO2- solubility in this case is low. 0.4 % of CO2 in synthesis gas has been solved in the water quench. The deviations between the equilibrium and the measurement/balancing results are caused by the unavoidable measurement errors in the experimental setup and experimentally non-accessible heat loss, the resulting difference between the temperatures TWGS and TWB and the water gas shift reaction.