Title : Development of auto-thermal catalytic reforming of tars and hydrocarbon gases derived from pressurized fluidized-bed gasification of wood residues
One of the major global energy challenges is the need for decarbonizing transportation, which will require new sustainable alternatives to replace fossil-based fuels in all transport sectors. While electric vehicles may become the key solution for light-duty transport, there is still a growing demand for renewable fuels in the heavy-duty road transport, maritime and air traffic sectors that cannot be electrified. Highly efficient tri-generation concepts have been developed in Finland for converting biomass residues and wastes into renewable transport fuels or chemicals through gasification and synthesis, while the by-product heat from the process and synthesis off-gases are utilized for generating energy in the combined-heat and power plants.
Fluidized-bed gasification is a feedstock-flexible technology, which is especially suitable for high volatile and highly reactive feedstocks, which can be readily gasified at 800-950 °C. However, in low-temperature gasification an abundance of tars and hydrocarbon gases are produced in addition to targeted carbon monoxide and hydrogen. Consequently, autothermal catalytic reforming is a key front-end conversion technology enabling high syngas yields and making it possible to apply conventional final gas cleaning and synthesis technologies developed for coal and oil gasification.
This paper highlights the ten-year R&D programme carried out in Finland on developing catalytic reforming technology as part of a pressurized fluidised-bed gasification process. Different reactor designs applying monolith catalyst elements as well as granular catalyst in fixed beds are described and the results from pilot-scale test facility are presented. In this process, the raw gas is led into a high temperature filter unit, where the ash and char particles are removed. Then the particulate-free gas is reformed in a multi-stage catalytic reformer. One of the key technical challenges, soot formation resulting from thermal cracking reactions, has been avoided by using staged reforming and innovative combination of different catalysts. In addition, the way of oxygen and steam introduction turned out to be a critical design factor. The key results and conclusions from 4000 hours of pilot-scale testing are summarised and best practical designs suggested. Typical raw gas of fluidised-bed biomass gasifier contains 5-10 vol% methane, 1-3 vol% C2-hydrocarbon gases and 10- 25 g/m3n benzene and 10-15 g/m3n tars. Under optimal operating conditions, 100 % conversion of C2-hydrocarbon gases, over 99 % conversion of tars and benzene and up to 80 % conversion of methane were achieved at relatively mild conditions with the reformer outlet temperature of 900 °C. Scaling-up of the technology as well as the long-term stability of one of the developed reforming concepts as well as the used catalyst materials was also verified at an industrial demonstration plant producing syngas from forest residues and bark.
Audience Take Away:
- Description of a promising concept for converting various biomass residues into transport fuels by a gasification-based technology.
- Highlights and main results from a 10 year R&D program on the pilot-scale development of reforming of tars and hydrocarbon gases from biomass-derived syngas.
- Comparison of various reactor alternatives and catalyst materials.
- Present a practical solution for solving the key challenge of biomass gasification - converting also tars and hydrocarbon gases into syngas components H2 and CO.
- Show the significant effect of reforming technology on the competiveness of gasification based routes to renewable transport fuels and chemicals.