In this project we have worked to develop new technology for producing liquid fuels from biomass via gasification. Gasification is the conversion of the raw material to synthesis gas, consisting mainly of hydrogen and carbon monoxide. This is done at high temperatures, and the route is called thermochemical conversion. In the chosen process route the synthesis gas (syngas) is the feedstock for the Fischer-Tropsch synthesis (FTS), where it is catalytically converted to a synthetic crude oil that can be further refined to high-quality products. The FTS is a well-known process that is used commercially to convert syngas from coal or natural gas to synthetic hydrocarbon, but significant changes and improvements are needed to be able to utilize biomass as the feedstock. The key advantages of this route is that the products can be applied directly as fuels for existing engines (ships, road vehicles or aviation), and by using forestry residues or agricultural wastes as the raw material the reduction in CO2 emissions are considerable. The liquid products are very well suited to produce aviation fuels, and are free from sulfur or other unwanted species. Even though the process is commercially available and the main elements of the technology can be converted to use biomass as the feedstock, there are still many technical and economic challenges that need to be overcome, many related to the scale of production and size of the plant. In order to make the process economically viable we need to find solutions that reduce the investment cost and improve efficiencies, squeezing more product out of each unit of raw materials fed to the process. The idea is to improve the synthesis step by improving the reactor and process technology. The new technology we are working on is a novel reactor arrangement where the feed gas is ?staged?, i.e. that the feedstock addition is distributed through the reactor system, and possibly combined with the addition of extra hydrogen. Hydrogen is a key component, and the addition of extra hydrogen, e.g. produced from renewable energy via electrolysis, contributes to increase the amount of products. The changes have the potential to improve the energy- and carbon efficiency of the biomass conversion. Through the work we will build expertise in fields of high relevance for the utilization of Norwegian biomass resources for energy and industrial purposes.
We have achieved important results in all parts of the project. Comprehensive experimental studies of the FTS establishing the kinetic foundation for further modelling has been performed. The rate of reaction, the selectivities to the key products as well as the catalyst deactivation has been investigated in detail over a broad range of the key variables (residence time, syngas composition and reaction temperature). A total of 3500 hours of continuous experiments have been logged. In addition we have also performed specific experiments with staged operation of the FTS reactor system as a basis for the process modelling work investigating the staging concept. The results achieved are being treated and fitted to kinetic models, and new models that improve the description of the FTS synthesis have been developed. An important improvement is the inclusion of the effect of water, a key reaction product, in the kinetic models. This is not available in the existing literature. We have also done process modelling of parts of the complete BTL plant. Thermal reactions involving biomass (pyrolysis) has been modelled using Aspen Plus, and entrained flow gasification and new, improved gasification schemes have been simulated. The kinetics of the FTS reactor must be modelled separately, e.g. using Fortran modelling, and such a model has been developed and implemented in the process modelling tool Aspen Plus. A tool for the optimization of the staging concept has been developed, and the process layout has been optimized. Techno-economical analysis of a complete plant using the staging concept has also been done. The work shows that it is possible to design a plant that provides synthesis gas with the ?correct? composition for the FTS over a cobalt-based catalyst. This, however, requires the addition of steam and energy in the gasification step (entrained flow gasification at high temperature). Separate production and addition of hydrogen has also been investigated, and for systems with energy and hydrogen addition the distribution between direct energy addition (heat) and addition of hydrogen (from electrolysis) has been optimized. The optimal distribution for the system studied is that approximately 30% of the energy is added to the gasifier, the rest is added as hydrogen into the synthesis step. Several new concepts have been investigated, showing that a carbon efficiency up to 98-99% is achievable.
We believe the work provides important contributions to the technology for thermochemical conversion of biomass to biofuels. We have developed new process concepts, including process configurations. The staging concept can significantly help in the search for an economically viable conversion process, and the idea of integrating additional renewable energy in order to achieve better overall efficiency can be necessary in order to maximize the use of biological carbon for fuel purposes. These results will be of great interest to other academics, working on developing technology for thermochemical conversion, but most importantly the results will be available to industry developing new processes. For society as a whole the main benefit is the importance and novelty of the results, but also the competence available in the form of 3 highly skilled candidates.
The project is cooperative project between NTNU, SINTEF and Avinor to develop new technology of a biomass-to-liquid fuel process via Fischer-Tropsch synthesis (BtL FT). It combines a novel conceptual design of the BtL fuel concept, a detailed kinetic study for the development of kinetic model describing product distribution of the FT process and experimental validation of staged reactor and distributed hydrogen feed concept in the FT process to maximize syngas conversion and production of heavy hydrocarbons. The proposed project bio Fischer-Tropsch (BioFT) aim to achive energy efficiency of more than 60% and carbon efficiency of more than 55% by integration of a renewable energy source (hydro/solar power), hot syngas cleaning and, in the concept of staging of FT reactors and multiple hydrogen feed. The results from the experimental and system design could provide a BioFT process which could be deployed in small as well as large scale applications on Norwegian context for sustainable production of bio fuel from biomass.