For the production of Fischer-Tropsch diesel the main technological challenges are in the production of the synthesis gas (entrained flow gasifier). These barriers also apply to other gasification-derived biofuels, i.e. bio-methanol, bio-DME and biohydrogen. The synthesis gas is produced by a high-temperature gasification, which is already used for coal gasification. Biomass has different properties than coal and, therefore, several process changes are necessary. First, the biomass pre-treatment and feeding need a different process, because milling biomass to small particles is too energy-intensive.
The Fischer-Tropsch synthesis is composed of three subsystems: gasification, Fischer-Tropsch synthesis (FTS), and upgrading to commercial products (). Based on the initial investment, the gasification system represents about 50% of the investment cost, with FTS representing 35% and upgrading 15%. The percentage of the investment for the gasification step increases to 65–70% for coal, with the remaining two systems divided in the same ratio as for natural gas. About 1.5% of the coal that is produced worldwide is gasified, and about half of this is used by Sasol (South African Synthetic Oils) FTS plants. It is expected that the cost for gasification of biomass will be similar to, or even higher than, that for coal, depending upon the biomass used.
Fischer-Tropsch Synthesis Research
Moreover, small biomass particles can also aggregate and plug feeding lines. Pre-treatment processes like torrefaction or pyrolysis (which produces a liquid oil) could be developed to overcome these problems. Second, due to the higher reactivity of biomass (compared to coal) the gasification temperature might be decreased, resulting in higher efficiencies, but this will require different gasification and burner design. Third, the ash composition in biomass is different from that in coal, which results in different ash and slag behaviour, which is an important factor in the gasifier and still needs to be studied thoroughly. This ash and slag behaviour is also important for the cooling of the syngas, for which innovative development is desired. Other research topics are the cleaning and conditioning of synthesis gas, development of several types of catalysts, and the utilisation of by-products such as electricity, heat and steam. In Germany, a pilot production facility for Fischer-Tropsch liquids from biomass is currently in operation.
Biorefineries - Essential Chemical Industry
The core technology of commercial-scale indirect coal liquefaction was first mastered in South Africa. Over the last decade, China has made breakthroughs in commercial indirect coal liquefaction through independent R&D. Three 160–180-ktpa indirect liquefaction projects have been placed in operation. Now efforts are being made to speed up the implementation of a large demonstration project, which is focused on solving key technical issues such as the design and manufacturing of large-scale Fischer–Tropsch (F-T) synthesis slurry bed reactors, catalytic oxidation of alcohol byproducts, methane conversion and utilization of synthesis tail gas, production and application of new F-T synthesis catalysts, process optimization and integration of a heat recovery system, and engineering design for major project deployment. Progress is also being made to improve process integration and optimization, further reduce the required unit investment, reduce water and coal consumption per unit product, establish a high-temperature F-T synthesis demonstration plant, and achieve safe and stable long-term operation of large (e.g., >1 MMtpa) plants.