Scale-up and Demonstration of Fischer-Tropsch Technology

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6 D. Schanke et al. To date, more than 100 tonnes of catalyst have been produced for use in the semicommercial demo plant. The scale of production (up to 1 ton/d) ensures minimal scaleup risk for the catalyst manufacturing plant for a commercial project. 5. Performance of the demonstration plant 5.1. Catalytic performance During the catalyst manufacturing campaigns, an extensive program of quality control was carried out, using a pilot plant and other catalyst test reactors. After developing and optimising the catalyst manufacturing procedures, the activity and selectivity of catalyst produced at large scale does not differ from catalyst produced in the laboratory. Furthermore, it was found that the catalyst activity and selectivity in the semicommercial demo plant was similar to what is usually observed in the pilot plant. Table 2. Example demo plant performance Feed gas composition H2 CO CO2+CH4+N2 58 mol % 27 mol % Balance Reactor pressure 1600 kPa Reactor temperature 232 o C Gas hourly space velocity 3950 Nm 3 /toncatalyst/h Conversion per pass H2 CO 66 % 67 % 5.2. Wax separation Predictably, the separation of wax from the slurry has been the most challenging aspect of the technology development. After very good results in smaller scale pilot reactors, the first trials in the semi-commercial demo plant gave low wax separation performance after some time of operation and higher than expected levels of catalyst fines in the wax product. After several modifications to the wax separation system as well as the introduction of a 2 nd generation FT catalyst, the plant was able to be operated at sustainable, high wax separation rates with minimal catalyst fines in the wax product (see fig. 4). The performance of the wax separation system is known to be strongly dependent on the particle size distribution of the catalyst in the reactor slurry. It became apparent that the attrition characteristics of the catalyst are a function of the scale of operation, the operating conditions as well as the properties of the catalyst (Wagner, 2008). This is
Scale-up and demonstration of Fischer-Tropsch technology 7 illustrated in Table 3. Similar observations have been made by Zennaro (2006). Using the 2 nd generation catalyst gives very low attrition rates in all reactors tested. Table 3. Attrition rates measured for different catalysts measured in slurry bubble columns of varying scale and type. Relative attrition rate (1 st gen. cat. In pilot plant = 1.0) Pilot plant Cold-flow column Semi-commercial plant 1 st gen. catalyst 1.0 0.3 5 2 nd gen. catalyst 0.03 0.01 0.03 SUSTAINABLE WAX SEPARATION RATE (relative) 4,0 3,0 2,0 1,0 0,0 1st gen. cat. 2nd gen. cat. Pilot plant Cold-flow Semi-commercial Fig. 4. Relative wax separation rates (wax output/filter surface area, time) for different catalysts in slurry bubble columns of varying scale and type. 5.3. Hydrodynamics The hydrodynamics of the semi-commercial reactor was studied using different methods: - Overall and local gas hold-up was estimated using differential pressure measurements - Catalyst concentration profiles were calculated from slurry sampling at several axial locations - Temperature profiles were compared with simulation models
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