Abstract
Small-scale Fischer-Tropsch Synthesis (FTS) plants for waste or biomass to liquid applications are more appropriate than mega-scale FTS plants because of different drivers, including environmental protection, economic development, and social progress. A novel design approach for multi-tube reactors for small-scale FTS plants was proposed where the activity of the catalyst was varied so that when the reactor tubes are scaled up, the maximum temperature in the reactor tube never exceeds a set upper limit. When designing multi-tube reactors in conventional commercial FTS plants, typically a suitable catalyst is identified using experiments run in laboratory reactors. The laboratory data is scaled up, and the measured catalyst activity is used directly in the design; however, this could result in the maximum temperature in the catalyst bed exceeding the safe catalyst operating range. The new design method was demonstrated by designing a multi-tube reactor for a mobile FTS plant that can fit into a commercial container. The performance for reactor tubes of different diameters, including CO conversion and productivity, was firstly predicted using CFD simulations. Simulations were conducted at the same safety constraint for temperature rise in order to utilize the corresponding heat removal capabilities efficiently. Catalyst activity and space velocity were set as controllable parameters in each simulation to ensure that the maximum temperature in the catalyst bed would meet, but not exceed, the temperature rise limit. Thereafter the diameter of single tube was optimized for total productivity, under the same space limit of the multi-tube reactor and tube bundle arrangement of the multi-tube reactor. According to the simulation results, the designed multi-tube reactor can obtain a productivity of 15.3 kg/h at the conditions: tube diameter of 3/4’, SV of 300/h, and catalyst activity of 695% of that in the base case. In the optimized case, approximately 2.2 tons of municipal solid waste or 2.0 tons of wood chips per day will be consumed by the containerized FTS plant.
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•A tubular reactor design for small-scale Fischer-Tropsch applications was proposed.•Designing the reactor for a containerized plant was taken as example.•Selection of tube diameter and optimization of catalyst activity were integrated.•A limit for temperature rise was set for maximum heat removal of tube and safety.•Productivity for reactor with a given space was optimized by simulation.