The paper presents the conceptual design of a castor oil biorefinery. Castor oil contains over 90% ricinoleic acid (12-hydroxy-9-octadecenoic) triglyceride, a versatile functional molecule. Fatty methyl ricinoleic ester (FAMRE) is the key building block. This can be valorised as biodiesel, but more profitable is making biochemicals, namely high-value polyamides. The goal is the conceptual design, simulation and economic analysis of a biorefinery processing 80 ktpy castor oil, equally shared between biodiesel and biochemicals. The process synthesis work is based on research papers and patents, supported by simulation with Aspen Plus (TM). The biorefinery involves three plants: transesterification, pyrolysis and amination. Two innovative technologies are developed for transesterification, by heterogeneous catalysis in variable-time PFR and by homogeneous catalysis in reactive-extraction device. The reactors are simulated by employing detailed kinetics such that the ester composition fulfils the specifications set by the quality norms for biodiesel. Both methods result in compact and low energy processes, but the first delivers more valuable high-purity glycerol. FAMRE pyrolysis supplies heptanal, a valuable intermediate for specialities, and methyl undecenoate, converted further to omega-aminoundecanoic acid. Energy saving of 77% is achieved by employing mechanical vapour recompression. The amination is complex as chemistry and processing, involving aqueous solutions and solids. The economic analysis estimates capital costs and minimum product prices for 20% ROI. The performance and contribution of each process is highlighted. The bottleneck in design is the amination plant, capital-intensive and handling large amounts of process water. This stage makes necessary high equipment and energy costs but delivers a high-value monomer that boost the profitability. The result is that at equal throughput the biochemicals bring 2.5 times more revenues than biodiesel. By a synergy effect, high-value biochemicals sustain the profitability of commodity biodiesel, which in turn offers a broader market and secures stable revenues for farmers. (C) 2018 Published by Elsevier B.V. on behalf of Institution of Chemical Engineers.