Heat Transfer Enhancement Of Tubular Flow Reactor

Author : Steven Wiryadinata
Publisher :
ISBN 13 : 9780438291454
Total Pages : pages
Book Rating : 4.2/5 (914 download)

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Download or read book Heat and Mass Transfer Enhancement of the Packed Bed Fischer-Tropsch Reactor written by Steven Wiryadinata and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This experimental work investigates the effect of flow field alteration in the packed bed Fischer-Tropsch (FT) reactor through the use of flow disturbers (bluff body) and varying the reactor aspect ratio using packed beds of two length-to-diameter ratios. The FT process is limited by heat and mass transfer and chemical kinetics as prescribed by the reactor geometry, flow and temperature fields, and catalyst properties. Exothermicity and uneven reaction rates lead to radial temperature and concentration gradients, which may increase conversion at the expense of high short-chain HC production (defined as C7 in this work) undesirable for the production of HC liquids. The present work investigates the influence of aspect ratio, flow rate and application of passive flow disturber packages in the fixed bed FT reactor on conversion and C[subscript 7+] productivity. Additional data acquisition at elevated temperatures and higher catalyst mass loading were performed. Empirical models as functions of aspect ratio, flow and number of bluff body packages were developed to enable predictions of conversion and productivity for a range of input values with minimum required data. Experiments were carried out using two 188 cm3 reactors with 3.8 and 30.8 aspect ratios (length-to-diameter ratios) loaded with equivalent mass of 20% cobalt/Al2O3 catalyst and controlled at 200°C at the exterior wall. The feed flow at constant 2.2 H2/CO ratio was varied between 300 and 800 GHSV. Reactor pressure was maintained at 2.75 bar. The effect of increased control temperature and increased reactor catalyst load were also investigated. Results show that the bluff bodies (enhanced case) have significant positive impact on conversion and productivity across the experimental space. The individual effect of the bluff bodies, the interaction between bluff bodies and flow rate, and the interaction between aspect ratio and bluff bodies are the statistically most significant factors influencing CO conversion, C[subscript 7+] yield and total C[subscript 7+] production rate, respectively. Conversion, yield and production rate of the enhanced reactor were increased by as much as 2.5x, 2.7x, and 5.4x of the baseline case, respectively. The bluff bodies were observed to increase effective residence times by 2.3x and 2.2x compared to the baseline wide and thin reactors, respectively, due to an imposed lengthening of the reaction path length. Compared to the baseline thin reactor, the enhanced wide reactor exhibited as much as 1.1x, 2.7x and 3x better conversion, yield and productivity, respective, and demonstrates that passive flow enhancement can reduce reactor length. This reduction in reactor length, which is accompanied by an increase in diameter, improves the cost effectiveness of FT at the small scale since state-of-the-art industrial packed bed FT has always employed high aspect ratio (L/D 200, > 5 cm inner diameter) multi-tubular reactors which cannot be replicated in the small scale. Furthermore, the combination of high flow, high reactor aspect ratio and use of bluff bodies at the normal catalyst load resulted in C[subscript 7+] productivity that approached the productivity of a reactor with 1.67x the catalyst load, thus indicating that the combined bluff body and aspect ratio adjustment can significantly boost productivity without additional use of expensive catalyst materials. The combination of 1) marked improvement in single pass productivity, 2) reduction in reactor length, and 3) reduction in reactor catalyst loading suggests that the use of internal flow disturbers in the packed bed had significant influence in lowering the heat and mass transfer resistances of the FT process, and can improve the cost-competitiveness of FT liquids production in the small scale.