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Efficient Removal and Processing of Tar from Biomass Gasification Gas
2014 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

During the last decade the gasification industry has had a steady upswing. The upswing has its roots in the rapid industrialization and increasing energy demand in Asia. The most widely used feedstock for gasification is coal. The use of biomass as feedstock for gasification is being more and more recognized, but the feedstock puts some limitations on the process. Tar compounds formed in the gasifier can cause downstream process failures. Tar reforming and removing process units are currently being developed. Three different kinds of tar reforming/removal technologies were investigated in this work; an oil scrubber system, a plasma system and a catalytic tar reforming system. Some of the parameters compared were process efficiency, technology maturity and investment costs. In addition, a catalytic test on steam reforming of oxygenated hydrocarbons was performed. The aim was to see which of the process(es) were more suitable to act as a tar reforming stage to an end product where methane were desired and to an end product where no methane were desired. Also, it was also desired to see which one of the processes that was most efficient in terms of tar removal alone, given the same inlet gas composition. The scrubber system was simulated in the software Invensys PRO/II for determining scrubber size and flows. Simulation data showed that the tar removal efficiency is strongly correlated to the oil-to-gas ratio. Regeneration of the oil can be achieved by utilizing a hot air stripper, for best results a gravimetrical separation is recommended. The plasma system market for tar reforming are mostly based on thermal plasma, non-thermal plasma is, however, considered to be a prominent technology for future tar reforming. The two previously mentioned technologies were then compared to a Haldor Topsøe owned tar reforming catalyst. The tar reforming catalyst utilizes steam reforming to crack tar compounds into smaller components. It was found that the three systems were more or less efficient, depending on the end-product of the process. For example, if an end-product with low contents of methane is required the plasma and the catalytic system are more suitable. If end-products with high methane levels are required, then a scrubber system may be more efficient. It was however concluded that each specific system needs to be individually assessed for a specific case in order to make a more certain system recommendation. The steam reforming showed complete conversion for a number of oxygenated hydrocarbons. The most resistant oxygenates against steam reforming was phenol and p-cresol. Large amounts of carbon formation were built up in the reactor. Some complications during the experiment may have affected the results.

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URN: urn:nbn:se:ltu:diva-44221Local ID: 2042ff17-7da8-4784-b46a-a1eff79cc604OAI: diva2:1017497
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Subject / course
Student thesis, at least 30 credits
Educational program
Sustainable Process Engineering, master's level
Validerat; 20140918 (global_studentproject_submitter)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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