Biomassapohjaisen kaasutuskaasun suodatus korkeissa lämpötiloissa

Literature part of the thesis concerns the combination of biomass gasification process and Fischer-Tropsch synthesis, which can be used to produce liquid biofuels. Cleaning of the gasification gas by filtration and tar reforming is the focus of the work. It is essential to develop an effective and profitable process concept for hot gas cleaning to achieve competitive biofuel production route. The main challenge is to develop stable filtration process that is resistant towards tar components and carbon formation at high temperatures. Heavy tar compounds are decomposed either in the filtration unit or in the following reformer unit. At high temperatures, formed filter cakes are sticky and cleaning of filter medium is challenging. Additionally, the contaminants in the gasification gas complicate the usage of some catalysts. Different catalysts have been studied for gasification gas cleaning applications and catalyst modifications have been tested including different support and promoter additives. The aim of the experimental part of the thesis was to study the suitability of novel metal filters for hot gasification gas cleaning purpose. Furthermore, the Atomic Layer Deposition (ALD) coating technique was tested in the experiments with nickel catalyst and alumina support. Different process conditions and gas face velocities were studied. It was also tested how sulfur in the gas affects the process. The best result was 55 % conversion for naphthalene and it was achieved with the combination of nickel catalyst and alumina support at 5 bar and at 900 ˚C. The applied gas face velocity was 15 cm/s. However, at these conditions, there occurred carbon formation on the surfaces and finally the reactor was blocked. Without a nickel catalyst, the best conversion achieved for naphthalene was 29 % at same process conditions with the gas face velocity of 12 cm/s. Without a catalyst, less carbon was accumulated on the filter surface and there were no problems related to the reactor clogging.Diplomityön kirjallisuusosio käsittelee nestemäisten polttoaineiden valmistusta biomassan kaasutuksen ja Fischer-Tropsch-synteesin avulla. Työ keskittyy tutkimaan kaasutuskaasun puhdistuslinjan suodatus- ja reformointiprosesseja. Merkittävä haaste biomassan valmistusprosessin tehokkuuden parantamisessa on saavuttaa stabiili suodatusprosessi. Suodatusprosessin tulisi kestää vaativat prosessiolosuhteet sekä kaasun sisältämien epäpuhtauksien vaikutukset. Raskaat tervayhdisteet hajotetaan joko suodatusvaiheessa tai sitä seuraavassa reformointiyksikössä. Korkeissa lämpötiloissa muodostuvat suodatuskakut ovat tyypillisesti tahmeita ja suodatin on hankala puhdistaa. Korkeissa lämpötiloissa hiiltä kertyy prosessilaitteen pinnoille, mikä voi lopulta johtaa reaktorin tukkeutumiseen. Monia erilaisia katalyyttejä on tutkittu kuuman kaasutuskaasun puhdistamista varten ja katalyyttejä on muokattu esimerkiksi erilaisten tuki- ja lisämateriaalien avulla. Kokeellisen osion tarkoituksena oli testata uusien metallifilttereiden soveltuvuutta kaasutuskaasun kuumasuodatusta varten. Lisäksi koeajoissa testattiin atomikerroskasvatuksella valmistettuja nikkeliä sekä alumiinioksidia sisältäviä katalyyttipinnoituksia. Myös erilaisia prosessiolosuhteita sekä kaasun pintanopeuksia tutkittiin. Koeajojen avulla saatiin myös lisätietoa rikkiyhdisteiden vaikutuksesta nikkelikatalyytin toimintaan. Paras naftaleenin hajoamiselle saavutettu konversio oli 55 % ja se saavutettiin paksuimmalla nikkelipinnoituksella alumiinioksidin päällä 5 bar paineessa sekä 900 ˚C lämpötilassa. Kaasun pintanopeus oli 15 cm/s. Näissä olosuhteissa reaktorin hiiltyminen aiheutti kuitenkin ongelmia ja neljän tunnin ajon jälkeen reaktori tukkeutui. Ilman katalyyttiä korkein saavutettu naftaleenin konversio oli 29 % samoissa olosuhteissa, mutta 12 cm/s pintanopeudella. Ilman katalyyttiä, hiiltä kertyi reaktoriin huomattavasti vähemmän eikä reaktorin tukkeutumista tapahtunut

Atomic Layer Deposition Coated Filters in Catalytic Filtration of Gasification Gas

Steel filter discs were catalytically activated by ALD, using a coating of supporting Al2O3 layer and an active NiO layer for gas cleaning. Prepared discs were tested for model biomass gasification and gas catalytic filtration to reduce or eliminate the need for a separate reforming unit for gasification gas tars and lighter hydrocarbons. Two different coating methods were tested. The method utilizing the stop-flow setting was shown to be the most suitable for the preparation of active and durable catalytic filters, which significantly decreases the amount of tar compounds in gasification gas. A pressure of 5 bar and temperatures of over 850 °C are required for efficient tar reforming. In optimal conditions, applying catalytic coating to the filter resulted in a seven-fold naphthalene conversion increase from 7% to 49%

Atomic Layer Deposition Coated Filters in Catalytic Filtration of Gasification Gas

Steel filter discs were catalytically activated by ALD, using a coating of supporting Al2O3 layer and an active NiO layer for gas cleaning. Prepared discs were tested for model biomass gasification and gas catalytic filtration to reduce or eliminate the need for a separate reforming unit for gasification gas tars and lighter hydrocarbons. Two different coating methods were tested. The method utilizing the stop-flow setting was shown to be the most suitable for the preparation of active and durable catalytic filters, which significantly decreases the amount of tar compounds in gasification gas. A pressure of 5 bar and temperatures of over 850 °C are required for efficient tar reforming. In optimal conditions, applying catalytic coating to the filter resulted in a seven-fold naphthalene conversion increase from 7% to 49%