Production of activated carbon within the indirect gasification process
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Typ
Examensarbete för masterexamen
Master Thesis
Master Thesis
Program
Publicerad
2012
Författare
Shabanzadeh, Amir
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
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Sammanfattning
III Abstract Activated carbon is one of the most attractive adsorbent which has a wide area of application. One of these areas of application is in the adsorption of impurities from the product gas resulting from biomass gasification. An impurity such as H2S in the product gas cause poisoning of catalysts used in downstream processes in which the product gas is used. Tars in the product gas condense on cold engine, turbine, and downstream pipelines causing fouling. These impurities should be eliminated before the product gas is subjected to downstream processes. One way of removing or at least decreasing the concentration of these impurities from the product gas is by the use of activated carbon in a fixed bed. The operating conditions under which activated carbon is produced are somewhat similar to those that prevail during the gasification step of indirect gasification. It may thus be cost effective to produce activated carbon within the indirect gasification processes so it can be used for the cleaning system of the product gas. In this work the possibility of the production of activated carbon within the indirect gasification process is investigated. To evaluate the use of char from a gasification process as activated carbon, samples of char were produced in laboratory scale reactors under gasification conditions using two methods. In the first method called two-steps activation, virgin biomass was first pyrolysis and the resulting char was subsequently activated with steam. During the pyrolysis stage, the temperature was varied from 750 - 900°C and the residence time was fixed at 5 minutes. The char samples obtained during the pyrolysis stage were activated at the same temperatures with steam. The steam flow rate and the residence time were varied to study their effects on the quality and yield of activated carbon. In the second method called one-step activation, the virgin biomass was carbonized and activated simultaneously by gasifying it with steam. The temperature was varied from 750 to 900ºC and residence time was varied from 10 to 25 minutes. The burn off rates of the carbonization and the activation processes, as well as the char and activated carbon yields were calculated on dry basis. A qualitative analysis of both the samples of char and activated carbon produced was done by: 1- the determination of the BET (Brunaure, Emmett, and Teller) internal pore surface area and volume, 2- structural analysis of the carbon crystals and pore bodies by the SEM (Scan Electron Microscopy). The results showed that the yield of activated carbon generally decreased as the temperature, residence time, and steam flow rate increased for both the one and two-steps activation methods. In contrast, the total internal surface area and volume of the pores in the samples of activated carbon increased when the operating temperature, residence time and steam flow rate were increased. However, the surface area and volume of the micropores decreased. The amount of the micropore volume is a good indication for the adsorption capacity of the activated carbon. For a fixed temperature, residence time and steam flow rate, there was a marginal increase in the total pore surface area and volume of the samples of activated carbon produced by the two -steps method relative to those in the samples of activated carbon produced by the one-step method. Given that activated carbon is commercially produced mostly by the two-steps method, the comparable total surface area and volume for both the samples of activated carbon produced by the one and two-steps methods suggest that activated carbon can effectively be produced during indirect gasification by the one-step method.
Beskrivning
Ämne/nyckelord
Kemisk energiteknik , Energi , Hållbar utveckling , Chemical energy engineering , Energy , Sustainable Development