Effects of sand composition on CO oxidation in FBC

Abstract

Fluidized bed sand is usually treated as an inert material though it is the main solid component in the bed. The sand can consist of a wide range of different components. In this study the effects of the fluidized bed sand on carbon monoxide conversion were investigated. The changes in the sand during the reactions in FBC were also studied. Test runs were conducted in the laboratory scale fluidized bed reactor in the Laboratory of Energy and Process Engineering at Tampere University of Technology. Temperature and gas concentrations were measured during the test runs. - The oxidation of carbon monoxide was investigated with different natural sands as bed particles. Noticeable differences were found in the oxidation rate of CO with different sands. The sands with relatively high iron content seem to have a greater catalytic effect than the others. - The influence of the reductive conditions on the sand was tested because carbon monoxide is a strong reducing agent and present in most combustion conditions. The test runs in strongly reductive conditions indicated that carbon monoxide can reduce the oxides of iron in the sand. The oxidation rate of carbon monoxide was improved after the fluidized bed had been in reductive conditions. The more iron was contained in the sand the more the oxidation rate improved. It is obvious that iron is more active as a catalyst in its reduced state. - The change in the colour of the sand was observed. The colour of the sand was reddish after CO was oxidized by air. The colour was a darker grey than fresh sand after reductive conditions. The colour change is mainly a result of reduction and oxidation of iron compounds in the sand.

AB3:Työssä tutkittiin leijukerroshiekan vaikutusta CO:n palamiseen. Työssä on mukana kokeellinen osuus. Työssä havaittiin leijukerroshiekan koostumuksella olevan vaikutusta CO:n palamiseen, mitä rautapitoisempaa hiekkaa, sitä tehokkaampaa palaminen.