Abstract
Oxygen Carrier Aided Combustion (OCAC) is realized by using an active oxygen-carrying bed material in fluidized bed boilers. The active material is reduced in fuel rich parts of the boiler and oxidized in air rich parts. Advantages could be achieved such as new mechanisms for oxygen transport in space and time. Here calcined manganese ore has been used as active bed material in a 12 MWth circulating fluidized bed boiler. The fuel was wood chips and the campaign lasted more than two weeks. From an operational point of view, manganese ore worked excellently. From the temperature profile of the boiler it can be concluded that fuel conversion was facilitated, especially in the dense bottom bed. The effect did not always translate to reduced emissions, which suggests that final combustion in the cyclone outlet was also influenced. Substituting 10% of the sand bed with manganese ore made it possible to reduce the air to fuel ratio without generating large amounts of CO. The use of 100% manganese ore resulted in higher emissions of CO than the sand reference, but, when combined sulphur feeding, dramatic reductions in CO emissions, up to 90% compared to sand reference, was achieved.
Highlights
Mixing of fuel and air is one of the most important aspects affecting the combustion performance in thermal power plants
The aims of the study were: (i) to study the use of manganese ore as bed material for Oxygen Carrier Aided Combustion (OCAC) in a circulating fluidized bed boiler with respect to operability and general behaviour; and (ii) to establish whether OCAC with manganese ore as bed material would provide benefits with respect to emissions compared to sand, especially at reduced air-to-fuel ratio
Regeneration means that alkali metals and other ash components absorbed by the bed material is continuously removed
Summary
Mixing of fuel and air is one of the most important aspects affecting the combustion performance in thermal power plants. Combustion facilities operate with an excess of air compared to what is needed for stoichiometric combustion. This is undesirable for several reasons: . In CLC, fuel is oxidized with oxygen from a solid oxygen carrier material in particle form, exemplified below by oxidation of methane with manganese (II,III) oxide, see Reaction (1). The products are carbon dioxide, steam and manganese (II) oxide, of which the latter is oxidized to its initial state with air in a separate reactor vessel, see Reaction (2). The oxidized material can be returned to the first reactor vessel and oxidize more fuel This way fuel and air is never mixed and the flue gas will be undiluted by N2.
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