Method and arrangement for feeding fuel into a circulating fluidized bed boiler

Abstract

The present invention relates to a method and an apparatus for feeding fuel into a circulating fluidized bed boiler. The invention is specifically concerned on feeding fine, light and / or moist fuel into the boiler. The method and apparatus for feeding light, fine, volatile and / or moist fuel into a circulating fluidized bed boiler is based on collecting circulating bed material to a return flow and introducing the return flow into communication with the fuel being introduced in the furnace (12) so that the bed material return flow and the fuel are mixed together and flow downwards in the furnace (12) for increasing the residence time of the fuel in the furnace (12).

Description

technical field [0001] The present invention relates to a method and an apparatus for feeding fuel into a circulating fluidized bed boiler. The invention specifically relates to the feeding of fine, light volatile and / or moist fuels into boilers. Background technique [0002] A circulating fluidized bed boiler (CFB) generally comprises a combustion chamber having a bottom, side walls and a roof and at least one particle separator connected in flow communication with the upper part of said combustion chamber. At least some walls of the bottom of the combustion chamber may be sloped such that the cross-section of the combustion chamber increases in an upward direction - ie the part of the combustion chamber with sloped walls may be referred to as a converging bottom. In practice, the roof and all walls of the boiler, as well as the separator, include water pipes to collect heat from the combustion chamber. The bottom of the combustion chamber is provided with a grate for int...

AI Technical Summary

Problems solved by technology

Especially at low load conditions this can lead to very low bed temperatures and high temperatures in the upper part of the combustion chamber which can cause problems with boiler emissions and load rate changes

[0006] In a similar way, for somewhat different reasons, the use of wet fuel can lead to similar problems

Whilst wet fuel may not be too light, it takes a while for the wet fuel to dry, which makes the fuel light again, although the fuel becomes dry and cannot be ignited, it is lifted to combustion by the fluidizing gases upper chamber

When the fuel is finally dry enough and ignited to eventually be burned, there may not be enough combustible fuel in the lower bed area, so the bed temperature may become lower again and cause the problems already described above

[0007] A further problematic fuel type is that which in most cases contains volatile components with a small amount of solid carbon

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