Solid fuels in Chemical-Looping Combustion – Feeding of fuel and distribution of volatiles

• Conventional CO2 capture processes have large costs and energy penalties associated with gasseparation. Chemical-looping combustion (CLC) uses interconnected fluidized beds and a metal oxideto transfer oxygen from air to fuel. Thus, fuel is oxidized without mixing fuel and air and thecombustion products, CO2 and H2O, are recovered in a separate flow. After H2O condensationessentially pure CO2 is obtained, thus avoiding the high costs and penalties of an active gasseparation.CLC of solid fuels has important similarities to well-established combustion in circulating fluidized bed(CFB), and a comparison indicates an added cost of 16-26 €/tonne CO2. The major cost besides CO2compression is oxygen-polishing of the gas from the fuel reactor, indicating that high gas conversion isbeneficial.Today, >2000 h of solid-fuel CLC operation in smaller pilots have been accomplished worldwide. Theexperiences show that the concept works in practice and that high gas conversion is reached with lowvolatilefuels, typically 95%. However, fuels with more volatiles show lower conversion, highlighting theneed to feed the fuel in way that provides good contact between volatiles and bed material, i.e. themetal oxide oxygen-carrier.For a larger size CLC the fuel should be fed in a way that make the volatiles enter the bed in the lowerpart and well distributed over the horizontal cross-section. Here, a system for distribution of volatiles ispresented. It is based on a fundamental principle of fluidization, that a box immersed in a fluidized bedwith the opening downward becomes empty. Moreover, if such a box has holes in its sides the bedlevel inside the box will rise but not above the holes and gas added will exit through these holes. Sucha box in the form of a system of arms is proposed to distribute volatiles over the cross-section.The paper discusses principles and possible design of such a volatiles distributor and how it can beimplemented in a large-scale CLC.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Energiteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Energy Engineering (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Kemiteknik -- Annan kemiteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Chemical Engineering -- Other Chemical Engineering (hsv//eng)

Nyckelord

fluidized bed

Chemical-Looping Combustion

solid fuels

distributor of volatiles

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