Solid fuels in Chemical-Looping Combustion – Feeding of fuel and distribution of volatiles
Konferensbidrag (offentliggjort, men ej förlagsutgivet), 2015
Conventional CO2 capture processes have large costs and energy penalties associated with gas
separation. Chemical-looping combustion (CLC) uses interconnected fluidized beds and a metal oxide
to transfer oxygen from air to fuel. Thus, fuel is oxidized without mixing fuel and air and the
combustion products, CO2 and H2O, are recovered in a separate flow. After H2O condensation
essentially pure CO2 is obtained, thus avoiding the high costs and penalties of an active gas
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 CO2
compression is oxygen-polishing of the gas from the fuel reactor, indicating that high gas conversion is
Today, >2000 h of solid-fuel CLC operation in smaller pilots have been accomplished worldwide. The
experiences show that the concept works in practice and that high gas conversion is reached with lowvolatile
fuels, typically 95%. However, fuels with more volatiles show lower conversion, highlighting the
need to feed the fuel in way that provides good contact between volatiles and bed material, i.e. the
metal 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 lower
part and well distributed over the horizontal cross-section. Here, a system for distribution of volatiles is
presented. It is based on a fundamental principle of fluidization, that a box immersed in a fluidized bed
with the opening downward becomes empty. Moreover, if such a box has holes in its sides the bed
level inside the box will rise but not above the holes and gas added will exit through these holes. Such
a 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 be
implemented in a large-scale CLC.
distributor of volatiles