Characteristics of hematite and fly ash during chemical looping combustion of sewage sludge

Biomass-based chemical looping technologies: the good, the bad and the future

“…It is noteworthy that dewatered sewage sludge was used as biomass feedstock in SEU-2015b and the Z cc reached almost 100% at 800-900 1C, which indicates that no char bypassed to the air reactor. 59 For case SEU-2015a, which was also sewage-sludge-based, the efficiency oscillated between 75% and 84%. The different reactor designs, OCs used, and ash properties may contribute to this discrepancy.…”

“…The reduction of Fe 2 O 3 to Fe 3 O 4 was utilised for iron oxide reduction with biomass syngas. 53 More recently, in cases SEU-2015a and 2015b, dewatered sewage sludge was investigated for CLC 59,60 using Fe-based or Ni-based OCs. Increasing the fuel reactor temperature intensified the gasification step and the subsequent reduction process, thus increasing the carbon conversion and combustion efficiency.…”

“…No sintering/agglomeration issues were reported during 20 redox cycles. SEU-2015b (1 kW th ) 59 De-watered sewage sludge (Ash: 36% Si, 20% Fe, 15% Al, 11% P, etc. )…”

“…Although OC particles are separable from fuel ash owing to the differences in their density and size, ash deposition cannot be ignored. Ash with a large content of high melting point Ca shows no agglomeration or sintering problems, 59,148 but low melting point Na or K can promote agglomeration. 148,149 The presence of Ca or Fe can lead to a positive effect on OC capacity owing to their ability to serve as OCs.…”

“…11,12 Ash with a low melting point remaining in the fuel reactor can cause agglomeration and even defluidisation. 59,60,77 By continuous removal of alkali metal laden bed particles from the system, a quasi-steady state of stable operation could be achieved by keeping the alkali metal content of the carrier particles below a critical level for stickiness and consequent agglomeration and breakdown of fluidisation. This suggested method of operation, which sacrifices the carrier material due to the withdrawal of alkali metals from the system, requires a low cost carrier such as ilmenite and excludes the more expensive specially designed oxygen carriers.…”