Investigation of biomass alkali release in a dual circulating fluidized bed chemical looping combustion system

Ivan Gogolev (Corresponding Author), Toni Pikkarainen, Juho Kauppinen, Carl Linderholm, Britt Marie Steenari, Anders Lyngfelt

Research output: Contribution to journalArticleScientificpeer-review

Abstract

Chemical looping combustion (CLC) of biomass is a promising technology for power generation with integrated carbon capture. In CLC, alkali content of biomass poses potential issues of bed agglomeration, as well as heat exchanger fouling and corrosion. The fate of biomass alkalis was investigated in a dual-interconnected circulating fluidized bed CLC system. Experiments were conducted in oxygen carrier aided combustion (OCAC) and CLC modes. Ilmenite and braunite oxygen carriers and three biomass fuels (wood pellets, wood char, straw pellets) were tested. Flue gas alkali emissions in the air reactor (AR) and fuel reactor (FR) were measured with a surface ionization detector (SID). Results showed that CLC operation yields gas-phase alkali emissions that are up to 15 times higher than in comparable OCAC operation. Results analysis concluded that increased alkali emissions in CLC arise from the steam atmosphere in the FR, whereby steam accelerates the decomposition of alkali compounds in the biomass. Retention of alkalis in the condensed phase was found to be >97% for ilmenite and >92% for braunite CLC operation. Up to 60–80% of the retention was attributed to fuel ash formation. The residual retention was attributed to absorption of alkalis by the oxygen carriers. Absorption likely occurred mainly through formation of alkali manganates and silicates in braunite, and formation of alkali silicates, aluminosilicates, manganates, and titanates in ilmenite. Gas-phase alkali emissions in the AR, although less than in the FR, were found to occur due to combustion of unconverted fuel carried over from the FR to the AR.

Original languageEnglish
Article number120743
JournalFuel
Volume297
DOIs
Publication statusPublished - 1 Aug 2021
MoE publication typeA1 Journal article-refereed

Keywords

  • Alkali
  • Biomass
  • Chemical looping combustion
  • Oxygen carriers

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