New combustion technique could unlock carbon capture in biomass power plants
Researchers have successfully demonstrated oxy-fuel combustion of wood in a pilot reactor, a process that could enable power plants to capture carbon directly from biomass burning—potentially achieving negative emissions. The findings, which map how potassium behaves during this high-temperature process, remove a major technical barrier to commercializing the technology at industrial scale.
Originaltitel: Oxy-fuel combustion of softwood in a pilot-scale down-fired pulverized combustor: fate of potassium
<p>Oxy-fuel biomass combustion can facilitate carbon capture in heat and power plants and enable negative carbon dioxide (CO<sub>2</sub>) emissions. We demonstrate oxy-fuel combustion (OFC) of softwood powder in a 100-kW atmospheric down-fired pulverized combustor run at a global oxidizer-fuel equivalence ratio of around 1.25. The simulated oxidizer was varied between oxygen (O<sub>2</sub>)/CO<sub>2</sub> mixtures of 23/77, 30/70, 40/60 and 54/46, and artificial air. The concentrations of the main gaseous potassium (K) species: atomic K, potassium hydroxide (KOH) and potassium chloride (KCl), were measured at two positions in the reactor core using photofragmentation tunable diode laser absorption spectroscopy (PF-TDLAS). Major species were quantified by TDLAS in the reactor core and with Fourier transform infrared spectroscopy and mass spectrometry at the exhaust. Flue gas particles were collected at the exhaust employing a low-pressure impactor and analyzed by X-ray powder diffraction and scanning electron microscopy. The measured individual K species concentrations in the reactor core agreed with predictions by thermodynamic equilibrium calculations (TEC) within one order of magnitude and the sum of K in the gas phase agreed within a factor of three for all cases. Atomic K was underpredicted, while the dominating KOH and KCl were slightly overpredicted. The ratios of measured to predicted total K were similar in artificial air and OFC, but the distributions of the individual species differed at the upper reactor position. The gaseous K species and fine particle concentrations in the flue gas were directly proportional to the O<sub>2</sub> content in the oxidizer. The crystalline phase compositions of the coarse mode particles were rich in K- and calcium-containing species. The fine mode particles, which contained most of the K, consisted mainly of K<sub>2</sub>SO<sub>4</sub> (94%) and K<sub>3</sub>Na(SO<sub>4</sub>)<sub>2</sub>, which is in excellent agreement with TECs of gas phase condensation. As supported by the solid phase analysis, complete sulfation of K species was achieved for all studied cases. A CO<sub>2</sub> purity (dry) of up to 94% was achieved for OFC.</p>