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Tampere, Finland

Bajamundi C.J.E.,VTT Technical Research Center of Finland | Bajamundi C.J.E.,University of Jyvaskyla | Vainikka P.,VTT Technical Research Center of Finland | Hedman M.,Valmet Power | Konttinen J.,University of Jyvaskyla
Fuel | Year: 2014

A staged equilibrium process model was developed for a bubbling fluidized bed boiler firing SRF, bark and sludge. The model was used to study the influence of sulfur addition strategies (S-pellet additive and peat co-firing) on the behavior of copper, bromine, and alkalis. Aerosol samples collected from the backpass of the boiler were used to validate the chemistry predicted by the model. The model revealed that Cu existed as Cu2S(s3) in the reducing zone, and CuCl(g) (for all test cases) and CuO (s) (during peat co-firing) in the oxidation zones. CuBr 3(g) was also present after the introduction of tertiary air. However the model failed to predict the formation of CuSO4, an important passive species of Cu necessary for PCDD/F abatement. The modes of occurrence of Cu were classified as either active or passive with respect to de novo synthesis and an active/passive species molar ratio (APR) was introduced. APR showed high correlation with the PCDD/F production levels. Sensitivity analysis revealed that excessive Cu in the fuel mixture decreased the volatility of the element due to the formation of CuO(s). Simulation for peat co-firing with low Cu content showed that PCDD/F concentration is decreased and is comparable to that of S-pellet addition. Sensitivity analysis revealed that increasing the energy share of sludge can likewise lower PCDD/F production. © 2014 Elsevier Ltd. All rights reserved. Source


Bajamundi C.J.E.,VTT Technical Research Center of Finland | Bajamundi C.J.E.,University of Jyvaskyla | Vainikka P.,VTT Technical Research Center of Finland | Hyytiainen I.,Valmet Power | And 4 more authors.
Fuel | Year: 2014

PCDD/F abatement strategies - sulfur pellet addition and peat co-combustion - were tested for a BFB boiler facility utilizing SRF-bark-sludge as fuel. In this paper chemical and physical analyses of electrostatic precipitator (ESP) fly ashes were used to explain the differences in the performance of these strategies. These analyses revealed a difference between the coarse and fine fly ashes collected in the ESP. Chemical analysis of the fine fly ashes revealed high concentration of easily volatilized elements while the SEM micrographs showed that fine ash are composed of clusters of spherical particles, thereby leading to a conclusion that fine ashes were originally in a gas phase in the high temperature zones of the boiler. Variation in the distribution of active and passive forms of Cu in fly ashes was revealed using X-ray absorption spectroscopy (XANES mode). It was also found that peat co-combustion led to increased formation of Cu oxides that may act as active catalysts in de novo synthesis. Furthermore, XANES revealed the formation of CuSO4 for all the test cases. By applying the empirical ratio between mole fractions of the active and passive species of Cu, the role of Cu speciation to PCDD/F production was emphasized. It is concluded that sulfur pellet addition is more effective than peat addition as a PCDD/F abatement strategy for the BFB facility understudy. © 2014 Elsevier Ltd. All rights reserved. Source


Bajamundi C.J.E.,VTT Technical Research Center of Finland | Bajamundi C.J.E.,University of Jyvaskyla | Vainikka P.,VTT Technical Research Center of Finland | Hedman M.,Valmet Power | And 5 more authors.
Fuel | Year: 2014

Levels of PCDD/F production in a 140 MWth bubbling fluidized bed boiler were measured. The boiler uses solid recovered fuel, bark and sludge. Homologue distribution patterns suggest the de novo mechanism is the main pathway for the generation of dioxin and furans in the post combustion zones of the boiler. Two modes of sulfur addition were tested to induce the deactivation of Cu which has been identified as the prime catalyst of this mechanism. First, S-pellet promoted Cu sulfation as supported by aerosol sampling data and resulted in a decrease in PCDD/F levels. The second approach was adding sulfur through peat; this resulted in an increase in PCDD/F concentration. Factors such as high Cu content in the SRF-peat-sludge fuel mixture and reduced volatilization of Cu may have contributed to the said increase. For all test cases, phase redistribution of PCDD/F was observed in the electrostatic precipitator favoring more gaseous PCDD/F at the outlet. The homologue distribution pattern did not change in the flue gas path, suggesting that further synthesis and/or chlorination in the stream were minimized. There is however evidence for subsequent reactions happening in the ESP fly ash. The homologue distribution pattern in the latter was different from that of the flue gas, and more highly chlorinated PCDD/Fs were present. Furthermore, the ratio of PCDD and PCDF was different from that of the samples in the flue gas path. © 2014 Elsevier Ltd. All rights reserved. Source

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