Modeling the Use of Sulfate Additives for Potassium Chloride Destruction in Biomass Combustion

Abstract

Potassium chloride, KCl, formed from biomass combustion may lead to ash deposition and corrosion problems in boilers. Sulfates are effective additives for converting KCl to the less harmful K 2 SO 4 and HCl. In the present study, the rate constants for decomposition of ammonium sulfate and aluminum sulfate were obtained from experiments in a fast heating rate thermogravimetric analyzer. The yields of SO 2 and SO 3 from the decomposition were investigated in a tube reactor at 600−900°C , revealing a constant distribution of about 15% SO 2 and 85% SO 3 from aluminum sulfate decomposition and a temperaturedependent distribution of SO 2 and SO 3 from ammonium sulfate decomposition. On the basis of these data as well as earlier results, a detailed chemical kinetic model for sulfation of KCl by a range of sulfate additives was established. Modeling results were compared to biomass combustion experiments in a bubbling fluidized-bed reactor using ammonium sulfate, aluminum sulfate, and ferric sulfate as additives. The simulation results for ammonium sulfate and ferric sulfate addition compared favorably to the experiments. The predictions for aluminum sulfate addition were only partly in agreement with the experimental results, implying a need for further investigations. Predictions for the effectiveness of the sulfur-based additives indicate that ferric sulfate and ammonium sulfate have similar effectiveness at temperatures ranging from approximately 850 to 900°C, whereas ferric sulfate is more efficient at higher temperatures and ammonium sulfate is more effective at lower temperatures.

Selective Noncatalytic Reduction of NOx Using Ammonium Sulfate

“…The assumption that ammonium sulfate decomposes into NH 3 , SO 3 , and H 2 O as the sole products, even at the highest temperatures studied, is supported by the present experimental results, as discussed below. However, it is not consistent with the findings of Wu et al, who reported that sulfur is mainly released as SO 2 at temperatures above 900 °C. Since the dissociation reaction conceivably occurs in the condensed phase, it is possible that differences in droplet size and reaction conditions may affect the SO 2 /SO 3 ratio, but more work is required to resolve this issue.…”

“…A decomposition reaction for ammonium sulfate was included in the mechanism, with the rate constant k 1 = 9.2 × 10 6 exp­(−13 040/ T ) s –1 drawn from Wu et al The low values for the pre-exponential factor and the activation energy indicate that the decomposition occurs in the condensed state. The assumption that ammonium sulfate decomposes into NH 3 , SO 3 , and H 2 O as the sole products, even at the highest temperatures studied, is supported by the present experimental results, as discussed below.…”

“…Ammonium sulfate (AS), (NH 4 ) 2 SO 4 , has been proposed as an additive, which upon decomposition yields NH 3 for the reduction of NO and SO 2 /SO 3 for sulfating metals. The results for the use of AS as the SNCR agent are reported for pilot-scale conditions, , while its use for sulfation of alkali metals has been studied in pilot and full scales. ,, These results provide an understanding of the overall behavior and the potential of the additive, but due to the complexities of flow and mixing on a larger scale, they are less useful for kinetic model development and validation. In the present work, SNCR experiments using ammonium sulfate were conducted in a laboratory flow reactor as a function of temperature, AS/NO ratio, and residence time.…”

Potassium Capture by Kaolin, Part 1: KOH

“…The basic principle of additive use is that the additives are injected to boilers to react with the problematic gaseous K-salts (such as KOH and KCl), forming K-species (such as K-aluminosilicates) with low corrosivity and high melting temperatures. 2,23,26,27,29,[39][40][41][42][43][44][45][46] Biomass firing additives can generally be categorized into Al-Si based, S-based, P-based and Ca-based, according to the major elements present in the additives. 2,42,[47][48][49][50] Kaolin [51][52][53][54][55] and coal fly ash 52 are typical Al-Si based additives for biomass combustion and have been studied in laboratory-scale experiments.…”

Multifunctional Additives for NOX Abatement in Fluidized Bed Biomass Combustion

“…47−49 In the case of (NH 4 ) 2 HPO 4 , the formation of P 4 O 10 , which melts at 562 °C, could have led to defluidization by sticking the bed material 37 The presence of S during combustion could convert the fuel-K to less harmful species such as K 2 SO 4 . 50 In addition, Al and Fe may increase the melting point of the compounds leading to agglomeration. 51 Of the examined additives, AlNH 4 (SO 4 ) 2 and NH 4 MgPO 4 were capable of reducing NO emission (approximately 40% reduction) while preventing defluidization.…”