Papers by Flemming Frandsen
Energy & Fuels, May 16, 2013
The interaction between alkali chloride and sulfur oxides has important implications for depositi... more The interaction between alkali chloride and sulfur oxides has important implications for deposition and corrosion in combustion of biomass. In the present study, the sulfation of particulate KCl (90-125 μm) by SO 2 was studied in a fixed bed reactor in the temperature range 673-1023 K and with reactant concentrations of 500-3000 ppm SO 2 , 1-20% O 2 , and 4-15% H 2 O. The degree of sulfation was monitored by measuring the formation of HCl. Analysis of the solid residue confirmed that the reaction proceeds according to a shrinking core model and showed the formation of an eutectic at higher temperatures. On the basis of the experimental results, a rate expression for the sulfation reaction was derived. The model compared well with literature data for sulfation of KCl and NaCl, and the results indicate that it may be applied at even higher SO 2 concentrations and temperatures than those of the present study. Simulations of sulfation of KCl particles with different size indicate that only for very small KCl particles, below 1 μm, a considerable in-flight sulfation is achievable at the short gas residence times typical of combustion systems.
Sulfates, such as ammonium sulfate, aluminum sulfate and ferric sulfate, are effective additives ... more Sulfates, such as ammonium sulfate, aluminum sulfate and ferric sulfate, are effective additives for converting the alkali chlorides released from biomass combustion to the less harmful alkali sulfates. Optimization of the use of these additives requires knowledge on their decomposition rate and product distribution under high temperature conditions. In the present work, the decomposition of ammonium sulfate, aluminum sulfate and ferric sulfate was studied respectively in a fast-heating rate thermogravimetric analyzer for deriving a kinetic model to describe the process. The yields of SO 2 and SO 3 from the decomposition were investigated experimentally in a tube reactor under different conditions, revealing that the ratio of the SO 3 /SO 2 released varied for different sulfate and the ratio could be influenced by the decomposition temperature. The proposed decomposition model of ferric sulfate was combined with a detailed gas-phase kinetic model of KCl sulfation and a model of K 2 SO 4 condensation to simulate the sulfation of KCl by ferric sulfate addition. The simulation results showed good agreements with the experiments conducted in a biomass grate-firing combustor, where ferric sulfate and elemental sulfur were used as additives. The results indicated that the SO 3 released from ferric sulfate decomposition was the main contributor to KCl sulfation and that the effectiveness of ferric sulfate addition was sensitive to the applied temperature conditions. Comparison of the effectiveness of different sulfates indicated that ammonium sulfate has clearly strongest sulfation power towards KCl at temperatures below 800 o C, whereas the sulfation power of ferric and aluminum sulfates exceeds clearly that of ammonium sulfate between 900 and 1000 o C. However, feeding gaseous SO 3 was found to be most effective to destroy KCl with a comparable dosage. Overall, the models developed in this work would facilitate an optimal use of sulfate additives in biomass combustion.
Energy & Fuels, Nov 11, 2013
Potassium chloride, KCl, formed from biomass combustion may lead to ash deposition and corrosion ... more 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 . In the present study, the decomposition of ammonium sulfate, aluminum sulfate and ferric sulfate was studied respectively in a fastheating rate thermogravimetric analyzer (TGA) for deriving a kinetic model. The yields of SO 2 and SO 3 from the decomposition were studied in a tube reactor, revealing that the ratio of the SO 3 /SO 2 released varied for different sulfate and for ammonium sulfate the ratio was affected by the decomposition temperature. Based on the experimental data, a model was proposed to simulate the sulfation of KCl by different sulfate addition, and the simulation results were compared with pilot-scale experiments conducted in a bubbling fluidized bed reactor. The simulation results of ammonium sulfate addition and ferric sulfation addition compared favorably with the experimental results. However, the model for aluminum sulfate addition under-predicted significantly the high sulfation degree of KCl observed in the experiments, possibly because of an under-estimation of the decomposition rate of aluminum. Under the boiler conditions of the present work, the simulation results suggested that the desirable temperature for the ferric sulfate injection was around 950-900 o C, whereas for ammonium sulfate the preferable injection temperature was below 800 o C.
Potassium chloride, KCl, formed from critical ash-forming elements released during combustion may... more Potassium chloride, KCl, formed from critical ash-forming elements released during combustion may lead to severe ash deposition and corrosion problems in biomass-fired boilers. Ferric sulfate, Fe 2 (SO 4 ) 3 is an effective additive, which produces sulfur oxides (SO 2 and SO 3 ) to convert KCl to the less harmful K 2 SO 4 . In the present study the decomposition of ferric sulfate is studied in a fast-heating rate thermogravimetric analyzer (TGA), and a kinetic model is proposed to describe the decomposition process. The yields of SO 2 and SO 3 from ferric sulfate decomposition are investigated in a laboratory-scale tube reactor. It is revealed that approximately 40% of the sulfur is released as SO 3 , the remaining fraction being released as SO 2 . The proposed decomposition model of ferric sulfate is combined with a detailed gas phase kinetic model of KCl sulfation, and a simplified model of K 2 SO 4 condensation in order to simulate the sulfation of KCl by ferric sulfate addition during grate-firing of biomass. The simulation results show good agreements with the experimental data obtained in a pilot-scale biomass grate-firing reactor, where different amounts of ferric sulfate was injected on the grate or into the freeboard. In addition, the simulations of elemental sulfur addition on the grate fit well with the experimental data. The results suggest that the SO 3 released from ferric sulfate decomposition is the main contributor to KCl sulfation, and that the effectiveness of the ferric sulfate addition is sensitive to actual temperature in the system. When the ferric sulfate is injected on the grate, the majority of the released SO 3 is rapidly converted to SO 2 due to the high temperatures, resulting in a low effectiveness similar to that of elementary sulfur addition on the grate. On the other hand, when the ferric sulfate is injected into the freeboard where the temperatures are below 1050 o C, the majority of the released SO 3 contributes to the formation of K 2 SO 4 , leading to a high effectiveness in KCl destruction. Overall, the model developed in this work facilitates an optimal use of ferric sulfate in biomass combustion.
European Biomass Conference and Exhibition Proceedings, 2016
A method to simulate the reaction between gaseous K-species and solid additives, at suspension fi... more A method to simulate the reaction between gaseous K-species and solid additives, at suspension fired conditions has been developed, using an entrained flow reactor (EFR). A water slurry containing solid additives (kaolin or coal fly ash) and KCl, is injected into the EFR and the solid products are collected from the cyclone and filter. The K-capture reaction is evaluated by determining the fraction of water-insoluble K in the products. The results showed that KCl can effectively be captured by kaolin and coal fly ash, forming water-insoluble Kaluminosilicates. The amount of K, captured per gram of additives, rose when increasing the molar ratio of K/(Al+Si) in the reactants. A change of the reaction temperature, from 1100 °C to 1450 °C, did not significantly influence the extent of the reaction, which is in contradiction to the trend observed in previous fixed-bed reactor studies. The method using the EFR, developed in this study, will be applied for further studies on the reaction of different additives and alkali species.
Energy & Fuels, Feb 1, 2018
Users may download and print one copy of any publication from the public portal for the purpose... more Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
Fuel Processing Technology, 2013
Trace element partitioning in co-combustion of a bituminous coal and a solid recovered fuel (SRF)... more Trace element partitioning in co-combustion of a bituminous coal and a solid recovered fuel (SRF) was studied in an entrained flow reactor. The experiments were carried out at conditions similar to pulverized coal combustion, with SRF shares of 7.9 wt.% (wet basis), 14.8 wt.% and 25.0 wt.%. In addition, the effect of additives such as NaCl, PVC, ammonium sulphate, and kaolinite on trace element partitioning was investigated. The trace elements studied were As, Cd, Cr, Pb, Sb and Zn, since these elements were significantly enriched in SRF as compared to coal. During the experiments, bottom ash was collected in a chamber, large fly ash particles were collected by a cyclone with a cutoff diameter of~2.5 μm, and the remaining fly ash particles were gathered in a filter. It was found that when coal was co-fired with SRF, the As, Cd, Pb, Sb and Zn content in filter ash/cyclone ash increased almost linearly with their content in fuel ash. This linear tendency was affected when the fuels were mixed with additives. The volatility of trace elements during combustion was assessed by applying a relative enrichment (RE) factor, and TEM-EDS analysis was conducted to provide qualitative interpretations. The results indicated that As, Cd, Pb, Sb and Zn were highly volatile when co-firing coal and SRF, whereas the volatility of Cr was relatively low. Compared with coal combustion, co-firing of coal and SRF slightly enhanced the volatility of Cd, Pb and Zn, but reduced the volatility of Cr and Sb. The Cl-based additives increased the volatility of Cd, Pb and As, whereas addition of ammonium sulphate generally decreased the volatility of trace elements. Addition of kaolinite reduced the volatility of Pb, while the influence on other trace elements was insignificant. The results from the present work imply that trace element emission would be significantly increased when coal is co-fired with SRF, which may greatly enhance the toxicity of the dusts from coal-fired power plant.
Energy & Fuels, Feb 20, 2018
Users may download and print one copy of any publication from the public portal for the purpose... more Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
Users may download and print one copy of any publication from the public portal for the purpose... more Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
Fuel, Apr 1, 2019
Users may download and print one copy of any publication from the public portal for the purpose... more Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
Energy & Fuels, Jun 14, 2011
The release and transformation of inorganic elements during grate-firing of bran was studied via ... more The release and transformation of inorganic elements during grate-firing of bran was studied via experiments in a laboratory-scale reactor, analysis of fly ash from a grate-fired plant, and equilibrium modeling. It was found that K, P, S, and to a lesser extent Cl and Na were released to the gas phase during bran combustion. Laboratory-scale experiments showed that S was almost fully vaporized during pyrolysis below 700°C. Sixty to seventy percent of the K and P in bran was released during combustion, in the temperature range 900À1100°C. The release of K and P was presumably attributed to the vaporization of KPO 3 generated from thermal decomposition of inositol phosphates, which were considered to be a major source of P and K in bran. The influence of additives such as CaCO 3 , Ca(OH) 2 , and kaolinite on the release was also investigated. Ca-based additives generally increased the molar ratio of the released K/P, whereas kaolinite showed an opposite effect. Thermodynamic modeling indicated that the fly ash chemistry was sensitive to the molar ratio of the released K/P. When the molar ratio of the released K/P was below 1, KPO 3 and P 4 O 10 (g) were the main stable K and P species at temperatures higher than 500°C. Below 500°C, the KPO 3 and P 4 O 10 (g) may be converted to H 3 PO 4 (l), which may cause severe deposit build-up in the economizers of a grate-fired boiler. By increasing the molar ratio of the released K/P to above 2, the equilibrium distribution of the K and P species was significantly changed and the formation of H 3 PO 4 (l) was not predicted by thermodynamic modeling.
In the present study a method to simulate the reaction between gaseous KCl and kaolin at suspensi... more In the present study a method to simulate the reaction between gaseous KCl and kaolin at suspension fired condition was developed using a pilot-scale entrained flow reactor (EFR). Kaolin was injected into the EFR for primary test of this method. By adding kaolin, KCl can effectively be captured, forming water-insoluble K-aluminosilicate. The amount of K captured by 1 g kaolin rose when increasing the molar ratio of K/Si in the reactant. Changing of reaction temperature from 1100 °C to 1300 °C did not influence the extent of reaction, which is different from the results observed in previous fixed-bed reactor. The method using the EFR developed in this study will be applied for further systematic investigation of different additives.
A water slurry, consisting of KCl and Al-Si based additives (kaolin and coal fly ash) was fed int... more A water slurry, consisting of KCl and Al-Si based additives (kaolin and coal fly ash) was fed into an entrained flow reactor (EFR) to study the K-capturing reaction of the additives at suspension-fired conditions. Solid products collected from the reactor were analysed with respect to total and water-soluble K content to quantify the extent of the K-capturing reaction. The results showed that under suspension-fired conditions (1100 °C-1450 °C), kaolin and coal fly ash can effectively capture gaseous KCl. When increasing the mass ratio of KCl to Al-Si additives in the reactants, the conversion of KCl to K-aluminosilicate decreased. When reaction temperature increased from 1100 °C to 1450 °C, the conversion of KCl does not change significantly, which differs from the trend observed in fixed-bed reactor.
Social Science Research Network, 2022
Users may download and print one copy of any publication from the public portal for the purpose... more Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
Users may download and print one copy of any publication from the public portal for the purpose... more Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
insights from laboratory scale studies DTU Orbit (18/01/2019) Alkali chloride induced corrosion o... more insights from laboratory scale studies DTU Orbit (18/01/2019) Alkali chloride induced corrosion of superheaters under biomass firing conditions: Improved insights from laboratory scale studies One of the major operational challenges experienced by power plants firing biomass is the high corrosion rate of superheaters. This limits the outlet steam temperature of the superheaters and consequently, the efficiency of the power plants. The high corrosion rates have been attributed to the formation of corrosive deposits (rich in alkali chlorides) on the surfaces of the superheaters. Accordingly, an extensive number of fundamental investigations have been undertaken to understand the basic mechanisms behind the alkali chloride induced high temperature corrosion of superheaters (for example, [1–3]). However, complete understanding of the corrosion mechanism under biomass-firing conditions has not yet been achieved. This is attributed partly to the complex nature of the corrosion process sin...
Surface Engineering, 2016
Superheater tubes in biomass-fired power plants experience high corrosion rates due to condensati... more Superheater tubes in biomass-fired power plants experience high corrosion rates due to condensation of corrosive alkali chloride rich deposits. To explore the possibility of reducing the corrosion attack by the formation of an initial protective oxide layer, the corrosion resistance of pre-oxidized Al and Ti-containing alloys (Kanthal APM and Nimonic 80A, respectively) was investigated under laboratory conditions mimicking biomass-firing. The alloys were pre-oxidized at 900 o C for 1 week. Afterwards, pre-oxidized samples, and virgin non-pre-oxidized samples as reference, were coated with a synthetic deposit of KCl and exposed at 560 o C for 1 week to a gas mixture typical of biomass firing. Results show that pre-oxidation could hinder the corrosion attack; however the relative success was different for the two alloys. While corrosion attack was observed on the preoxidized Kanthal APM, the morphology of the preoxidized Nimonic 80A was significantly unaffected suggesting protection of the alloy from the corrosive environment.
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Papers by Flemming Frandsen