| 1. |
- Derda, Patrycja, et al.
(författare)
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Fate of Alkali Metals during Co-Combustion of Biodiesel Residues with Coal in a Semi-Industrial CFB Boiler
- 2008
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Ingår i: 9th International Conference on Circulating Fluidized Beds, CFB 2008, in Conjunction with the 4th International VGB Workshop on Operating Experience with Fluidized Bed Firing Systems; Hamburg; Germany; 13 May 2008 through 16 May 2008. - 9783930400577
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Konferensbidrag (refereegranskat)abstract
- The use of biodiesel, especially of Rapeseed Methyl Ester (RME), has recently increased inthe European countries. This gives rise to an increasing amount of after production residues. Rapeseedcake is the main residue of the RME production process, and may become available in large amounts forenergy recovery. Since rapeseed cake contains high levels of alkali metals, it may cause bedagglomeration, deposit formation and corrosion upon combustion in fluidized beds.This paper presents the fate of alkali metals formed during co-combustion of coal and up to 25% ofrapeseed cake pellets in a 12 MW Circulating Fluidized Bed Boiler at Chalmers University ofTechnology (Sweden). Standard fuel analyses combined with sequential leaching and SEM/EDX, showedthe alkali entering the boiler. Gaseous emissions, bed samples, fly ash and deposits were analyzed inorder to monitor the alkali metals distribution. Gaseous alkali chlorides were measured upstream from theconvective pass at a flue gas temperature of 800 oC using an In-situ Alkali Chloride Monitor (IACM). Inthe same location, deposits were collected on a deposit probe fitted with rings for SEM/EDX analysis.Re-circulated bed material was analyzed as well.Two-day tests showed successful co-firing of up to 25% rapeseed cake on energy basis in the semiindustrialfluidized-bed boiler. Alkali metals were enriched in fly ash. No significant difference could benoticed in the distribution of alkali metals when increasing the share of rapeseed cake from 15% to 25%on energy basis. In the near future, further studies will be carried out to determine the influence oflimestone on the performed tests.
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| 2. |
- Kassman, Håkan, 1962, et al.
(författare)
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Ammonium Sulphate and Co-Combustion with Peat – Two Strategies to Reduce Gaseous KCl and Chlorine in Deposits during Biomass Combustion
- 2010
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Ingår i: In Proceedings from: "Impacts of Fuel Quality on Power Production & Environment", Lapland, Finland, August 29th - September 3rd 2010.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Combustion of a biomass with an enhanced content of chlorine (Cl) can result in operational problems including deposit formation and superheater corrosion. The strategies to reduce such problems include co-combustion and the use of additives. The positive effects of such measures are mainly due to sulphation of the alkali chlorides (KCl for biomass) to less corrosive alkali sulphates or capture of released alkali (K) in components such as potassium aluminium silicates. A mixture of wood pellets and straw pellets was fired in a 12 MW circulation fluidised bed (CFB) boiler. PVC was added to the fuel in order to achieve a further enhanced reference level of gaseous KCl during certain tests. Two strategies were applied to decrease the risk for superheater corrosion by reducing gaseous KCl and content of chlorine in deposits. The strategies were sulphation of KCl by injection of ammonium sulphate and co-combustion with peat. During co-combustion of biomass with peat both sulphation of KCl and capture of released K in ash components can be of importance. The results were evaluated by means of several advanced measurement tools including IACM (on-line measurements of gaseous KCl), deposit measurements (chemical composition in collected deposits, initial corrosion), ash analysis (chemical composition in fly ashes). The overall performance was better for ammonium sulphate, which significantly reduced gaseous KCl. Meanwhile almost no chlorine was found in the deposits. Only a minor reduction of gaseous KCl was obtained during co-combustion of biomass with peat although the chlorine content in the deposits was greatly reduced.
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| 3. |
- Kassman, Håkan, 1962, et al.
(författare)
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Gas Phase Alkali Chlorides and Deposits during Co-Combustion of Coal and Biomass
- 2006
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Ingår i: Proccedings 19th FBC Conference from May 21 -May 24 2006 in Vienna/AUSTRIA. - 3200006455 ; 2
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Konferensbidrag (refereegranskat)abstract
- Straw pellets have been co-fired with a bituminous coal with a high chlorine content. The tests were carried out in a 12 MW circulating fluidized bed (CFB) boiler located at Chalmers University of Technology in Sweden. The tests focused on variation of the ratio of straw to coal in combination with different feeding rates of limestone to the bed. Three test series were carried out: Lime – the fuel was a constant mixture of coal and straw pellets, with an increasing lime supply; Coal – the fuel was coal only, with an increasing lime supply. Alkali – the fuel was coal and straw pellets and constant lime supply. The fraction of straw pellets (alkali) was increased. An In-situ Alkali Chloride Monitor (IACM) was used during the tests to measure the on-line concentration of alkali chlorides and SO2 before the convection section of the boiler. Deposit measurements were also carried out and the deposits were analysed by means of SEM-EDX. It was found that an increased fraction of straw pellets in the fuel mix results in increased level of alkali chlorides in the gas phase as well as in collected deposits.
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| 4. |
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| 5. |
- Kassman, Håkan, 1962, et al.
(författare)
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Measures to reduce chlorine in deposits: Application in a large-scale circulating fluidised bed boiler firing biomass
- 2011
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Ingår i: Fuel. - Amsterdam : Elsevier BV. - 0016-2361 .- 1873-7153. ; 90:4, s. 1325-1334
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Tidskriftsartikel (refereegranskat)abstract
- Combustion of biomass with a high content of alkali (mainly potassium, K) and chlorine (Cl) can result in operational problems including deposit formation and superheater corrosion. Among the measures applied to decrease such problems are co-combustion and the use of additives. The positive effects of these measures are to a large extent either sulphation of the alkali chlorides (KCl) to less corrosive alkali sulphates or capture of alkali from KCl during release of HCl. A test campaign was carried out in a large-scale circulating fluidised boiler fired with biomass where the measures applied were sulphation by ammonium sulphate and co-combustion with peat. Their performance was evaluated by means of several advanced measurement tools including: IACM (on-line measurements of gaseous KCl); a low-pressure impactor (size distribution and chemical composition of extracted fly ash particles) and deposit measurements (chemical composition in collected deposits). The overall performance was better for ammonium sulphate, which significantly lowered KCl in the flue gas. Meanwhile no chlorine was found in the deposits. Only a minor reduction of gaseous KCl was obtained during co-combustion with peat although the chlorine content in the deposits was greatly reduced. These findings were supported by the results from the impactor measurements. (C) 2010 Elsevier Ltd. All rights reserved.
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| 6. |
- Kassman, Håkan, 1962, et al.
(författare)
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Nitrogen Containing Additives for Simultaneous Reduction of KCl and NOx during Biomass Combustion in a CFB Boiler
- 2009
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Ingår i: Proceedings of the 9th International Conference on Circulating Fluidized Beds, May, 13 - 16, 2008, Hamburg, Germany.
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Konferensbidrag (refereegranskat)abstract
- High levels of alkali chlorides in the flue gas can cause enhanced deposit formation and superheater corrosion during combustion of biofuels. These alkali chlorides mainly originate from potassium chloride (KCl). A challenge during combustion of biofuels is to simultaneously reduce NOx and KCl. The ChlorOut concept has been developed by Vattenfall to minimise deposit formation and corrosion. It consists of IACM, an instrument for on-line measurements of gaseous alkali chlorides, and a sulphate-containing additive that converts alkali chlorides to less corrosive alkali sulphates. The sulphate-containing additive is often ammonium sulphate, (NH4)2SO4, and, therefore, a significant NOx reduction is also achieved. This paper presents the results from a comparison of the conventional SNCR additives (ammonia or urea) and (NH4)2SO4 for reduction of NOx and/or KCl during combustion in a CFB boiler. The fuel consisted of either a mixture of wood chips and wood pellets with added PVC or with straw pellets. Of special interest was the influence of sulphation of KCl in parallel to the reduction of NO and if these processes interact. The results show that there are rather small differences in performance concerning NOx reduction between the additives.
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| 7. |
- Kassman, Håkan, 1962, et al.
(författare)
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Secondary effects in sampling ammonia during measurements in a circulationg fluidised-bed combustor
- 1997
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Ingår i: Journal of the Institute of Energy. ; :70, s. 95-101
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Tidskriftsartikel (refereegranskat)abstract
- A previous paper presented the results of measuring the ammonia (NH3) concentration in the combustion chamber of a circulating fluidised-bed (CFB) boiler. Two sampling techniques were used: a gas-quenching (GQ) probe where the sample is quenched directly in the probe tip by a circulating trapper solution, and a gas-sampling probe connected to a Fourier-transform infra-red (FTIR) instrument. In this paper, an attempt is made to estimate the influence of potential secondary reactions with NH3 in the GQ probe tip by means of a plug-flow model. The calculations showed that heterogeneous and homogeneous reactions could be of importance to the accuracy of the measurement. This contradicts the almost identical results relative to the parallel FTIR measurement, and the conversion of NH3 is probably overestimated by the model. In addition, transients obtained during the FTIR measurement were used to study the accuracy of the gas-sampling probe.
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| 8. |
- Kassman, Håkan, 1962
(författare)
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Strategies to reduce gaseous KCl and chlorine in deposits during combustion of biomass in fluidised bed boilers
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Combustion of a biomass with an enhanced content of alkali and chlorine (Cl) can result in operational problems including deposit formation and superheater corrosion. The strategies applied to reduce such problems include co-combustion and the use of additives. In this work, measures were investigated in order to decrease the risk of superheater corrosion by reducing gaseous KCl and the content of chlorine in deposits. The strategies applied were sulphation of KCl by sulphur/sulphate containing additives (i.e. elemental sulphur (S) and ammonium sulphate (AS)) and co-combustion with peat. Both sulphation of KCl and capture of potassium (K) in ash components can be of importance when peat is used. The experiments were mainly performed in a 12 MW circulation fluidised bed (CFB) boiler equipped for research purposes but also in a full-scale CFB boiler. The results were evaluated by means of IACM (on-line measurements of gaseous KCl), conventional gas analysis, deposit and corrosion probe measurements and ash analysis.Ammonium sulphate performed significantly better than elemental sulphur. Thus the presence of SO3 (i.e. AS) is of greater importance than that of SO2 (i.e. S) for sulphation of gaseous KCl and reduction of chlorine in deposits. Only a minor reduction of gaseous KCl was obtained during co-combustion with peat although chlorine in the deposits was greatly reduced. This reduction was supposedly due to capture of K by reactive components from the peat ash in parallel to sulphation of KCl. These compounds remained unidentified. The effect of volatile combustibles on the sulphation of gaseous KCl was investigated. The poorest sulphation was attained during injection of ammonium sulphate in the upper part of the combustion chamber during the lowest air excess ratio. The explanation for this is that SO3 was partly consumed by side reactions due to the presence of combustibles. These experimental results were supported by modelling, although the sulphation of KCl in the presence of combustibles were somewhat overestimated in the chemical kinetic model. Oxygen also had an effect on the sulphation when injecting AS in the cyclone. Less gaseous KCl was reduced during air excess ratio λ = 1.1 compared to the higher air excess ratios. A correlation was also observed between the sulphation of gaseous KCl and reduced chlorine content in the deposits.
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| 9. |
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| 10. |
- Kassman, Håkan, 1962, et al.
(författare)
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The effect of oxygen and volatile combustibles on the sulphation of gaseous KCl
- 2013
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Ingår i: Combustion and Flame. - : Elsevier BV. - 1556-2921 .- 0010-2180. ; 160:10, s. 2231-2241
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Tidskriftsartikel (refereegranskat)abstract
- Sulphur/sulphate containing additives, such as elemental sulphur (S) and ammonium sulphate (NH4)(2)SO4), can be used for sulphation of KCl during biomass combustion. These additives convert KCl to an alkali sulphate and a more efficient sulphation is normally achieved for ammonium sulphate compared to sulphur. The presence of SO3 is thus of greater importance than that of SO2. Oxygen and volatile combustibles could also have an effect on the sulphation of gaseous KCl. This paper is based on results obtained during co-combustion of wood chips and straw pellets in a 12 MW circulating fluidised bed (CFB) boiler. Ammonium sulphate was injected at three positions in the boiler i.e. in the upper part of the combustion chamber, in the cyclone inlet, and in the cyclone. The sulphation of KCl was investigated at three air excess ratios (lambda = 1.1, 1.2 and 1.4). Several measurement tools were applied including IACM (on-line measurements of gaseous alkali chlorides), deposit probes (chemical composition in deposits collected) and gas analysis. The position for injection of ammonium sulphate had a great impact on the sulphation efficiency for gaseous KCl at the different air excess ratios. There was also an effect of oxygen on the sulphation efficiency when injecting ammonium sulphate in the cyclone. Less gaseous KCl was reduced during air excess ratio lambda = 1.1 compared to the higher air excess ratios. The optimal position and conditions for injection of ammonium sulphate were identified by measuring KCl with IACM. A correlation was observed between the sulphation of gaseous KCl and reduced chlorine content in the deposits. The experimental observations were evaluated using a detailed reaction mechanism. It was used to model the effect of volatile combustibles on the sulphation of gaseous MCI by SO3. The calculations supported the proposition that the presence of combustibles at the position of SO3 injection (i.e. AS) causes reduction of SO3 to SO2.
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| 11. |
- Kassman, Håkan, 1962, et al.
(författare)
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The importance of SO2 and SO3 for sulphation of gaseous KCl - An experimental investigation in a biomass fired CFB boiler
- 2010
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Ingår i: Combustion and Flame. - : Elsevier BV. - 1556-2921 .- 0010-2180. ; 157:9, s. 1649-1657
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Tidskriftsartikel (refereegranskat)abstract
- This paper is based on results obtained during co-combustion of wood pellets and straw in a 12 MW circulating fluidised bed (CFB) boiler. Elemental sulphur (S) and ammonium sulphate ((NH4)(2)SO4) were used as additives to convert the alkali chlorides (mainly KCl) to less corrosive alkali sulphates. Their performance was then evaluated using several measurement tools including, IACM (on-line measurements of gaseous alkali chlorides), a low-pressure impactor (particle size distribution and chemical composition of extracted fly ash particles), and deposit probes (chemical composition in deposits collected). The importance of the presence of either SO2 or SO3 for gas phase sulphation of KCl is also discussed. Ammonium sulphate performed significantly better than elemental sulphur. A more efficient sulphation of gaseous KCl was achieved with (NH4)(2)SO4 even when the S/Cl molar ratio was less than half compared to sulphur. Thus the presence of gaseous SO3 is of greater importance than that of SO2 for the sulphation of gaseous KCl. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 12. |
- Kassman, Håkan, 1962, et al.
(författare)
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Two Strategies to Reduce Gaseous KCl and Chlorine in Deposits during Biomass Combustion - Injection of Ammonium Sulphate and Co-Combustion with Peat
- 2013
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Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820. ; 105, s. 170-180
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Tidskriftsartikel (refereegranskat)abstract
- Combustion of a biomass with an enhanced content of chlorine can result in operational problems including deposit formation and superheater corrosion. The strategies applied to reduce such problems include co-combustion and the use of additives. In this work a mixture of wood pellets and straw pellets was fired in a circulating fluidised bed boiler. Two strategies were applied to decrease the risk of superheater corrosion by reducing gaseous KCl and content of chlorine in deposits: sulphation of KCl by injection of ammonium sulphate and co-combustion with peat. During co-combustion of biomass with peat both sulphation of KCl and capture of released potassium in ash components can be of importance. The results were evaluated by means of IACM (on-line measurements of gaseous KCl), deposit probe measurements (chemical composition in collected deposits, initial corrosion) and ash analysis (chemical composition in fly ashes). The best overall performance was achieved with ammonium sulphate, which significantly reduced KCl. Meanwhile almost no chlorine was found in the deposits. Only a minor reduction of gaseous KCl was obtained during co-combustion although the chlorine content in the deposits was greatly reduced. The resistance to initial corrosion was improved during both injection of ammonium sulphate and co-combustion with peat.
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| 13. |
- Viklund, P., et al.
(författare)
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Deposit chemistry and initial corrosion during biomass combustion - The influence of excess O-2 and sulphate injection
- 2015
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Ingår i: Materials and Corrosion - Werkstoffe und Korrosion. - : Wiley. - 1521-4176 .- 0947-5117. ; 66:2, s. 118-127
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Tidskriftsartikel (refereegranskat)abstract
- Corrosion of superheater tubes is a serious problem during combustion of fuels with a high content of chlorine, such as waste and certain biomasses. The alkali chlorides are released to the flue gas and may condense on the heat exchanger tubes forming corrosive, chloride-rich deposits. In this work the effect of ammonium sulphate ((NH4)(2)SO4) injection on gaseous alkali chlorides, deposit chemistry and initial corrosion attack of superheater tubes during biomass combustion have been investigated. The investigation was carried out at three different sulphate injection rates (reference, low and high) and at three air excess ratios (lambda = 1.1, 1.2 and 1.4). Short-term exposures of Sanicro 28 specimens, using temperature controlled probes, were used for deposit collection and to study the initial corrosion attack. The results showed reduced concentrations of potassium chloride in the flue gas when injecting ammonium sulphate and in particular in combination with high air excess ratios. A decrease of chlorine was also observed in the deposit, but the concentrations did not always correlate to the flue gas measurements. In particular, it was evident that a subsequent sulphation occurred on the tube surface at low air excess ratios. Metallography revealed that sulphation reactions on the tube surface, rather than in the flue gas, had a detrimental effect on the initial corrosion attack. As a consequence, the corrosion attack correlated more clearly to the KCl(g) concentration in the flue gas than the chlorine content in the deposit.
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| 14. |
- Åmand, Lars-Erik, 1957, et al.
(författare)
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Measurement of the concentration of ammonia and ethene in the combustion chamber of a circulating fluidised-bed boiler
- 1997
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Ingår i: Journal of the Institute of Energy. ; :70, s. 25-30
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the results of measuring the ammonia and ethene concentration profiles in the combustion chamber of a circulating fluidised-bed boiler. The boiler was operated in three air-staging conditions with peat as fuel, and with the addition of lime. Two sampling techniques were used for the analysis of ammonia: gas-sampling probe connected to a Fourier transformed infra-red (FTIR) instrument, and a gas-quenching (GQ) probe where the sample was quenched directly in the probe tip by a trapper solution. Both techniques are accurate enough to distinguish the influence on air staging of the level of ammonia in the combustion chamber. Comparison of the concentration profiles for ammonia measured by the two procedures shows similar results. The levels of ammonia and ethene measured by FTIR follow each other in the combustion chamber for all three staging conditions. The FTIR spectra were evaluated by three methods: spectral subtraction, differential absorbance and the multiple variable analysis method named 'partial least square' (PLS). Almost equal levels of concentration of ammonia and ethene were found, regardless of the method employed. The measurement error from reactions with ammonia at the GO probe tip was estimated in a simple model.
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