| 1. |
- Davidsson, Kent, 1967, et al.
(författare)
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Potassium, chlorine, and sulfur in ash, particles, deposits, and corrosion during wood combustion in a circulating fluidized-bed boiler
- 2007
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 21:1, s. 71-81
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the addition of chlorine and/or sulfur to the fuel on fly ash composition, deposit formation, and superheater corrosion has been studied during biomass combustion in a circulating fluidized-bed boiler. The chlorine (HCl (aq)) and sulfur (SO2 (g)) were added in proportions of relevance for the potassium chemistry. The composition of the bottom and the fly ashes was analyzed. Gas and particle measurements were performed downstream of the cyclone before the convection pass and the flue gas composition was recorded in the stack with a series of standard instruments and an FTIR analyzer. At the position downstream of the cyclone, a deposit probe was situated, simulating a superheater tube. Deposits on the probe and initial corrosion were examined. It is concluded that addition of sulfur and chlorine increases the formation of submicron particles leading to deposition of potassium sulfate and chloride. The results compare well with earlier work based on laboratory-scale experiments concerning effects of chlorine and sulfur on potassium chemistry.
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| 2. |
- Herstad-Svärd, S., et al.
(författare)
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Ramprogram – Åtgärder för samtidig minimering av alkalirelaterade driftproblem, Etapp 2
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Combustion of an increasing amount of biofuel and waste woods has resulted in certainenvironmental advantages, including decreased emissions of fossil CO2, SO2 andmetals. On the other hand, a number of chloride and alkali related operational problemshave occurred which are related to combustion of these fuels.Alkali related operational problems have been studied in a project consisting of twoparts. The overall scope has been to characterise the operational problems and to studymeasures to minimise them. The first part was reported in Värmeforsk report 997 wherethe results were summarised in a table of different measures. In part two, additionalmeasures have been included in the test plan and initial corrosion has been studiedlinked to the different measures. The tests have also in part two been carried out at the12 MW CFB boiler at Chalmers. The effect of the selected measures has beeninvestigated concerning both deposit formation and bed agglomeration, and at the sametime emissions and other operational conditions were characterised.The second part of the project has among other things focused on:• To investigate measures which decrease the content of alkali and chloride in thedeposits, and consequently decrease the risk for corrosion (by investigating theinitial corrosion). Focus was also on trying to explain favourable effects.• To investigate if it is possible to combine a rather low dosage of kaolin and injectionof ammonium sulphate. This was done in order to reduce both bed agglomerationand problems from deposits during combustion of fuels rich in chlorine.• To investigate if co-combustion with sewage sludge, de-inking sludge or peat withhigh ash content, could give similar advantages as conventional additives.• Investigate if ash from PFBC is possible to use as an alternative bed material.By comparing the different measures in part two, it could be concluded that cocombustionof sewage sludge gave the best overall effect. The judgement was based onthe effects concerning bed agglomeration, level of alkali chloride in the flue gas,deposits and initial corrosion. Simultaneous addition of kaolin and ammonia sulphatealso had a favourable impact both in the bed and on the alkali chlorides in the gas phase.Dosage of kaolin did not reduce the effect of injected ammonium sulphate. Cocombustionof peat could also be a very attractive alternative, but it is critical to select asuitable peat type. It is of special concern to avoid peat with a high content of calcium,since it can increase the level of alkali chlorides by reacting with available sulphur.Change of bed material to ash from PFBC can decrease problems with bedagglomeration, but there is a risk of increased deposit formation and corrosion. A boileroperated with high steam data should consequently combine the change of bed materialwith injection of ammonium sulphate or another source of sulphur.Co-combustion of de-inking sludge from pulp and paper production can reduceproblems with bed agglomeration. There is, however, an increased chance of corrosiondue to the high content of calcium. Injection of sulphates may improve the situationconcerning corrosion. The results also showed that low potassium chlorine content in the flue gas decreasesthe risk of corrosion. Increased amount of potassium chlorine content in the flue gaswill not necessary give a high amount of chlorine content in the deposits if there is sulphur in the system.Key words: agglomeration, deposits, corrosion, alkali, kaolin, ammonium sulphate,sludge
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| 3. |
- Karlsson, Sofia, 1982, et al.
(författare)
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Reducing High Temperature Corrosion when Burning Waste by Adding Digested Sewage Sludge
- 2011
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Ingår i: Swedish - Finnish Flame Days, January 26-27 2011 in Piteå, Sweden, The Swedish and Finnish National Committees of the International Flame Research Foundation (IFRF) and The Scandinavian - Nordic Section of the Combustion Institute (SNCI).
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The presence of alkali chlorides are well known to cause high temperature corrosion during combustion of biomass and waste. Low alloyed steels as well as stainless steels are experiencing an accelerated corrosion attack in such environments. Even though more highly alloyed steels (i.e. higher Cr/Fe ratio in the steel) are being used, there is only a small decrease in corrosion rate compared to low alloyed steels. To maintain the corrosion rates at an acceptable level the temperature of the superheaters (used for steam production to the steam turbine) of the boiler have been lowered. However, this causes a decrease in power production when the driving force for waste-to-energy boilers in the future is to increase the power production by increasing the temperatures of the steam from the final superheater stage.One of the reasons for the corrosive behavior of alkali chlorides towards stainless steels is the formation of alkali chromates. It has been shown that alkali chlorides react with chromium in the initial formed protective oxide on stainless steel:1/2Cr2O3(s) + 3/4O2(g) + H2O(g) + 2KCl(s) K2CrO4 (s) + 2 HCl(g) This result in a chromium depleted oxide which is converted into an iron-rich fast-growing oxide. This oxide has much poorer protective properties as it has higher diffusion rates compared to chromium rich oxides. Furthermore, the iron rich oxide is also more susceptible towards chlorine induced corrosion by chlorine ions penetrating the oxide scale. This leads to the formation of transition metal chlorides (e.g. FeCl2) at the metal/oxide interface causing poor scale adherence.A way to mitigate the alkali chloride induced corrosion is by introducing fuel additives and thus, changing the flue gas chemistry and furthermore the deposit composition. In this study, the effect of digested sewage sludge as fuel additive was investigated at the 12MW circulating fluidized bed (CFB) boiler at Chalmers University of Technology. The initial corrosion attack of the stainless steel 304L(Fe18Cr10Ni exposed at 600°C (material temperature) was investigated during 24h exposure of three different environments. Deposit analysis by means of XRD and IC were carried out using Sanicro 28 (Fe35Cr27Ni31) as sample ring. The exposures were denoted “RDF” (a reference exposure 80%Bark + 20%RDF), “SjöMed” (80%Bark + 20%RDF with sewage sludge from Sjölundaverket (medium dosage)) and “HimHög” (80%Bark + 20%RDF with sewage sludge from Himmerfjärdsverket (high dosage)).The results showed that the most severe corrosion attack of 304L occurred in the “RDF” exposure. The corrosion attack was characterized by an up to 100µm thick corrosion product layer and signs of internal corrosion of the steel. The deposit in the RDF exposure was dominated by alkali chlorides. The exposures with sewage sludge additions, “SjöMed” and “HimHög”, showed a remarkable decrease in corrosion rate. 304L performed especially well in the “HimHög” exposure, the steel ring was protected by a thin oxide, less than 0.3µm in thickness. Furthermore, the deposit was dominated by sulphate- and phosphate containing compounds. The presence of alkali chlorides was low.
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| 4. |
- 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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| 5. |
- 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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| 6. |
- Nordin, Andreas, et al.
(författare)
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Co-Combustion of Municipal Sewage Sludge and Biomass in a Grate Fired Boiler for Phosphorus Recovery in Bottom Ash
- 2020
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Ingår i: Energies. - : MDPI. - 1996-1073. ; 13:7
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Tidskriftsartikel (refereegranskat)abstract
- Phosphorus has been identified as a critical element by the European Union and recycling efforts are increasingly common. An important phosphorus-containing waste stream for recycling is municipal sewage sludge (MSS), which is used directly as fertilizer to farmland. However, it contains pollutants such as heavy metals, pharmaceutical residues, polychlorinated bi-phenyls (PCBs) and nano-plastics. The interest in combustion of MSS is continuously growing, as it both reduces the volume as well as destroys the organic materials and could separate certain heavy metals from the produced ashes. This results in ashes with a potential for either direct use as fertilizer or as a suitable feedstock for upgrading processes. The aim of this study was to investigate co-combustion of MSS and biomass to create a phosphorus-rich bottom ash with a low heavy metal content. A laboratory-scale fixed-bed reactor in addition to an 8 MWth grate-boiler was used for the experimental work. The concentration of phosphorus and selected heavy metals in the bottom ashes were compared to European Union regulation on fertilizers, ash application to Swedish forests and Swedish regulations on sewage sludge application to farmland. Element concentrations were determined by ICP-AES complemented by analysis of spatial distribution with SEM-EDS and XRD analysis to determine crystalline compounds. The results show that most of the phosphorus was retained in the bottom ash, corresponding to 9-16 wt.% P2O5, while the concentration of cadmium, mercury, lead and zinc was below the limits of the regulations. However, copper, chromium and nickel concentrations exceeded these standards.
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| 7. |
- Pettersson, Anita, et al.
(författare)
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Application of chemical fractionation methods for characterisation of biofuels, waste derived fuels and CFB co-combustion fly ashes
- 2008
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Ingår i: Fuel. - : Elsevier Ltd. - 0016-2361 .- 1873-7153. ; 87:15-16, s. 3183-3193
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Tidskriftsartikel (refereegranskat)abstract
- In the important efforts to decrease the net CO2 emissions to the atmosphere, new, alternative fuels are being included in the fuel mixes used in utility boilers. However, these fuels have ash properties that are different from those of the traditionally used fuels and in some cases technical problems, such as ash fouling and corrosion occur due to this. Therefore, diagnostic and predictive methods are developed and used to avoid such problems. Determination of the chemical association forms of important elements, such as potassium and sodium, in the fuel by chemical fractionation is a method well defined for coal and biofuels, such as wood pellets, bark and forest residues. Chemical fractionation is a step by step leaching method extracting water soluble salts in the first step, ion exchangeable elements, such as organically associated sodium, calcium and magnesium in the second step and acid soluble compounds such as carbonates and sulfates in the third step. The solid residue fraction consists of silicates, oxides, sulfides and other minerals. The compound extracted in the two first steps is considered reactive in the combustion with a few exceptions. In this work, it has been applied to some waste fuels, i.e. sewage sludge, straw and refuse derived fuel (RDF), as well as to coal and wood. The present work also includes results from combustion tests in a fluidised bed boiler where three blends of the investigated fuels were used. The fractionation results for the fuel blends are weighted results of the fractionations of the pure fuels discussed above which are compared with fractionations of their corresponding fly ashes. The co-combustion strategy gave very good results in reducing ash problems. Possible chemical mechanisms involved are discussed in the article.
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| 8. |
- Pettersson, Anita, et al.
(författare)
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Chemical fractionation for the characterisation of fly ashes from co-combustion of biofuels using different methods for alkali reduction
- 2009
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 88:9, s. 1758-1772
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Tidskriftsartikel (refereegranskat)abstract
- a b s t r a c tChemical fractionation, SEM–EDX and XRD was used for characterisation of fly ashes from different cocombustiontests in a 12MW circulating fluidized bed boiler. The fuels combusted were wood pellets asbase fuel and straw pellets as co-fuel in order to reach a fuel blend with high alkali and chlorine concentrations.This fuel blend causes severe problems with both agglomeration of bed material if silica sand isused and with deposits in the convection section of the boiler. Counter measures to handle this situationand avoiding expensive shut downs, tests with alternative bed materials and additives were performed.Three different bed materials were used; silica sand, Olivine sand and blast furnace slag (BFS) and differentadditives were introduced to the furnace of the boiler; Kaolin, Zeolites and Sulphur with silica sand asbed material. The results of the study are that BFS gives the lowest alkali load in the convection pass comparedwith Silica and Olivine sand. In addition less alkali and chlorine was found in the fly ashes in theBFS case. The Olivine sand however gave a higher alkali load in the convection section and the chemicalfractionation showed that the main part of the alkali in the fly ashes was soluble, thus found as KCl whichwas confirmed by the SEM–EDX and XRD.The comparison of the different additives gave that addition of Kaolin and Zeolites containing aluminium-silicates captured 80% of the alkali in the fly ash as insoluble alkali–aluminium-silikates and reducedthe KCl load on the convection section. Addition of sulphur reduced the KCl load in the flue gas even morebut the K2SO4 concentration was increased and KCl was found in the fly ashes anyhow. The chemical fractionationshowed that 65% of the alkali in the fly ashes of the Sulphur case was soluble.
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| 10. |
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