| 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. |
- Johnsson, Jan-Erik, et al.
(författare)
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Modeling N2O Reduction and Decomposition in a Circulating Fluidized Bed Boiler
- 1996
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Ingår i: Energy & Fuels. - 1520-5029 .- 0887-0624. ; 10:4, s. 970-979
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Tidskriftsartikel (refereegranskat)abstract
- The N2O concentration was measured in a circulating fluidized bed boiler of commercial size. Kinetics for N2O reduction by char and catalytic reduction and decomposition over bed material from the combustor were determined in a laboratory fixed bed reactor. The destruction rate of N2O in the combustion chamber and the cyclone was calculated taking three mechanisms into account: reduction by char, catalytic decomposition over bed material, and thermal decomposition. The calculated destruction rate was in good agreement with the measured destruction of N2O injected at different levels in the boiler. The conclusion is that in the bottom part of the combustor, where the solids concentration is about 1000 kg/m3 (voidage 0.6) and the char content in solids 2 wt %, heterogeneous reactions were the most important N2O destruction mechanisms. Reduction by char accounted for 80% of the N2O destruction, 20% was due to catalytic decomposition over bed material, and homogeneous thermal decomposition was negligible. However, at higher levels in the combustor, the solids concentration is lower: at the top 60% of the N2O destruction was due to thermal decomposition and in the cyclone heterogeneous destruction of N2O was insignificant. It was estimated that more than one-half of the formation of N2O in the combustion chamber takes place above the secondary air inlet.
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| 4. |
- Johnsson, Jan-Erik, et al.
(författare)
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Modelling of N2O reduction in a circulating fluidized bed boiler
- 1996
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Ingår i: Proc of the 5th International Conference on Circulating Fluidized Bed. ; 5, s. 338-343
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Konferensbidrag (refereegranskat)abstract
- The N2O was measured in a circulating fluidized bed boiler of commercial size. Kinetics of N2O reduction and decomposition by char and over bed material from the combustor were determined in a laboratory fixed bed reactor. A mathematical model of the N2O chemistry in the combustor was set up, and the results from the simulation of N2O destruction were in good agreement with measurements of the N2O destruction from injection at different levels in the furnace of the boiler.
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| 5. |
- Johnsson, Jan-Erik, et al.
(författare)
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Modelling of NOx Formation in a Circulating Fluidized Bed Boiler
- 1990
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Ingår i: Proceedings 3rd International Conference on Circulating Fluidized Beds held October 15-18, 1990 in Nagoya, Japan.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A detailed kinetic model for the oxidation of NH3 and reduction of NO in FBC is used to model the NO concentration profile in an 8 MW CFB. Three different fuels were burned in the full scale tests: Bituminous coal, brown coal and petroleum coke. Kinetics were measured in a laboratory reactor using samples of char and bed material from the boiler. The simulation results show that char is an important catalyst for the oxidation of NH3 and reduction of NO when burning bituminous coal and petroleum coke. The char content in the brown coal bed is low and very active bed material with a high ash content is the important catalyst in this case. Homogeneous gas phase reactions were found to have only a minor influence. The levels of NO concentration calculated are in agreement with the experimental results. It is concluded that modelling the fuel-N conversion using kinetics measured for the specific chars and bed materials is a considerable step towards a better understanding of the formation and reduction of NO in FBC.
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| 6. |
- Lyckeskog, Huyen, 1985, et al.
(författare)
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Catalytic depolymerisation and conversion of Kraft lignin into liquid products using near-critical water
- 2014
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Ingår i: Journal of Supercritical Fluids. - : Elsevier BV. - 0896-8446. ; 86, s. 67-75
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Tidskriftsartikel (refereegranskat)abstract
- A high-pressure pilot plant was developed to study the conversion of LignoBoost Kraft lignin into bio-oil and chemicals in near-critical water (350◦C, 25 MPa). The conversion takes place in a continuous fixed-bed catalytic reactor (500 cm3) filled with ZrO2 pellets. Lignin (mass fraction of approximately 5.5%) is dispersed in an aqueous solution containing K2CO3(from 0.4% to 2.2%) and phenol (approximately 4.1%).The feed flow rate is 1 kg/h (reactor residence time 11 min) and the reaction mixture is recirculated internally at a rate of approximately 10 kg/h. The products consist of an aqueous phase, containing phenolic chemicals, and a bio-oil, showing an increased heat value (32 MJ/kg) with respect to the lignin feed. The 1-ring aromatic compounds produced in the process are mainly anisoles, alkylphenols, guaiacols and catechols: their overall yield increases from 17% to 27% (dry lignin basis) as K2CO3 is increased.
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| 7. |
- Lyckeskog, Huyen, 1985, et al.
(författare)
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Storage Stability of Bio-oils Derived from the Catalytic Conversion of Softwood Kraft Lignin in Subcritical Water
- 2016
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 30:4, s. 3097-3106
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Tidskriftsartikel (refereegranskat)abstract
- The stability of lignin-derived bio-oil obtained from a continuous process [base (K2CO3)-catalyzed, using phenol as a capping agent] under subcritical conditions of water (25 MPa, 290-370 degrees C) was investigated. The lignin-derived bio-oil obtained was stored at ambient temperature for 2 years. Our results show that the base concentration in the feed solution affects the stability of this lignin-derived bio-oil during its long-term storage. It was found that, at low base concentrations (i.e., 0.4%-1.0%), the yields of all lignin-derived bio-oil fractions were relatively stable. At high base concentrations (i.e., 1.6%-2.2%), however, the yield of high-molecular-weight (high-Mw) structures increased and that of low-molecular-weight (low-Mw) structures decreased after storage. This indicated that the low-Mw materials had been polymerized to form high-Mw materials. In addition, it was found that the yield of gas chromatography-mass spectrometry (GC-MS)-identified compounds (excluding phenol) in this lignin-derived bio-oil decreased from 15% to 11%. This is probably due to the presence of solids in these lignin derived bio-oils, which promotes the catalytic polymerization reactions, suggesting that it is beneficial to remove the solids from this lignin-derived bio-oil in order to enhance its stability. Compared to the results obtained from bio-oil derived from biomass pyrolysis, our results show that bio-oil derived from the conversion of lignin in subcritical water has better chemical stability during long-term storage.
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| 8. |
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| 9. |
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| 10. |
- Andersson, Bengt-Åke, et al.
(författare)
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Fluidized bed combustion of coals and alternative fuels
- 1985
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Ingår i: Proc of the 8th International Conference on Fluidized-Bed Combustion held in Houston Texas USA, March 18-21, 1985. ; 2, s. 1019-1029
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Konferensbidrag (refereegranskat)abstract
- The 16 MW demonstration plant at Chalmers University of Technology was designed to burn coal but measures were taken also to allow the use of alternative fuels. Results of comparative tests, with bituminous coal and alternative fuels, brown coal, peat, and wood chips, are presented. The combustion characteristics of the various fuels are illustrated with temperature and heat flux profiles in the freeboard. It is found that the volatile fuels tend to burn to a large extent above the bed and secondary air is necessary to complete the combustion. However, -if secondary air is used, a combustion efficiency close to 100% is easily obtained. Bituminous coal, on the other hand, does not readily burn with a high combustion efficiency in the boiler used.
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