| 1. |
- Davidsson, Kent, 1967, et al.
(författare)
-
Potassium, chlorine, and sulfur in ash, particles, deposits, and corrosion during wood combustion in a circulating fluidized-bed boiler
- 2007
-
Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 21:1, s. 71-81
-
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.
|
|
| 2. |
- Herstad-Svärd, S., et al.
(författare)
-
Ramprogram – Åtgärder för samtidig minimering av alkalirelaterade driftproblem, Etapp 2
- 2007
-
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
|
|
| 3. |
- Johnsson, Jan-Erik, et al.
(författare)
-
Modeling N2O Reduction and Decomposition in a Circulating Fluidized Bed Boiler
- 1996
-
Ingår i: Energy & Fuels. - 1520-5029 .- 0887-0624. ; 10:4, s. 970-979
-
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.
|
|
| 4. |
- Johnsson, Jan-Erik, et al.
(författare)
-
Modelling of N2O reduction in a circulating fluidized bed boiler
- 1996
-
Ingår i: Proc of the 5th International Conference on Circulating Fluidized Bed. ; 5, s. 338-343
-
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.
|
|
| 5. |
- Johnsson, Jan-Erik, et al.
(författare)
-
Modelling of NOx Formation in a Circulating Fluidized Bed Boiler
- 1990
-
Ingår i: Proceedings 3rd International Conference on Circulating Fluidized Beds held October 15-18, 1990 in Nagoya, Japan.
-
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.
|
|
| 6. |
- Lyckeskog, Huyen, 1985, et al.
(författare)
-
Catalytic depolymerisation and conversion of Kraft lignin into liquid products using near-critical water
- 2014
-
Ingår i: Journal of Supercritical Fluids. - : Elsevier BV. - 0896-8446. ; 86, s. 67-75
-
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.
|
|
| 7. |
- Lyckeskog, Huyen, 1985, et al.
(författare)
-
Storage Stability of Bio-oils Derived from the Catalytic Conversion of Softwood Kraft Lignin in Subcritical Water
- 2016
-
Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 30:4, s. 3097-3106
-
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.
|
|
| 8. |
|
|
| 9. |
|
|
| 10. |
- Andersson, Bengt-Åke, et al.
(författare)
-
Fluidized bed combustion of coals and alternative fuels
- 1985
-
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
-
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.
|
|
| 11. |
- Andersson, Sven B, 1952, et al.
(författare)
-
N2O-Emissions from Fluidized Bed Combustion
- 1988
-
Ingår i: Proceedings of IEA AFBC Technical Meting held in November 1988 in Amsterdam, The Netherlands.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Nitrous oxide, N20, is formed during combustion. In flames the N20 is removed because of the fast destruction at high temperatures. At the temperatures of fluidized bed combustion the destruction is much slower and N20 will leave the system, normally at a concentration of 50-200 ppm when burning coal. Using the results of the preliminary model in a CFB, it can be assumed that:- N20 is formed from char nitrogen in the bottom bed because of reactions in the pores of the particle. - Only some N20 is formed when NO is reduced during its journey up through the combustion chamber. - N20 is formed from HCN. This is a slow process (taking seconds) and it therefore takes place principally above the bottom bed.
|
|
| 12. |
- Barisic, Vesna, et al.
(författare)
-
The Role of Limestone in Preventing Agglomeration and Slagging during CFB Combustion of High-Phosphorous Fuels
- 2008
-
Ingår i: Proceedings Poster Session for World BioEnergy 2008 Conference & Exhibition on Biomass for Energy, 27-29 May 2008, Jönköping - Sweden. ; , s. 259-263
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- ABSTRACT: This paper presents key observations on the role of limestone in preventing bed agglomeration during combustion of a high-phosphorous fuel in CFB boilers. Composition of the bed material samples was analyzed using X-ray fluorescence, and scanning electron microscope combined with an energy dispersive X-ray analyzer (SEM/EDXA). It has been demonstrated that during combustion of the high-phosphorous fuel in CFB conditions, addition of limestone reduces or prevents bed agglomeration and formation of slag by interfering with the ash chemistry, and not by simple dilution of the reacting system. The role of limestone can be summarized as: 1) to provide calcium for the reaction with phosphorous forming high-temperature-melting calcium phosphates instead of low-temperature-melting potassium phosphates, and 2) to coat silica particles preventing the reaction of potassium (calcium) phosphates and silica from fluidizing sand, which can form low-temperature-melting potassium (calcium) silicates, especially relevant for fluidized bed combustion conditions.
|
|
| 13. |
- Belkheiri, Tallal, 1985, et al.
(författare)
-
Effect of pH on Kraft Lignin Depolymerisation in Subcritical Water
- 2016
-
Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 30:6, s. 4916-4924
-
Tidskriftsartikel (refereegranskat)abstract
- Softwood kraft lignin was depolymerized using subcritical water (623 K and 25 MPa) in a continuous small pilot unit. ZrO2 and K2CO3 were used as catalysts, and phenol was used as capping agent to suppress repolymerization. The effect of pH was investigated by adding KOH in five steps to the feed. The yield of water-soluble organics increased with pH. The yield of bio-oil was also influenced by the pH and varied between 28 and 32 wt %. The char yield on the zirconia catalyst showed a minimum at pH 8.1. The yield of suspended solids was low at pH below 8.1 but increased at higher pH values. The oxygen content in the bio-oil was only 15 wt %, compared to about 26 wt % in the kraft lignin.
|
|
| 14. |
- Belkheiri, Tallal, 1985, et al.
(författare)
-
Kraft Lignin Depolymerization in Near-Critical Water: Effect of Changing Co-Solvent
- 2014
-
Ingår i: Cellulose Chemistry and Technology. - 0576-9787. ; 48:9-10, s. 813-818
-
Tidskriftsartikel (refereegranskat)abstract
- As part of developing a process to valorize lignin in a pulp mill with lignin separation, the depolymerisation of lignin to valuable chemicals was investigated in near-critical water. This was done by using methanol as co-solvent and hydrogen donor, phenol to suppress repolymerization (e.g. formation of char), and ZrO2 as a heterogeneous catalyst, with potassium carbonate as a co-catalyst. The reaction was carried out in a continuous flow fixed-bed reactor (500 cm(3)), at 280-350 degrees C and 25MPa. An important aspect is to suppress char formation. Therefore, the char formation was studied by using different concentrations of methanol and phenol. The char yield varied between 14% and 26%. When using methanol as the only co-solvent, the char yield decreased with increasing methanol concentration. Adding phenol resulted in a further decrease. The reactor outlet consisted mainly of two liquid phases, an aqueous and an oil phase, mixed together. The chemical analysis of the aqueous phase showed the presence of mainly phenolic compounds, for instance guaiacol, catechol, phenol and cresol.
|
|
| 15. |
- Berglin, Niklas, et al.
(författare)
-
Pilot-scale combustion studies with kraft lignin as a solid biofuel
- 2008
-
Ingår i: Engineering, Pulping and Environmental Conference 2008. - : TAPPI Press. - 9781605605081 ; , s. 2571-2580
-
Konferensbidrag (refereegranskat)abstract
- Processing of kraft lignin precipitated from black liquor to produce a solid biofuel with high energy density and low ash content has been developed in research programs by STFI-Packforsk and partners. In preparation for full-scale combustion trials, tests were carried out on pilot scale in a 150 kW powder burner and in a 12 MWfluidized bed (CFB) boiler. Lignin powder could be fired in a powder burner with good combustion performance after some trimming of the airflows to reduce swirl. Lignin dried to 10 % moisture content was easy to feed smoothly and had less bridging tendencies in the feeding system than wood/bark powder. In the CFB boiler lignin was easily handled and co-fired together with bark. Although the filter cake was broken into smaller pieces and fines the combustion was not disturbed. When co-firing lignin with bark, the sulfur emission increased compared to bark firing only, but most of the sulfur was captured by calcium in the bark ash. Conventional sulfur capture with addition of limestone to the bed was also demonstrated. The sulfur content in the lignin had a significantly positive effect on reducing the alkali chloride content in the deposits, thus reducing the high temperature corrosion risk.
|
|
| 16. |
- Berglin, N., et al.
(författare)
-
Pilot-scale combustion studies with kraft lignin in a powder burner and a CFB boiler
- 2010
-
Ingår i: Tappi Journal. - 0734-1415. ; 9:6, s. 24-30
-
Tidskriftsartikel (refereegranskat)abstract
- Processes have been developed to produce a solid biofuel with high energy density and low ash content from kraft lignin precipitated from black liquor. Pilot-scale tests of the lignin biofuel were carried out with a 150 kW powder burner and a 12 MW circulating fluidized bed (CFB) boiler. Lignin powder could be fired in a powder burner with good combustion performance after some trimming of the air flows to reduce swirl. Lignin dried to 10% moisture content was easy to feed smoothly and had less bridging tendencies in the feeding system than did wood/bark powder. In the CFB boiler, lignin was easily handled and cofired together with bark. Although the filter cake was broken into smaller pieces and fines, the combustion was not disturbed. When cofiring lignin with bark, the sulfur emission increased compared with bark firing only, but most of the sulfur was captured by calcium in the bark ash. Conventional sulfur capture also occurred with addition of limestone to the bed. The sulfur content in the lignin had a significantly positive effect on reducing the alkali chloride content in the deposits, thus reducing the high temperature corrosion risk.
|
|
| 17. |
- Boëlle, A., et al.
(författare)
-
Coal Comminution Characterization for Industrial Scale Circulating Fluidized Bed
- 2002
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The management of the bed solids inventory and particle size distribution in fluidized bed combustors has long been recognized as a key factor for the efficient and trouble-free operation of industrial scale fluidized bed ombustors. From a coal particle to an ash particle getting out the circulating loop, the particle size reduction factor can be hundred. Detailed pilot scale test observations related to the size of circulating particles and ash particles, show very different behaviours for different coals. In order to describe those behaviours related to a large particle size spectrum, a general frame work is proposed based on several concepts. The key concept is represented by the Primary Ash Particle Size Distribution (PAPSD). According to this concept, Primary Ash Particles are liberated from the carbon matrix under the combined action of Combustion and Primary Attrition of the mother fuel particles. By Primary Attrition it is meant here a complex of particle comminution phenomena closely associated with the progress of reactions (devolatilization/char combustion), along pathways and with mechanisms that are extensively discussed by Chirone et al. (1991). Further (Secondary) attrition of ash particles can occur after char combustion is complete and is not associated with the parallel progress of chemical reactions but to mechanical attrition only. Those concepts are associated with coal characterization procedures in order to have information on the size reduction of a coal particle and the final size istribution of ash. The measurement obtained on a lab scale is validated by the analysis of some results of industrial-scale tests. In association with procedure definition, a qualitative approach allows prediction and inter-coal comparison. A modelisation work is also presented considering however that quantitative predictions of the particle size distribution inside a CFBC is still a far objective.
|
|
| 18. |
- Dam-Johansen, Kim, et al.
(författare)
-
Influence of SO2 on the NO/N2O chemistry in fluidized bed combustion 2. Interpretation of full-scale observations based on laboratory experiments
- 1993
-
Ingår i: Fuel. - 0016-2361. ; 72:4, s. 565-571
-
Tidskriftsartikel (refereegranskat)abstract
- In circulating fluidized bed combustion of coal, significant interactions between desulfurization by limestone and emissions of nitrogen oxides (NO, N2O) are generally observed. In order to facilitate interpretation of experimental results obtained in a 12 MW circulating fluidized bed boiler, a series of laboratory tests have been carried out. The tests include homogeneous CO and HCN oxidation in the presence of different concentrations of SO2, CO oxidation catalysed by calcined and partly sulfated limestone particles, and formation and reduction of NO and N20 over bed material containing char. The presence of SO2 in the gas is shown to decrease the rate of homogeneous CO and HCN oxidation and thereby change the product distribution of the nitrogen-containing species. Unlike sulfated limestone, calcined limestone (CaO) is shown to be a good catalyst for oxidation of CO. A lower mean CO concentration is therefore expected in fluidized bed combustors during injection oflimestone. This indirectly influences the nitrogen chemistry. Finally, the influence of NO and O2 on the formation of N2O from char was studied.
|
|
| 19. |
- Davidsson, Kent, 1967, et al.
(författare)
-
Countermeasures against alkali-related problems during combustion of biomass in a circulating fluidized bed boiler
- 2008
-
Ingår i: Chemical Engineering Science. ; 63, s. 5314-5329
-
Tidskriftsartikel (refereegranskat)abstract
- The purpose of this work was to study different ways to mitigate alkali-related problems during combustionof biomass in circulating fluidized beds. Wood chips and wood pellets were fired together withstraw pellets, while the tendency to agglomerate and form deposits was monitored. In addition to areference case, a number of countermeasures were applied in related tests. Those were addition of elementalsulphur, ammonium sulphate and kaolin to a bed of silica sand, as well as use of olivine sand andblast-furnace slag as alternative bed materials. The agglomeration temperature, composition and structureof bed-ash samples were examined. The flue-gas composition, including gaseous alkali chlorides, wasmeasured in the hot flue gases and in the stack. Particles in the flue gas were collected and analysed forsize distribution and composition. Deposits were collected on a probe in hot flue gases and their amountand composition were analysed. Addition of kaolin was found to be the best method to counteract theagglomeration problem. The deposition problem is effectively counteracted with addition of ammoniumsulphate, while kaolin is too expensive to be used commercially against deposits, and sulphur is lesseffective than ammonium sulphate.
|
|
| 20. |
|
|
| 21. |
- Derda, Patrycja, et al.
(författare)
-
Fate of Alkali Metals during Co-Combustion of Biodiesel Residues with Coal in a Semi-Industrial CFB Boiler
- 2008
-
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
-
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.
|
|
| 22. |
- Edvardsson, Elin, 1976, et al.
(författare)
-
Measuring the External Solids Flux in a CFB boiler
- 2006
-
Ingår i: Proceedings 19th FBC Conferance, May 21-24, Vienna Austria. - 3200006455
-
Konferensbidrag (refereegranskat)abstract
- In circulating fluidized bed (CFB) boilers, the flow rate of externally recirculated bed material is important, since it influences combustion, fluid dynamics, solids segregation and heat transfer. However, in CFB boilers (as well as in other industrial CFB units), the solids recirculation rate is difficult to determine, as no standard method is available to measure it directly. In this work, a methodology for measurement of the external solid flux is developed, based on heat and mass balances over parts of the return loop of a CFB boiler. Continuous measurements of temperatures and flow rates of gas and water entering and exiting different sections of the return loop are needed to determine both instantaneous and time-averaged solids recirculation rates. The method was evaluated in the Chalmers 12 MWth CFB boiler with good results.
|
|
| 23. |
- Edvardsson, Elin, 1976, et al.
(författare)
-
Solids Distribution and Gas Concentrations in the Furnace of a CFB Boiler during Co-Combustion of Bituminous Coal with Municipal Sewage Sludge
- 2006
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this work, bituminous coal was co-fired with municipal sewage sludge in a 12 MWth circulating fluidized bed (CFB) research boiler. The fraction of sewage sludge(both wet and dry) in the feed was varied in the range 0-67 % (on dry mass). The impact of co-combustion on ash leaving the boiler, bed material in the furnace and concentrations of O2, CO2, CO and total hydrocarbons throughout the furnace was studied. In order to evaluate the influence of the wide size distribution of the coal on the results, the coal was pre-sieved into a fine and a coarse size fraction and separately burned. The higher ash content in the sewage sludge resulted in increasing fly ash flows and lower combustible content in the fly ash with increasing fraction of sludge in the fuel mix. The bottom ash flow and combustible content were more sensitive to the feed coal size distribution than to the sludge supply. Compared to coal combustion, co-combustion of coal with sewage sludge was found to lead to a higher concentration of fine solids in the furnace, caused by attrition of sludge ash particles. Furthermore, as the density of sewage sludge ash is lower than that of coal ash, coarser sludge ash particles than coal ash particles could be entrained from the bottom bed. These two phenomena contributed to wider solids size distributions throughout the furnace in the case of co-combustion with sewage sludge. The effect of theentering coal size distribution on the size distribution of the inert ashes was negligible compared to the impact of the sludge fraction in the feed. The size distributions of the combustible solids in the bed material, on the other hand, were dependent on variations in feed size distribution of the coal rather than on sludge supply. Theintroduction of sewage sludge in the fuel mix resulted in greater measured concentrations of CO and total hydrocarbons in the furnace, leading to an increasedcombustion of volatiles above the bottom bed and higher temperatures in the top of the furnace.
|
|
| 24. |
- Elled, Anna-Lena, 1975, et al.
(författare)
-
Composition of agglomerates in fluidized bed reactors for thermochemical conversion of biomass and waste fuels Experimental data in comparison with predictions by a thermodynamic equilibrium model
- 2013
-
Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 111, s. 696-708
-
Tidskriftsartikel (refereegranskat)abstract
- Controlled combustion tests of biomass were performed in the 12 MWth circulating fluidized bed (CFB) boiler located on the campus of Chalmers University of Technology. The aim was twofold: to investigate the composition of agglomerated material and also to highlight the reasons for sintering and agglomeration during thermochemical conversion of biomass and wastes in fluidized bed reactors using quartz sand as bed material. Bed ash from three different tests regarding fuel or fuel mixtures (wood with straw, bark, and bark with refused derived fuel) was analysed to determine the ash elements using: (a) inductive coupled plasma (ICP) equipped with optical emission spectroscopy (OES) and (b) scanning electron microscopy equipped with an electron dispersive X-ray spectrometer (SEM-EDX). Chemical equilibrium calculations were also performed to support the interpretation of the experimental findings. It was found that the combination of (i) well controlled full-scale tests in a fluidized bed boiler, (ii) the use of line-scans by the EDX spectrometer of the SEM on bed samples and (iii) thermodynamic equilibrium modelling is a powerful tool in understanding the phenomena of bed agglomeration using quartz sand.
|
|
| 25. |
- Elled, Anna-Lena, 1975, et al.
(författare)
-
Influence of phosphorus on sulphur capture during co-firing
- 2006
-
Ingår i: Fuel. ; 85, s. 1671-1678
-
Tidskriftsartikel (refereegranskat)abstract
- Interference from phosphorus on sulphur capture during co-firing of sludge with wood has been investigated in a circulating fluidised bed boiler.Chemical equilibrium analyses were performed on the combustion system to complement the experimental results. It was found that the relativelyhigh content of phosphorus in municipal sewage sludge interferes with the sulphur capture by occupying calcium, which otherwise would beavailable for reaction with sulphur. This fact must be taken into account when sulphur capture strategies are decided for reduction of sulphurdioxide emissions from sewage sludge as an additional fuel.q 2006 Elsevier Ltd. All rights reserved.
|
|
| 26. |
- Elled, Anna-Lena, et al.
(författare)
-
Phosphorous in ash from co-combustion of municipal sewage sludge with wood in a CFB boiler: a comparison of experimental data with predictions by a thermodynamic equilibrium model
- 2005
-
Ingår i: In Proceedings of the 18th International Conference on Fluidized Bed Combustion--FBC2005 held in Toronto, Ontario, Canada, May 22-25, 2005. - 0791837556 ; 18, s. FBC2005-78072
-
Konferensbidrag (refereegranskat)abstract
- Combustion tests have been carried out in a circulating fluidised bed (CFB) boiler co-firing wood and municipal, digested and mechanical dewatered sewage sludge from two Swedish wastewater treatment plants, using either iron sulphate or aluminium sulphate as precipitating chemicals. Experimental data on the concentration of various phosphorous compounds in the ashes are compared with theoretical equilibrium predictions. A clear relationship is not found between the employed precipitation chemical and the formation of phosphorous compounds in the ash. Hematite (Fe2O3(s)) is predicted to be the stable iron compound, and even in the sludge precipitated by iron sulphate, the aluminium content is sufficient to form aluminium phosphate (AlPO4(s)) in similar amounts as in the sludge precipitated by aluminium sulphate. Lime addition to the bed gives a decreased formation of AlPO4(s) in favour of calcium orthophosphate (Ca3(PO4)2(s)), which interferes with the sulphur capture efficiency of lime.
|
|
| 27. |
- Elled, Anna-Lena, 1975, et al.
(författare)
-
Sewage sludge as a deposit inhibitor when co-fired with high potassium fuels
- 2010
-
Ingår i: Biomass and Bioenergy. - : Elsevier BV. - 1873-2909 .- 0961-9534. ; 34:11, s. 1546-1554
-
Tidskriftsartikel (refereegranskat)abstract
- The objective of this work is to survey the fate of potassium in the gas phase of a fluidised bed boiler and gain deeper understanding of the involved mechanisms during co-firing of municipal sewage sludge with biomass containing high amounts of potassium and chlorine. The results show that formation of alkali chlorides in the flue gas and corrosive deposits on heat transfer surfaces can be controlled by addition of municipal sewage sludge even though the fuel is highly contaminated with chlorine. The beneficial effects are partly due to the content of sulphur in the sludge, partly to the properties of the sludge ash. The sludge ash consists of both crystalline and amorphous phases. It contains silica, aluminium, calcium, iron and phosphorus which all are involved in the capture of potassium. (c) 2010 Elsevier Ltd. All rights reserved.
|
|
| 28. |
- Elled, Anna-Lena, et al.
(författare)
-
The fate of trace elements in fluidised bed combustion of sewage sludge and wood
- 2007
-
Ingår i: Fuel. ; 86:5-6, s. 843-852
-
Tidskriftsartikel (refereegranskat)abstract
- Combustion tests have been carried out in a fluidised bed boiler to investigate the fate of trace elements during co-combustion of wood and municipal sewage sludge. The approach was to collect fuel and ash samples and to perform thermodynamic equilibrium calculations for gasification (reducing) and combustion (oxidising) conditions. Trace elements are found in the ash. Even most of the highlyvolatile Hg is captured in the bag filter ash. The bag filter ash offers higher surface area than the secondary cyclone ash and enhances the capture of Hg. There is no obvious correlation between capture and parameters investigated (sludge precipitation agent and lime addition).As, Cd, Hg, Pb, Se, Sb and Tl are predicted by equilibrium calculations to be volatile in the combustion chamber under oxidising conditions and Hg even at the filter temperature (150°C). Reducing conditions promote, in some case more than others, the volatility of As, Cd, Pb, Sb, Se, Tl and Zn. The opposite effect was observed for Cu and Ni. Data points to the necessity of including bag filter in thegas cleaning system in order to achieve good removal of toxic trace elements.
|
|
| 29. |
- Elled, Anna-Lena, et al.
(författare)
-
The fate of zinc during combustion of demolition wood in a fluidized bed boiler
- 2007
-
Ingår i: Energy & Fuels. - : American Chemical Society. - 0887-0624 .- 1520-5029. ; 22:3
-
Tidskriftsartikel (refereegranskat)abstract
- Demolition wood can be used as a fuel in heat and power plants. However, it may contain elevated amounts of zinc, originating from white paint, which can cause problems related to deposit formation and corrosion on heat transfer surfaces. In this work, combustion tests with zinc addition were carried out in a fluidized bed boiler to investigate its effect on deposit formation. Thermodynamic equilibrium calculations were performed to complement the experimental data. The results show that combustion of demolition wood only contaminated with zinc generates a modest amount of deposit. Combustion of demolition wood contaminated with both zinc and chlorine promotes the deposit formation due to the increased amount of submicron particles in the flue gas. The thermodynamic equilibrium analyses show further that reducing conditions increase the release of zinc to the flue gas. On the other hand, in the case of oxidizing conditions, the retention of zinc in the ash is strong. Zinc, in combination with chlorine, gives rise to formation of zinc chloride in the flue gas. The formation is, at reducing conditions, thermodynamically favored between 450 and 850 °C. At oxidizing conditions, the formation is initiated at 400 °C and gradually increased with the temperature.
|
|
| 30. |
|
|
| 31. |
|
|
| 32. |
|
|
| 33. |
- Gulyurtlu, Ibrahim, et al.
(författare)
-
Co-firing of biomass and other wastes in fluidized bed systems
- 2006
-
Ingår i: 19th International Conference on Fluidized Bed Combustion.
-
Konferensbidrag (refereegranskat)abstract
- A project on co-firing in large-scale power plants burning coal is currently funded by the European Commission. It is called COPOWER. The project involves 10 organisations from 6 countries. The project involves combustion studies over the full spectrum of equipment size, ranging from small laboratory-scale reactors and pilot plants, to investigate fundamentals and operating parameters, to proving trials on a commercial power plant in Duisburg. The power plant uses a circulating fluidized bed boiler. The results to be obtained are to be compared as function of scale-up. There are two different coals, 3 types of biomass and 2 kinds of waste materials are to be used for blending with coal for co-firing tests. The baseline values are obtained during a campaign of one month at the power station and the results are used for comparison with those to be obtained in other units of various sizes. Future tests will be implemented with the objective to achieve improvement on baseline values. The fuels to be used are already characterized. There are ongoing studies to determine reactivities of fuels and chars produced from the fuels. Reactivities are determined not only for individual fuels but also for blends to be used. Presently pilot-scale combustion tests are also undertaken to study the effect of blending coal with different types of biomass and waste materials. The potential for synergy to improve combustion is investigated. Simultaneously, studies to verify the availability of biomass and waste materials in Portugal, Turkey and Italy have been undertaken. Techno-economic barriers for the future use of biomass and other waste materials are identified. The potential of using these materials in coal fired power stations has been assessed. The conclusions will also be reported.
|
|
| 34. |
- Gulyurtlu, Ibrahim, et al.
(författare)
-
PRODUCTION OF FINES DURING CO-COMBUSTION OF COAL WITH BIOMASS FUELS BY FRAGMENTATION AND ATTRITION
- 2005
-
Ingår i: Proceedings of the 8th International Conference on Circulating Fluidized Beds Hangzhou, China, May 10-13, 2005. - 7506274426 ; , s. 565-573
-
Konferensbidrag (refereegranskat)abstract
- Results are reported from a project funded by the RFCS Programme of the European Union. The aim is to investigate, experimentally and by modeling, the production of fine char and ash particles during co-combustion of coal with wastes and biofuels in circulating fluidized bed. Work was undertaken at installations of different scales. Polish and Colombian coals were base fuels. The additional fuels were two sewage sludges. Bed temperature, feeding system, sand particle size, devolatilisation behaviour and char burn-out were studied to verify their influence on the fine particle production. Modeling was also carried out to understand the mechanisms of fragmentation and attrition. Samples from bed and cyclone were collected to determine particle size distributions.
|
|
| 35. |
- Hansson, Karl-Martin, 1973, et al.
(författare)
-
Formation of HNCO, HCN, and NH3 from the pyrolysis of bark and nitrogen-containing model compounds
- 2004
-
Ingår i: Combustion and Flame. - 1556-2921 .- 0010-2180. ; 137, s. 265-277
-
Tidskriftsartikel (refereegranskat)abstract
- Bark pellets have been pyrolyzed in a fluidized bed reactor at temperatures between 700 and 1000C. Identifiednitrogen-containing species were hydrogen cyanide (HCN), ammonia (NH3), and isocyanic acid (HNCO). Quantification of HCN and to some extent of NH3 was unreliable at 700 and 800C due to low concentrations. HNCO could not be quantified with any accuracy at any temperature for bark, due to the low concentrations found. Since most of the nitrogen in biomass is bound in proteins, various protein-rich model compounds were pyrolyzed with the aim of finding features that are protein-specific, making conclusions regarding the model compounds applica-ble for biomass fuels in general. The model compounds used were a whey protein isolate, soya beans, yellow peas,and shea nut meal. The split between HCN and NH3 depends on the compound and temperature. It was found that the HCN/NH3 ratio is very sensitive to temperature and increases with increasing temperature for all compounds, including bark. Comparing the ratio for the different compounds at a fixed temperature, the ratio was found to decrease with decreasing release of volatile nitrogen. The temperature dependence implies that heating rate andthereby particle size affect the split between HCN and NH3. For whey, soya beans, and yellow peas, HNCO was also quantified. It is suggested that most HCN and HNCO are produced from cracking of cyclic amides formed as primary pyrolysis products. The dependence of the HNCO/HCN ratio on the compound is fairly small, but the temperature dependence of the ratio is substantial, decreasing with increasing temperature. The release of nitrogen-containing species does not seem to be greatly affected by the other constituents of the fuel, and proteins appear to be suitable model compounds for the nitrogen in biomass.
|
|
| 36. |
- Hansson, Karl-Martin, 1973, et al.
(författare)
-
Pyrolysis of poly-L-leucine under combustion-like conditions
- 2003
-
Ingår i: Fuel. - 0016-2361. ; 82, s. 653-660
-
Tidskriftsartikel (refereegranskat)abstract
- The protein poly-L-leucine has been used as a model compound for the nitrogen in biomass fuels. It was pyrolysed in a fluidised bed at 700 and 800C and the pyrolysis gases were analysed with a FT-IR spectrometer. HCN, NH3 and HNCO were identified as the main nitrogen-containing species, while neither NO nor N2O were found among the pyrolysis gases. At 700C, as much as 58% of the nitrogen content was converted into HCN and 31% into NH3. The HCN/NH3 ratio increased from about 1.9 at 700C to above 2.2 at 800C. Pyrolysis of another protein, poly-L-proline, at 800C gave a HCN/NH3 ratio close to 10. This revealed that the protein’s amino acid composition has a marked impact on the composition of the pyrolysate.
|
|
| 37. |
- Hansson, Karl-Martin, 1973, et al.
(författare)
-
The temperature’s influence on the selectivity between HNCO and HCN from pyrolysis of 2,5-diketopiperazine and 2-pyridone
- 2003
-
Ingår i: Fuel. - 0016-2361. ; 82, s. 2163-2172
-
Tidskriftsartikel (refereegranskat)abstract
- Two cyclic amides, 2-pyridone and 2,5-diketopiperazine (DKP), were pyrolysed at temperatures ranging from 700 to 1100C. Pyridone is the only one of the four main nitrogen functionalities found in coal that is likely to form HNCO under pyrolysis. DKP is a primary pyrolysis product from proteins, which are the main nitrogen source in biomass. The formation of HNCO from biomass has been suggested to originate from DKP and other cyclic amides. The aromatic 2-pyridone was thermally more stable than the non-aromatic DKP. Both amides formed HCN, HNCO and NH3. The NH3 yields, about 3–4% for 2-pyridone and 10% for DKP, were almost independent of temperature. The HCN yield on the other hand showed strong temperature dependence and increased with temperature for both of the cyclic amides. The HNCO yield decreased with increasing temperature for DKP over the whole temperature interval. For 2-pyridone, the pyrolysis was incomplete at the lowest temperature in the investigation. Between 900 and 1100C, the pyrolysis of 2-pyridone was complete and the HNCO yield decreased with increasing temperature. The HNCO/HCN ratio for both of the cyclic amides decreased with increasing temperature over the whole investigated temperature range. The finding in literature that the HNCO formation from cracking of coal tars produced a maximum HNCO yield at an intermediate temperature, is explained by the thermal stability of pyridone at low temperatures and the selectivity towards HCN at high temperatures.
|
|
| 38. |
- Johansson, Andreas, et al.
(författare)
-
Dynamics of furnace processes in a CFB boiler
- 2007
-
Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509 .- 1873-4405. ; 62:1-2, s. 550-560
-
Tidskriftsartikel (refereegranskat)abstract
- With the aim of understanding the dynamics of combustion, this work examines simultaneous fluctuations in fluid dynamic parameters and gas composition measured in a CFB furnace operated with coal as a fuel. The fluid dynamic parameters investigated are pressure and air flow entering the furnace. Gas composition was recorded by a zirconia-cell probe and a gas suction probe connected to a mass spectrometer having a high time resolution (10 Hz). The principal fluctuations detected are around I Hz and below 0.3 Hz. The fluctuations below 0.3 Hz mostly originate from variations in the fuel-feed rate. These variations create periods of reducing conditions caused by a momentarily high fuel input accompanied by a pressure rise in the furnace and a reduction of the air feed, which occurs concurrent with the release of an enhanced quantity of volatiles. Modelled pressure fluctuations based on the relation between volatile release and pressure in the furnace give similar pressure fluctuations as the measured pressure fluctuations, with respect to amplitude and characteristic time scale of the fluctuations. There is also a correlation between reducing conditions and the concentration of hydrocarbons. (c) 2006 Elsevier Ltd. All rights reserved.
|
|
| 39. |
- Johansson, Andreas, 1980, et al.
(författare)
-
DYNAMICS OF IN-FURNACE PROCESSES IN A CFB BOILER
- 2005
-
Ingår i: Proceedings of the 8th International Conference on Circulating Fluidized Beds. - 7506274426 ; , s. 159-166
-
Konferensbidrag (refereegranskat)abstract
- With the aim of understanding the dynamics of combustion, this work examines simultaneous fluctuations in fluid dynamic parameters and gas composition in a CFB furnace operated with coal as a fuel. Fluid dynamic parameters are pressure and air flow to the furnace. Gas composition was obtained by a zirconia-cell probe and a gas suction probe connected to a mass spectrometer having a high time resolution (10 Hz). The fluctuations of interest are around 1 Hz and below 0.3 Hz. The fluctuations below 0.3 Hz, which have not been investigated previously, are found to originate from irregularities in the fuel feed. These irregularities give rise to periods of reducing conditions because high inputs of fuel yield an increased pressure in the furnace and a decreased air feed to the furnace, which then occurs concurrent with the release of a high amount of volatiles. There is also a correlation between reducing conditions and the concentration of hydrocarbons.
|
|
| 40. |
- Johansson, Linda S., et al.
(författare)
-
Properties of Particles in the Fly Ash of a Biofuel-Fired Circulating Fluidized Bed (CFB) Boiler
- 2008
-
Ingår i: Energy & Fuels. ; 22:5, s. 3015-3015
-
Tidskriftsartikel (refereegranskat)abstract
- A quench/dilution probe was designed and used for sampling of particles and vapors in the flue gas upstream of the convective path in a circulating fluidized bed boiler. Downstream of the convective path, flue gas was sampled by a heated probe. The sampled gas was lead through low-pressure impactors for analysis of the mass size distribution of particles. The particles were analyzed for Cl, S, K, Na, Ca, Mg, P, Al, Fe, Ba, Mn, and Si. A series of tests was carried out to study minimization of problems originating from the alkali content in the fuel, including the effect of additives to the fuel, change of bed material, and co-combustion with sewage sludge. Particle concentration and composition were compared to deposit growth and composition on a deposit probe, which represents a superheater. Alkali chloride in the particles was compared to online measurements of gaseous alkali chlorides. The continuous mass deposition on the heat-transfer surface in the convective path was illustrated by calculation of the reduction of heat transfer by means of the temperature drop of the flue gas. Fine particles ( 1 μm) particles increased. These test cases also showed the lowest deposit growth on the superheater probe. The particles deposited in the convective path were mostly coarse ones. The most favorable case with respect to low deposits was co-combustion with sewage sludge.
|
|
| 41. |
- Kallio, S., et al.
(författare)
-
Sensitivity study of fluid dynamic effects on nitric oxide formation in CFB combustion of wood
- 2002
-
Ingår i: Proc. of the 7th International Circulating Fluidized Bed. - 0920804985 ; , s. 757-764
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The paper presents results from simulations by a 1.5D numerical model developed to study the formation of the NO and N2O emissions in a circulating fluidized bed combustor (CFBC) under different operating conditions and burning different fuels. A comprehensive kinetic scheme for the homogeneous chemistry and a single particle model for char combustion are used. Fluiddynamic factors, including gas mixing and release of volatiles, are investigated in the case of wood combustion under normal air staging conditions. The pattern of release of volatiles, the mixing of secondary air, and the lateral mixing of gas are observed to play significant roles in the formation of the relatively high NO emissions from combustion of wood. Comparisons are made with measurement data and also with coal combustion.
|
|
| 42. |
- Karlsson, Sofia, 1982, et al.
(författare)
-
Reducing high-temperature corrosion on high- alloyed stainless steel superheaters by co-combustion of municipal sewage sludge in a fluidised bed boiler
- 2015
-
Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 139, s. 482-493
-
Tidskriftsartikel (refereegranskat)abstract
- One way of mitigating alkali chloride induced corrosion in biomass and waste-fired boilers is by using additives or by co-combustion and thereby decreasing the corrosiveness of the flue gas and deposits. The effect of co-firing digested sewage sludge with a mixture of biomass and waste (78% bark pellets + 22% Solid Recovered Fuel, denoted "SRF'') was investigated in a 12 MW circulating fluidised bed (CFB) boiler. The initial corrosion attack of the stainless steel 304L at 600 degrees C (material temperature) was investigated during 24 h exposures. The exposures were carried out in the flue gas environment from three fuel-mixes: SRF, MSS1- low (SRF with municipal sewage sludge, low dosage) and MSS2- high (SRF with municipal sewage sludge, high dosage). The results showed that the most severe corrosion attack on 304L occurred without sewage sludge in the SRF exposure. This attack was characterised by a corrosion product layer up to 100 mu m in thickness and signs of internal corrosion of the steel. The deposit in the SRF case was dominated by alkali chlorides. The exposures with co- combustion of sewage sludge, MSS1-low and MSS2- high, showed a significant decrease in corrosion. The steel sample of 304L performed especially well in the latter case when it was protected by a thin oxide of less than 0.3 mu m in thickness. This deposit was dominated by sulphate- and phosphate- containing compounds but traces of aluminium silicate compounds where also found. Furthermore, the concentration of alkali chlorides was low. Thus, the initial corrosion attack was greatly reduced by co- combustion of digested sewage sludge with SRF.
|
|
| 43. |
- Karlsson, Sofia, 1982, et al.
(författare)
-
Reducing High Temperature Corrosion when Burning Waste by Adding Digested Sewage Sludge
- 2011
-
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).
-
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.
|
|
| 44. |
- Kassman, Håkan, 1962, et al.
(författare)
-
Ammonium Sulphate and Co-Combustion with Peat – Two Strategies to Reduce Gaseous KCl and Chlorine in Deposits during Biomass Combustion
- 2010
-
Ingår i: In Proceedings from: "Impacts of Fuel Quality on Power Production & Environment", Lapland, Finland, August 29th - September 3rd 2010.
-
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.
|
|
| 45. |
- Kassman, Håkan, 1962, et al.
(författare)
-
Gas Phase Alkali Chlorides and Deposits during Co-Combustion of Coal and Biomass
- 2006
-
Ingår i: Proccedings 19th FBC Conference from May 21 -May 24 2006 in Vienna/AUSTRIA. - 3200006455 ; 2
-
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.
|
|
| 46. |
- Kassman, H., et al.
(författare)
-
Influence of air-staging on the concentration profiles of NH3 and HCN in the combustion chamber of a CFB boiler burning coal
- 1999
-
Ingår i: 15th Int. Conf. on Fluidized Bed Combustion / Reuther, R.B..
-
Konferensbidrag (refereegranskat)abstract
- The characterisation of the concentration profiles of NH3 and HCN are of great importance for increasing the knowledge of the formation and destruction pathways of NO and N2O in a fluidized bed boiler. Further improvements of the sampling methods for the determination of both NH3 and HCN in the combustion chamber in full-scale CFB boilers are also needed. A gas-sampling probe connected to a Fourier Transform Infra Red (FTIR) instrument and a gas-quenching (GQ) probe in which the sample is quenched directly in the probe tip by a circulating trapper solution were used. The FTIR technique is based on analysis of hot combustion gases, whereas the trapper solutions from the GQ probe were analysed by means of wet chemistry.The tests were performed during coal combustion in a 12 MW CFB boiler, which was operated at three air-staging cases with the addition of limestone for sulphur capture. The concentration profiles of NH3 and HCN in the combustion chamber showed a different pattern concerning the influence of air-staging. The highest levels of NH3 were observed during reducing conditions (severe air-staging), and the lowest were found under oxidising conditions (no air-staging). The levels of HCN were much lower than those measured for NH3. The highest levels of HCN were observed for reversed air-staging and severe air-staging showed almost no HCN. The potential reactions involving NH3 and HCN in the combustion chamber as well as the potential measurement errors in each sampling technique are discussed for the three air-staging cases.
|
|
| 47. |
|
|
| 48. |
- Kassman, Håkan, 1962, et al.
(författare)
-
Measures to reduce chlorine in deposits: Application in a large-scale circulating fluidised bed boiler firing biomass
- 2011
-
Ingår i: Fuel. - Amsterdam : Elsevier BV. - 0016-2361 .- 1873-7153. ; 90:4, s. 1325-1334
-
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.
|
|
| 49. |
- Kassman, Håkan, et al.
(författare)
-
Nitrogen containing additives for simultaneous reduction of KCL and NOx during biomass combustion in a CFB boiler
- 2008
-
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 ; , s. Paper 14_13-
-
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 mainlyoriginate from potassium chloride (KCl). A challenge during combustion of biofuels is to simultaneously reduce NOx and KCl. The ChlorOut concept has been developed by Vattenfallto 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 oftenammonium 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.
|
|
| 50. |
- Kassman, Håkan, 1962, et al.
(författare)
-
Nitrogen Containing Additives for Simultaneous Reduction of KCl and NOx during Biomass Combustion in a CFB Boiler
- 2009
-
Ingår i: Proceedings of the 9th International Conference on Circulating Fluidized Beds, May, 13 - 16, 2008, Hamburg, Germany.
-
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.
|
|
