| 1. |
- 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.
|
|
| 2. |
- 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.
|
|
| 3. |
- 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.
|
|
| 4. |
- 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.
|
|
| 5. |
- Pettersson, Anita, et al.
(författare)
-
Application of chemical fractionation methods for characterisation of biofuels, waste derived fuels and CFB co-combustion fly ashes
- 2008
-
Ingår i: Fuel. - : Elsevier Ltd. - 0016-2361 .- 1873-7153. ; 87:15-16, s. 3183-3193
-
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.
|
|
| 6. |
- Pettersson, Anita, et al.
(författare)
-
Chemical fractionation for the characterisation of fly ashes from co-combustion of biofuels using different methods for alkali reduction
- 2009
-
Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 88:9, s. 1758-1772
-
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.
|
|
| 7. |
|
|
| 8. |
|
|
| 9. |
- Pettersson, Anita, 1965, et al.
(författare)
-
The impact of zeolites during co-combustion of municipal sewage sludge with alkali and chlorine rich fuels
- 2009
-
Ingår i: Proceedings of the 20th International Conference on Fluidized Bed Combustion in Xi:an, China May 18-20, 2009. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 9787302201465 ; 2, s. 903-909, s. 902-909
-
Konferensbidrag (refereegranskat)abstract
- Municipal sewage sludge has proven to eliminate alkali metals and chlorine related problems during combustion of straw and refuse derived fuels (RDF). However, the mechanisms involved have not been clarified. The aim of this work was to gain more knowledge about the behaviour of sewage sludge and detergent zeolites in combustion and about their effects on alkali metal chemistry. Co-combustion tests with combinations of municipal sewage sludge, wood and straw were carried out in a 12 MW fluidised bed (FB) boiler. In addition, a detergent zeolite, Doucil A24, was used as additive during co-combustion of wood and straw. The chemical characteristics of fuels and fly ashes were studied using several methods, such as chemical fractionation and scanning electron microscopy with element analysis by energy dispersive fluorescence detection (SEM-EDX) and X-ray diffraction (XRD). In the co-combustion tests involving sewage sludge no KCl was found in the flue gas prior to the convection pass. The zeolite addition was less effective but the KCl concentration was reduced to some degree in favour of HCl compared to the reference case. Both SEM-EDX and XRD confirmed the presence of potassium-aluminium-silicates in the fly ash fraction in all cases. In addition, the laboratory study showed that Doucil A24 had the ability to capture potassium and KCl at temperatures in the range of 700-900°C.
|
|
