| 1. |
- Bellais, Michel, et al.
(författare)
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Pyrolysis of large wood particles : a study of shrinkage importance in simulations
- 2003
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Ingår i: Fuel. - 0016-2361 .- 1873-7153. ; 82:12, s. 1541-1548
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Tidskriftsartikel (refereegranskat)abstract
- Shrinkage models have been developed and included in a model for the pyrolysis of large wood particles. Shrinkage is modelled in three different ways: uniform shrinkage, shrinking shell and shrinking cylinders. These models and a reference model without shrinkage are compared with experimental data for mass loss versus time during pyrolysis of birch cylinders at different temperatures. In the experiments a wood particle was introduced into a pyrolysis furnace held at constant temperature. The particle mass and volume were recorded using a balance and a video camera. Uniform shrinkage slows down the pyrolysis whereas shrinking shell and cylinder models enhance the pyrolysis rate. The effect was sufficiently small to be neglected given the uncertainty about some wood physical properties.
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| 2. |
- Brackmann, Christian, et al.
(författare)
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Optical and mass spectrometric study of the pyrolysis gas of wood particles
- 2003
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Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 57:2, s. 216-222
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Tidskriftsartikel (refereegranskat)abstract
- A detailed experimental investigation has been made of the pyrolysis-the first step in biomass combustion-of single birchwood particles. In addition to mass spectrometric and gravimetric analysis, the pyrolysis volatiles were characterized by different optical techniques. Absorption measurements showed a nearly featureless absorption in the ultraviolet spectral region with a continuously stronger absorption for shorter wavelengths. Using different excitation wavelengths, laser-induced fluorescence measurements revealed generally broad spectra in the spectral region from 300-500 nm, which are characteristic spectral signatures for larger hydrocarbons. The optical data were monitored at different times in the pyrolysis process of the particles and compared with the results from the mass spectrometric and gravimetric analysis. The sensitivity of the optical techniques for differentiation between specific molecules was rather low, although formaldehyde could be observed both in absorption and fluorescence spectra. Laser-induced fluorescence measurements were also made for two-dimensional visualization of the pyrolysis volatiles; emitted from heated birchwood particles, indicating much higher flows along the fiber direction than across.
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| 3. |
- Davidsson, K.O., et al.
(författare)
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Countermeasures against alkali-related problems during combustion of biomass in a circulating fluidized bed boiler
- 2008
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Ingår i: Chemical Engineering Science. - : Elsevier. - 0009-2509 .- 1873-4405. ; 63:21, s. 5314-5329
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this work was to study different ways to mitigate alkali-related problems during combustion of biomass in circulating fluidized beds. Wood chips and wood pellets were fired together with straw pellets, while the tendency to agglomerate and form deposits was monitored. In addition to a reference case, a number of countermeasures were applied in related tests. Those were addition of elemental sulphur, ammonium sulphate and kaolin to a bed of silica sand, as well as use of olivine sand and blast-furnace slag as alternative bed materials. The agglomeration temperature, composition and structure of bed-ash samples were examined. The flue-gas composition, including gaseous alkali chlorides, was measured in the hot flue gases and in the stack. Particles in the flue gas were collected and analysed for size distribution and composition. Deposits were collected on a probe in hot flue gases and their amount and composition were analysed. Addition of kaolin was found to be the best method to counteract the agglomeration problem. The deposition problem is effectively counteracted with addition of ammonium sulphate, while kaolin is too expensive to be used commercially against deposits, and sulphur is less effective than ammonium sulphate.
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| 4. |
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| 5. |
- Davidsson, K.O., et al.
(författare)
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Effect of Cofiring Coal and Biofuel with sewage Sludge on Alkali Problems in a Circulating Fluidized Bed Boilder
- 2007
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Ingår i: Energy & Fuels. - : American Chemical Society. - 0887-0624 .- 1520-5029. ; 21:6, s. 3180-3188
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Tidskriftsartikel (refereegranskat)abstract
- Cofiring experiments were performed in a 12 MW circulating fluidized bed boiler. The fuel combinations were biofuel (wood+straw), coal+biofuel, coal+sewage sludge+biofuel, and sewage sludge+biofuel. Limestone or chlorine (PVC) was added in separate experiments. Effects of feed composition on bed ash and fly ash were examined. The composition of flue gas was measured, including on-line measurement of alkali chlorides. Deposits were collected on a probe simulating a superheater tube. It was found that the fuel combination, as well as addition of limestone, has little effect on the alkali fraction in bed ash, while chlorine decreases the alkali fraction in bed ash. Sewage sludge practically eliminates alkali chlorides in flue gas and deposits. Addition of enough limestone to coal and sludge for elimination of the SO2 emission does not change the effect of chlorine. Chlorine addition increases the alkali chloride in flue gas, but no chlorine was found in the deposits with sewage sludge as a cofuel. Cofiring of coal and biofuel lowers the alkali chloride concentration in the flue gas to about a third compared with that of pure biofuel. This is not affected by addition of lime or chlorine. It is concluded that aluminum compounds in coal and sludge are more important than sulfur to reduce the level of KCl in flue gas and deposits.
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| 6. |
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| 7. |
- Davidsson, K. O., et al.
(författare)
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The Pyrolysis Kinetics of a Single Wood Particle
- 2008
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Ingår i: Progress in Thermochemical Biomass Conversion. - Oxford, UK : Wiley-Blackwell. - 9780470694954 ; , s. 1129-1142
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Experimental results from birchwood and pinewood pyrolysis in a new single particle reactor are presented. Apparent lunetic parameters for the mass-loss of wood particles (5-800 mg) at temperatures from 300 to 860°C are determined. Kinetic parameters for the evolution of CO, CO2, H2O, H2 and CH4, are also established. The drylng process was examined and it was found that drying and pyrolysis increasingly overlap in time as temperature rises and that the overlap is substantial above 450 °C.
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| 8. |
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| 9. |
- Tchoffor Atongka, Placid, 1981, et al.
(författare)
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Production of Activated Carbon within the Dual Fluidized Bed Gasification Process
- 2015
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 54:15, s. 3761-3766
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Tidskriftsartikel (refereegranskat)abstract
- A key step in the production of clean energy from biomass gasification is the cleaning of the product gas to remove impurities, such as tars, H2S, HCl, particulates, and alkali compounds. Some gas cleaning systems employ activated carbon (AC), with Brunauer-Ernmett-Teller (BET) surface areas in the range of 800-1300 m(2)/g. Because the operational conditions for the production of AC are similar to those applied in the gasification chamber of a dual fluidized bed gasifier, the possibility to produce AC within the dual fluidized bed gasification (DFBG) process was investigated in the present work. Wood pellets were gasified with steam in a fluidized bed reactor at 800 and 840 degrees C. Part of the unconverted char from this process was further activated with steam in a fixed bed reactor at 850 degrees C. The results obtained indicate that if >= 44% of the char that results from the devolatilization of the wood pellets is gasified (the extent of char conversion), the unconverted char acquires a BET surface area >900 m(2)/g, which makes it suitable for use in gas cleaning processes. Achieving this extent of char conversion in the gasification chamber of industrial dual fluidized gasification plants would remove the need and cost for a second reactor for further activation of the unconverted char. The cost of the produced activated carbon (AC) has been estimated as being 15-fold lower than that of commercially available AC. This suggests that the production of AC as part of the dual fluidized bed gasification process would be cost-effective.
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