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- Johansson, Andreas, et al.
(author)
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Dynamics of furnace processes in a CFB boiler
- 2007
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In: Chemical Engineering Science. - : Elsevier BV. - 0009-2509 .- 1873-4405. ; 62:1-2, s. 550-560
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Journal article (peer-reviewed)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.
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| 2. |
- Johansson, Andreas, et al.
(author)
-
Solids back-mixing in CFB boiler
- 2007
-
In: Chemical Engineering Science. - : Elsevier. - 0009-2509 .- 1873-4405. ; 62, s. 561-573
-
Journal article (peer-reviewed)abstract
- The furnaces of circulating fluidized bed (CFB) boilers have substantially lower height-to-width ratios than most of the laboratory CFB risers from which experimental investigations on riser fluid dynamics are published. Therefore, it is uncertain whether literature expressions for prediction of the distribution of solids and the thickness of the wall layers, derived from investigations in laboratory units, are applicable to boilers. In this work, data from laboratory units are compared with boiler data, and the accuracy of literature expressions for prediction of solids distribution, solids flow and wall layer thickness is reviewed. It is found that the height-to-width ratio does have a significant impact on the flow properties. Correlations based on experiments in laboratory units show poor agreement when applied to boilers. Modifications of literature expressions for prediction of solids flow and solids distribution are proposed, and an improved expression is formulated for prediction of the thickness of the wall layer.
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