Unburned carbon in the circulating fluidised bed boiler fly ash

2011 ◽  
Vol 32 (4) ◽  
pp. 255-266 ◽  
Author(s):  
Rafał Kobyłecki
Keyword(s):  
Fly Ash ◽  
Separation Efficiency ◽  
Unburned Carbon ◽  
Fuel Particle ◽  
Fluidised Bed ◽  
Bed Temperature ◽  
Grid Design ◽  
Cfbc Fly Ash ◽  
Boiler Fly Ash ◽  
Circulating Fluidised Bed

Unburned carbon in the circulating fluidised bed boiler fly ash The paper describes the results of various actions and industrial tests conducted in order to decrease the content of unburned carbon in the fly ash of a circulating fluidised bed combustor (CFBC). Several attempts to improve the situation were made and the effects of several parameters on the unburned carbon content in the fly ash were investigated (e.g. bed temperature, cyclone separation efficiency, fuel particle size distribution, boiler hydrodynamics, grid design, and fuel data). Unfortunately, no satisfactory solution to these problems was found. Probably, apart from attrition and char fragmentation, additional factors also contributed to the formation of unburned carbon in the CFBC fly ash.

"Recent Patents on the Triboelectrostatic Separation of Fly Ash"

2019 ◽  
Vol 13 ◽  
Author(s):  
Haisheng Li ◽  
Wenping Wang ◽  
Yinghua Chen ◽  
Xinxi Zhang ◽  
Chaoyong Li
Keyword(s):  
Fly Ash ◽  
Power Plants ◽  
High Efficiency ◽  
Separation Efficiency ◽  
High Reliability ◽  
Operating Conditions ◽  
Security Requirements ◽  
Unburned Carbon ◽  
Efficient Operation ◽  
Triboelectrostatic Separation

Background: The fly ash produced by coal-fired power plants is an industrial waste. The environmental pollution problems caused by fly ash have been widely of public environmental concern. As a waste of recoverable resources, it can be used in the field of building materials, agricultural fertilizers, environmental materials, new materials, etc. Unburned carbon content in fly ash has an influence on the performance of resource reuse products. Therefore, it is the key to remove unburned carbon from fly ash. As a physical method, triboelectrostatic separation technology has been widely used because of obvious advantages, such as high-efficiency, simple process, high reliability, without water resources consumption and secondary pollution. Objective: The related patents of fly ash triboelectrostatic separation had been reviewed. The structural characteristics and working principle of these patents are analyzed in detail. The results can provide some meaningful references for the improvement of separation efficiency and optimal design. Methods: Based on the comparative analysis for the latest patents related to fly ash triboelectrostatic separation, the future development is presented. Results: The patents focused on the charging efficiency and separation efficiency. Studies show that remarkable improvements have been achieved for the fly ash triboelectrostatic separation. Some patents have been used in industrial production. Conclusion: According to the current technology status, the researches related to process optimization and anti-interference ability will be beneficial to overcome the influence of operating conditions and complex environment, and meet system security requirements. The intelligent control can not only ensure the process continuity and stability, but also realize the efficient operation and management automatically. Meanwhile, the researchers should pay more attention to the resource utilization of fly ash processed by triboelectrostatic separation.

scholarly journals MINERALOGICAL AND CHEMICAL COMPOSITION OF CFB FLY ASH DERIVED FROM CO-COMBUSTION OF XYLITE AND BIOMASS

2007 ◽  
Vol 40 (2) ◽  
pp. 859
Author(s):  
N. Koukouzas ◽  
J. Hämäläinen ◽  
D. Papanikolaou ◽  
A. Tourunen ◽  
T. Jäntti
Keyword(s):  
Fly Ash ◽  
Mineralogical Composition ◽  
Fluidised Bed ◽  
Chemical Analyses ◽  
X Ray Diffraction ◽  
Mineral Phase ◽  
X Ray ◽  
Mineral Phases ◽  
Circulating Fluidised Bed ◽  
Different Parts

The chemical and mineralogical composition of fly ash samples collected from different parts of two Circulating Fluidised Bed (CFB) facilities has been investigated. The fuels used, were Greek xylite/suhbituminous coal (from the Fiorina basin), Polish coal (from the Catowice region - Poland) and wood chips (Swedish conifer). The characterisation of the fly ash samples included chemical analyses, particle size distribution and X-ray diffraction. According to the chemical analyses the produced fly ashes are rich in CaO. Moreover, S1O2 is the dominant oxide in fly ash with Al203 and Fe2Oi found in considerable quantities. Finally, results obtained by XRD showed that the major mineral phase of fly ash is quartz, while other mineral phases that are occurred are maghemite, hematite, periclase, rutile, gehlenite and anhydrite, while the aforementioned mineral phases were identified by scanning electron microscope (SEM).

Bed-To-Wall Heat Transfer in a Supercritical Circulating Fluidised Bed Boiler

2014 ◽  
Vol 35 (2) ◽  
pp. 191-204 ◽  
Author(s):  
Artur Błaszczuk ◽  
Wojciech Nowak ◽  
Szymon Jagodzik
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Pressure Measurements ◽  
Fluidised Bed ◽  
Cfb Boiler ◽  
Suspension Density ◽  
Bed Temperature ◽  
Circulating Fluidised Bed ◽  
The Heat Transfer Coefficient

Abstract The purpose of this work is to find a correlation for heat transfer to walls in a 1296 t/h supercritical circulating fluidised bed (CFB) boiler. The effect of bed-to-wall heat transfer coefficient in a long active heat transfer surface was discussed, excluding the radiation component. Experiments for four different unit loads (i.e. 100% MCR, 80% MCR, 60% MCR and 40% MCR) were conducted at a constant excess air ratio and high level of bed pressure (ca. 6 kPa) in each test run. The empirical correlation of the heat transfer coefficient in a large-scale CFB boiler was mainly determined by two key operating parameters, suspension density and bed temperature. Furthermore, data processing was used in order to develop empirical correlation ranges between 3.05 to 5.35 m·s-1 for gas superficial velocity, 0.25 to 0.51 for the ratio of the secondary to the primary air, 1028 to 1137K for bed temperature inside the furnace chamber of a commercial CFB boiler, and 1.20 to 553 kg·m-3 for suspension density. The suspension density was specified on the base of pressure measurements inside the boiler’s combustion chamber using pressure sensors. Pressure measurements were collected at the measuring ports situated on the front wall of the combustion chamber. The obtained correlation of the heat transfer coefficient is in agreement with the data obtained from typical industrial CFB boilers.

scholarly journals Design of High Volume CFBC Fly Ash Based Calcium Sulphoaluminate Type Binder in Mixtures with Ordinary Portland Cement

Materials ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 5798
Author(s):  
Peeter Paaver ◽  
Oliver Järvik ◽  
Kalle Kirsimäe
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Portland Cement ◽  
Building Materials ◽  
Ordinary Portland Cement ◽  
High Volume ◽  
Cementitious Materials ◽  
Fluidised Bed ◽  
Complete Replacement ◽  
Cfbc Fly Ash

Growing concerns on global industrial greenhouse gas emissions have boosted research for developing alternative, less CO2 intensive binders for partial to complete replacement of ordinary Portland cement (OPC) clinker. Unlike slag and pozzolanic siliceous low-Ca class F fly ashes, the Ca- and S-rich class C ashes, particularly these formed in circulating fluidised bed combustion (CFBC) boilers, are typically not considered as viable cementitious materials for blending with or substituting the OPC. We studied the physical, chemical-mineralogical characteristics of the mechanically activated Ca-rich CFBC fly ash pastes and mortars with high volume OPC substitution rates to find potential alternatives for OPC in building materials and composites. Our findings indicate that compressive strength of pastes and mortars made with partial to complete replacement of the mechanically activated CFBC ash to OPC is comparable to OPC concrete, showing compared to OPC pastes reduction in compressive strength only by <10% at 50% and <20% at 75% replacement rates. Our results show that mechanically activated Ca-rich CFBC fly ash can be successfully used as an alternative CSA-cement type binder.

Effects of pressure on flow regimes transition velocities and bubble properties in a pilot-scale pressurised circulating fluidised bed

2021 ◽  
Vol 410 ◽  
pp. 128438
Author(s):  
Xiaoli Zhu ◽  
Pengfei Dong ◽  
Zhiping Zhu ◽  
Raffaella Ocone ◽  
Wuqiang Yang ◽  
...  
Keyword(s):  
Flow Regimes ◽  
Pilot Scale ◽  
Fluidised Bed ◽  
Circulating Fluidised Bed ◽  
Bubble Properties

scholarly journals Recovery of Cenospheres and Fine Fraction from Coal Fly Ash by a Novel Dry Separation Method

Energies ◽  
2020 ◽  
Vol 13 (14) ◽  
pp. 3576
Author(s):  
Jan Wrona ◽  
Witold Żukowski ◽  
Dariusz Bradło ◽  
Piotr Czupryński
Keyword(s):  
Fly Ash ◽  
Coal Fly Ash ◽  
Fine Fraction ◽  
Free Fall ◽  
Raw Material ◽  
Fluidised Bed ◽  
Air Chamber ◽  
Pneumatic Separation ◽  
Bed Separation ◽  
Separation Product

Aluminosilicate microspheres are a valuable fraction of coal fly ash with diverse applications due to their low density. Currently, there is no efficient and ecologically rational method of cenosphere recovery from fly ash. A combination of dry methods for the recovery of both fine ash particles and aluminosilicate microspheres from coal fly ash is presented. It is comprised of fluidised bed separation followed by screening and pneumatic separation in a free-fall air chamber. Fluidised bed separation was assisted by a mechanical activator to prevent agglomeration. This step reduced the portion of material that required further treatment by 52–55 wt.%, with the recovery of microspheres exceeding 97%. Then, the concentrates were individually subjected to pneumatic separation. The final separation product for the fly ash containing 0.64 wt.% cenospheres was a cenosphere concentrate that constituted about 17 wt.% of the initial fly ash. The recovery of cenospheres was around 81%. Usage of a combination of dry methods allowed for maintaining almost 83 wt.% of the raw material in its dry form. Furthermore, the produced fly ash grain fractions could be used for different industrial purposes.

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