Latest Papers

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Article Number 201002, June 2010

Reuse of Partially Sulphated CFBC Ash as an SO2 Sorbent

Yinghai Wu¹, Lufei Jia¹, Edward J. Anthony¹, Marianna Nobili², Antonio Telesca², Fabio Montagnaro³

(PDF article, 0.94 MB)

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Abstract:

Ashes produced from fluidized bed combustors (FBC) burning high-sulphur fuels often contain 20 – 30 % unreacted CaO because of the limestone added to remove SO2 in situ. This paper presents the results from experiments into reactivating partially sulphated FBC ash (both bed ash and fly ash) with liquid water, steam and sodium carbonate. The water- or steam-hydrated ashes were subsequently re-sulphated in a thermogravimetric analyzer (TGA) with simulated flue gas. The TGA results show that, while liquid water and steam successfully hydrate and reactivate the unreacted CaO in the bed ash, the treated ashes sulphated to widely different extents. Attempts to reactivate fly ash with hydration failed, although fly ash by itself is extremely reactive. A pilot-scale mini-circulating FBC (CFBC) was also used to evaluate the results of reactivation on the bed ash by hydrating with liquid water and admixtures of inorganic salt (Na2CO3) in the form of either powder or solution. When the treated ash was re-injected into the combustor with the fuel, the effect on SO2 removal efficiency was negligible if Na2CO3 was added as powder. Doping with aqueous solution resulted in enhanced SO2 removal; however, the extent was lower than the level achieved if only water hydration was employed. Increasing the amount of water (from 10 % to 30 %) to reactivate the ash did not improve the sulphur capture capacity in the mini-CFBC. Overall, this study suggests that the most practical way for re-use of the partially sulphated bed ash as a sulphur sorbent is reactivation by water. A proposal for utilization of the fly ash in an economically reasonable way is also discussed.

Keywords:

FBC, CFBC ash, reactivation, hydration, sulphation

* Corresponding Author:

Yinghai Wu CanmetENERGY, 1 Haanel Drive, Ottawa, Ontario, K1A1M1, Canada Tel: +1 613 943 7773; Fax: +1 992 9335;

Article Number 201001, April 2010

On the Potential of Flameless Oxidation to Reduce NOx Emissions from Pulverized Coal Combustion

D. Ristic¹, A. Schuster¹, G. Scheffknecht¹

(PDF article, 0.55 MB)

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Abstract:

This paper examines the potential of flameless oxidation (FLOX®) to reduce NOx emissions from pulverized coal combustion. The experiments were carried out at a 20 kWt experimental furnace at the University of Stuttgart. Systematic parameter studies of the air ratio at the burner, the coal type and the secondary air velocity were made for flameless oxidation and flame combustion. The results of these tests are discussed and the potential of flameless oxidation technology to reduce NOx emissions from pulverized coal combustion is presented. Experiments have shown a considerable NOx reduction capability with the current FLOX®-coal burner design. These reductions depend mainly on the burner air ratio and the coal type.

Keywords:

Flameless oxidation, coal combustion, NOx emissions.

* Corresponding Author:

D. Ristic Dragisa Ristic Institute of Process Engineering and Power Plant Technology (IVD), University of Stuttgart, Pfaffenwaldring 23, 70569 Stuttgart, GERMANY. Tel.: +49-(0)711/685-68922 Fax: +49-(0)711/685-63491

Article Number 200903, August 2009

Emissions performance of a 40 MW pulverised wood fired boiler

Olof Stålnacke^1,2, Björn Zethræus³

(PDF article, 4.32 MB)

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Abstract:

In this paper we study the characteristics of combustion in a 40 MW pulverised wood fired boiler in order to find measures that would enhance its performance in regards to the emissions of carbon monoxide (CO) and nitrogen oxides (NOx), as well as the amount of unburned carbon in the ash. The latter has historically been observed to be high, which led to this study. The main flows in the furnace were studied with a Plexiglas model. The residence time, temperature, oxygen level, mixing rate and the fuel’s particle size distribution were measured and correlated to the responses of the boiler performance. NOx was found to be formed mainly by conversion of fuel nitrogen as is common for biomass combustion. We conclude that CO burnout was limited by insufficient mixing and CO production by entrained particles in the combustion chamber exhaust. The reason for the high amount of unburned carbon in the ash was that the fuel particles were too large. Our results are in agreement with the flow studied in the Plexiglas model. To improve mixing and the staging of the combustion, we recommend changing the design of the secondary air inlets. Our study predicts that both NOx and CO emissions can be lowered by taking this measure.

Keywords:

Pulverised wood combustion, Carbon monoxide, Nitrogen oxides, Unburned carbon, Ash

* Corresponding Author:

Olof Stålnacke TPS Termiska processer AB Box 624 SE-611 10 Nyköping Sweden. TEL: +46 8 535 248 10 FAX: + 46 155 26 30 52