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1. School of Pure and Applied Natural Sciences, University of Kalmar, Sweden

2. TPS Termiska processer AB, Nyköping, Sweden.

3. School of Technology and Design, Växjö University, Sweden.

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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.

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

1. Department of Mechanical Engineering, University of La Plata

Department of Mechanical Engineering, Faculty of Engineering, University of La Plata, La Plata, Argentina

2. Dept. Mechanical Engineering, Vrije Universiteit Brussel

Research Group Fluid Mechanics and Thermodynamics, Dept. Mechanical Engineering, Vrije Universiteit Brussel, Brussels, Belgium

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The computation of the Beta PDF is discussed and algorithms are described which permit calculation of the PDF over the full range of its parameters without recourse to approximations or polynomial expansions. This is achieved by giving simple rules for the treatment of the trivial cases and a new algorithm for the general cases, particularly for the cases where the PDF becomes infinity at the extremes of the range. The problems of underflow and overflow when performing the calculations on a digital computer are also addressed, and a general prescaling procedure is presented which overcomes these problems. It is shown that the new algorithms perform more efficiently than commercial mathematical packages.

CARS and Heat Flux Measurements in Regenerative and Conventional Industrial-Scale Burners

P. M. Hughes¹, R. J. Lacelle¹, A. Idris¹, M. Legere¹, D. Percy¹, J. Wong¹, T. Parameswaran¹

1. CANMET

CANMET Energy Technology Centre, Natural Resources Canada Ottawa, Ontario Canada

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There has been an increased interest in high temperature air combustion provided by the current regenerative burners for many industrial processes. Initially, the interest was focused on processes in the steel industry; however, because of the high efficiency, low emissions and even heat distribution, this technology is envisioned for other industrial applications as well. To this end, a detailed characterization of the regenerative burner flame is required to understand the combustion performance and to develop the models used to simulate different industrial furnaces. The measurements discussed in this paper come from an ongoing project to compare conventional and regenerative burner flames and their application to different industrial processes. This paper describes the in-situ temperature, composition and radiative flux measurements taken in these flames.

The flames studied here are produced by a conventional low NOx burner with and without pre-heat and a self regenerative burner. The burners were operated at 200 kW with an excess oxygen of between 4 and 5%. The flame temperatures were measured with the laser-based CARS technique and suction pyrometer. The radiant flux at the wall was measured with a 2 pi and a narrow angle radiometer. A thermal load was applied to the combustion products with the intent of simulating an industrial process. The temperature measurements show that the regenerative flame has a lower mean temperature and an even distribution throughout the furnace. The fluctuating component of temperature is shown to be significantly smaller for the regenerative flame as compared to the conventional flames. The radiant properties of the flames are different as well. The regenerative flame is shown to have a slightly higher emissivity than does the conventional flame. The incident radiant flux from the regenerative flame is much higher than that of the conventional flame (with and without preheat).

Flameless, HITAC, regenerative, CARS, emissivity, radiative heat flux, heat flux

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