Biomass combustion research studying the impact factors of NOx formation and reduction

T. Sereika¹,*, K. Buinevičius¹,², E. Puida¹ and A. Jančauskas²

¹ Kaunas University of Technology, Faculty of Mechanical Engineering and Design, Department of Thermal and Nuclear Energy, Studentų st. 56, LT–51424 Kaunas, Lithuania
²UAB ‘Enerstena’ Centre of Research and Development, Partizanų st. 89, LT–50312 Kaunas, Lithuania
*Correspondence: titas.sereika@ktu.edu

Abstract:

Aim of this study was to identify potential NO_x reduction factors and determine impact of nitrogen quantity in the fuel, during combustion process and conversion to nitrogen oxides. Experiments were performed using moving grate biofuel boiler with two staged air inlets, which represents industrial boiler operating principles. Combustion was performed using agricultural wastes: grain middlings, buckwheat hulls, corn pellets and mixtures with wood pellets. These types of fuels in combustion process generate about two times bigger amount of nitrogen oxides than wood pellets. The result of research shows, that the amount of nitrogen in the fuel has the greatest impact for NO_x generation compared to all NO_x formation forms. It was found that a smaller quantity of nitrogen, has bigger impact factor, than higher quantity of nitrogen, in biomass, for NO_x formation during combustion. It was noticed that during combustion process the amount of carbon monoxide is inversely proportional to NO_x values. The impact factor of nitrogen conversion to NO_x and CO potential of reducing NO_x is presented by formula in this paper.

Key words:

Comparison of technologic parameters of pellets and other solid fuels produced from various raw materials

T. Ivanova¹, M. Kaválek¹,*, B. Havrland¹, M. Kolaříková¹ and P. Skopec²

¹Czech University of Life Sciences Prague, Faculty of Tropical AgriSciences, Kamycka 129, CZ16521 Prague 6 – Suchdol, Czech Republic
²Czech Technical University in Prague, Faculty of Mechanical Engineering, Zikova 1903/4, CZ16636 Prague 6, Czech Republic *Correspondence: michal.kavalek@seznam.cz

Abstract:

The article relates results of experiments and problem studies, the main goal of which was comparing four alternatives of solid biofuels suitable for heating private houses by low-power boilers. The results were obtained by burning of selected biofuels in an automatic pellet boiler specifically designed for combustion of pelletized fuels with high ash content. The emissions were set up related to the mass of burnt fuels and to the fuels’ net calorific value (specific emissions), they were measured and analysed. Based on the emission concentration measurements and stoichiometric calculations, the fuel gas emissions’ properties and boiler efficiency were compared at a range of power outputs of 7.5 kW, 12.5 kW and 18.5 kW. With regard to fuel properties and boiler outputs, the emissions of carbon monoxide (CO) were determined as well as emissions of nitrogen oxides (NOx) and sulfur dioxide (SO2) were measured and compared too. The results permitted to formulate conclusions that the wood pellets were having the lowest values of measured emissions, whereby Jatropha seed cakes showed several times higher emissions in comparison with emissions from wood pellets, oil palm shells and wheat straw pellets, where the last one is a typical representative of the agricultural biomass with relatively high nitrogen content and as was shown higher emissions of NOX as compared to wood pellets. Oil palm shells measured emissions were relatively similar to wood pellets emissions, especially concerning emissions of SO2 and CO. All tested materials were having very low combustible sulphur contents and therefore the specific SO2 emissions were negligible at all these fuels. A very important finding was that the amount of emissions was dependent on boiler output, where with the output decreasing the amount of emissions was growing. The other linkage – dependence of the boiler efficiency on power output was also proved in the present paper.

Key words:

biomass combustion., emissions., Jatropha seed cake, oil palm shell, wheat straw, wood pellet