Experimental Investigation on NOx Reduction by Primary Measures in Biomass Combustion: Straw, Peat, Sewage Sludge, Forest Residues and Wood Pellets

Abstract

An experimental investigation was carried out to study the NO x formation and reduction by primary measures for five types of biomass (straw, peat, sewage sludge, forest residues/Grot, and wood pellets) and their mixtures. To minimize the NO x level in biomass-fired boilers, combustion experiments were performed in a laboratory scale multifuel fixed grate reactor using staged air combustion. Flue gas was extracted to measure final levels of CO, CO 2 , C x H y , O 2 , NO, NO 2 , N 2 O, and other species. The fuel gas compositions between the first and second stage were also monitored. The experiments showed good combustion quality with very low concentrations of unburnt species in the flue gas. Under optimum conditions, a NO x reduction of 50-80% was achieved, where the highest reduction represents the case with the highest fuel-N content. The NO x emission levels were very sensitive to the primary excess air ratio and an optimum value for primary excess air ratio was seen at about 0.9. Conversion of fuel nitrogen to NO x showed great dependency on the initial fuel-N content, where the blend with the highest nitrogen content had lowest conversion rate. Between 1-25% of the fuel-N content is converted to NO x depending on the fuel blend and excess air ratio. Sewage sludge is suggested as a favorable fuel to be blended with straw. It resulted in a higher NO x reduction and low fuel-N conversion to NO x . Tops and branches did not show desirable NO x reduction and made the combustion also more unstable. N 2 O emissions were very low, typically below 5 ppm at 11% O 2 in the dry flue gas, except for mixtures with high nitrogen content, where values up to 20 ppm were observed. The presented results are part of a larger study on OPEN ACCESSEnergies 2012, 5 271 problematic fuels, also considering ash content and corrosive compounds which have been discussed elsewhere.

Air staging to reduce emissions from energy crop combustion in small scale applications

“…Previously, it had been suggested that the combustion of herbaceous biomass should be confined to larger combustion plants [3]. However, recent research work has shown that air staging can be successfully used to reduce emissions from the combustion of problematic fuels in small scale combustion systems [11,17]. Consequently, three air staging strategies (adjustment of primary air, adjustment of total excess air and adjustment of combustion temperature) were studied as potential means to reduce gaseous and particulate emissions from the combustion of four energy crops of relevance to Irish conditions (miscanthus, willow, tall fescue and cocksfoot) and wood.…”

Extensive Operating Experiments on the Conversion of Fuel-Bound Nitrogen into Nitrogen Oxides in the Combustion of Wood Fuel

“…A similar trend was observed in Pleckaitine and Buinevicius's model (2011) [8], according to which conversion was expressed by the equation X NOx = 11.312 × (N K ) −0.6196 (where N K is the nitrogen content in fuel, expressed as a percentage). Another graphically similar shape was produced by laboratory measurements of biomass combustion in an electrically heated reactor, where obtained values were considerably lower than the generally recognized values [24]. It follows from this that the results of laboratory modeled experiments cannot always be used for accurate calculations in real practice.…”

Fire Performance of Sandwich Panels in a Modified ISO 13784-1 Small Room Test: The Influence of Increased Fire Load for Different Insulation Materials

“…Wood itself has very low nitrogen content (the three main components, cellulose, hemicellulose and lignin, contain no nitrogen at all). The nitrogen content of dry wood has been quantified [24] as 0.11%, thus the burning wooden crib would not be expected to contribute significantly to the HCN yield.…”