Effect of Excess Air Ratio and Temperature on NOx Emission from Grate Combustion of Biomass in the Staged Air Combustion Scenario

The combustion of biomass, in this case demolition wood, has been investigated in a grate combustion multifuel reactor. In this work a temperature range of 850-1000 degrees C is applied both for staged air combustion and nonstaged combustion of biomass to investigate the effects of these parameters on the emission levels of NOx, N(2)O, CO, hydrocarbons (C(x)H(y)),) and different other components. The composition of the flue gas is measured by four advanced continuous gas analyzers including gas chromatograph (GC), two Fourier transform infrared (FTIR) analyzers, and a conventional multispecies gas analyzer with fast response time. The experiments show the effects of staged air combustion, compared to nonstaged combustion, on the emission levels clearly. A NOx reduction of up to 85% is reached with staged air combustion. An optimum primary excess air ratio of 0.8-0.95 is found as a minimizing parameter for the NOx emissions for staged air combustion. Air staging has, however, a negative effect on N(2)O emissions. Even though the trends show a very small reduction in the NOx level as temperature increases in nonstaged combustion, the effect of temperature is not significant for NOx and C(x)H(y), neither in staged air combustion or nonstaged combustion, while it has a great influence on the N(2)O and CO emissions, with decreasing levels with increasing temperature

NOx emission reduction by staged combustion in grate combustion of biomass fuels and fuel mixtures

NOx and N2O emissions have been investigated for different pelletized biomass fuels and fuel mixtures thereof both with and without air staging in a grate fired multi-fuel reactor. The fuels investigated are wood, demolition wood and coffee waste, and selected mixtures of these. The multi-fuel reactor was operated at close to constant operating conditions due to impactor (ELPI) measurements, with a total excess air ratio of about 1.6, and a primary excess air ratio of about 0.8 in the air staging experiments. The reactor set point temperature was held constant at 850 degrees C. NOx emission levels as a function of air supply mode and fuel nitrogen content are reported, showing a large NOx reduction potential, up to 91% and corresponding to less than 20 ppm NOx at 11% O-2 for a fuel containing about 3 wt.% fuel-N, using air staging. The effect on N2O, however, is adverse at the selected set point temperature and optimum primary excess air ratio for NOx reduction. The effect of fuel mixing and fuel nitrogen content on the conversion of fuel nitrogen to NOx is also reported and discussed. Fuel mixing has a positive influence on the NOx emission level, but a negative influence on the overall conversion factor for fuel-N to NOx and N2O

The effect of kaolin on the combustion of demolition wood under well-controlled conditions

In an attempt to look at means for reduction of corrosion in boilers, combustion experiments are performed on demolition wood with kaolin as additive. The experiments were performed in a multi-fuel reactor with continuous feed of pellets and by applying staged air combustion. A total characterization of the elemental composition of the fuel, the bottom ash and some particle size stages of fly ash was performed. This was done in order to follow the fate of some of the problematic compounds in demolition wood as a function of kaolin addition and other combustion-related parameters. In particular chlorine and potassium distribution between the gas phase, the bottom ash and the fly ash is reported as a function of increased kaolin addition, reactor temperature and air staging. Kaolin addition of 5 and 10% were found to give the least aerosol load in the fly ash. In addition, the chlorine concentration in aerosol particles was at its lowest levels for the same addition of kaolin, although the difference between 5 and 10% addition was minimal. The reactor temperature was found to have a minimal effect on both the fly ash and bottom ash properties

The effect of peat ash addition to demolition wood on the formation of alkali, lead and zinc compounds at staged combustion conditions

Combustion experiments were performed in a multi-fuel reactor with continuous feed of pellets by applying staged air combustion. Total characterization of the elemental composition of the fuel, the bottom ash and some particle size stages of fly ash was performed. This was done in order to follow the fate of some of the problematic compounds in demolition wood as a function of peat-ash addition and other combustion related parameters. A method was developed to estimate the composition and speciation of the salt part of aerosols based on SEM/EDX analysis. The results show that the concentrations of zinc and lead account for 40-50% of the salts produced for the small particles (0.093 mu m) and up to 90% for the larger particles (1.59 mu m). A considerable part of these metals are chemically bound to chlorides and sulfates together with potassium and sodium indicating extensive volatilization of zinc and lead. The experiments show that the reactions of potassium, zinc and lead are the most affected. This gives rise to higher concentrations of zinc and lead in the aerosols. The chloride content in the aerosols decreases with increased peat ash addition. This will have an inhibiting effect on corrosion, but the higher Zn and especially Pb concentrations will lead to a lower first melting point of the aerosol particles. This may promote deposition and cause corrosion

Ash related behaviour in staged and non-staged combustion of biomass fuels and fuel mixtures

The fate of selected elements (with focus on the important players in corrosion i.e. Na, K, Pb, Zn, Cl and S) are investigated for three biomasses (wood, demolition wood and coffee waste) and six mixtures of these as pellets both with and without air staging in a laboratory reactor. In order to get a complete overview of the combustion products, both online and offline analytical methods are used. Information is collected about: flue gas composition, particle (fly ash) size distribution and composition, bottom ash composition and melting properties. The main findings are: (1) complex interactions are taking place between the mixed fuels during combustion; (2) the mode of occurrence of an element as well as the overall structure of the fuel are important for speciation; (3) the pelletisation process, by bringing chemical elements into intimate contact, may affect partitioning and speciation; (4) staging and mixing might simultaneously have positive and negative effects on operation; (5) staging affects the governing mechanisms of fly ash (aerosols) formation

Host range of enterococcal vanA plasmids among Gram-positive intestinal bacteria

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