Pulverized coal combustion: the influence of flame temperature and coal composition on thermal and fuel NOx

Journal ArticleA laboratory combustor was used to investigate the factors that influence the conversion of fuel nitrogen in coal during coal combustion. Fuel NO was isolated by experimentation utilizing Argon / Oxygen / Carbon Dioxide mixtures as the oxidant, and care was taken to compare cases with air at matched conditions. For both well mixed and slowly mixed flame types, fuel NO contributed over 75% of the total NO emissions for all conditions examined. Fuel NO was insensitive to temperature changes except when the adiabatic flame temperatures were above 2480°K (4000°F). At the highest adiabatic flame temperature, 2580°K (4200°F), a 10% increase in fuel NO was observed

Pulverized coal combustion: NOx formation mechanisms under fuel rich and staged combustion conditions

Journal ArticleA 2 Kg/h pulverized fuel one dimensional flame combustor was used to determine time resolved NO profiles under fuel rich and staged combustion conditions. Seven solid fuels, including two coal chars, were investigated. Results show that at all fuel rich conditions NO is formed rapidly and then is slowly destroyed

Influence of coal composition on the fate of volatile and char nitrogen during combustion

Journal ArticleFifty coals from North America, Europe, Asia, South Africa and Australia were burned in a 21 kW, refractory-lined tunnel furnace to determine the influence of coal properties on the fate of volatile and char nitrogen. Excess air fuel NO emissions (as determined by combustion in Ar/02/C02) ranged from 415 ppm to 1380 ppm with a premixed burner. These results correlated with total fuel nitrogen, inert pyrolysis HCN yield, and non-volatile nitrogen content, rather than with the geographic origin of the coal. Minimum staged NO emissions (at optimum first stage stoichiometry) ranged from 140 ppm to 380 ppm. Detailed in-flame measurements indicated that as first stage stoichiometry (air/fuel) was reduced, first stage NO formation decreased, but was ultimately offset by increases in oxidizable gaseous nitrogen species and solid phase nitrogen retention. TFN (NH3 + NO + HCN) generally increased with increasing fuel nitrogen and the species distribution was dependent upon coal rank. In general, HCN was greater than NH3 with bituminous coals, but less than NH3 with subbituminous and lignite coals. Second stage TFN conversion to exhaust NO decreased as the TFN distribution was shifted in favor of HCN and NH3. Char nitrogen conversion was generally low (less than 20 percent). Exhaust emissions were correlated in terms of the gas phase TFN and the char nitrogen entering the second stage

Biomass combustion: relationship between pollutant formation and fuel composition

Journal ArticleA 65-kW refractory-walled reactor was used to study biomass combustion under conditions typical of the suspension-burning phase in a spreader-stoker-fired boiler. Isothermal combustion data and nitric oxide (NO) emission rates were obtained as a function of temperature, local oxygen concentration, and vertical velocity for sized biomass fuels. Two softwoods, a hardwood, and a North Carolina peat were studied

Investigation of first- and second-stage variables on control of NOx emissions using staged combustion in a pulverized coal wall-fired furnace

Journal ArticleRecent tests on an EPA 1- to 1.5 x 106 Btu/hr pilot-scale pulverized coal furnace show that N0X emissions of 100 ppm to 150 ppm (zero percent 02) are achievable with the use of two-stage combustion. Comparable N0X emission levels were obtained with three different coal types fired in either the single-wall or tangential configuration

Mechanisms of NOx formation and control: alternative and petroleum-derived liquid fuels

Journal ArticlePetroleum-, coal- and shale-derived liquid fuels were burned in a downfired tunnel furnace to assess the impact of fuel properties on the formation and control of NOx emissions. A nitrogen-free oxidant mixture (Ar, C02 , 02) was used to isolate fuel NOx formation. Under excess air conditions fuel NOx correlated well with total fuel nitrogen content for both the petroleum and alternate fuels. Under staged combustion conditions the influence of fuel nitrogen content was much less pronounced but equally highly correlated except in the case of a coal-derived liquid

Influence of fuel composition and flame temperature on the formation of thermal and fuel NOx in residual oil flames

Journal ArticleA 900 kw model package boiler and a 20 kw laboratory tunnel furnace were used to study fuel and thermal NO, formation during heavy oil combustion. Package boiler results indicated that atomizer design, spray/ flow field interactions, and fuel composition were significant, dependent parameters. These effects were then investigated in detail in the laboratory furnace. One distillate and nine heavy oils were studied. Fuel NO.,., isolated with an argon/oxygen/carbon dioxide oxidant, was found to be a major source of NOx emissions. Fuel NOx formation increased approximately linearily with increasing nitrogen content from 0.05 to 0.79 wt. percent nitrogen. Fuel nitrogen oxidation was insensitive to temperature changes (over the theoretical temperature range of 2100 to 2500°K) except for one oil which exhibited a sudden increase at the highest temperature. Fuel NOx was insensitive to drop size, but thermal NOx increased with decreased mean droplet size. Percentage conversion of bound nitrogen decreased with increasing nitrogen content except for one oil containing substantial refractory nitrogen. Doping studies indicated that fuel sulfur can enhance fuel NOx formation and that nitrogen and hydrocarbon volatility are not first order parameters with a rapid mix burner under fuel-lean conditions

Parameters influencing the evolution and oxidation of sulfur in suspension phase coal combustion

Journal ArticleStoker coal-fired boiler furnaces are significant in terms of coal consumption and environmental impact; however, they have received relatively little research attention. This paper describes the results of a two-year study on the formation of sulfur oxides in the suspension phase of a coal-fired spreader-stoker system. An eight foot, drop-tube furnace with upward hot-gas flow was used to define the evolution and oxidation of fuel sulfur in the suspension phase and to establish the influence of the combustion parameters on S02 formation. The results indicate that coal particles greater than approximately 0.1 inch fall to the stoker grate essentially unreacted. Thus, only between 8 and 20 percent of the coal feed actually burns in the suspension phase. In general, the evolution and oxidation of sulfur lags hydrogen but leads carbon. The behavior of the organic sulfur closely follows that of carbon; however, the decomposition of the sulfate sulfur depends primarily on the local temperature and oxygen concentration. The behavior of the sulfate sulfur is of major importance because of the high sulfate content of the natural coal fines

Formation and control of NO emissions from coal-fired spreader-stoker boilers

Journal ArticleStoker coal-fired furnaces are significant in terms of coal consumption and environmental impact; however, they have received little research attention. This paper describes the results of a study on the formation and control of nitrogen oxides in coal-fired spreader-stoker systems. Three scales of experimental equipment were used to define the evolution and oxidation of fuel nitrogen in the fuel suspension phase, the conversion of fuel nitrogen during fixed-bed combustion, and the coupling between the two combustion phases. The results indicate that NO emissions from spreader-stoker-fired coal furnaces are the result of relatively high conversions of fuel nitrogen evolved from particles less than 0.1 inches in the suspension phase and low conversion of fuel nitrogen during the bed combustion. In the suspension phase, nitrogen is evolved at approximately the same rate as carbon is oxidized. Local oxygen availability is the primary control parameter for both phases of the combustion. Minimum overall fuel nitrogen conversions of 6 percent were achieved in the pilot scale facility by controlling the stoichiometry in both combustion zones

Bench and pilot scale process evaluation of reburning for in-furnace NOx reduction

Journal ArticleThis paper describes a combined experimental and theoretical study which was undertaken to quantify the impact of fuel and process parameters on reburning effectiveness and provide the scaling information required for commercial application of reburning under highly varied industrial conditions. Initially parametric screening studies were conducted in a 25 KW refractory- lined tunnel furnace. These studies were supported by large scale testing in a 3.0 MW pilot scale facility. The work at both scales focused on the importance and the fate of the reactive nitrogen species within the reburning zone