Combination of Primary Measures on Flue Gas Emissions in Grate-Firing Biofuel Boiler

Abstract

Increasingly stringent limits for NOx and SO2 emission are forcing the investigation of new reduction methods. This study was conducted to determine the combination of primary measures, i.e., flue gas recirculation (FGR) and excess air effects on sulfur, nitrogen and hydrocarbon emissions, in boiler flue gas. Experimental research was performed using an experimental, small-scale (20 kW) model of an industrial biofuel boiler. During combustion of sunflower seed hulls at different FGR ratios and incomplete combustion regimes, the composition of flue gas (NO, NO2, N2O, HCN, NH3, SO2, SO3, H2S, CO, and CxHy) was compared, allowing an explanation of the determinants of emission concentration changes to be provided. Increasing the flue gas recirculation ratio in the primary air had a positive effect on reducing NOX and CO with certain organic compounds. However, an opposite effect on SO2 was observed. NOX and SO2 concentrations were found to be approximately 500 mg/m3 and 150 mg/m3 under a regular combustion regime. When the FGR ratio of 50% NOX concentration decreased by 110 mg/m3, the SO2 concentration increased by 60 mg/m3. The incomplete combustion regime reduced NOX concentration by 70 mg/m3, whereas SO2 concentration increased by 100 mg/m3. The influence of primary measures presented an unclear relationship to hydrocarbon emissions, with concentrations not exceeding 18 mg/m3.

The Effect of Mixing Recirculated Flue Gas with Primary or Secondary Air during Biomass Combustion in Grate-Firing Boiler as the Primary Measure for NOx Reduction

“…Prompt NOx is formed during the reaction of an incomplete combustion hydrocarbon radical with a nitrogen atom. This is a two-way reaction and the amount of prompt NOx is negligible [4]. However, the biggest amount of NOx is formed from fuel nitrogen N during biomass combustion in the process of oxidation of char-N and volatile N [5].…”

“…The emissions in biomass combustion products that are limited by the new EU legislations for the rates of medium combustion plants are nitrogen oxides, while carbon monoxide emissions are no longer limited. A lot of studies propose that biomass combustion by burning it by gasification mode with recirculating flue gas is an appropriate way to reduce the NOx emissions as a primary measure [4,6,[16][17][18][19].…”

“…In this case, similar results to those with different fuels were achieved, as the emissions of NOx were reduced by 40% to 80 mg/nm³. Again, it can be assumed that in order to achieve significant results on nitrogen oxides reduction by mixing secondary air with FGR it needs to decrease oxygen level more than in primary air and FGR mixture as the main combustion processes are already completed, but a reaction between CO and NO is still happening, where breakdown of NO and oxidation of CO to CO2 takes place [4]. The results of the Fig.…”

Ionic liquids and deep eutectic solvents for NH3 absorption and separation: a review

“…14–16 With the rapid enhancement of environmental awareness, people have progressively realized that the emission of NH 3 will result in environmental pollution and ecological damage. The alkaline NH 3 released into the atmosphere can react with acid gases (NO x , SO x ) to generate ammonium salts (NH 4 + ), 12,17,18 resulting in severe air pollution via the formation of fine particulate matter (PM2.5) (the formation process of PM2.5 is shown in Fig. 1).…”

Applying the Random Forest Method to Improve Burner Efficiency

“…FGR is being actively introduced to reduce emissions in biofuel boilers of various capacities [34][35][36]. Much attention is currently paid to the use of hydrogen, methanehydrogen fractions, fuel mixtures based on landfill gases and thermal decomposition products of industrial and municipal waste as fuel in power plants [37][38][39].…”