Effects of lignite dewatering treatment on the surface behaviour and NO emission characteristics during the combustion process

Abstract

Hailaer lignite (HLE) with a uniform particle size distribution (3-6 mm) was employed to investigate the parameters of the low-temperature dewatering process influencing the emission of gaseous pollutants (NO x ) during their combustion process. The combustion of HLE original/dried samples obtained from a COMBD ry drying system were carried out in a fixed bed horizontal furnace under an air atmosphere at the reaction temperature of 1100 8C. The dewatering treatment led to the enhancement of the relative amount of the volatile and fixed carbon content in the upgraded coal sample. The deconvolution of the Raman spectra of each sample showed that the increased degree of drying led to an enhancement of the defects in aromatic structures, indicating an enhancement in the number of active sites or oxygen-containing complexes on particle surface. The devolatilization and combustion experimental results showed the following: (1) with the increase in the degree of drying, more HCN and NH 3 were released during the devolatilization process, and both HCN and NH 3 molecules had positive effects on the consumption of NO under high temperature conditions; (2) due to the enhancement of the specific surface area and total amount of surface active sites (C f ) after the drying treatment, the combustion and reduction reactivity of the dried HLE samples increased significantly; and (3) the conversion ratio of fuel-N to NO during the combustion process decreased significantly with the increase of the degree of dewatering. Therefore, it could be concluded that the removal of moisture content in lignite particles in advance had positive effects on lignite high efficiency combustion with low NO emission.

Effects of Upgrading Treatment on the Physicochemical Structure, Moisture Re-Adsorption Ability, and NOx Emission Characteristic of Lignite Particles

“…The SEM images in Figure illustrated that tube-like structures were generated on the surface of lignite particles after upgrading treatment. Meanwhile, with the enhancement of drying temperature, this phenomenon became more obvious . Because the upgrading treatments were performed at the temperatures not exceeding 483 K, which were not high enough for the occurrence of lignite devolatilization, the irreversible variations in the surface morphology of lignite particles during the drying process could be wholly attributed to the precipitation of moisture content in the particles.…”

“…The nitrogen content in both volatile matters and char particles were the primary source of NO generated in the process of coal combustion. NO released from the combustion of volatile matters accounting for approximately 70% of the total amount of NO, and the other part of NO results from the gasification of nitrogen content in char particles. , Moreover, previous researchers demonstrated that HCN was a main nitrogen-containing gaseous product generating during the lignite devolatilization process, which could also reduce NO into N 2 . , Therefore, the conversion ratio of fuel N to HCN in the stage of rapid devolatilization played a vital role in affecting and inhibiting the NO emission characteristics of coal during the combustion process.…”

“…H 2 O molecules could decompose into hydroxyl groups and hydrogen free radicals under high temperature conditions, and then react with the volatiles and char promoting the emission of NO during the combustion process. , Previous results illustrated that the enhancement of the upgrading degree could promote the emission of nitrogen content in volatiles into HCN and NH 3 , which could accelerate the consumption of NO in the atmosphere under high-temperature conditions. Moreover, the total amount of active site on the surface of dried lignite particles was more than that on the surface of the parent coal particles, illustrating that reducibility of upgraded lignite particles was normally strengthened after upgrading treatments . Consequently, it could be assumed that preventing the participation of moisture content in the combustion of coal-based fuel by upgrading treatments or re-adsorption prevention could obviously inhibit the release of NO during the utilization of low-rank coal …”

Experimental methods in chemical engineering: Raman spectroscopy

“…Eng. published 11 articles: six are directly related to catalysis, [27][28][29][30][31] three are in the area of combustion, [32] one combined Raman and EDS to identify a low melting lithium phosphate phase in lithium iron phosphate ingots, [33] and another applied confocal Raman to measure solute concentrations in a hanging droplet (mass transfer). [34] Raman spectrographs now record the whole spectral range (Raman shifts from 100 cm −1 to 4000 cm −1 ) at subsecond resolution and are applied to pulse experiments with isotopes, to measure reaction kinetics and spectroscopic characteristics.…”

“…Eng . published 11 articles: six are directly related to catalysis, [ 27–31 ] three are in the area of combustion, [ 32 ] one combined Raman and EDS to identify a low melting lithium phosphate phase in lithium iron phosphate ingots, [ 33 ] and another applied confocal Raman to measure solute concentrations in a hanging droplet (mass transfer). [ 34 ]…”