N migration and transformation during the co-combustion of sewage sludge and coal slime

Investigation of Combustion and NO/SO2 Emission Characteristics during the Co-Combustion Process of Torrefied Biomass and Lignite

This paper investigates the combustion characteristics and pollutant emission patterns of the mixed combustion of lignite (L) and torrefied pine wood (TPW) under different blending ratios. Isothermal combustion experiments were conducted in a fixed bed reaction system at 800 °C, and pollutant emission concentrations were measured using a flue gas analyzer. Using scanning electron microscopy (SEM) and BET (nitrogen adsorption) experiments, it was found that torrefied pine wood (TPW) has a larger specific surface area and a more developed pore structure, which can facilitate more complete combustion of the sample. The results of the non-isothermal thermogravimetric analysis show that with the TPW blending ratio increase, the entire combustion process advances, and the ignition temperature, maximum peak temperature, and burnout temperature all show a decreasing trend. The kinetic equations of the combustion reaction process of mixed gas were calculated by Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) kinetic equations. The results show that the blending of TPW reduces the activation energy of the combustion reaction of the mixed fuel. When the TPW blending ratio is 80%, the activation energy values of the mixed fuel are the lowest at 111.32 kJ/mol and 104.87 kJ/mol. The abundant alkali metal ions and porous structure in TPW reduce the conversion rates of N and S elements in the fuel to NO and SO2, thus reducing the pollutant emissions from the mixed fuel.

Mechanical pretreatment of typical agricultural biomass on shape characterization and NO emissions during combustion

The impact of mechanical pretreatment of corn straw (CS), pea straw (PS), and wheat straw (WS), on shape characterization and NO emissions during combustion were investigated in this research. Particle size ranges were obtained and characterized their shape factors using Image J correction. The thermal properties and NO emissions of the different-sized particles were investigated by TG-MS and fixed-bed reactor. Compared with CS and PS, WS is more likely to break into smaller particles due to its moderate strength. Amine-N completely disappeared after pyrolysis, whereas pyrrolic-N and pyridinic-N were the main N functionalities in char-N. During the volatile burning stage, the maximum peak of NO concentration was 270, 354 and 311 ppm for CS, PS and WS, respectively. NO was detected at a steady level during the semicoke combustion stage, and the duration increased with particle size. The NO concentration decreased sharply in a short duration during the fixed carbon combustion stage.

Effecting mechanisms of iron-rich sludge on ash fusion characteristics of coal with high ash fusion temperature under reducing atmosphere

Co-gasification is crucial for large-scale clean conversion of coal and sludge. In this study, the effects of municipal sewage sludge (MSS, Fe2O3:48.11 %) and pharmaceutical sewage sludge (PSS, Fe2O3: 67.80 %) on ash fusion temperature (AFT) of high AFT Xiangyuan coal (XY) were explored using an AFT analysis, X-ray fluorescence spectrometry, X-ray diffraction, scanning electronic microscopy, and thermodynamics FactSage calculation. The results showed that when MSS or PSS ash mass ratios reached 20 % or 16 % (for XY mixtures, the mass ratio of MSS or PSS should be >5.81 wt% or 5.07 wt%), respectively, the AFT met the requirement of liquid-slag discharge for entrained-flow bed gasification. Under a reducing atmosphere (6:4, CO/CO2, volume ratio), Fe2+ destroyed the bridging-oxygen bonds in the network structure and generated low melting-point (MP) hercynite (FeAl2O4). This resulted in the AFT decreases in the XY mixtures with the additions of PSS or MSS. Meanwhile, the high calcium content (CaO: 13.40 %) easily reacted with Al2O3 and SiO2 and formed anorthite (CaAl2SiO8), which inhibited high-MP mullite formation and decreased the mixed XY AFT. With the increasing SS mass ratio, the surface of the ash sample and thermodynamic FactSage calculation were in good agreement with the experimental results.

Investigation of interaction mechanisms during co-combustion of sewage sludge and coal slime: Combustion characteristics and NO/SO2 emission behavior

Co-combustion of sewage sludge (SS) and coal slime (CS) is a promising method to achieve resource utilization of both solid wastes. However, the emission characteristics of NO/SO₂ and the interaction mechanisms between SS and CS are unclear. In this paper, the co-combustion characteristics and NO/SO₂ emission behavior of SS and CS were investigated using a thermogravimetric analyzer and a tube furnace combustion system, and the interactions between SS and CS were explored. The results revealed the presence of remarkable interactions between SS and CS during the co-combustion. For the combustion characteristics, non-catalytic factors (interaction between volatiles and heat synergy) and catalytic factors (catalysis of inorganic components) controlled the combustion stage of the heavy volatiles and fixed carbon of the blends, respectively, leading to an earlier combustion process. For NO and SO₂ emission characteristics, SS-CS co-combustion had significant NO in-situ reduction and self-desulphurization characteristics at 800 °C and 900 °C. The best inhibition occurred at 900 °C and 50 % CS ratio, and NO and SO₂ emission amounts were reduced by 0.25 mg/g and 1.37 mg/g, respectively, compared to the theoretical values. At 1000 °C, co-combustion promoted the emissions of both NO and SO₂. The interaction mechanisms suggested that the reducing atmosphere created and the reducing gases released by SS combustion promoted the reduction of CS-NO, while the char formed by CS exhibited a significant reduction of SS-NO. In addition, the effect of CS addition on the mass transfer process enhanced the sulfur fixation of inorganic components in SS, which led to the suppression of SO₂ production. These findings provide a better understanding of the interactions between SS and CS during SS-CS co-combustion.