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Gasification and combustion are two common methods for Zhundong (ZD) coal utilization. In the present study, it was intended to investigate the thermal transformation of Na in ZD coal at the Lurgi fixed bed gasifier (Lurgi) and circulating fluidized bed boiler (CFBB). To this end, raw coal samples before gasification and gasified slags were gathered from Lurgi, and the raw coal before combustion, burned slag, and fly ash were collected from CFBB. The occurrence form of Na was analyzed by extraction experiments, and the samples were analyzed by inductively coupled plasma‐optical emission spectrometry (ICP‐OES), X‐ray diffraction (XRD), and scanning electron microscopy (SEM). The obtained results revealed that insoluble Na in Lurgi slag exceeded 90% under the high‐pressure gasification process. It was found that the high temperatures and high in Lurgi intensify the conversion of sodium to Na2Ca3Si2O8 and NaAlSiO4. The performed analyses revealed that the insoluble Na content in CFBB slag and fly ash was above 92%, and Na2SiO3 and NaAlSi3O8 were the main sodium minerals in CFBB solid residue. It was found that 76.64% of the initial Na content of raw coal in Lurgi migrated into slag after the gasification process, which was 7.05% higher than the sum of slag and fly ash in CFBB after combustion. During the sodium thermal transformation in Lurgi and CFBB, high pressures significantly reduce the release of gaseous Na from coal ash so more Na was retained in slag. [ABSTRACT FROM AUTHOR]

To explore the effect of pressure on the transformation characteristics of inorganic minerals Na/S in Zhundong (ZD) coal ash, the ZD coal ash were calcined by a high-pressure tubular furnace at different pressures (0.1 MPa, 2 MPa and 4 MPa) and temperatures (600–1000 °C every 100 °C intervals). XRF and XRD were used to analyze the mass of each element and inorganic minerals in ash samples. SEM and EDS analyzed the morphological features and elemental distribution. The average crystal size of Na 2 Ca(SO 4) 2 and Na 2 SO 4 crystals were calculated, and two crystal structure phases of Na 2 SO 4 were discussed. The possible mechanism of the inorganic Na/S transformation during 0.1 MPa and 4 MPa were established. The results showed that inorganic substances Na/S mainly existed as Na 2 Ca(SO 4) 2 , Na 2 SO 4 and CaSO 4 in ash samples. With the increase of pressure, the inorganic mineral species including Na/S did not change, and the release ratio of elements Na/S were decreased gradually. Under 4 MPa at 1000 °C, the release ratio of Na/S were 16.80% and 47.23% in raw coal respectively, which were less than 0.1 MPa at 1000 °C (38.68% and 72.37%). High pressure inhibited the release of Na/S in ash, significantly. Na 2 SO 4 crystals were ordered at room temperature, whereas at high temperature there were disordered O atoms. The pressure promoted the coalescence of Na 2 SO 4 and CaSO 4 into Na 2 Ca(SO 4) 2 , but accelerates the reduction of crystallite size. • Higher pressure inhibited the release of Na/S inorganic substances significantly. • Temperature rising promoted structural phase transition of Na 2 SO 4. • Higher pressure accelerated the crystallite size of Na 2 SO 4 and Na 2 Ca(SO 4) 2 smaller. • Higher pressure promoted the coalescence of Na 2 SO 4 and CaSO 4 into Na 2 Ca(SO 4) 2. [ABSTRACT FROM AUTHOR]

Aiming at alleviating the difficulties of extracting vanadium from high-carbon stone coal and solving the relevant pollution problem, a new synergetic and cleaner method combining concentration of vanadium with clean utilization of carbon was proposed and corroborated. Firstly, Fe 2 O 3 , acting as the source for the catalytic of carbon gasification and the capturer of vanadium, was added to the raw ore. Then, the carbon within the raw ore was gasified by water vapor at 800–900 °C under the catalysis of reducing product of Fe 2 O 3 (Fe 3 O 4) to generate synthesis gas (CO + H 2), and subsequently the vanadium dispersive occurred in the ore was captured by Fe 3 O 4 at 1100–1200 °C under Ar atmosphere to form Fe x V 3-x O 4. Finally, the Fe x V 3-x O 4 phase was separated magnetically, and a high-grade vanadium concentrate was obtained. The experimental results show that the Fe 3 O 4 effectively promoted the gasification rate and ratio of carbon. When 10 mass% Fe 2 O 3 relative to raw ore was added and roasted at 850 °C for 2 h, the gasification ratio of carbon increased by 26%. The gasification ratio of carbon could reach up to 90.2%. Besides, the Fe 3 O 4 could react with the V3+ components to form magnetic V-rich phase, Fe x V 3-x O 4 , and the vanadium concentrate was obtained by magnetic separation. Under the optimal conditions, the vanadium concentrate with a metallic vanadium content of 6.35 mass% was obtained by magnetic separation, which was 23.5 times higher than the raw ore. The recovery ratio of vanadium reached 85.6%. • A synergetic method for cleaner utilization of high-carbon stone coal is proposed. • Fe 2 O 3 acts as the source for the catalytic of C gasification and the capturer of V. • Water vapor is used to gasify carbon, and CO and H 2 can be formed at 800–900 °C. • Magnetic V-rich phase can be formed at 1200 °C and extracted by magnetic separation. • C/V in the raw ore can be cleanly and synergistically utilized by one-step roasting. [ABSTRACT FROM AUTHOR]

• Iron existed in the form of excluded minerals in Zhundong coal was found. • The spherical particles in the raw coal were the main source of the coal ash. • The slagging mechanism of high iron Zhundong coal on water-wall was proposed. Due to the wide region of Zhundong mining area, the coal properties of different mines are quite different. In this paper, a Zhundong coal containing red and cyan spherical particles (named as RP and CP) which can be observed by naked eye was studied. To better understand the characteristics of coal and spherical particles, the raw coal with spherical particles was directly ground for density classification, and then ashed. Besides, the raw coal was also separated according to the macroscopic appearance, and then the separated samples were ground and then burned at different temperature. The results showed that 91.57% of the coal mass was contained in classes with density less than 1.50 g/cm3, but the ash mass only occupied 46.74% of the total ash mass. On the contrary, the mass ratio of pulverized coal which density greater than 1.50 g/cm3 was occupied 8.43%, but its ash content was more than half of the total ash content. Iron was the main element in CP and RP ashes, but there was still a high iron content (reached 6.58%) in the ash of the coal without CP and RP. Finally, the slagging mechanism of high iron Zhundong coal on water-wall during combustion process was proposed. [ABSTRACT FROM AUTHOR]

In the combustion process of Zhundong coal, many factors had obvious influence on slagging process. In this paper, the influence of particle system on slag formation and shedding process was evaluated. Two slags were sampled at two CFBBs super heaters which temperatures were similar and the ash particles size and concentration were different. The collected slags were separated, and the inner layer was analyzed by XRF, XRD, and Nano-CT. The results suggested that the area ratio of particles smaller than 2 μm to the region area was above 80% in each region, indicating that the inner layer was dominated by fine particles. Furthermore, the proportion of particles decreased in each region of two slags with the increase of particle size. The influence of particle system on the slag formation and shedding process was proposed. The accumulation of small particles was the cause of slag formation, while large particles had great influence on slag shedding. The presence of large particles increased the porosity and reduced the contact area between particles, the binding force between the particles was weaker than that between particles and tubes. Therefore, the fracture location of two slags was different, which made the internal surface presented different appearances. • The effect of ash particle size in gas on slagging and shedding was studied in CFBB. • The 3D structure of the slag was reconstructed by the Nano-CT technology firstly. • The large particles in slag weakened the binging force between ash particles. [ABSTRACT FROM AUTHOR]