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This work investigates the effects of two kinds of iron ore on the pyrolysis characteristics of a low-rank bituminous coal from Hami, China. The pyrolysis and its product distribution were studied using a thermogravimetric analyzer and a fixed bed reactor. A gas chromatograph and a gas chromatograph–mass spectrometer were employed to test the properties and composition of the pyrolytic products. Results showed that the pyrolysis temperature of the raw coal ranged mainly from 350 to 650 °C. The weight-loss rate reached a maximum of 6.95%/min at 443 °C. The weight loss was 44.27% at the final pyrolysis temperature of 750 °C. The tar yield of raw coal was 9.51% in the fixed bed reactor at 600 °C. Adding iron ore, which was intended for a lower tar yield and a higher fraction of light tar (boiling point <360 °C), had a catalytic effect on the pyrolysis of raw coal. With separate addition of hematite and specularite, both having a mass of 20% of the raw coal, coal weight loss increased by 3.86% and 5.56%, respectively, when the catalytic upgrading was at 600 °C, and good upgrading effect was obtained. Meanwhile, benzene homologue in tar increased slightly, by 0.62% and 1.44%, compared to that in the tar of the raw coal. The upgrading effects of iron ore on tar also lowered element O content in the resulting tar, by 36.89% with the addition of hematite and by 43.16% with specularite. The iron concentrate recovered was measured by magnetic separation method. The iron concentrate grade was 52.97% with hematite added in coal when the residence time of ultimate pyrolysis temperature was 25 min and the magnetic field strength was 96.48 kA/m, while it was 58.02% with specularite added when the residence time was 35 min and the magnetic field strength was 109.27 kA/m, both with a char grinding fineness of less than 0.074 mm (ground char accounting for approximately 80% of total char); iron concentrate recovery rate was 85.31% and 76.74%, respectively. The experimental results proved the feasibility of recovering iron ore in char by magnetic separation.

In this work, four slag samples were collected from the OMB CWS gasification, and the mineral behavior and morphology were studied to explore the formation mechanism of blockage slag. Results showed that amorphous phase is dominant in all slag samples, which was mainly glassy substances rich in low-temperature eutectic of iron. The precipitation of metallic iron and the crystals of SiC, calcite, and quartz were found in slags which were taken from the bottom of the combustion chamber (S-b). The quench slag collected from stable operation conditions (S-s) had a low content of quartz crystalline. While slag from the down pipe of the quench chamber (S-b) and bulk slag from the water-cooled pool (S-p) had observed the precipitation of crystals. Comparing to S-s, carbon matters in S-b had a higher order degree of carbon structure. By comparing the slag sample obtained during stable operation (S-s) with slag blocking occurs (S-b, S-d, S-p), it is found that the blockage of the OMB CWS gasifier was strongly related to unreacted residual carbon and the high content of sodium and iron in coal. They will interact with each other and form small number of crystals and most of the amorphous material.

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