Effect of OP/TX emulsifiers on the effectiveness of pressurised dewatering of coal slurry and the structure of the filter cake

The effect of two surfactants, octylphenol ethoxylate (OP-10) and nonylphenol ethoxylate (TX-10), on the pressurised dewatering of coal slurry, was investigated by using a new intelligent monitoring test device designed independently to monitor the effect of pressurised dewatering, The mechanism of the effect of surfactants on the dewatering effect of coal slurry was analysed by means of filter press dewatering tests, average mass-specific resistance measurements, Capillary absorption time (CST) measurements, wetting heat measurements, compression dewatering index measurements and CT tests. The results of the filter press dewatering test, average mass-specific resistance measurement and CST measurement showed that both OP-10 and TX-10 can improve the dewatering effect of coal slurry under pressure, and the best dosage of OP-10 is 200 g/t, at which time the average mass-specific resistance of the filter cake is 5.21×10⁶ m/kg, the maximum CST reduction rate is 14.25%, the filtration speed is 88.45% higher than that of the original coal slurry, and the moisture content is 16.7%. The optimum dosage of TX-10 was 400 g/t, which resulted in an average mass-specific resistance of 9.31×10⁶ m/kg, a maximum CST reduction of 13.36%, an increase in filtration speed of 76.57% and a moisture content of 18.2% compared to the original coal slurry. The wetting heat measurement results showed that the wetting heat of OP-10 was 1.196 J/g and that of TX-10 was 4.11 J/g. The hydrophilicity of TX-10 was higher than that of OP-10 and it was difficult to dewater compared with OP-10, so the filter press dewatering effect of OP-10 surfactant was better than TX-10. The three stages of the filter cake forming process were obtained through the analysis of the pressure-deformation relationship of the filter cake, and it was found that the compression dewatering stage was closely related to the dewatering effect, and the compression dewatering index CDI was further defined. The lower the CDI, the higher the compressibility of the filter cake, the greater the reduction of the thickness of the filter cake under the same pressure, and the lower the moisture, and the compression dewatering index under the action of OP-10 and TX-10 at the optimal concentration were 147.18 and 155.35 respectively. The effective porosity of the original sample was 11.96% with poor connectivity and a large proportion of isolated pores, while the effective porosity of the filter cake was 20.43% with good connectivity and a significant decrease in tortuosity to 1.9 when OP-10 was added at a concentration of 200 g/t. The permeability of the filter cake gradually increases, and the average mass specific resistance is smaller, so it can improve the dewatering effect.