Xuemin Ye

Preparing coal slurry from coking wastewater to achieve resource utilization: Slurrying mechanism of coking wastewater–coal slurry

Coking wastewater is used to prepare coal slurry, which can be used as combustion and gasification fuel. This promising technology simultaneously achieves resource utilization and wastewater management. Slurrying properties are essential to the industrial application of coal slurry. These properties are considerably influenced by coal surface properties and the adsorption of an additive by coal. In this study, the effects of the internal components (e.g., phenol, ammonia nitrogen, and metal ions) of coking wastewater on the adsorption of an additive by coal and on coal surface properties were measured. Results showed that the competitive adsorption between phenol and the additive reduced the amount of additive adsorbed on coal. However, phenol acted as an additive to improve the wettability of coal particles. Cations (Ca2+, NH4+, and Na+) adversely affected the slurrying because they weakened the negative charges of coal. Furthermore, a large amount of water was adsorbed due to the ionic bonding effects, thereby reducing the free water in the coal slurry system. The maximum slurrying concentration of CWCS was 0.8 percentage points higher than that of CWS, suggesting that coking wastewater enhanced the slurrying capability of the coal slurry by integrating the various effects induced by the different internal components.

Improving the slurry fuel preparation performance to recycle municipal sewage sludge by combined alkali and ultrasonication pretreatment

Municipal wastewater sludge (hereafter, sludge) is economically recycled by mixing with coal to prepare slurry fuels, called coal sludge slurry (CSS). However, raw sludge needs to be pretreated before being prepared as CSS because of its high viscosity. Alkali and ultrasonication pretreatment can effectively disrupt the sludge flocs and improve slurrying performance. The alkali pretreatment method takes a long time but has a low cost, whereas the ultrasonication pretreatment method needs a high energy input but takes a short time. This study combined these two methods with complementary advantages to reduce the sludge pretreatment time and ultrasonication energy demand to improve the slurrying performance for sludge. Results showed that, compared with only alkali and only ultrasonication, the combined alkali and ultrasonication pretreatment method had stronger effects on reducing slurry viscosity. The characteristic viscosity ηc of CSS prepared by raw sludge was 1663.60xa0mPaxa0s. It was reduced to 1033.44 and 1472.10xa0mPaxa0s, respectively, after the sludge was only pretreated by NaOH and Ca(OH)2 at a dosage of 10xa0% dry sludge (DS) for 2xa0h, while it was reduced to 1205.43xa0mPaxa0s after the sludge was only pretreated by ultrasonication of 30xa0kJ/g DS. After combined pretreatment, ηc of CSS was reduced to 774.98xa0mPaxa0s (NaOH of 10xa0% DS for 2xa0hxa0+xa0ultrasonication of 30xa0kJ/g DS) and 1083.24xa0mPaxa0s (Ca(OH)2 of 10xa0% DS for 2xa0hxa0+xa0ultrasonication of 30xa0kJ/g DS), respectively. Apparently, the combined method can effectively decrease the alkali dosage or the ultrasonication energy input.