Environmental mitigation of sludge combustion via two opposite modifying strategies: Kinetics and stabilization effect. (1st September 2018)

• Record Type: Journal Article
• Authors: Chen, Jingjing; Sun, Yongqi; Shao, Ningning; Zhang, Zuotai
• Is Part Of: Fuel. Volume 227(2018)
• Page Start: 346
• Page End: 354
• Publication Date: 2018-09-01
• Subjects: Sludge combustion -- Kinetic mechanism -- TG-MS -- Polluting gas -- Trace element; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2018.04.113
• Languages: English
• ISSNs: 0016-2361

Abstract

Graphical abstract: In this study we deepened the understanding of distribution behaviors of hazardous elements including trace elements and polluting gases during sludge combustion. The acidic kaolin and alkaline CaO additives were used for pollutant stabilizations, representing two general strategies. The additives themselves underwent great phase changes as the temperature increases, so there are different mechanisms of reaction and adsorption about trace elements and polluting gases in different temperature ranges. Highlights: Sludge combustion was characterized using an advanced TG-MS system. Two opposite additives, CaO and kaolin, were employed for pollutant stabilization. The specific stages during sludge combustion were clarified kinetically. Kaolin showed a better role controlling volatility of trace elements than CaO. We provided two general strategies for pollution mitigations. Abstract: Nowadays, environmental mitigation remains a key issue challenging sludge combustion toward its clean utilization. Herein, two opposite additives, CaO and kaolin, representing two different strategies, were employed for environmental mitigation of sludge combustion. An advanced TG-MS (thermogravimetric-mass spectrometer) system was used. The online MS analysis indicated that kaolin remarkably decreased the release of NOx whereas the fixation effect of CaO on SO2 was more pronounced. Furthermore, the experiments using a fixed tube furnace proved that overall kaolin had a better role controlling volatility of trace elements (Cr, Ni, Cu, Zn, Pb, As and Ba) than CaO and we found that the fixation mechanism of CaO changed at 750 °C, whereas that of kaolin changed at 500 °C. Then the kinetics of the various stages during sludge combustion were investigated. We found that low temperature stages were along with the formation of new phases, whereas, at high temperatures, the diffusion could be rate-controlling step. The present study thus provides not only a deep understanding of sludge combustion mechanisms but also two effective modifying strategies toward the environmental mitigation of sludge combustion.