Analysis of D2 law in case of Shengli lignite drying under inert and uninert environment. Issue 4 (12th March 2018)

• Record Type: Journal Article
• Authors: Chen, Wei; Lei, Yafeng; Annamalai, Kalyan; Sun, Jiafeng
• Is Part Of: Drying technology. Volume 36:Issue 4(2018)
• Page Start: 448
• Page End: 458
• Publication Date: 2018-03-12
• Subjects: D2 law -- drying -- evaporation constant -- lignite -- moisture; FC: fixed carbon -- HHV: higher heating value -- HTD: hydrothermal dewatering -- SEM: scanning electron microscopy -- TGA: thermal gravimetric analysis -- VM: volatile matter; Drying -- Periodicals; Desiccation; 660.28426
• DOI: 10.1080/07373937.2017.1340304
• Languages: English
• ISSNs: 0737-3937

Abstract

ABSTRACT: Shengli lignite coal, originated from inner Mongolia China, contains significantly high amount of moisture (more than 30%) which can cause spontaneous combustion or other application problems. Thus, it is of interest to understand the heat and mass transfer mechanism of the low-rank lignite drying under different drying environments such as N2, CO2, air, argon, and helium. In this study, fundamental drying experiments with different drying agents were performed on coal samples using thermogravimetric analysis (TGA) method. Lignites with size of 0.045–0.075 mm were heated up from ambient temperature to a target temperature of 175°C under different environments at heating rates of 5, 10, 20, 40, and 80 °C/min, respectively. It was found that thermal conductivity of drying media, heating rate, and initial moisture content are three most significant factors affecting lignite drying process. The highest moisture release rate and the lowest T peak (when maximum moisture release rate occurred) were observed when drying with helium due to its highest evaporation constant (i.e., highest thermal conductivity). Moreover, higher heating rate and moisture content resulted in higher evaporation rate and T peak . In the meantime, the classical D 2 law, which is used to simulate the liquid fuel droplet combustion, was further developed to describe the "group effect" of moisture evaporation process of solid fuel during drying. The D 2 law well explains the experiment results. Finally, the structures of the dried lignite samples under different drying mediums were investigated through scanning electron microscopy studies. It was found that lignite coals shrank and became more compact when dried out, especially with drying agent CO2 .