Upgrading of Low-Grade Colombian Coals via Low-Cost and Sustainable Calcium Nitrate Dense Media Separation

Abstract

Wet coal beneficiation in Colombia is prohibitive due to the high cost and scarcity of commonly used dense media. The practical value of this study is that it demonstrates for the first time that a common fertilizer, calcium nitrate, can be used in the beneficiation of low-grade Colombian coals. Three high-ash low-grade Colombian coals (Valle, Cundinamarca, and Antioquia) commonly used in Colombian sugar mill stoker furnaces were tested. Coal mineralogy and prevalence were analyzed before and after washing using mineral liberation analysis. The swelling potential of the coals was assessed using a novel application of thermal mechanical analysis (TMA) and an ash fusion oven (AFO). Calcium nitrate reduced ash levels across all size fractions, even for highash coals like Valle (29% to below 7%) to acceptable levels for coke manufacturing or pulverized fuel combustion. The novel use of TMA and AFO to analyze coal swelling demonstrated that swelling varies under constrained and unconstrained conditions and the small sample size allows for rapid testing of coal swelling. This study has demonstrated that the use of common fertilizers can allow beneficiation to become a processing option for low-grade coals in Official Development Assistance countries where conventional dense media is prohibitively expensive.

Novel Thermal and Microscopic Techniques To Determine the Causes of Suboptimal Combustion Performance at Colombian Stoker Furnaces

“… 35 Above 600 °C, below 0.5 g of the sample remained, which resulted in it being sensitive to any fluctuations, as the linearity deviation of the balance is up to 0.2 g. Furthermore, Cundinamarca and Valle were known to swell during combustion, which is discussed further in Section 4 with reference to the literature. 36 This explosive swelling behavior also led to fluctuations in the mass recorded during the tests.…”

“…A tared empty crucible test was conducted, and this base line data were subtracted from the weight of each run to remove drift in the measurements. Due to the explosive nature of some of the samples during combustion, 36 weight data were smoothed in Matlab 2019a using the smoothn.m script by Garcia, 53 which is an automated smoothing procedure for uniformly sampled data sets based on a penalized least squared method, which allows smoothing of the results in one or higher dimensions by means of the discrete cosine function. Figure 12 shows the temperature ramp profile and mass change for an empty tared crucible from atmospheric conditions to 800 °C in the macro-TGA at a ramp rate of 10 °C/min.…”

Triboelectric characteristics and separation of magnesite and quartz

“…Flotation is currently considered the most effective way to separate magnesite and remove impurities (Brezáni et al, 2017;Sun et al, 2021c;Zhu et al, 2015). However, this method has strict requirements on particle size and is associated with high processing costs (Fan et al, 2021;Williams et al, 2022;Zhang et al, 2020;Zhang et al, 2023). Moreover, the wastewater and chemicals generated during the separation process lead to environmental pollution and resource waste, which is not in line with the government's green and low-carbon economic plan (Bentli et al, 2017;Wu et al, 2004).…”

A physical coal cleaning approach for clean energy production from low grade Lakhra coal of Pakistan using diester table

“…The specific gravity of clean coal is usually between 1.3 and 1.7 whereas the specific gravity of the mineral matter is between 3.5 and 5.0 [19]. There are many studies for coal cleaning by physical and physicochemical methods like froth flotation [20,21] heavy media separation [22] coal-oil agglomeration [23] but there is hardly any literature available for the cleaning of coal by diester table. This work aims to investigate coal cleaning efficiency of a laboratory diester table in terms of ash and sulfur reduction on Lakhra coal sample.…”