Indonesian low rank coal (LRC) was upgraded by the addition of palm acid oil (PAO), and the efficiency of the inhibition of spontaneous combustion, as well as the resistance to moisture readsorption, was compared with raw coal. Fluorescence microscopy images revealed that PAO was well distributed in the coal matrix during the drying process. The PAO coating the surface of coal decreased the pore volume and the surface area of the upgraded coal and improved its stability. The upgraded LRCs had higher heat calorimetry values, greater resistance to moisture readsorption, and a reduced tendency toward spontaneous combustion when compared to raw coal. In upgraded coal briquettes, PAO was present in the form of a network-like structure, which led to an increase in the compressive strength by binding the coal particles. The upgraded LRCs showed less susceptibility to isothermal oxidation due to the PAO coating on the coal particles, which suppressed the reaction of active functional groups with oxygen in the air.
− Fry-drying of coal slurry is one of the upgrading low rank coal processes. It consists of slurry mixing, slurry dewatering, solvent recovery and briquetting. Cost estimation and economic feasibility are examined for the upgrading low rank coal process based on capacity of 1 million ton/yr. In case that investment costs are $100,000,000, discount rate is 12%, and service life is 20 years, the results of economic analysis are enough to satisfy the evaluation criteria of investment such as IRR, B/C ratio, NPV and discounted payback period. According to sensitivity analysis, investment value are very sensitive to raw material cost and product price. Since the bituminous coal price is currently soaring, it is expected that the investment value will increase more and more.
:Vapor adsorption of hydrocarbon has been studied for stabilization after drying low-rank coal. The surface characteristics and the propensity of spontaneous combustion were observed for stabilized coal which was maintained with hydrocarbons as stabilizer at several conditions of residence time and temperature. Surface area of micropores in coal mainly decreased after vapor adsorption. As residence time and temperature of adsorption process increased, the propensity of spontaneous combustion decreased. The type of hydrocarbons did not effect on the propensity of spontaneous combustion. As the analysis results of this work, the amount of hydrocarbon adsorbates required to stabilize dried coal was 0.5 wt% or less of coal, and the stabilizing effect was induced by adsorption of low-molecular-weight hydrocarbons.
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