Abstract
Each year the pulp and paper industries generate enormous amounts of effluent treatment sludge. The sludge is made up of various fractions including primary, secondary, deinked, fiber rejects sludge, etc. The goal of this study was to evaluate the fuel properties of the hydrochars produced from various types of paper mill sludges (PMS) at 180 °C, 220 °C, and 260 °C. The hydrochars, as well as the raw feedstocks, were characterized by means of ultimate analysis, proximate analysis, moisture, ash, lignin, sugar, and higher heating value (HHVdaf) measurements. Finally, combustion indices of selected hydrochars were evaluated and compared with bituminous coal. The results showed that HHVdaf of hydrochar produced at 260 °C varied between 11.4 MJ/kg and 31.5 MJ/kg depending on the feedstock. This implies that the fuel application of hydrochar produced from PMS depends on the quality of feedstocks rather than the hydrothermal carbonization (HTC) temperature. The combustion indices also showed that when hydrochars are co-combusted with coal, they have similar combustion indices to that of coal alone. However, based on the energy and ash contents in the produced hydrochars, Primary and Secondary Sludge (PPS2) could be a viable option for co-combustion with coal in an existing coal-fired power plant.
Highlights
The world energy demand continues to grow with the increase of populations
The increase of liquids resulted from the decomposition reactions that occur during hydrothermal carbonization (HTC); mainly in the form of dehydration, polymerization, and aromatization reactions [21,51]
Six different paper mill sludges have been hydrothermally carbonized at 180 ◦ C, 220 ◦ C, and 260 ◦ C
Summary
The world energy demand continues to grow with the increase of populations. The energy demand is projected to reach up to 42 quadrillion British Thermal Unit (BTU) in 2040 to fulfill the needs of 10 billion people [1,2]. In order to ensure this energy supply is provided in a sustainable manner, fossil fuel industries need to begin integrating with renewable energy sources. One of the major electricity producers in the U.S, are still expected to provide 17.6% more electricity in 2040 compared to today [2]. This sustainability problem provides extraordinary potential for coal-like fuels generated from renewable resources. Wet waste biomass, such as paper mill sludges (PMS), is one of the largest and most abundant sources of renewable energy [3].
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