Abstract
The utilization of biomass as a solid fuel for co-firing has received great attention from boiler manufacturers as a clean coal technology (CCT) option. This research aimed to produce biocoal pellets, as a clean energy fuel, using hydrochar from trees planted to rehabilitate acid mine drainage (AMD) water and fine coal discards. The hydrochar was synthesized by hydrothermal carbonization of Searsia lancea harvested from AMD-contaminated land at a temperature of 280°C and a residence time of 90 minutes. It was blended with discard coal (-1 mm) at ratios of 25% and 50% hydrochar to produce different forms of solid pelletized biocoal (BC). The physicochemical and mechanical properties of each of the biocoal pellet blends were determined. The 100% hydrochar had the highest calorific value of 29.99 MJ/kg, while the raw discard coal had a calorific value of 16.73 MJ/kg. The ash content decreased from 42% in the discard coal to 25% in the blend of 50% coal and 50% hydrochar biocoal pellets. Biocoal pellets comprising 25% hydrochar and 75% discard coal (BC25HC/75COAL) displayed the best mechanical properties (compressive strength 3.06 MPa) of all the fuels, but the physicochemical properties were inferior to the BC50HC/50 COAL pellets. This research has demonstrated that hydrochar synthesized from a tree species planted for hydraulic control of AMD has the capability to act as a binder for improving the mechanical properties and energy characteristics of fine discard coal.
Highlights
IntroductionThe world population in 2017 was estimated to be around 7.3 billion and is projected to increase to 10.5 billion by the year 2040 (EIA, 2016; Saba, Sha, and Reza, 2017)
The increase in human population will inevitably require an increase in energy production, necessitating more fossil fuels and biomass to be added to the global energy mix
The biocoals made from the blend of 50% hydrochar and 50% coal are denoted as (BC50 HC/50 C), whereas the 25% hydrochar and 75% coal blend is denoted as BC25 HC/75 C
Summary
The world population in 2017 was estimated to be around 7.3 billion and is projected to increase to 10.5 billion by the year 2040 (EIA, 2016; Saba, Sha, and Reza, 2017). Since South Africa is obliged to use its remaining low-grade coal, the use of biomass as a clean co-fired fuel is an attractive option for use in these power plants in order to meet the stipulated emission standards. The utilization of biomass and refuse-derived fuels (RDF) for co-firing has received great attention from researchers and boiler manufacturers as a clean coal technology (CCT) option worldwide (Rousset et al, 2011; Kerina, and Bada 2020). Such products are seen as potential alternative renewable energy sources for electricity generation, with low emissions and low ash contents among other beneficial fuel characteristics (Teixeira et al, 2012; Ndou, Bada, and Falcon, 2020)
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