South Africa’s first continuous hydrothermal liquefaction plant was launched at North-West University (NWU) earlier this month, which will result in the production of bio-oils, bio-char, biochemicals and biogas.
The plant is one of the outputs of the Department of Science and Technology- and the National Research Foundation-supported South African Research Chairs Initiative (Sarchi), particularly of the the Biofuels Sarchi at NWU headed by Professor Sanette Marx.
She explains that the plant can process dry plant matter, or lignocellulose biomass, in water feed of 150 ℓ/h at a residence time of 10 min. The plant is designed to operate at 350 C and pressures of 100 bar.
The closest comparable plant, at the University of Sydney, in Australia, has a maximum capacity of 90 ℓ/h. This plant is designed to process a liquid feed of micro-algae in water at 280 C and pressures of 610 bar.
The local plant will be used for the production of products for research applications and is the first of its kind in the world to use biomass as feedstock.
Bio-oil produced at the plant has a calorific content of about 30 MJ/kg, similar to that of coal typically used in coal-fired power stations. The oil will be upgraded using the continuous hydrotreatment reactor of the liquefaction plant to produce renewable diesel with characteristics and a calorific content similar to that of fossil-based diesel, which has a calorific content of about 45 MJ/kg.
The plant has demonstrated the possibility of co-feeding such oils with the crude oil currently used by refineries, to reduce the sulphur content in liquid fuels, thereby decreasing environmental impact.
In September last year the plant produced its first batch of bio-char, a form of charcoal produced from plant matter, using sweet sorghum bagasse as the feedstock.
Bio-char can be used in a number of applications, including cogeneration or cogasification with coal to reduce the sulphur footprint of coal combustion or gasification. Bio-char can also be used as a soil remediation agent in the agricultural industry or as an adsorbent to remove heavy metals and organic pollutants from industrial water effluent streams.
Marx and fellow professors John Bunt and Frans Waanders registered a patent in October last year on the use of bio-char with fine discard coal for catalytic cogasification. The bio-char produced at the plant will provide opportunities to further investigate cogasification applications.
The plant at NWU was designed, constructed and commissioned by Johannesburg-based design and engineering company Mass and Heat Transfer Technology.
The design was based on the work of several NWU alumni over a nine-year period, including two PhD, six master’s, and nine chemical engineering undergraduate students.