Abstract
Japanese wireweed, Sargassum muticum is an invasive species to Great Britain, which might be controlled by harvesting it for energy and chemicals. Pyrolysis is the thermal decomposition of the organic components of dry biomass by heating in the absence of air. The distribution of matter between solid, liquid and syngas depends on the biomass and the pyrolysis temperature and time. Slow pyrolysis with lower temperatures (~ 400⁰ C) tends to produce more solid char. Pyrolysis char can be an effective soil ameliorant, a sequestration agent due to its stability or burned as a fuel. The research attempts to answer the question: Could slow pyrolysis be an energy efficient means for the destruction of Japanese wireweed and produce a potential product, biochar? A simple test rig was developed to establish the yield of biochar, biocrude and syngas from the slow pyrolysis of Sargassum muticum. An energy balance was calculated using compositional data from the analysis of the seaweed feedstock, higher heating values (HHV) from bomb-calorimetry and literature values. The energy required to heat 1 kg of dry seaweed by 400⁰ C for slow pyrolysis was estimated at 0.5 MJ. The HHV of syngas and biocrude produced from the pyrolysis totalled 2.9 MJ. There is, therefore, sufficient energy in the biocrude and syngas fractions produced by the pyrolysis of seaweed to power the process and produce useful biochar, but insufficient energy for drying.
Highlights
The environmental and economic impacts of biological invasions of non-native species were estimated to be in early part of the last decade ~ US$ 1.4 trillion per year, equivalent 5 % of the world economy (Engelen & Santos, 2009)
There is, sufficient energy in the biocrude and syngas fractions produced by the pyrolysis of seaweed to power the process and produce useful biochar, but insufficient energy for drying
The oxygen content was established by difference. 2.5 Slow Pyrolysis Approximately 50 g of seaweed was subject to slow pyrolysis in a test-rig made from standard laboratory glassware, shown in Figure 2, which attempts to simulate the conditions in a commercial biochar retort, where biomass is heated externally in the absence of a flow of air
Summary
The environmental and economic impacts of biological invasions of non-native species were estimated to be in early part of the last decade ~ US$ 1.4 trillion per year, equivalent 5 % of the world economy (Engelen & Santos, 2009). Under the EU’s Water Framework Directive the UK has identified it as a species of high priority (Davison, 2009) It is causing considerable problems in certain areas of the Kent coast, especially on chalk ledges, and is spreading, possibly displacing native algae (Kent Wildlife Trust, 2006; Medway Swale Estuary Partnership, ND; The River Stour (Kent) Internal Drainage Board, 2012). The char from the pyrolysis of algae, has been found to be an effective soil ameliorant and fertiliser and could be an additional revenue stream (Bird & Benson, 1987), but the thermal behaviour of seaweeds is complex with a myriad of diverse reactions and thermolysis pathways (Rowbotham, Dyer, Greenwell, Selby, & Theodorou, 2013) It is suggested considerable further study is required to discover if and how this could be exploited to commercialise seaweed for fuel and chemicals (Ross, Jones, Kubacki, & Bridgeman, 2008). Could the destruction of the invasive species to the UK, Sargassum muticum, by slow pyrolysis be energy efficient and produce a valuable product biochar?
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