Climate models from the Intergovernmental Panel on Climate Change (IPCC) have predicted that the global surface temperature will increase between 0.3 °C and 4.8 °C in the 21st century [1
]. Between 1880 and 2012, the mean surface temperature increased by 0.85 °C, which is alarming and needs to be controlled. Human interventions such as using fossil fuels for energy and transportation, emissions from agricultural practices, and industrial developments are reported to be the major contributors to climate change [1
]. More than 40% of the emissions could be reduced if the demands of energy supply and transportation sectors are met through clean energy sources [1
]. The quest for alternative energy sources have resulted in wind, solar, geothermal, tidal, hydroelectric and bioenergy sources. However, wind and solar have problems including storage and transmission losses.
Islands like Hawaii are deprived of resources for power generation. In Hawaii, more than 70% of electricity is produced from imported oil and 13% from coal [2
]. By contrast, the mainland United States generated only 1% of its electricity from oil, which shows the dependency on fossil-fuel resources in these islands. At present, 3% of the electricity produced in Hawaii comes from biomass [3
]. Lignocelluloses are plentiful organics accessible today, accounting for up to 50 billion tons in dry weight [4
Different technology routes are available for processing biomass to energy. Lignocellulosic ethanol is one of the possible alternatives for producing clean energy, which requires a pre-treatment process [5
]. This pre-treatment step increases the production cost, in addition to technical hindrances such as effective sugar release and inhibitor formation. Some attempts have been made to integrate first- and second-generation ethanol production to reduce production costs [6
]. However, the economic feasibility and the need for electricity cannot be satisfied with liquid fuels. Unlike biochemical processes, thermochemical processes offer access to clean energy with fewer technical hindrances. In addition, thermochemical processes satisfy the needs of electricity production for a state like Hawaii that is devoid of resources. Thermochemical processing routes for producing energy include gasification, combustion, pyrolysis, hydrothermal carbonization, and hydrothermal liquefaction [7
]. In combustion, an exothermic reaction happens between the fuel and an oxidant, which produces steam and other gases. Using these hot gases in a turbine or combined cycle results in potential applications such as heat and power [8
]. The state of Hawaii owns 1.3 million acres of land, of which only 8% is used for cultivation [9
]. Utilizing the unused land for the cultivation of energy crops helps produce green electricity. This green electricity reduces the economic burden, dependence on oil, and environmental impacts.
Thermochemical processes yield higher efficiencies when the moisture content of the biomass is lower. Failing to do so consumes energy to vaporize the moisture, thus reducing the efficiency of the process. For the same reason, dried biomass such as wood chips are usually preferred in thermochemical processes. When energy crops are used, field drying them reduces the moisture content of the biomass [11
]. Previous studies have investigated the effect of varying moisture content in the biomass for alternative fuel production [12
]. Striugas et al. used an indirect method to calculate the heat balance that controls the reciprocating grate using wet woody biomass [15
]. The variation in the moisture content affects the overall viability of the process and needs further investigation.
No previous research has considered the variation of moisture content on trifold sustainability metrics including techno-economic and environmental impact analysis. These tri-fold sustainability metrics check the feasibility of a process from a multi-disciplinary angle, ensuring the process is environmentally friendly, technically feasible, and economically viable.
The objectives of this study include:
analyzing the effect of varying moisture content of two lignocelluloses (banagrass and energycane) for electricity production;
evaluating the techno-economic potential of power production in Maui (Hawaii);
carrying out an energy analysis to understand the energy flow;
conducting a life-cycle assessment to identify the environmental impacts of the thermochemical process.
Lignocellulosic electricity production was evaluated through a holistic approach, including techno-economic analysis and life-cycle assessments, under varying moisture contents. The results suggest that drying energycane on the field was the most sustainable scenario in terms of technology, economics and environmental impacts. The most profitable scenario (ECLM) could yield investments after 11 years with a capacity of 60,000 dry MT/year. Biomass cost ($80/dry MT) was identified as the main factor affecting the profitability of the plant, followed by electricity-selling prices. The GHG emissions from different scenarios ranged between 16 gCO2/MJ and 29 gCO2/MJ. For an island like Hawaii, electricity generation from biomass could be sustainable in terms of technology, economics and environmental impact in comparison with fossil-fuel sources.