Ralph E.H. Sims

An overview of second generation biofuel technologies.

The recently identified limitations of 1st-generation biofuels produced from food crops (with perhaps the exception of sugarcane ethanol) have caused greater emphasis to be placed on 2nd-generation biofuels produced from ligno-cellulosic feedstocks. Although significant progress continues to be made to overcome the technical and economic challenges, 2nd-generation biofuels production will continue to face major constraints to full commercial deployment. The logistics of providing a competitive, all-year-round, supply of biomass feedstock to a commercial-scale plant is challenging, as is improving the performance of the conversion process to reduce costs. The biochemical route, being less mature, probably has a greater cost reduction potential than the thermo-chemical route, but here a wider range of synthetic fuels can be produced to better suit heavy truck, aviation and marine applications. Continued investment in research and demonstration by both public and private sectors, coupled with appropriate policy support mechanisms, are essential if full commercialisation is to be achieved within the next decade. After that, the biofuel industry will grow only at a steady rate and encompass both 1st- and 2nd-generation technologies that meet agreed environmental, sustainability and economic policy goals.

CARBON EMISSION AND MITIGATION COST COMPARISONS BETWEEN FOSSIL FUEL, NUCLEAR AND RENEWABLE ENERGY RESOURCES FOR ELECTRICITY GENERATION

A study was conducted to compare the electricity generation costs of a number of current commercial technologies with technologies expected to become commercially available within the coming decade or so. The amount of greenhouse gas emissions resulting per kWh of electricity generated were evaluated. A range of fossil fuel alternatives (with and without physical carbon sequestration),were compared with the baseline case of a pulverised coal,steam cycle power plant. Nuclear,hydro,wind,bioenergy and solar generating plants were also evaluated. The objectives were to assess the comparative costs of mitigation per tonne of carbon emissions avoided,and to estimate the total amount of carbon mitigation that could result from the global electricity sector by 2010 and 2020 as a result of fuel switching,carbon dioxide sequestration and the greater uptake of renewable energy. Most technologies showed potential to reduce both generating costs and carbon emission avoidance by 2020 with the exception of solar power and carbon dioxide sequestration. The global electricity industry has potential to reduce its carbon emissions by over 15% by 2020 together with cost saving benefits compared with existing generation. r 2002 Elsevier Science Ltd. All rights reserved.

Fuel characteristics of short rotation forest biomass

Abstract Fuel characteristics of biomass from 12 tree species grown under a short rotation forestry regime were analysed. E. globulus, E. nitens and A. dealbata had the biggest trees while A. glutinosa, P. tomentosa and S. matsudana × alba 1002 had the smallest trees when the trees were harvested at the age of 3, 4 and 5 years. Higher heating value (HHV) ranged from 19.6–20.5 MJ/kg for wood, 17.4–20.6 MJ/kg for bark, and 19.5–24.1 MJ/kg for leaves, with the highest values for wood and bark being obtained from Pinus radiata . Wood basic density ranged from 250–500 kg/m 3 ; ash content, 0.7–1.4%; volatile matter content, 91.5–95.1%; fixed carbon content, 4.2–7.3%; and extractives content, 3.3–11.9%. Wood properties were significantly different from those of bark, and also different from those of leaves. Except basic density and the proportion of bark on the stem, properties of wood did not vary with either cutting age or stocking density. Wood from coppice crops did not differ from that of single stem, first harvest crops. Differences in tree size for species planted at similar plant populations determine species yields. Variations in properties between species and between tree parts have implications for feedstock handling, transport, drying, storage, and on the design of conversion systems.

Renewable Energy: A Response to Climate Change

Abstract “We recognize the importance of renewable energy for sustainable development, diversification of energy supply, and preservation of the environment. We will ensure that renewable energy sources are adequately considered in our national plans and encourage others to do so as well. We encourage continuing research and investment in renewable energy technology, throughout the world”. Communique from the G8 Leaders’ Summit, Genoa, July 2001. The Third Assessment Report of the IPCC confirmed that the Earth’s climate is changing as a result of human activities, particularly from energy use, and that further change is inevitable. Natural ecosystems are already adapting to change, some are under threat, and it is evident that human health and habitats will be affected world-wide. Such climate changes could also affect the present supplies of renewable energy sources and the performance and reliability of the conversion technologies. This paper concentrates on the reduction of carbon dioxide emissions and the role that the global renewable energy industry might play in this regard. (The five other major greenhouse gases are given less emphasis here.) The paper compares the costs of renewable energy systems with fossil fuel-derived energy services and considers how placing a value on carbon emissions will help provide convergence. The move towards a de-carbonised world, driven partly by climate change science and partly by the business opportunities it offers, will need to occur sooner rather than later if an acceptable stabilisation level of atmospheric carbon dioxide is to be achieved. Government policy decisions made now will determine the sort of future world we wish our children to inherit. The renewable energy era has begun.

Biomass production and nutrient cycling in Eucalyptus short rotation energy forests in New Zealand. I: Biomass and nutrient accumulation.

Accumulation of biomass and nutrients (N, P, K, Ca, Mg and Mn) was measured during the first 3-year rotation of three Eucalyptus short rotation forest species (E. botryoides, E. globulus and E. ovata) irrigated with meatworks effluent compared with no irrigation. E. globulus had the highest biomass and nutrient accumulation either irrigated with effluent or without irrigation. After 3-year growth, E. globulus stands irrigated with effluent accumulated 72 oven dry t/ha of above-ground total biomass with a total of 651 kg N, 55 kg P, 393 kg K, 251 kg Ca, 35 kg Mg and 67 kg Mn. Effluent irrigation increased the accumulation of biomass, N, P, K and Mn, but tended to reduce the leaf area index and leaf biomass, and decreased the accumulation of Ca and Mg.

Litter decomposition and nutrient release via litter decomposition in New Zealand eucalypt short rotation forests

Abstract Litter decomposition plays a major role in the cycling of energy and nutrients in woodland ecosystems. The rates of leaf litter decomposition and the resulting nutrient (nitrogen and phosphorus) release were monitored over a 12-month period for Eucalyptus brookerana and two types of E. botryoides leaf litter under one population density trial of eucalypt short rotation forests. The results showed that the tree density had little influence on the rates of litter decomposition and nitrogen release, but had a significant effect on phosphorus release. The higher the population density, the slower the release. The total nitrogen and phosphorus retention in the litter increased at first, particularly for phosphorus under the highest tree density (9803 trees ha−1). There were significant differences between the rates of both litter decomposition and nutrient release among the three studied leaf litter types. Litter dry weight loss and nutrient release were faster from E. brookerana litter than from E. botryoides litter. Autumn was the main season for litter decomposition and nutrient release. Overall, short rotation forests should be managed rationally based on the fluctuation of litter decomposition, and nutrient cycling in the system to ensure a sustainable production system of land use.

All-year-round harvesting of short rotation coppice eucalyptus compared with the delivered costs of biomass from more conventional short season, harvesting systems

Abstract This study attempted to define the optimum harvesting, processing and transport system in terms of the cost per tonne of delivering biomass produced from a commercial short rotation coppice crop to a 10 MW e bioenergy conversion plant 25 km away. Harvesting the crop during one short seasonal period of the year results in the need to store most of the material for between one to 12 months in order to provide a continual supply of feedstock. Storage of large volumes of biomass is costly and also results in dry matter losses over time. An alternative system would be to harvest small areas as required every few weeks throughout the year. This would enable cheaper, lower performance equipment to be used and hence provide a continual supply of biomass feedstock for delivery to the plant. Four systems of conventionally harvesting the biomass during one short seasonal period of 8–10 weeks were compared with two systems of harvesting it continually throughout the year. Whether the biomass is stored on the farms after harvest to allow for transpirational drying or at the plant was also compared. All-year-round harvesting using a simple tractor-mounted circular saw showed cost benefits in terms of

Eucalypt litter decomposition and nutrient release under a short rotation forest regime and effluent irrigation treatments in New Zealand: II. internal effects

/GJ of energy delivered to the bioenergy plant but the performance assumptions made will require confirmation by field monitoring. A sensitivity analysis was conducted on several key parameters.

Eucalyptus species for biomass energy in New Zealand—Part II: Coppice performance

Nutrient cycling in a short rotation forest system can be manipulated to give sustainable biomass production and land use. External factors, such as irrigation of meatworks effluent and age of plantation, could play some special role when managing litter in plantation forests to provide biomass sustainably for use as a fuel. These factors were examined for their effects on eucalypt leaf litter decomposition and nutrient release under 1, 2 and 3-year-old short rotation forest plantations grown in New Zealand. Both factors had significant effects on the rate of decomposition and nutrient release. Effluent irrigation significantly increased litter decomposition (from 46 to 62%) and nutrient release under 1-year-old stands, made no significant difference under 2-year-old stands (decomposition: 68 and 66%) and retarded the process under 3-year-old stands (decomposition: from 75 to 42%). In stands without irrigation, the decomposition and nutrient release occurred least under 1-year-old stands compared with 2- and 3-year-old stands. Conversely, in stands irrigated with effluent, the decomposition and nutrient release occurred least under 3-year-old stands. Phosphorus, magnesium, and nitrogen accumulated more than their initial amount in the litter, particularly under 3-year-old stands irrigated with effluent. The effects of these external factors should be considered when managing litter in plantation forests to give sustainable biomass production.

Bioenergy — a renewable carbon sink

Abstract Coppice re-growth and related yields of twelve species of the subgenus Symphyomyrtus and seven species of the subgenus Monocalyptus were monitored over five 3-year rotations. Planted in small plots at an original planting density equivalent to 2200 stems/ha, the resulting population densities (trees/ha and shoots/ha) varied with species and with each rotation as tree mortality increased to varying degrees following every successive harvest. Only eight of the 19 species planted had survival rates exceeding 50% of the initial population density after the fifth and final harvest. E. brookerana and E. ovata were the most vigorous species with survival rates exceeding 80% of the original planting. Eight of the species had died out completely before the final harvest. Overall, species from the sub-genus Symphyomyrtus had higher survival rates than those from the sub-genus Monocalyptus . Tree height, shoot stump diameter and above ground biomass dry weights varied between species, between sub-genera, and also between harvests. Biomass yields at comparative population densities tended to increase with subsequent coppice harvests, even though no irrigation, fertiliser, pest management systems or weed control methods were applied. Six species— E. brookerana, E. botryoides, E. botryoides × saligna and E. ovata of the sub-genus Symphyomyrtus , and E. elata and E. obliqua of the sub-genus Monocalyptus —gave satisfactory yields which exceeded 10 ODt/ha/y in any one of the five harvests. This provided mean annual incremental yields over the 15 year period ranging between 12-34 ODt/ha/y for these species when grown in the small plots. Commercial scale crop yields are likely to be considerably lower. However the six top yielding Eucalyptus species identified can be recommended for consideration in commercial plantings of short rotation coppice forestry schemes when grown on fertile soils in a temperate climate.