Comparative evaluation of GHG emissions from the use of Miscanthus for bio-hydrocarbon production via fast pyrolysis and bio-oil upgrading

This study examines the GHG emissions associated with producing bio-hydrocarbons via fast pyrolysis of Miscanthus. The feedstock is then upgraded to bio-oil products via hydroprocessing and zeolite cracking. Inventory data for this study were obtained from current commercial cultivation practices of Miscanthus in the UK and state-of-the-art process models developed in Aspen Plus®. The system boundary considered spans from the cultivation of Miscanthus to conversion of the pyrolysis-derived bio-oil into bio-hydrocarbons up to the refinery gate. The Miscanthus cultivation subsystem considers three scenarios for soil organic carbon (SOC) sequestration rates. These were assumed as follows: (i) excluding (SOC), (ii) low SOC and (iii) high (SOC) for best and worst cases. Overall, Miscanthus cultivation contributed moderate to negative values to GHG emissions, from analysis of excluding SOC to high SOC scenarios. Furthermore, the rate of SOC in the Miscanthus cultivation subsystem has significant effects on total GHG emissions. Where SOC is excluded, the fast pyrolysis subsystem shows the highest positive contribution to GHG emissions, while the credit for exported electricity was the main ‘negative’ GHG emission contributor for both upgrading pathways. Comparison between the bio-hydrocarbons produced from the two upgrading routes and fossil fuels indicates GHG emission savings between 68% and 87%. Sensitivity analysis reveals that bio-hydrocarbon yield and nitrogen gas feed to the fast pyrolysis reactor are the main parameters that influence the total GHG emissions for both pathways

Radiation sensitive optical fibres for radiation detection and dosimetry

Optical fibre-based alpha and beta particle sensing devices have been investigated for the purpose of detecting low levels of Uranium-238 and its decay products in liquids for mineral processing applications. Both sensors operate using the mechanism of scintillation produced within scintillating polymer optical fibres. The prototype devices which have been created are capable of performing direct, real-time, semi-continuous measurements of alpha and beta particle emitting radionuclides within solutions or suspensions, which is not possible with current measurement techniques. This work aims to help improve current processing techniques for the production of high quality copper concentrates from ore by monitoring the quantities and distributions of nontarget minerals throughout various mineral processing stages. Using the fibre fabrication facilities at IPAS, optical fibres have been drawn in-house from the commercial bulk scintillators EJ204 and EJ262 from ELJEN Technologies. Fibres with outer diameters of 160 μm were fabricated for alpha particle detection, and through refinement of the fabrication conditions, a transmission loss of 14 dB/m at 440 nm (EJ204) was achieved, down from > 30 dB/m in an earlier trial. 1 mm diameter canes were fabricated for beta particle detection, with transmission losses of 5 dB/m at 450 nm (EJ204), comparable to similar commercial fibre varieties. In-house fabricated fibres were tested alongside commercially available scintillating optical fibres in radiation sensing experiments, where their response to X-rays, alpha and beta particles were evaluated. Optical fibres have been tested under laboratory-simulated environmental conditions analogous to those encountered during mineral processing, where commercial fibres with outer claddings displayed the best performance. Prototype devices have been created and tested in real-world mineral processing solutions. Both alpha and beta particle sensors have demonstrated detection limits below the 1 Bq/ml per isotope of 238U target level. The work which has been presented shows the concept of using scintillating polymer fibres for low level radionuclide detection in liquids has been proven, and successful prototype alpha and beta particle sensors have been developed.Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 201

Testing the use of static chamber boxes to monitor greenhouse gas emissions from wood chip storage heaps

This study explores the use of static chamber boxes to detect whether there are fugitive emissions of greenhouse gases (GHGs) from a willow chip storage heap. The results from the boxes were compared with those from 3-m stainless steel probes inserted into the core of the heap horizontally and vertically at intervals. The results from probes showed that there were increases of carbon dioxide (CO2) concentrations in the heap over the first 10 days after heap establishment, which were correlated with a temperature rise to 60 °C. As the CO2 declined, there was a small peak in methane (CH4) concentration in probes orientated vertically in the heap. Static chambers positioned at the apex of the heap detected some CO2 fluxes as seen in the probes; however, the quantities were small and random in nature. A small (maximum 5 ppm) flux in CH4 occurred at the same time as the probe concentrations peaked. Overall, the static chamber method was not effective in monitoring fluxes from the heap as there was evidence that gases could enter and leave around the edges of the chambers during the course of the experiment. In general, the use of standard (25 cm high) static chambers for monitoring fluxes from wood chip heaps is not recommended

Energy and greenhouse gas balance of the use of forest residues for bioenergy production in the UK

Life cycle analysis is used to assess the energy requirements and greenhouse gas (GHG) emissions associated with extracting UK forest harvesting residues for use as a biomass resource. Three forest harvesting residues were examined (whole tree thinnings, roundwood and brash bales), and each have their own energy and emission profile. The whole forest rotation was examined, including original site establishment, forest road construction, biomass harvesting during thinning and final clear-fell events, chipping and transportation. Generally, higher yielding sites give lower GHG emissions per 'oven dried tonne' (ODT) forest residues, but GHG emissions 'per hectare' are higher as more biomass is extracted. Greater quantities of biomass, however, ultimately mean greater displacement of conventional fuels and therefore greater potential for GHG emission mitigation. Although forest road construction and site establishment are " one off" events they are highly energy-intensive operations associated with high diesel fuel consumption, when placed in context with the full forest rotation, however, their relative contributions to the overall energy requirements and GHG emissions are small. The lower bulk density of wood chips means that transportation energy requirements and GHG emissions are higher compared with roundwood logs and brash bales, suggesting that chipping should occur near the end-user of application. © 2011 Elsevier Ltd

Understanding the greenhouse gas balances of bioenergy systems.

Bioenergy systems play a key role in the UK’s energy future because they offer the triple benefits of being renewable, sustainable and incurring lower greenhouse gas (GHG) emissions than fossil fuels, such as coal, oil or gas.When biomass is utilized as an energy source, carbon dioxide (CO2) that was recently captured from the atmosphere by plant growth is re-released. As this has been recently sequestered, it is often ignored as not contributing to net increases in long term atmospheric concentrations. However, that neutrality is dependent on the biomass growth vegetation recapturing the equivalent over ashort time horizon, otherwise the balance between carbon in the atmosphere and biosphere is shifted. In the natural world, every unit of greenhouse gas (GHG) emitted has an impact that needs to be considered and, given the tight carbon budget constraints faced by the UK, this must be considered in assessment.Bioenergy is expected to deliver 8-11% of the UK’s primary energy demand by 2020 and around 12% by 2050 (DECC 2012), playing a key role in delivering policy commitments on greenhouse gas reductions. See section 1 – Why is bioenergy important in the future UK energy mix?Bioenergy systems achieve GHG reductions by displacing a relatively high carbon intensity existing fuel with a biomass feedstock that has incurred lower GHG emissions along its supply chain than the (usually fossil fuel) incumbent. Verifying GHG reductions therefore requires consideration of the whole supply chain and awareness of the wider impacts of bioenergy implementation. Techniques such as life cycle assessment (LCA) can be used to verify this. When this is done the yield of usable material produced is nearly always important; fertilizer use is often important for annual crops; changes in carbon stocks may be very significant for forestry systems and land-use change can have very large impacts for perennial crops. A summary of which issues tend to be most important for which crops and why is given in section 2 – What are the key differences between different bioenergy systems?Every bioenergy system is different and their GHG balances must be independently verified. Nevertheless, there are many examples of UK bioelectricity systems achieving substantial GHG savings, while relatively low carbon intensity natural gas is dominant in the UK heating sector, making substantial reductions more difficult to achieve. Biomass-derived liquid transport fuels with existing technologies offer lower potential for savings and there are many reported examples that do not result in greenhouse gas savings. Section 3 – Can bioenergy systems achieve “real” greenhouse gas reductions? shows that real GHG savings can be achieved, but certain factors,including land-use and the reference comparison can substantially alter the calculated GHG savings.Section 4 – How can different reports reach different conclusions about the GHG balances of bioenergy systems? examines and classifies the main drivers of variation in LCA of bioenergy systems. Some variation is “real”, where different systems may actually give rise to different physical levels of GHG emissions. Other sources of variation may be methodological – this can oftenbe thought of as using LCA to answer a “different question” about the same bioenergy system. It is therefore absolutely critical that the “LCA question” being asked is clearly and adequately defined. Section 5 –What should be considered when assessing if bioenergy is delivering real greenhouse gas reductions? gives guidance on formulating LCA questions and what needs to be considered by policy makers in defining GHG reduction objectives e.g. it is important to consider which demand is being displaced, from whose perspective “reductions” are framed, when emissions are incurred and whether reduced sequestration can be considered equivalent to increased emissions.Section 6 – What are the methodological issues that make bioenergy LCA calculations difficult and their results contested? then focuses particularly on the methodological issues that result in different LCA analyses of the same system producing different results and the most appropriate context for applying different methods is outlined. There is particular focus on our understanding of temporal aspects of biomass feedstocks. This issue is most significant for forestry systems and it is noted that often the issue is not one of a carbon debt, but foregone future sequestration, which perhaps should be considered differently when assessing the system GHG balance.Finally section 7 –What are the implications of our understanding of bioenergy system greenhouse gas balances for policy initiatives or “How can policy frameworks incentivize “real” greenhouse gas reductions? synthesizes the policy implications for assessing GHG balances of bioenergy systems and promoting greenhouse gas reductions. It emphasizes the importance of land-use and land-use change for some systems and recognizes the need to better understand the future food-fuel interface for climate policy development. It also identifies a key gap in knowledge surrounding the impact of forest management on carbon stocks and perceives a need for closer examination ofcarbon dynamics. It notes the fact that importing biomass is effectively equivalent to exporting our carbon reduction obligations, but notes that this occurs in many sectors where the UK imports goods. <br/