Arbre Monitoring - the Fuel Supply Chain
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dti ARBRE MONITORING - THE FUEL SUPPLY CHAIN CONTRACT NUMBER: B/U1/00626/00/00 NUMBER: 05/1077 The DTI drives our ambition of 'prosperity for all' by working to create the best environment for business success in the UK. We help people and companies become more productive by promoting enterprise, innovation and creativity. We champion UK business at home and abroad. We invest heavily in world-class science and technology. We protect the rights of working people and consumers. And we stand up for fair and open markets in the UK, Europe and the world. ii ARBRE MONITORING - THE FUEL SUPPLY CHAIN B/U1/00626/REP URN 05/1077 Contractors ADAS Consulting Limited Transport Research Laboratory (TRL) Prepared by Barbara Hilton John Garstang Simon Groves John King Phil Metcalfe Tim Pepper Ian McCrae (TRL) The work described in this report was carried out under contract as part of the DTI Technology Programme: New and Renewable Energy, which is managed by Future Energy Solutions. The views and judgements expressed in this report are those of the contractor and do not necessarily reflect those of the DTI or Future Energy Solutions. First published 2005 © Crown copyright 2005 iii EXECUTIVE SUMMARY Objectives The objectives of this project were to monitor the entire fuel supply chain for the ARBRE power plant from crop husbandry and yield, through the performance of harvesting machinery, to all handling and transport elements of the fuel supply chain from source to store and store to power plant. In doing this emissions from harvesting, processing and transport machinery were monitored, along with dust and spore emissions from the wood fuel through the store-chipping-handling chain. In addition to the above, water use of short rotation coppice (SRC) was monitored along with site drainage characteristics. The objective data resulting from the work were to be used to establish confidence in the fuel supply chain for the ARBRE plant and future similar operations by verifying the environmental balance, the technical efficiency and overall performance. Introduction The use of renewable biofuels to generate part of the UK's energy requirements is central to the Government's current objectives of reducing CO2 emissions by 12.5% by 2010 (DTI, 1999) thereby honouring its obligations under the Kyoto Treaty of 1997. A further domestic target of reducing CO2 levels in particular to 20% below 1990 levels has also been set. To achieve these targets the Government envisages that 10% of the UK's energy demand will be met from renewables by 2010 with an aspiration that this will increase to 20% by 2020 and that a significant proportion will be biomass generated. Currently, just 3% of UK electricity is generated from renewable sources as a whole. The Energy White Paper (DTI, 2003a) accepted the Royal Commission on Environmental Pollution's (RCEP, 2000) recommendation that the UK should also have a longer term goal of reducing CO2 emissions by 60% by about 2050 compared to today's levels, "with real progress by 2020". In order to achieve this 60% reduction, it is envisaged that at least 30% to 40% of the UK's electricity generation should come from renewable sources (DTI, 2003b) with biomass energy again a significant proportion. In 2001 ARBRE Energy Ltd completed construction of what was due to be the first commercial state-of-the-art wood-fuelled electricity generating plant of its type in Europe. The plant was of the Biomass Integrated Gasification-Combined Cycle (BIG- CC) design based on circulating fluidised bed gasification technology the principal benefits including high plant efficiency and a reduction in emissions to atmosphere from the combustion process. Commissioning was underway when, in July 2002 and for a number of reasons, ARBRE went into liquidation. The power plant would have generated 10MWe with 8MWe being exported to the local grid, providing enough electricity for the domestic consumption of 33,500 people. The fuel, in the form of wood chips, was from two sources: forest residues and specifically grown SRC with a requirement of 43,500 oven dry tonnes (odt) per annum. The wood chips would arrive at the power plant at or below 30% moisture content with a nominal 30mm size (30 x 30 x 30mm). The chips would then have been dried to 10% iv moisture content using waste heat from the generation process prior to being fed into the gasifier. To ensure the long-term viability of currently proposed biomass energy projects it is essential that all aspects of the production chain be run at optimal efficiency. This in turn should ensure that the energy balance of the heat and/or electricity generated is optimally positive. Large scale cropping of SRC for fuel, as was proposed for ARBRE and as is now taking place for a number of heat and/or power projects, and the burning of large quantities of biomass require comprehensive environmental monitoring to ensure that both plant operators and the general public are not exposed to any unnecessary hazards. Work summary The work carried out was as follows: • The fuel supply chain was described from crop establishment through management and harvesting to final storage of the harvested materials. Changes in production methods were noted. • Exhaust emissions and energy consumption from vehicles and equipment were either monitored in the field or obtained from Transport Research Laboratory's (TRL) Emissions Database. • Vehicle performance at crop establishment, harvesting and delivery were monitored including the verification of planter efficiency. Any design faults or inadequacies on the harvesters were noted including cutting height variability and field losses. • SRC water uptake was determined on sand and clay sites using the ADAS water use programme Irriguide. • Drainage water from sand sites, treated and untreated with sewage sludge as fertiliser, and a clay site was monitored working from baseline data obtained prior to planting. The quantity of nitrate-N leached was calculated using the Irriguide model. • Changes in soil nutrient status and carbon accumulation within both sand and clay soils were assessed. • Overall performance of a number of the plantations was monitored including machinery used, herbicide and pesticide applications, fertiliser inputs, pests and diseases identified to general level and scored for severity, mammalian grazing activity and weed burden assessments. Field estimates of yield were also made plus percentage dry matter content. • The quality of water draining from piles of stored harvested material was determined by BOD analysis and tannin levels. • The runoff from the storage piles was also quantified using an automated sampler. • The spores and dust produced during storage and handling of the harvested material were determined using personal dust monitors attached to operators plus passive spore traps within the storage piles and at 10 and 50m distances from the piles. v Conclusions • Increased SRC yield reduces the emissions per oven dry tonne harvested for planting and cutback operations but not for harvesting operations nor field and road transport. • Planting and cutback operations contribute the least emissions at 1% or less of the total emissions for SRC production. • Harvesting operations, field and on-farm transport were the predominant sources of emissions during SRC production. • The SRC energy ratio does not alter radically between harvesting methods or lifetime of the crop but the higher the yield the more positive the energy ratio becomes. • The energy ratio for SRC production ranged from 19.7 (16 year crop yielding 9odt ha" 1yr"1) to 28.2 (30 year crop yielding 12odt ha" 1yr"1). • There was no major increase in levels of bio-aerosols above the upwind background concentrations when the chip storage piles were moved. • Bio-aerosol emissions from the chips in store were very low. • Dust exposure to staff and release to the environment during movement of the chip storage piles were within exposure limits for similar dusts encountered in grain stores. • The levels of dust emission are low enough to suggest that there is low general risk to the environment from wood chip storage facilities. • There were no apparent differences in the runoff patterns observed from storage piles of either SRC or forest residue chips. • Biological oxygen demand values recorded for runoff from stored wood chips are unlikely to cause problems provided some dilution occurs before any discharge to a watercourse. • Nitrate-N concentrations in runoff water from the chip storage piles were consistently low during the entire monitoring period, within the range 0.5 to 5.6mg l-1 (EC limit for potable water = 11.6mg l-1), with the highest values recorded in low volumes of runoff. • As shown in previous work, water-use in willows proved higher than continuous cereals, grass or bare soil. • This work confirmed that winter drainage under SRC might be limited to <60mm per winter compared with c. 150-240mm for grass or wheat. • Drainage water from a clay site where no sewage sludge had been applied showed nitrate-N concentrations declining rapidly in the winter following SRC establishment and continuing to decline during the second and third years after planting. Levels were generally below 1mg l-118 months after planting, much lower than would be expected from arable land and similar to values measured in MAFF's Nitrate Sensitive Area scheme when land was converted to nil- fertilised grassland. These concentrations were also 30 times lower than that recorded at the start of the study and a factor of ten lower than the EC limit for potable water. vi • On a sand site, where no sewage sludge had been applied, nitrate-N concentrations again declined rapidly in the first year following planting to around 1mg l-1 and remained below this level for the following two years. • In contrast, nitrate-N concentrations, where slurry had been applied to a sand site, increased through the first winter, peaking at over 80mg l-1, with the pattern repeated during the following two winters with peaks of 176mg l-1 and 248mg l-1 respectively.